WorldWideScience

Sample records for atomic layer graphene

  1. Atomic layer deposition of high-k oxides on graphene

    OpenAIRE

    Alles, Harry; Aarik, Jaan; Kozlova, Jekaterina; Niilisk, Ahti; Rammula, Raul; Sammelselg, Väino

    2011-01-01

    Comment: Graphene - Synthesis, Characterization, Properties and Applications, Jian Ru Gong (Ed.), ISBN: 978-953-307-292-0, InTech, Available from: http://www.intechopen.com/articles/show/title/atomic-layer-deposition-of-high-k-oxides-on-graphene

  2. Interfacial Atomic Structure of Twisted Few-Layer Graphene

    OpenAIRE

    Ryo Ishikawa; Nathan R. Lugg; Kazutoshi Inoue; Hidetaka Sawada; Takashi Taniguchi; Naoya Shibata; Yuichi Ikuhara

    2016-01-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterize...

  3. A DFT study of halogen atoms adsorbed on graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros, Paulo V C; De Brito Mota, F; De Castilho, Caio M C [Grupo de Fisica de Superfcies e Materiais, Instituto de Fisica, Universidade Federal da Bahia, Campus Universitario da Federacao/Ondina, 40170-115 Salvador, Bahia (Brazil); Mascarenhas, Artur J S, E-mail: caio@ufba.br [Instituto Nacional de Ciencia e Tecnologia em Energia e Ambiente-INCT-E and A, Universidade Federal da Bahia, 40170-280 Salvador, Bahia (Brazil)

    2010-12-03

    In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp{sup 2} to sp{sup 3} transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16 eV at the {Gamma} point, which is a value that is close to the value of 3.50 eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.

  4. Plasma enhanced atomic layer deposition of ultrathin oxides on graphene

    Science.gov (United States)

    Trimble, Christie J.; Zaniewski, Anna M.; Kaur, Manpuneet; Nemanich, Robert J.

    2015-03-01

    Graphene, a single atomic layer of sp2 bonded carbon atoms, possesses extreme material properties that point toward a plethora of potential electronic applications. Many of these possibilities require the combination of graphene with dielectric materials such as metal oxides. Simultaneously, there is interest in new physical properties that emerge when traditionally three dimensional materials are constrained to ultrathin layers. For both of these objectives, we explore deposition of ultrathin oxide layers on graphene. In this project, we perform plasma enhanced atomic layer deposition (PEALD) of aluminum oxide on graphene that has been grown by chemical vapor deposition atop copper foil and achieve oxide layers that are <1.5 nm. Because exposure to oxygen plasma can cause the graphene to deteriorate, we explore techniques to mitigate this effect and optimize the PEALD process. Following deposition, the graphene and oxide films are transferred to arbitrary substrates for further analysis. We use x-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy to assess the quality of the resulting films. This work is supported by the National Science Foundation under Grant # DMR-1206935.

  5. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    Science.gov (United States)

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A

    2015-08-27

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  6. Interfacial Atomic Structure of Twisted Few-Layer Graphene.

    Science.gov (United States)

    Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene. PMID:26888259

  7. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides

    Science.gov (United States)

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeißer, Dieter; van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; de Gendt, Stefan

    2015-06-01

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the

  8. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling.

    Science.gov (United States)

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2016-01-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene. PMID:26645468

  9. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling

    Science.gov (United States)

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2015-12-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene. Electronic supplementary information (ESI) available: Three TEM movies, additional TEM data corresponding to movies, calculated models, and lifetime results. See DOI: 10.1039/c5nr05913e

  10. Atomic layer deposition of HfO2 on graphene through controlled ion beam treatment

    Science.gov (United States)

    Kim, Ki Seok; Oh, Il-Kwon; Jung, Hanearl; Kim, Hyungjun; Yeom, Geun Young; Kim, Kyong Nam

