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Sample records for pseudomorphic semiconducting heterostructures

  1. InGaAsGaAs pseudomorphic heterostructure transistors prepared by MOVPE

    Science.gov (United States)

    Liu, Wen-Chau; Laih, Lih-Wen; Tsai, Jung-Hui; Lin, Kun-Wei; Cheng, Chin-Chuan

    1997-01-01

    In this paper, we will demonstrate two new InGaAs-GaAs pseudomorphic heterostructure transistors prepared by MOVPE technology, i.e. InGaAs-GaAs graded-concentration doping-channel MIS-like field effect transistors (FET) and heterostructure-emitter and heterostructure-base (InGaAs-GaAs) transistors (HEHBT). For the doping-channel MIS-like FET, the graded In 0.15Ga 0.85As doping-channel structure is employed as the active channel. For a 0.8 × 100 μm 2 gate device, a breakdown voltage of 15 V, a maximum transconductance of 200 mS/mm, and a maximum drain saturation current of 735 mA/mm are obtained. For the HEHBT, the confinement effect for holes is enhanced owing to the presence of GaAs/InGaAs/GaAs quantum wells. Thus, the emitter injection efficiency is increased and a high current gain can be obtained. Also, due to the lower surface recombination velocity of InGaAs base layers, the potential spike of the emitter-base (E-B) junction can be reduced significantly. This can provide a lower collector-emitter offset voltage. For an emitter area of 4.9 × 10 -5 cm 2, the common emitter current gain of 120 and the collector-emitter offset voltage of 100 mV are obtained.

  2. High-performance InP/InGaAs co-integrated metamorphic heterostructure bipolar and field-effect transistors with pseudomorphic base-emitter spacer and channel layers

    Science.gov (United States)

    Wu, Yi-Chen; Tsai, Jung-Hui; Chiang, Te-Kuang; Chiang, Chung-Cheng; Wang, Fu-Min

    2014-02-01

    In the InP/InGaAs metamorphic co-integrated heterostructure bipolar and field-effect transistors (BiFETs), the field-effect transistor (FET) with pseudomorphic channel layer was stacked on the top of the metamorphic heterostructure bipolar transistor (HBT) with pseudomorphic base-emitter spacer layers. In the FET, a relatively thin as well as heavily doped In0.65Ga0.35As pseudomorphic channel layer between two undoped InP layers was employed to enhance the gate forward operation voltage, drain current, and transconductance, simultaneously. On the other hand, after removing the top four layers of material structures, the studied HBT was fabricated on the metamorphic buffer layer. In the metamorphic HBT, the valence band discontinuity at InP/In0.65Ga0.35As heterojunction and emitter injection efficiency could be further extended than the conventional InP/In0.53Ga0.47As lattice-matched HBTs. Furthermore, the delta doping layer between two In0.65Ga0.35As spacer layers at emitter side could effectively eliminate the potential spike at base-emitter junction for reducing the collector-emitter offset voltage. Consequently, the co-integrated metamorphic devices show a good potential for mixed signal integrated circuits and systems applications.

  3. High-performance polymer semiconducting heterostructure devices by nitrene-mediated photocrosslinking of alkyl side chains

    Science.gov (United States)

    Png, Rui-Qi; Chia, Perq-Jon; Tang, Jie-Cong; Liu, Bo; Sivaramakrishnan, Sankaran; Zhou, Mi; Khong, Siong-Hee; Chan, Hardy S. O.; Burroughes, Jeremy H.; Chua, Lay-Lay; Friend, Richard H.; Ho, Peter K. H.

    2010-02-01

    Heterostructures are central to the efficient manipulation of charge carriers, excitons and photons for high-performance semiconductor devices. Although these can be formed by stepwise evaporation of molecular semiconductors, they are a considerable challenge for polymers owing to re-dissolution of the underlying layers. Here we demonstrate a simple and versatile photocrosslinking methodology based on sterically hindered bis(fluorophenyl azide)s. The photocrosslinking efficiency is high and dominated by alkyl side-chain insertion reactions, which do not degrade semiconductor properties. We demonstrate two new back-infiltrated and contiguous interpenetrating donor-acceptor heterostructures for photovoltaic applications that inherently overcome internal recombination losses by ensuring path continuity to give high carrier-collection efficiency. This provides the appropriate morphology for high-efficiency polymer-based photovoltaics. We also demonstrate photopatternable polymer-based field-effect transistors and light-emitting diodes, and highly efficient separate-confinement-heterostructure light-emitting diodes. These results open the way to the general development of high-performance polymer semiconductor heterostructures that have not previously been thought possible.

  4. Low frequency noise and electrical transport properties of pseudomorphic Si/Si sub 1 sub - xGe sub x heterostructures

    CERN Document Server

    Prest, M J

    2001-01-01

    Growth of high germanium content (x=0.44) pseudomorphic Si/Si sub 1 sub - sub x Ge sub x structures at low temperature, followed by a high temperature anneal, was optimised for low temperature mobility. The optimum was found for growth at 380 deg C with an ex-situ anneal at 800 deg C which gave a 10K mobility of 1030cm sup 2 V sup - sup 1 s sup - sup 1 with a sheet density of 1.2x10 sup 1 sup 2 cm sup - sup 2. A sample grown at 380 deg C with an in-situ anneal at 800 deg C gave an even higher 10K mobility of 1985cm sup 2 V sup - sup 1 s sup - sup 1 with a sheet density of 1.0x10 sup 1 sup 2 cm sup - sup 2. Chemical etching was used to fully deplete the dopant supply layer so that a room temperature Hall mobility of 255cm sup 2 V sup - sup 1 s sup - sup 1 was measured. Variation of the Hall coefficient was used to determine the room temperature Hall scattering factor as 0.58 which gave a Drift mobility of 440cm sup 2 V sup - sup 1 s sup - sup 1 (about twice that of a conventional Si pMOS device at the same ver...

  5. Submilliampere threshold current pseudomorphic InGaAs/AlGaAs buried-heterostructure quantum well lasers grown by molecular beam epitaxy

    OpenAIRE

    Eng, L. E.; Chen, T. R.; Sanders, S.; Zhuang, Y. H.; Zhao, B.; Yariv, A.; Morkoç, H.

    1989-01-01

    We report on low threshold current strained InGaAs/AlGaAs single quantum well lasers grown by molecular beam epitaxy. Broad-area threshold current densities of 114 A/cm2 at 990 nm were measured for 1540-µm-long lasers. Threshold currents of 2.4 mA at 950 nm were obtained for an uncoated buried-heterostructure device with a 2-µm-wide stripe and 425-µm-long cavity. With reflective coatings the best device showed 0.9 mA threshold current (L=225 µm). Preliminary modulation measurements show bandw...

  6. Pseudomorphic Semiconducting Heterostructures from Combinations of AIN, GaN and Selected SiC Polytypes: Theoretical Advancement and its Coordination with Experimental Studies of Nucleation, Growth, Characterization and Device Development.

    Science.gov (United States)

    1992-12-01

    c-BN) corresponding to diamond, and a rare hexagonal wurtzite structure (w-BN) which corresponds to Lonsdaleite . The layered hexagonal structure is...structure (w-BN) corresponding to Lonsdaleite . The last two phases are metastable under normal environmental conditions. An amorphous phase (a-BN) is

  7. Pseudomorphic Bipolar Quantum Resonant-Tunneling Transistor

    National Research Council Canada - National Science Library

    Seabaugh, Alan C; Frensley, William R; Randall, John N; Reed, Mark A; Farrington, Dewey L; Matyi, Richard J

    1989-01-01

    ...+ InGaAs quantum well of a double-barrier resonant-tunneling structure. The heterojunction transistor consists of an n-GaAs emitter and collector, undoped AlAs tunnel barriers, and a pseudomorphic p...

  8. CdSe colloidal nanocrystals monolithically integrated in a pseudomorphic semiconductor epilayer

    Energy Technology Data Exchange (ETDEWEB)

    Larramendi, Erick M. [Physics Faculty-ICTM, University of Havana, Colina Universitaria, C.P. 10400 Havana (Cuba); Institut fuer Optik und Atomare Physik, Technische Universitaet Berlin, Strasse des 17. Juni 135, D-10623 Berlin (Germany); Department Physik, Center for Optoelectronics and Photonics Paderborn (CeOPP), Universitaet Paderborn, Warburger Strasse 100, D-33098 Paderborn (Germany); Schoeps, Oliver; Woggon, Ulrike [Institut fuer Optik und Atomare Physik, Technische Universitaet Berlin, Strasse des 17. Juni 135, D-10623 Berlin (Germany); Artemyev, Mikhail V. [Institute for Physico-Chemical Problems, Belarussian State University, Minsk 220080 (Belarus); Schikora, Detlef; Lischka, Klaus [Department Physik, Center for Optoelectronics and Photonics Paderborn (CeOPP), Universitaet Paderborn, Warburger Strasse 100, D-33098 Paderborn (Germany)

    2013-01-14

    As optically active emitters in a semiconductor matrix, core/shell and bare CdSe colloidal nanocrystals (CNCs) were monolithically incorporated in ZnSe pseudomorphic epilayers by molecular beam epitaxy (MBE). A suspension of wet chemically synthesized CNCs was sprayed ex-situ over a pseudomorphic ZnSe/GaAs(001) heterostructure using a nebulizer. Subsequently, the matrix material growth was resumed to form a capping layer by a slow MBE growth mode. Structural investigations show high crystalline quality and pseudomorphic epitaxial character of the whole hybrid CNC-matrix structure. The core/shell CNCs remain optically active following the embedding process. Their emission is blue shifted without a significant change on the spectral shape, and shows the same temperature dependence as that of the free exciton peak energy in zinc-blende CdSe at temperatures above 80 K. Our optical characterization of the samples showed that the embedded CNCs were stable and that the structure of the host was preserved. These results are encouraging for the fabrication of more complex optoelectronic devices based on CNCs.

  9. CdSe colloidal nanocrystals monolithically integrated in a pseudomorphic semiconductor epilayer

    Science.gov (United States)

    Larramendi, Erick M.; Schöps, Oliver; Artemyev, Mikhail V.; Schikora, Detlef; Lischka, Klaus; Woggon, Ulrike

    2013-01-01

    As optically active emitters in a semiconductor matrix, core/shell and bare CdSe colloidal nanocrystals (CNCs) were monolithically incorporated in ZnSe pseudomorphic epilayers by molecular beam epitaxy (MBE). A suspension of wet chemically synthesized CNCs was sprayed ex-situ over a pseudomorphic ZnSe/GaAs(001) heterostructure using a nebulizer. Subsequently, the matrix material growth was resumed to form a capping layer by a slow MBE growth mode. Structural investigations show high crystalline quality and pseudomorphic epitaxial character of the whole hybrid CNC-matrix structure. The core/shell CNCs remain optically active following the embedding process. Their emission is blue shifted without a significant change on the spectral shape, and shows the same temperature dependence as that of the free exciton peak energy in zinc-blende CdSe at temperatures above 80 K. Our optical characterization of the samples showed that the embedded CNCs were stable and that the structure of the host was preserved. These results are encouraging for the fabrication of more complex optoelectronic devices based on CNCs.

  10. PREFACE: Semiconducting oxides Semiconducting oxides

    Science.gov (United States)

    Catlow, Richard; Walsh, Aron

    2011-08-01

    Semiconducting oxides are amongst the most widely studied and topical materials in contemporary condensed matter science, with interest being driven both by the fundamental challenges posed by their electronic and magnetic structures and properties, and by the wide range of applications, including those in catalysis and electronic devices. This special section aims to highlight recent developments in the physics of these materials, and to show the link between developing fundamental understanding and key application areas of oxide semiconductors. Several aspects of the physics of this wide and expanding range of materials are explored in this special section. Transparent semiconducting oxides have a growing role in several technologies, but challenges remain in understanding their electronic structure and the physics of charge carriers. A related problem concerns the nature of redox processes and the reactions which interconvert defects and charge carriers—a key issue which may limit the extent to which doping strategies may be used to alter electronic properties. The magnetic structures of the materials pose several challenges, while surface structures and properties are vital in controlling catalytic properties, including photochemical processes. The field profits from and exploits a wide range of contemporary physical techniques—both experimental and theoretical. Indeed, the interplay between experiment and computation is a key aspect of contemporary work. A number of articles describe applications of computational methods whose use, especially in modelling properties of defects in these materials, has a long and successful history. Several papers in this special section relate to work presented at a symposium within the European Materials Research Society (EMRS) meeting held in Warsaw in September 2010, and we are grateful to the EMRS for supporting this symposium. We would also like to thank the editorial staff of Journal of Physics: Condensed Matter for

  11. Semiconducting polymeric materials

    NARCIS (Netherlands)

    de Boer, Bert; Facchetti, Antonio

    2008-01-01

    (Semi)conducting polymers with a pi-conjugated (hetero)aromatic backbone are capable of transporting charge and interact efficiently with light enabling their utilization in a variety of opto-electronic devices. In this report and in the additional papers of this special issue, several classes of

  12. Nano semiconducting materials

    CERN Document Server

    Saravanan, R

    2016-01-01

    The main focus of the present book is the characterization of a number of nano-semiconducting materials, using such techniques as powder X-ray diffraction, UV-visible spectrophotometry, Raman spectrometry, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. The materials studied include ZnS, TiO2, NiO, Ga doped ZnO, Mn doped SnO2, Mn doped CeO2 and Mn doped ZrO2.

  13. Intermetallic semiconducting films

    CERN Document Server

    Wieder, H H

    1970-01-01

    Intermetallic Semiconducting Films introduces the physics and technology of AшВv compound films. This material is a type of a polycrystalline semiconductor that is used for galvanomagnetic device applications. Such material has a high electron mobility that is ideal for generators and magnetoresistors. The book discusses the available references on the preparation and identification of the material. An assessment of its device applications and other possible use is also enumerated. The book describes the structures and physical parts of different films. A section of the book covers the three t

  14. Semiconducting transition metal oxides

    Science.gov (United States)

    Lany, Stephan

    2015-07-01

    Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using

  15. Non-coherent growth patches in pseudomorphic films: Unusual strain relief in electrodeposited Co on Cu(001)

    DEFF Research Database (Denmark)

    Schindler, W.; Koop, T.; Kazimirov, A.

    2000-01-01

    The critical thickness for pseudomorphic Co growth on Cu(001) is found to be independent of the onset of lattice constant relaxation. The pseudomorphic film relieves strain by local formation of orthomorphic growth patches within the pseudomorphic matrix. This unusual relaxation mechanism of elec...

  16. High-power single-element pseudomorphic InGaAs/GaAs/AlGaAs single quantum well lasers for pumping Er-doped fiber amplifiers

    Science.gov (United States)

    Larsson, A.; Forouhar, S.; Cody, J.; Lang, R. J.; Andrekson, P. A.

    1991-01-01

    A 980-nm-ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs single-quantum-well laser with a maximum single-ended output power of 240 mW from a facet-coated device is fabricated from a graded-index separate-confinement heterostructure grown by molecular-beam epitaxy. The laser oscillates in the fundamental spatial mode, allowing 22 percent coupling efficiency into a 1.55-micron single-mode optical fiber. Life testing at an output power of 30 mW per facet from uncoated devices reveals a superior reliability to GaAs/AlGaAs quantum-well lasers but also the need for protective facet coatings for long term reliability at power levels required for pumping Er-doped fiber amplifiers.

  17. Millimeter-wave and optoelectronic applications of heterostructure integrated circuits

    Science.gov (United States)

    Pavlidis, Dimitris

    1991-01-01

    The properties are reviewed of heterostructure devices for microwave-monolithic-integrated circuits (MMICs) and optoelectronic integrated circuits (OICs). Specific devices examined include lattice-matched and pseudomorphic InAlAs/InGaAs high-electron mobility transistors (HEMTs), mixer/multiplier diodes, and heterojunction bipolar transistors (HBTs) developed with a number of materials. MMICs are reviewed that can be employed for amplification, mixing, and signal generation, and receiver/transmitter applications are set forth for OICs based on GaAs and InP heterostructure designs. HEMTs, HBTs, and junction-FETs can be utilized in combination with PIN, MSM, and laser diodes to develop novel communication systems based on technologies that combine microwave and photonic capabilities.

  18. Graphene encapsulated gold nanoparticle-quantum dot heterostructures and their electrochemical characterization

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yuan [Metallurgical and Materials Engineering Department, Center for Materials for Information Technology (MINT), The University of Alabama, Tuscaloosa, AL 35487 (United States); Chopra, Nitin, E-mail: nchopra@eng.ua.edu [Metallurgical and Materials Engineering Department, Center for Materials for Information Technology (MINT), The University of Alabama, Tuscaloosa, AL 35487 (United States); Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487 (United States); Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487 (United States)

    2015-07-30

    Highlights: • Patterning of multilayer graphene shell encapsulated gold nanoparticles (GNPs). • Binding of quantum dots to GNPs resulted in GNP-QD heterostructures. • The heterostructures were characterized for their electrochemical properties. - Abstract: A simple technique for patterning multilayer graphene shell encapsulated gold nanoparticles (GNPs) on the silicon substrate and their further surface decoration with semiconducting quantum dots (QDs) is reported. This leads to the fabrication of a novel silicon electrode decorated with GNP-QD hybrids or heterostructures. The morphology, structure, and composition of the GNPs and GNP-QD heterostructures were evaluated using microscopic and spectroscopic techniques. The heterostructures decorated silicon electrode was also evaluated for the electronic and electrochemical properties. The results showed that the electrical characteristics of the silicon substrate were significantly improved by decorating with GNPs and quantum dots. Furthermore, GNP-QD heterostructure electrode was observed to show significantly increased electrochemical charge transfer activity.

  19. Charge Transport in Two-Photon Semiconducting Structures for Solar Fuels

    OpenAIRE

    LIU Guohua; Du, Kang; Haussener, Sophia; Wang, Kaiying

    2016-01-01

    Semiconducting heterostructures are emerging as promising light absorbers and offer effective electron–hole separation to drive solar chemistry. This technology relies on semiconductor composites or photoelectrodes that work in the presence of a redox mediator and that create cascade junctions to promote surface catalytic reactions. Rational tuning of their structures and compositions is crucial to fully exploit their functionality. In this review, we describe the possibilities of applying th...

  20. Manufacturing of calcium phosphate scaffolds by pseudomorphic transformation of gypsum

    Energy Technology Data Exchange (ETDEWEB)

    Araujo Batista, H. de.; Batista Cardoso, M.; Sales Vasconcelos, A.; Vinicius Lia Fook, M.; Rodriguez Barbero, M. A.; Garcia Carrodeguas, R.

    2016-08-01

    Carbonated hydroxyapatite (CHAp) and β-tricalcium phosphate (β-TCP) have been employed for decades as constituents of scaffolds for bone regeneration because they chemically resemble bone mineral. In this study, the feasibility to manufacture CHAp/β-TCP scaffolds by pseudomorphic transformation of casted blocks of gypsum was investigated. The transformation was carried out by immersing the precursor gypsum block in 1 M (NH{sub 4}){sub 2}HPO{sub 4}/1.33 M NH{sub 4}OH solution with liquid/solid ratio of 10 mL/g and autoclaving at 120 degree centigrade and 203 kPa (2 atm) for 3 h at least. Neither shape nor dimensions significantly changed during transformation. The composition of scaffolds treated for 3 h was 70 wt.% CHAp and 30 wt.% β-TCP, and their compressive and diametral compressive strengths were 6.5 ± 0.7 and 5.3 ±0.7 MPa, respectively. By increasing the time of treatment to 6 h, the composition of the scaffold enriched in β-TCP (60 wt.% CHAp and 40 wt.% β-TCP) but its compressive and diametral compressive strengths were not significantly affected (6.7 ± 0.9 and 5.4 ± 0.6 MPa, respectively). On the basis of the results obtained, it was concluded that this route is a good approach to the manufacturing of biphasic (CHAp/β-TCP) scaffolds from previously shaped pieces of gypsum. (Author)

  1. Field Effect in Graphene-Based van der Waals Heterostructures: Stacking Sequence Matters

    DEFF Research Database (Denmark)

    Stradi, Daniele; Papior, Nick Rübner; Hansen, Ole

    2017-01-01

    Stacked van der Waals (vdW) heterostructures where semiconducting two-dimensional (2D) materials are contacted by overlaid graphene electrodes enable atomically thin, flexible electronics. We use first-principles quantum transport simulations of graphene-contacted MoS2 devices to show how...

  2. Semiconducting III-V compounds

    CERN Document Server

    Hilsum, C; Henisch, Heinz R

    1961-01-01

    Semiconducting III-V Compounds deals with the properties of III-V compounds as a family of semiconducting crystals and relates these compounds to the monatomic semiconductors silicon and germanium. Emphasis is placed on physical processes that are peculiar to III-V compounds, particularly those that combine boron, aluminum, gallium, and indium with phosphorus, arsenic, and antimony (for example, indium antimonide, indium arsenide, gallium antimonide, and gallium arsenide).Comprised of eight chapters, this book begins with an assessment of the crystal structure and binding of III-V compounds, f

  3. Scalable Fabrication of 2D Semiconducting Crystals for Future Electronics

    Directory of Open Access Journals (Sweden)

    Jiantong Li

    2015-12-01

    Full Text Available Two-dimensional (2D layered materials are anticipated to be promising for future electronics. However, their electronic applications are severely restricted by the availability of such materials with high quality and at a large scale. In this review, we introduce systematically versatile scalable synthesis techniques in the literature for high-crystallinity large-area 2D semiconducting materials, especially transition metal dichalcogenides, and 2D material-based advanced structures, such as 2D alloys, 2D heterostructures and 2D material devices engineered at the wafer scale. Systematic comparison among different techniques is conducted with respect to device performance. The present status and the perspective for future electronics are discussed.

  4. Luminescent Organic Semiconducting Langmuir Monolayers.

    Science.gov (United States)

    Agina, Elena V; Mannanov, Artur A; Sizov, Alexey S; Vechter, Olga; Borshchev, Oleg V; Bakirov, Artem V; Shcherbina, Maxim A; Chvalun, Sergei N; Konstantinov, Vladislav G; Bruevich, Vladimir V; Kozlov, Oleg V; Pshenichnikov, Maxim S; Paraschuk, Dmitry Yu; Ponomarenko, Sergei A

    2017-05-31

    In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene-phenylene dimer D2-Und-PTTP-TMS (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices.

  5. Optical dating of relict sand wedges and composite-wedge pseudomorphs in Flanders, Belgium

    DEFF Research Database (Denmark)

    Buylaert, Jan-Pieter; Ghysels, Günther; Murray, Andrew S.

    2009-01-01

    We report on quartz Optically Stimulated Luminescence (OSL) dating of the infill of 14 relict sand wedges and composite-wedge pseudomorphs at 5 different sites in Flanders, Belgium. A laboratory dose recovery test indicates that the single-aliquot regenerative-dose (SAR) procedure is suitable...

  6. Semiconducting silicon nanowires for biomedical applications

    CERN Document Server

    Coffer, JL

    2014-01-01

    Biomedical applications have benefited greatly from the increasing interest and research into semiconducting silicon nanowires. Semiconducting Silicon Nanowires for Biomedical Applications reviews the fabrication, properties, and applications of this emerging material. The book begins by reviewing the basics, as well as the growth, characterization, biocompatibility, and surface modification, of semiconducting silicon nanowires. It goes on to focus on silicon nanowires for tissue engineering and delivery applications, including cellular binding and internalization, orthopedic tissue scaffol

  7. Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures.

    Science.gov (United States)

    Lee, Jae Yoon; Shin, Jun-Hwan; Lee, Gwan-Hyoung; Lee, Chul-Ho

    2016-10-27

    Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDCs) and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW) heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures.

  8. Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Jae Yoon Lee

    2016-10-01

    Full Text Available Two-dimensional (2D semiconductors such as transition metal dichalcogenides (TMDCs and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures.

  9. Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures

    Science.gov (United States)

    Lee, Jae Yoon; Shin, Jun-Hwan; Lee, Gwan-Hyoung; Lee, Chul-Ho

    2016-01-01

    Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDCs) and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW) heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures. PMID:28335321

  10. Graphene encapsulated gold nanoparticle-quantum dot heterostructures and their electrochemical characterization

    Science.gov (United States)

    Li, Yuan; Chopra, Nitin

    2015-07-01

    A simple technique for patterning multilayer graphene shell encapsulated gold nanoparticles (GNPs) on the silicon substrate and their further surface decoration with semiconducting quantum dots (QDs) is reported. This leads to the fabrication of a novel silicon electrode decorated with GNP-QD hybrids or heterostructures. The morphology, structure, and composition of the GNPs and GNP-QD heterostructures were evaluated using microscopic and spectroscopic techniques. The heterostructures decorated silicon electrode was also evaluated for the electronic and electrochemical properties. The results showed that the electrical characteristics of the silicon substrate were significantly improved by decorating with GNPs and quantum dots. Furthermore, GNP-QD heterostructure electrode was observed to show significantly increased electrochemical charge transfer activity.

  11. Tunable Band Gaps of Mono-layer Hexagonal BNC Heterostructures

    OpenAIRE

    Peng, Qing; Zamiri, Amir; De, Suvranu

    2011-01-01

    Bandgap engineering by substituting C with B and N atoms in graphene has been shown to be a promising way to improve semiconducting properties of graphene. Such hybridized monolayers consisting of hexagonal BN phases in graphene (h-BNC) have been recently synthesized and char- acterized. In this paper, we present an ab initio density functional theory (DFT)-based study of h-BN domain size effect on band gap of mono-layer h-BNC heterostructures. The atomic structures, electronic band structure...

  12. Assembly of ordered carbon shells on semiconducting nanomaterials

    Science.gov (United States)

    Sutter, Eli Anguelova; Sutter, Peter Werner

    2010-05-11

    In some embodiments of the invention, encapsulated semiconducting nanomaterials are described. In certain embodiments the nanostructures described are semiconducting nanomaterials encapsulated with ordered carbon shells. In some aspects a method for producing encapsulated semiconducting nanomaterials is disclosed. In some embodiments applications of encapsulated semiconducting nanomaterials are described.

  13. Assembly of ordered carbon shells on semiconducting nanomaterials

    Science.gov (United States)

    Sutter, Eli Anguelova; Sutter, Peter Werner

    2012-10-02

    In some embodiments of the invention, encapsulated semiconducting nanomaterials are described. In certain embodiments the nanostructures described are semiconducting nanomaterials encapsulated with ordered carbon shells. In some aspects a method for producing encapsulated semiconducting nanomaterials is disclosed. In some embodiments applications of encapsulated semiconducting nanomaterials are described.

  14. Heterostructures and quantum devices

    CERN Document Server

    Einspruch, Norman G

    1994-01-01

    Heterostructure and quantum-mechanical devices promise significant improvement in the performance of electronic and optoelectronic integrated circuits (ICs). Though these devices are the subject of a vigorous research effort, the current literature is often either highly technical or narrowly focused. This book presents heterostructure and quantum devices to the nonspecialist, especially electrical engineers working with high-performance semiconductor devices. It focuses on a broad base of technical applications using semiconductor physics theory to develop the next generation of electrical en

  15. Separation of Metallic and Semiconducting Carbon Nanotubes.

    Science.gov (United States)

    Tambraparni, Madhava B; Wang, Shiren

    2010-01-01

    Carbon nanotubes are currently the focus of intense interest due to their extraordinary properties. However, as-grown nanotubes exist as bundles of metallic and semiconducting. This hinders their widespread applications. Much progress has been made to overcome this limitation. Many separation methods have been investigated, including combination of physical, chemical, or biochemical methods. These methods have demonstrated their own advantages and limitations. This paper reviews recent patents progress made for the separation of metallic and semiconducting nanotubes.

  16. One-step synthesis of van der Waals heterostructures of graphene and two-dimensional superconducting α -M o2C

    Science.gov (United States)

    Qiao, Jia-Bin; Gong, Yue; Zuo, Wei-Jie; Wei, Yi-Cong; Ma, Dong-Lin; Yang, Hong; Yang, Ning; Qiao, Kai-Yao; Shi, Jin-An; Gu, Lin; He, Lin

    2017-05-01

    Assembling different two-dimensional (2D) crystals, covering a very broad range of properties, into van der Waals (vdW) heterostructures enables unprecedented possibilities for combining the best of different ingredients in one objective material. So far, metallic, semiconducting, and insulating 2D crystals have been used successfully in making functional vdW heterostructures with properties by design. Here, we expand 2D superconducting crystals as a building block of vdW hererostructures. One-step growth of large-scale high-quality vdW heterostructures of graphene and 2D superconducting α -M o2C by using chemical vapor deposition is reported. The superconductivity and its 2D nature of the heterostructures are characterized by our scanning tunneling microscopy measurements. This adds 2D superconductivity, the most attractive property of condensed matter physics, to vdW heterostructures.

  17. Ab initio exploration of d0 digital magnetic heterostructures: the case of MgO and CaO δ-doped with potassium

    Science.gov (United States)

    Du, Jiangtao; Dong, Shengjie; Lu, Yi-Lin; Zhao, Hui; Wang, Liying; Feng, Liefeng

    2017-06-01

    Previous studies of digital magnetic heterostructures have mainly focused on 3 d transition metal δ-doped semiconductors. In this work, sp-electron digital magnetic heterostructures without magnetic ions are proposed. Based on a theoretical density functional investigation, electronic structures and magnetic properties of MgO and CaO δ-doped with K were reported. The results show that these heterostructures are half-metallic ferromagnetic materials having semiconducting up spins and metallic down spins, with an exchange interaction much stronger than that of a random alloy with similar K concentration. Our first-principles calculations show that the carriers at the Fermi level are strongly confined within a few monolayers around the KO plane. This strong confinement is responsible for the large exchange coupling and the two-dimensional half-metallic behavior. The thickness of the host semiconducting spacer does not significantly change the global electric and magnetic features.

  18. Trends of semiconductivity in 3d oxides

    Science.gov (United States)

    Lany, Stephan

    2015-03-01

    Open shell transition metal oxides are usually described as Mott insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a Mott gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g., for energy applications. This presentation gives an overview for the band-structure trends of 3d oxides with special attention on the hybridization between the 3d crystal field symmetries with the sp bands, and on how this interactions affect the effective masses and the likelihood of self-trapping of electrons or holes. Supported by DOE-SC-BES as part on an Energy Frontier Research Center.

  19. Structural and Electrical Investigation of C60-Graphene Vertical Heterostructures.

    Science.gov (United States)

    Kim, Kwanpyo; Lee, Tae Hoon; Santos, Elton J G; Jo, Pil Sung; Salleo, Alberto; Nishi, Yoshio; Bao, Zhenan

    2015-06-23

    Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C60 thin film on graphene. The assembled film structure of C60 on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C60 film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C60 crystal and graphene lattice directions are found, and van der Waals ab initio calculations support the observed phenomena. Moreover, using C60-graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10(3). Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications.

  20. Synthetic Nanosheets of Natural van der Waals Heterostructures.

    Science.gov (United States)

    Banik, Ananya; Biswas, Kanishka

    2017-11-13

    Creation of new van der Waals heterostructures by stacking different two dimensional (2D) crystals on top of each other in a chosen sequence is the next challenge after the discovery of graphene, mono/few layer of h-BN, and transition-metal dichalcogenides. However, chemical syntheses of van der Waals heterostructures are rarer than the physical preparation techniques. Herein, we demonstrate the kinetic stabilization of 2D ultrathin heterostructure (ca. 1.13-2.35 nm thick) nanosheets of layered intergrowth SnBi 2 Te 4 , SnBi 4 Te 7 , and SnBi 6 Te 10 , which belong to the Sn m Bi 2n Te 3n+m homologous series, by a simple solution based synthesis. Few-layer nanosheets exhibit ultralow lattice thermal conductivity (κ lat ) of 0.3-0.5 W m -1  K -1 and semiconducting electron-transport properties with high carrier mobility. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Solid-state semiconducting polymer lasers

    Science.gov (United States)

    Hide, Fumitomo

    A comprehensive review of the recent emergence of semiconducting pi-conjugated polymers as solid-state laser materials is presented. With the notable exception of semiconducting polymer laser diodes, high performance photonic and electronic devices have been fabricated from semiconducting polymers, with their performance parameters approaching or even surpassing those of their inorganic counterparts in some cases. As the first step in exploring the feasibility of 'plastic' laser diodes, optically pumped stimulated emission, gain, and lasing have recently been observed in over a dozen different semiconducting polymers representing a variety of molecular structures with emission wavelengths spanning the visible spectrum. Resonant structures for providing the feedback required for lasing or gain narrowing in submicron thick films, neat and undiluted, of photoluminescent thin solid films of conjugated polymers include: planar waveguides, microcavities, distributed feedback (DFB) structures, and high-Q microresonators. Lasing and gain narrowing have been compared using two of these structures: waveguides and microcavities. In both cases, the gain narrowing or lasing threshold is at 0.05-0.1 muJ per 10 ns pulse focused to ˜1.5 mm. Single-mode microcavity lasers are obtained when a microcavity resonance occurs at the wavelength where the gain of the polymer is maximum. High efficiency Stokes-shifted photoluminescence (PL) and high gain are features that make undiluted semiconducting polymers uniquely attractive as solid-state laser materials. These features also make the same polymers attractive as active components in InGaN/semiconducting polymer hybrid LEDs, where the blue emission from the InGaN LED provides the blue component, and simultaneously, serves as the short wavelength pump source for exciting the PL of the polymer film(s). White, green, green-yellow, and yellow emitting InGaN/polymer hybrid LED prototypes have been demonstrated simply by dip-coating pre

  2. The paleomagnetism of the salt pseudomorph beds of middle cambrian age from the salt range, West Pakistan

    NARCIS (Netherlands)

    Wensink, H.

    1972-01-01

    Oriented cores for a paleomagnetic investigation were collected from ten sites in the sedimentary redbeds of the Salt Pseudomorph Beds of Middle Cambrian age m the Salt Range near Khcwra. All samples were subjected to progressive, thermal demagnetization procedures which revealed the

  3. In-plane polarization of GaN-based heterostructures with arbitrary crystal orientation

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Q.Y.; Li, T.; Wu, Z.H.; Ponce, F.A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

    2010-10-15

    The total polarization fields of pseudomorphic In{sub x}Ga{sub 1-x}N/GaN and Al{sub x}Ga{sub 1-x}N/GaN heterostructures with 0 {<=} x {<=} 0.4 have been calculated as a function of the crystal orientation. Especial attention is placed on the direction and magnitude of in-plane piezoelectric polarization, which is not negligible for the non-polar and semi-polar growth. For an arbitrary crystal orientation, the piezoelectric polarization prevails in the InGaN/GaN system while the spontaneous polarization prevails in the AlGaN/GaN system. The in-plane potential due to polarization fields in non-polar epilayers is found to depend on the degree of planarity of the heterojunctions, and on the respective lateral dimensions. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  4. The origin of low-frequency negative transconductance dispersion in a pseudomorphic HEMT

    Science.gov (United States)

    Balakrishnan, V. R.; Kumar, Vikram; Ghosh, Subhasis

    2005-08-01

    Measurements of low-frequency transconductance dispersion at different temperatures and conductance deep level transient spectroscopic (CDLTS) studies of an AlGaAs/InGaAs pseudomorphic high electron mobility transistor (p-HEMT) were carried out. The experimental results show the presence of defect states at the AlGaAs/InGaAs hetero-interface. A mobility degradation model was developed to explain the low-frequency negative transconductance dispersion as well as the apparent 'hole' like peaks observed in the CDLTS spectra. This model incorporates a time-dependent change in the two-dimensional electron gas mobility due to ionized impurity scattering by the remaining charge states at the adjoining AlGaAs/InGaAs hetero-interface.

  5. Stability of semiconducting transition metal dichalcogenides irradiated by soft X-rays and low energy electrons

    Science.gov (United States)

    Walker, Roger C.; Bhimanapati, Ganesh R.; Shi, Tan; Zhang, Kehao; Eichfeld, Sarah M.; Jovanovic, Igor; Robinson, Joshua A.

    2017-04-01

    Semiconducting two-dimensional materials (2DMs) such as molybdenum disulfide and tungsten diselenide have attracted significant attention due to their unique electronic properties. Understanding their nanoscale radiation tolerance is needed for developing radiation-hardened nanoelectronics. Here, we report that the XPS environment of soft X-ray (E = 1.486 keV) exposure in a vacuum combined with a low energy electron flood gun leads to charge accumulation in the 2D layers over time, with little impact on layer chemistry. Additionally, the charging that induced the 2DM/substrate heterostructure depends more on the growth technique, the size of as-grown domains, and the surface coverage of the 2DM than the conductivity of the substrate. Charging is minimized for the combination of a continuous 2DM film and strong coupling between the 2DM and the substrate.

  6. Low-temperature performance of semiconducting asymmetric nanochannel diodes

    Science.gov (United States)

    Akbas, Y.; Savich, G. R.; Jukna, A.; Plecenik, T.; Ďurina, P.; Plecenik, A.; Wicks, G. W.; Sobolewski, Roman

    2017-10-01

    We present our studies on fabrication and electrical and optical characterization of semiconducting asymmetric nanochannel diodes (ANCDs), focusing mainly on the temperature dependence of their current–voltage (I–V) characteristics in the range from room temperature to 77 K. These measurements enable us to elucidate the electron transport mechanism in a nanochannel. Our test devices were fabricated in a GaAs/AlGaAs heterostructure with a two-dimensional electron gas layer and were patterned using electron-beam lithography. The 250-nm-wide, 70-nm-deep trenches that define the nanochannel were ion-beam etched using the photoresist as a mask, so the resulting nanostructure consisted of approximately ten ANCDs connected in parallel with 2-µm-long, 230-nm-wide nanochannels. The ANCD I–V curves collected in the dark exhibited nonlinear, diode-type behavior at all tested temperatures. Their forward-biased regions were fitted to the classical diode equation with a thermionic barrier, with the ideality factor n and the saturation current as fitting parameters. We have obtained very good fits, but with n as large as ∼50, suggesting that there must be a substantial voltage drop likely at the contact pads. The thermionic energy barrier was determined to be 56 meV at high temperatures. We have also observed that under optical illumination our ANCDs at low temperatures exhibited, at low illumination powers, a very strong photoresponse enhancement that exceeded that at room temperature. At 78 K, the responsivity was of the order of 104 A/W at the nW-level light excitation.

  7. Mixed Dimensional Van der Waals Heterostructures for Opto-Electronics.

    Science.gov (United States)

    Jariwala, Deep

    The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into ``all-2D'' van der Waals heterostructures, this concept is not limited to 2D materials alone. Given that any passivated, dangling bond-free surface will interact with another via vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through noncovalent interactions. In the first part of this talk I will present our work on emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices performed at Northwestern University. I will present two distinct examples of gate-tunable p-n heterojunctions 1. Single layer n-type MoS2\\ (2D) combined with p-type semiconducting single walled carbon nanotubes (1D) and 2. Single layer MoS2 combined with 0D molecular semiconductor, pentacene. I will present the unique electrical properties, underlying charge transport mechanisms and photocurrent responses in both the above systems using a variety of scanning probe microscopy techniques as well as computational analysis. This work shows that van der Waals interactions are robust across different dimensionalities of materials and can allow fabrication of semiconductor devices with unique geometries and properties unforeseen in bulk semiconductors. Finally, I will briefly discuss our recent work from Caltech on near-unity absorption in atomically-thin photovoltaic devices. This work is supported by the Materials Research Center at Northwestern University, funded by the National Science Foundation (NSF DMR-1121262) and the Resnick Sustainability Institute at Caltech.

  8. Layer-Controlled Chemical Vapor Deposition Growth of MoS2 Vertical Heterostructures via van der Waals Epitaxy.

    Science.gov (United States)

    Samad, Leith; Bladow, Sage M; Ding, Qi; Zhuo, Junqiao; Jacobberger, Robert M; Arnold, Michael S; Jin, Song

    2016-07-26

    The fascinating semiconducting and optical properties of monolayer and few-layer transition metal dichalcogenides, as exemplified by MoS2, have made them promising candidates for optoelectronic applications. Controllable growth of heterostructures based on these layered materials is critical for their successful device applications. Here, we report a direct low temperature chemical vapor deposition (CVD) synthesis of MoS2 monolayer/multilayer vertical heterostructures with layer-controlled growth on a variety of layered materials (SnS2, TaS2, and graphene) via van der Waals epitaxy. Through precise control of the partial pressures of the MoCl5 and elemental sulfur precursors, reaction temperatures, and careful tracking of the ambient humidity, we have successfully and reproducibly grown MoS2 vertical heterostructures from 1 to 6 layers over a large area. The monolayer MoS2 heterostructure was verified using cross-sectional high resolution transmission electron microscopy (HRTEM) while Raman and photoluminescence spectroscopy confirmed the layer-controlled MoS2 growth and heterostructure electronic interactions. Raman, photoluminescence, and energy dispersive X-ray spectroscopy (EDS) mappings verified the uniform coverage of the MoS2 layers. This reaction provides an ideal method for the scalable layer-controlled growth of transition metal dichalcogenide heterostructures via van der Waals epitaxy for a variety of optoelectronic applications.

  9. Synthesis and Applications of Semiconducting Graphene

    Directory of Open Access Journals (Sweden)

    Shahrima Maharubin

    2016-01-01

    Full Text Available Semimetal-to-semiconductor transition in graphene can bestow graphene with numerous novel and enhanced structural, electrical, optical, and physicochemical characteristics. The scope of graphene and its prospective for an array of implications could be significantly outspread by this transition. In consideration of the recent advancements of semiconducting graphene, this article widely reviews the properties, production, and developing operations of this emergent material. The comparisons among the benefits and difficulties of current methods are made, intending to offer evidences to develop novel and scalable synthesis approaches. The emphasis is on the properties and applications resulting from various conversion methods (doping, controlled reduction, and functionalization, expecting to get improved knowledge on semiconducting graphene materials. Intending to motivate further efficient implications, the mechanisms leading to their beneficial usages for energy conversion and storage are also emphasized.

  10. Polarization-coupled tunable resistive behavior in oxide ferroelectric heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Gruverman, Alexei [Univ. of Nebraska, Lincoln, NE (United States); Tsymbal, Evgeny Y. [Univ. of Nebraska, Lincoln, NE (United States); Eom, Chang-Beom [Univ. of Wisconsin, Madison, WI (United States)

    2017-05-03

    This research focuses on investigation of the physical mechanism of the electrically and mechanically tunable resistive behavior in oxide ferroelectric heterostructures with engineered interfaces realized via a strong coupling of ferroelectric polarization with tunneling electroresistance and metal-insulator (M-I) transitions. This report describes observation of electrically conductive domain walls in semiconducting ferroelectrics, voltage-free control of resistive switching and demonstration of a new mechanism of electrical control of 2D electron gas (2DEG) at oxide interfaces. The research goals are achieved by creating strong synergy between cutting-edge fabrication of epitaxial single-crystalline complex oxides, nanoscale electrical characterization by scanning probe microscopy and theoretical modeling of the observed phenomena. The concept of the ferroelectric devices with electrically and mechanically tunable nonvolatile resistance represents a new paradigm shift in realization of the next-generation of non-volatile memory devices and low-power logic switches.

  11. Degadation of semiconducting polymers by concentrated sunlight

    DEFF Research Database (Denmark)

    Tromholt, Thomas; Manceau, Matthieu; Petersen, Martin Helgesen

    2011-01-01

    A lens based sunlight concentration setup was used to accelerate the degradation of semiconducting polymers. Sunlight was collected outdoor and focused into an optical fiber bundle allowing for indoor experimental work. Photo-degradation of several polymers was studied by UV–vis absorbance...... was carried out in a materials study employing five different conjugated polymers relevant to polymer solar cells for which acceleration factors in the range 19–55 were obtained....

  12. Atomically Thin Heterostructures Based on Single-Layer Tungsten Diselenide and Graphene

    KAUST Repository

    Lin, Yu-Chuan

    2014-11-10

    Heterogeneous engineering of two-dimensional layered materials, including metallic graphene and semiconducting transition metal dichalcogenides, presents an exciting opportunity to produce highly tunable electronic and optoelectronic systems. In order to engineer pristine layers and their interfaces, epitaxial growth of such heterostructures is required. We report the direct growth of crystalline, monolayer tungsten diselenide (WSe2) on epitaxial graphene (EG) grown from silicon carbide. Raman spectroscopy, photoluminescence, and scanning tunneling microscopy confirm high-quality WSe2 monolayers, whereas transmission electron microscopy shows an atomically sharp interface, and low energy electron diffraction confirms near perfect orientation between WSe2 and EG. Vertical transport measurements across the WSe2/EG heterostructure provides evidence that an additional barrier to carrier transport beyond the expected WSe2/EG band offset exists due to the interlayer gap, which is supported by theoretical local density of states (LDOS) calculations using self-consistent density functional theory (DFT) and nonequilibrium Green\\'s function (NEGF).

  13. Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Bongjun; Jang, Seonpil; Dodabalapur, Ananth, E-mail: ananth.dodabalapur@engr.utexas.edu [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States); Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Geier, Michael L.; Prabhumirashi, Pradyumna L. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Hersam, Mark C. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Department of Chemistry, Northwestern University, Evanston, Illinois 60208 (United States); Department of Medicine, Northwestern University, Evanston, Illinois 60208 (United States)

    2014-02-10

    We report ambipolar field-effect transistors (FETs) consisting of inkjet printed semiconductor bilayer heterostructures utilizing semiconducting single-walled carbon nanotubes (SWCNTs) and amorphous zinc tin oxide (ZTO). The bilayer structure allows for electron transport to occur principally in the amorphous oxide layer and hole transport to occur exclusively in the SWCNT layer. This results in balanced electron and hole mobilities exceeding 2 cm{sup 2} V{sup −1} s{sup −1} at low operating voltages (<5 V) in air. We further show that the SWCNT-ZTO hybrid ambipolar FETs can be integrated into functional inverter circuits that display high peak gain (>10). This work provides a pathway for realizing solution processable, inkjet printable, large area electronic devices, and systems based on SWCNT-amorphous oxide heterostructures.

  14. Comparative Study between Direct and Pseudomorphic Transformation of Rice Husk Ash into MFI-Type Zeolite.

    Science.gov (United States)

    Alyosef, Hallah Ahmad; Roggendorf, Hans; Schneider, Denise; Inayat, Alexandra; Welscher, Julia; Schwieger, Wilhelm; Münster, Tom; Kloess, Gert; Ibrahim, Suzan; Enke, Dirk

    2017-12-21

    Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy.

  15. Pseudomorphic synthesis of monodisperse magnetic mesoporous silica microspheres for selective enrichment of endogenous peptides.

    Science.gov (United States)

    Zhu, Gang-Tian; Li, Xiao-Shui; Gao, Qiang; Zhao, Ning-Wei; Yuan, Bi-Feng; Feng, Yu-Qi

    2012-02-10

    In this work, we describe a novel synthetic strategy of magnetic mesoporous silica spheres (Fe3O4@mSiO2) for the selective enrichment of endogenous peptides. Fe3O4 particles were coated with silica shell by a sol-gel method, followed by pseudomorphic synthesis to transform nonporous silica shell into ordered mesoporous silica shell. The core/shell structure and mesostructure were individually fabricated in two steps, which can be expedient to independently optimize the properties of monodispersion, magnetization and mesostructure. Actually, it was confirmed that the produced Fe3O4@mSiO2 particles possess good monodispersion, high magnetization, superparamagnetism, uniform accessible mesopores, and large surface area and pore volume. With these good properties, Fe3O4@mSiO2 spheres were applied to the rapid enrichment of peptides. Based on the size-exclusion mechanism and hydrophobic interaction with siloxane bridge group mainly on the surface of inside pores, Fe3O4@mSiO2 can selectively capture peptides and exclude high-MW proteins and salts. Furthermore, peptides in human plasma were successfully enriched by Fe3O4@mSiO2. Copyright © 2011 Elsevier B.V. All rights reserved.

  16. Crystal structure refinements of the 2H and 2M pseudomorphs of ferric carbonate-hydroxyapatite.

    Science.gov (United States)

    Low, H R; Ritter, C; White, T J

    2010-07-28

    The crystal structures of the ferric carbonate-hydroxyapatite (Fe-CHAp) and oxyapatite (Fe-OAp) pseudomorphs were investigated by powder neutron diffraction and Fourier transform infrared spectroscopy. At low iron loadings, Fe-CHAp (x = 0.1) is A-B type carbonate apatite-2H, where atmospheric CO(2) displaces tunnel hydroxyl and framework phosphate (Ca(2+) + 2PO(4)(3-) --> square(Ca) + 2CO(3)(2-) and Ca(2+) + OH(-) --> Fe(3+) + CO(3)(2-)), while Fe-CHAp (x = 0.2) is A type carbonate apatite-2M. For high iron loadings (x = 0.5), near the solubility limit, Fe(3+) incorporation includes concomitant oxidation of hydroxyl groups (Ca(2+) + OH(-) --> Fe(3+) + O(2-)). The discontinuity in the lattice metric at x approximately 0.2 together with a progressive reduction of OH(-) and CO(3)(2-), substantiates these incorporation mechanisms. The general formula of Fe-CHAp is [Ca(4-x)(F)Fe(x)][Ca(6-y)(T) square(y)][(PO(4))(6-y)(CO(3))(y)][(OH(4))(2-x)(CO(3))(x)] (0 27.(0) degrees, monoclinic and triclinic structures are preferable.

  17. Strain profile in nitride based multilayer nano-heterostructures

    Science.gov (United States)

    Gupta, Sapna; Rahman, F.; Siddiqui, M. J.; Alvi, P. A.

    2013-02-01

    This article has focused on the behavior of strain produced in the III-nitride based multilayer nano-heterostructure such as GaN/AlGaN, InN/AlInN, and InN/GaInN. Moreover, the variations in the strain with different material compositions for the proposed structures have also been reported. In this paper, the eight band k.p method has been utilized to compute the strain produced due to lattice mismatch between the binary and ternary semiconducting thin epitaxial layers in the multilayer nano-heterostructure. The strain has been simulated for entire model of size 288 nm, but the significant strain has been observed only in the quantum region that lies between 100 nm and 188 nm. For all models under simulation, the strain in the quantum region is found to be tensile along both x and y directions, while compressive in nature along z-direction. The correlation between strain and bandgap for the structures has also been reported. The Results presented in the paper may be beneficial for entire nano-optoelectronics community.

  18. Magnetic monolayers on semiconducting substrates. An in situ FMR study of Fe-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zakeri Lori, K.

    2007-10-18

    The growth, magnetic anisotropy, g-factor, and magnetization of Fe monolayers grown on GaAs(001), InAs(001), and InP(001) are investigated by a combination of in situ ferromagnetic resonance and SQUID magnetometry as a function of temperature and film thickness. The effect of stress caused by the lattice mismatch and the surface reconstruction on the magnetic anisotropy is quantified. An in-plane spin reorientation transition as a function of film thickness is observed at room temperature for all systems. A magneto-elastic model is used to explain the direction of the easy axis, the spin reorientation transition, and the contributions to the magnetic anisotropy terms using the stress components measured directly by in situ IV-low-energy electron diffraction. While the model gives a quantitative explanation of the out-of-plane magnetic anisotropy, changes of the electronic interface structure have to be taken into account for the in-plane magnetic anisotropy. The influence of Ag and Au buffer and cap layers on the magnetic anisotropy terms are determined. The temperature dependence of the total magnetic anisotropy, as well as the surface-interface and volume contribution to the magnetic anisotropy are determined for Fe monolayers on GaAs(001). It is demonstrated that the temperature dependence of the magnetic anisotropy is correlated with the temperature dependence of the magnetization according to the Callen-Callen model. The temperature dependence of the volume contribution to the perpendicular magnetic anisotropy is fully explained by the temperature dependence of the magneto-elastic anisotropy. A temperature-driven morphological transformation occurring at a temperature higher than 550 K depending on the film thickness is observed. The thin Fe3Si binary Heusler structure epitaxially grown on MgO(001) is investigated. In addition to the structural properties, magnetic anisotropy, magnetization, g-factor, spin, and orbital magnetism, the magnetic relaxation mechanisms are determined as a function of Si concentration, sample treatment, and film thickness. The Arias and Mills model is confirmed yielding a quantitative explanation for the magnetic relaxation parameters from the ferromagnetic resonance linewidth. Two relaxation channels, i.e. dissipative isotropic Gilbert damping as well as anisotropic two-magnon scattering are simultaneously identified. It is demonstrated that changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influences the relaxation channels and can be used to tune the relaxation rates. (orig.)

  19. Electronic properties of blue phosphorene/graphene and blue phosphorene/graphene-like gallium nitride heterostructures.

    Science.gov (United States)

    Sun, Minglei; Chou, Jyh-Pin; Yu, Jin; Tang, Wencheng

    2017-07-05

    Blue phosphorene (BlueP) is a graphene-like phosphorus nanosheet which was synthesized very recently for the first time [Nano Lett., 2016, 16, 4903-4908]. The combination of electronic properties of two different two-dimensional materials in an ultrathin van der Waals (vdW) vertical heterostructure has been proved to be an effective approach to the design of novel electronic and optoelectronic devices. Therefore, we used density functional theory to investigate the structural and electronic properties of two BlueP-based heterostructures - BlueP/graphene (BlueP/G) and BlueP/graphene-like gallium nitride (BlueP/g-GaN). Our results showed that the semiconducting nature of BlueP and the Dirac cone of G are well preserved in the BlueP/G vdW heterostructure. Moreover, by applying a perpendicular electric field, it is possible to tune the position of the Dirac cone of G with respect to the band edge of BlueP, resulting in the ability to control the Schottky barrier height. For the BlueP/g-GaN vdW heterostructure, BlueP forms an interface with g-GaN with a type-II band alignment, which is a promising feature for unipolar electronic device applications. Furthermore, we discovered that both G and g-GaN can be used as an active layer for BlueP to facilitate charge injection and enhance the device performance.

  20. Interfacial properties of semiconducting transition metal chalcogenides

    Science.gov (United States)

    Jaegermann, W.; Tributsch, H.

    This review is aimed at the correlation of structural and electronic properies of semiconducting transition metal chalcogenides with molecular surface processes and mechanisms in photoelectrochemistry, (photo)catalysis, geochemistry and hydrometallurgy. Layer-type, pyrite structured and transition metal cluster containing chalcogenides are selected as model systems to explain the principles involved. Special emphasis is given to the discussion of materials which involve transition metal d- states in the interfacial reaction pathways of holes and electrons. Since they initiate and control heterogeneous coordination chemistry at the surfaces they may provide the possibility of tailoring selective and catalytically demanding reactions. Examples of such mechanisms are presented and discussed in relation to surface properties involved.

  1. Theoretical prediction of high electron mobility in multilayer MoS2 heterostructured with MoSe2.

    Science.gov (United States)

    Ji, Liping; Shi, Juan; Zhang, Z Y; Wang, Jun; Zhang, Jiachi; Tao, Chunlan; Cao, Haining

    2018-01-07

    Two-dimensional (2D) MoS2 has been considered to be one of the most promising semiconducting materials with the potential to be used in novel nanoelectronic devices. High carrier mobility in the semiconductor is necessary to guarantee a low power dissipation and a high switch speed of the corresponding electronic device. Strain engineering in 2D materials acts as an important approach to tailor and design their electronic and carrier transport properties. In this work, strain is introduced to MoS2 through perpendicularly building van der Waals heterostructures MoSe2-MoS2. Our first-principles calculations demonstrate that acoustic-phonon-limited electron mobility can be significantly enhanced in the heterostructures compared with that in pure multilayer MoS2. It is found that the effective electron mass and the deformation potential constant are relatively smaller in the heterostructures, which is responsible for the enhancement in the electron mobility. Overall, the electron mobility in the heterostructures is about 1.5 times or more of that in pure multilayer MoS2 with the same number of layers for the studied structures. These results indicate that MoSe2 is an excellent material to be heterostructured with multilayer MoS2 to improve the charge transport property.

  2. Physical Properties of semiconducting/magnetic nanocomposites

    Directory of Open Access Journals (Sweden)

    Petra eGranitzer

    2015-01-01

    Full Text Available In this review the fabrication of porous silicon/magnetic nanocomposite materials and their physical properties are elucidated. Especially the investigation of the presented systems with respect to their magnetic properties is reported. Furthermore the influence of the semiconducting matrix on the properties of the nanocomposites is highlighted. The main focus will be put on silicon used as template-material. In general the nanocomposite systems are fabricated in a two-step process, first by anodization of a silicon wafer to achieve porous silicon structures, and second by electrodeposition of a magnetic material into the pores. The morphology of the porous silicon template offers straight pores, grown perpendicular to the wafer surface. The magnetic nanostructures deposited within the pores lead to specific properties of the composite dependent on their size and shape. Due to their mutual arrangement magnetic coupling between these structures can occur whereas, coupling between adjacent pores depends on the porous silicon morphology. In a first section different types of such template/metal systems are reviewed and second an experimental part follows implying the porous silicon formation as well as the subsequent metal deposition process. Third the magnetic and optical properties of the systems are described. In a forth chapter the influence of the semiconducting matrix on these properties is elucidated and finally some prospects and conclusions are addressed.

  3. 270 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Over 60 mW Continuous Wave Output Power

    Science.gov (United States)

    Grandusky, James R.; Chen, Jianfeng; Gibb, Shawn R.; Mendrick, Mark C.; Moe, Craig G.; Rodak, Lee; Garrett, Gregory A.; Wraback, Michael; Schowalter, Leo J.

    2013-03-01

    In this letter, the achievement of over 60 mW output power from pseudomorphic ultraviolet light-emitting diodes in continuous wave operation is reported. Die thinning and encapsulation improved the photon extraction efficiency to over 15%. Improved thermal management and a high characteristic temperature resulted in a low thermal rolloff up to 300 mA injection current with an output power of 67 mW, an external quantum efficiency (EQE) of 4.9%, and a wall plug efficiency (WPE) of 2.5% for a single-chip device emitting at 271 nm in continuous wave operation.

  4. Intersubband transitions in pseudomorphic InGaAs/GaAs/AlGaAs multiple step quantum wells

    OpenAIRE

    Li, H. S.; Chen, Y. W.; Wang, K. L.; Lie, D. Y. C.

    1993-01-01

    Intersubband transitions from the ground state to the first and second excited states in pseudomorphic AlGaAs/InGaAs/GaAs/AlGaAs multiple step quantum wells have been observed. The step well structure has a configuration of two AlGaAs barriers confining an InGaAs/GaAs step. Multiple step wells were grown on GaAs substrate with each InGaAs layer compressively strained. During the growth, a uniform growth condition was adopted so that inconvenient long growth interruptions and fast temperature ...

  5. Precise characterization of self-catalyzed III-V nanowire heterostructures via optical second harmonic generation

    Science.gov (United States)

    Yu, Ying; Wang, Jing; Wei, Yu-Ming; Zhou, Zhang-Kai; Ni, Hai-Qiao; Niu, Zhi-Chuan; Wang, Xue-Hua; Yu, Si-Yuan

    2017-09-01

    We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of self-assembled zinc-blende/wurtzite III-V nanowire heterostructures. By analyzing four anisotropic SHG polarimetric patterns, we distinguish between wurtzite (WZ), zinc-blende (ZB) and ZB/WZ mixing III-V semiconducting crystal structures in nanowire systems. By neglecting the surface contributions and treating the bulk crystal within the quasi-static approximation, we can well explain the optical SHG polarimetry from the NWs with diameter from 200-600 nm. We show that the optical in-coupling and out-coupling coefficients arising from depolarization field can determine the polarization of the SHG. We also demonstrate micro-photoluminescence of GaAs quantum dots in related ZB and ZB/WZ mixing sections of core-shell NW structure, in agreement with the SHG polarimetry results. The ability to perform in situ SHG-based crystallographic study of semiconducting single and multi-crystalline nanowire heterostructures will be useful in displaying structure-property relationships of nanodevices.

  6. Thiolated Gold Nanowires: Metallic versus Semiconducting

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Deen [ORNL; Luo, Weidong [ORNL; Nobusada, Katsuyuki [Institute for Molecular Science, Japan; Whetten, Robert L [Georgia Institute of Technology

    2009-01-01

    Tremendous research efforts have been spent on thiolated gold nanoparticles and self-assembled monolayers of thiolate (RS-) on gold, but thiolated gold nanowires have received almost no attention. Here we computationally design two such one-dimensional nanosystems by creating a linear chain of Au icosahedra, fused together by either vertex sharing or face sharing. Then neighboring Au icosahedra are bridged by five thiolate groups for the vertex-sharing model and three RS?Au?SR motifs for the face-sharing model. We show that the vertex-sharing thiolated gold nanowire can be made either semiconducting or metallic by tuning the charge, while the face-sharing one is always metallic. We explain this difference between the two nanowires by examining their band structures and invoking a previously proposed electron-count rule. Implications of our findings for previous experimentation of gold nanowires are discussed, and a potential way to make thiolated gold nanowires is proposed.

  7. Thiolated gold nanowires: metallic versus semiconducting.

    Science.gov (United States)

    Jiang, De-en; Nobusada, Katsuyuki; Luo, Weidong; Whetten, Robert L

    2009-08-25

    Tremendous research efforts have been spent on thiolated gold nanoparticles and self-assembled monolayers of thiolate (RS-) on gold, but thiolated gold nanowires have received almost no attention. Here we computationally design two such one-dimensional nanosystems by creating a linear chain of Au icosahedra, fused together by either vertex sharing or face sharing. Then neighboring Au icosahedra are bridged by five thiolate groups for the vertex-sharing model and three RS-Au-SR motifs for the face-sharing model. We show that the vertex-sharing thiolated gold nanowire can be made either semiconducting or metallic by tuning the charge, while the face-sharing one is always metallic. We explain this difference between the two nanowires by examining their band structures and invoking a previously proposed electron-count rule. Implications of our findings for previous experimentation of gold nanowires are discussed, and a potential way to make thiolated gold nanowires is proposed.

  8. Nanogenerator comprising piezoelectric semiconducting nanostructures and Schottky conductive contacts

    Science.gov (United States)

    Wang, Zhong L. (Inventor); Wang, Xudong (Inventor); Song, Jinhui (Inventor); Zhou, Jun (Inventor); He, Jr-Hau (Inventor)

    2011-01-01

    A semiconducting device includes a substrate, a piezoelectric wire, a structure, a first electrode and a second electrode. The piezoelectric wire has a first end and an opposite second end and is disposed on the substrate. The structure causes the piezoelectric wire to bend in a predetermined manner between the first end and the second end so that the piezoelectric wire enters a first semiconducting state. The first electrode is coupled to the first end and the second electrode is coupled to the second end so that when the piezoelectric wire is in the first semiconducting state, an electrical characteristic will be exhibited between the first electrode and the second electrode.

  9. Light-matter interaction in transition metal dichalcogenides and their heterostructures

    Science.gov (United States)

    Wurstbauer, Ursula; Miller, Bastian; Parzinger, Eric; Holleitner, Alexander W.

    2017-05-01

    The investigation of two-dimensional (2D) van der Waals materials is a vibrant, fast-moving and still growing interdisciplinary area of research. These materials are truly 2D crystals with strong covalent in-plane bonds and weak van der Waals interaction between the layers, and have a variety of different electronic, optical and mechanical properties. Transition metal dichalcogenides are a very prominent class of 2D materials, particularly the semiconducting subclass. Their properties include bandgaps in the near-infrared to the visible range, decent charge carrier mobility together with high (photo-) catalytic and mechanical stability, and exotic many-body phenomena. These characteristics make the materials highly attractive for both fundamental research as well as innovative device applications. Furthermore, the materials exhibit a strong light-matter interaction, providing a high sunlight absorbance of up to 15% in the monolayer limit, strong scattering cross section in Raman experiments, and access to excitonic phenomena in van der Waals heterostructures. This review focuses on the light-matter interaction in MoS2, WS2, MoSe2 and WSe2, which is dictated by the materials’ complex dielectric functions, and on the multiplicity of studying the first-order phonon modes by Raman spectroscopy to gain access to several material properties such as doping, strain, defects and temperature. 2D materials provide an interesting platform for stacking them into van der Waals heterostructures without the limitation of lattice mismatch, resulting in novel devices for applications but also to enable the study of exotic many-body interaction phenomena such as interlayer excitons. Future perspectives of semiconducting transition metal dichalcogenides and their heterostructures for applications in optoelectronic devices will be examined, and routes to study emergent fundamental problems and many-body quantum phenomena under excitations with photons will be discussed.

  10. Heterostructures of transition metal dichalcogenides

    KAUST Repository

    Amin, Bin

    2015-08-24

    The structural, electronic, optical, and photocatalytic properties of out-of-plane and in-plane heterostructures of transition metal dichalcogenides are investigated by (hybrid) first principles calculations. The out-of-plane heterostructures are found to be indirect band gap semiconductors with type-II band alignment. Direct band gaps can be achieved by moderate tensile strain in specific cases. The excitonic peaks show blueshifts as compared to the parent monolayer systems, whereas redshifts occur when the chalcogen atoms are exchanged along the series S-Se-Te. Strong absorption from infrared to visible light as well as excellent photocatalytic properties can be achieved.

