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Sample records for 6h-sic mos structures

  1. Power mos devices: structures and modelling procedures

    Energy Technology Data Exchange (ETDEWEB)

    Rossel, P.; Charitat, G.; Tranduc, H.; Morancho, F.; Moncoqut

    1997-05-01

    In this survey, the historical evolution of power MOS transistor structures is presented and currently used devices are described. General considerations on current and voltage capabilities are discussed and configurations of popular structures are given. A synthesis of different modelling approaches proposed last three years is then presented, including analytical solutions, for basic electrical parameters such as threshold voltage, on-resistance, saturation and quasi-saturation effects, temperature influence and voltage handling capability. The numerical solutions of basic semiconductor devices is then briefly reviewed along with some typical problems which can be solved this way. A compact circuit modelling method is finally explained with emphasis on dynamic behavior modelling

  2. Design method for a digitally trimmable MOS transistor structure

    DEFF Research Database (Denmark)

    Ning, Feng; Bruun, Erik

    1996-01-01

    A digitally trimmable MOS transistor is a MOS transistor consisting of a drain, a source, and a main gate as well as several subgates. The transconductance of the transistor is tunabledigitally by means of connecting subgates either to the main gate or to the source terminal. In this paper......, a systematic design method for a digitally trimmable MOS transistor structure is proposed. Using the proposed method, we have designed a digitally trimmable MOS transistor structure and prototype devices were fabricated in a 2.4 micron n-well CMOS technology. Through measurements on these devices, the design...... method has been experimentally confirmed. The trimmable MOS transistor structure has been applied to a high precision current mirror to reduce mismatch in the current mirror. With the trimmable transistor structure, the mismatch can be reduced by more than one order of magnitude....

  3. C- V characterization of MOS capacitors in SOI structures

    Science.gov (United States)

    Rustagi, S. C.; Mohsen, Z. O.; Chandra, S.; Chand, A.

    1996-06-01

    The capacitance-voltage characterization of a MOS structure in the SOI film has been carried out and the results have been interpreted with the help of a numerical solution to the one-dimensional Laplace-Poisson's equation. Various parameters characterizing the SOI MOS structures have been extracted. It has been shown that the C- V data on a simple three-terminal SOI MOS capacitor structure can yield all the information such as the thickness of the gate oxide, buried-oxide as well as the SOI film, along with the doping density in the film and the substrate.

  4. Atomic and electronic structure of MoS2 nanoparticles

    DEFF Research Database (Denmark)

    Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet

    2003-01-01

    Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized at the e......Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized...

  5. Effects of radiation on MOS structures and silicon devices

    International Nuclear Information System (INIS)

    A comprehensive view of radiation effects on MOS structures and silicon devices is given. In the introduction, the interaction of radiation with semiconductor material is presented. In the next section, the electrical degradation of semiconductor devices due to this interaction is discussed. The commonly used hardening techniques are shown. The last section deals with testing of radiation hardness of devices. (orig.)

  6. Atomic and electronic structure of MoS2 nanoparticles

    OpenAIRE

    Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet

    2003-01-01

    Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized at the edges. The electronic structure of the edge states is studied and we discuss their influence on the chemical properties of the edges. In particular, we study the reactivity towards hydrogen and show th...

  7. ELECTRONIC PROPERTIES OF MOS 2 MONOLAYER AND RELATED STRUCTURES

    OpenAIRE

    ENYASHIN A.N.; Seifert, G.

    2014-01-01

    The present review provides an overview of the transition metal dichalcogenides discovered newly at the level of two dimensions. A special emphasis is given to the electronic structure of semiconducting representatives of this family, which can depend on many factors like thickness, environment, mechanical strain and structural imperfections of the layers. Both calculations and experimental data available to date on example of MoS 2 compound evidence that, semiconducting dichalcogenide layers...

  8. Band structural properties of MoS2 (molybdenite)

    International Nuclear Information System (INIS)

    Semiconductivity and superconductivity in MoS2 (molybdenite) can be understood in terms of the band structure of MoS2. The band structural properties of MoS2 are presented here. The energy dependence of nsub(eff) and epsilon(infinity)sub(eff) is investigated. Using calculated values of nsub(eff) and epsilon(infinity)sub(eff), the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of Esub(G)[(deltaEsub(G)/deltaT)sub(P)], which are in agreement with the experimental data, and the contribution to (deltaEsub(G)/deltaT)sub(P) due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation. (author)

  9. Characterization of degradation processes in MOS VLSI structures

    Science.gov (United States)

    Brozek, Tomasz; Jakubowski, Andrzej; Majkusiak, Bogdan

    1992-08-01

    The detailed investigations of degradation processes, their characterization and understanding of mechanisms responsible for degradation is of great technological interest, both from the fabrication point of view, and as a long-term reliability concern. Some of the effects usually need investigation in the completed MOS transistor structure (hot carrier degradation, threshold voltage, and channel mobility deterioration), but others should be studied with the special test structures so that effects can be investigated independently (electromigration, radiation effects, oxide wear-out). The paper presents a review of problems related to reliability of VLSI ICs, degradation processes, and their characterization.

  10. Modeling of A-DLTS Spectra of MOS Structures

    Directory of Open Access Journals (Sweden)

    Peter Hockicko

    2008-01-01

    Full Text Available Acquisition of basic characteristic of defects has become possible through a wide class of measurement techniqueswhich probe the interface, the near interface, as well as the bulk of semiconductor. Results presented here are basedessentially on the acoustic version of Deep Level Transient Spectroscopy (A-DLTS measurements. This method is based onthe acoustoelectric response effect observed at the interface. The A-DLTS uses the acoustoelectric response signal (ARSproduced by MOS structure interface when a longitudal acoustic wave propagates through a structure. The ARS is extremelysensitive to external conditions of the structure and reflects any changes in the charge distribution connected with chargedtraps. The temperature dependence of ARS after bias voltage step application is investigated and the activation energies andsome other parameters of traps at the insulator – semiconductor interface are determined. The results obtained formArrhenius plots of A-DLTS spectra of selected MOS structures are compared with results obtained from modeling of ADLTS spectra using theoretical model.

  11. Correspondence between MOS and modulation-doped structures

    Science.gov (United States)

    Pierret, R. F.; Lundstrom, M. S.

    1984-03-01

    There is currently considerable interest in the development of modulation-doped field-effect transistors suitable for high-speed applications. A promising version of the modulation-doped FET consists of a Schottky-barrier contact atop a thin Al(x)Ga(1-x)As layer on a lightly doped GaAs underlayer. It is pointed out that for a n-AlGaAs/p-GaAs structure, the conduction band discontinuity at the AlGaAs-GaAs interface gives rise to an inversion layer at the GaAs surface. The present paper is concerned with the physical correspondence between n-AlGaAs/p-GaAs modulation-doped structures and MOS structures. It is shown that certain key modulation-doped relationships can be obtained directly from MOSFET relationships.

  12. Atomic-scale structure of single-layer MoS2 nanoclusters

    DEFF Research Database (Denmark)

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.;

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2...

  13. Graphene gate electrode for MOS structure-based electronic devices.

    Science.gov (United States)

    Park, Jong Kyung; Song, Seung Min; Mun, Jeong Hun; Cho, Byung Jin

    2011-12-14

    We demonstrate that the use of a monolayer graphene as a gate electrode on top of a high-κ gate dielectric eliminates mechanical-stress-induced-gate dielectric degradation, resulting in a quantum leap of gate dielectric reliability. The high work function of hole-doped graphene also helps reduce the quantum mechanical tunneling current from the gate electrode. This concept is applied to nonvolatile Flash memory devices, whose performance is critically affected by the quality of the gate dielectric. Charge-trap flash (CTF) memory with a graphene gate electrode shows superior data retention and program/erase performance that current CTF devices cannot achieve. The findings of this study can lead to new applications of graphene, not only for Flash memory devices but also for other high-performance and mass-producible electronic devices based on MOS structure which is the mainstream of the electronic device industry.

  14. First-principles study of the structural and electronic properties of MoS2-WS2 and MoS2-MoTe2 monolayer heterostructures

    Science.gov (United States)

    Wang, Qianwen; Wu, Ping; Cao, Gengyu; Huang, Min

    2013-12-01

    Using first-principles calculations, we have systematically investigated the geometric and electronic structure of MoS2-WS2 and MoS2-MoTe2 monolayer (ML) heterostructures. Analysis of the variation of the total density of states and partial density of states of the specific atoms in the interfaces demonstrates that the two heterostructures show rather different properties and different changes from the initial MoS2 ML. The MoS2-WS2 ML heterostructure is still a semiconductor with a band gap of 1.58 eV, which is smaller than that of MoS2 and WS2 MLs. However, the strong interactions between MoS2and MoTe2 at the interfacial sites induce the MoS2-MoTe2 ML heterostructure to display metallic characteristics. Our results indicate that the ML heterostructures of MoS2-WS2 and MoS2-MoTe2 are expected to be a possible way to extend the application of the transition-metal dichalcogenides.

  15. Preparation and tunneling characteristics of MOS structures for Si-based IR light emitters

    Energy Technology Data Exchange (ETDEWEB)

    Suckow, Stephan [IHP/BTU Joint Lab., Cottbus (Germany); Kittler, Martin; Seifert, Winfried; Arguirov, Tzanimir [IHP/BTU Joint Lab., Cottbus (Germany); IHP, Frankfurt (Oder) (Germany); Schmidt, Manfred; Stegemann, Bert; Angermann, Heike [Hahn-Meitner-Institut Berlin (Germany)

    2008-07-01

    Si based light emitters, such as MOS structures based on dislocation networks, are attractive candidates for the generation of electroluminescence in the IR spectral range to be applied e.g. in optical on-chip interconnects. In the present work the preparation of an appropriate MOS structure that facilitates efficient charge carrier injection is explored and its charge carrier tunneling and recombination characteristics are analyzed. In this respect MOS structures with ultra-thin tunnel oxides fabricated by wet-chemical oxidation of Si wafers and thermally deposited Ti contacts turned out to produce the most efficient and reliable results. Moreover, electroluminescence measurements revealed an anomalous temperature behavior of band-to-band recombination with enhanced intensity at higher temperature (300 K). As photoluminescence intensity inversely increases with decreasing temperature, this effect is clearly correlated to efficient minority charge carrier injection via the MOS contact and points towards an application as room temperature IR light emitter.

  16. Influence of Deposition Conditions on the Crystal Structure of MoS2 Coating

    Institute of Scientific and Technical Information of China (English)

    Jihui WANG; Yang XIA; E.Wieers; L.M.Stals; X.Zhang; J.P.Celis

    2006-01-01

    MoS2 coatings were prepared using an unbalanced bipolar pulsed DC (direct current) magnetron sputtering apparatus under different targets, cathode current densities, power modes and bias voltages. The morphology,structure and growth characteristics of MoS2 coatings were observed and identified respectively by scanning electron microscopy, X-ray diffractometry and mass spectrometry. The results show that MoS2 coatings evolve with the (002) basal plane parallel to the surface by using cold pressed target with lower density, lower cathodic current density, bipolar pulse DC power and minus bias voltage, whereas the coatings deposited under hot pressed target, higher cathodic current density, simple DC power and positive bias voltage have the (002)basal plane perpendicular to the surface. The influence of deposition conditions on the crystal structure of MoS2 coating is implemented by altering its growth rate and the energy of sputtering-deposition particles.

  17. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2.

    Science.gov (United States)

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-12-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries.

  18. Sulfur bonding in MoS2 and Co-Mo-S structures

    DEFF Research Database (Denmark)

    Byskov, Line Sjolte; Hammer, Bjørk; Nørskov, Jens Kehlet;

    1997-01-01

    The structure and bonding in small MoS2 structures with and without Co is studied theoretically using self-consistent density functional theory with a non-local exchange-correlation energy. The structures model the catalysts used extensively in hydrotreating. We study in detail the structure...... and binding energies as a function of the amount of sulfur. The calculations show that extensive reconstructions occur at the two types of MoS2 edges where the sulfur dimerizes and occupies non-lattice positions. These structures are shown to be in good agreement with available experimental data. We also...

  19. High-pressure structure, decomposition, and superconductivity of MoS2

    Science.gov (United States)

    Kohulák, Oto; MartoÅák, Roman; Tosatti, Erio

    2015-04-01

    The high pressure structural and electronic evolution of bulk MoS2, an important transition metal layered dichalchogenide, is currently under active investigation, particularly in search of superconductivity. Recent theoretical and experimental work predicted and verified a 2 Hc→2 Ha layer sliding structural transition at 20 GPa and a band overlap semiconductor-semimetal transition in the same pressure range. The poorly metallic and nonsuperconducting 2 Ha structure is known to persist up to a pressure of 81 GPa, but properties at higher pressures remain experimentally unknown. Here we predict, with a first-principles evolutionary search, that major structural and electronic transformations should take place in equilibrium at higher pressures near 130-140 GPa. The main motif is a decomposition into MoS + S, also heralded in a small bimolecular cell by the appearance of a metastable nonlayered metallic MoS2 structure with space group P 4 /m m m . Unlike semimetallic 2 Ha -MoS2, the new high pressure phases are expected to be fully metallic and superconducting with higher critical temperatures than even alkali-intercalated MoS2.

  20. Capturing Ion-Solid Interactions with MOS structures

    Science.gov (United States)

    Shyam, R.; Harrell, W. R.; Harriss, J. E.; Sosolik, C. E.

    2012-02-01

    We have fabricated metal-oxide-semiconductor (MOS) devices for a study of implantation rates and damage resulting from low energy ion-solid impacts. Specifically, we seek to capture ion irradiation effects on oxides by exposing as-grown SiO2 layers (50 nm to 200 nm) to incident beams of alkali ions with energies in the range of 100 eV to 10 keV. The oxide is analyzed post exposure by encapsulating the irradiated region under a top metallic contact or within a finished MOS device. Characterization of the resulting ion-modified MOS device involves the standard techniques of room temperature and bias-dependent capacitance-voltage (C-V) measurements. The C-V results reveal alkali ion-induced changes in the flatband voltage of irradiated devices which can be used to extract both the range and implantation probabilities of the ions. Biased C-V measurements are utilized to confirm the concentration or dosage of ions in the oxide. A triangular voltage sweep (TVS) measurement at elevated temperatures also reveals the total ionic space charge in the oxide and can be used to extract a mobility for the ions as they pass through the damaged oxide. Comparisons of these measurements to standard device models as well as to ion range calculations in the oxide are presented.

  1. Fabrication and atomic structure of size-selected, layered MoS2 clusters for catalysis.

    Science.gov (United States)

    Cuddy, Martin J; Arkill, Kenton P; Wang, Zhi Wei; Komsa, Hannu-Pekka; Krasheninnikov, Arkady V; Palmer, Richard E

    2014-11-01

    Well defined MoS2 nanoparticles having a layered structure and abundant edges would be of considerable interest for applications including photocatalysis. We report the atomic structure of MoS2 size-selected clusters with mass in a range all the way from 50 to ∼2000 MoS2 units. The clusters were prepared by magnetron sputtering and gas condensation prior to size selection and soft landing on carbon supports. Aberration-corrected scanning transmission electron microscopy (STEM) in high-angle annular dark-field (HAADF) mode reveals a layered structure and Mo-Mo spacing similar to the bulk material. The mean number of layers in these lamellar clusters increases from one to three with increasing mass, consistent with density functional theory calculations of the balance between edge energies and interlayer binding. PMID:25226541

  2. Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)

    Science.gov (United States)

    2016-01-01

    Monolayers of transition metal dichalcogenides are interesting materials for optoelectronic devices due to their direct electronic band gaps in the visible spectral range. Here, we grow single layers of MoS2 on Au(111) and find that nanometer-sized patches exhibit an electronic structure similar to their freestanding analogue. We ascribe the electronic decoupling from the Au substrate to the incorporation of vacancy islands underneath the intact MoS2 layer. Excitation of the patches by electrons from the tip of a scanning tunneling microscope leads to luminescence of the MoS2 junction and reflects the one-electron band structure of the quasi-freestanding layer. PMID:27459588

  3. Van der Waals trilayers and superlattices: Modification of electronic structures of MoS2 by intercalation

    OpenAIRE

    Lu, N.; Guo, H. Y.; L. Wang; Wu, X. J.; Zeng, X. C.

    2014-01-01

    We perform a comprehensive first-principles study of the electronic properties of van der Waals (vdW) trilayers via intercalating a two-dimensional (2D) monolayer (ML = BN, MoSe2, WS2, or WSe2) between MoS2 bilayer to form various MoS2/ML/MoS2 sandwich trilayers. We find that the BN monolayer is the most effective sheet to decouple the interlayer vdW coupling of the MoS2 bilayer, and the resulting sandwich trilayer can recover the electronic structures of the MoS2 monolayer, particularly the ...

  4. Software structure and its performance on FOCAS instrument control, a MOS design, and an analyzing package

    Science.gov (United States)

    Yoshida, Michitoshi; Shimizu, Yasuhiro; Sasaki, Toshiyuki; Kosugi, George; Takata, Tadafumi; Sekiguchi, Kazuhiro; Kashikawa, Nobunari; Aoki, Kentaro; Asai, Ryo; Ohyama, Youichi; Kawabata, Koji; Inata, Motoko; Saito, Yoshihiko; Taguchi, Hiroko; Ebizuka, Noboru; Yadoumaru, Yasushi; Ozawa, Tomohiko; Iye, Masanori

    2000-06-01

    Faint Object Camera And Spectrograph (FOCAS) is completed and now waiting for a commissioning run on the Subaru Telescope atop Mauna Kea. We have developed a software system that includes the control of FOCAS instruments, Multiple Object Slits (MOS) design, and an analyzing package especially for evaluating performances of FOCAS. The control software system consists of several processes: a network interface process, user interface process, a central control engine process, a command dispatcher process, local control units, and a data acquisition system. These processes are mutually controlled by passing messages of commands and their status each other. The control system is also connected to Subaru Observation Software System to achieve high efficiency and reliability of observations. We have two off-line systems: a MOS design program, MDP, and an analyzing package. The MDP is a utility software to select spectroscopy targets in the field of view of FOCAS easily through its GUI and to design MOS plates efficiently. The designed MOS parameters are sent to a laser cutter to make a desirable MOS plate. A special package enables prompt performance check and evaluation of the FOCAS itself during a commissioning period. We describe the overall structure of FOCAS software with some GUI samples.

  5. Atomic-scale structure of single-layer MoS2 nanoclusters

    OpenAIRE

    Helveg, S.; Lauritsen, J.V.; Lægsgaard, E.; Stensgaard, I.; Nørskov, Jens Kehlet; Clausen, B.S, Helveg S; Topsøe, H.; Besenbacher, Flemming

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2 nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in ...

  6. Effect of monolayer supports on the electronic structure of single-layer MoS2

    Science.gov (United States)

    Ramirez-Torres, Alfredo; Le, Duy; Rahman, Talat S.

    2015-03-01

    We present results of density functional theory based calculations of the electronic structure of a single-layer of MoS2, as modified by three different single-layer materials used as support: hexagonal boron nitride (h-BN), graphene, and silicene, using the local density approximation (LDA), on the one hand, and a functional that explicitly includes van der Waals interactions (optB88-vdW), on the other hand. Because the lattice mismatch between the primitive cell of MoS2 and those of the supports is large, calculations are performed with as large a supercell as computationally feasible, so as to reduce the incommensurability between lattices. Even though van der Waals interactions are expected to play an important role in the binding between MoS2, and h-BN and graphene, we find that the band structure and related conclusions obtained by optB88-vdW and LDA are quite similar for the three heterostructures considered here. Single-layer MoS2 interacts weakly with h-BN and graphene, while covalent bonds are formed with silicene. Detailed analysis of the electronic density of states also indicates little effect of h-BN and graphene, while silicene severely modifies it by introducing additional states within the band gap. Furthermore, adsorption on graphene brings the conduction bands of MoS2 down to the Fermi level of graphene as a result of charge transfer from graphene to MoS2, while adsorption on silicene shifts both valence and conduction bands towards the Fermi level, in addition to inducing a gap of ~50 meV in silicene itself.

  7. Modeling of tunneling current in ultrathin MOS structure with interface trap charge and fixed oxide charge

    Institute of Scientific and Technical Information of China (English)

    Hu Bo; Huang Shi-Hua; Wu Feng-Min

    2013-01-01

    A model based on analysis of the self-consistent Poisson-Schrodinger equation is proposed to investigate the tunneling current of electrons in the inversion layer of a p-type metal-oxide-semiconductor (MOS) structure.In this model,the influences of interface trap charge (ITC) at the Si-SiO2 interface and fixed oxide charge (FOC) in the oxide region are taken into account,and one-band effective mass approximation is used.The tunneling probability is obtained by employing the transfer matrix method.Further,the effects of in-plane momentum on the quantization in the electron motion perpendicular to the Si-SiO2 interface of a MOS device are investigated.Theoretical simulation results indicate that both ITC and FOC have great influence on the tunneling current through a MOS structure when their densities are larger than 1012 cm-2,which results from the great change of bound electrons near the Si-SiO2 interface and the oxide region.Therefore,for real ultrathin MOS structures with ITC and FOC,this model can give a more accurate description for the tunneling current in the inversion layer.

  8. Defect assisted coupling of a MoS2/TiO2 interface and tuning of its electronic structure

    Science.gov (United States)

    Chen, Guifeng; Song, Xiaolin; Guan, Lixiu; Chai, Jianwei; Zhang, Hui; Wang, Shijie; Pan, Jisheng; Tao, Junguang

    2016-09-01

    Although MoS2 based heterostructures have drawn increased attention, the van der Waals forces within MoS2 layers make it difficult for the layers to form strong chemical coupled interfaces with other materials. In this paper, we demonstrate the successful strong chemical attachment of MoS2 on TiO2 nanobelts after appropriate surface modifications. The etch-created dangling bonds on TiO2 surfaces facilitate the formation of a steady chemically bonded MoS2/TiO2 interface. With the aid of high resolution transmission electron microscope measurements, the in-plane structure registry of MoS2/TiO2 is unveiled at the atomic scale, which shows that MoS2[1-10] grows along the direction of TiO2[001] and MoS2[110] parallel to TiO2[100] with every six units of MoS2 superimposed on five units of TiO2. Electronically, type II band alignments are realized for all surface treatments. Moreover, the band offsets are delicately correlated to the surface states, which plays a significant role in their photocatalytic performance.

  9. Asymmetric Gate(AG)MOS Device:A Novel Field Effect Transistor(FET) Structure

    Institute of Scientific and Technical Information of China (English)

    YANGShengqi; HEJin; HUANGRu; ZHANGXing

    2003-01-01

    A novel fleld effect transistor(FET),named asymmetric gate(AG)MOS device,is proposed in this paper and its excellent performance is demonstrated numericall.Compared with the conventional MOSFET,the presented AG one benefits more from the special design of gate oxide which is divided into two regions,with one region at the source side thicker than that at the drain side.Two-dimensional (2-D)numerical simulations have proved that the short-channel effects(SCE)and the draininduced barrier lowering(DIBL)can be greatly suppressed just because the channel is screened from the drain potential variations via the unique gate oxide design.Also,a significant electron velocity overshoot is achieved,resulting in higher driving current in the novel structure.It shows that the AG structure will be one of the promising structures in design of MOS devices.

  10. MOS structure fabrication by thermal oxidation of multilayer metal thin films

    Institute of Scientific and Technical Information of China (English)

    Mohammad Orvatiniat; Atefeh Chahkoutahi

    2011-01-01

    A novel approach for the fabrication of a metal oxide semiconductor (MOS) structure was reported.The process comprises electrochemical deposition of aluminum and zinc layers on a base of nickel-chromium alloy.This two-layer structure was thermally oxidized at 400 ℃ for 40 min to produce thin layers of aluminum oxide as an insulator and zinc oxide as a semiconductor on a metallic substrate.Using deposition parameters,device dimensions and SEM micrographs of the layers,the device parameters were calculated.The resultant MOS structure was characterized by a C-V curve method.From this curve,the device maximum capacitance and threshold voltage were estimated to be about 0.74 nF and -2.9 V,respectively,which are in the order of model-based calculations.

  11. Surface Passivation of Germanium Using NH3 Ambient in RTP for High Mobility MOS Structure

    Directory of Open Access Journals (Sweden)

    Anil G. Khairnar

    2013-05-01

    Full Text Available Ge CMOS is very striking for the post Si-CMOS technology. However, we have to attempt a number of challenges with regard to materials and their interface control. In this paper we have investigated the control of the interfacial properties of SiO2 / Ge gate stack structures by the thermal nitridation technique. Structural and electrical properties of SiO2 gate-dielectric metal-oxide-semiconductor (MOS capacitors deposited by sputtering on germanium are studied. The structural characterization confirmed that the thin film was free of physical defects and smooth surface of the films after PDA at 500 °C in N2 ambient. The smooth surface SiO2 thin films were used for Pt / SiO2 / GeON / Ge MOS structures fabrication. The MOS structure yields a low leakage current density of 9.16 × 10 – 6Acm – 2 at 1 V.

  12. New strategy of modeling inversion layer characteristics in MOS structure for ULSI applications

    Institute of Scientific and Technical Information of China (English)

    马玉涛; 李志坚; 刘理天

    2001-01-01

    With the development of ULSI silicon technology, metal oxide semiconductor field effect transistor (MOSFET) devices are scaling down to nanometer regime. Energy of carriers in inversion layer in MOS structure is quantized and consequently, the physics and then the transport characteristics of inversion layer carriers are different from those in semi-classical theory. One essential matter is that the widely used concept of conduction band (valence band as well) effective density-of-states is no longer valid in quantized inversion layer. In this paper, an alternative concept, called surface layer effective density-of-states, is used to model the characteristics of MOS structure including threshold voltage, carrier sheet density, surface potential as well as capacitance.

  13. C-VCharacterization in MOS Structure Inversion Layer Including Quantum Mechanical Effects

    Institute of Scientific and Technical Information of China (English)

    马玉涛; 刘理天; 李志坚

    2000-01-01

    A simplified method to calculate the band bending and subband energy is presented to investigate the Quantum Mechanical Effects (QMEs) in MOS structure inversion layer. The method is fairly unique compared with the published methods in the reversed nature of the iteration procedure. It has high efficiency and good convergence characteristics. Gate capacitance in MOS structure inversion region is formulated in both quantum mechanical cases and semi-classical cases and Quantum Mechanical Effects on gate capacitance have been analyzed. Results of different substrate doping levels are compared and the substrate doping concentration dependence of QMEs on gate capacitance is studied. It is shown that QMEs lead to a substantial decrease in gate capacitance in the strong inversion region. Results of different substrate doping levels indicate that the QMEs on gate capacitance are different substantially in the threshold region at different substrate doping levels but almost the same in the strong inversion region.

  14. Effects of Organic Molecules with Different Structures and Absorption Bandwidth on Modulating Photoresponse of MoS2 Photodetector.

    Science.gov (United States)

    Huang, Yanmin; Zheng, Wei; Qiu, Yunfeng; Hu, PingAn

    2016-09-01

    Organic dye molecules possessing modulated optical absorption bandwidth and molecular structures can be utilized as sensitizing species for the enhancement of photodetector performance of semiconductor via photoinduced charge transfer mechanism. MoS2 photodetector were modified by drop-casting of methyl orange (MO), rhodamine 6G (R6G), and methylene blue (MB) with different molecular structures and extinction coefficients, and enhanced photodetector performance in terms of photocurrent, photoresponsity, photodetectivity, and external quantum efficiency were obtained after modification of MO, R6G, and MB, respectively. Furthermore, dyes showed different modulating abilities for photodetector performance after combination with MoS2, mainly due to the variation of molecular structures and optical absorption bandwidth. Among tested dyes, deposition of MB onto monolayer MoS2 grown by CVD resulted in photocurrent ∼20 times as high as pristine MoS2 due to favorable photoinduced charge transfer of photoexcited electrons from flat MB molecules to the MoS2 layer. Meanwhile, the corresponding photoresponsivity, photodetectivity, and an external quantum efficiency are 9.09 A W(1-), 2.2 × 10(11) Jones, 1729% at 610 nm, respectively. Photoinduced electron-transfer measurements of the pristine MoS2 and dye-modified MoS2 indicated the n-doping effect of dye molecules on the MoS2. Additionally, surface-enhanced Raman measurements also confirmed the direct correlation with charge transfer between organic dyes and MoS2 taking into account the chemically enhanced Raman scattering mechanism. Present work provides a new clue for the manipulation of high-performance of two-dimensional layered semiconductor-based photodetector via the combination of organic dyes.

  15. Utilization of monolayer MoS2 in Bragg stacks and metamaterial structures as broadband absorbers

    Science.gov (United States)

    Mukherjee, Bablu; Simsek, Ergun

    2016-06-01

    We numerically study the possibility of using atomically thin transition metal dichalcogenides (TMDs) for applications requiring broadband absorption in the visible range of the electromagnetic spectrum. We demonstrate that when monolayer TMDs are positioned into a finite-period of multilayer Bragg stack geometry, they make broadband, wide-angle, almost polarization-independent absorbers. In our study, we consider molybdenum disulfide (MoS2) and silicon dioxide (SiO2) as semiconducting and dielectric thin film of alternate high- and low- index films, respectively. By optimizing the thickness of the SiO2 film, we find that monolayer MoS2 based Bragg stacks can absorb 94.7% of the incident energy in the visible (350-700 nm). Similar structures can be engineered to make perfect reflectors for saturable absorption applications. We also demonstrate that bandwidth of metamaterial absorbers can be expanded using monolayer TMDs.

  16. Formation of oxide-trapped charges in 6H-SiC MOS structures

    Energy Technology Data Exchange (ETDEWEB)

    Yoshikawa, Masahito; Ohshima, Takeshi; Itoh, Hisayoshi; Nashiyama, Isamu [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; Okumura, Hajime; Yoshida, Sadafumi

    1997-03-01

    The silicon and the carbon faces of hexagonal silicon carbide (6H-SiC) substrates were oxidized pyrogenically at 1100degC, and the metal-oxide-semiconductor structures were formed on these faces. The MOS capacitors developed using the silicon and the carbon faces were irradiated with {sup 60}Co gamma-rays under argon atmosphere at room temperature. The bias voltages with the different polarity were applied to the gate electrode during irradiation to examine the formation mechanisms of the trapped charges in the oxides of these MOS capacitors. The amount of the trapped charges in the oxide were obtained from capacitance pulse voltage characteristics. The generation of the trapped charges are affects with not only the absorbed dose but also the bias polarity applied to the gate electrodes during irradiation. The formation mechanisms of the trapped charges in the oxides were estimated in conjunction with the surface orientation of 6H-SiC substrates. (author)

  17. Surface Passivation of Germanium Using NH3 Ambient in RTP for High Mobility MOS Structure

    OpenAIRE

    Anil G. Khairnar; Y.S. Mhaisagar; A.M. Mahajan

    2013-01-01

    Ge CMOS is very striking for the post Si-CMOS technology. However, we have to attempt a number of challenges with regard to materials and their interface control. In this paper we have investigated the control of the interfacial properties of SiO2 / Ge gate stack structures by the thermal nitridation technique. Structural and electrical properties of SiO2 gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering on germanium are studied. The structural characterizatio...

  18. Fundamental insights into the electronic structure of zigzag MoS2 nanoribbons.

    Science.gov (United States)

    Yu, Shansheng; Zheng, Weitao

    2016-02-14

    The structural and electronic properties of zigzag MoS2 nanoribbons are investigated using first-principles density functional theory. Our models are motivated by the experimental observations, in which both Mo edges are terminated by S atoms. Our calculations show that the edge can introduce some extra states into the energy gap, which lead nanoribbons to exhibit a metallic characteristic. Such extra states around the Fermi level are flat or dispersed. Through detailed analyses, we identify and discriminate them based on the major contributors. By applying an external transverse electric field, Eext the extra states around the Fermi level can shift apparently, especially for those attributed to Mo-edge atoms. It can be explained by the charge redistribution in the MoS2 nanoribbons due to Eext. In addition, the nanoribbon can be changed from metal to an n/p-type semiconductor according to different edge hydrogenation. After full edge hydrogenation, we observe a characteristic of anti-bonding orbitals between H and S atoms at the Mo-edge. Interestingly, the energy of anti-bonding orbitals and electric conductivity of nanoribbons can be tailored by Eext. The results suggest a strategy controlling the performance of MoS2 for hydrogen evolution. PMID:26799649

  19. A MOS tunneling structure used as a photosensitive device with internal gain

    International Nuclear Information System (INIS)

    Avalanche photodiodes used in photosensitive devices with internal gain suffer some limitations due to their doping profiles and the reproducibility of their internal gain. Experiments were made on devices using very thin layers of SiO2. The basic structure being a MOS capacitance, it was shown that such a structure provides an internal gain when minority carriers are injected within the deep depletion layer just beneath the thin oxide in the silicon. Experimal results obtained on devices built using either aluminum and chromium electrodes are presented

  20. Toward epitaxially grown two-dimensional crystal hetero-structures: Single and double MoS2/graphene hetero-structures by chemical vapor depositions

    Science.gov (United States)

    Lin, Meng-Yu; Chang, Chung-En; Wang, Cheng-Hung; Su, Chen-Fung; Chen, Chi; Lee, Si-Chen; Lin, Shih-Yen

    2014-08-01

    Uniform large-size MoS2/graphene hetero-structures fabricated directly on sapphire substrates are demonstrated with layer-number controllability by chemical vapor deposition (CVD). The cross-sectional high-resolution transmission electron microscopy (HRTEM) images provide the direct evidences of layer numbers of MoS2/graphene hetero-structures. Photo-excited electron induced Fermi level shift of the graphene channel are observed on the single MoS2/graphene hetero-structure transistors. Furthermore, double hetero-structures of graphene/MoS2/graphene are achieved by CVD fabrication of graphene layers on top of the MoS2, as confirmed by the cross-sectional HRTEM. These results have paved the possibility of epitaxially grown multi-hetero-structures for practical applications.

  1. Prediction of new stable structure, promising electronic and thermodynamic properties of MoS3: Ab initio calculations

    Science.gov (United States)

    Pan, Yong; Guan, Weiming

    2016-09-01

    MoS3 has attracted considerable attention as potential hydrogen storage material due to the interaction between the hydrogen and unsaturated sulfur atoms. However, its structure and physical properties are unknown. By means of first-principles approach and Inorganic crystal structure Database (ISCD), we systematically investigated the structure, relevant physical and thermodynamic properties of MoS3. Phonon dispersion, electronic structure, band structure and heat capacity are calculated in detail. We predicted the orthorhombic B2ab (SrS3-type) and tetragonal P-421m (BaS3-type) structures of MoS3, which prefers to form the SrS3-type (Space group: B2ab, No.41) structure at the ground state. High pressure results in structural transition from SrS3-type structure to BaS3-type structure. This sulfide exhibits a degree of metallic behavior. The calculated heat capacity of MoS3 with SrS3-type structure is about of 39 J/(mol·K).

  2. Synthesis and Structural Characterization of Al2O3-Coated MoS2 Spheres for Photocatalysis Applications

    Directory of Open Access Journals (Sweden)

    S. V. Prabhakar Vattikuti

    2015-01-01

    Full Text Available This paper reports the synthesis of novel monodisperse Al2O3-coated molybdenum disulfide nanospheres (i.e., core-shell structures using a one-step facile hydrothermal method. XPS analysis confirmed the purity and stable structure of the Al2O3-coated MoS2 nanospheres. A possible growth mechanism of the core-shell structure is also reported, along with their influence on the photodegradation process of rhodamine B (RhB. The Al2O3-coated MoS2 nanospheres demonstrate good photocatalytic activity and chemical stability compared to MoS2 spheres. TG-DTA analysis provided insight into the decomposition process of the precursor solution and the stability of the nanoparticles. The enhanced photocatalytic activity makes the Al2O3-coated MoS2 nanospheres a promising candidate as a photocatalyst that could be used in place of traditional Al2O3/MoS2 photocatalyst for the removal of pollutants from waste water.

  3. Evolution of band structures in MoS2-based homo- and heterobilayers

    International Nuclear Information System (INIS)

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  −  Q C) and ΔE(K V  −  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  −  Q C) and ΔE(K V  −  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  −1.6% to  −1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices. (paper)

  4. Evolution of band structures in MoS2-based homo- and heterobilayers

    Science.gov (United States)

    Zhu, H. L.; Zhou, C. J.; Huang, X. J.; Wang, X. L.; Xu, H. Z.; Lin, Yong; Yang, W. H.; Wu, Y. P.; Lin, W.; Guo, F.

    2016-02-01

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  -  Q C) and ΔE(K V  -  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  -  Q C) and ΔE(K V  -  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  -1.6% to  -1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices.

  5. Exploring biological effects of MoS2 nanosheets on native structures of α-helical peptides

    Science.gov (United States)

    Gu, Zonglin; Li, Weifeng; Hong, Linbi; Zhou, Ruhong

    2016-05-01

    Recent reports of mono- and few-layer molybdenum disulfide (MoS2), a representative transition metal dichacogenide (TMD), as antibacterial and anticancer agents have shed light on their potential in biomedical applications. To better facilitate these promising applications, one needs to understand the biological effects of these TMDs as well, such as their potential adverse effects on protein structure and function. Here, we sought to understand the interaction of MoS2 nanosheets with peptides using molecular dynamics simulations and a simple model polyalanine with various lengths (PAn, n = 10, 20, 30, and 40; mainly α - helices). Our results demonstrated that MoS2 monolayer has an exceptional capability to bind all peptides in a fast and strong manner. The strong attraction from the MoS2 nanosheet is more than enough to compensate the energy needed to unfold the peptide, regardless of the length, which induces drastic disruptions to the intra-peptide hydrogen bonds and subsequent secondary structures of α - helices. This universal phenomenon may point to the potential nanotoxicity of MoS2 when used in biological systems. Moreover, these results aligned well with previous findings on the potential cytotoxicity of TMD nanomaterials.

  6. Monolithic Silicon Photodetector - Detector of Ionizing Radiation Based on Functional Integrated MOS Structures

    Directory of Open Access Journals (Sweden)

    S.A. Legotin

    2014-07-01

    Full Text Available This paper describes the principle of operation, construction, architecture and fabrication of a new type of monolithic silicon coordinate photodetector - detector of optical and ionizing radiation (MSCP on the basis of functional integrated MOS structures. The analytical estimation of electrophysical characteristics MSCP is given. It is shown that MSCP is a specialized monolithic silicon VLSI containing two-dimensional pixel array with high and low voltage functionally integrated structures (FIS and peripheral electronic circuits of amplification and signal processing matrix. Estimations and presents comparative characteristics are presented. They show potential MSCP possibilities for registration of optical and ionizing radiation. Experimental results of α-particles and electrons registration. The possible areas of application, with the possibility of its use in a wide X-ray panels medical supplies, X-rays, etc are considered.

  7. High frequency characteristics and modelling of p-type 6H-silicon carbide MOS structures

    Science.gov (United States)

    Fernández, J.; Godignon, P.; Berberich, S.; Rebollo, J.; Brezeanu, G.; Millán, J.

    1996-09-01

    This paper presents the high frequency electrical characteristics and modelling of Al/SiO 2/ p-type 6HSiC structures. The oxide was thermally grown under dry conditions. Capacitance and conductance vs bias and frequency measurements have been performed in daylight and exposing the capacitors to u.v. light. The experimental Cm- Vg and Gm- Vg characteristics show hysteresis effects, which are more important when the samples are exposed to 254 nm u.v. light. This behaviour can be explained in terms of interface traps. The MOS structure modelling is based on an interface trap model in which the interface trap levels are considered to be continuously distributed in the SiC bandgap and only charge exchange between interface trap levels and the SiC bands is allowed. From this formulation and from the Gm- f characteristics, the interface state density and the interface trap time constant have been determined.

  8. The intrinsic defect structure of exfoliated MoS2 single layers revealed by Scanning Tunneling Microscopy

    Science.gov (United States)

    Vancsó, Péter; Magda, Gábor Zsolt; Pető, János; Noh, Ji-Young; Kim, Yong-Sung; Hwang, Chanyong; Biró, László P.; Tapasztó, Levente

    2016-01-01

    MoS2 single layers have recently emerged as strong competitors of graphene in electronic and optoelectronic device applications due to their intrinsic direct bandgap. However, transport measurements reveal the crucial role of defect-induced electronic states, pointing out the fundamental importance of characterizing their intrinsic defect structure. Transmission Electron Microscopy (TEM) is able to image atomic scale defects in MoS2 single layers, but the imaged defect structure is far from the one probed in the electronic devices, as the defect density and distribution are substantially altered during the TEM imaging. Here, we report that under special imaging conditions, STM measurements can fully resolve the native atomic scale defect structure of MoS2 single layers. Our STM investigations clearly resolve a high intrinsic concentration of individual sulfur atom vacancies, and experimentally identify the nature of the defect induced electronic mid-gap states, by combining topographic STM images with ab intio calculations. Experimental data on the intrinsic defect structure and the associated defect-bound electronic states that can be directly used for the interpretation of transport measurements are essential to fully understand the operation, reliability and performance limitations of realistic electronic devices based on MoS2 single layers. PMID:27445217

  9. Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board the XMM/NEWTON satellite

    International Nuclear Information System (INIS)

    We have used a mesh experiment in order to measure the sub-pixel structure of the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40 μm-square pixels which have an open electrode structure in order to improve the detection efficiency for low-energy X-rays. We obtained restored pixel images for various X-ray event grades (e.g. split-pixel events, single pixel events, etc.) at various X-ray energies. We confirmed that the open electrode structure results in a distorted horizontal pixel boundary. The open electrode region generates both single pixel events and vertically split events, but no horizontally split events. Because the single pixel events usually show the best energy resolution, we discuss a method of increasing the fraction of single pixel events from the open electrode region. Furthermore, we have directly measured the thickness of the electrodes and dead-layers by comparing spectra from the open electrode region with those from the other regions: electrodes, electrode finger and channel stop. We can say that EPIC MOS CCDs are more radiation hard than front-illumination chips of ACIS on-board Chandra X-ray Observatory because of their extra absorption thickness above the charge transfer channel. We calculated the mean pixel response and found that our estimation has a good agreement with that of the ground calibration of EPIC MOS CCD

  10. Effect of size and position of gold nanocrystals embedded in gate oxide of SiO2/Si MOS structures

    Science.gov (United States)

    Chakraborty, Chaitali; Bose, Chayanika

    2016-02-01

    The influence of single and double layered gold (Au) nanocrystals (NC), embedded in SiO2 matrix, on the electrical characteristics of metal-oxide-semiconductor (MOS) structures is reported in this communication. The size and position of the NCs are varied and study is made using Sentaurus TCAD simulation tools. In a single NC-layered MOS structure, the role of NCs is more prominent when they are placed closer to SiO2/Si‑substrate interface than to SiO2/Al-gate interface. In MOS structures with larger NC dots and double layered NCs, the charge storage capacity is increased due to charging of the dielectric in the presence of NCs. Higher breakdown voltage and smaller leakage current are also obtained in the case of dual NC-layered MOS device. A new phenomenon of smearing out of the capacitance-voltage curve is observed in the presence of dual NC layer indicating generation of interface traps. An internal electric field developed between these two charged NC layers is expected to generate such interface traps at the SiO2/Si interface.

  11. Interface studies of the MOS-structure by transfer-admittance measurements

    NARCIS (Netherlands)

    Koomen, Jan

    1974-01-01

    The transfer-admittance of n- and p-channel MOS transistors has been measured under the condition of a uniform channel. These MOS transistors all showed a measurable “slow interface state drift” <0·1–0·2 V. The transfer-susceptance has been found to show a significant peak value in moderate inversio

  12. Structural Phase Transition Effect on Resistive Switching Behavior of MoS2 -Polyvinylpyrrolidone Nanocomposites Films for Flexible Memory Devices.

    Science.gov (United States)

    Zhang, Peng; Gao, Cunxu; Xu, Benhua; Qi, Lin; Jiang, Changjun; Gao, Meizhen; Xue, Desheng

    2016-04-01

    The 2H phase and 1T phase coexisting in the same molybdenum disulfide (MoS2 ) nanosheets can influence the electronic properties of the materials. The 1T phase of MoS2 is introduced into the 2H-MoS2 nanosheets by two-step hydrothermal synthetic methods. Two types of nonvolatile memory effects, namely write-once read-many times memory and rewritable memory effect, are observed in the flexible memory devices with the configuration of Al/1T@2H-MoS2 -polyvinylpyrrolidone (PVP)/indium tin oxide (ITO)/polyethylene terephthalate (PET) and Al/2H-MoS2 -PVP/ITO/PET, respectively. It is observed that structural phase transition in MoS2 nanosheets plays an important role on the resistive switching behaviors of the MoS2 -based device. It is hoped that our results can offer a general route for the preparation of various promising nanocomposites based on 2D nanosheets of layered transition metal dichalcogenides for fabricating the high performance and flexible nonvolatile memory devices through regulating the phase structure in the 2D nanosheets.

  13. Effects of particle size and edge structure on the electronic structure, spectroscopic features, and chemical properties of Au(111)-supported MoS2 nanoparticles.

    Science.gov (United States)

    Bruix, Albert; Lauritsen, Jeppe V; Hammer, Bjørk

    2016-07-01

    Materials based on MoS2 are widely used as catalysts and their structure usually consists of single-layered MoS2 nanoparticles whose edges are known to constitute the catalytically active sites. Methods based on density functional theory are used in this work to calculate the electronic structure of representative computational models of MoS2 nanoparticles supported on Au(111). By considering nanoparticles with different edge-terminations, compositions, and sizes, we describe how the electronic structure, Mo3d core-level shifts, and chemical properties (i.e. H adsorption and S vacancy formation) depend on the MoS2 nanoparticle size and structure. In addition, site-specific properties, largely inaccessible when using only slab models of MoS2 edges, are reported, which reveal that the edge sites are not uniform along the nanoparticle and largely depend on the proximity to the corners of the triangular NPs, especially when interacting with a metallic support. Furthermore, a structural motif where H atoms adsorb favourably in a bridging position between two Mo atoms is proposed as an active site for the hydrogen evolution reaction. PMID:27076269

  14. Changes in the composition, structure and friction property of sputtered MoS2 films by LEO environment exposure

    International Nuclear Information System (INIS)

    Highlights: • Sputtered MoS2 films were exposed in real low earth orbit (LEO) environment. • LEO exposure resulted in the oxidation and S loss of MoS2 film surface. • Depth affected by the LEO exposure was limited within 10 nm. • The exposed MoS2 film exhibited a slight increase in friction coefficient at initial sliding stage. - Abstract: Radio frequency-sputtered MoS2 films had been exposed for 43.5 h in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard China Shenzhou-7 manned spaceship. The composition, morphology, phase structure and friction property of the exposed films were investigated using X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray energy-dispersive spectroscopy (EDS) and ball-on-disk tribometer. XRD and EDS results revealed that the as-deposited MoS2 films were characterized by a MoSxOy phase structure, in which x and y values were determined to be ∼0.65 and 1.24, respectively. XPS analysis revealed that due to space atomic oxygen attack, the film surface was oxidized to MoO3 and MoSxOy with higher O concentration, while the partial S was lost. However, the affected depth was restricted within the surface layer because of protective function of the oxidation layer. As a result, the friction coefficient only exhibited a slight increase at initial stage of sliding friction

  15. Nanoimprint-Assisted Shear Exfoliation (NASE) for Producing Multilayer MoS2 Structures as Field-Effect Transistor Channel Arrays.

    Science.gov (United States)

    Chen, Mikai; Nam, Hongsuk; Rokni, Hossein; Wi, Sungjin; Yoon, Jeong Seop; Chen, Pengyu; Kurabayashi, Katsuo; Lu, Wei; Liang, Xiaogan

    2015-09-22

    MoS2 and other semiconducting transition metal dichalcogenides (TMDCs) are of great interest due to their excellent physical properties and versatile chemistry. Although many recent research efforts have been directed to explore attractive properties associated with MoS2 monolayers, multilayer/few-layer MoS2 structures are indeed demanded by many practical scale-up device applications, because multilayer structures can provide sizable electronic/photonic state densities for driving upscalable electrical/optical signals. Currently there is a lack of processes capable of producing ordered, pristine multilayer structures of MoS2 (or other relevant TMDCs) with manufacturing-grade uniformity of thicknesses and electronic/photonic properties. In this article, we present a nanoimprint-based approach toward addressing this challenge. In this approach, termed as nanoimprint-assisted shear exfoliation (NASE), a prepatterned bulk MoS2 stamp is pressed into a polymeric fixing layer, and the imprinted MoS2 features are exfoliated along a shear direction. This shear exfoliation can significantly enhance the exfoliation efficiency and thickness uniformity of exfoliated flakes in comparison with previously reported exfoliation processes. Furthermore, we have preliminarily demonstrated the fabrication of multiple transistors and biosensors exhibiting excellent device-to-device performance consistency. Finally, we present a molecular dynamics modeling analysis of the scaling behavior of NASE. This work holds significant potential to leverage the superior properties of MoS2 and other emerging TMDCs for practical scale-up device applications. PMID:26302003

  16. Depth profiling of oxide-trapped charges in 6H-SiC MOS structures by slant etching method

    Energy Technology Data Exchange (ETDEWEB)

    Saitoh, Kazunari; Takahashi, Yoshihiro; Ohnishi, Kazunori [Nihon Univ., Tokyo (Japan). Coll. of Science and Technology; Yoshikawa, Masahito; Ohshima, Takeshi; Itoh, Hisayoshi; Nashiyama, Isamu

    1997-03-01

    In this paper, we propose a method to evaluate the depth profile of trapped charges in an oxide layer on SiC. Using this method, 6H-SiC MOS structures with different oxide thickness were fabricated on the same substrate under the same oxidation condition, and the depth profile of oxide-trapped charges before and after {sup 60}Co-gamma ray irradiation were obtained. It is found, from the depth profiling, that the trapping mechanism of electrons and holes in the oxide strongly depends on the bias polarity during irradiation, and these charges are trapped near 6H-SiC/SiO{sub 2} interface. We believe that this method is very useful for estimation of the oxide-trapped charges in 6H-SiC MOS structures. (author)

  17. DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/-Si MOS structures

    Indian Academy of Sciences (India)

    N Shashank; Sanjeev K Gupta; K V Madhu; J Akhtar; R Damle

    2011-12-01

    This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO2/-Si MOS structures fabricated on -type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO2/-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at C = 0.49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (C = 0.43, 0.46 and 0.34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.

  18. Structural and Electronic Properties of Germanene on MoS2

    Science.gov (United States)

    Zhang, L.; Bampoulis, P.; Rudenko, A. N.; Yao, Q.; van Houselt, A.; Poelsema, B.; Katsnelson, M. I.; Zandvliet, H. J. W.

    2016-06-01

    To date germanene has only been synthesized on metallic substrates. A metallic substrate is usually detrimental for the two-dimensional Dirac nature of germanene because the important electronic states near the Fermi level of germanene can hybridize with the electronic states of the metallic substrate. Here we report the successful synthesis of germanene on molybdenum disulfide (MoS2), a band gap material. Preexisting defects in the MoS2 surface act as preferential nucleation sites for the germanene islands. The lattice constant of the germanene layer (3.8 ±0.2 Å ) is about 20% larger than the lattice constant of the MoS2 substrate (3.16 Å). Scanning tunneling spectroscopy measurements and density functional theory calculations reveal that there are, besides the linearly dispersing bands at the K points, two parabolic bands that cross the Fermi level at the Γ point.

  19. Hierarchical MoS2 tubular structures internally wired by carbon nanotubes as a highly stable anode material for lithium-ion batteries

    Science.gov (United States)

    Chen, Yu Ming; Yu, Xin Yao; Li, Zhen; Paik, Ungyu; Lou, Xiong Wen (David)

    2016-01-01

    Molybdenum disulfide (MoS2), a typical two-dimensional material, is a promising anode material for lithium-ion batteries because it has three times the theoretical capacity of graphite. The main challenges associated with MoS2 anodes are the structural degradation and the low rate capability caused by the low intrinsic electric conductivity and large strain upon cycling. Here, we design hierarchical MoS2 tubular structures internally wired by carbon nanotubes (CNTs) to tackle these problems. These porous MoS2 tubular structures are constructed from building blocks of ultrathin nanosheets, which are believed to benefit the electrochemical reactions. Benefiting from the unique structural and compositional characteristics, these CNT-wired MoS2 tubular structures deliver a very high specific capacity of ~1320 mAh g−1 at a current density of 0.1 A g−1, exceptional rate capability, and an ultralong cycle life of up to 1000 cycles. This work may inspire new ideas for constructing high-performance electrodes for electrochemical energy storage. PMID:27453938

  20. Hierarchical MoS2 tubular structures internally wired by carbon nanotubes as a highly stable anode material for lithium-ion batteries.

    Science.gov (United States)

    Chen, Yu Ming; Yu, Xin Yao; Li, Zhen; Paik, Ungyu; Lou, Xiong Wen David

    2016-07-01

    Molybdenum disulfide (MoS2), a typical two-dimensional material, is a promising anode material for lithium-ion batteries because it has three times the theoretical capacity of graphite. The main challenges associated with MoS2 anodes are the structural degradation and the low rate capability caused by the low intrinsic electric conductivity and large strain upon cycling. Here, we design hierarchical MoS2 tubular structures internally wired by carbon nanotubes (CNTs) to tackle these problems. These porous MoS2 tubular structures are constructed from building blocks of ultrathin nanosheets, which are believed to benefit the electrochemical reactions. Benefiting from the unique structural and compositional characteristics, these CNT-wired MoS2 tubular structures deliver a very high specific capacity of ~1320 mAh g(-1) at a current density of 0.1 A g(-1), exceptional rate capability, and an ultralong cycle life of up to 1000 cycles. This work may inspire new ideas for constructing high-performance electrodes for electrochemical energy storage. PMID:27453938

  1. Dispersion-Corrected Density Functional Theory Investigations of Structural and Electronic Properties of Bulk MoS2: Effect of Uniaxial Strain.

    Science.gov (United States)

    Nguyen, Chuong V; Hieu, Nguyen N; Nguyen, Duong T

    2015-12-01

    Strain-dependent structural and electronic properties of MoS2 materials are investigated using first principles calculations. The structural and electronic band structures of the MoS2 with relaxed unit cells are optimized and calculated by the dispersion-corrected density functional theory (DFT-D2). Calculations within the local density approximation (LDA) and GGA using PAW potentials were also performed for specific cases for the purpose of comparison. The effect of strain on the band gap and the dependence of formation energy on strain of MoS2 are also studied and discussed using the DFT-D2 method. In bulk MoS2, the orbitals shift towards the higher/lower energy area when strain is applied along the z/x direction, respectively. The energy splitting of Mo4d states is in the range from 0 to 2 eV, which is due to the reduction of the electronic band gap of MoS2.

  2. Structures of a 17,19-hexatriacontadiyne and sashlike polydiacetylene monolayer on MoS2(0001) studied by UHV-STM

    International Nuclear Information System (INIS)

    We have observed a 17,19-hexatriacontadiyne (HTDY) monolayer on MoS2(0001) and sashlike polydiacetylene atomic sash (AS) molecules derived from the monolayer by scanning tunnelling microscopy under ultrahigh vacuum. HTDY molecules adsorbed at 150 K start to move around on the surface above 240 K to form relatively unstable columnar structures. The column is converted into the AS by UV irradiation. In most AS molecules on MoS2(0001), the alkyl chains are in all-trans conformation but their carbon planes are tilted to the polydiacetylene backbone. This conformer, which is one of the most stable structures for an isolated AS molecule, appears on MoS2(0001) because of very weak molecule-substrate interactions

  3. Capacitance transients in p-type GaAs MOS structures and application to lifetime mapping during solar cell fabrication

    Science.gov (United States)

    Vitale, G.; Loferski, J. J.; Ercil, Y.

    1979-01-01

    Fabrication on p-type GaAs of MOS structures in which the quality of the oxide is such that the surface can be driven into deep inversion by a voltage pulse is reported. The capacitance transients in such MOS capacitors as a function of step amplitude and temperature were measured and the transients were analyzed by an extension of a method for silicon. The oxides were produced by plasma oxidation on an LPE-grown p-type GaAs specimen with N sub A of 3x10 to the 17th power/cu cm. The capacitors were produced by depositing 50 microns-diameter gold dots over the native oxide and, therefore, the lifetime is localized to the area under the dot. The method permits extraction of both the bulk lifetime and the interface recombination velocity. These parameters on samples with different N sub A were measured and a correlation between tau sub g and N sub A was found.

  4. Controlled, defect-guided, metal-nanoparticle incorporation onto MoS2 via chemical and microwave routes: electrical, thermal, and structural properties.

    Science.gov (United States)

    Sreeprasad, T S; Nguyen, Phong; Kim, Namhoon; Berry, Vikas

    2013-09-11

    Ultrathin (0.3-3 nm) metal dichalcogenides exhibit confinement of carriers, evolution of band-structure and photophysical properties with thickness, high on/off rectification (in MoS2, WS2, and so forth) and high thermal absorption. Here, we leverage the stable sulfur/nobel-metal binding to incorporate highly capacitive gold nanoparticles (Au NPs) onto MoS2 to raise the effective gate-voltage by an order of magnitude. Functionalization is achieved via both diffusion limited aggregation and instantaneous reaction arresting (using microwaves) with selective deposition on crystallographic edges (with 60° displacement). The electrical, thermal, and Raman studies show a highly capacitive interaction between Au NP and MoS2 flakes (CAu-MoS2 = 2.17 μF/cm(2)), a low Schottky barrier (14.52 meV), a reduced carrier-transport thermal-barrier (253 to 44.18 meV after Au NP functionalization), and increased thermal conductivity (from 15 to 23 W/mK post NP deposition). The process could be employed to attach electrodes to heterostructures of graphene and MoS2, where a gold film could be grown to act as an electron-tunneling gate-electrode connected to MoS2. PMID:23927716

  5. Thiol click chemistry on gold-decorated MoS2: elastomer composites and structural phase transitions

    Science.gov (United States)

    Topolovsek, Peter; Cmok, Luka; Gadermaier, Christoph; Borovsak, Milos; Kovac, J.; Mrzel, Ales

    2016-05-01

    We show that gold decorated MoS2 flakes are amenable to thiol chemistry by blending them with a cross-linkable thiolated polysiloxane (PMMS). PMMS prevents restacking of dispersed MoS2 when transforming the metallic to the semiconducting phase. Cross-linking PMMS yields an elastomer of good optical quality, containing individual, mostly single-layer MoS2 flakes.We show that gold decorated MoS2 flakes are amenable to thiol chemistry by blending them with a cross-linkable thiolated polysiloxane (PMMS). PMMS prevents restacking of dispersed MoS2 when transforming the metallic to the semiconducting phase. Cross-linking PMMS yields an elastomer of good optical quality, containing individual, mostly single-layer MoS2 flakes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01490a

  6. Electronic structure of MoSe2, MoS2, and WSe2. I. Band-structure calculations and photoelectron spectroscopy

    OpenAIRE

    Coehoorn, R.; Haas, C.; Dijkstra, J.; Flipse, C.J.F.; de Groot, R. A.; Wold, A.