    2016-05-01

    The polymer residue generated during the graphene transfer process to the substrate tends to cause problems (e.g., a decrease in electron mobility, unwanted doping, and non-uniform deposition of the dielectric material). In this study, by using a controllable low-energy Ar+ ion beam, we cleaned the polymer residue without damaging the graphene network. HfO2 grown by atomic layer deposition on graphene cleaned using an Ar+ ion beam showed a dense uniform structure, whereas that grown on the transferred graphene (before Ar+ ion cleaning) showed a non-uniform structure. A graphene-HfO2-metal capacitor fabricated by growing 20-nm thick HfO2 on graphene exhibited a very low leakage current (graphene, whereas a similar capacitor grown using the transferred graphene showed high leakage current.

  11. Visualization of arrangements of carbon atoms in graphene layers by Raman mapping and atomic-resolution TEM

    KAUST Repository

    Cong, Chunxiao

    2013-02-01

    In-plane and out-of-plane arrangements of carbon atoms in graphene layers play critical roles in the fundamental physics and practical applications of these novel two-dimensional materials. Here, we report initial results on the edge/crystal orientations and stacking orders of bi-and tri-layer graphene (BLG and TLG) from Raman spectroscopy and transmission electron microscopy (TEM) experiments performed on the same sample. We introduce a new method of transferring graphene flakes onto a normal TEM grid. Using this novel method, we probed the BLG and TLG flakes that had been previously investigated by Raman scattering with high-resolution (atomic) TEM.

  12. Graphene Coatings: Probing the Limits of the One Atom Thick Protection Layer

    DEFF Research Database (Denmark)

    Nilsson, Louis; Andersen, Mie; Balog, Richard;

    2012-01-01

    The limitations of graphene as an effective corrosion-inhibiting coating on metal surfaces, here exemplified by the hex-reconstructed Pt(100) surface, are probed by scanning tunneling microscopy measurements and density functional theory calculations. While exposure of small molecules directly onto...... the Pt(100) surface will lift the reconstruction, a single graphene layer is observed to act as an effective coating, protecting the reactive surface from O2 exposure and thus preserving the reconstruction underneath the graphene layer in O2 pressures as high as 104 mbar. A similar protective effect...... against CO is observed at CO pressures below 106 mbar. However, at higher pressures CO is observed to intercalate under the graphene coating layer, thus lifting the reconstruction. The limitations of the coating effect are further tested by exposure to hot atomic hydrogen. While the coating can withstand...

  13. Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

    International Nuclear Information System (INIS)

    Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy. The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS2) and graphene-like BN sheets

  14. Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Chunqiang, E-mail: chunqiang.zhuang@bjut.edu.cn [Beijing Key Laboratory of Microstructure and Properties of Advanced Materials, Beijing University of Technology, Beijing 100124 (China); Liu, Lei [Institute of Earthquake Science, China Earthquake Administration, Beijing 10036 (China)

    2015-03-21

    Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy. The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS{sub 2}) and graphene-like BN sheets.

  15. Growth of Few-Layer Graphene on Sapphire Substrates by Directly Depositing Carbon Atoms

    Institute of Scientific and Technical Information of China (English)

    KANG Chao-Yang; TANG Jun; LIU Zhong-Liang; LI Li-Min; YAN Wen-Sheng; WEI Shi-Qiang; XU Peng-Shou

    2011-01-01

    Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300℃ in a molecular beam epitaxy chamber.The reflection high energy diffraction,Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample,which confirm the formation of graphene layers.The mean domain size of FLG is around 29.2 nm and the layer number is about 2-3.The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated a-SiC surface.Graphene,a monolayer of sp2-bonded carbon atoms,is a quasi two-dimensional (2D) material.It has attracted great interest because of its distinctive band structure and physical properties.[1] Graphene can now be obtained by several different approaches including micromechanical[1] and chemical[2] exfoliation of graphite,epitaxial growth on hexagonal SiC substrates by Si sublimation in vacuum,[3] and CVD growth on metal substrates.[4] However,these preparation methods need special substrates,otherwise,in order to design microelectronic devices,the prepared graphene should be transferred to other appropriate substrates.Thus the growth of graphene on the suitable substrates is motivated.%Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300℃ in a molecular beam epitaxy chamber. The reflection high energy diffraction, Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample, which confirm the formation of graphene layers. The mean domain size of FLG is around 29.2nm and the layer number is about 2-3. The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated α-SiC surface.