  11. Thermal stability and thermal conductivity of phosphorene in phosphorene/graphene van der Waals heterostructures.

    Science.gov (United States)

    Pei, Qing-Xiang; Zhang, Xiaoliang; Ding, Zhiwei; Zhang, Ying-Yan; Zhang, Yong-Wei

    2017-07-14

    Phosphorene, a new two-dimensional (2D) semiconducting material, has attracted tremendous attention recently. However, its structural instability under ambient conditions poses a great challenge to its practical applications. A possible solution for this problem is to encapsulate phosphorene with more stable 2D materials, such as graphene, forming van der Waals heterostructures. In this study, using molecular dynamics simulations, we show that the thermal stability of phosphorene in phosphorene/graphene heterostructures can be enhanced significantly. By sandwiching phosphorene between two graphene sheets, its thermally stable temperature is increased by 150 K. We further study the thermal transport properties of phosphorene and find surprisingly that the in-plane thermal conductivity of phosphorene in phosphorene/graphene heterostructures is much higher than that of the free-standing one, with a net increase of 20-60%. This surprising increase in thermal conductivity arises from the increase in phonon group velocity and the extremely strong phonon coupling between phosphorene and the graphene substrate. Our findings have an important meaning for the practical applications of phosphorene in nanodevices.

  12. Growth and electronic structure of graphene on semiconducting Ge(110)

    OpenAIRE

    Tesch, Julia; Voloshina, Elena; Fonin, Mikhail; Dedkov, Yuriy S.

    2017-01-01

    The direct growth of graphene on semiconducting or insulating substrates might help to overcome main drawbacks of metal-based synthesis, like metal-atom contaminations of graphene, transfer issues, etc. Here we present the growth of graphene on n-doped semiconducting Ge(110) by using an atomic carbon source and the study of the structural and electronic properties of the obtained interface. We found that graphene interacts weakly with the underlying Ge(110) substrate that keeps graphene's ele...

  13. Escher-like quasiperiodic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Barriuso, A G; Monzon, J J; Sanchez-Soto, L L [Departamento de Optica, Facultad de Fisica, Universidad Complutense, 28040 Madrid (Spain); Costa, A F [Departamento de Matematicas Fundamentales, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia, Senda del Rey 9, 28040 Madrid (Spain)

    2009-05-15

    Quasiperiodic heterostructures present unique structural, electronic and vibrational properties, connected to the existence of incommensurate periods. We go beyond previous schemes, such as Fibonacci or Thue-Morse, based on substitutional sequences, by introducing construction rules generated by tessellations of the unit disc by regular polygons. We explore some of the properties exhibited by these systems. (fast track communication)

  14. Thermoelectric Properties of Semiconducting Silicide Nanowires

    Science.gov (United States)

    Jin, Song; Sczech, Jeannine; Higgins, Jeremy; Zhou, Feng; Shi, Li

    2008-03-01

    Semiconducting silicides are promising thermoelectric materials. In addition to their respectable thermoelectric figure-of-merit (ZT up to 0.8), silicides have the advantages of low cost, excellent thermal stability and mechanical strength, and outstanding oxidation resistance, making them suitable for high temperature applications. We have developed general synthetic approaches to single crystal nanowires of silicides to investigate the enhancement of thermoelectric properties due to the reduced nanoscale dimension and to explore their applications in thermoelectrics. We will discuss the synthesis and structural characterization of nanowires of chromium disilicide (CrSi2) prepared via a chemical vapor transport (CVT) method and chemical vapor deposition (CVD) of organometallic precursors to synthesize the Novontony Chimney ladder phase MnSi1.75. The Seebeck coefficient, electrical conductivity, and thermal conductivity of individual CrSi2 nanowires were characterized using a suspended microdevice and correlated with the structural information obtained by microscopy on the same nanowires. This combined Seebeck coefficient and electrical conductivity measurements also provide an effective approach to probing the Fermi level, carrier concentration and mobility in nanowires. We will also discuss our progress in using individual nanostructures combined well-defined structural characterization to conclusively investigate the complex thermoelectric behaviors of silicide materials.

  15. Charge Transport in Two-Photon Semiconducting Structures for Solar Fuels.

    Science.gov (United States)

    Liu, Guohua; Du, Kang; Haussener, Sophia; Wang, Kaiying

    2016-10-20

    Semiconducting heterostructures are emerging as promising light absorbers and offer effective electron-hole separation to drive solar chemistry. This technology relies on semiconductor composites or photoelectrodes that work in the presence of a redox mediator and that create cascade junctions to promote surface catalytic reactions. Rational tuning of their structures and compositions is crucial to fully exploit their functionality. In this review, we describe the possibilities of applying the two-photon concept to the field of solar fuels. A wide range of strategies including the indirect combination of two semiconductors by a redox couple, direct coupling of two semiconductors, multicomponent structures with a conductive mediator, related photoelectrodes, as well as two-photon cells are discussed for light energy harvesting and charge transport. Examples of charge extraction models from the literature are summarized to understand the mechanism of interfacial carrier dynamics and to rationalize experimental observations. We focus on a working principle of the constituent components and linking the photosynthetic activity with the proposed models. This work gives a new perspective on artificial photosynthesis by taking simultaneous advantages of photon absorption and charge transfer, outlining an encouraging roadmap towards solar fuels. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Chronology and palaeoenvironmental implications of the ice-wedge pseudomorphs and composite-wedge casts on the Magdalen Islands (eastern Canada)

    DEFF Research Database (Denmark)

    Remillard, A.M.; Hetu, B.; Bernatchez, P.

    2015-01-01

    The Magdalen Islands are a valuable terrestrial record, evidencing the complex glacial and periglacial history of the Gulf of St. Lawrence. Thirteen structures interpreted as ice-wedge pseudomorphs or composite-wedge casts were observed at four sites on the southern Magdalen Islands and testify t...

  17. Temperature Effects on The Electrical Characteristics of In0.15Ga0.85As Pseudomorphic High-Electron-Mobility Transistors

    Directory of Open Access Journals (Sweden)

    BECHLAGHEM Fatima Zohra

    2017-10-01

    Full Text Available Nowadays, GaAs-based HEMTs and pseudomorphic HEMTs are speedily replacing conventional MESFET technology in military and commercial applications including, communication, radar and automotive technologies having need of high gain, and low noise figures especially at millimeter-wave frequencies. In this work, a short gate length pseudomorphic HEMT "p-HEMT" on GaAs substrate is treated. As temperature dependence study is a very important part of the complete characterization on active devices, the impact of temperature variation on the electrical properties of our 30nm short gate length pseudomorphic high-electron mobility In0.15Ga0.85As device is investigated. All our static DC device characteristics and RF response have been obtained using a device simulator that is Silvaco software to examine temperature impact on our device output current, transconductance and cutoff frequency. The 30nm gate pseudomorphic HEMT reported here exhibit superior DC and RF performances, Our results reveals a maximum drain-source current IDS up to 537.16 mA/mm, a peak extrinsic transconductance Gm of 345.4 mS/mm, a cutoff frequency Ft of 285.9 GHz, and a maximum frequency Fmax of 1580 GHz at room temperature.

  18. Pseudomorphs of Neotethyan Evaporites in Anatolia's HP/LT belts - Aptian basin-wide pelagic gypsum deposits

    Science.gov (United States)

    Scheffler, Franziska; Oberhänsli, Roland; Pourteau, Amaury; Immenhauser, Adrian; Candan, Osman

    2015-04-01

    Rosetta Marble was defined in SW Anatolia as 3D-radiating textures of dm-to-m-long calcite rods in the HP/LT metamorphosed Mid-Cretaceous pelagic carbonate sequence of the Ören Unit. Rosetta Marble in the type locality are interbedded with meta-chert beds, and may constitute entire carbonate beds. Rare aragonite relicts and Sr-rich, fibrous calcite pseudomorphs after aragonite witness the HP metamorphic imprint of this sequence during the closure of a Neotethyan oceanic domain during latest Cretaceous-Palaeocene times. We investigated the Rosetta Marble of the Ören Unit, as well as other known and newly found localities in the Tavşanlı and Afyon zones, and the Alanya Massif and Malatya area, to decipher the metamorphic, diagenetic and sedimentologic significance of these uncommon textures. Based on field, petrographic and geochemical investigations, we document a wide variety of Rosetta-type textures. A striking resemblance with well-known gypsum morphologies (e.g. shallow-tail, palm-tree textures) leads us to argue that Rosetta Marble was initially composed of giant gypsum crystals (selenite). The absence of anhydrite relicts of pseudomorphs indicate that gypsum transformed into calcite soon after the deposition by the mean of a sulphate reduction reaction. The gypsum-to-calcite transformation requires that organic matter intervened as a reactant phase. Mid Cretaceous oceanic domains in the Tethyan realm are characterised by overall anoxic conditions that allowed the preservation of organic material. Rosetta Marble exposures are widely distributed over 600 km along the Neotethyan suture zone. During deepening of the Neotethyan ocean in Mid Cretaceous times, basin-wide and cyclic sedimentation of gypsum and radiolarite occurred. The origin of high-salinity waters needed for gypsum precipitation was located at shelf levels. Density and gravity effects forced the brines to cascade downwards into the deep ocean. Favorable climatic conditions trigger the formation

  19. Analysis of the damage threshold of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

    Science.gov (United States)

    Xi, Xiao-Wen; Chai, Chang-Chun; Liu, Yang; Yang, Yin-Tang; Fan, Qing-Yang; Shi, Chun-Lei

    2016-08-01

    An electromagnetic pulse (EMP)-induced damage model based on the internal damage mechanism of the GaAs pseudomorphic high electron mobility transistor (PHEMT) is established in this paper. With this model, the relationships among the damage power, damage energy, pulse width and signal amplitude are investigated. Simulation results show that the pulse width index from the damage power formula obtained here is higher than that from the empirical formula due to the hotspot transferring in the damage process of the device. It is observed that the damage energy is not a constant, which decreases with the signal amplitude increasing, and then changes little when the signal amplitude reaches up to a certain level. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

  20. Detection of lead ions with AlGaAs/InGaAs pseudomorphic high electron mobility transistor

    Science.gov (United States)

    Jiqiang, Niu; Yang, Zhang; Min, Guan; Chengyan, Wang; Lijie, Cui; Qiumin, Yang; Yiyang, Li; Yiping, Zeng

    2016-11-01

    Lead poisoning is a serious environmental concern, which is a health threat. Existing technologies always have some drawbacks, which restrict their application ranges, such as real time monitoring. To solve this problem, glutathione was functionalized on the Au-coated gate area of the pseudomorphic high electron mobility transistor (pHEMT) to detect trace amounts of Pb2+. The positive charge of lead ions will cause a positive potential on the Au gate of the pHEMT sensor, which will increase the current between the source and the drain. The response range for Pb2+ detection has been determined in the concentrations from 0.1 pmol/L to 10 pmol/L. To our knowledge, this is currently the best result for detecting lead ions. Project supported by the National Natural Science Foundation of China (Nos. 61204012, 61274049, 61376058), the Beijing Natural Science Foundation (Nos. 4142053, 4132070), and the Beijing Nova Program (Nos. 2010B056, xxhz201503).

  1. High transconductance InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

    Science.gov (United States)

    Ketterson, A.; Moloney, M.; Masselink, W. T.; Klem, J.; Fischer, R.

    1985-01-01

    Pseudomorphic In0.15Ga0.85As/A10.15Ga0.85As modulation-doped field effect transistors (MODFET's) exhibiting extremely good dc characteristics have been successfully fabricated. dc transconductance in these strained-layer structures of 270 mS/mm was measured for 1-micron gate, normally-on devices at 300 K. Maximum drain current levels are 290 mA/mm, with excellent pinch-off and saturation characteristics. The transconductance increased to 360 mS/mm at 77 K while no persistent photoconductivity or drain collapse was observed. Preliminary microwave results indicate a 300-K current gain cutoff frequency of about 20 GHz. These results are equivalent to the best GaAs/AlGaAs MODFET results and are due in part to the improved transport properties and carrier confinement in the InGaAs quantum well.

  2. Electroluminescence from a forward-biased Schottky barrier diode on modulation Si {delta}-doped GaAs/InGaAs/AlGaAs heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, Adam; Witczak, P.; Twardowski, A.; Baranowski, J. M.

    2001-06-18

    Electroluminescence (EL) from a forward-biased Schottky barrier diode on modulation Si {delta}-doped pseudomorphic GaAs/InGaAs/AlGaAs heterostructure with high mobility electron gas is investigated in this work. It has been found that the EL from the InGaAs quantum well can be observed at temperatures up to 90 K. The EL line shape depends on the current density, which reflects the filling of the InGaAs channel with electrons. The total integrated EL intensity depends linearly on the current density. We propose that hole diffusion from an inversion layer at the Schottky barrier is responsible for the observed optical recombination with electrons in the InGaAs quantum well. {copyright} 2001 American Institute of Physics.

  3. Physical Properties of Thin Film Semiconducting Materials

    Science.gov (United States)

    Bouras, N.; Djebbouri, M.; Outemzabet, R.; Sali, S.; Zerrouki, H.; Zouaoui, A.; Kesri, N.

    2005-10-01

    The physics and chemistry of semiconducting materials is a continuous question of debate. We can find a large stock of well-known properties but at the same time, many things are not understood. In recent years, porous silicon (PS-Si), diselenide of copper and indium (CuInSe2 or CIS) and metal oxide semiconductors like tin oxide (SnO2) and zinc oxide (ZnO) have been subjected to extensive studies because of the rising interest their potential applications in fields such as electronic components, solar panels, catalysis, gas sensors, in biocompatible materials, in Li-based batteries, in new generation of MOSFETS. Bulk structure and surface and interface properties play important roles in all of these applications. A deeper understanding of these fundamental properties would impact largely on technological application performances. In our laboratory, thin films of undoped and antimony-doped films of tin oxide have been deposited by chemical vapor deposition. Spray pyrolysis was used for ZnO. CIS was prepared by flash evaporation or close-space vapor transport. Some of the deposition parameters have been varied, such as substrate temperature, time of deposition (or anodization), and molar concentration of bath preparation. For some samples, thermal annealing was carried out under oxygen (or air), under nitrogen gas and under vacuum. Deposition and post-deposition parameters are known to strongly influence film structure and electrical resistivity. We investigated the influence of film thickness and thermal annealing on structural optical and electrical properties of the films. Examination of SnO2 by x-ray diffraction showed that the main films are polycrystalline with rutile structure. The x-ray spectra of ZnO indicated a hexagonal wurtzite structure. Characterizations of CIS films with compositional analysis, x-ray diffraction, scanning microscopy, spectrophotometry, and photoluminescence were carried out.

  4. Development of N- and P- Types of Semiconducting Polymers

    Science.gov (United States)

    2015-03-05

    Heterostructures for Potential Thermoelectric Applications. Nano Letters ( Impact factor 13.025), 2012, 12, 3627-3633. 2. Wu, Yue*; Finefrock, Scott W.; Yang...Haoran Nanostructured Thermoelectric: Opportunities and Challenges. Invited Opinion, Nano Energy ( Impact factor 10.211), 2012, 1, 651-653. 3. Fang...Heterostructures. Nano Letters ( Impact factor 13.025), 2013, 13, 2058-2063. 4. Yadav, Gautam G.; David, Anand; Favaloro, Tela; Yang, Haoran; Shakouri

  5. Ultraviolet photodetectors with high photosensitivity based on type-II ZnS/SnO2 core/shell heterostructured ribbons.

    Science.gov (United States)

    Huang, Xing; Yu, Yong-Qiang; Xia, Jing; Fan, Hua; Wang, Lei; Willinger, Marc-Georg; Yang, Xiao-Ping; Jiang, Yang; Zhang, Tie-Rui; Meng, Xiang-Min

    2015-03-12

    Semiconducting heterostructures with type-II band structure have attracted much attention due to their novel physical properties and wide applications in optoelectronics. Herein, we report, for the first time, a controlled synthesis of type-II ZnS/SnO2 heterostructured ribbon composed of SnO2 nanoparticles that uniformly cover the surface of ZnS ribbon via a simple and versatile thermal evaporation approach. Structural analysis indicated that the majority of SnO2 nanoparticles have an equivalent zone axis, i.e., of rutile SnO2, which is perpendicular to ±(2-1-10) facets (top/down surfaces) of ZnS ribbon. For those SnO2 nanoparticles decorated on ±(01-10) facets (side surfaces) of ZnS ribbon, an epitaxial relationship of (01-10)ZnO//(020)SnO2 and [2-1-10]ZnO//[001]SnO2 was identified. To explore their electronic and optoelectronic properties, we constructed field-effect transistors from as-prepared new heterostructures, which exhibited an n-type characteristic with an on/off ratio of ∼10(3) and a fast carrier mobility of ∼33.2 cm2 V(-1) s(-1). Owing to the spatial separation of photogenerated electron-hole pairs from type-II band alignment together with the good contacts between electrodes and ribbon, the resultant photodetector showed excellent photoresponse properties, including large photocurrent, high sensitivity (external quantum efficiency as high as ∼2.4×10(7)%), good stability and reproducibility, and relatively fast response speed. Our results suggest great potential of ZnS/SnO2 heterostructures for efficient UV light sensing, and, more importantly, signify the advantages of type-II semiconducting heterostructures for construction of high-performance nano-photodetectors.

  6. Photoluminescence from quantum dots in cubic GaN/InGaN/GaN double heterostructures

    Science.gov (United States)

    Husberg, O.; Khartchenko, A.; As, D. J.; Vogelsang, H.; Frey, T.; Schikora, D.; Lischka, K.; Noriega, O. C.; Tabata, A.; Leite, J. R.

    2001-08-01

    We have measured photoluminescence spectra of molecular-beam-epitaxy-grown cubic GaN/InxGa1-xN/GaN double heterostructures with x between 0.09 and 0.33. We observe a luminescence peak at about 2.3-2.4 eV which is almost independent of the InGaN layer composition. High-resolution x-ray diffraction measurements revealed a pseudomorphic In-rich phase with x=0.56±0.02 embedded in the InGaN layers. Including strain effects we calculate a gap energy Eg=2.13 eV of this phase. In cubic InGaN, spontaneous polarization and strain-induced piezoelectric fields are negligible. Therefore, the observed difference between the luminescence energy and the gap of the In-rich phase is assumed to be due to the localization of excitons at quantum-dot-like structures with a size of about 15 nm.

  7. Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Kai Ding

    2017-10-01

    Full Text Available We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV light-emitting diodes (LEDs, with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice- and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p- and n-type conductivity of high Al-molar fraction AlGaN are reviewed.

  8. Semiconducting graphene: converting graphene from semimetal to semiconductor.

    Science.gov (United States)

    Lu, Ganhua; Yu, Kehan; Wen, Zhenhai; Chen, Junhong

    2013-02-21

    Interest in graphene has grown extensively in the last decade or so, because of its extraordinary physical properties, chemical tunability, and potential for various applications. However, graphene is intrinsically a semimetal with a zero bandgap, which considerably impedes its use in many applications where a suitable bandgap is required. The transformation of graphene into a semiconductor has attracted significant attention, because the presence of a sizable bandgap in graphene can vastly promote its already-fascinating potential in an even wider range of applications. Here we review major advances in the pursuit of semiconducting graphene materials. We first briefly discuss the electronic properties of graphene and some theoretical background for manipulating the band structure of graphene. We then summarize many experimental approaches proposed in recent years for producing semiconducting graphene. Despite the relatively short history of research in semiconducting graphene, the progress has been remarkable and many significant developments are highly anticipated.

  9. Superconductivity in an Inhomogeneous Bundle of Metallic and Semiconducting Nanotubes

    Directory of Open Access Journals (Sweden)

    Ilya Grigorenko

    2013-01-01

    Full Text Available Using Bogoliubov-de Gennes formalism for inhomogeneous systems, we have studied superconducting properties of a bundle of packed carbon nanotubes, making a triangular lattice in the bundle's transverse cross-section. The bundle consists of a mixture of metallic and doped semiconducting nanotubes, which have different critical transition temperatures. We investigate how a spatially averaged superconducting order parameter and the critical transition temperature depend on the fraction of the doped semiconducting carbon nanotubes in the bundle. Our simulations suggest that the superconductivity in the bundle will be suppressed when the fraction of the doped semiconducting carbon nanotubes will be less than 0.5, which is the percolation threshold for a two-dimensional triangular lattice.

  10. Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

    Directory of Open Access Journals (Sweden)

    Han Huang

    2016-09-01

    Full Text Available Two dimensional atomic crystals, like grapheme (G and molybdenum disulfide (MoS2, exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress in the understanding of the interfaces of van der Waals (vdW heterostructures between small organic molecules (pentacene, copper phthalocyanine (CuPc, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA, and dioctylbenzothienobenzothiophene (C8-BTBT and layered substrates (G, MoS2 and hexagonal boron nitride (h-BN. The influences of the underlying layered substrates on the molecular arrangement, electronic and vibrational properties will be addressed.

  11. EUO-Based Multifunctional Heterostructures

    Science.gov (United States)

    2015-06-06

    MULTIFUNCTIONAL HETEROSTRUCTURES Final Report (June, 2015) 5 5 A. Melville, T. Mairoser, A. Schmehl, D.E. Shai, E.J. Monkman, J.W. Harter , T. Heeg...Europium Oxide,” J. Appl. Phys. 109 (2011) 07C309. 13 D.E. Shai, A.J. Melville, J.W. Harter , E.J. Monkman, D.W. Shen, A. Schmehl, D.G. Schlom, and...A. Schmehl, D.E. Shai, E.J. Monkman, J.W. Harter , T. Heeg, B. Holländer, J. Schubert, K.M. Shen, J. Mannhart, and D.G. Schlom, “Lutetium-doped EuO

  12. Damage effect and mechanism of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

    Science.gov (United States)

    Xiao-Wen, Xi; Chang-Chun, Chai; Gang, Zhao; Yin-Tang, Yang; Xin-Hai, Yu; Yang, Liu

    2016-04-01

    The damage effect and mechanism of the electromagnetic pulse (EMP) on the GaAs pseudomorphic high electron mobility transistor (PHEMT) are investigated in this paper. By using the device simulation software, the distributions and variations of the electric field, the current density and the temperature are analyzed. The simulation results show that there are three physical effects, i.e., the forward-biased effect of the gate Schottky junction, the avalanche breakdown, and the thermal breakdown of the barrier layer, which influence the device current in the damage process. It is found that the damage position of the device changes with the amplitude of the step voltage pulse. The damage appears under the gate near the drain when the amplitude of the pulse is low, and it also occurs under the gate near the source when the amplitude is sufficiently high, which is consistent with the experimental results. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900), and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

  13. Structure, chemical bonding states, and optical properties of the hetero-structured ZnO/CuO prepared by using the hydrothermal and the electrospinning methods

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Kyong-Soo; Kim, Jong Wook; Bae, Jong-Seong; Hong, Tae Eun; Jeong, Euh Duck; Jin, Jong Sung; Ha, Myoung Gyu; Kim, Jong-Pil, E-mail: jpkim@kbsi.re.kr

    2017-01-01

    ZnO-branched nanostructures have recently attracted considerable attention due to their rich architectures and promising applications in the field of optoelectronics. Contrary to n-type semiconducting metal oxides, cupric oxide is a p-type semiconductor which can be applied to high-critical-temperature superconductors, photovoltaic materials, field emission, and catalysis. We report the synthesis of the ZnO nanorods on the CuO nanofibers prepared by using the electrospinning method along with the hydrothermal method. As the growing time increases, emission spectra of the hetero-structured ZnO/CuO show that the observed band in the UV region is slightly increased, while the intensity of the green emission is highly enhanced. The hetero-structured ZnO/CuO is found to be a promising candidate for developing renewable devices with photoluminescent behavior and the increased surface to volume ratio.

  14. Quantum-Confined Stark Effect in a MoS2Monolayer van der Waals Heterostructure.

    Science.gov (United States)

    Roch, Jonas G; Leisgang, Nadine; Froehlicher, Guillaume; Makk, Peter; Watanabe, Kenji; Taniguchi, Takashi; Schönenberger, Christian; Warburton, Richard J

    2018-02-14

    The optics of dangling-bond-free van der Waals heterostructures containing transition metal dichalcogenides are dominated by excitons. A crucial property of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a heterostructure is used to probe the QCSE by applying a uniform vertical electric field across a molybdenum disulfide (MoS 2 ) monolayer. The photoluminescence emission energies of the neutral and charged excitons shift quadratically with the applied electric field, provided that the electron density remains constant, demonstrating that the exciton can be polarized. Stark shifts corresponding to about half the homogeneous linewidth were achieved. Neutral and charged exciton polarizabilities of (7.8 ± 1.0) × 10 -10 and (6.4 ± 0.9) × 10 -10 D m V -1 at relatively low electron density (∼10 12 cm -2 ) have been extracted, respectively. These values are one order of magnitude lower than the previously reported values but in line with theoretical calculations. The methodology presented here is versatile and can be applied to other semiconducting layered materials.

  15. Stabilized thin film heterostructure for electrochemical applications

    DEFF Research Database (Denmark)

    2015-01-01

    The invention provides a method for the formation of a thin film multi-layered heterostructure upon a substrate, said method comprising the steps of: a. providing a substrate; b. depositing a buffer layer upon said substrate, said buffer layer being a layer of stable ionic conductor (B); c...... or less; and e. repeating steps b. and c. a total of N times, such that N repeating pairs of layers (A/B) are built up, wherein N is 1 or more. The invention also provides a thin film multi-layered heterostructure as such, and the combination of a thin film multi-layered heterostructure and a substrate...

  16. Probing the Interlayer Exciton Physics in a MoS2/MoSe2/MoS2 van der Waals Heterostructure

    Science.gov (United States)

    Baranowski, M.; Surrente, A.; Klopotowski, L.; Urban, J. M.; Zhang, N.; Maude, D. K.; Wiwatowski, K.; Mackowski, S.; Kung, Y. C.; Dumcenco, D.; Kis, A.; Plochocka, P.

    2017-10-01

    Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of inter-layer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe$_2$/WSe$_2$ heterostructures. Here we report on the observation of long lived inter-layer exciton emission in a MoS$_2$/MoSe$_2$/MoS$_2$ trilayer van der Waals heterostructure. The inter-layer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power and temperature dependence of the inter-layer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long lived valley polarization of inter-layer exciton. Intriguingly, the inter-layer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the inter-layer exciton emission.

  17. Probing the Interlayer Exciton Physics in a MoS2/MoSe2/MoS2van der Waals Heterostructure.

    Science.gov (United States)

    Baranowski, M; Surrente, A; Klopotowski, L; Urban, J M; Zhang, N; Maude, D K; Wiwatowski, K; Mackowski, S; Kung, Y C; Dumcenco, D; Kis, A; Plochocka, P

    2017-10-11

    Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of interlayer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe 2 /WSe 2 heterostructures. Here we report on the observation of long-lived interlayer exciton emission in a MoS 2 /MoSe 2 /MoS 2 trilayer van der Waals heterostructure. The interlayer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power, and temperature dependence of the interlayer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long-lived valley polarization of interlayer exciton. Intriguingly, the interlayer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the interlayer exciton emission.

  18. Optically transparent semiconducting polymer nanonetwork for flexible and transparent electronics

    Science.gov (United States)

    Yu, Kilho; Park, Byoungwook; Kim, Geunjin; Kim, Chang-Hyun; Park, Sungjun; Kim, Jehan; Jung, Suhyun; Jeong, Soyeong; Kwon, Sooncheol; Kang, Hongkyu; Kim, Junghwan; Yoon, Myung-Han; Lee, Kwanghee

    2016-01-01

    Simultaneously achieving high optical transparency and excellent charge mobility in semiconducting polymers has presented a challenge for the application of these materials in future “flexible” and “transparent” electronics (FTEs). Here, by blending only a small amount (∼15 wt %) of a diketopyrrolopyrrole-based semiconducting polymer (DPP2T) into an inert polystyrene (PS) matrix, we introduce a polymer blend system that demonstrates both high field-effect transistor (FET) mobility and excellent optical transparency that approaches 100%. We discover that in a PS matrix, DPP2T forms a web-like, continuously connected nanonetwork that spreads throughout the thin film and provides highly efficient 2D charge pathways through extended intrachain conjugation. The remarkable physical properties achieved using our approach enable us to develop prototype high-performance FTE devices, including colorless all-polymer FET arrays and fully transparent FET-integrated polymer light-emitting diodes. PMID:27911774

  19. Semiconducting phase in borophene: role of defect and strain

    Science.gov (United States)

    Bhattacharyya, Gargee; Mahata, Arup; Choudhuri, Indrani; Pathak, Biswarup

    2017-10-01

    Boron is an interesting element due to its chemical and structural complexity. Recent synthesis of borophene led scientists to study boron monolayer-based materials for various applications. Using density functional theory calculations, nineteen different phases of boron monolayer (with hexagonal hole densities from 1/32-8/32) are studied to understand their origin of buckling, stability, and planarity. Projected densities of states of various phases of borophene-based systems with defect are plotted into in-plane (s  +  p x   +  p y ) and out-of-plane (p z ) orbitals to understand the role of the σ and π-bands towards their geometry and stability. Interestingly, the λ 5-sheet shows semiconducting properties under uniaxial/biaxial tensile/compressive strains and it shows excellent dynamical, thermal, and mechanical properties and is thus a promising semiconducting phase for electronic devices.

  20. Electronic properties of semiconducting silicides: fundamentals and recent predictions

    Energy Technology Data Exchange (ETDEWEB)

    Ivanenko, L.I.; Shaposhnikov, V.L.; Filonov, A.B.; Krivosheeva, A.V.; Borisenko, V.E.; Migas, D.B.; Miglio, L.; Behr, G.; Schumann, J

    2004-08-02

    This review emphasizes progress in theoretical simulation and experiments that have been performed in the past years for semiconducting silicides. New fundamental electronic and optical properties of Ca{sub 2}Si and BaSi{sub 2}, recently found RuSi{sub 2} phase, ternaries in Fe-Os-Si and Ru-Os-Si systems, {beta}-FeSi{sub 2}, Mg{sub 2}Si and CrSi{sub 2} with stretched and compressed lattices as well as transport properties of {beta}-FeSi{sub 2}, ReSi{sub 1.75}, Ru{sub 2}Si{sub 3} are presented. Prospects for practical applications of semiconducting silicides are discussed.

  1. Meso-/Nanoporous Semiconducting Metal Oxides for Gas Sensor Applications

    OpenAIRE

    Nguyen Duc Hoa; Nguyen Van Duy; Sherif A. El-Safty; Nguyen Van Hieu,

    2015-01-01

    Development and/or design of new materials and/or structures for effective gas sensor applications with fast response and high sensitivity, selectivity, and stability are very important issues in the gas sensor technology. This critical review introduces our recent progress in the development of meso-/nanoporous semiconducting metal oxides and their applications to gas sensors. First, the basic concepts of resistive gas sensors and the recent synthesis of meso-/nanoporous metal oxides for gas...

  2. Syntheses of Nanostructure Bundles Based on Semiconducting Metal Silicides

    Science.gov (United States)

    Li, Wen; Ishikawa, Daisuke; Tatsuoka, Hirokazu

    2013-08-01

    A variety of nanostructure bundles and arrays based on semiconducting metal silicides have been synthesized using abundant and non-toxic starting materials. Three types of fabrication techniques of the nanostructure bundles or arrays, including direct growth, template synthesis using natural nanostructured materials and template synthesis using artificially fabricated nanostructured materials are demonstrated. CrSi2 nanowire bundles were directly grown by the exposure of Si substrates to CrCl2 vapor at atmospheric pressure. A hexagonal MoSi2 nanosheet, Mg2Si/MgO composite nanowire and Mg2Si nanowire bundles and MnSi1.7 nanowire array were synthesized using a MoS2 layered material, a SiOx nanofiber bundle, a Si nanowire array, and a Si nanowire array as the templates, respectively. Additionally, the fabrication phenomenon and structural properties of the nanostructured semiconducting metal silicides were investigated. These reactions provided the low-cost and controllable synthetic techniques to synthesize large scale and one-dimensional semiconducting metal silicides for thermoelectric applications.

  3. Spin Dependent Transport Properties of Metallic and Semiconducting Nanostructures

    Science.gov (United States)

    Sapkota, Keshab R.

    Present computing and communication devices rely on two different classes of technologies; information processing devices are based on electrical charge transport in semiconducting materials while information storage devices are based on orientation of electron spins in magnetic materials. A realization of a hybrid-type device that is based on charge as well as spin properties of electrons would perform both of these actions thereby enhancing computation power to many folds and reducing power consumptions. This dissertation focuses on the fabrication of such spin-devices based on metallic and semiconducting nanostructures which can utilize spin as well as charge properties of electrons. A simplified design of the spin-device consists of a spin injector, a semiconducting or metallic channel, and a spin detector. The channel is the carrier of the spin signal from the injector to the detector and therefore plays a crucial role in the manipulation of spin properties in the device. In this work, nanostructures like nanowires and nanostripes are used to function the channel in the spin-device. Methods like electrospinning, hydrothermal, and wet chemical were used to synthesize nanowires while physical vapor deposition followed by heat treatment in controlled environment was used to synthesis nanostripes. Spin-devices fabrication of the synthesized nanostructures were carried out by electron beam lithography process. The details of synthesis of nanostructures, device fabrication procedures and measurement techniques will be discussed in the thesis. We have successfully fabricated the spin-devices of tellurium nanowire, indium nanostripe, and indium oxide nanostripe and studied their spin transport properties for the first time. These spin-devices show large spin relaxation length compared to normal metals like copper and offer potentials for the future technologies. Further, Heusler alloys nanowires like nanowires of Co 2FeAl were synthesized and studied for electrical

  4. Dependence of the photovoltaic performance of pseudomorphic InGaN/GaN multiple-quantum-well solar cells on the active region thickness

    Energy Technology Data Exchange (ETDEWEB)

    Mukhtarova, Anna; Valdueza-Felip, Sirona; Redaelli, Luca; Durand, Christophe; Monroy, Eva; Eymery, Joël, E-mail: joel.eymery@cea.fr [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS group “Nanophysique et semiconducteurs”, CEA-INAC-PHELIQS, 17 av. des Martyrs, 38054 Grenoble (France); Bougerol, Catherine [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS group “Nanophysique et semiconducteurs”, Institut Néel-CNRS, 25 av. des Martyrs, 38042 Grenoble (France)

    2016-04-18

    We investigate the photovoltaic performance of pseudomorphic In{sub 0.1}Ga{sub 0.9}N/GaN multiple-quantum well (MQW) solar cells as a function of the total active region thickness. An increase in the number of wells from 5 to 40 improves the short-circuit current and the open-circuit voltage, resulting in a 10-fold enhancement of the overall conversion efficiency. Further increasing the number of wells leads to carrier collection losses due to an incomplete depletion of the active region. Capacitance-voltage measurements point to a hole diffusion length of 48 nm in the MQW region.

  5. Vertical-Cavity In-plane Heterostructures: Physics and Applications

    DEFF Research Database (Denmark)

    Taghizadeh, Alireza; Mørk, Jesper; Chung, Il-Sug

    2015-01-01

    We show that the in-plane heterostructures realized in vertical cavities with high contrast grating(HCG) reflector enables exotic configurations of heterostructure and photonic wells. In photonic crystal heterostructures forming a photonic well, the property of a confined mode is determined by th...... to discuss the rich potential of this heterostructure as a platform for various physics studies and propose a system of two laterally coupled cavities which shows the breaking of parity-time symmetry as an example....

  6. Dual distributions for the metallic and semiconducting single-walled carbon nanotubes observed by Raman spectroscopy.

    Directory of Open Access Journals (Sweden)

    Yosuke Sakai

    2008-06-01

    Full Text Available The prospective applicability of single-walled carbon nanotubes (SWNT is highly dependent on its controlled synthesis.Effects of few macroscopic growth-conditions (such as catalyst composition, temperature of deposition etc. reflected on thedistributions of SWNT (diameter, chiralities and semiconducting-metallic nature, are studied by Raman spectroscopicanalysis. We report the presence of two different diameter distributions for as-grown metallic and semiconducting SWNT, themetallic tubes having larger average diameters than their semiconducting counterpart. We hope that, in future, it should bepossible to selectively synthesize SWNT with pre-determined chirality, diameter and metallic/semiconducting nature.

  7. Pseudomorphic growth mode of Pb on the Al{sub 13}Fe{sub 4}(0 1 0) approximant surface

    Energy Technology Data Exchange (ETDEWEB)

    Ledieu, J., E-mail: Julian.ledieu@univ-lorraine.fr [Institut Jean Lamour (UMR 7198 CNRS-Université de Lorraine), Parc de Saurupt, CS50840, 54011 Nancy Cedex (France); Weerd, M.-C de [Institut Jean Lamour (UMR 7198 CNRS-Université de Lorraine), Parc de Saurupt, CS50840, 54011 Nancy Cedex (France); Hahne, M.; Gille, P. [Department of Earth and Environmental Sciences, Crystallography Section, Ludwig-Maximilians-Universität München, Theresienstr. 41, D-80333 München (Germany); Fournée, V. [Institut Jean Lamour (UMR 7198 CNRS-Université de Lorraine), Parc de Saurupt, CS50840, 54011 Nancy Cedex (France)

    2015-11-30

    Highlights: • Pb adsorption has been characterised on the Al{sub 13}Fe{sub 4}(0 1 0) approximant surface. • A pseudomorphic Pb monolayer is formed at 300 K on this highly corrugated template. • The Pb atomic arrangement replicates the motifs observed on the clean surface. • The formation of surface alloys and intermixing can be disregarded. • Efficient energy dissipation of impinging adatoms allows additional layer deposition. - Abstract: We report the adsorption of lead adatoms on the pseudo-10-fold Al{sub 13}Fe{sub 4}(0 1 0) surface using low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). For the submonolayer regime, Pb adatoms remain highly mobile across the surface at 300 K. STM analysis indicates the formation of irregularly shaped islands of monoatomic height. The latter do not coalesce with increasing coverage. At 0.95 MLE coverage, the LEED patterns are consistent with a pseudomorphic growth of the adatoms. This is confirmed by STM measurements which reveal local motifs qualitatively similar to those observed on the clean Al{sub 13}Fe{sub 4}(0 1 0) surface, i.e. prior to dosing. Apart from the absence of plasmons, the XPS measurements of Pb 4f and Al 2s core levels are comparable to those observed for the Pb/Al(1 1 1) system.

  8. Terahertz semiconductor-heterostructure laser.

    Science.gov (United States)

    Köhler, Rüdeger; Tredicucci, Alessandro; Beltram, Fabio; Beere, Harvey E; Linfield, Edmund H; Davies, A Giles; Ritchie, David A; Iotti, Rita C; Rossi, Fausto

    2002-05-09

    Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

  9. Ultraviolet optical absorptions of semiconducting copper phosphate glasses

    Science.gov (United States)

    Bae, Byeong-Soo; Weinberg, Michael C.

    1993-01-01

    Results are presented of a quantitative investigation of the change in UV optical absorption in semiconducting copper phosphate glasses with batch compositions of 40, 50, and 55 percent CuO, as a function of the Cu(2+)/Cu(total) ratio in the glasses for each glass composition. It was found that optical energy gap, E(opt), of copper phosphate glass is a function of both glass composition and Cu(2+)/Cu(total) ratio in the glass. E(opt) increases as the CuO content for fixed Cu(2+)/Cu(total) ratio and the Cu(2+)/Cu(total) ratio for fixed glass composition are reduced.

  10. Leaching mechanism of semiconducting minerals a historical note

    Directory of Open Access Journals (Sweden)

    Habashi F.

    2012-01-01

    Full Text Available mechanism of leaching of semiconducting minerals such as CuS, ZnS, UO2, etc., has been the subject of intensive speculation by hydrometallurgy researchers in the early 1950s who assumed the formation of intermediate surface complexes that could be neither separated nor identified by physico-chemical techniques. The electrochemical theory of leaching introduced in the late 1960s resolved this problem by comparing the leaching process to a corrosion phenomenon similar to the corrosion of metals. A historical summary of these proposals is presented.

  11. Enhancement of semiconducting single-wall carbon nanotubes photoluminescence

    OpenAIRE

    Gaufrès, Etienne; Izard, Nicolas; Vivien, Laurent; Kazaoui, Saïd; Marris-Morini, Delphine; Cassan, Eric

    2009-01-01

    International audience; Photoluminescence properties of semiconducting single wall carbon nanotubes (s-SWNT) thin films with different metallic single wall carbon nanotubes (m-SWNT) concentrations are reported. s-SWNT purified samples are obtained by polymer assisted selective extraction. We show that a few m-SWNT in the sample generates a drastic quenching of the emission. Therefore, highly purified s-SWNT films are a strongly luminescent material and a good candidate for future applications in p...

  12. Thin-film structure of semiconducting end-capped oligothiophenes

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimoto, N [Graduate School of Engineering, Iwate University, Ueda Morioka 020-8551 (Japan); Li, W Y [JST Innovation Satellite Iwate, Iiokashinden Morioka 020-0852 (Japan); Omote, K [Rigaku Corporation, 3-9-12 Matsubara-cho Akishima, Tokyo 196-8666 (Japan); Ackermann, J [Laboratoire des Materiaux Moleculaires et des Biomateriaux, GCOM2 UMR CNRS 6114 Faculte des Sciences de Luminy, Case 901, F-13288, Marseille cedex 09 (France); Videlot-Ackermann, C [Laboratoire des Materiaux Moleculaires et des Biomateriaux, GCOM2 UMR CNRS 6114 Faculte des Sciences de Luminy, Case 901, F-13288, Marseille cedex 09 (France); Brisset, H [Laboratoire des Materiaux Moleculaires et des Biomateriaux, GCOM2 UMR CNRS 6114 Faculte des Sciences de Luminy, Case 901, F-13288, Marseille cedex 09 (France); Fages, F [Laboratoire des Materiaux Moleculaires et des Biomateriaux, GCOM2 UMR CNRS 6114 Faculte des Sciences de Luminy, Case 901, F-13288, Marseille cedex 09 (France)

    2007-10-15

    Distyryl-oligothiophenes (DS-nT) is one of the promising semiconducting materials that use for organic thin-film transistors (OTFTs). The in-plane structures of vapor deposited ultrathin films of DS-4T, and its derivatives with different end-cap groups, on SiO{sub 2}substrate were characterized by grazing incidence x-ray diffractometry (GIXD). The morphology and film structure change with the nature of end-cap groups. The increase in volume of end-cap group causes the decrease in crystallinity and increase in frequency in nucleation. These characteristics could affect to the transport properties in OTFTs.

  13. Magnetism in (Semi)Conducting Macrocycles of pi conjugated Polymers

    Science.gov (United States)

    2016-12-09

    AFRL-AFOSR-JP-TR-2017-0006 Magnetism in (Semi)Conducting Macrocycles of pi-conjugated Polymers Andre Persoons KATHOLIEKE UNIVERSITEIT TE LEUVEN INST...Macrocycles of pi-conjugated Polymers 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-15-1-4051 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Andre Persoons...the investigation of potential magnetic properties of macrocycles of pi-conjugated polymers . This research was initially motivated by the observation

  14. Manipulation of magnetic exchange in iridate heterostructures

    Science.gov (United States)

    Meyers, D.; Fabbris, G.; Yin, Weiguo; Casa, D.; Cao, Yue; Hao, Lin; Schmitt, T.; Liu, Jian; Dean, M. P. M.

    Artificial layering of disparate materials into superlattices is an emerging method that promises unparalleled versatility in accessing ground states unavailable to bulk synthesis. Heterostructures composed of paramagnetic, metallic SrIrO3 interspaced with band insulating SrTiO3 were found to host a canted antiferromagnetic ground state, mirroring the Ruddlesen-Popper series iridates with enhanced tunability. We investigate the magnetic excitation spectrum of these artificial systems using resonant inelastic x-ray scattering and directly infer the interlayer and intralayer magnetic exchange interactions. Understanding how interfacial effects modify magnetic interactions is a vital prerequisite for efforts to controllably target different ground states within complex oxide-heterostructures.

  15. Molecular Strategies for Morphology Control in Semiconducting Polymers for Optoelectronics.

    Science.gov (United States)

    Rahmanudin, Aiman; Sivula, Kevin

    2017-06-28

    Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.

  16. Multicomponent semiconducting polymer systems with low crystallization-induced percolation threshold

    DEFF Research Database (Denmark)

    Goffri, S.; Müller, C.; Stingelin-Stutzmann, N.

    2006-01-01

    –crystalline/semiconducting–insulating multicomponent systems offer expanded flexibility for realizing high-performance semiconducting architectures at drastically reduced materials cost with improved mechanical properties and environmental stability, without the need to design all performance requirements into the active semiconducting polymer...

  17. Structural, mechanical and electronic properties of in-plane 1T/2H phase interface of MoS2 heterostructures

    Directory of Open Access Journals (Sweden)

    Xiaoyan Guo

    2015-09-01

    Full Text Available Two-dimensional (2D molybdenum disulfide (MoS2 phase hybrid system composed by 2H and 1T phase is a natural metal/semiconductor heterostructures and promised a wide range of potential applications. Here, we report the first principle investigations on the structural, mechanical and electronic properties of hybrid system with armchair (AC and zigzag (ZZ interfaces. The ZZ type 1T/2H interface are more energy favorable than AC type interface with 3.39 eV/nm. Similar with that of bulked 1T MoS2, the intrinsic strengths of the heterostructures are lower than that of the bulk 2H, especially for that with ZZ interface. Analysis of density of states shows that the electronic properties gradually transmitted from the metallic 1T phase to the semiconducting 2H phase for the structural abrupt interface. The present theoretical results constitute a useful picture for the 2D electronic devices using current MoS2 1T/2H heterostructures and provide vital insights into the other 2D hybrid materials.

  18. Stacked mechanical nanogenerator comprising piezoelectric semiconducting nanostructures and Schottky conductive contacts

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhong L [Marietta, GA; Xu, Sheng [Atlanta, GA

    2011-08-23

    An electric power generator includes a first conductive layer, a plurality of semiconducting piezoelectric nanostructures, a second conductive layer and a plurality of conductive nanostructures. The first conductive layer has a first surface from which the semiconducting piezoelectric nanostructures extend. The second conductive layer has a second surface and is parallel to the first conductive layer so that the second surface faces the first surface of the first conductive layer. The conductive nanostructures depend downwardly therefrom. The second conductive layer is spaced apart from the first conductive layer at a distance so that when a force is applied, the semiconducting piezoelectric nanostructures engage the conductive nanostructures so that the piezoelectric nanostructures bend, thereby generating a potential difference across the at semiconducting piezoelectric nanostructures and also thereby forming a Schottky barrier between the semiconducting piezoelectric nanostructures and the conductive nanostructures.

  19. Van der Waals Epitaxy of Two-Dimensional MoS2-Graphene Heterostructures in Ultrahigh Vacuum.

    Science.gov (United States)

    Miwa, Jill A; Dendzik, Maciej; Grønborg, Signe S; Bianchi, Marco; Lauritsen, Jeppe V; Hofmann, Philip; Ulstrup, Søren

    2015-06-23

    In this work, we demonstrate direct van der Waals epitaxy of MoS2-graphene heterostructures on a semiconducting silicon carbide (SiC) substrate under ultrahigh vacuum conditions. Angle-resolved photoemission spectroscopy (ARPES) measurements show that the electronic structure of free-standing single-layer (SL) MoS2 is retained in these heterostructures due to the weak van der Waals interaction between adjacent materials. The MoS2 synthesis is based on a reactive physical vapor deposition technique involving Mo evaporation and sulfurization in a H2S atmosphere on a template consisting of epitaxially grown graphene on SiC. Using scanning tunneling microscopy, we study the seeding of Mo on this substrate and the evolution from nanoscale MoS2 islands to SL and bilayer (BL) MoS2 sheets during H2S exposure. Our ARPES measurements of SL and BL MoS2 on graphene reveal the coexistence of the Dirac states of graphene and the expected valence band of MoS2 with the band maximum shifted to the corner of the Brillouin zone at K̅ in the SL limit. We confirm the 2D character of these electronic states via a lack of dispersion with photon energy. The growth of epitaxial MoS2-graphene heterostructures on SiC opens new opportunities for further in situ studies of the fundamental properties of these complex materials, as well as perspectives for implementing them in various device schemes to exploit their many promising electronic and optical properties.

  20. Low-noise AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor recessed by electron cyclotron resonance plasma etching

    CERN Document Server

    Lee, J H; Lee, C W; Yoon, H S; Park, B S; Park, C S

    1999-01-01

    GaAs pseudomorphic high electron mobility transistor recessed by electron cyclotron resonance (ECR) plasma etching have been investigated. We used a BCl sub 3 /SF sub 6 gas mixture to implement the gate recess process. We obtained a uniformity of the threshold voltage to within 50 mV in 3-inch wafers. The GaAs PHEMTs with a 0.2-mu m gate length recessed by the ECR plasma exhibited a minimum noise figure (NF sub m sub i sub n) as low as 0.26 dB with an associated gain (G sub a) of 13 dB at 12 GHz. At 18 GHz, the NF sub m sub i sub n was 0.47 dB with a Ga of 11.66 dB. These results suggest that the ECR plasma etching process reported here is suitable as a manufacturing process for gate recess of a GaAs PHEMT.

  1. Nanoscale semiconducting silicon as a nutritional food additive

    Energy Technology Data Exchange (ETDEWEB)

    Canham, L T [pSiNutria Ltd, Malvern Hills Science Park, Geraldine Road, Malvern, Worcestershire WR14 3SZ (United Kingdom)

    2007-05-09

    Very high surface area silicon powders can be realized by high energy milling or electrochemical etching techniques. Such nanoscale silicon structures, whilst biodegradable in the human gastrointestinal tract, are shown to be remarkably stable in most foodstuffs and beverages. The potential for using silicon to improve the shelf life and bioavailability of specific nutrients in functional foods is highlighted. Published drug delivery data implies that the nanoentrapment of hydrophobic nutrients will significantly improve their dissolution kinetics, through a combined effect of nanostructuring and solid state modification. Nutrients loaded to date include vitamins, fish oils, lycopene and coenzyme Q10. In addition, there is growing published evidence that optimized release of orthosilicic acid, the biodegradation product of semiconducting silicon in the gut, offers beneficial effects with regard bone health. The utility of nanoscale silicon in the nutritional field shows early promise and is worthy of much further study.

  2. Quantum Capacitance Modifies Interionic Interactions in Semiconducting Nanopores

    CERN Document Server

    Lee, Alpha A; Goriely, Alain

    2016-01-01

    Nanopores made with low dimensional semiconducting materials, such as carbon nanotubes and graphene slit pores, are used in supercapacitors. In theories and simulations of their operation, it is often assumed that such pores screen ion-ion interactions like metallic pores, i.e. that screening leads to an exponential decay of the interaction potential with ion separation. By introducing a quantum capacitance that accounts for the density of states in the material, we show that ion-ion interactions in carbon nanotubes and graphene slit pores actually decay algebraically with ion separation. This result suggests a new avenue of capacitance optimization based on tuning the electronic structure of a pore: a marked enhancement in capacitance might be achieved by developing nanopores made with metallic materials or bulk semimetallic materials.

  3. Fused electron deficient semiconducting polymers for air stable electron transport

    KAUST Repository

    Onwubiko, Ada

    2018-01-23

    Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

  4. 14th Conference on "Microscopy of Semiconducting Materials"

    CERN Document Server

    Hutchison, J

    2005-01-01

    This is a long-established international biennial conference series, organised in conjunction with the Royal Microscopical Society, Oxford, the Institute of Physics, London and the Materials Research Society, USA. The 14th conference in the series focused on the most recent advances in the study of the structural and electronic properties of semiconducting materials by the application of transmission and scanning electron microscopy. The latest developments in the use of other important microcharacterisation techniques were also covered and included the latest work using scanning probe microscopy and also X-ray topography and diffraction. Developments in materials science and technology covering the complete range of elemental and compound semiconductors are described in this volume.

  5. Coexistence of negative photoconductivity and hysteresis in semiconducting graphene

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Shendong; Tang, Nujiang; Chen, Zhuo, E-mail: zchen@nju.edu.cn [School of Physics, National Laboratory of Solid State Microstructures, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, No. 22 Hankou Road, Nanjing, Jiangsu, 210093 (China); Chen, Yan; Xia, Yidong [Department of Materials Science and Engineering, National Laboratory of Solid State Microstructures, and Collaborative Innovation Center of Advanced Microstructures, No. 22 Hankou Road, Nanjing University, Nanjing, Jiangsu, 210093 (China); Xu, Xiaoyong; Hu, Jingguo, E-mail: jghu@yzu.edu.cn [School of Physics Science and Technology, Yangzhou University, No. 180 Siwangting Road, Yangzhou, Jiangsu, 225002 (China)

    2016-04-15

    Solution-processed graphene quantum dots (GQDs) possess a moderate bandgap, which make them a promising candidate for optoelectronics devices. However, negative photoconductivity (NPC) and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices. So far, their origins and relations have remained elusive. Here, we investigate experimentally the origins of the NPC and hysteresis in GQDs. By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions, we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture. We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation. Considering the pervasive moisture adsorption, our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices.

  6. Search for Majorana Fermions in Multiband Semiconducting Nanowires

    Science.gov (United States)

    Lutchyn, Roman M.; Stanescu, Tudor D.; Das Sarma, S.

    2011-03-01

    We study multiband semiconducting nanowires proximity-coupled with an s-wave superconductor. We show that, when an odd number of subbands are occupied, the system realizes a nontrivial topological state supporting Majorana modes. We study the topological quantum phase transition in this system and calculate the phase diagram as a function of the chemical potential and magnetic field. Our key finding is that multiband occupancy not only lifts the stringent constraint of one-dimensionality but also allows one to have higher carrier density in the nanowire, and as such multisubband nanowires are better suited for observing the Majorana particle. We study the robustness of the topological phase by including the effects of the short- and long-range disorder. We show that there is an optimal regime in the phase diagram (“sweet spot”) where the topological state is to a large extent insensitive to the presence of disorder.

  7. Coexistence of negative photoconductivity and hysteresis in semiconducting graphene

    Directory of Open Access Journals (Sweden)

    Shendong Zhuang

    2016-04-01

    Full Text Available Solution-processed graphene quantum dots (GQDs possess a moderate bandgap, which make them a promising candidate for optoelectronics devices. However, negative photoconductivity (NPC and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices. So far, their origins and relations have remained elusive. Here, we investigate experimentally the origins of the NPC and hysteresis in GQDs. By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions, we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture. We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation. Considering the pervasive moisture adsorption, our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices.

  8. Imaging heterogeneous ultrafast exciton dynamics in organic semiconducting thin films

    Science.gov (United States)

    Ginsberg, Naomi S.

    2013-03-01

    In solid state semiconducting molecular materials used in electro-optical applications, relatively long exciton diffusion lengths hold the promise to boost device performance by relaxing proximity constraints on the locations for light absorption and interfacial charge separation. The architecture of such materials determines their optical and electronic properties as a result of spacing- and orientation-dependent Coulomb couplings between adjacent molecules. Exciton character and dynamics are generally inferred from bulk optical measurements, which can present a severe limitation on our understanding of these films because their constituent molecules are not perfectly ordered. Rather, films of small organic molecules are composed of multiple microcrystalline domains, and this deposition-dependent microstructure can have profound impacts on transport properties. Using ultrafast transient absorption microscopy, we track the time evolution of excitons, domain by domain, in solid state thin films of TIPS-pentacene, a small soluble molecule that has recently been used in organic semiconducting devices because of its high hole mobility. The results from this spatially-resolved nonlinear optical spectroscopy support our hypothesis that bulk optical measurements deleteriously average over heterogeneities in both spatial and electronic structure; we have revealed significant inhomogeneity in exciton dynamics. Domains that appear homogeneous in linear optical microscopy are shown to have spatial variation and defects, and notable differences in exciton character and behavior are observed at domain boundaries. To interpret the contrast we observe with ultrafast dynamics, we correlate our data to local linear absorption, polarization analysis, profilometry, and atomic force microscopy. With this combined approach, we aim to ultimately understand fundamental structure-function relationship in molecular materials to provide predictive power to material development and device

  9. Heterostructures based on inorganic and organic van der Waals systems

    Directory of Open Access Journals (Sweden)

    Gwan-Hyoung Lee

    2014-09-01

    Full Text Available The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organic-inorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

  10. Analysis of Critical Dimensions for Nanowire Core-Multishell Heterostructures

    OpenAIRE

    Yan, Xin; Fan, Shuyu; Zhang, Xia; Ren, Xiaomin

    2015-01-01

    Critical dimensions for nanowire core-multishell heterostructures are analyzed by using finite-element method based on the energy equilibrium criteria. Results show that the nanowire core-shell heterostructure can sufficiently reduce the strain in the shell and increase the critical shell thickness. The critical dimensions for the nanowire core-multishell heterostructure are determined by the stress fields generated at two heterointerfaces. For thin barrier, the critical dimensions decrease a...

  11. A review of nano-optics in metamaterial hybrid heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mahi R. [Department of Physics and Astronomy, Western University, London N6G 3K7 (Canada)

    2014-03-31

    We present a review for the nonlinear nano-optics in quantum dots doped in a metamaterial heterostructure. The heterostructure is formed by depositing a metamaterial on a dielectric substrate and ensemble of noninteracting quantum dots are doped near the heterostructure interface. It is shown that there is enhancement of the second harmonic generation due to the surface plasmon polaritons field present at the interface.

  12. Nanocrystalline TiO2/SnO2 heterostructures for gas sensing.

    Science.gov (United States)

    Lyson-Sypien, Barbara; Kusior, Anna; Rekas, Mieczylaw; Zukrowski, Jan; Gajewska, Marta; Michalow-Mauke, Katarzyna; Graule, Thomas; Radecka, Marta; Zakrzewska, Katarzyna

    2017-01-01

    The aim of this research is to study the role of nanocrystalline TiO2/SnO2 n-n heterojunctions for hydrogen sensing. Nanopowders of pure SnO2, 90 mol % SnO2/10 mol % TiO2, 10 mol % SnO2/90 mol % TiO2 and pure TiO2 have been obtained using flame spray synthesis (FSS). The samples have been characterized by BET, XRD, SEM, HR-TEM, Mössbauer effect and impedance spectroscopy. Gas-sensing experiments have been performed for H2 concentrations of 1-3000 ppm at 200-400 °C. The nanomaterials are well-crystallized, anatase TiO2, rutile TiO2 and cassiterite SnO2 polymorphic forms are present depending on the chemical composition of the powders. The crystallite sizes from XRD peak analysis are within the range of 3-27 nm. Tin exhibits only the oxidation state 4+. The H2 detection threshold for the studied TiO2/SnO2 heterostructures is lower than 1 ppm especially in the case of SnO2-rich samples. The recovery time of SnO2-based heterostructures, despite their large responses over the whole measuring range, is much longer than that of TiO2-rich samples at higher H2 flows. TiO2/SnO2 heterostructures can be intentionally modified for the improved H2 detection within both the small (1-50 ppm) and the large (50-3000 ppm) concentration range. The temperature Tmax at which the semiconducting behavior begins to prevail upon water desorption/oxygen adsorption depends on the TiO2/SnO2 composition. The electrical resistance of sensing materials exhibits a power-law dependence on the H2 partial pressure. This allows us to draw a conclusion about the first step in the gas sensing mechanism related to the adsorption of oxygen ions at the surface of nanomaterials.

  13. Nanocrystalline TiO2/SnO2 heterostructures for gas sensing

    Directory of Open Access Journals (Sweden)

    Barbara Lyson-Sypien

    2017-01-01

    Full Text Available The aim of this research is to study the role of nanocrystalline TiO2/SnO2 n–n heterojunctions for hydrogen sensing. Nanopowders of pure SnO2, 90 mol % SnO2/10 mol % TiO2, 10 mol % SnO2/90 mol % TiO2 and pure TiO2 have been obtained using flame spray synthesis (FSS. The samples have been characterized by BET, XRD, SEM, HR-TEM, Mössbauer effect and impedance spectroscopy. Gas-sensing experiments have been performed for H2 concentrations of 1–3000 ppm at 200–400 °C. The nanomaterials are well-crystallized, anatase TiO2, rutile TiO2 and cassiterite SnO2 polymorphic forms are present depending on the chemical composition of the powders. The crystallite sizes from XRD peak analysis are within the range of 3–27 nm. Tin exhibits only the oxidation state 4+. The H2 detection threshold for the studied TiO2/SnO2 heterostructures is lower than 1 ppm especially in the case of SnO2-rich samples. The recovery time of SnO2-based heterostructures, despite their large responses over the whole measuring range, is much longer than that of TiO2-rich samples at higher H2 flows. TiO2/SnO2 heterostructures can be intentionally modified for the improved H2 detection within both the small (1–50 ppm and the large (50–3000 ppm concentration range. The temperature Tmax at which the semiconducting behavior begins to prevail upon water desorption/oxygen adsorption depends on the TiO2/SnO2 composition. The electrical resistance of sensing materials exhibits a power-law dependence on the H2 partial pressure. This allows us to draw a conclusion about the first step in the gas sensing mechanism related to the adsorption of oxygen ions at the surface of nanomaterials.

  14. Effects of energetic ion irradiation on WSe2/SiC heterostructures.

    Science.gov (United States)

    Shi, Tan; Walker, Roger C; Jovanovic, Igor; Robinson, Joshua A

    2017-06-23

    The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (TMDs) make them promising candidates for next-generation ultrathin, low-power, high-speed electronics. It has been suggested that electronics based upon ultra-thin TMDs may be appropriate for use in high radiation environments such as space. Here, we present the effects of irradiation by protons, iron, and silver ions at MeV-level energies on a WSe2/6H-SiC vertical heterostructure studied using XPS and UV-Vis-NIR spectroscopy. It was found that with 2 MeV protons, a fluence of 10(16) protons/cm(2) was necessary to induce a significant charge transfer from SiC to WSe2, where a reduction of valence band offset was observed. Simultaneously, a new absorption edge appeared at 1.1 eV below the conduction band of SiC. The irradiation with heavy ions at 10(16) ions/cm(2) converts WSe2 into a mixture of WOx and Se-deficient WSe2. The valence band is also heavily altered due to oxidation and amorphization. However, these doses are in excess of the doses needed to damage TMD-based electronics due to defects generated in common dielectric and substrate materials. As such, the radiation stability of WSe2-based electronics is not expected to be limited by the radiation hardness of WSe2, but rather by the dielectric and substrate.

  15. Thermal response in van der Waals heterostructures

    KAUST Repository

    Gandi, Appala

    2016-11-21

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation. © 2016 IOP Publishing Ltd.

  16. Phonon engineering in proximity enhanced superconductor heterostructures.

    Science.gov (United States)

    Tang, Yong-Chao; Kwon, Sangil; Mohebbi, Hamid R; Cory, David G; Miao, Guo-Xing

    2017-06-27

    In this research, we tailor the phonon density of states (DOS) in thin superconducting films to suppress quasiparticle losses. We examine a model system of a proximity-enhanced three-layered Al/Nb/Al heterostructure and show that the local quantized phonon spectrum of the ultrathin Al cladding layers in the heterostructure has a pronounced effect on the superconducting resonator's quality factors. Instead of a monotonic increase of quality factors with decreasing temperatures, we observe the quality factor reaches a maximum at 1.2 K in 5/50/5 nm Al/Nb/Al microstrip resonators, because of a quantized phonon ladder. The phonon DOS may be engineered to enhance the performance of quantum devices.

  17. Electrical and optoelectrical monolithically integrated circuits on InP based heterostructures; Elektrische und optoelektrische monolithisch integrierte Schaltungen auf InP-basierenden Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Hodel, U.

    2001-03-01

    A key element in long distance data communication systems is the optoelectrical detector system for light with a wavelength between 1.3 {mu}m and 1.55 {mu}m, the dispersion and absorption minimum of a typical glasfiber. In this thesis InP-based heterostructures for integrating high frequency photodetectors and transistors for applications in data communication systems have been investigated. Rf-optimized pseudomorphic HEMTs have been produced on an InAlAs/InGaAs layer system and characterized. The addition of an InGaAs absorption layer to the HEMT layer system allows the production of transistors and photodetectors in parallel. The influence of the additional layer on the performance of the photodetectors and the transistors was investigated and the properties of the layer system has been optimized so that both devices still show a good high frequency performance. To demonstrate the capability for a monolithical integration a photoreceiver, consisting of an MSM-photodiode and a traveling wave amplifier with two HEMTS has been produced. The optoelectrical circuit reached a bandwidth of 13.5 GHz and a response of 0.7 A/W. It has been shown that the presented InGaAs/InAlAs layer system with an additional absorption layer provides a solution for a monolithical integration of MSM photodiodes and HEMTs. A demonstration circuit showed results comparable to existing solutions for integrating photodetectors with HEMTs while minimizing the technological effort. (orig.)