    1987-01-01

    The band structures of the semiconducting layered compounds MoSe2, MoS2, and WSe2 have been calculated self-consistently with the augmented-spherical-wave method. Angle-resolved photoelectron spectroscopy of MoSe2 using He I, He II, and Ne I radiation, and photon-energy-dependent normal-emission photoelectron spectroscopy using synchrotron radiation, show that the calculational results give a good description of the valence-band structure. At about 1 eV below the top of the valence band a dis...

  7. Strain-Gated Field Effect Transistor of a MoS2-ZnO 2D-1D Hybrid Structure.

    Science.gov (United States)

    Chen, Libo; Xue, Fei; Li, Xiaohui; Huang, Xin; Wang, Longfei; Kou, Jinzong; Wang, Zhong Lin

    2016-01-26

    Two-dimensional (2D) molybdenum disulfide (MoS2) is an exciting material due to its unique electrical, optical, and piezoelectric properties. Owing to an intrinsic band gap of 1.2-1.9 eV, monolayer or a-few-layer MoS2 is used for fabricating field effect transistors (FETs) with high electron mobility and on/off ratio. However, the traditional FETs are controlled by an externally supplied gate voltage, which may not be sensitive enough to directly interface with a mechanical stimulus for applications in electronic skin. Here we report a type of top-pressure/force-gated field effect transistors (PGFETs) based on a hybrid structure of a 2D MoS2 flake and 1D ZnO nanowire (NW) array. Once an external pressure is applied, the piezoelectric polarization charges created at the tips of ZnO NWs grown on MoS2 act as a gate voltage to tune/control the source-drain transport property in MoS2. At a 6.25 MPa applied stimulus on a packaged device, the source-drain current can be tuned for ∼25%, equivalent to the results of applying an extra -5 V back gate voltage. Another type of PGFET with a dielectric layer (Al2O3) sandwiched between MoS2 and ZnO also shows consistent results. A theoretical model is proposed to interpret the received data. This study sets the foundation for applying the 2D material-based FETs in the field of artificial intelligence.

  8. Synthesis and Crystal Structure of a Novel Mixed Nido-like and Half-open Cubane-like Cluster [(n-Bu)4N]3[MoS4Cu5Br6

    Institute of Scientific and Technical Information of China (English)

    LIU,Quai(刘泉); XU,Qing-Feng(徐庆锋); ZHANG,Yong(张勇); CHEN,Jin-Xiang(陈金香); ZHOU,Zhi-Feng(周志峰); LANG,Jian-Ping(郎建平)

    2002-01-01

    Reaction of (NH4)2MoS4 with [Cu(MeCN)4] (BF4) and (nBu)4NBr in CH2Cl2 afforded a new hexanuclear cluster [ ( nBu)4N]3[MoS4Cu5Br6] (1). 1 crystallizes in the monoclinic system, space group P21/c, with lattice parameters a =1.17383(4) nm, b = 2.40136(4) nm, c = 2.64112(5) nm,β =94.2020(5)°, V=7.4247(5) nm3andZ=4. The structure of the [MoS4Cu5Br6]3- trianion of 1 is composed of one nidolike [MoS3Cu3] core and one half-open cubane-like [MoS3Cu3Br] core, which are interconnected by sharing the of 0.2622(6)-0.2692(5) nm.

  9. Structural and electrical characteristics of RF-sputtered HfO 2 high-k based MOS capacitors

    Science.gov (United States)

    Tirmali, P. M.; Khairnar, Anil G.; Joshi, Bhavana N.; Mahajan, A. M.

    2011-08-01

    The HfO 2 high-k thin films have been deposited on p-type (1 0 0) silicon wafer using RF magnetron sputtering technique. The XRD, AFM and Ellipsometric characterizations have been performed for crystal structure, surface morphology and thickness measurements respectively. The monoclinic structured, smooth surface HfO 2 thin films with 9.45 nm thickness have been used for Al/HfO 2/p-Si metal-oxide-semiconductor (MOS) structures fabrication. The fabricated Al/HfO2/Si structure have been used for extracting electrical properties viz dielectric constant, EOT, barrier height, doping concentration and interface trap density through capacitance voltage and current-voltage measurements. The dielectric constant, EOT, barrier height, effective charge carriers, interface trap density and leakage current density are determined are 22.47, 1.64 nm, 1.28 eV, 0.93 × 10 10, 9.25 × 10 11 cm -2 eV -1 and 9.12 × 10 -6 A/cm 2 respectively for annealed HfO 2 thin films.

  10. Structures of exfoliated single layers of WS2, MoS2, and MoSe2 in aqueous suspension

    Science.gov (United States)

    Gordon, R. A.; Yang, D.; Crozier, E. D.; Jiang, D. T.; Frindt, R. F.

    2002-03-01

    Single layers of the transition-metal dichalcogenides WS2, MoS2, and MoSe2 were formed as aqueous suspensions by lithium intercalation and exfoliation of crystalline powders and examined by x-ray diffraction and x-ray absorption fine structure (XAFS) spectroscopy. The two-dimensional characteristics of these systems were readily apparent through the absence of any (hkl) peaks (l≠0) and in the strong asymmetry of the (hk0) peaks in the diffraction patterns. Indexing the diffraction patterns with rectangular unit cells revealed the diselenide as the most distorted from the hexagonal structures of the parent materials, with the Mo atoms forming a ``zigzag'' structure which is also corrugated perpendicular to the layers. Mo K-edge and W L3-edge XAFS analysis using WTe2-related structural models enabled the determination of the short, intermediate, and long metal-metal near-neighbor distances with the shortest metal-metal distances contracted approximately 0.4 Å compared to parent reference materials. Shifts in the Mo K-absorption-edge energy in MoSe2 correlated with changing Se-Se interactions. Combining the XAFS and diffraction results enabled an estimation of the layer puckering and atomic positions in three-dimensional models of the unit cells. Selenium K-edge XAFS also identified two selenium-oxygen scattering paths from water or OH- ions coordinating the layers of exfoliated MoSe2.

  11. Three-Dimensional Structures of MoS2@Ni Core/Shell Nanosheets Array toward Synergetic Electrocatalytic Water Splitting.

    Science.gov (United States)

    Xing, Zhicai; Yang, Xiurong; Asiri, Abdullah M; Sun, Xuping

    2016-06-15

    Hydrogen evolution reaction (HER) in alkaline media using non-noble metal catalysts with great efficiency represents a critical challenge in current water-alkaline and chlor-alkali electrolyzers. Herein, we demonstrate that the MoS2@Ni core/shell nanosheets array vertically aligned on carbon cloth (MoS2@Ni/CC) is a highly active electrocatalyst for HER. In alkaline solutions, MoS2@Ni/CC needs overpotentials of 91, 118, and 196 mV to approach current densities of 10, 20, and 100 mA cm(-2), respectively, exceeding behavior of commercial Pt/C catalyst at high current densities. Additionally, this catalyst also exhibits excellent electrocatalytic activity toward HER in neutral electrolytes. Such high hydrogen evolution activities are due to synergistic electrocatalytic effects between MoS2 core and Ni shell. PMID:27211232

  12. Structure design and film process optimization for metal-gate stress in 20 nm nMOS devices

    International Nuclear Information System (INIS)

    The optimizations to metal gate structure and film process were extensively investigated for great metal-gate stress (MGS) in 20 nm high-k/metal-gate-last (HK/MG-last) nMOS devices. The characteristics of advanced MGS technologies on device performances were studied through a process and device simulation by TCAD tools. The metal gate electrode with different stress values (0 to −6 GPa) was implemented in the device simulation along with other traditional process-induced-strain (PIS) technologies like e-SiC and nitride capping layer. The MGS demonstrated a great enhancing effect on channel carriers transporting in the device as device pitch scaling down. In addition, the novel structure for a tilted gate electrode was proposed and relationships between the tilt angle and channel stress were investigated. Also with a new method of fully stressed replacement metal gate (FSRMG) and using plane-shape-HfO to substitute U-shape-HfO, the effect of MGS was improved. For greater film stress in the metal gate, the process conditions for physical vapor deposition (PVD) TiNx were optimized. The maximum compressive stress of −6.5 GPa TiNx was achieved with thinner film and greater RF power as well as about 6 sccm N ratio. (semiconductor technology)

  13. Electron microscopy studies on MoS2 nanocrystals

    DEFF Research Database (Denmark)

    Hansen, Lars Pilsgaard

    Industrial-style MoS2-based hydrotreating catalysts are studied using electron microscopy. The MoS2 nanostructures are imaged with single-atom sensitivity to reveal the catalytically important edge structures. Furthermore, the in-situ formation of MoS2 crystals is imaged for the first time....

  14. A Novel Depletion-Mode MOS Gated Emitter Shorted Thyristor

    Institute of Scientific and Technical Information of China (English)

    张鹤鸣; 戴显英; 张义门; 马晓华; 林大松

    2000-01-01

    A Novel MOS-gated thyristor, depletion-mode MOS gated emitter shorted thyristor (DMST),and its two structures are proposed. In DMST,the channel of depletion-mode MOS makes the thyristor emitter-based junction inherently short. The operation of the device is controlled by the interruption and recovery of the depletion-mode MOS P channel. The perfect properties have been demonstrated by 2-D numerical simulations and the tests on the fabricated chips.

  15. In Situ XPS Chemical Analysis of MnSiO3 Copper Diffusion Barrier Layer Formation and Simultaneous Fabrication of Metal Oxide Semiconductor Electrical Test MOS Structures.

    Science.gov (United States)

    Byrne, Conor; Brennan, Barry; McCoy, Anthony P; Bogan, Justin; Brady, Anita; Hughes, Greg

    2016-02-01

    Copper/SiO2/Si metal-oxide-semiconductor (MOS) devices both with and without a MnSiO3 barrier layer at the Cu/SiO2 interface have been fabricated in an ultrahigh vacuum X-ray photoelectron spectroscopy (XPS) system, which allows interface chemical characterization of the barrier formation process to be directly correlated with electrical testing of barrier layer effectiveness. Capacitance voltage (CV) analysis, before and after tube furnace anneals of the fabricated MOS structures showed that the presence of the MnSiO3 barrier layer significantly improved electric stability of the device structures. Evidence of improved adhesion of the deposited copper layer to the MnSiO3 surface compared to the clean SiO2 surface was apparent both from tape tests and while probing the samples during electrical testing. Secondary ion mass spectroscopy (SIMS) depth profiling measurements of the MOS test structures reveal distinct differences of copper diffusion into the SiO2 dielectric layers following the thermal anneal depending on the presence of the MnSiO3 barrier layer. PMID:26732185

  16. Study of various technological parameters on the C-Vg and the G-Vg characteristics of MOS structures

    Science.gov (United States)

    Rejaiba, Omar; Braña, Alejandro F.; Matoussi, Adel

    2016-08-01

    This paper was devoted to study the effects of some technological parameters (gate, oxide and doping density N a on the electrical properties of MOS structures. The conductance and capacitance were determined from a proposed admittance model. Results showed a frequency dispersion of C- V g and G- V g curves in inversion regime. This modeling takes into account the influence of series and parallel resistances ( R s, R p), thickness of oxide layer, the work function of gate electrode and the doping density ( N a). The C- V g and G- V g characteristics have been simulated at high frequency (100 kHz-1 MHz).With increasing frequency, the inversion capacitance is decreased whereas the conductance is strongly increased. A degradation of their shapes is shown in the operating accumulation and depletion modes. The accumulation capacitance seems to be strong for titanium oxide (TiO2) and for the oxide thickness is very small. Interestingly, the change of metal gate causes C- V g shifting and variation of the values of the flat band and threshold voltages. In the inversion mode, the C - V g and G- V g decreases with the increase of the doping density ( N a). There is a shift of the flat-band and threshold voltage ( V fb, V th) when N a increase. Excellent agreement was observed between the calculated and the measured C- V g curves obtained at high frequency.

  17. Photo-induced tunneling currents in MOS structures with various HfO2/SiO2 stacking dielectrics

    Directory of Open Access Journals (Sweden)

    Chin-Sheng Pang

    2014-04-01

    Full Text Available In this study, the current conduction mechanisms of structures with tandem high-k dielectric in illumination are discussed. Samples of Al/SiO2/Si (S, Al/HfO2/SiO2/Si (H, and Al/3HfO2/SiO2/Si (3H were examined. The significant observation of electron traps of sample H compares to sample S is found under the double bias capacitance-voltage (C-V measurements in illumination. Moreover, the photo absorption sensitivity of sample H is higher than S due to the formation of HfO2 dielectric layer, which leads to larger numbers of carriers crowded through the sweep of VG before the domination of tunneling current. Additionally, the HfO2 dielectric layer would block the electrons passing through oxide from valance band, which would result in less electron-hole (e−-h+ pairs recombination effect. Also, it was found that both of the samples S and H show perimeter dependency of positive bias currents due to strong fringing field effect in dark and illumination; while sample 3H shows area dependency of positive bias currents in strong illumination. The non-uniform tunneling current through thin dielectric and through HfO2 stacking layers are importance to MOS(p tunneling photo diodes.

  18. 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.

  19. Electrical characteristics of MoS2 field-effect transistor with ferroelectric vinylidene fluoride-trifluoroethylene copolymer gate structure

    Science.gov (United States)

    Kobayashi, Takuhei; Hori, Naoki; Nakajima, Takashi; Kawae, Takeshi

    2016-03-01

    Ferroelectric field-effect transistors (FeFET) based on MoS2 have recently been shown to exhibit considerable potential for use in nano sized non-volatile memory devices. Here, we demonstrated fabrication and characterization of FeFET based on MoS2 channel with vinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer as back-gate insulator. In this device, counterclockwise hysteresis behavior was observed in the drain current-gate voltage curve, which is indicative of interaction between MoS2 carrier modulation and ferroelectric polarization switching. Furthermore, our VDF-TrFE/MoS2 FeFET exhibited only n-type behavior, a maximum linear mobility of 625 cm2/V s, a large memory window width of 16 V, and a high on/off current ratio of 8 × 105.

  20. MOS integrated circuit design

    CERN Document Server

    Wolfendale, E

    2013-01-01

    MOS Integral Circuit Design aims to help in the design of integrated circuits, especially large-scale ones, using MOS Technology through teaching of techniques, practical applications, and examples. The book covers topics such as design equation and process parameters; MOS static and dynamic circuits; logic design techniques, system partitioning, and layout techniques. Also featured are computer aids such as logic simulation and mask layout, as well as examples on simple MOS design. The text is recommended for electrical engineers who would like to know how to use MOS for integral circuit desi

  1. Reliability study of ultra-thin gate oxides on strained-Si/SiGe MOS structures

    Energy Technology Data Exchange (ETDEWEB)

    Varzgar, John B. [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom)]. E-mail: j.b.varzgar@newcastle.ac.uk; Kanoun, Mehdi [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Uppal, Suresh [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Chattopadhyay, Sanatan [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Tsang, Yuk Lun [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Escobedo-Cousins, Enrique [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Olsen, Sarah H. [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); O' Neill, Anthony [School of Electrical, Electronic and Computer Engineering, Merz Court, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE1 7RU (United Kingdom); Hellstroem, Per-Erik [KTH, Royal Institute of Technology, Department of Microelectronics and Information Technology, Electrum 229, SE-164 40 Kista (Sweden); Edholm, Jonas; Ostling, Mikael [KTH, Royal Institute of Technology, Department of Microelectronics and Information Technology, Electrum 229, SE-164 40 Kista (Sweden); Lyutovich, Klara; Oehme, Michael; Kasper, Erich [Institute of Semiconductor Engineering, University of Stuttgart, Pfaffenwaldring 47, Stuttgart D-70569 (Germany)

    2006-12-15

    The reliability of gate oxides on bulk Si and strained Si (s-Si) has been evaluated using constant voltage stressing (CVS) to investigate their breakdown characteristics. The s-Si architectures exhibit a shorter life time compared to that of bulk Si, which is attributed to higher bulk oxide charges (Q {sub ox}) and increased surface roughness in the s-Si structures. The gate oxide in the s-Si structure exhibits a hard breakdown (HBD) at 1.9 x 10{sup 4} s, whereas HBD is not observed in bulk Si up to a measurement period of 1.44 x 10{sup 5} s. The shorter lifetime of the s-Si gate oxide is attributed to a larger injected charge (Q {sub inj}) compared to Q {sub inj} in bulk Si. Current-voltage (I-V) measurements for bulk Si samples at different stress intervals show an increase in stress induced leakage current (SILC) of two orders in the low voltage regime from zero stress time to up to 5 x 10{sup 4} s. In contrast, superior performance enhancements in terms of drain current, maximum transconductance and effective channel mobility are observed in s-Si MOSFET devices compared to bulk Si. The results from this study indicate that further improvement in gate oxide reliability is needed to exploit the sustained performance enhancement of s-Si devices over bulk Si.

  2. Electronic structure of MoSe2, MoS2, and WSe2. II. The nature of the optical band gaps

    OpenAIRE

    Coehoorn, R.; Haas, C.; de Groot, R. A.

    1987-01-01

    From band-structure calculations it is shown that MoSe2, MoS2, and WSe2 are indirect-gap semiconductors. The top of the valence band is at the Γ point and the bottom of the conduction band is along the line T of the hexagonal Brillouin zone, halfway between the points Γ and K. The A and B excitons correspond to the smallest direct gap at the K point. This assignment of the exciton peaks is shown to be consistent with the polarization dependence of their intensities, their effective masses, an...

  3. Electronic Structures and Magnetic Properties of MoS2 Nanostructures: Atomic Defects, Nanoholes, Nanodots and Antidots

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yungang; Yang, Ping; Zu, Haoyue; Gao, Fei; Zu, Xiaotao

    2013-04-24

    MoS2-based nanostructures, including atomic defect, nanohole, nanodot and antidot, are characterized with spin-polarized density functional theory. The S-vacancy defect is more likely to form than the Mo-vacancy defect due to the formation of Mo-Mo metallic bonds. Among different shaped nanoholes and nanodots, triangle ones associated with ferromagnetic characteristic are the most energetically favorable, and exhibit unexpected large spin moment that is scaled linearly with edged length.

  4. Degradation of the electrical characteristics of MOS structures with erbium, gadolinium, and dysprosium oxides under the effect of an electric field

    International Nuclear Information System (INIS)

    The degradation of the characteristics of silicon metal-oxide-semiconductor (MOS) structures with oxides of rare-earth elements under the effect of electric fields with intensities of 0.1–4 MV/cm during the course of electroforming is studied. A specific feature of electroforming consists in the possibility of multiple switching of the structures from the insulating state to the low-resistivity one and back. The temporal characteristics of the degradation of MOS structures during the course of electroforming are exponential. The current-voltage characteristics follow the power law in the range of 0.2–3 V; the effect of an electric field brings about a variation in the distribution of the energy density of traps responsible for currents limited by space charge. It is established that multiple cycles of electroforming lead to an increase in the density of surface states at the Si-oxide interface and to a variation in the energy position of the trap levels, which affects the charge state of the traps

  5. Folded MoS2 layers with reduced interlayer coupling

    OpenAIRE

    Castellanos-Gomez, Andres; van der Zant, Herre S. J.; Steele, Gary A.

    2013-01-01

    We study molybdenum disulfide (MoS2) structures generated by folding single- and bilayer MoS2 flakes. We find that this modified layer stacking leads to a decrease in the interlayer coupling and an enhancement of the photoluminescence emission yield. We additionally find that folded single-layer MoS2 structures show a contribution to photoluminescence spectra of both neutral and charged excitons, which is a characteristic feature of single-layer MoS2 that has not been observed in multilayer M...

  6. Structural, optical and compositional stability of MoS2 multi-layer flakes under high dose electron beam irradiation

    Science.gov (United States)

    Rotunno, E.; Fabbri, F.; Cinquanta, E.; Kaplan, D.; Longo, M.; Lazzarini, L.; Molle, A.; Swaminathan, V.; Salviati, G.

    2016-06-01

    MoS2 multi-layer flakes, exfoliated from geological molybdenite, have been exposed to high dose electron irradiation showing clear evidence of crystal lattice and stoichiometry modifications. A massive surface sulfur depletion is induced together with the consequent formation of molybdenum nanoislands. It is found that a nanometric amorphous carbon layer, unwillingly deposited during the transmission electron microscope experiments, prevents the formation of the nanoislands. In the absence of the carbon layer, the formation of molybdenum grains proceeds both on the top and bottom surfaces of the flake. If carbon is present on both the surfaces then the formation of Mo grains is completely prevented.

  7. The pristine atomic structure of MoS2 monolayer protected from electron radiation damage by graphene

    Science.gov (United States)

    Algara-Siller, Gerardo; Kurasch, Simon; Sedighi, Mona; Lehtinen, Ossi; Kaiser, Ute

    2013-11-01

    Materials can, in principle, be imaged at the level of individual atoms with aberration-corrected transmission electron microscopy. However, such resolution can be attained only with very high electron doses. Consequently, radiation damage is often the limiting factor when characterizing sensitive materials. Here, we demonstrate a simple and an effective method to increase the electron radiation tolerance of materials by using graphene as protective coating. This leads to an improvement of three orders of magnitude in the radiation tolerance of monolayer MoS2. Further on, we construct samples in different heterostructure configurations to separate the contributions of different radiation damage mechanisms.

  8. Optical and Electrical Performance of MOS-Structure Silicon Solar Cells with Antireflective Transparent ITO and Plasmonic Indium Nanoparticles under Applied Bias Voltage

    Directory of Open Access Journals (Sweden)

    Wen-Jeng Ho

    2016-08-01

    Full Text Available This paper reports impressive improvements in the optical and electrical performance of metal-oxide-semiconductor (MOS-structure silicon solar cells through the incorporation of plasmonic indium nanoparticles (In-NPs and an indium-tin-oxide (ITO electrode with periodic holes (perforations under applied bias voltage. Samples were prepared using a plain ITO electrode or perforated ITO electrode with and without In-NPs. The samples were characterized according to optical reflectance, dark current voltage, induced capacitance voltage, external quantum efficiency, and photovoltaic current voltage. Our results indicate that induced capacitance voltage and photovoltaic current voltage both depend on bias voltage, regardless of the type of ITO electrode. Under a bias voltage of 4.0 V, MOS cells with perforated ITO and plain ITO, respectively, presented conversion efficiencies of 17.53% and 15.80%. Under a bias voltage of 4.0 V, the inclusion of In-NPs increased the efficiency of cells with perforated ITO and plain ITO to 17.80% and 16.87%, respectively.

  9. Torsional Deformations in Subnanometer MoS Interconnecting Wires.

    Science.gov (United States)

    Koh, Ai Leen; Wang, Shanshan; Ataca, Can; Grossman, Jeffrey C; Sinclair, Robert; Warner, Jamie H

    2016-02-10

    We use aberration-corrected transmission electron microscopy to track the real time atomic level torsional dynamics of subnanometer wires of MoS interconnecting monolayer regions of MoS2. An in situ heating holder is used inside the transmission electron microscope to raise the temperature of the sample to 400 °C to increase crystallization rates of the wires and reduce contamination effects. Frequent rotational twisting of the MoS wire is captured, demonstrating elastic torsional deformation of the MoS wires. We show that torsional rotations of the crystal structure of the MoS wires depend upon the specific atomic structure of the anchored sections of the suspended wire and the number of unit cells that make up the wire length. Elastic torsional flexibility of the MoS wires is revealed to help their self-adapting connectivity during the structural changes. Plastic torsional deformation is also seen for MoS wires that contain defects in their crystal structure, which produce small scale rotational disorder within the wires. Upon removal of the defects, the wire returns back to pristine form. These results provide detailed insights into how the atomic structure of the anchoring site significantly influences the nanowire configurations relative to the monolayered MoS2. PMID:26785319

  10. Vertically Conductive MoS2 Spiral Pyramid.

    Science.gov (United States)

    Ly, Thuc Hue; Zhao, Jiong; Kim, Hyun; Han, Gang Hee; Nam, Honggi; Lee, Young Hee

    2016-09-01

    MoS2 spirals grown by the chemical vapor deposition method, driven by a threading dislocation, has a peculiar rhombohedral-like structure. This threading dislocation can carry helical current in the vertical direction and greatly enhances the vertical conductance in the MoS2 multilayer samples.

  11. The creation of the magnetic and metallic characteristics in low-width MoS 2 nanoribbon (1D MoS 2): A DFT study

    Science.gov (United States)

    Shidpour, Reza; Manteghian, Merhrdad

    2009-06-01

    A basic understanding of the catalytic performance is needed to probe the physical properties that change with a reduction in the catalytic clusters size. It has been shown that the edge of low-width MoS2 nanoribbon has a metallic characteristic, while that of bulk MoS2 has a semi-conductive characteristic. For probing the observations, we constructed the models representing the surface atoms and the edge atoms of the MoS2 nanoribbon. The nanoribbon-like model can also be used to model the edge atoms of the nanocluster MoS2 .Then we calculated the density of states (DOS) of infinitely two-dimensional MoS2 and of the structure corresponding to the edge atoms of the MoS2 nanoribbon-like structure with Wien2K software. The magnetic moment of structures was calculated for identifying the magnetic structure. We found that the bulk MoS2 and infinitely two-dimensional MoS2 are semi-conductive and not magnetic, while the computation model corresponding to MoS2 nanoribbon is metallic. The calculation anticipates that the edges of the MoS2 nanocluster and the low-width MoS2 nanoribbon are strongly magnetic.

  12. Two-bit memory and quantized storage phenomenon in conventional MOS structures with double-stacked Pt-NCs in an HfAlO matrix.

    Science.gov (United States)

    Zhou, Guangdong; Wu, Bo; Liu, Xiaoqin; Li, Ping; Zhang, Shuangju; Sun, Bai; Zhou, Ankun

    2016-03-01

    A two-bit memory and quantized storage phenomenon are observed at room temperature for a device based on the traditional MOS structure with double-stacked Pt-nanocrystals (Pt-NCs). A 2.68 and 1.72 V flat band voltage shift (memory window) has been obtained when applying a ±7 V programming/erasing voltage to the structures with double-stacked Pt-NCs. The memory windows of 2.40 and 1.44 V can be retained after stress for 10(5) seconds, which correspond to 89.55% and 83.72% stored charges reserved. The quantized charge storage phenomenon characterized by current-voltage (J-V) hysteresis curves was detected at room temperature. The shrinkage of the memory window results from the decreasing tunneling probability, which strongly depends on the number of stacks. The traps, de-traps and quantum confinement effects of Pt-NCs may contribute to the improvement of dielectric characteristics and the two-bit memory behavior. The multi-bit memory and quantized storage behavior observed in the Pt-NCs stacks structure at room temperature might provide a feasible method for realizing the multi-bit storage in non-volatile flash memory devices. PMID:26864686

  13. Darstellung und Charakterisierung von MoS2 Cokatalysatoren für die H2-Entwicklung

    OpenAIRE

    Djamil, John

    2015-01-01

    Die hergestellten MoS2 Cokatalysatoren wurden hinsichtlich der chemischen Zusammensetzung, der strukturellen und fotokatalytischen Eigenschaften untersucht. MoS2 Cocatalysts were prepared and characterised in their chemical composition, structural and photocatalytic properties.

  14. Synthesis and characterization of MoS2 nanosheets.

    Science.gov (United States)

    Deokar, G; Vignaud, D; Arenal, R; Louette, P; Colomer, J-F

    2016-02-19

    Here, we report on the synthesis of MoS2 nanosheets using a simple two-step additive-free growth technique. The as-synthesized nanosheets were characterized to determine their structure and composition, as well as their optical properties. The MoS2 nanosheets were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), including high-resolution scanning TEM imaging and energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL). The as-produced MoS2 nanosheets are vertically aligned with curved edges and are densely populated. The TEM measurements confirmed that the nanosheets have the 2H-MoS2 crystal structure in agreement with the Raman results. The XPS results revealed the presence of high purity MoS2. Moreover, a prominent PL similar to mechanically exfoliated few and mono-layer MoS2 was observed for the as-grown nanosheets. For the thin (≤50 nm) nanosheets, the PL feature was observed at the same energy as that for a direct band-gap monolayer MoS2 (1.83 eV). Thus, the as-produced high-quality, large-area, MoS2 nanosheets could be potentially useful for various optoelectronic and catalysis applications.

  15. Photoconductivities in MoS2 Nanoflake Photoconductors

    Science.gov (United States)

    Shen, Wei-Chu; Chen, Ruei-San; Huang, Ying-Sheng

    2016-03-01

    Photoconductivities in molybdenum disulfide (MoS2) layered nanostructures with two-hexagonal crystalline structure prepared by mechanical exfoliation were investigated. The photoconductor-type MoS2 nanoflakes exhibit remarkable photoresponse under the above bandgap excitation wavelength of 532 nm at different optical intensity. The photocurrent responsivity and photoconductive gain of nanoflakes can reach, respectively, 30 AW-1 and 103 at the intensity of 50 Wm-2, which are several orders of magnitude higher than those of their bulk counterparts. The vacuum-enhanced photocurrent and power-independent responsivity/gain indicate a surface-controlled photoconduction mechanism in the MoS2 nanomaterial.

  16. DLTS analysis of amphoteric interface defects in high-TiO2 MOS structures prepared by sol-gel spin-coating

    Directory of Open Access Journals (Sweden)

    Arvind Kumar

    2015-11-01

    Full Text Available High-κ TiO2 thin films have been fabricated from a facile, combined sol – gel spin – coating technique on p and n type silicon substrate. XRD and Raman studies headed the existence of anatase phase of TiO2 with a small grain size of 18 nm. The refractive index ‘n’ quantified from ellipsometry is 2.41. AFM studies suggest a high quality, pore free films with a fairly small surface roughness of 6 Å. The presence of Ti in its tetravalent state is confirmed by XPS analysis. The defect parameters observed at the interface of Si/TiO2 were studied by capacitance – voltage (C – V and deep level transient spectroscopy (DLTS. The flat – band voltage (VFB and the density of slow interface states estimated are – 0.9, – 0.44 V and 5.24×1010, 1.03×1011 cm−2; for the NMOS and PMOS capacitors, respectively. The activation energies, interface state densities and capture cross – sections measured by DLTS are EV + 0.30, EC – 0.21 eV; 8.73×1011, 6.41×1011 eV−1 cm−2 and 5.8×10−23, 8.11×10−23 cm2 for the NMOS and PMOS structures, respectively. A low value of interface state density in both P- and N-MOS structures makes it a suitable alternate dielectric layer for CMOS applications. And also very low value of capture cross section for both the carriers due to the amphoteric nature of defect indicates that the traps are not aggressive recombination centers and possibly can not contribute to the device operation to a large extent.

  17. DLTS analysis of amphoteric interface defects in high-TiO2 MOS structures prepared by sol-gel spin-coating

    Science.gov (United States)

    Kumar, Arvind; Mondal, Sandip; Rao, K. S. R. Koteswara

    2015-11-01

    High-κ TiO2 thin films have been fabricated from a facile, combined sol - gel spin - coating technique on p and n type silicon substrate. XRD and Raman studies headed the existence of anatase phase of TiO2 with a small grain size of 18 nm. The refractive index `n' quantified from ellipsometry is 2.41. AFM studies suggest a high quality, pore free films with a fairly small surface roughness of 6 Å. The presence of Ti in its tetravalent state is confirmed by XPS analysis. The defect parameters observed at the interface of Si/TiO2 were studied by capacitance - voltage (C - V) and deep level transient spectroscopy (DLTS). The flat - band voltage (VFB) and the density of slow interface states estimated are - 0.9, - 0.44 V and 5.24×1010, 1.03×1011 cm-2; for the NMOS and PMOS capacitors, respectively. The activation energies, interface state densities and capture cross - sections measured by DLTS are EV + 0.30, EC - 0.21 eV; 8.73×1011, 6.41×1011 eV-1 cm-2 and 5.8×10-23, 8.11×10-23 cm2 for the NMOS and PMOS structures, respectively. A low value of interface state density in both P- and N-MOS structures makes it a suitable alternate dielectric layer for CMOS applications. And also very low value of capture cross section for both the carriers due to the amphoteric nature of defect indicates that the traps are not aggressive recombination centers and possibly can not contribute to the device operation to a large extent.

  18. Hydrogen intercalation in MoS2

    Science.gov (United States)

    Zhu, Zhen; Peelaers, Hartwin; Van de Walle, Chris G.

    2016-08-01

    We investigate the structure and energetics of interstitial hydrogen and hydrogen molecules in layered 2 H -MoS2, an issue of interest both for hydrogen storage applications and for the use of MoS2 as an (opto)electronic material. Using first-principles density functional theory we find that hydrogen interstitials are deep donors. H2 molecules are electrically inactive and energetically more stable than hydrogen interstitials. Their equilibrium position is the hollow site of the MoS2 layers. The migration barrier of a hydrogen molecule is calculated to be smaller than 0.6 eV. We have also explored the insertion energies of hydrogen molecules as a function of hydrogen concentration in MoS2. For low concentrations, additional inserted H2 molecules prefer to be located in hollow sites (on top of the center of a hexagon) in the vicinity of an occupied site. Once two molecules have been inserted, the energy cost for inserting additional H2 molecules becomes much lower. Once all hollow sites are filled, the energy cost increases, but only by a modest amount. We find that up to 13 H2 molecules can be accommodated within the same interlayer spacing of an areal 3 ×3 supercell.

  19. Stability and Electronic Properties of Hydrogenated MoS2 Monolayer: A First-Principles Study.

    Science.gov (United States)

    Zhang, Weibin; Zhang, Zhijun; Yang, Woochul

    2015-10-01

    First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-Hx) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-Hx is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-Hx forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-Hx on the electronic structure of the compound is also investigated. The MoS2-Hx band structure exhibits a dispersion and the MoS2-Hx band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.

  20. Interfacial chemical reactions between MoS2 lubricants and bearing materials

    Science.gov (United States)

    Zabinski, J. S.; Tatarchuk, B. J.

    1989-01-01

    XPS and conversion-electron Moessbauer spectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides, depending on the level of excess S in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to the MoS2 basal plane, and that alignment (and potentially adhesion) could be varied by appropriate high-temperature annealing procedures.

  1. Electron Emission from Ultra-Large Area MOS Electron Emitters

    DEFF Research Database (Denmark)

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm;

    2009-01-01

    Ultralarge metal-oxide-semiconductor (MOS) devices with an active oxide area of 1 cm2 have been fabricated for use as electron emitters. The MOS structures consist of a Si substrate, a SiO2 tunnel barrier (~5 nm), a Ti wetting layer (3–10 Å), and a Au top layer (5–60 nm). Electron emission from....... Electron emission under high pressures (up to 2 bars) of Ar was observed. ©2009 American Vacuum Society...

  2. First-principle and experiment investigation of MoS2@SnO2 nano-heterogeneous structures with enhanced humidity sensing performance

    Science.gov (United States)

    Lei, Xiang; Yu, Ke; Li, Honglin; Tang, Zheng; Guo, Bangjun; Li, Jinzhu; Fu, Hao; Zhang, Qingfeng; Zhu, Ziqiang

    2016-04-01

    In this work, we report the First-principle investigation and synthesis of MoS2@SnO2 heterostructure as high-performance humidity sensor by a two-step hydrothermal method. The first-principles calculations were performed to explain water molecule adsorption mechanism by applying density of state model to simulate the interaction between water molecule and sensing base material. The higher specific surface and the lower adsorption energy theoretically predicted the improvement on humidity sensing performance, which was confirmed by experiments testing. The MoS2@SnO2 heterostructure exhibited promoted humidity sensing characteristics on response time of 53 s and recovery time of 21 s, while switching the humidity between 11% relative humidity (RH) and 95% RH. The corresponding humidity sensing mechanisms of MoS2@SnO2 were elaborately interpreted. This work could bring forward a new design method on practical humidity sensing devices with an excellent stability and fast response by using MoS2@SnO2 heterostructure.

  3. Synthesis and characterization of vertically standing MoS2 nanosheets

    Science.gov (United States)

    Li, Han; Wu, Huaqiang; Yuan, Shuoguo; Qian, He

    2016-01-01

    Molybdenum disulfide (MoS2) has been attracting much attentions due to its excellent electrical and optical properties. We report here the synthesis of large-scale and uniform MoS2 nanosheets with vertically standing morphology using chemical vapor deposition method. TEM observations clearly reveal the growth mechanism of these vertical structures. It is suggested that the vertical structures are caused by the compression and extrusion between MoS2 islands. More importantly, the vertical morphology of two dimensional (2D) materials hold many promising potential applications. We demonstrate here the as-synthesized vertically standing MoS2 nanosheets could be used for hydrogen evolution reaction, where the exchange current density is about 70 times of bulk MoS2. The field emission performance of vertically standing MoS2 were also improved due to the abundantly exposed edges. PMID:26888690

  4. Broadband ultra-high transmission of terahertz radiation through monolayer MoS$_{2}$

    CERN Document Server

    Deng, Xue-Yong; Su, Fu-Hai; Liu, Nian-Hua; Liu, Jiang-Tao

    2015-01-01

    In this study, terahertz (THz) absorption and transmission of monolayer MoS$_{2}$ was calculated under different carrier concentrations. Results showed that the THz absorption of monolayer MoS$_{2}$ is very small even under high carrier concentrations and large incident angle. Equivalent loss of the THz absorption is the total sum of reflection and absorption that is one to three grades lower than that of graphene. The monolayer MoS$_{2}$ transmission is much larger than that of the traditional GaAs and InAs two-dimensional electron gas. The field-effect tubular structure formed by the monolayer MoS$_{2}$-insulation-layer-graphene is investigated. In this structure the THz absorption of graphene to reach saturation under low voltage. Meantime, the maximum THz absorption of monolayer MoS$_{2}$ was limited to approximately 5\\%. Thus, monolayer MoS$_{2}$ is a kind of ideal THz Transparent Electrodes.

  5. DLTS analysis of amphoteric interface defects in high-TiO{sub 2} MOS structures prepared by sol-gel spin-coating

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Arvind; Mondal, Sandip; Rao, K. S. R. Koteswara, E-mail: ksrkrao@physics.iisc.ernet.in, E-mail: raoksrk@gmail.com [Department of Physics, Indian Institute of Science, Bangalore, 560012 (India)

    2015-11-15

    High-κ TiO{sub 2} thin films have been fabricated from a facile, combined sol – gel spin – coating technique on p and n type silicon substrate. XRD and Raman studies headed the existence of anatase phase of TiO{sub 2} with a small grain size of 18 nm. The refractive index ‘n’ quantified from ellipsometry is 2.41. AFM studies suggest a high quality, pore free films with a fairly small surface roughness of 6 Å. The presence of Ti in its tetravalent state is confirmed by XPS analysis. The defect parameters observed at the interface of Si/TiO{sub 2} were studied by capacitance – voltage (C – V) and deep level transient spectroscopy (DLTS). The flat – band voltage (V{sub FB}) and the density of slow interface states estimated are – 0.9, – 0.44 V and 5.24×10{sup 10}, 1.03×10{sup 11} cm{sup −2}; for the NMOS and PMOS capacitors, respectively. The activation energies, interface state densities and capture cross – sections measured by DLTS are E{sub V} + 0.30, E{sub C} – 0.21 eV; 8.73×10{sup 11}, 6.41×10{sup 11} eV{sup −1} cm{sup −2} and 5.8×10{sup −23}, 8.11×10{sup −23} cm{sup 2} for the NMOS and PMOS structures, respectively. A low value of interface state density in both P- and N-MOS structures makes it a suitable alternate dielectric layer for CMOS applications. And also very low value of capture cross section for both the carriers due to the amphoteric nature of defect indicates that the traps are not aggressive recombination centers and possibly can not contribute to the device operation to a large extent.

  6. The impact of ultrathin Al2O3 films on the electrical response of p-Ge/Al2O3/HfO2/Au MOS structures

    Science.gov (United States)

    Botzakaki, M. A.; Skoulatakis, G.; Kennou, S.; Ladas, S.; Tsamis, C.; Georga, S. N.; Krontiras, C. A.

    2016-09-01

    It is well known that the most critical issue in Ge CMOS technology is the successful growth of high-k gate dielectrics on Ge substrates. The high interface quality of Ge/high-k dielectric is connected with advanced electrical responses of Ge based MOS devices. Following this trend, atomic layer deposition deposited ultrathin Al2O3 and HfO2 films were grown on p-Ge. Al2O3 acts as a passivation layer between p-Ge and high-k HfO2 films. An extensive set of p-Ge/Al2O3/HfO2 structures were fabricated with Al2O3 thickness ranging from 0.5 nm to 1.5 nm and HfO2 thickness varying from 2.0 nm to 3.0 nm. All structures were characterized by x-ray photoelectron spectroscopy (XPS) and AFM. XPS analysis revealed the stoichiometric growth of both films in the absence of Ge sub-oxides between p-Ge and Al2O3 films. AFM analysis revealed the growth of smooth and cohesive films, which exhibited minimal roughness (~0.2 nm) comparable to that of clean bare p-Ge surfaces. The electrical response of all structures was analyzed by C-V, G-V, C-f, G-f and J-V characteristics, from 80 K to 300 K. It is found that the incorporation of ultrathin Al2O3 passivation layers between p-Ge and HfO2 films leads to superior electrical responses of the structures. All structures exhibit well defined C-V curves with parasitic effects, gradually diminishing and becoming absent below 170 K. D it values were calculated at each temperature, using both Hill-Coleman and Conductance methods. Structures of p-Ge/0.5 nm Al2O3/2.0 nm HfO2/Au, with an equivalent oxide thickness (EOT) equal to 1.3 nm, exhibit D it values as low as ~7.4  ×  1010 eV-1 cm-2. To our knowledge, these values are among the lowest reported. J-V measurements reveal leakage currents in the order of 10-1 A cm-2, which are comparable to previously published results for structures with the same EOT. A complete mapping of the energy distribution of D its into the energy bandgap of p-Ge, from the valence band

  7. Highly stretchable MoS2 kirigami

    Science.gov (United States)

    Hanakata, Paul Z.; Qi, Zenan; Campbell, David K.; Park, Harold S.

    2015-12-01

    We report the results of classical molecular dynamics simulations focused on studying the mechanical properties of MoS2 kirigami. Several different kirigami structures were studied based upon two simple non-dimensional parameters, which are related to the density of cuts, as well as the ratio of the overlapping cut length to the nanoribbon length. Our key findings are significant enhancements in tensile yield (by a factor of four) and fracture strains (by a factor of six) as compared to pristine MoS2 nanoribbons. These results, in conjunction with recent results on graphene, suggest that the kirigami approach may be generally useful for enhancing the ductility of two-dimensional nanomaterials.

  8. Formation Energies of the Lithium Intercalations in MoS2

    Institute of Scientific and Technical Information of China (English)

    Aiyu LI; Huiying LIU; Zizhong ZHU; Meichun HUANG; Yong YANG

    2006-01-01

    First-principles calculations have been performed to study the lithium intercalations in MoS2. The formation energies, changes of volumes, electronic structures and charge densities of the lithium intercalations in MoS2 are presented. Our calculations show that during lithium intercalations in MoS2, the lithium intercalation formation energies per lithium atom are between 2.5 eV to 3.0 eV, The volume expansions of MoS2 due to lithium intercalations are relatively small

  9. Hierarchical MoS2-rGO nanosheets with high MoS2 loading with enhanced electro-catalytic performance

    Science.gov (United States)

    Zhou, Jing; Xiao, Han; Zhou, Bowen; Huang, Feifan; Zhou, Shoubin; Xiao, Wei; Wang, Dihua

    2015-12-01

    Incorporation of high-loading redox-active materials with small amounts of graphene is a general protocol to achieve high-performance catalysts. Herein, hierarchical MoS2-reduced graphene oxide nanosheet (denoted as MoS2-rGO nanosheets) hybrids with a loading of MoS2 as high as 94 wt% are synthesized. The obtained hierarchical MoS2-rGO nanosheets simultaneously integrate the structural and compositional design rationales for high-efficiency and durable electrocatalysts based on high weight ratio of MoS2 in hybrid composite, highly stable/conducting rGO, well-dispersed two-dimensional ultrathin MoS2 nanosheets, more exposed edge sites and micro/nano hierarchical structure. When evaluated as electrocatalysts for hydrogen evolution and oxygen reduction reactions, the hierarchical MoS2-rGO nanosheets demonstrates enhanced activity and excellent stability, promising their applications in MoS2 based electrochemical, photo-catalytic and photo-elecrocatalytic cells.

  10. Electron irradiation effects on power MOS transistors

    Energy Technology Data Exchange (ETDEWEB)

    Frisina, F.; Tavolo, N. (S.G.S. Thomson Microelectronics, Catania (Italy)); Gombia, E.; Mosca, R. (Consiglio Nazionale delle Ricerche, Parma (Italy). Ist. MASPEC); Chirco, P.; Fuochi, P.G. (Consiglio Nazionale delle Ricerche, Bologna (Italy). Lab. di Fotochimica e Radiazioni d' Alta Energia)

    1990-01-01

    Electron irradiation has been used to enhance the switching speed of the internal diode in high-voltage power MOS structures (BV{sub DSS} > 500 V). By using 12 MeV electron irradiation at room temperature it has been found that the reverse recovery time and the reverse recovery charge of power MOS internal diode can be reduced in a well controlled manner up to 70% and 90% of their initial value respectively increasing the radiation dose from 0 to 15 Mrads. Anyway an undesirable decrease of about 3V has been observed in the gate threshold voltage. This effect has been ascribed to the damage produced in the gate oxide of the device due to the electron irradiation. By annealing the device at temperature >315{sup 0}C it has been possible to restore the threshold voltage without heavily enhancing the carrier lifetime. DLTS measurements have been performed on electron-irradiated devices to identify the recombination centres introduced in the forbidden gap of the silicon. A comparison has been made with gold-diffused devices. The results obtained confirm that electron irradiation is feasible for power MOS transistors. (author).

  11. Band gap engineering of MoS2 upon compression

    Science.gov (United States)

    López-Suárez, Miquel; Neri, Igor; Rurali, Riccardo

    2016-04-01

    Molybdenum disulfide (MoS2) is a promising candidate for 2D nanoelectronic devices, which shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS2 upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e., ±0.15). However, compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS2, show semi-conductor to metal transition upon compressive strain without bucking.

  12. Effects of plasma treatment on surface properties of ultrathin layered MoS2

    Science.gov (United States)

    Kim, Suhhyun; Choi, Min Sup; Qu, Deshun; Ra, Chang Ho; Liu, Xiaochi; Kim, Minwoo; Song, Young Jae; Jong Yoo, Won

    2016-09-01

    This work investigates the use of oxygen plasma (O2) treatment, applied as an inductively coupled plasma, to control the thickness and work function of a MoS2 layer. Plasma-etched MoS2 exhibited a surface roughness similar to that of the pristine MoS2. The MoS2 field effect transistors fabricated using the plasma-etched MoS2 displayed a higher n-type doping concentration than that of pristine MoS2. The x-ray photoelectron spectroscopy was performed to analyze chemical composition to demonstrate the minimum level of chemical reactions occurred upon plasma treatment. Moreover, Kelvin probe force microscopy measurements were conducted to probe the changes in the work function that could be attributed to the changes in the surface potential. The measured work functions suggest the modification of a band structure and n-doping effect after plasma treatments that depended on the number of MoS2 layers. This study suggests that the O2 plasma can control the layer number of the MoS2 as well as the electronic properties of a MoS2 film.

  13. Effects of La, Ce and Nd doping on the electronic structure of monolayer MoS2%La,Ce,Nd掺杂对单层MoS2电子结构的影响

    Institute of Scientific and Technical Information of China (English)

    雷天民; 吴胜宝; 张玉明; 郭辉; 陈德林; 张志勇

    2014-01-01

    To study the effect of rare earth element doping on the electronic structure of monolayer MoS2, the lattice parame-ters, band structures, density of states, and electron density differences of La, Ce and Nd doped and intrinsic monolayer MoS2 are calculated, respectively, using first-principles density functional theory based on the plane wave pseudopoten-tial method in this paper. Calculations indicate that variations of bond length near La impurity are maximum, but they are the minimum near Nd impurity. Analysis points out that lattice distortion in doped monolayer of MoS2 is relative to the magnitude of the covalent radius of doping atom. Analysis of band structure shows that La, Ce and Nd doping can induce three, six and four energy levels, respectively, in the forbidden band of MoS2, and that the properties of impurity levels are analyzed. Rare earth doped monolayer MoS2 make change in electron distribution through the analysis of electron density difference, and especially, the existence of f electrons can induce the electron density difference to exhibit a physical image with a great contrast.%为了研究稀土掺杂对单层MoS2电子结构的影响,文章基于密度泛函理论框架下的第一性原理,采用平面波赝势方法分别计算了本征及La, Ce, Nd掺杂单层MoS2的晶格参数、能带结构、态密度和差分电荷密度。计算发现,稀土掺杂所引起的晶格畸变与杂质原子的共价半径大小有关, La杂质附近的键长变化最大, Nd杂质附近的键长变化最小。能带结构分析表明, La掺杂可以在MoS2的禁带中引入3个能级, Ce掺杂可以形成6个新能级, Nd掺杂可以形成4个能级,并对杂质能级属性进行了初步分析。差分电荷密度分布显示,稀土掺杂可以使单层MoS2中的电子分布发生改变,尤其是f电子的存在会使差分电荷密度呈现出反差极大的物理图象。

  14. Conduction quantization in monolayer MoS2

    Science.gov (United States)

    Li, T. S.

    2016-10-01

    We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

  15. Surface Defects on Natural MoS2.

    Science.gov (United States)

    Addou, Rafik; Colombo, Luigi; Wallace, Robert M

    2015-06-10

    Transition metal dichalcogenides (TMDs) are being considered for a variety of electronic and optoelectronic devices such as beyond complementary metal-oxide-semiconductor (CMOS) switches, light-emitting diodes, solar cells, as well as sensors, among others. Molybdenum disulfide (MoS2) is the most studied of the TMDs in part because of its availability in the natural or geological form. The performance of most devices is strongly affected by the intrinsic defects in geological MoS2. Indeed, most sources of current transition metal dichalcogenides have defects, including many impurities. The variability in the electrical properties of MoS2 across the surface of the same crystal has been shown to be correlated with local variations in stoichiometry as well as metallic-like and structural defects. The presence of impurities has also been suggested to play a role in determining the Fermi level in MoS2. The main focus of this work is to highlight a number of intrinsic defects detected on natural, exfoliated MoS2 crystals from two different sources that have been often used in previous reports for device fabrication. We employed room temperature scanning tunneling microscopy (STM) and spectroscopy (STS), inductively coupled plasma mass spectrometry (ICPMS), as well as X-ray photoelectron spectroscopy (XPS) to study the pristine surface of MoS2(0001) immediately after exfoliation. ICPMS used to measure the concentration of impurity elements can in part explain the local contrast behavior observed in STM images. This work highlights that the high concentration of surface defects and impurity atoms may explain the variability observed in the electrical and physical characteristics of MoS2. PMID:25980312

  16. Synthesis of coaxial nanotubes of MoS2 and carbon

    International Nuclear Information System (INIS)

    The di chalcogenides WS2 and MoS2 by their tubular properties were combined. It was synthesized coaxial structures of MoS2 with C with the purpose to studying the possible structural changes of the MoS2 nano tubes at was submitted to a propylene gas flux as carbon precursor in a thermal treatment. Studies of structural characterization by Transmission Electron Microscopy (Tem) were realized. The theoretical simulation of the structure was realized using an algorithm type multilayer. The possibility of the nano tubes are applied to gas storage as can be the hydrogen arouse interest by the energy production. (Author)

  17. Hydrothermal synthesis of flower-like MoS2 nanospheres for electrochemical supercapacitors.

    Science.gov (United States)

    Zhou, Xiaoping; Xu, Bin; Lin, Zhengfeng; Shu, Dong; Ma, Lin

    2014-09-01

    Flower-like MoS2 nanospheres were synthesized by a hydrothermal route. The structure and surface morphology of the as-prepared MoS2 was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of MoS2 in 1 M KCl electrolyte was studied by means of cyclic voltammetry (CV), constant current charge-discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD results indicate that the as-prepared MoS2 has good crystallinity. SEM images show that the MoS2 nanospheres have uniform sizes with mean diameter about 300 nm. Many nanosheets growing on the surface make the MoS2 nanospheres to be a flower-like structure. The specific capacitance of MoS2 is 122 F x g(-1) at 1 A x g(-1) or 114 F x g(-1) at 2 mv s(-1). All the experimental results indicate that MoS2 is a promising electrode material for electrochemical supercapacitors. PMID:25924398

  18. First-principles analysis of MoS2/Ti2C and MoS2/Ti2CY2 (Y=F and OH) all-2D semiconductor/metal contacts

    KAUST Repository

    Gan, Li-Yong

    2013-06-13

    First-principles calculations are used to explore the geometry, bonding, and electronic properties of MoS2/Ti2C and MoS2/Ti2CY2 (Y = F and OH) semiconductor/metal contacts. The structure of the interfaces is determined. Strong chemical bonds formed at the MoS2/Ti2C interface result in additional states next to the Fermi level, which extend over the three atomic layers of MoS2 and induce a metallic character. The interaction in MoS2/Ti2CY2, on the other hand, is weak and not sensitive to the specific geometry, and the semiconducting nature thus is preserved. The energy level alignment implies weak and strong n-type doping of MoS2 in MoS2/Ti2CF2 and MoS2/Ti2C(OH)2, respectively. The corresponding n-type Schottky barrier heights are 0.85 and 0.26 eV. We show that the MoS2/Ti2CF2 interface is close to the Schottky limit. At the MoS2/Ti2C(OH)2 interface, we find that a strong dipole due to charge rearrangement induces the Schottky barrier. The present interfaces are well suited for application in all-two-dimensional devices.

  19. Photoconductivities in MoS2 Nanoflake Photoconductors.

    Science.gov (United States)

    Shen, Wei-Chu; Chen, Ruei-San; Huang, Ying-Sheng

    2016-12-01

    Photoconductivities in molybdenum disulfide (MoS2) layered nanostructures with two-hexagonal crystalline structure prepared by mechanical exfoliation were investigated. The photoconductor-type MoS2 nanoflakes exhibit remarkable photoresponse under the above bandgap excitation wavelength of 532 nm at different optical intensity. The photocurrent responsivity and photoconductive gain of nanoflakes can reach, respectively, 30 AW(-1) and 103 at the intensity of 50 Wm(-2), which are several orders of magnitude higher than those of their bulk counterparts. The vacuum-enhanced photocurrent and power-independent responsivity/gain indicate a surface-controlled photoconduction mechanism in the MoS2 nanomaterial. PMID:26935304

  20. Thermoelectric performance of restacked MoS2 nanosheets thin-film.

    Science.gov (United States)

    Wang, Tongzhou; Liu, Congcong; Xu, Jingkun; Zhu, Zhengyou; Liu, Endou; Hu, Yongjing; Li, Changcun; Jiang, Fengxing

    2016-07-15

    MoS2 has been predicted to be an excellent thermoelectric material due to its large intrinsic band gap and high carrier mobility. In this work, we exfoliated bulk MoS2 by the assistance of lithium intercalation and fabricated the restacked MoS2 thin-film using a simple filtration technique. These MoS2 thin-films with different thickness showed different thermoelectric performance. It was found that with the increase of thickness, carrier concentration, electrical conductivity and Seebeck coefficient all showed an increasing trend. In particular, the maximum Seebeck coefficient was able to reach 93.5 μV K(-1). This high thermopower indicates that MoS2 will have ideal thermoelectric performance in the future through optimizing its structure. The highest figure of merit (ZT = 0.01) is calculated in this experiment.

  1. Thermoelectric performance of restacked MoS2 nanosheets thin-film

    Science.gov (United States)

    Wang, Tongzhou; Liu, Congcong; Xu, Jingkun; Zhu, Zhengyou; Liu, Endou; Hu, Yongjing; Li, Changcun; Jiang, Fengxing

    2016-07-01

    MoS2 has been predicted to be an excellent thermoelectric material due to its large intrinsic band gap and high carrier mobility. In this work, we exfoliated bulk MoS2 by the assistance of lithium intercalation and fabricated the restacked MoS2 thin-film using a simple filtration technique. These MoS2 thin-films with different thickness showed different thermoelectric performance. It was found that with the increase of thickness, carrier concentration, electrical conductivity and Seebeck coefficient all showed an increasing trend. In particular, the maximum Seebeck coefficient was able to reach 93.5 μV K‑1. This high thermopower indicates that MoS2 will have ideal thermoelectric performance in the future through optimizing its structure. The highest figure of merit (ZT = 0.01) is calculated in this experiment.

  2. Graphite edge controlled registration of monolayer MoS2 crystal orientation

    International Nuclear Information System (INIS)

    Transition metal dichalcogenides such as the semiconductor MoS2 are a class of two-dimensional crystals. The surface morphology and quality of MoS2 grown by chemical vapor deposition are examined using atomic force and scanning tunneling microscopy techniques. By analyzing the moiré patterns from several triangular MoS2 islands, we find that there exist at least five different superstructures and that the relative rotational angles between the MoS2 adlayer and graphite substrate lattices are typically less than 3°. We conclude that since MoS2 grows at graphite step-edges, it is the edge structure which controls the orientation of the islands, with those growing from zig-zag (or armchair) edges tending to orient with one lattice vector parallel (perpendicular) to the step-edge

  3. Large-Area Buckled MoS2 Films on the Graphene Substrate.

    Science.gov (United States)

    Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae

    2016-06-01

    In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications. PMID:27144288

  4. Large-Area Buckled MoS2 Films on the Graphene Substrate.

    Science.gov (United States)

    Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae

    2016-06-01

    In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications.

  5. The OverMOS project

    Science.gov (United States)

    Das, D.; Dopke, J.; McMahon, S. J.; Turchetta, R.; Villani, G.; Wilson, F.; Worm, S.

    2016-07-01

    The OverMOS project aims to create a fast radiation hard tracking detector sensor, based on High Resistivity CMOS technology. In a first prototype submission, different pixel and charge collection node geometries have been produced, which have lately been returned from fabrication and are currently under test.

  6. BATMAN: MOS Spectroscopy on Demand

    Science.gov (United States)

    Molinari, E.; Zamkotsian, F.; Moschetti, M.; Spano, P.; Boschin, W.; Cosentino, R.; Ghedina, A.; González, M.; Pérez, H.; Lanzoni, P.; Ramarijaona, H.; Riva, M.; Zerbi, F.; Nicastro, L.; Valenziano, L.; Di Marcantonio, P.; Coretti, I.; Cirami, R.