  16. Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina

    OpenAIRE

    Johns, James E.; Karmel, Hunter J.; Alaboson, Justice M. P.; Hersam, Mark C.

    2012-01-01

    The superlative electronic properties of graphene suggest its use as the foundation of next generation integrated circuits. However, this application requires precise control of the interface between graphene and other materials, especially the metal oxides that are commonly used as gate dielectrics. Towards that end, organic seeding layers have been empirically shown to seed ultrathin dielectric growth on graphene via atomic layer deposition (ALD), although the underlying chemical mechanisms...

  17. Seeding atomic layer deposition of high-k dielectric on graphene with ultrathin poly(4-vinylphenol) layer for enhanced device performance and reliability

    Science.gov (United States)

    Cheol Shin, Woo; Yong Kim, Taek; Sul, Onejae; Jin Cho, Byung

    2012-07-01

    We demonstrate that ultrathin poly(4-vinylphenol) (PVP) acts as an effective organic seeding layer for atomic layer deposition (ALD) of high-k dielectric on large-scale graphene fabricated by chemical vapor deposition (CVD). While identical ALD conditions result in incomplete and rough dielectric deposition on CVD graphene, the reactive groups provided by the PVP seeding layer yield conformal and pinhole-free dielectric films throughout the large-scale graphene. Top-gate graphene field effect transistors fabricated with the high quality, PVP-seeded Al2O3 gate dielectric show superior carrier mobility and enhanced reliability performance, which are desirable for graphene nanoelectronics.

  18. High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

    Energy Technology Data Exchange (ETDEWEB)

    Mu, Haichuan; Zhang, Zhiqiang; Wang, Keke; Xie, Haifen, E-mail: hfxie@ecust.edu.cn [Department of Physics, School of Science, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Zhao, Xiaojing; Liu, Feng [Department of Physics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

    2014-07-21

    Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

  19. High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

    Science.gov (United States)

    Mu, Haichuan; Zhang, Zhiqiang; Zhao, Xiaojing; Liu, Feng; Wang, Keke; Xie, Haifen

    2014-07-01

    Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

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

    KAUST Repository

    Lin, Yu-Chuan

    2014-11-10

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

  1. Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone.

    Science.gov (United States)

    Jandhyala, Srikar; Mordi, Greg; Lee, Bongki; Lee, Geunsik; Floresca, Carlo; Cha, Pil-Ryung; Ahn, Jinho; Wallace, Robert M; Chabal, Yves J; Kim, Moon J; Colombo, Luigi; Cho, Kyeongjae; Kim, Jiyoung

    2012-03-27

    Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.

  2. Quantitative Assessment of Friction Characteristics of Single-Layer MoS2 and Graphene Using Atomic Force Microscopy.

    Science.gov (United States)

    Khac, Bien-cuong tran; Chung, Koo-hyun

    2016-05-01

    Atomically thin layered materials such as MoS2 and graphene have attracted a lot of interest as protective coating layers for micro- and nano-electromechanical devices based on their superior mechanical properties and chemical inertness. In this work, the frictional characteristics of single layer MoS2 and graphene prepared by the mechanical exfoliation method were quantitatively investigated using atomic force microscopy. The results showed that both MoS2 and graphene exhibited relatively low friction forces of 1-3 nN under normal forces ranging from 1 to 30 nN. However, a higher increase in the friction force as the normal force increased was observed in the case of MoS2. The differences in the adhesion characteristics and mechanical properties of atomically thin layered materials may influence the puckering of the layer, which in turn influences the frictional behavior. PMID:27483768