  18. Proximity coupling in superconductor-graphene heterostructures

    OpenAIRE

    Lee, Gil-Ho; Lee, Hu-Jong

    2017-01-01

    This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene...

  19. Voltage control of magnetism in multiferroic heterostructures.

    Science.gov (United States)

    Liu, Ming; Sun, Nian X

    2014-02-28

    Electrical tuning of magnetism is of great fundamental and technical importance for fast, compact and ultra-low power electronic devices. Multiferroics, simultaneously exhibiting ferroelectricity and ferromagnetism, have attracted much interest owing to the capability of controlling magnetism by an electric field through magnetoelectric (ME) coupling. In particular, strong strain-mediated ME interaction observed in layered multiferroic heterostructures makes it practically possible for realizing electrically reconfigurable microwave devices, ultra-low power electronics and magnetoelectric random access memories (MERAMs). In this review, we demonstrate this remarkable E-field manipulation of magnetism in various multiferroic composite systems, aiming at the creation of novel compact, lightweight, energy-efficient and tunable electronic and microwave devices. First of all, tunable microwave devices are demonstrated based on ferrite/ferroelectric and magnetic-metal/ferroelectric composites, showing giant ferromagnetic resonance (FMR) tunability with narrow FMR linewidth. Then, E-field manipulation of magnetoresistance in multiferroic anisotropic magnetoresistance and giant magnetoresistance devices for achieving low-power electronic devices is discussed. Finally, E-field control of exchange-bias and deterministic magnetization switching is demonstrated in exchange-coupled antiferromagnetic/ferromagnetic/ferroelectric multiferroic hetero-structures at room temperature, indicating an important step towards MERAMs. In addition, recent progress in electrically non-volatile tuning of magnetic states is also presented. These tunable multiferroic heterostructures and devices provide great opportunities for next-generation reconfigurable radio frequency/microwave communication systems and radars, spintronics, sensors and memories.

  20. Strain engineering of van der Waals heterostructures.

    Science.gov (United States)

    Vermeulen, Paul A; Mulder, Jefta; Momand, Jamo; Kooi, Bart J

    2018-01-18

    Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS2, and Bi2Te3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals interfaces. Here we present direct observations of the contrary by showing growth of vdWaals heterostructures with persistent in-plane strains up to 5% and we show that strain relaxation follows a not yet reported process distinctly different from strain relaxation in three-dimensionally bonded (3D) materials. For this, 2D bonded Bi2Te3-Sb2Te3 and 2D/3D bonded Bi2Te3-GeTe multilayered films are grown using Pulsed Laser Deposition (PLD) and their structure is monitored in situ using Reflective High Energy Electron Diffraction (RHEED) and post situ analysis is performed using Transmission Electron Microscopy (TEM). Strain relaxation is modeled and found to solely depend on the layer being grown and its initial strain. This insight demonstrates that strain engineering of 2D bonded heterostructures obeys different rules than hold for epitaxial 3D materials and opens the door to precise tuning of the strain state of the individual layers to optimize functional performance of vdWaals heterostructures.

  1. Electroluminescence from chirality-sorted (9,7)-semiconducting carbon nanotube devices

    National Research Council Canada - National Science Library

    Pfeiffer, Martin H P; Stürzl, Ninette; Marquardt, Christoph W; Engel, Michael; Dehm, Simone; Hennrich, Frank; Kappes, Manfred M; Lemmer, Uli; Krupke, Ralph

    2011-01-01

    We have measured the electroluminescence and photoluminescence of (9,7)-semiconducting carbon nanotube devices and demonstrate that the electroluminescence wavelength is determined by the nanotube's chiral index (n,m...

  2. Organic small molecule semiconducting chromophores for use in organic electronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Welch, Gregory C.; Hoven, Corey V.; Nguyen, Thuc-Quyen

    2018-02-13

    Small organic molecule semi-conducting chromophores containing a pyridalthiadiazole, pyridaloxadiazole, or pyridaltriazole core structure are disclosed. Such compounds can be used in organic heterojunction devices, such as organic small molecule solar cells and transistors.

  3. Biomedical Detection via Macro- and Nano-Sensors Fabricated with Metallic and Semiconducting Oxides

    OpenAIRE

    Hahm, Jong-In

    2013-01-01

    Originally developed as gas sensors, the benefits of metallic and semiconducting oxide materials are now being realized in other areas of sensing, such as chemical, environmental, and biomedical monitoring and detection. Metallic and semiconducting oxides have continuously expanded their roles to date, and have also established their significance in biosensing by utilizing a variety of modes for signal generation and detection mechanism. These sensors are typically based either on their optic...

  4. Structural Distortion Stabilizing the Antiferromagnetic and Semiconducting Ground State of BaMn2As2

    Directory of Open Access Journals (Sweden)

    Ekkehard Krüger

    2016-09-01

    Full Text Available We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn 2 As 2 are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn 2 As 2 . In addition, we find that a (small tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally.

  5. Influence of the electric polarization on carrier transport and recombinaton dynamics in ZnO-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, Matthias

    2010-08-16

    The present thesis deals with the influence of the electric polarization on properties of free carriers in ZnO-based semiconductor heterostructures. Thereby especially transport properties of free carriers as well as their recombination dynamics are studied. The thesis treats four main topics. The first main topic lies on the phsical properties of the applied materials, here the connection of the band gap and the lattice constant of thin Mg{sub x}Zn{sub 1-x}O films and their magnesium content is described. Furthermore the morphology of such films is discussed. Different substrates and deposition conditions are thereby detailedly considered. The second main topic treats the properties of undoped and phosphorus doped thin ZnO and Mg{sub x}Zn{sub 1-x}O films. The structural, transport, and luminescence properties are here compared and conclusions drawn on the growth conditions. In the third main topic quantum effects on ZnO/Mg{sub x}Zn{sub 1-x}O interfaces are treated. Hereby especially the influence of the electric polarization is considered. The presence of a two-dimensional electron gas is proved, and the necessary conditions for the generation of the so-called confined Stark effect are explained. Especially the growth-relevant parameters are considered. The fourth main topic represent coupling phenomena in ZnO/BaTiO{sub 3} heterostructures. Thereby first the experimentally observed properties of different heterostructures are shown, which were grown on different substrates. Here structural and transport properties hold the spotlight. A model for the description of the formation of space-charge zones in such heterostructures is introduced and applied for the description of the experimental results. The usefulness of the ferroelectric properties of the material BaTiO{sub 3} in combination with semiconducting ZnO were studied. For this ferroelectric field effect transistors were fabricated under application of both materials. The principle suitedness of the

  6. Failure mechanisms and electromechanical coupling in semiconducting nanowires

    Directory of Open Access Journals (Sweden)

    Peng B.

    2010-06-01

    Full Text Available One dimensional nanostructures, like nanowires and nanotubes, are increasingly being researched for the development of next generation devices like logic gates, transistors, and solar cells. In particular, semiconducting nanowires with a nonsymmetric wurtzitic crystal structure, such as zinc oxide (ZnO and gallium nitride (GaN, have drawn immense research interests due to their electromechanical coupling. The designing of the future nanowire-based devices requires component-level characterization of individual nanowires. In this paper, we present a unique experimental set-up to characterize the mechanical and electromechanical behaviour of individual nanowires. Using this set-up and complementary atomistic simulations, mechanical properties of ZnO nanowires and electromechanical properties of GaN nanowires were investigated. In ZnO nanowires, elastic modulus was found to depend on nanowire diameter decreasing from 190 GPa to 140 GPa as the wire diameter increased from 5 nm to 80 nm. Inconsistent failure mechanisms were observed in ZnO nanowires. Experiments revealed a brittle fracture, whereas simulations using a pairwise potential predicted a phase transformation prior to failure. This inconsistency is addressed in detail from an experimental as well as computational perspective. Lastly, in addition to mechanical properties, preliminary results on the electromechanical properties of gallium nitride nanowires are also reported. Initial investigations reveal that the piezoresistive and piezoelectric behaviour of nanowires is different from bulk gallium nitride.

  7. Meso-/Nanoporous Semiconducting Metal Oxides for Gas Sensor Applications

    Directory of Open Access Journals (Sweden)

    Nguyen Duc Hoa

    2015-01-01

    Full Text Available Development and/or design of new materials and/or structures for effective gas sensor applications with fast response and high sensitivity, selectivity, and stability are very important issues in the gas sensor technology. This critical review introduces our recent progress in the development of meso-/nanoporous semiconducting metal oxides and their applications to gas sensors. First, the basic concepts of resistive gas sensors and the recent synthesis of meso-/nanoporous metal oxides for gas sensor applications are introduced. The advantages of meso-/nanoporous metal oxides are also presented, taking into account the crystallinity and ordered/disordered porous structures. Second, the synthesis methods of meso-/nanoporous metal oxides including the soft-template, hard-template, and temple-free methods are introduced, in which the advantages and disadvantages of each synthetic method are figured out. Third, the applications of meso-/nanoporous metal oxides as gas sensors are presented. The gas nanosensors are designed based on meso-/nanoporous metal oxides for effective detection of toxic gases. The sensitivity, selectivity, and stability of the meso-/nanoporous gas nanosensors are also discussed. Finally, some conclusions and an outlook are presented.

  8. Gas Sensors Based on Semiconducting Nanowire Field-Effect Transistors

    Directory of Open Access Journals (Sweden)

    Ping Feng

    2014-09-01

    Full Text Available One-dimensional semiconductor nanostructures are unique sensing materials for the fabrication of gas sensors. In this article, gas sensors based on semiconducting nanowire field-effect transistors (FETs are comprehensively reviewed. Individual nanowires or nanowire network films are usually used as the active detecting channels. In these sensors, a third electrode, which serves as the gate, is used to tune the carrier concentration of the nanowires to realize better sensing performance, including sensitivity, selectivity and response time, etc. The FET parameters can be modulated by the presence of the target gases and their change relate closely to the type and concentration of the gas molecules. In addition, extra controls such as metal decoration, local heating and light irradiation can be combined with the gate electrode to tune the nanowire channel and realize more effective gas sensing. With the help of micro-fabrication techniques, these sensors can be integrated into smart systems. Finally, some challenges for the future investigation and application of nanowire field-effect gas sensors are discussed.

  9. Engineering the Kondo state in two-dimensional semiconducting phosphorene

    Science.gov (United States)

    Babar, Rohit; Kabir, Mukul

    2018-01-01

    Correlated interaction between dilute localized impurity electrons and the itinerant host conduction electrons in metals gives rise to the conventional many-body Kondo effect below sufficiently low temperature. In sharp contrast to these conventional Kondo systems, we report an intrinsic, robust, and high-temperature Kondo state in two-dimensional semiconducting phosphorene. While absorbed at a thermodynamically stable lattice defect, Cr impurity triggers an electronic phase transition in phosphorene to provide conduction electrons, which strongly interact with the localized moment generated at the Cr site. These manifest into the intrinsic Kondo state, where the impurity moment is quenched in multiple stages and at temperatures in the 40-200 K range. Further, along with a much smaller extension of the Kondo cloud, the predicted Kondo state is shown to be robust under uniaxial strain and layer thickness, which greatly simplifies its future experimental realization. We predict the present study will open up new avenues in Kondo physics and trigger further theoretical and experimental studies.

  10. Advanced Branching Control and Characterization of Inorganic Semiconducting Nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Steven Michael [Univ. of California, Berkeley, CA (United States)

    2007-01-01

    The ability to finely tune the size and shape of inorganic semiconducting nanocrystals is an area of great interest, as the more control one has, the more applications will be possible for their use. The first two basic shapes develped in nanocrystals were the sphere and the anistropic nanorod. the II_VI materials being used such as Cadmium Selenide (CdSe) and Cadmium Telluride (CdTe), exhibit polytypism, which allows them to form in either the hexagonally packed wurtzite or cubically packed zinc blende crystalline phase. The nanorods are wurtzite with the length of the rod growing along the c-axis. As this grows, stacking faults may form, which are layers of zinc blende in the otherwise wurtzite crystal. Using this polytypism, though, the first generation of branched crystals were developed in the form of the CdTe tetrapod. This is a nanocrystal that nucleates in the zincblend form, creating a tetrahedral core, on which four wurtzite arms are grown. This structure opened up the possibility of even more complex shapes and applications. This disseration investigates the advancement of branching control and further understanding the materials polytypism in the form of the stacking faults in nanorods.

  11. Gas Sensors Based on Semiconducting Nanowire Field-Effect Transistors

    Science.gov (United States)

    Feng, Ping; Shao, Feng; Shi, Yi; Wan, Qing

    2014-01-01

    One-dimensional semiconductor nanostructures are unique sensing materials for the fabrication of gas sensors. In this article, gas sensors based on semiconducting nanowire field-effect transistors (FETs) are comprehensively reviewed. Individual nanowires or nanowire network films are usually used as the active detecting channels. In these sensors, a third electrode, which serves as the gate, is used to tune the carrier concentration of the nanowires to realize better sensing performance, including sensitivity, selectivity and response time, etc. The FET parameters can be modulated by the presence of the target gases and their change relate closely to the type and concentration of the gas molecules. In addition, extra controls such as metal decoration, local heating and light irradiation can be combined with the gate electrode to tune the nanowire channel and realize more effective gas sensing. With the help of micro-fabrication techniques, these sensors can be integrated into smart systems. Finally, some challenges for the future investigation and application of nanowire field-effect gas sensors are discussed. PMID:25232915

  12. Synthesis and spectroscopic properties of a soluble semiconducting porphyrin polymer.

    Science.gov (United States)

    Schmitz, Robert A; Liddell, Paul A; Kodis, Gerdenis; Kenney, Michael J; Brennan, Bradley J; Oster, Nolan V; Moore, Thomas A; Moore, Ana L; Gust, Devens

    2014-09-07

    A semiconducting porphyrin polymer that is solution processable and soluble in organic solvents has been synthesized, and its spectroscopic and electrochemical properties have been investigated. The polymer consists of diarylporphyrin units that are linked at meso-positions by aminophenyl groups, thus making the porphyrin rings an integral part of the polymer backbone. Hexyl chains on two of the aryl groups impart solubility. The porphyrin units interact only weakly in the ground electronic state. Excitation produces a local excited state that rapidly evolves into a state with charge-transfer character (CT) involving the amino nitrogen and the porphyrin macrocycle. Singlet excitation energy is transferred between porphyrin units in the chain with a time constant of ca. 210 ps. The final CT state has a lifetime of several nanoseconds, and the first oxidation of the polymer occurs at ca. 0.58 V vs. SCE. These properties make the polymer a suitable potential excited state electron donor to a variety of fullerenes or other acceptor species, suggesting that the polymer may find use in organic photovoltaics, sensors, and similar applications.

  13. Nanochannel-directed growth of multi-segment nanowire heterojunctions of metallic Au(1-x)Ge(x) and semiconducting Ge.

    Science.gov (United States)

    Li, Xiangdong; Meng, Guowen; Qin, Shengyong; Xu, Qiaoling; Chu, Zhaoqin; Zhu, Xiaoguang; Kong, Mingguang; Li, An-Ping

    2012-01-24

    We report on the synthesis of multi-segment nanowire (NW) junctions of Au(1-x)Ge(x) and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au(1-x)Ge(x)/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au(1-x)Ge(x)NW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au(1-x)Ge(x) segments, respectively. The high yield of multiple segment NW junctions of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces. © 2011 American Chemical Society

  14. Nanochannel-Directed Growth of One-Dimensional Multi-Segment Heterojunctions of Metallic Au1-xGex and Semiconducting Ge

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiangdong [Chinese Academy of Sciences; Meng, Guowen [Chinese Academy of Sciences; Qin, Shengyong [ORNL; Xu, Qiaoling [Chinese Academy of Sciences; Chu, Zhaoqin [Chinese Academy of Sciences; Zhu, Xiaoguang [Chinese Academy of Sciences; Kong, Mingguang [Chinese Academy of Sciences; Li, An-Ping [ORNL

    2012-01-01

    We report on the synthesis of multi-segment nanowire (NW) junctions of Au{sub 1-x}Ge{sub x} and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au{sub 1-x}Ge{sub x}/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au{sub 1-x}Ge{sub x}NW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au{sub 1-x}Ge{sub x} segments, respectively. The high yield of multiple segment NW junctions of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces.

  15. Flow induced/ refined solution crystallization of a semiconducting polymer

    Science.gov (United States)

    Nguyen, Ngoc A.

    Organic photovoltaics, a new generation of solar cells, has gained scientific and economic interests due to the ability of solution-processing and potentially low-cost power production. Though, the low power conversion efficiency of organic/ plastic solar cells is one of the most pertinent challenges that has appealed to research communities from many different fields including materials science and engineering, electrical engineering, chemical engineering, physics and chemistry. This thesis focuses on investigating and controlling the morphology of a semi-conducting, semi-crystalline polymer formed under shear-flow. Molecular structures and processing techniques are critical factors that significantly affect the morphology formation in the plastic solar cells, thus influencing device performance. In this study, flow-induced solution crystallization of poly (3-hexylthiophene) (P3HT) in a poor solvent, 2-ethylnapthalene (2-EN) was utilized to make a paint-like, structural liquid. The polymer crystals observed in this structured paint are micrometers long, nanometers in cross section and have a structure similar to that formed under quiescent conditions. There is pi-pi stacking order along the fibril axis, while polymer chain folding occurs along the fibril width and the order of the side-chain stacking is along fibril height. It was revealed that shear-flow not only induces P3HT crystallization from solution, but also refines and perfects the P3HT crystals. Thus, a general strategy to refine the semiconducting polymer crystals from solution under shear-flow has been developed and employed by simply tuning the processing (shearing) conditions with respect to the dissolution temperature of P3HT in 2-EN. The experimental results demonstrated that shear removes defects and allows more perfect crystals to be formed. There is no glass transition temperature observed in the crystals formed using the flow-induced crystallization indicating a significantly different

  16. Fabrication and characterization of semiconducting nanowires for tunnel field transistors

    Science.gov (United States)

    Vallett, Aaron Lee

    The scaling of traditional metal-oxide-semiconductor field-effect transistors (MOSFETs) is hitting a limit, not due to difficulties in fabricating short gate lengths, but rather to an ongoing power crisis. As channel lengths have been reduced power densities of integrated circuits have risen dramatically. While supply voltage scaling would alleviate many power concerns, the MOSFET structure fundamentally limits the amount that voltages can be reduced. Because MOSFET operation is governed by thermal emission of carriers over a potential barrier, the subthreshold swing from the off to on current is limited to a minimum of 60 mV/decade of current. Therefore, reductions in the supply voltage will degrade the on/off current ratio. The tunnel field-effect transistor (TFET) has emerged as a potential solution to these problems. Current is controlled by band-to-band tunneling through a barrier that is modulated by the gate, and subthreshold swings below 60 mV/dec. can be achieved. While TFET simulations are quite promising, subthreshold swings below 60 mV/dec. at technically relevant on-currents have yet to be demonstrated experimentally. Nanowire geometries and III-V semiconductor channel materials are predicted to improve TFET performance by increasing gate control and tunneling current. In this dissertation the fabrication of TFETs from semiconducting nanowires will be investigated. First, axially doped silicon (Si) nanowire in situ p-n junctions will be studied. By controlling the nanowire growth, separate p and n-type segments can be formed to create a rectifying junction. While as-grown nanowire junctions do not have the abruptness necessary to facilitate band-to-band tunneling, thermally oxidized nanowires are shown to have a p-n-n+ profile with an abrupt n-n+ junction. By gating the nanowires an abrupt electrostatically-doped p +- n+ junction can be formed that permits reverse-biased tunneling. These p-n-n+ nanowires will be integrated into a top-gated lateral TFET

  17. Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors

    Science.gov (United States)

    Datta, Kanak; Shadman, Abir; Rahman, Ehsanur; Khosru, Quazi D. M.

    2017-02-01

    Two dimensional materials such as transition metal dichalcogenides (TMDC) and their bi-layer/tri-layer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M = Mo or, W and X = S or, Se) metal oxide semiconductor field effect transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device `on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate field effect transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.

  18. Improving carrier injection in colloidal CdSe nanocrystals by embedding them in a pseudomorphic ZnSe/ZnMgSe quantum well structure

    Science.gov (United States)

    Larramendi, E. M.; Schöps, O.; Artemyev, M. V.; Schikora, D.; Lischka, K.; Woggon, U.

    2013-11-01

    The incorporation of colloidal nanocrystals in a high crystalline quality semiconductor matrix, the efficient carrier injection into the embedded nanocrystals and the fast optical response are key features for the fabrication of novel optoelectronic nanodevices based on colloidal nanostructures as active optical material. Using a novel growth approach, colloidal bare CdSe and core-shell CdSe/ZnS nanocrystals were monolithically incorporated in pseudomorphic ZnSe/ZnMgSe quantum wells in order to control and enhance the carrier transfer into the nanocrystals. The photoluminescence for bare CdSe nanocrystals incorporated in ZnSe/ZnMgSe quantum well structures is substantially enhanced in comparison to nanocrystals sandwiched in ZnSe epilayers, which we attribute to increased carrier injection into the embedded nanocrystals via the quantum well, resembling the function of a wetting layer in Stranski-Krastanov-grown quantum dots. Core-shell CdSe/ZnS nanocrystals embedded in quantum well structures do not show considerable PL modifications because the ZnS shell prevents the efficient carrier migration between the nanocrystal and the matrix. Systematic investigations of structural and optical properties by high-resolution x-ray diffraction, temperature-dependent photoluminescence and time-resolved emission are presented.

  19. Magnetotransport measurements on modulation Si {delta}-doped pseudomorphic In{sub 0.2}Ga{sub 0.8}As/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, A.; Li, G.; Jagadish, C. [The Australian National University, ACT (Australia). Institute of Advanced Studies, Research School of Physical Sciences and Engineering, Department of Electronic Materials Engineering

    1998-07-01

    The effect of doping concentration on electrical properties of Si {delta}-doped pseudomorphic In{sub 0} {sub .2}Ga{sub 0.} {sub 8}As/GaAs quantum wells (QWs) was examined in this work. Magnetotransport measurements were carried out in the magnetic fields up to 12 T in the dark at the temperature of T=1.7 K. The results were analysed using the fast Fourier transform (FFT). It was found that one electron subband was occupied in the QW with the doping concentrations of 2.3 x 10{sup 12} or 6.0 x 10{sup 12} cm{sup -2}. The parallel conduction was present in both samples, which increased with an increase of Si {delta}-doping concentration. The well-developed plateaus arising from the quantised Hall effect were observed in the Si {delta}-doped In{sub 0.} {sub 2}Ga{sub 0.} {sub 8}As/GaAs QW with reduced parallel conduction. The two subbands remain occupied within the V-shaped potential well formed at the Si doping plane when the Si {delta}-doping concentration was high. The results of measurements in tilted magnetic fields, confirming the attribution of FFT peaks to the particular 2DEG systems, are also presented.

  20. Room- and low-temperature assessment of pseudomorphic AlGaAs/InGaAs/GaAS high-electron-mobility transistor structures by photoluminescence spectroscopy

    Science.gov (United States)

    Gilperez, J. M.; Sanchez-Rojas, J. L.; Munoz, E.; Calleja, E.; David, J. P. R.; Reddy, M.; Hill, G.; Sanchez-Dehesa, J.

    1994-11-01

    The use of room- and low-temperature photoluminescence (PL) spectroscopy for the assessment of n-type pseudomorphic AlGaAs/InGaAs/GaAs high-electron-mobility transistor stransitor structures is reported. We describe a method to determine the InAs mole fraction x, the channel layer thickness L, and the confined two-dimensional electron gas density (n(sub s)), based on the comparison between the PL transitions and the recombination energies derived from self-consistent calculations of the subband structure. A detailed analysis of the optical transitions and their dependence on the Fermi level position and temperature is performed. It is shown that, in real devices, the high sensitivity of the recombination energies and intensities on small changes of the parameters x, L, and n(sub s) allows us to detect deviations from their nominal structural parameters within the uncertainty of the molecular beam epitaxy growth technique. The present assessment procedure has been applied to a significant number of samples, and it has been backed by independent measurements of these parameters by more sophisticated techniques such as Shubnikov-de Haas and PL excitation in standard and gated samples, and by physical techniques like transmission electron microscopy and Auger spectroscopy.

  1. Charged-particle spectroscopy in organic semiconducting single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ciavatti, A.; Basiricò, L.; Fraboni, B. [Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna (Italy); Sellin, P. J. [Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Fraleoni-Morgera, A. [ELETTRA-Sincrotrone Trieste, Strada Statale 14, Km 163.5, Basovizza, Trieste (Italy); Department of Engineering and Architecture, University of Trieste, V. Valerio 10, 34100 Trieste (Italy); CNR-Nano S3 Institute, Via Campi 213/A, 41125 Modena (Italy)

    2016-04-11

    The use of organic materials as radiation detectors has grown, due to the easy processability in liquid phase at room temperature and the possibility to cover large areas by means of low cost deposition techniques. Direct charged-particle detectors based on solution-grown Organic Semiconducting Single Crystals (OSSCs) are shown to be capable to detect charged particles in pulse mode, with very good peak discrimination. The direct charged-particle detection in OSSCs has been assessed both in the planar and in the vertical axes, and a digital pulse processing algorithm has been used to perform pulse height spectroscopy and to study the charge collection efficiency as a function of the applied bias voltage. Taking advantage of the charge spectroscopy and the good peak discrimination of pulse height spectra, an Hecht-like behavior of OSSCs radiation detectors is demonstrated. It has been possible to estimate the mobility-lifetime value in organic materials, a fundamental parameter for the characterization of radiation detectors, whose results are equal to μτ{sub coplanar} = (5 .5 ± 0.6 ) × 10{sup −6} cm{sup 2}/V and μτ{sub sandwich} = (1 .9 ± 0.2 ) × 10{sup −6} cm{sup 2}/V, values comparable to those of polycrystalline inorganic detectors. Moreover, alpha particles Time-of-Flight experiments have been carried out to estimate the drift mobility value. The results reported here indicate how charged-particle detectors based on OSSCs possess a great potential as low-cost, large area, solid-state direct detectors operating at room temperature. More interestingly, the good detection efficiency and peak discrimination observed for charged-particle detection in organic materials (hydrogen-rich molecules) are encouraging for their further exploitation in the detection of thermal and high-energy neutrons.

  2. Antimonide Heterostructure Nanowires - Growth, Physics and Devices

    OpenAIRE

    Borg, Mattias

    2012-01-01

    This thesis investigates the growth and application of antimonide heterostructure nanowires for low-power electronics. In the first part of the thesis, GaSb, InSb and InAsSb nanowire growth is presented, and the distinguishing features of the growth are described. It is found that the presence of Sb results in more than 50 at. % group-III concentration in the Au seed particle on top of the nanowires. It is further concluded that the effective V/III ratio inside the seed particle is reduced co...

  3. Exciton broadening in WS2/graphene heterostructures

    Science.gov (United States)

    Hill, Heather M.; Rigosi, Albert F.; Raja, Archana; Chernikov, Alexey; Roquelet, Cyrielle; Heinz, Tony F.

    2017-11-01

    We have used optical spectroscopy to observe spectral broadening of WS2 exciton reflectance peaks in heterostructures of monolayer WS2 capped with mono- to few-layer graphene. The broadening is found to be similar for the A and B excitons and on the order of 5-10 meV. No strong dependence on the number of graphene layers was observed within experimental uncertainty. The broadening can be attributed to charge- and energy-transfer processes between the two materials, providing an observed lower bound for the corresponding time scales of 65 fs.

  4. Photoresponse of Natural van der Waals Heterostructures.

    Science.gov (United States)

    Ray, Kyle; Yore, Alexander E; Mou, Tong; Jha, Sauraj; Smithe, Kirby K H; Wang, Bin; Pop, Eric; Newaz, A K M

    2017-06-27

    Van der Waals heterostructures consisting of two-dimensional materials offer a platform to obtain materials by design and are very attractive owing to unique electronic states. Research on 2D van der Waals heterostructures (vdWH) has so far been focused on fabricating individually stacked atomically thin unary or binary crystals. Such systems include graphene, hexagonal boron nitride, and members of the transition metal dichalcogenide family. Here we present our experimental study of the optoelectronic properties of a naturally occurring vdWH, known as franckeite, which is a complex layered crystal composed of lead, tin, antimony, iron, and sulfur. We present here that thin film franckeite (60 nm < d < 100 nm) behaves as a narrow band gap semiconductor demonstrating a wide-band photoresponse. We have observed the band-edge transition at ∼1500 nm (∼830 meV) and high external quantum efficiency (EQE ≈ 3%) at room temperature. Laser-power-resolved and temperature-resolved photocurrent measurements reveal that the photocarrier generation and recombination are dominated by continuously distributed trap states within the band gap. To understand wavelength-resolved photocurrent, we also calculated the optical absorption properties via density functional theory. Finally, we have shown that the device has a fast photoresponse with a rise time as fast as ∼1 ms. Our study provides a fundamental understanding of the optoelectronic behavior in a complex naturally occurring vdWH, and may pave an avenue toward developing nanoscale optoelectronic devices with tailored properties.

  5. Probing charge transfer in a novel class of luminescent perovskite-based heterostructures composed of quantum dots bound to RE-activated CaTiO3 phosphors

    Science.gov (United States)

    Lewis, Crystal S.; Liu, Haiqing; Han, Jinkyu; Wang, Lei; Yue, Shiyu; Brennan, Nicholas A.; Wong, Stanislaus S.

    2016-01-01

    We report on the synthesis and structural characterization of novel semiconducting heterostructures composed of cadmium selenide (CdSe) quantum dots (QDs) attached onto the surfaces of novel high-surface area, porous rare-earth-ion doped alkaline earth titanate micron-scale spherical motifs, i.e. both Eu-doped and Pr-doped CaTiO3, composed of constituent, component nanoparticles. These unique metal oxide perovskite building blocks were created by a multi-pronged synthetic strategy involving molten salt and hydrothermal protocols. Subsequently, optical characterization of these heterostructures indicated a clear behavioral dependence of charge transfer in these systems upon a number of parameters such as the nature of the dopant, the reaction temperature, and particle size. Specifically, 2.7 nm diameter ligand-functionalized CdSe QDs were anchored onto sub-micron sized CaTiO3-based spherical assemblies, prepared by molten salt protocols. We found that both the Pr- and Eu-doped CaTiO3 displayed pronounced PL emissions, with maximum intensities observed using optimized lanthanide concentrations of 0.2 mol% and 6 mol%, respectively. Analogous experiments were performed on Eu-doped BaTiO3 and SrTiO3 motifs, but CaTiO3 still performed as the most effective host material amongst the three perovskite systems tested. Moreover, the ligand-capped CdSe QD-doped CaTiO3 heterostructures exhibited effective charge transfer between the two individual constituent nanoscale components, an assertion corroborated by the corresponding quenching of their measured PL signals.We report on the synthesis and structural characterization of novel semiconducting heterostructures composed of cadmium selenide (CdSe) quantum dots (QDs) attached onto the surfaces of novel high-surface area, porous rare-earth-ion doped alkaline earth titanate micron-scale spherical motifs, i.e. both Eu-doped and Pr-doped CaTiO3, composed of constituent, component nanoparticles. These unique metal oxide perovskite

  6. PREFACE: 18th Microscopy of Semiconducting Materials Conference (MSM XVIII)

    Science.gov (United States)

    Walther, T.; Hutchison, John L.

    2013-11-01

    YRM logo This volume contains invited and contributed papers from the 18th international conference on 'Microscopy of Semiconducting Materials' held at St Catherine's College, University of Oxford, on 7-11 April 2013. The meeting was organised under the auspices of the Royal Microscopical Society and supported by the Institute of Physics as well as the Materials Research Society of the USA. This conference series deals with recent advances in semiconductor studies carried out by all forms of microscopy, with an emphasis on electron microscopy and scanning probe microscopy with high spatial resolution. This time the meeting was attended by 109 delegates from 17 countries world-wide. We were welcomed by Professor Sir Peter Hirsch, who noted that this was the first of these conferences where Professor Tony Cullis was unable to attend, owing to ill-health. During the meeting a card containing greetings from many of Tony's friends and colleagues was signed, and duly sent to Tony afterwards. As semiconductor devices shrink further new routes for device processing and characterisation need to be developed, and, for the latter, methods that offer sub-nanometre spatial resolution are particularly valuable. The various forms of imaging, diffraction and spectroscopy available in modern microscopes are powerful tools for studying the microstructure, electronic structure, chemistry and also electric fields in semiconducting materials. Recent advances in instrumentation, from lens aberration correction in both TEM and STEM instruments, to the development of a wide range of scanning probe techniques, as well as new methods of signal quantification have been presented at this conference. Two topics that have at this meeting again highlighted the interesting contributions of aberration corrected transmission electron microscopy were: contrast quantification of annular dark-field STEM images in terms of chemical composition (Z-contrast), sample thickness and strain, and the study of

  7. Influence of semiconducting properties of nanoparticle coating on the electrochemical actuation of liquid metal marble

    Science.gov (United States)

    Sivan, Vijay; Tang, Shi-Yang; O'Mullane, Anthony P.; Petersen, Phred; Kalantar-zadeh, Kourosh; Khoshmanesh, Khashayar; Mitchell, Arnan

    2014-09-01

    Semiconducting properties of nanoparticle coating on liquid metal marbles can present opportunities for an additional dimension of control on these soft objects with functional surfaces in aqueous environments. We show the unique differences in the electrochemical actuation mechanisms of liquid metal marbles with n- and p-type semiconducting nanomaterial coating. A systematic study on such liquid metal marbles shows voltage dependent nanoparticle cluster formation and morphological changes of the liquid metal core during electrochemical actuations and these observations are unique to p-type nanomaterial coated liquid metal marbles.

  8. Gas Sensors Based on Semiconducting Metal Oxide One-Dimensional Nanostructures

    Directory of Open Access Journals (Sweden)

    Jin Huang

    2009-12-01

    Full Text Available This article provides a comprehensive review of recent (2008 and 2009 progress in gas sensors based on semiconducting metal oxide one-dimensional (1D nanostructures. During last few years, gas sensors based on semiconducting oxide 1D nanostructures have been widely investigated. Additionally, modified or doped oxide nanowires/nanobelts have also been synthesized and used for gas sensor applications. Moreover, novel device structures such as electronic noses and low power consumption self-heated gas sensors have been invented and their gas sensing performance has also been evaluated. Finally, we also point out some challenges for future investigation and practical application.

  9. Modeling carrier density dependent charge transport in semiconducting carbon nanotube networks

    Science.gov (United States)

    Schießl, Stefan P.; de Vries, Xander; Rother, Marcel; Massé, Andrea; Brohmann, Maximilian; Bobbert, Peter A.; Zaumseil, Jana

    2017-09-01

    Charge transport in a network of only semiconducting single-walled carbon nanotubes is modeled as a random-resistor network of tube-tube junctions. Solving Kirchhoff's current law with a numerical solver and taking into account the one-dimensional density of states of the nanotubes enables the evaluation of carrier density dependent charge transport properties such as network mobility, local power dissipation, and current distribution. The model allows us to simulate and investigate mixed networks that contain semiconducting nanotubes with different diameters, and thus different band gaps and conduction band edge energies. The obtained results are in good agreement with available experimental data.

  10. Ge/Si core/multi shell heterostructure FETs

    Energy Technology Data Exchange (ETDEWEB)

    Picraux, Samuel T [Los Alamos National Laboratory; Dayeh, Shadi A [Los Alamos National Laboratory

    2010-01-01

    Concentric heterostructured materials provide numerous design opportunities for engineering strain and interfaces, as well as tailoring energy band-edge combinations for optimal device performance. Key to the realization of such novel device concepts is the complete understanding and full control over their growth, crystal structure, and hetero-epitaxy. We report here on a new route for synthesizing Ge/Si core/multi-shell heterostructure nanowires that eliminate Au seed diffusion on the nanowire sidewalls by engineering the interface energy density difference. We show that such control over core/shell synthesis enable experimental realization of heterostructure FET devices beyond those available in the literature with enhanced transport characteristics. We provide a side-by-side comparison on the transport properties of Ge/Si core/multi-shell nanowires grown with and without Au diffusion and demonstrate heterostructure FETs with drive currents that are {approx} 2X higher than record results for p-type FETs.

  11. Engineering charge transport by heterostructuring solution-processed semiconductors

    Science.gov (United States)

    Voznyy, Oleksandr; Sutherland, Brandon R.; Ip, Alexander H.; Zhitomirsky, David; Sargent, Edward H.

    2017-06-01

    Solution-processed semiconductor devices are increasingly exploiting heterostructuring — an approach in which two or more materials with different energy landscapes are integrated into a composite system. Heterostructured materials offer an additional degree of freedom to control charge transport and recombination for more efficient optoelectronic devices. By exploiting energetic asymmetry, rationally engineered heterostructured materials can overcome weaknesses, augment strengths and introduce emergent physical phenomena that are otherwise inaccessible to single-material systems. These systems see benefit and application in two distinct branches of charge-carrier manipulation. First, they influence the balance between excitons and free charges to enhance electron extraction in solar cells and photodetectors. Second, they promote radiative recombination by spatially confining electrons and holes, which increases the quantum efficiency of light-emitting diodes. In this Review, we discuss advances in the design and composition of heterostructured materials, consider their implementation in semiconductor devices and examine unexplored paths for future advancement in the field.

  12. Magnetic Heterostructures Advances and Perspectives in Spinstructures and Spintransport

    CERN Document Server

    Bader, Samuel D

    2008-01-01

    Magnetic heterostructures constitute an important field in magnetism and nanotechnology, which has developed over the past fifteen years due to important advances in epitaxial- growth techniques and lithographic processes. Magnetic heterostructures combine different physical properties which do not exist in nature. Examples are semiconductors/ferromagnets, superconductors/ferromagnets, and ferromagnets/antiferromagnets. These combinations display rich and novel physical properties different from those that exit in any single one of them. Interlayer exchange coupling, exchange bias, proximity effects, giant magneto-resistance, tunneling magneto-resistance, spininjection and spintransport are examples of new physical phenomena that rely on the combination of different materials layers. Since the literature on magnetic heterostructures is widely spread and highly specialized, the situation calls for a book that provides an overview of the basics and the state of the art of magnetic heterostructures. These contri...

  13. Organic heterostructures deposited by MAPLE on AZO substrate

    Science.gov (United States)

    Socol, M.; Preda, N.; Stanculescu, A.; Breazu, C.; Florica, C.; Stanculescu, F.; Iftimie, S.; Girtan, M.; Popescu-Pelin, G.; Socol, G.

    2017-09-01

    Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence (PL) and current-voltage (I-V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode.

  14. Quantum and field effects of oxide heterostructures

    DEFF Research Database (Denmark)

    Trier, Felix

    . In these multi-plexed devices, several inputs aretranslated into several outputs through the multiple physical functionalities.A highly prominent example of such an oxide interface is the one between LaAlO3 and SrTiO3. Although both LaAlO3 and SrTiO3 in the bulk are electrically insulating and non...... aspects of sample preparation will initially be covered. Here, the growth of amorphous-LaAlO3 on SrTiO3 will be addressed in a modified pulsed laser deposition setup. This is followed by an investigation of two high-electron mobility interfaces in SrTiO3-based heterostructures. Specifically...

  15. Magnetoelectric imaging of multiferroic heterostructures (Presentation Recording)

    Science.gov (United States)

    Ghidini, Massimo; Lesaine, Arnaud; Zhu, Bonan; Moya, Xavier; Yan, Wenjing; Crossley, Sam; Nair, Bhasi; Mansell, Rhodri; Cowburn, Russell P.; Barnes, Crispin H. W.; Kronast, Florian; Valencia, Sergio; Maccherozzi, Francesco; Dhesi, Sarnjeet S.; Mathur, Neil

    2015-09-01

    Electrical control of magnetism has been demonstrated in multiferroic compounds and ferromagnetic semiconductors, but electrical switching of a substantial net magnetization at room temperature has not been demonstrated in these materials. This goal has instead been achieved in heterostructures comprising ferromagnetic films in which electrically driven magnetic changes arise due to strain or exchange bias from ferroic substrates, or due to charge effects induced by a gate. However, previous work focused on electrical switching of an in-plane magnetization or involved the assistance of applied magnetic fields. In heterostructures made of juxtaposed ferroelectric and ferromagnetic layers, we have shown electrical control with no applied magnetic field of the perpendicular magnetization of small features [1] and of magnetic stripe domains patterns [2]. Here we investigate Ni81Fe19 films on ferroelectric substrates with and without buffer layers of Cu, whose presence precludes charge-mediated coupling. Ni81Fe19 has virtually zero magnetostriction, but sufficiently thin films show large magnetostriction, and thus, on increasing film thickness through the threshold for zero magnetostriction, we have seeked the crossover from charge- to strain-mediated coupling. We will then show that strain associated with the motion of 90°- ferroelectric domain walls in a BaTiO3 substrate, can switch the magnetization of an array of overlying single-domain Ni dots. [1] M. Ghidini, R. Pellicelli, J. L. Prieto, X. Moya, J. Soussi, J. Briscoe, S. Dunn and N. D. Mathur, Nature Communications 4 (2013) 1453. [2] M. Ghidini, F.Maccherozzi, X. Moya, L. C. Phillips, W.Yan, J. Soussi, N. Métallier, M.Vickers, , N. -J.Steinke, R. Mansell, C. H. W. Barnes, S. S. Dhesi, and N. D. Mathur, Adv. Mater.doi: 10.1002/adma.201404799 (2015).

  16. Planar heterostructures of single-layer transition metal dichalcogenides: Composite structures, Schottky junctions, tunneling barriers, and half metals

    Science.gov (United States)

    Aras, Mehmet; Kılıç, ćetin; Ciraci, S.

    2017-02-01

    Planar composite structures formed from the stripes of transition metal dichalcogenides joined commensurately along their zigzag or armchair edges can attain different states in a two-dimensional (2D), single-layer, such as a half metal, 2D or one-dimensional (1D) nonmagnetic metal and semiconductor. Widening of stripes induces metal-insulator transition through the confinements of electronic states to adjacent stripes, that results in the metal-semiconductor junction with a well-defined band lineup. Linear bending of the band edges of the semiconductor to form a Schottky barrier at the boundary between the metal and semiconductor is revealed. Unexpectedly, strictly 1D metallic states develop in a 2D system along the boundaries between stripes, which pins the Fermi level. Through the δ doping of a narrow metallic stripe one attains a nanowire in the 2D semiconducting sheet or narrow band semiconductor. A diverse combination of constituent stripes in either periodically repeating or finite-size heterostructures can acquire critical fundamental features and offer device capacities, such as Schottky junctions, nanocapacitors, resonant tunneling double barriers, and spin valves. These predictions are obtained from first-principles calculations performed in the framework of density functional theory.

  17. Fabrication of poly(methyl methacrylate)-MoS{sub 2}/graphene heterostructure for memory device application

    Energy Technology Data Exchange (ETDEWEB)

    Shinde, Sachin M.; Tanemura, Masaki [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

    2014-12-07

    Combination of two dimensional graphene and semi-conducting molybdenum disulfide (MoS{sub 2}) is of great interest for various electronic device applications. Here, we demonstrate fabrication of a hybridized structure with the chemical vapor deposited graphene and MoS{sub 2} crystals to configure a memory device. Elongated hexagonal and rhombus shaped MoS{sub 2} crystals are synthesized by sulfurization of thermally evaporated molybdenum oxide (MoO{sub 3}) thin film. Scanning transmission electron microscope studies reveal atomic level structure of the synthesized high quality MoS{sub 2} crystals. In the prospect of a memory device fabrication, poly(methyl methacrylate) (PMMA) is used as an insulating dielectric material as well as a supporting layer to transfer the MoS{sub 2} crystals. In the fabricated device, PMMA-MoS{sub 2} and graphene layers act as the functional and electrode materials, respectively. Distinctive bistable electrical switching and nonvolatile rewritable memory effect is observed in the fabricated PMMA-MoS{sub 2}/graphene heterostructure. The developed material system and demonstrated memory device fabrication can be significant for next generation data storage applications.

  18. Polaron hopping mediated by nuclear tunnelling in semiconducting polymers at high carrier density

    NARCIS (Netherlands)

    Asadi, Kamal; Kronemeijer, Auke J.; Cramer, Tobias; Koster, L. Jan Anton; Blom, Paul W. M.; de Leeuw, Dago M.

    The transition rate for a single hop of a charge carrier in a semiconducting polymer is assumed to be thermally activated. As the temperature approaches absolute zero, the predicted conductivity becomes infinitesimal in contrast to the measured finite conductivity. Here we present a uniform

  19. Surface-roughness fractality effects in electrical conductivity of single metallic and semiconducting films

    NARCIS (Netherlands)

    Palasantzas, G.; Barnaś, J.

    1997-01-01

    Surface-roughness effects in electrical conductivity of thin metallic and semiconducting films with self-affine fractal surfaces are considered in the framework of the Born approximation. The surface roughness is described by the k-correlation model, and is characterized by the roughness exponent H

  20. Interface Roughness Fractality Effects on the Electron Mobility in Semiconducting Quantum Wells

    NARCIS (Netherlands)

    Palasantzas, G.; Barnaś, J.

    1998-01-01

    The influence of interface electron scattering on electron mobility in semiconducting quantum wells is analyzed theoretically in the Born approximation. The interface roughness is assumed to be random self-affine fractal characterized by roughness exponent H, correlation length ξ, and rms amplitude

  1. Highly Efficient and Scalable Separation of Semiconducting Carbon Nanotubes via Weak Field Centrifugation

    Science.gov (United States)

    Reis, Wieland G.; Weitz, R. Thomas; Kettner, Michel; Kraus, Alexander; Schwab, Matthias Georg; Tomović, Željko; Krupke, Ralph; Mikhael, Jules

    2016-05-01

    The identification of scalable processes that transfer random mixtures of single-walled carbon nanotubes (SWCNTs) into fractions featuring a high content of semiconducting species is crucial for future application of SWCNTs in high-performance electronics. Herein we demonstrate a highly efficient and simple separation method that relies on selective interactions between tailor-made amphiphilic polymers and semiconducting SWCNTs in the presence of low viscosity separation media. High purity individualized semiconducting SWCNTs or even self-organized semiconducting sheets are separated from an as-produced SWCNT dispersion via a single weak field centrifugation run. Absorption and Raman spectroscopy are applied to verify the high purity of the obtained SWCNTs. Furthermore SWCNT - network field-effect transistors were fabricated, which exhibit high ON/OFF ratios (105) and field-effect mobilities (17 cm2/Vs). In addition to demonstrating the feasibility of high purity separation by a novel low complexity process, our method can be readily transferred to large scale production.

  2. Biomedical Detection via Macro- and Nano-Sensors Fabricated with Metallic and Semiconducting Oxides

    Science.gov (United States)

    Hahm, Jong-In

    2013-01-01

    Originally developed as gas sensors, the benefits of metallic and semiconducting oxide materials are now being realized in other areas of sensing, such as chemical, environmental, and biomedical monitoring and detection. Metallic and semiconducting oxides have continuously expanded their roles to date, and have also established their significance in biosensing by utilizing a variety of modes for signal generation and detection mechanism. These sensors are typically based either on their optical, electrochemical, electrical, gravimetric, acoustic, and magnetic properties for signal transduction. This article reviews such biosensors that employ metallic and semiconducting oxides as active sensing elements to detect nucleic acids, proteins, cells, and a variety of important biomarkers, both in thin film and one-dimensional forms. Specific oxide materials (Mx Oy ) examined comprehensively in this article include M = Fe, Cu, Si, Zn, Sn, In. The derivatives of these oxide materials resulting from incorporation of dopants are examined as well. The crystalline structures and unique properties that may be exploited for various biosensing applications are discussed, and recent efforts investigating the feasibility of using these oxide materials in biosensor technology are described. Key biosensor characteristics resulting from reduced dimensionality are overviewed under the motif of planar and one-dimensional sensors. This article also provides insight into current challenges facing biosensor applications for metallic and semiconducting oxides. In addition, future outlook in this particular field as well as different impacts on biology and medicine are addressed. PMID:23627064

  3. Selecting Semiconducting Single-Walled Carbon Nanotubes with Narrow Bandgap Naphthalene Diimide-Based Polymers

    NARCIS (Netherlands)

    Salazar-Rios, Jorge Mario; Gomulya, Widianta; Derenskyi, Vladimir; Yang, Jie; Bisri, Satria Zulkarnaen; Chen, Zhihua; Facchetti, Antonio; Loi, Maria Antonietta

    Noncovalent functionalization of carbon nanotubes by wrapping them using pi-conjugated polymers is one of the most promising techniques to sort, separate, and purify semiconducting nanotube species for applications in optoelectronic devices. However, wide energy bandgap polymers commonly used in

  4. Synthesis, Characterization, and Properties of the Two-Dimensional Chalcogenides: Monolayers, Alloys, and Heterostructures

    Science.gov (United States)

    Cain, Jeffrey D.

    monolayer transition metal dichalcogenides materials (TMDs), MX2. Specifically, synthetic protocols for monolayers of the semiconducting TMDs, MoS2, WS2, and MoSe2, are presented and the layers are completely characterized with a full suite of techniques including scanning/transmission electron microscopy, scanning probe microscopy, and photo-spectroscopy (photoluminescence, Raman scattering) among others. Furthermore, the nucleation and growth processes in CVD grown TMD monolayers is investigated using aberration-corrected scanning transmission electron microscopy and a step-by-step nucleation and growth mechanism for monolayer TMDs is elucidated. Third, the use of monolayers as building blocks for more complex structures is explored and a predictive approach for the synthesis of van der Waals heterostructures and monolayer alloys is designed. This is accomplished using an intellectual framework analogous to the Time-Temperature-Transformation (TTT) diagrams that are ubiquitous in traditional materials science and metallurgy. These are called Time-Temperature-Architecture (TTA) diagrams, wherein the term "architecture" defines the specific conformation of the 2D components. These diagrams provide process guidance to synthesize a library of heterostructures with a range of morphologies and monolayer alloys within both the transition metal sulfide and selenide systems. Lastly, some next steps for future research are outlined. An appendix of summaries of collaborative studies of the optical and electronic properties of CVD grown monolayers TMDs is appended.

  5. Transition of single-walled carbon nanotubes from metallic to semiconducting in field-effect transistors by hydrogen plasma treatment.

    Science.gov (United States)

    Zheng, Gang; Li, Qunqing; Jiang, Kaili; Zhang, Xiaobo; Chen, Jia; Ren, Zheng; Fan, Shoushan

    2007-06-01

    We report hydrogen plasma treatment results on converting the metallic single-walled carbon nanotubes to semiconducting single-walled carbon nanotubes. We found that the as-grown single-walled carbon nanotubes (SWNTs) can be sorted as three groups which behave as metallic, as-metallic, and semiconducting SWNTs. These three groups have different changes under hydrogen plasma treatment and successive annealing process. The SWNTs can be easily hydrogenated in the hydrogen plasma environment and the as-metallic SWNTs can be transformed to semiconducting SWNTs. The successive annealing process can break the C-H bond, so the conversion is reversible.

  6. Organic heterostructures based on arylenevinylene oligomers deposited by MAPLE

    Science.gov (United States)

    Socol, M.; Preda, N.; Vacareanu, L.; Grigoras, M.; Socol, G.; Mihailescu, I. N.; Stanculescu, F.; Jelinek, M.; Stanculescu, A.; Stoicanescu, M.

    2014-05-01

    Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV-vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550-800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. I-V characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 × 10-6 A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material.

  7. Structural properties of ZnSy Se1-yZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

    Science.gov (United States)

    Zhang, X. G.; Kalisetty, S.; Robinson, J.; Zhao, G.; Parent, D. W.; Ayers, J. E.; Jain, F. C.

    1997-06-01

    ZnSySe1-yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSyySe1-y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is hc ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnSySe1-y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnSySe1-y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ˜ 5.9%), rather than growth temperature lattice matching (y ˜ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by

  8. Graphene/Si-nanowire heterostructure molecular sensors.

    Science.gov (United States)

    Kim, Jungkil; Oh, Si Duk; Kim, Ju Hwan; Shin, Dong Hee; Kim, Sung; Choi, Suk-Ho

    2014-06-20

    Wafer-scale graphene/Si-nanowire (Si-NW) array heterostructures for molecular sensing have been fabricated by vertically contacting single-layer graphene with high-density Si NWs. Graphene is grown in large scale by chemical vapour deposition and Si NWs are vertically aligned by metal-assisted chemical etching of Si wafer. Graphene plays a key role in preventing tips of vertical Si NWs from being bundled, thereby making Si NWs stand on Si wafer separately from each other under graphene, a critical structural feature for the uniform Schottky-type junction between Si NWs and graphene. The molecular sensors respond very sensitively to gas molecules by showing 37 and 1280% resistance changes within 3.5/0.15 and 12/0.15 s response/recovery times under O2 and H2 exposures in air, respectively, highest performances ever reported. These results together with the sensor responses in vacuum are discussed based on the surface-transfer doping mechanism.

  9. Proximity coupling in superconductor-graphene heterostructures.

    Science.gov (United States)

    Lee, Gil-Ho; Lee, Hu-Jong

    2018-02-16

    This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable two-dimensional platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given. © 2018 IOP Publishing Ltd.

  10. Theory of unidirectional magnetoresistance in magnetic heterostructures

    Science.gov (United States)

    Zhang, Steven S.-L.; Vignale, Giovanni

    2017-09-01

    We present a general drift-diffusion theory beyond linear response to explain the unidirectional magnetoresistance (UMR) observed in recent experiments in various magnetic heterostructures. In general, such nonlinear magnetoresistance may originate from the concerted action of current-induced spin accumulation and spin asymmetry in electron mobility. As a case study, we calculate the UMR in a bilayer system consisting of a heavy-metal (HM) and a ferromagnetic metal (FM), where the spin accumulation is induced via the spin Hall effect in the bulk of the HM layer. Our previous formulation [cf. PRB 94, 140411(R) (2016)] is generalized to include the interface resistance and spin memory loss, which allows us to analyze in details their effects on the UMR. We found that the UMR turns out to be independent of the spin asymmetry of the interfacial resistance, at variance with the linear giant-magnetoresistance (GMR) effect. A linear relation between the UMR and the conductivity-spin asymmetry is revealed, which provides an alternative way to control the sign and magnitude of the UMR and hence may serve as an experimental signature of our proposed mechanism.

  11. Highly Confined Electronic and Ionic Conduction in Oxide Heterostructures

    DEFF Research Database (Denmark)

    Pryds, Nini

    2015-01-01

    The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. In this talk I will present our recent results both on ionic and electronic conductivity at different heterostructures systems. In the first...... unattainable for Bi2O3-based materials, is achieved[1]. These confined heterostructures provide a playground not only for new high ionic conductivity phenomena that are sufficiently stable but also uncover a large variety of possible technological perspectives. At the second part, I will discuss and show our...... recent results of high mobile samples realized by, interface confined redox reactions[2], strain induced polarization[3]and modulation doping at complex oxide interfaces. This collection of samples offers unique opportunities for a wide range of rich world of mesoscopic physics. [1] S. Sanne et al...

  12. Epitaxial growth and physical properties of Heusler/perovskite heterostructures

    Science.gov (United States)

    Kobayashi, K.; Ueda, K.; Fukatani, N.; Kawada, H.; Sakuma, K.; Asano, H.

    2013-08-01

    Multiferroic heterostructures of the ferromagnetic, half-metallic Heusler Fe2CrSi (FCS) and the ferroelectric perovskite Ba0.7Sr0.3TiO3 (BSTO) have been formed by magnetron sputtering, and their magnetic and ferroelectric properties have been investigated. FCS/BSTO bilayer structures were epitaxially grown on LaAlO3 substrates with epitaxial relationships of FCS (001)[110]//BSTO (001)[100]. Multiferroic properties with a remanent polarization of 10.6 µC/cm2 and a saturation magnetization of 417 emu/cc were observed for the FCS/BSTO heterostructures at room temperature. These results suggest that the Heusler/perovskite epitaxial heterostructure is a promising candidate for fabricating multiferroic devices.

  13. Interface-engineered oxygen octahedral coupling in manganite heterostructures

    Science.gov (United States)

    Huijben, M.; Koster, G.; Liao, Z. L.; Rijnders, G.

    2017-12-01

    Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low

  14. Broad-Band-Emissive Organic-Inorganic Hybrid Semiconducting Nanowires Based on an ABX3-Type Chain Compound.

    Science.gov (United States)

    Wu, Zhenyue; Li, Lina; Ji, Chengmin; Lin, Guoming; Wang, Sasa; Shen, Yaoguo; Sun, Zhihua; Zhao, Sangen; Luo, Junhua

    2017-08-07

    Organic-inorganic hybrid lead halide (e.g., CH3NH3PbX3, where X = CI, Br, and I) nanowires (NWs) with remarkable electric and optical properties have recently garnered increasing attention, owing to their structural flexibility and tunability compared to inorganic semiconducting NWs. While most recently reported NWs are limited to methylammonium/formamidinium three-dimensional lead halide perovskites, it is urgent to develop new organic-inorganic hybrid semiconducting NWs. Here, broad-band-emissive single-crystal semiconductive NWs based on a new ABX3-type organic-inorganic chain hybrid, (2-methylpiperidine)lead tribromide, are reported. It is believed that this work will enrich the organic-inorganic hybrid semiconducting NWs and may provide potential applications for LED displaying.

  15. Empirical Equation Based Chirality (n, m Assignment of Semiconducting Single Wall Carbon Nanotubes from Resonant Raman Scattering Data

    Directory of Open Access Journals (Sweden)

    Md Shamsul Arefin

    2012-12-01

    Full Text Available This work presents a technique for the chirality (n, m assignment of semiconducting single wall carbon nanotubes by solving a set of empirical equations of the tight binding model parameters. The empirical equations of the nearest neighbor hopping parameters, relating the term (2n, m with the first and second optical transition energies of the semiconducting single wall carbon nanotubes, are also proposed. They provide almost the same level of accuracy for lower and higher diameter nanotubes. An algorithm is presented to determine the chiral index (n, m of any unknown semiconducting tube by solving these empirical equations using values of radial breathing mode frequency and the first or second optical transition energy from resonant Raman spectroscopy. In this paper, the chirality of 55 semiconducting nanotubes is assigned using the first and second optical transition energies. Unlike the existing methods of chirality assignment, this technique does not require graphical comparison or pattern recognition between existing experimental and theoretical Kataura plot.

  16. A semiconducting microporous framework of Cd6Ag4(SPh)16 clusters interlinked using rigid and conjugated bipyridines.

    Science.gov (United States)

    Xu, Chao; Hedin, Niklas; Shi, Hua-Tian; Zhang, Qian-Feng

    2014-04-11

    Ternary supertetrahedral chalcogenolate clusters were interlinked with bipyridines into a microporous semiconducting framework with properties qualitatively different from those of the original clusters. Both the framework and the clusters were effective photocatalysts, and rapidly degraded the dye rhodamine B.

  17. Formation of single-walled carbon nanotube thin films enriched with semiconducting nanotubes and their application in photoelectrochemical devices.

    Science.gov (United States)

    Wei, Li; Tezuka, Noriyasu; Umeyama, Tomokazu; Imahori, Hiroshi; Chen, Yuan

    2011-04-01

    Single-walled carbon nanotube (SWCNT) thin films, containing a high-density of semiconducting nanotubes, were obtained by a gel-centrifugation method. The agarose gel concentration and centrifugation force were optimized to achieve high semiconducting and metallic nanotube separation efficiency at 0.1 wt% agarose gel and 18,000g. The thickness of SWCNT films can be precisely controlled from 65 to 260 nm with adjustable transparency. These SWCNT films were applied in photoelectrochemical devices. Photocurrents generated by semiconducting SWCNT enriched films are 15-35% higher than those by unsorted SWCNT films. This is because of reducing exciton recombination channels as a result of the removal of metallic nanotubes. Thinner films generate higher photocurrents because charge carriers have less chances going in metallic nanotubes for recombination, before they can reach electrodes. Developing more scalable and selective methods for high purity semiconducting SWCNTs is important to further improve the photocurrent generation efficiency by using SWCNT-based photoelectrochemical devices.

  18. Electronic homogeneity of nanowire heterostructure Light Emitting Diodes (LEDs)

    Science.gov (United States)

    Selcu, Camelia; May, Brelon J.; Sarwar, A. T. M. Golam; Myers, Roberto C.

    In addition to low defect densities and great tunability bandgap within a single heterostructure, the possibility of growing (Al, In,_) GaN nanowire heterostructure LEDs on different substrates while maintaining their high electronic and optical properties makes them very attractive. We investigated the electronic homogeneity of the (Al, In,_) GaN nanowire ensemble by acquiring current maps at certain applied biases using conductive AFM. By taken IVs on individual nanowires, we found that different wires have different turn on voltages and that some of the nanowires degrade due to the applied bias.

  19. Electric field control of magnetism in multiferroic heterostructures.

    Science.gov (United States)

    Vaz, C A F

    2012-08-22

    We review the recent developments in the electric field control of magnetism in multiferroic heterostructures, which consist of heterogeneous materials systems where a magnetoelectric coupling is engineered between magnetic and ferroelectric components. The magnetoelectric coupling in these composite systems is interfacial in origin, and can arise from elastic strain, charge, and exchange bias interactions, with different characteristic responses and functionalities. Moreover, charge transport phenomena in multiferroic heterostructures, where both magnetic and ferroelectric order parameters are used to control charge transport, suggest new possibilities to control the conduction paths of the electron spin, with potential for device applications.

  20. Linear ac transport in graphene semiconducting nanosystem with normal-metal electrodes

    Science.gov (United States)

    Ye, En-Jia; Sun, Yun-Lei; Lan, Jin; Shi, Yi-Jian

    2016-03-01

    Linear ac transport properties are investigated in a graphene semiconducting nanosystem, with the effect of normal-metal electrodes taken into account. We use a tight-binding approach and ac transport theory to study the dc conductance and ac emittance in normal-metal/graphene (NG) and normal-metal/graphene/normal-metal (NGN) systems with armchair-edge graphene. We find that the resonant and semiconducting behaviors in NG and NGN systems are closely related to the spatial-resolved local density of states. Furthermore, features of the size-dependent emittances in the NGN system are investigated. The results suggest a positive correlation between the width and capacitive response, and the capacitive response is robust as the size of the system increases proportionally.

  1. Measurement of the photobleaching kinetics of semiconducting polymer films by the pump - probe method

    Energy Technology Data Exchange (ETDEWEB)

    Ozimova, A E; Bruevich, V V; Parashchuk, D Yu [International Laser Center, M. V. Lomonosov Moscow State University, Moscow (Russian Federation)

    2011-12-31

    A phenomenological model of the laser photobleaching dynamics of a semiconducting polymer in a dual-beam scheme for different wavelengths of the burning and probe beams is developed. An experimental method is implemented based on this model, which allows one to investigate materials with significantly different photodegradation rates. The photodegradation quantum yield in mixtures of a semiconducting polymer belonging to polyparaphenylene vinylenes (MEH-PPV) with a low-molecular electron acceptor 2,4,7-trinitrofluorenone (TNF) is measured at burning wavelengths of 488 and 514 nm for different component ratios of MEHPPV : TNF. It is found that adding the acceptor decreases the polymer photodegradation quantum yield by at least four orders of magnitude in the MEH-PPV : TNF = 1 : 0.4 mixture; the photodegradation quantum yields are the same at both wavelengths. It is shown that the photodegradation rates of the MEH-PPV : TNF films measured by laser photobleaching and IR spectroscopy are in good agreement.

  2. Photoelectric Property Modulation by Nanoconfinement in the Longitude Direction of Short Semiconducting Nanorods.

    Science.gov (United States)

    Tang, Chaolong; Jiang, Chengming; Bi, Sheng; Song, Jinhui

    2016-05-04

    Photoelectric property change in half-dimensional (0.5D) semiconducting nanomaterials as a function of illumination light intensity and materials geometry has been systematically studied. Through two independent methods, conductive atomic force microscopy (C-AFM) direct current-voltage acquisition and scanning kelvin probe microscopy (SKPM) surface potential mapping, photoelectric property of 0.5D ZnO nanomaterial has been characterized with exceptional behaviors compared with bulk/micro/one-dimensional (1D) nanomaterial. A new model by considering surface effect, quantum effect, and illumination effect has been successfully built, which could more accurately predict the photoelectric characteristics of 0.5D semiconducting nanomaterials. The findings reported in this study could potentially impact three-dimensional (3D) photoelectronics.