    2016-10-01

    Multi-Object Spectrographs (MOS) are the major instruments for studying primary galaxies and remote and faint objects. Current object selection systems are limited and/or difficult to implement in next generation MOS for space and ground-based telescopes. A promising solution is the use of MOEMS devices such as micromirror arrays, which allow the remote control of the multi-slit configuration in real time. TNG is hosting a novelty project for real-time, on-demand MOS masks based on MOEMS programmable slits. We are developing a 2048×1080 Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Galileo telescope, called BATMAN. It is a two-arm instrument designed for providing in parallel imaging and spectroscopic capabilities. With a field of view of 6.8×3.6 arcmin and a plate scale of 0.2 arcsec per micromirror, this astronomical setup can be used to investigate the formation and evolution of galaxies. The wavelength range is in the visible and the spectral resolution is R=560 for a 1 arcsec object, and the two arms will have 2k × 4k CCD detectors. ROBIN, a BATMAN demonstrator, has been designed, realized and integrated. We plan to have BATMAN first light by mid-2016.

  7. A 77 K MOS magnetic field detector

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, R S; Torres, A. [Instituto Nacional de Astrofisica Optica y Electronica, Puebla (Mexico); Garcia, P.J. [Universidad Veracruzana, Veracruz (Mexico); Gutierrez, E.A. [Motorola, Puebla (Mexico)

    2001-12-01

    An integrated MOS (metal-oxide-semiconductor)-compatible magnetic field detector (split-drain MAGFET) for operation at liquid-nitrogen temperature LNT (77 K) is presented. The measured relative magnetic sensibility (S{sub a}) is approximately 14%/T (double the value ever reported) using a non-optimized MAGFET structure (W/L) = (100 mm/125 mm). The cryo-magnetic structure was tested without a built-in preamplifier. It presents a power consumption of the order of mW. [Spanish] A traves de este articulo se presenta un detector de campo magnetico (split-drain MAGFET), basado en el transistor de efecto de campo MOS (metal-oxido-semiconductor), y totalmente compatible con procesos de fabricacion de circuitos integrados CMOS. La operacion optima de este detector es a temperaturas criogenicas. Aqui se presentan los resultados experimentales de la caracterizacion de una estructura no optimizada con dimensiones (W / L) = (100 mm/125 mm) a la temperatura del nitrogeno liquido (77 K). La sensibilidad relativa medida es de cerca del 14 % T, casi el doble del valor maximo antes reportado en la literatura. El dispositivo se midio sin un pre-amplificador integrado, mostrando un consumo de potencia del orden de microwatts.

  8. Large-Area Growth of Uniform Single-Layer MoS2 Thin Films by Chemical Vapor Deposition.

    Science.gov (United States)

    Baek, Seung Hyun; Choi, Yura; Choi, Woong

    2015-12-01

    We report the largest-size thin films of uniform single-layer MoS2 on sapphire substrates grown by chemical vapor deposition based on the reaction of gaseous MoO3 and S evaporated from solid sources. The as-grown thin films of single-layer MoS2 were continuous and uniform in thickness for more than 4 cm without the existence of triangular-shaped MoS2 clusters. Compared to mechanically exfoliated crystals, the as-grown single-layer MoS2 thin films possessed consistent chemical valence states and crystal structure along with strong photoluminescence emission and optical absorbance at high energy. These results demonstrate that it is possible to scale up the growth of uniform single-layer MoS2 thin films, providing potentially important implications on realizing high-performance MoS2 devices.

  9. Effect of MoO3 constituents on the growth of MoS2 nanosheets by chemical vapor deposition

    Science.gov (United States)

    Wang, Xuan; Zhang, Yong Ping; Qian Chen, Zhi

    2016-06-01

    The highly crystalline and uniform MoS2 film was grown on Si substrate by a low-pressure chemical vapor deposition method using S and MoO3 as precursors at an elevated temperature. The structures and properties of MoS2 nanosheets vary greatly with the content of MoO3 constituents in the films. The nanostructured MoS2 film exhibits strong photoluminescence in the visible range. This work may provide a pathway to synthesizing MoS2 nanosheets and facilitate the development of applicable devices.

  10. Plasma nanocoating of thiophene onto MoS2 nanotubes

    Science.gov (United States)

    Türkaslan, Banu Esencan; Dikmen, Sibel; Öksüz, Lütfi; Öksüz, Aysegul Uygun

    2015-12-01

    MoS2 nanotubes were coated with conductive polymer thiophene by atmospheric pressure radio-frequency (RF) glow discharge. MoS2 nanotubes were prepared by thermal decomposition of hexadecylamine (HDA) intercalated laminar MoS2 precursor on anodized aluminum oxide template and the thiophene was polymerized directly on surface of these nanotubes as in situ by plasma method. The effect of plasma power on PTh/MoS2 nanocomposite properties has been investigated by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM and EDX), and X-ray diffraction spectroscopy (XRD). The presence of PTh bands in the FTIR spectra of PTh/MoS2 nanotube nanocomposites corresponding XRD results indicates that the polythiophene coating onto MoS2 nanotube. The chemical structure of PTh is not changed when the plasma power of discharge differ from 117 to 360 W. SEM images of nanocomposites show that when the discharge power is increased between 117 and 360 W the average diameter of PTh/MoS2 nanotube nanocomposites are changed and the structure become more uniformly.

  11. Thermal conductivity of MoS2 polycrystalline nanomembranes

    Science.gov (United States)

    Sledzinska, M.; Graczykowski, B.; Placidi, M.; Saleta Reig, D.; El Sachat, A.; Reparaz, J. S.; Alzina, F.; Mortazavi, B.; Quey, R.; Colombo, L.; Roche, S.; Sotomayor Torres, C. M.

    2016-09-01

    Heat conduction in 2D materials can be effectively engineered by means of controlling nanoscale grain structure. A favorable thermal performance makes these structures excellent candidates for integrated heat management units. Here we show combined experimental and theoretical studies for MoS2 nanosheets in a nanoscale grain-size limit. We report thermal conductivity measurements on 5 nm thick polycrystalline MoS2 by means of 2-laser Raman thermometry. The free-standing, drum-like MoS2 nanomembranes were fabricated using a novel polymer- and residue-free, wet transfer, in which we took advantage of the difference in the surface energies between MoS2 and the growth substrate to transfer the CVD-grown nanosheets. The measurements revealed a strong reduction in the in-plane thermal conductivity down to about 0.73 ± 0.25 {{{W}}{{m}}}-1 {{{K}}}-1. The results are discussed theoretically using finite elements method simulations for a polycrystalline film, and a scaling trend of the thermally conductivity with grain size is proposed.

  12. Electronic and magnetic properties of MoS2 nanoribbons with sulfur line vacancy defects

    Science.gov (United States)

    Han, Yang; Zhou, Jian; Dong, Jinming

    2015-08-01

    Motivated by the recent experimental result that single sulfur vacancies in monolayer MoS2 are mobile under the electron beam and easily agglomerate into the sulfur line vacancy defects [Physical Review B 88, 035301(2013)] , the structural, electronic and magnetic properties of one dimensional zigzag (ZZ) and armchair (AC) edge MoS2 nanoribbons with single or double staggered sulfur line vacancy defects (hereafter, abbreviated as SV or DV, respectively), parallel to their edges, have been investigated systematically by density functional theory calculations. It is very interesting to find that the bond strains induced by the sulfur line vacancy defect can cause a much larger out-of plane distortions in the ZZ edge MoS2 nanoribbon than in the AC edge counterpart. Besides, the defective ZZ edge MoS2 nanoribbons with SV or DV are both metals, having their two respective degenerate ground states with the same energy, among which one is ferromagnetic (FM " + +") and the other is antiferromagnetic (AFM " + -"). But the AC edge MoS2 nanoribbons with SV or DV are both nonmagnetic semiconductors, having very different gap values. Finally, the sulfur line vacancy defects would induce some defect states in the electronic structures of the defective MoS2 nanoribbons. All these important results could provide a new route of tuning the electronic properties of MoS2 nanoribbons and its derivatives for their promising applications in nanoelectronics and optoelectronics.

  13. A Multiple—Valued Algebra for Modeling MOS VLSI Circuits at Switch—Level

    Institute of Scientific and Technical Information of China (English)

    胡谋

    1992-01-01

    A multiple-valued algebra for modeling MOS VLSI circuits at switch-level is proposed in this paper,Its structure and properties are studied.This algebra can be used to transform a MOS digital circuit to a swith-level algebraic expression so as to generate the truth table for the circuit and to derive a Boolean expression for it.In the paper,methods to construct a switch-level algebraic expression for a circuit and methods to simplify expressions are given.This algebra provides a new tool for MOS VLSI circuit design and analysis.

  14. Synthesis of Vertically Standing MoS2 Triangles on SiC

    Science.gov (United States)

    Lan, Feifei; Lai, Zhanping; Xu, Yongkuan; Cheng, Hongjuan; Wang, Zaien; Qi, Chengjun; Chen, Jianli; Zhang, Song

    2016-08-01

    Layered material MoS2 has been attracting much attention due to its excellent electronical properties and catalytic property. Here we report the synthesis of vertically standing MoS2 triangles on silicon carbon(SiC), through a rapid sulfidation process. Such edge-terminated films are metastable structures of MoS2, which may find applications in FinFETs and catalytic reactions. We have confirmed the catalytic property in a hydrogen evolution reaction(HER). The Tafel slope is about 54mV/decade.

  15. Synthesis of Vertically Standing MoS2 Triangles on SiC.

    Science.gov (United States)

    Lan, Feifei; Lai, Zhanping; Xu, Yongkuan; Cheng, Hongjuan; Wang, Zaien; Qi, Chengjun; Chen, Jianli; Zhang, Song

    2016-01-01

    Layered material MoS2 has been attracting much attention due to its excellent electronical properties and catalytic property. Here we report the synthesis of vertically standing MoS2 triangles on silicon carbon(SiC), through a rapid sulfidation process. Such edge-terminated films are metastable structures of MoS2, which may find applications in FinFETs and catalytic reactions. We have confirmed the catalytic property in a hydrogen evolution reaction(HER). The Tafel slope is about 54mV/decade. PMID:27550237

  16. All Chemical Vapor Deposition Growth of MoS2:h-BN Vertical van der Waals Heterostructures.

    Science.gov (United States)

    Wang, Shanshan; Wang, Xiaochen; Warner, Jamie H

    2015-05-26

    Vertical van der Waals heterostructures are formed when different 2D crystals are stacked on top of each other. Improved optical properties arise in semiconducting transition metal dichalcogenide (TMD) 2D materials, such as MoS2, when they are stacked onto the insulating 2D hexagonal boron nitride (h-BN). Most work to date has required mechanical exfoliation of at least one of the TMDs or h-BN materials to form these semiconductor:insulator structures. Here, we report a direct all-CVD process for the fabrication of high-quality monolayer MoS2:h-BN vertical heterostructured films with isolated MoS2 domains distributed across 1 cm. This is enabled by the use of few-layer h-BN films that are more robust against decomposition than monolayer h-BN during the MoS2 growth process. The MoS2 domains exhibit different growth dynamics on the h-BN surfaces compared to bare SiO2, confirming that there is strong interaction between the MoS2 and underlying h-BN. Raman and photoluminescence spectroscopies of CVD-grown MoS2 are compared to transferred MoS2 on both types of substrates, and our results show directly grown MoS2 on h-BN films have smaller lattice strain, lower doping level, cleaner and sharper interfaces, and high-quality interlayer contact. PMID:25895108

  17. A MOS for all seasons

    Science.gov (United States)

    Bryant, Larry

    1993-01-01

    From a systems perspective, this paper examines the challenges of a single system to support multiple JPL space exploration missions and the need for unitary responsibility for the system. The focus is a Mission Operations System (MOS), which is effectively a mission management organization with direct authority over data system operations, command sequencing, flight operations control, data management, trajectory determination, telemetry and data acquisition, and spacecraft analysis. Stratagems for training and the approach to processes, procedures, and interfaces to facilitate the transition from the present situation to a truly multimission operational environment are developed. The outcome is a paradigm for a MOS that is achievable, that can effectively support multiple projects, and that can take advantage of technological changes without perturbing the entire system.

  18. MoS2 spaser

    Science.gov (United States)

    Jayasekara, Charith; Premaratne, Malin; Gunapala, Sarath D.; Stockman, Mark I.

    2016-04-01

    We present a comprehensive analysis of a spaser made of a circular shaped highly doped molybdenum disulfide (MoS2) resonator. "Spaser" is an acronym for "surface plasmon amplification by stimulated emission of radiation"-a nanoscale source of surface plasmons generated by stimulated emission in a plasmonic resonator which receives energy nonradiatively. By considering localized surface plasmon modes, operation characteristics of the model are analysed, and tunability of the design is demonstrated. We find the optimum geometric and material parameters of the spaser that provides efficient outputs and carryout a comparative analysis with a similar circular spaser made of graphene. Owing to physical and chemical properties of MoS2 and the active medium, the proposed design delivers efficient outputs in terms of spaser mode energy, operating thresholds, Q-factor, and electric field amplitude. Lower operating thresholds and higher mode energies are notable advantages of the design. Owing to having many superior features to existing similar designs, this MoS2 spaser may be much suited for applications in nanoplasmonic devices.

  19. Single-layer MoS2 transistors.

    Science.gov (United States)

    Radisavljevic, B; Radenovic, A; Brivio, J; Giacometti, V; Kis, A

    2011-03-01

    Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting. PMID:21278752

  20. Lubrication with sputtered MoS2 films: Principles, operation, limitations

    Science.gov (United States)

    Spalvins, T.

    1991-01-01

    The present practices, limitations, and understanding of thin sputtered MoS2 films are reviewed. Sputtered MoS2 films can exhibit remarkable tribological properties such as ultralow friction coefficients (0.01) and enhanced wear lives (millions of cycles) when used in vacuum or dry air. To achieve these favorable tribological characteristics, the sputtering conditions during deposition must be optimized for adequate film adherence and appropriate structure (morphology) and composition.

  1. Facile Hydrothermal Synthesis of Monodispersed MoS2 Ultrathin Nanosheets Assisted by Ionic Liquid Brij56

    Directory of Open Access Journals (Sweden)

    Guan-Qun Han

    2015-01-01

    Full Text Available Monodispersed MoS2 ultrathin nanosheets have been successfully fabricated by a facile hydrothermal process assisted by ionic liquid Brij56. The effect of Brij56 on the morphology and structure of MoS2 has been obviously observed. XRD shows that the as-prepared MoS2 assisted by Brij56 has the weak and broad peak of (002 planes, which implies the small size and well dispersed structure of MoS2 nanosheets. TEM and SEM images reveal that MoS2 ultrathin nanosheets have small size and few stacking layers with the adding of Brij56. HRTEM images prove that MoS2 appears to have a highly monodispersed morphology and to be monolayer ultrathin nanosheets with the length about 5–8 nm, which can provide more exposed rims and edges as active sites for hydrogen evolution reaction. Brij56 has played a crucial role in preparing monodispersed MoS2 ultrathin nanosheets as excellent electrocatalysts. The growth mechanism of monodispersed MoS2 has been discussed in detail.

  2. Cluster-support interactions and morphology of MoS2 nanoclusters in a graphite-supported hydrotreating model catalyst.

    Science.gov (United States)

    Kibsgaard, Jakob; Lauritsen, Jeppe V; Laegsgaard, Erik; Clausen, Bjerne S; Topsøe, Henrik; Besenbacher, Flemming

    2006-10-25

    Supported MoS(2) nanoparticles constitute the active component of the important hydrotreating catalysts used for industrial upgrading and purification of the oil feedstock for the production of fossil fuels with a low environmental load. We have synthesized and studied a model system of the hydrotreating catalyst consisting of MoS(2) nanoclusters supported on a graphite surface in order to resolve a number of very fundamental questions related to the atomic-scale structure and morphology of the active clusters and in particular the effect of a substrate used in some types of hydrotreating catalysts. Scanning tunneling microscopy (STM) is used to image the atomic-scale structure of graphite-supported MoS(2) nanoclusters in real space. It is found that the pristine graphite (0001) surface does not support a high dispersion of MoS(2), but by introducing a small density of defects in the surface, highly dispersed MoS(2) nanoclusters could be synthesized on the graphite. From high-resolution STM images it is found that MoS(2) nanoclusters synthesized at low temperature in a sulfiding atmosphere preferentially grow as single-layer clusters, whereas clusters synthesized at 1200 K grow as multilayer slabs oriented with the MoS(2)(0001) basal plane parallel to the graphite surface. The morphology of both single-layer and multilayer MoS(2) nanoclusters is found to be preferentially hexagonal, and atom-resolved images of the top facet of the clusters provide new atomic-scale information on the MoS(2)-HOPG bonding. The structure of the two types of catalytically interesting edges terminating the hexagonal MoS(2) nanoclusters is also resolved in atomic detail in STM images, and from these images it is possible to reveal the atomic structure of both edges and the location and coverage of sulfur and hydrogen adsorbates.

  3. Graphene decorated with MoS2 nanosheets: a synergetic energy storage composite electrode for supercapacitor applications.

    Science.gov (United States)

    Thangappan, R; Kalaiselvam, S; Elayaperumal, A; Jayavel, R; Arivanandhan, M; Karthikeyan, R; Hayakawa, Y

    2016-02-14

    The two-dimensional (2D) transition metal dichalcogenide nanosheet-carbon composite is an attractive material for energy storage because of its high Faradaic activity, unique nanoconstruction and electronic properties. In this work, a facile one step preparation of a molybdenum disulfide (MoS2) nanosheet-graphene (MoS2/G) composite with the in situ reduction of graphene oxide is reported. The structure, morphology and composition of the pure MoS2 and composites were comparatively analyzed by various characterization techniques. The electrochemical performance of the pure MoS2, graphene oxide and the MoS2/G composite electrode materials was evaluated by cyclic voltammogram, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The MoS2/G composite showed a higher specific capacitance (270 F g(-1) at a current density of 0.1 A g(-1)) compared to the pure MoS2 (162 F g(-1)) in a neutral aqueous electrolyte. Moreover, the energy density of the composite electrode is also higher (12.5 Wh kg(-1)) with a high power density (2500 W kg(-1)) compared to the pure MoS2. In addition, the MoS2/G composite electrode showed excellent cyclic stability even after 1000 cycles. The enhancement in specific capacitance, excellent cyclic stability and high energy density of the composite electrode are mainly due to the interconnected conductive network of the composite as well as the synergetic effect of the pure MoS2 and graphene. The experimental results demonstrated that the MoS2/G composite is a promising electrode material for high-performance supercapacitors.

  4. Operation and modeling of the MOS transistor

    CERN Document Server

    Tsividis, Yannis

    2011-01-01

    Operation and Modeling of the MOS Transistor has become a standard in academia and industry. Extensively revised and updated, the third edition of this highly acclaimed text provides a thorough treatment of the MOS transistor - the key element of modern microelectronic chips.

  5. Large-area MoS2 grown using H2S as the sulphur source

    Science.gov (United States)

    Dumcenco, Dumitru; Ovchinnikov, Dmitry; Lopez Sanchez, Oriol; Gillet, Philippe; Alexander, Duncan T. L.; Lazar, Sorin; Radenovic, Aleksandra; Kis, Andras

    2015-12-01

    We report on the growth of molybdenum disulphide (MoS2) using H2S as a gas-phase sulfur precursor that allows controlling the domain growth direction of domains in both vertical (perpendicular to the substrate plane) and horizontal (within the substrate plane), depending on the H2S:H2 ratio in the reaction gas mixture and temperature at which they are introduced during growth. Optical and atomic force microscopy measurements on horizontal MoS2 demonstrate the formation of monolayer triangular-shape domains that merge into a continuous film. Scanning transmission electron microscopy of monolayer MoS2 shows a regular atomic structure with a hexagonal symmetry. Raman and photoluminescence spectra confirm the monolayer thickness of the material. Field-effect transistors fabricated on MoS2 domains that are transferred onto Si/SiO2 substrates show a mobility similar to previously reported exfoliated and chemical vapor deposition-grown materials.

  6. Monolayers of MoS2 and WS2 as oxidation protective nanocoating materials

    Science.gov (United States)

    Sen, Huseyin Sener; Durgun, Engin; Sahin, Hasan; Peeters, Francois

    2014-03-01

    First-principles simulation techniques are employed to analyse the interaction of oxygen with MoS2 and WS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulphur atoms, oxygen molecule only weakly interact with the system. The penetration of oxygen atom and molecule through MoS2 monolayer require a very high energy barrier indicating that MoS2 can serve as protective layer from oxidation. Not only ideal structures but also possible defect formations are considered and penetration/diffusion barriers of oxygen are calculated for each case. The study is extended for WS2 as well, and obtained results are compared. Our predictions indicate that ideal and/or defected MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be used as an efficient nanocoating material.

  7. Z2 Invariance of Germanene on MoS2 from First Principles

    Science.gov (United States)

    Amlaki, Taher; Bokdam, Menno; Kelly, Paul J.

    2016-06-01

    We present a low energy Hamiltonian generalized to describe how the energy bands of germanene (Ge ¯ ) are modified by interaction with a substrate or a capping layer. The parameters that enter the Hamiltonian are determined from first-principles relativistic calculations for Ge ¯ |MoS2 bilayers and MoS2|Ge ¯ |MoS2 trilayers and are used to determine the topological nature of the system. For the lowest energy, buckled germanene structure, the gap depends strongly on how germanene is oriented with respect to the MoS2 layer(s). Topologically nontrivial gaps for bilayers and trilayers can be almost as large as for a freestanding germanene layer.

  8. Thickness dependent interlayer transport in vertical MoS2 Josephson junctions

    Science.gov (United States)

    Island, Joshua O.; Steele, Gary A.; van der Zant, Herre S. J.; Castellanos-Gomez, Andres

    2016-09-01

    We report on observations of thickness dependent Josephson coupling and multiple Andreev reflections (MAR) in vertically stacked molybdenum disulfide (MoS2)—molybdenum rhenium (MoRe) Josephson junctions. MoRe, a chemically inert superconductor, allows for oxide free fabrication of high transparency vertical MoS2 devices. Single and bilayer MoS2 junctions display relatively large critical currents (up to 2.5 μA) and the appearance of sub-gap structure given by MAR. In three and four layer thick devices we observe orders of magnitude lower critical currents (sub-nA) and reduced quasiparticle gaps due to proximitized MoS2 layers in contact with MoRe. We anticipate that this device architecture could be easily extended to other 2D materials.

  9. MoS2 Enhanced T-Phase Stabilization and Tunability Through Alloying.

    Science.gov (United States)

    Raffone, Federico; Ataca, Can; Grossman, Jeffrey C; Cicero, Giancarlo

    2016-07-01

    Two-dimensional MoS2 is a promising material for nanoelectronics and catalysis, but its potential is not fully exploited since proper control of its multiple phases (H, T, ZT) and electronic properties is lacking. In this theoretical study, alloying is proposed as a method to stabilize the MoS2 T-phase. In particular, MoS2 is alloyed with another material that is known to exist in a monolayer MX2 T-structure, and we show that the formation energy difference among phases decreases even for low impurity concentrations in MoS2, and a relationship between impurity concentration and alloy band gap is established. This method can be potentially applied to many two-dimensional materials to tune/enhance their electronic properties and stabilities in order to suit the desired application. PMID:27225447

  10. A magnetic resonance study of MoS2 fullerene-like nanoparticles

    International Nuclear Information System (INIS)

    We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS2 nanoparticles. Spectra of bulk 2H-MoS2 samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS2 reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS2 exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS2 ones.

  11. Density functional studies on edge-contacted single-layer MoS2 piezotronic transistors

    Science.gov (United States)

    Liu, Wei; Zhang, Aihua; Zhang, Yan; Wang, Zhong Lin

    2015-08-01

    The piezotronic effect uses strain-induced piezoelectric charges at interfaces and junctions to tune and/or control carrier transport in piezoelectric semiconductor devices. This effect has recently been observed in single-layer 2D MoS2 materials. However, previous work had found that metallic states are generated at the edge of a free-standing MoS2 flat sheet, and these states may screen the piezoelectric charges. Using density functional theory simulations, we found that the metal-MoS2 interface structure plays an important role in enhancing both the piezoelectric and piezotronic effects in MoS2 transistors by breaking the metallic state screening effect at the MoS2 edge. This study not only provides an understanding of the piezoelectric and piezotronic effects based on first principles calculations but also offers guidance for the design of two-dimensional piezotronic devices.

  12. Performance Analysis of Strained Monolayer MoS$_{2}$ MOSFET

    OpenAIRE

    Sengupta, Amretashis; Ghosh, Ram Krishna; Mahapatra, Santanu

    2013-01-01

    We present a computational study on the impact of tensile/compressive uniaxial ($\\varepsilon_{xx}$) and biaxial ($\\varepsilon_{xx}=\\varepsilon_{yy}$) strain on monolayer MoS$_{2}$ NMOS and PMOS FETs. The material properties like band structure, carrier effective mass and the multi-band Hamiltonian of the channel, are evaluated using the Density Functional Theory (DFT). Using these parameters, self-consistent Poisson-Schr\\"{o}dinger solution under the Non-Equilibrium Green's Function (NEGF) fo...

  13. Two-dimensional lateral heterojunction through bandgap engineering of MoS2 via oxygen plasma

    Science.gov (United States)

    Choudhary, Nitin; Islam, Muhammad R.; Kang, Narae; Tetard, Laurene; Jung, Yeonwoong; Khondaker, Saiful I.

    2016-09-01

    The present study explores the structural, optical (photoluminescence (PL)), and electrical properties of lateral heterojunctions fabricated by selective exposure of mechanically exfoliated few layer two-dimensional (2D) molybdenum disulfide (MoS2) flakes under oxygen (O2)-plasma. Raman spectra of the plasma exposed MoS2 flakes show a significant loss in the structural quality due to lattice distortion and creation of oxygen-containing domains in comparison to the pristine part of the same flake. The PL mapping evidences the complete quenching of peak A and B consistent with a change in the exciton states of MoS2 after the plasma treatment, indicating a significant change in its band gap properties. The electrical transport measurements performed across the pristine and the plasma-exposed MoS2 flake exhibit a gate tunable current rectification behavior with a rectification ratio up to 1.3  ×  103 due to the band-offset at the pristine and plasma-exposed MoS2 interface. Our Raman, PL, and electrical transport data confirm the formation of an excellent lateral heterojunction in 2D MoS2 through its bandgap modulation via oxygen plasma.

  14. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential.

  15. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential. PMID:27281693

  16. Advances in MoS2-Based Field Effect Transistors (FETs)

    Institute of Scientific and Technical Information of China (English)

    Xin Tong; Eric Ashalley; Feng Lin; Handong Li; Zhiming M. Wang

    2015-01-01

    This paper reviews the original achievements and advances regarding the field effect transistor (FET) fabricated from one of the most studied transition metal dichalcogenides: two-dimensional MoS2. Not like graphene, which is highlighted by a gapless Dirac cone band structure, Monolayer MoS2 is featured with a 1.9 eV gapped direct energy band thus facilitates convenient electronic and/or optoelectronic modulation of its physical properties in FET structure. Indeed, many MoS2 devices based on FET architecture such as phototransistors, memory devices, and sensors have been studied and extraordinary properties such as excellent mobility, ON/OFF ratio, and sensitivity of these devices have been ex-hibited. However, further developments in FET device applications depend a lot on if novel physics would be involved in them. In this review, an overview on advances and developments in the MoS2-based FETs are presented. Engineering of MoS2-based FETs will be discussed in details for understanding contact physics, formation of gate dielectric, and doping strategies. Also reported are demonstrations of device behaviors such as low-frequency noise and photoresponse in MoS2-based FETs, which is crucial for developing electronic and optoelectronic devices.

  17. MoS2 Nanosheets Vertically Grown on Graphene Sheets for Lithium-Ion Battery Anodes.

    Science.gov (United States)

    Teng, Yongqiang; Zhao, Hailei; Zhang, Zijia; Li, Zhaolin; Xia, Qing; Zhang, Yang; Zhao, Lina; Du, Xuefei; Du, Zhihong; Lv, Pengpeng; Świerczek, Konrad

    2016-09-27

    A designed nanostructure with MoS2 nanosheets (NSs) perpendicularly grown on graphene sheets (MoS2/G) is achieved by a facile and scalable hydrothermal method, which involves adsorption of Mo7O24(6-) on a graphene oxide (GO) surface, due to the electrostatic attraction, followed by in situ growth of MoS2. These results give an explicit proof that the presence of oxygen-containing groups and pH of the solution are crucial factors enabling formation of a lamellar structure with MoS2 NSs uniformly decorated on graphene sheets. The direct coupling of edge Mo of MoS2 with the oxygen from functional groups on GO (C-O-Mo bond) is proposed. The interfacial interaction of the C-O-Mo bonds can enhance electron transport rate and structural stability of the MoS2/G electrode, which is beneficial for the improvement of rate performance and long cycle life. The graphene sheets improve the electrical conductivity of the composite and, at the same time, act not only as a substrate to disperse active MoS2 NSs homogeneously but also as a buffer to accommodate the volume changes during cycling. As an anode material for lithium-ion batteries, the manufactured MoS2/G electrode manifests a stable cycling performance (1077 mAh g(-1) at 100 mA g(-1) after 150 cycles), excellent rate capability, and a long cycle life (907 mAh g(-1) at 1000 mA g(-1) after 400 cycles).

  18. Synergistic effect of bias and target currents for magnetron sputtered MoS2-Ti composite films

    International Nuclear Information System (INIS)

    In terms of modification of the properties of MoS2-Ti composite films, especially tribological properties, significant advances have recently been recorded. However, the commercially production of MoS2-Ti composite films is still limited, because the production of desirable MoS2-Ti composite coating is only possible by using closed field unbalanced magnetron systems and by the selection of convenient deposition parameters. This requirement has focused the researchers' attention on optimization of deposition parameters. This study is concentrating on the effect of the bias voltage and the target currents for MoS2-Ti composite films deposited by pulsed magnetron sputtering (PMS). It is found that the bias and the target currents clearly affect the mechanical, structural and tribological properties of MoS2-Ti films.

  19. An Anomalous Formation Pathway for Dislocation-Sulfur Vacancy Complexes in Polycrystalline Monolayer MoS2.

    Science.gov (United States)

    Yu, Zhi Gen; Zhang, Yong-Wei; Yakobson, Boris I

    2015-10-14

    Two-dimensional (2D) molybdenum disulfide (MoS2) has attracted significant attention recently due to its direct bandgap semiconducting characteristics. Experimental studies on monolayer MoS2 show that S vacancy concentration varies greatly; while recent theoretical studies show that the formation energy of S vacancy is high and thus its concentration should be low. We perform density functional theory calculations to study the structures and energetics of vacancy and interstitial in both grain boundary (GB) and grain interior (GI) in monolayer MoS2 and uncover an anomalous formation pathway for dislocation-double S vacancy (V2S) complexes in MoS2. In this pathway, a (5|7) defect in an S-polar GB energetically favorably converts to a (4|6) defect, which possesses a duality: dislocation and double S vacancy. Its dislocation character allows it to glide into GI through thermal activation at high temperatures, bringing the double vacancy with it. Our findings here not only explain why VS is predominant in exfoliated 2D MoS2 and V2S is predominant in chemical vapor deposition (CVD)-grown 2D MoS2 but also reproduce GB patterns in CVD-grown MoS2. The new pathway for sulfur vacancy formation revealed here provides important insights and guidelines for controlling the quality of monolayer MoS2.

  20. Robust Denaturation of Villin Headpiece by MoS2 Nanosheet: Potential Molecular Origin of the Nanotoxicity.

    Science.gov (United States)

    Gu, Zonglin; Yang, Zaixing; Kang, Seung-Gu; Yang, Jerry R; Luo, Judong; Zhou, Ruhong

    2016-01-01

    MoS2 nanosheet, a new two-dimensional transition metal dichalcogenides nanomaterial, has attracted significant attentions lately due to many potential promising biomedical applications. Meanwhile, there is also a growing concern on its biocompatibility, with little known on its interactions with various biomolecules such as proteins. In this study, we use all-atom molecular dynamics simulations to investigate the interaction of a MoS2 nanosheet with Villin Headpiece (HP35), a model protein widely used in protein folding studies. We find that MoS2 exhibits robust denaturing capability to HP35, with its secondary structures severely destroyed within hundreds of nanosecond simulations. Both aromatic and basic residues are critical for the protein anchoring onto MoS2 surface, which then triggers the successive protein unfolding process. The main driving force behind the adsorption process is the dispersion interaction between protein and MoS2 monolayer. Moreover, water molecules at the interface between some key hydrophobic residues (e.g. Trp-64) and MoS2 surface also help to accelerate the process driven by nanoscale drying, which provides a strong hydrophobic force. These findings might have shed new light on the potential nanotoxicity of MoS2 to proteins with atomic details, which should be helpful in guiding future biomedical applications of MoS2 with its nanotoxicity mitigated.

  1. Robust Denaturation of Villin Headpiece by MoS2 Nanosheet: Potential Molecular Origin of the Nanotoxicity.

    Science.gov (United States)

    Gu, Zonglin; Yang, Zaixing; Kang, Seung-Gu; Yang, Jerry R; Luo, Judong; Zhou, Ruhong

    2016-01-01

    MoS2 nanosheet, a new two-dimensional transition metal dichalcogenides nanomaterial, has attracted significant attentions lately due to many potential promising biomedical applications. Meanwhile, there is also a growing concern on its biocompatibility, with little known on its interactions with various biomolecules such as proteins. In this study, we use all-atom molecular dynamics simulations to investigate the interaction of a MoS2 nanosheet with Villin Headpiece (HP35), a model protein widely used in protein folding studies. We find that MoS2 exhibits robust denaturing capability to HP35, with its secondary structures severely destroyed within hundreds of nanosecond simulations. Both aromatic and basic residues are critical for the protein anchoring onto MoS2 surface, which then triggers the successive protein unfolding process. The main driving force behind the adsorption process is the dispersion interaction between protein and MoS2 monolayer. Moreover, water molecules at the interface between some key hydrophobic residues (e.g. Trp-64) and MoS2 surface also help to accelerate the process driven by nanoscale drying, which provides a strong hydrophobic force. These findings might have shed new light on the potential nanotoxicity of MoS2 to proteins with atomic details, which should be helpful in guiding future biomedical applications of MoS2 with its nanotoxicity mitigated. PMID:27312409

  2. Reductive hybridization route with exfoliated graphene oxide and MoS2 nanosheets to efficient electrode materials

    International Nuclear Information System (INIS)

    Highlights: • Homogeneous hybridization of MoS2 and graphene can occur with exfoliated nanosheet precursors. • Graphene oxide is more effective for hybridization with MoS2 than reduced graphene oxide. • Mesoporous MoS2-graphene nanohybrid shows excellent anode performance in Li-ion battery. - Abstract: Mesoporous MoS2–graphene nanohybrid with excellent electrode activity can be synthesized by the reductive hybridization of exfoliated MoS2 and graphene oxide (G-O) nanosheets under hydrothermal condition. The use of G-O precursor is crucial in synthesizing homogeneously hybridized MoS2–graphene materials with mesoporous stacking structure. The MoS2–graphene nanohybrid prepared with G-O shows promising electrode performance for lithium ion batteries with large discharge capacity of ∼1400 mA h g−1 for the 100th cycle and excellent rate performance, which is much superior to that of the homologue prepared with rG-O precursor and also restacked MoS2 nanosheets. The present results clearly demonstrate the usefulness of G-O precursor in the hydrothermal synthesis of graphene-based hybrid materials

  3. Highly Stretchable MoS2 and Phosphorene Kirigami

    Science.gov (United States)

    Campbell, David; Hanakata, Paul; Park, Harold

    Several recent works have shown how nanomesh and kirigami patterning can be used to increase the ductility of monolayer graphene and thin film electrodes, suggesting that this approach should be useful for other 2D materials. We have studied the effects of kirigami patterning on the mechanical properties of MoS2 and phosphorene ``monolayers,'' using classical molecular dynamics simulations. We have explored several different kirigami structures, focusing on two simple non-dimensional parameters found to be relevant in our previous study of graphene. These parameters are related to the density of cuts and to the ratio of the overlapping cut length to the nanoribbon length. We found that these membranes, despite not having the single atomic layer planar structure of graphene, show a significantly enhanced ductility that can be understood in terms of the two geometric parameters. For instance, fracture strains of MoS2 kirigami can be enhanced by a factor of six relative to pristine MoS2 nanoribbons. Our findings suggest that the kirigami cuts are the key to changing the morphology of 2D membranes to allow out of plane deflection and to prevent early failure

  4. Mouse Mos protooncogene product is present and functions during oogenesis.

    OpenAIRE

    Paules, R S; Buccione, R; Moschel, R C; Vande Woude, G F; Eppig, J.J.

    1989-01-01

    We have identified the mouse Mos-encoded protein product, p39mos, in maturing mouse oocytes and have shown that it is indistinguishable from the product expressed in Mos-transformed NIH 3T3 cells. p39mos is detected in oocytes arrested in the first meiotic prophase, during germinal-vesicle breakdown, metaphase I, anaphase I, and in ovulated eggs. We show that microinjection of three different Mos antisense (but not sense) oligodeoxyribonucleotides into germinal vesicle-stage oocytes prevents ...

  5. Ionizing radiation effects in MOS oxides

    CERN Document Server

    Oldham, Timothy R

    1999-01-01

    This volume is intended to serve as an updated critical guide to the extensive literature on the basic physical mechanisms controlling the radiation and reliability responses of MOS oxides. The last such guide was Ionizing Radiation Effects in MOS Devices and Circuits, edited by Ma and Dressendorfer and published in 1989. While that book remains an authoritative reference in many areas, there has been a significant amount of more recent work on the nature of the electrically active defects in MOS oxides which are generated by exposure to ionizing radiation. These same defects are also critical

  6. Growth characteristics of MoS2 coatings prepared by unbalanced bipolar DC magnetron sputtering

    Institute of Scientific and Technical Information of China (English)

    WANG Ji-hui; XIA Yang; E.Wieers; L.M.Stals; J.P.Celis

    2005-01-01

    MoS2 coatings were prepared by unbalanced bipolar DC magnetron sputtering under different argon pressures and for different deposition times, and the structure and morphology of MoS2 coatings were determined and observed respectively by X-ray diffractometry and scanning electron microscopy. The results show that at lower argon pressures of 0.15Pa and 0.40Pa, MoS2 coatings are formed with the (002) basal plane parallel to the surface, whereas the coating deposited at the argon pressure above 0.60Pa has the (002) basal plane perpendicular to the surface. Two stages can be classified for the formation of MoS2 coating. At the initial stage of coating formation, the (002) basal plane with S-Mo-S layer structure grows on the substrate whatever the argon pressure is. And then the coating under 0.40Pa argon pressure still grows with (002) laminate structure, but the coatings under 0.88Pa and 1.60Pa argon pressures turn to grow with the mixed basal and edge orientations. The morphology and structure of MoS2 coatings are highly related to their growth rate and the energy of sputtered particles.

  7. Memristive Phenomena in Polycrystalline Single Layer MoS2

    Science.gov (United States)

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, single layer transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high electrical conductivity, tunable band-gap, and strong light-matter interaction. However, available growth methods produce large-area polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Complementary electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism.

  8. Scalable Patterning of MoS2 Nanoribbons by Micromolding in Capillaries.

    Science.gov (United States)

    Hung, Yu-Han; Lu, Ang-Yu; Chang, Yung-Huang; Huang, Jing-Kai; Chang, Jeng-Kuei; Li, Lain-Jong; Su, Ching-Yuan

    2016-08-17

    In this study, we report a facile approach to prepare dense arrays of MoS2 nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH4)2MoS4) as the printing ink. The obtained MoS2 nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS2 nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10(8) were achieved. The MoS2 pattern can be printed on versatile substrates, such as SiO2/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS2 was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS2 nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS2. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoSx structure (x ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoSx was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm(2) and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS2. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS2/MoSx nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials.

  9. Scalable Patterning of MoS2 Nanoribbons by Micromolding in Capillaries.

    Science.gov (United States)

    Hung, Yu-Han; Lu, Ang-Yu; Chang, Yung-Huang; Huang, Jing-Kai; Chang, Jeng-Kuei; Li, Lain-Jong; Su, Ching-Yuan

    2016-08-17

    In this study, we report a facile approach to prepare dense arrays of MoS2 nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH4)2MoS4) as the printing ink. The obtained MoS2 nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS2 nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10(8) were achieved. The MoS2 pattern can be printed on versatile substrates, such as SiO2/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS2 was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS2 nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS2. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoSx structure (x ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoSx was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm(2) and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS2. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS2/MoSx nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials. PMID:27462874

  10. A generic tight-binding model for monolayer, bilayer and bulk MoS2

    Directory of Open Access Journals (Sweden)

    Ferdows Zahid

    2013-05-01

    Full Text Available Molybdenum disulfide (MoS2 is a layered semiconductor which has become very important recently as an emerging electronic device material. Being an intrinsic semiconductor the two-dimensional MoS2 has major advantages as the channel material in field-effect transistors. In this work we determine the electronic structures of MoS2 with the highly accurate screened hybrid functional within the density functional theory (DFT including the spin-orbit coupling. Using the DFT electronic structures as target, we have developed a single generic tight-binding (TB model that accurately produces the electronic structures for three different forms of MoS2 - bulk, bilayer and monolayer. Our TB model is based on the Slater-Koster method with non-orthogonal sp3d5 orbitals, nearest-neighbor interactions and spin-orbit coupling. The TB model is useful for atomistic modeling of quantum transport in MoS2 based electronic devices.

  11. Location and coordination of promoter atoms in Co- and Ni-promoted MoS2-based hydrotreating catalysts

    DEFF Research Database (Denmark)

    Lauritsen, J.V.; Kibsgaard, J.; Olesen, G.H.;

    2007-01-01

    In this study, we used scanning tunneling microscopy (STM) and density functional theory (DFT) to investigate the atomic-scale structure of the active Co- or Ni-promoted MoS2 nanoclusters in hydrotreating catalysts. Co-promoted MoS2 nanoclusters (Co–Mo–S) are found to adopt a hexagonal shape......, with Co atoms preferentially located at () edges with a 50% sulfur coverage. The first atom-resolved STM images of the Ni-promoted MoS2 nanoclusters (Ni–Mo–S) reveal that the addition of Ni also leads to truncated morphologies, but the degree of truncation and the Ni sites are observed to depend...

  12. Radiation damage in MOS varactors at low temperatures

    International Nuclear Information System (INIS)

    A description of the build-up of charges at low temperatures (T = 80 K) in SiO2 (MOS-structures) induced by ionizing radiation is presented. The damage is characterized by CV measurements and an expanded analysis is developed. A non-homogeneous distribution of frozen holes in the SiO2 appears corresponding to the energy deposition. When the radiation is terminated a field dependent (≥ 2 MV/cm) hole transport to the interfaces is observed. Only after warming (T ≥ 240 K) the structure interface states are created. (orig./HP)

  13. High-k Al2O3 MOS structures with Si interface control layer formed on air-exposed GaAs and InGaAs wafers

    International Nuclear Information System (INIS)

    This paper attempts to realize unpinned high-k insulator-semiconductor interfaces on air-exposed GaAs and In0.53Ga0.47As by using the Si interface control layer (Si ICL). Al2O3 was deposited by ex situ atomic layer deposition (ALD) as the high-k insulator. By applying an optimal chemical treatment using HF acid combined with subsequent thermal cleaning below 500 deg. C in UHV, interface bonding configurations similar to those by in situ UHV process were achieved both for GaAs and InGaAs after MBE growth of the Si ICL with no trace of residual native oxide components. As compared with the MIS structures without Si ICL, insertion of Si ICL improved the electrical interface quality, a great deal both for GaAs and InGaAs, reducing frequency dispersion of capacitance, hysteresis effects and interface state density (Dit). A minimum value of Dit of 2 x 1011 eV-1 cm-2 was achieved both for GaAs and InGaAs. However, the range of bias-induced surface potential excursion within the band gap was different, making formation of electron layer by surface inversion possible in InGaAs, but not possible in GaAs. The difference was explained by the disorder induced gap state (DIGS) model.

  14. Attapulgite-CeO2/MoS2 ternary nanocomposite for photocatalytic oxidative desulfurization

    Science.gov (United States)

    Li, Xiazhang; Zhang, Zuosong; Yao, Chao; Lu, Xiaowang; Zhao, Xiaobing; Ni, Chaoying

    2016-02-01

    Novel attapulgite(ATP)-CeO2/MoS2 ternary nanocomposites were synthesized by microwave assisted assembly method. The structures of the nanocomposites were characterized by XRD, FT-IR, UV-vis, XPS and in situ TEM. The photocatalytic activities of ATP-CeO2/MoS2 composites were investigated by degradating dibenzothiophene (DBT) in gasoline under visible light irradiation. The effect of the mass ratio of CeO2 to MoS2 on photocatalytic activity was investigated. The results indicate that the three-dimensional network structure is firmly constructed by ATP skeleton, CeO2 particles and MoS2 nanosheet which effectively increase the surface area of the composites and promote the separation of electrons and holes by resulting electronic transmission channels of multi-channel in space. The degradation rate of DBT can reach 95% under 3 h irradiation when the mass ratio of CeO2/MoS2 is 4/10. A plausible mechanism for the photocatalytic oxidative desulfurization of this nanocomposite is put forward.

  15. Direct TEM observations of growth mechanisms of two-dimensional MoS2 flakes

    Science.gov (United States)

    Fei, Linfeng; Lei, Shuijin; Zhang, Wei-Bing; Lu, Wei; Lin, Ziyuan; Lam, Chi Hang; Chai, Yang; Wang, Yu

    2016-07-01

    A microscopic understanding of the growth mechanism of two-dimensional materials is of particular importance for controllable synthesis of functional nanostructures. Because of the lack of direct and insightful observations, how to control the orientation and the size of two-dimensional material grains is still under debate. Here we discern distinct formation stages for MoS2 flakes from the thermolysis of ammonium thiomolybdates using in situ transmission electron microscopy. In the initial stage (400 °C), vertically aligned MoS2 structures grow in a layer-by-layer mode. With the increasing temperature of up to 780 °C, the orientation of MoS2 structures becomes horizontal. When the growth temperature reaches 850 °C, the crystalline size of MoS2 increases by merging adjacent flakes. Our study shows direct observations of MoS2 growth as the temperature evolves, and sheds light on the controllable orientation and grain size of two-dimensional materials.

  16. Direct TEM observations of growth mechanisms of two-dimensional MoS2 flakes.

    Science.gov (United States)

    Fei, Linfeng; Lei, Shuijin; Zhang, Wei-Bing; Lu, Wei; Lin, Ziyuan; Lam, Chi Hang; Chai, Yang; Wang, Yu

    2016-01-01

    A microscopic understanding of the growth mechanism of two-dimensional materials is of particular importance for controllable synthesis of functional nanostructures. Because of the lack of direct and insightful observations, how to control the orientation and the size of two-dimensional material grains is still under debate. Here we discern distinct formation stages for MoS2 flakes from the thermolysis of ammonium thiomolybdates using in situ transmission electron microscopy. In the initial stage (400 °C), vertically aligned MoS2 structures grow in a layer-by-layer mode. With the increasing temperature of up to 780 °C, the orientation of MoS2 structures becomes horizontal. When the growth temperature reaches 850 °C, the crystalline size of MoS2 increases by merging adjacent flakes. Our study shows direct observations of MoS2 growth as the temperature evolves, and sheds light on the controllable orientation and grain size of two-dimensional materials. PMID:27412892

  17. Ab Initio Study of Quasiparticle and Excitonic Properties of MoS2

    Science.gov (United States)

    Qiu, Diana; Jornada, Felipe; Louie, Steven

    2013-03-01

    MoS2 is a layered, transition-metal dichalcogenide that can be cleaved into single-layer sheets, in a manner similar to graphene. Monolayer MoS2 has a direct band gap, strong spin-orbit coupling and strongly enhanced photoluminescence, compared with the bulk. MoS2's interesting electronic and optical properties mean that it could have many applications in single-layer electronic devices, but on the theoretical level, when many-electron interaction effects are included, there is still some uncertainty about the quasiparticle and excitonic properties of MoS2. We use first-principles calculations to study the quasiparticle band structure and optical absorption spectrum of MoS2 at the GW +BSE level. We include spin-orbit coupling as a perturbation either before or after the GW calculation of the band structure, and we demonstrate that our calculations are fully converged with respect to the dielectric cutoff and summation over empty bands. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by NERSC.

  18. Few-layer MoS2: a promising layered semiconductor.

    Science.gov (United States)

    Ganatra, Rudren; Zhang, Qing

    2014-05-27

    Due to the recent expanding interest in two-dimensional layered materials, molybdenum disulfide (MoS2) has been receiving much research attention. Having an ultrathin layered structure and an appreciable direct band gap of 1.9 eV in the monolayer regime, few-layer MoS2 has good potential applications in nanoelectronics, optoelectronics, and flexible devices. In addition, the capability of controlling spin and valley degrees of freedom makes it a promising material for spintronic and valleytronic devices. In this review, we attempt to provide an overview of the research relevant to the structural and physical properties, fabrication methods, and electronic devices of few-layer MoS2. Recent developments and advances in studying the material are highlighted. PMID:24660756

  19. Three-Dimensional Heterostructures of MoS2 Nanosheets on Conducting MoO2 as an Efficient Electrocatalyst To Enhance Hydrogen Evolution Reaction.

    Science.gov (United States)

    Nikam, Revannath Dnyandeo; Lu, Ang-Yu; Sonawane, Poonam Ashok; Kumar, U Rajesh; Yadav, Kanchan; Li, Lain-Jong; Chen, Yit-Tsong

    2015-10-21

    Molybdenum disulfide (MoS2) is a promising catalyst for hydrogen evolution reaction (HER) because of its unique nature to supply active sites in the reaction. However, the low density of active sites and their poor electrical conductivity have limited the performance of MoS2 in HER. In this work, we synthesized MoS2 nanosheets on three-dimensional (3D) conductive MoO2 via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO2 structure can create structural disorders in MoS2 nanosheets (referred to as 3D MoS2/MoO2), which are responsible for providing the superior HER activity by exposing tremendous active sites of terminal disulfur of S2(-2) (in MoS2) as well as the backbone conductive oxide layer (of MoO2) to facilitate an interfacial charge transport for the proton reduction. In addition, the MoS2 nanosheets could protect the inner MoO2 core from the acidic electrolyte in the HER. The high activity of the as-synthesized 3D MoS2/MoO2 hybrid material in HER is attributed to the small onset overpotential of 142 mV, a largest cathodic current density of 85 mA cm(-2), a low Tafel slope of 35.6 mV dec(-1), and robust electrochemical durability.

  20. MOS OF CANADA: A FOODSERVICE INDUSTRY ANALYSIS OF GREATER VANCOUVER

    OpenAIRE

    Ryomoto, Craig

    2009-01-01

    This paper analyzes the Greater Vancouver commercial food industry and whether the market is ideal for MOS Food Services to fulfil its “MOS of the World” strategy by opening a MOS Burger restaurant in Greater Vancouver. To assess the future viability of MOS Burger opening in Greater Vancouver, this paper identifies and analyzes market size, drivers of demand, various customer segments, key competitors, the strength of key industry forces, and the key sources of advantage for the foodservice i...

  1. MOSFET and MOS capacitor responses to ionizing radiation

    Science.gov (United States)

    Benedetto, J. M.; Boesch, H. E., Jr.

    1984-01-01

    The ionizing radiation responses of metal oxide semiconductor (MOS) field-effect transistors (FETs) and MOS capacitors are compared. It is shown that the radiation-induced threshold voltage shift correlates closely with the shift in the MOS capacitor inversion voltage. The radiation-induced interface-state density of the MOSFETs and MOS capacitors was determined by several techniques. It is shown that the presence of 'slow' states can interfere with the interface-state measurements.

  2. 应变对单层二硫化钼能带影响的第一性原理研究%The effect of strain on band structure of single-layer MoS2: an ab initio study

    Institute of Scientific and Technical Information of China (English)

    吴木生; 徐波; 刘刚; 欧阳楚英

    2012-01-01

    We study the electronic properties of single-layer MoS2 with biaxial tensile strain by using an ab initio method of plane wave potential technique based on the density function theory. Our results show that a smalL tensile strain (0.5%) will result in the transition from direct to indirect gap for ingle-layer MoS2. With the increase of strain, the feature of the indirect gap can be preserved but the gap decreases linearly. Based on the further analysis of the density of states and the projected charge density for single-layer MoS2, the reason of the change of band structure is revealed.%采用密度泛函理论框架下的第一性原理平面波赝势方法,研究了双轴拉应变下单层二硫化钼晶体的电子结构性质.本文的计算结果表明对单层二硫化钼晶体施加一个很小的应变(0.5%)时,其能带结构由直接带隙转变为间接带隙.随着应变的增加,能带仍然保持间接带隙的特征,且禁带宽度呈现线性下降的趋势.通过对单层二硫化钼晶体态密度和投影电荷密度的进一步分析,揭示了单层二硫化钼晶体能带变化的原因.

  3. Recent Advancement on the Optical Properties of Two-Dimensional Molybdenum Disulfide (MoS2 Thin Films

    Directory of Open Access Journals (Sweden)

    Mingxiao Ye

    2015-03-01

    Full Text Available The emergence of two-dimensional (2D materials has led to tremendous interest in the study of graphene and a series of mono- and few-layered transition metal dichalcogenides (TMDCs. Among these TMDCs, the study of molybdenum disulfide (MoS2 has gained increasing attention due to its promising optical, electronic, and optoelectronic properties. Of particular interest is the indirect to direct band-gap transition from bulk and few-layered structures to mono-layered MoS2, respectively. In this review, the study of these properties is summarized. The use of Raman and Photoluminescence (PL spectroscopy of MoS2 has become a reliable technique for differentiating the number of molecular layers in 2D MoS2.

  4. Perspective: Highly ordered MoS2 thin films grown by multi-step chemical vapor deposition process

    Directory of Open Access Journals (Sweden)

    S. N. Heo

    2016-03-01

    Full Text Available We established a process for growing highly ordered MoS2 thin films. The process consists of four steps: MoO3 thermal evaporation, first annealing, sulfurization, and second annealing. The main feature of this process is that thermally deposited MoO3 thin films are employed as a precursor for the MoS2 films. The first deposition step enabled us to achieve precise control of the resulting thickness of the MoS2 films with high uniformity. The crystalline structures, surface morphologies, and chemical states at each step were characterized by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Based on these characterizations and a careful optimization of the growth conditions, we successfully produced a highly oriented MoS2 thin film with a thickness of five monolayers over an entire one-centimeter-square sapphire substrate.

  5. A density functional study of strong local magnetism creation on MoS2 nanoribbon by sulfur vacancy

    Science.gov (United States)

    Shidpour, Reza; Manteghian, Merhrdad

    2010-08-01

    In this study a low-width MoS2 ribbon has been used for probing the electronic structure and local magnetic moment near vacancies. A theoretical study with the full-potential Density Functional Theory (DFT) approach (Wien2K code) have shown that when the dimension of MoS2 is reduced from 2-D to 1-D the nonmagnetic semi-conductor MoS2 becomes a magnetic conductor. Our study has shown that a vacancy on the S-edge with 50% coverage intensifies the magnetization of the edge of the MoS2 nanoribbon but such a vacancy on S-edge with 100% coverage causes this magnetic property to disappear. It is concluded that in both of them, there are positive or negative strong gradients of local magnetic moment near the vacancy. This may explain why lattice defects are essential for catalysis processes.

  6. Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance

    Science.gov (United States)

    Li, Xu; Tang, Aiwei; Li, Jiantao; Guan, Li; Dong, Guoyi; Teng, Feng

    2016-03-01

    Molybdenum disulfide (MoS2) nanosheets were synthesized by using a simple heating-up approach, in which 1-dodecanethiol (DDT) was used not only as a sulfur source but also as the surface ligand. The sheet-like morphology was confirmed by the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results, and the X-ray diffraction (XRD) patterns and Raman spectrum were employed to characterize the structure of the as-synthesized MoS2 nanosheets. The as-obtained MoS2 nanosheets blending with a polymer could be used to fabricate an electrically bistable device through a simple spin-coating method, and the device exhibited an obvious electrical bistability in the I-V curve. The charge transport of the device was discussed based on the organic electronic models.

  7. Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance.

    Science.gov (United States)

    Li, Xu; Tang, Aiwei; Li, Jiantao; Guan, Li; Dong, Guoyi; Teng, Feng

    2016-12-01

    Molybdenum disulfide (MoS2) nanosheets were synthesized by using a simple heating-up approach, in which 1-dodecanethiol (DDT) was used not only as a sulfur source but also as the surface ligand. The sheet-like morphology was confirmed by the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results, and the X-ray diffraction (XRD) patterns and Raman spectrum were employed to characterize the structure of the as-synthesized MoS2 nanosheets. The as-obtained MoS2 nanosheets blending with a polymer could be used to fabricate an electrically bistable device through a simple spin-coating method, and the device exhibited an obvious electrical bistability in the I-V curve. The charge transport of the device was discussed based on the organic electronic models. PMID:27033847

  8. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    KAUST Repository

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  9. Growth and Tunable Surface Wettability of Vertical MoS2 Layers for Improved Hydrogen Evolution Reactions.

    Science.gov (United States)

    Bhimanapati, Ganesh R; Hankins, Trevor; Lei, Yu; Vilá, Rafael A; Fuller, Ian; Terrones, Mauricio; Robinson, Joshua A

    2016-08-31

    Layered materials, especially the transition metal dichalcogenides (TMDs), are of interest for a broad range of applications. Among the class of TMDs, molybdenum disulfide (MoS2) is perhaps the most studied because of its natural abundance and use in optoelectronics, energy storage and energy conversion applications. Understanding the fundamental structure-property relations is key for tailoring the enhancement in the above-mentioned applications. Here, we report a controlled powder vaporization synthesis of MoS2 flower-like structures consisting of vertically grown layers of MoS2 exhibiting exposed edges. This growth is readily achievable on multiple substrates, such as graphite, silicon, and silicon dioxide. The resulting MoS2 flowers are highly crystalline and stoichiometric. Further observations using contact angle indicate that MoS2 flowers exhibit the highest reported contact angle of ∼160 ± 10°, making the material super hydrophobic. This surface wettability was further tuned by changing the edge chemistry of the MoS2 flowers using an ozone etching treatment. Hydrogen evolution reaction (HER) measurements indicate that the surface treated with UV-ozone showed a reduction in the Tafel slope from 185 to 54 mV/dec, suggesting an increase in the amount of reactive surface to generate hydrogen.

  10. Analysis of electron beam damage of exfoliated MoS2 sheets and quantitative HAADF-STEM imaging

    International Nuclear Information System (INIS)

    In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200 kV. Structural damage of the MoS2 sheets has been controlled at 80 kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron–matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80 kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers. - Highlights: • MoS2 sheets were exfoliated by using hydrogen gas flow to separate the MoS2 layers. • The optimum energy to avoid structural damage was calculated. • Cs-corrected STEM imaging was used to obtain atomic resolution images. • Three energies were used in STEM imaging: 80, 120 and 200 kV. • A quantitative method for determining the number of layers has been applied

  11. Photo-Promoted Platinum Nanoparticles Decorated MoS2@Graphene Woven Fabric Catalyst for Efficient Hydrogen Generation.