  3. Interactions between fluorescence of atomically layered graphene oxide and metallic nanoparticles

    Science.gov (United States)

    Wang, Yu; Li, Shao-Sian; Yeh, Yun-Chieh; Yu, Chen-Chieh; Chen, Hsuen-Li; Li, Feng-Chieh; Chang, Yu-Ming; Chen, Chun-Wei

    2013-01-01

    Graphene oxide (GO) demonstrates interesting photoluminescence (PL) because of its unique heterogeneous atomic structure, which consists of variable sp2- and sp3-bonded carbons. In this study, we report the interaction between the luminescence of GO ranging from a single atomic layer to few-layered thin films and localized surface plasmon resonance (LSPR) from silver nanoparticles (Ag NPs). The photoluminescence of GO in the vicinity of the Ag NPs is enhanced significantly due to the near-field plasmonic effect by coupling electron-hole pairs of GO with oscillating electrons in Ag NPs, leading to an increased PL intensity and a decreased PL decay lifetime. The maxima 30-fold enhancement in PL intensity is obtained with an optimized film thickness of GO, and the luminescence image from a single atomic layer GO sheet is successfully observed with the assistance of the LSPR effect. The results provide an ideal platform for exploring the interactions between the fluorescence of two-dimensional layered materials and the LSPR effect.Graphene oxide (GO) demonstrates interesting photoluminescence (PL) because of its unique heterogeneous atomic structure, which consists of variable sp2- and sp3-bonded carbons. In this study, we report the interaction between the luminescence of GO ranging from a single atomic layer to few-layered thin films and localized surface plasmon resonance (LSPR) from silver nanoparticles (Ag NPs). The photoluminescence of GO in the vicinity of the Ag NPs is enhanced significantly due to the near-field plasmonic effect by coupling electron-hole pairs of GO with oscillating electrons in Ag NPs, leading to an increased PL intensity and a decreased PL decay lifetime. The maxima 30-fold enhancement in PL intensity is obtained with an optimized film thickness of GO, and the luminescence image from a single atomic layer GO sheet is successfully observed with the assistance of the LSPR effect. The results provide an ideal platform for exploring the

  4. Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition.

    Science.gov (United States)

    Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Shaygan, Mehrdad; Turner, Kevin T; Bargatin, Igor

    2016-04-15

    We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al2O3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young's modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young's modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

  5. Single-Atom Pd₁/Graphene Catalyst Achieved by Atomic Layer Deposition: Remarkable Performance in Selective Hydrogenation of 1,3-Butadiene.

    Science.gov (United States)

    Yan, Huan; Cheng, Hao; Yi, Hong; Lin, Yue; Yao, Tao; Wang, Chunlei; Li, Junjie; Wei, Shiqiang; Lu, Junling

    2015-08-26

    We reported that atomically dispersed Pd on graphene can be fabricated using the atomic layer deposition technique. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy both confirmed that isolated Pd single atoms dominantly existed on the graphene support. In selective hydrogenation of 1,3-butadiene, the single-atom Pd1/graphene catalyst showed about 100% butenes selectivity at 95% conversion at a mild reaction condition of about 50 °C, which is likely due to the changes of 1,3-butadiene adsorption mode and enhanced steric effect on the isolated Pd atoms. More importantly, excellent durability against deactivation via either aggregation of metal atoms or carbonaceous deposits during a total 100 h of reaction time on stream was achieved. Therefore, the single-atom catalysts may open up more opportunities to optimize the activity, selectivity, and durability in selective hydrogenation reactions. PMID:26268551

  6. Wafer-scale single-domain-like graphene by defect-selective atomic layer deposition of hexagonal ZnO

    Science.gov (United States)

    Park, Kyung Sun; Kim, Sejoon; Kim, Hongbum; Kwon, Deokhyeon; Koo Lee, Yong-Eun; Min, Sung-Wook; Im, Seongil; Choi, Hyoung Joon; Lim, Seulky; Shin, Hyunjung; Koo, Sang Man; Sung, Myung Mo