  3. Titania nanotubes self-assembled by electrochemical anodization: Semiconducting and electrochemical properties

    Energy Technology Data Exchange (ETDEWEB)

    Giorgi, L., E-mail: leonardo_giorgi@libero.it [Materials Science & Electrochemistry, Via Mantova 11, 00042, Anzio, Roma (Italy); Salernitano, E. [ENEA, Faenza Laboratories, Via Ravegnana 186, 48018 Faenza, Ravenna (Italy); Dikonimos Makris, Th.; Giorgi, R.; Leoni, E.; Grilli, M.L.; Lisi, N. [ENEA, Casaccia Research Centre, Via Anguillarese 301, 00123, S. Maria di Galeria, Roma (Italy)

    2016-02-29

    Titania nanotubes (TNT), thanks to their semiconducting properties, have received wide attention for application in many fields such as photoelectrolysis, dye sensitized solar cells, photocatalysis, and sensors. In this work, highly ordered TNT were grown by controlled electrochemical anodization of titanium sheets. Scanning electron microscope equipped with a field emission gun and electrochemical DC/AC techniques was used to characterize the TNT. Semiconducting properties were investigated through linear sweep voltammetry and electrochemical impedance spectroscopy. Donor concentration (N{sub ed}) was obtained by recording Mott–Schottky plots. The high N{sub ed} of TNT (around 10{sup 26} m{sup −3}) allows an optimal electron transfer when used as photoelectrode. Frequency dispersion of flat band potential from Mott–Schottky plots (− 0.38 ÷ + 0.40 V vs. saturated calomel electrode, SCE) was used as an indicator of the amorphous semiconductor behaviour. The dispersion of flat band in heat treated samples was extremely reduced (0.48–0.51 V vs. SCE) because of the conversion to crystalline semiconductor. The depth of space charge was comparable to the TNT wall thickness, meaning that the entire TiO{sub 2} nanotube walls formed the space charge layer. Considering the high charge carrier concentration, we can hypothesise a high density of electronic defects (e.g., surface states) that enhances the electron transport by percolation inside a porous photoelectrode. The transition from amorphous to crystalline structure of TNT was detected from the change of semiconducting properties and confirmed by Raman spectroscopy. - Highlights: • Highly ordered self-assembled TiO{sub 2} nanotubes were synthesized by electrochemical anodization. • The electrochemical and semiconducting properties were studied. • An electrical model was developed for titania nanotubes/electrolyte interface. • Thermal treatment changed electronic properties of TiO{sub 2} nanotubes.

  4. Tuning the band gap of semiconducting carbon nanotube by an axial magnetic field

    OpenAIRE

    G. Fedorov

    2010-01-01

    We have investigated the magnetic field dependence of transfer characteristics of a device fabricated in a configuration of a field-effect transistor with a conduction channel formed by a semiconducting multiwalled carbon nanotube. Our results unambiguously indicate that an axial magnetic field suppresses the band gap of the nanotube. Quantitative analysis of the data indicates linear dependence of the band gap on magnetic field as well as a linear splitting between the K and K′ subbands of t...

  5. Zonal flow magnetic field interaction in the semi-conducting region of giant planets

    Science.gov (United States)

    Cao, Hao; Stevenson, David J.

    2017-11-01

    All four giant planets in the Solar System feature zonal flows on the order of 100 m/s in the cloud deck, and large-scale intrinsic magnetic fields on the order of 1 Gauss near the surface. The vertical structure of the zonal flows remains obscure. The end-member scenarios are shallow flows confined in the radiative atmosphere and deep flows throughout the entire planet. The electrical conductivity increases rapidly yet smoothly as a function of depth inside Jupiter and Saturn. Deep zonal flows will inevitably interact with the magnetic field, at depth with even modest electrical conductivity. Here we investigate the interaction between zonal flows and magnetic fields in the semi-conducting region of giant planets. Employing mean-field electrodynamics, we show that the interaction will generate detectable poloidal magnetic field perturbations spatially correlated with the deep zonal flows. Assuming the peak amplitude of the dynamo α-effect to be 0.1 mm/s, deep zonal flows on the order of 0.1-1 m/s in the semi-conducting region of Jupiter and Saturn would generate poloidal magnetic perturbations on the order of 0.01%-1% of the background dipole field. These poloidal perturbations should be detectable with the in-situ magnetic field measurements from the Juno mission and the Cassini Grand Finale. This implies that magnetic field measurements can be employed to constrain the properties of deep zonal flows in the semi-conducting region of giant planets.

  6. Intrinsic nature of visible-light absorption in amorphous semiconducting oxides

    Directory of Open Access Journals (Sweden)

    Youngho Kang

    2014-03-01

    Full Text Available To enlighten microscopic origin of visible-light absorption in transparent amorphous semiconducting oxides, the intrinsic optical property of amorphous InGaZnO4 is investigated by considering dipole transitions within the quasiparticle band structure. In comparison with the crystalline InGaZnO4 with the optical gap of 3.6 eV, the amorphous InGaZnO4 has two distinct features developed in the band structure that contribute to significant visible-light absorption. First, the conduction bands are down-shifted by 0.55 eV mainly due to the undercoordinated In atoms, reducing the optical gap between extended states to 2.8 eV. Second, tail states formed by localized oxygen p orbitals are distributed over ∼0.5 eV near the valence edge, which give rise to substantial subgap absorption. The fundamental understanding on the optical property of amorphous semiconducting oxides based on underlying electronic structure will pave the way for resolving instability issues in recent display devices incorporating the semiconducting oxides.

  7. Nonvolatile Transistor Memory with Self-Assembled Semiconducting Polymer Nanodomain Floating Gates.

    Science.gov (United States)

    Wang, Wei; Kim, Kang Lib; Cho, Suk Man; Lee, Ju Han; Park, Cheolmin

    2016-12-14

    Organic field effect transistor based nonvolatile memory (OFET-NVM) with semiconducting nanofloating gates offers additional benefits over OFET-NVMs with conventional metallic floating gates due to the facile controllability of charge storage based on the energetic structure of the floating gate. In particular, an all-in-one tunneling and floating-gate layer in which the semiconducting polymer nanodomains are self-assembled in the dielectric tunneling layer is promising. In this study, we utilize crystals of a p-type semiconducting polymer in which the crystalline lamellae of the polymer are spontaneously developed and embedded in the tunneling matrix as the nanofloating gate. The widths and lengths of the polymer nanodomains are approximately 20 nm and a few hundred nanometers, respectively. An OFET-NVM containing the crystalline nanofloating gates exhibits memory performance with a large memory window of 10 V, programming/erasing switching endurance for over 500 cycles, and a long retention time of 5000 s. Moreover, the device performance is improved by comixing with an n-type semiconductor; thus, the solution-processed p- and n-type double floating gates capable of storing both holes and electrons allow for the multilevel operation of our OFET-NVM. Four highly reliable levels (two bits per cell) of charge trapping and detrapping are achieved using this OFET-NVM by accurately choosing the programming/erasing voltages.

  8. Semiconducting nanodimer as a photonic cavity: Large and well-defiined Rabi splitting

    Science.gov (United States)

    Uemoto, Mitsuharu; Ajiki, Hiroshi

    2015-03-01

    A metallic nanodimer acts as a photonic cavity because a strong light field appears at the gap region due to a surface plasmon resonance. In this talk, we propose a photonic cavity consisting of a semiconducting nanodimer with a small gap, and theoretically demonstrate large and well-defined vacuum Rabi splitting of a two-level emitter placed at the photonic cavity. A light field is strongly enhanced at the gap region of the semiconducting nanodimer due to an exciton resonance. The interaction between the enhanced light and the emitter is significantly larger than that in a conventional photonic cavity, because the semiconducting nanodimer has a small cavity-mode volume beyond the diffraction limit as well as the metallic nanodimer. In contrast to the metallic nanodimer, the exciton decay rate at low temperature is very small, and as a result, the quality factor reaches Q ~104 which is about 100 times larger than that of the metallic nanodimer. Consequently, the large Rabi splitting energy (~ 1 . 7 meV) appears for the small dipole moment (~ 25 Debye) of the emitter, and the splitting energy is two times larger than the spectral width. Such a well-defined Rabi splitting is highly suited for both fundamental researches and applications. Supported by the Grant-in-Aid for Scientific Reearch (C), No. 25400325 of the Japan Society for Promotion of Science (JSPS).

  9. Tracking Ultrafast Carrier Dynamics in Single Semiconductor Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Taylor A.J.

    2013-03-01

    Full Text Available An understanding of non-equilibrium carrier dynamics in silicon (Si nanowires (NWs and NW heterostructures is very important due to their many nanophotonic and nanoelectronics applications. Here, we describe the first measurements of ultrafast carrier dynamics and diffusion in single heterostructured Si nanowires, obtained using ultrafast optical microscopy. By isolating individual nanowires, we avoid complications resulting from the broad size and alignment distribution in nanowire ensembles, allowing us to directly probe ultrafast carrier dynamics in these quasi-one-dimensional systems. Spatially-resolved pump-probe spectroscopy demonstrates the influence of surface-mediated mechanisms on carrier dynamics in a single NW, while polarization-resolved femtosecond pump-probe spectroscopy reveals a clear anisotropy in carrier lifetimes measured parallel and perpendicular to the NW axis, due to density-dependent Auger recombination. Furthermore, separating the pump and probe spots along the NW axis enabled us to track space and time dependent carrier diffusion in radial and axial NW heterostructures. These results enable us to reveal the influence of radial and axial interfaces on carrier dynamics and charge transport in these quasi-one-dimensional nanosystems, which can then be used to tailor carrier relaxation in a single nanowire heterostructure for a given application.

  10. Exciton diffusion and dissociation in conjugated polymer/fullerene heterostructures

    NARCIS (Netherlands)

    Markov, D.E.; Amsterdam, E.; Blom, P.W.M.; Sieval, A.B.; Hummelen, J.C.; Heremans, PL; Muccini, M; Hofstraat, H

    2004-01-01

    Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly(p-phenylene vinylene) (PPV) based derivatives. Exciton density distribution upon photoexcitation in polymer/fullerene heterostructures has been modeled and exciton diffusion length values of

  11. Topological superconductivity in metal/quantum-spin-ice heterostructures

    Science.gov (United States)

    She, Jian-Huang; Kim, Choong H.; Fennie, Craig J.; Lawler, Michael J.; Kim, Eun-Ah

    2017-11-01

    We propose a strategy to achieve an unconventional superconductor in a heterostructure: use a quantum paramagnet (QPM) as a substrate for heterostructure growth of metallic films to design exotic superconductors. The proposed setup allows us to "customize" electron-electron interaction imprinted on the metallic layer. The QPM material of our choice is quantum spin ice. Assuming the metallic layer forms a single isotropic Fermi pocket, we predict its coupling to spin fluctuations in quantum spin ice will drive topological odd-parity pairing. We further present guiding principles for materializing the suitable heterostructure using ab initio calculations and describe the band structure we predict for the case of Y2Sn2-xSbxO7 grown on the (111) surface of Pr2Zr2O7. Using this microscopic information, we predict topological odd-parity superconductivity at a few Kelvin in this heterostructure, which is comparable to the Tc of the only other confirmed odd-parity superconductor Sr2RuO4.

  12. High ionic conductivity in confined bismuth oxide-based heterostructures

    DEFF Research Database (Denmark)

    Sanna, Simone; Esposito, Vincenzo; Christensen, Mogens

    2016-01-01

    Bismuth trioxide in the cubic fluorite phase (δ-Bi2O3) exhibits the highest oxygen ionic conductivity. In this study, we were able to stabilize the pure -Bi2O3 at low temperature with no addition of stabilizer but only by engineering the interface, using highly coherent heterostructures made...

  13. Photosensitive heterostructures made of sulfonamide zinc phthalocyanine and organic semiconductor

    Czech Academy of Sciences Publication Activity Database

    Lutsyk, P.; Vertsimakha, Ya.; Nešpůrek, Stanislav; Pomaz, I.

    2011-01-01

    Roč. 535, - (2011), s. 18-29 ISSN 1542-1406 Institutional research plan: CEZ:AV0Z40500505 Keywords : heterostructure * reversal of sign in photovoltage spectra * sulphonamide-substituted phthalocyanine Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.580, year: 2011

  14. The dielectric genome of van der Waals heterostructures

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Latini, Simone; Thygesen, Kristian Sommer

    2015-01-01

    Vertical stacking of two-dimensional (2D) crystals, such as graphene and hexagonal boron nitride, has recently lead to a new class of materials known as van der Waals heterostructures (vdWHs) with unique and highly tunable electronic properties. Abinitio calculations should in principle provide...

  15. Excitons in van der Waals Heterostructures: A theoretical study

    DEFF Research Database (Denmark)

    Latini, Simone

    Van der Waals heterostructures (vdWHs) represent a novel and largely unexplored class of materials. Since 2013, when Geim and Grigorieva first conceived the stacking of 2D (two-dimensional) materials to create artificial layered structures with tailored properties, a number of promising (opto...

  16. High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures.

    Science.gov (United States)

    Wong, Joeson; Jariwala, Deep; Tagliabue, Giulia; Tat, Kevin; Davoyan, Artur R; Sherrott, Michelle C; Atwater, Harry A

    2017-07-25

    We report experimental measurements for ultrathin (van der Waals heterostructures exhibiting external quantum efficiencies exceeding 50% and show that these structures can achieve experimental absorbance >90%. By coupling electromagnetic simulations and experimental measurements, we show that pn WSe 2 /MoS 2 heterojunctions with vertical carrier collection can have internal photocarrier collection efficiencies exceeding 70%.

  17. Effective mechanical properties of multilayer nano-heterostructures.

    Science.gov (United States)

    Mukhopadhyay, T; Mahata, A; Adhikari, S; Zaeem, M Asle

    2017-11-17

    Two-dimensional and quasi-two-dimensional materials are important nanostructures because of their exciting electronic, optical, thermal, chemical and mechanical properties. However, a single-layer nanomaterial may not possess a particular property adequately, or multiple desired properties simultaneously. Recently a new trend has emerged to develop nano-heterostructures by assembling multiple monolayers of different nanostructures to achieve various tunable desired properties simultaneously. For example, transition metal dichalcogenides such as MoS2 show promising electronic and piezoelectric properties, but their low mechanical strength is a constraint for practical applications. This barrier can be mitigated by considering graphene-MoS2 heterostructure, as graphene possesses strong mechanical properties. We have developed efficient closed-form expressions for the equivalent elastic properties of such multi-layer hexagonal nano-hetrostructures. Based on these physics-based analytical formulae, mechanical properties are investigated for different heterostructures such as graphene-MoS2, graphene-hBN, graphene-stanene and stanene-MoS2. The proposed formulae will enable efficient characterization of mechanical properties in developing a wide range of application-specific nano-heterostructures.

  18. Inorganic nanostructure-organic polymer heterostructures useful for thermoelectric devices

    Energy Technology Data Exchange (ETDEWEB)

    See, Kevin C.; Urban, Jeffrey J.; Segalman, Rachel A.; Coates, Nelson E.; Yee, Shannon K.

    2017-11-28

    The present invention provides for an inorganic nanostructure-organic polymer heterostructure, useful as a thermoelectric composite material, comprising (a) an inorganic nanostructure, and (b) an electrically conductive organic polymer disposed on the inorganic nanostructure. Both the inorganic nanostructure and the electrically conductive organic polymer are solution-processable.

  19. Elastic and piezoelectric properties of zincblende and wurtzite crystalline nanowire heterostructures.

    Science.gov (United States)

    Boxberg, Fredrik; Søndergaard, Niels; Xu, H Q

    2012-09-04

    The elastic and piezoelectric properties of zincblende and wurtzite crystalline InAs/InP nanowire heterostructures have been studied using electro-elastically coupled continuum elasticity theory. A comprehensive comparison of strains, piezoelectric potentials and piezoelectric fields in the two crystal types of nanowire heterostructures is presented. For each crystal type, three different forms of heterostructures-core-shell, axial superlattice, and quantum dot nanowire heterostructures-are considered. In the studied nanowire heterostructures, the principal strains are found to be insensitive to the change in the crystal structure. However, the shear strains in the zincblende and wurtzite nanowire heterostructures can be very different. All the studied nanowire heterostructures are found to exhibit a piezoelectric field along the nanowire axis. The piezoelectric field is in general much stronger in a wurtzite nanowire heterostructure than in its corresponding zincblende heterostructure. Our results are expected to be particularly important for analyzing and understanding the properties of epitaxially grown nanowire heterostructures and for applications in nanowire electronics, optoelectronics, and biochemical sensing. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Elastic and piezoelectric properties of zincblende and wurtzite crystalline nanowire heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Boxberg, Fredrik [Division of Solid State Physics, Lund University (Sweden); Soendergaard, Niels [Division of Mathematical Physics, Lund University (Sweden); Xu, H.Q. [Department of Electronics and Key Laboratory for the Physics and Chemistry of Nanodevices, Peking University, Beijing (China); Division of Solid State Physics, Lund University (Sweden)

    2012-09-04

    The elastic and piezoelectric properties of zincblende and wurtzite crystalline InAs/InP nanowire heterostructures have been studied using electro-elastically coupled continuum elasticity theory. A comprehensive comparison of strains, piezoelectric potentials and piezoelectric fields in the two crystal types of nanowire heterostructures is presented. For each crystal type, three different forms of heterostructures - core-shell, axial superlattice, and quantum dot nanowire heterostructures - are considered. In the studied nanowire heterostructures, the principal strains are found to be insensitive to the change in the crystal structure. However, the shear strains in the zincblende and wurtzite nanowire heterostructures can be very different. All the studied nanowire heterostructures are found to exhibit a piezoelectric field along the nanowire axis. The piezoelectric field is in general much stronger in a wurtzite nanowire heterostructure than in its corresponding zincblende heterostructure. Our results are expected to be particularly important for analyzing and understanding the properties of epitaxially grown nanowire heterostructures and for applications in nanowire electronics, optoelectronics, and biochemical sensing. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Epitaxial Growth, Surface, and Electronic Properties of Unconventional Semiconductors: RE-V/III-V Nanocomposites and Semiconducting Half Heusler Alloys

    Science.gov (United States)

    2014-09-01

    groundwork for future studies on all-Heusler heterostructures . 2 UNIVERSITY of CALIFORNIA Santa Barbara Epitaxial growth, surface, and electronic...Schultz, and C. J. Palmstrøm. Growth and transport properties of epitaxial lattice matched Half Heusler Co- TiSb/InAlAs/InP(001) heterostructures . Appl...and nanowires via directed electrochemical nanowire assembly. Nano Lett., 11, 191901 (2011). 5. N. Ferralis, J. K. Kawasaki, R. Maboudian, and C

  2. Synthesis, characterization and photovoltaic integration of type II nanorod heterostructures

    Science.gov (United States)

    McDaniel, Hunter Y.

    Motivated by a desire to control the actions of charges within materials in new and productive ways, researchers have increasingly focused their efforts on engineering materials on the nanometer scale where the laws of quantum mechanics rule supreme. Novel properties emerge when a semiconductor crystal is prepared at sizes below the hydrogenic ground state of the material, also known as the exciton Bohr radius. In addition to effects of quantum confinement, the large fraction of surface atoms can play a significant role in determining nanocrystal properties and applications. By combining two or more nanometer scale semiconductor crystals together to form a nanocrystal heterostructure, new avenues for materials engineering are opened up as nascent properties emerge. The high fraction of surface atoms means that much larger degrees of strain are possible than in the bulk. The large fraction of interface atoms means that the heterojunction properties can dominate the properties of the entire structure. Along with engineering these novel multi component properties comes new unexplored areas of science to be investigated and understood. New techniques are needed for studying these materials that require resolution of features much smaller than the wavelength of (visible) light. Along with this research comes a responsibility to share findings with the scientific community and to pursue directions that can positively impact humanity. At the same time, we should take a long term view when judging the applications of this or any new technology as we are only beginning to understand what is possible. After an introduction to the field in chapter one where we motivate our focus on anisotropic nanocrystal heterostructures, we discuss the formation of Fe3O4/CdS structures from spherical seeds in chapter two. In chapter three we turn our focus to type II CdSe/CdTe nanorod heterostructures where the anisotropy is inherent. The type II system is of particular interest because

  3. Advanced Semiconductor Heterostructures Novel Devices, Potential Device Applications and Basic Properties

    CERN Document Server

    Stroscio, Michael A

    2003-01-01

    This volume provides valuable summaries on many aspects of advanced semiconductor heterostructures and highlights the great variety of semiconductor heterostructures that has emerged since their original conception. As exemplified by the chapters in this book, recent progress on advanced semiconductor heterostructures spans a truly remarkable range of scientific fields with an associated diversity of applications. Some of these applications will undoubtedly revolutionize critically important facets of modern technology. At the heart of these advances is the ability to design and control the pr

  4. Abnormal room temperature ferromagnetism in CuO-ZnO heterostructures: interface related or not?

    Science.gov (United States)

    Gao, Daqiang; Zhang, Zhipeng; Li, You; Xia, Baorui; Shi, Shoupeng; Xue, Desheng

    2015-01-21

    We report the new functionality of room temperature ferromagnetism in CuO-ZnO heterostructures. Magnetic measurement results indicate the CuO-ZnO heterostructures show enhanced ferromagnetism contrary to the pure CuO (ZnO) and the observed ferromagnetism is proportional to the interface counts for the film-heterostructures, providing proof of interface related ferromagnetism. Our study suggests that magnetically functional interfaces could be an entirely new and novel design of magnetic materials for emergent devices.

  5. Nano-scale polar-nonpolar oxide heterostructures for photocatalysis

    Science.gov (United States)

    Guo, Hongli; Saidi, Wissam A.; Yang, Jinlong; Zhao, Jin

    2016-03-01

    We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates ferroelectric instability in STO. The proposed setup is ideal for tandem oxide photocatalysts especially when combined with photoactive polar materials.We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates

  6. Semiconducting Polymer Photodetectors with Electron and Hole Blocking Layers: High Detectivity in the Near-Infrared

    Directory of Open Access Journals (Sweden)

    Xiong Gong

    2010-07-01

    Full Text Available Sensing from the ultraviolet-visible to the infrared is critical for a variety of industrial and scientific applications. Photodetectors with broad spectral response, from 300 nm to 1,100 nm, were fabricated using a narrow-band gap semiconducting polymer blended with a fullerene derivative. By using both an electron-blocking layer and a hole-blocking layer, the polymer photodetectors, operating at room temperature, exhibited calculated detectivities greater than 1013 cm Hz1/2/W over entire spectral range with linear dynamic range approximately 130 dB. The performance is comparable to or even better than Si photodetectors.

  7. Highly fluorescent semiconducting polymer dots for single-molecule imaging and biosensing

    Science.gov (United States)

    Sun, Wei; Yu, Jiangbo; Ye, Fangmao; Rong, Yu; Chiu, Daniel T.

    2013-09-01

    This paper describes the preparation of semiconducting polymer dots (Pdots) and their application for single-molecule imaging and biosensing. The Pdots possessed high fluorescence brightness, with a 16 nm Pdot being ~9 times brighter than 13 nm Quantum Dots (Qdots). The surface of Pdots was successfully conjugated with streptavidin, which made Pdots suitable for specific subcellular labeling and targeting. The interior composition of Pdots was also successfully modified, through which the Pdots obtained additional functionalities. We demonstrated the utility of gold nanoparticle embedded Pdots in dual-modality imaging. We also demonstrated that Rhodamine B embedded Pdots were able to function as ratiometric temperature sensor in live-cell imaging mode.

  8. Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

    Science.gov (United States)

    Apostol, I.; Stefan, N.; Luculescu, C. R.; Birjega, R.; Socol, M.; Miroiu, M.; Mihailescu, I. N.

    2011-02-01

    We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates. The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements. We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.

  9. CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

    OpenAIRE

    Chapelle, Audrey; Oudrhiri-Hassani, Fahd; Presmanes, Lionel; Barnabé, Antoine; Tailhades, Philippe

    2010-01-01

    A new active layer for CO2 sensing based on semiconducting CuO–CuxFe3−xO4 (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO2 target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite–spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures ...

  10. Room temperature ferromagnetic and semiconducting properties of graphene adsorbed with cobalt oxide using electrochemical method

    Science.gov (United States)

    Park, Chang-Soo; Lee, Kyung Su; Chu, Dongil; Lee, Juwon; Shon, Yoon; Kim, Eun Kyu

    2017-12-01

    We report the room temperature ferromagnetic properties of graphene adsorbed by cobalt oxide using electrochemical method. The cobalt oxide doping onto graphene was carried out in 0.1 M LiCoO2/DI-water solution. The doped graphene thin film was determined to be a single layer from Raman analysis. The CoO doped graphene has a clear ferromagnetic hysteresis at room temperature and showed a remnant magnetization, 128.2 emu/cm3. The temperature dependent conductivity of the adsorbed graphene showed the semiconducting behavior and a band gap opening of 0.12 eV.

  11. Role of Molecular Weight Distribution on Charge Transport in Semiconducting Polymers

    KAUST Repository

    Himmelberger, Scott

    2014-10-28

    © 2014 American Chemical Society. Model semiconducting polymer blends of well-controlled molecular weight distributions are fabricated and demonstrated to be a simple method to control intermolecular disorder without affecting intramolecular order or degree of aggregation. Mobility measurements exhibit that even small amounts of low molecular weight material are detrimental to charge transport. Trends in charge carrier mobility can be reproduced by a simple analytical model which indicates that carriers have no preference for high or low molecular weight chains and that charge transport is limited by interchain hopping. These results quantify the role of long polymer tie-chains and demonstrate the need for controlled polydispersity for achieving high carrier mobilities.

  12. Scaling analysis of Schottky barriers at metal-embedded semiconducting carbon nanotube interfaces

    OpenAIRE

    Xue, Yongqiang; Ratner, Mark A.

    2004-01-01

    We present an atomistic self-consistent tight-binding study of the electronic and transport properties of metal-semiconducting carbon nanotube interfaces as a function of the nanotube channel length when the end of the nanotube wire is buried inside the electrodes. We show that the lineup of the nanotube band structure relative to the metal Fermi-level depends strongly on the metal work function but weakly on the details of the interface. We analyze the length-dependent transport characterist...

  13. Synthesis and applications of heterostructured semiconductor nanocrystals

    Science.gov (United States)

    Khon, Elena

    Semiconductor nanocrystals (NCs) have been of great interest to researchers for several decades due to their unique optoelectronic properties. These nanoparticles are widely used for a variety of different applications. However, there are many unresolved issues that lower the efficiency and/or stability of devices which incorporate these NCs. Our research is dedicated to addressing these issues by identifying potential problems and resolving them, improving existing systems, generating new synthetic strategies, and/or building new devices. The general strategies for the synthesis of different nanocrystals were established in this work, one of which is the colloidal growth of gold domains onto CdS semiconductor nanocrystals. Control of shape and size was achieved simply by adjusting the temperature and the time of the reaction. Depending on the exact morphology of Au and CdS domains, fabricated nano-composites can undergo evaporation-induced self-assembly onto a substrate, which is very useful for building devices. CdS/Au heterostructures can assemble in two different ways: through end-to-end coupling of Au domains, resulting in the formation of one-dimensional chains; and via side-by-side packing of CdS nanorods, leading to the onset of two-dimensional superlattices. We investigated the nature of exciton-plasmon interactions in Au-tipped CdS nanorods using femtosecond transient absorption spectroscopy. The study demonstrated that the key optoelectronic properties of electrically coupled metal and semiconductor domains are significantly different from those observed in systems with weak inter-domain coupling. In particular, strongly-coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton carrier excitations. Colloidal QDs are starting to replace organic molecules in many different applications, such as organic light emmiting diods (OLEDs), due to their

  14. Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures

    Science.gov (United States)

    Lu, Peipei; Shang, Dashan; Shen, Jianxin; Chai, Yisheng; Yang, Chuansen; Zhai, Kun; Cong, Junzhuang; Shen, Shipeng; Sun, Young

    2016-12-01

    Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroic heterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.

  15. In-plane heterostructures of Sb/Bi with high carrier mobility

    Science.gov (United States)

    Zhao, Pei; Wei, Wei; Sun, Qilong; Yu, Lin; Huang, Baibiao; Dai, Ying

    2017-06-01

    In-plane two-dimensional (2D) heterostructures have been attracting public attention due to their distinctive properties. However, the pristine materials that can form in-plane heterostructures are reported only for graphene, hexagonal BN, transition-metal dichalcogenides. It will be of great significance to explore more suitable 2D materials for constructing such ingenious heterostructures. Here, we demonstrate two types of novel seamless in-plane heterostructures combined by pristine Sb and Bi monolayers by means of first-principle approach based on density functional theory. Our results indicate that external strain can serve as an effective strategy for bandgap engineering, and the transition from semiconductor to metal occurs when a compressive strain of -8% is applied. In addition, the designed heterostructures possess direct band gaps with high carrier mobility (˜4000 cm2 V-1 s-1). And the mobility of electrons and holes have huge disparity along the direction perpendicular to the interface of Sb/Bi in-plane heterostructures. It is favorable for carriers to separate spatially. Finally, we find that the band edge positions of Sb/Bi in-plane heterostructures can meet the reduction potential of hydrogen generation in photocatalysis. Our results not only offer alternative materials to construct versatile in-plane heterostructures, but also highlight the applications of 2D in-plane heterostructures in diverse nanodevices and photocatalysis.

  16. Synthesis, optical and electrochemical properties of ZnO nanowires/graphene oxide heterostructures

    National Research Council Canada - National Science Library

    Zeng, Huidan; Cao, Ying; Xie, Shufan; Yang, Junhe; Tang, Zhihong; Wang, Xianying; Sun, Luyi

    2013-01-01

    .... Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising...

  17. Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis

    National Research Council Canada - National Science Library

    Gong, Ming; Zhou, Wu; Tsai, Mon-Che; Zhou, Jigang; Guan, Mingyun; Lin, Meng-Chang; Zhang, Bo; Hu, Yongfeng; Wang, Di-Yan; Yang, Jiang; Pennycook, Stephen J; Hwang, Bing-Joe; Dai, Hongjie

    2014-01-01

    .... Here we report nanoscale nickel oxide/nickel heterostructures formed on carbon nanotube sidewalls as highly effective electrocatalysts for hydrogen evolution reaction with activity similar to platinum...

  18. Observation of long-lived interlayer excitons in monolayer MoSe2-WSe2 heterostructures

    National Research Council Canada - National Science Library

    Rivera, Pasqual; Schaibley, John R; Jones, Aaron M; Ross, Jason S; Wu, Sanfeng; Aivazian, Grant; Klement, Philip; Seyler, Kyle; Clark, Genevieve; Ghimire, Nirmal J; Yan, Jiaqiang; Mandrus, D G; Yao, Wang; Xu, Xiaodong

    2015-01-01

    ..., that is, interlayer excitons. Here, we report the observation of interlayer excitons in monolayer MoSe2-WSe2 heterostructures by photoluminescence and photoluminescence excitation spectroscopy...

  19. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures

    Science.gov (United States)

    Renshaw Wang, X.; Sun, L.; Huang, Z.; Lü, W. M.; Motapothula, M.; Annadi, A.; Liu, Z. Q.; Zeng, S. W.; Venkatesan, T.; Ariando

    2015-12-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context.

  20. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures.

    Science.gov (United States)

    Kral, S; Zeiner, C; Stöger-Pollach, M; Bertagnolli, E; den Hertog, M I; Lopez-Haro, M; Robin, E; El Hajraoui, K; Lugstein, A

    2015-07-08

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor-liquid-solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I-V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying capacity of about 0.8 MA/cm(2). Transmission electron microscopy (TEM) characterization has confirmed both the composition and crystalline nature of the pure Al nanowire segments. A very sharp interface between the ⟨111⟩ oriented Ge nanowire and the reacted Al part was observed with a Schottky barrier height of 361 meV. To demonstrate the potential of this approach, a monolithic Al/Ge/Al heterostructure was used to fabricate a novel impact ionization device.

  1. Novel heterostructured Ge nanowires based on polytype transformation.

    Science.gov (United States)

    Vincent, Laetitia; Patriarche, Gilles; Hallais, Géraldine; Renard, Charles; Gardès, Cyrille; Troadec, David; Bouchier, Daniel

    2014-08-13

    We report on a strain-induced phase transformation in Ge nanowires under external shear stresses. The resulted polytype heterostructure may have great potential for photonics and thermoelectric applications. ⟨111⟩-oriented Ge nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal diamond phase referred as the 2H-allotrope. The phase transformation occurs heterogeneously on shear bands along the length of the nanowire. The structure meets the common phenomenological criteria of a martensitic phase transformation. This point is discussed to initiate an on going debate on the transformation mechanisms. The process results in unprecedented quasiperiodic heterostructures 3C/2H along the Ge nanowire. The thermal stability of those 2H domains is also studied under annealing up to 650 °C by in situ TEM.

  2. Photoresponsive memory device based on Graphene/Boron Nitride heterostructure

    Science.gov (United States)

    Kahn, Salman; Velasco, Jairo, Jr.; Ju, Long; Wong, Dillon; Lee, Juwon; Tsai, Hsin Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael

    2015-03-01

    Recent technological advancements have allowed the stacking of two dimensional layered material in order to create van der Waals heterostructures (VDH), enabling the design of novel properties by exploiting the proximal interaction between layers with different electronic properties. We report the creation of an optoelectronic memory device using a Graphene/Boron Nitride (hBN) heterostructure. Using the photo-induced doping phenomenon, we are able to spatially ``write'' a doping profile on graphene and ``read'' the profile through electrical transport and local probe techniques. We then utilize defect engineering to enhance the optoelectronic response of graphene and explore the effect of defects in hBN. Our work introduces a simple device architecture to create an optoelectronic memory device and contributes towards understanding the proximal effects of hBN on Graphene.

  3. Multifunctional high-performance van der Waals heterostructures

    Science.gov (United States)

    Huang, Mingqiang; Li, Shengman; Zhang, Zhenfeng; Xiong, Xiong; Li, Xuefei; Wu, Yanqing

    2017-12-01

    A range of novel two-dimensional materials have been actively explored for More Moore and More-than-Moore device applications because of their ability to form van der Waals heterostructures with unique electronic properties. However, most of the reported electronic devices exhibit insufficient control of multifunctional operations. Here, we leverage the band-structure alignment properties of narrow-bandgap black phosphorus and large-bandgap molybdenum disulfide to realize vertical heterostructures with an ultrahigh rectifying ratio approaching 106 and on-off ratio up to 107. Furthermore, we design and fabricate tunable multivalue inverters, in which the output logic state and window of the mid-logic can be controlled by specific pairs of channel length and, most importantly, by the electric field, which shifts the band-structure alignment across the heterojunction. Finally, high gains over 150 are achieved in the inverters with optimized device geometries, showing great potential for future logic applications.

  4. Prismatic quantum heterostructures on MBE grown GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Fontcuberta i Morral, Anna [Walter Schottky Institut, TU Muenchen, Garching (Germany)

    2008-07-01

    Semiconductor nanowires are believed to play a decisive role in the electronic and optoelectronic devices of the XXI century. Their synthesis is a rapidly expanding field, due to the expectations that nanoscale objects and their associated phenomena have to offer to basic and applied science. Here we report on a new method for the growth of GaAs nanowires and related prismatic quantum heterostructures using Molecular Beam Epitaxy (MBE), by avoiding the use of gold as seed for the nanowires. The use of Molecular Beam Epitaxy presents an additional interest, as this technique allows us to produce ultra-pure nanowires and quantum heterostructures on the nanowire facets with very high crystalline quality and atomically sharp interfaces. This new versatility of MBE in the growth of nanostructures opens great possibilities for the generation of novel devices with additional optical and electronic functionalities, as it has been previously shown in planar structures.

  5. Axial Ge/Si nanowire heterostructure tunnel FETs

    Energy Technology Data Exchange (ETDEWEB)

    Picraux, Sanuel T [Los Alamos National Laboratory; Daych, Shadi A [Los Alamos National Laboratory

    2010-01-01

    The vapor-liquid-solid (VLS) growth of semiconductor nanowires allows doping and composition modulation along their axis and the realization of axial 1 D heterostructures. This provides additional flexibility in energy band-edge engineering along the transport direction which is difficult to attain by planar materials growth and processing techniques. We report here on the design, growth, fabrication, and characterization of asymmetric heterostructure tunnel field-effect transistors (HTFETs) based on 100% compositionally modulated Si/Ge axial NWs for high on-current operation and low ambipolar transport behavior. We discuss the optimization of band-offsets and Schottky barrier heights for high performance HTFETs and issues surrounding their experimental realization. Our HTFET devices with 10 nm PECVD SiN{sub x} gate dielectric resulted in a measured current drive exceeding 100 {mu}A/{mu}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios.

  6. High ionic conductivity in confined bismuth oxide-based heterostructures

    DEFF Research Database (Denmark)

    Sanna, Simone; Esposito, Vincenzo; Christensen, Mogens

    2016-01-01

    Bismuth trioxide in the cubic fluorite phase (δ-Bi2O3) exhibits the highest oxygen ionic conductivity. In this study, we were able to stabilize the pure -Bi2O3 at low temperature with no addition of stabilizer but only by engineering the interface, using highly coherent heterostructures made...... of alternative layers of δ-Bi2O3 and Yttria Stabilized Zirconia (YSZ), deposited by pulsed laser deposition. The resulting [δ-Bi2O3=YSZ] heterostructures are found to be stable over a wide temperature range (500-750 °C) and exhibits stable high ionic conductivity over a long time comparable to the value...... of the pure δ-Bi2O3, which is approximately two orders of magnitude higher than the conductivity of YSZ bulk....

  7. Band structure engineering in topological insulator based heterostructures.

    Science.gov (United States)

    Menshchikova, T V; Otrokov, M M; Tsirkin, S S; Samorokov, D A; Bebneva, V V; Ernst, A; Kuznetsov, V M; Chulkov, E V

    2013-01-01

    The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.

  8. Optoelectronics based on 2D TMDs and heterostructures

    Science.gov (United States)

    Huo, Nengjie; Yang, Yujue; Li, Jingbo

    2017-03-01

    2D materials including graphene and TMDs have proven interesting physical properties and promising optoelectronic applications. We reviewed the growth, characterization and optoelectronics based on 2D TMDs and their heterostructures, and demonstrated their unique and high quality of performances. For example, we observed the large mobility, fast response and high photo-responsivity in MoS2, WS2 and WSe2 phototransistors, as well as the novel performances in vdW heterostructures such as the strong interlayer coupling, am-bipolar and rectifying behaviour, and the obvious photovoltaic effect. It is being possible that 2D family materials could play an increasingly important role in the future nano- and opto-electronics, more even than traditional semiconductors such as silicon.

  9. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures

    OpenAIRE

    Kral, S.; Zeiner, C.; St?ger-Pollach, M.; Bertagnolli, E.; Den Hertog, M.I.; Lopez-Haro, M.; Robin, E.; El Hajraoui, K.; Lugstein, A.

    2015-01-01

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor?liquid?solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I?V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying...

  10. Liquid phase epitaxial growth of heterostructured hierarchical MOF thin films

    KAUST Repository

    Chernikova, Valeriya

    2017-05-10

    Precise control of epitaxial growth of MOF-on-MOF thin films, for ordered hierarchical tbo-type structures is demonstrated. The heterostructured MOF thin film was fabricated by successful sequential deposition of layers from two different MOFs. The 2-periodic layers, edge-transitive 4,4-square lattices regarded as supermolecular building layers, were commendably cross-linked using a combination of inorganic/organic and organic pillars.

  11. Double-heterostructure cavities: from theory to design

    CERN Document Server

    Mahmoodian, Sahand; Poulton, Christopher G; Dossou, Kokou B; Botten, Lindsay C; McPhedran, Ross C; de Sterke, C Martijn

    2012-01-01

    We derive a frequency-domain-based approach for radiation (FAR) from double-heterostructure cavity (DHC) modes. We use this to compute the quality factors and radiation patterns of DHC modes. The semi-analytic nature of our method enables us to provide a general relationship between the radiation pattern of the cavity and its geometry. We use this to provide general designs for ultrahigh quality factor DHCs with radiation patterns that are engineered to emit vertically.

  12. Ag/CdS heterostructural composites: Fabrication, characterizations and photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yang [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China); Chi, Mei [Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning 110016 (China); Dong, Hailiang; Jia, Husheng; Xu, Bingshe [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China); Zhang, Zhuxia, E-mail: zhangzhuxia@tyut.edu.cn [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China)

    2014-09-15

    Highlights: • Novel Ag/CdS core–shell heterostructural composites were fabricated using a two-step chemical method. • A formation mechanism of Ag/CdS heterostructural composites. • The photocatalytic activity of Ag/CdS heterostructural composites was found to be improved. • PL emissions are markedly quenched in the Ag/CdS composites than in CdS nanoparticles. - Abstract: Ag/CdS heterostructural materials were successfully synthesized by ultrasound-assisted polyols and hydrothermal method. Under hydrothermal condition, thiourea adsorbed on Ag nanowires releases S{sup 2−} ions, which react with vicinal Cd{sup 2+} ions to form CdS clusters on Ag nanowires. Thereafter, the Ag/CdS composites grow into core–shell structure through CdS aggregation, Ostwald ripening, and preferential growth. The obtained core–shell structures and morphologies were investigated by XRD, SEM, and TEM; the experimental results indicate that the composites are composed of Ag nanowires serving as the core and CdS particles as the shell. The photocatalytic property of Ag/CdS core–shell materials was then investigated in detail. Comparing studies on the degradation of methylene blue were employed by using pure CdS, pure Ag, and Ag/CdS composites, respectively. The results show that the Ag/CdS composites possess higher photocatalytic degradation efficiency. Moreover, the Ag/CdS composites show improved stability, and the photocatalytic activity remains almost unchanged after four recycles. The enhanced photocatalytic effect for Ag/CdS composites is mainly attributed to the photogenerated electron transfer from CdS to Ag nanowire, while photogenerated holes still remain in CdS's valence band. Consequently, the effective separation of photogenerated electrons and holes and the resulting OH radicals improve the photocatalytic efficiency of Ag/CdS composites greatly.

  13. Band gap dependence of semiconducting nano-wires on cross-sectional shape and size

    Science.gov (United States)

    Arora, Neha; Joshi, Deepika P.

    2017-12-01

    Applicability of three different thermodynamic models based on classical (Qi model) as well as quantum approach (Lu et al. and Jiang et al. models) have been discussed to search out the exact description of band gap variation with size in semiconducting nanowires. All considered models showed an increment in the band gap as diametric size of the wire decreases. To study band gap and the band edge shift of nanowires, a novel approach has been proposed by incorporating shape effect with size in Jiang et al. model due to its accuracy or consistency with the experimental results. Hence a unified model without any adjustable parameter has been established for studying the combined effect of size and shape on band edges shift [ΔEc (D), ΔEv (D)] and the band gap expansion [ΔEG (D)] of the semiconducting nanowires. Present study reveals that for small-sized nanowires band gap expansion and edge shift is not only governed by size but also varies with the cross-sectional shape. Band gap expansion and edge shift showed rising behavior due to the enhancement in surface area.

  14. Synthesis, characterization, and transistor and solar cell applications of a naphthobisthiadiazole-based semiconducting polymer.

    Science.gov (United States)

    Osaka, Itaru; Shimawaki, Masafumi; Mori, Hiroki; Doi, Iori; Miyazaki, Eigo; Koganezawa, Tomoyuki; Takimiya, Kazuo

    2012-02-22

    We report the synthesis and characterization of a novel donor-acceptor semiconducting polymer bearing naphthobisthiadiazole (NTz), a doubly benzothiadiazole (BTz)-fused ring, and its applications to organic field-effect transistors and bulk heterojunction solar cells. With NTz's highly π-extended structure and strong electron affinity, the NTz-based polymer (PNTz4T) affords a smaller bandgap and a deeper HOMO level than the BTz-based polymer (PBTz4T). PNTz4T exhibits not only high field-effect mobilities of ~0.56 cm(2)/(V s) but also high photovoltaic properties with power conversion efficiencies of ~6.3%, both of which are significantly high compared to those for PBTz4T. This is most likely due to the more suitable electronic properties and, importantly, the more highly ordered structure of PNTz4T in the thin film than that of PBTz4T, which might originate in the different symmetry between the cores. NTz, with centrosymmetry, can lead to a more linear backbone in the present polymer system than BTz with axisymmetry, which might be favorable for better molecular ordering. These results demonstrate great promise for using NTz as a bulding unit for high-performance semiconducting polymers for both transistors and solar cells.

  15. Challenges Found When Patterning Semiconducting Polymers with Electric Fields for Organic Solar Cell Applications

    Directory of Open Access Journals (Sweden)

    Fernando A. de Castro

    2012-01-01

    Full Text Available A material-independent, contactless structuring method of semiconducting organic materials for the fabrication of interface-enhanced bilayer solar cells is not available so far. Patterning of thin films using electrohydrodynamic instabilities possesses many desired characteristics and has convincingly been used as a simple method to structure and replicate patterns of nonconducting polymers on submicrometer length scales. However, the applicability of this technique to a wider range of materials has not been demonstrated yet. Here, we report attempts to structure poly(p-phenylene vinylene in a similar way. We found that thin films of poly(2-methoxy-5-(2′-ethylhexyl-oxy-1,4-phenylene-vinylene (MEH-PPV and poly(2-methoxy-5-(3′,7′-dimethyloctyloxy-1,4-phenylene-vinylene (MDMO-PPV could not be destabilized at all in the limited accessible range of the experimental parameters set by the delicate chemical nature of these materials. We discuss failure origins and present possible loopholes for the patterning of semiconducting polymers using electric fields.

  16. Synthesis and morphological modification of semiconducting Mg(Zn)Al(Ga)–LDH/ITO thin films

    Energy Technology Data Exchange (ETDEWEB)

    Valente, Jaime S., E-mail: jsanchez@imp.mx [Instituto Mexicano del Petróleo, Eje Central # 152, 07730 México D.F. (Mexico); López-Salinas, Esteban [Instituto Mexicano del Petróleo, Eje Central # 152, 07730 México D.F. (Mexico); Prince, Julia [Universidad Anáhuac México Norte, Av. Universidad Anáhuac # 46, Huixquilucan, Edo. de México 52786 (Mexico); González, Ignacio; Acevedo-Peña, Prospero [Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Apdo. Postal 55-534, 09340 México D.F. (Mexico); Ángel, Paz del [Instituto Mexicano del Petróleo, Eje Central # 152, 07730 México D.F. (Mexico)

    2014-09-15

    Layered double hydroxide (LDH) thin films with different chemical compositions (MgZnAl, MgZnGa, MgGaAl) and varying thicknesses were easily prepared by sol–gel method followed by dip-coating. Films were chemically uniform, transparent and well adhered to a conductive indium tin oxide (ITO) substrate. Structure, chemical composition and morphology of the thin films were characterized by XRD-GADDS, SEM-EDS and AFM. Additionally, the semiconducting properties of all the prepared films were studied through the Mott–Schottky relationship; such properties were closely related to the chemical compositions of the film. The films were characterized after electrochemical treatment and important modifications regarding surface morphology, particle and crystal sizes were observed. An in-depth study was conducted in order to investigate the effect of several different electrochemical treatments on the morphology, particle size distribution and crystal size of LDH thin films. Upon electrochemical treatment, the films' surface became smooth and the particles forming the films were transformed from flaky open LDH platelets to uniformly distributed close-packed LDH nanoparticles. - Highlights: • Semiconducting Mg(Zn)Al(Ga)–LDH/ITO thin films prepared by sol–gel. • LDH thin films show a turbostratic morphology made up of porous flakes. • Electrochemical treatments change the flaky structure into a nanoparticle array.

  17. 5,10-linked naphthodithiophenes as the building block for semiconducting polymers

    Science.gov (United States)

    Osaka, Itaru; Komatsu, Koki; Koganezawa, Tomoyuki; Takimiya, Kazuo

    2014-04-01

    We present new semiconducting polymers incorporating naphtho[1, 2-b:5, 6-b‧] dithiophene (NDT3) and naphtho[2, 1-b:6, 5-b‧] dithiophene (NDT4), which are linked at the naphthalene positions, in the polymer backbone. It is interesting that the trend in the ordering structure and thus charge transport properties are quite different from what were observed in the isomeric polymers where the NDT3 and NDT4 cores are linked at the thiophene α-positions. In the thiophene-linked NDT system, the NDT3-based polymer (PNDT3BT) gave the better ordering in thin films and thus the high charge carrier mobility compared to the NDT4-based polymer (PNDT4BT). In the meantime, in the naphthalene-linked NDT system, the NDT4-based polymer (PNDT4iBT) provided the superior properties. Considering that PNDT4iBT has relatively low highest occupied molecular orbital (HOMO) energy level (-5.2 eV) and moderately high mobilities in the order of 10-2 cm2 V-1 s-1, the NDT4 core, when linked at the naphthalene positions, can be a good building unit for the development of high-performance semiconducting polymers for both organic field-effect transistors and photovoltaic devices.

  18. Vanadium sesquioxide (V2O3)-based semiconducting temperature sensitive resistors for uncooled microbolometers

    Science.gov (United States)

    Abdel-Rahman, Mohamed; Alduraibi, Mohammad; Zia, Muhammad Fakhar; Bahidra, Esme; Alasaad, Amr

    2017-05-01

    This paper reports on a semiconducting resistor material based on vanadium sesquioxide (V2O3) with electrical resistivity and temperature coefficient of resistance (TCR) appropriate for microbolometer applications. In this work, V2O3-based semiconducting resistor material was synthesized and electrically characterized. The developed material was prepared by annealing, in O2 and N2 atmospheres, a cascaded multilayer structure composed of V2O3 (10 nm) and V (5 nm) room temperature sputter coated thin films. The developed 55 nm thin film microbolometer resistor material possessed high temperature sensitivity from 20∘C to 45∘C with a TCR of -3.68%/∘C and room temperature resistivity of 0.57 Ω ṡcm for O2 annealed samples and a TCR of -3.72%/∘C and room temperature resistivity of 0.72 Ω ṡcm for N2 annealed samples. The surface morphologies of the synthesized thin films were studied using atomic force microscopy showing no significant post-growth annealing effect on the smoothness of the samples surfaces.

  19. Defects in individual semiconducting single wall carbon nanotubes: Raman spectroscopic and in situ Raman spectroelectrochemical study.

    Science.gov (United States)

    Kalbac, Martin; Hsieh, Ya-Ping; Farhat, Hootan; Kavan, Ladislav; Hofmann, Mario; Kong, Jing; Dresselhaus, Mildred S

    2010-11-10

    Raman spectroscopy and in situ Raman spectroelectrochemistry have been used to study the influence of defects on the Raman spectra of semiconducting individual single-walled carbon nanotubes (SWCNTs). The defects were created intentionally on part of an originally defect-free individual semiconducting nanotube, which allowed us to analyze how defects influence this particular nanotube. The formation of defects was followed by Raman spectroscopy that showed D band intensity coming from the defective part and no D band intensity coming from the original part of the same nanotube. It is shown that the presence of defects also reduces the intensity of the symmetry-allowed Raman features. Furthermore, the changes to the Raman resonance window upon the introduction of defects are analyzed. It is demonstrated that defects lead to both a broadening of the Raman resonance profile and a decrease in the maximum intensity of the resonance profile. The in situ Raman spectroelectrochemical data show a doping dependence of the Raman features taken from the defective part of the tested SWCNT.

  20. New anthracene-based-phtalocyanine semi-conducting materials: Synthesis and optoelectronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Kahouech, M.S. [Laboratoire de Chimie Organique et Analytique, Institut Supérieur de l' Education et de la Formation Continue (Université El Manar), Bardo 2000 (Tunisia); Hriz, K., E-mail: khaledhriz@gmail.com [Laboratoire des Interfaces et Matériaux Avancés (LIMA), Faculté des Sciences de Monastir (Université de Monastir), Bd. de l' Environnement, Monastir 5019 (Tunisia); Touaiti, S.; Bassem, J. [Laboratoire de Chimie Organique et Analytique, Institut Supérieur de l' Education et de la Formation Continue (Université El Manar), Bardo 2000 (Tunisia)

    2016-03-15

    Highlights: • Synthesis of tow phtalocyanines based on the anthracene and tetrazole. • Semi-conducting supramolecular material. • Good PL quantum yield. • The film morphology of the phtalocynine containing tetrazole group enhanced the carrier mobility. - Abstract: A new anthracene-based semi-conducting phtalocyanines AnPc and AnPc-Tr were synthesized in solvent-free conditions. The supramolecular structure of these compounds was confirmed by NMR and FT-IR spectroscopies. Their optical properties were investigated by UV–vis and photoluminescence spectroscopies. The optical gaps were estimated from the absorption-onsets films, and the obtained values were of 1.50 eV and 1.47 eV for AnPc-Tr and AnPc respectively. In solid state, a weaker π–π-interactions of conjugated systems were obtained in the case of AnPc-Tr in comparison with AnPc. This behavior was explained by steric hindrance of triazol groups, which decrease the planarity of macromolecular structure. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis; two phtalocyanine derivatives show a comparable ionization potential. The phtalacyanine containing triazole groups (AnPc-Tr) reveals a higher electron affinity in comparison with AnPc. Single-layer diode devices were fabricated and showed relatively low turn-on voltages.

  1. Universal Selective Dispersion of Semiconducting Carbon Nanotubes from Commercial Sources Using a Supramolecular Polymer.

    Science.gov (United States)

    Chortos, Alex; Pochorovski, Igor; Lin, Pei; Pitner, Gregory; Yan, Xuzhou; Gao, Theodore Z; To, John W F; Lei, Ting; Will, John W; Wong, H-S Philip; Bao, Zhenan

    2017-06-27

    Selective extraction of semiconducting carbon nanotubes is a key step in the production of high-performance, solution-processed electronics. Here, we describe the ability of a supramolecular sorting polymer to selectively disperse semiconducting carbon nanotubes from five commercial sources with diameters ranging from 0.7 to 2.2 nm. The sorting purity of the largest-diameter nanotubes (1.4 to 2.2 nm; from Tuball) was confirmed by short channel measurements to be 97.5%. Removing the sorting polymer by acid-induced disassembly increased the transistor mobility by 94 and 24% for medium-diameter and large-diameter carbon nanotubes, respectively. Among the tested single-walled nanotube sources, the highest transistor performance of 61 cm2/V·s and on/off ratio >104 were realized with arc discharge carbon nanotubes with a diameter range from 1.2 to 1.7 nm. The length and quality of nanotubes sorted from different sources is compared using measurements from atomic force microscopy and Raman spectroscopy. The transistor mobility is found to correlate with the G/D ratio extracted from the Raman spectra.

  2. On-Chip Sorting of Long Semiconducting Carbon Nanotubes for Multiple Transistors along an Identical Array.

    Science.gov (United States)

    Otsuka, Keigo; Inoue, Taiki; Maeda, Etsuo; Kometani, Reo; Chiashi, Shohei; Maruyama, Shigeo

    2017-11-13

    Ballistic transport and sub-10 nm channel lengths have been achieved in transistors containing one single-walled carbon nanotube (SWNT). To fill the gap between single-tube transistors and high-performance logic circuits for the replacement of silicon, large-area, high-density, and purely semiconducting (s-) SWNT arrays are highly desired. Here we demonstrate the fabrication of multiple transistors along a purely semiconducting SWNT array via an on-chip purification method. Water- and polymer-assisted burning from site-controlled nanogaps is developed for the reliable full-length removal of metallic SWNTs with the damage to s-SWNTs minimized even in high-density arrays. All the transistors with various channel lengths show large on-state current and excellent switching behavior in the off-state. Since our method potentially provides pure s-SWNT arrays over a large area with negligible damage, numerous transistors with arbitrary dimensions could be fabricated using a conventional semiconductor process, leading to SWNT-based logic, high-speed communication, and other next-generation electronic devices.

  3. Tunable Semiconducting Polymer Nanoparticles with INDT-Based Conjugated Polymers for Photoacoustic Molecular Imaging.

    Science.gov (United States)

    Stahl, Thomas; Bofinger, Robin; Lam, Ivan; Fallon, Kealan J; Johnson, Peter; Ogunlade, Olumide; Vassileva, Vessela; Pedley, R Barbara; Beard, Paul C; Hailes, Helen C; Bronstein, Hugo; Tabor, Alethea B

    2017-06-21

    Photoacoustic imaging combines both excellent spatial resolution with high contrast and specificity, without the need for patients to be exposed to ionizing radiation. This makes it ideal for the study of physiological changes occurring during tumorigenesis and cardiovascular disease. In order to fully exploit the potential of this technique, new exogenous contrast agents with strong absorbance in the near-infrared range, good stability and biocompatibility, are required. In this paper, we report the formulation and characterization of a novel series of endogenous contrast agents for photoacoustic imaging in vivo. These contrast agents are based on a recently reported series of indigoid π-conjugated organic semiconductors, coformulated with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, to give semiconducting polymer nanoparticles of about 150 nm diameter. These nanoparticles exhibited excellent absorption in the near-infrared region, with good photoacoustic signal generation efficiencies, high photostability, and extinction coefficients of up to three times higher than those previously reported. The absorption maximum is conveniently located in the spectral region of low absorption of chromophores within human tissue. Using the most promising semiconducting polymer nanoparticle, we have demonstrated wavelength-dependent differential contrast between vasculature and the nanoparticles, which can be used to unambiguously discriminate the presence of the contrast agent in vivo.

  4. Template-based preparation of free-standing semiconducting polymeric nanorod arrays on conductive substrates.

    Science.gov (United States)

    Haberkorn, Niko; Weber, Stefan A L; Berger, Rüdiger; Theato, Patrick

    2010-06-01

    We describe the synthesis and characterization of a cross-linkable siloxane-derivatized tetraphenylbenzidine (DTMS-TPD), which was used for the fabrication of semiconducting highly ordered nanorod arrays on conductive indium tin oxide or Pt-coated substrates. The stepwise process allow fabricating of macroscopic areas of well-ordered free-standing nanorod arrays, which feature a high resistance against organic solvents, semiconducting properties and a good adhesion to the substrate. Thin films of the TPD derivate with good hole-conducting properties could be prepared by cross-linking and covalently attaching to hydroxylated substrates utilizing an initiator-free thermal curing at 160 degrees C. The nanorod arrays composed of cross-linked DTMS-TPD were fabricated by an anodic aluminum oxide (AAO) template approach. Furthermore, the nanorod arrays were investigated by a recently introduced method allowing to probe local conductivity on fragile structures. It revealed that more than 98% of the nanorods exhibit electrical conductance and consequently feature a good electrical contact to the substrate. The prepared nanorod arrays have the potential to find application in the fabrication of multilayered device architectures for building well-ordered bulk-heterojunction solar cells.

  5. Half-cell potentials of semiconductive simple binary sulphides in aqueous solution

    Science.gov (United States)

    Sato, M.

    1966-01-01

    Theoretical consideration of the charge-transfer mechanism operative in cells with an electrode of a semiconductive binary compound leads to the conclusion that the half-cell potential of such a compound is not only a function of ionic activities in the electrolytic solution, but also a function of the activities of the component elements in the compound phase. The most general form of the electrode equation derived for such a compound with a formula MiXj which dissociates into Mj+ and Xi- ions in aqueous solution is. EMiXj = EMiXj0 + R T 2 ij ln [ (sua Mj+)aqi ?? (suaX)jMiXj/ (suaXi-)aqj ?? (suaM)iMiXj],. where. EMiXj0 = 1 2(EM,Mj+0 + EXi-,X). The equation can be modified to other forms. When applied to semiconductive simple binary sulphides, these equations appear to give better descriptions of the observed electrode potentials of such sulphides than any other proposed equations. ?? 1966.

  6. Evaluation of polarization rotation in the scattering responses from individual semiconducting oxide nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Daniel S.; Singh, Manpreet; Zhou, Hebing; Milchak, Marissa; Monahan, Brian; Hahm, Jong-in, E-mail: jh583@georgetown.edu [Department of Chemistry, Georgetown University, 37" t" h & O Sts. NW., Washington, DC 20057 (United States)

    2016-04-15

    We investigate the interaction of visible light with the solid matters of semiconducting oxide nanorods (NRs) of zinc oxide (ZnO), indium tin oxide (ITO), and zinc tin oxide (ZTO) at the single nanomaterial level. We subsequently identify an intriguing, material-dependent phenomenon of optical rotation in the electric field oscillation direction of the scattered light by systematically controlling the wavelength and polarization direction of the incident light, the NR tilt angle, and the analyzer angle. This polarization rotation effect in the scattered light is repeatedly observed from the chemically pure and highly crystalline ZnO NRs, but absent on the chemically doped NR variants of ITO and ZTO under all measurement circumstances. We further elucidate that the phenomenon of polarization rotation detected from single ZnO NRs is affected by the NR tilt angle, while the phenomenon itself occurs irrespective of the wavelength and incident polarization direction of the visible light. Combined with the widespread optical and optoelectronic use of the semiconducting oxide nanomaterials, these efforts may provide much warranted fundamental bases to tailor material-specific, single nanomaterial-driven, optically modulating functionalities which, in turn, can be beneficial for the realization of high-performance integrated photonic circuits and miniaturized bio-optical sensing devices.

  7. XRD- and infrared-probed anisotropic thermal expansion properties of an organic semiconducting single crystal.

    Science.gov (United States)

    Mohanraj, J; Capria, E; Benevoli, L; Perucchi, A; Demitri, N; Fraleoni-Morgera, A

    2018-01-17

    The anisotropic thermal expansion properties of an organic semiconducting single crystal constituted by 4-hydroxycyanobenzene (4HCB) have been probed by XRD in the range 120-300 K. The anisotropic thermal expansion coefficients for the three crystallographic axes and for the crystal volume have been determined. A careful analysis of the crystal structure revealed that the two different H-bonds stemming from the two independent, differently oriented 4HCB molecules composing the unit cell have different rearrangement patterns upon temperature variations, in terms of both bond length and bond angle. Linearly Polarized Mid InfraRed (LP-MIR) measurements carried out in the same temperature range, focused on the O-H bond spectral region, confirm this finding. The same LP-MIR measurements, on the basis of a semi-empirical relation and of geometrical considerations and assumptions, allowed calculation of the -CNH-O- hydrogen bond length along the a and b axes of the crystal. In turn, the so-calculated -CNH-O- bond lengths were used to derive the thermal expansion coefficients along the corresponding crystal axes, as well as the volumetric one, using just the LP-MIR data. Reasonable to good agreement with the same values obtained from XRD measurements was obtained. This proof-of-principle opens interesting perspectives about the possible development of a rapid, low cost and industry-friendly assessment of the thermal expansion properties of organic semiconducting single crystals (OSSCs) involving hydrogen bonds.

  8. Selective Growth of Metal-Free Metallic and Semiconducting Single-Wall Carbon Nanotubes.

    Science.gov (United States)

    Zhang, Lili; Sun, Dong-Ming; Hou, Peng-Xiang; Liu, Chang; Liu, Tianyuan; Wen, Jianfeng; Tang, Nujiang; Luan, Jian; Shi, Chao; Li, Jin-Cheng; Cong, Hong-Tao; Cheng, Hui-Ming

    2017-08-01

    A major obstacle for the use of single-wall carbon nanotubes (SWCNTs) in electronic devices is their mixture of different types of electrical conductivity that strongly depends on their helical structure. The existence of metal impurities as a residue of a metallic growth catalyst may also lower the performance of SWCNT-based devices. Here, it is shown that by using silicon oxide (SiO x ) nanoparticles as a catalyst, metal-free semiconducting and metallic SWCNTs can be selectively synthesized by the chemical vapor deposition of ethanol. It is found that control over the nanoparticle size and the content of oxygen in the SiO x catalyst plays a key role in the selective growth of SWCNTs. Furthermore, by using the as-grown semiconducting and metallic SWCNTs as the channel material and source/drain electrodes, respectively, all-SWCNT thin-film transistors are fabricated to demonstrate the remarkable potential of these SWCNTs for electronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Using nanoscale thermocapillary flows to create arrays of purely semiconducting single-walled carbon nanotubes.

    Science.gov (United States)

    Jin, Sung Hun; Dunham, Simon N; Song, Jizhou; Xie, Xu; Kim, Ji-Hun; Lu, Chaofeng; Islam, Ahmad; Du, Frank; Kim, Jaeseong; Felts, Johnny; Li, Yuhang; Xiong, Feng; Wahab, Muhammad A; Menon, Monisha; Cho, Eugene; Grosse, Kyle L; Lee, Dong Joon; Chung, Ha Uk; Pop, Eric; Alam, Muhammad A; King, William P; Huang, Yonggang; Rogers, John A

    2013-05-01

    Among the remarkable variety of semiconducting nanomaterials that have been discovered over the past two decades, single-walled carbon nanotubes remain uniquely well suited for applications in high-performance electronics, sensors and other technologies. The most advanced opportunities demand the ability to form perfectly aligned, horizontal arrays of purely semiconducting, chemically pristine carbon nanotubes. Here, we present strategies that offer this capability. Nanoscale thermocapillary flows in thin-film organic coatings followed by reactive ion etching serve as highly efficient means for selectively removing metallic carbon nanotubes from electronically heterogeneous aligned arrays grown on quartz substrates. The low temperatures and unusual physics associated with this process enable robust, scalable operation, with clear potential for practical use. We carry out detailed experimental and theoretical studies to reveal all of the essential attributes of the underlying thermophysical phenomena. We demonstrate use of the purified arrays in transistors that achieve mobilities exceeding 1,000 cm(2) V(-1) s(-1) and on/off switching ratios of ∼10,000 with current outputs in the milliamp range. Simple logic gates built using such devices represent the first steps toward integration into more complex circuits.