    Science.gov (United States)

    Li, Xiao; Zhang, Li; Zang, Xiaobei; Li, Xinming; Zhu, Hongwei

    2016-05-01

    Hydrogen production from water splitting has been considered as an effective and sustainable method to solve future energy related crisis. Molybdenum sulfides (e.g., MoS2) show promising catalytic ability in hydrogen evolution reaction (HER). Combining MoS2 with conductive carbon-based materials has aroused tremendous research interest recently. In this work, a highly efficient multiple-catalyst is developed for HER by decorating Pt nanoparticles (Pt NPs) on MoS2@graphene protected nickel woven fabrics (NiWF) substrate, which comprises the following components: (i) Graphene protected NiWF acts as the underlying substrate, supporting the whole structure; (ii) MoS2 nanoplates serve as a central and essential photosensitive component, forming a heterostructure with graphene simultaneously; and (iii) on the basis of the intrinsic photoluminescence effect of MoS2, together with the photoelectric response at the MoS2/graphene interface, Pt NPs are successfully deposited on the whole structure under illumination. Particularly and foremost, this work emphasizes on discussion and verification of the underlying mechanism for photopromoted electroless Pt NPs deposition. Due to this assembly approach, the usage amount of Pt is controlled at ∼5 wt % (∼0.59 at. %) with respect to the whole catalyst. MoS2@Substrate with Pt NPs deposited under 643 nm illumination, with the synergistic effect of MoS2 active sites and Pt NPs, demonstrates the most superior electrocatalytic performance, with negligible overpotential and low Tafel slope of 39.4 mV/dec. PMID:27070762

  12. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    Science.gov (United States)

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4. PMID:26797320

  13. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    Science.gov (United States)

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

  14. Photo-Promoted Platinum Nanoparticles Decorated MoS2@Graphene Woven Fabric Catalyst for Efficient Hydrogen Generation.

    Science.gov (United States)

    Li, Xiao; Zhang, Li; Zang, Xiaobei; Li, Xinming; Zhu, Hongwei

    2016-05-01

    Hydrogen production from water splitting has been considered as an effective and sustainable method to solve future energy related crisis. Molybdenum sulfides (e.g., MoS2) show promising catalytic ability in hydrogen evolution reaction (HER). Combining MoS2 with conductive carbon-based materials has aroused tremendous research interest recently. In this work, a highly efficient multiple-catalyst is developed for HER by decorating Pt nanoparticles (Pt NPs) on MoS2@graphene protected nickel woven fabrics (NiWF) substrate, which comprises the following components: (i) Graphene protected NiWF acts as the underlying substrate, supporting the whole structure; (ii) MoS2 nanoplates serve as a central and essential photosensitive component, forming a heterostructure with graphene simultaneously; and (iii) on the basis of the intrinsic photoluminescence effect of MoS2, together with the photoelectric response at the MoS2/graphene interface, Pt NPs are successfully deposited on the whole structure under illumination. Particularly and foremost, this work emphasizes on discussion and verification of the underlying mechanism for photopromoted electroless Pt NPs deposition. Due to this assembly approach, the usage amount of Pt is controlled at ∼5 wt % (∼0.59 at. %) with respect to the whole catalyst. MoS2@Substrate with Pt NPs deposited under 643 nm illumination, with the synergistic effect of MoS2 active sites and Pt NPs, demonstrates the most superior electrocatalytic performance, with negligible overpotential and low Tafel slope of 39.4 mV/dec.

  15. Direct synthesis of large-scale hierarchical MoS2 films nanostructured with orthogonally oriented vertically and horizontally aligned layers.

    Science.gov (United States)

    Zhang, Xiaoyan; Zhang, Saifeng; Chen, Bohua; Wang, Hao; Wu, Kan; Chen, Yang; Fan, Jintai; Qi, Shen; Cui, Xiaoli; Zhang, Long; Wang, Jun

    2016-01-01

    Hierarchical MoS2 thin films nanostructured with orthogonally oriented vertically and horizontally aligned layers were designed and excellent passive Q-switching behavior in a fiber laser was demonstrated. A special solvothermal system containing a small amount of water was applied to synthesize such hierarchical MoS2 nanofilms, in which the reaction rate is carefully controlled by the diffusion rate of the sulfur precursor. Wafer-scale MoS2 thin films with hierarchical structures are formed on various substrates. Moreover, the hierarchical MoS2 thin films consisting of both vertical and horizontal layers can be tuned to possess only horizontally aligned layers by controlling the solvothermal time. To show the potential application proof-of-concept, the nonlinear optical performance of the hierarchical MoS2 was investigated. Superior passive Q-switching behavior in a fiber laser with a minimum pulse width of 2.2 μs was observed. PMID:26620263

  16. Edge termination of MoS2 and CoMoS catalyst particles

    DEFF Research Database (Denmark)

    Byskov, Line Sjolte; Nørskov, Jens Kehlet; Clausen, B. S.;

    2000-01-01

    The edge termination of MoS2 and CoMoS catalyst particles is studied by density functional calculations. We show that for structures without vacancies Mo-terminated edges have the lowest edge energies. Creation of vacancies, which are believed to be active sites in these catalyst systems, leads...

  17. An offset-trimmable array of magnetic-field-sensitive MOS transistors (MAGFETs)

    DEFF Research Database (Denmark)

    Ning, Feng; Bruun, Erik

    1997-01-01

    . In this paper we present a new combination of an offset compensating circuit and a MAGFET cascade circuit with increased sensitivity. The offset compensation utilizes a digitally trimmable current mirror implemented by a multiple-gate MOS transistor structure. A prototype circuit has been fabricated in a 2.4 mu...

  18. Low Noise Bias Current/Voltage References Based on Floating-Gate MOS Transistors

    DEFF Research Database (Denmark)

    Igor, Mucha

    1997-01-01

    The exploitation of floating-gate MOS transistors as reference current and voltage sources is investigated. Test structures of common source and common drain floating-gate devices have been implemented in a commercially available 0.8 micron double-poly CMOS process. The measurements performed...

  19. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates

    Science.gov (United States)

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J.; Atkin, Paul; Berean, Kyle J.; Clark, Rhiannon M.; Cole, Ivan S.; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-01

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4]2- anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of

  20. Enhancement of photodetection characteristics of MoS2 field effect transistors using surface treatment with copper phthalocyanine

    Science.gov (United States)

    Pak, Jinsu; Jang, Jingon; Cho, Kyungjune; Kim, Tae-Young; Kim, Jae-Keun; Song, Younggul; Hong, Woong-Ki; Min, Misook; Lee, Hyoyoung; Lee, Takhee

    2015-11-01

    Recently, two-dimensional materials such as molybdenum disulfide (MoS2) have been extensively studied as channel materials for field effect transistors (FETs) because MoS2 has outstanding electrical properties such as a low subthreshold swing value, a high on/off ratio, and good carrier mobility. In this study, we characterized the electrical and photo-responsive properties of MoS2 FET when stacking a p-type organic copper phthalocyanine (CuPc) layer on the MoS2 surface. We observed that the threshold voltage of MoS2 FET could be controlled by stacking the CuPc layers due to a charge transfer phenomenon at the interface. Particularly, we demonstrated that CuPc/MoS2 hybrid devices exhibited high performance as a photodetector compared with the pristine MoS2 FETs, caused by more electron-hole pairs separation at the p-n interface. Furthermore, we found the optimized CuPc thickness (~2 nm) on the MoS2 surface for the best performance as a photodetector with a photoresponsivity of ~1.98 A W-1, a detectivity of ~6.11 × 1010 Jones, and an external quantum efficiency of ~12.57%. Our study suggests that the MoS2 vertical hybrid structure with organic material can be promising as efficient photodetecting devices and optoelectronic circuits.Recently, two-dimensional materials such as molybdenum disulfide (MoS2) have been extensively studied as channel materials for field effect transistors (FETs) because MoS2 has outstanding electrical properties such as a low subthreshold swing value, a high on/off ratio, and good carrier mobility. In this study, we characterized the electrical and photo-responsive properties of MoS2 FET when stacking a p-type organic copper phthalocyanine (CuPc) layer on the MoS2 surface. We observed that the threshold voltage of MoS2 FET could be controlled by stacking the CuPc layers due to a charge transfer phenomenon at the interface. Particularly, we demonstrated that CuPc/MoS2 hybrid devices exhibited high performance as a photodetector compared

  1. Interface properties of CVD grown graphene transferred onto MoS2(0001)

    Science.gov (United States)

    Coy Diaz, Horacio; Addou, Rafik; Batzill, Matthias

    2013-12-01

    Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ~300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ~0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ~0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties.Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting

  2. Quantitative evaluation of slow traps near Ge MOS interfaces by using time response of MOS capacitance

    Science.gov (United States)

    Tanaka, Katsuhisa; Zhang, Rui; Takenaka, Mitsuru; Takagi, Shinichi

    2015-04-01

    Time-dependent changes in current and threshold voltage due to slow traps near Ge metal-oxide-semiconductor (MOS) interfaces is one of the most serious problems in Ge metal-oxide-semiconductor field-effect transistors (MOSFETs). In this study, we propose a new evaluation method of slow traps near MOS interfaces utilizing the time response of capacitance in MOS capacitors at a constant gate voltage, allowing us to evaluate the density and time constant of slow traps. We apply this method to Au/Al2O3/GeOx/Ge MOS capacitors and evaluate the density and average time constant of slow traps. The slow trap density of n-Ge MOS capacitors is found to be much larger than that of p-Ge MOS capacitors, indicating that a higher density of slow traps exists near the conduction band edge. We also examine the effects of post deposition annealing in a variety of ambient gases, including several hydrogen-based species, on the properties of slow traps.

  3. Reconfigurable Threshold Logic Element with SET and MOS Transistors

    Institute of Scientific and Technical Information of China (English)

    WEI Rong-Shan; CHEN Jin-Feng; CHEN Shou-Chang; HE Ming-Hua

    2012-01-01

    A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide semiconductor (MOS) transistors is proposed.The proposed TLE is highly reconfigurable,which can perform all two-variable logic functions directly or indirectly,including OR,NOR,AND,NAND,XOR and XNOR.The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters.The design methodology can also be applied in the design of a multi-variable TLE.The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation.The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.%A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors is proposed. The proposed TLE is highly reconfigurable, which can perform all two-variable logic functions directly or indirectly, including OR, NOR, AND, NAND, XOR and XNOR. The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters. The design methodology can also be applied in the design of a multi-variable TLE. The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation. The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.

  4. 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.

  5. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates.

    Science.gov (United States)

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J; Atkin, Paul; Berean, Kyle J; Clark, Rhiannon M; Cole, Ivan S; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-16

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.

  6. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates.

    Science.gov (United States)

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J; Atkin, Paul; Berean, Kyle J; Clark, Rhiannon M; Cole, Ivan S; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-16

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications. PMID:27263805

  7. Monolayer MoS2-Graphene Hybrid Aerogels with Controllable Porosity for Lithium-Ion Batteries with High Reversible Capacity.

    Science.gov (United States)

    Jiang, Lianfu; Lin, Binghui; Li, Xiaoming; Song, Xiufeng; Xia, Hui; Li, Liang; Zeng, Haibo

    2016-02-01

    Monolayer MoS2 nanosheets (NSs) are promising anode materials for lithium-ion batteries because all redox reactions take place at the surface without lithium-ion diffusion limit. However, the expanded band gap of monolayer MoS2 NSs (∼1.8 eV) compared to their bulk counterparts (∼1.2 eV) and restacking tendency due to the van der Waals forces result in poor electron transfer and loss of the structure advantage. Here, a facile approach is developed to fabricate the MoS2-graphene aerogels comprising controlled three-dimensional (3D) porous architectures constructed by interconnected monolayer MoS2-graphene hybrid NSs. The robust 3D architectures combining with the monolayer feature of the hybrid NSs not only prevent the MoS2 and graphene NSs from restacking, but also enable fast electrode kinetics due to the surface reaction mechanism and highly conductive graphene matrix. As a consequence, the 3D porous monolayer MoS2-graphene composite aerogels exhibit a large reversible capacity up to 1200 mAh g(-1) as well as outstanding cycling stability and rate performance, making them promising as advanced anode materials for lithium-ion batteries.

  8. Covalent Nitrogen Doping and Compressive Strain in MoS2 by Remote N2 Plasma Exposure.

    Science.gov (United States)

    Azcatl, Angelica; Qin, Xiaoye; Prakash, Abhijith; Zhang, Chenxi; Cheng, Lanxia; Wang, Qingxiao; Lu, Ning; Kim, Moon J; Kim, Jiyoung; Cho, Kyeongjae; Addou, Rafik; Hinkle, Christopher L; Appenzeller, Joerg; Wallace, Robert M

    2016-09-14

    Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism. Furthermore, the electrical characterization demonstrates that p-type doping of MoS2 is achieved by nitrogen doping, which is in agreement with theoretical predictions. Notably, we found that the presence of nitrogen can induce compressive strain in the MoS2 structure, which represents the first evidence of strain induced by substitutional doping in a transition metal dichalcogenide material. Finally, our first principle calculations support the experimental demonstration of such strain, and a correlation between nitrogen doping concentration and compressive strain in MoS2 is elucidated.

  9. The origin of the enhanced performance of nitrogen-doped MoS2 in lithium ion batteries.

    Science.gov (United States)

    Liu, Qiuhong; Weijun, Xia; Wu, Zhenjun; Huo, Jia; Liu, Dongdong; Wang, Qiang; Wang, Shuangyin

    2016-04-29

    MoS2 with a similar layered structure to graphene has been widely applied in various areas including lithium ion batteries. However, low conductivity, capacity fading and poor rate performance are still the main challenges for MoS2 anode materials. In this work, for the first time, we prepared nitrogen-doped MoS2 (N-MoS2) nanosheets through a simple two-step method involving the preparation of MoS2 with defects by the hydrothermal method, followed by sintering in a NH3 atmosphere. Our electrochemical characterizations and density functional theory calculations demonstrated that nitrogen doping could enhance the electron conductivity and showed higher specific capacity than pristine MoS2 as anode materials of lithium ion batteries, which can be attributed to the faster transportation of electrons and ions because of nitrogen doping. This work helps us understand the origin of the enhanced performance of N-doped MoS2 in lithium ion batteries.

  10. Covalent Nitrogen Doping and Compressive Strain in MoS2 by Remote N2 Plasma Exposure.

    Science.gov (United States)

    Azcatl, Angelica; Qin, Xiaoye; Prakash, Abhijith; Zhang, Chenxi; Cheng, Lanxia; Wang, Qingxiao; Lu, Ning; Kim, Moon J; Kim, Jiyoung; Cho, Kyeongjae; Addou, Rafik; Hinkle, Christopher L; Appenzeller, Joerg; Wallace, Robert M

    2016-09-14

    Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism. Furthermore, the electrical characterization demonstrates that p-type doping of MoS2 is achieved by nitrogen doping, which is in agreement with theoretical predictions. Notably, we found that the presence of nitrogen can induce compressive strain in the MoS2 structure, which represents the first evidence of strain induced by substitutional doping in a transition metal dichalcogenide material. Finally, our first principle calculations support the experimental demonstration of such strain, and a correlation between nitrogen doping concentration and compressive strain in MoS2 is elucidated. PMID:27494551

  11. Interface properties of CVD grown graphene transferred onto MoS2(0001).

    Science.gov (United States)

    Coy Diaz, Horacio; Addou, Rafik; Batzill, Matthias

    2014-01-21

    Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ~300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ~0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ~0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties. PMID:24297086

  12. Ab-initio study of gold nanoparticles supported on defect-laden single-layer MoS2

    Science.gov (United States)

    Rawal, Takat B.; Le, Duy; Rahman, Talat S.

    We have investigated the geometry, electronic structure, and catalytic properties of gold nanoparticles on defect-laden single-layer MoS2 using density functional theory (DFT) based calculations with semi-empirical van der Waals interaction (DFT-D3). Our results show that the two-dimensional planar structure, the most favorable one for unsupported Au13 nanoparticle, transforms into a distorted three-dimensional (3D) structure when supported on single-layer MoS2 with single S-vacancy which is more favorable than the icosahedral, decahedron and cuboctahedron forms. The MoS2 support substantially alters the electronic structure of Au13 nanoparticle near the Fermi level, owing to the strong interaction of MoS2 support with Au13 in the presence of an S-vacancy. The modified electronic structure remarkably affects the catalytic activity of the MoS2-supported Au13, offering enhanced activity towards methanol synthesis reaction via CO hydrogenation reaction - a contrast from that of titania-supported Au13 nanoparticlewhich promotes methanol decomposition. This work is supported in part by U.S. Department of Energy (DOE DE-FG02-07ER15842).

  13. Mechanistic Insight into the Stability of HfO2 -Coated MoS2 Nanosheet Anodes for Sodium Ion Batteries.

    Science.gov (United States)

    Ahmed, Bilal; Anjum, Dalaver H; Hedhili, Mohamed N; Alshareef, Husam N

    2015-09-01

    It is demonstrated for the first time that surface passivation of 2D nanosheets of MoS2 by an ultrathin and uniform layer of HfO2 can significantly improve the cyclic performance of sodium ion batteries. After 50 charge/discharge cycles, bare MoS2 and HfO2 coated MoS2 electrodes deliver the specific capacity of 435 and 636 mAh g(-1) , respectively, at current density of 100 mA g(-1) . These results imply that batteries using HfO2 coated MoS2 anodes retain 91% of the initial capacity; in contrast, bare MoS2 anodes retain only 63%. Also, HfO2 coated MoS2 anodes show one of the highest reported capacity values for MoS2 . Cyclic voltammetry and X-ray photoelectron spectroscopy results suggest that HfO2 does not take part in electrochemical reaction. The mechanism of capacity retention with HfO2 coating is explained by ex situ transmission electron microscope imaging and electrical impedance spectroscopy. It is illustrated that HfO2 acts as a passivation layer at the anode/electrolyte interface and prevents structural degradation during charge/discharge process. Moreover, the amorphous nature of HfO2 allows facile diffusion of Na ions. These results clearly show the potential of HfO2 coated MoS2 anodes, which performance is significantly higher than previous reports where bulk MoS2 or composites of MoS2 with carbonaceous materials are used. PMID:26061915

  14. First principles study and empirical parametrization of twisted bilayer MoS2 based on band-unfolding

    Science.gov (United States)

    Tan, Yaohua; Chen, Fan W.; Ghosh, Avik W.

    2016-09-01

    We explore the band structure and ballistic electron transport in twisted bilayer MoS2 using the density functional theory. The sphagetti like bands are unfolded to generate band structures in the primitive unit cell of the original 2H MoS2 bilayer and projected onto the original bands of an individual layer. The corresponding twist angle dependent bandedges are extracted from the unfolded band structures. Based on a comparison within the same primitive unit cell, an efficient two band effective mass model for indirect ΓV and ΛC valleys is created and parametrized by fitting to the unfolded band structures. With the two band effective mass model, we calculate transport properties—specifically, the ballistic transmission in arbitrarily twisted bilayer MoS2 .

  15. Prebiotic (Mannanoligosaccharide- MOS in fish nutrition: effects on nile-tilapia Oreochromis niloticus performance

    Directory of Open Access Journals (Sweden)

    Flávio Endrigo Cechim

    2012-12-01

    observed no influence of this prebiotic on fish growth. The use of prebiotics as mannanoligosaccharides to improve growth and health status in fish still needs further research for better explanation of contradictory results. The complex carbohydrate structure in the cell wall of yeast, different strains and fermentation conditions, processing methods can all alter their function, as well as MOS concentration, administration period and population status (age, sex, gonadal maturation. For instance, in this experiment, dietary MOS supplementation did not show prebiotic properties such as positive effects on juvenile Nile tilapia growth.

  16. Beneficial effect of Re doping on the electrochemical HER activity of MoS2 fullerenes.

    Science.gov (United States)

    Chhetri, Manjeet; Gupta, Uttam; Yadgarov, Lena; Rosentsveig, Rita; Tenne, Reshef; Rao, C N R

    2015-10-01

    Electrochemical generation of hydrogen by non-precious metal electrocatalysts at a lower overpotential is a focus area of research directed towards sustainable energy. The exorbitant costs associated with Pt-based catalysts is the major bottleneck associated with commercial-scale hydrogen generation. Strategies for the synthesis of cost-effective and stable catalysts are thus key for a prospective 'hydrogen economy'. In this report, we highlight a novel and general strategy to enhance the electrochemical activity of molybdenum disulfide (MoS2) in a fullerene structure (IF-). In particular, pristine (undoped) and rhenium-doped nanoparticles of MoS2 with fullerene-like structures (IF-MoS2) were studied, and their performance as catalysts for the hydrogen evolution reaction (HER) was compared to that of 2H-MoS2 particles (platelets). The current density of the IF-MoS2 was higher by one order of magnitude than that of few-layer (FL-) MoS2, due to the enhanced density of the edge sites. Furthermore, Re doping of as low as 100 ppm in IF-MoS2 decreased the onset potential by 60-80 mV and increased the activity by 60 times compared with that of the FL-MoS2. The combined synergistic effect of Re doping and the IF structure not only changes the intrinsic nature of the MoS2 but also increases its reactivity. This strategy highlights the potential use of the IF structure and Re doping in electrocatalytic hydrogen evolution using MoS2-based catalysts. PMID:26308554

  17. Enhancement of photovoltaic response in multilayer MoS2 induced by plasma doping.

    Science.gov (United States)

    Wi, Sungjin; Kim, Hyunsoo; Chen, Mikai; Nam, Hongsuk; Guo, L Jay; Meyhofer, Edgar; Liang, Xiaogan

    2014-05-27

    Layered transition-metal dichalcogenides hold promise for making ultrathin-film photovoltaic devices with a combination of excellent photovoltaic performance, superior flexibility, long lifetime, and low manufacturing cost. Engineering the proper band structures of such layered materials is essential to realize such potential. Here, we present a plasma-assisted doping approach for significantly improving the photovoltaic response in multilayer MoS2. In this work, we fabricated and characterized photovoltaic devices with a vertically stacked indium tin oxide electrode/multilayer MoS2/metal electrode structure. Utilizing a plasma-induced p-doping approach, we are able to form p-n junctions in MoS2 layers that facilitate the collection of photogenerated carriers, enhance the photovoltages, and decrease reverse dark currents. Using plasma-assisted doping processes, we have demonstrated MoS2-based photovoltaic devices exhibiting very high short-circuit photocurrent density values up to 20.9 mA/cm(2) and reasonably good power-conversion efficiencies up to 2.8% under AM1.5G illumination, as well as high external quantum efficiencies. We believe that this work provides important scientific insights for leveraging the optoelectronic properties of emerging atomically layered two-dimensional materials for photovoltaic and other optoelectronic applications.

  18. Additional electric field in real trench MOS barrier Schottky diode

    Science.gov (United States)

    Mamedov, R. K.; Aslanova, A. R.

    2016-04-01

    In real trench MOS barrier Schottky diode (TMBS diode) additional electric field (AEF) the whole is formed in the near contact region of the semiconductor and its propagation space is limited with the barrier metal and the metallic electrodes of MOS structures. Effective potential barrier height TMBS diode is formed via resulting electric field of superposition AEF and electric field of space charge region (SCR) semiconductor. The dependence of the resulting electric field intensity of the distance towards the inside the semiconductor is nonlinear and characterized by a peak at a certain distance from the interface. The thickness of the SCR in TMBS diode becomes equal to the trench depth. Force and energy parameters of the AEF, and thus resulting electric field in the SCR region, become dependent on the geometric design parameters TMBS diode. The forward I-V characteristic TMBS diode is described by the thermionic emission theory as in conventional flat Scottky diode, and in the reverse bias, current is virtually absent at initial voltage, appears abruptly at a certain critical voltage.

  19. Synthesis of MoS2/g-C3N4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of nitric oxide (NO).

    Science.gov (United States)

    Wen, M Q; Xiong, T; Zang, Z G; Wei, W; Tang, X S; Dong, F

    2016-05-16

    Molybdenum disulfide and graphitic carbon nitride (MoS2-g-C3N4) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS2-g-C3N4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS2 nanosheets and g-C3N4 nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS2-g-C3N4 composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS2 content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C3N4 nanoparticles. A possible photocatalytic mechanism for the MoS2-g-C3N4 nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS2 and g-C3N4. PMID:27409846

  20. Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films

    Science.gov (United States)

    Vangelista, Silvia; Cinquanta, Eugenio; Martella, Christian; Alia, Mario; Longo, Massimo; Lamperti, Alessio; Mantovan, Roberto; Basso Basset, Francesco; Pezzoli, Fabio; Molle, Alessandro

    2016-04-01

    Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm2-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

  1. Rolling Up a Monolayer MoS2 Sheet.

    Science.gov (United States)

    Meng, Jianling; Wang, Guole; Li, Xiaomin; Lu, Xiaobo; Zhang, Jing; Yu, Hua; Chen, Wei; Du, Luojun; Liao, Mengzhou; Zhao, Jing; Chen, Peng; Zhu, Jianqi; Bai, Xuedong; Shi, Dongxia; Zhang, Guangyu

    2016-07-01

    MoS2 nanoscrolls are formed by argon plasma treatment on monolayer MoS2 sheet. The nanoscale scroll formation is attributed to the partial removal of top sulfur layer in MoS2 during the argon plasma treatment process. This convenient, solvent-free, and high-yielding nanoscroll formation technique is also feasible for other 2D transition metal dichalcogenides.

  2. MoS2 coated hollow carbon spheres for anodes of lithium ion batteries

    Science.gov (United States)

    Zhang, Yufei; Wang, Ye; Yang, Jun; Shi, Wenhui; Yang, Huiying; Huang, Wei; Dong, Xiaochen

    2016-06-01

    With the assistance of resorcinol-formaldehyde, MoS2 coated hollow carbon spheres (C@MoS2) were synthesized through a facile hydrothermal route followed by heat and alkali treatments. The measurements indicate that the hollow carbon spheres with an average diameter of 300 nm and shell thickness of 20 nm. And the hollow core are uniformly covered by ultrathin MoS2 nanosheets with a length increased to 400 nm. The unique hollow structure and the synergistic effect between carbon layer and MoS2 nanosheets significantly enhance the rate capability and electrochemical stability of C@MoS2 spheres as anode material of lithium-ion battery. The synthesized C@MoS2 delivered a capacity of 750 mAh g-1 at a current density of 100 mA g-1. More importantly, the C@MoS2 maintained a reversible capacity of 533 mAh g-1 even at a high current density of 1000 mA g-1. The study indicated that MoS2 coated hollow carbon spheres can be promising anode material for next generation high-performance lithium-ion batteries.

  3. Ultrafast charge transfer in MoS2/WSe2 p–n Heterojunction

    Science.gov (United States)

    Peng, Bo; Yu, Guannan; Liu, Xinfeng; Liu, Bo; Liang, Xiao; Bi, Lei; Deng, Longjiang; Chien Sum, Tze; Loh, Kian Ping

    2016-06-01

    Atomically thin and sharp van der Waals heterojunction can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) onto n-type molybdenum disulfide (MoS2). Theory predicts that stacked MoS2 and WSe2 monolayer forms type II p–n junction, creating a built-in electric field across the interface which facilitates electron–hole separation and transfer. Gaining insights into the dynamics of charge transfer across van der Waals heterostructure is central to understanding light-photocurrent conversion at these ultrathin interfaces. Herein, we investigate the exciton dissociation and charge transfer in a MoS2/WSe2 van der Waals hetero-structure. Our results show that ultrafast electron transfer from WSe2 to MoS2 take place within 470 fs upon optical excitation with 99% charge transfer efficiency, leading to drastic photoluminescence quenching and decreased lifetime. Our findings suggest that van der Waals heterostructure may be useful as active components in ultrafast optoelectronic devices.

  4. Three-dimensional spirals of atomic layered MoS2.

    Science.gov (United States)

    Zhang, Liming; Liu, Kaihui; Wong, Andrew Barnabas; Kim, Jonghwan; Hong, Xiaoping; Liu, Chong; Cao, Ting; Louie, Steven G; Wang, Feng; Yang, Peidong

    2014-11-12

    Atomically thin two-dimensional (2D) layered materials, including graphene, boron nitride, and transition metal dichalcogenides (TMDs), can exhibit novel phenomena distinct from their bulk counterparts and hold great promise for novel electronic and optoelectronic applications. Controlled growth of such 2D materials with different thickness, composition, and symmetry are of central importance to realize their potential. In particular, the ability to control the symmetry of TMD layers is highly desirable because breaking the inversion symmetry can lead to intriguing valley physics, nonlinear optical properties, and piezoelectric responses. Here we report the first chemical vapor deposition (CVD) growth of spirals of layered MoS2 with atomically thin helical periodicity, which exhibits a chiral structure and breaks the three-dimensional (3D) inversion symmetry explicitly. The spirals composed of tens of connected MoS2 layers with decreasing areas: each basal plane has a triangular shape and shrinks gradually to the summit when spiraling up. All the layers in the spiral assume an AA lattice stacking, which is in contrast to the centrosymmetric AB stacking in natural MoS2 crystals. We show that the noncentrosymmetric MoS2 spiral leads to a strong bulk second-order optical nonlinearity. In addition, we found that the growth of spirals involves a dislocation mechanism, which can be generally applicable to other 2D TMD materials. PMID:25343743

  5. Resonant Raman spectroscopy study of swift heavy ion irradiated MoS2

    Science.gov (United States)

    Guo, Hang; Sun, Youmei; Zhai, Pengfei; Zeng, Jian; Zhang, Shengxia; Hu, Peipei; Yao, Huijun; Duan, Jinglai; Hou, Mingdong; Liu, Jie

    2016-08-01

    Molybdenum disulphide (MoS2) crystal samples were irradiated by swift heavy ions (209Bi and 56Fe). Hillock-like latent tracks were observed on the surface of irradiated MoS2 by atomic force microscopy. The modifications of properties of irradiated MoS2 were investigated by resonant Raman spectroscopy and ultraviolet-visible spectroscopy (UV-Vis). A new peak (E1u2, ∼385.7 cm-1) occurs near the in-plane E2g1 peak (∼383.7 cm-1) after irradiation. The two peaks shift towards lower frequency and broaden due to structural defects and stress with increasing fluence. When irradiated with high fluence, two other new peaks appear at ∼ 190 and ∼ 230 cm-1. The peak at ∼230 cm-1 is disorder-induced LA(M) mode. The presence of this mode indicates defects induced by irradiation. The feature at ∼460 cm-1 is composed of 2LA(M) (∼458 cm-1) and A2u (∼466 cm-1) mode. With increasing fluence, the integrated intensity ratio between 2LA(M) and A2u increases. The relative enhancement of 2LA(M) mode is in agreement with the appearance of LA(M) mode, which both demonstrate structural disorder in irradiated MoS2. The ∼423-cm-1 peak shifts toward lower frequency due to the decrease in exciton energy of MoS2, and this was demonstrated by the results of UV-Vis spectra. The decrease in exciton energy could be due to introduction of defect levels into band gap.

  6. Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties.

    Science.gov (United States)

    Tan, Shu Min; Ambrosi, Adriano; Sofer, Zdenĕk; Huber, Štěpán; Sedmidubský, David; Pumera, Martin

    2015-05-01

    The layered structure of molybdenum disulfide (MoS2 ) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS2 : basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS2 by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS2 pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X-ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E2g and A1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k(0) of 4.96×10(-5) and 1.1×10(-3)  cm s(-1) for [Fe(CN)6 ](3-/4-) and [Ru(NH3 )6 ](3+/2+) redox probes, respectively, compared to the basal plane, which yielded k(0) tending towards zero for [Fe(CN)6 ](3-/4-) and about 9.3×10(-4)  cm s(-1) for [Ru(NH3 )6 ](3+/2+) . The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)6 ](3-/4-) in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS2 crystals is supported by DFT calculations. PMID:25821017

  7. Improved dehydrogenation performance of LiBH4 by 3D hierarchical flower-like MoS2 spheres additives

    Science.gov (United States)

    Zhao, Yan; Liu, Yongchang; Liu, Huiqiao; Kang, Hongyan; Cao, Kangzhe; Wang, Qinghong; Zhang, Chunling; Wang, Yijing; Yuan, Huatang; Jiao, Lifang

    2015-12-01

    In this work, 3D hierarchical flower-like MoS2 spheres are successfully fabricated via a hydrothermal method followed by a heat treatment. The obtained product is composed of few-layered MoS2 nanosheets with enlarged interlayer distance (ca. 0.66 nm) of the (002) plane. Meanwhile, the hydrogen storage properties of the as-prepared MoS2 ball milled with LiBH4 are systematically investigated. The results of temperature programmed desorption (TPD) and isothermal measurement suggest that the LiBH4-MoS2 (as-prepared) mixture exhibits favorable dehydrogenation properties in both lowering the hydrogen release temperature and improving kinetics of hydrogen release rate. LiBH4-MoS2 (as-prepared) sample (the preparation mass ratio is 1:1) starts to release hydrogen at 171 °C, and roughly 5.6 wt% hydrogen is released within 1 h when isothermally heated to 320 °C, which presents superior dehydrogenation performance compared to that of the bulk LiBH4. The excellent dehydrogenation performance of the LiBH4-MoS2 (as-prepared) mixture may be attributed to the high active site density and enlarged interlayer distance of the MoS2 nanosheets, 3D architectures and hierarchical structures.

  8. Facile one-pot synthesis of CoS2-MoS2/CNTs as efficient electrocatalyst for hydrogen evolution reaction

    Science.gov (United States)

    Liu, Yan-Ru; Hu, Wen-Hui; Li, Xiao; Dong, Bin; Shang, Xiao; Han, Guan-Qun; Chai, Yong-Ming; Liu, Yun-Qi; Liu, Chen-Guang

    2016-10-01

    Ternary hybrid cobalt disulfide-molybdenum disulfides supported on carbon nanotubes (CoS2-MoS2/CNTs) electrocatalysts have been prepared via a simple hydrothermal method. CNTs as support may provide good conductivity and low the agglomeration of layered MoS2 structure. CoS2 with intrinsic metallic conductivity may enhance the activity of the ternary hybrid electrocatalysts for hydrogen evolution reaction (HER). X-ray diffraction (XRD) data confirm the formation of ternary hybrid nanocomposites composed of CNTs, CoS2 and amorphous MoS2. Scanning electron microscopy (SEM) images show that strong combination between MoS2, CNTs and regular orthohexagonal CoS2 has been obtained. The dispersion of each component is good and no obvious agglomeration can be observed. It is found that compared with CoS2/CNTs and MoS2/CNTs, the ternary CoS2-MoS2/CNTs have the better activity for HER with a low onset potential of 70 mV (vs. RHE) and a small Talel slope of 67 mV dec-1, and are extremely stable after 1000 cycles. In addition, the optimal doping ratio of Co to Mo is 2:1, which have better HER activity. It is proved that the introduction of carbon materials and Co atoms could improve the performances of MoS2-based electrocatalysts for HER.

  9. Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films.

    Science.gov (United States)

    Vangelista, Silvia; Cinquanta, Eugenio; Martella, Christian; Alia, Mario; Longo, Massimo; Lamperti, Alessio; Mantovan, Roberto; Basset, Francesco Basso; Pezzoli, Fabio; Molle, Alessandro

    2016-04-29

    Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm(2)-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

  10. Origin of the n -type and p -type conductivity of MoS 2 monolayers on a SiO 2 substrate

    KAUST Repository

    Dolui, Kapildeb

    2013-04-02

    Ab initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO 2 substrate in the presence of interface impurities and defects. When MoS2 is placed on a defect-free substrate, the oxide plays an insignificant role since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from n- to p-type. Our results show that the conductive properties of MoS2 deposited on SiO 2 are mainly determined by the detailed structure of the MoS 2/SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2-based devices. © 2013 American Physical Society.

  11. High pressure effect on MoS2 and MoSe2 single crystals grown by CVT method

    Indian Academy of Sciences (India)

    Madhavi Dave; Rajiv Vaidya; S G Patel; A R Jani

    2004-04-01

    Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.

  12. In-Situ hydrothermal synthesis of a MoS2 nanosheet electrode for electrochemical energy storage applications

    Science.gov (United States)

    Patel, Rajkumar; Inamdar, Akbar I.; Kim, Hyung Bae; Im, Hyunsik; Kim, Hyungsang

    2016-06-01

    A molybdenum disulfide (MoS2) nanosheet film was grown directly on a stainless-steel substrate by using an in-situ hydrothermal growth technique at 200 °C. The formation of an MoS2 hexagonal structure with a nanosheet-like morphology was confirmed by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) while a layered MoS2 nanosheet structure was observed under an energy-filtering transmission electron microscope (EF-TEM). The electrochemical supercapacitor properties of the MoS2 nanosheet electrode were measured in 1-M aqueous Na2SO4 electrolyte by using cyclic voltammetry (CV) and charge/discharge technique, and the electrode's specific capacitances were 91.29 F/g and 146.15 F/g, respectively. The concurrent double-layer capacitance and pseudo-capacitance behaviors of the electrode manifested themselves in the rectangular shape and redox peaks of the CV curve. The mesoporous MoS2 nanosheets were electrochemically stable for up to 1000 charge/discharge cycles.

  13. Magnetoresistance in Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions.

    Science.gov (United States)

    Zhang, Han; Ye, Meng; Wang, Yangyang; Quhe, Ruge; Pan, Yuanyuan; Guo, Ying; Song, Zhigang; Yang, Jinbo; Guo, Wanlin; Lu, Jing

    2016-06-28

    Semiconducting single-layer (SL) and few-layer MoS2 have a flat surface, free of dangling bonds. Using density functional theory coupled with non-equilibrium Green's function method, we investigate the spin-polarized transport properties of Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions with MoS2 layer numbers of N = 1, 3, and 5. Well-defined interfaces are formed between MoS2 and metal electrodes. The junctions with a SL MoS2 spacer are almost metallic owing to the strong coupling between MoS2 and the ferromagnets, while those are tunneling with a few layer MoS2 spacer. Both large magnetoresistance and tunneling magnetoresistance are found when fcc or hcp Co is used as an electrode. Therefore, flat single- and few-layer MoS2 can serve as an effective nonmagnetic spacer in a magnetoresistance or tunneling magnetoresistance device with a well-defined interface.

  14. Magnetoresistance in Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions.

    Science.gov (United States)

    Zhang, Han; Ye, Meng; Wang, Yangyang; Quhe, Ruge; Pan, Yuanyuan; Guo, Ying; Song, Zhigang; Yang, Jinbo; Guo, Wanlin; Lu, Jing

    2016-06-28

    Semiconducting single-layer (SL) and few-layer MoS2 have a flat surface, free of dangling bonds. Using density functional theory coupled with non-equilibrium Green's function method, we investigate the spin-polarized transport properties of Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions with MoS2 layer numbers of N = 1, 3, and 5. Well-defined interfaces are formed between MoS2 and metal electrodes. The junctions with a SL MoS2 spacer are almost metallic owing to the strong coupling between MoS2 and the ferromagnets, while those are tunneling with a few layer MoS2 spacer. Both large magnetoresistance and tunneling magnetoresistance are found when fcc or hcp Co is used as an electrode. Therefore, flat single- and few-layer MoS2 can serve as an effective nonmagnetic spacer in a magnetoresistance or tunneling magnetoresistance device with a well-defined interface. PMID:27257639

  15. Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review

    Directory of Open Access Journals (Sweden)

    Yufei Zhao, Yuxia Zhang, Zhiyu Yang, Yiming Yan and Kening Sun

    2013-01-01

    Full Text Available Scientists increasingly witness the applications of MoS2 and MoO2 in the field of energy conversion and energy storage. On the one hand, MoS2 and MoO2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS2 and MoO2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS2 and MoO2 are briefly summarized according to their applications for H2 generation and lithium ion batteries. Firstly, we overview the recent advancements in the morphology control of MoS2 and MoO2 and their applications as electrocatalysts for hydrogen evolution reactions. Secondly, we focus on the photo-induced water splitting for H2 generation, in which MoS2 acts as an important co-catalyst when combined with other semiconductor catalysts. The newly reported research results of the significant functions of MoS2 nanocomposites in photo-induced water splitting are presented. Thirdly, we introduce the advantages of MoS2 and MoO2 for their enhanced cyclic performance and high capacity as electrode materials of lithium ion batteries. Recent key achievements in MoS2- and MoO2-based lithium ion batteries are highlighted. Finally, we discuss the future scope and the important challenges emerging from these fascinating materials.

  16. Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review

    International Nuclear Information System (INIS)

    Scientists increasingly witness the applications of MoS2 and MoO2 in the field of energy conversion and energy storage. On the one hand, MoS2 and MoO2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS2 and MoO2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS2 and MoO2 are briefly summarized according to their applications for H2 generation and lithium ion batteries. Firstly, we overview the recent advancements in the morphology control of MoS2 and MoO2 and their applications as electrocatalysts for hydrogen evolution reactions. Secondly, we focus on the photo-induced water splitting for H2 generation, in which MoS2 acts as an important co-catalyst when combined with other semiconductor catalysts. The newly reported research results of the significant functions of MoS2 nanocomposites in photo-induced water splitting are presented. Thirdly, we introduce the advantages of MoS2 and MoO2 for their enhanced cyclic performance and high capacity as electrode materials of lithium ion batteries. Recent key achievements in MoS2- and MoO2-based lithium ion batteries are highlighted. Finally, we discuss the future scope and the important challenges emerging from these fascinating materials. (review)

  17. Luminescence from Er and Tb implanted into MOS tunnel diodes

    International Nuclear Information System (INIS)

    We have demonstrated the 1.5 μm electroluminescence from implanted Er ions inside the SiO2 insulator of a silicon metal-oxide-semiconductor (MOS) structure under forward bias. The Er ions are excited by the direct impact from electrons tunneling through the oxide at electric fields larger than 6 MV/cm. We measured an excitation cross-section of 6x10-15 cm2 and a total lifetime of 1.5 ms. In order to change the emission wavelength into the visible regime, we changed to Tb ions. Photoluminescence data show a broad defect luminescence band and several sharp lines due to the Tb transitions. We find a noticeable influence of Tb-Tb-cross-relaxation which favours the green lines over the blue luminescence lines

  18. Bonding between graphene and MoS2 monolayers without and with Li intercalation

    International Nuclear Information System (INIS)

    We performed density functional theory (DFT) calculations for a bi-layered heterostructure combining a graphene layer with a MoS2 layer with and without intercalated Li atoms. Our calculations demonstrate the importance of the van der Waals (vdW) interaction, which is crucial for forming stable bonding between the layers. Our DFT calculation correctly reproduces the linear dispersion, or Dirac cone, feature at the Fermi energy for the isolated graphene monolayer and the band gap for the MoS2 monolayer. For the combined graphene/MoS2 bi-layer, we observe interesting electronic structure and density of states (DOS) characteristics near the Fermi energy, showing both the gap like features of the MoS2 layer and in-gap states with linear dispersion contributed mostly by the graphene layer. Our calculated total DOS in this vdW heterostructure reveals that the graphene layer significantly contributes to pinning the Fermi energy at the center of the band gap of MoS2. We also find that intercalating Li ions in between the layers of the graphene/MoS2 heterostructure enhances the binding energy through orbital hybridizations between cations (Li adatoms) and anions (graphene and MoS2 monolayers). Moreover, we calculate the dielectric function of the Li intercalated graphene/MoS2 heterostructure, the imaginary component of which can be directly compared with experimental measurements of optical conductivity in order to validate our theoretical prediction. We observe sharp features in the imaginary component of the dielectric function, which shows the presence of a Drude peak in the optical conductivity, and therefore metallicity in the lithiated graphene/MoS2 heterostructure

  19. Spin-dependent transport properties of Fe3O4/MoS2/Fe3O4 junctions

    Science.gov (United States)

    Wu, Han-Chun; Coileáin, Cormac Ó.; Abid, Mourad; Mauit, Ozhet; Syrlybekov, Askar; Khalid, Abbas; Xu, Hongjun; Gatensby, Riley; Jing Wang, Jing; Liu, Huajun; Yang, Li; Duesberg, Georg S.; Zhang, Hong-Zhou; Abid, Mohamed; Shvets, Igor V.

    2015-11-01

    Magnetite is a half-metal with a high Curie temperature of 858 K, making it a promising candidate for magnetic tunnel junctions (MTJs). Yet, initial efforts to exploit its half metallic nature in Fe3O4/MgO/Fe3O4 MTJ structures have been far from promising. Finding suitable barrier layer materials, which keep the half metallic nature of Fe3O4 at the interface between Fe3O4 layers and barrier layer, is one of main challenges in this field. Two-dimensional (2D) materials may be good candidates for this purpose. Molybdenum disulfide (MoS2) is a transition metal dichalcogenide (TMD) semiconductor with distinctive electronic, optical, and catalytic properties. Here, we show based on the first principle calculations that Fe3O4 keeps a nearly fully spin polarized electron band at the interface between MoS2 and Fe3O4. We also present the first attempt to fabricate the Fe3O4/MoS2/Fe3O4 MTJs. A clear tunneling magnetoresistance (TMR) signal was observed below 200 K. Thus, our experimental and theoretical studies indicate that MoS2 can be a good barrier material for Fe3O4 based MTJs. Our calculations also indicate that junctions incorporating monolayer or bilayer MoS2 are metallic.

  20. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    Science.gov (United States)

    Khan, Abdul Karim; Lee, Byoung Hun

    2016-09-01

    Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT) phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range) over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

  1. Adsorption of gas molecules on Cu impurities embedded monolayer MoS2: A first- principles study

    Science.gov (United States)

    Zhao, B.; Li, C. Y.; Liu, L. L.; Zhou, B.; Zhang, Q. K.; Chen, Z. Q.; Tang, Z.

    2016-09-01

    Adsorption of small gas molecules (O2, NO, NO2 and NH3) on transition-metal Cu atom embedded monolayer MoS2 was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS2 with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS2 embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS2 with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH3 molecule acts as electron donor after adsorption, which is different from the other gas molecules (O2, NO, and NO2). The results suggest that MoS2-Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene.

  2. Thermally activated trap charges responsible for hysteresis in multilayer MoS2 field-effect transistors

    Science.gov (United States)

    Park, Youngseo; Baac, Hyoung Won; Heo, Junseok; Yoo, Geonwook

    2016-02-01

    Hysteresis, which is induced by both extrinsic and intrinsic causes, is often observed in molybdenum disulphide (MoS2) field-effect transistors (FETs), and several extrinsic hysteresis effects have been reported in unpassivated bottom-gate MoS2 device structures. In this study, interface-trap-induced hysteresis and other electrical properties are examined. We experimentally investigate thermally activated trap charges near a silicon-dioxide (SiO2)-MoS2 interface that gives rise to hysteresis in a multilayer MoS2 FET in a temperature region of 10-300 K. The threshold voltage (VTH) and field-effect mobility (μFE) decrease with the increase in temperature, regardless of the gate-bias sweep direction. The hysteresis that coincides with the trend of subthreshold swing increases sharply above T = 150 K as the released charges from interface traps become dominant over the fixed charges. Based on a temperature-dependent hysteresis analysis, we discussed the activation energy of interface traps and maximum interface trap density of the fabricated multilayer MoS2 FET.

  3. Photoluminescence of MoS2 quantum dots quenched by hydrogen peroxide: A fluorescent sensor for hydrogen peroxide

    Science.gov (United States)

    Gan, Zhixing; Gui, Qingfeng; Shan, Yun; Pan, Pengfei; Zhang, Ning; Zhang, Lifa

    2016-09-01

    By cutting MoS2 microcrystals to quantum dots (QDs) of sizes below 10 nm, the photoluminescence (PL) at ca. 450 nm can be detected easily due to the quantum confinement effects across the 2D planes. The PL is stable under continuous irradiation of UV light but gradually quenches when treated with an increasing concentration of hydrogen peroxide. Time-resolved PL and Raman spectra imply that H2O2 causes the partial oxidation of MoS2 QDs. First-principles calculations reveal that the MoS2 QDs with oxygen impurity are of indirect bandgap structures showing no notable PL. And absorption spectra verify that the PL of MoS2 QDs quenched by H2O2 is attributed to the oxidation. The integrated PL intensity and H2O2 concentration show an exponential relationship in the range of 2-20 μM, suggesting that MoS2 QDs are potential fluorescent probes for hydrogen peroxide sensing in a physiological environment.

  4. MOS: The Critical Elements of Doing Effective Classroom Demonstrations

    Science.gov (United States)

    Shmaefsky, Brian R.

    2005-01-01

    MOS, or Minds-On-Science, is the foundation of conducting educationally valuable science demonstrations. It is a teaching strategy equally effective as hands-on-learning. Plus, it proves much more effective at reinforcing abstract science concepts than traditional lectures, readings, and audiovisual presentations. Adding MOS to a demonstration…

  5. Heterostructures based on graphene and MoS2 layers decorated by C60 fullerenes

    Science.gov (United States)

    Chernozatonskii, Leonid A.; Kvashnin, Alexander G.; Sorokin, Pavel B.

    2016-09-01

    Here we present a comprehensive investigation of various novel composite structures based on graphene (G) and molybdenum disulphide (MoS2) monolayers decorated by C60 fullerenes, which can be successfully applied in photovoltaics as a solar cell unit. Theoretical studies of the atomic structure, stability and electronic properties of the proposed G/C60, MoS2/C60 and G/MoS2/C60/G nanostructures were carried out. We show that making the G/MoS2/C60/G heterostructure from the 2D films considered here will lead to the appearance of particular properties suitable for application in photovoltaics due to the broad energetic region of high electronic density of states.

  6. Covalent functionalization of MoS2

    Directory of Open Access Journals (Sweden)

    Stanislav Presolski

    2016-04-01

    Full Text Available MoS2 nanosheets have been used extensively in catalytic, electronic, optoelectronic and electrochemical research due to their diverse properties that are often determined by the method of fabrication. Fine tuning of the colloidal behaviour, specific interactions and further reactivity of the materials is typically achieved by subsequent surface modifications. Arguably the most permanent of these involve covalent attachment of molecules to either the molybdenum or the sulphur atoms in the lattice. Here we review of the nascent field of transition metal dichalcogenide (TMD covalent functionalization and explore the prospective avenues for hybrid organic-inorganic nanomaterials.

  7. UHV-STM manipulation of single flat gold nano-islands for constructing interconnection nanopads on MoS2

    International Nuclear Information System (INIS)

    We demonstrate manipulation of metallic islands containing nearly a million atoms with a precision of one lattice spacing on a MoS2 surface, one at a time. Optimizing the growth conditions yields triangular shape metallic nano-islands 40 nm in lateral size and 12 nm in height on the MoS2 surface. The manipulation of these nano-islands is done one at a time using the scanning tunneling microscope, and a fully planar 4 pad nanostructure is demonstrated, where one apex of each triangular nano-island is pointing towards a central working MoS2 area of 12 nm x 24 nm in which atomic cleanliness is preserved. The feedback loop conditions to achieve this manipulation are discussed. This fully planar 4 pads nano-structure is ready to be interconnected by a multi-tip system

  8. Van der Waals epitaxial growth of MoS2 on SiO2/Si by chemical vapor deposition

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    Recently, single layer MoS2 with a direct band gap of 1.9 eV has been proposed as a candidate for two dimensional nanoelectronic devices. However, the synthetic approach to obtain high-quality MoS2 atomic thin layers is still problematic. Spectroscopic and microscopic results reveal that both single layers and tetrahedral clusters of MoS2 are deposited directly on the SiO2/Si substrate by chemical vapor deposition. The tetrahedral clusters are mixtures of 2H- and 3R-MoS2. By ex situ optical analysis, both the single layers and tetrahedral clusters can be attributed to van der Waals epitaxial growth. Due to the similar layered structures we expect the same growth mechanism for other transition-metal disulfides by chemical vapor deposition. © 2013 The Royal Society of Chemistry.

  9. Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process,a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design,better interface property,lower leakage current,and smaller capacitance-voltage (C-V) hysteresis were obtained,and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.

  10. Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

    Institute of Scientific and Technical Information of China (English)

    YUE YuanZheng; HAO Yue; FENG Qian; ZHANG JinCheng; MA XiaoHua; NI JinYu

    2009-01-01

    We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AIGaN/GaN HEMT of similar design, better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis were obtained, and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.

  11. A route to synthesis molybdenum disulfide-reduced graphene oxide (MoS2-RGO) composites using supercritical methanol and their enhanced electrochemical performance for Li-ion batteries

    Science.gov (United States)

    Choi, Mugyeom; Koppala, Siva Kumar; Yoon, Dohyeon; Hwang, Jieun; Kim, Seung Min; Kim, Jaehoon

    2016-03-01

    A simple and effective approach for the tight anchoring of molybdenum disulfide (MoS2) to the surface of supercritical-alcohol-reduced graphene oxide (SRGO) is developed. The MoS2-SRGO composites are synthesized by the one-pot deposition of MoO2 on SRGO and simultaneous reduction of GO to SRGO in supercritical methanol followed by sulfurization. The obtained MoS2-SRGO composites contain a crystalline MoS2 phase comprising 11-14 layers of MoS2. In addition, the composites have mesoporous structures with high porosities, ranging between 55 and 57%. In comparison with bare MoS2 and SRGO, the MoS2-SRGO composites have enhanced electrochemical performances due to their mesoporous structures and the synergetic effect between MoS2 and SRGO sheets. When tested as the anode in a secondary lithium battery, it shows high reversible capacity of 896 mAh g-1 at 50 mA g-1 after 50 cycles, a high rate capacity of 320 mAh g-1 at a high charge-discharge rate of 2.5 A g-1, and long-term cycling of 724 mAh g-1 at 50 mA g-1 after 200 cycles. This unique synthetic approach effectively and tightly anchors MoS2 nanoparticles to the SRGO surface, resulting in improved structural integrity, electron transfer efficiency between the SRGO sheets and MoS2, and Li-ion diffusion kinetics.

  12. Atomic and electronic properties of quasi-one-dimensional MoS2 nanowires

    OpenAIRE

    Fernandez Seivane, Lucas; Barron, Hector; Botti, Silvana; Lopes Marques, Miguel Alexandre; Rubio Secades, Ángel; López-Lozano, Xóchitl

    2013-01-01

    The structural, electronic, and magnetic properties of quasi-one-dimensional MoS2nanowires (NWs), passivated by extra sulfur, have been determined using ab initio density functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images and theoretical literature. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo edge, quasi-one-dimensional metallic states are predominant in a...

  13. Analytical Charge Voltage Model in MOS Inversion Layer Based on Space Charge Capacitance

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The concept of Space Charge Capacitance (SCC) is proposed and used to make a novel analytical charge model of quantized inversion layer in MOS structures. Based on SCC,continuous expressions of surface potential and inversion layer carrier density are derived.Quantum mechanical effects on both inversion layer carrier density and surface potential are extensively included. The accuracy of the model is verified by the numerical solution to Schrodinger and Poisson equation and the model is demonstrated,too.

  14. Metallic and ferromagnetic MoS2 nanobelts with vertically aligned edges

    Institute of Scientific and Technical Information of China (English)

    Guanchen Xu[1,2; Xinsheng Wang[1; Yupeng Sun[1; Xiao Chen[2; Jingying Zheng[1; Lifei Sun[1; Liying Jiao[1; Jinghong Li[1

    2015-01-01

    Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional (2D) and three-dimensional (3D) 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional (1D) MoS2 material will enable its applications in electronics, spintronics, and catalysis.

  15. Imaging spectroscopic ellipsometry of MoS2

    Science.gov (United States)

    Funke, S.; Miller, B.; Parzinger, E.; Thiesen, P.; Holleitner, A. W.; Wurstbauer, U.

    2016-09-01

    Micromechanically exfoliated mono- and multilayers of molybdenum disulfide (MoS2) are investigated by spectroscopic imaging ellipsometry. In combination with knife edge illumination, MoS2 flakes can be detected and classified on arbitrary flat and also transparent substrates with a lateral resolution down to 1-2 µm. The complex dielectric functions from mono- and trilayer MoS2 are presented. They are extracted from a multilayer model to fit the measured ellipsometric angles employing an anisotropic and an isotropic fit approach. We find that the energies of the critical points of the optical constants can be treated to be independent of the utilized model, whereas the magnitude of the optical constants varies with the used model. The anisotropic model suggests a maximum absorbance for a MoS2 sheet supported by sapphire of about 14% for monolayer and of 10% for trilayer MoS2. Furthermore, the lateral homogeneity of the complex dielectric function for monolayer MoS2 is investigated with a spatial resolution of 2 µm. Only minor fluctuations are observed. No evidence for strain, for a significant amount of disorder or lattice defects can be found in the wrinkle-free regions of the MoS2 monolayer from complementary µ-Raman spectroscopy measurements. We assume that the minor lateral variation in the optical constants are caused by lateral modification in the van der Waals interaction presumably caused by the preparation using micromechanical exfoliation and viscoelastic stamping.

  16. A compact plasmonic MOS-based 2x2 electro-optic switch

    CERN Document Server

    Ye, Chenran; Soref, Richard A; Sorger, Volker J

    2015-01-01

    We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, Indium-Tin-Oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 dB (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with Siliconon- Insulator platforms to for low-cost manufacturing.

  17. Photoluminescence of MoS2 Prepared by Effective Grinding-Assisted Sonication Exfoliation

    Directory of Open Access Journals (Sweden)

    Jing-Yuan Wu

    2014-01-01

    Full Text Available Exfoliation of bulk molybdenum disulfide (MoS2 using sonication in appropriate solvent is a promising route to large-scale preparation of few-layered or monolayered crystals. Grinding-assisted sonication exfoliation was used for preparing monolayered MoS2 nanosheets from natural mineral molybdenite. By controlling the sonication time, larger crystallites could be further exfoliated to smaller as well as thinner nanosheets without damaging their structures. The concentration of 1.6 mg mL−1 of final solution could be achieved. Several microscopic techniques like scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were employed to evaluate the exfoliation results. Strong photoluminescence with the peak centered at 440 nm was also observed in the resulting dispersion which included several small lateral-sized (~3 nm nanostructures.

  18. MoS2 nanoflowers and their field-emission properties

    Science.gov (United States)

    Li, Y. B.; Bando, Y.; Golberg, D.

    2003-03-01

    Elegant three-dimensional MoS2 nanoflowers were uniformly formed via heating a MoO2 thin film in a vapor sulfur atmosphere. Tens to hundreds of petals were self-assembled within a single nanoflower. Each petal, 100-300 nm wide and only several nanometers thick, exhibited a hexagonal structure. The number of petal layers gradually decreased towards the edges, resulting in uniquely thin edges, typically less than 3 nm. The MoS2 nanoflowers appeared to be excellent field emitters displaying a current density of 0.01 and 10 mA/cm2 at macroscopic fields of 4.5-5.5 and 7.6-8.6 V/μm, respectively; the electron field emission was consistent with the Fowler-Nordheim theory.

  19. A compact plasmonic MOS-based 2×2 electro-optic switch

    Science.gov (United States)

    Ye, Chenran; Liu, Ke; Soref, Richard A.; Sorger, Volker J.

    2015-01-01

    We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, indium-tin-oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with silicon-on-insulator platforms for low-cost manufacturing.