    2015-10-01

    Large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain numerous grain boundaries that can greatly degrade their performance and produce inhomogeneous properties. A better grain boundary engineering in CVD graphene is essential to realize the full potential of graphene in large-scale applications. Here, we report a defect-selective atomic layer deposition (ALD) for stitching grain boundaries of CVD graphene with ZnO so as to increase the connectivity between grains. In the present ALD process, ZnO with a hexagonal wurtzite structure was selectively grown mainly on the defect-rich grain boundaries to produce ZnO-stitched CVD graphene with well-connected grains. For the CVD graphene film after ZnO stitching, the inter-grain mobility is notably improved with only a little change in the free carrier density. We also demonstrate how ZnO-stitched CVD graphene can be successfully integrated into wafer-scale arrays of top-gated field-effect transistors on 4-inch Si and polymer substrates, revealing remarkable device-to-device uniformity.Large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain numerous grain boundaries that can greatly degrade their performance and produce inhomogeneous properties. A better grain boundary engineering in CVD graphene is essential to realize the full potential of graphene in large-scale applications. Here, we report a defect-selective atomic layer deposition (ALD) for stitching grain boundaries of CVD graphene with ZnO so as to increase the connectivity between grains. In the present ALD process, ZnO with a hexagonal wurtzite structure was selectively grown mainly on the defect-rich grain boundaries to produce ZnO-stitched CVD graphene with well-connected grains. For the CVD graphene film after ZnO stitching, the inter-grain mobility is notably improved with only a little change in the free carrier density. We also

  7. Seeding Atomic Layer Deposition of High-k Dielectrics on Epitaxial Graphene with Organic Self-assembled Monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Alaboson, Justice M. P.; Wang, Qing Hua; Emery, J.D.; Lipson, Albert L; Bedzyk, M.J.; Elam, Jeffrey W.; Pellin, Michael J.; Hersam, Mark C.

    2011-06-28

    The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO₂ and Al₂O₃ on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al₂O₃ and 10 nm HfO₂ dielectric stack show high capacitance values of ~700 nF/cm² and low leakage currents of ~5 × 10{sup –9} A/cm² at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics.

  8. Seeding atomic layer deposition of high-k dielectrics on epitaxial graphene with organic self-assembled monolayers.

    Science.gov (United States)

    Alaboson, Justice M P; Wang, Qing Hua; Emery, Jonathan D; Lipson, Albert L; Bedzyk, Michael J; Elam, Jeffrey W; Pellin, Michael J; Hersam, Mark C

    2011-06-28

    The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO(2) and Al(2)O(3) on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al(2)O(3) and 10 nm HfO(2) dielectric stack show high capacitance values of ∼700 nF/cm(2) and low leakage currents of ∼5 × 10(-9) A/cm(2) at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics. PMID:21553842

  9. Tunnel spin injection into graphene using Al{sub 2}O{sub 3} barrier grown by atomic layer deposition on functionalized graphene surface

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, Takehiro, E-mail: yamatake@iis.u-tokyo.ac.jp [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Masubuchi, Satoru [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Iguchi, Kazuyuki [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Machida, Tomoki [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012 (Japan)

    2012-03-15

    We demonstrate electrical tunnel spin injection from a ferromagnet to graphene through a high-quality Al{sub 2}O{sub 3} grown by atomic layer deposition (ALD). The graphene surface is functionalized with a self-assembled monolayer of 3,4,9,10-perylene tetracarboxylic acid (PTCA) to promote adhesion and growth of Al{sub 2}O{sub 3} with a smooth surface. Using this composite tunnel barrier of ALD-Al{sub 2}O{sub 3} and PTCA, a spin injection signal of {approx}30 {Omega} has been observed from non-local magnetoresistance measurements at 45 K, revealing potentially high performance of ALD-Al{sub 2}O{sub 3}/PTCA tunnel barrier for spin injection into graphene. - Highlights: Black-Right-Pointing-Pointer Graphene spin-valve devices using Ni{sub 81}Fe{sub 19}/Al{sub 2}O{sub 3} electrodes are fabricated. Black-Right-Pointing-Pointer Atomic layer deposition (ALD) is used to fabricate Al{sub 2}O{sub 3} tunnel barrier. Black-Right-Pointing-Pointer Graphene surface is terminated with a 3,4,9,10-perylene tetracarboxylic acid (PTCA). Black-Right-Pointing-Pointer Non-local magneto-resistance (MR) as large as 30 {Omega} is demonstrated. Black-Right-Pointing-Pointer Tunnel spin injection into the graphene is achieved with ALD-grown tunnel barrier.