  10. Observing Imperfection in Atomic Interfaces for van der Waals Heterostructures

    Science.gov (United States)

    Rooney, Aidan. P.; Kozikov, Aleksey; Rudenko, Alexander N.; Prestat, Eric; Hamer, Matthew J.; Withers, Freddie; Cao, Yang; Novoselov, Kostya S.; Katsnelson, Mikhail I.; Gorbachev, Roman; Haigh, Sarah J.

    2017-09-01

    Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS2 or WS2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe2 and WSe2, our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN: interfaces which are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe2 from bulk to monolayer we see a systematic increase in the interlayer separation. We attribute these differences to the thinnest TMDC flakes being flexible and hence able to deform mechanically around a sparse population of protruding interfacial impurities. We show that the air sensitive two dimensional (2D) crystal NbSe2 can be fabricated into heterostructures with pristine interfaces by processing in an inert-gas environment. Finally we find that adopting glove-box transfer significantly improves the quality of interfaces for WSe2 compared to processing in air.

  11. Pulsed laser deposition of yttria stabilized zirconia based heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Pascu, R. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Somacescu, S. [Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest (Romania); Epurescu, G.; Filipescu, M.; Luculescu, C.; Colceag, D. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Osiceanu, P. [Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest (Romania); Birjega, R. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Mitu, B., E-mail: mitub@infim.ro [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania)

    2014-02-28

    Yttria stabilized zirconia (YSZ), nickel-doped yttria stabilized zirconia (NiYSZ) thin films and NiYSZ/YSZ anode–electrolyte heterostructure have been synthesized on Si(100) substrate by pulsed laser deposition technique. Atomic Force Microscopy, Scanning Electron Microscopy, and Variable Angle Spectroscopic Ellipsometry studies have been applied to determine the surface topography, film morphology and thickness. The X-ray diffraction measurements evidenced a highly textured growth along (111) direction for NiYSZ/YSZ heterostructure with crystallite dimension of 18 nm. The X-ray photoelectron spectroscopy analysis showed a displacement of Ni oxidation states along the depth profile, with Ni{sup 3+} oxidation state on the surface, a very thin layer containing Ni{sup 2+} associated to NiO buried under the surface, while metallic Ni is predominant in the bulk. The presence of an intermix layer at the interface between the NiYSZ and YSZ, suggested by the ellipsometric measurements, was confirmed by Secondary Neutral Mass Spectrometry data. - Highlights: • Crystalline NiYSZ/YSZ heterostructure with cubic phase was obtained by PLD at 873 K. • The structure presents an intermix layer at the interface between the NiYSZ and YSZ films. • Ni is present on the surface as Ni{sub 2}O{sub 3}, while in the bulk metallic Ni is predominant.

  12. Gating of high-mobility InAs metamorphic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Shabani, J. [California NanoSystems Institute, University of California, Santa Barbara, California 93106 (United States); McFadden, A. P. [Department of Electrical Engineering, University of California, Santa Barbara, California 93106 (United States); Shojaei, B. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Palmstrøm, C. J. [California NanoSystems Institute, University of California, Santa Barbara, California 93106 (United States); Department of Electrical Engineering, University of California, Santa Barbara, California 93106 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States)

    2014-12-29

    We investigate the performance of gate-defined devices fabricated on high mobility InAs metamorphic heterostructures. We find that heterostructures capped with In{sub 0.75}Ga{sub 0.25}As often show signs of parallel conduction due to proximity of their surface Fermi level to the conduction band minimum. Here, we introduce a technique that can be used to estimate the density of this surface charge that involves cool-downs from room temperature under gate bias. We have been able to remove the parallel conduction under high positive bias, but achieving full depletion has proven difficult. We find that by using In{sub 0.75}Al{sub 0.25}As as the barrier without an In{sub 0.75}Ga{sub 0.25}As capping, a drastic reduction in parallel conduction can be achieved. Our studies show that this does not change the transport properties of the quantum well significantly. We achieved full depletion in InAlAs capped heterostructures with non-hysteretic gating response suitable for fabrication of gate-defined mesoscopic devices.

  13. Electron dynamics in MoS2-graphite heterostructures.

    Science.gov (United States)

    Zhang, Xinwu; He, Dawei; Yi, Lixin; Zhao, Siqi; He, Jiaqi; Wang, Yongsheng; Zhao, Hui

    2017-10-05

    The electron dynamics in heterostructures formed by multilayer graphite and monolayer or bulk MoS2 were studied by femtosecond transient absorption measurements. Samples of monolayer MoS2-multilayer graphite and bulk MoS2-multilayer graphite were fabricated by exfoliation and dry transfer techniques. Ultrafast laser pulses were used to inject electron-hole pairs into monolayer or bulk MoS2. The transfer of these photocarriers to the adjacent multilayer graphite was time resolved by measuring the differential reflection of a probe pulse. We found that photocarriers injected into monolayer MoS2 transfer to graphite on an ultrafast time scale shorter than 400 fs. Such an efficient charge transfer is key to the development of high performance optoelectronic devices with MoS2 as the light absorbing layer and graphite as electrodes. The absorption coefficient of monolayer MoS2 can be controlled by the carriers in graphite. This process can be used for interlayer coupling and control. In a bulk MoS2-graphite heterostructure, the photocarrier transfer time is about 220 ps, due to the inefficient interlayer charge transport in bulk MoS2. These results provide useful information for developing optoelectronic devices based on MoS2-graphite heterostructures.

  14. Evolutionary design of interfacial phase change van der Waals heterostructures.

    Science.gov (United States)

    Kalikka, Janne; Zhou, Xilin; Behera, Jitendra; Nannicini, Giacomo; Simpson, Robert E

    2016-10-27

    We use an evolutionary algorithm to explore the design space of hexagonal Ge 2 Sb 2 Te 5 ; a van der Waals layered two dimensional crystal heterostructure. The Ge 2 Sb 2 Te 5 structure is more complicated than previously thought. Predominant features include layers of Ge 3 Sb 2 Te 6 and Ge 1 Sb 2 Te 4 two dimensional crystals that interact through Te-Te van der Waals bonds. Interestingly, (Ge/Sb)-Te-(Ge/Sb)-Te alternation is a common feature for the most stable structures of each generation's evolution. This emergent rule provides an important structural motif that must be included in the design of high performance Sb 2 Te 3 -GeTe van der Waals heterostructure superlattices with interfacial atomic switching capability. The structures predicted by the algorithm agree well with experimental measurements on highly oriented, and single crystal Ge 2 Sb 2 Te 5 samples. By analysing the evolutionary algorithm optimised structures, we show that diffusive atomic switching is probable by Ge atoms undergoing a transition at the van der Waals interface from layers of Ge 3 Sb 2 Te 6 to Ge 1 Sb 2 Te 4 thus producing two blocks of Ge 2 Sb 2 Te 5 . Evolutionary methods present an efficient approach to explore the enormous multi-dimensional design parameter space of van der Waals bonded heterostructure superlattices.

  15. Franckeite as a naturally occurring van der Waals heterostructure

    Science.gov (United States)

    Molina-Mendoza, Aday J.; Giovanelli, Emerson; Paz, Wendel S.; Niño, Miguel Angel; Island, Joshua O.; Evangeli, Charalambos; Aballe, Lucía; Foerster, Michael; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agraït, Nicolás; Palacios, J. J.; Pérez, Emilio M.; Castellanos-Gomez, Andres

    2017-01-01

    The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors. PMID:28194037

  16. Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Vieira, Kayo Oliveira [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Bettini, Jefferson [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970, Campinas, SP (Brazil); Ferrari, Jefferson Luis [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil)

    2015-01-15

    The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs.

  17. Axial Ge/Si nanowire heterostructure tunnel FETs.

    Energy Technology Data Exchange (ETDEWEB)

    Dayeh, Shadi A. (Los Alamos National Laboratory); Gin, Aaron V.; Huang, Jian Yu; Picraux, Samuel Thomas (Los Alamos National Laboratory)

    2010-03-01

    Axial Ge/Si heterostructure nanowires (NWs) allow energy band-edge engineering along the axis of the NW, which is the charge transport direction, and the realization of asymmetric devices for novel device architectures. This work reports on two significant advances in the area of heterostructure NWs and tunnel FETs: (i) the realization of 100% compositionally modulated Si/Ge axial heterostructure NWs with lengths suitable for device fabrication and (ii) the design and implementation of Schottky barrier tunnel FETs on these NWs for high-on currents and suppressed ambipolar behavior. Initial prototype devices with 10 nm PECVD SiN{sub x} gate dielectric resulted in a very high current drive in excess of 100 {micro}A/{micro}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios. Prior work on the synthesis of Ge/Si axial NW heterostructures through the VLS mechanism have resulted in axial Si/Si{sub 1-x}Ge{sub x} NW heterostructures with x{sub max} {approx} 0.3, and more recently 100% composition modulation was achieved with a solid growth catalyst. In this latter case, the thickness of the heterostructure cannot exceed few atomic layers due to the slow axial growth rate and concurrent radial deposition on the NW sidewalls leading to a mixture of axial and radial deposition, which imposes a big challenge for fabricating useful devices form these NWs in the near future. Here, we report the VLS growth of 100% doping and composition modulated axial Ge/Si heterostructure NWs with lengths appropriate for device fabrication by devising a growth procedure that eliminates Au diffusion on the NW sidewalls and minimizes random kinking in the heterostructure NWs as deduced from detailed microscopy analysis. Fig. 1 a shows a cross-sectional SEM image of epitaxial Ge/Si axial NW heterostructures grown on a Ge(111) surface. The interface abruptness in these Ge/Si heterostructure NWs is of the order of the NW diameter. Some of these NWs develop a crystallographic kink that is {approx

  18. Interface-Confined High Crystalline Growth of Semiconducting Polymers at Graphene Fibers for High-Performance Wearable Supercapacitors.

    Science.gov (United States)

    Padmajan Sasikala, Suchithra; Lee, Kyung Eun; Lim, Joonwon; Lee, Ho Jin; Koo, Sung Hwan; Kim, In Ho; Jung, Hong Ju; Kim, Sang Ouk

    2017-09-26

    We report graphene@polymer core-shell fibers (G@PFs) composed of N and Cu codoped porous graphene fiber cores uniformly coated with semiconducting polymer shell layers with superb electrochemical characteristics. Aqueous/organic interface-confined polymerization method produced robust highly crystalline uniform semiconducting polymer shells with high electrical conductivity and redox activity. When the resultant core-shell fibers are utilized for fiber supercapacitor application, high areal/volume capacitance and energy densities are attained along with long-term cycle stability. Desirable combination of mechanical flexibility, electrochemical properties, and facile process scalability makes our G@PFs particularly promising for portable and wearable electronics.

  19. Enrichment of semiconducting single-walled carbon nanotubes by carbothermic reaction for use in all-nanotube field effect transistors.

    Science.gov (United States)

    Li, Shisheng; Liu, Chang; Hou, Peng-Xiang; Sun, Dong-Ming; Cheng, Hui-Ming

    2012-11-27

    Selective removal of metallic single-walled carbon nanotubes (SWCNTs) and consequent enrichment of semiconducting SWCNTs were achieved through an efficient carbothermic reaction with a NiO thin film at a relatively low temperature of 350 °C. All-SWCNT field effect transistors (FETs) were fabricated with the aid of a patterned NiO mask, in which the as-grown SWCNTs behaving as source/drain electrodes and the remaining semiconducting SWCNTs that survive in the carbothermic reaction as a channel material. The all-SWCNT FETs demonstrate improved current ON/OFF ratios of ∼10(3).

  20. Semiconducting III-V nanowires with nanogaps for molecular junctions: DFT transport simulations

    DEFF Research Database (Denmark)

    Kallesøe, Christian; Fürst, Joachim Alexander; Mølhave, Kristian

    2009-01-01

    We consider here the possibility of using III–V heterostructure nanowires as electrodes for molecular electronics instead of metal point contacts. Using ab initio electronic structure and transport calculations, we study the effect on electronic properties of placing a small molecule with thiol...... linking groups, benzene-di-thiol (BDT), within a nanosize gap in a III–V nanowire. Furthermore, it is investigated how surface states affect the transport through pristine III–V nanowires and through the BDT molecule situated within the nanogap. Using GaAs and GaP as III–V materials we find that the BDT...

  1. Dynamics of exciton diffusion in poly(p-phenylene vinylene)/fullerene heterostructures

    NARCIS (Netherlands)

    Markov, D.E.; Hummelen, J.C.; Blom, P.W.M.; Sieval, A.B.

    The exciton diffusion process in a poly(p-phenylene vinylene)- (PPV-)based derivative is investigated using time-resolved photoluminescence in conjugated polymer/fullerene heterostructures. The decay of the luminescence in the polymer/fullerene heterostructures is governed by exciton diffusion and

  2. Interface engineering of CsPbI3-black phosphorus van der Waals heterostructure

    Science.gov (United States)

    Liu, Biao; Long, Mengqiu; Cai, Meng-Qiu; Yang, Junliang

    2018-01-01

    Interface Engineering is an effective route to tune structural and electrical properties in semiconductor heterostructures. Two kinds of typical van der Waals (vdW)-type electrical contacts, i.e., the electrical contacts of the Pb-I interface and Cs-I interface with a black phosphorus (BP) monolayer, respectively, in CsPbI3-BP heterostructures are studied by first-principles calculations. The electronic band structures of both CsPbI3 slabs and the BP monolayer are preserved in the combined vdW CsPbI3-BP heterostructures. The heterostructure of the Pb-I interface contacting with BP demonstrates the type-I band alignment, and the Cs-I interface contacting with the BP heterostructure demonstrates the type-II band alignment. The reason for the energy level shift is the work function difference of CsPbI3 slabs relative to the BP monolayer, which drives electrons and holes to move spontaneously. In addition, the CsPbI3-BP heterostructures show much better optical properties than CsPbI3 slabs. The light absorptions are enhanced in the CsPbI3-BP heterostructures, especially in the infrared region, which would improve the use of infrared light in CsPbI3 perovskite solar cells. This work suggests that such inorganic perovskite-BP heterostructures have significant potential for future optoelectronic applications and can enable broad possibilities with compositional tunability in inorganic perovskites.

  3. Page 1 i i ZnSe-GaAs heterostructures by MOVPE 357 Deep levels ...

    Indian Academy of Sciences (India)

    ZnSe-GaAs heterostructures by MOVPE 357. Deep levels in heterostructures often act as recombination and/or nonradiative centres and degrade their carrier transport and/or optical properties, We study the nature of deep traps in the HD by means of deep-level transient spectroscopy (DLTS), which provides a very ...

  4. PHOTOELECTRIC PROPERTIES OF HETEROSTRUCTURES BASED ON PEPC AND MEH-PPV FILMS DOPED WITH ZINC OCTABUTYLPHTHALOCYANINE

    Directory of Open Access Journals (Sweden)

    Nicolay Davidenko

    2016-06-01

    Full Text Available Planar organic heterostructures were prepared using poly-N- epoxypropylcarbazole films and poly[2-methoxy-5-(2’-ethylhexyloxy-1,4-phenylenevinylene] by the method of successive deposition adding 2,3,9,10,16,17,23,24-zinc octabutylphthalocyanine. Photoelectric, photodielectric and photovoltaic properties of the heterostructures were studied.

  5. Electronic structure and optical signatures of semiconducting transition metal dichalcogenide nanosheets.

    Science.gov (United States)

    Zhao, Weijie; Ribeiro, Ricardo Mendes; Eda, Goki

    2015-01-20

    CONSPECTUS: Two-dimensional (2D) crystals derived from transition metal dichalcogenides (TMDs) are intriguing materials that offer a unique platform to study fundamental physical phenomena as well as to explore development of novel devices. Semiconducting group 6 TMDs such as MoS2 and WSe2 are known for their large optical absorption coefficient and their potential for high efficiency photovoltaics and photodetectors. Monolayer sheets of these compounds are flexible, stretchable, and soft semiconductors with a direct band gap in contrast to their well-known bulk crystals that are rigid and hard indirect gap semiconductors. Recent intense research has been motivated by the distinct electrical, optical, and mechanical properties of these TMD crystals in the ultimate thickness regime. As a semiconductor with a band gap in the visible to near-IR frequencies, these 2D MX2 materials (M = Mo, W; X = S, Se) exhibit distinct excitonic absorption and emission features. In this Account, we discuss how optical spectroscopy of these materials allows investigation of their electronic properties and the relaxation dynamics of excitons. We first discuss the basic electronic structure of 2D TMDs highlighting the key features of the dispersion relation. With the help of theoretical calculations, we further discuss how photoluminescence energy of direct and indirect excitons provide a guide to understanding the evolution of the electronic structure as a function of the number of layers. We also highlight the behavior of the two competing conduction valleys and their role in the optical processes. Intercalation of group 6 TMDs by alkali metals results in the structural phase transformation with corresponding semiconductor-to-metal transition. Monolayer TMDs obtained by intercalation-assisted exfoliation retains the metastable metallic phase. Mild annealing, however, destabilizes the metastable phase and gradually restores the original semiconducting phase. Interestingly, the

  6. Gate-Tunable Spin Transport and Giant Electroresistance in Ferromagnetic Graphene Vertical Heterostructures

    Science.gov (United States)

    Myoung, Nojoon; Park, Hee Chul; Lee, Seung Joo

    2016-04-01

    Controlling tunneling properties through graphene vertical heterostructures provides advantages in achieving large conductance modulation which has been known as limitation in lateral graphene device structures. Despite of intensive research on graphene vertical heterosturctures for recent years, the potential of spintronics based on graphene vertical heterostructures remains relatively unexplored. Here, we present an analytical device model for graphene-based spintronics by using ferromagnetic graphene in vertical heterostructures. We consider a normal or ferroelectric insulator as a tunneling layer. The device concept yields a way of controlling spin transport through the vertical heterostructures, resulting in gate-tunable spin-switching phenomena. Also, we revealed that a ‘giant’ resistance emerges through a ferroelectric insulating layer owing to the anti-parallel configuration of ferromagnetic graphene layers by means of electric fields via gate and bias voltages. Our findings discover the prospect of manipulating the spin transport properties in vertical heterostructures without use of magnetic fields.

  7. Effect of roughness on the conductivity of semiconducting thin films/quantum wells with double rough boundaries

    NARCIS (Netherlands)

    Palasantzas, G; De Hosson, JTM

    2003-01-01

    We have investigated the influence of surface/interface roughness on the electrical conductivity in semiconducting thin films/quantum wells with double self-affine rough interface boundaries. The self-affine boundary roughness is characterized by the roughness exponent H, the in-plane correlation

  8. Selective synthesis and device applications of semiconducting single-walled carbon nanotubes using isopropyl alcohol as feedstock.

    Science.gov (United States)

    Che, Yuchi; Wang, Chuan; Liu, Jia; Liu, Bilu; Lin, Xue; Parker, Jason; Beasley, Cara; Wong, H-S Philip; Zhou, Chongwu

    2012-08-28

    The development of guided chemical vapor deposition (CVD) growth of single-walled carbon nanotubes provides a great platform for wafer-scale integration of aligned nanotubes into circuits and functional electronic systems. However, the coexistence of metallic and semiconducting nanotubes is still a major obstacle for the development of carbon-nanotube-based nanoelectronics. To address this problem, we have developed a method to obtain predominantly semiconducting nanotubes from direct CVD growth. By using isopropyl alcohol (IPA) as the carbon feedstock, a semiconducting nanotube purity of above 90% is achieved, which is unambiguously confirmed by both electrical and micro-Raman measurements. Mass spectrometric study was performed to elucidate the underlying chemical mechanism. Furthermore, high performance thin-film transistors with an on/off ratio above 10(4) and mobility up to 116 cm(2)/(V·s) have been achieved using the IPA-synthesized nanotube networks grown on silicon substrate. The method reported in this contribution is easy to operate and the results are highly reproducible. Therefore, such semiconducting predominated single-walled carbon nanotubes could serve as an important building block for future practical and scalable carbon nanotube electronics.

  9. Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors

    KAUST Repository

    Nielsen, Christian B.

    2016-07-22

    The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous envi-ronment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially availa-ble conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, we present a series of semiconducting polymers designed to elucidate important structure-property guidelines required for accumulation mode OECT operation. We discuss key aspects relating to OECT performance such as ion and hole transport, elec-trochromic properties, operational voltage and stability. The demonstration of our molecular design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT based devices, and show stability under aqueous oper-ation without the need for formulation additives and cross-linkers.

  10. Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

    Energy Technology Data Exchange (ETDEWEB)

    Apostol, I. [S.C. IPEE ATI S.A. Curtea de Arges, RO-115300 (Romania); Stefan, N.; Luculescu, C.R.; Birjega, R. [Laser Department, National Institute for Laser, Plasma and Radiation Physics, Bucharest - Magurele, P.O. Box MG-54, RO-077125 (Romania); Socol, M. [National Institute of Materials Physics, Bucharest - Magurele, RO-77125 (Romania); Miroiu, M. [Laser Department, National Institute for Laser, Plasma and Radiation Physics, Bucharest - Magurele, P.O. Box MG-54, RO-077125 (Romania); Mihailescu, I.N., E-mail: ion.mihailescu@inflpr.ro [Laser Department, National Institute for Laser, Plasma and Radiation Physics, Bucharest - Magurele, P.O. Box MG-54, RO-077125 (Romania)

    2011-02-01

    We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO{sub 3} and (Ba,Pb,Y)TiO{sub 3} thin films on mechanically polished nickel substrates. The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements. We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.

  11. Half-metallic ferromagnetism in Cr-doped semiconducting Ge-chalcogenide: Density functional approach

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S., E-mail: hardevdft@gmail.com [Department of Physics, National Institute of Technology, Kurukshetra-136119, Haryana (India); Singh, Mukhtiyar; Thakur, Jyoti; Kashyap, Manish K. [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2014-04-24

    A supercell approach has been used to calculate the electronic and magnetic properties of Cr-doped Ge chalcogenide, Ge{sub 1−x}Cr{sub x}Te (x = 0.25 and 0.125). The calculations have been performed using full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potential. The calculated results show that the doping of Cr induces the 100% spin polarization at Fermi level (EF) and showed the robust half metallic ferromagnetism in this compound. Thus, the compound at both dopant concentrations behave as dilute magnetic semiconductor (DMS) showing metallic property in majority and semiconducting for minority spin channels which is best suited for spintronic applications. The total magnetic moments of this compound are mainly due to Cr-d states present at E{sup F} with negligible contribution from electronic states of other atoms.

  12. Phase Separation in Bulk Heterojunctions of Semiconducting Polymers and Fullerenes for Photovoltaics

    Science.gov (United States)

    Treat, Neil D.; Chabinyc, Michael L.

    2014-04-01

    Thin-film solar cells are an important source of renewable energy. The most efficient thin-film solar cells made with organic materials are blends of semiconducting polymers and fullerenes called the bulk heterojunction (BHJ). Efficient BHJs have a nanoscale phase-separated morphology that is formed during solution casting. This article reviews recent work to understand the nature of the phase-separation process resulting in the formation of the domains in polymer-fullerene BHJs. The BHJ is now viewed as a mixture of polymer-rich, fullerene-rich, and mixed polymer-fullerene domains. The formation of this structure can be understood through fundamental knowledge of polymer physics. The implications of this structure for charge transport and charge generation are given.

  13. Transparent ferrimagnetic semiconducting CuCr2O4 thin films by atomic layer deposition

    Science.gov (United States)

    Tripathi, T. S.; Yadav, C. S.; Karppinen, M.

    2016-04-01

    We report the magnetic and optical properties of CuCr2O4 thin films fabricated by atomic layer deposition (ALD) from Cu(thd)2, Cr(acac)3, and ozone; we deposit 200 nm thick films and anneal them at 700 °C in oxygen atmosphere to crystallize the spinel phase. A ferrimagnetic transition at 140 K and a direct bandgap of 1.36 eV are determined for the films from magnetic and UV-vis spectrophotometric measurements. Electrical transport measurements confirm the p-type semiconducting behavior of the films. As the ALD technique allows the deposition of conformal pin-hole-free coatings on complex 3D surfaces, our CuCr2O4 films are interesting material candidates for various frontier applications.

  14. Transparent ferrimagnetic semiconducting CuCr2O4 thin films by atomic layer deposition

    Directory of Open Access Journals (Sweden)

    T. S. Tripathi

    2016-04-01

    Full Text Available We report the magnetic and optical properties of CuCr2O4 thin films fabricated by atomic layer deposition (ALD from Cu(thd2, Cr(acac3, and ozone; we deposit 200 nm thick films and anneal them at 700 °C in oxygen atmosphere to crystallize the spinel phase. A ferrimagnetic transition at 140 K and a direct bandgap of 1.36 eV are determined for the films from magnetic and UV-vis spectrophotometric measurements. Electrical transport measurements confirm the p-type semiconducting behavior of the films. As the ALD technique allows the deposition of conformal pin-hole-free coatings on complex 3D surfaces, our CuCr2O4 films are interesting material candidates for various frontier applications.

  15. Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics

    Science.gov (United States)

    Lei, Ting; Guan, Ming; Liu, Jia; Lin, Hung-Cheng; Pfattner, Raphael; McGuire, Allister F.; Huang, Tsung-Ching; Shao, Leilai; Cheng, Kwang-Ting; Tok, Jeffrey B.-H.; Bao, Zhenan

    2017-01-01

    Increasing performance demands and shorter use lifetimes of consumer electronics have resulted in the rapid growth of electronic waste. Currently, consumer electronics are typically made with nondecomposable, nonbiocompatible, and sometimes even toxic materials, leading to serious ecological challenges worldwide. Here, we report an example of totally disintegrable and biocompatible semiconducting polymers for thin-film transistors. The polymer consists of reversible imine bonds and building blocks that can be easily decomposed under mild acidic conditions. In addition, an ultrathin (800-nm) biodegradable cellulose substrate with high chemical and thermal stability is developed. Coupled with iron electrodes, we have successfully fabricated fully disintegrable and biocompatible polymer transistors. Furthermore, disintegrable and biocompatible pseudo-complementary metal–oxide–semiconductor (CMOS) flexible circuits are demonstrated. These flexible circuits are ultrathin (electronics. PMID:28461459

  16. Crystalline Stratification in Semiconducting Polymer Thin Film Quantified by Grazing Incidence X-ray Scattering

    Science.gov (United States)

    Gann, Eliot; Caironi, Mario; Noh, Yong-Young; Kim, Yun-Hi; McNeill, Christopher R.

    The depth dependence of crystalline structure within thin films is critical for many technological applications, but has been impossible to measure directly using common techniques. In this work, by monitoring diffraction peak intensity and location and utilizing the highly angle-dependent waveguiding effects of X-rays near grazing incidence we quantitatively measure the thickness, roughness and orientation of stratified crystalline layers within thin films of a high-performance semiconducting polymer. In particular, this diffractive X-ray waveguiding reveals a self-organized 5-nm-thick crystalline surface layer with crystalline orientation orthogonal to the underlying 65-nm-thick layer. While demonstrated for an organic semiconductor film, this approach is applicable to any thin film material system where stratified crystalline structure and orientation can influence important interfacial processes such as charge injection and field-effect transport.

  17. Excitons in semiconducting quantum filaments of CdS and CdSe with dielectric barriers

    CERN Document Server

    Dneprovskij, V S; Shalygina, O A; Lyaskovskij, V L; Mulyarov, E A; Gavrilov, S A; Masumoto, I

    2002-01-01

    The peculiarities of the luminescence spectra obtained by different polarization and intensity of the pumping excitation and luminescence kinetics of the CdS and CdSe nanocrystals are explained by the exciton transitions in the semiconducting quantum threads with dielectric barriers. The exciton transition energies correspond to the calculated ones with an account of both their dimensional quantization and the effect of the excitons dielectric intensification. It is shown that the excitons transition energies do not change by the change in the quantum threads diameter within the wide range, while the increase in the one-dimensional forbidden zone width of quantum thread by the decrease in its diameter is compensated through the decrease in the excitons binding energy

  18. Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors

    KAUST Repository

    Chen, Hu

    2017-07-19

    The charge-carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene (IDT) repeat unit, which have both a low Urbach energy and a high mobility in thin-film-transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin-film morphology evaluated, with the co-benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm2 V−1 s−1 in bottom-gate top-contact organic field-effect transistors.

  19. Realizing the semiconducting state of delafossite AgFeO{sub 2} by GGA + U calculations

    Energy Technology Data Exchange (ETDEWEB)

    Ong, Khuong P. [Institute of High Performance Computing, 1 Science Park Road, 01-01 The Capricorn Singapore Science Park II, Singapore 117528 (Singapore)], E-mail: ongpk@ihpc.a-star.edu.sg; Bai Kewu; Wu Ping [Institute of High Performance Computing, 1 Science Park Road, 01-01 The Capricorn Singapore Science Park II, Singapore 117528 (Singapore)

    2008-01-31

    The electronic structures of delafossite-type oxide AgFeO{sub 2} have been calculated by using the full potential linearlized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) and GGA + U. It was found that the GGA calculations lead to a metallic state for AgFeO{sub 2} which is in contradiction with the experiment that AgFeO{sub 2} is a semiconductor. By taking into account the Hubbard interaction parameter U, the GGA + U calculations produce a semiconducting state for AgFeO{sub 2} when U > 0.68 eV. An energy band gap which is the gap between the highest occupied valance band of Ag-3d and the lowest upper Hubbard band of Fe-3d was predicted to be 1.15 eV with an effective U{sub eff} = 7.86 eV.

  20. Itinerant magnetism in doped semiconducting β-FeSi₂ and CrSi₂.

    Science.gov (United States)

    Singh, David J; Parker, David

    2013-12-17

    Novel or unusual magnetism is a subject of considerable interest, particularly in metals and degenerate semiconductors. In such materials the interplay of magnetism, transport and other Fermi liquid properties can lead to fascinating physical behavior. One example is in magnetic semiconductors, where spin polarized currents may be controlled and used. We report density functional calculations predicting magnetism in doped semiconducting β-FeSi₂ and CrSi₂ at relatively low doping levels particularly for n-type. In this case, there is a rapid cross-over to a half-metallic state as a function of doping level. The results are discussed in relation to the electronic structure and other properties of these compounds.

  1. Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

    Science.gov (United States)

    Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir

    2013-01-01

    The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of electron density for na individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closet neighbors reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

  2. High-performance radio frequency transistors based on diameter-separated semiconducting carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Yu; Che, Yuchi; Zhou, Chongwu, E-mail: chongwuz@usc.edu [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Seo, Jung-Woo T.; Hersam, Mark C. [Department of Materials Science and Engineering and Department of Chemistry, Northwestern University, Evanston, Illinois 60208 (United States); Gui, Hui [Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States)

    2016-06-06

    In this paper, we report the high-performance radio-frequency transistors based on the single-walled semiconducting carbon nanotubes with a refined average diameter of ∼1.6 nm. These diameter-separated carbon nanotube transistors show excellent transconductance of 55 μS/μm and desirable drain current saturation with an output resistance of ∼100 KΩ μm. An exceptional radio-frequency performance is also achieved with current gain and power gain cut-off frequencies of 23 GHz and 20 GHz (extrinsic) and 65 GHz and 35 GHz (intrinsic), respectively. These radio-frequency metrics are among the highest reported for the carbon nanotube thin-film transistors. This study provides demonstration of radio frequency transistors based on carbon nanotubes with tailored diameter distributions, which will guide the future application of carbon nanotubes in radio-frequency electronics.

  3. Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

    Directory of Open Access Journals (Sweden)

    VLADIMIR D. JOVIC

    2008-03-01

    Full Text Available In this paper, the results of the potentiostatic formation of homogeneous and heterogeneous, nano-crystalline passive films of Nb2O5 onto an Nb electrode in NaOH solutions of different concentrations at potentials lower than 3.0 V vs. SCE are presented. The semiconducting properties of such films were investigated by EIS measurements. After fitting the EIS results by appropriate equivalent circuits, the space charge capacitance (Csc and space charge resistance (Rsc of these films were determined. The donor density (Nsc, flat band potential (Efb and thickness of the space charge layer (dsc for such oxide films were determined from the corresponding Mott–Schottky (M–S plots. It is shown that all oxide films were n-type semiconductors in a certain potential range.

  4. Recent Advances of Activatable Molecular Probes Based on Semiconducting Polymer Nanoparticles in Sensing and Imaging

    Science.gov (United States)

    Lyu, Yan

    2017-01-01

    Molecular probes that change their signals in response to the target of interest have a critical role in fundamental biology and medicine. Semiconducting polymer nanoparticles (SPNs) have recently emerged as a new generation of purely organic photonic nanoagents with desirable properties for biological applications. In particular, tunable optical properties of SPNs allow them to be developed into photoluminescence, chemiluminescence, and photoacoustic probes, wherein SPNs usually serve as the energy donor and internal reference for luminescence and photoacoustic probes, respectively. Moreover, facile surface modification and intraparticle engineering provide the versatility to make them responsive to various biologically and pathologically important substances and indexes including small‐molecule mediators, proteins, pH and temperature. This article focuses on recent advances in the development of SPN‐based activatable molecular probes for sensing and imaging. The designs and applications of these probes are discussed in details, and the present challenges to further advance them into life science are also analyzed. PMID:28638783

  5. Lanthanide-Coordinated Semiconducting Polymer Dots Used for Flow Cytometry and Mass Cytometry.

    Science.gov (United States)

    Wu, Xu; DeGottardi, Quinn; Wu, I-Che; Yu, Jiangbo; Wu, Li; Ye, Fangmao; Kuo, Chun-Ting; Kwok, William W; Chiu, Daniel T

    2017-11-20

    Simultaneous monitoring of biomarkers as well as single-cell analyses based on flow cytometry and mass cytometry are important for investigations of disease mechanisms, drug discovery, and signaling-network studies. Flow cytometry and mass cytometry are complementary to each other; however, probes that can satisfy all the requirements for these two advanced technologies are limited. In this study, we report a probe of lanthanide-coordinated semiconducting polymer dots (Pdots), which possess fluorescence and mass signals. We demonstrated the usage of this dual-functionality probe for both flow cytometry and mass cytometry in a mimetic cell mixture and human peripheral blood mononuclear cells as model systems. The probes not only offer high fluorescence signal for use in flow cytometry, but also show better performance in mass cytometry than the commercially available counterparts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Evaluation Methods of Contamination Flashover Voltage Performance of Cylindrical Type Semi-conducting Glaze Porcelain Insulators

    Science.gov (United States)

    Yamada, Kazuma; Hayashi, Akio; Saka, Chiharu; Sakanishi, Kenji; Matsuoka, Ryosuke; Ito, Susumu; Fujii, Osamu

    Higher contamination flashover voltage of a semi-conducting glaze (SG) insulator owes primarily to the drying effect by leakage current flowing in the glaze. Significant reduction in contamination flashover voltage was confirmed on a cylindrical SG insulator when fog density was increased from 0.5g/m3 to 13g/m3 in clean fog test. The effect of de-energized duration between trip-out and re-energization on the contamination flashover voltage of a cylindrical SG insulator under cold-wet switch-on conditions was investigated. As the de-energized duration becomes shorter, the flashover voltage of a cylindrical SG insulator becomes higher. Higher contamination design voltages may be adopted even under cold-wet switch-on conditions.

  7. The biostimulation of anaerobic digestion with (semi)conductive ferric oxides: their potential for enhanced biomethanation.

    Science.gov (United States)

    Baek, Gahyun; Kim, Jaai; Cho, Kyungjin; Bae, Hyokwan; Lee, Changsoo

    2015-12-01

    The effect of biostimulation with ferric oxides, semiconductive ferric oxyhydroxide, and conductive magnetite on the anaerobic digestion of dairy wastewater was examined in a batch mode. The reactors supplemented with ferric oxyhydroxide (R2) and magnetite (R3) showed significantly enhanced biomethanation performance compared with the control (R1). The removal of chemical oxygen demand (COD) after 30 days was 31.9, 59.3, and 82.5% in R1, R2, and R3, respectively. The consumed COD was almost fully recovered as biogas in R2 and R3, while only 79% was recovered in R1. The total energy production as biogas was accordingly 32.2, 71.0, and 97.7 kJ in R1, R2, and R3, respectively. The reactors also differed in the acid formation profile with more propionate and butyrate found in R1 and more acetate found in R3. The enhanced biomethanation seems to be associated with variations in the bacterial community structure supposedly induced by the ferric oxides added. In contrast, no evident variation was observed in the archaeal community structure among the reactors. The potential electric syntrophy formed between Methanosaeta concilii-like methanogens and electroactive iron-reducing bacteria, particularly Trichococcus, was likely responsible for the enhanced performance. The stimulated growth of fermentative iron reducers may also have contributed by altering the metabolic characteristics of the bacterial communities to produce more favorable acidogenic products for methanogenesis. The overall results suggest the potential of biostimulation with (semi)conductive ferric oxides to enhance the rate and efficiency of the biomethanation of organic wastes. This seems to be potentially attractive, as increasing attention is being paid to the energy self-sufficiency of waste/wastewater treatment processes today.

  8. Structure-Property Relationships of Semiconducting Polymers for Flexible and Durable Polymer Field-Effect Transistors.

    Science.gov (United States)

    Kim, Min Je; Jung, A-Ra; Lee, Myeongjae; Kim, Dongjin; Ro, Suhee; Jin, Seon-Mi; Nguyen, Hieu Dinh; Yang, Jeehye; Lee, Kyung-Koo; Lee, Eunji; Kang, Moon Sung; Kim, Hyunjung; Choi, Jong-Ho; Kim, BongSoo; Cho, Jeong Ho

    2017-11-09

    We report high-performance top-gate bottom-contact flexible polymer field-effect transistors (FETs) fabricated by flow-coating diketopyrrolopyrrole (DPP)-based and naphthalene diimide (NDI)-based polymers (P(DPP2DT-T2), P(DPP2DT-TT), P(DPP2DT-DTT), P(NDI2OD-T2), P(NDI2OD-F2T2), and P(NDI2OD-Se2)) as semiconducting channel materials. All of the polymers displayed good FET characteristics with on/off current ratios exceeding 10(7). The highest hole mobility of 1.51 cm(2) V(-1) s(-1) and the highest electron mobility of 0.85 cm(2) V(-1) s(-1) were obtained from the P(DPP2DT-T2) and P(NDI2OD-Se2) polymer FETs, respectively. The impacts of the polymer structures on the FET performance are well-explained by the interplay between the crystallinity, the tendency of the polymer backbone to adopt an edge-on orientation, and the interconnectivity of polymer fibrils in the film state. Additionally, we demonstrated that all of the flexible polymer-based FETs were highly resistant to tensile stress, with negligible changes in their carrier mobilities and on/off ratios after a bending test. Conclusively, these high-performance, flexible, and durable FETs demonstrate the potential of semiconducting conjugated polymers for use in flexible electronic applications.

  9. Semiconducting polymer encapsulated mesoporous silica particles with conjugated Europium complexes: toward enhanced luminescence under aqueous conditions.

    Science.gov (United States)

    Zhang, Jixi; Prabhakar, Neeraj; Näreoja, Tuomas; Rosenholm, Jessica M

    2014-01-01

    Immobilization of lanthanide organic complexes in meso-organized hybrid materials for luminescence applications have attracted immense interest due to the possibility of controlled segregation at the nanoscopic level for novel optical properties. Aimed at enhancing the luminescence intensity and stability of the hybrid materials in aqueous media, we developed polyvinylpyrrolidone (PVP) stabilized, semiconducting polymer (poly(9-vinylcarbazole), PVK) encapsulated mesoporous silica hybrid particles grafted with Europium(III) complexes. Monosilylated β-diketonate ligands (1-(2-naphthoyl)-3,3,3-trifluoroacetonate, NTA) were first co-condensed in the mesoporous silica particles as pendent groups for bridging and anchoring the lanthanide complexes, resulting in particles with an mean diameter of ∼ 450 nm and a bimodal pore size distribution centered at 3.5 and 5.3 nm. PVK was encapsulated on the resulted particles by a solvent-induced surface precipitation process, in order to seal the mesopores and protect Europium ions from luminescence quenching by producing a hydrophobic environment. The obtained polymer encapsulated MSN-EuLC@PVK-PVP particles exhibit significantly higher intrinsic quantum yield (Φ(Ln) = 39%) and longer lifetime (τ(obs) = 0.51 ms), as compared with those without polymer encapsulation. Most importantly, a high luminescence stability was realized when MSN-EuLC@PVK-PVP particles were dispersed in various aqueous media, showing no noticeable quenching effect. The beneficial features and positive attributes of both mesoporous silica and semiconducting polymers as lanthanide-complex host were merged in a single hybrid carrier, opening up the possibility of using these hybrid luminescent materials under complex aqueous conditions such as biological/physiological environments.

  10. Resonant Tunneling in Photonic Double Quantum Well Heterostructures

    Directory of Open Access Journals (Sweden)

    Cox Joel

    2010-01-01

    Full Text Available Abstract Here, we study the resonant photonic states of photonic double quantum well (PDQW heterostructures composed of two different photonic crystals. The heterostructure is denoted as B/A/B/A/B, where photonic crystals A and B act as photonic wells and barriers, respectively. The resulting band structure causes photons to become confined within the wells, where they occupy discrete quantized states. We have obtained an expression for the transmission coefficient of the PDQW heterostructure using the transfer matrix method and have found that resonant states exist within the photonic wells. These resonant states occur in split pairs, due to a coupling between degenerate states shared by each of the photonic wells. It is observed that when the resonance energy lies at a bound photonic state and the two photonic quantum wells are far away from each other, resonant states appear in the transmission spectrum of the PDQW as single peaks. However, when the wells are brought closer together, coupling between bound photonic states causes an energy-splitting effect, and the transmitted states each have two peaks. Essentially, this means that the system can be switched between single and double transparent states. We have also observed that the total number of resonant states can be controlled by varying the width of the photonic wells, and the quality factor of transmitted peaks can be drastically improved by increasing the thickness of the outer photonic barriers. It is anticipated that the resonant states described here can be used to develop new types of photonic-switching devices, optical filters, and other optoelectronic devices.

  11. Spin-polarized photoemission from SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F. [LNESS-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2013-12-04

    We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

  12. Band Offsets Engineering for van der Waals Heterostructure Devices

    Science.gov (United States)

    Koda, Daniel S.; Bechstedt, Friedhelm; Marques, Marcelo; Teles, Lara K.

    Two-dimensional crystals (2D) and their stacks in van der Waals heterostructures became prospective for novel devices and physics. To surmount commensurability limitations within first-principles investigations, the coincidence lattice method is developed, enabling studies on interlayer twist and quasiparticle corrections despite limited computational resources. Interesting properties are observed within stacked systems, such as structural deformation on contact, strong orbital hybridization, and tunable band offsets by application of pressure and vertical electric fields. These studies could help to develop versatile electronic and optoelectronic devices and unravel new physics within 2D interfaces.

  13. Control of Interfacial Phenomena in Artificial Oxide Heterostructures

    Science.gov (United States)

    2015-09-01

    pathway to realizing new classes of devices that exhibit  functionalities not found in conventional technologies. New materials based on  perovskite ...approach to achieving high carrier densities is to use  interfaces involving  perovskite  oxide ABO3 heterostructures. So far, only SrTiO3 (STO) has been...conventional technologies. New materials based on perovskite oxides are promising because of their wide variety of properties, including electronic

  14. SWCNT-MoS2 -SWCNT Vertical Point Heterostructures.

    Science.gov (United States)

    Zhang, Jin; Wei, Yang; Yao, Fengrui; Li, Dongqi; Ma, He; Lei, Peng; Fang, Hehai; Xiao, Xiaoyang; Lu, Zhixing; Yang, Juehan; Li, Jingbo; Jiao, Liying; Hu, Weida; Liu, Kaihui; Liu, Kai; Liu, Peng; Li, Qunqing; Lu, Wei; Fan, Shoushan; Jiang, Kaili

    2017-02-01

    A vertical point heterostructure (VPH) is constructed by sandwiching a two-dimensional (2D) MoS2 flake with two cross-stacked metallic single-walled carbon nanotubes. It can be used as a field-effect transistor with high on/off ratio and a light detector with high spatial resolution. Moreover, the hybrid 1D-2D-1D VPHs open up new possibilities for nanoelectronics and nano-optoelectronics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Tuning the Carrier Confinement in GeS/Phosphorene van der Waals Heterostructures.

    Science.gov (United States)

    Wang, Chan; Peng, Lei; Qian, Qi; Du, Jinyan; Wang, Sufan; Huang, Yucheng

    2018-01-11

    Van der Waals (vdW) heterostructures, which have the advantage of integrating excellent properties of the stacked 2D materials by vdW interactions, have gained increasing attention recently. In this work, within the framework of density functional theory calculations, the electronic properties of vdW heterostructure composed of phosphorene (BP) in black phosphorus phase and GeS monolayer are systematically explored. The results show that the carriers are not separated for both lattice-match and lattice-mismatch heterostructures. For the lattice-match heterostructure, it is found that changing monolayer of GeS to bilayer can increase the energy difference of valence band offsets between GeS and BP, thus realizing electron-hole separation. For the lattice-mismatch heterostructure, altering the layer distance can transform the heterostructure into a typical type-I alignment, but applying the electric field or doping with 2, 3, 5, 6-tetrafluoro-7, 7, 8, 8-tetracyanoquinodimethane (F4TCNQ) can make it display a perfect desirable type-II alignment, where holes migration and electrons transfer are revealed to account respectively for the phenomenon of carrier separation. It is believed that the work would greatly enlarge the potential application of the BP-based heterostructures in photoelectronics and further stimulate the investigation enthusiasms on other fashionable heterostructures and even unassuming heterostructures in which the charming electronic properties can be modulated to emerge by various general methods. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Semiconductor-oxide heterostructured nanowires using postgrowth oxidation.

    Science.gov (United States)

    Wallentin, Jesper; Ek, Martin; Vainorious, Neimantas; Mergenthaler, Kilian; Samuelson, Lars; Pistol, Mats-Erik; Reine Wallenberg, L; Borgström, Magnus T

    2013-01-01

    Semiconductor-oxide heterointerfaces have several electron volts high-charge carrier potential barriers, which may enable devices utilizing quantum confinement at room temperature. While a single heterointerface is easily formed by oxide deposition on a crystalline semiconductor, as in MOS transistors, the amorphous structure of most oxides inhibits epitaxy of a second semiconductor layer. Here, we overcome this limitation by separating epitaxy from oxidation, using postgrowth oxidation of AlP segments to create axial and core-shell semiconductor-oxide heterostructured nanowires. Complete epitaxial AlP-InP nanowire structures were first grown in an oxygen-free environment. Subsequent exposure to air converted the AlP segments into amorphous aluminum oxide segments, leaving isolated InP segments in an oxide matrix. InP quantum dots formed on the nanowire sidewalls exhibit room temperature photoluminescence with small line widths (down to 15 meV) and high intensity. This optical performance, together with the control of heterostructure segment length, diameter, and position, opens up for optoelectrical applications at room temperature.

  17. Epitaxial Heterostructures of Lead Selenide Quantum Dots on Hematite Nanowires.

    Science.gov (United States)

    Selinsky, Rachel S; Shin, Sanghun; Lukowski, Mark A; Jin, Song

    2012-06-21

    We present a novel method for synthesizing epitaxial quantum dot-nanowire (QD-NW) heterostructures using the example of colloidal PbSe QDs decorated on furnace-grown hematite (α-Fe2O3) NWs. The direct heterogeneous nucleation of QDs on Fe2O3 NWs relies upon an aggressive surface dehydration of the as-synthesized Fe2O3 NWs at 350 °C under vacuum and subsequent introduction of colloidal reactants resulting in direct growth of PbSe QDs on Fe2O3. The synthesis is tunable: the QD diameter distribution and density of QDs on the NWs increase with increased dehydration time, and QD diameters and size distributions decrease with decreased injection temperature of the colloidal synthesis. Transmission electron microscopy (TEM) structural analysis reveals direct heteroepitaxial heterojunctions where the matching faces can be PbSe (002) and Fe2O3 (003) with their respective [11̅0] crystallographic directions aligned. This can be a general approach for integrating colloidal and furnace synthetic techniques, thus broadening possible material combinations for future high-quality, epitaxial nanoscale heterostructures for solar applications.

  18. The direct magnetoelectric effect in ferroelectric-ferromagnetic epitaxial heterostructures.

    Science.gov (United States)

    Fina, I; Dix, N; Rebled, J M; Gemeiner, P; Martí, X; Peiró, F; Dkhil, B; Sánchez, F; Fàbrega, L; Fontcuberta, J

    2013-09-07

    Ferroelectric (FE) and ferromagnetic (FM) materials engineered in horizontal heterostructures allow interface-mediated magnetoelectric coupling. The so-called converse magnetoelectric effect (CME) has been already demonstrated by electric-field poling of the ferroelectric layers and subsequent modification of the magnetic state of adjacent ferromagnetic layers by strain effects and/or free-carrier density tuning. Here we focus on the direct magnetoelectric effect (DME) where the dielectric state of a ferroelectric thin film is modified by a magnetic field. Ferroelectric BaTiO3 (BTO) and ferromagnetic CoFe2O4 (CFO) oxide thin films have been used to create epitaxial FE/FM and FM/FE heterostructures on SrTiO3(001) substrates buffered with metallic SrRuO3. It will be shown that large ferroelectric polarization and DME can be obtained by appropriate selection of the stacking order of the FE and FM films and their relative thicknesses. The dielectric permittivity, at the structural transitions of BTO, is strongly modified (up to 36%) when measurements are performed under a magnetic field. Due to the insulating nature of the ferromagnetic layer and the concomitant absence of the electric-field effect, the observed DME effect solely results from the magnetostrictive response of CFO elastically coupled to the BTO layer. These findings show that appropriate architecture and materials selection allow overcoming substrate-induced clamping in multiferroic multi-layered films.

  19. THz investigations of graphene-complex-oxide heterostructures

    Science.gov (United States)

    Jnawali, Giriraj; Chen, Lu; Irvin, Patrick; Levy, Jeremy; Ryu, Sangwoo; Eom, Chang-Beom; Ghahari, Fereshte; Ravichandran, Jayakanth; Kim, Philip

    2014-03-01

    The unique and multifaceted properties of graphene have fascinated scientists and engineers for a decade now. A new frontier in research concerns properties of graphene in the THz-IR region, where the collective excitation of graphene 2D electron gas (2DEG) into plasmonic waves has proven the salient feature.[2] Complex oxide heterostructures (e.g., LaAlO3/SrTiO3, LAO/STO) also support a 2DEG with high carrier densities and expected plasmonic behavior. A unique feature of the LAO/STO system is the ability to control the electron density with nanoscale precision.[3] In addition, a method for sourcing and detecting broadband THz emission from LAO/STO nanojunctions has been recently demonstrated.[4] Here we describe initial efforts to investigate the THz properties of graphene-complex oxide (GCO) heterostructures. We envision that the proposed graphene plasmonic devices in the GCO will help to lay the foundation for a host of powerful THz-IR technologies for signal processing, imaging, spectroscopy and chemical sensing. We gratefully acknowledge support for this work from ONR (N00014-13-1-0806) and AFOSR (FA9550-12-1-0268).

  20. Fabrication and transport studies of graphene-superconductor heterostructures

    Science.gov (United States)

    Hu, Jiuning; Wu, Tailung; Tian, Jifa; Chen, Yong

    2014-03-01

    Recently, graphene based stacked heterostructures, e.g., graphene and boron nitride (BN) multi-layers, have attracted much attention as a system to study novel interaction-driven physics (e.g., excitonic condensation) and perform interesting measurements (eg. Coulomb drag and tunneling). The realm of graphene-superconductor heterostructures remains less unexplored, while such a system offers various interesting prospects (effects of superconductor vortices lattices on over-layering graphene and quantum Hall states, where novel phenomena such as anionic excitations have been predicted). We have used polyvinyl alcohol (PVA) based carrier films and a micro-manipulator to transfer mechanically exfoliated flakes and fabricated graphene/BN/NbSe2 structures to study the transport properties of graphene in close proximity to electrically isolated superconducting NbSe2 films. The NbSe2 film shows the superconducting transition temperature of ~7 K and upper critical field of ~3.5 T after device fabrication. We will present results from magneto-transport in graphene and graphene-NbSe2 Coulomb drag and tunneling measurements.

  1. Band offsets in ITO/Ga2O3 heterostructures

    Science.gov (United States)

    Carey, Patrick H.; Ren, F.; Hays, David C.; Gila, B. P.; Pearton, S. J.; Jang, Soohwan; Kuramata, Akito

    2017-11-01

    The valence band offsets in rf-sputtered Indium Tin Oxide (ITO)/single crystal β-Ga2O3 (ITO/Ga2O3) heterostructures were measured with X-Ray Photoelectron Spectroscopy using the Kraut method. The bandgaps of the component materials in the heterostructure were determined by Reflection Electron Energy Loss Spectroscopy as 4.6 eV for Ga2O3 and 3.5 eV for ITO. The valence band offset was determined to be -0.78 ± 0.30 eV, while the conduction band offset was determined to be -0.32 ± 0.13 eV. The ITO/Ga2O3 system has a nested gap (type I) alignment. The use of a thin layer of ITO between a metal and the Ga2O3 is an attractive approach for reducing contact resistance on Ga2O3-based power electronic devices and solar-blind photodetectors.

  2. Resonant Photonic States in Coupled Heterostructure Photonic Crystal Waveguides

    Directory of Open Access Journals (Sweden)

    Sabarinathan J

    2010-01-01

    Full Text Available Abstract In this paper, we study the photonic resonance states and transmission spectra of coupled waveguides made from heterostructure photonic crystals. We consider photonic crystal waveguides made from three photonic crystals A, B and C, where the waveguide heterostructure is denoted as B/A/C/A/B. Due to the band structure engineering, light is confined within crystal A, which thus act as waveguides. Here, photonic crystal C is taken as a nonlinear photonic crystal, which has a band gap that may be modified by applying a pump laser. We have found that the number of bound states within the waveguides depends on the width and well depth of photonic crystal A. It has also been found that when both waveguides are far away from each other, the energies of bound photons in each of the waveguides are degenerate. However, when they are brought close to each other, the degeneracy of the bound states is removed due to the coupling between them, which causes these states to split into pairs. We have also investigated the effect of the pump field on photonic crystal C. We have shown that by applying a pump field, the system may be switched between a double waveguide to a single waveguide, which effectively turns on or off the coupling between degenerate states. This reveals interesting results that can be applied to develop new types of nanophotonic devices such as nano-switches and nano-transistors.

  3. Excellent valleytronic properties and nontrivial topological phase in germanene heterostructure

    Science.gov (United States)

    Qu, Jinfeng; Peng, Xiangyang; Luo, Chaobo; Zhong, Jianxin

    2017-10-01

    In comparison with transition metal dichalcogenides (TMDs), germanene is not an ideal valleytronic material due to its very weak spin–orbit coupling (SOC) and tiny band gap. By performing density functional calculations, we studied the heterostructures of germanene/Sb and germanene/SbF in order to augment the valleytronic properties of germanene to a level similar to that of TMDs. Although germanene/Sb has large spin splittings, the system is found to be gapless. By proximity with the fluorine-adsorbed Sb layer, germanene can acquire large SOC. Germanene/SbF has a sizable direct band gap at Dirac points and the Dirac valleys of SbF and germanene are preserved in the heterostructure. The Ge–SbF interaction breaks the inversion symmetry, leading to large spin splittings and Berry curvatures, which are valley contrasting due to time reversal symmetry. We studied the interband optical transitions and found that valley polarization is achievable via valley-selective circular dichroism. The calculated Z 2 topological invariant further confirms that Ge/SbF is a topological insulator. Our studies illustrate that weak SOC materials can be converted into good valleytronic material and that nontrivial topological phase and valleytronic properties can be simultaneously realized.

  4. Graphene/CdTe heterostructure solar cell and its enhancement with photo-induced doping

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Shisheng, E-mail: shishenglin@zju.edu.cn; Chen, Hongsheng [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China); State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China); Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China)

    2015-11-09

    We report a type of solar cell based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.10%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by field effect transport, Raman, photoluminescence, and quantum efficiency measurements. This work demonstrates a feasible way of improving the performance of graphene/semiconductor heterostructure solar cells by combining one dimensional with two dimensional materials.

  5. Interlayer coupling effects on Schottky barrier in the arsenene-graphene van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Congxin, E-mail: xiacongxin@htu.edu.cn; Xue, Bin; Wang, Tianxing; Peng, Yuting [Department of Physic, Henan Normal University, Xinxiang 453007 (China); Jia, Yu [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-11-09

    The electronic characteristics of arsenene-graphene van der Waals (vdW) heterostructures are studied by using first-principles methods. The results show that a linear Dirac-like dispersion relation around the Fermi level can be quite well preserved in the vdW heterostructures. Moreover, the p-type Schottky barrier (0.18 eV) to n-type Schottky barrier (0.31 eV) transition occurs when the interlayer distance increases from 2.8 to 4.5 Å, which indicates that the Schottky barrier can be tuned effectively by the interlayer distance in the vdW heterostructures.

  6. High-Purity Semiconducting Single-Walled Carbon Nanotubes: A Key Enabling Material in Emerging Electronics.

    Science.gov (United States)

    Lefebvre, Jacques; Ding, Jianfu; Li, Zhao; Finnie, Paul; Lopinski, Gregory; Malenfant, Patrick R L

    2017-10-17

    Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are emerging as a promising material for high-performance, high-density devices as well as low-cost, large-area macroelectronics produced via additive manufacturing methods such as roll-to-roll printing. Proof-of-concept demonstrations have indicated the potential of sc-SWCNTs for digital electronics, radiofrequency circuits, radiation hard memory, improved sensors, and flexible, stretchable, conformable electronics. Advances toward commercial applications bring numerous opportunities in SWCNT materials development and characterization as well as fabrication processes and printing technologies. Commercialization in electronics will require large quantities of sc-SWCNTs, and the challenge for materials science is the development of scalable synthesis, purification, and enrichment methods. While a few synthesis routes have shown promising results in making near-monochiral SWCNTs, gram quantities are available only for small-diameter sc-SWCNTs, which underperform in transistors. Most synthesis routes yield mixtures of SWCNTs, typically 30% metallic and 70% semiconducting, necessitating the extraction of sc-SWCNTs from their metallic counterparts in high purity using scalable postsynthetic methods. Numerous routes to obtain high-purity sc-SWCNTs from raw soot have been developed, including density-gradient ultracentrifugation, chromatography, aqueous two-phase extraction, and selective DNA or polymer wrapping. By these methods (termed sorting or enrichment), >99% sc-SWCNT content can be achieved. Currently, all of these approaches have drawbacks and limitations with respect to electronics applications, such as excessive dilution, expensive consumables, and high ionic impurity content. Excess amount of dispersant is a common challenge that hinders direct inclusion of sc-SWCNTs into electronic devices. At present, conjugated polymer extraction may represent the most practical route to sc-SWCNTs. By the use of

  7. Chemical changes in carbon Nanotube-Nickel/Nickel Oxide Core/Shell nanoparticle heterostructures treated at high temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, Nitin, E-mail: nchopra@eng.ua.edu [Metallurgical and Materials Engineering, Center for Materials for Information Technology (MINT), Box 870202, University of Alabama, Tuscaloosa, AL 35487 (United States); McWhinney, Hylton G. [Prairie View A and M University, TX 77446 (United States); Shi Wenwu [Metallurgical and Materials Engineering, Center for Materials for Information Technology (MINT), Box 870202, University of Alabama, Tuscaloosa, AL 35487 (United States)

    2011-06-15

    Heterostructures composed of carbon nanotube (CNT) coated with Ni/NiO core/shell nanoparticles (denoted as CNC heterostructures) were synthesized in a wet-chemistry and single-step synthesis route involving direct nucleation of nanoparticles on CNT surface. Two different aspects of CNC heterostructures were studied here. First, it was observed that the nanoparticle coatings were more uniform on the as-produced and non-purified CNTs compared to purified (or acid treated) CNTs. These heterostructures were characterized using electron microscopy, Raman spectroscopy, and energy dispersive spectroscopy. Second, thermal stability of CNC heterostructures was studied by annealing them in N{sub 2}-rich (O{sub 2}-lean) environment between 125 and 750 deg. C for 1 h. A detailed X-ray photoelectron spectroscopy and Raman spectroscopy analysis was performed to evaluate the effects of annealing temperatures on chemical composition, phases, and stability of the heterostructures. It was observed that the CNTs present in the heterostructures completely decomposed and core Ni nanoparticle oxidized significantly between 600 and 750 deg. C. - Research Highlights: {yields} Heterostructures composed of CNTs coated with Ni/NiO core/shell nanoparticles. {yields} Poor nanoparticle coverage on purified CNT surface compared to non-purified CNTs. {yields} CNTs in heterostructures decompose between 600 and 750 deg. C in N{sub 2}-rich atmosphere. {yields} Metallic species in heterostructures were oxidized at higher temperatures.

  8. Narrow bandgap semiconducting silicides: Intrinsic infrared detectors on a silicon chip

    Science.gov (United States)

    Mahan, John E.

    1990-01-01

    Work done during the final report period is presented. The main technical objective was to achieve epitaxial growth on silicon of two semiconducting silicides, ReSi2 and CrSi2. ReSi2 thin films were grown on (001) silicon wafers by vacuum evaporation of rhenium onto hot substrates in ultrahigh vacuum. The preferred epitaxial relationship was found to be ReSi2(100)/Si(001) with ReSi2(010) parallel to Si(110). The lattice matching consists of a common unit mesh of 120 A(sup 2) area, and a mismatch of 1.8 percent. Transmission electron microscopy revealed the existence of rotation twins corresponding to two distinct but equivalent azimuthal orientations of the common unit mesh. MeV He(+) backscattering spectrometry revealed a minimum channeling yield of 2 percent for an approximately 1,500 A thick film grown at 650 C. Although the lateral dimension of the twins is on the order of 100 A, there is a very high degree of alignment between the ReSi2(100) and the Si(001) planes. Highly oriented films of CrSi2 were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi2(001)/Si(111). The reflection high-energy electron diffraction (RHEED) patterns of the films consist of sharp streaks, symmetrically arranged. The predominant azimuthal orientation of the films was determined to be CrSi2(210) parallel to Si(110). This highly desirable heteroepitaxial relationship has been obtained previously by others; it may be described with a common unit mesh of 51 A(sup 2) and mismatch of 0.3 percent. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi2(110) parallel to Si(110). A channeling effect for MeV He(+) ions was not found for this material. Potential commercial applications of this research may be found in silicon-integrated infrared detector arrays. Optical characterizations showed that semiconducting ReSi2 is a strong absorber of infrared radiation, with the adsorption constant increasing above 2 x

  9. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity.

    Science.gov (United States)

    Kang, Kibum; Xie, Saien; Huang, Lujie; Han, Yimo; Huang, Pinshane Y; Mak, Kin Fai; Kim, Cheol-Joo; Muller, David; Park, Jiwoong

    2015-04-30

    The large-scale growth of semiconducting thin films forms the basis of modern electronics and optoelectronics. A decrease in film thickness to the ultimate limit of the atomic, sub-nanometre length scale, a difficult limit for traditional semiconductors (such as Si and GaAs), would bring wide benefits for applications in ultrathin and flexible electronics, photovoltaics and display technology. For this, transition-metal dichalcogenides (TMDs), which can form stable three-atom-thick monolayers, provide ideal semiconducting materials with high electrical carrier mobility, and their large-scale growth on insulating substrates would enable the batch fabrication of atomically thin high-performance transistors and photodetectors on a technologically relevant scale without film transfer. In addition, their unique electronic band structures provide novel ways of enhancing the functionalities of such devices, including the large excitonic effect, bandgap modulation, indirect-to-direct bandgap transition, piezoelectricity and valleytronics. However, the large-scale growth of monolayer TMD films with spatial homogeneity and high electrical performance remains an unsolved challenge. Here we report the preparation of high-mobility 4-inch wafer-scale films of monolayer molybdenum disulphide (MoS2) and tungsten disulphide, grown directly on insulating SiO2 substrates, with excellent spatial homogeneity over the entire films. They are grown with a newly developed, metal-organic chemical vapour deposition technique, and show high electrical performance, including an electron mobility of 30 cm(2) V(-1) s(-1) at room temperature and 114 cm(2) V(-1) s(-1) at 90 K for MoS2, with little dependence on position or channel length. With the use of these films we successfully demonstrate the wafer-scale batch fabrication of high-performance monolayer MoS2 field-effect transistors with a 99% device yield and the multi-level fabrication of vertically stacked transistor devices for three

  10. Electrical behavior of Langmuir-Blodgett networks of sorted metallic and semiconducting single-walled carbon nanotubes.