  20. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    KAUST Repository

    Chiu, Ming-Hui

    2015-07-16

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

  1. Remote Plasma Oxidation and Atomic Layer Etching of MoS2.

    Science.gov (United States)

    Zhu, Hui; Qin, Xiaoye; Cheng, Lanxia; Azcatl, Angelica; Kim, Jiyoung; Wallace, Robert M

    2016-07-27

    Exfoliated molybdenum disulfide (MoS2) is shown to chemically oxidize in a layered manner upon exposure to a remote O2 plasma. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) are employed to characterize the surface chemistry, structure, and topography of the oxidation process and indicate that the oxidation mainly occurs on the topmost layer without altering the chemical composition of underlying layer. The formation of S-O bonds upon short, remote plasma exposure pins the surface Fermi level to the conduction band edge, while the MoOx formation at high temperature modulates the Fermi level toward the valence band through band alignment. A uniform coverage of monolayer amorphous MoO3 is obtained after 5 min or longer remote O2 plasma exposure at 200 °C, and the MoO3 can be completely removed by annealing at 500 °C, leaving a clean ordered MoS2 lattice structure as verified by XPS, LEED, AFM, and scanning tunneling microscopy. This work shows that a remote O2 plasma can be useful for both surface functionalization and a controlled thinning method for MoS2 device fabrication processes. PMID:27386734

  2. Oscillating edge states in one-dimensional MoS2 nanowires

    Science.gov (United States)

    Xu, Hai; Liu, Shuanglong; Ding, Zijing; Tan, Sherman J. R.; Yam, Kah Meng; Bao, Yang; Nai, Chang Tai; Ng, Man-Fai; Lu, Jiong; Zhang, Chun; Loh, Kian Ping

    2016-10-01

    Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge density wave and quantum correlation effects arising from edge states. The greater flexibility of a molecular scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topology. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact atomic force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topographical modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.

  3. Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam.

    Science.gov (United States)

    Fox, Daniel S; Zhou, Yangbo; Maguire, Pierce; O'Neill, Arlene; Ó'Coileáin, Cormac; Gatensby, Riley; Glushenkov, Alexey M; Tao, Tao; Duesberg, Georg S; Shvets, Igor V; Abid, Mohamed; Abid, Mourad; Wu, Han-Chun; Chen, Ying; Coleman, Jonathan N; Donegan, John F; Zhang, Hongzhou

    2015-08-12

    We report subnanometer modification enabled by an ultrafine helium ion beam. By adjusting ion dose and the beam profile, structural defects were controllably introduced in a few-layer molybdenum disulfide (MoS2) sample and its stoichiometry was modified by preferential sputtering of sulfur at a few-nanometer scale. Localized tuning of the resistivity of MoS2 was demonstrated and semiconducting, metallic-like, or insulating material was obtained by irradiation with different doses of He(+). Amorphous MoSx with metallic behavior has been demonstrated for the first time. Fabrication of MoS2 nanostructures with 7 nm dimensions and pristine crystal structure was also achieved. The damage at the edges of these nanostructures was typically confined to within 1 nm. Nanoribbons with widths as small as 1 nm were reproducibly fabricated. This nanoscale modification technique is a generalized approach that can be applied to various two-dimensional (2D) materials to produce a new range of 2D metamaterials. PMID:26154305

  4. Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors.

    Science.gov (United States)

    Chen, Chuanmeng; Feng, Zhihong; Feng, Yiyu; Yue, Yuchen; Qin, Chengqun; Zhang, Daihua; Feng, Wei

    2016-07-27

    The large-scale synthesis of atomically thin, layered MoS2/graphene heterostructures is of great interest in optoelectronic devices because of their unique properties. Herein, we present a scalable synthesis method to prepare centimeter-scale, continuous, and uniform films of bilayer MoS2 using low-pressure chemical vapor deposition. This growth process was utilized to assemble a heterostructure by growing large-scale uniform films of bilayer MoS2 on graphene (G-MoS2/graphene). Atomic force microscopy, Raman spectra, and transmission electron microscopy characterization demonstrated that the large-scale bilayer MoS2 film on graphene exhibited good thickness uniformity and a polycrystalline nature. A centimeter-scale phototransistor prepared using the G-MoS2/graphene heterostructure exhibited a high responsivity of 32 mA/W with good cycling stability; this value is 1 order of magnitude higher than that of transferred MoS2 on graphene (2.5 mA/W). This feature results from efficient charge transfer at the interface enabled by intimate contact between the grown bilayer MoS2 (G-MoS2) and graphene. The ability to integrate multilayer materials into atomically thin heterostructures paves the way for fabricating multifunctional devices by controlling their layer structure. PMID:27381011

  5. Photoelectron spectroscopic imaging and device applications of large-area patternable single-layer MoS2 synthesized by chemical vapor deposition.

    Science.gov (United States)

    Park, Woanseo; Baik, Jaeyoon; Kim, Tae-Young; Cho, Kyungjune; Hong, Woong-Ki; Shin, Hyun-Joon; Lee, Takhee

    2014-05-27

    Molybdenum disulfide (MoS2) films, which are only a single atomic layer thick, have been synthesized by chemical vapor deposition (CVD) and have gained significant attention due to their band-gap semiconducting properties. However, in order for them to be useful for the fabrication of practical devices, patterning processes that can be used to form specific MoS2 structures must be integrated with the existing synthetic approaches. Here, we report a method for the synthesis of centimeter-scale, high-quality single-layer MoS2 that can be directly patterned during CVD, so that postpatterning processes can be avoided and device fabrication can be streamlined. Utilizing X-ray photoelectron spectroscopic imaging, we characterize the chemical states of these CVD-synthesized single-layer MoS2 films and demonstrate that the triangular-shaped MoS2 are single-crystalline single-domain monolayers. We also demonstrate the use of these high-quality and directly patterned MoS2 films in electronic device applications by fabricating and characterizing field effect transistors. PMID:24730654

  6. Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors.

    Science.gov (United States)

    Chen, Chuanmeng; Feng, Zhihong; Feng, Yiyu; Yue, Yuchen; Qin, Chengqun; Zhang, Daihua; Feng, Wei

    2016-07-27

    The large-scale synthesis of atomically thin, layered MoS2/graphene heterostructures is of great interest in optoelectronic devices because of their unique properties. Herein, we present a scalable synthesis method to prepare centimeter-scale, continuous, and uniform films of bilayer MoS2 using low-pressure chemical vapor deposition. This growth process was utilized to assemble a heterostructure by growing large-scale uniform films of bilayer MoS2 on graphene (G-MoS2/graphene). Atomic force microscopy, Raman spectra, and transmission electron microscopy characterization demonstrated that the large-scale bilayer MoS2 film on graphene exhibited good thickness uniformity and a polycrystalline nature. A centimeter-scale phototransistor prepared using the G-MoS2/graphene heterostructure exhibited a high responsivity of 32 mA/W with good cycling stability; this value is 1 order of magnitude higher than that of transferred MoS2 on graphene (2.5 mA/W). This feature results from efficient charge transfer at the interface enabled by intimate contact between the grown bilayer MoS2 (G-MoS2) and graphene. The ability to integrate multilayer materials into atomically thin heterostructures paves the way for fabricating multifunctional devices by controlling their layer structure.

  7. Growth and characteristics of self-assembled MoS2/Mo-S-C nanoperiod multilayers for enhanced tribological performance

    Science.gov (United States)

    Xu, Jiao; He, Tengfei; Chai, Liqiang; Qiao, Li; Wang, Peng; Liu, Weimin

    2016-05-01

    Highly ordered MoS2/Mo-S-C nanoperiod multilayers are synthesized by a novel self-assembling mechanism in simultaneous sputtering of MoS2 and graphite targets. The sequential formation of MoS2-riched domain layers and Mo-S-C compositional mixed capping layers reveals no correspondence to the sample stage rotation but is caused by the low energy ion bombardment enhanced interdiffusion. The HRTEM observation shows that the phase segregation normal to the film surface is initiated from substrate-film interlayer with clear contrasts in the first few bi-layers, and then diffuses mutually in a quasiperiodic pattern between two altered sub-layers. Compared with sputtered MoS2 film, the bulk film of multilayers exhibit largely improved toughness under a normal load, and the preferential orientation of sputtered MoS2 in (002) basal planes is significantly enhanced, both of which render the film excellent loads-bearing capacity and lubricant properties. The nano-scratching tests performed on a nanoindentation system suggest that the nano-tribological performance of multilayers is directly determined by the altered structure and properties of neighboring sub-layers until stable tribofilms are formed. Meanwhile, the pin-on-disk tribotests in ambient air, low vacuum and high vacuum provide comparably low friction coefficient yet distinct wear lives in different atmospheres due to the partially restricted humid-sensitivity of sputtered MoS2 phase.

  8. The capacity fading mechanism and improvement of cycling stability in MoS2-based anode materials for lithium-ion batteries.

    Science.gov (United States)

    Shu, Haibo; Li, Feng; Hu, Chenli; Liang, Pei; Cao, Dan; Chen, Xiaoshuang

    2016-02-01

    Two-dimensional (2D) layered MoS2 nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of electrode materials depends on a deep understanding of their dynamic structural evolution and reaction kinetics in the lithiation process. Herein, thermodynamic phase diagrams and the lithiation dynamics of MoS2-based nanostructures with the intercalation of lithium ions are studied by using first-principles calculations and ab initio molecular dynamics simulations. Our results demonstrate that the continuous intercalation of Li ions induces structural destruction of 2H phase MoS2 nanosheets in the discharge process that follows a layer-by-layer dissociation mechanism. Meanwhile, the intercalation of Li ions leads to a structural transition of MoS2 nanosheets from the 2H to the 1T phase due to the ultralow transition barriers (∼0.1 eV). We find that the phase transition can slow down the dissociation of MoS2 nanosheets during lithiation. The result can be applied to explain extensive experimental observation of the fast capacity fading of MoS2-based anode materials between the first and the subsequent discharges. To suppress the dissociation of MoS2 nanosheets in the lithiation process, we propose a strategy by constructing a sandwich-like graphene/MoS2/graphene structure that indicates high chemical stability, superior conductivity, and high Li-ion mobility in the charge/discharge process, implying the possibility to induce an improvement in the anode cycling performance. This work opens a new route to rational design layered transition-metal disulfide (TMD) anode materials for LIBs with superior cycling stability and electrochemical performance.

  9. Sensitivity of MOS transistors to gamma and electron doses

    Energy Technology Data Exchange (ETDEWEB)

    Petr, I. (Ceske Vysoke Uceni Technicke, Prague (Czechoslovakia). Fakulta Jaderna a Fysikalne Inzenyrska); Gilar, O. (Tesla, Premysleni (Czechoslovakia). Vyzkumny Ustav Pristroju Jaderne Techniky)

    1985-03-01

    The threshold shift has been as a function of the properties of the SiO/sub 2/ layer, viz. oxide thickness and diffusion length of the charge carriers formed in the oxide layer. Experimental results obtained from gamma, fast electron, and fast neutron irradiation of MOS transistors having different oxide thickness are given. The theoretical results are compared with the measured data. The sensitivity of MOS transistors to gamma rays and fast electrons is given together with the energy dependence of radiation doses. The application of MOS transistors as dosemeters is discussed.

  10. Chemical sensitivity of Mo gate Mos capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Lombardi, R.M.; Aragon, R. [Laboratorio de Peliculas delgadas, Facultad de Ingenieria, Paseo Colon 850, 1063, Buenos Aires (Argentina)

    2006-07-01

    Mo gate Mos capacitors exhibit a negative shift of their C-V characteristic by up to 240 mV, at 125 C, in response to 1000 ppm hydrogen, in controlled nitrogen atmospheres. The experimental methods for obtaining capacitance and conductance, as a function of polarisation voltage, as well as the relevant equivalent circuits are reviewed. The single-state interface state density, at the semiconductor-dielectric interface, decreases from 2.66 x 10{sup 11} cm{sup -2} e-v{sup -1}, in pure nitrogen, to 2.5 x 10{sup 11} cm{sup -2} e-v{sup -1} in 1000 ppm hydrogen in nitrogen mixtures, at this temperature. (Author)

  11. Enhanced saturation current sensitivities to charge trapping and illumination in MOS tunnel diode by inserting metal in gate dielectric

    Science.gov (United States)

    Chen, Jun-Yao; Kao, Wei-Chih; Hwu, Jenn-Gwo

    2016-06-01

    The enlarged two-state phenomenon in the current-voltage (I-V) characteristic of metal-oxide-semiconductor (MOS) tunnel diode (TD) after negative/positive constant voltage stress (negative/positive CVS) was investigated. It was found that the reverse saturation tunnel current of MOS TD is proportional to the Schottky barrier height of holes, which is determined by the intensity of fringing field (FF) at device edge. With the aid of high permittivity dielectric and screening effect by embedded metal in the MOS structure, the FF was enhanced, which was confirmed by TCAD simulations. Because of the FF enhancement, after proper electrical treatments of voltage stressing, the intensified quantity of electron trapping/de-trapping was found at device edge, which augmented the modulation of Schottky barrier height of holes. As a result, much variation of reverse saturation tunnel current was exhibited, and hence, the enlarged two-state behavior was achieved. The endurance characteristics were also demonstrated to show that the trapped electrons are more stable in the MOS structure with embedded aluminum. Moreover, benefited from FF enhancement, the enlarged photosensitivity of the I-V characteristics of the sample with high permittivity dielectric and embedded aluminum was obtained. The mechanisms of the enlarged split of current behaviors after suitable CVS and illumination treatments are also discussed for these observations.

  12. Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS2 thin film

    Science.gov (United States)

    Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

    2015-08-01

    Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03046c

  13. Polystyrene-Templated Aerosol Synthesis of MoS2 -Amorphous Carbon Composite with Open Macropores as Battery Electrode.

    Science.gov (United States)

    Choi, Seung Ho; Kang, Yun Chan

    2015-07-01

    MoS2 -amorphous carbon (MoS2 -AC) composite microspheres with macroporous structure were fabricated by one-pot spray pyrolysis. Single- or few-layered MoS2 were uniformly dispersed and oriented in random directions in the amorphous carbon microsphere with macropores sizes between 50 and 90 nm. The macroporous microspheres having a high contact area with liquid electrolyte exhibited overall superior Li- and Na-ion storage properties compared with those of the dense microspheres. After 250 charge/discharge cycles at a current density of 1.5 A g(-1) , the discharge capacities of the MoS2 -AC microspheres with dense and macroporous structures for Li-ion storage were 694 and 896 mAh g(-1) , respectively. In the case of Na-ion storage, discharge capacities of 336 and 425 mAh g(-1) were achieved for the dense and macroporous microspheres, respectively, after 100 cycles at 0.3 A g(-1) . PMID:26098539

  14. Monolayer MoS2 heterojunction solar cells

    KAUST Repository

    Tsai, Menglin

    2014-08-26

    We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS 2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS 2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices. © 2014 American Chemical Society.

  15. Photovoltaic heterojunctions of fullerenes with MoS2 and WS 2 monolayers

    KAUST Repository

    Gan, Liyong

    2014-04-17

    First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS2 or WS2 monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C60/MoS 2 and C60/WS2 systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron-hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS2 and preserves it only in one spin channel on WS2, which is unsuitable for excitonic solar cells. Our results suggest that the C60/WS 2 system is highly promising for excitonic solar cells. © 2014 American Chemical Society.

  16. Extraordinary Bending Effects in MoS2 , Phosphorene, and Graphene Nanoribbons

    Science.gov (United States)

    Yu, Liping; Ruzsinszky, Adrienn; Perdew, John

    The two-dimensional (2D) materials show great potential for flexible electronics and energy applications. They have remarkable mechanical, electronic, thermal and optical properties, which are often coupled to each other. In this talk, we shall present our first principles study on the bending effects in the electronic structure of MoS2, phosphorene, and graphene nanoribbons. We predict that mechanical bending, as a unique attribute of thin 2D materials, can be used to control conductivity and Fermi-level shift. We find that bending can control the charge localization of top valence bands in both MoS2 and phosphorene nanoribbons. The donor-like in-gap edge-states of armchair MoS2 ribbon and their associated Fermi-level pinning can be removed by bending. A bending-controllable new in-gap state and accompanying direct-indirect gap transition are predicted in armchair phosphorene nanoribbon. We demonstrate that such emergent bending effects are realizable in experiment and can be attributed to the highly non-uniform and enormously large local in-plane strains induced by bending. The bending stiffness as wells as the effective thickness of 2D materials are also derived from first principles. The work was supported as part of the Center for the Computational Design of Functional Layered Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

  17. Ab-initio study of dynamical properties of two dimensional MoS2 under strain

    Directory of Open Access Journals (Sweden)

    Himadri Soni

    2015-10-01

    Full Text Available In this paper, we report the biaxial strain induced modifications in the phonon dispersion curves of monolayer MoS2 using first principles calculations in the framework of density functional perturbation theory. We have used the ultrasoft psedopotentials and the exchange correlation energies have been approximated by the local density approximation. There are significant changes in the phonon dispersion curves under strain. A systematic decrease in the optical phonon modes is observed with strain percentage. The longitudinal and transverse acoustic phonon modes of monolayer MoS2 show linear dependency for both without and with strain cases. However, the out of plane acoustic mode (ZA which behaves quadratically with wave vector k- turns linear under strain. We have also linked ripple in single layer (SL MoS2 by ZA mode with strain using shell elasticity theory. The strain induced softening of linear behaviour of ZA mode with strain indicates the absence of rippling under strain. At a very high strain there is a possibility of structural phase transition as the ZA mode at zone centre turns imaginary above 15% strain. Our results indicate a close relationship between the morphology and properties enabling the device tailoring and bandgap engineering in SL-MoS2 by manipulating the strain.

  18. Direct synthesis of large-scale hierarchical MoS2 films nanostructured with orthogonally oriented vertically and horizontally aligned layers

    Science.gov (United States)

    Zhang, Xiaoyan; Zhang, Saifeng; Chen, Bohua; Wang, Hao; Wu, Kan; Chen, Yang; Fan, Jintai; Qi, Shen; Cui, Xiaoli; Zhang, Long; Wang, Jun

    2015-12-01

    Hierarchical MoS2 thin films nanostructured with orthogonally oriented vertically and horizontally aligned layers were designed and excellent passive Q-switching behavior in a fiber laser was demonstrated. A special solvothermal system containing a small amount of water was applied to synthesize such hierarchical MoS2 nanofilms, in which the reaction rate is carefully controlled by the diffusion rate of the sulfur precursor. Wafer-scale MoS2 thin films with hierarchical structures are formed on various substrates. Moreover, the hierarchical MoS2 thin films consisting of both vertical and horizontal layers can be tuned to possess only horizontally aligned layers by controlling the solvothermal time. To show the potential application proof-of-concept, the nonlinear optical performance of the hierarchical MoS2 was investigated. Superior passive Q-switching behavior in a fiber laser with a minimum pulse width of 2.2 μs was observed.Hierarchical MoS2 thin films nanostructured with orthogonally oriented vertically and horizontally aligned layers were designed and excellent passive Q-switching behavior in a fiber laser was demonstrated. A special solvothermal system containing a small amount of water was applied to synthesize such hierarchical MoS2 nanofilms, in which the reaction rate is carefully controlled by the diffusion rate of the sulfur precursor. Wafer-scale MoS2 thin films with hierarchical structures are formed on various substrates. Moreover, the hierarchical MoS2 thin films consisting of both vertical and horizontal layers can be tuned to possess only horizontally aligned layers by controlling the solvothermal time. To show the potential application proof-of-concept, the nonlinear optical performance of the hierarchical MoS2 was investigated. Superior passive Q-switching behavior in a fiber laser with a minimum pulse width of 2.2 μs was observed. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05938k

  19. Preparation of Nanocrystalline MoS2 Hollow Spheres

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Nanocrystalline MoS2 with hollow spherical morphology has been prepared by the hydrothermal method. The products are characterized by means of X-ray powder diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The experimental results give the evidence that the sample is consists of hollow spheres 400~600 nm in diameter, and there is much whisker on the surface of MoS2 hollow sphere.

  20. Translational regulation of MOS messenger RNA in pig oocytes.

    Science.gov (United States)

    Dai, Yanfeng; Newman, Barbara; Moor, Robert

    2005-11-01

    The temporal and spatial translation control of stored mRNA in oocytes is regulated by elements in their 3'-untranslated region (3'-UTR). The MOS 3'-UTR in pig oocytes is both heterogeneous (180, 480, or 530 nucleotides), and it contains multiple U-rich elements and extensive A-rich sequences (CA13CA5CA5CA6). We have examined the role of these potential regulatory elements by fusing wild-type or mutant MOS 3'-UTRs to luciferase mRNA and then injecting these chimeric transcripts into oocytes. We draw six main conclusions. First, the length of the MOS 3'-UTR tightly controls the level of translation of luciferase during oocyte maturation. Second, two U-rich (U5A) elements and the hexanucleotide signal (AAUAAA) are required for translation. Third, mutations, duplications, or relocations of the A-rich sequence reduce or block translation. Fourth, the relative importance of the A-rich and U-rich elements in controlling the level of translation differs. Fifth, none of our MOS 3'-UTR manipulations relieved translational repression before germinal vesicle breakdown. Sixth, all the MOS mRNA variants underwent polyadenylation during maturation. Whereas mutations to the hexanucleotide signal block both polyadenylation and translation, mutations to either the A-rich sequence or the U-rich elements block translation without fully blocking polyadenylation. We conclude that MOS mRNA translation in pig oocytes is subject to a more extensive series of controls than that in lower vertebrates.

  1. Spin polarized transport in MoS2

    Science.gov (United States)

    Dankert, André; Pashaei, Parham; Mutta, Venkata Kamalakar; Dash, Saroj Prasad; Spintronic SPD Team

    The two-dimensional (2D) semiconductor MoS2 possesses a high potential for spintronic devices due to a rich spin-valley physics and large spin-orbit coupling. While there have been significant advances in studying the spin and valley dynamics in MoS2 using optical spectroscopy techniques, electronic spin transport in semiconducting MoS2 or its heterostructures have not yet been demonstrated. Here we report the electronic and spin transport properties in MoS2 employing ferromagnetic electrodes in a vertical device geometry. Such vertical devices with MoS2 channel length defined by the thickness of the 2D layer allow to investigate the spin injection, transport and detection. We observe a magnetoresistance effect over a large temperature range up to 300 K and investigate the temperature and bias dependence behavior. Using magnetotransport data and calculations we extract spin parameters in the MoS2 spin valve devices. These findings can open new avenues for exploring spin functionalities in 2D semiconductor heterostructures for spin logic applications.

  2. The Effect of VMoS3 Point Defect on the Elastic Properties of Monolayer MoS2 with REBO Potentials.

    Science.gov (United States)

    Li, Minglin; Wan, Yaling; Tu, Liping; Yang, Yingchao; Lou, Jun

    2016-12-01

    Structural defects in monolayer molybdenum disulfide (MoS2) have significant influence on the electric, optical, thermal, chemical, and mechanical properties of the material. Among all the types of structural defects of the chemical vapor phase-grown monolayer MoS2, the VMoS3 point defect (a vacancy complex of Mo and three nearby S atoms) is another type of defect preferentially generated by the extended electron irradiation. Here, using the classical molecular dynamics simulation with reactive empirical bond-order (REBO) potential, we first investigate the effect of VMoS3 point defects on the elastic properties of monolayer MoS2 sheets. Under the constrained uniaxial tensile test, the elastic properties of monolayer MoS2 sheets containing VMoS3 vacancies with defect fraction varying from 0.01 to 0.1 are obtained based on the plane anisotropic constitutive relations of the material. It is found that the increase of VMoS3 vacancy concentration leads to the noticeable decrease in the elastic modulus but has a slight effect on Poisson's ratio. The maximum decrease of the elastic modulus is up to 25 %. Increasing the ambient temperature from 10 K to 500 K has trivial influences on the elastic modulus and Poisson's ratio for the monolayer MoS2 without defect and with 5 % VMoS3 vacancies. However, an anomalous parabolic relationship between the elastic modulus and the temperature is found in the monolayer MoS2 containing 0.1 % VMoS3 vacancy, bringing a crucial and fundamental issue to the application of monolayer MoS2 with defects.

  3. The Effect of VMoS3 Point Defect on the Elastic Properties of Monolayer MoS2 with REBO Potentials.

    Science.gov (United States)

    Li, Minglin; Wan, Yaling; Tu, Liping; Yang, Yingchao; Lou, Jun

    2016-12-01

    Structural defects in monolayer molybdenum disulfide (MoS2) have significant influence on the electric, optical, thermal, chemical, and mechanical properties of the material. Among all the types of structural defects of the chemical vapor phase-grown monolayer MoS2, the VMoS3 point defect (a vacancy complex of Mo and three nearby S atoms) is another type of defect preferentially generated by the extended electron irradiation. Here, using the classical molecular dynamics simulation with reactive empirical bond-order (REBO) potential, we first investigate the effect of VMoS3 point defects on the elastic properties of monolayer MoS2 sheets. Under the constrained uniaxial tensile test, the elastic properties of monolayer MoS2 sheets containing VMoS3 vacancies with defect fraction varying from 0.01 to 0.1 are obtained based on the plane anisotropic constitutive relations of the material. It is found that the increase of VMoS3 vacancy concentration leads to the noticeable decrease in the elastic modulus but has a slight effect on Poisson's ratio. The maximum decrease of the elastic modulus is up to 25 %. Increasing the ambient temperature from 10 K to 500 K has trivial influences on the elastic modulus and Poisson's ratio for the monolayer MoS2 without defect and with 5 % VMoS3 vacancies. However, an anomalous parabolic relationship between the elastic modulus and the temperature is found in the monolayer MoS2 containing 0.1 % VMoS3 vacancy, bringing a crucial and fundamental issue to the application of monolayer MoS2 with defects. PMID:27000023

  4. Stability and electronic properties of SiC nanowire adsorbed on MoS2 monolayer

    Science.gov (United States)

    Sharma, Munish; Pooja, Kumar, Ashok; Ahluwalia, P. K.

    2015-06-01

    Structural stability and electronic properties of silicon carbide (SiC) nano-wire on MoS2 monolayer are investigated within the framework of density functional theory (DFT). The preferred binding site for the SiC nano-wire is predicted to be hollow site of monolayer. In the electronic band structure the states in valence band near Fermi level are mainly due to nano-wire leading to reduction of band gap relative to monolayer. These results provide a platform for their applications in optoelectronic devices.

  5. Characterization of the system MoS2 + C, HAADF vs Tem conventional

    International Nuclear Information System (INIS)

    A study is presented about the synthesis and characterization of unidimensional nano systems composed of MoS2 and C with potential use as solid lubricant. The synthesis process was developed for the mold method, via thermal decomposition, which uses a film of nano porous aluminium oxide. Such systems were characterized by two analysis methods that involve Transmission Electron Microscopy, HRTEM (Conventional TEM) and HAADF (Z Contrast). The results obtained in the structural and morphological characterization were supplemented to determine the structure type obtained in the unidimensional systems. (Author)

  6. High photocatalytic performance of a type-II α-MoO3@MoS2 heterojunction: from theory to experiment.

    Science.gov (United States)

    Li, Honglin; Yu, Ke; Tang, Zheng; Fu, Hao; Zhu, Ziqiang

    2016-05-18

    For the first time, a systematic study using density functional theory (DFT) has been employed to survey the synergistic effect of α-MoO3@MoS2 with the aim of gaining insights into the role of this heterogeneous structure in a relevant photocatalytic reaction. The geometry, electronic structures and the band edge positions of the α-MoO3@MoS2 composite were computed to explore the characteristics of the heterojunction. This revealed that the established heterogeneous structure could facilitate the separation of the photoinduced carriers into two parts around the interface. The photoinduced electron carriers injected into the conduction band minimum (CBM) of α-MoO3 from the CBM of MoS2 while the hole carriers transferred from the valence band maximum (VBM) of α-MoO3 to the VBM of MoS2. This separation process could markedly restrain the photogenerated electron-hole pair recombination and was further verified by photocurrent and photoluminescence (PL) surveys. Based on the results obtained from computation, we then synthesized the α-MoO3@MoS2 hybrid rod@sphere structure via a facile two-step hydrothermal method. A reasonable formation mechanism of this rod@sphere structured composite was proposed. The enhanced photocatalytic performance originated from the synergistic effect between α-MoO3 and MoS2. On the one hand, the unique structural characteristics of the composite possessed massive MoS2 spheres closely attached to α-MoO3 rods. On the other hand, the staggered type-II band formation also contributed to the effective separation of photoinduced carriers and thus the corresponding photocatalytic activity was far superior to that of the pristine α-MoO3/MoS2 structures. In brief, the general analyses could fully explain the inner mechanism for the improved photocatalytic activity of the composite structure and provide a reference for the research of composite structures in the future.

  7. Monolayer MoS2/GaAs heterostructure self-driven photodetector with extremely high detectivity

    CERN Document Server

    Xu, Zhijuan; Li, Xiaoqiang; Zhang, Shengjiao; Wu, Zhiqian; Xu, Wenli; Lu, Yanghua; Xu, Sen

    2015-01-01

    Two dimensional material/semiconductor heterostructures offer alternative platforms for optoelectronic devices other than conventional Schottky and p-n junction devices. Herein, we use MoS2/GaAs heterojunction as a self-driven photodetector with wide response band width from ultraviolet to visible light, which exhibits high sensitivity to the incident light of 650 nm with responsivity as 446 mA/W and detectivity as 5.9E13 Jones (Jones = cm Hz^1/2 W^-1), respectively. Employing interface design by inserting h-BN and photo-induced doping by covering Si quantum dots on the device, the responsivity is increased to 582 mA/W for incident light of 650 nm. Distinctly, attributing to the low dark current of the MoS2/h-BN/GaAs sandwich structure based on the self-driven operation condition, the detectivity shows extremely high value of 3.2E14 Jones for incident light of 650 nm, which is higher than all the reported values of the MoS2 based photodetectors. Further investigations reveal that the MoS2/GaAs based photodete...

  8. Lithography-free plasma-induced patterned growth of MoS2 and its heterojunction with graphene.

    Science.gov (United States)

    Chen, Xiang; Park, Yong Ju; Das, Tanmoy; Jang, Houk; Lee, Jae-Bok; Ahn, Jong-Hyun

    2016-08-18

    Application-oriented patterned growth of transition metal dichalcogenides (TMDCs) and their heterojunctions is of critical importance for sophisticated, customized two-dimensional (2D) electronic and optoelectronic devices; however, it is still difficult to fabricate these patterns in a simple, clean, and high controllability manner without using optical lithography. Here, we report the direct synthesis of patterned MoS2 and graphene-MoS2 heterojunctions via selective plasma treatment of a SiO2/Si substrate and chemical vapor deposition of MoS2. This method has multiple merits, such as simple steps, a short operating time, easily isolated MoS2 layers with clean surfaces and controllable locations, shapes, sizes and thicknesses, which enable their integration into the device structure without using a photoresist. In addition, we demonstrate the direct growth of patterned graphene-MoS2 heterojunctions for the fabrication of transistor. This study reveals a novel method to fabricate and use patterned MoS2 and graphene-MoS2 heterojunctions, which could be generalized to the rational design of other 2D materials, heterojunctions and devices in the future.

  9. Back-gated Nb-doped MoS2 junctionless field-effect-transistors

    Directory of Open Access Journals (Sweden)

    Gioele Mirabelli

    2016-02-01

    Full Text Available Electrical measurements were carried out to measure the performance and evaluate the characteristics of MoS2 flakes doped with Niobium (Nb. The flakes were obtained by mechanical exfoliation and transferred onto 85 nm thick SiO2 oxide and a highly doped Si handle wafer. Ti/Au (5/45 nm deposited on top of the flake allowed the realization of a back-gate structure, which was analyzed structurally through Scanning Electron Microscopy (SEM and Transmission Electron Microscopy (TEM. To best of our knowledge this is the first cross-sectional TEM study of exfoliated Nb-doped MoS2 flakes. In fact to date TEM of transition-metal-dichalcogenide flakes is extremely rare in the literature, considering the recent body of work. The devices were then electrically characterized by temperature dependent Ids versus Vds and Ids versus Vbg curves. The temperature dependency of the device shows a semiconductor behavior and, the doping effect by Nb atoms introduces acceptors in the structure, with a p-type concentration 4.3 × 1019 cm−3 measured by Hall effect. The p-type doping is confirmed by all the electrical measurements, making the structure a junctionless transistor. In addition, other parameters regarding the contact resistance between the top metal and MoS2 are extracted thanks to a simple Transfer Length Method (TLM structure, showing a promising contact resistivity of 1.05 × 10−7 Ω/cm2 and a sheet resistance of 2.36 × 102 Ω/sq.

  10. MoS2 nanoribbons as promising thermoelectric materials

    Science.gov (United States)

    Fan, D. D.; Liu, H. J.; Cheng, L.; Jiang, P. H.; Shi, J.; Tang, X. F.

    2014-09-01

    The thermoelectric properties of MoS2 armchair nanoribbons with different width are studied by using first-principles calculations and Boltzmann transport theory, where the relaxation time is predicted from deformation potential theory. Due to the dangling bonds at the armchair edge, there is obvious structure reconstruction of the nanoribbons which plays an important role in governing the electronic and transport properties. The investigated armchair nanoribbons are found to be semiconducting with indirect gaps, which exhibit interesting width-dependent oscillation behavior. The smaller gap of nanoribbon with width N = 4 (Here, N represents the number of dimer lines or zigzag chains across the ribbon width) leads to a much larger electrical conductivity at 300 K, which outweighs the relatively larger electronic thermal conductivity when compared with those of N = 5, 6. As a result, the ZT values can be optimized to 3.4 (p-type) and 2.5 (n-type) at room temperature, which significantly exceed the performance of most laboratory results reported in the literature.

  11. Comparative analysis of nanoscale MOS device architectures for RF applications

    Science.gov (United States)

    Kranti, Abhinav; Armstrong, G. Alastair

    2007-05-01

    The suitability of nanoscale non-planar FinFETs and classical planar single and double gate SOI MOSFETs for rf applications is examined via extensive 3D device simulations and detailed interpretation. It is shown that although nanoscale FinFETs achieve higher values of intrinsic dc gain (nearly 20 dB higher than planar SG devices), they also present higher gate capacitance that severely undermines their rf performance. We also show that at large values of drain currents, well-designed conventional planar single and double gate SOI MOSFETs attain higher values of cut-off frequency compared to FinFETs, whereas at lower drain currents, a well-aligned planar double gate SOI MOSFET is the optimal structure. The reason for higher parasitic capacitance in FinFETs as compared to planar MOSFETs is examined in detail. An assessment of the impact of back gate misalignment on the rf performance of a 25 nm gate length planar double gate MOSFET indicates that a misalignment of 12 nm towards the source end is acceptable to give superior performance to a FinFET. The importance of source/drain extension region engineering in nanoscale FinFETs for ultra-low voltage analogue applications is also investigated. RF figures of merit for planar and vertical MOS devices are also compared based on layout-area calculations. The paper provides valuable design insights for optimizing device parameters for nanoscale planar and vertical MOSFETs.

  12. Electric field effects on armchair MoS2 nanoribbons.

    Science.gov (United States)

    Dolui, Kapildeb; Pemmaraju, Chaitanya Das; Sanvito, Stefano

    2012-06-26

    Ab initio density functional theory calculations are performed to investigate the electronic structure of MoS(2) armchair nanoribbons in the presence of an external static electric field. Such nanoribbons, which are nonmagnetic and semiconducting, exhibit a set of weakly interacting edge states whose energy position determines the band gap of the system. We show that, by applying an external transverse electric field, E(ext), the nanoribbon band gap can be significantly reduced, leading to a metal-insulator transition beyond a certain critical value. Moreover, the presence of a sufficiently high density of states at the Fermi level in the vicinity of the metal-insulator transition leads to the onset of Stoner ferromagnetism that can be modulated, and even extinguished, by E(ext). In the case of bilayer nanoribbons we further show that the band gap can be changed from indirect to direct by applying a transverse field, an effect that might be of significance for opto-electronics applications. PMID:22546015

  13. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence.

    Science.gov (United States)

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen

    2015-11-01

    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis.

  14. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence.

    Science.gov (United States)

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen

    2015-11-01

    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis. PMID:26439853

  15. Identification of protein tyrosine phosphatase 1B and casein as substrates for 124-v-Mos

    Directory of Open Access Journals (Sweden)

    Stabel Silvia

    2002-04-01

    Full Text Available Abstract Background The mos proto-oncogene encodes a cytoplasmic serine/threonine-specific protein kinase with crucial function during meiotic cell division in vertebrates. Based on oncogenic amino acid substitutions the viral derivative, 124-v-Mos, displays constitutive protein kinase activity and functions independent of unknown upstream effectors of mos protein kinase. We have utilized this property of 124-v-Mos and screened for novel mos substrates in immunocomplex kinase assays in vitro. Results We generated recombinant 124-v-Mos using the baculovirus expression system in Spodoptera frugiperda cells and demonstrated constitutive kinase activity by the ability of 124-v-Mos to auto-phosphorylate and to phosphorylate vimentin, a known substrate of c-Mos. Using this approach we analyzed a panel of acidic and basic substrates in immunocomplex protein kinase assays and identified novel in vitro substrates for 124-v-Mos, the protein tyrosine phosphatase 1B (PTP1B, alpha-casein and beta-casein. We controlled mos-specific phosphorylation of PTP1B and casein in comparative assays using a synthetic kinase-inactive 124-v-Mos mutant and further, tryptic digests of mos-phosphorylated beta-casein identified a phosphopeptide specifically targeted by wild-type 124-v-Mos. Two-dimensional phosphoamino acid analyses showed that 124-v-mos targets serine and threonine residues for phosphorylation in casein at a 1:1 ratio but auto-phosphorylation occurs predominantly on serine residues. Conclusion The mos substrates identified in this study represent a basis to approach the identification of the mos-consensus phosphorylation motif, important for the development of specific inhibitors of the Mos protein kinase.

  16. Protection of MOS capacitors during anodic bonding

    Science.gov (United States)

    Schjølberg-Henriksen, K.; Plaza, J. A.; Rafí, J. M.; Esteve, J.; Campabadal, F.; Santander, J.; Jensen, G. U.; Hanneborg, A.

    2002-07-01

    We have investigated the electrical damage by anodic bonding on CMOS-quality gate oxide and methods to prevent this damage. n-type and p-type MOS capacitors were characterized by quasi-static and high-frequency CV-curves before and after anodic bonding. Capacitors that were bonded to a Pyrex wafer with 10 μm deep cavities enclosing the capacitors exhibited increased leakage current and interface trap density after bonding. Two different methods were successful in protecting the capacitors from such damage. Our first approach was to increase the cavity depth from 10 μm to 50 μm, thus reducing the electric field across the gate oxide during bonding from approximately 2 × 105 V cm-1 to 4 × 104 V cm-1. The second protection method was to coat the inside of a 10 μm deep Pyrex glass cavity with aluminium, forming a Faraday cage that removed the electric field across the cavity during anodic bonding. Both methods resulted in capacitors with decreased interface trap density and unchanged leakage current after bonding. No change in effective oxide charge or mobile ion contamination was observed on any of the capacitors in the study.

  17. Antibacterial activity of two-dimensional MoS2 sheets

    Science.gov (United States)

    Yang, Xi; Li, Jie; Liang, Tao; Ma, Chunyan; Zhang, Yingying; Chen, Hongzheng; Hanagata, Nobutaka; Su, Huanxing; Xu, Mingsheng

    2014-08-01

    Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders used for the synthesis of ce-MoS2 sheets possibly due to the 2D planar structure (high specific surface area) and higher conductivity of the ce-MoS2. We investigated the antibacterial mechanisms of the ce-MoS2 sheets and proposed their antibacterial pathways. We found that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from a previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behaviour of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane and oxidation stress. The antibacterial pathways include MoS2-bacteria contact induced membrane stress, superoxide anion (O2&z.rad;-) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. Our study thus indicates that the tailoring of the dimension of nanomaterials and their electronic properties would manipulate antibacterial activity.Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders

  18. Phonon thermal conductivity of monolayer MoS2

    Science.gov (United States)

    Wang, Xiaonan; Tabarraei, Alireza

    2016-05-01

    We use nonequilibrium molecular dynamics modeling using Stillinger-Weber interatomic potential to investigate the thermal properties of monolayer molybdenum disulfide (MoS2) nanoribbons. We study the impact of factors such as length, edge chirality, monovacancies, and uniaxial stretching on the thermal conductivity of MoS2 nanoribbons. Our results show that longer ribbons have a higher thermal conductivity, and the thermal conductivity of infinitely long zigzag and armchair MoS2 nanoribbons is, respectively, 54 W/mK and 33 W/mK. This is significantly lower than the thermal conductivity of some other graphene-like two-dimensional materials such as graphene and boron nitride. While the presence of molybdenum or sulfur vacancies reduces the thermal conductivity of ribbons, molybdenum vacancies have a more deteriorating effect on thermal conductivities. We also have studied the impact of uniaxial stretching on the thermal conductivity of MoS2 nanoribbons. The results show that in contrast to three dimensional materials, thermal conductivity of MoS2 is fairly insensitive to stretching. We have used the phonon dispersion curves and group velocities to investigate the mechanism of this unexpected behavior. Our results show that tensile strain does not alter the phonon dispersion curves and hence the thermal conductivity does not change.

  19. Microinjection of antisense c-mos oligonucleotides prevents meiosis II in the maturing mouse egg.

    OpenAIRE

    O'Keefe, S J; Wolfes, H; Kiessling, A A; Cooper, G M

    1989-01-01

    Injection of antisense oligonucleotides was used to investigate the function of c-mos in murine oocytes. Oocytes injected with antisense c-mos oligonucleotides completed the first meiotic division but failed to initiate meiosis II. Instead, loss of c-mos function led to chromosome decondensation, reformation of a nucleus after meiosis I, and cleavage to two cells. Therefore, c-mos is required for meiosis II during murine oocyte maturation.

  20. Fabrication of TiO2/MoS2@zeolite photocatalyst and its photocatalytic activity for degradation of methyl orange under visible light

    Science.gov (United States)

    Zhang, Weiping; Xiao, Xinyan; Zheng, Lili; Wan, Caixia

    2015-12-01

    TiO2/MoS2@zeolite composite photocatalysts with visible-light activity were fabricated via a simple ultrasonic-hydrothermal synthesis method, using TiCl4 as Ti source, MoS2 as a direct sensitizer, glycerol water solution with certain dispersion agent as hydrolytic agent, and zeolite as carrier. The structure, morphology, composition, optical properties, and specific surface area of the as-prepared photocatalysts were characterized by using XRD, FTIR, SEM-EDS, TEM, XPS, UV-vis, PL and BET analyzer, respectively. And the photocatalytic degradation of methyl orange (MO) in aqueous suspension has been employed to evaluate the photocatalytic activity and degradation kinetics of as-prepared photocatalysts with xenon lamp as irradiation source. The results indicate that: (1) TiO2/MoS2@zeolite composite photocatalysts exhibit enhanced photocatalytic activities for methyl orange (MO) degradation compared to Degussa P25; (2) photocatalytic degradation of MO obeys Langmuir-Hinshelwood kinetic model (pseudo-first order reaction), and its degradation rate constant (kapp) (2.304 h-1) is higher than that of Degussa P25 (0.768 h-1); (3) the heterostructure consisted of zeolite, MoS2 and TiO2 nanostructure could provide synergistic effect for degradation of MO due to the efficient electron transfer process and better absorption property of TiO2/MoS2@zeolite composite photocatalyst.

  1. Tunable electronic and magnetic properties of a MoS2 monolayer with vacancies under elastic planar strain: Ab initio study

    Science.gov (United States)

    Salami, N.; Shokri, A. A.; Elahi, S. M.

    2016-03-01

    Electronic and magnetic properties of a molybdenum disulfide (MoS2) monolayer with some intrinsic and extrinsic vacancies are investigated using ab initio method in the presence of planar strain distributions. The calculations are carried out within the density functional theory (DFT) as implemented in SIESTA package. By using fully relaxed structures and applying a full spin-polarized description to the system, we concentrate on created magnetic moment due to the vacancies under different planar strains. The results show that the extrinsic MoS6 vacancy induces a net magnetic moment of 6.00 μB per supercell. Also, it is found that the pure MoS2 monolayer for the most cases does not show any magnetic properties under the planar strain. While the net magnetic moment of MoS2 monolayer with the vacancies enhances as the planar tensile strain is applied. The tunable magnetic moment of MoS2 monolayer may be utilized for the development of spintronic and flexible electronic nano-devices.

  2. MoS2/CdS Nanosheets-on-Nanorod Heterostructure for Highly Efficient Photocatalytic H2 Generation under Visible Light Irradiation.

    Science.gov (United States)

    Yin, Xing-Liang; Li, Lei-Lei; Jiang, Wen-Jie; Zhang, Yun; Zhang, Xiang; Wan, Li-Jun; Hu, Jin-Song

    2016-06-22

    Semiconductor-based photocatalytic H2 generation as a direct approach of converting solar energy to fuel is attractive for tackling the global energy and environmental issues but still suffers from low efficiency. Here, we report a MoS2/CdS nanohybrid as a noble-metal-free efficient visible-light driven photocatalyst, which has the unique nanosheets-on-nanorod heterostructure with partially crystalline MoS2 nanosheets intimately but discretely growing on single-crystalline CdS nanorod. This heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction, shorter radial transfer path, and fewer defects in single-crystalline nanorod, thus effectively reducing the charge recombination, but also provides plenty of active sites for hydrogen evolution reaction due to partially crystalline structure of MoS2 as well as enough room for hole extraction. As a result, the MoS2/CdS nanosheets-on-nanorod exhibits a state-of-the-art H2 evolution rate of 49.80 mmol g(-1) h(-1) and an apparent quantum yield of 41.37% at 420 nm, which is the advanced performance among all MoS2/CdS composites and CdS/noble metal photocatalysts. These findings will open opportunities for developing low-cost efficient photocatalysts for water splitting. PMID:27237623

  3. Near-infrared light triggered superior photocatalytic activity from MoS2-NaYF4:Yb(3+)/Er(3+) nanocomposites.

    Science.gov (United States)

    Chatti, Manjunath; Adusumalli, Venkata N K B; Ganguli, Sagar; Mahalingam, Venkataramanan

    2016-08-01

    A near infrared (NIR) responsive photocatalyst, composed of a narrow band gap semiconductor (i.e. MoS2) and an optical material possessing upconverting ability (i.e. NaYF4:Yb(3+)/Er(3+)) has been successfully prepared via a simple hydrothermal method. The latter has the ability to convert NIR light into visible light while the MoS2 uses the light to degrade organic pollutants. Upon near infrared (NIR) excitation of the MoS2-NaYF4:Yb(3+)/Er(3+) nanocomposites, the energy of the strong green and the red emissions along with the weak violet emissions from the NaYF4:Yb(3+)/Er(3+) nanocrystals (NCs) is transferred to MoS2. This results in enhanced NIR light triggered photocatalytic performance, as verified by studying the degradation of Rhodamine B (RhB) dye under 980 nm laser excitation. The strong photocatalytic activity of MoS2-NaYF4:Yb(3+)/Er(3+) composites is attributed to the layered nature of the photocatalyst which leads to the efficient separation of photogenerated carriers (electron-hole pairs) and excellent upconversion properties of NaYF4:Yb(3+)/Er(3+) NCs. The study also shows the importance of the composite formation, as the physical mixture leads to only very low photocatalytic activity. Our results can be helpful in the structural design and development of high-performance photocatalysts. PMID:27424735

  4. A novel technique to measure interface trap density in a GaAs MOS capacitor using time-varying magnetic fields

    Science.gov (United States)

    Choudhury, Aditya N. Roy; Venkataraman, V.

    2016-05-01

    Interface trap density (Dit) in a GaAs metal-oxide-semiconductor (MOS) capacitor can be measured electrically by measuring its impedance, i.e. by exciting it with a small signal voltage source and measuring the resulting current through the circuit. We propose a new method of measuring Dit where the MOS capacitor is subjected to a (time-varying) magnetic field instead, which produces an effect equivalent to a (time-varying) voltage drop across the sample. This happens because the electron chemical potential of GaAs changes with a change in an externally applied magnetic field (unlike that of the gate metal); this is not the voltage induced by Faraday's law of electromagnetic induction. So, by measuring the current through the MOS, Dit can be found similarly. Energy band diagrams and equivalent circuits of a MOS capacitor are drawn in the presence of a magnetic field, and analyzed. The way in which a magnetic field affects a MOS structure is shown to be fundamentally different compared to an electrical voltage source.

  5. Magnetic edge states in MoS2 characterized using density-functional theory

    OpenAIRE

    Vojvodic, Aleksandra; Hinnemann, B; Nørskov, Jens Kehlet

    2009-01-01

    It is known that the edges of a two-dimensional slab of insulating MoS2 exhibit one-dimensional metallic edge states, the so-called "brim states." Here, we find from density-functional theory calculations that several edge structures, which are relevant for the hydrodesulfurization process, are magnetic. The magnetism is an edge phenomenon associated with certain metallic edge states. Interestingly, we find that among the two low-index edges, only the S edge displays magnetism under hydrodesu...

  6. Magnetic edge states in MoS2 characterized using density-functional theory

    DEFF Research Database (Denmark)

    Vojvodic, Aleksandra; Hinnemann, B.; Nørskov, Jens Kehlet

    2009-01-01

    It is known that the edges of a two-dimensional slab of insulating MoS2 exhibit one-dimensional metallic edge states, the so-called "brim states." Here, we find from density-functional theory calculations that several edge structures, which are relevant for the hydrodesulfurization process......, are magnetic. The magnetism is an edge phenomenon associated with certain metallic edge states. Interestingly, we find that among the two low-index edges, only the S edge displays magnetism under hydrodesulfurization conditions. In addition, the implications of this on the catalytic activity are investigated...

  7. MoS2 nanotube field effect transistors

    Directory of Open Access Journals (Sweden)

    M. Strojnik

    2014-09-01

    Full Text Available We report on electric field effects on electron transport in multi-walled MoS2 nanotubes (NTs, fabricated using a two-step synthesis method from Mo6SxI9-x nanowire bundle precursors. Transport properties were measured on 20 single nanotube field effect transistor (FET devices, and compared with MoS2 layered crystal devices prepared using identical fabrication techniques. The NTs exhibited mobilities of up to 0.014 cm2V−1s−1 and an on/off ratio of up to 60. As such they are comparable with previously reported WS2 nanotube FETs, but materials defects and imperfections apparently limit their performance compared with multilayer MoS2 FETs with similar number of layers.

  8. Plasmons on the edge of MoS2 nanostructures

    Science.gov (United States)

    Andersen, Kirsten; Jacobsen, Karsten W.; Thygesen, Kristian S.

    2014-10-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated spatially resolved electron energy loss spectrum owing to the different plasmonic properties of the two edges. The edge plasmons could potentially be utilized for tuning the photocatalytic activity of MoS2 nanoparticles.

  9. Synthesis of Large Scale MoS2 -Graphene Heterostructures

    Science.gov (United States)

    McCreary, Kathleen; Hanbicki, Aubrey; Friedman, Adam; Robinson, Jeremy; Jonker, Berend

    2014-03-01

    A rapidly progressing field involves the stacking of multiple two dimensional materials to form heterostructures. These heterosctructures have exhibited unique and interesting properties. For the most part, heterostructure devices are produced via mechanical exfoliation followed by careful aligning and stacking of the various components, limiting dimensions to micron-scale devices. Chemical vapor deposition (CVD) has proven to be a useful tool in the production of graphene and has very recently been investigated as a means for the growth of other 2D materials such as MoS2, hexagonal boron nitride and WS2. Using a two-step CVD process we are able to synthesize MoS2 on CVD grown graphene. AFM and Raman microscopy of the MoS2-graphene heterostructure show a uniform and continuous film on the cm scale.

  10. Shallow donor in natural MoS2

    International Nuclear Information System (INIS)

    Using electron paramagnetic resonance and density functional theory calculations, we show that the shallow donor responsible for the n-type conductivity in natural MoS2 is rhenium (Re) with a typical concentration in the low 1017 cm-3 range and the g -values: g parallel = 2.0274 and g perpendicular to = 2.2642. In bulk MoS2, the valley-orbit (VO) splitting and ionization energy of the Re shallow donor are determined to be ∝3 meV and ∝27 meV, respectively. Calculations show that the VO splitting of Re approaches the value in bulk if the number of MoS2 layers is larger than four and increases to 97.9 meV in a monolayer. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Plasmons on the edge of MoS2 nanostructures

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2014-01-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis...... of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated spatially...... resolved electron energy loss spectrum owing to the different plasmonic properties of the two edges. The edge plasmons could potentially be utilized for tuning the photocatalytic activity of MoS2 nanoparticles....

  12. Rendering high charge density of states in ionic liquid-gated MoS 2 transistors

    NARCIS (Netherlands)

    Lee, Y.; Lee, J.; Kim, S.; Park, H.S.

    2014-01-01

    We investigated high charge density of states (DOS) in the bandgap of MoS2 nanosheets with variable temperature measurements on ionic liquid-gated MoS2 transistors. The thermally activated charge transport indicates that the electrical current in the two-dimensional MoS 2 nanosheets under high charg

  13. MoS2/Nitrogen-doped graphene as efficient electrocatalyst for oxygen reduction reaction

    International Nuclear Information System (INIS)

    Graphical abstract: A simple yet effective method was developed for generating an electrocatalyst for oxygen reduction reaction by deposited MoS2 sheets on nitrogen-doped graphene (NG). Due to the synergistic effect of MoS2 and NG, enhancement of electrocatalytic oxygen-reduction was realized. Display Omitted -- Highlights: • MoS2/Nitrogen-doped graphene (NG) composites were obtained by physically mixing method. • MoS2 sheets deposited NG could be used as effective electrocatalyst for ORR. • Enhanced electrocatalytic activity is due to the synergistic effect of MoS2 and NG. • The ORR is a four-electron process based on Koutecky-Levich equation. -- Abstract: A simple yet effective strategy was developed to generate a non-precious oxygen electrode electrocatalyst of MoS2/nitrogen-doped graphene (NG) by physical mixing MoS2 sheets with NG. The micrometer-sized MoS2 sheets were obtained through ultrasonication exfoliation of the bulk MoS2, only showing little oxygen reduction reaction (ORR) activity. MoS2/NG hybrid was obtained by loading MoS2 sheets onto NG through ultrasonication, and the resulting nanocomposites exhibited improved electrocatalytic activity for ORR with dominant 4 electron pathway in alkaline solutions. The exposed active edges as well as the synergistic effect and reduced resistance connection jointly make the MoS2/NG composite a highly competitive ORR catalyst

  14. A method for the measurement of the turn-on condition in MOS transistors

    NARCIS (Netherlands)

    Wallinga, H.

    1971-01-01

    Metal-oxide-silicon (MOS) integrated circuits usually consist of MOS transistors and interconnections. Both, interconnections and MOS transistors are built up of diffused regions in the bulk substrate and conductive strips (metal or polycrystalline silicon) on top of the oxide. For proper electrical

  15. Large-Area Epitaxial Monolayer MoS2.

    Science.gov (United States)

    Dumcenco, Dumitru; Ovchinnikov, Dmitry; Marinov, Kolyo; Lazić, Predrag; Gibertini, Marco; Marzari, Nicola; Lopez Sanchez, Oriol; Kung, Yen-Cheng; Krasnozhon, Daria; Chen, Ming-Wei; Bertolazzi, Simone; Gillet, Philippe; Fontcuberta i Morral, Anna; Radenovic, Aleksandra; Kis, Andras

    2015-04-28

    Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photodetectors. Even though the interaction between the growth substrate and MoS2 is strong enough to induce lattice alignment via van der Waals interaction, we can easily transfer the grown material and fabricate devices. Local potential mapping along channels in field-effect transistors shows that the single-crystal MoS2 grains in our film are well connected, with interfaces that do not degrade the electrical conductivity. This is also confirmed by the relatively large and length-independent mobility in devices with a channel length reaching 80 μm. PMID:25843548

  16. Ultrafast Li-storage of MoS2 nanosheets grown on metal-organic framework-derived microporous nitrogen-doped carbon dodecahedrons

    Science.gov (United States)

    Shao, Jie; Gao, Tian; Qu, Qunting; Shi, Qiang; Zuo, Zhichen; Zheng, Honghe

    2016-08-01

    The nanocomposites of MoS2 nanosheets and microporous nitrogen-doped carbon dodecahedron (MNCD) are prepared through the pyrolysis of metal-organic framework (MOF) and subsequent growth of MoS2. The porous and active surface of MNCDs enables uniform growth of ultrathin MoS2 nanosheets. When the MNCD@MoS2 composite is used as the anode material of Li-ion batteries, a reversible capacity of 915 mAh g-1 can be obtained even at the extremely high current density of 10 A g-1. The ultrafast charge/discharge ability of MNCD@MoS2 can be attributed to its unique core-shell structure with the inner MNCDs serving as the reservoir of Li-ions and transport media of electrons.

  17. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface

    Science.gov (United States)

    Li, Ming-Yang; Shi, Yumeng; Cheng, Chia-Chin; Lu, Li-Syuan; Lin, Yung-Chang; Tang, Hao-Lin; Tsai, Meng-Lin; Chu, Chih-Wei; Wei, Kung-Hwa; He-Hau, Jr.; Chang, Wen-Hao; Suenaga, Kazu; Li, Lain-Jong

    2015-07-01

    Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.

  18. Ferromagnetism in Transitional Metal-Doped MoS2 Monolayer.

    Science.gov (United States)

    Fan, Xiao-Li; An, Yu-Rong; Guo, Wen-Jun

    2016-12-01

    Manipulating electronic and magnetic properties of two-dimensional (2D) transitional-metal dichalcogenides (TMDs) MX2 by doping has raised a lot of attention recently. By performing the first-principles calculations, we have investigated the structural, electronic, and magnetic properties of transitional metal (TM)-doped MoS2 at low and high impurity concentrations. Our calculation result indicates that the five elements of V-, Mn-, Fe-, Co-, and Cu-doped monolayer MoS2 at low impurity concentration all give rise to the good diluted magnetic semiconductors. By studying various configurations with different TM-TM separations, we found that the impurity atoms prefer to stay together in the nearest neighboring (NN) configuration, in which the doped TM atoms are FM coupling except for Fe doping at 12 % concentration. For V, Mn, and Fe doping, the total magnetic moment is smaller than the local magnetic moment of the dopants because the induced spins on the nearby host atoms are antiparallel to that of the doped atoms. In contrast, Co and Cu doping both give the higher total magnetic moment. Especially, Cu doping induces strong ferromagnetism relative to the local spins. However, the atomic structures of Co- and Cu-doped MoS2 deviate from the original prismatic configuration, and the magnetic moments of the doped systems decrease at 12 % impurity concentration although both elements give higher magnetic moments at 8 % impurity concentration. Our calculations indicate that V and Mn are promising candidates for engineering and manipulating the magnetism of the 2D TMDs. PMID:27000022

  19. Nanocrystalline MoS2 through directional growth along the (0 0 2) crystal plane under high pressure

    International Nuclear Information System (INIS)

    Highlights: · MoS2 crystals are uncovered to grow along (0 0 2) plane by XRD techniques. · XRD peaks abnormal broadening is attributed to the layers disorder of MoS2. ·Scherrer equation could not be suitable for layer-disordered nano-MoS2. - Abstract: The directional growth experiments of graphite-like structured MoS2 crystallites have been conducted by utilizing a designed sample cell assembly under high pressure (2.0 and 5.0 GPa) and high temperature (700 deg. C). X-ray diffraction (XRD) and scanning electron microscope (SEM) are used to characterize the samples. The results show that the prepared nanocrystalline MoS2 (n-MoS2) crystals have a hexagonal layered structure. The crystal is uncovered to grow preferentially along the (0 0 2) plane, which indicates that the low-energy surface is the (0 0 2) plane of the crystal. The striking diffuse/broadening nature of Bragg reflection is also analyzed in details, and considered to be associated with the defect structures of the layers stacking and rotational disorder. Measurements of crystallite/grain size are performed by using XRD technique and SEM observation. The measurement results suggest that the traditional peak broadening analysis techniques, including Williamson-Hall formula and Scherrer equation, may not be suitable for the present poorly crystallized n-MoS2 situation. The results may be conducive to have an insight into the growth mechanism and defects analysis of the layer-structured materials.