  10. Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina.

    Science.gov (United States)

    Johns, James E; Karmel, Hunter J; Alaboson, Justice M P; Hersam, Mark C

    2012-07-11

    The superlative electronic properties of graphene suggest its use as the foundation of next generation integrated circuits. However, this application requires precise control of the interface between graphene and other materials, especially the metal oxides that are commonly used as gate dielectrics. Towards that end, organic seeding layers have been empirically shown to seed ultrathin dielectric growth on graphene via atomic layer deposition (ALD), although the underlying chemical mechanisms and structural details of the molecule/dielectric interface remain unknown. Here, confocal resonance Raman spectroscopy is employed to quantify the structure and chemistry of monolayers of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on graphene before and after deposition of alumina with the ALD precursors trimethyl aluminum (TMA) and water. Photoluminescence measurements provide further insight into the details of the growth mechanism, including the transition between layer-by-layer growth and island formation. Overall, these results reveal that PTCDA is not consumed during ALD, thereby preserving a well-defined and passivating organic interface between graphene and deposited dielectric thin films. PMID:22905282

  11. Enhanced Breakdown Reliability and Spatial Uniformity of Atomic Layer Deposited High-k Gate Dielectrics on Graphene via Organic Seeding Layers

    Science.gov (United States)

    Sangwan, Vinod; Jariwala, Deep; Filippone, Stephen; Karmel, Hunter; Johns, James; Alaboson, Justice; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark

    2013-03-01

    Ultra-thin high- κ top-gate dielectrics are essential for high-speed graphene-based nanoelectronic circuits. Motivated by the need for high reliability and spatial uniformity, we report here the first statistical analysis of the breakdown characteristics of dielectrics grown on graphene. Based on these measurements, a rational approach is devised that simultaneously optimizes the gate capacitance and the key parameters of large-area uniformity and dielectric strength. In particular, vertically heterogeneous oxide stacks grown via atomic-layer deposition (ALD) seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) organic monolayer result in improved reliability (Weibull shape parameter β > 25) compared to the control dielectric directly grown on graphene without PTCDA (β 7 MV/cm) that is comparable to that of the control dielectric grown on Si substrates.

  12. Bottom-gate coplanar graphene transistors with enhanced graphene adhesion on atomic layer deposition Al{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Park, Dong-Wook; Mikael, Solomon; Chang, Tzu-Hsuan; Ma, Zhenqiang, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Gong, Shaoqin [Department of Biomedical Engineering, and Wisconsin Institute for Discovery, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2015-03-09

    A graphene transistor with a bottom-gate coplanar structure and an atomic layer deposition (ALD) aluminum oxide (Al{sub 2}O{sub 3}) gate dielectric is demonstrated. Wetting properties of ALD Al{sub 2}O{sub 3} under different deposition conditions are investigated by measuring the surface contact angle. It is observed that the relatively hydrophobic surface is suitable for adhesion between graphene and ALD Al{sub 2}O{sub 3}. To achieve hydrophobic surface of ALD Al{sub 2}O{sub 3}, a methyl group (CH{sub 3})-terminated deposition method has been developed and compared with a hydroxyl group (OH)-terminated deposition. Based on this approach, bottom-gate coplanar graphene field-effect transistors are fabricated and characterized. A post-thermal annealing process improves the performance of the transistors by enhancing the contacts between the source/drain metal and graphene. The fabricated transistor shows an I{sub on}/I{sub off} ratio, maximum transconductance, and field-effect mobility of 4.04, 20.1 μS at V{sub D} = 0.1 V, and 249.5 cm{sup 2}/V·s, respectively.