    Science.gov (United States)

    Massey, Mark K; Rosamond, Mark C; Pearson, Christopher; Zeze, Dagou A; Petty, Michael C

    2012-10-30

    Langmuir-Blodgett deposition has been used to form thin film networks of both metallic and semiconducting single-walled carbon nanotubes. These have been investigated to understand their physical, optical, and morphological properties. The electrical conductivities over the temperature range 80-350 K and across electrode gaps of 220 nm and 2 mm have been explored. In the case of semiconducting tubes, the results suggest that Poole-Frenkel conduction is the dominant electrical process at temperatures below 150 K and electric fields of greater than 1 MV m(-1). Metallic nanotube networks exhibit a decrease in resistance with a reduction in temperature. This can be approximated by a linear relationship, giving a temperature coefficient of resistance of 10(-3) K(-1).

  11. Organic Semiconducting Materials in Film and Powder Forms from a Co-polymeric Elastomer-Styrene Butadiene Rubber

    Science.gov (United States)

    Santhamma, G.; Predeep, P.

    2008-04-01

    Semiconducting materials in both film and powder forms are prepared by Antimony Pentachloride (SBCl5) doping in Styrene Butadiene Rubber (SBR). SBR is a synthetic co-polymeric elastomer, insulating in undoped state, is mainly used for manufacturing tires, tubes etc. Synthesized conducting materials are proposed to have tremendous application potentials in optoelectronic, electronic and electrical industries. For example conducting films can be used as active elements for fabrication of organic light emitting diodes, photovoltaic cells etc. Electrical and optical properties of prepared samples are studied by measuring electrical conductivity and analyzing spectroscopic data. Electrical conductivity of samples lies in the range of that of semi-conducting materials. Presence of conjugated sequences in the back bone of prepared conducting materials, which is regarded as pre-requisite condition for a polymer to conductive, is confirmed by studying UV/Vis spectra.

  12. Semiconducting ZnSnxGe1−xN2 alloys prepared by reactive radio-frequency sputtering

    Directory of Open Access Journals (Sweden)

    Amanda M. Shing

    2015-07-01

    Full Text Available We report on the fabrication and structural and optoelectronic characterization of II-IV-nitride ZnSnxGe1−xN2 thin-films. Three-target reactive radio-frequency sputtering was used to synthesize non-degenerately doped semiconducting alloys having <10% atomic composition (x = 0.025 of tin. These low-Sn alloys followed the structural and optoelectronic trends of the alloy series. Samples exhibited semiconducting properties, including optical band gaps and increasing in resistivities with temperature. Resistivity vs. temperature measurements indicated that low-Sn alloys were non-degenerately doped, whereas alloys with higher Sn content were degenerately doped. These films show potential for ZnSnxGe1−xN2 as tunable semiconductor absorbers for possible use in photovoltaics, light-emitting diodes, or optical sensors.

  13. Selective landing of semiconducting single-wall carbon nanotubes onto tetrathiafulvalene moiety self-assembled on ITO substrate

    Directory of Open Access Journals (Sweden)

    Jin-Sun Kim

    2010-03-01

    Full Text Available Semiconducting single-wall carbon nanotubes (SWCNTs were selecively interacted with tetrathiafulvalene (TTF moiety self-assembled on indium tin oxide (ITO substrate by charge-transfer interaction. The charge-transfer phenomena between two molecules were elucidated by cyclic voltammetry (CV and Raman spectroscopy. CV measurement of TTF-modified ITO substrate as a working electrode presented the difference between heat-treated system and untreated one. The two redox potentials, which are typically related to redox behavior of TTF, were shown in the unheated system during both oxidation and reduction cycles, while the two oxidation peaks were disappeared in the heated system. Raman spectra indicated that the intensities of RBM originated from metallic SWCNTs were much reduced in the heat-treated system, while there were little change in the unheated one. These results revealed that only semiconducting SWNTs were selectively adsorbed on the TTF moiety self-assembled on ITO when the system with heat treatment.

  14. Stable solar-driven oxidation of water by semiconducting photoanodes protected by transparent catalytic nickel oxide films

    KAUST Repository

    Sun, Ke

    2015-03-11

    Reactively sputtered nickel oxide (NiOx) films provide transparent, antireflective, electrically conductive, chemically stable coatings that also are highly active electrocatalysts for the oxidation of water to O2(g). These NiOx coatings provide protective layers on a variety of technologically important semiconducting photoanodes, including textured crystalline Si passivated by amorphous silicon, crystalline n-type cadmium telluride, and hydrogenated amorphous silicon. Under anodic operation in 1.0 M aqueous potassium hydroxide (pH 14) in the presence of simulated sunlight, the NiOx films stabilized all of these self-passivating, high-efficiency semiconducting photoelectrodes for >100 h of sustained, quantitative solar-driven oxidation of water to O2(g). © 2015, National Academy of Sciences. All rights reserved.

  15. Cu{sub 2}O/TiO{sub 2} heterostructures on a DVD as easy&cheap photoelectrochemical sensors

    Energy Technology Data Exchange (ETDEWEB)

    Zanatta, Michele; Calvillo, Laura; Zheng, Jian; Rizzi, Gian Andrea, E-mail: gianandrea.rizzi@unipd.it; Durante, Christian; Giallongo, Giuseppe; Chirkov, Dymitrov; Colazzo, Luciano; Marega, Carla; Gennaro, Armando; Granozzi, Gaetano

    2016-03-31

    Cu{sub 2}O nanoparticles have been grown by pulse-electrochemical deposition on a Digital Versatile Disk (DVD) which acts as a nanostructured electrode. Prior to Cu{sub 2}O deposition, the silver-coated rectangular-shaped grooves of the disassembled DVD were coated with a TiO{sub 2} thin film by a modified sol–gel method, where oxalic acid is used in place of the usual mineral acids to peptize the precipitated hydrous titania formed from the hydrolysis of titanium iso-propoxide. This procedure leaves no inorganic residues after UV-curing, resulting in a high quality film, mainly composed of TiO{sub 2}-anatase. As demonstrated by Atomic Force Microscopy (AFM) measurements, the DVD grooves are filled by a 120–130 nm thick TiO{sub 2} film, while the thickness of the TiO{sub 2} deposit on the crests is only ca. 50 nm. This inhomogeneous thickness leads to an inhomogeneous electric field when the DVD is used as an electrode for depositing Cu{sub 2}O nanoparticles, which eventually leads to the growth of Cu{sub 2}O nanoparticles only on the DVD crests. A highly regular and reproducible Cu{sub 2}O/TiO{sub 2} stripe-like heterostructure is obtained where both semiconducting oxides are aside. This system has been characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray photoemission spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, Raman spectroscopy and photocurrent measurements. A possible use of this easy&cheap electrode as a visible light responsive sensor to water soluble organics in basic solution is suggested. - Highlights: • A commercial DVD is recycled to prepare cheap photo-electrochemical sensors. • The sensing elements are Cu{sub 2}O nanostripes grown on a nanostructured TiO{sub 2} thin film obtained at room temperature. • Water soluble organics can be detected by dissolved O{sub 2} activation with visible light.

  16. Design of L2_1-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT+GW study

    OpenAIRE

    Tas, M.; Sasioglu, E.; Friedrich, C.; Blugel, S.; Galanakis, I.

    2016-01-01

    Antiferromagnetic spintronics is an on-going growing field of research. Employing both standard density functional theory and the $GW$ approximation within the framework of the FLAPW method, we study the electronic and magnetic properties of seven potential antiferromagnetic semiconducting Heusler compounds with 18 (or 28 when Zn is present) valence electrons per unit cell. We show that in these compounds G-type antiferromagnetism is the ground state and that they are all either emiconductors...

  17. Semiconducting polymer dots doped with europium complexes showing ultranarrow emission and long luminescence lifetime for time-gated cellular imaging.

    Science.gov (United States)

    Sun, Wei; Yu, Jiangbo; Deng, Ruiping; Rong, Yu; Fujimoto, Bryant; Wu, Changfeng; Zhang, Hongjie; Chiu, Daniel T

    2013-10-18

    Bright dots: Semiconducting polymer dots (Pdots) doped with europium complexes possess line-like fluorescence emission, high quantum yield, and long fluorescence lifetime. The Pdots successfully labeled receptors on cells. The long fluorescence lifetime of the Pdots was used to distinguish them from other red fluorescence emitting nanoparticles, and improve the signal-to-noise ratio for time-gated cellular imaging. PVK=poly(9-vinylcarbazole). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review

    Science.gov (United States)

    Romero, Cristina; Noyola, Juan C.; Santiago, Ulises; Valladares, Renela M.; Valladares, Alexander; Valladares, Ariel A.

    2010-01-01

    We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists first of constructing crystalline supercells with a large number of atoms and a density close to the real value and then lowering the density by increasing the volume. The resulting supercells are subjected to either ab initio or parameterized—Tersoff-based—molecular dynamics processes at various temperatures, all below the corresponding bulk melting points, followed by geometry relaxations. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions without the need of incorporating ad hoc semiconducting atomic structural elements such as graphene-like sheets and/or chain-like patterns (reconstructive simulations) or of reproducing the experimental processes (mimetic simulations). We report radial (pair) distribution functions, nanoporous structures of C and Si, and some computational predictions for their vibrational density of states. We present numerical estimates and discuss possible applications of semiconducting materials for hydrogen storage in potential fuel tanks. Nanopore structures for metallic elements like Al and Au also obtained through the expanding lattice method are reported.

  19. Study of the Natural Auger Suppression Mechanism in Heterostructures through Heteroboundary Engineering.

    Science.gov (United States)

    Slonopas, Andre; Tomkinson, David

    2017-10-12

    Planar superlattice devices revolutionized our approach to solid-state technology by reducing the Shockley-Read-Hall losses to negligible levels. Despite these achievements, significant efficiency losses are found in current devices presumably caused by the Auger recombinations. This work present the theoretical considerations of the Auger recombination suppression through heterostructure engineering. It is found that Auger recombinations are suppressed through the heterobarrier-carrier interactions. It is shown that a minima in Auger recombinations exists in type-II and III heterostructures, and can be reached through proper conduction and valence band alignments. Furthermore, the careful consideration of the heterostructure enables natural Auger suppression for high operating temperatures. Dark current based on the optimized heterostructure was computed and found to be over an order of magnitude below the currently reported measurements for the superlattice and QD devices. This research provides crucial information about the underlying physics behind the Auger recombination, enabling future superlattice and quantum dot device optimization.

  20. Comparative analysis of hole transport in compressively strained InSb and Ge quantum well heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Agrawal, Ashish; Barth, Michael; Madan, Himanshu; Datta, Suman [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Lee, Yi-Jing; Lin, You-Ru; Wu, Cheng-Hsien; Ko, Chih-Hsin; Wann, Clement H. [Taiwan Semiconductor Manufacturing Company, Hsinchu 30078, Taiwan (China); Loubychev, Dmitri; Liu, Amy; Fastenau, Joel [IQE, Inc., Bethlehem, Pennsylvania 18015 (United States); Lindemuth, Jeff [Lake Shore Cryotronics, Westerville, Ohio 43082 (United States)

    2014-08-04

    Compressively strained InSb (s-InSb) and Ge (s-Ge) quantum well heterostructures are experimentally studied, with emphasis on understanding and comparing hole transport in these two-dimensional confined heterostructures. Magnetotransport measurements and bandstructure calculations indicate 2.5× lower effective mass for s-InSb compared to s-Ge quantum well at 1.9 × 10{sup 12} cm{sup –2}. Advantage of strain-induced m* reduction is negated by higher phonon scattering, degrading hole transport at room temperature in s-InSb quantum well compared to s-Ge heterostructure. Consequently, effective injection velocity is superior in s-Ge compared to s-InSb. These results suggest s-Ge quantum well heterostructure is more favorable and promising p-channel candidate compared to s-InSb for future technology node.

  1. Synthesis, fabrication and characterization of Ge/Si axial nanowire heterostructure tunnel FETs

    Energy Technology Data Exchange (ETDEWEB)

    Picraux, Samuel T [Los Alamos National Laboratory; Dayeh, Shadi A [Los Alamos National Laboratory

    2010-01-01

    Axial Ge/Si heterostructure nanowires allow energy band-edge engineering along the axis of the nanowire, which is the charge transport direction, and the realization of asymmetric devices for novel device architectures. This work reports on two advances in the area of heterostructure nanowires and tunnel FETs: (i) the realization of 100% compositionally modulated Si/Ge axial heterostructure nanowires with lengths suitable for device fabrication and (ii) the design and implementation of Schottky barrier tunnel FETs on these nanowires for high-on currents and suppressed ambipolar behavior. Initial prototype devices resulted in a current drive in excess of 100 {micro}A/{micro}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios. These results demonstrate the potential of such asymmetric heterostructures (both in the semiconductor channel and metal-semiconductor barrier heights) for low-power and high performance electronics.

  2. Heterostructures based on two-dimensional layered materials and their potential applications

    KAUST Repository

    Li, Ming-yang

    2015-12-04

    The development of two-dimensional (2D) layered materials is driven by fundamental interest and their potential applications. Atomically thin 2D materials provide a wide range of basic building blocks with unique electrical, optical, and thermal properties which do not exist in their bulk counterparts. The van der Waals interlayer interaction enables the possibility to exfoliate and reassemble different 2D materials into arbitrarily and vertically stacked heterostructures. Recently developed vapor phase growth of 2D materials further paves the way of directly synthesizing vertical and lateral heterojunctions. This review provides insights into the layered 2D heterostructures, with a concise introduction to preparative approaches for 2D materials and heterostructures. These unique 2D heterostructures have abundant implications for many potential applications.

  3. Microwave assisted green synthesis and characterization of silver/montmorillonite heterostructures with improved antimicrobial properties

    CSIR Research Space (South Africa)

    Kesavan Pillai, Sreejarani

    2013-10-01

    Full Text Available Silver (Ag)/montmorillonite (Mt) heterostructures were effectively synthesized utilising microwave (MW) irradiation technique in the absence of any reducing agent. Compared to conventional thermal reduction processes, this approach is simple, faster...

  4. Scanning probe microscopy investigation of complex-oxide heterostructures

    Science.gov (United States)

    Bi, Feng

    Advances in the growth of precisely tailored complex-oxide heterostructures have led to new emergent behavior and associated discoveries. One of the most successful examples consists of an ultrathin layer of LaAlO 3 (LAO) deposited on TiO2-terminated SrTiO3 (STO), where a high mobility quasi-two dimensional electron liquid (2DEL) is formed at the interface. Such 2DEL demonstrates a variety of novel properties, including field tunable metal-insulator transition, superconductivity, strong spin-orbit coupling, magnetic and ferroelectric like behavior. Particularly, for 3-unit-cell (3 u.c.) LAO/STO heterostructures, it was demonstrated that a conductive atomic force microscope (c-AFM) tip can be used to "write" or "erase" nanoscale conducting channels at the interface, making LAO/STO a highly flexible platform to fabricate novel nanoelectronics. This thesis is focused on scanning probe microscopy studies of LAO/STO properties. We investigate the mechanism of c-AFM lithography over 3 u.c. LAO/STO in controlled ambient conditions by using a vacuum AFM, and find that the water molecules dissociated on the LAO surface play a critical role during the c-AFM lithography process. We also perform electro-mechanical response measurements over top-gated LAO/STO devices. Simultaneous piezoresponse force microscopy (PFM) and capacitance measurements reveal a correlation between LAO lattice distortion and interfacial carrier density, which suggests that PFM could not only serve as a powerful tool to map the carrier density at the interface but also provide insight into previously reported frequency dependence of capacitance enhancement of top-gated LAO/STO structures. To study magnetism at the LAO/STO interface, magnetic force microscopy (MFM) and magnetoelectric force microscopy (MeFM) are carried out to search for magnetic signatures that depend on the carrier density at the interface. Results demonstrate an electronicallycontrolled ferromagnetic phase on top-gated LAO

  5. Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy.

    Science.gov (United States)

    Mehlenbacher, Randy D; McDonough, Thomas J; Grechko, Maksim; Wu, Meng-Yin; Arnold, Michael S; Zanni, Martin T

    2015-04-13

    Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Förster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap separation, whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.

  6. Multinuclear Phthalocyanine-Fused Molecular Nanoarrays: Synthesis, Spectroscopy, and Semiconducting Property.

    Science.gov (United States)

    Shang, Hong; Xue, Zheng; Wang, Kang; Liu, Huibiao; Jiang, Jianzhuang

    2017-06-27

    The post-cyclization strategy rather than the conventional ante-cyclotetramerization method was employed for the synthesis of multinuclear phthalocyanine-fused molecular nanoarrays. Reaction of 2,3,9,10,16,17-hexakis(2,6-dimethylphenoxy)-23,24-diaminophthalocyaninato zinc(II) with 2,7-di-tert-butylpyrene-4,5-dione, 2,7-di-tert-butylpyrene-4,5,9,10-tetraone, and hexaketocyclohexane in refluxing acetic acid afforded the corresponding mono-, bi-, and trinuclear phthalocyanine-fused zinc complexes (Pz-pyrene){Zn[Pc(OC8 H9 )6 ]} (1), (Pz2 -pyrene){Zn[Pc(OC8 H9 )6 ]}2 (2), {(HAT){Zn[Pc(OC8 H9 )6 ]}3 } (3) in 46, 13, and 25 % yield, respectively, which extend the scope of multinuclear phthalocyanine-fused nanoarrays with different molecular skeletons. The self-assembly behavior of trinuclear phthalocyanine 3 in THF/CH3 CN was investigated by electronic absorption spectroscopy and SEM, and the fabricated nanorods showed interesting semiconducting properties, which suggest good application potential of these multinuclear phthalocyanine-fused molecular nanoarrays. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Extended π-conjugated molecules derived from naphthalene diimides toward organic emissive and semiconducting materials.

    Science.gov (United States)

    Li, Yonghai; Zhang, Guanxin; Yang, Ge; Guo, Yunlong; Di, Chong'an; Chen, Xin; Liu, Zitong; Liu, Huiying; Xu, Zhenzhen; Xu, Wei; Fu, Hongbing; Zhang, Deqing

    2013-04-05

    In this paper, a new synthetic way to modify naphthalene diimide (NDI) at "shoulder" positions is reported. The key step of the transformation is the intramolecular cyclization involving ethynyl and imidecarbonyl groups. The structure of the intermediate pyrylium cation was confirmed by X-ray crystal structural analysis. New conjugated molecules 1a-g were successfully synthesized in acceptable yields. Their absorption and fluorescence spectra were measured. Among them 1c-f are strongly emissive in solutions. Furthermore, 1b-f are also fluorescent in their solid states; in particular, 1b exhibits a typical aggregation-induced enhanced emission feature. Yellow-emissive microfibrils of 1d show potential optical waveguide behavior. HOMO/LUMO energies of 1a-f were determined based on their cyclic voltammograms. The results also reveal that HOMO/LUMO energies of these new conjugated molecules are influenced by the two flanking moieties. Notably, the thin film of 1c that is emissive shows p-type semiconducting behavior with hole mobility up to 0.0063 cm(2) V(-1) s(-1) based on the transfer and output characteristics of the OFET (organic field effect transistor).

  8. Dissociating excitons photogenerated in semiconducting carbon nanotubes at polymeric photovoltaic heterojunction interfaces.

    Science.gov (United States)

    Bindl, Dominick J; Safron, Nathaniel S; Arnold, Michael S

    2010-10-26

    Semiconducting single-walled carbon nanotubes (s-SWCNTs) have strong near-infrared and visible absorptivity and exceptional charge transport characteristics, rendering them highly attractive semiconductor absorbers for photovoltaic and photodetector technologies. However, these applications are limited by a poor understanding of how photogenerated charges, which are bound as excitons in s-SWCNTs, can be dissociated in large-area solid-state devices. Here, we measure the dissociation of excitons in s-SWCNT thin films that form planar heterojunction interfaces with polymeric photovoltaic materials using an exciton dissociation-sensitive photocapacitor measurement technique that is advantageously insensitive to optically induced thermal photoconductive effects. We find that fullerene and polythiophene derivatives induce exciton dissociation, resulting in electron and hole transfer, respectively, away from optically excited s-SWCNTs. Significantly weaker or no charge transfer is observed using wider gap polymers due to insufficient energy offsets. These results are expected to critically guide the development of thin film s-SWCNT-based photosensitive devices.

  9. Passivity and Semiconducting Behavior of a High Nitrogen Stainless Steel in Acidic NaCl Solution

    Directory of Open Access Journals (Sweden)

    Yanxin Qiao

    2016-01-01

    Full Text Available The passivity and semiconducting behaviors of a high nitrogen-containing nickel-free stainless steel (HNSS in 0.05 mol/L H2SO4 + 0.5 mol/L NaCl have been investigated. Results indicated that HNSS offered excellent pitting corrosion resistance in corrosive environments. Three corrosion potential values were observed in potentiodynamic polarization response, indicating the existence of an unstable system. The current transient and Mott-Schottky plots demonstrated that the stability of passive films decreased with the increase of applied potentials. The angle resolved X-ray photoelectron spectrometric results revealed that the primary constituents of passive films formed in 0.05 mol/L H2SO4 + 0.5 mol/L NaCl solution were composed of iron oxides, manganese oxides, Cr2O3, and Cr(OH3. Meanwhile, it indicated that molybdenum oxides did not exist in the oxide layer, but chloride ions were present in the passive films.

  10. Critical behavior of quasi-two-dimensional semiconducting ferromagnet Cr2Ge2Te6

    Science.gov (United States)

    Liu, Yu; Petrovic, C.

    2017-08-01

    The critical properties of the single-crystalline semiconducting ferromagnet Cr2Ge2Te6 were investigated by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. Critical exponents β =0.200 ±0.003 with a critical temperature Tc=62.65 ±0.07 K and γ =1.28 ±0.03 with Tc=62.75 ±0.06 K are obtained by the Kouvel-Fisher method whereas δ =7.96 ±0.01 is obtained by a critical isotherm analysis at Tc=62.7 K. These critical exponents obey the Widom scaling relation δ =1 +γ /β , indicating self-consistency of the obtained values. With these critical exponents the isotherm M (H ) curves below and above the critical temperatures collapse into two independent universal branches, obeying the single scaling equation m =f±(h ) , where m and h are renormalized magnetization and field, respectively. The determined exponents match well with those calculated from the results of the renormalization group approach for a two-dimensional Ising system coupled with a long-range interaction between spins decaying as J (r ) ≈r-(d +σ ) with σ =1.52 .

  11. Optoelectronic properties of Mg{sub 2}Si semiconducting layers with high absorption coefficients

    Energy Technology Data Exchange (ETDEWEB)

    Kato, Takashi; Sago, Yuichiro; Fujiwara, Hiroyuki [Center of Innovative Photovoltaic Systems (CIPS), Gifu University, 1-1 Yanagido, Gifu 501-1193 (Japan)

    2011-09-15

    In an attempt to develop a low-cost material for solar cell devices, polycrystalline magnesium silicide (poly-Mg{sub 2}Si) semiconducting layers have been prepared by applying rf magnetron sputtering using a Mg{sub 2}Si target. The optimum substrate temperature for the poly-Mg{sub 2}Si growth was found to be T{sub s} = 200 deg. C; the film deposition at higher temperatures leads to desorption of Mg atoms from the growing surface, while the amorphous phase formation occurs at room temperature. The poly-Mg{sub 2}Si layer deposited at T{sub s} = 200 deg. C shows the (111) preferential orientation with a uniform grain size of {approx}50 nm. The dielectric function of the poly-Mg{sub 2}Si layer has been determined accurately by spectroscopic ellipsometry. From the analysis, quite high absorption coefficients and an indirect gap of 0.77 eV in the poly-Mg{sub 2}Si layer have been confirmed. The above poly-Mg{sub 2}Si layer shows clear photoconductivity and can be applied as a narrow-gap bottom layer in multi-junction solar cell devices.

  12. Photochemical Creation of Fluorescent Quantum Defects in Semiconducting Carbon Nanotube Hosts.

    Science.gov (United States)

    Wu, Xiaojian; Kim, Mijin; Kwon, Hyejin; Wang, YuHuang

    2018-01-15

    Quantum defects are an emerging class of synthetic single-photon emitters that hold vast potential for near-infrared imaging, chemical sensing, materials engineering, and quantum information processing. Herein, we show that it is possible to optically direct the synthetic creation of molecularly tunable fluorescent quantum defects in semiconducting single-walled carbon nanotube hosts through photochemical reactions. By exciting the host semiconductor with light that resonates with its electronic transition, we find that halide-containing aryl groups can covalently bond to the sp2 carbon lattice. The introduced quantum defects generate bright photoluminescence that allows tracking of the reaction progress in situ. We show that the reaction is independent of temperature but correlates strongly with the photon energy used to drive the reaction, suggesting a photochemical mechanism rather than photothermal effects. This type of photochemical reactions opens the possibility to control the synthesis of fluorescent quantum defects using light and may enable lithographic patterning of quantum emitters with electronic and molecular precision. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Thermal conductivity of organic semi-conducting materials using 3omega and photothermal radiometry techniques

    Directory of Open Access Journals (Sweden)

    Reisdorffer Frederic

    2014-01-01

    Full Text Available Organic semiconductors for opto-electronic devices show several defects which can be enhanced while increasing the operating temperature. Their thermal management and especially the reduction of their temperature are of great interest. For the heat transfer study, one has to measure the thermal conductivity of thin film organic materials. However the major difficulty for this measurement is the very low thickness of the films which needs the use of very specific techniques. In our work, the 3-omega and photothermal radiometric methods were used to measure the thermal conductivity of thin film organic semiconducting material (Alq3. The measurements were performed as function of the thin film thickness from 45 to 785 nm and also of its temperature from 80 to 350 K. With the 3 omega method, a thermal conductivity value of 0.066 W.m−1K−1 was obtained for Alq3 thin film of 200 nm at room temperature, in close agreement with the photothermal value. Both techniques appear to be complementary: the 3 omega method is easier to implement for large temperature range and small thicknesses down to a few tens of nanometers whereas the photothermal method is more suitable for thicknesses over 200nm since it provides additional information such as the thin film volumetric heat capacity.

  14. Purification of semiconducting single-walled carbon nanotubes by spiral counter-current chromatography.

    Science.gov (United States)

    Knight, Martha; Lazo-Portugal, Rodrigo; Ahn, Saeyoung Nate; Stefansson, Steingrimur

    2017-02-03

    Over the last decade man-made carbon nanostructures have shown great promise in electronic applications, but they are produced as very heterogeneous mixtures with different properties so the achievement of a significant commercial application has been elusive. The dimensions of single-wall carbon nanotubes are generally a nanometer wide, up to hundreds of microns long and the carbon nanotubes have anisotropic structures. They are processed to have shorter lengths but they need to be sorted by diameter and chirality. Thus counter-current chromatography methods developed for large molecules are applied to separate these compounds. A modified mixer-settler spiral CCC rotor made with 3 D printed disks was used with a polyethylene glycol-dextran 2-phase solvent system and a surfactant gradient to purify the major species in a commercial preparation. We isolated the semi-conducting single walled carbon nanotube chiral species identified by UV spectral analysis. The further development of spiral counter-current chromatography instrumentation and methods will enable the scalable purification of carbon nanotubes useful for the next generation electronics. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. OCT imaging detection of brain blood vessels in mouse, based on semiconducting polymer nanoparticles.

    Science.gov (United States)

    Yang, Shaozhuang; Chen, Haobin; Liu, Liwei; Chen, Bingling; Yang, Zhigang; Wu, Changfeng; Hu, Siyi; Lin, Huiyun; Li, Buhong; Qu, Junle

    2017-11-20

    Optical Coherence Tomography (OCT) is a valuable technology that has been used to obtain microstructure images of tissue, and has several advantages, though its applications are limited in high-scattering tissues. Therefore, semiconducting polymer nanoparticles (SPNs) that possess strong absorption characteristics are applied to decrease light scattering in tissues and used as exogenous contrast agents for enhancing the contrast of OCT imaging detection. In this paper, we prepared two kinds of SPNs, termed PIDT-TBZ SPNs and PBDT-TBZ SPNs, as the contrast agents for OCT detection to enhance the signal. Firstly, we proved that they were good contrast agents for OCT imaging in agar-TiO 2 . After that, the contrast effects of these two SPNs were quantitatively analyzed, and then cerebral blood vessels were monitored by a home-made SD-OCT system. Finally, we created OCT images in vitro and in vivo with these two probes and performed quantitative analysis using the images. The results indicated that these SPNs created a clear contrast enhancement of small vessels in the OCT imaging process, which provides a basis for the application of SPNs as contrast agents for bioimaging studies.

  16. Efficient Naphthalenediimide-Based Hole Semiconducting Polymer with Vinylene Linkers between Donor and Acceptor Units

    KAUST Repository

    Zhang, Lei

    2016-11-04

    We demonstrate a new method to reverse the polarity and charge transport behavior of naphthalenediimide (NDI)-based copolymers by inserting a vinylene linker between the donor and acceptor units. The vinylene linkers minimize the intrinsic steric congestion between the NDI and thiophene moieties to prompt backbone planarity. The polymers with vinylene linkers exhibit electron n-channel transport characteristics under vacuum, similar to the benchmark polymer, P(NDI2OD-T2). To our surprise, when the polymers are measured in air, the dominant carrier type switches from n- to p-type and yield hole mobilities up to 0.45 cm(2) s(-1) with hole to electron mobility ratio of three (mu(h)/mu(e), similar to 3), which indicates that the hole density in the active layer can be significantly increased by exposure to air. This increase is consistent with the intrinsic more delocalized nature of the highest occupied molecular orbital of the charged vinylene polymer, as estimated by density functional theory (DFT) calculations, which facilitates hole transport within the polymer chains. This is the first demonstration of an efficient NDI-based hole semiconducting polymer, which will enable new developments in all-polymer solar cells, complementary circuits, and dopable polymers for use in thermoelectrics.

  17. Correlation of Disorder and Charge Transport in a Range of Indacenodithiophene-Based Semiconducting Polymers

    KAUST Repository

    Nikolka, Mark

    2017-12-13

    Over the past 25 years, various design motifs have emerged for the development of organic semiconductors for demanding applications in flexible organic light emitting diode display backplanes or even printed organic logic. Due to their large area uniformity paired with high charge carrier mobilities, conjugated polymers have attracted increasing attention in this respect. However, the performances delivered by current generation conjugated polymers still fall short of many industrial requirements demanding devices with ideal transistor characteristics and higher mobilities. The discovery of conjugated polymers with low energetic disorder, such as the indacenodithiophene-based polymer indacenodithiophene-co-benzothiadiazole, represent an exciting opportunity to breach this chasm if these materials can be further optimized while maintaining their low disorder. Here, it is shown how both the charge transport properties as well as the energetic disorder are affected by tuning the molecular structure of a large range of indacenodithiophene-based semiconducting polymer derivatives. This study allows to understand better the interplay between molecular design and structure of the polymer backbone and the degree of energetic disorder that governs the charge transport properties in thin polymer films.

  18. Excited-State Interaction of Semiconducting Single-Walled Carbon Nanotubes with Their Wrapping Polymers.

    Science.gov (United States)

    Kahmann, Simon; Salazar Rios, Jorge M; Zink, Matthias; Allard, Sybille; Scherf, Ullrich; Dos Santos, Maria C; Brabec, Christoph J; Loi, Maria A

    2017-11-16

    We employ photoluminescence and pump-probe spectroscopy on films of semiconducting single-walled carbon nanotubes (CNTs) of different chirality wrapped with either a wide band gap polyfluorene derivative (PF12) or a polythiophene with narrower gap (P3DDT) to elucidate the excited states' interplay between the two materials. Excitation above the polymer band gap gives way to an ultrafast electron transfer from both polymers toward the CNTs. By monitoring the hole polaron on the polymer via its mid infrared signature, we show that also illumination below the polymer band gap leads to the formation of this fingerprint and infer that holes are also transferred toward the polymer. As this contradicts the standard way of discussing the involved energy levels, we propose that polymer-wrapped CNTs should be considered as a single hybrid system, exhibiting states shared between the two components. This proposition is validated through quantum chemical calculations that show hybridization of the first excited states, especially for the thiophene-CNT sample.

  19. Glutathione responsive micelles incorporated with semiconducting polymer dots and doxorubicin for cancer photothermal-chemotherapy

    Science.gov (United States)

    Cai, Zhixiong; Zhang, Da; Lin, Xinyi; Chen, Yunzhu; Wu, Ming; Wei, Zuwu; Zhang, Zhenxi; Liu, Xiaolong; Yao, Cuiping

    2017-10-01

    Nanoplatform integrated with photothermal therapy (PTT) and chemotherapy has been recognized a promising agent for enhancing cancer therapeutic outcomes, but still suffer from less controllability for optimizing their synergistic effects. We fabricated glutathione (GSH) responsive micelles incorporated with semiconducting polymer dots and doxorubicin (referred as SPDOX NPs) for combining PTT with chemotherapy to enhance cancer therapeutic efficiency. These micelles, with excellent water dispersibility, comprises of three distinct functional components: (1) the monomethoxy-poly(ethylene glycol)-S-S-hexadecyl (mPEG-S-S-C16), which forms the micelles, can render hydrophobic substances water-soluble and improve the colloidal stability; (2) disulfide linkages can be cleaved in a reductive environment for tumor specific drug release due to the high GSH concentrations of tumor micro-environment; (3) PCPDTBT dots and anti-cancer drug DOX that are loaded inside the hydrophobic core of the micelle can be applied to simultaneously perform PTT and chemotherapy to achieve significantly enhanced tumor killing efficiency both in vitro and in vivo. In summary, our studies demonstrated that our SPDOX NPs with simultaneous photothermal-chemotherapy functions could be a promising platform for a tumor specific responsive drug delivery system.

  20. Thin sensing layer based on semi-conducting β-cyclodextrin rotaxane for toxic metals detection

    Energy Technology Data Exchange (ETDEWEB)

    Teka, S.; Gaied, A.; Jaballah, N. [Laboratoire des Interfaces et Matériaux Avancés (LIMA), Université de Monastir, Faculté des Sciences de Monastir, Bd. de l' Environnement, 5019 Monastir (Tunisia); Xiaonan, S. [Université Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS, 15 rue J-A de Baı̈ f, 75205 Paris Cedex 13 (France); Majdoub, M., E-mail: mustapha.majdoub@fsm.rnu.tn [Laboratoire des Interfaces et Matériaux Avancés (LIMA), Université de Monastir, Faculté des Sciences de Monastir, Bd. de l' Environnement, 5019 Monastir (Tunisia)

    2016-02-15

    Highlights: • Microwave-assisted synthesis of rotaxane based on anthracene and β-cyclodextrin. • Morphological and optical characterization of thin solid film. • Elaboration of impedimetric gold/rotaxane sensor. • Investigation of the membrane sensitivity towards Hg{sup 2+}, Cu{sup 2+} and Pb{sup 2+} cations. - Abstract: An impedimetric sensor based on a new semi-conducting rotaxane has been described for detection of toxic cations. The rotaxane, consists on a π-conjugated material encapsulated into β-cyclodextrin (β-CD); it has been synthesized via the Williamson reaction under microwaves irradiation. The supramolecular structure of the compound was confirmed by NMR and FT-IR spectroscopies. A thin solid film of the rotaxane was deposited by spin-coating to develop a new electrochemical sensor. The morphological properties of the organic membrane were evaluated using contact angle measurements and atomic force microscopy. The gold/rotaxane/solution interfaces were investigated by electrochemical impedance spectroscopy and the obtained data were fitted using an equivalent electrical circuit. The response of the gold/rotaxane membrane towards Hg{sup 2+}, Cu{sup 2+} and Pb{sup 2+} cations was studied and the results showed a good sensitivity to the mercury cations.

  1. Evaluation of metallic and semiconducting single-walled carbon nanotube characteristics.

    Science.gov (United States)

    Wu, Bin; Geng, Dechao; Liu, Yunqi

    2011-05-01

    The nature of the mixed electronic type metallic (M-) and semiconducting (S-) single-walled carbon nanotubes (SWNTs) synthesized by current methods has posed a key challenge for the development of high performance SWNT-based electronic devices. The precise measurements of M- to S-SWNT ratio in as-grown or separated samples are of paramount importance for the controlled synthesis, separation and the realization of various applications. The objective of this review is to provide comprehensive overview of the progress achieved so far for measuring the M/S ratio both on individual and collective levels of SWNT states. We begin with a brief introduction of SWNT structures/properties and discussion of the problems and difficulties associated with precise measurement of the M/S ratio, and then introduce the principles for obtaining distinguished signals from M-and S-SWNTs. These techniques are classified into different groups based either on the single/ensemble detection of SWNT samples or on the principles of techniques themselves. We then present the M/S ratio evaluation results of these methods, with emphasis on scanning probe microscopy (SPM)-based detection techniques. Finally, the prospects of precise and large-scale measurement of M/S ratio in achieving controlled synthesis and understanding growth mechanism of SWNTs are discussed. © The Royal Society of Chemistry 2011

  2. Radiation-Hard Complementary Integrated Circuits Based on Semiconducting Single-Walled Carbon Nanotubes.

    Science.gov (United States)

    McMorrow, Julian J; Cress, Cory D; Gaviria Rojas, William A; Geier, Michael L; Marks, Tobin J; Hersam, Mark C

    2017-03-28

    Increasingly complex demonstrations of integrated circuit elements based on semiconducting single-walled carbon nanotubes (SWCNTs) mark the maturation of this technology for use in next-generation electronics. In particular, organic materials have recently been leveraged as dopant and encapsulation layers to enable stable SWCNT-based rail-to-rail, low-power complementary metal-oxide-semiconductor (CMOS) logic circuits. To explore the limits of this technology in extreme environments, here we study total ionizing dose (TID) effects in enhancement-mode SWCNT-CMOS inverters that employ organic doping and encapsulation layers. Details of the evolution of the device transport properties are revealed by in situ and in operando measurements, identifying n-type transistors as the more TID-sensitive component of the CMOS system with over an order of magnitude larger degradation of the static power dissipation. To further improve device stability, radiation-hardening approaches are explored, resulting in the observation that SWNCT-CMOS circuits are TID-hard under dynamic bias operation. Overall, this work reveals conditions under which SWCNTs can be employed for radiation-hard integrated circuits, thus presenting significant potential for next-generation satellite and space applications.

  3. Progression in sensing cardiac troponin biomarker charge transductions on semiconducting nanomaterials

    Energy Technology Data Exchange (ETDEWEB)

    Fathil, M.F.M., E-mail: faris.fathil@gmail.com [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); Md Arshad, M.K., E-mail: mohd.khairuddin@unimap.edu.my [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); School of Microelectronic Engineering, Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); Ruslinda, A.R., E-mail: ruslinda@unimap.edu.my [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); Nuzaihan, M.N.M., E-mail: m.nuzaihan@unimap.edu.my [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); Gopinath, Subash C.B., E-mail: subash@unimap.edu.my [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); School of Bioprocess Engineering, Universiti Malaysia Perlis, 02600, Arau, Perlis (Malaysia); Adzhri, R., E-mail: adzhri@gmail.com [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); Hashim, U., E-mail: uda@unimap.edu.my [Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia); School of Microelectronic Engineering, Universiti Malaysia Perlis, 01000, Kangar, Perlis (Malaysia)

    2016-09-07

    A real-time ability to interpret the interaction between targeted biomolecules and the surface of semiconductors (metal transducers) into readable electrical signals, without biomolecular modification involving fluorescence dyes, redox enzymes, and radioactive labels, created by label-free biosensors has been extensively researched. Field-effect transistor (FET)- and capacitor-based biosensors are among the diverse electrical charge biosensing architectures that have drawn much attention for having charge transduction; thus, enabling the early and rapid diagnosis of the appropriate cardiac biomarkers at lower concentrations. These semiconducting material-based transducers are very suitable to be integrated with portable electronic devices for future online collection, transmission, reception, analysis, and reporting. This overview elucidates and clarifies two major electrical label-free systems (FET- and capacitor-based biosensors) with cardiac troponin (cTn) biomarker-mediated charge transduction for acute myocardial infarction (AMI) diagnosis. Advances in these systems are highlighted by their progression in bridging the laboratory and industry; the foremost technologies have made the transition from benchtop to bedside and beyond. - Highlights: • The progression of cardiac troponin detection from past to future are presented. • Electrical label-free biosensors for cardiac troponin are discussed. • The discussion focused on field-effect transistor-and capacitor-based devices. • Surface functionalization, sensitivity, and innovation of devices are highlighted. • They presented high sensitivity and specificity of real-time AMI determination.

  4. Energetic fluctuations in amorphous semiconducting polymers: Impact on charge-carrier mobility

    Science.gov (United States)

    Gali, Sai Manoj; D'Avino, Gabriele; Aurel, Philippe; Han, Guangchao; Yi, Yuanping; Papadopoulos, Theodoros A.; Coropceanu, Veaceslav; Brédas, Jean-Luc; Hadziioannou, Georges; Zannoni, Claudio; Muccioli, Luca

    2017-10-01

    We present a computational approach to model hole transport in an amorphous semiconducting fluorene-triphenylamine copolymer (TFB), which is based on the combination of molecular dynamics to predict the morphology of the oligomeric system and Kinetic Monte Carlo (KMC), parameterized with quantum chemistry calculations, to simulate hole transport. Carrying out a systematic comparison with available experimental results, we discuss the role that different transport parameters play in the KMC simulation and in particular the dynamic nature of positional and energetic disorder on the temperature and electric field dependence of charge mobility. It emerges that a semi-quantitative agreement with experiments is found only when the dynamic nature of the disorder is taken into account. This study establishes a clear link between microscopic quantities and macroscopic hole mobility for TFB and provides substantial evidence of the importance of incorporating fluctuations, at the molecular level, to obtain results that are in good agreement with temperature and electric field-dependent experimental mobilities. Our work makes a step forward towards the application of nanoscale theoretical schemes as a tool for predictive material screening.

  5. Formation and Device Application of Ge Nanowire Heterostructures via Rapid Thermal Annealing

    OpenAIRE

    Tang, Jianshi; Wang, Chiu-Yen; Xiu, Faxian; Zhou, Yi; Chen, Lih-Juann; Wang, Kang L.

    2011-01-01

    We reviewed the formation of Ge nanowire heterostructure and its field-effect characteristics by a controlled reaction between a single-crystalline Ge nanowire and Ni contact pads using a facile rapid thermal annealing process. Scanning electron microscopy and transmission electron microscopy demonstrated a wide temperature range of 400~500°C to convert the Ge nanowire to a single-crystalline Ni2Ge/Ge/Ni2Ge nanowire heterostructure with atomically sharp interfaces. More importantly, we studie...

  6. Graphene-Nanodiamond Heterostructures and their application to High Current Devices

    OpenAIRE

    Fang Zhao; Andrei Vrajitoarea; Qi Jiang; Xiaoyu Han; Aysha Chaudhary; Welch, Joseph O.; Jackman, Richard B.

    2015-01-01

    Graphene on hydrogen terminated monolayer nanodiamond heterostructures provides a new way to improve carrier transport characteristics of the graphene, offering up to 60% improvement when compared with similar graphene on SiO2/Si substrates. These heterostructures offers excellent current-carrying abilities whilst offering the prospect of a fast, low cost and easy methodology for device applications. The use of ND monolayers is also a compatible technology for the support of large area graphe...

  7. Band structure engineering in van der Waals heterostructures via dielectric screening: the GΔW method

    DEFF Research Database (Denmark)

    Winther, Kirsten Trøstrup; Thygesen, Kristian Sommer

    2017-01-01

    The idea of combining different two-dimensional (2D) crystals in van der Waals heterostructures (vdWHs) has led to a new paradigm for band structure engineering with atomic precision. Due to the weak interlayer couplings, the band structures of the individual 2D crystals are largely preserved upon...... with the polarisability of the 2D material. Our work demonstrates that dielectric engineering via van der Waals heterostructuring represents a promising strategy for tailoring the band structure of 2D materials....

  8. Gate-Controlled Electron Spin Resonance in a GaAs/AlGaAs Heterostructure

    OpenAIRE

    Jiang, H. W.; Yablonovitch, E.

    2001-01-01

    The electron spin resonance (ESR) of two-dimensional electrons is investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR resonance frequency can be turned by means of a gate voltage. The front and back gates of the heterostructure produce opposite g-factor shift, suggesting that electron g-factor is being electrostatically controlled by shifting the equilibrium position of the electron wave function from one epitaxial layer to another with different g-factors.

  9. Self-assembly of electronically abrupt borophene/organic lateral heterostructures

    OpenAIRE

    Liu, Xiaolong; Wei, Zonghui; Balla, Itamar; Mannix, Andrew J.; Guisinger, Nathan P.; Luijten, Erik; Hersam, Mark C.

    2017-01-01

    Two-dimensional boron sheets (that is, borophene) have recently been realized experimentally and found to have promising electronic properties. Because electronic devices and systems require the integration of multiple materials with well-defined interfaces, it is of high interest to identify chemical methods for forming atomically abrupt heterostructures between borophene and electronically distinct materials. Toward this end, we demonstrate the self-assembly of lateral heterostructures betw...

  10. Controllable growth of semiconductor heterostructures mediated by bifunctional Ag2S nanocrystals as catalyst or source-host.

    Science.gov (United States)

    Zhu, Guoxing; Xu, Zheng

    2011-01-12

    We demonstrate that Ag(2)S nanocrystals are the bifunctional mediator for controllable growth of semiconductor heterostructures including more complicated multisegments heterostructures in solution-phase, which is a new type of nanomediator and quite different from the metal nanoparticle catalyst. The intrinsic high Ag(+) ion mobility makes Ag(2)S nanocrystals not only exhibit excellent catalytic function for growth of metal sulfide heterostructures but also act as a source-host for growth of ternary semiconductor heterostructures, for example, Ag(2)S-AgInS(2). The semiconductors grow epitaxially from or inward in Ag(2)S nanocrystals forming single-crystalline heterostructures. Moreover, the method developed here also can construct multisegments heterostructures, for example, Ag(2)S-CdS-ZnS, AgInS(2)-Ag(2)S-AgInS(2). The interfacial structure is still stable even if the lattice mismatch is quite large, which is a unique feature of this method.

  11. Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications.

    Science.gov (United States)

    Akkari, Marwa; Aranda, Pilar; Ben Haj Amara, Abdessalem; Ruiz-Hitzky, Eduardo

    2016-01-01

    In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica-organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica-organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay-SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite-silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants.

  12. Effect of silicon doping in InGaN/GaN heterostructure grown by MOCVD

    Science.gov (United States)

    Surender, S.; Pradeep, S.; Prabakaran, K.; Singh, Shubra; Baskar, K.

    2017-05-01

    In this work the effect of Si doped InGaN/GaN heterostructure is systematically studied. The n-InGaN /GaN heterostructure are grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD). The heterostructure samples are investigated by structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature Photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. The composition of indium in n-InGaN/GaN heterostructure was calculated as 15.9% using epitaxy smooth fit software. The energy band gap (Eg) of the InGaN epilayer has been calculated as 2.78 eV using vigard's law. PL emission obtained at 446 nm for n-InGaN epilayer. AFM results indicate that the Si doped InGaN/GaN heterostructure has the root mean square (rms) roughness of about 0.59 nm for a scan area of 5×5 µm2 which has island like growth. Moreover, Hall measurements results shows that Si doped InGaN/GaN heterostructure possess carrier concentration of 4.2 × 1018cm-3 and mobility of 257 cm2/V s at room temperature.

  13. Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides.

    Science.gov (United States)

    Fang, Hui; Battaglia, Corsin; Carraro, Carlo; Nemsak, Slavomir; Ozdol, Burak; Kang, Jeong Seuk; Bechtel, Hans A; Desai, Sujay B; Kronast, Florian; Unal, Ahmet A; Conti, Giuseppina; Conlon, Catherine; Palsson, Gunnar K; Martin, Michael C; Minor, Andrew M; Fadley, Charles S; Yablonovitch, Eli; Maboudian, Roya; Javey, Ali

    2014-04-29

    Semiconductor heterostructures are the fundamental platform for many important device applications such as lasers, light-emitting diodes, solar cells, and high-electron-mobility transistors. Analogous to traditional heterostructures, layered transition metal dichalcogenide heterostructures can be designed and built by assembling individual single layers into functional multilayer structures, but in principle with atomically sharp interfaces, no interdiffusion of atoms, digitally controlled layered components, and no lattice parameter constraints. Nonetheless, the optoelectronic behavior of this new type of van der Waals (vdW) semiconductor heterostructure is unknown at the single-layer limit. Specifically, it is experimentally unknown whether the optical transitions will be spatially direct or indirect in such hetero-bilayers. Here, we investigate artificial semiconductor heterostructures built from single-layer WSe2 and MoS2. We observe a large Stokes-like shift of ∼ 100 meV between the photoluminescence peak and the lowest absorption peak that is consistent with a type II band alignment having spatially direct absorption but spatially indirect emission. Notably, the photoluminescence intensity of this spatially indirect transition is strong, suggesting strong interlayer coupling of charge carriers. This coupling at the hetero-interface can be readily tuned by inserting dielectric layers into the vdW gap, consisting of hexagonal BN. Consequently, the generic nature of this interlayer coupling provides a new degree of freedom in band engineering and is expected to yield a new family of semiconductor heterostructures having tunable optoelectronic properties with customized composite layers.

  14. Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications

    Directory of Open Access Journals (Sweden)

    Marwa Akkari

    2016-12-01

    Full Text Available In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM. The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants.

  15. Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications

    Science.gov (United States)

    Akkari, Marwa; Aranda, Pilar; Ben Haj Amara, Abdessalem

    2016-01-01

    In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants. PMID:28144545

  16. Graphene/blue-phosphorus heterostructure as potential anode materials for sodium-ion batteries

    Science.gov (United States)

    Fan, Kaimin; Tang, Ting; Wu, Shiyun; Zhang, Zhiyuan

    2018-01-01

    The first-principles calculations based on density functional theory (DFT) have been implemented to investigate the graphene/blue-phosphorus (G/BP) heterostructure as potential anode material for SIBs. The adsorption and diffusion behaviors of sodium (Na) in G/BP heterostructure and the effect of external electric field on Na adsorption have been investigated. The results indicate that G/BP heterostructure with Na adsorption is metallic due to Na incorporation, which is of benefit for electronic conductivity as anode material. The results show that the design of G/BP heterostructure is an efficient scheme to enhance the Na adsorption in G/BP without affecting the high mobility of Na in the G/BP heterostructure surface. The present work demonstrates that the external electric field can effectively modulate the adsorption of Na, and the adsorption behavior of Na is more sensitive to the external electric field when E > 0.10 V Å‑1 in G/BP heterostructure. The Mulliken population analysis and DOS calculations have been performed to explore the charge transfer and the interaction between Na and G/BP.

  17. Band engineering of the MoS2/stanene heterostructure: strain and electrostatic gating

    Science.gov (United States)

    Xiong, Wenqi; Xia, Congxin; Du, Juan; Wang, Tianxing; Peng, Yuting; Wei, Zhongming; Li, Jingbo

    2017-05-01

    In a fast developing field, it has been found that van der Waals heterostructures can overcome the weakness of single two-dimensional layered materials and extend their electronic and optoelectronic applications. Through first-principles methods, the studied MoS2/stanene heterostructure preserves high-speed carrier characteristics and opens the direct band gap. Simultaneously, the band alignment shows that the electrons transfer from stanene to MoS2, which forms an internal electric field. As an effective strategy, the out-of-plane strain remarkably changes the band gaps of the heterostructure and enhances its carrier concentration. In addition, the combined effects of the internal and external electric fields can further open the band gaps and induce a direct-to-indirect gap transition in the heterostructure. More interestingly, when the external electric field is equal to the reverse internal one, the heterostructure regains a Dirac cone. Our results show that the MoS2/stanene heterostructure has potential applications in high-speed optoelectronic devices.

  18. Size-tunable band alignment and optoelectronic properties of transition metal dichalcogenide van der Waals heterostructures

    Science.gov (United States)

    Zhao, Yipeng; Yu, Wangbing; Ouyang, Gang

    2018-01-01

    2D transition metal dichalcogenide (TMDC)-based heterostructures exhibit several fascinating properties that can address the emerging market of energy conversion and storage devices. Current achievements show that the vertical stacked TMDC heterostructures can form type II band alignment and possess significant optoelectronic properties. However, a detailed analytical understanding of how to quantify the band alignment and band offset as well as the optimized power conversion efficiency (PCE) is still lacking. Herein, we propose an analytical model to exhibit the PCEs of TMDC van der Waals (vdW) heterostructures and explore the intrinsic mechanism of photovoltaic conversion based on the detailed balance principle and atomic-bond-relaxation correlation mechanism. We find that the PCE of monolayer MoS2/WSe2 can be up to 1.70%, and that of the MoS2/WSe2 vdW heterostructures increases with thickness, owing to increasing optical absorption. Moreover, the results are validated by comparing them with the available evidence, providing realistic efficiency targets and design principles. Highlights • Both electronic and optoelectronic models are developed for vertical stacked MoS2/WSe2 heterostructures. • The underlying mechanism on size effect of electronic and optoelectronic properties for vertical stacked MoS2/WSe2 heterostructures is clarified. • The macroscopically measurable quantities and the microscopical bond identities are connected.

  19. Structurally Analogous Degradable Version of Fluorene-Bipyridine Copolymer with Exceptional Selectivity for Large-Diameter Semiconducting Carbon Nanotubes.

    Science.gov (United States)

    Kanimozhi, Catherine; Brady, Gerald J; Shea, Matthew J; Huang, Peishen; Joo, Yongho; Arnold, Michael S; Gopalan, Padma

    2017-11-22

    Separation of electronically pure, narrowly dispersed, pristine, semiconducting single-walled carbon nanotubes (CNTs) from a heterogeneous as-synthesized mixture is essential for various semiconducting technologies and biomedical applications. Although conjugated polymer wrappers are often utilized to facilitate electronic-type sorting, it is highly desirable to remove organic residues from the resulting devices. We report here the design and synthesis of a mild acid-degradable π-conjugated polyimine polymer, poly[(9,9-di-n-octyl-2,7-fluoren-dinitrilomethine)-alt-co-(6,6'-{2,2'-bipyridyl-dimethine})] (PFO-N-BPy), that is structurally analogous to the commonly used and commercially available poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-(2,2'-bipyridine))] (PFO-BPy). An acid cleavable imine link (-HC═N-) was introduced in the PFO-N-BPy backbone to impart degradability, which is absent in PFO-BPy. PFO-N-BPy was synthesized via a metal catalyst-free aza-Wittig reaction in high yields. PFO-N-BPy with a degree of polymerization of just ∼10 showed excellent (>99% electronic purity) selectivity for both large-diameter (1.3-1.7 nm) arc-discharge semiconducting CNTs (S-CNTs) and smaller diameter (0.8-1.2 nm) high-pressure carbon monoxide disproportionation reaction S-CNTs. Overall, the selectivity for the semiconducting species is similar to that of PFO-BPy but with an advantage of complete depolymerization under mild acidic conditions into recyclable monomers. We further show by ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy that the PFO-N-BPy-wrapped S-CNTs can be aligned into a monolayer array on gate dielectrics using a floating evaporative self-assembly process from which the polymer can be completely removed. Short channel field effect transistors were fabricated from the polymer-stripped aligned S-CNT arrays, which further confirmed the semiconducting purity on the order of 99.9% or higher.

  20. Epitaxial growth of Fe/BaTiO3 heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Brivio, S., E-mail: m.gooley@elsevier.com [LNESS, Dipartimento di Fisica, Politecnico di Milano, via Anzani 42, 22100, Como (Italy); Rinaldi, C.; Petti, D.; Bertacco, R. [LNESS, Dipartimento di Fisica, Politecnico di Milano, via Anzani 42, 22100, Como (Italy); Sanchez, F. [Institut de Ciencia de Materials de Barcelona, Consejo Superior de Investigaciones Cientificas, Campus Universitat Autonoma de Barcelona, Bellaterra 08193, Catalunya (Spain)

    2011-06-30

    The realization of epitaxial heterostructures involving ferroelectric (FE) and ferromagnetic (FM) materials is one of the possible routes towards the realization of devices exploiting sizable magnetoelectric effects. In this paper we demonstrate the epitaxial growth of Fe on BaTiO{sub 3}(001) as this system represents a prototypical example of interface between well known FE and FM materials with bcc and perovskite structure respectively, both with Curie temperature well above 300 K. Fe grows on BaTiO{sub 3} with 45 deg. rotation of its cubic lattice with respect to that of the substrate in order to reduce the lattice mismatch. Negligible interdiffusion of Ba and Ti cations or Fe atoms is found by X-ray photoemission spectroscopy, while a sizable Fe oxidation occurs within an interfacial layer with thicknesses thinner than 3 nm.

  1. Evanescent channels and scattering in cylindrical nanowire heterostructures

    Science.gov (United States)

    Racec, P. N.; Racec, E. R.; Neidhardt, H.

    2009-04-01

    We investigate the scattering phenomena produced by a general finite-range nonseparable potential in a multichannel two-probe cylindrical nanowire heterostructure. The multichannel current scattering matrix is efficiently computed using the R -matrix formalism extended for cylindrical coordinates. Considering the contribution of the evanescent channels to the scattering matrix, we are able to put in evidence the specific dips in the tunneling coefficient in the case of an attractive potential. The cylindrical symmetry cancels the “selection rules” known for Cartesian coordinates. If the attractive potential is superposed over a nonuniform potential along the nanowire then resonant transmission peaks appear. We can characterize them quantitatively through the poles of the current scattering matrix. Detailed maps of the localization probability density sustain the physical interpretation of the resonances (dips and peaks). Our formalism is applied to a variety of model systems such as a quantum dot, a core/shell quantum ring, or a double barrier embedded into the nanocylinder.

  2. Transient photoreflectance of AlInN/GaN heterostructures

    Directory of Open Access Journals (Sweden)

    S. Marcinkevičius

    2012-12-01

    Full Text Available Time-resolved photoreflectance (PR in AlInN/GaN heterostructures was applied to study carrier dynamics at energies extending from the uniform AlInN alloy band gap to the band gap of GaN. PR at the AlInN band gap has been found to have subpicosecond decay. Such ultrafast carrier relaxation from the extended to the sub-band edge states implies that the localization sites are small and dense, most probably originating from the In-rich clusters. At energies below the AlInN band gap, a complicated energy dependence of the PR signal is attributed to the properties of the localized states and to the modulation of the interface electric field by photoexcitation.

  3. Nanometer-scale sharpness in corner-overgrown heterostructures.

    Energy Technology Data Exchange (ETDEWEB)

    Steinke, L.; Cantwell, P.; Zakharov, D.; Stach, E.; Zaluzec, N. J.; Fontcuberta i Morral, A.; Bichler, M.; Abstreiter, G.; Grayson, M.; Materials Science Division; Technische Univ. Munchen; Purdue Univ.; Northwestern Univ.

    2008-11-10

    A corner-overgrown GaAs/AlGaAs heterostructure is investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile 3.5 nm wide. In the AlGaAs layers, we observe self-ordered diagonal stripes, precipitating exactly at the corner, which show increased Al content measured with x-ray spectroscopy. A quantitative model for self-limited growth is adapted to the present case of faceted molecular beam epitaxial growth, and the corner sharpness is discussed in relation to quantum confined structures. We note that corner overgrowth maintains nanometer sharpness after microns of growth, allowing corner-shaped nanostructures.

  4. Thermal conductance of graphene/hexagonal boron nitride heterostructures

    Science.gov (United States)

    Lu, Simon; McGaughey, Alan J. H.

    2017-03-01

    The lattice-based scattering boundary method is applied to compute the phonon mode-resolved transmission coefficients and thermal conductances of in-plane heterostructures built from graphene and hexagonal boron nitride (hBN). The thermal conductance of all structures is dominated by acoustic phonon modes near the Brillouin zone center that have high group velocity, population, and transmission coefficient. Out-of-plane modes make their most significant contributions at low frequencies, whereas in-plane modes contribute across the frequency spectrum. Finite-length superlattice junctions between graphene and hBN leads have a lower thermal conductance than comparable junctions between two graphene leads due to lack of transmission in the hBN phonon bandgap. The thermal conductances of bilayer systems differ by less than 10% from their single-layer counterparts on a per area basis, in contrast to the strong thermal conductivity reduction when moving from single- to multi-layer graphene.

  5. Giant thermopower in superconducting heterostructures with spin-active interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kalenkov, Mikhail S. [I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute, 119991 Moscow (Russian Federation); Laboratory of Cryogenic Nanoelectronics, Nizhny Novgorod State Technical University, 603950 Nizhny Novgorod (Russian Federation); Zaikin, Andrei D. [Institut für Nanotechnologie, Karlsruher Institut für Technologie (KIT), 76021 Karlsruhe (Germany); I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute, 119991 Moscow (Russian Federation)

    2015-06-01

    We predict parametrically strong enhancement of the thermoelectric effect in metallic bilayers consisting of two superconductors separated by a spin-active interface. The physical mechanism for such an enhancement is directly related to electron–hole imbalance generated by spin-sensitive quasiparticle scattering at the interface between superconducting layers. We explicitly evaluate the thermoelectric currents flowing in the system and demonstrate that they can reach maximum values comparable to the critical ones for superconductors under consideration. - Highlights: • Strong enhancement of the thermoelectric effect in superconducting heterostructures. • Generation of the electron-hole imbalance by spin-sensitive quasiparticle scattering. • Thermoelectric currents can reach maximum values comparable to the critical ones.

  6. A.E.S. characterisation of small dimensional heterostructures

    CERN Document Server

    Gelsthorpe, A J

    2001-01-01

    the surface. The CMA also incorporates an electrostatic lens that deflects electrons onto the detectors along the same path independent of their energy. The operation and characterisation of the modified CMA and its electrostatic lens is described. Application to topographical features that show artefacts is also described. The CMA system can also be used to perform depth profiling by ion beam bevelling. This technique is applied to multi-layered heterostructures and a comparison is made between this, ion beam milling and chemical bevelling. Surface analysis is used to examine the outer layers of solid material to determine their properties and composition, and has many applications in industry. Atomic composition of the surface can be determined by Auger analysis. Depth profiles can also be obtained by exposing layers buried within a structure and then analysing them. This thesis presents improved techniques for analysing complex structures that have multiple thin layers or have significant topographical fea...

  7. Robust electromagnetic absorption by graphene/polymer heterostructures.

    Science.gov (United States)

    Lobet, Michaël; Reckinger, Nicolas; Henrard, Luc; Lambin, Philippe

    2015-07-17

    Polymer/graphene heterostructures present good shielding efficiency against GHz electromagnetic perturbations. Theory and experiments demonstrate that there is an optimum number of graphene planes, separated by thin polymer spacers, leading to maximum absorption for millimeter waves Batrakov et al (2014 Sci. Rep. 4 7191). Here, electrodynamics of ideal polymer/graphene multilayered material is first approached with a well-adapted continued-fraction formalism. In a second stage, rigorous coupled wave analysis is used to account for the presence of defects in graphene that are typical of samples produced by chemical vapor deposition, namely microscopic holes, microscopic dots (embryos of a second layer) and grain boundaries. It is shown that the optimum absorbance of graphene/polymer multilayers does not weaken to the first order in defect concentration. This finding testifies to the robustness of the shielding efficiency of the proposed absorption device.

  8. Photocatalytic Applications of Colloidal Heterostructured Nanocrystals: What's Next?

    Science.gov (United States)

    Razgoniaeva, Natalia; Moroz, Pavel; Lambright, Scott; Zamkov, Mikhail

    2015-11-05

    Recent progress in the colloidal synthesis of inorganic nanocrystals has led to the realization of complex, multidomain nanoparticle morphologies that give rise to advanced optoelectronic properties. Such nanocomposites are particularly appealing for photocatalytic applications where tunable absorption, extensive charge separation, and large surface-to-volume ratios are important. To date, heterostructured nanocrystals featuring a metal catalyst and a semiconductor "chromophore" component have shown compelling efficiencies in photoreduction reactions, including sacrificial hydrogen production. Time-resolved optical studies have attributed their success to a near-complete separation of photoinduced charges across dissimilar nanoparticle domains. The spectroscopy approach has also identified the key performance-limiting factors of nanocrystal catalysts that arise from inefficient extraction of photoinduced charges to catalytic sites. Along these lines, the main scope of present-day efforts targets the improvement of interstitial charge transfer pathways across the chromophore-catalyst assembly through the design of high-quality stoichiometric interfaces.

  9. The Origin of Tc Enhancement in Heterostructure Cuprate Superconductors

    Directory of Open Access Journals (Sweden)

    Doron L. Bergman

    2011-10-01

    Full Text Available Recent experiments on heterostructures composed of two or more films of cuprate superconductors of different oxygen doping levels have shown a remarkable Tc enhancement (up to 50% relative to single compound films. We provide a simple explanation of the enhancement which arises naturally from a collection of experimental works. We show that the enhancement could be caused by a structural change in the lattice, namely an increase in the distance of the apical oxygen from the copper-oxygen plane. This increase modifies the effective off-site interaction in the plane which in turn enhances the d-wave superconductivity order parameter. To illustrate this point we study the extended Hubbard model using the fluctuation exchange approximation.