  20. Online MOS Capacitor Characterization in LabVIEW Environment

    Directory of Open Access Journals (Sweden)

    Chinmay K Maiti

    2009-08-01

    Full Text Available We present an automated evaluation procedure to characterize MOS capacitors involving high-k gate dielectrics. Suitability of LabVIEW environment for online web-based semiconductor device characterization is demonstrated. Developed algorithms have been successfully applied to automate the MOS capacitor measurements for Capacitance-Voltage, Conductance-Voltage and Current-Voltage characteristics. Implementation of the algorithm for use as a remote internet-based characterization tool where the client and server communicate with each other via web services is also shown.

  1. MOS2 has redundant function with its homolog MOS2H and is required for proper splicing of SNC1

    OpenAIRE

    Copeland, Charles; Xu, Shaohua; Qi, Yijun; Li, Xin

    2013-01-01

    Plant immunity is essential for plant survival and resistance (R) proteins serve essential roles in pathogen detection and defense signal initiation. A gain-of-function mutation in SNC1, a TIR-type R gene, results in a characteristic autoimmune phenotype in Arabidopsis. From a forward genetic suppressor screen using snc1, MOS2 (MODIFIER of snc1), which encodes an RNA-binding protein, was identified. When MOS2 function is lost, the autoimmunity caused by snc1 is abolished and basal resistance ...

  2. How dielectric screening in two-dimensional crystals affects the convergence of excited-state calculations: Monolayer MoS2

    DEFF Research Database (Denmark)

    Hüser, Falco; Olsen, Thomas; Thygesen, Kristian Sommer

    2013-01-01

    We present first-principles many-body calculations of the dielectric constant, quasiparticle band structure, and optical absorption spectrum of monolayer MoS2 using a supercell approach. As the separation between the periodically repeated layers is increased, the dielectric function of the layer...

  3. Theoretical analysis of the combined effects of sulfur vacancies and analyte adsorption on the electronic properties of single-layer MoS2

    Science.gov (United States)

    Akdim, Brahim; Pachter, Ruth; Mou, Shin

    2016-05-01

    We report a first-principles theoretical investigation on the electronic structure and electron transport of defective single-layer (SL) MoS2, as well as of corresponding structures adsorbed with benzyl viologen (BV), which was shown to provide improved performance of a field effect transistor. O2 adsorption was included to gain an understanding of the response upon air-exposure. Following analysis of the structure and stability of sulfur single vacancy and line defects in SL MoS2, we investigated the local transport at the adsorbed sites via a transport model that mimics a scanning tunneling spectroscopy experiment. Distinct current-voltage characteristics were indicated for adsorbed oxygen species at a sulfur vacancy. The electronic structures of defective MoS2 indicated the emergence of impurity states in the bandgap due to sulfur defects and oxygen adsorption. Electron transport calculations for the MoS2 surface with an extended defect in a device setting demonstrated that physisorption of BV enhances the output current, while facile chemisorption by O2 upon air-exposure causes degradation of electron transport.

  4. Photoluminescence of freestanding single- and few-layer MoS2

    OpenAIRE

    Scheuschner, Nils; Ochedowski, Oliver; Kaulitz, Anne-Marie; Gillen, Roland; Schleberger, Marika; Maultzsch, Janina

    2013-01-01

    We present a photoluminescence study of freestanding and Si/SiO2 supported single- and few-layer MoS2. The single-layer exciton peak (A) is only observed in freestanding MoS2. The photoluminescence of supported single-layer MoS2 is instead originating from the A- (trion) peak as the MoS2 is n-type doped from the substrate. In bilayer MoS2, the van der Waals interaction with the substrate is decreasing the indirect band gap energy by up to ~ 80 meV. Furthermore, the photoluminescence spectra o...

  5. Enhanced absorption of monolayer MoS2 with resonant back reflector

    CERN Document Server

    Liu, Jiang-Tao; Li, Xiao-Jing; Liu, Nian-Hua

    2014-01-01

    By extracting the permittivity of monolayer MoS2 from experiments, the optical absorption of monolayer MoS2 prepared on top of one-dimensional photonic crystal (1DPC) or metal films is investigated theoretically. The 1DPC and metal films act as resonant back reflectors that can enhance absorption of monolayer MoS2 substantially over a broad spectral range due to the Fabry-Perot cavity effect. The absorption of monolayer MoS2 can also be tuned by varying either the distance between the monolayer MoS2 and the back reflector or the thickness of the cover layers.

  6. Structural and optical properties of ZnO films grown on silicon and their applications in MOS devices in conjunction with ZrO2 as a gate dielectric

    Indian Academy of Sciences (India)

    S K Nandi; S Chakraborty; M K Bera; C K Maiti

    2007-06-01

    Photoluminescence (PL) properties of undoped ZnO thin films grown by rf magnetron sputtering on silicon substrates have been investigated. ZnO/Si substrates are characterized by Rutherford backscattering (RBS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). ZrO2 thin films have been deposited on ZnO using microwave plasma enhanced chemical vapour deposition at a low temperature (150°C). Using metal insulator semiconductor (MIS) capacitor structures, the reliability and the leakage current characteristics of ZrO2 films have been studied both at room and high temperatures. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Good electrical and reliability properties suggest the suitability of deposited ZrO2 thin films as an alternative as gate dielectric on ZnO/-Si heterostructure for future device applications.

  7. Characterization of atomic-layer MoS2 synthesized using a hot filament chemical vapor deposition method

    Science.gov (United States)

    Ying-Zi, Peng; Yang, Song; Xiao-Qiang, Xie; Yuan, Li; Zheng-Hong, Qian; Ru, Bai

    2016-05-01

    Atomic-layer MoS2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS2 under our experimental conditions. Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LY16F040003 and LY16A040007) and the National Natural Science Foundation of China (Grant Nos. 51401069 and 11574067).

  8. MOS11: a new component in the mRNA export pathway.

    Directory of Open Access Journals (Sweden)

    Hugo Germain

    Full Text Available Nucleocytoplasmic trafficking is emerging as an important aspect of plant immunity. The three related pathways affecting plant immunity include Nuclear Localization Signal (NLS-mediated nuclear protein import, Nuclear Export Signal (NES-dependent nuclear protein export, and mRNA export relying on MOS3, a nucleoporin belonging to the Nup107-160 complex. Here we report the characterization, identification, and detailed analysis of Arabidopsis modifier of snc1, 11 (mos11. Mutations in MOS11 can partially suppress the dwarfism and enhanced disease resistance phenotypes of snc1, which carries a gain-of-function mutation in a TIR-NB-LRR type Resistance gene. MOS11 encodes a conserved eukaryotic protein with homology to the human RNA binding protein CIP29. Further functional analysis shows that MOS11 localizes to the nucleus and that the mos11 mutants accumulate more poly(A mRNAs in the nucleus, likely resulting from reduced mRNA export activity. Epistasis analysis between mos3-1 and mos11-1 revealed that MOS11 probably functions in the same mRNA export pathway as MOS3, in a partially overlapping fashion, before the mRNA molecules pass through the nuclear pores. Taken together, MOS11 is identified as a new protein contributing to the transfer of mature mRNA from the nucleus to the cytosol.

  9. MOS11: A New Component in the mRNA Export Pathway

    Science.gov (United States)

    Cheng, Yu Ti; Lee, EunKyoung; Huang, Yan; Dong, Oliver Xiaoou; Gannon, Patrick; Huang, Shuai; Ding, Pingtao; Li, Yingzhong; Sack, Fred; Zhang, Yuelin; Li, Xin

    2010-01-01

    Nucleocytoplasmic trafficking is emerging as an important aspect of plant immunity. The three related pathways affecting plant immunity include Nuclear Localization Signal (NLS)–mediated nuclear protein import, Nuclear Export Signal (NES)–dependent nuclear protein export, and mRNA export relying on MOS3, a nucleoporin belonging to the Nup107–160 complex. Here we report the characterization, identification, and detailed analysis of Arabidopsis modifier of snc1, 11 (mos11). Mutations in MOS11 can partially suppress the dwarfism and enhanced disease resistance phenotypes of snc1, which carries a gain-of-function mutation in a TIR-NB-LRR type Resistance gene. MOS11 encodes a conserved eukaryotic protein with homology to the human RNA binding protein CIP29. Further functional analysis shows that MOS11 localizes to the nucleus and that the mos11 mutants accumulate more poly(A) mRNAs in the nucleus, likely resulting from reduced mRNA export activity. Epistasis analysis between mos3-1 and mos11-1 revealed that MOS11 probably functions in the same mRNA export pathway as MOS3, in a partially overlapping fashion, before the mRNA molecules pass through the nuclear pores. Taken together, MOS11 is identified as a new protein contributing to the transfer of mature mRNA from the nucleus to the cytosol. PMID:21203492

  10. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

    Science.gov (United States)

    Tadi, Kiran Kumar; Palve, Anil M; Pal, Shubhadeep; Sudeep, P M; Narayanan, Tharangattu N

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here. PMID:27231837

  11. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

    Science.gov (United States)

    Tadi, Kiran Kumar; Palve, Anil M; Pal, Shubhadeep; Sudeep, P M; Narayanan, Tharangattu N

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

  12. Layer-by-layer self-assembly of polyelectrolyte functionalized MoS2 nanosheets.

    Science.gov (United States)

    Shen, Jianfeng; Pei, Yu; Dong, Pei; Ji, Jin; Cui, Zheng; Yuan, Junhua; Baines, Robert; Ajayan, Pulickel M; Ye, Mingxin

    2016-05-01

    Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems.

  13. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis

    Science.gov (United States)

    Tadi, Kiran Kumar; Palve, Anil M.; Pal, Shubhadeep; Sudeep, P. M.; Narayanan, Tharangattu N.

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

  14. Ambipolar MoS2 Thin Flake Transistors

    NARCIS (Netherlands)

    Zhang, Yijin; Ye, Jianting; Matsuhashi, Yusuke; Iwasa, Yoshihiro

    2012-01-01

    Field effect transistors (FETs) made of thin flake single crystals isolated from layered materials have attracted growing interest since the success of graphene. Here, we report the fabrication of an electric double layer transistor (EDLT, a FET gated by ionic liquids) using a thin flake of MoS2, a

  15. Simulation of vertical merged MOS elements with optical power supply

    NARCIS (Netherlands)

    Bubennikov, AN; Rakitin, VV; Zykov, AV

    2002-01-01

    Functional optoelectronic vertical merged MOS (OVMMOS) elements with optical power supply increasing the packaging density for advanced high-speed low-voltage low-power deep-submicron ULSI are considered. Two types of new OVVMOS logical elements are proposed, analyzed and simulated. The simple reduc

  16. Magnetoresistance in molybdenite (MoS2) crystals

    International Nuclear Information System (INIS)

    The principal magnetoresistance ratios of molybdenite (MoS2), the naturally occurring semiconducting crystal, have been investigated at magnetic fields ranging from 4.5 KOe and within the temperature range 3000K to 7000K. Unlike some previous observations, magnetoresistance has been found to be negative. (author)

  17. Ultralarge area MOS tunnel devices for electron emission

    DEFF Research Database (Denmark)

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm;

    2007-01-01

    A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxid...

  18. Few-layer MoS2-anchored graphene aerogel paper for free-standing electrode materials.

    Science.gov (United States)

    Lee, Wee Siang Vincent; Peng, Erwin; Loh, Tamie Ai Jia; Huang, Xiaolei; Xue, Jun Min

    2016-04-21

    To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic stability.

  19. Few-layer MoS2-anchored graphene aerogel paper for free-standing electrode materials.

    Science.gov (United States)

    Lee, Wee Siang Vincent; Peng, Erwin; Loh, Tamie Ai Jia; Huang, Xiaolei; Xue, Jun Min

    2016-04-21

    To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic stability. PMID:27020143

  20. Atomic layer deposition of a high-k dielectric on MoS2 using trimethylaluminum and ozone.

    Science.gov (United States)

    Cheng, Lanxia; Qin, Xiaoye; Lucero, Antonio T; Azcatl, Angelica; Huang, Jie; Wallace, Robert M; Cho, Kyeongjae; Kim, Jiyoung

    2014-08-13

    We present an Al2O3 dielectric layer on molybdenum disulfide (MoS2), deposited using atomic layer deposition (ALD) with ozone/trimethylaluminum (TMA) and water/TMA as precursors. The results of atomic force microscopy and low-energy ion scattering spectroscopy show that using TMA and ozone as precursors leads to the formation of uniform Al2O3 layers, in contrast to the incomplete coverage we observe when using TMA/H2O as precursors. Our Raman and X-ray photoelectron spectroscopy measurements indicate minimal variations in the MoS2 structure after ozone treatment at 200 °C, suggesting its excellent chemical resistance to ozone.

  1. Nitrogen-Doped Carbon Embedded MoS2 Microspheres as Advanced Anodes for Lithium- and Sodium-Ion Batteries.

    Science.gov (United States)

    Xie, Dong; Xia, Xinhui; Wang, Yadong; Wang, Donghuang; Zhong, Yu; Tang, Wangjia; Wang, Xiuli; Tu, Jiangping

    2016-08-01

    Rational design and synthesis of advanced anode materials are extremely important for high-performance lithium-ion and sodium-ion batteries. Herein, a simple one-step hydrothermal method is developed for fabrication of N-C@MoS2 microspheres with the help of polyurethane as carbon and nitrogen sources. The MoS2 microspheres are composed of MoS2 nanoflakes, which are wrapped by an N-doped carbon layer. Owing to its unique structural features, the N-C@MoS2 microspheres exhibit greatly enhanced lithium- and sodium-storage performances including a high specific capacity, high rate capability, and excellent capacity retention. Additionally, the developed polyurethane-assisted hydrothermal method could be useful for the construction of many other high-capacity metal oxide/sulfide composite electrode materials for energy storage. PMID:27355199

  2. Nanoscale mapping of excitonic processes in single-layer MoS2 using tip-enhanced photoluminescence microscopy.

    Science.gov (United States)

    Su, Weitao; Kumar, Naresh; Mignuzzi, Sandro; Crain, Jason; Roy, Debdulal

    2016-05-19

    In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural and excitonic properties.

  3. Tribological Performance of MoS2 Coatings in Various Environments

    Directory of Open Access Journals (Sweden)

    Thomas Gradt

    2016-09-01

    Full Text Available Molybdenum disulfide (MoS2 is a well-known solid lubricant for tribosystems running in vacuum or dry gases. Problems arise due to its sensitivity to humidity, which is a drawback for its application under ambient conditions. However, by using a physical vapor deposition (PVD process, deposition parameters can be optimized not only to gain a coatings structure with favorable frictional properties but also to minimize the sensitivity to attack by water molecules. Therefore, an improved tribological behavior even under moist conditions can be achieved. MoS2 coatings are also candidates for being applied at cryogenic temperatures. They already have proven their suitability, e.g., for sliding support elements between superconducting magnets of the nuclear fusion-experiment Wendelstein 7-X. However, these coatings were exclusively produced for this particular application and the utilization for more common tribosystems may be precluded due to cost considerations. In view of a wider range of applications, pure and Cr containing PVD-MoS2 coatings with an optimized structure were tested under varying environments including hydrogen gas and cryogenic temperatures. Results of the most promising variant are presented in this paper.

  4. Thermal transport properties of MoS2 and MoSe2 monolayers

    Science.gov (United States)

    Kandemir, Ali; Yapicioglu, Haluk; Kinaci, Alper; Çağın, Tahir; Sevik, Cem

    2016-02-01

    The isolation of single- to few-layer transition metal dichalcogenides opens new directions in the application of two-dimensional materials to nanoelectronics. The characterization of thermal transport in these new low-dimensional materials is needed for their efficient implementation, either for general overheating issues or specific applications in thermoelectric devices. In this study, the lattice thermal conductivities of single-layer MoS2 and MoSe2 are evaluated using classical molecular dynamics methods. The interactions between atoms are defined by Stillinger-Weber-type empirical potentials that are developed to represent the structural, mechanical, and vibrational properties of the given materials. In the parameterization of the potentials, a stochastic optimization algorithm, namely particle swarm optimization, is utilized. The final parameter sets produce quite consistent results with density functional theory in terms of lattice parameters, bond distances, elastic constants, and vibrational properties of both single-layer MoS2 and MoSe2. The predicted thermal properties of both materials are in very good agreement with earlier first-principles calculations. The discrepancies between the calculations and experimental measurements are most probably caused by the pristine nature of the structures in our simulations.

  5. Tunable Molecular MoS2 Edge-Site Mimics for Catalytic Hydrogen Production.

    Science.gov (United States)

    Garrett, Benjamin R; Polen, Shane M; Click, Kevin A; He, Mingfu; Huang, Zhongjie; Hadad, Christopher M; Wu, Yiying

    2016-04-18

    Molybdenum sulfides represent state-of-the-art, non-platinum electrocatalysts for the hydrogen evolution reaction (HER). According to the Sabatier principle, the hydrogen binding strength to the edge active sites should be neither too strong nor too weak. Therefore, it is of interest to develop a molecular motif that mimics the catalytic sites structurally and possesses tunable electronic properties that influence the hydrogen binding strength. Furthermore, molecular mimics will be important for providing mechanistic insight toward the HER with molybdenum sulfide catalysts. In this work, a modular method to tune the catalytic properties of the S-S bond in MoO(S2)2L2 complexes is described. We studied the homogeneous electrocatalytic hydrogen production performance metrics of three catalysts with different bipyridine substitutions. By varying the electron-donating abilities, we present the first demonstration of using the ligand to tune the catalytic properties of the S-S bond in molecular MoS2 edge-site mimics. This work can shed light on the relationship between the structure and electrocatalytic activity of molecular MoS2 catalysts and thus is of broad importance from catalytic hydrogen production to biological enzyme functions. PMID:27022836

  6. Atomistic modeling of the metallic-to-semiconducting phase boundaries in monolayer MoS2

    Science.gov (United States)

    Saha, Dipankar; Mahapatra, Santanu

    2016-06-01

    Recent experimental demonstration on the coexistence of metallic and semiconducting phases in the same monolayer MoS2 crystal has attracted much attention for its use in ultra-low contact resistance-MoS2 transistors. However, the electronic structures of the metallic-to-semiconducting phase boundaries, which appear to dictate the carrier injection in such transistors, are not yet well understood. In this letter, interfacing the 2H and 1T' polytypes appropriately, we first model the "beta" (β) and the "gamma" (γ) phase boundaries, and demonstrate good agreement with experiential results. We then apply first-principles based density functional theory to calculate the electronic structures for those optimized geometries. We further employ non equilibrium Green's function formalism to evaluate the transmission spectra and the local density of states (LDOS) in order to assess the Schottky barrier nature of the phase boundaries. Our study reveals that while the γ boundary yields p-type Schottky barrier, the β boundary leads to the distinct symmetric Schottky barrier with an atomically sharp transition region. This understanding could be useful for designing high performance transistors using phase-engineered MoS2 crystals.

  7. Protecting the properties of monolayer MoS2 on silicon based substrates with an atomically thin buffer

    Science.gov (United States)

    Man, Michael K. L.; Deckoff-Jones, Skylar; Winchester, Andrew; Shi, Guangsha; Gupta, Gautam; Mohite, Aditya D.; Kar, Swastik; Kioupakis, Emmanouil; Talapatra, Saikat; Dani, Keshav M.

    2016-02-01

    Semiconducting 2D materials, like transition metal dichalcogenides (TMDs), have gained much attention for their potential in opto-electronic devices, valleytronic schemes, and semi-conducting to metallic phase engineering. However, like graphene and other atomically thin materials, they lose key properties when placed on a substrate like silicon, including quenching of photoluminescence, distorted crystalline structure, and rough surface morphology. The ability to protect these properties of monolayer TMDs, such as molybdenum disulfide (MoS2), on standard Si-based substrates, will enable their use in opto-electronic devices and scientific investigations. Here we show that an atomically thin buffer layer of hexagonal-boron nitride (hBN) protects the range of key opto-electronic, structural, and morphological properties of monolayer MoS2 on Si-based substrates. The hBN buffer restores sharp diffraction patterns, improves monolayer flatness by nearly two-orders of magnitude, and causes over an order of magnitude enhancement in photoluminescence, compared to bare Si and SiO2 substrates. Our demonstration provides a way of integrating MoS2 and other 2D monolayers onto standard Si-substrates, thus furthering their technological applications and scientific investigations.

  8. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals

    Science.gov (United States)

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  9. Nucleoporin MOS7/Nup88 is required for mitosis in gametogenesis and seed development in Arabidopsis.

    Science.gov (United States)

    Park, Guen Tae; Frost, Jennifer M; Park, Jin-Sup; Kim, Tae Ho; Lee, Jong Seob; Oh, Sung Aeong; Twell, David; Brooks, Janie Sue; Fischer, Robert L; Choi, Yeonhee

    2014-12-23

    Angiosperm reproduction is characterized by alternate diploid sporophytic and haploid gametophytic generations. Gametogenesis shares similarities with that of animals except for the formation of the gametophyte, whereby haploid cells undergo several rounds of postmeiotic mitosis to form gametes and the accessory cells required for successful reproduction. The mechanisms regulating gametophyte development in angiosperms are incompletely understood. Here, we show that the nucleoporin Nup88-homolog MOS7 (Modifier of Snc1,7) plays a crucial role in mitosis during both male and female gametophyte formation in Arabidopsis thaliana. Using a mutagenesis screen, we identify the mos7-5 mutant allele, which causes ovule and pollen abortion in MOS7/mos7-5 heterozygous plants, and preglobular stage embryonic lethality in homozygous mos7-5 seeds. During interphase, we show that MOS7 is localized to the nuclear membrane but, like many nucleoporins, is associated with the spindle apparatus during mitosis. We detect interactions between MOS7 and several nucleoporins known to control spindle dynamics, and find that in pollen from MOS7/mos7-5 heterozygotes, abortion is accompanied by a failure of spindle formation, cell fate specification, and phragmoplast activity. Most intriguingly, we show that following gamete formation by MOS7/mos7-5 heterozygous spores, inheritance of either the MOS7 or the mos7-5 allele by a given gamete does not correlate with its respective survival or abortion. Instead, we suggest a model whereby MOS7, which is highly expressed in the Pollen- and Megaspore Mother Cells, enacts a dosage-limiting effect on the gametes to enable their progression through subsequent mitoses.

  10. High Efficient Photo-Fenton Catalyst of α-Fe2O3/MoS2 Hierarchical Nanoheterostructures: Reutilization for Supercapacitors

    Science.gov (United States)

    Yang, Xijia; Sun, Haiming; Zhang, Lishu; Zhao, Lijun; Lian, Jianshe; Jiang, Qing

    2016-08-01

    A novel three-dimensional (3D) α-Fe2O3/MoS2 hierarchical nanoheterostructure is effectively synthesized via a facile hydrothermal method. The zero-dimensional (0D) Fe2O3 nanoparticles guide the growth of two-dimensional (2D) MoS2 nanosheets and formed 3D flower-like structures, while MoS2 facilitates the good dispersion of porous Fe2O3 with abundant oxygen vacancies. This charming 3D-structure with perfect match of non-equal dimension exhibits high recyclable photo-Fenton catalytic activity for Methyl orange pollutant and nice specific capacity in reusing as supercapacitor after catalysis. The synergistic effect between Fe2O3 and MoS2, the intermediate nanointerfaces, the 3D porous structures, and the abundant oxygen vacancies both contribute to highly active catalysis, nice electrochemical performance and stable cycling. This strategy is simple, cheap, and feasible for maximizing the value of the materials, as well as eliminating the secondary pollution.

  11. Few-layer MoS2-anchored graphene aerogel paper for free-standing electrode materials

    Science.gov (United States)

    Lee, Wee Siang Vincent; Peng, Erwin; Loh, Tamie Ai Jia; Huang, Xiaolei; Xue, Jun Min

    2016-04-01

    To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic stability.To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic

  12. Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite

    Science.gov (United States)

    Ding, Shuang-Shuang; Huang, Wei-Qing; Yang, Yin-Cai; Zhou, Bing-Xin; Hu, Wang-Yu; Long, Meng-Qiu; Peng, P.; Huang, Gui-Fang

    2016-05-01

    The enhanced photocatalytic performance of various MoS2-based nanomaterials has recently been observed, but the role of monolayer MoS2 is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS2/SnO2 nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS2 as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ˜0.49 eV exists between monolayer MoS2 and SnO2 with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO2, thus enhancing the reduction activity of latter, indicating that the monolayer MoS2 is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS2, turn into catalytic active sites, making the monolayer MoS2 to be a highly active co-catalyst in the composite. The dual role of monolayer MoS2 is expected to arise in other MoS2-semiconductor nanocomposites. The calculated absorption spectra can be rationalized by available experimental results. These findings provide theoretical evidence supporting the experimental reports and pave the way for developing highly efficient MoS2-based photocatalysts.

  13. Modeling accumulation capacitance-voltage characteristic of MoS2 thin flake transistors

    International Nuclear Information System (INIS)

    We report a theoretical investigation on the accumulation capacitance in MoS2 thin flake transistors using a two-valley band structure. To obtain the relevant two-valley band structure parameters, first-principles calculations are performed. Then, the capacitance-voltage characteristic in the accumulation layer is simulated by a self-consistent Poisson–Schrödinger solution. It is found that the occupation of the K valley in the conduction band has a significant contribution to the accumulation capacitance, especially in the strong accumulation layer. More importantly, the calculated results using a two-valley band structure is in good agreement with the published experimental data without any fitting parameters, highlighting that the inclusion of both the Q and K conduction band valley is necessary to understand the accumulation capacitance in the strong accumulation region. (paper)

  14. The capacity fading mechanism and improvement of cycling stability in MoS2-based anode materials for lithium-ion batteries

    Science.gov (United States)

    Shu, Haibo; Li, Feng; Hu, Chenli; Liang, Pei; Cao, Dan; Chen, Xiaoshuang

    2016-01-01

    Two-dimensional (2D) layered MoS2 nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of electrode materials depends on a deep understanding of their dynamic structural evolution and reaction kinetics in the lithiation process. Herein, thermodynamic phase diagrams and the lithiation dynamics of MoS2-based nanostructures with the intercalation of lithium ions are studied by using first-principles calculations and ab initio molecular dynamics simulations. Our results demonstrate that the continuous intercalation of Li ions induces structural destruction of 2H phase MoS2 nanosheets in the discharge process that follows a layer-by-layer dissociation mechanism. Meanwhile, the intercalation of Li ions leads to a structural transition of MoS2 nanosheets from the 2H to the 1T phase due to the ultralow transition barriers (~0.1 eV). We find that the phase transition can slow down the dissociation of MoS2 nanosheets during lithiation. The result can be applied to explain extensive experimental observation of the fast capacity fading of MoS2-based anode materials between the first and the subsequent discharges. To suppress the dissociation of MoS2 nanosheets in the lithiation process, we propose a strategy by constructing a sandwich-like graphene/MoS2/graphene structure that indicates high chemical stability, superior conductivity, and high Li-ion mobility in the charge/discharge process, implying the possibility to induce an improvement in the anode cycling performance. This work opens a new route to rational design layered transition-metal disulfide (TMD) anode materials for LIBs with superior cycling stability and electrochemical performance.Two-dimensional (2D) layered MoS2 nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of

  15. Enhanced second harmonic generation of MoS2 layers on a thin gold film.

    Science.gov (United States)

    Zeng, Jianhua; Yuan, Maohui; Yuan, Weiguang; Dai, Qiaofeng; Fan, Haihua; Lan, Sheng; Tie, Shaolong

    2015-08-28

    The linear and nonlinear optical properties of thin MoS2 layers exfoliated on an Au/SiO2 substrate were investigated both numerically and experimentally. It was found that the MoS2 layers with different thicknesses exhibited different colors on the gold film. The reflection spectra of the MoS2 layers with different thicknesses were calculated by using the finite-difference time-domain technique and the corresponding chromaticity coordinates were derived. The electric field enhancement factors at both the fundamental light and the second harmonic were calculated and the enhancement factors for second harmonic generation (SHG) were estimated for the MoS2 layers with different thicknesses. Different from the MoS2 layers on a SiO2/Si substrate where the maximum SHG was observed in the single-layer MoS2, the maximum SHG was achieved in the 17 nm-thick MoS2 layer on the Au/SiO2 substrate. As compared with the MoS2 layers on the SiO2/Si substrate, a significant enhancement in SHG was found for the MoS2 layers on the Au/SiO2 substrate due to the strong localization of the electric field. More interestingly, it was demonstrated experimentally that optical data storage can be realized by modifying the SHG intensity of a MoS2 layer through thinning its thickness.

  16. Oxidation of atomically thin MoS2 on SiO2

    Science.gov (United States)

    Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

    2013-03-01

    Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

  17. Spatial and temporal expression of c-mos in mouse testis during postnatal development

    Institute of Scientific and Technical Information of China (English)

    Shao-Feng Cao; Ding Li; Qing Yuan; Xin Guan; Chen Xu

    2008-01-01

    Aim: To immunolocalize the c-mos gene product and to investigate its spatial and temporal expression in mouse testis during postnatal development. Methods: Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization techniques were used to examine c-mos mRNA and indirect immunofluorescence was used to localize c-Mos protein in mouse testis on postnatal days 14, 21, 25, 28, 30, 35, 49 and 70. Results: c-mos mRNA remained low on postnatal days 14-21, increased abruptly from day 25 and peaked on day 30. Its levels decreased a little on day 35 and became almost stable thereafter until day 70. c-mos mRNA was localized in the nucleus and cytoplasm of the spermatocytes and round spermatids. The nuclear staining was much stronger than the cytoplasmic staining. Using a polyclonal anti-c-Mos antibody, Western blotting detected a single band at 43 kDa in testis lysate, c-Mos protein was exclusively localized to the elongating spermatids and was first detected on postnatal day 30. The number of c-Mos-positive spermatids increased progressively till day 49 and stabilized thereafter.Conclusion: The c-mos gene displays a spatial and temporal expression pattern in the mouse testis during postnatal development at both the mRNA and protein level. This suggests that c-mos might play important roles in spermatogenesis.

  18. Enhanced second harmonic generation of MoS2 layers on a thin gold film.

    Science.gov (United States)

    Zeng, Jianhua; Yuan, Maohui; Yuan, Weiguang; Dai, Qiaofeng; Fan, Haihua; Lan, Sheng; Tie, Shaolong

    2015-08-28

    The linear and nonlinear optical properties of thin MoS2 layers exfoliated on an Au/SiO2 substrate were investigated both numerically and experimentally. It was found that the MoS2 layers with different thicknesses exhibited different colors on the gold film. The reflection spectra of the MoS2 layers with different thicknesses were calculated by using the finite-difference time-domain technique and the corresponding chromaticity coordinates were derived. The electric field enhancement factors at both the fundamental light and the second harmonic were calculated and the enhancement factors for second harmonic generation (SHG) were estimated for the MoS2 layers with different thicknesses. Different from the MoS2 layers on a SiO2/Si substrate where the maximum SHG was observed in the single-layer MoS2, the maximum SHG was achieved in the 17 nm-thick MoS2 layer on the Au/SiO2 substrate. As compared with the MoS2 layers on the SiO2/Si substrate, a significant enhancement in SHG was found for the MoS2 layers on the Au/SiO2 substrate due to the strong localization of the electric field. More interestingly, it was demonstrated experimentally that optical data storage can be realized by modifying the SHG intensity of a MoS2 layer through thinning its thickness. PMID:26204257

  19. Atomic defect states in monolayers of MoS2 and WS2

    Science.gov (United States)

    Salehi, Saboura; Saffarzadeh, Alireza

    2016-09-01

    The influence of atomic vacancy defects at different concentrations on electronic properties of MoS2 and WS2 monolayers is studied by means of Slater-Koster tight-binding model with non-orthogonal sp3d5 orbitals and including the spin-orbit coupling. The presence of vacancy defects induces localized states in the bandgap of pristine MoS2 and WS2, which have potential to modify the electronic structure of the systems, depending on the type and concentration of the defects. It is shown that although the contribution of metal (Mo or W) d orbitals is dominant in the formation of midgap states, the sulphur p and d orbitals have also considerable contribution in the localized states, when metal defects are introduced. Our results suggest that Mo and W defects can turn the monolayers into p-type semiconductors, while the sulphur defects make the system a n-type semiconductor, in agreement with ab initio results and experimental observations.

  20. DPFFs: C2MOS Direct Path Flip-Flops for Process-Resilient Ultradynamic Voltage Scaling

    Directory of Open Access Journals (Sweden)

    Myeong-Eun Hwang

    2016-01-01

    Full Text Available We propose two master-slave flip-flops (FFs that utilize the clocked CMOS (C2MOS technique with an internal direct connection along the main signal propagation path between the master and slave latches and adopt an adaptive body bias technique to improve circuit robustness. C2MOS structure improves the setup margin and robustness while providing full compatibility with the standard cell characterization flow. Further, the direct path shortens the logic depth and thus speeds up signal propagation, which can be optimized for less power and smaller area. Measurements from test circuits fabricated in 130 nm technology show that the proposed FF operates down to 60 mV, consuming 24.7 pW while improving the propagation delay, dynamic power, and leakage by 22%, 9%, and 13%, respectively, compared with conventional FFs at the iso-output-load condition. The proposed FFs are integrated into an 8×8 FIR filter which successfully operates all the way down to 85 mV.

  1. Graphene - ferroelectric and MoS2 - ferroelectric heterostructures for memory applications

    Science.gov (United States)

    Lipatov, Alexey; Sharma, Pankaj; Gruverman, Alexei; Sinitskii, Alexander

    In recent years there has been an unprecedented interest in two-dimensional (2D) materials with unique physical and chemical properties that cannot be found in their three-dimensional (3D) counterparts. One of the important advantages of 2D materials is that they can be easily integrated with other 2D materials and functional films, resulting in multilayered structures with new properties. We fabricated and tested electronic and memory properties of field-effect transistors (FETs) based on a single-layer graphene combined with lead zirconium titanate (PZT) substrate. Previously studied graphene-PZT devices exhibited an unusual electronic behavior such as clockwise hysteresis of electronic transport, in contradiction with counterclockwise polarization dependence of PZT. We investigated how the interplay of polarization and interfacial phenomena affects the electronic behavior and memory characteristics of graphene-PZT FETs, explain the origin of unusual clockwise hysteresis and experimentally demonstrate a reversed polarization-dependent hysteresis of electronic transport. In addition we fabricated and tested properties of MoS2-PZT FETs which exhibit a large hysteresis of electronic transport with high ON/OFF ratios. We demonstrate that MoS2-PZT memories have a number of advantages over commercial FeRAMs, such as nondestructive data readout, low operation voltage, wide memory window and the possibility to write and erase them both electrically and optically.

  2. Pd-gate MOS sensor for detection of methanol and propanol

    Institute of Scientific and Technical Information of China (English)

    Preeti Pandey; J.K.Srivastava; V.N.Mishra; R.Dwivedi

    2011-01-01

    The present paper focused on the detection of methanol and propanol using Pd-gate metal-oxide-semiconductor(MOS)sensor.Surface morphology and composition of the gate film were studied by scanning electron microscopy(SEM)and atomic force microscopy(AFM).The response of the sensor for propanol and methanol was measured as shift in capacitance-voltage(C-V) and conductance-voltage(G-V) curves of the MOS structure.The sensitivity of the sensor towards methanol was found to be greater than that towards propanol.It was 58.2% for methanol and 32% for propanol(at 0.6 V,1 MHz)in terms of capacitance measurements,while in terms of conductance results the sensitivity was found to be 57.2% for methanol and 38.9% for propanol at 1 kHz.The discontinuities or cracks present in the microstructure of the gate material are believed to be mainly responsible for the high sensitivity of the sensor,going with the decomposition of gas molecules and subsequent hydrogen permeation through Pd.

  3. Broadband and enhanced nonlinear optical response of MoS2/graphene nanocomposites for ultrafast photonics applications

    Science.gov (United States)

    Jiang, Yaqin; Miao, Lili; Jiang, Guobao; Chen, Yu; Qi, Xiang; Jiang, Xiao-Fang; Zhang, Han; Wen, Shuangchun

    2015-11-01

    Due to their relatively high compatibility with specific photonic structures, strong light-matter interactions and unique nonlinear optical response, two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, are attractive for ultrafast photonics applications. Here, we fabricate MoS2/graphene nanocomposites by a typical hydrothermal method. In addition, we systematically investigate their nonlinear optical responses. Our experiments indicate that the combined advantages of ultrafast relaxation, a broadband response from graphene, and the strong light-matter interaction from MoS2, can be integrated together by composition. The optical properties in terms of carrier relaxation dynamics, saturation intensity and modulation depth suggest great potential for the MoS2/graphene nanocomposites in photonics applications. We have further fabricated 2D nanocomposites based optical saturable absorbers and integrated them into a 1.5 μm Erbium-doped fiber laser to demonstrate Q-switched and mode-locked pulse generation. The fabrication of 2D nanocomposites assembled from different types of 2D materials, via this simple and scalable growth approach, paves the way for the formation and tuning of new 2D materials with desirable photonic properties and applications.

  4. New quantum spin Hall insulator in two-dimensional MoS2 with periodically distributed pores.

    Science.gov (United States)

    Liu, Peng-Fei; Zhou, Liujiang; Frauenheim, Thomas; Wu, Li-Ming

    2016-03-01

    MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications.

  5. Self-assembled lamellar MoS2, SnS2 and SiO2 semiconducting polymer nanocomposites.

    Science.gov (United States)

    Kirmayer, Saar; Aharon, Eyal; Dovgolevsky, Ekaterina; Kalina, Michael; Frey, Gitti L

    2007-06-15

    Lamellar nanocomposites based on semiconducting polymers incorporated into layered inorganic matrices are prepared by the co-assembly of organic and inorganic precursors. Semiconducting polymer-incorporated silica is prepared by introducing the semiconducting polymers into a tetrahydrofuran (THF)/water homogeneous sol solution containing silica precursor species and a surface-active agent. Semiconducting polymer-incorporated MoS(2) and SnS(2) are prepared by Li intercalation into the inorganic compound, exfoliation and restack in the presence of the semiconducting polymer. All lamellar nanocomposite films are organized in domains aligned parallel to the substrate surface plane. The incorporated polymers maintain their semiconducting properties, as evident from their optical absorption and photoluminescence spectra. The optoelectronic properties of the nanocomposites depend on the properties of both the inorganic host and the incorporated guest polymer as demonstrated by integrating the nanocomposite films into light-emitting diodes. Devices based on polymer-incorporated silica and polymer-incorporated MoS(2) show no diode behaviour and no light emission due to the insulating and metallic properties of the silica and MoS(2) hosts. In contrast, diode performance and electroluminescence are obtained from devices based on semiconducting polymer-incorporated semiconducting SnS(2), demonstrating that judicious selection of the composite components in combination with the optimization of material synthesis conditions allows new hierarchical structures to be tailored for electronic and optoelectronic applications.

  6. GaN MOS-HEMT Using Ultra-Thin Al2O3 Dielectric Grown by Atomic Layer Deposition

    Institute of Scientific and Technical Information of China (English)

    YUE Yuan-Zheng; HAO Yue; FENG Qian; ZHANG Jin-Cheng; MA Xiao-Hua; NI Jin-Yu

    2007-01-01

    @@ We report a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with atomic layer deposited (ALD) Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 (2005) 063501] of Ye et al. By decreeing the thickness of the gate oxide to 3.5nm and optimizing the device fabrication process, the device with maximum transconductance of 150mS/mm is produced and discussed in comparison with the result of 100mS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800mA/mm at the gate bias of 3.0 V. The gate leakage is two orders of magnitude lower than that of the conventional AlGaN/GaN HEMT. The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented.

  7. Polymer-Derived Ceramic Functionalized MoS2 Composite Paper as a Stable Lithium-Ion Battery Electrode

    Science.gov (United States)

    David, L.; Bhandavat, R.; Barrera, U.; Singh, G.

    2015-04-01

    A facile process is demonstrated for the synthesis of layered SiCN-MoS2 structure via pyrolysis of polysilazane functionalized MoS2 flakes. The layered morphology and polymer to ceramic transformation on MoS2 surfaces was confirmed by use of electron microscopy and spectroscopic techniques. Tested as thick film electrode in a Li-ion battery half-cell, SiCN-MoS2 showed the classical three-stage reaction with improved cycling stability and capacity retention than neat MoS2. Contribution of conversion reaction of Li/MoS2 system on overall capacity was marginally affected by the presence of SiCN while Li-irreversibility arising from electrolyte decomposition was greatly suppressed. This is understood as one of the reasons for decreased first cycle loss and increased capacity retention. SiCN-MoS2 in the form of self-supporting paper electrode (at 6 mg.cm-2) exhibited even better performance, regaining initial charge capacity of approximately 530 mAh.g-1 when the current density returned to 100 mA.g-1 after continuous cycling at 2400 mA.g-1 (192 mAh.g-1). MoS2 cycled electrode showed mud-cracks and film delamination whereas SiCN-MoS2 electrodes were intact and covered with a uniform solid electrolyte interphase coating. Taken together, our results suggest that molecular level interfacing with precursor-derived SiCN is an effective strategy for suppressing the metal-sulfide/electrolyte degradation reaction at low discharge potentials.

  8. New quantum spin Hall insulator in two-dimensional MoS2 with periodically distributed pores

    Science.gov (United States)

    Liu, Peng-Fei; Zhou, Liujiang; Frauenheim, Thomas; Wu, Li-Ming

    2016-02-01

    MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications.MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications. Electronic supplementary information (ESI) available: Geometry for graphene, T-graphene, graphenylene, h-MoS2, so-MoS2 and g-MoS2, ab initio molecular dynamics simulations, shapes of the three

  9. MoS2/a-C复合薄膜在高/低湿度环境下的摩擦学性能研究%Tribological Properties of MoS2/a-C Composite Films under High/Low Humidity Environments

    Institute of Scientific and Technical Information of China (English)

    耿中荣; 李霞; 张广安; 李浩

    2016-01-01

    In this study,the MoS2 film and MoS2/a-C films with two C contents were deposited by unbalanced magnetron sputtering.The structure,mechanical and tribological properties were investigated by X-ray diffraction,scanning electron microscopy,nanoindentor and CSM tribometer.The results show that MoS2 film presented loose columnar structure with well crystalline state,while the MoS2/a-C composite films appeared amorphous state with much dense microstructure.Moreover,the MoS2/a-C composite films possessed relatively higher hardness compared to the MoS2 film.The friction coefficient and wear rate of the films were all found to be very low,and there were no obviously variations with the change of C content under low humidity (RH 15%).However,under high humidity (RH 75%),the friction coefficient of the MoS2 film and the MoS2/a-C composite film with low C content was relatively high and unstable with rather high wear rate as the serious oxidization.The MoS2/a-C composite film with high C content exhibited relatively lower and stable friction coefficient,as well as relatively lower wear rate compared to the MoS2 film and the MoS2/a-C composite film with low C content.The film also provided stable performance and recovery of low friction in multiple humidity cycles.The excellent properties of the MoS2/a-C composite film were attributed to the relatively denser microstructure,high hardness and excellent oxidation resistance properties.%采用磁控溅射方法制备了MoS2薄膜与不同碳含量的MoS2/a-C复合薄膜,利用XRD、SEM、Raman光谱仪、纳米压痕仪和CSM摩擦试验机等分析了复合薄膜的结构、力学和摩擦学性能.结果表明:MoS2薄膜为疏松的柱状结构,MoS2/a-C复合薄膜为无定形的致密结构,硬度较高.低湿环境下MoS2薄膜与MoS2/a-C复合薄膜的摩擦性能差别不明显;高湿环境下薄膜的摩擦系数和磨损率均有所升高,其中MoS2薄膜与低碳含量的MoS2/a-C复合薄膜氧化

  10. Covalent Modification of MoS2 with Poly(N-vinylcarbazole) for Solid-State Broadband Optical Limiters.

    Science.gov (United States)

    Cheng, Hongxia; Dong, Ningning; Bai, Ting; Song, Yi; Wang, Jun; Qin, Yuanhao; Zhang, Bin; Chen, Yu

    2016-03-18

    New soluble MoS2 nanosheets covalently functionalized with poly(N-vinylcarbazole) (MoS2-PVK) were in situ synthesized for the first time. In contrast to MoS2 and MoS2 /PVK blends, both the solution of MoS2 -PVK in DMF and MoS2-PVK/poly(methyl methacrylate) (PMMA) film show superior nonlinear optical and optical limiting responses. The MoS2-PVK/PMMA film shows the largest nonlinear coefficients (βeff) of about 917 cm GW(-1) at λ=532 nm (cf. 100.69 cm GW(-1) for MoS2/PMMA and 125.12 cm GW(-1) for MoS2/PVK/PMMA) and about 461 cm GW(-1) at λ=1064 nm (cf. -48.92 cm GW(-1) for MoS2/PMMA and 147.56 cm GW(-1) for MoS2/PVK/PMMA). A larger optical limiting effect, with thresholds of about 0.3 GW cm(-2) at λ=532 nm and about 0.5 GW cm(-2) at λ=1064 nm, was also achieved from the MoS2-PVK/PMMA film. These values are among the highest reported for MoS2-based nonlinear optical materials. These results show that covalent functionalization of MoS2 with polymers is an effective way to improve nonlinear optical responses for efficient optical limiting devices.

  11. Covalent Modification of MoS2 with Poly(N-vinylcarbazole) for Solid-State Broadband Optical Limiters.

    Science.gov (United States)

    Cheng, Hongxia; Dong, Ningning; Bai, Ting; Song, Yi; Wang, Jun; Qin, Yuanhao; Zhang, Bin; Chen, Yu

    2016-03-18

    New soluble MoS2 nanosheets covalently functionalized with poly(N-vinylcarbazole) (MoS2-PVK) were in situ synthesized for the first time. In contrast to MoS2 and MoS2 /PVK blends, both the solution of MoS2 -PVK in DMF and MoS2-PVK/poly(methyl methacrylate) (PMMA) film show superior nonlinear optical and optical limiting responses. The MoS2-PVK/PMMA film shows the largest nonlinear coefficients (βeff) of about 917 cm GW(-1) at λ=532 nm (cf. 100.69 cm GW(-1) for MoS2/PMMA and 125.12 cm GW(-1) for MoS2/PVK/PMMA) and about 461 cm GW(-1) at λ=1064 nm (cf. -48.92 cm GW(-1) for MoS2/PMMA and 147.56 cm GW(-1) for MoS2/PVK/PMMA). A larger optical limiting effect, with thresholds of about 0.3 GW cm(-2) at λ=532 nm and about 0.5 GW cm(-2) at λ=1064 nm, was also achieved from the MoS2-PVK/PMMA film. These values are among the highest reported for MoS2-based nonlinear optical materials. These results show that covalent functionalization of MoS2 with polymers is an effective way to improve nonlinear optical responses for efficient optical limiting devices. PMID:26891470

  12. Nanoscale plasmonic phenomena in CVD-grown MoS(2) monolayer revealed by ultra-broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy.

    Science.gov (United States)

    Patoka, Piotr; Ulrich, Georg; Nguyen, Ariana E; Bartels, Ludwig; Dowben, Peter A; Turkowski, Volodymyr; Rahman, Talat S; Hermann, Peter; Kästner, Bernd; Hoehl, Arne; Ulm, Gerhard; Rühl, Eckart

    2016-01-25

    Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS(2)) on silicon dioxide (SiO(2)) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO(2)-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS(2) islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS(2). The influence of MoS(2) islands on the SiO(2) phonon resonance is discussed. The results reveal the plasmonic character of the MoS(2) structures and their interaction with the SiO(2) phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS(2) optical plasmon mode to the SiO(2) surface phonons does not affect the infrared spectrum significantly. For two-layer MoS(2), the coupling of the extra inter-plane acoustic plasmon mode with the SiO(2) surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm(-1). This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non-homogeneous structures. PMID:26832499

  13. Rare-earth implanted MOS devices for silicon photonics. Microstructural, electrical and optoelectronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Rebohle, Lars; Skorupa, Wolfgang [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany). Inst. fuer Ionenstrahlphysik und Materialforschung

    2010-07-01

    The book concentrates on the microstructural, electric and optoelectronic properties of rare-earth implanted MOS structures and their use as light emitters in potential applications. It describes the structural formation processes in the gate oxide during fabrication and under operation, how this microstructure development will affect the electrical device performance and how both microstructure and electrical characteristics determine the optoelectronic features of the light emitters. However, most of the discussed physical processes as well as the described fabrication methods and device characterization techniques are of general interest and are beyond the scope of this type of light emitter. The book will be of value to engineers, physicists, and scientists dealing either with Si based photonics in particular or optoelectronic device fabrication and characterization in general. (orig.)

  14. Diffusion-Mediated Synthesis of MoS2/WS2 Lateral Heterostructures.

    Science.gov (United States)

    Bogaert, Kevin; Liu, Song; Chesin, Jordan; Titow, Denis; Gradečak, Silvija; Garaj, Slaven

    2016-08-10

    Controlled growth of two-dimensional transition metal dichalcogenide (TMD) lateral heterostructures would enable on-demand tuning of electronic and optoelectronic properties in this new class of materials. Prior to this work, compositional modulations in lateral TMD heterostructures have been considered to depend solely on the growth chronology. We show that in-plane diffusion can play a significant role in the chemical vapor deposition of MoS2/WS2 lateral heterostructures leading to a variety of nontrivial structures whose composition does not necessarily follow the growth order. Optical, structural, and compositional studies of TMD crystals captured at different growth temperatures and in different diffusion stages suggest that compositional mixing versus segregation are favored at high and low growth temperatures, respectively. The observed diffusion mechanism will expand the realm of possible lateral heterostructures, particularly ones that cannot be synthesized using traditional methods. PMID:27438807

  15. Analysis of displacement damage effects on MOS capacitors

    Science.gov (United States)

    Fernández-Martínez, P.; Palomo, F. R.; Hidalgo, S.; Fleta, C.; Campabadal, F.; Flores, D.

    2013-12-01

    Displacement damage effect on MOS capacitors is analyzed in this work with the aid of TCAD simulations. A noticeable capacitance reduction in the accumulation mode is observed in the High Frequency C-V characteristic curve after a 24 GeV proton irradiation. This effect is clearly distinguishable from ionizing damage effects, otherwise negligible under the specific conditions of the experiment. The capacitance reduction is identified with the increase of the substrate resistivity, due to the modification of its effective doping concentration. Supported on a well-established traps model, the expected displacement damage defects are simulated as a function of the fluence, allowing the identification of donor trap levels as the responsible of the phenomenon for p-type substrate MOS capacitors.

  16. Flowerlike MoS2 nanoparticles: solvothermal synthesis and characterization

    Institute of Scientific and Technical Information of China (English)

    Yanli SUN; Shiming WANG; Qiongsheng WANG

    2009-01-01

    Flowerlike MoS2 nanoparticles have been successfully synthesized through a mild solvothermal reaction with the aid of ethanol aqueous solution, and the samples have been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and low temperature nitrogen adsorption-desorption. The nanometer flower MoS2 is composed of ultrathin nanosheets of approximately 10 nanometers in thickness. The influence of the reaction temperature and the reaction time on the formation of the flowerlike M0S2 nanoparticles were evaluated. The optimal experimental conditions were determined as follows: the molar ratio of 1:1 between ethanol and water, the reaction temperature of 190°C, and the reaction time of 24 h.

  17. Effects on focused ion beam irradiation on MOS transistors

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, A.N.; Peterson, K.A.; Fleetwood, D.M.; Soden, J.M.

    1997-04-01

    The effects of irradiation from a focused ion beam (FIB) system on MOS transistors are reported systematically for the first time. Three MOS transistor technologies, with 0.5, 1, and 3 {mu}m minimum feature sizes and with gate oxide thicknesses ranging from 11 to 50 nm, were analyzed. Significant shifts in transistor parameters (such as threshold voltage, transconductance, and mobility) were observed following irradiation with a 30 keV Ga{sup +} focused ion beam with ion doses varying by over 5 orders of magnitude. The apparent damage mechanism (which involved the creation of interface traps, oxide trapped charge, or both) and extent of damage were different for each of the three technologies investigated.

  18. Microwave irradiation induced band gap tuning of MoS2-TiO2 nanocomposites

    Science.gov (United States)

    Shakya, Jyoti; Mohanty, T.

    2016-05-01

    The MoS2-TiO2 nanocomposites have been synthesized by sol-gel method and characterized by different microscopic and spectroscopic techniques. The crystallinity of these nanocomposites has been confirmed by X-ray diffraction (XRD) analysis. The Raman spectrum of MoS2-TiO2 nanocomposites consists of three distinct peaks (E1 g, E1 2g and A1g) which are associated with TiO2 and MoS2. The morphological study is carried out by scanning electron microscope. The effect of microwave irradiation on the band gap of MoS2-TiO2 nanocomposites has been investigated; it is observed that the microwave irradiation causes decrease in the band gap of MoS2-TiO2 nanocomposites. The microwave treated MoS2-TiO2 thin films offers a novel process route in treating thin films for commercial applications.

  19. Enhancement mode AlGaN/GaN MOS high-electron-mobility transistors with ZrO2 gate dielectric deposited by atomic layer deposition

    Science.gov (United States)

    Anderson, Travis J.; Wheeler, Virginia D.; Shahin, David I.; Tadjer, Marko J.; Koehler, Andrew D.; Hobart, Karl D.; Christou, Aris; Kub, Francis J.; Eddy, Charles R., Jr.

    2016-07-01

    Advanced applications of AlGaN/GaN high-electron-mobility transistors (HEMTs) in high-power RF and power switching are driving the need for insulated gate technology. We present a metal-oxide-semiconductor (MOS) gate structure using atomic-layer-deposited ZrO2 as a high-k, high-breakdown gate dielectric for reduced gate leakage and a recessed barrier structure for enhancement mode operation. Compared to a Schottky metal-gate HEMT, the recessed MOS-HEMT structure demonstrated a reduction in the gate leakage current by 4 orders of magnitude and a threshold voltage shift of +6 V to a record +3.99 V, enabled by a combination of a recessed barrier structure and negative oxide charge.

  20. Micro-irradiation experiments in MOS transistors using synchrotron radiation

    International Nuclear Information System (INIS)

    Spatially-resolved total-dose degradation has been performed in MOS transistors by focusing x-ray synchrotron radiation on the gate electrode with micrometer resolution. The influence of the resulting permanent degradation on device electrical properties has been analyzed using current-voltage and charge pumping measurements, in concert with optical characterization (hot-carrier luminescence) and one-dimensional device simulation. (authors)

  1. Unusual reactivity of MoS2 nanosheets

    Science.gov (United States)

    Mondal, Biswajit; Som, Anirban; Chakraborty, Indranath; Baksi, Ananya; Sarkar, Depanjan; Pradeep, Thalappil

    2016-05-01

    The reactivity of the 2D nanosheets of MoS2 with silver ions in solution, leading to their spontaneous morphological and chemical transformations, is reported. This unique reactivity of the nanoscale form of MoS2 was in stark contrast to its bulk counterpart. While the gradual morphological transformation involving several steps has been captured with an electron microscope, precise chemical identification of the species involved was achieved by electron spectroscopy and mass spectrometry. The energetics of the system investigated supports the observed chemical transformation. The reaction with mercury and gold ions shows similar and dissimilar reaction products, respectively and points to the stability of the metal-sulphur bond in determining the chemical compositions of the final products.The reactivity of the 2D nanosheets of MoS2 with silver ions in solution, leading to their spontaneous morphological and chemical transformations, is reported. This unique reactivity of the nanoscale form of MoS2 was in stark contrast to its bulk counterpart. While the gradual morphological transformation involving several steps has been captured with an electron microscope, precise chemical identification of the species involved was achieved by electron spectroscopy and mass spectrometry. The energetics of the system investigated supports the observed chemical transformation. The reaction with mercury and gold ions shows similar and dissimilar reaction products, respectively and points to the stability of the metal-sulphur bond in determining the chemical compositions of the final products. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00878j

  2. MOS PARAMETER EXTRACTION AND OPTIMIZATION WITH GENETIC ALGORITHM

    OpenAIRE

    BAŞAK, M.Emin; KUNTMAN, Ayten; Kuntman, Hakan

    2010-01-01

    Extracting an optimal set of parameter values for a MOS device is great importance in contemporary technology is acomplex problem. Traditional methods of parameter extraction can produce far from optimal solutions because of thepresence of local optimum in the solution space. Genetic algorithms are well suited for finding near optimal solutions inirregular parameter spaces.In this study*, We have applied a genetic algorithm to the problem of device model parameter extraction and are able topr...

  3. Results of the verification of the NIR MOS EMIR

    Science.gov (United States)

    Garzón, F.; Castro-Rodríguez, N.; Insausti, M.; López-Martín, L.; Hammersley, Peter; Barreto, M.; Fernández, P.; Joven, E.; López, P.; Mato, A.; Moreno, H.; Núñez, M.; Patrón, J.; Rasilla, J. L.; Redondo, P.; Rosich, J.; Pascual, S.; Grange, R.