  13. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    Science.gov (United States)

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

  14. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    Science.gov (United States)

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts. PMID:27124605

  15. Atomic layer deposition of ZrO2 for graphene-based multilayer structures: In situ and ex situ characterization of growth process

    International Nuclear Information System (INIS)

    Real time monitoring of atomic layer deposition by quartz crystal microbalance (QCM) was used to follow the growth of ZrO2 thin films on graphene. The films were grown from ZrCl4 and H2O on graphene prepared by chemical vapor deposition method on 100-nm thick nickel film or on Cu-foil and transferred onto QCM sensor. The deposition was performed at a substrate temperature of 190 C. The growth of the dielectric film on graphene was significantly retarded compared to the process carried out on QCM without graphene. After the deposition of dielectric films, the basic structure of graphene was retained. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors.

    Science.gov (United States)

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-01-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8" glass wafer. PMID:26861833

  17. Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors

    Science.gov (United States)

    Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

    2016-02-01

    The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer.

  18. Discrete atomic layers at the molecular level

    International Nuclear Information System (INIS)

    In this review, we deal with the syntheses of large discrete atomic layers at the molecular level. Spectroscopic measurements as well as X-ray crystallographic analyses lead to unambiguous characterizations of these layers. The molecular atomic layers can be considered to be parts of graphenes and related atomic layers, thereby helping to understand such indefinitely huge atomic layers or serving as seeds for the controlled synthesis of nanocarbons. (author)

  19. Dispersion coefficients for the interactions of the alkali and alkaline-earth ions and inert gas atoms with a graphene layer

    CERN Document Server

    Kaur, Kiranpreet; Sahoo, B K

    2015-01-01

    Largely motivated by a number of applications, the van der Waals dispersion coefficients ($C_3$s) of the alkali ions (Li$^+$, Na$^+$, K$^+$ and Rb$^+$), the alkaline-earth ions (Ca$^+$, Sr$^+$, Ba$^+$ and Ra$^+$) and the inert gas atoms (He, Ne, Ar and Kr) with a graphene layer are determined precisely within the framework of Dirac model. For these calculations, we have evaluated the dynamic polarizabilities of the above atomic systems very accurately by evaluating the transition matrix elements employing relativistic many-body methods and using the experimental values of the excitation energies. The dispersion coefficients are, finally, given as functions of the separation distance of an atomic system from the graphene layer and the ambiance temperature during the interactions. For easy extraction of these coefficients, we give a logistic fit to the functional forms of the dispersion coefficients in terms of the separation distances at the room temperature.

  20. Dispersion coefficients for the interactions of the alkali-metal and alkaline-earth-metal ions and inert-gas atoms with a graphene layer

    Science.gov (United States)

    Kaur, Kiranpreet; Arora, Bindiya; Sahoo, B. K.

    2015-09-01

    Largely motivated by a number of applications, the van der Waals dispersion coefficients C3 of the alkali-metal ions Li+,Na+,K+, and Rb+, the alkaline-earth-metal ions Ca+,Sr+,Ba+, and Ra+, and the inert-gas atoms He, Ne, Ar, and Kr with a graphene layer are determined precisely within the framework of the Dirac model. For these calculations, we evaluate the dynamic polarizabilities of the above atomic systems very accurately by evaluating the transition matrix elements employing relativistic many-body methods and using the experimental values of the excitation energies. The dispersion coefficients are given as functions of the separation distance of an atomic system from the graphene layer and the ambiance temperature during the interactions. For easy extraction of these coefficients, we give a logistic fit to the functional forms of the dispersion coefficients in terms of the separation distances at room temperature.