  10. Biaxial Compressive Strain Engineering in Graphene/Boron Nitride Heterostructures

    Science.gov (United States)

    Pan, Wei; Xiao, Jianliang; Zhu, Junwei; Yu, Chenxi; Zhang, Gang; Ni, Zhenhua; Watanabe, K.; Taniguchi, T.; Shi, Yi; Wang, Xinran

    2012-11-01

    Strain engineered graphene has been predicted to show many interesting physics and device applications. Here we study biaxial compressive strain in graphene/hexagonal boron nitride heterostructures after thermal cycling to high temperatures likely due to their thermal expansion coefficient mismatch. The appearance of sub-micron self-supporting bubbles indicates that the strain is spatially inhomogeneous. Finite element modeling suggests that the strain is concentrated on the edges with regular nano-scale wrinkles, which could be a playground for strain engineering in graphene. Raman spectroscopy and mapping is employed to quantitatively probe the magnitude and distribution of strain. From the temperature-dependent shifts of Raman G and 2D peaks, we estimate the TEC of graphene from room temperature to above 1000K for the first time.

  11. Imaging the motion of electrons in 2D semiconductor heterostructures

    Science.gov (United States)

    Dani, Keshav

    Technological progress since the late 20th century has centered on semiconductor devices, such as transistors, diodes, and solar cells. At the heart of these devices, is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. In this talk, we combine femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy to image the motion of photoexcited electrons from high-energy to low-energy states in a 2D InSe/GaAs heterostructure exhibiting a type-II band alignment. At the instant of photoexcitation, energy-resolved photoelectron images reveal a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observe the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we make a movie lasting a few tens of picoseconds of the electron transfer process in the photoexcited type-II heterostructure - a fundamental phenomenon in semiconductor devices like solar cells. Quantitative analysis and theoretical modeling of spatial variations in the video provide insight into future solar cells, electron dynamics in 2D materials, and other semiconductor devices.

  12. Novel Heterostructure Devices for Ultra-Scaled Logic

    Science.gov (United States)

    Fay, Patrick

    Continuing increases in circuit complexity and capability for logic and computational applications as well as for emerging low-power distributed systems require fundamental advances in device technology and scaling. Dimensional scaling of conventional devices are approaching fundamental limitations. In addition, due to power constraints, devices capable of achieving switching slopes (SS) steeper than 60 mV/decade are essential if conventional computational architectures are to continue scaling. Similarly, low power systems such as distributed sensing applications also benefit from devices capable of delivering high performance in low-voltage operation. Tunneling field effect transistors (TFETs) are one promising alternative to achieve these objectives. A great deal of work has been devoted to realizing TFETs in Si, Ge, and narrow-gap III-V materials, but the use of two-dimensional materials and III-N heterostructures offer unique opportunities. From physics-based simulations, GaN/InGaN/GaN heterostructure TFETs offer the potential for achieving switching slopes approaching 20 mV/decade with on-current densities approaching 1 mA/ μm in nanowire configurations, while recent results in two-dimensional materials have also shown potential for sub-thermionic switching slopes. In this talk, the operational principles of candidate devices for steep switching will be described, and device design and performance considerations will be discussed. In addition, experimental efforts demonstrating these devices will be reviewed, and the future prospects for these and related devices to enable future generations of scaled technologies will be discussed. This work is sponsored in part by LEAST, a funded center of STARnet, a Semiconductor Research Corporation (SRC) program sponsored by MARCO and DARPA.

  13. GaN heterostructures for biosensing and radiation detection

    Energy Technology Data Exchange (ETDEWEB)

    Howgate, John D.

    2012-12-11

    In this thesis I show the results from our investigation of the interface between gallium nitride wide bandgap semiconductor heterostructures and (bio)molecular systems on their surfaces for biosensing, bioelectronics, and photoelectric applications, with a large emphasis on the processes arising from high energy ionizing irradiation, including heterostructure photoelectric gain mechanisms. Wide bandgap semiconductors, such as gallium nitride, have received increasing attention as potential components in advanced organic/inorganic hybrid systems. Working to further this topic, we determine a new semiconductor alignment required for low energy photo-induced charge transfer ionization of alkyl chains well below the energy normally required for molecular cleavage, show original results of the influence of binding methods on enzyme functionality in conjunction with a novel electrochemical and environmental control system and demonstrate new possibilities to significantly improve upon pH measurements through the use of high sensitivity devices. Furthermore, based on the extension of this work to support future studies of radiation effects on cell systems, we present a detailed characterization of new simultaneous chemical sensing and ionizing radiation dosimetry using single devices. We found that their pH sensitivity was retained during X-ray irradiation and that the fundamental characteristics can be used to separate the irradiation signal from the pH response without compromising operational stability. These data provide clear indications of the separate response mechanism tied to the presence of a two-dimensional electron gas channel. Here, we found new results exhibiting exceptionally high gains and independence of the well-known persistent photoconductivity for soft X-rays and high energy particles in the ultralow dose-rate regime. This material system provides the capability for high sensitivity and resolution real time monitoring, which is competitive with and

  14. Multilayer Graphene–WSe2 Heterostructures for WSe2 Transistors

    KAUST Repository

    Tang, Hao-Ling

    2017-11-29

    Two-dimensional (2D) materials are drawing growing attention for next-generation electronics and optoelectronics owing to its atomic thickness and unique physical properties. One of the challenges posed by 2D materials is the large source/drain (S/D) series resistance due to their thinness, which may be resolved by thickening the source and drain regions. Recently explored lateral graphene–MoS21−3 and graphene–WS21,4 heterostructures shed light on resolving the mentioned issues owing to their superior ohmic contact behaviors. However, recently reported field-effect transistors (FETs) based on graphene–TMD heterostructures have only shown n-type characteristics. The lack of p-type transistor limits their applications in complementary metal-oxide semiconductor electronics. In this work, we demonstrate p-type FETs based on graphene–WSe2 lateral heterojunctions grown with the scalable CVD technique. Few-layer WSe2 is overlapped with the multilayer graphene (MLG) at MLG–WSe2 junctions such that the contact resistance is reduced. Importantly, the few-layer WSe2 only forms at the junction region while the channel is still maintained as a WSe2 monolayer for transistor operation. Furthermore, by imposing doping to graphene S/D, 2 orders of magnitude enhancement in Ion/Ioff ratio to ∼108 and the unipolar p-type characteristics are obtained regardless of the work function of the metal in ambient air condition. The MLG is proposed to serve as a 2D version of emerging raised source/drain approach in electronics.

  15. PREFACE: 17th International Conference on Microscopy of Semiconducting Materials 2011

    Science.gov (United States)

    Walther, T.; Midgley, P. A.

    2011-11-01

    This volume contains invited and contributed papers from the 17th international conference on 'Microscopy of Semiconducting Materials' held at Churchill College, University of Cambridge, on 4-7 April 2011. The meeting was organised under the auspices of the Institute of Physics and supported by the Royal Microscopical Society as well as the Materials Research Society of the USA. This conference series deals with recent advances in semiconductor studies carried out by all forms of microscopy, with an emphasis on electron microscopy and related techniques with high spatial resolution. This time the meeting was attended by 131 delegates from 25 countries world-wide, a record in terms of internationality. As semiconductor devices shrink further new routes of device processing and characterisation need to be developed, and, for the latter, methods that offer sub-nanometre spatial resolution are particularly valuable. The various forms of imaging, diffraction and spectroscopy available in modern microscopes are powerful tools for studying the microstructure, the electronic structure, the chemistry and also electric fields in semiconducting materials. Recent advances in instrumentation, from lens aberration correction in both TEM and STEM instruments, to the development of a wide range of scanning probe techniques, as well as new methods of signal quantification have been presented at this conference. Two examples of topics at this meeting that have attracted a number of interesting studies were: the correlation of microstructural, optical and chemical information at atomic resolution with nanometre-scale resolved maps of the local electrical fields in (In,Al)GaN based semiconductors and tomographic approaches to characterise ensembles of nanowires and stacks of processed layers in devices Figure 1 Figure 1. Opening lecture by Professor Sir Colin J Humphreys. Each manuscript submitted for publication in this proceedings volume has been independently reviewed and revised

  16. Microscopic parameters of heterostructures containing nanoclusters and thin layers of Ge in Si matrix

    CERN Document Server

    Erenburg, S B; Stepina, N P; Nikiforov, A I; Nenashev, A V; Mazalov, L N

    2001-01-01

    GeK XAFS measurements have been performed using the total electron yield detection mode for pseudomorphous Ge films deposited on Si(0 0 1) substrate via molecular beam epitaxy at 300 deg. C. The samples have been produced by thrice repeating the growing procedure separated by deposition of blocking Si layers at 500 deg. C. The local microstructure parameters (interatomic distances, Ge coordination numbers) are linked to nanostructure morphology and adequate models are suggested and discussed. It was established that pseudomorphous 4-monolayer Ge films contain 50% of Si atoms on the average. Pyramid-like, pure Ge islands formed in the Stranski-Krastanov growth are characterized by the interatomic Ge-Ge distances of 2.41 A (by 0.04 A less than in bulk Ge) and the Ge-Si distances of 2.37 A. It was revealed that the pure Ge nanoclusters are covered by a 1-2-monolayer film with admixture on the average of a 50% Si atom impurity from blocking Si layers.

  17. Polymer-Free Electronic-Grade Aligned Semiconducting Carbon Nanotube Array.

    Science.gov (United States)

    Joo, Yongho; Brady, Gerald J; Kanimozhi, Catherine; Ko, Jaehyoung; Shea, Matthew J; Strand, Michael T; Arnold, Michael S; Gopalan, Padma

    2017-08-30

    Conjugated polymers are used commonly to selectively sort semiconducting carbon nanotubes (S-CNTs) from their metallic counterparts in organic solvents. The polymer-wrapped S-CNTs can be easily processed from organic solvents into arrays of CNTs for scalable device fabrication. Though the conjugated polymers are essential for sorting and device fabrication, it is highly desirable to remove them completely as they limit the electronic properties of the device. Here, we use a commercially available polymer, namely, poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-(2,2'-bipyridine))] (PFO-BPy), to sort large-diameter S-CNTs with ultrahigh selectivity and fabricate CNT-array-based field effect transistors (FETs) via a floating evaporative self-assembly (FESA) process. We report quantitative removal of the polymer wrapper from the FESA aligned S-CNT arrays using a metal-chelation-assisted polymer removal (McAPR) process. The implementation of this process on FESA films requires the selective thermal degradation of the polymer into oligomers, combined with optimization of the solvent type and temperature of the metal complexation reaction. Resulting S-CNT array FET devices show that the electronic properties of pristine CNT are preserved through this process. Optical microscopy, UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to characterize the quantitative polymer removal. We quantitatively describe the FET devices to analyze the fundamental characteristics of FETs (mobility (μ), on-conductance (Gon), and contact resistance (2Rc)) by comparing before and after polymer removal. The ability to completely remove the polymer wrapper in aligned CNT arrays without adversely affecting the device properties opens up applications beyond FETs into photovoltaics and biosensing.

  18. Linear and Nonlinear Rheology Combined with Dielectric Spectroscopy of Hybrid Polymer Nanocomposites for Semiconductive Applications

    Directory of Open Access Journals (Sweden)

    Roland Kádár

    2017-01-01

    Full Text Available The linear and nonlinear oscillatory shear, extensional and combined rheology-dielectric spectroscopy of hybrid polymer nanocomposites for semiconductive applications were investigated in this study. The main focus was the influence of processing conditions on percolated poly(ethylene-butyl acrylate (EBA nanocomposite hybrids containing graphite nanoplatelets (GnP and carbon black (CB. The rheological response of the samples was interpreted in terms of dispersion properties, filler distortion from processing, filler percolation, as well as the filler orientation and distribution dynamics inside the matrix. Evidence of the influence of dispersion properties was found in linear viscoelastic dynamic frequency sweeps, while the percolation of the nanocomposites was detected in nonlinearities developed in dynamic strain sweeps. Using extensional rheology, hybrid samples with better dispersion properties lead to a more pronounced strain hardening behavior, while samples with a higher volume percentage of fillers caused a drastic reduction in strain hardening. The rheo-dielectric time-dependent response showed that in the case of nanocomposites containing only GnP, the orientation dynamics leads to non-conductive samples. However, in the case of hybrids, the orientation of the GnP could be offset by the dispersing of the CB to bridge the nanoplatelets. The results were interpreted in the framework of a dual PE-BA model, where the fillers would be concentrated mainly in the BA regions. Furthermore, better dispersed hybrids obtained using mixing screws at the expense of filler distortion via extrusion processing history were emphasized through the rheo-dielectric tests.

  19. Thiophene-Thiazole-Based Semiconducting Copolymers for High-Performance Polymer Field-Effect Transistors.

    Science.gov (United States)

    Chung, Jong Won; Park, Won-Tae; Park, Jeong-Il; Yun, Youngjun; Gu, Xiaodan; Lee, Jiyoul; Noh, Yong-Young

    2017-11-08

    We report a newly synthesized donor (D)-acceptor (A)type semiconducting copolymer, consisting of thiophene as an electron-donating unit and thiazole as an electron-accepting unit (PQTBTz-TT-C8) for the active layer of the organic field-effect transistors (OFETs). Specifically, this study investigates the structure and electrical property relationships of PQTBTz-TT-C8 with comprehensive analyses on the charge-transporting properties corresponding to the spin rate of the spin coater during the formation of the PQTBTz-TT-C8 film. The crystallinity of PQTBTz-TT-C8 films is examined with grazing incidence X-ray diffraction. Temperature-dependent transfer measurements of the OFETs are conducted to extract the density of states (DOS) and characterize the charge-transport properties. Comparative analyses on charge transports within the framework of the physical model, based on polaron hopping and Gaussian DOS, reveal that the prefactors of both physical charge-transport models are independent of the spin-coating condition for the films. For staggered structural transistors, however, the thickness of the PQTBTz-TT-C8 films, which strongly affect the series resistance along the charge-transfer path in a vertical direction, is changed in accordance with the spin-coating rate. In other words, the spin-coating rate of the PQTBTz-TT-C8 films influences the thickness of the polymer films, yet any significant changes in the crystallinity of the film or electronic coupling between the neighboring molecules upon the spin-coating condition were barely noticeable. Because the PQTBTz-TT-C8 backbone chains inside the thin film are stacked up with the edge-on, the series resistances are changed according to the thickness of the film and thus the performance of the device varies depending on the thickness.

  20. Rapid Construction of ZnO@ZIF-8 Heterostructures with Size-Selective Photocatalysis Properties.

    Science.gov (United States)

    Wang, Xianbiao; Liu, Jin; Leong, Sookwan; Lin, Xiaocheng; Wei, Jing; Kong, Biao; Xu, Yongfei; Low, Ze-Xian; Yao, Jianfeng; Wang, Huanting

    2016-04-13

    To selectively remove heavy metal from dye solution, inspired by the unique pore structure of ZIF-8, we developed a synthetic strategy for rapid construction of ZnO@ZIF-8 heterostructure photocatalyst for selective reduction of Cr(VI) between Cr(VI) and methylene blue (MB). In particular, ZnO@ZIF-8 core-shell heterostructures were prepared by in situ ZIF-8 crystal growth using ZnO colloidal spheres as template and zinc source within 8-60 min. The shell of the resulting ZnO@ZIF-8 core-shell heterostructure with a uniform thickness of around 30 nm is composed of ZIF-8 crystal polyhedrons. The concentration of organic ligand 2-methylimidazole (Hmim) was found to be crucial for the formation of ZnO@ZIF-8 core-shell heterostructures. Different structures, ZnO@ZIF-8 core-shell spheres and separate ZIF-8 polyhedrons could be formed by altering Hmim concentration, which significantly influences the balance between rate of Zn(2+) release from ZnO and coordinate rate. Importantly, such ZnO@ZIF-8 core-shell heterostructures exhibit size-selective photocatalysis properties due to selective adsorption and permeation effect of ZIF-8 shell. The as-synthesized ZnO@ZIF-8 heterostructures exhibited enhanced selective reduction of Cr(VI) between Cr(VI) and MB, which may find application in the dye industry. This work not only provides a general route for rapid fabrication of such core-shell heterostructures but also illustrates a strategy for selectively enhanced photocatalysis performance by utilizing adsorption and size selectivity of ZIF-8 shell.

  1. Solvothermal synthesis of Ag hybrid BiPO4 heterostructures with enhanced photodegradation activity and stability.

    Science.gov (United States)

    Huang, Chang-Wei; Wu, Mei-Yao; Lin, Yang-Wei

    2017-03-15

    In this study, Ag hybrid BiPO4 (Ag/BiPO4) heterostructures were synthesized using a solvothermal method. The morphologies and optical properties of the Ag/BiPO4 heterostructures were drastically different from those of BiPO4 and were highly dependent on the AgNO3:BiPO4 weight percent during the synthesis. The three formulated heterostructures were evaluated for their photocatalytic degradation of methylene blue (MB) under UV light illumination; the 0.5%Ag/BiPO4 heterostructure was observed to result in 99% degradation of MB within 60min, a remarkably higher level of photodegradation activity than the levels caused by TiO2 and BiPO4. Furthermore, even after use for five cycles of MB degradation, the 0.5%Ag/BiPO4 heterostructure showed no observable loss in photodegradation activity and no change in XRD patterns, demonstrating its chemical and structural stability. According to the results of a systematic experimental investigation, the enhanced photodegradation activity of this Ag/BiPO4 heterostructure could be ascribed to the high position of its valence band and the highly efficient separation of photogenerated electrons and holes. Moreover, hydroxyl radicals and holes were found to be the major reactive species. Successful photodegradation of standard dye solutions, including acid blue 1, methyl orange, fast green, rhodamine B, rhodamine 6G, and MB, in real water samples was demonstrated with the 0.5%Ag/BiPO4 heterostructure, providing clear evidence of its utility for treating waste water containing organic dyes. Copyright © 2016 Elsevier Inc. All rights reserved.

  2. Effect of natural homointerfaces on the magnetic properties of pseudomorphic La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin film: Phase separation vs split domain structure

    Energy Technology Data Exchange (ETDEWEB)

    Congiu, Francesco [Dipartimento di Fisica e CNISM, Università di Cagliari, S.P. Monserrato-Sestu, km 0.700, I 09042 Monserrato, Cagliari (Italy); Sanna, Carla [Sardegna Ricerche, Laboratorio Energetica Elettrica, VI Strada Ovest - Z.I.Macchiareddu, I 09010 Uta, Cagliari (Italy); Maritato, Luigi [CNR-SPIN, UOS Salerno, I 84084 Fisciano, Salerno (Italy); Dipartimento di Ingegneria dell’Informazione, Ingegneria Elettrica e Matematica Applicata, Università di Salerno, I 84084 Fisciano, Salerno (Italy); Orgiani, Pasquale [CNR-SPIN, UOS Salerno, I 84084 Fisciano, Salerno (Italy); Geddo Lehmann, Alessandra, E-mail: lehmann@dsf.unica.it [Dipartimento di Fisica e CNISM, Università di Cagliari, S.P. Monserrato-Sestu, km 0.700, I 09042 Monserrato, Cagliari (Italy)

    2016-12-15

    We studied the effect of naturally formed homointerfaces on the magnetic and electric transport behavior of a heavily twinned, 40 nm thick, pseudomorphic epitaxial film of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} deposited by molecular beam epitaxy on ferroelastic LaAlO{sub 3}(001) substrate. As proved by high resolution X-ray diffraction analysis, the lamellar twin structure of the substrate is imprinted in La{sub 0.7}Sr{sub 0.3}MnO{sub 3}. In spite of the pronounced thermomagnetic irreversibility in the DC low field magnetization, spin-glass-like character, possibly related to the structural complexity, was ruled out, on the base of AC susceptibility results. The magnetic characterization indicates anisotropic ferromagnetism, with a saturation magnetization M{sub s} = 3.2 μ{sub B}/Mn, slightly reduced with respect to the fully polarized value of 3.7 μ{sub B}/Mn. The low field DC magnetization vs temperature is non bulklike, with a two step increase in the field cooled M{sub FC}(T) branch and a two peak structure in the zero field cooled M{sub ZFC}(T) one. Correspondingly, two peaks are present in the resistivity vs temperature ρ(T) curve. With reference to the behavior of epitaxial manganites deposited on bicrystal substrates, results are discussed in terms of a two phase model, in which each couple of adjacent ferromagnetic twin cores, with bulklike T{sub C} = 370 K, is separated by a twin boundary with lower Curie point T{sub C} = 150 K, acting as barrier for spin polarized transport. The two phase scenario is compared with the alternative one based on a single ferromagnetic phase with the peculiar ferromagnetic domains structure inherent to twinned manganites films, reported to be split into interconnected and spatially separated regions with in-plane and out-of-plane magnetization, coinciding with twin cores and twin boundaries respectively.

  3. NiO nanosheet/TiO{sub 2} nanorod-constructed p–n heterostructures for improved photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Bin [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Key Laboratory of Fine Chemicals in Universities of Shandong, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353 (China); Zhou, Guowei, E-mail: guoweizhou@hotmail.com [Key Laboratory of Fine Chemicals in Universities of Shandong, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353 (China); Gao, Tingting [Key Laboratory of Fine Chemicals in Universities of Shandong, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353 (China); Zhang, Huaijin, E-mail: hjzhang@icm.sdu.edu.cn [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Yu, Haohai [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

    2016-02-28

    Graphical abstract: - Highlights: • NiO nanosheet/acid-corroded TiO{sub 2} nanorod p–n heterostructures were fabricated. • The heterostructures enhanced the separation of photogenerated electron–hole pairs. • The heterostructures shown high photocatalytic activity. • A schematic of the energy band structure of the heterostructures was proposed. - Abstract: NiO nanosheet/acid-corroded TiO{sub 2} nanorod (A-TiO{sub 2} nanorod) heterostructures with high photocatalytic activity were successfully fabricated via a facile and low-cost hydrothermal route. The as-prepared heterostructures featured NiO nanosheets with uniformly assembled A-TiO{sub 2} nanorods and a rough surface. The morphology, structure, and photoelectric properties of the pristine NiO nanosheets and TiO{sub 2}-based nanomaterials were characterized in detail, and results revealed that secondary NiO nanosheets were successfully grown on TiO{sub 2} nanorod substrates to achieve a p–n heterostructure between the cubic structure NiO and the TiO{sub 2} anatase phase. In comparison with P25, NiO nanosheets, TiO{sub 2} nanorods, and A-TiO{sub 2} nanorods, the proposed heterostructures exhibited markedly enhanced photocatalytic activity for the degradation of methyl orange under UV light irradiation. Specifically, the NiO nanosheet/A-TiO{sub 2} nanorod heterostructures exhibited the best photocatalytic activity, achieving 100% photocatalytic efficiency within 20 min. The observed enhancement in photocatalytic activity was attributed to the synergetic contributions of p–n heterostructures and the large specific surface area of the catalyst, which may improve the separation of photogenerated electron–hole pairs and prolong the lifetime of charge carriers. The heterostructures could be easily recycled without observable decreases in photocatalytic activity because of their one-dimensional nanostructural property.

  4. Basal-Plane Ligand Functionalization on Semiconducting 2H-MoS2 Monolayers.

    Science.gov (United States)

    Ding, Qi; Czech, Kyle J; Zhao, Yuzhou; Zhai, Jianyuan; Hamers, Robert J; Wright, John C; Jin, Song

    2017-04-12

    Molybdenum disulfide (MoS2) is a two-dimensional material promising for electronic, optical, and catalytic applications. To fully harness its potential, functionalization is essential to controlling its properties. However, MoS2 functionalization has been mostly limited to either 1T-phase MoS2 or the edges of 2H-phase MoS2, and the chemistry of covalent functionalization on the basal plane of 2H-MoS2 is poorly understood. Here, we report a facile approach to covalently functionalize chemical vapor deposition (CVD) grown 2H-MoS2 monolayers (MLs), as well as mechanically exfoliated MoS2, via thiol conjugation at sulfur vacancies on the basal plane. Thorough characterization confirmed the functionalization by thiol molecules on MoS2 MLs, and we experimentally proved that sulfur vacancies in MoS2 MLs play a key role in the functionalization of basal planes. By the controlling of the amount of sulfur vacancies via sulfur annealing, the degree of MoS2 functionalization was effectively tuned. Because thiol conjugation partially repairs or passivates sulfur vacancies, enhanced photoluminescence response and decreased active sites for hydrogen evolution catalysis were observed for functionalized MoS2. Moreover, such functionalization can be utilized for making MoS2-based heterostructures, an example of which was demonstrated using a dithiol molecule to link MoS2 layers and PbSe quantum dots. These results provide new understanding and insights on the surface chemistry of MoS2 and open up more opportunities for MoS2 MLs with well-controlled properties and broader applications.

  5. General Considerations of the Electrostatic Boundary Conditions in Oxide Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Higuchi, Takuya

    2011-08-19

    When the size of materials is comparable to the characteristic length scale of their physical properties, novel functionalities can emerge. For semiconductors, this is exemplified by the 'superlattice' concept of Esaki and Tsu, where the width of the repeated stacking of different semiconductors is comparable to the 'size' of the electrons, resulting in novel confined states now routinely used in opto-electronics. For metals, a good example is magnetic/non-magnetic multilayer films that are thinner than the spin-scattering length, from which giant magnetoresistance (GMR) emerged, used in the read heads of hard disk drives. For transition metal oxides, a similar research program is currently underway, broadly motivated by the vast array of physical properties that they host. This long-standing notion has been recently invigorated by the development of atomic-scale growth and probe techniques, which enables the study of complex oxide heterostructures approaching the precision idealized in Fig. 1(a). Taking the subset of oxides derived from the perovskite crystal structure, the close lattice match across many transition metal oxides presents the opportunity, in principle, to develop a 'universal' heteroepitaxial materials system. Hand-in-hand with the continual improvements in materials control, an increasingly relevant challenge is to understand the consequences of the electrostatic boundary conditions which arise in these structures. The essence of this issue can be seen in Fig. 1(b), where the charge sequence of the sublayer 'stacks' for various representative perovskites is shown in the ionic limit, in the (001) direction. To truly 'universally' incorporate different properties using different materials components, be it magnetism, ferroelectricity, superconductivity, etc., it is necessary to access and join different charge sequences, labelled here in analogy to the designations 'group IV, III-V, II

  6. Optically pumped lasing in solution-processed perovskite semiconducting materials: Self-assembled Fabry-Pérot microcavity

    Science.gov (United States)

    Sasaki, Fumio; Zhou, Ying; Sonoda, Yoriko; Azumi, Reiko; Mochizuki, Hiroyuki; Nguyen, Van-Cao; Yanagi, Hisao

    2017-04-01

    Optically pumped lasing has been observed in solution-processed perovskite semiconducting materials, CH3NH3PbX3 (X = Cl, Br, I). Self-assembled Fabry-Pérot (FP) cavities have been easily obtained by using a simple “cast-capping method”, where we can obtain single-crystal-like optical cavities. The observed spectra show clear multimode lasing of the FP cavities under pulsed optical excitation. The mode intervals are well explained by the optical constants with large dispersions of the materials. The obtained refractive index around the lasing area coincides with the results in the previous reports.

  7. Communication: electronic band gaps of semiconducting zig-zag carbon nanotubes from many-body perturbation theory calculations.

    Science.gov (United States)

    Umari, P; Petrenko, O; Taioli, S; De Souza, M M

    2012-05-14

    Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy.

  8. Semiconductor nanowires and nanowire heterostructures: Nanoscience from the bottom up

    Science.gov (United States)

    Zhong, Zhaohui

    2005-07-01

    Nanoscale science and technology involves interdisciplinary research at the interface of chemistry, physics, biology, and engineering sciences. By developing and following a unique intellectual path---the bottom-up paradigm of nanoscale science and technology---it is possible to assemble integrated nanoscale systems with novel functionalities beyond the conventional lithography limit. In this thesis, I present research efforts focused on fundamental aspects of this bottom-up paradigm using semiconductor nanowires (NWs) and nanowire heterostructures as nanoscale building blocks. We first present studies conducted on one of the most important semiconductor materials, silicon nanowires (SiNWs). SiNWs are rationally synthesized via a metal cluster-catalyzed vapor-liquid-solid (VLS) growth mechanism. Room temperature electrical transport studies carried out on SiNW field effect transistors (FETs) show exceptional device performance; estimated hole mobilities in p-SiNWs are significantly higher than bulk silicon at similar doping levels. Furthermore, low temperature transport studies on molecular scale SiNWs reveal phase coherent single charge transport through discrete single particle quantum levels with length scales up to several hundred nanometers. Finally, we show that SiNWs can be assembled into functional nanoelectronic devices. We then discuss two types of nanowire heterostructures: modulation doped silicon nanowires, and branched and hyper-branched nanowire structures. All key properties of modulation doped nanowires can be controlled during the synthesis, including the number, size and periodicity of the differentially doped regions. Their potential applications are also discussed. Moreover, branched and hyper-branched nanowire structures are synthesized via a multi-step nanocluster-catalyzed VLS approach, with branch density controlled by the nanocluster catalyst concentration. Lastly, we describe the realization of complementary doping in gallium nitride

  9. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays

    Directory of Open Access Journals (Sweden)

    Liu Jian

    2009-01-01

    Full Text Available Abstract Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondary nanostructures of SiO2 nanowires are highly dense grown on the primary Cd4SiS6 core-SiO2 sheath nanowires and formed hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays which stand vertically on silicon substrates. The possible growth mechanism of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays is proposed. The optical properties of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays are investigated using Raman and Photoluminescence spectroscopy.

  10. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays.

    Science.gov (United States)

    Liu, Jian; Wang, Chunrui; Xie, Qingqing; Cai, Junsheng; Zhang, Jing

    2009-10-29

    Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondary nanostructures of SiO2 nanowires are highly dense grown on the primary Cd4SiS6 core-SiO2 sheath nanowires and formed hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays which stand vertically on silicon substrates. The possible growth mechanism of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays is proposed. The optical properties of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays are investigated using Raman and Photoluminescence spectroscopy.

  11. Augmented Photoelectrochemical Efficiency of ZnO/TiO2 Nanotube Heterostructures

    Science.gov (United States)

    Boda, Muzaffar Ahmad; Shah, Mohammad Ashraf

    2017-11-01

    ZnO/TiO2 nanotube heterostructures have been fabricated by electrodeposition of ZnO microcrystals over electrochemically anodized TiO2 nanotube arrays. The resulting ZnO/TiO2 nanotube heterostructures showed enhanced photocurrent density of 5.72 mA cm-2, about 1.5 times the value of 3.68 mA cm-2 shown by bare compact TiO2 nanotubes. This enhanced photocurrent density of the ZnO/TiO2 nanotube heterostructures is due to high electron mobility in the ZnO crystals, thereby decreasing the electron-hole recombination process, good interfacial quality between the ZnO and TiO2 structures, and a proposed smooth charge-transfer mechanism due to band bending at the interface. The morphological features of the as-prepared heterostructures were determined by field-emission scanning electron microscopy (FESEM). The crystallinity and phase purity of the samples were confirmed by x-ray diffraction (XRD) analysis. The light absorption properties of the prepared samples were investigated by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The photoelectrochemical efficiency of bare and ZnO-modified TiO2 nanotube heterostructures was determined by electrochemical analyzer.

  12. Au@MoS2 Core-Shell Heterostructures with Strong Light-Matter Interactions.

    Science.gov (United States)

    Li, Yuan; Cain, Jeffrey D; Hanson, Eve D; Murthy, Akshay A; Hao, Shiqiang; Shi, Fengyuan; Li, Qianqian; Wolverton, Chris; Chen, Xinqi; Dravid, Vinayak P

    2016-12-14

    There are emerging opportunities to harness diverse and complex geometric architectures based on nominal two-dimensional atomically layered structures. Herein we report synthesis and properties of a new core-shell heterostructure, termed Au@MoS2, where the Au nanoparticle is snugly and contiguously encapsulated by few shells of MoS2 atomic layers. The heterostructures were synthesized by direct growth of multilayer fullerene-like MoS2 shell on Au nanoparticle cores. The Au@MoS2 heterostructures exhibit interesting light-matter interactions due to the structural curvature of MoS2 shell and the plasmonic effect from the underlying Au nanoparticle core. We observed significantly enhanced Raman scattering and photoluminescence emission on these heterostructures. We attribute these enhancements to the surface plasmon-induced electric field, which simulations show to mainly localize within the MoS2 shell. We also found potential evidence for the charge transfer-induced doping effect on the MoS2 shell. The DFT calculations further reveal that the structural curvature of MoS2 shell results in a modification of its electronic structure, which may facilitate the charge transfer from MoS2 to Au. Such Au@MoS2 core-shell heterostructures have the potential for future optoelectronic devices, optical imaging, and other energy-environmental applications.

  13. Strain-Induced Electronic Structure Changes in Stacked van der Waals Heterostructures.

    Science.gov (United States)

    He, Yongmin; Yang, Yang; Zhang, Zhuhua; Gong, Yongji; Zhou, Wu; Hu, Zhili; Ye, Gonglan; Zhang, Xiang; Bianco, Elisabeth; Lei, Sidong; Jin, Zehua; Zou, Xiaolong; Yang, Yingchao; Zhang, Yuan; Xie, Erqing; Lou, Jun; Yakobson, Boris; Vajtai, Robert; Li, Bo; Ajayan, Pulickel

    2016-05-11

    Vertically stacked van der Waals heterostructures composed of compositionally different two-dimensional atomic layers give rise to interesting properties due to substantial interactions between the layers. However, these interactions can be easily obscured by the twisting of atomic layers or cross-contamination introduced by transfer processes, rendering their experimental demonstration challenging. Here, we explore the electronic structure and its strain dependence of stacked MoSe2/WSe2 heterostructures directly synthesized by chemical vapor deposition, which unambiguously reveal strong electronic coupling between the atomic layers. The direct and indirect band gaps (1.48 and 1.28 eV) of the heterostructures are measured to be lower than the band gaps of individual MoSe2 (1.50 eV) and WSe2 (1.60 eV) layers. Photoluminescence measurements further show that both the direct and indirect band gaps undergo redshifts with applied tensile strain to the heterostructures, with the change of the indirect gap being particularly more sensitive to strain. This demonstration of strain engineering in van der Waals heterostructures opens a new route toward fabricating flexible electronics.

  14. Self-assembly of electronically abrupt borophene/organic lateral heterostructures.

    Science.gov (United States)

    Liu, Xiaolong; Wei, Zonghui; Balla, Itamar; Mannix, Andrew J; Guisinger, Nathan P; Luijten, Erik; Hersam, Mark C

    2017-02-01

    Two-dimensional boron sheets (that is, borophene) have recently been realized experimentally and found to have promising electronic properties. Because electronic devices and systems require the integration of multiple materials with well-defined interfaces, it is of high interest to identify chemical methods for forming atomically abrupt heterostructures between borophene and electronically distinct materials. Toward this end, we demonstrate the self-assembly of lateral heterostructures between borophene and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). These lateral heterostructures spontaneously form upon deposition of PTCDA onto submonolayer borophene on Ag(111) substrates as a result of the higher adsorption enthalpy of PTCDA on Ag(111) and lateral hydrogen bonding among PTCDA molecules, as demonstrated by molecular dynamics simulations. In situ x-ray photoelectron spectroscopy confirms the weak chemical interaction between borophene and PTCDA, while molecular-resolution ultrahigh-vacuum scanning tunneling microscopy and spectroscopy reveal an electronically abrupt interface at the borophene/PTCDA lateral heterostructure interface. As the first demonstration of a borophene-based heterostructure, this work will inform emerging efforts to integrate borophene into nanoelectronic applications.

  15. Stacking order dependent mechanical properties of graphene/MoS{sub 2} bilayer and trilayer heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Elder, Robert M., E-mail: robert.elder26.ctr@mail.mil, E-mail: mahesh.neupane.ctr@mail.mil; Neupane, Mahesh R., E-mail: robert.elder26.ctr@mail.mil, E-mail: mahesh.neupane.ctr@mail.mil; Chantawansri, Tanya L. [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)

    2015-08-17

    Transition metal dichalcogenides (TMDC) such as molybdenum disulfide (MoS{sub 2}) are two-dimensional materials that show promise for flexible electronics and piezoelectric applications, but their weak mechanical strength is a barrier to practical use. In this work, we perform nanoindentation simulations using atomistic molecular dynamics to study the mechanical properties of heterostructures formed by combining MoS{sub 2} with graphene. We consider both bi- and tri-layer heterostructures formed with MoS{sub 2} either supported or encapsulated by graphene. Mechanical properties, such as Young's modulus, bending modulus, ultimate tensile strength, and fracture strain, are extracted from nanoindentation simulations and compared to the monolayer and homogeneous bilayer systems. We observed that the heterostructures, regardless of the stacking order, are mechanically more robust than the mono- and bi-layer MoS{sub 2}, mainly due to the mechanical reinforcement provided by the graphene layer. The magnitudes of ultimate strength and fracture strain are similar for both the bi- and tri-layer heterostructures, but substantially larger than either the mono- and bi-layer MoS{sub 2}. Our results demonstrate the potential of graphene-based heterostructures to improve the mechanical properties of TMDC materials.

  16. Strain-induced structural defects and their effects on the electrochemical performances of silicon core/germanium shell nanowire heterostructures.

    Science.gov (United States)

    Lin, Yung-Chen; Kim, Dongheun; Li, Zhen; Nguyen, Binh-Minh; Li, Nan; Zhang, Shixiong; Yoo, Jinkyoung

    2017-01-19

    We report on strain-induced structural defect formation in core Si nanowires of a Si/Ge core/shell nanowire heterostructure and the influence of the structural defects on the electrochemical performances in lithium-ion battery anodes based on Si/Ge core/shell nanowire heterostructures. The induced structural defects consisting of stacking faults and dislocations in the core Si nanowire were observed for the first time. The generation of stacking faults in the Si/Ge core/shell nanowire heterostructure is observed to prefer settling in either only the Ge shell region or in both the Ge shell and Si core regions and is associated with the increase of the shell volume fraction. The relaxation of the misfit strain in the [112] oriented core/shell nanowire heterostructure leads to subsequent gliding of Shockley partial dislocations, preferentially forming the twins. The observation of crossover of defect formation is of great importance for understanding heteroepitaxy in radial heterostructures at the nanoscale and for building three dimensional heterostructures for the various applications. Furthermore, the effect of the defect formation on the nanomaterial's functionality is investigated using electrochemical performance tests. The Si/Ge core/shell nanowire heterostructures enhance the gravimetric capacity of lithium ion battery anodes under fast charging/discharging rates compared to Si nanowires. However, the induced structural defects hamper lithiation of the Si/Ge core/shell nanowire heterostructure.

  17. CuO/ZnO core/shell heterostructure nanowire arrays: synthesis, optical property, and energy application.

    Science.gov (United States)

    Zhao, Xinhong; Wang, Peng; Li, Baojun

    2010-09-28

    Aligned CuO nanowires (NWs) were synthesized by a simple cost-effective oxidation method. They act as cores; high density CuO/ZnO core/shell heterostructure NWs were fabricated by thermal decomposition. Using the core/shell heterostructure NWs as a photoelectrode, a 0.71% photo-to-hydrogen conversion efficiency was obtained from photoelectrochemical water decomposition.

  18. Photodiode-like behavior and excellent photoresponse of vertical Si/monolayer MoS2 heterostructures.

    Science.gov (United States)

    Li, Yang; Xu, Cheng-Yan; Wang, Jia-Ying; Zhen, Liang

    2014-11-26

    Monolayer transition metal dichalcogenides (TMDs) and their van der Waals heterostructures have been experimentally and theoretically demonstrated as potential candidates for photovoltaic and optoelectronic devices due to the suitable bandgap and excellent light absorption. In this work, we report the observation of photodiode behavior in (both n- and p- type) silicon/monolayer MoS2 vertical heterostructures. The photocurrent and photoresponsivity of heterostructures photodiodes were dependent both on the incident light wavelength and power density, and the highest photoresponsivity of 7.2 A/W was achieved in n-Si/monolayer MoS2 vertical heterostructures photodiodes. Compared with n-Si/MoS2 heterostructures, the photoresponsivity of p-Si/MoS2 heterostructure was much lower. Kelvin probe microscope (KFM) results demonstrated the more efficient separation of photogenerated excitons in n-Si/MoS2 than that in p-Si/MoS2. Coupling KFM results with band alignments of (p-, n-) Si/MoS2 heterostructures, the origins of photodiode-like phenomena of p-Si/MoS2 and n-Si/MoS2 have been unveiled, that is intrinsic built-in electric field in p-n junction, and modulated barrier height and width at the interface in n-n junction. Our work may benefit to the deep understanding of the integration of two-dimensional materials with more conventional three-dimensional semiconductors, and then contribute to the developments in the area of van der Waals heterostructures.

  19. First-Principles Study of Double Perovskite Sr2FeXO6 (X = Mo, Re) Ultrathin Films and Heterostructures

    Science.gov (United States)

    Suzuki, Shugo; Tsuyama, Makoto

    2017-12-01

    We study double perovskite Sr2FeXO6 (X = Mo, Re) ultrathin films (UTFs) and their heterostructures with a SrTiO3 substrate by first-principles calculations based on density functional theory. It is found that the UTFs and their heterostructures are all half-metallic despite being extremely thin.

  20. Universal chitosan-assisted synthesis of Ag-including heterostructured nanocrystals for label-free in situ SERS monitoring.

    Science.gov (United States)

    Cai, Kai; Xiao, Xiaoyan; Zhang, Huan; Lu, Zhicheng; Liu, Jiawei; Li, Qin; Liu, Chen; Foda, Mohamed F; Han, Heyou

    2015-12-07

    A universal chitosan-assisted method was developed to synthesize various Ag-including heterostructured nanocrystals, in which chelation probably plays a vital role. The as-prepared Ag/Pd heterostructured nanocrystals show outstanding properties when used as bifunctional nanocomposites in label-free in situ SERS monitoring of Pd-catalyzed reaction.

  1. Understanding and improving the mechanical stability of semiconducting polymers for flexible and stretchable electronics

    Science.gov (United States)

    Printz, Adam David

    -aggregate model---a spectroscopic model which estimates the quantity and quality of aggregates in a polymer film---is used to determine how the microstructure of a semiconducting polymer thin film evolves with repetitive strain. Samples strained below the yield point undergo little microstructural evolution, while samples strained above the yield point exhibit a significant decrease in aggregation and tensile modulus. Appendix C describes the invention of an environmentally-friendly fabrication technique, abrasion lithography.

  2. Competition between deformability and charge transport in semiconducting polymers for flexible and stretchable electronics

    Energy Technology Data Exchange (ETDEWEB)

    Printz, Adam D.; Lipomi, Darren J., E-mail: dlipomi@ucsd.edu [Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448 (United States)

    2016-06-15

    The primary goal of the field concerned with organic semiconductors is to produce devices with performance approaching that of silicon electronics, but with the deformability—flexibility and stretchability—of conventional plastics. However, an inherent competition between deformability and charge transport has long been observed in these materials, and achieving the extreme (or even moderate) deformability implied by the word “plastic” concurrently with high charge transport may be elusive. This competition arises because the properties needed for high carrier mobilities—e.g., rigid chains in π-conjugated polymers and high degrees of crystallinity in the solid state—are antithetical to deformability. On the device scale, this competition can lead to low-performance yet mechanically robust devices, or high-performance devices that fail catastrophically (e.g., cracking, cohesive failure, and delamination) under strain. There are, however, some observations that contradict the notion of the mutual exclusivity of electronic and mechanical performances. These observations suggest that this problem may not be a fundamental trade-off, but rather an inconvenience that may be negotiated by a logical selection of materials and processing conditions. For example, the selection of the poly(3-alkylthiophene) with a critical side-chain length—poly(3-heptylthiophene) (n = 7)—marries the high deformability of poly(3-octylthiophene) (n = 8) with the high electronic performance (as manifested in photovoltaic efficiency) of poly(3-hexylthiophene) (n = 6). This review explores the relationship between deformability and charge transport in organic semiconductors. The principal conclusions are that reducing the competition between these two parameters is in fact possible, with two demonstrated routes being: (1) incorporation of softer, insulating material into a stiffer, semiconducting material and (2) increasing disorder in a highly ordered film, but not

  3. Understanding and Controlling Nanoscale Morphology in Self-Assembled Semiconducting Materials

    Science.gov (United States)

    Kang, Hyeyeon

    Self-assembled semiconducting materials have been rapidly developed for a range of applications. This work aims to control the morphology of nanostructured semiconductors to understand how their functions arise from the structural properties. The first part of this dissertation focuses on the formation of a bulk-heterojunction (BHJ) in the active layer of organic photovoltaics (OPV). A BHJ is a bicontinuous interpenetrating network of organic components. The phase separation of the electron donor and the acceptor is required to achieve a BHJ structure in the nanostructured morphology, which promotes an efficient charge transportation. The use of solvent additive is one of the strategies to control the spontaneous phase separation during the film formation. Low vapor pressure solvent additives are introduced to a polymer casting solution in a sequentially processed OPV system, to study the swelling effect on the phase separation. In particular, the change in crystallinity and vertical mixing will be intensively studied upon polymer swelling. As another strategy, we introduce a molecular structure change to fullerene derivatives. A small structural variation leads to a large enough contrast of their surface energy, which is attributed to different vertical phase separation in the active layer. It eventually allows us to examine photovoltaic performance and device physics. In the second part, mesoporous inorganic films are investigated by preparation from a nanocrystal solution or sol-gel precursors for solar energy applications. Mesoporous nanocrystal-based titania is synthesized for inorganic/organic hybrid solar cells. The effect of surface modification is examined by anchoring a fullerene derivative on to titania surface. 3D interconnected mesoporous tantalum nitride films are prepared via sol-gel method as photoanodes in solar water splitting. The simple synthetic method using polymer template enables us to successfully prepare nitride films with excellent pore

  4. Optical and electronic properties of semiconducting nanoparticles; Optische und elektronische Eigenschaften von halbleitenden Nanopartikeln

    Energy Technology Data Exchange (ETDEWEB)

    Gondorf, Andreas

    2011-10-07

    In the present thesis, the electronic properties of semiconducting nanoparticles are investigated. The I-V-characteristics of a submonolayer of silicon nanoparticles, embedded in a Si{sub 3}N{sub 4}-matrix are calculated. The calculated results are compared to those found experimentally by Cho et al. It is investigated whether quantization effects, like the Coulomb blockade, can also be observed in systems, which contain many particles. Compacted silicon and germanium nanoparticle powders are analyzed by reflection measurements. The goal is to determine the carrier density and to find how the core-shell-structure (Ge/Si core and Ge/Si oxide shell) affects the reflection spectra. Furthermore, the influence of doping on the properties of the nanoparticles is investigated. Optical spectroscopy and magneto-transport measurements are performed on thin films, consisting of indium tin oxide nanoparticles (ITO nanoparticles). In optical spectroscopy the dielectric function in the high frequency region is determined. With the known dielectric function the charge carrier concentration as well as the mobility can be calculated. With magnetotransport measurements it is possible to measure the Hall voltage and the macroscopic conductivity. By taking into account the theoretically derived correction factor [Kharitonov, 2008] the carrier density and macroscopic mobility can be determined. Thus, the combination of the two measurement methods allows an insight into the electronic structure of this system. Additionally, layers consisting of ITO nanoparticles exhibit a decreasing resistivity when a magnetic field is applied perpendicular to the current orientation. This effect is called negative transverse magnetoresistance. The experimental results can be explained by the weak localization theory of granular systems. For the dephasing time {tau}{sub H}, however, we find a different dependence on the magnetic field than predicted by theory (experiment: 1/{tau}{sub H} {proportional

  5. Impact of biaxial compressive strain on the heterostructures of paraelectrics KTaO3 and SrTiO3

    Directory of Open Access Journals (Sweden)

    Yi Yang

    2015-05-01

    Full Text Available We have performed density functional theory calculations to explore the impact of biaxial compressive strain on the heterostructures of paraelectrics KTaO3 and SrTiO3. We find that the strain induces strong ferroelectric distortion in KTaO3/SrTiO3 heterostructures and it stabilizes the heterostructures in ferroelectric states.The strain influences the distribution of doped holes and leads to the localization of holes in TiO2 layer. It is very interesting that ferroelectricity and ferromagnetism simultaneously present in the strained heterostructures formed by the paraelectrics KTaO3 and SrTiO3. The reversal of ferroelectric polarization changes the interface magnetization and thus results in magnetoelectric coupling effect in the heterostructures.

  6. Modulation of electronic structures of MoSe2/WSe2 van der Waals heterostructure by external electric field

    Science.gov (United States)

    Zhang, Fang; Li, Wei; Dai, Xianqi

    2017-10-01

    By using first-principles calculations, we investigate the electronic structures of MoSe2/WSe2 van der Waals(vdW) heterostructure by applying external electric field(Eext) perpendicular to the layers. It is demonstrated that MoSe2/WSe2 heterostructure is a type-II vdW heterostructure. The band gap of MoSe2/WSe2 is significantly modulated by Eext, eventually a semiconductor-to-metal transition can be realized. The positive and negative Eext have different effects on the band gap due to the intrinsic spontaneous electric polarization in MoSe2/WSe2 heterostructure. Moreover, MoSe2/WSe2 heterobilayer experiences transitions from type-II to type-I and then to type-II under various Eext. The present study provides great application potential of ultrathin MoSe2/WSe2 heterostructure in future nano- and optoelectronics.

  7. Precipitation growth of graphene under exfoliated hexagonal boron nitride to form heterostructures on cobalt substrate by molecular beam epitaxy

    Science.gov (United States)

    Zheng, Renjing; Khanaki, Alireza; Tian, Hao; He, Yanwei; Cui, Yongtao; Xu, Zhongguang; Liu, Jianlin

    2017-07-01

    Research on graphene/hexagonal boron nitride (h-BN) heterostructures has attracted much attention for band engineering and device performance optimization of graphene. However, the growth of graphene/h-BN heterostructure is still challenging, which usually requires high growth temperature and long growth duration. In this paper, we demonstrate graphene/h-BN heterostructures by growing graphene onto the substrates which consist of exfoliated h-BN flakes on Co thin films using molecular beam epitaxy. The heterostructure samples grown at different temperatures and growth times were characterized by Raman, optical microscopy, atomic force microscopy, microwave impedance microscopy, and scanning tunneling microscopy. It is found that the graphene/h-BN heterostructures were formed by the formation of graphene underneath rather than on top of the h-BN flakes. The growth mechanism is discussed.

  8. Interfacial coupling and polarization of perovskite ABO3 heterostructures

    Science.gov (United States)

    Wu, Lijun; Wang, Zhen; Zhang, Bangmin; Yu, Liping; Chow, G. M.; Tao, Jing; Han, Myung-Geun; Guo, Hangwen; Chen, Lina; Plummer, E. W.; Zhang, Jiandi; Zhu, Yimei

    2017-02-01

    Interfaces with subtle difference in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. In this article, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 (PSMO) films and La0.67Sr0.33MnO3 (LSMO) films of various thicknesses on SrTiO3 (STO) substrate. In particular, using atomically resolved imaging and electron energy-loss spectroscopy (EELS), we measured interface related local lattice distortion, BO6 octahedral rotation and cation-anion displacement induced polarization. In the very thin PSMO film, an unexpected interface-induced ferromagnetic polaronic insulator phase was observed during the cubic-to-tetragonal phase transition of the substrate STO, due to the enhanced electron-phonon interaction and atomic disorder in the film. On the other hand, for the very thin LSMO films we observed a remarkably deep polarization in non-ferroelectric STO substrate near the interface. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by an electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties of transition metal oxides.

  9. Analysis of Si/SiGe Heterostructure Solar Cell

    Directory of Open Access Journals (Sweden)

    Ashish Kumar Singh

    2014-01-01

    Full Text Available Sunlight is the largest source of carbon-neutral energy. Large amount of energy, about 4.3 × 1020 J/hr (Lewis, 2005, is radiated because of nuclear fusion reaction by sun, but it is unfortunate that it is not exploited to its maximum level. Various photovoltaic researches are ongoing to find low cost, and highly efficient solar cell to fulfil looming energy crisis around the globe. Thin film solar cell along with enhanced absorption property will be the best, so combination of SiGe alloy is considered. The paper presented here consists of a numerical model of Si/Si1-xGex heterostructure solar cell. The research has investigated characteristics such as short circuit current density (Jsc, generation rate (G, absorption coefficient (α, and open circuit voltage (Voc with optimal Ge concentration. The addition of Ge content to Si layer will affect the property of material and can be calculated with the use of Vegard’s law. Due to this, short circuit current density increases.

  10. Growth kinetics of heterostructured GaP-GaAs nanowires.

    Science.gov (United States)

    Verheijen, Marcel A; Immink, George; de Smet, Thierry; Borgström, Magnus T; Bakkers, Erik P A M

    2006-02-01

    We have studied the vapor-liquid-solid (VLS) growth dynamics of GaP and GaAs in heterostructured GaP-GaAs nanowires. The wires containing multiple GaP-GaAs junctions were grown by the use of metal-organic vapor phase-epitaxy (MOVPE) on SiO(2), and the lengths of the individual sections were obtained from transmission electron microscopy. The growth kinetics has been studied as a function of temperature and the partial pressures of the precursors. We found that the growth of the GaAs sections is limited by the arsine (AsH(3)) as well as the trimethylgallium (Ga(CH(3))(3)) partial pressures, whereas the growth of GaP is a temperature-activated, phosphine(PH(3))-limited process with an activation energy of 115 +/- 6 kJ/mol. The PH(3) kinetics obeys the Hinshelwood-Langmuir mechanism, indicating that the dissociation reaction of adsorbed PH(3) into PH(2) and H on the catalytic gold surface is the rate-limiting step for the growth of GaP. In addition, we have studied the competitive thin layer growth on the sidewalls of the nanowires. Although the rate of this process is 2 orders of magnitude lower than the growth rate of the VLS mechanism, it competes with VLS growth and results in tapered nanowires at elevated temperatures.

  11. Quantum and Ionic Transport Across Superconductor-based Heterostructures

    Science.gov (United States)

    Nayfeh, Osama; Dinh, Son; Taylor, Benjamin; de Andrade, Marcio; Swanson, Paul; Offord, Bruce; de Escobar, Anna Leese; Claussen, Stephanie; Kassegne, Sam

    2015-03-01

    We present analysis of quantum and ionic transport across superconductor/barrier/ionic/barrier/superconductor (SBIBS) heterostructures. Calculations for various ionic configurations demonstrate modification of the quantum transport coherence length and energy profile with moderate ionic transport away from the superconductor-barrier interface. The effect of electric field and cryogenic temperature on the stability of the ionic configurations for quantum information state storage is examined. Characterization and analysis of constructed Al and Nb-based device structures are presented. Acknowledgements: We acknowledge the support of the SSC Pacific In-house Laboratory Independent Research Science and Technology Program managed by Dr. Dave Rees, the Naval Innovative Science and Engineering Program managed by Mr. Robin Laird, and the ONR Summer Faculty Research Program. Interactions with Dr. Van Vechten (ONR) and Dr. Manheimer (IARPA) are appreciated. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of SPAWAR or the U.S. Government. Approved for Public Release; distribution is unlimited.

  12. Heterostructures for Increased Quantum Efficiency in Nitride LEDs

    Energy Technology Data Exchange (ETDEWEB)

    Davis, Robert F. [Carnegie Mellon Univ., Pittsburgh, PA (United States)

    2010-09-30

    Task 1. Development of an advanced LED simulator useful for the design of efficient nitride-based devices. Simulator will contain graphical interface software that can be used to specify the device structure, the material parameters, the operating conditions and the desired output results. Task 2. Theoretical and experimental investigations regarding the influence on the microstructure, defect concentration, mechanical stress and strain and IQE of controlled changes in the chemistry and process route of deposition of the buffer layer underlying the active region of nitride-based blue- and greenemitting LEDs. Task 3. Theoretical and experimental investigations regarding the influence on the physical properties including polarization and IQE of controlled changes in the geometry, chemistry, defect density, and microstructure of components in the active region of nitride-based blue- and green-emitting LEDs. Task 4. Theoretical and experimental investigations regarding the influence on IQE of novel heterostructure designs to funnel carriers into the active region for enhanced recombination efficiency and elimination of diffusion beyond this region. Task 5. Theoretical and experimental investigations regarding the influence of enhanced p-type doping on the chemical, electrical, and microstructural characteristics of the acceptor-doped layers, the hole injection levels at Ohmic contacts, the specific contact resistivity and the IQE of nitride-based blue- and green-emitting LEDs. Development and optical and electrical characterization of reflective Ohmic contacts to n- and p-type GaN films.

  13. Electrotunable artificial molecules based on van der Waals heterostructures.

    Science.gov (United States)

    Zhang, Zhuo-Zhi; Song, Xiang-Xiang; Luo, Gang; Deng, Guang-Wei; Mosallanejad, Vahid; Taniguchi, Takashi; Watanabe, Kenji; Li, Hai-Ou; Cao, Gang; Guo, Guang-Can; Nori, Franco; Guo, Guo-Ping

    2017-10-01

    Quantum confinement has made it possible to detect and manipulate single-electron charge and spin states. The recent focus on two-dimensional (2D) materials has attracted significant interests on possible applications to quantum devices, including detecting and manipulating either single-electron charging behavior or spin and valley degrees of freedom. However, the most popular model systems, consisting of tunable double-quantum-dot molecules, are still extremely difficult to realize in these materials. We show that an artificial molecule can be reversibly formed in atomically thin MoS2 sandwiched in hexagonal boron nitride, with each artificial atom controlled separately by electrostatic gating. The extracted values for coupling energies at different regimes indicate a single-electron transport behavior, with the coupling strength between the quantum dots tuned monotonically. Moreover, in the low-density regime, we observe a decrease of the conductance with magnetic field, suggesting the observation of Coulomb blockade weak anti-localization. Our experiments demonstrate for the first time the realization of an artificial quantum-dot molecule in a gated MoS2 van der Waals heterostructure, which could be used to investigate spin-valley physics. The compatibility with large-scale production, gate controllability, electron-hole bipolarity, and new quantum degrees of freedom in the family of 2D materials opens new possibilities for quantum electronics and its applications.

  14. Emergent ultrafast phenomena in correlated oxides and heterostructures

    Science.gov (United States)

    Gandolfi, M.; Celardo, G. L.; Borgonovi, F.; Ferrini, G.; Avella, A.; Banfi, F.; Giannetti, C.

    2017-03-01

    The possibility of investigating the dynamics of solids on timescales faster than the thermalization of the internal degrees of freedom has disclosed novel non-equilibrium phenomena that have no counterpart at equilibrium. Transition metal oxides (TMOs) provide an interesting playground in which the correlations among the charges in the metal d-orbitals give rise to a wealth of intriguing electronic and thermodynamic properties involving the spin, charge, lattice and orbital orders. Furthermore, the physical properties of TMOs can be engineered at the atomic level, thus providing the platform to investigate the transport phenomena on timescales of the order of the intrinsic decoherence time of the charge excitations. Here, we review and discuss three paradigmatic examples of transient emerging properties that are expected to open new fields of research: (i) the creation of non-thermal magnetic states in spin-orbit Mott insulators; (ii) the possible exploitation of quantum paths for the transport and collection of charge excitations in heterostructures; (iii) the transient wave-like behavior of the temperature field in strongly anisotropic TMOs.

  15. Transport spectroscopy in bilayer graphene using double layer heterostructures

    Science.gov (United States)

    Lee, Kayoung; Jung, Jeil; Fallahazad, Babak; Tutuc, Emanuel

    2017-09-01

    We provide a comprehensive study of the chemical potential of bilayer graphene in a wide range of carrier density, at zero and high magnetic (B)-fields, and at different transverse electric (E)-fields, using high quality double bilayer graphene heterostructures. Using a direct thermodynamic transport spectroscopic technique, we probe the chemical potential as a function of carrier density in six samples. The data clearly reveal the non-parabolicity and electron-hole asymmetry of energy-momentum dispersion in bilayer graphene. The tight-binding hopping amplitudes, t 0, t 1, and t 4, renormalized by electron-electron interaction are extracted from the chemical potential versus density dependence. A diverse set of electron-electron interaction driven phenomena were also clearly discerned at zero and high B-fields. We measure the gaps at integer fillings with orbital index N  =  0, 1, and discuss about the dependence of the N  =  0, 1 quantum Hall phases on the carrier density (or filling factor), E-field, and B-field.

  16. High-power disk lasers based on dilute nitride heterostructures

    Science.gov (United States)

    Guina, M.; Leinonen, T.; Härkönen, A.; Pessa, M.

    2009-12-01

    We report the development of InGaAsN-based gain mirrors for high-power optically pumped semiconductor disk lasers with direct emission at wavelengths around 1180 nm. The gain mirrors were fabricated by molecular beam epitaxy. They consist of 10 dilute nitride quantum wells, which were placed within a GaAs micro-cavity on top of a GaAs/AlAs distributed Bragg reflector. We demonstrated laser operation at ~1180 nm with record high output power (~7 W). The differential efficiency was ~30% for operation at 5 °C and ~28% when operating at 15 °C. The lasers exhibited excellent tuning characteristics, delivering an output power of more than 5 W in a narrow spectrum and providing over 30 nm tuning band. These features represent significant progress towards demonstration of practical high-power lasers with frequency-doubled yellow emission required for laser guide stars, life sciences and spectroscopy. At the same time the results emphasize the importance of dilute nitride heterostructures in the development of novel optoelectronic devices.

  17. Temperature Dependence of the Resonant Magnetoelectric Effect in Layered Heterostructures

    Directory of Open Access Journals (Sweden)

    Dmitrii A. Burdin

    2017-10-01

    Full Text Available The dependence of the resonant direct magnetoelectric effect on temperature is studied experimentally in planar composite structures. Samples of rectangular shapes with dimensions of 5 mm × 20 mm employed ferromagnetic layers of either an amorphous (metallic glass alloy or nickel with a thickness of 20–200 μm and piezoelectric layers of single crystalline langatate material or lead zirconate titanate piezoelectric ceramics with a thickness of 500 μm. The temperature of the samples was varied in a range between 120 and 390 K by blowing a gaseous nitrogen stream around them. It is shown that the effective characteristics of the magnetoelectric effect—such as the mechanical resonance frequency fr, the quality factor Q and the magnitude of the magnetoelectric coefficient αE at the resonance frequency—are contingent on temperature. The interrelations between the temperature changes of the characteristics of the magnetoelectric effect and the temperature variations of the following material parameters—Young’s modulus Y, the acoustic quality factor of individual layers, the dielectric constant ε, the piezoelectric modulus d of the piezoelectric layer as well as the piezomagnetic coefficients λ(n of the ferromagnetic layer—are established. The effect of temperature on the characteristics of the nonlinear magnetoelectric effect is observed for the first time. The results can be useful for designing magnetoelectric heterostructures with specified temperature characteristics, in particular, for the development of thermally stabilized magnetoelectric devices.

  18. Exchange coupling in permalloy/BiFeO3 heterostructures

    Science.gov (United States)

    Heron, John; Wang, Chen; Carlton, David; Nowakowski, Mark; Gajek, Martin; Awschalom, David; Bokor, Jeff; Ralph, Dan; Ramesh, R.

    2010-03-01

    BiFeO3 is a ferroelectric and antiferromagnetic multiferroic with the ferroelectric and antiferromagnetic order parameters coupled at room temperature. This coupling results in the reorientation of the ferroelectric and magnetic domains as applied voltages switch the electric polarization. Previous studies using ferromagnet/BiFeO3 heterostructures have shown that the anisotropy of the ferromagnetic layer can be tuned by the ferroelectric domain structure of the BiFeO3 film [1, 2]. The physical mechanism driving this exchange bias with BiFeO3 is still under investigation. We use patterned permalloy structures, with varying aspect ratios, on BiFeO3 thin films to investigate the physics of this interaction. The results of our studies using MFM, PEEM, and MOKE to understand this mechanism as a means to electric field control of magnetic structures will be presented. [4pt] [1] H. Bea et al., Physical Review Letters 100, 017204 (2008).[0pt] [2] L.W. Martin et al., Nanoletters 8, 2050 (2008).