    2014-07-01

    EMIR is one of the first common user instruments for the GTC, the 10 meter telescope operating at the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofísica de Canarias (IAC). EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 μm. This contribution reports on the results achieved so far during the verification phase at the IAC prior to its shipment to the GTC for being commissioned, which is due by mid 2015. After a long period of design and fabrication, EMIR finally entered into its integration phase by mid 2013. Soon after this, the verification phase at the IAC was initiated aimed at configuring and tuning the EMIR functions, mostly the instrument control system, which includes a sophisticated on line data reduction pipeline, and demonstrating the fulfillment of the top level requirements. We have designed an ambitious verification plan structured along the three kind of detectors at hand: the MUX and the engineering and scientific grade arrays. The EMIR subsystems are being integrated as they are needed for the purposes of the verification plan. In the first stage, using the MUX, the full optical system, but with a single dispersive element out of the three which form the EMIR suite, the two large wheels mounting the filters and the pseudo-grisms, plus the detector translation unit holding the MUX, were mounted. This stage was mainly devoted to learn about the capabilities of the instrument, define different settings for its basic operation modes and test the accuracy, repeatability and reliability of the mechanisms. In the second stage, using the engineering Hawaii2 FPA, the full set of pseudo-grisms and band filters are mounted, which means that the instrument is fully assembled

  4. Electrical Transport Properties of Polymorphic MoS2.

    Science.gov (United States)

    Kim, Jun Suk; Kim, Jaesu; Zhao, Jiong; Kim, Sungho; Lee, Jin Hee; Jin, Youngjo; Choi, Homin; Moon, Byoung Hee; Bae, Jung Jun; Lee, Young Hee; Lim, Seong Chu

    2016-08-23

    The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2 is locally converted into metallic 1T-MoS2 through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T' phases coexisting in Li-treated MoS2, which result in unusual transport phenomena. Although multiphase MoS2 shows no transistor-gating response, the channel resistance decreases in proportion to the temperature, similar to the behavior of a typical semiconductor. Transmission electron microscopy images clearly show that the 1T and 1T' phases are randomly distributed and intervened with 2H-MoS2, which is referred to as the 1T and 1T' puddling phenomenon. The resistance curve fits well with 2D-variable range-hopping transport behavior, where electrons hop over 1T domains that are bounded by semiconducting 2H phases. However, near 30 K, electrons hop over charge puddles. The large temperature coefficient of resistance (TCR) of multiphase MoS2, -2.0 × 10(-2) K(-1) at 300 K, allows for efficient IR detection at room temperature by means of the photothermal effect.

  5. Monolayer MoS2 self-switching diodes

    International Nuclear Information System (INIS)

    This paper presents a new molybdenum disulphide (MoS2) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70

  6. Monolayer MoS2 self-switching diodes

    Science.gov (United States)

    Al-Dirini, Feras; Hossain, Faruque M.; Mohammed, Mahmood A.; Hossain, Md Sharafat; Nirmalathas, Ampalavanapillai; Skafidas, Efstratios

    2016-01-01

    This paper presents a new molybdenum disulphide (MoS2) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.

  7. Electrical Transport Properties of Polymorphic MoS2.

    Science.gov (United States)

    Kim, Jun Suk; Kim, Jaesu; Zhao, Jiong; Kim, Sungho; Lee, Jin Hee; Jin, Youngjo; Choi, Homin; Moon, Byoung Hee; Bae, Jung Jun; Lee, Young Hee; Lim, Seong Chu

    2016-08-23

    The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2 is locally converted into metallic 1T-MoS2 through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T' phases coexisting in Li-treated MoS2, which result in unusual transport phenomena. Although multiphase MoS2 shows no transistor-gating response, the channel resistance decreases in proportion to the temperature, similar to the behavior of a typical semiconductor. Transmission electron microscopy images clearly show that the 1T and 1T' phases are randomly distributed and intervened with 2H-MoS2, which is referred to as the 1T and 1T' puddling phenomenon. The resistance curve fits well with 2D-variable range-hopping transport behavior, where electrons hop over 1T domains that are bounded by semiconducting 2H phases. However, near 30 K, electrons hop over charge puddles. The large temperature coefficient of resistance (TCR) of multiphase MoS2, -2.0 × 10(-2) K(-1) at 300 K, allows for efficient IR detection at room temperature by means of the photothermal effect. PMID:27399325

  8. c-Mos forces the mitotic cell cycle to undergo meiosis II to produce haploid gametes

    OpenAIRE

    Tachibana, Kazunori; Tanaka, Daisuke; Isobe, Tomohiro; Kishimoto, Takeo

    2000-01-01

    The meiotic cycle reduces ploidy through two consecutive M phases, meiosis I and meiosis II, without an intervening S phase. To maintain ploidy through successive generations, meiosis must be followed by mitosis after the recovery of diploidy by fertilization. However, the coordination from meiotic to mitotic cycle is still unclear. Mos, the c-mos protooncogene product, is a key regulator of meiosis in vertebrates. In contrast to the previous observation that Mos f...

  9. Magnetic MoS2 pizzas and sandwiches with Mnn (n = 1-4) cluster toppings and fillings: A first-principles investigation.

    Science.gov (United States)

    Zhang, Meng; Huang, Zhongjia; Wang, Xiao; Zhang, Hongyu; Li, Taohai; Wu, Zhaolong; Luo, Youhua; Cao, Wei

    2016-01-01

    The inorganic layered crystal (ILC) MoS2 in low dimensions is considered as one of the most promising and efficient semiconductors. To enable the magnetism and keep intrinsic crystal structures, we carried out a first-principles study of the magnetic and semiconductive monolayer MoS2 adsorbed with the Mnn (n = 1-4) clusters, and bilayer MoS2 intercalated with the same clusters. Geometric optimizations of the Mnn@MoS2 systems show the complexes prefer to have Mnn@MoS2(M) pizza and Mnn@MoS2(B) sandwich forms in the mono- and bi-layered cases, respectively. Introductions of the clusters will enhance complex stabilities, while bonds and charge transfers are found between external Mn clusters and the S atoms in the hosts. The pizzas have medium magnetic moments of 3, 6, 9, 4 μB and sandwiches of 3, 2, 3, 2 μB following the manganese numbers. The pizzas and sandwiches are semiconductors, but with narrower bandgaps compared to their corresponding pristine hosts. Direct bandgaps were found in the Mnn@MoS2(M) (n = 1,4) pizzas, and excitingly in the Mn1@MoS2(B) sandwich. Combining functional clusters to the layered hosts, the present work shows a novel material manipulation strategy to boost semiconductive ILCs applications in magnetics.

  10. Effect of processing parameters on microstructure of MoS2 ultra-thin films synthesized by chemical vapor deposition method

    Directory of Open Access Journals (Sweden)

    Yang Song

    2015-06-01

    Full Text Available MoS2 ultra-thin layers are synthesized using a chemical vapor deposition method based on the sulfurization of molybdenum trioxide (MoO3. The ultra-thin layers are characterized by X-ray diffraction (XRD, photoluminescence (PL spectroscopy and atomic force microscope (AFM. Based on our experimental results, all the processing parameters, such as the tilt angle of substrate, applied voltage, heating time and the weight of source materials have effect on the microstructures of the layers. In this paper, the effects of such processing parameters on the crystal structures and morphologies of the as-grown layers are studied. It is found that the film obtained with the tilt angle of 0.06° is more uniform. A larger applied voltage is preferred to the growth of MoS2 thin films at a certain heating time. In order to obtain the ultra-thin layers of MoS2, the weight of 0.003 g of source materials is preferred. Under our optimal experimental conditions, the surface of the film is smooth and composed of many uniformly distributed and aggregated particles, and the ultra-thin MoS2 atomic layers (1∼10 layers covers an area of more than 2 mm×2 mm.

  11. Simultaneous Hosting of Positive and Negative Trions and the Enhanced Direct Band Emission in MoSe2/MoS2 Heterostacked Multilayers.

    Science.gov (United States)

    Kim, Min Su; Seo, Changwon; Kim, Hyun; Lee, Jubok; Luong, Dinh Hoa; Park, Ji-Hoon; Han, Gang Hee; Kim, Jeongyong

    2016-06-28

    Heterostacking of layered transition-metal dichalcogenide (LTMD) monolayers (1Ls) offers a convenient way of designing two-dimensional exciton systems. Here we demonstrate the simultaneous hosting of positive trions and negative trions in heterobilayers made by vertically stacking 1L MoSe2 and 1L MoS2. The charge transfer occurring between the 1Ls of MoSe2 and MoS2 converted the polarity of trions in 1L MoSe2 from negative to positive, resulting in the presence of positive trions in the 1L MoSe2 and negative trions in the 1L MoS2 of the same heterostacked bilayer. Significantly enhanced MoSe2 photoluminescence (PL) in the heterostacked bilayers compared to the PL of 1L MoSe2 alone suggests that, unlike other previously reported heterostacked bilayers, direct band transition of 1L MoSe2 in heterobilayer was enhanced after the vertical heterostacking. Moreover, by inserting hexagonal BN monolayers between 1L MoSe2 and 1L MoS2, we were able to adjust the charge transfer to maximize the MoSe2 PL of the heteromultilayers and have achieved a 9-fold increase of the PL emission. The enhanced optical properties of our heterostacked LTMDs suggest the exciting possibility of designing LTMD structures that exploit the superior optical properties of 1L LTMDs. PMID:27187667

  12. Flower-like N-doped MoS2 for photocatalytic degradation of RhB by visible light irradiation

    Science.gov (United States)

    Liu, Peitao; Liu, Yonggang; Ye, Weichun; Ma, Ji; Gao, Daqiang

    2016-06-01

    In this paper, the photocatalytic performance and reusability of N-doped MoS2 nanoflowers with the specific surface area of 114.2 m2 g‑1 was evaluated by discoloring of RhB under visible light irradiation. Results indicated that the 20 mg fabricated catalyst could completely degrade 50 ml of 30 mg l‑1 RhB in 70 min with excellent recycling and structural stability. The optimized N-doped MoS2 nanoflowers showed a reaction rate constant (k) as high as 0.06928 min‑1 which was 26.4 times that of bare MoS2 nanosheets (k = 0.00262). In addition, it was about seven times that of P25 (k = 0.01) (Hou et al 2015 Sci. Rep. 5 15228). The obtained outstanding photocatalytic performance of N-doped MoS2 nanoflowers provides potential applications in water pollution treatment, as well as other related fields.

  13. Potential application of mono/bi-layer molybdenum disulfide (MoS2) sheet as an efficient transparent conducting electrode in silicon heterojunction solar cells

    Science.gov (United States)

    Chaudhary, Rimjhim; Patel, Kamlesh; Sinha, Ravindra K.; Kumar, Sanjeev; Tyagi, Pawan K.

    2016-07-01

    In this paper, we have simulated the structure of n-type MoS2/silicon heterojunction solar cell and studied its function under different conditions. The optimization of parameters of the cell's layer has been carried out by using AFORS-HET software. In the present study, MoS2 has been considered as 3-D in nature instead of the reported 2-D nature. In order to ensure the formation of Schottky junction, electric contact has been made along the c-axis to collect the minority charge carriers. After optimizing the various parameters of n-type single layer MoS2, power efficiency of 12.44% has been achieved at the room temperature, which has further decreased to 9.042% as the layer number has increased up to 40. Furthermore, after optimizing the parameters of silicon wafer maximum efficiency of 16.4% has been achieved. Temperature dependence of the cell performance has also been studied and the maximum efficiency has been achieved at 300 K. In the present study, we have demonstrated that n-type ultrathin layer of MoS2 can be used as an excellent transparent conducting electrode.

  14. Magnetic MoS2 pizzas and sandwiches with Mnn (n = 1-4) cluster toppings and fillings: A first-principles investigation

    Science.gov (United States)

    Zhang, Meng; Huang, Zhongjia; Wang, Xiao; Zhang, Hongyu; Li, Taohai; Wu, Zhaolong; Luo, Youhua; Cao, Wei

    2016-01-01

    The inorganic layered crystal (ILC) MoS2 in low dimensions is considered as one of the most promising and efficient semiconductors. To enable the magnetism and keep intrinsic crystal structures, we carried out a first-principles study of the magnetic and semiconductive monolayer MoS2 adsorbed with the Mnn (n = 1-4) clusters, and bilayer MoS2 intercalated with the same clusters. Geometric optimizations of the Mnn@MoS2 systems show the complexes prefer to have Mnn@MoS2(M) pizza and Mnn@MoS2(B) sandwich forms in the mono- and bi-layered cases, respectively. Introductions of the clusters will enhance complex stabilities, while bonds and charge transfers are found between external Mn clusters and the S atoms in the hosts. The pizzas have medium magnetic moments of 3, 6, 9, 4 μB and sandwiches of 3, 2, 3, 2 μB following the manganese numbers. The pizzas and sandwiches are semiconductors, but with narrower bandgaps compared to their corresponding pristine hosts. Direct bandgaps were found in the Mnn@MoS2(M) (n = 1,4) pizzas, and excitingly in the Mn1@MoS2(B) sandwich. Combining functional clusters to the layered hosts, the present work shows a novel material manipulation strategy to boost semiconductive ILCs applications in magnetics.

  15. Solvent-Assisted Oxygen Incorporation of Vertically Aligned MoS2 Ultrathin Nanosheets Decorated on Reduced Graphene Oxide for Improved Electrocatalytic Hydrogen Evolution.

    Science.gov (United States)

    Liu, Aiping; Zhao, Li; Zhang, Junma; Lin, Liangxu; Wu, Huaping

    2016-09-28

    Three-dimensional oxygen-incorporated MoS2 ultrathin nanosheets decorated on reduced graphene oxide (O-MoS2/rGO) had been successfully fabricated through a facile solvent-assisted hydrothermal method. The origin of the incorporated oxygen and its incorporation mechanism into MoS2 were carefully investigated. We found that the solvent N,N-dimethylformamide (DMF) was the key as the reducing agent and the oxygen donor, expanding interlayer spaces and improving intrinsic conductivity of MoS2 sheets (modulating its electronic structure and vertical edge sites). These O dopants, vertically aligned edges and decoration with rGO gave effectively improved double-layer capacitance and catalytic performance for hydrogen evolution reaction (HER) of MoS2. The prepared O-MoS2/rGO catalysts showed an exceptional small Tafel slope of 40 mV/decade, a high current density of 20 mA/cm(2) at the overpotential of 200 mV and remarkable stability even after 2000th continuous HER test in the acid media.

  16. Cross-Calibration of the XMM-Newton EPIC pn & MOS On-Axis Effective Areas Using 2XMM Sources

    OpenAIRE

    Read, A. M.; Guainazzi, M.; Sembay, S.

    2014-01-01

    We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a sample of 46 bright, high-count, non-piled-up isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) ...

  17. Hierarchical MoS2 nanosheet/active carbon fiber cloth as a binder-free and free-standing anode for lithium-ion batteries.

    Science.gov (United States)

    Wang, Chao; Wan, Wang; Huang, Yunhui; Chen, Jitao; Zhou, Heng Hui; Zhang, Xin Xiang

    2014-05-21

    Owing to the layered structure and high theoretical capacity, MoS2 has attracted more and more interest as a potential anode material for lithium-ion batteries. However, it suffers from rapid capacity decay and low rate capability. In this work, we introduce a novel hierarchical material consisting of ultrathin MoS2 nanosheets grown on the surface of an active carbon fiber (ACF) cloth fabricated by a facile morphogenetic process. The ACF cloth acts as both a template and a stabilizer. The obtained MoS2/ACF cloth composite possesses hierarchical porosity and an interconnected framework. Serving as a free-standing and binder-free anode, it shows high specific capacity and excellent reversibility. A discharge capacity as high as 971 mA h g(-1) is attained at a current density of 0.1 A g(-1), and the capacity fade is only 0.15% per cycle within 90 cycles. Even after 200 cycles at a high current density of 0.5 A g(-1), the composite still shows a capacity of 418 mA h g(-1). The superior electrochemical performance of MoS2/ACF can be attributed to its robust structure and to the synergistic effects of ultrathin MoS2 nanosheets and ACF. This single-component anode that we propose benefits from a simplified electrode preparation process. The morphogenetic strategy used for the material production is facile but effective, and can be extended to prepare other metal sulfides with elaborate textural characteristics.

  18. Molecular beam epitaxy of the van der Waals heterostructure MoTe2 on MoS2: phase, thermal, and chemical stability

    Science.gov (United States)

    Coy Diaz, Horacio; Chaghi, Redhouane; Ma, Yujing; Batzill, Matthias

    2015-12-01

    (Sub)monolayer MoTe2 is grown by molecular beam epitaxy on a bulk MoS2 substrate. The film morphology, the thermally induced transformation of structural and compositional phases, as well as the chemical stability upon exposure to atmosphere are investigated by scanning tunneling microscopy and photoemission spectroscopy. Predominantly, semiconducting α-MoTe2 islands are obtained under tellurium rich growth conditions and a substrate temperature of 200 °C. Under less tellurium-rich conditions, elongated and meandering MoTe2-x strands are formed rather than compact islands. Similarly, annealing of initial α-MoTe2 islands to above 500 °C causes the loss of tellurium and possibly transformation into the same MoTe2-x strands. Consequently, under vacuum conditions the the transformation of α-MoTe2 monolayers into the semimetallic β -MoTe2 high temperature phase is accompanied by a loss of Te and formation of MoTe2-x phase. The obtained tellurium deficient MoTe2-x phase is almost metallic but a small band gap of a few tens meV remains. The as-grown α-MoTe2 islands exhibit a moiré structure with ˜2.6 nm periodicity. This periodicity implies a rotation of ˜56° between the MoTe2 and MoS2. We assign the observation of a specific rotation angle for the grown MoTe2 islands with respect to the MoS2 substrate to the lowest energy adsorption configuration for MoTe2 monolayers on MoS2 substrates. Exposure of the as grown films to atmosphere results in oxidation of the MoTe2 film. The oxidized film maintains the two-dimensional island morphology of the initial film and thus is a candidate for a 2D (amorphous) oxide layer on MoS2.

  19. Identification of Active Edge Sites for Electrochemical H2 Evolution from MoS2 Nanocatalysts

    DEFF Research Database (Denmark)

    Jaramillo, Thomas; Jørgensen, Kristina Pilt; Bonde, Jacob;

    2007-01-01

    The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically...... resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy....... Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst....

  20. Density functional theory calculation of edge stresses in monolayer MoS2

    Science.gov (United States)

    Qi, Zenan; Cao, Penghui; Park, Harold S.

    2013-10-01

    We utilize density functional theory to calculate the edge energy and edge stress for monolayer MoS2 nanoribbons. In contrast to previous reports for graphene, for both armchair and zigzag chiralities, the edge stresses for MoS2 nanoribbons are found to be tensile, indicating that their lowest energy configuration is one of compression in which Mo-S bond lengths are shorter than those in a bulk, periodic MoS2 monolayer. The edge energy and edge stress is found to converge for both chiralities for nanoribbon widths larger than about 1 nm.

  1. Controlling the Spontaneous Emission Rate of Monolayer MoS$_2$ in a Photonic Crystal Nanocavity

    CERN Document Server

    Gan, Xuetao; Mak, Kin Fai; Yao, Xinwen; Shiue, Ren-Jye; van der Zande, Arend; Trusheim, Matthew; Hatami, Fariba; Heinz, Tony F; Hone, James; Englund, Dirk

    2013-01-01

    We report on controlling the spontaneous emission (SE) rate of a molybdenum disulfide (MoS$_2$) monolayer coupled with a planar photonic crystal (PPC) nanocavity. Spatially resolved photoluminescence (PL) mapping shows strong variations of emission when the MoS$_2$ monolayer is on the PPC cavity, on the PPC lattice, on the air gap, and on the unpatterned gallium phosphide substrate. Polarization dependences of the cavity-coupled MoS$_2$ emission show a more than 5 times stronger extracted PL intensity than the un-coupled emission, which indicates an underlying cavity mode Purcell enhancement of MoS$_2$ SE rate exceeding a factor of 70.

  2. Towards intrinsic phonon transport in single-layer MoS2

    Science.gov (United States)

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuanfeng; Zhang, Xiangchao; Zhu, Heyuan

    2016-06-01

    The intrinsic lattice thermal conductivity of MoS$_2$ is an important aspect in the design of MoS$_2$-based nanoelectronic devices. We investigate the lattice dynamics properties of MoS$_2$ by first principles calculations. The intrinsic thermal conductivity of single-layer MoS$_2$ is calculated using the Boltzmann transport equation for phonons. The obtained thermal conductivity agrees well with the measurements. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. The size dependence of thermal conductivity is investigated as well.

  3. Photothermoelectric and photovoltaic effects both present in MoS2

    Science.gov (United States)

    Zhang, Youwei; Li, Hui; Wang, Lu; Wang, Haomin; Xie, Xiaomin; Zhang, Shi-Li; Liu, Ran; Qiu, Zhi-Jun

    2015-01-01

    As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

  4. Self-Assembly-Induced Alternately Stacked Single-Layer MoS2 and N-doped Graphene: A Novel van der Waals Heterostructure for Lithium-Ion Batteries.

    Science.gov (United States)

    Zhao, Chenyang; Wang, Xu; Kong, Junhua; Ang, Jia Ming; Lee, Pooi See; Liu, Zhaolin; Lu, Xuehong

    2016-01-27

    In this article, a simple self-assembly strategy for fabricating van der Waals heterostructures from isolated two-dimensional atomic crystals is presented. Specifically, dopamine (DOPA), an excellent self-assembly agent and carbon precursor, was adsorbed on exfoliated MoS2 monolayers through electrostatic interaction, and the surface-modified monolayers self-assembled spontaneously into DOPA-intercalated MoS2. The subsequent in situ conversion of DOPA to highly conductive nitrogen-doped graphene (NDG) in the interlayer space of MoS2 led to the formation of a novel NDG/MoS2 nanocomposite with well-defined alternating structure. The NDG/MoS2 was then studied as an anode for lithium-ion batteries (LIBs). The results show that alternating arrangement of NDG and MoS2 triggers synergistic effect between the two components. The kinetics and cycle life of the anode are greatly improved due to the enhanced electron and Li(+) transport as well as the effective immobilization of soluble polysulfide by NDG. A reversible capacity of more than 460 mAh/g could be delivered even at 5 A/g. Moreover, the abundant voids created at the MoS2-NDG interface also accommodate the volume change during cycling and provide additional active sites for Li(+) storage. These endow the NDG/MoS2 heterostructure with low charge-transfer resistance, high sulfur reservation, and structural robustness, rendering it an advanced anode material for LIBs.

  5. Cross-Calibration of the XMM-Newton EPIC pn & MOS On-Axis Effective Areas Using 2XMM Sources

    CERN Document Server

    Read, A M; Sembay, S

    2014-01-01

    We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a sample of 46 bright, high-count, non-piled-up isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) and 0-3% (MOS2/pn). Above 3 keV, the MOS/pn ratio is consistent with energy-independent (or only mildly increasing) excesses of 7-8% (MOS1/pn) and 5-8% (MOS2/pn). In addition, between 1-2 keV there is a `silicon bump' - an enhancement at a level of 2-4% (MOS1/pn) and 3-5% (MOS2/pn). Tests suggest that the methods employed here are stable and robust. The results presented here provide the most accurate cross-calibration of the effective areas of the XMM-Newton EPIC pn and MOS instruments to date. They suggest areas of furt...

  6. First-principle study of hydrogenation on monolayer MoS2

    Science.gov (United States)

    Xu, Yong; Li, Yin; Chen, Xi; Zhang, Chunfang; Zhang, Ru; Lu, Pengfei

    2016-07-01

    The structural and electronic properties of hydrogenation on 1H-MoS2 and 1T-MoS2 have been systematically explored by using density functional theory (DFT) calculations. Our calculated results indicate an energetically favorable chemical interaction between H and MoS2 monolayer for H adsorption when increasing concentration of H atoms. For 1H-MoS2, single H atom adsorption creates midgap approaching the fermi level which increases the n-type carrier concentration effectively. As a consequence, its electrical conductivity is expected to increase significantly. For 1T-MoS2, H atoms adsorption can lead to the opening of a direct gap of 0.13eV compared to the metallic pristine 1T-MoS2.

  7. Hybrid MOS-PN photodiode with positive feedback for pulse-modulation imaging.

    Science.gov (United States)

    Sallin, Denis; Koukab, Adil; Kayal, Maher

    2014-06-16

    A new type of CMOS compatible photodetector, exhibiting intrinsic light-to-time conversion, is proposed. Its main objective is to start the time-to-digital conversion directly at its output, thereby avoiding the cumbersome analog processing. The operation starts with an internal charge integration, followed by a positive feedback, and a sharp switching-current. The device, consisting of a deeply depleted MOS structure controlling the conduction of a forward-based PN diode, is presented and its operation explained. TCAD simulations are used to show the effects of semiconductor parameters and bias conditions. The photodetector and its detection circuit are designed and fabricated in a 0.18µm CMOS process. Measurements of this new device under different biasing and illumination conditions show highly promising properties in terms of linearity, internal gain, and noise performances.

  8. Giant valley drifts in uniaxially strained monolayer MoS2

    KAUST Repository

    Zhang, Qingyun

    2013-12-30

    Using first-principles calculations, we study the electronic structure of monolayer MoS2 under uniaxial strain. We show that the energy valleys drift far off the corners of the Brillouin zone (K points), about 12 times the amount observed in graphene. Therefore, it is essential to take this effect into consideration for a correct identification of the band gap. The system remains a direct band gap semiconductor up to 4% uniaxial strain, while the size of the band gap decreases from 1.73 to 1.54 eV. We also demonstrate that the splitting of the valence bands due to inversion symmetry breaking and spin-orbit coupling is not sensitive to strain.

  9. Hydrogenation-induced edge magnetization in armchair MoS2 nanoribbon and electric field effects

    Science.gov (United States)

    Ouyang, Fangping; Yang, Zhixiong; Ni, Xiang; Wu, Nannan; Chen, Yu; Xiong, Xiang

    2014-02-01

    We performed density functional theory study on the electronic and magnetic properties of armchair MoS2 nanoribbons (AMoS2NR) with different edge hydrogenation. Although bare and fully passivated AMoS2NRs are nonmagnetic semiconductors, it was found that hydrogenation in certain patterns can induce localized ferromagnetic edge state in AMoS2NRs and make AMoS2NRs become antiferromagnetic semiconductors or ferromagnetic semiconductors. Electric field effects on the bandgap and magnetic moment of AMoS2NRs were investigated. Partial edge hydrogenation can change a small-sized AMoS2NR from semiconductor to metal or semimetal under a moderate transverse electric field. Since the rate of edge hydrogenation can be controlled experimentally via the temperature, pressure and concentration of H2, our results suggest edge hydrogenation is a useful method to engineer the band structure of AMoS2NRs.

  10. Reaction mechanism of core–shell MoO2/MoS2 nanoflakes via plasma-assisted sulfurization of MoO3

    Science.gov (United States)

    Kumar, Prabhat; Singh, Megha; Sharma, Rabindar K.; Reddy, G. B.

    2016-05-01

    The sulfurization of MoO3 in an H2S/Ar plasma atmosphere has been experimentally studied and a reaction mechanism has been proposed based on the results obtained. Nanostructured thin films (NTFs) of MoO3 were sulfurized at different temperatures varying from 150 °C to 550 °C. High-resolution transmission electron microscopy (TEM) images depict core–shell nanoflakes with varying shell thicknesses as the sulfurization temperature (T sn) is varied. The shells consist of MoS2 and the core is MoO2/MoO3. X-ray diffraction (XRD) and Raman analysis have been used to study the structural changes as MoO3 is sulfurized. The analyses showed two phases, MoO2 and MoS2, at low temperatures (≤350 °C), whereas the films sulfurized at higher temperatures show predominantly MoS2. The scanning electron microscopy (SEM) results show no noticeable changes in the surface morphology of the NTFs after sulfurization. X-ray photoelectron spectroscopy (XPS) was carried out to calculate the relative percentages of MoO3, MoO2 and MoS2. It is revealed that sulfurization of MoO3 in the plasma is affected by T sn. The sulfurization process occurs in two steps, involving the reduction of MoO3 to form MoO2 in the first step, followed by MoO2 being converted into MoS2. It is also evident that the reduction of MoO3 is more a result of the reactive species of hydrogen (H*) than the replacement of oxygen by sulfur in the second step.

  11. Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors

    Directory of Open Access Journals (Sweden)

    Ji Heon Kim

    2016-06-01

    Full Text Available We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ∼107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ∼10 to ∼18 cm2V−1s−1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

  12. Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors

    Science.gov (United States)

    Kim, Ji Heon; Kim, Tae Ho; Lee, Hyunjea; Park, Young Ran; Choi, Woong; Lee, Cheol Jin

    2016-06-01

    We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ˜107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ˜10 to ˜18 cm2V-1s-1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

  13. Efficient exfoliation of MoS2 with volatile solvents and their application for humidity sensor. .

    Science.gov (United States)

    Zhang, Shao-Lin; Jung, Hyun; Huh, Jeung-Soo; Yu, Joon-Boo; Yang, Woo-Chul

    2014-11-01

    Liquid-phase exfoliation is likely to be feasible for practical fabrication of few-layer MoS2 nanosheets in large quantities. However, this method generally involves the organic solvents with high boiling point; new strategy using low-boiling-point solvents to obtain high MoS2 concentration is still highly required. In this study, using the strategy of Hansen solubility parameters (HSP), a method based on exfoliation of MoS2 in chloroform/acetonitrile mixtures is demonstrated to fabricate high concentration MoS2 nanosheet solution. The highest concentration of few-layer MoS2 nanosheets and nanoparticles up to 0.4 mg/ml is achieved with the optimum composition of mixture. The MoS2 nanosheet thin film is also investigated in terms of their sensing properties towards humidity. The exfoliated MoS2 based thin film sensor exhibited excellent sensitivity, quick response and recovery, and good reproducibility comparing to their bulk counterpart. The excellent sensing performance of exfoliated MoS2 is generally attributed to the high surface-to-volume-ratio and increased ratio of edge sites and basal plane sites after exfoliation. PMID:25958556

  14. Tunable volatile organic compounds sensor by using thiolated ligand conjugation on MoS2.

    Science.gov (United States)

    Kim, Jong-Seon; Yoo, Hae-Wook; Choi, Hyung Ouk; Jung, Hee-Tae

    2014-10-01

    One of the most important issues in the development of gas sensors for breath analysis is the fabrication of gas sensor arrays that possess different responses for recognizing patterns for volatile organic compounds (VOCs). Here, we develop a high-performance chemiresistor with a tunable sensor response and high sensitivity for representative VOC groups by using molybdenum disulfide (MoS2) and by conjugating a thiolated ligand (mercaptoundecanoic acid (MUA)) to MoS2 surface. Primitive and MUA-conjugated MoS2 sensing channels exhibit distinctly different sensor responses toward VOCs. In particular, the primitive MoS2 sensor presents positive responses for oxygen-functionalized VOCs, while the MUA-conjugated MoS2 sensor presents negative responses for the same analytes. Such characteristic sensor responses demonstrate that ligand conjugation successfully adds functionality to a MoS2 matrix. Thus, this will be a promising approach to constructing a versatile sensor array, by conjugating a wide variety of thiolated ligands on the MoS2 surface. Furthermore, these MoS2 sensors in this study exhibit high sensitivity to representative VOCs down to a concentration of 1 ppm. This approach to fabricating a tunable and sensitive VOC sensor may lead to a valuable real-world application for lung cancer diagnosis by breath analysis. PMID:25191976

  15. Atomic-layer soft plasma etching of MoS2.

    Science.gov (United States)

    Xiao, Shaoqing; Xiao, Peng; Zhang, Xuecheng; Yan, Dawei; Gu, Xiaofeng; Qin, Fang; Ni, Zhenhua; Han, Zhao Jun; Ostrikov, Kostya Ken

    2016-01-01

    Transition from multi-layer to monolayer and sub-monolayer thickness leads to the many exotic properties and distinctive applications of two-dimensional (2D) MoS2. This transition requires atomic-layer-precision thinning of bulk MoS2 without damaging the remaining layers, which presently remains elusive. Here we report a soft, selective and high-throughput atomic-layer-precision etching of MoS2 in SF6 + N2 plasmas with low-energy (MoS2 layers are removed uniformly across domains with vastly different initial thickness, without affecting the underlying SiO2 substrate and the remaining MoS2 layers. The etching rates can be tuned to achieve complete MoS2 removal and any desired number of MoS2 layers including monolayer. Layer-dependent vibrational and photoluminescence spectra of the etched MoS2 are also demonstrated. This soft plasma etching technique is versatile, scalable, compatible with the semiconductor manufacturing processes, and may be applicable for a broader range of 2D materials and intended device applications.

  16. Mechanical properties of freely suspended semiconducting graphene-like layers based on MoS2

    NARCIS (Netherlands)

    Castellanos-Gomez, A.; Poot, M.; Steele, G.A.; Van der Zant, H.S.J.; Agrait, N.; Rubio-Bollinger, G.

    2012-01-01

    We fabricate freely suspended nanosheets of molybdenum disulphide (MoS2) which are characterized by quantitative optical microscopy and high-resolution friction force microscopy. We study the elastic deformation of freely suspended nanosheets of MoS2 using an atomic force microscope. The Young’s mod

  17. General Thermal Texturization Process of MoS2 for Efficient Electrocatalytic Hydrogen Evolution Reaction.

    Science.gov (United States)

    Kiriya, Daisuke; Lobaccaro, Peter; Nyein, Hnin Yin Yin; Taheri, Peyman; Hettick, Mark; Shiraki, Hiroshi; Sutter-Fella, Carolin M; Zhao, Peida; Gao, Wei; Maboudian, Roya; Ager, Joel W; Javey, Ali

    2016-07-13

    Molybdenum disulfide (MoS2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS2 because the pristine MoS2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is achieved through a simple thermal annealing procedure in a hydrogen environment, removing sulfur from the MoS2 surface to form edge sites. As a result, the process generates high HER catalytic performance in pristine MoS2 across various morphologies such as the bulk mineral, films composed of micron-scale flakes, and even films of a commercially available spray of nanoflake MoS2. The lowest overpotential (η) observed for these samples was η = 170 mV to obtain 10 mA/cm(2) of HER current density.

  18. Patterned Peeling 2D MoS2 off the Substrate.

    Science.gov (United States)

    Zhao, Jing; Yu, Hua; Chen, Wei; Yang, Rong; Zhu, Jianqi; Liao, Mengzhou; Shi, Dongxia; Zhang, Guangyu

    2016-07-01

    The performance of two-dimensional (2D) MoS2 devices depends largely on the quality of the MoS2 itself. Existing fabrication process for 2D MoS2 relies on lithography and etching. However, it is extremely difficult to achieve clean patterns without any contaminations or passivations. Here we report a peel-off pattering of MoS2 films on substrates based on a proper interface engineering. The peel-off process utilizes the strong adhesion between gold and MoS2 and removes the MoS2 film contact with gold directly, leading to clean MoS2 pattern generation without residuals. Significantly improved electrical performances including high mobility ∼17.1 ± 8.3 cm(2)/(V s) and on/off ratio ∼5.6 ± 3.6 × 10(6) were achieved. Such clean fabrication technique paves a way to high quality MoS2 devices for various electrical and optical applications.

  19. MOS current gain cells with electronically variable gain and constant bandwidth

    NARCIS (Netherlands)

    Klumperink, Eric A.M.; Seevinck, Evert

    1989-01-01

    Two MOS current gain cells are proposed that provide linear amplification of currents supplied by several linear MOS V-I converters. The gain is electronically variable by a voltage or a current and can be made insensitive to temperature and IC processing. The gain cells have a constant (gain-indepe

  20. MOS current gain cells with electronically variable gain and constant bandwidth

    OpenAIRE

    Klumperink, Eric A.M.; Seevinck, Evert

    1989-01-01

    Two MOS current gain cells are proposed that provide linear amplification of currents supplied by several linear MOS V-I converters. The gain is electronically variable by a voltage or a current and can be made insensitive to temperature and IC processing. The gain cells have a constant (gain-independent) bandwidth

  1. Patterned Peeling 2D MoS2 off the Substrate.

    Science.gov (United States)

    Zhao, Jing; Yu, Hua; Chen, Wei; Yang, Rong; Zhu, Jianqi; Liao, Mengzhou; Shi, Dongxia; Zhang, Guangyu

    2016-07-01

    The performance of two-dimensional (2D) MoS2 devices depends largely on the quality of the MoS2 itself. Existing fabrication process for 2D MoS2 relies on lithography and etching. However, it is extremely difficult to achieve clean patterns without any contaminations or passivations. Here we report a peel-off pattering of MoS2 films on substrates based on a proper interface engineering. The peel-off process utilizes the strong adhesion between gold and MoS2 and removes the MoS2 film contact with gold directly, leading to clean MoS2 pattern generation without residuals. Significantly improved electrical performances including high mobility ∼17.1 ± 8.3 cm(2)/(V s) and on/off ratio ∼5.6 ± 3.6 × 10(6) were achieved. Such clean fabrication technique paves a way to high quality MoS2 devices for various electrical and optical applications. PMID:27314173

  2. General Thermal Texturization Process of MoS2 for Efficient Electrocatalytic Hydrogen Evolution Reaction.

    Science.gov (United States)

    Kiriya, Daisuke; Lobaccaro, Peter; Nyein, Hnin Yin Yin; Taheri, Peyman; Hettick, Mark; Shiraki, Hiroshi; Sutter-Fella, Carolin M; Zhao, Peida; Gao, Wei; Maboudian, Roya; Ager, Joel W; Javey, Ali

    2016-07-13

    Molybdenum disulfide (MoS2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS2 because the pristine MoS2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is achieved through a simple thermal annealing procedure in a hydrogen environment, removing sulfur from the MoS2 surface to form edge sites. As a result, the process generates high HER catalytic performance in pristine MoS2 across various morphologies such as the bulk mineral, films composed of micron-scale flakes, and even films of a commercially available spray of nanoflake MoS2. The lowest overpotential (η) observed for these samples was η = 170 mV to obtain 10 mA/cm(2) of HER current density. PMID:27322506

  3. Mos1 transposon-based transformation of fish cell lines using baculoviral vectors

    Energy Technology Data Exchange (ETDEWEB)

    Yokoo, Masako [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Fujita, Ryosuke [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Innate Immunity Laboratory, Graduate School of Life Science and Creative Research Institution, Hokkaido University, Sapporo 001-0021 (Japan); Nakajima, Yumiko [Functional Genomics Group, COMB, Tropical Biosphere Research Center, University of the Ryukyus, Okinawa 903-0213 (Japan); Yoshimizu, Mamoru; Kasai, Hisae [Faculty of Fisheries Sciences, Hokkaido University, Hakodate 041-8611 (Japan); Asano, Shin-ichiro [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Bando, Hisanori, E-mail: hban@abs.agr.hokudai.ac.jp [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan)

    2013-09-13

    Highlights: •The baculovirus vector infiltrates the cells of economic important fishes. •Drosophila Mos1 transposase expressed in fish cells maintains its ability to localize to the nucleus. •The baculoviral vector carrying Mos1 is a useful tool to stably transform fish cells. -- Abstract: Drosophila Mos1 belongs to the mariner family of transposons, which are one of the most ubiquitous transposons among eukaryotes. We first determined nuclear transportation of the Drosophila Mos1-EGFP fusion protein in fish cell lines because it is required for a function of transposons. We next constructed recombinant baculoviral vectors harboring the Drosophila Mos1 transposon or marker genes located between Mos1 inverted repeats. The infectivity of the recombinant virus to fish cells was assessed by monitoring the expression of a fluorescent protein encoded in the viral genome. We detected transgene expression in CHSE-214, HINAE, and EPC cells, but not in GF or RTG-2 cells. In the co-infection assay of the Mos1-expressing virus and reporter gene-expressing virus, we successfully transformed CHSE-214 and HINAE cells. These results suggest that the combination of a baculovirus and Mos1 transposable element may be a tool for transgenesis in fish cells.

  4. Re-Engineering the Mission Operations System (MOS) for the Prime and Extended Mission

    Science.gov (United States)

    Hunt, Joseph C., Jr.; Cheng, Leo Y.

    2012-01-01

    One of the most challenging tasks in a space science mission is designing the Mission Operations System (MOS). Whereas the focus of the project is getting the spacecraft built and tested for launch, the mission operations engineers must build a system to carry out the science objectives. The completed MOS design is then formally assessed in the many reviews. Once a mission has completed the reviews, the Mission Operation System (MOS) design has been validated to the Functional Requirements and is ready for operations. The design was built based on heritage processes, new technology, and lessons learned from past experience. Furthermore, our operational concepts must be properly mapped to the mission design and science objectives. However, during the course of implementing the science objective in the operations phase after launch, the MOS experiences an evolutional change to adapt for actual performance characteristics. This drives the re-engineering of the MOS, because the MOS includes the flight and ground segments. Using the Spitzer mission as an example we demonstrate how the MOS design evolved for both the prime and extended mission to enhance the overall efficiency for science return. In our re-engineering process, we ensured that no requirements were violated or mission objectives compromised. In most cases, optimized performance across the MOS, including gains in science return as well as savings in the budget profile was achieved. Finally, we suggest a need to better categorize the Operations Phase (Phase E) in the NASA Life-Cycle Phases of Formulation and Implementation

  5. DNA base detection using a single-layer MoS2.

    Science.gov (United States)

    Farimani, Amir Barati; Min, Kyoungmin; Aluru, Narayana R

    2014-08-26

    Nanopore-based DNA sequencing has led to fast and high-resolution recognition and detection of DNA bases. Solid-state and biological nanopores have low signal-to-noise ratio (SNR) ( 5 nm) to be able to read at single-base resolution. A nanopore in graphene, a 2-D material with sub-nanometer thickness, has a SNR of ∼3 under DNA ionic current. In this report, using atomistic and quantum simulations, we find that a single-layer MoS2 is an extraordinary material (with a SNR > 15) for DNA sequencing by two competing technologies (i.e., nanopore and nanochannel). A MoS2 nanopore shows four distinct ionic current signals for single-nucleobase detection with low noise. In addition, a single-layer MoS2 shows a characteristic change/response in the total density of states for each base. The band gap of MoS2 is significantly changed compared to other nanomaterials (e.g., graphene, h-BN, and silicon nanowire) when bases are placed on top of the pristine MoS2 and armchair MoS2 nanoribbon, thus making MoS2 a promising material for base detection via transverse current tunneling measurement. MoS2 nanopore benefits from a craftable pore architecture (combination of Mo and S atoms at the edge) which can be engineered to obtain the optimum sequencing signals. PMID:25007098

  6. Exfoliated MoS2 in Water without Additives.

    Directory of Open Access Journals (Sweden)

    Viviane Forsberg

    Full Text Available Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2 in pure water at high concentration (i.e., 0.14 ± 0.01 g L-1. This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.

  7. Exfoliated MoS2 in Water without Additives

    Science.gov (United States)

    Forsberg, Viviane; Zhang, Renyun; Bäckström, Joakim; Dahlström, Christina; Andres, Britta; Norgren, Magnus; Andersson, Mattias; Hummelgård, Magnus; Olin, Håkan

    2016-01-01

    Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2) in pure water at high concentration (i.e., 0.14 ± 0.01 g L−1). This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable. PMID:27120098

  8. Layer-by-layer self-assembly of polyelectrolyte functionalized MoS2 nanosheets

    Science.gov (United States)

    Shen, Jianfeng; Pei, Yu; Dong, Pei; Ji, Jin; Cui, Zheng; Yuan, Junhua; Baines, Robert; Ajayan, Pulickel M.; Ye, Mingxin

    2016-05-01

    Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems.Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems. Electronic supplementary information (ESI) available: SEM, AFM and TEM characterization of PAA-MoS2 and PAM-MoS2 nanocomposites. More characterization and electrochemical properties of LBL films

  9. DAG Telescope: A New Potential for MOS Observations

    Science.gov (United States)

    Alis, S.; Yesilyaprak, C.; Yerli, S. K.

    2016-10-01

    East Anatolian Observatory (aka. DAG) is a national project supported by the Turkish Government for building a 4 m class telescope which will be working in the optical and near-IR domain. As the tender process has been completed and kick-off to the telescope and the mirror production has been initiated, the project team is looking for possible collaborations for the focal plane instrumentation. This contribution is intended to describe the DAG project and to show its opportunities for a state-of-the-art MOS instrument.

  10. Plasmons on the edge of MoS2 nanostructures

    OpenAIRE

    Andersen, Kirsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2015-01-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduct...

  11. A νMOS soft-maximum current mirror

    OpenAIRE

    Minch, Bradley A.; Diorio, Chris; Hasler, Paul; Mead, Carver

    1995-01-01

    In this paper, we describe a novel circuit consisting of N+1 MOS transistors and a single floating gate which computes a soft maximum of N current inputs and reflects the result in the output transistor. An intuitive description of the operation of the circuit is given. Data from a working two-input version of the circuit is presented and discussed. The circuit features a high output voltage swing and an interesting feedback mechanism which causes its output impedance to be comparable to that...

  12. 650V CoolMOS CFD2:MOSFET

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    英飞凌推出了650V CoolMOS CFD2,它是漏源击穿电压为650V并且集成了快速体二极管的高压晶体管。器件延续了600VCFD产品的特点,不仅可以提高能效,而且具备更软的交换功能,从而降低了电磁干扰(EMI)。

  13. Variability of electrical contact properties in multilayer MoS2 thin-film transistors

    Science.gov (United States)

    Kim, Seong Yeoul; Park, Seonyoung; Choi, Woong

    2014-09-01

    We report the variability of electrical properties of Ti contacts in back-gated multilayer MoS2 thin-film transistors based on mechanically exfoliated flakes. By measuring current-voltage characteristics from room temperature to 240 °C, we demonstrate the formation of both ohmic and Schottky contacts at the Ti-MoS2 junctions of MoS2 transistors fabricated using identical electrode materials under the same conditions. While MoS2 transistors with ohmic contacts exhibit a typical signature of band transport, those with Schottky contacts indicate thermally activated transport behavior for the given temperature range. These results provide the experimental evidence of the variability of Ti metal contacts on MoS2, highlighting the importance of understanding the variability of electronic properties of naturally occurring MoS2 for further investigation.

  14. Plasma treatment introduced memory properties in MoS2 field-effect transistors

    Science.gov (United States)

    Zhang, Miaomiao; Tong, Yanhong; Tang, Qingxin; Liu, Yichun

    2016-01-01

    We present a facile method to obtain MoS2-based nonvolatile memory field-effect transistors by oxygen plasma treatment on the MoS2 surface that is in contact with a dielectric. The oxygen plasma treatment provides a way of introducing deep defects into the MoS2 surface. Only those deep defects located at the semiconductor/dielectric interface can behave as charge trapping sites to develop the memory capability. No memory properties can be observed when the MoS2 surface far from the conductive channel was treated with oxygen plasma. This method brings promising advantages to MoS2-based memory devices obtained using a simple fabrication method and small device dimensions.

  15. Optically pumped terahertz wave modulation in MoS2-Si heterostructure metasurface

    Science.gov (United States)

    Zheng, Wei; Fan, Fei; Chen, Meng; Chen, Sai; Chang, Sheng-Jiang

    2016-07-01

    An optically pumped terahertz (THz) modulator based on a MoS2-Si heterostructure metasurface are fabricated and investigated in this paper. The THz wave modulation in MoS2 metasurface has been demonstrated by THz time domain spectroscopy experiment and numerical simulation, which can reach over 90% under the continuous wave laser pumping of 4W/cm2 power density. Importantly, the catalysis of photocarrier generation in MoS2-Si heterostructure has been proved by the comparsion between the modulation depth of metasurface with and without MoS2 nanosheet under the same pumping power, and we found that the strcuture of metasurface and polariztion direction can also influence the photocarrier density in MoS2 metasurface. This novel THz modulator based on 2D material has a high effective modulation on THz waves under a low pumping power, which has a bright potential in THz applications.

  16. Laser-Induced Particle Adsorption on Atomically Thin MoS2.

    Science.gov (United States)

    Tran Khac, Bien Cuong; Jeon, Ki-Joon; Choi, Seung Tae; Kim, Yong Soo; DelRio, Frank W; Chung, Koo-Hyun

    2016-02-10

    Atomically thin molybdenum disulfide (MoS2) shows great potential for use in nanodevices because of its remarkable electronic, optoelectronic, and mechanical properties. These material properties are often dependent on the thickness or the number of layers, and hence Raman spectroscopy is widely used to characterize the thickness of atomically thin MoS2 due to the sensitivity of the vibrational spectrum to thickness. However, the lasers used in Raman spectroscopy can increase the local surface temperature and eventually damage the upper layers of the MoS2, thereby changing the aforementioned material properties. In this work, the effects of lasers on the topography and material properties of atomically thin MoS2 were systematically investigated using Raman spectroscopy and atomic force microscopy. In detail, friction force microscopy was used to study the friction characteristics of atomically thin MoS2 as a function of laser powers from 0.5 to 20 mW and number of layers from 1 to 3. It was found that particles formed on the top surface of the atomically thin MoS2 due to laser-induced thermal effects. The degree of particle formation increased as the laser power increased, prior to the thinning of the atomically thin MoS2. In addition, the degree of particle formation increased as the number of MoS2 layers increased, which suggests that the thermal behavior of the supported MoS2 may differ depending on the number of layers. The particles likely originated from the atmosphere due to laser-induced heating, but could be eliminated via appropriate laser powers and exposure times, which were determined experimentally. The outcomes of this work indicate that thermal management is crucial in the design of reliable nanoscale devices based on atomically thin MoS2.

  17. Thermal Conductance at the 2D MoS2-hexagonal Boron Nitride Interface

    Science.gov (United States)

    Liu, Yi; Hippalgaonkar, Kedar; Ong, Zhun Yong; Thong, John Tl; Qiu, Chengwei

    In recent years, a number of 2D heterostructure devices have emerged, including graphene/hexagonal boron nitride (h-BN), graphene/MoS2 and MoS2/ h-BN. Among them, MoS2/ h-BN field-effect transistors with MoS2 channels and h-BN dielectric have been reported to have higher carrier mobility and reduced hysteresis compared to MoS2 on SiO2. Despite relatively high in-plane thermal conductivity of MoS2 and h-BN, heat dissipation from these 2D devices is mainly limited by heat transfer in the vertical direction. Consequently, their operating temperatures are strongly influenced by the interface thermal conductance. In this work, we demonstrate the measurement of interface thermal conductance between MoS2 and h-BN. This is realized by electrically heating MoS2 and monitoring their temperatures through Raman spectroscopy. The obtained interface thermal conductance between MoS2 and h-BN is 1.77 MW/m2K, smaller than the reported value for the graphene/ h-BN interface, due to the weak coupling of phonon modes between MoS2 and h-BN based on our NEGF calculation. The low interface thermal conductance value suggests this interface is not favorable for heat dissipation, and should be considered carefully for the design of electronic and optoelectronic devices based on MoS2/ h-BN heterostructures.

  18. An infant with mos45,X/46,XY/47,XYY/48,XYYY: Genetic and clinical findings

    Energy Technology Data Exchange (ETDEWEB)

    Fox, J.; Blumenthal, D.; Brock, W. [Long Island Jewish Medical Center, New Hyde Park, NY (United States)] [and others

    1994-09-01

    We report on an infant with mos45,X/46,XY/47,XYY/48,XYYY who presented with ambiguous genitalia. The patient was the 2,637 gram product of a 38 week gestation and elective repeat C-section born to a 35 year old G3P2 mother. The pregnancy was complicated by placenta previa. There was no history of maternal health problems or drug or steroid use. At birth bilateral epicanthal folds and overfolded helices were noted without webbing of the neck or lymphedema. There was a phallic structure measuring 1.5 cm with dorsal hood and midline cleft with a normal female introitus, urethra, and vagina. Congenital adrenal hyperplaxia was excluded. Renal ultrasound was normal. Periperal blood chromosomes revealed a mos45,X(38%)/47,XYY(29%)/48,XYYY(33%) karyotype. Echocardiography revealed coarctation of the aorta and a bicuspid aortic valve. An additional cell line, 46,XY, was identified in aortic tissue obtained at the time of surgery. At age 15 months she was 25% in height and weight and had bilateral ptosis. Her development was within normal limits, but no words except {open_quotes}Mama{close_quotes} or {open_quotes}Dada{close_quotes} were spoken. A left intraabdominal testis with epididymis and dilated tubules and bilateral Fallopian tubes were removed at laparoscopy/reconstruction. Cell cultures were initiated from gonadal tissue, and karyotypes are pending. Patients with mosaic Y chromosome aneuploidy involving 2 Y chromosomes are rare. Eighteen patients with 45,X/47,XYY have been described; prenatally diagnosed cases appeared to be normal male whereas cases diagnosed postnally presented with ambiguous genitalia and/or other anomalies. The phenotype of Y chromosome aneuploidy with 3 Y chromosomes is even more unpredictable due to the paucity of reported cases. To our knowledge this is the first patient described with this unusual karyotype, thus adding to the limited information of patients with rare mosaic Y chromosome aneuploidy.

  19. ELT-MOS White Paper: Science Overview & Requirements

    CERN Document Server

    Evans, Chris; Barbuy, Beatriz; Bastian, Nate; Bonifacio, Piercarlo; Caffau, Elisabetta; Cuby, Jean-Gabriel; Dalton, Gavin; Davies, Ben; Dunlop, Jim; Flores, Hector; Hammer, Francois; Kaper, Lex; Lemasle, Bertrand; Morris, Simon; Pentericci, Laura; Petitjean, Patrick; Schaerer, Daniel; Telles, Eduardo; Welikala, Niraj; Ziegler, Bodo

    2013-01-01

    The workhorse instruments of the 8-10m class observatories have become their multi-object spectrographs (MOS), providing comprehensive follow-up to both ground-based and space-borne imaging. With the advent of deeper imaging surveys from, e.g., the HST and VISTA, there are a plethora of spectroscopic targets which are already beyond the sensitivity limits of current facilities. This wealth of targets will grow even more rapidly in the coming years, e.g., after the completion of ALMA, the launch of the JWST and Euclid, and the advent of the LSST. Thus, one of the key requirements underlying plans for the next generation of ground-based telescopes, the Extremely Large Telescopes (ELTs), is for even greater sensitivity for optical and infrared spectroscopy. Here we revisit the scientific motivation for a MOS capability on the European ELT, combining updated elements of science cases advanced from the Phase A instrument studies with new science cases which draw on the latest results and discoveries. These science...

  20. MoS2 memristor with photoresistive switching

    Science.gov (United States)

    Wang, Wei; Panin, Gennady N.; Fu, Xiao; Zhang, Lei; Ilanchezhiyan, P.; Pelenovich, Vasiliy O.; Fu, Dejun; Kang, Tae Won

    2016-08-01

    A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques.

  1. MoS2 memristor with photoresistive switching.

    Science.gov (United States)

    Wang, Wei; Panin, Gennady N; Fu, Xiao; Zhang, Lei; Ilanchezhiyan, P; Pelenovich, Vasiliy O; Fu, Dejun; Kang, Tae Won

    2016-01-01

    A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques. PMID:27492593

  2. Analytical models for total dose ionization effects in MOS devices.

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, Phillip Montgomery; Bogdan, Carolyn W.

    2008-08-01

    MOS devices are susceptible to damage by ionizing radiation due to charge buildup in gate, field and SOI buried oxides. Under positive bias holes created in the gate oxide will transport to the Si / SiO{sub 2} interface creating oxide-trapped charge. As a result of hole transport and trapping, hydrogen is liberated in the oxide which can create interface-trapped charge. The trapped charge will affect the threshold voltage and degrade the channel mobility. Neutralization of oxidetrapped charge by electron tunneling from the silicon and by thermal emission can take place over long periods of time. Neutralization of interface-trapped charge is not observed at room temperature. Analytical models are developed that account for the principal effects of total dose in MOS devices under different gate bias. The intent is to obtain closed-form solutions that can be used in circuit simulation. Expressions are derived for the aging effects of very low dose rate radiation over long time periods.

  3. MEGARA, the new IFU and MOS for the GTC

    Science.gov (United States)

    Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias-Páramo, J.; Sánchez Moreno, F. M.; Vílchez, J. M.; García Vargas, M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; Cedazo, R.; Eliche-Moral, M. C.; Ferrusca, D.; González-Guardia, E.; Lefort, B.; Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Guzmán, R.; Herrero, A.; Huélamo, N., Hughes, D.; Jiménez-Vicente, J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya, Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O.; Villar, V.

    2015-05-01

    MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the future intermediate-resolution optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) of the 10.4m GTC telescope. The instrument can be used to observe either a contiguous (100% filling factor) field-of-view of 12.5×11.3 arcsec^{2} or 92 objects anywhere in a 3.5×3.5 arcmin^{2} field patrolled by robotic actuactors attached to optical-fiber minibundles, respectively in its IFU and MOS modes. The MEGARA Consortium is led by the Universidad Complutense de Madrid (UCM, Spain) and also includes the Instituto Nacional de Astrofísica, óptica y Electrónica (INAOE, Mexico), the Instituto de Astrofísica de Andalucía (IAA-CSIC, Spain) and the Universidad Politécnica de Madrid (UPM, Spain). The instrument passed its Critical Design Review (CDR) on late 2014 and is currently in construction phase with a planned date for the start of operations at GTC on early 2017. In this paper we summarize the main characteristics of the instrument and the status of the project.

  4. Germanium MOS technology for infra-red detectors

    Energy Technology Data Exchange (ETDEWEB)

    Ruddell, Fred H. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom)]. E-mail: f.ruddell@qub.ac.uk; Montgomery, John H. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom); Gamble, Harold S. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom); Denvir, Donal [Andor Technology, 7 Millenium Way, Springvale Business Park, Belfast BT12 7AL (United Kingdom)

    2007-04-01

    Fabrication of an electrically stable dielectric is a key enabling technology in the production of a Ge detector with enhanced response in the near infra-red spectrum. This work investigates the physical and electrical properties of silicon dioxide (SiO{sub 2}) dielectrics deposited on Ge substrates. The deposited SiO{sub 2} (silox) layers have been densified at 600 and 800 deg. C. Significant Ge outdiffusion from the substrate into the densifying silox layer has been observed for the 800 deg. C process, and the diffusivity has been estimated as 1.5x10{sup -4} {mu}m{sup 2}/min. The C-V characteristics of Ge MOS capacitors incorporating this silox dielectric display the onset of 'low frequency' operation at a relatively high frequency of 100 kHz, and the capacitor C-t response suggests that Ge carrier lifetime is much shorter than that measured for Si MOS capacitors. These phenomena are shown to result from the narrow band gap of Ge, and this work therefore emphasises that increased cooling will be required to exploit the infra-red detector properties of a practical Ge device.

  5. MOS Mapping of the NIR Outflow HH 223

    Science.gov (United States)

    López, R.; Acosta-Pulido, J. A.; Estalella, R.; Gómez, G.; García-Lorenzo, B.

    2016-10-01

    The Multi-Object-Spectroscopy (MOS) mode of LIRIS was used to map the near-IR stellar outflow HH 223, in the dark cloud Lynds 723 (L723). HH 223 spatially coincides with the east-west component of the L723 quadrupolar CO outflow. The radio continuum source SMA2, towards the center of the quadrupolar CO outflow, hides the YSO that seems to power both the near-IR and the CO outflows. To map the S-shaped, near-IR emission of HH 223, extending ˜ 5', an appropriate mask was designed, with 16 rectangular slitlets. J, H and K-band spectra (R ˜eq 2500) were obtained through the mask. The kinematics of the neutral (H2) and ionized ([FeII]) gas outflow was derived from these data. The results confirm that both the near-IR and the CO outflows have a common driving source. To our knowledge, this is the first use of the MOS-LIRIS observing mode with the mask designed ad hoc to fit several extended, nonaligned targets.