  19. Magnetic coupling in Fe/(Ga,Mn)As based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sperl, M.; Soda, M.; Eigenmann, F.; Utz, M.; Woltersdorf, G.; Bougeard, D.; Back, C.H. [Institut fuer Experimentelle Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Torelli, P.; Panaccione, G. [Laboratorio Nazionale TASC, INFM-CNR, in Area Science Park, S.S. 14, Km 163.5, I-34012 Trieste (Italy); Polesya, S. [Department of Chemistry, Ludwig-Maximilians University Munich (Germany)

    2011-07-01

    (Ga,Mn)As is one of the most promising diluted magnetic semiconductors (DMS) for spintronics due to the compatibility with the GaAs MBE technology. Despite the promising features (Ga,Mn)As has a Curie temperature well below room temperature limiting its possible applications. One potential direction to tailor novel properties of DMS thus making integration in real devices feasible is to exploit interface effects in highly controlled heterostructures (HS). Following this route FM behaviour of Mn at room temperature in both epitaxial and non-epitaxial Fe/(Ga,Mn)As interfaces has been demonstrated. We report results obtained with Synchrotron Radiation techniques, where we were able to monitor the evolution of the magnetic coupling between Fe and Mn as a function of Mn doping, temperature and thickness. In particular, XMCD experiments show a peculiar thickness dependence of the room temperature magnetic coupling between Fe and Mn, namely a switching from antiparallel to parallel, thus opening the possibility of controlling the magnetization state of the interface.

  20. Spin-torque generation in topological insulator based heterostructures

    KAUST Repository

    Fischer, Mark H.

    2016-03-11

    Heterostructures utilizing topological insulators exhibit a remarkable spin-torque efficiency. However, the exact origin of the strong torque, in particular whether it stems from the spin-momentum locking of the topological surface states or rather from spin-Hall physics of the topological-insulator bulk, remains unclear. Here, we explore a mechanism of spin-torque generation purely based on the topological surface states. We consider topological-insulator-based bilayers involving ferromagnetic metal (TI/FM) and magnetically doped topological insulators (TI/mdTI), respectively. By ascribing the key theoretical differences between the two setups to location and number of active surface states, we describe both setups within the same framework of spin diffusion of the nonequilibrium spin density of the topological surface states. For the TI/FM bilayer, we find large spin-torque efficiencies of roughly equal magnitude for both in-plane and out-of-plane spin torques. For the TI/mdTI bilayer, we elucidate the dominance of the spin-transfer-like torque. However, we cannot explain the orders of magnitude enhancement reported. Nevertheless, our model gives an intuitive picture of spin-torque generation in topological-insulator-based bilayers and provides theoretical constraints on spin-torque generation due to topological surface states.

  1. Tunable band offset and recombination in ZnO nanowire-CdTe quantum dot heterostructures

    Science.gov (United States)

    He, Haiping; Gan, Lu; Sun, Luwei; Ye, Zhizhen

    2017-10-01

    ZnO nanowire (NW)-CdTe quantum dot (QD) type-II heterostructures were constructed using hydrothermally grown ZnO and colloidal CdTe QDs. Photoluminescence (PL) spectroscopy was used to investigate the charge transfer and band offset between CdTe QDs and ZnO NWs. The results demonstrated that the PL shows obvious redshift and prolonged lifetime in the heterostructure, indicating that it originates from recombination between electrons localized in ZnO and holes localized in CdTe. The results reveal that the band offset and charge recombination can be tuned by the growth time or size of CdTe QDs. Our results demonstrate that PL can be a useful tool to evaluate the band alignment and charge recombination in type-II semiconductor heterostructures.

  2. Piezoelectric potential in axial (In,Ga)N/GaN nanowire heterostructures

    Science.gov (United States)

    Kaganer, Vladimir M.; Marquardt, Oliver; Brandt, Oliver

    2016-04-01

    We derive analytic expressions for the built-in electrostatic potential arising from piezo- and pyroelectricity in a cylindrical axial In x Ga{}1-xN/GaN nanowire (NW) heterostructure. Our simulations show that, for sufficiently thin NWs, a significant reduction of the built-in potential is reached in comparison to the planar heterostructure of the same In content, thickness, and orientation. This specific feature of axial NW heterostructures makes the aspect ratio of the embedded In x Ga{}1-xN disks an important additional degree of freedom to control the recombination energies. We furthermore show that the magnitude of the polarization potential decreases again above a certain value of the aspect ratio and that the extrema of the potential move from the central axis of the NW towards the side facets when the thickness of the disk is increased.

  3. Integration, gap formation, and sharpening of III-V heterostructure nanowires by selective etching

    DEFF Research Database (Denmark)

    Kallesoe, C.; Mølhave, Kristian; Larsen, K. F.

    2010-01-01

    Epitaxial growth of heterostructure nanowires allows for the definition of narrow sections with specific semiconductor composition. The authors demonstrate how postgrowth engineering of III-V heterostructure nanowires using selective etching can form gaps, sharpening of tips, and thin sections...... simultaneously on multiple nanowires. They investigate the potential of combining nanostencil deposition of catalyst, epitaxial III-V heterostructure nanowire growth, and selective etching, as a road toward wafer scale integration and engineering of nanowires with existing silicon technology. Nanostencil...... lithography is used for deposition of catalyst particles on trench sidewalls and the lateral growth of III-V nanowires is achieved from such catalysts. The selectivity of a bromine-based etch on gallium arsenide segments in gallium phosphide nanowires is examined, using a hydrochloride etch to remove the III...

  4. Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures.

    Science.gov (United States)

    Gamucci, A; Spirito, D; Carrega, M; Karmakar, B; Lombardo, A; Bruna, M; Pfeiffer, L N; West, K W; Ferrari, A C; Polini, M; Pellegrini, V

    2014-12-19

    Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

  5. Laterally Stitched Heterostructures of Transition Metal Dichalcogenide: Chemical Vapor Deposition Growth on Lithographically Patterned Area

    KAUST Repository

    Li, Henan

    2016-10-31

    Two-dimensional transition metal dichalcogenides (TMDCs) have shown great promise in electronics and optoelectronics due to their unique electrical and optical properties. Heterostructured TMDC layers such as the laterally stitched TMDCs offer the advantages of better electronic contact and easier band offset tuning. Here, we demonstrate a photoresist-free focused ion beam (FIB) method to pattern as-grown TMDC monolayers by chemical vapor deposition, where the exposed edges from FIB etching serve as the seeds for growing a second TMDC material to form desired lateral heterostructures with arbitrary layouts. The proposed lithographic and growth processes offer better controllability for fabrication of the TMDC heterostrucuture, which enables the construction of devices based on heterostructural monolayers. © 2016 American Chemical Society.

  6. Uniform photoresponse in thermally oxidized Ni and MoS{sub 2} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Wei [College of Science, National University of Defense Technology, Changsha (China); National Laboratory of Solid State Microstructures, School of Physics, Nanjing University (China); Peng, Gang; Wang, Fei [College of Science, National University of Defense Technology, Changsha (China); Miao, Feng [National Laboratory of Solid State Microstructures, School of Physics, Nanjing University (China); Zhang, Xue-Ao; Qin, Shiqiao [College of Science, National University of Defense Technology, Changsha (China); State Key Laboratory of High Performance Computing, National University of Defense Technology, Changsha (China)

    2017-09-15

    Non-uniform photocurrent is usually generated at the overlapped region of the heterostructures, and its potential applications may be hindered by the spatial uniformity issue of the device photoresponse. Here, nearly a uniform photoresponse at the overlapped region of the thermally oxidized Ni and molybdenum disulphide (MoS{sub 2}) heterostructures is obtained. Further characterizations reveal that several nanometers Ni is rightly under the NiO{sub x} layer formed at the surface of the film in the oxidation process. The heterostructures based on layered MoS{sub 2}/NiO{sub x}/Ni with highly conductive bottom Ni show a high uniform photoresponse with an external quantum efficiency (EQE) of 1.4% at 532 nm. Moreover, successful integration of multiple devices suggests a great priority for such a structure for highly integrated uniform photodetectors. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Periodic potentials in hybrid van der Waals heterostructures formed by supramolecular lattices on graphene.

    Science.gov (United States)

    Gobbi, Marco; Bonacchi, Sara; Lian, Jian X; Liu, Yi; Wang, Xiao-Ye; Stoeckel, Marc-Antoine; Squillaci, Marco A; D'Avino, Gabriele; Narita, Akimitsu; Müllen, Klaus; Feng, Xinliang; Olivier, Yoann; Beljonne, David; Samorì, Paolo; Orgiu, Emanuele

    2017-03-21

    The rise of 2D materials made it possible to form heterostructures held together by weak interplanar van der Waals interactions. Within such van der Waals heterostructures, the occurrence of 2D periodic potentials significantly modifies the electronic structure of single sheets within the stack, therefore modulating the material properties. However, these periodic potentials are determined by the mechanical alignment of adjacent 2D materials, which is cumbersome and time-consuming. Here we show that programmable 1D periodic potentials extending over areas exceeding 10 4  nm 2 and stable at ambient conditions arise when graphene is covered by a self-assembled supramolecular lattice. The amplitude and sign of the potential can be modified without altering its periodicity by employing photoreactive molecules or their reaction products. In this regard, the supramolecular lattice/graphene bilayer represents the hybrid analogue of fully inorganic van der Waals heterostructures, highlighting the rich prospects that molecular design offers to create ad hoc materials.

  8. Engineering multiple topological phases in nanoscale Van der Waals heterostructures: realisation of α-antimonene

    Science.gov (United States)

    Märkl, T.; Kowalczyk, P. J.; Le Ster, M.; Mahajan, I. V.; Pirie, H.; Ahmed, Z.; Bian, G.; Wang, X.; Chiang, T.-C.; Brown, S. A.

    2018-01-01

    Van der Waals heterostructures have recently been identified as providing many opportunities to create new two-dimensional materials, and in particular to produce materials with topologically-interesting states. Here we show that it is possible to create such heterostructures with multiple topological phases in a single nanoscale island. We discuss their growth within the framework of diffusion-limited aggregation, the formation of moiré patterns due to the differing crystallographies of the materials comprising the heterostructure, and the potential to engineer both the electronic structure as well as local variations of topological order. In particular we show that it is possible to build islands which include both the hexagonal β- and rectangular α-forms of antimonene, on top of the topological insulator α-bismuthene. This is the first experimental realisation of α-antimonene, and we show that it is a topologically non-trivial material in the quantum spin Hall class.

  9. Green's function formalism for spin transport in metal-insulator-metal heterostructures

    Science.gov (United States)

    Zheng, Jiansen; Bender, Scott; Armaitis, Jogundas; Troncoso, Roberto E.; Duine, Rembert A.

    2017-11-01

    We develop a Green's function formalism for spin transport through heterostructures that contain metallic leads and insulating ferromagnets. While this formalism in principle allows for the inclusion of various magnonic interactions, we focus on Gilbert damping. As an application, we consider ballistic spin transport by exchange magnons in a metal-insulator-metal heterostructure with and without disorder. For the former case, we show that the interplay between disorder and Gilbert damping leads to spin current fluctuations. For the case without disorder, we obtain the dependence of the transmitted spin current on the thickness of the ferromagnet. Moreover, we show that the results of the Green's function formalism agree in the clean and continuum limit with those obtained from the linearized stochastic Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a natural starting point for numerical studies of magnon transport in heterostructures that contain normal metals and magnetic insulators.

  10. Effect of strain on voltage-controlled magnetism in BiFeO3-based heterostructures

    Science.gov (United States)

    Wang, J. J.; Hu, J. M.; Yang, T. N.; Feng, M.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

    2014-01-01

    Voltage-modulated magnetism in magnetic/BiFeO3 heterostructures can be driven by a combination of the intrinsic ferroelectric-antiferromagnetic coupling in BiFeO3 and the antiferromagnetic-ferromagnetic exchange interaction across the heterointerface. However, ferroelectric BiFeO3 film is also ferroelastic, thus it is possible to generate voltage-induced strain in BiFeO3 that could be applied onto the magnetic layer across the heterointerface and modulate magnetism through magnetoelastic coupling. Here, we investigated, using phase-field simulations, the role of strain in voltage-controlled magnetism for these BiFeO3-based heterostructures. It is predicted, under certain condition, coexistence of strain and exchange interaction will result in a pure voltage-driven 180° magnetization reversal in BiFeO3-based heterostructures. PMID:24686503

  11. Dynamic in situ visualization of voltage-driven magnetic domain evolution in multiferroic heterostructures.

    Science.gov (United States)

    Gao, Ya; Hu, Jia-Mian; Wu, Liang; Nan, C W

    2015-12-23

    Voltage control of magnetism in multiferroic heterostructures provides a promising solution to the excessive heating in spintronic devices. Direct observation of voltage-modulated magnetic domain evolution dynamics is desirable for studying the mechanism of the voltage control of magnetism at mesoscale, but has remained challenging. Here we explored a characterization method for the dynamic in situ evolution of pure voltage modulated magnetic domains in the heterostructures by employing the scanning Kerr microscopy function in the magneto optic Kerr effect system. The local magnetization reorientation of a Ni/PMN-PT heterostructure were characterized under sweeping applied voltage on the PMN-PT single crystal, and the results show that the magnetization rotation angle in the local regions is much greater than that obtained from macroscopic magnetization hysteresis loops.

  12. High-Sensitive Ultraviolet Photodetectors Based on ZnO Nanorods/CdS Heterostructures.

    Science.gov (United States)

    Lam, Kin-Tak; Hsiao, Yu-Jen; Ji, Liang-Wen; Fang, Te-Hua; Hsiao, Kai-Hua; Chu, Tung-Te

    2017-12-01

    The ultraviolet (UV) photodetectors with ZnO nanorods (NRs)/CdS thin film heterostructures on glass substrates have been fabricated and characterized. It can be seen that the UV photoresponsivity of such a device became higher as the ZnO NR length was increased in the investigation. With an incident wavelength of 350 nm and 5 V applied bias, the responsivity of photodetectors based on ZnO NR/CdS heterostructures with the ZnO NR length at 500, 350, and 200 nm and traditional CdS film were at 12.86, 3.83, 0.91, and 0.75 A/W, respectively. The measurement results of the fabricated photodetectors based on ZnO nanorods (NRs)/CdS heterostructures have shown a significant high sensitivity in the range of UV light, which can be useful for the application of UV detection.

  13. Spin-Orbit Torque from a Magnetic Heterostructure of High-Entropy Alloy

    Science.gov (United States)

    Chen, Tian-Yue; Chuang, Tsao-Chi; Huang, Ssu-Yen; Yen, Hung-Wei; Pai, Chi-Feng

    2017-10-01

    High-entropy alloy (HEA) is a family of metallic materials with nearly equal partitions of five or more metals, which might possess mechanical and transport properties that are different from conventional binary or tertiary alloys. In this work, we demonstrate current-induced spin-orbit torque (SOT) magnetization switching in a Ta-Nb-Hf-Zr-Ti HEA-based magnetic heterostructure with perpendicular magnetic anisotropy. The maximum dampinglike SOT efficiency from this particular HEA-based magnetic heterostructure is further determined to be |ζDLHEA | ≈0.033 by hysteresis-loop-shift measurements, while that for the Ta control sample is |ζDLTa | ≈0.04 . Our results indicate that HEA-based magnetic heterostructures can serve as an alternative group of potential candidates for SOT device applications due to the possibility of tuning buffer-layer properties with more than two constituent elements.

  14. Effect of strain on voltage-controlled magnetism in BiFeO₃-based heterostructures.

    Science.gov (United States)

    Wang, J J; Hu, J M; Yang, T N; Feng, M; Zhang, J X; Chen, L Q; Nan, C W

    2014-04-01

    Voltage-modulated magnetism in magnetic/BiFeO3 heterostructures can be driven by a combination of the intrinsic ferroelectric-antiferromagnetic coupling in BiFeO3 and the antiferromagnetic-ferromagnetic exchange interaction across the heterointerface. However, ferroelectric BiFeO3 film is also ferroelastic, thus it is possible to generate voltage-induced strain in BiFeO3 that could be applied onto the magnetic layer across the heterointerface and modulate magnetism through magnetoelastic coupling. Here, we investigated, using phase-field simulations, the role of strain in voltage-controlled magnetism for these BiFeO3-based heterostructures. It is predicted, under certain condition, coexistence of strain and exchange interaction will result in a pure voltage-driven 180° magnetization reversal in BiFeO3-based heterostructures.

  15. Laser treatment of Se/Bi heterostructure: Bi2Se3 nanofilm formation

    Science.gov (United States)

    Mikheev, K. G.; Kogai, V. Ya; Mikheev, G. M.

    2017-11-01

    Thin films of Se/Bi heterostructure were obtained by the by thermal vaporization of Se and Bi powders in a vacuum camera. A focused He-Ne laser beam at 632.8 nm is shown to cause local darkening of Se/Bi heterostructure at incident power densities above 3.5 kW/cm2. The possibility of laser recording of diffraction grating by this technique is demonstrated. It is shown that the resistance between the electrical contacts on the heterostructure reduces as the lines between these contacts are recorded. Data obtained from Raman spectra before and after laser treatment indicate that the darkening is accompanied by Bi2Se3 formation.

  16. Characterization of Inx Ga1-x As-GaAs heterostructures via electron beam techniques

    Science.gov (United States)

    Gomez-Barojas, Estela; Silva-Gonzalez, Rutilo; Serrano-Rojas, Rosa Maria; Vidal-Borbolla, Miguel Angel

    2005-03-01

    In the case of strained superlattices abrupt heterointerfaces are required because compositional fluctuations at heterointerfaces results in uncertainty in both composition and lattice constant. The aim of this work is to study exsitu the surface morphology, the periodicity and elemental composition of a set of 3 InGaAs-GaAs heterostructures grown on GaAs (100) substrates by a molecular beam epitaxy system. The heterostructures are formed by 10 periods of InGaAs-GaAs epitaxially grown on GaAs substrates with nominal thickness of 500 and 1000 å, respectively. The techniques used for this purpose are the scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The In content in the heterostructures is determined from corresponding Auger depth profiles. This work has been supported by VIEP-BUAP, Project No. II53G02.

  17. Semiconducting-metallic transition of singlecrystalline ferromagnetic Hf-doped CuCr2Se4 spinels

    Science.gov (United States)

    Maciążek, E.; Malicka, E.; Gągor, A.; Stokłosa, Z.; Groń, T.; Sawicki, B.; Duda, H.; Gudwański, A.

    2017-09-01

    Chalcogenide spinels show a variety of physical properties and are very good candidates for electronic and high-frequency applications. We report the measurements of magnetic susceptibility, magnetic isotherm, electrical conductivity, thermoelectric power and calculations of the superexchange and double-exchange integrals made for singlecrystalline Cu[CrxHfy]Se4 spinels. The results showed a ferromagnetic order of magnetic moments below the Curie temperatures of 390 K and, an increase in the splitting of the zero-field cooled and field cooled susceptibilities with increasing Hf-content below the room temperature suggesting a slight spin-frustration and a rapid transition from semiconducting to metallic state at room temperature. A quantitative evaluation of the exchange Hamiltonian showed that the total hopping integral rapidly decreased and the bandwidth of the 3d t2g band due to Cr3+ and Cr4+ ions strongly narrowed from 0.76 eV for y = 0 to 0.28 eV for y = 0.14. The narrowing of this band appears to be responsible for semiconducting properties of the Hf-doped CuCr2Se4 spinels below the room temperature.

  18. Design of Semiconducting Tetrahedral Mn_{1−x}Zn_{x}O Alloys and Their Application to Solar Water Splitting

    Directory of Open Access Journals (Sweden)

    Haowei Peng

    2015-05-01

    Full Text Available Transition metal oxides play important roles as contact and electrode materials, but their use as active layers in solar energy conversion requires achieving semiconducting properties akin to those of conventional semiconductors like Si or GaAs. In particular, efficient bipolar carrier transport is a challenge in these materials. Based on the prediction that a tetrahedral polymorph of MnO should have such desirable semiconducting properties, and the possibility to overcome thermodynamic solubility limits by nonequilibrium thin-film growth, we exploit both structure-property and composition-structure relationships to design and realize novel wurtzite-structure Mn_{1−x}Zn_{x}O alloys. At Zn compositions above x≈0.3, thin films of these alloys assume the tetrahedral wurtzite structure instead of the octahedral rocksalt structure of MnO, thereby enabling semiconductor properties that are unique among transition metal oxides, i.e., a band gap within the visible spectrum, a band-transport mechanism for both electron and hole carriers, electron doping, and a band lineup suitable for solar hydrogen generation. A proof of principle is provided by initial photo-electrocatalytic device measurements, corroborating, in particular, the predicted favorable hole-transport properties of these alloys.

  19. Effect of the semi-conductive properties of the passive layer on the current provided by stainless steel microbial cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Pons, Liz; Delia, Marie-Line; Basseguy, Regine [Laboratoire de Genie Chimique, CNRS - Universite de Toulouse, 4 allee Emile Monso BP 84234, 31030 Toulouse (France); Bergel, Alain, E-mail: alain.bergel@ensiacet.f [Laboratoire de Genie Chimique, CNRS - Universite de Toulouse, 4 allee Emile Monso BP 84234, 31030 Toulouse (France)

    2011-02-15

    Geobacter sulfurreducens biofilms were formed under constant polarisation at -0.6 V vs. Ag/AgCl on stainless steel cathodes to catalyse the reduction of fumarate. The time-evolution of the current strongly depended on the quality of the inoculum. Inoculating with young cells significantly shortened the initial lag-phase and using the same inoculum improved the reproducibility of the current-time curves. The whole set of experiments showed that 254SMO stainless steel provided higher current densities (on average 14.1 A/m{sup 2}) than biofilms formed on 316L stainless steel (on average 4.5 A/m{sup 2}). Biofilm coverage assessed by epifluorescent microscopy showed that coverage ratios were generally higher for 316L than for 254SMO. It must be concluded that 254SMO is more efficient in transferring electrons to bacterial cells than 316L. Mott-Schottky diagrams recorded on both materials under conditions of electrolysis in the absence of microorganisms showed that the surface oxide layers had similar n-type semi-conductive behaviour for potential values higher than the flat band potential. In contrast, 316L exhibited slight p-type behaviour at potential lower than the flat band potential, while 254SMO did not. The higher electrochemical performances of biocathodes formed on 254SMO are explained by semi-conductive properties of its passive layer, which prevented the p-type behaviour occurring in cathodic electrolysis conditions.

  20. The growth, characterization, and application of highly ordered small molecule semiconducting thin films

    Science.gov (United States)

    Lunt, Richard Royal, III

    Organic semiconductors have gained tremendous attention recently as their use in field effect transistors, sensors, solar cells, lasers, and organic light emitting diodes have been demonstrated, offering the potential for low-cost alternatives. Since renewable energy remains one the greatest challenges of the 21st century, the possibility for low-cost and flexible organic photovoltaics is particularly exciting. In the first part of this thesis, we demonstrate a route to the controlled growth of oriented crystalline films through organic vapor-phase deposition (OVPD), in conjunction with organic-inorganic, and organic-organic quasi-epitaxy. This method for producing highly ordered crystalline thin-film heterostructures combines the control of film growth with the electronic properties expected to approach that of organic single crystals, making them potentially useful for high efficiency organic thin-film devices and solar cells. We further demonstrate OVPD as a method for the deposition of large-scale organic electronics with low material waste, a key ability in fulfilling the promise of low-cost organic devices. The second part of this thesis is focused on understanding factors that govern energy (i.e. exciton) transport. The two single most important and fundamental properties of organic semiconductors are the transport of charge and energy. While charge mobility has been extensively studied and convincingly linked to the degree of crystalline order and orientation, the principles governing energy transport, i.e. exciton migration, in this class of materials and the subsequent connection to crystalline properties still remain ambiguous. Therefore, we aim to understand key aspects governing exciton motion in organic materials to better engineer materials, film morphologies, and film architectures for organic electronics with improved performance. To this end, we have developed a new method for measuring exciton diffusion and characterize a range of archetypal

  1. Ultra-high optical responsivity of semiconducting asymmetric nano-channel diodes for photon detection

    Science.gov (United States)

    Akbas, Y.; Plecenik, T.; Durina, P.; Plecenik, A.; Jukna, A.; Wicks, G.; Sobolewski, Roman

    2017-05-01

    The asymmetric nano-channel diode (ANCD) is the 2-dimensional electron gas (2DEG) semiconductor nanodevice that, unlike a conventional diode, relies on the device nanostructure and field-controlled transport in a ballistic nanometerwidth channel instead of barriers to develop its asymmetric, diode-like current-voltage (I-V) characteristics. We focus on ANCD optoelectronic properties, and demonstrate that the devices can act as very sensitive, single-photon-level, visiblelight photodetectors. Our test structures consist of 2-μm-long and 230-nm-wide channels and were fabricated using electron-beam lithography on a GaAs/AlGaAs heterostructure with a 2DEG layer, followed by reactive ion etching. The I-V curves were collected by measuring the transport current under the voltage-source biasing condition, both in the dark and under light illumination. The experiments were conducted inside a cryostat, in a temperature range from 300 K to 78 K. As an optical excitation, we used a 800-nm-wavelength, generated by a commercial Ti:sapphire laser operated either at a quasi-continuous-wave mode or as a source of 100-fs-wide pulses. The impact of the light illumination was very clear, and at low temperatures we observed a significant photocurrent Iph 0.25 μA at temperature 78 K for the incident optical power as low as 1 nW, with a limited dark-current background. The magnitude of the device optical responsivity increased linearly with the decrease of the optical power, reaching for 1-nW optical excitation the value as high as 400 A/W at room temperature and >800 A/W at 78K. The physics of the photoresponse gain mechanism in the ANCD arises from a vast disparity between the sub-picosecond transit time of photo-excited electrons travelling in the 2DEG nanochannel and the up to microsecond lifetime of photo-excited holes pushed towards the device substrate.

  2. Nanoscale Engineering of Heterostructured Anode Materials for Boosting Lithium-Ion Storage.

    Science.gov (United States)

    Chen, Gen; Yan, Litao; Luo, Hongmei; Guo, Shaojun

    2016-09-01

    Rechargeable lithium-ion batteries (LIBs), as one of the most important electrochemical energy-storage devices, currently provide the dominant power source for a range of devices, including portable electronic devices and electric vehicles, due to their high energy and power densities. The interest in exploring new electrode materials for LIBs has been drastically increasing due to the surging demands for clean energy. However, the challenging issues essential to the development of electrode materials are their low lithium capacity, poor rate ability, and low cycling stability, which strongly limit their practical applications. Recent remarkable advances in material science and nanotechnology enable rational design of heterostructured nanomaterials with optimized composition and fine nanostructure, providing new opportunities for enhancing electrochemical performance. Here, the progress as to how to design new types of heterostructured anode materials for enhancing LIBs is reviewed, in the terms of capacity, rate ability, and cycling stability: i) carbon-nanomaterials-supported heterostructured anode materials; ii) conducting-polymer-coated electrode materials; iii) inorganic transition-metal compounds with core@shell structures; and iv) combined strategies to novel heterostructures. By applying different strategies, nanoscale heterostructured anode materials with reduced size, large surfaces area, enhanced electronic conductivity, structural stability, and fast electron and ion transport, are explored for boosting LIBs in terms of high capacity, long cycling lifespan, and high rate durability. Finally, the challenges and perspectives of future materials design for high-performance LIB anodes are considered. The strategies discussed here not only provide promising electrode materials for energy storage, but also offer opportunities in being extended for making a variety of novel heterostructured nanomaterials for practical renewable energy applications. © 2016

  3. On the optimization of asymmetric barrier layers in InAlGaAs/AlGaAs laser heterostructures on GaAs substrates

    DEFF Research Database (Denmark)

    Zhukov, A. E.; Asryan, L. V.; Semenova, Elizaveta

    2015-01-01

    Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost...

  4. 3C-SiC/ZnS heterostructured nanospheres with high photocatalytic activity and enhancement mechanism

    Directory of Open Access Journals (Sweden)

    J. Zhang

    2015-03-01

    Full Text Available 3C-SiC/n-type ZnS heterostructured nanospheres synthesized hydrothermally deliver enhanced photocatalytic performance under visible light excitation. The heterostructured catalysts consisting of 3C-SiC and ZnS nanocrystals with a mean size being less than 5 nm exhibit extended light absorption to the visible range. The proper band structure of the 3C-SiC and ZnS nanocrystals and intrinsic electric field induced by the heterojunction promote separation of photoexcited electrons and holes in the ZnS and 3C-SiC nanocrystals resulting in the increased photocatalytic efficiency. The associated mechanism is studied and proposed.

  5. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays

    OpenAIRE

    Liu, Jian; Wang, Chunrui; Xie, Qingqing; Cai, Junsheng; Zhang, Jing

    2009-01-01

    Abstract Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondar...

  6. Cu particle seeded InP-InAs axial nanowire heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hillerich, Karla; Ghidini, Dario S.; Deppert, Knut; Johansson, Jonas [Solid State Physics, Lund University, Lund (Sweden); Dick, Kimberly A. [Solid State Physics, Lund University, Lund (Sweden); Polymer and Materials Chemistry, Lund University, Lund (Sweden)

    2013-10-15

    We demonstrate the epitaxial growth of alternating InP-InAs nanowire heterostructures using Cu seed particles in MOVPE. We observe extraordinary early stages in the formation of InAs segments, e.g. three-dimensional nucleation instead of step-flow growth. Furthermore, InAs segments of thin nanowires exhibit extended 4H crystal structure. Color coded XEDS elemental map of a typical InP-InAs nanowire heterostructure seeded by a Cu particle. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Space concentrator solar cells based on multilayer LPE grown AlGaAs/GaAs heterostructure

    Science.gov (United States)

    Khvostikov, V. P.; Larionov, V. R.; Paleeva, E. V.; Sorokina, S. V.; Chosta, O. I.; Shvarts, M. Z.; Zimogorova, N. S.

    1995-01-01

    The high efficiency solar cells based on multilayer AlGaAs/GaAs heterostructures, prepared by low temperature liquid phase epitaxy (LPE), were developed and tested. An investigation of the low temperature LPE process for the crystallization of AlGaAs heterostructures of as high as 24.0 to 24.7 percent under AMO conditions at concentration ratios of 20 to 100x, were reached. Developed solar cells show substantial radiation resistance to the damage induced by 3.75 MeV electrons.

  8. High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures.

    Science.gov (United States)

    Mudd, Garry W; Svatek, Simon A; Hague, Lee; Makarovsky, Oleg; Kudrynskyi, Zakhar R; Mellor, Christopher J; Beton, Peter H; Eaves, Laurence; Novoselov, Kostya S; Kovalyuk, Zakhar D; Vdovin, Evgeny E; Marsden, Alex J; Wilson, Neil R; Patanè, Amalia

    2015-07-01

    High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures is achieved by exploiting the broad-band transparency of graphene, the direct bandgap of InSe, and the favorable band line up of InSe with graphene. The photoresponsivity exceeds that for other van der Waals heterostructures and the spectral response extends from the near-infrared to the visible spectrum. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

    KAUST Repository

    Lin, Yu-Chuan

    2015-06-19

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2–WSe2–graphene and WSe2–MoS2–graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

  10. Study of dual color infrared photodetection from n-GaSb/n-InAsSb heterostructures

    Directory of Open Access Journals (Sweden)

    Jinchao Tong

    2016-02-01

    Full Text Available We report detailed investigation of n-GaSb/n-InAsSb heterostructure photodetectors for infrared photodetection at different temperatures and biases. Our results show that the heterostructure photodetectors are capable of dual color photodetections at a fixed forward bias with its highest responsivity occurred at room temperature; With the decrease of the forward bias, a turning point, at which the photocurrent changes its direction, exist and the corresponding voltage values increases with the decrease of temperature; At all reverse biases, the photocurrents flow in the same direction but the maximum current occurs at about 205 K. A new model is proposed, which can well explain all the observations.

  11. Temperature Dependence of Photoluminescence in InGaAs/InP Strained MQW Heterostructures

    Science.gov (United States)

    Raisky, O. Y.; Wang, W. B.; Alfano, R. R.; Reynolds, C. L., Jr.; Swaminathan, V.

    1996-01-01

    Multiple quantum well (MQW) InGaAsP/InP heterostructure systems have been drawn considerable research interest in recent years due to its suitability for long wavelength optoelectronic devices. The performance of such devices is strongly affected by peculiarities of recombination processes in the quantum wells (QW). The goal of this study was to investigate the effect of barrier width on the radiative recombination of carriers. In our study, the photoluminescence spectra from InGaAsP/lnP MQW double heterostructures have been measured in the 77-290 K temperature range with different excitation intensities.

  12. AlN/GaN heterostructures for normally-off transistors

    Energy Technology Data Exchange (ETDEWEB)

    Zhuravlev, K. S., E-mail: zhur@isp.nsc.ru; Malin, T. V.; Mansurov, V. G.; Tereshenko, O. E. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Abgaryan, K. K.; Reviznikov, D. L. [Dorodnicyn Computing Centre of the Russian Academy of Sciences (Russian Federation); Zemlyakov, V. E.; Egorkin, V. I. [National Research University of Electronic Technology (MIET) (Russian Federation); Parnes, Ya. M.; Tikhomirov, V. G. [Joint Stock Company “Svetlana-Electronpribor” (Russian Federation); Prosvirin, I. P. [Russian Academy of Sciences, Boreskov Institute of Catalysis, Siberian Branch (Russian Federation)

    2017-03-15

    The structure of AlN/GaN heterostructures with an ultrathin AlN barrier is calculated for normally-off transistors. The molecular-beam epitaxy technology of in situ passivated SiN/AlN/GaN heterostructures with a two-dimensional electron gas is developed. Normally-off transistors with a maximum current density of ~1 A/mm, a saturation voltage of 1 V, a transconductance of 350 mS/mm, and a breakdown voltage of more than 60 V are demonstrated. Gate lag and drain lag effects are almost lacking in these transistors.

  13. Study of organic-inorganic hetero-interfaces and electrical transport in semiconducting nanostructures

    Science.gov (United States)

    Wagner, Sean Robert

    As the electronics industry continues to evolve and move towards functional electronic devices with increasing complexity and functionality, it becomes important to explore materials outside the regime of conventional semiconductors. Organic semiconducting small molecules have received a large amount of attention due to their high degree of flexibility, the option to perform molecular synthesis to modify their electronic and magnetic properties, and their ability to organize into highly-ordered functionalized nanostructures and thin films. Being able to form complex nanostructures and thin films with molecular precision, while maintaining the ability to tune properties through modifications in the molecular chemistry could result in vast improvements in conventional device architectures. However, before this is realized, there still remains a significant lack of understanding regarding how these molecules interact with various substrate surfaces as well as their intermolecular interactions. The interplay between these interactions can produce drastic changes in the molecular orientation and ordering at the hetero-interface, which can affect the transport properties of the molecular thin film and ultimately modify the performance of the organic electronic device. This study first focuses on the growth dynamics, molecular ordering, and molecular orientation of metal phthalocyanine (MPc) molecules, particularly on Si, a substrate which is notoriously difficult to form an organized organic thin film on due to the surface dangling bonds. By deactivating these bonds, the formation of a highly ordered organic molecular thin film becomes possible. Combining scanning tunneling microscopy, scanning tunneling spectroscopy, low-energy electron diffraction, and density functional theory calculations, the growth evolution of MPc molecules ( M = Zn, Cu, Co) from the single molecule level to multilayered films on the deactivated Si(111)-B surface is investigated. Initial tests are

  14. Spin-Dependent Transport Phenomena in Ferromagnet/Semiconductor Heterostructures

    Science.gov (United States)

    Geppert, Chad Christopher

    This dissertation examines several aspects of spin-dependent transport phenomena in epitaxially grown ferromagnet/n-GaAs heterostructures. Further maturation of the field of semiconductor-based spintronics is hindered by difficulties in evaluating device performance across materials systems. Using Fe/n-GaAs and Co2MnSi/n-GaAs heterostructures as a test case, the main goal of this work is to demonstrate how such difficulties may be overcome by (1) specifying a more quantitative framework for evaluating transport parameters and (2) the introduction of a new spin-to-charge conversion phenomenon which may be parameterized by bulk semiconductor parameters. In the introductory chapter, this work is placed in the broader context of developing improved methods for the generation, modulation, and detection of spins. The lateral spin-valve geometry is presented as a concrete example of the typical measurement procedures employed. Chapter 2 presents the charge-based transport properties of these samples and establishes the notation and calculation techniques to be employed in subsequent chapters. In particular, we examine in detail the calculation of the electrochemical potential for a given carrier concentration. Chapter 3 provides a full derivation of the equations governing spin-dependent transport in the large polarization regime. This is applied to the case of extracting spin lifetimes and diffusion rates, demonstrating how quantitative agreement with theoretical predictions may be obtained upon properly accounting for both device geometry and material parameters. Further examination of the boundary conditions applicable to the heterojunctions of these samples demonstrates to what extent device performance may be parameterized across materials systems. Chapter 4 presents experimental observations of a new spin-to-charge conversion phenomenon using a non-magnetic probe. In the presence of a large non-equilibrium spin accumulation, the combination of a non-constant density

  15. Effect of ferromagnetism on superconductivity in manganite/cuprate heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Pang, B.S.H. [Device Materials Group, Department of Materials Science and Metallurgy, University of Cambridge, New Museum Site, Pembroke St., Cambridge CB2 3QZ (United Kingdom)]. E-mail: bshp2@cam.ac.uk; Tomov, R.I. [Device Materials Group, Department of Materials Science and Metallurgy, University of Cambridge, New Museum Site, Pembroke St., Cambridge CB2 3QZ (United Kingdom); Bell, C. [Device Materials Group, Department of Materials Science and Metallurgy, University of Cambridge, New Museum Site, Pembroke St., Cambridge CB2 3QZ (United Kingdom); Blamire, M.G. [Device Materials Group, Department of Materials Science and Metallurgy, University of Cambridge, New Museum Site, Pembroke St., Cambridge CB2 3QZ (United Kingdom)

    2004-10-15

    In this investigation, we deposited multilayers of [(La{sub 0.67}Sr{sub 0.33}MnO{sub 3}){sub d}/(YBa{sub 2}Cu{sub 3}O{sub y}){sub x}], [(La{sub 0.7}Ca{sub 0.3}MnO{sub 3}){sub 4}/(YBa{sub 2}Cu{sub 3}O{sub 7}){sub x}]{sub 180nm} and [(La{sub 0.45}Ca{sub 0.55}MnO{sub 3} ){sub 4}/(YBa{sub 2}Cu{sub 3}O{sub 7}){sub x}]{sub 180nm} of varying individual layer thicknesses using the 'eclipse' pulsed laser deposition technique. Transport measurements were performed to obtain the films' critical temperatures (T{sub c}). We study the interaction between superconductivity and magnetism within these heterostructures, paying attention to the superconducting and ferromagnetic coherence lengths, {xi}{sub F} and {xi}{sub S} respectively, of the materials in the system, and analyzing how these parameters affect the suppression of T{sub c}, eliminating stray field as a possible cause of T{sub c} suppression. We compared our data to previous work to achieve a more comprehensive study of oxide F/S multilayers. We observe that the magnetic nature of the manganite layers do not have much influence on T{sub c} suppression in the multilayers. We show that within certain limits, the thicknesses of both the superconducting and ferromagnetic layers individually affect the T{sub c} of the multilayers. The critical thickness of YBCO in our multilayers was estimated to be {approx}20 nm.

  16. Micromagnetic sensors and Dirac fermions in HgTe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Buettner, Bastian

    2012-08-06

    Within the scope of this thesis two main topics have been investigated: the examination of micromagnetic sensors and transport of massive and massless Dirac fermions in HgTe quantum wells. For the investigation of localized, inhomogeneous magnetic fields, the fabrication and characterization of two different non-invasive and ultra sensitive sensors has been established at the chair ''Experimentelle Physik'' of the University of Wuerzburg. The first sensor is based on the young technique named micro-Hall magnetometry. The necessary semiconductor devices (Hall cross structures) were fabricated by high-resolution electron beam lithography based on two different two dimensional electron gases (2DEGs), namely InAs/(Al,Ga)Sb- and HgTe/(Hg,Cd)Te-heterostructures. The characteristics have been examined in two different ways. Measurements in homogeneous magnetic fields served for characterization of the sensors, whereas the investigation of artificially produced sub-{mu}m magnets substantiates the suitability of the devices for the study of novel nanoscale magnetic materials (e.g. nanowires). Systematic experiments with various magnets are in accordance with the theory of single-domain particles and anisotropic behavior due to shapes with high aspect ratio. The highest sensitivity for strongly localized fields was obtained at T=4.2 K for a (200.200) nm{sup 2} Hall cross - made from shallow, high mobility HgTe 2DEG. Although the field resolution was merely {delta}B{approx}100 {mu}T, the nanoscale sensor size yields an outstanding flux resolution of {delta}{Phi}=2.10{sup -3} {Phi}{sub 0}, where {Phi}{sub 0}=h/2e is the flux quantum. Translating this result in terms of magnetic moment, the sensitivity allows for the detection of magnetization changes of a particle centered on top of the sensor as low as {delta}M{approx}10{sup 2} {mu}{sub B}, with the magnetic moment of a single electron {mu}{sub B}, the Bohr magneton. The further examination of a permalloy

  17. Black phosphorene/monolayer transition-metal dichalcogenides as two dimensional van der Waals heterostructures: a first-principles study.

    Science.gov (United States)

    You, Baiqing; Wang, Xiaocha; Zheng, Zhida; Mi, Wenbo

    2016-03-14

    The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p-n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc.

  18. Strongly Coupled High-Quality Graphene/2D Superconducting Mo2C Vertical Heterostructures with Aligned Orientation.

    Science.gov (United States)

    Xu, Chuan; Song, Shuang; Liu, Zhibo; Chen, Long; Wang, Libin; Fan, Dingxun; Kang, Ning; Ma, Xiuliang; Cheng, Hui-Ming; Ren, Wencai

    2017-06-27

    Vertical heterostructures of two-dimensional (2D) crystals have led to the observations of numerous exciting physical phenomena and presented the possibilities for technological applications, which strongly depend on the quality, interface, relative alignment, and interaction of the neighboring 2D crystals. The heterostructures or hybrids of graphene and superconductors offer a very interesting platform to study mesoscopic superconductivity and the interplay of the quantum Hall effect with superconductivity. However, so far the heterostructures of graphene and 2D superconductors are fabricated by stacking, and consequently suffer from random relative alignment, weak interfacial interaction, and unavoidable interface contaminants. Here we report the direct growth of high-quality graphene/2D superconductor (nonlayered ultrathin α-Mo2C crystal) vertical heterostructures with uniformly well-aligned lattice orientation and strong interface coupling by chemical vapor deposition. In the heterostructure, both graphene and 2D α-Mo2C crystal show no defect, and the graphene is strongly compressed. Different from the previously reported graphene/superconductor heterostructures or hybrids, the strong interface coupling leads to a phase diagram of superconducting transition with multiple voltage steps being observed in the transition regime. Furthermore, we demonstrate the realization of highly transparent Josephson junction devices based on these strongly coupled high-quality heterostructures, in which a clear magnetic-field-induced Fraunhofer pattern of the critical supercurrent is observed.

  19. Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of KxFe2-ySe2

    Science.gov (United States)

    Zhao, Jun; Cao, Huibo; Bourret-Courchesne, E.; Lee, D.-H.; Birgeneau, R. J.

    2012-12-01

    The recently discovered K-Fe-Se high-temperature superconductor has caused heated debate regarding the nature of its parent compound. Transport, angle-resolved photoemission spectroscopy, and STM measurements have suggested that its parent compound could be insulating, semiconducting, or even metallic [M. H. Fang, H.-D. Wang, C.-H. Dong, Z.-J. Li, C.-M. Feng, J. Chen, and H. Q. Yuan, Europhys. Lett. 94, 27009 (2011)EULEEJ0295-507510.1209/0295-5075/94/27009; F. Chen , Phys. Rev. X 1, 021020 (2011)PRXHAE2160-330810.1103/PhysRevX.1.021020; and W. Li , Phys. Rev. Lett. 109, 057003 (2012)PRLTAO0031-900710.1103/PhysRevLett.109.057003]. Because the magnetic ground states associated with these different phases have not yet been identified and the relationship between magnetism and superconductivity is not fully understood, the real parent compound of this system remains elusive. Here, we report neutron-diffraction experiments that reveal a semiconducting antiferromagnetic (AFM) phase with rhombus iron vacancy order. The magnetic order of the semiconducting phase is the same as the stripe AFM order of the iron pnictide parent compounds. Moreover, while the 5×5 block AFM phase coexists with superconductivity, the stripe AFM order is suppressed by it. This leads us to conjecture that the new semiconducting magnetic ordered phase is the true parent phase of this superconductor.

  20. Strain and Water Effects on the Electronic Structure and Chemical Activity of In-Plane Graphene/Silicene Heterostructure

    OpenAIRE

    Kistanov, Andrey A; Cai, Yongqing; Zhang, Yong-Wei; Dmitriev, Sergey V; Zhou, Kun

    2016-01-01

    By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from -7% (compression) to +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding...

  1. Formation and Device Application of Ge Nanowire Heterostructures via Rapid Thermal Annealing

    Directory of Open Access Journals (Sweden)

    Jianshi Tang

    2011-01-01

    Full Text Available We reviewed the formation of Ge nanowire heterostructure and its field-effect characteristics by a controlled reaction between a single-crystalline Ge nanowire and Ni contact pads using a facile rapid thermal annealing process. Scanning electron microscopy and transmission electron microscopy demonstrated a wide temperature range of 400~500°C to convert the Ge nanowire to a single-crystalline Ni2Ge/Ge/Ni2Ge nanowire heterostructure with atomically sharp interfaces. More importantly, we studied the effect of oxide confinement during the formation of nickel germanides in a Ge nanowire. In contrast to the formation of Ni2Ge/Ge/Ni2Ge nanowire heterostructures, a segment of high-quality epitaxial NiGe was formed between Ni2Ge with the confinement of Al2O3 during annealing. A twisted epitaxial growth mode was observed in both two Ge nanowire heterostructures to accommodate the large lattice mismatch in the NixGe/Ge interface. Moreover, we have demonstrated field-effect transistors using the nickel germanide regions as source/drain contacts to the Ge nanowire channel. Our Ge nanowire transistors have shown a high-performance p-type behavior with a high on/off ratio of 105 and a field-effect hole mobility of 210 cm2/Vs, which showed a significant improvement compared with that from unreacted Ge nanowire transistors.

  2. Designing Diameter-Modulated Heterostructure Nanowires of PbTe/Te by Controlled Dewetting.

    Science.gov (United States)

    Kumar, Abinash; Kundu, Subhajit; Samantaray, Debadarshini; Kundu, Paromita; Zanaga, Daniele; Bals, Sara; Ravishankar, N

    2017-12-13

    Heterostructures consisting of semiconductors with controlled morphology and interfaces find applications in many fields. A range of axial, radial, and diameter-modulated nanostructures have been synthesized primarily using vapor phase methods. Here, we present a simple wet chemical routine to synthesize heterostructures of PbTe/Te using Te nanowires as templates. A morphology evolution study for the formation of these heterostructures has been performed. On the basis of these control experiments, a pathway for the formation of these nanostructures is proposed. Reduction of a Pb precursor to Pb on Te nanowire templates followed by interdiffusion of Pb/Te leads to the formation of a thin shell of PbTe on the Te wires. Controlled dewetting of the thin shell leads to the formation of cube-shaped PbTe that is periodically arranged on the Te wires. Using control experiments, we show that different reactions parameters like rate of addition of the reducing agent, concentration of Pb precursor and thickness of initial Te nanowire play a critical role in controlling the spacing between the PbTe cubes on the Te wires. Using simple surface energy arguments, we propose a mechanism for the formation of the hybrid. The principles presented are general and can be exploited for the synthesis of other nanoscale heterostructures.

  3. A solid-state cation exchange reaction to form multiple metal oxide heterostructure nanowires.

    Science.gov (United States)

    Chen, Y H; Huang, C W; Yeh, P H; Chen, J Y; Lin, T Y; Chang, C F; Wu, W W

    2016-09-29

    Metal oxide nanostructures have been investigated extensively due to their wide range of physical properties; zinc oxide is one of the most promising materials. It exhibits fascinating functional properties and various types of morphologies. In particular, ZnO heterostructures have attracted great attention because their performance can be modified and further improved by the addition of other materials. In this study, we successfully transformed ZnO nanowires (NWs) into multiple ZnO/Al 2 O 3 heterostructure NWs via a solid-state cation exchange reaction. The experiment was carried out in situ via an ultrahigh vacuum transmission electron microscope (UHV-TEM), which was equipped with a video recorder. Moreover, we analyzed the structure and composition of the heterostructure NWs by Cs-corrected STEM equipped with EDS. Based on these experimental results, we inferred a cation exchange reaction ion path model. Additionally, we investigated the defects that appeared after the cation reaction, which resulted from the remaining zinc ions. These multiple heterostructure ZnO/Al 2 O 3 NWs exhibited excellent UV sensing sensitivity and efficiency.

  4. Control and understanding of kink formation in InAs-InP heterostructure nanowires.

    Science.gov (United States)

    Fahlvik Svensson, S; Jeppesen, S; Thelander, C; Samuelson, L; Linke, H; Dick, K A

    2013-08-30

    Nanowire heterostructures are of special interest for band structure engineering due to an expanded range of defect-free material combinations. However, the higher degree of freedom in nanowire heterostructure growth comes at the expense of challenges related to nanowire-seed particle interactions, such as undesired composition, grading and kink formation. To better understand the mechanisms of kink formation in nanowires, we here present a detailed study of the dependence of heterostructure nanowire morphology on indium pressure, nanowire diameter, and nanowire density. We investigate InAs-InP-InAs heterostructure nanowires grown with chemical beam epitaxy, which is a material system that allows for very abrupt heterointerfaces. Our observations indicate that the critical parameter for kink formation is the availability of indium, and that the resulting morphology is also highly dependent on the length of the InP segment. It is shown that kinking is associated with the formation of an inclined facet at the interface between InP and InAs, which destabilizes the growth and leads to a change in growth direction. By careful tuning of the growth parameters, it is possible to entirely suppress the formation of this inclined facet and thereby kinking at the heterointerface. Our results also indicate the possibility of producing controllably kinked nanowires with a high yield.

  5. Single crystalline PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices.

    Science.gov (United States)

    Lin, Yung-Chen; Lu, Kuo-Chang; Wu, Wen-Wei; Bai, Jingwei; Chen, Lih J; Tu, K N; Huang, Yu

    2008-03-01

    We report the formation of PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices from such heterostructures. Scanning electron microscopy studies show that silicon nanowires can be converted into PtSi nanowires through controlled reactions between lithographically defined platinum pads and silicon nanowires. High-resolution transmission electron microscopy studies show that PtSi/Si/PtSi heterostructure has an atomically sharp interface with epitaxial relationships of Si[110]//PtSi[010] and Si(111)//PtSi(101). Electrical measurements show that the pure PtSi nanowires have low resistivities approximately 28.6 microOmega.cm and high breakdown current densities>1x10(8) A/cm2. Furthermore, using single crystal PtSi/Si/PtSi nanowire heterostructures with atomically sharp interfaces, we have fabricated high-performance nanoscale field-effect transistors from intrinsic silicon nanowires, in which the source and drain contacts are defined by the metallic PtSi nanowire regions, and the gate length is defined by the Si nanowire region. Electrical measurements show nearly perfect p-channel enhancement mode transistor behavior with a normalized transconductance of 0.3 mS/microm, field-effect hole mobility of 168 cm2/V.s, and on/off ratio>10(7), demonstrating the best performing device from intrinsic silicon nanowires.

  6. Barrier formation at organic interfaces in a Cu(100)-benzenethiolate-pentacene heterostructure

    DEFF Research Database (Denmark)

    Betti, M.G.; Kanjilal, A.; Mariani, C.

    2008-01-01

    The energy level alignment at the metal-organic and organic-organic interfaces of the Cu(100)/benzenethiolate/pentacene heterostructure is studied by photoemission spectroscopy and discussed theoretically using a model that includes, in a consistent way, charge transfer, Pauli repulsion, intrinsic...

  7. Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction.

    Science.gov (United States)

    Ross, Jason S; Rivera, Pasqual; Schaibley, John; Lee-Wong, Eric; Yu, Hongyi; Taniguchi, Takashi; Watanabe, Kenji; Yan, Jiaqiang; Mandrus, David; Cobden, David; Yao, Wang; Xu, Xiaodong

    2017-02-08

    Semiconductor heterostructures are backbones for solid-state-based optoelectronic devices. Recent advances in assembly techniques for van der Waals heterostructures have enabled the band engineering of semiconductor heterojunctions for atomically thin optoelectronic devices. In two-dimensional heterostructures with type II band alignment, interlayer excitons, where Coulomb bound electrons and holes are confined to opposite layers, have shown promising properties for novel excitonic devices, including a large binding energy, micron-scale in-plane drift-diffusion, and a long population and valley polarization lifetime. Here, we demonstrate interlayer exciton optoelectronics based on electrostatically defined lateral p-n junctions in a MoSe 2 -WSe 2 heterobilayer. Applying a forward bias enables the first observation of electroluminescence from interlayer excitons. At zero bias, the p-n junction functions as a highly sensitive photodetector, where the wavelength-dependent photocurrent measurement allows the direct observation of resonant optical excitation of the interlayer exciton. The resulting photocurrent amplitude from the interlayer exciton is about 200 times smaller than the resonant excitation of intralayer exciton. This implies that the interlayer exciton oscillator strength is 2 orders of magnitude smaller than that of the intralayer exciton due to the spatial separation of electron and hole to the opposite layers. These results lay the foundation for exploiting the interlayer exciton in future 2D heterostructure optoelectronic devices.

  8. Ga self-diffusion in isotopically enriched GaAs heterostructures doped with Si and Zn

    Energy Technology Data Exchange (ETDEWEB)

    Norseng, Marshall Stephen [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    This study attempts to advance the modeling of AlGaAs/GaAs/AlAs diffusion by experimental investigation of Ga self-diffusion in undoped, as-grown doped and Zinc diffused structures. We utilize novel, isotopically enriched superlattice and heterostructure samples to provide direct observation and accurate measurement of diffusion with a precision not possible using conventional techniques.

  9. Synthesis of ZnO-based nanostructures for heterostructure photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Lashkova, N. A.; Maximov, A. I.; Ryabko, A. A.; Bobkov, A. A.; Moshnikov, V. A.; Terukov, E. I., E-mail: eug.terukov@mail.ioffe.ru [St. Petersburg State Electrotechnical University “LETI” (Russian Federation)

    2016-09-15

    A model describing heterostructure solar cells based on zinc and copper oxides is developed. Seed layers of ZnO and CuO are synthesized by spray pyrolysis. To form a bulk heterojunction, ZnO nanorods are grown by hydrothermal synthesis. The morphological, electrical and optical properties of the fabricated structures are investigated.

  10. Rational design and controlled synthesis of Te/Bi2Te3 heterostructure nanostring composites

    Science.gov (United States)

    Zhang, Yuzhuo; Chen, Hong; Li, Zhiliang; Huang, Ting; Zheng, Shuqi

    2015-07-01

    Te/Bi2Te3 heterostructure nanostring composites composed of several Bi2Te3 nanoplates, which were perpendicularly strung together by Te nanorod, were rationally designed and synthesized via a facile solvothermal method on a large scale. The X-ray diffraction (XRD) characterization demonstrated that the Bi2Te3 nanoplates were rhombohedral phase and the Te nanorods were trigonal phase. The uniform nanostring morphologies were well characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Detailed heterostructures were proved via energy dispersive spectrometer (EDS) and high-resolution transmission electron microscope (HRTEM). The morphology transformation from Bi2Te3 nanoplates to Te/Bi2Te3 heterostructure nanostrings could be controlled by adjusting the ratio of bismuth oxide to tellurium oxide. NaOH, serving as catalytic reduction agent and morphology controlling agent, played an important role in the synthesis of Te/Bi2Te3 heterostructure nanostrings. The reaction mechanism was also proposed to explain the formation process of the composites and the specific function of reagents in this reaction system.

  11. First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures.

    Science.gov (United States)

    Wang, Xiaoming; Zebarjadi, Mona; Esfarjani, Keivan

    2016-08-21

    This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling-dominated transport to thermionic-dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The use of layered van der Waals heterostructures has two advantages: (a) thermionic transport barriers can be tuned by changing the number of layers, and (b) thermal conductance across these non-covalent structures is very weak. The phonon thermal conductance of the present van der Waals heterostructure is found to be 4.1 MW m(-2) K(-1) which is one order of magnitude lower than the lowest value for that of covalently-bonded interfaces. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices. This study shows that layered van der Waals structures have great potential to be used as solid-state energy-conversion devices.

  12. Dielectric Engineering of Electronic Correlations in a van der Waals Heterostructure.

    Science.gov (United States)

    Steinleitner, Philipp; Merkl, Philipp; Graf, Alexander; Nagler, Philipp; Watanabe, Kenji; Taniguchi, Takashi; Zipfel, Jonas; Schüller, Christian; Korn, Tobias; Chernikov, Alexey; Brem, Samuel; Selig, Malte; Berghäuser, Gunnar; Malic, Ermin; Huber, Rupert

    2018-02-14

    Heterostructures of van der Waals bonded layered materials offer unique means to tailor dielectric screening with atomic-layer precision, opening a fertile field of fundamental research. The optical analyses used so far have relied on interband spectroscopy. Here we demonstrate how a capping layer of hexagonal boron nitride (hBN) renormalizes the internal structure of excitons in a WSe 2 monolayer using intraband transitions. Ultrabroadband terahertz probes sensitively map out the full complex-valued mid-infrared conductivity of the heterostructure after optical injection of 1s A excitons. This approach allows us to trace the energies and line widths of the atom-like 1s-2p transition of optically bright and dark excitons as well as the densities of these quasiparticles. The excitonic resonance red shifts and narrows in the WSe 2 /hBN heterostructure compared to the bare monolayer. Furthermore, the ultrafast temporal evolution of the mid-infrared response function evidences the formation of optically dark excitons from an initial bright population. Our results provide key insight into the effect of nonlocal screening on electron-hole correlations and open new possibilities of dielectric engineering of van der Waals heterostructures.

  13. Large area molybdenum disulphide- epitaxial graphene vertical Van der Waals heterostructures

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Naylor, Carl H.; Sediri, Haikel; Lhuillier, Emmanuel; Balan, Adrian; Rault, Julien E.; Dappe, Yannick J.; Bertran, François; Fèvre, Patrick Le; Johnson, A. T. Charlie; Ouerghi, Abdelkarim

    2016-01-01

    Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design. PMID:27246929

  14. Parabolic negative magnetoresistance in p-Ge/Ge1-xSix heterostructures

    NARCIS (Netherlands)

    Arapov, YG; Harus, GI; Neverov, VN; Shelushinina, NG; Kuznetsov, OA

    Quantum corrections for the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge1-xSex heterostructures at T=(0.1-20) K in magnetic field B up to 1.5 T. Negative magnetoresistance with

  15. Strain-engineered optoelectronic properties of 2D transition metal dichalcogenide lateral heterostructures

    Science.gov (United States)

    Lee, Jaekwang; Huang, Jingsong; Sumpter, Bobby G.; Yoon, Mina

    2017-06-01

    Compared with their bulk counterparts, 2D materials can sustain much higher elastic strain at which optical quantities such as bandgaps and absorption spectra governing optoelectronic device performance can be modified with relative ease. Using first-principles density functional theory and quasiparticle GW calculations, we demonstrate how uniaxial tensile strain can be utilized to optimize the electronic and optical properties of transition metal dichalcogenide lateral (in-plane) heterostructures such as MoX2/WX2 (X  =  S, Se, Te). We find that these lateral-type heterostructures may facilitate efficient electron-hole separation for light detection/harvesting and preserve their type II characteristic up to 12% of uniaxial strain. Based on the strain-dependent bandgap and band offset, we show that uniaxial tensile strain can significantly increase the power conversion efficiency of these lateral heterostructures. Our results suggest that these strain-engineered lateral heterostructures are promising for optimizing optoelectronic device performance by selectively tuning the energetics of the bandgap.

  16. Controllable Schottky barrier in GaSe/graphene heterostructure: the role of interface dipole

    Science.gov (United States)

    Si, Chen; Lin, Zuzhang; Zhou, Jian; Sun, Zhimei

    2017-03-01

    The discoveries of graphene and other related two-dimensional crystals have recently led to a new technology: van der Waals (vdW) heterostructures based on these atomically thin materials. Such a paradigm has been proved promising for a wide range of applications from nanoelectronics to optoelectronics and spintronics. Here, using first-principles calculations, we investigate the electronic structure and interface characteristics of a newly synthesized GaSe/graphene (GaSe/g) vdW heterostructure. We show that the intrinsic electronic properties of GaSe and graphene are both well preserved in the heterostructure, with a Schottky barrier formed at the GaSe/g interface. More interestingly, the band alignment between graphene and GaSe can be effectively modulated by tuning the interfacial distance or applying an external electric filed. This makes the Schottky barrier height (SBH) controllable, which is highly desirable in the electronic and optoelectronic devices based on vdW heterostructures. In particular, the tunability of the interface dipole and potential step is further uncovered to be the underlying mechanism that ensures this controllable tuning of SBH.

  17. Graphene-Hexagonal Boron Nitride Heterostructure as a Tunable Phonon–Plasmon Coupling System

    Directory of Open Access Journals (Sweden)

    Sheng Qu

    2017-02-01

    Full Text Available The layered van der Waals (vdW heterostructure, assembled from monolayer graphene, hexagonal boron nitride (h-BN and other atomic crystals in various combinations, is emerging as a new paradigm with which to attain desired electronic and optical properties. In this paper, we study theoretically the mid-infrared optical properties of the vdW heterostructure based on the graphene–h-BN system. The light–matter interaction of this heterostructure system is described by the hyperbolic phonon–plasmon polaritons which originate from the coupling modes of surface plasmon polaritons (SPPs in graphene with hyperbolic phonon polaritons (HPPs in h-BN. By numerical simulation, we find that the coupling modes are governed by the Fermi level of monolayer graphene, the thickness of the h-BN slab and the mode excitation sequence of SPPs and HPPs. Moreover, the response of the coupling modes of the graphene–h-BN heterostructure on a noble metal layer is also proposed in this paper.

  18. In situ catalytic growth of large-area multilayered graphene/MoS2 heterostructures

    Science.gov (United States)

    Fu, Wei; Du, Fei-Hu; Su, Juan; Li, Xin-Hao; Wei, Xiao; Ye, Tian-Nan; Wang, Kai-Xue; Chen, Jie-Sheng

    2014-04-01

    Stacking various two-dimensional atomic crystals on top of each other is a feasible approach to create unique multilayered heterostructures with desired properties. Herein for the first time, we present a controlled preparation of large-area graphene/MoS2 heterostructures via a simple heating procedure on Mo-oleate complex coated sodium sulfate under N2 atmosphere. Through a direct in situ catalytic reaction, graphene layer has been uniformly grown on the MoS2 film formed by the reaction of Mo species with S pecies, which is from the carbothermal reduction of sodium sulfate. Due to the excellent graphene ``painting'' on MoS2 atomic layers, the significantly shortened lithium ion diffusion distance and the markedly enhanced electronic conductivity, these multilayered graphene/MoS2 heterostructures exhibit high specific capacity, unprecedented rate performance and outstanding cycling stability, especially at a high current density, when used as an anode material for lithium batteries. This work provides a simple but efficient route for the controlled fabrication of large-area multilayered graphene/metal sulfide heterostructures with promising applications in battery manufacture, electronics or catalysis.

  19. Interface ordering and phase competition in a model Mott-insulator--band-insulator heterostructure

    OpenAIRE

    Okamoto, Satoshi; Andrew J. Millis

    2005-01-01

    The phase diagram of model Mott-insulator--band-insulator heterostructures is studied using the semiclassical approximation to the dynamical-mean-field method as a function of thickness, coupling constant, and charge confinement. An interface-stabilized ferromagnetic phase is found, allow the study of its competition and possible coexistence with the antiferromagnetic order characteristic of the bulk Mott insulator.

  20. Size and structure dependent ultrafast dynamics of plasmonic gold nanosphere heterostructures on poly (ethylene glycol) brushes

    Science.gov (United States)

    Karatay, Ahmet; Küçüköz, Betül; Pekdemir, Sami; Onses, Mustafa Serdar; Elmali, Ayhan

    2017-11-01

    We have investigated the plasmonic properties of heterostructures that consist of gold nanosphere (NSs) with average diameters of 60 nm, 40 nm and 20 nm on poly (ethylene glycol) (PEG) brushes by using ultrafast pump-probe spectroscopy experiments. Gold NSs start to behave like gold nanorods with increasing number of immobilization cycles due to the close proximity. Gold NSs immobilized by 3 and 5 deposition cycles show longitudinal modes of plasmon bands at long wavelengths which are characteristic behaviors for gold nanorods. Increasing the number of immobilization cycle also increase relaxation times of samples due to the close proximity. Linear absorption spectra and scanning electron microscopy images show that there are close packing assemblies for heterostructures containing 20 nm gold NSs as the small particle. Ultrafast electron transfer (<100 fs) occurs between transverse and longitudinal modes by exciting the samples at both 520 nm and 650 nm. Further, experimental results indicate that, heterostructures with the small particles have faster relaxation times than other heterostructures due to closed packing of 20 nm gold NSs.