  6. Commentaryon using the SF-36 or MOS-HIV in studies of persons with HIV disease

    Directory of Open Access Journals (Sweden)

    Hays Ron D

    2003-07-01

    Full Text Available Abstract The purposewas to compare and comment on use of the SF-36 and MOS-HIV instrumentsin studies of persons with HIV disease. Three medical informationdatabases were searched to identify examples of HIV studies thatincluded the MOS-HIV or SF-36. Thirty-nine and 14 published articleswere identified for illustration in comparing the use of the MOS-HIVand SF-36 in HIV disease, respectively. Support for the reliabilityand construct validity of the MOS-HIV and SF-36 was found. Ceilingand floor effects were reported for both the MOS-HIV and SF-36;however, ceiling effects were more common for the MOS-HIV, in partdue to fewer items in the physical, social, and role functioningdomains. The MOS-HIV measures three domains hypothesized to be associatedwith the health deterioration of HIV disease not measured by theSF-36; however, these domains may not assess aspects of HIV diseasethat typify the majority of the persons with HIV disease today.National norms for the U.S. adult population (and other nationsare available for the SF-36. In addition, the SF-36 has been usedin a wide variety of patient populations, enabling comparisons ofHIV-infected persons with persons with other health conditions.No national norms for the MOS-HIV are available. We conclude thatthere is currently insufficient evidence in the literature to recommendthe use of the MOS-HIV over the SF-36 in HIV-infected persons. Althoughthe SF-36 is not targeted at HIV, it may be preferable to use theSF-36 over the MOS-HIV due to fewer ceiling effects, availabilityof national norms, and the vast amount of data for other populationsin the U.S. and around the world. Head-to-head comparisons demonstratingthe unique value of the MOS-HIV over the SF-36 are clearly needed.More importantly, additional work needs to be directed at comparingthe MOS-HIV and other putatively HIV-targeted instruments to oneanother to help demarcate aspects of HRQOL that are truly genericversus specific to HIV disease

  7. Single-Step Exfoliation and Covalent Functionalization of MoS2 Nanosheets by an Organosulfur Reaction.

    Science.gov (United States)

    Gonçalves, Ricardo H; Fiel, Rodrigo; Soares, Mario R S; Schreiner, Wido H; Silva, Caio M P; Leite, Edson R

    2015-10-26

    A simple approach to exfoliate and functionalize MoS2 in a single-step is described, which combines the dispersion of MoS2 in polybutadiene solution and ultrasonication processes. The great advantage of this process is that a colloidal stability of MoS2 in nonpolar solvent is achieved by chemically bonding polybutadiene on the perimeter edge sites of MoS2 sheets. In addition, elastomeric nanocomposite has been prepared with singular mechanical properties using functionalized MoS2 as nanofiller in a polybutadiene matrix with a subsequent vulcanization reaction. PMID:26367390

  8. Nanoscale mapping of excitonic processes in single-layer MoS2 using tip-enhanced photoluminescence microscopy

    Science.gov (United States)

    Su, Weitao; Kumar, Naresh; Mignuzzi, Sandro; Crain, Jason; Roy, Debdulal

    2016-05-01

    In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural and excitonic properties.In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural

  9. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Directory of Open Access Journals (Sweden)

    Wei-Ting eLai

    2016-02-01

    Full Text Available We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5−90 nm, the SiO2 thickness (3−4 nm, and as well the SiGe-shell thickness (2−15 nm has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5 in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge MOS nanoelectronic and nanophotonic applications.

  10. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Science.gov (United States)

    Lai, Wei-Ting; Yang, Kuo-Ching; Liao, Po-Hsiang; George, Tom; Li, Pei-Wen

    2016-02-01

    We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5‑90 nm), the SiO2 thickness (3‑4 nm), and as well the SiGe-shell thickness (2‑15 nm) has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

  11. Fluorescent MoS2 Quantum Dots: Ultrasonic Preparation, Up-Conversion and Down-Conversion Bioimaging, and Photodynamic Therapy.

    Science.gov (United States)

    Dong, Haifeng; Tang, Songsong; Hao, Yansong; Yu, Haizhu; Dai, Wenhao; Zhao, Guifeng; Cao, Yu; Lu, Huiting; Zhang, Xueji; Ju, Huangxian

    2016-02-10

    Small size molybdenum disulfide (MoS2) quantum dots (QDs) with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like Mo-S bond cleavage mode. The tunable up-bottom approach of precise fabrication of MoS2 QDs finally enables detailed experimental investigations of their optical properties. The synthesized MoS2 QDs present good down-conversion photoluminescence behaviors and exhibit remarkable up-conversion photoluminescence for bioimaging. The mechanism of the emerging photoluminescence was investigated. Furthermore, superior (1)O2 production ability of MoS2 QDs to commercial photosensitizer PpIX was demonstrated, which has great potential application for photodynamic therapy. These early affording results of tunable synthesis of MoS2 QDs with desired photo properties can lead to application in fields of biomedical and optoelectronics.

  12. Fluorescent MoS2 Quantum Dots: Ultrasonic Preparation, Up-Conversion and Down-Conversion Bioimaging, and Photodynamic Therapy.

    Science.gov (United States)

    Dong, Haifeng; Tang, Songsong; Hao, Yansong; Yu, Haizhu; Dai, Wenhao; Zhao, Guifeng; Cao, Yu; Lu, Huiting; Zhang, Xueji; Ju, Huangxian

    2016-02-10

    Small size molybdenum disulfide (MoS2) quantum dots (QDs) with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like Mo-S bond cleavage mode. The tunable up-bottom approach of precise fabrication of MoS2 QDs finally enables detailed experimental investigations of their optical properties. The synthesized MoS2 QDs present good down-conversion photoluminescence behaviors and exhibit remarkable up-conversion photoluminescence for bioimaging. The mechanism of the emerging photoluminescence was investigated. Furthermore, superior (1)O2 production ability of MoS2 QDs to commercial photosensitizer PpIX was demonstrated, which has great potential application for photodynamic therapy. These early affording results of tunable synthesis of MoS2 QDs with desired photo properties can lead to application in fields of biomedical and optoelectronics. PMID:26761391

  13. Unravelling merging behaviors and electrostatic properties of CVD-grown monolayer MoS2 domains.

    Science.gov (United States)

    Hao, Song; Yang, Bingchu; Gao, Yongli

    2016-08-28

    The presence of grain boundaries is inevitable for chemical vapor deposition (CVD)-grown MoS2 domains owing to various merging behaviors, which greatly limits its potential applications in novel electronic and optoelectronic devices. It is therefore of great significance to unravel the merging behaviors of the synthesized polygon shape MoS2 domains. Here we provide systematic investigations of merging behaviors and electrostatic properties of CVD-grown polycrystalline MoS2 crystals by multiple means. Morphological results exhibit various polygon shape features, ascribed to polycrystalline crystals merged with triangle shape MoS2 single crystals. The thickness of triangle and polygon shape MoS2 crystals is identical manifested by Raman intensity and peak position mappings. Three merging behaviors are proposed to illustrate the formation mechanisms of observed various polygon shaped MoS2 crystals. The combined photoemission electron microscopy and kelvin probe force microscopy results reveal that the surface potential of perfect merged crystals is identical, which has an important implication for fabricating MoS2-based devices.

  14. Ultra-broadband nonlinear saturable absorption of high-yield MoS2 nanosheets.

    Science.gov (United States)

    Wei, Rongfei; Zhang, Hang; Hu, Zhongliang; Qiao, Tian; He, Xin; Guo, Qiangbing; Tian, Xiangling; Chen, Zhi; Qiu, Jianrong

    2016-07-29

    High-yield MoS2 nanosheets with strong nonlinear optical (NLO) responses in a broad near-infrared range were synthesized by a facile hydrothermal method. The observation of saturable absorption, which was excited by the light with photon energy smaller than the gap energy of MoS2, can be attributed to the enhancement of the hybridization between the Mo d-orbital and S p-orbital by the oxygen incorporation into MoS2. High-yield MoS2 nanosheets with high modulation depth and large saturable intensity generated a stable, passively Q-switched fiber laser pulse at 1.56 μm. The high output power of 1.08 mW can be attained under a very low pump power of 30.87 mW. Compared to recently reported passively Q-switched fiber lasers utilizing exfoliated MoS2 nanosheets, the efficiency of the laser for our passive Q-switching operation is larger and reaches 3.50%. This research may extend the understanding on the NLO properties of MoS2 and indicate the feasibility of the high-yield MoS2 nanosheets to passively Q-switched fiber laser effectively at low pump strengths.

  15. Abnormal electrical characteristics of multi-layered MoS2 FETs attributed to bulk traps

    Science.gov (United States)

    Kim, Choong-Ki; Yu, Chan Hak; Hur, Jae; Bae, Hagyoul; Jeon, Seung-Bae; Park, Hamin; Kim, Yong Min; Choi, Kyung Cheol; Choi, Yang-Kyu; Choi, Sung-Yool

    2016-03-01

    Multiple layers of MoS2 are used as channel materials in a type of field-effect transistor (FET). It was found that the hysteresis in transfer curves and low-frequency noise (LFN) characteristics are varied by the number of layers in MoS2 due to the different influences of bulk traps. The LFN characteristics of a FET composed of a ‘bi-layer’ MoS2 channel, which was passivated with an atomic-layer-deposited (ALD) Al2O3 layer, follow the conventional carrier number fluctuation (CNF) model. However, FETs consisting of multi-layered MoS2 channels (4, 7, 9, and 18 layers) show abnormal LFN characteristics, which substantially deviate from well-established 1/f noise models such as the CNF and Hooge’s mobility fluctuation models. The bulk traps inside the MoS2 layers are the origin of the abnormal LFN characteristics and the large hysteresis of FETs with multi-layered MoS2 is due to its randomly embedded bulk traps. Secondary ion mass spectrometry (SIMS) confirms the existence of oxygen species that induce the electrical bulk trap in the MoS2 layers.

  16. Ultra-broadband nonlinear saturable absorption of high-yield MoS2 nanosheets

    Science.gov (United States)

    Wei, Rongfei; Zhang, Hang; Hu, Zhongliang; Qiao, Tian; He, Xin; Guo, Qiangbing; Tian, Xiangling; Chen, Zhi; Qiu, Jianrong

    2016-07-01

    High-yield MoS2 nanosheets with strong nonlinear optical (NLO) responses in a broad near-infrared range were synthesized by a facile hydrothermal method. The observation of saturable absorption, which was excited by the light with photon energy smaller than the gap energy of MoS2, can be attributed to the enhancement of the hybridization between the Mo d-orbital and S p-orbital by the oxygen incorporation into MoS2. High-yield MoS2 nanosheets with high modulation depth and large saturable intensity generated a stable, passively Q-switched fiber laser pulse at 1.56 μm. The high output power of 1.08 mW can be attained under a very low pump power of 30.87 mW. Compared to recently reported passively Q-switched fiber lasers utilizing exfoliated MoS2 nanosheets, the efficiency of the laser for our passive Q-switching operation is larger and reaches 3.50%. This research may extend the understanding on the NLO properties of MoS2 and indicate the feasibility of the high-yield MoS2 nanosheets to passively Q-switched fiber laser effectively at low pump strengths.

  17. Effect of precursor on growth and morphology of MoS2 monolayer and multilayer

    Science.gov (United States)

    Ganorkar, Shraddha; Kim, Jungyoon; Kim, Young-Hwan; Kim, Seong-II

    2015-12-01

    The rise of two-dimensional (2D) material is one of the results of successful efforts of researchers which laid the path to the new era of electronics. One of the most exciting materials is MoS2. Synthesis has been always a major issue as electronic devices need reproducibility along with similar properties for mass productions. Chemical vapor deposition (CVD) is one of the successful methods for 2D materials including graphene. Furthermore, the choice of starting materials for Mo and S source is crucial. The different source has different effects on the layers and morphology of MoS2 films. In this work, we have extensively studied the CVD technique to grow few layers of MoS2 with two precursors MoO3 and MoCl5, show remarkable changes. The MoO3 source gives a triangular shaped MoS2 monolayer while that of MoCl5 can achieve uniform MoS2 without triangle. The absence of geometric shapes with MoCl5 is poorly understood. We tried to explain with MoCl5 precursor, the formation of continuous monolayer of MoS2 without any triangle on the basis of chemical reaction formalism mostly due to one step reaction process and formation of MoS2 from gas phase to the solid phase. The film synthesized by MoCl5 is more continuous and it would be a good choice for device applications.

  18. High efficiency photocatalysis for pollutant degradation with MoS2/C3N4 heterostructures.

    Science.gov (United States)

    Li, Qian; Zhang, Ning; Yang, Yong; Wang, Guozhong; Ng, Dickon H L

    2014-07-29

    Porous graphitic carbon nitride was synthesized by controllable thermal polymerization of urea in air. Their textural, electrical, and optical properties were tuned by varying the heating rate. The presence of proper residual oxygen in carbon nitride matrix had enhanced light absorption and inhibited the recombination of charge carriers. Furthermore, the MoS2 nanosheets were coupled into the carbon nitride to form MoS2/C3N4 heterostructures via a facile ultrasonic chemical method. The optimized MoS2/C3N4 heterostructure with 0.05 wt % MoS2 showed a reaction rate constant as high as 0.301 min(-1), which was 3.6 times that of bare carbon nitride. As analyzed by SEM, TEM, UV-vis absorption, PL and photoelectrochemical measurements, intimate contact interface, extended light response range, enhanced separation speed of charge carriers, and high photocurrent density upon MoS2 coupling led to the photocatalytic promotion of the MoS2/C3N4 heterostructures. In this architecture, MoS2 served as electron trapper to extend the lifetime of separated electron-hole pairs. Meanwhile, the accumulated holes on the surface of carbon nitride oxidized the organic dye directly, which was a predominant process in the photodegradation of organic pollutants in water treatment. The promotional mechanisms and principles reported here would have great significance in heterogeneous photocatalysis.

  19. Unravelling merging behaviors and electrostatic properties of CVD-grown monolayer MoS2 domains.

    Science.gov (United States)

    Hao, Song; Yang, Bingchu; Gao, Yongli

    2016-08-28

    The presence of grain boundaries is inevitable for chemical vapor deposition (CVD)-grown MoS2 domains owing to various merging behaviors, which greatly limits its potential applications in novel electronic and optoelectronic devices. It is therefore of great significance to unravel the merging behaviors of the synthesized polygon shape MoS2 domains. Here we provide systematic investigations of merging behaviors and electrostatic properties of CVD-grown polycrystalline MoS2 crystals by multiple means. Morphological results exhibit various polygon shape features, ascribed to polycrystalline crystals merged with triangle shape MoS2 single crystals. The thickness of triangle and polygon shape MoS2 crystals is identical manifested by Raman intensity and peak position mappings. Three merging behaviors are proposed to illustrate the formation mechanisms of observed various polygon shaped MoS2 crystals. The combined photoemission electron microscopy and kelvin probe force microscopy results reveal that the surface potential of perfect merged crystals is identical, which has an important implication for fabricating MoS2-based devices. PMID:27586938

  20. Synthesis and characterization of MoS2/Ti composite coatings on Ti6Al4V prepared by laser cladding

    Directory of Open Access Journals (Sweden)

    Rongjuan Yang

    2013-02-01

    Full Text Available The MoS2/Ti composite coating with sub-micron grade structure has been prepared on Ti6Al4V by laser method under argon protection. The morphology, microstructure, microhardness and friction coefficient of the coating were examined. The results indicated that the molybdenum disulfide was decomposed during melting and resolidification. The phase organization of composite coating mainly consisted of ternary element sulfides, molybdenum sulfides and titanium sulfides. The friction coefficient of and the surface roughness the MoS2/Ti coating were lower than those of Ti6Al4V. The composite coating exhibits excellent adhesion to the substrates, less surface roughness, good wear resistance and harder surface.

  1. Synthesis of Highly Uniform Molybdenum-Glycerate Spheres and Their Conversion into Hierarchical MoS2 Hollow Nanospheres for Lithium-Ion Batteries.

    Science.gov (United States)

    Wang, Yawen; Yu, Le; Lou, Xiong Wen David

    2016-06-20

    Highly uniform Mo-glycerate solid spheres are synthesized for the first time through a solvothermal process. The size of these Mo-glycerate spheres can be easily controlled in the range of 400-1000 nm by varying the water content in the mixed solvent. As a precursor, these Mo-glycerate solid spheres can be converted into hierarchical MoS2 hollow nanospheres through a subsequent sulfidation reaction. Owing to the unique ultrathin subunits and hollow interior, the as-prepared MoS2 hollow nanospheres exhibit appealing performance as the anode material for lithium-ion batteries. Impressively, these hierarchical structures deliver a high capacity of about 1100 mAh g(-1) at 0.5 A g(-1) with good rate retention and long cycle life. PMID:27095261

  2. Fabrication of 3 D Mesoporous Black TiO2 /MoS2 /TiO2 Nanosheets for Visible-Light-Driven Photocatalysis.

    Science.gov (United States)

    Liu, Xuefeng; Xing, Zipeng; Zhang, Hang; Wang, Wenmei; Zhang, Yan; Li, Zhenzi; Wu, Xiaoyan; Yu, Xiujuan; Zhou, Wei

    2016-05-23

    A novel 3 D mesoporous black TiO2 (MBT)/MoS2 /MBT sandwich-like nanosheet was successfully fabricated using a facile mechanochemical process combined with an in situ solid-state chemical reduction approach, followed by mild calcination (350 °C) under an argon atmosphere. The MBT/MoS2 /MBT exhibits a 3 D sandwich-like nanosheet structure and heterojunctions are formed at the interfaces between MoS2 and black TiO2 . The significantly narrowed band gap of MBT/MoS2 /MBT is attributed to the introduction of MoS2 and the formed Ti(3+) species in the frameworks. The visible-light photocatalytic degradation rate of methyl orange and the hydrogen production rate are as high as 89.86 % and 0.56 mmol h(-1)  g(-1) , respectively. The introduction of MoS2 and Ti(3+) in the frameworks favors the visible-light absorption and the separation of photogenerated charges, and the 3 D sandwich-like heterojunction structure facilitates the transfer of photogenerated charges.

  3. Fabrication of 3 D Mesoporous Black TiO2 /MoS2 /TiO2 Nanosheets for Visible-Light-Driven Photocatalysis.

    Science.gov (United States)

    Liu, Xuefeng; Xing, Zipeng; Zhang, Hang; Wang, Wenmei; Zhang, Yan; Li, Zhenzi; Wu, Xiaoyan; Yu, Xiujuan; Zhou, Wei

    2016-05-23

    A novel 3 D mesoporous black TiO2 (MBT)/MoS2 /MBT sandwich-like nanosheet was successfully fabricated using a facile mechanochemical process combined with an in situ solid-state chemical reduction approach, followed by mild calcination (350 °C) under an argon atmosphere. The MBT/MoS2 /MBT exhibits a 3 D sandwich-like nanosheet structure and heterojunctions are formed at the interfaces between MoS2 and black TiO2 . The significantly narrowed band gap of MBT/MoS2 /MBT is attributed to the introduction of MoS2 and the formed Ti(3+) species in the frameworks. The visible-light photocatalytic degradation rate of methyl orange and the hydrogen production rate are as high as 89.86 % and 0.56 mmol h(-1)  g(-1) , respectively. The introduction of MoS2 and Ti(3+) in the frameworks favors the visible-light absorption and the separation of photogenerated charges, and the 3 D sandwich-like heterojunction structure facilitates the transfer of photogenerated charges. PMID:27111114

  4. Towards intrinsic MoS2 devices for high performance arsenite sensing

    Science.gov (United States)

    Li, Peng; Zhang, Dongzhi; Sun, Yan'e.; Chang, Hongyan; Liu, Jingjing; Yin, Nailiang

    2016-08-01

    Molybdenum disulphide (MoS2) is one of the most attractive two dimensional materials other than graphene, and the exceptional properties make it a promising candidate for bio/chemical sensing. Nevertheless, intrinsic properties and sensing performances of MoS2 are easily masked by the presence of the Schottky barrier (SB) at source/drain electrodes, and its impact on MoS2 sensors remains unclear. Here, we systematically investigated the influence of the SB on MoS2 sensors, revealing the sensing mechanism of intrinsic MoS2. By utilizing a small work function metal, Ti, to reduce the SB, excellent electrical properties of this 2D material were yielded with 2-3 times enhanced sensitivity. We experimentally demonstrated that the sensitivity of MoS2 is superior to that of graphene. Intrinsic MoS2 was able to realize rapid detection of arsenite down to 0.1 ppb without the influence of large SB, which is two-fold lower than the World Health Organization (WHO) tolerance level and better than the detection limit of recently reported arsenite sensors. Additionally, accurately discriminating target molecules is a great challenge for sensors based on 2D materials. This work demonstrates MoS2 sensors encapsulated with ionophore film which only allows certain types of molecules to selectively permeate through it. As a result, multiplex ion detection with superb selectivity was realized. Our results show prominent advantages of intrinsic MoS2 as a sensing material.

  5. Highly Selective and Efficient Removal of Heavy Metals by Layered Double Hydroxide Intercalated with the MoS4(2-) Ion.

    Science.gov (United States)

    Ma, Lijiao; Wang, Qing; Islam, Saiful M; Liu, Yingchun; Ma, Shulan; Kanatzidis, Mercouri G

    2016-03-01

    The MoS4(2-) ion was intercalated into magnesium-aluminum layered double hydroxide (MgAl-NO3-LDH) to produce a single phase material of Mg0.66Al0.34(OH)2(MoS4)0.17·nH2O (MgAl-MoS4-LDH), which demonstrates highly selective binding and extremely efficient removal of heavy metal ions such as Cu(2+), Pb(2+), Ag(+), and Hg(2+). The MoS4-LDH displays a selectivity order of Co(2+), Ni(2+), Zn(2+) metal ions. The enormous capacities for Hg(2+) (∼500 mg/g) and Ag(+) (450 mg/g) and very high distribution coefficients (Kd) of ∼10(7) mL/g place the MoS4-LDH at the top of materials known for such removal. Sorption isotherm for Ag(+) agrees with the Langmuir model suggesting a monolayer adsorption. It can rapidly lower the concentrations of Cu(2+), Pb(2+), Hg(2+), and Ag(+) from ppm levels to trace levels of ≤1 ppb. For the highly toxic Hg(2+) (at ∼30 ppm concentration), the adsorption is exceptionally rapid and highly selective, showing a 97.3% removal within 5 min, 99.7% removal within 30 min, and ∼100% removal within 1 h. The sorption kinetics for Cu(2+), Ag(+), Pb(2+), and Hg(2+) follows a pseudo-second-order model suggesting a chemisorption with the adsorption mechanism via M-S bonding. X-ray diffraction patterns of the samples after adsorption demonstrate the coordination and intercalation structures depending on the metal ions and their concentration. After the capture of heavy metals, the crystallites of the MoS4-LDH material retain the original hexagonal prismatic shape and are stable at pH ≈ 2-10. The MoS4-LDH material is thus promising for the remediation of heavy metal polluted water.

  6. Electrostatic properties of few-layer MoS2 films

    Directory of Open Access Journals (Sweden)

    Guolin Hao

    2013-04-01

    Full Text Available Two-dimensional MoS2-based materials are considered to be one of the most attractive materials for next-generation nanoelectronics. The electrostatic properties are important in designing and understanding the performance of MoS2-based devices. By using Kelvin probe force microscopy, we show that few-layer MoS2 sheets exhibit uniform surface potential and charge distributions on their surfaces but have relatively lower surface potentials on the edges, folded areas as well as defect grain boundaries.

  7. Two-step synthesis of luminescent MoS2-ZnS hybrid quantum dots

    Science.gov (United States)

    Clark, Rhiannon M.; Carey, Benjamin J.; Daeneke, Torben; Atkin, Paul; Bhaskaran, Madhu; Latham, Kay; Cole, Ivan S.; Kalantar-Zadeh, Kourosh

    2015-10-01

    A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing applications.A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing

  8. Bandgap engineering of rippled MoS2 monolayer under external electric field

    Science.gov (United States)

    Qi, Jingshan; Li, Xiao; Qian, Xiaofeng; Feng, Ji

    2013-04-01

    In this letter we propose a universal strategy combining external electric field with the ripple of membrane to tune the bandgap of semiconducting atomic monolayer. By first-principles calculations we show that the bandgap of rippled MoS2 monolayer can be tuned in a large range by vertical external electric field, which is expected to have little effect on MoS2 monolayer. This phenomenon can be explained from charge redistribution under external electric field by a simple model. This may open an avenue of optimizing monolayer MoS2 for electronic and optoelectronic applications by surface patterning.

  9. Mutation analysis of the c-mos proto-oncogene in human ovarian teratomas.

    OpenAIRE

    de Foy, K. A.; Gayther, S A; Colledge, W.H.; Crockett, S; Scott, I V; Evans, M.J.; Ponder, B A

    1998-01-01

    Female transgenic mice lacking a functional c-mos proto-oncogene develop ovarian teratomas, indicating that c-mos may behave as a tumour-suppressor gene for this type of tumour. We have analysed the entire coding region of the c-MOS gene in a series of human ovarian teratomas to determine whether there are any cancer-causing alterations. DNA from twenty teratomas was analysed by single-strand conformational analysis (SSCA) and heteroduplex analysis (HA) to screen for somatic and germline muta...

  10. Physics-based stability analysis of MOS transistors

    Science.gov (United States)

    Ferrara, A.; Steeneken, P. G.; Boksteen, B. K.; Heringa, A.; Scholten, A. J.; Schmitz, J.; Hueting, R. J. E.

    2015-11-01

    In this work, a physics-based model is derived based on a linearization procedure for investigating the electrical, thermal and electro-thermal instability of power metal-oxide-semiconductor (MOS) transistors. The proposed model can be easily interfaced with a circuit or device simulator to perform a failure analysis, making it particularly useful for power transistors. Furthermore, it allows mapping the failure points on a three-dimensional (3D) space defined by the gate-width normalized drain current, drain voltage and junction temperature. This leads to the definition of the Safe Operating Volume (SOV), a powerful frame work for making failure predictions and determining the main root of instability (electrical, thermal or electro-thermal) in different bias and operating conditions. A comparison between the modeled and the measured SOV of silicon-on-insulator (SOI) LDMOS transistors is reported to support the validity of the proposed stability analysis.

  11. MoS2 and semiconductors in the flatland

    Directory of Open Access Journals (Sweden)

    Oleg V. Yazyev

    2015-01-01

    Full Text Available The fascinating properties of graphene, the first two-dimensional (2D material, and the accompanying strong activity in the research community have sparked a renewed interest in related layered crystalline materials with unique electronic and optical properties. Their superb mechanical properties, optical transparency, direct band gap and large degree of electrostatic control due to their atomic scale thickness make them interesting inorganic nanosystems for a wide variety of applications. In this review we will present a short history of research in the synthesis, band properties and potential applications of 2D semiconductors with a particular emphasis on MoS2, the prototypical and best-studied material from this family.

  12. MoS2-Titanium Contact Interface Reactions.

    Science.gov (United States)

    McDonnell, Stephen; Smyth, Christopher; Hinkle, Christopher L; Wallace, Robert M

    2016-03-01

    The formation of the Ti-MoS2 interface, which is heavily utilized in nanoelectronic device research, is studied by X-ray photoelectron spectroscopy. It is found that, if deposition under high vacuum (∼1 × 10(-6) mbar) as opposed to ultrahigh vacuum (∼1 × 10(-9) mbar) conditions are used, TiO2 forms at the interface rather than Ti. The high vacuum deposition results in an interface free of any detectable reaction between the semiconductor and the deposited contact. In contrast, when metallic titanium is successfully deposited by carrying out depositions in ultrahigh vacuum, the titanium reacts with MoS2 forming Ti(x)S(y) and metallic Mo at the interface. These results have far reaching implications as many prior studies assuming Ti contacts may have actually used TiO2 due to the nature of the deposition tools used. PMID:26967016

  13. Fowler-Nordheim characteristics of electron irradiated MOS capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Candelori, A.; Paccagnella, A.; Cammarata, M. [Univ. di Padova (Italy). Dipt. di Elettronica e Informatica; Ghidini, G. [SGS-Thomson Microelectronics, Agrate Brianza (Italy); Fuochi, P.G. [CNR-FRAE, Bologna (Italy)

    1998-12-01

    MOS capacitors with 8 nm thick oxides have been irradiated by an 8 MeV LINAC electron beam. C-V and I-V measurements have shown a positive trapped charge, higher for irradiation performed under negative gate bias, as a consequence of preferential charge recombination at the cathodic interface. No saturation of the positive trapped charge is measured up to 20 Mrad(Si). Neutral defects induced by irradiation have been studied, by performing positive and negative Fowler-Nordheim injection. The distribution of neutral defects is similar to that of trapped holes, indicating a correlation between trapped holes and neutral defects. Electrical stresses performed after irradiation have shown that the accumulation kinetics of oxide defects is similar in both unirradiated and irradiated devices.

  14. Bandgap tuning in armchair MoS2 nanoribbon

    Science.gov (United States)

    Yue, Qu; Chang, Shengli; Kang, Jun; Zhang, Xueao; Shao, Zhengzheng; Qin, Shiqiao; Li, Jingbo

    2012-08-01

    We report on the first-principles calculations of bandgap modulation in armchair MoS2 nanoribbon (AMoS2NR) by transverse and perpendicular electric fields respectively. In the monolayer AMoS2NR case, it is shown that the bandgap can be significantly reduced and be closed by transverse field, whereas the bandgap modulation is absent under perpendicular field. The critical strength of transverse field for gap closure decreases as ribbon width increases. In the multilayer AMoS2NR case, in contrast, it is shown that the bandgap can be effectively reduced by both transverse and perpendicular fields. Nevertheless, it seems that the two fields exhibit different modulation effects on the gap. The critical strength of perpendicular field for gap closure decreases with increasing number of layers, while the critical strength of transverse field is almost independent of it.

  15. The Pore Confinement Effect of FDU-12 Mesochannels on MoS2 Active Phases and Their Hydrodesulfurization Performance

    Directory of Open Access Journals (Sweden)

    Cong Liu

    2016-01-01

    Full Text Available FDU-12 silica with highly ordered face-centered cubic mesoporous structure is developed as support to prepare Mo/FDU-12 catalysts for hydrodesulfurization (HDS of dibenzothiophene (DBT. A series of Mo/FDU-12 catalysts are synthesized by using incipient wetness impregnation method with different MoO3 loadings (6, 8, 10, 12, and 15 wt.%. The objective of this work is to explore the pore confinement effect of FDU-12 mesochannels on the MoS2 morphology with various metal loadings. It is found that, as increasing MoO3 loadings from 6 to 15 wt.%, the MoS2 nanocrystallites transform from monolayer to multilayer and the morphology changes from straight layered to curved and then to ring-like and finally to spherical-like morphology due to the restriction of cage-like pore channels of FDU-12 support. The HDS results show that the catalytic activity increases first and then decreases with the best HDS performance at the MoO3 loading of 10 wt.%. In addition, we compared the HDS activity of Mo catalyst supported on FDU-12 with that on the commercial γ-Al2O3 and SBA-15; the result exhibits that FDU-12 is superior to the other two supports due to its large pore size and ordered three-dimensional open pore channels.

  16. Ultrathin Co(Ni)-doped MoS2 nanosheets as catalytic promoters enabling efficient solar hydrogen production

    Institute of Scientific and Technical Information of China (English)

    Xiaoyan Ma; Jinquan Li; Changhua An; Juan Feng; Yuhua Chi; Junxue Liu; Jun Zhang

    2016-01-01

    The design of efficient artificial photosynthetic systems that harvest solar energy to drive the hydrogen evolution reaction via water reduction is of great importance from both the theoretical and practical viewpoints.Integrating appropriate co-catalyst promoters with strong light absorbing materials represents an ideal strategy to enhance the conversion efficiency of solar energy in hydrogen production.Herein,we report,for the first time,the synthesis of a class of unique hybrid structures consisting of ultrathin Co(Ni)-doped MoS2 nanosheets (co-catalyst promoter) intimately grown on semiconductor CdS nanorods (light absorber).The as-synthesized one-dimensional CdS@doped-MoS2 heterostructures exhibited very high photocatalytic activity (with a quantum yield of 17.3%) and stability towards H2 evolution from the photoreduction of water.Theoretical calculations revealed that Ni doping can increase the number of uncoordinated atoms at the edge sites of MoS2 nanosheets to promote electron transfer across the CdS/MoS2 interfaces as well as hydrogen reduction,leading to an efficient H2 evolution reaction.

  17. Versatile MoS2 Nanosheets in ITO-Free and Semi-transparent Polymer Power-generating Glass

    Science.gov (United States)

    Hu, Xiaotian; Chen, Lie; Tan, Licheng; Zhang, Yong; Hu, Lin; Xie, Bing; Chen, Yiwang

    2015-07-01

    Chemical exfoliated ultra-thin MoS2 nanosheets (NSs) with well 2D structure were demonstrated for interfacial layers and Ag nanowires composite transparent electrode in polymer solar cells (PSCs). The smooth and uniform n-type and p-type (after the plasma treatment) MoS2 NSs could improve fill factor of devices and light absorption in active layer. The optimized Ag nanowires-MoS2 NSs (AgNW-MoS2 NSs) transparent electrode presented a low sheet resistance of 9.8 Ω sq-1, and the corresponding transmittance also exhibited a high value of 93.1% at 550 nm. As a result, ITO-free PSCs based on AgNW-MoS2 NSs/n-MoS2 NSs cathode and p-MoS2 NSs/Ag anode achieved a highest PCE of 8.72%. Furthermore, a high efficiency (6.55%), large area and low cost semi-transparent power-generating glass was obtained, after reducing the thickness of top Ag electrode from 100 nm to 30 nm. To our best knowledge, it is the highest performance for semi-transparent PSCs devices reported up to now. The novel semi-transparent power-generating glass showed good performance and color purity for commercial applications in the near future.

  18. Ionic Liquid-Assisted Hydrothermal Method Synthesis of Flower-Like MoS2 and Their Electrochemical Performances.

    Science.gov (United States)

    Li, Maohua; Yang, Bo; Hao, Junying; Lu, Yi; Long, Zerong; Liu, Yumei

    2016-06-01

    Molybdenum disulfide (MoS2) was prepared successfully via hydrothermal reaction at 200 degrees C in water/ethanol (1:1) solvent system using the ammonium molybdate and sodium thiosulfate as the molybdenum sources and sulfur sources, 1-butyl-3-methylimidazolium chloride salt [BMIM][Cl] as the additive agent. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the morphology and structure of flower-like products. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy spectrum analysis results show that the as-prepared product is a pure phase of MoS2. The prepared products are used as electrode materials for Li-ion batteries and showed excellent cycle stability and high Coulombic efficiency at a current density of 200 mA x g(-1) in the voltage range of 0.01 - 3.00 V (vs. Li/Li+). In addition, this paper also examined the influence of the reaction time and the amount of template agent on morphology, and discussed the reaction mechanism of the formation of flower-like morphology.

  19. Electromechanical coupling and design considerations in single-layer MoS2 suspended-channel transistors and resonators

    Science.gov (United States)

    Yang, Rui; Islam, Arnob; Feng, Philip X.-L.

    2015-11-01

    We report on the analysis of electromechanical coupling effects in suspended doubly-clamped single-layer MoS2 structures, and the designs of suspended-channel field-effect transistors (FETs) and vibrating-channel nanoelectromechanical resonators. In DC gating scenario, signal transduction processes including electrostatic actuation, deflection, straining on bandgap, mobility, carrier density and their intricate cross-interactions, have been analyzed considering strain-enhanced mobility (by up to 4 times), to determine the transfer characteristics. In AC gating scenario and resonant operations (using 100 MHz and 1 GHz devices as relevant targets), we demonstrate that the vibrating-channel MoS2 devices can offer enhanced signals (than the zero-bandgap graphene counterparts), thanks to the resonant straining effects on electron transport of the semiconducting channel. We also show dependence of signal intensity and signal-to-background ratio (SBR) on device geometries and scaling effects, with SBR enhancement by a factor of ~8 for resonance signal, which provide guidelines toward designing future devices with desirable parameters.

  20. Synthesizing 2D MoS2 Nanofins on carbon nanospheres as catalyst support for Proton Exchange Membrane Fuel Cells

    Science.gov (United States)

    Hu, Yan; Chua, Daniel H. C.

    2016-06-01

    Highly dense 2D MoS2 fin-like nanostructures on carbon nanospheres were fabricated and formed the main catalyst support structure in the oxygen reduction reaction (ORR) for polymer electrolyte membrane (PEM) fuel cells. These nanofins were observed growing perpendicular to the carbon nanosphere surface in random orientations and high resolution transmission electron microscope confirmed 2D layers. The PEM fuel cell test showed enhanced electrochemical activity with good stability, generating over 8.5 W.mgPt‑1 as compared to standard carbon black of 7.4 W.mgPt‑1 under normal operating conditions. Electrochemical Impedance Spectroscopy confirmed that the performance improvement is highly due to the excellent water management of the MoS2 lamellar network, which facilitates water retention at low current density and flood prevention at high current density. Reliability test further demonstrated that these nanofins are highly stable in the electrochemical reaction and is an excellent ORR catalyst support.

  1. A low power cryogenic 512 × 512-pixel infrared readout integrated circuit with modified MOS device model

    Science.gov (United States)

    Zhao, Hongliang; Liu, Xinghui; Xu, Chao

    2013-11-01

    A low power cryogenic readout integrated circuit (ROIC) for 512 × 512-pixel infrared focal plane array (IRFPA) image system, is presented. In order to improve the precision of the circuit simulation at cryogenic temperatures, a modified MOS device model is proposed. The model is based on BSIM3 model, and uses correction parameters to describe carrier freeze-out effect at low temperatures to improve the fitting accuracy for low temperature MOS device simulation. A capacitive trans-impedance amplifier (CTIA) with inherent correlated double sampling (CDS) configuration is employed to realize a high performance readout interfacing circuit in a pixel area of 30 × 30 μm2. Optimized column readout timing and structure are applied to reduce the power consumption. The experimental chip fabricated by a standard 0.35 μm 2P4M CMOS process shows more than 10 MHz readout rate with less than 70 mW power consumption under 3.3 V supply voltage at 77-150 K operated temperatures. And it occupies an area of 18 × 17 mm2.

  2. Ionic Liquid-Assisted Hydrothermal Method Synthesis of Flower-Like MoS2 and Their Electrochemical Performances.

    Science.gov (United States)

    Li, Maohua; Yang, Bo; Hao, Junying; Lu, Yi; Long, Zerong; Liu, Yumei

    2016-06-01

    Molybdenum disulfide (MoS2) was prepared successfully via hydrothermal reaction at 200 degrees C in water/ethanol (1:1) solvent system using the ammonium molybdate and sodium thiosulfate as the molybdenum sources and sulfur sources, 1-butyl-3-methylimidazolium chloride salt [BMIM][Cl] as the additive agent. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the morphology and structure of flower-like products. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy spectrum analysis results show that the as-prepared product is a pure phase of MoS2. The prepared products are used as electrode materials for Li-ion batteries and showed excellent cycle stability and high Coulombic efficiency at a current density of 200 mA x g(-1) in the voltage range of 0.01 - 3.00 V (vs. Li/Li+). In addition, this paper also examined the influence of the reaction time and the amount of template agent on morphology, and discussed the reaction mechanism of the formation of flower-like morphology. PMID:27427696

  3. Strain engineering of selective chemical adsorption on monolayer MoS2

    Science.gov (United States)

    Kou, Liangzhi; Du, Aijun; Chen, Changfeng; Frauenheim, Thomas

    2014-04-01

    Nanomaterials are prone to influence by chemical adsorption because of their large surface to volume ratios. This enables sensitive detection of adsorbed chemical species which, in turn, can tune the properties of the host material. Recent studies discovered that single and multi-layer molybdenum disulfide (MoS2) films are ultra-sensitive to several important environmental molecules. Here we report new findings from ab inito calculations that reveal substantially enhanced adsorption of NO and NH3 on strained monolayer MoS2 with significant impact on the properties of the adsorbates and the MoS2 layer. The magnetic moment of adsorbed NO can be tuned between 0 and 1 μB strain also induces an electronic phase transition between the half-metal and the metal. Adsorption of NH3 weakens the MoS2 layer considerably, which explains the large discrepancy between the experimentally measured strength and breaking strain of MoS2 films and previous theoretical predictions. On the other hand, adsorption of NO2, CO, and CO2 is insensitive to the strain conditions in the MoS2 layer. This contrasting behavior allows sensitive strain engineering of selective chemical adsorption on MoS2 with effective tuning of mechanical, electronic, and magnetic properties. These results suggest new design strategies for constructing MoS2-based ultrahigh-sensitivity nanoscale sensors and electromechanical devices.Nanomaterials are prone to influence by chemical adsorption because of their large surface to volume ratios. This enables sensitive detection of adsorbed chemical species which, in turn, can tune the properties of the host material. Recent studies discovered that single and multi-layer molybdenum disulfide (MoS2) films are ultra-sensitive to several important environmental molecules. Here we report new findings from ab inito calculations that reveal substantially enhanced adsorption of NO and NH3 on strained monolayer MoS2 with significant impact on the properties of the adsorbates and the

  4. FETSIM user's manual and example. [D.C. and transient analysis of MOS circuits

    Science.gov (United States)

    1978-01-01

    A batch program written in FORTRAN IV which does D.C. and transient analysis of MOS circuits is presented. Circuits employing N-MOS transistors and/or P-MOS transistors in either a bulk technology or an SOS technology, or almost any combination of R-C elements may be analyzed. The program requires as input data the complete circuit topology, device parameters, process parameters, and control parameters. The user can specify initial node conditions and the input pulse format. For example, pulse rise time, fall time, width and time between succeeding pulses are all independently controllable. The program contains a sophisticated mathematical model that can accurately handle either NMOS, P-MOS, Bulk or SOS devices. Sensitivity to process changes is maintained by requiring such process parameters as threshold voltage and doping level as program inputs.

  5. Heterojunction hybrid devices from vapor phase grown MoS2.

    Science.gov (United States)

    Yim, Chanyoung; O'Brien, Maria; McEvoy, Niall; Riazimehr, Sarah; Schäfer-Eberwein, Heiko; Bablich, Andreas; Pawar, Ravinder; Iannaccone, Giuseppe; Downing, Clive; Fiori, Gianluca; Lemme, Max C; Duesberg, Georg S

    2014-01-01

    We investigate a vertically-stacked hybrid photodiode consisting of a thin n-type molybdenum disulfide (MoS2) layer transferred onto p-type silicon. The fabrication is scalable as the MoS2 is grown by a controlled and tunable vapor phase sulfurization process. The obtained large-scale p-n heterojunction diodes exhibit notable photoconductivity which can be tuned by modifying the thickness of the MoS2 layer. The diodes have a broad spectral response due to direct and indirect band transitions of the nanoscale MoS2. Further, we observe a blue-shift of the spectral response into the visible range. The results are a significant step towards scalable fabrication of vertical devices from two-dimensional materials and constitute a new paradigm for materials engineering. PMID:24975741

  6. Morphology evolution of MoS2: From monodisperse nanoparticles to self-assembled nanobelts

    Science.gov (United States)

    Yu, Ting; Luo, Xingfang; Han, Shuming; Cao, Yingjie; Yuan, Cailei; Yang, Yong; Li, Qinliang

    2016-02-01

    The MoS2 nanobelts were successfully synthesized on SiO2/Si substrates using a vapor phase sulfurization process. Atomic force microscopy (AFM) techniques are employed to comprehensively study the morphology evolution of MoS2 from monodisperse nanoparticles to self-assembled nanobelts on the SiO2/Si substrates. A possible three-step morphology evolution process, which includes initial nucleation process, self-assembly process, and subsequent crystal growth process (Ostwald ripening), is proposed to explain the formation of MoS2. Moreover, MoS2 nanobelts are characterized by Raman spectroscopy and photo-luminescence (PL). These results provide the possibility to develop an easier-to-cooperate and morphology-controllable approach to fabricate novel architectures.

  7. Monolayers of MoS2 as an oxidation protective nanocoating material

    International Nuclear Information System (INIS)

    First-principle calculations are employed to investigate the interaction of oxygen with ideal and defective MoS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulfur atoms, the oxygen molecule only weakly interacts with the surface. The penetration of oxygen atoms and molecules through a defect-free MoS2 monolayer is prevented by a very high diffusion barrier indicating that MoS2 can serve as a protective layer for oxidation. The analysis is extended to WS2 and similar coating characteristics are obtained. Our calculations indicate that ideal and continuous MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be considered as an efficient nanocoating material

  8. Monolayers of MoS2 as an oxidation protective nanocoating material

    Science.gov (United States)

    Sen, H. Sener; Sahin, H.; Peeters, F. M.; Durgun, E.

    2014-08-01

    First-principle calculations are employed to investigate the interaction of oxygen with ideal and defective MoS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulfur atoms, the oxygen molecule only weakly interacts with the surface. The penetration of oxygen atoms and molecules through a defect-free MoS2 monolayer is prevented by a very high diffusion barrier indicating that MoS2 can serve as a protective layer for oxidation. The analysis is extended to WS2 and similar coating characteristics are obtained. Our calculations indicate that ideal and continuous MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be considered as an efficient nanocoating material.

  9. First-principles study of the magnetism of Ni-doped MoS2 monolayer

    Science.gov (United States)

    Luo, Min; Hao Shen, Yu; Hao Chu, Jun

    2016-09-01

    The magnetic properties of Ni-doped monolayer MoS2 are investigated using the density function theory. The results show that two Ni-doped systems of the nearest-neighbor configuration are ferromagnetic. The p-d hybridization between the Ni dopant and its neighboring S atoms results in the splitting of energy levels near the Fermi energy. These results suggest the p-d hybridization mechanism for the magnetism of the Ni-doped MoS2 monolayer. The magnetic moment disappears with increasing Ni-Ni distance. Our studies predict the nearest two-Ni-doped MoS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations indicate that it would be easier to incorporate Ni atoms into a S-rich MoS2 monolayer in the experiment.

  10. Orientation Dependent Thermal Conductance in Single-Layer MoS2

    Science.gov (United States)

    Jiang, Jin-Wu; Zhuang, Xiaoying; Rabczuk, Timon

    2013-07-01

    We investigate the thermal conductivity in the armchair and zigzag MoS2 nanoribbons, by combining the non-equilibrium Green's function approach and the first-principles method. A strong orientation dependence is observed in the thermal conductivity. Particularly, the thermal conductivity for the armchair MoS2 nanoribbon is about 673.6 Wm-1 K-1 in the armchair nanoribbon, and 841.1 Wm-1 K-1 in the zigzag nanoribbon at room temperature. By calculating the Caroli transmission, we disclose the underlying mechanism for this strong orientation dependence to be the fewer phonon transport channels in the armchair MoS2 nanoribbon in the frequency range of [150, 200] cm-1. Through the scaling of the phonon dispersion, we further illustrate that the thermal conductivity calculated for the MoS2 nanoribbon is esentially in consistent with the superior thermal conductivity found for graphene.

  11. Tuning the hysteresis voltage in 2D multilayer MoS2 FETs

    Science.gov (United States)

    Jiang, Jie; Zheng, Zhouming; Guo, Junjie

    2016-10-01

    The hysteresis tuning is of great significance before the two-dimensional (2D) molybdenum disulfide (MoS2) field-effect transistors (FETs) can be practically used in the next-generation nanoelectronic devices. In this paper, a simple and effective annealing method was developed to tune the hysteresis voltage in 2D MoS2 transistors. It was found that high temperature (175 °C) annealing in air could increase the hysteresis voltage from 8.0 V (original device) to 28.4 V, while a next vacuum annealing would reduce the hysteresis voltage to be only 2.0 V. An energyband diagram model based on electron trapping/detrapping due to oxygen adsorption is proposed to understand the hysteresis mechanism in multilayer MoS2 FET. This simple method for tuning the hysteresis voltage of MoS2 FET can make a significant step toward 2D nanoelectronic device applications.

  12. MoS2/MX2 heterobilayers: bandgap engineering via tensile strain or external electrical field

    Science.gov (United States)

    Lu, Ning; Guo, Hongyan; Li, Lei; Dai, Jun; Wang, Lu; Mei, Wai-Ning; Wu, Xiaojun; Zeng, Xiao Cheng

    2014-02-01

    We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X = S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-bandgap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering the bandgap of the TMD heterobilayer materials via application of either a tensile strain or an external electric field. We find that with increasing either the biaxial or uniaxial tensile strain, the MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial tensile strain. Moreover, the bandgap of MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can be reduced by the vertical electric field. For two heterobilayers MSe2/MoS2 (M = Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect-direct bandgap transitions due to tensile strain or external electric field make the TMD heterobilayer materials a viable candidate for optoelectronic applications.We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For

  13. Laser Direct Writing Process for Making Electrodes and High-k Sol-Gel ZrO2 for Boosting Performances of MoS2 Transistors.

    Science.gov (United States)

    Kwon, Hyuk-Jun; Jang, Jaewon; Grigoropoulos, Costas P

    2016-04-13

    A series of two-dimensional (2D) transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS2), can be attractive materials for photonic and electronic applications due to their exceptional properties. Among these unique properties, high mobility of 2D TMDCs enables realization of high-performance nanoelectronics based on a thin film transistor (TFT) platform. In this contribution, we report highly enhanced field effect mobility (μ(eff) = 50.1 cm(2)/(V s), ∼2.5 times) of MoS2 TFTs through the sol-gel processed high-k ZrO2 (∼22.0) insulator, compared to those of typical MoS2/SiO2/Si structures (μ(eff) = 19.4 cm(2)/(V s)) because a high-k dielectric layer can suppress Coulomb electron scattering and reduce interface trap concentration. Additionally, in order to avoid costly conventional mask based photolithography and define the patterns, we employ a simple laser direct writing (LDW) process. This process allows precise and flexible control with reasonable resolution (up to ∼10 nm), depending on the system, and enables fabrication of arbitrarily patterned devices. Taking advantage of continuing developments in laser technology offers a substantial cost decrease, and LDW may emerge as a promising technology.

  14. Scalable fabrication of a hybrid field-effect and acousto-electric device by direct growth of monolayer MoS2/LiNbO3

    Science.gov (United States)

    Preciado, Edwin; Schülein, Florian J. R.; Nguyen, Ariana E.; Barroso, David; Isarraraz, Miguel; von Son, Gretel; Lu, I.-Hsi; Michailow, Wladislaw; Möller, Benjamin; Klee, Velveth; Mann, John; Wixforth, Achim; Bartels, Ludwig; Krenner, Hubert J.

    2015-10-01

    Lithium niobate is the archetypical ferroelectric material and the substrate of choice for numerous applications including surface acoustic wave radio frequencies devices and integrated optics. It offers a unique combination of substantial piezoelectric and birefringent properties, yet its lack of optical activity and semiconducting transport hamper application in optoelectronics. Here we fabricate and characterize a hybrid MoS2/LiNbO3 acousto-electric device via a scalable route that uses millimetre-scale direct chemical vapour deposition of MoS2 followed by lithographic definition of a field-effect transistor structure on top. The prototypical device exhibits electrical characteristics competitive with MoS2 devices on silicon. Surface acoustic waves excited on the substrate can manipulate and probe the electrical transport in the monolayer device in a contact-free manner. We realize both a sound-driven battery and an acoustic photodetector. Our findings open directions to non-invasive investigation of electrical properties of monolayer films.

  15. Laser Direct Writing Process for Making Electrodes and High-k Sol-Gel ZrO2 for Boosting Performances of MoS2 Transistors.

    Science.gov (United States)

    Kwon, Hyuk-Jun; Jang, Jaewon; Grigoropoulos, Costas P

    2016-04-13

    A series of two-dimensional (2D) transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS2), can be attractive materials for photonic and electronic applications due to their exceptional properties. Among these unique properties, high mobility of 2D TMDCs enables realization of high-performance nanoelectronics based on a thin film transistor (TFT) platform. In this contribution, we report highly enhanced field effect mobility (μ(eff) = 50.1 cm(2)/(V s), ∼2.5 times) of MoS2 TFTs through the sol-gel processed high-k ZrO2 (∼22.0) insulator, compared to those of typical MoS2/SiO2/Si structures (μ(eff) = 19.4 cm(2)/(V s)) because a high-k dielectric layer can suppress Coulomb electron scattering and reduce interface trap concentration. Additionally, in order to avoid costly conventional mask based photolithography and define the patterns, we employ a simple laser direct writing (LDW) process. This process allows precise and flexible control with reasonable resolution (up to ∼10 nm), depending on the system, and enables fabrication of arbitrarily patterned devices. Taking advantage of continuing developments in laser technology offers a substantial cost decrease, and LDW may emerge as a promising technology. PMID:27011225

  16. Density functional theory study of Li, Na, and Mg intercalation and diffusion in MoS2 with controlled interlayer spacing

    Science.gov (United States)

    Shuai, Jing; Deog Yoo, Hyun; Liang, Yanliang; Li, Yifei; Yao, Yan; Grabow, Lars C.

    2016-06-01

    Layered materials, such as the transition metal dichalcogenide molybdenum disulfide (MoS2), are promising materials for ion storage in electrodes of rechargeable batteries. To extend the application range of these materials to ions beyond lithium-ions, we used van der Waals corrected density functional theory simulations to study the intercalation and diffusion of lithium (Li), sodium (Na), and magnesium (Mg) in the 2H structure of MoS2 as a function of interlayer spacing. All three species exhibit an optimal intercalation energy, which is reached at about 11% expansion for Li and Mg, and 23% expansion for Na. Similarly, the slow diffusion kinetics of large Na and divalent Mg-ions can be improved by layer expansion. When the interlayer spacing is increased by about 35% from its equilibrium value, the diffusion of Na and Mg-ions becomes more facile than the diffusion of small, monovalent Li-ions, with diffusion barriers similar to those of Li in graphene. Our results indicate that interlayer expansion is a promising technique to improve intercalation kinetics and thermodynamics for large and/or multivalent ions in MoS2, which can be a major limitation to battery performance. The rationalization of our results in terms of bonding geometries forms the basis of a battery electrode design framework with applications for a wide range of layered materials.

  17. Free MoS2 Nanoflowers Grown on Graphene by Microwave-Assisted Synthesis as Highly Efficient Non-Noble-Metal Electrocatalysts for the Hydrogen Evolution Reaction

    Science.gov (United States)

    Cao, Jiamu; Zhang, Xuelin; Zhang, Yufeng; Zhou, Jing; Chen, Yinuo; Liu, Xiaowei

    2016-01-01

    Advanced approaches to preparing non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) are considered to be a significant breakthrough in promoting the exploration of renewable resources. In this work, a hybrid material of MoS2 nanoflowers (NFs) on reduced graphene oxide (rGO) was synthesized as a HER catalyst via an environmentally friendly, efficient approach that is also suitable for mass production. Small-sized MoS2 NFs with a diameter of ca. 190 nm and an abundance of exposed edges were prepared by a hydrothermal method and were subsequently supported on rGO by microwave-assisted synthesis. The results show that MoS2 NFs were distributed uniformly on the remarkably reduced GO and preserved the outstanding original structural features perfectly. Electrochemical tests show that the as-prepared hybrid material exhibited excellent HER activity, with a small Tafel slope of 80 mV/decade and a low overpotential of 170 mV. PMID:27556402

  18. 2D Space-Confined Synthesis of Few-Layer MoS2 Anchored on Carbon Nanosheet for Lithium-Ion Battery Anode.

    Science.gov (United States)

    Zhou, Jingwen; Qin, Jian; Zhang, Xiang; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun; Zhao, Naiqin; He, Chunnian

    2015-04-28

    A facile and scalable 2D spatial confinement strategy is developed for in situ synthesizing highly crystalline MoS2 nanosheets with few layers (≤5 layers) anchored on 3D porous carbon nanosheet networks (3D FL-MoS2@PCNNs) as lithium-ion battery anode. During the synthesis, 3D self-assembly of cubic NaCl particles is adopted to not only serve as a template to direct the growth of 3D porous carbon nanosheet networks, but also create a 2D-confined space to achieve the construction of few-layer MoS2 nanosheets robustly lain on the surface of carbon nanosheet walls. In the resulting 3D architecture, the intimate contact between the surfaces of MoS2 and carbon nanosheets can effectively avoid the aggregation and restacking of MoS2 as well as remarkably enhance the structural integrity of the electrode, while the conductive matrix of 3D porous carbon nanosheet networks can ensure fast transport of both electrons and ions in the whole electrode. As a result, this unique 3D architecture manifests an outstanding long-life cycling capability at high rates, namely, a specific capacity as large as 709 mAh g(-1) is delivered at 2 A g(-1) and maintains ∼95.2% even after 520 deep charge/discharge cycles. Apart from promising lithium-ion battery anode, this 3D FL-MoS2@PCNN composite also has immense potential for applications in other areas such as supercapacitor, catalysis, and sensors.

  19. Investigations on MgO-dielectric GaN/AlGaN/GaN MOS-HEMTs by using an ultrasonic spray pyrolysis deposition technique

    Science.gov (United States)

    Lee, Ching-Sung; Hsu, Wei-Chou; Liu, Han-Yin; Wu, Ting-Ting; Sun, Wen-Ching; Wei, Sung-Yen; Yu, Sheng-Min

    2016-05-01

    This work investigates GaN/Al0.24Ga0.76N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) grown on a Si substrate with MgO gate dielectric by using the non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. The oxide layer thickness is tuned to be 30 nm with the dielectric constant of 8.8. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), transmission electron microscopy (TEM), C-V, low-frequency noise spectra, and pulsed I-V measurements are performed to characterize the interface and oxide quality for the MOS-gate structure. Improved device performances have been successfully achieved for the present MOS-HEMT (Schottky-gate HEMT) design, consisting of a maximum drain-source current density (I DS, max) of 681 (500) mA/mm at V GS = 4 (2) V, I DS at V GS = 0 V (I DSS0) of 329 (289) mA/mm, gate-voltage swing (GVS) of 2.2 (1.6) V, two-terminal gate-drain breakdown voltage (BV GD) of -123 (-104) V, turn-on voltage (V on) of 1.7 (0.8) V, three-terminal off-state drain-source breakdown voltage (BV DS) of 119 (96) V, and on/off current ratio (I on/I off) of 2.5 × 108 (1.2 × 103) at 300 K. Improved high-frequency and power performances are also achieved in the present MOS-HEMT design.

  20. One-dimensional metallic edge states in MoS2

    DEFF Research Database (Denmark)

    Bollinger, Mikkel; Lauritsen, J.V.; Jacobsen, Karsten Wedel;

    2001-01-01

    By the use of density functional calculations it is shown that the edges of a two-dimensional slab of insulating MoS2 exhibit several metallic states. These edge states can be viewed as one-dimensional conducting wires, and we show that they can be observed directly using scanning tunneling...... microscopy for single-layer MoS2 nanoparticles grown on a support....