  1. Controlled direct growth of Al2O3-doped HfO2 films on graphene by H2O-based atomic layer deposition.

    Science.gov (United States)

    Zheng, Li; Cheng, Xinhong; Yu, Yuehui; Xie, Yahong; Li, Xiaolong; Wang, Zhongjian

    2015-02-01

    Graphene has been drawing worldwide attention since its discovery in 2004. In order to realize graphene-based devices, thin, uniform-coverage and pinhole-free dielectric films with high permittivity on top of graphene are required. Here we report the direct growth of Al2O3-doped HfO2 films onto graphene by H2O-based atom layer deposition (ALD). Al2O3-onto-HfO2 stacks benefited the doping of Al2O3 into HfO2 matrices more than HfO2-onto-Al2O3 stacks did due to the micro-molecular property of Al2O3 and the high chemical activity of trimethylaluminum (TMA). Al2O3 acted as a network modifier, maintained the amorphous structure of the film even to 800 °C, and made the film smooth with a root mean square (RMS) roughness of 0.8 nm, comparable to the surface of pristine graphene. The capacitance and the relative permittivity of Al2O3-onto-HfO2 stacks were up to 1.18 μF cm(-2) and 12, respectively, indicating the high quality of Al2O3-doped HfO2 films on graphene. Moreover, the growth process of Al2O3-doped HfO2 films introduced no detective defects into graphene confirmed by Raman measurements. PMID:25519447

  2. Charge Transfer Properties Through Graphene Layers in Gas Detectors

    CERN Document Server

    Thuiner, P; Jackman, R.B.; Müller, H.; Nguyen, T.T.; Oliveri, E.; Pfeiffer, D.; Resnati, F.; Ropelewski, L.; Smith, J.A.; van Stenis, M.; Veenhof, R.

    2015-01-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.

  3. Dual-protection of a graphene-sulfur composite by a compact graphene skin and an atomic layer deposited oxide coating for a lithium-sulfur battery.

    Science.gov (United States)

    Yu, Mingpeng; Wang, Aiji; Tian, Fuyang; Song, Hongquan; Wang, Yinshu; Li, Chun; Hong, Jong-Dal; Shi, Gaoquan

    2015-03-12

    A reduced graphene oxide (rGO)-sulfur composite aerogel with a compact self-assembled rGO skin was further modified by an atomic layer deposition (ALD) of ZnO or MgO layer, and used as a free-standing electrode material of a lithium-sulfur (Li-S) battery. The rGO skin and ALD-oxide coating worked as natural and artificial barriers to constrain the polysulfides within the cathode region. As a result, the Li-S battery based on this electrode material exhibited superior cycling stability, good rate capability and high coulombic efficiency. Furthermore, ALD-ZnO coating was tested for performance improvement and found to be more effective than ALD-MgO coating. The ZnO modified G-S electrode with 55 wt% sulfur loading delivered a maximum discharge capacity of 998 mA h g(-1) at a current density of 0.2 C. A high capacity of 846 mA h g(-1) was achieved after charging/discharging for 100 cycles with a coulombic efficiency of over 92%. In the case of using LiNO3 as a shuttle inhibitor, this electrode showed an initial discharge capacity of 796 mA h g(-1) and a capacity retention of 81% after 250 cycles at a current density of 1 C with an average coulombic efficiency higher than 99.7%.

  4. Physisorbed-precursor-assisted atomic layer deposition of reliable ultrathin dielectric films on inert graphene surfaces for low-power electronics

    Science.gov (United States)

    Jeong, Seong-Jun; Kim, Hyo Won; Heo, Jinseong; Lee, Min-Hyun; Song, Hyun Jae; Ku, JiYeon; Lee, Yunseong; Cho, Yeonchoo; Jeon, Woojin; Suh, Hwansoo; Hwang, Sungwoo; Park, Seongjun

    2016-09-01

    Among the most fundamental challenges encountered in the successful incorporation of graphene in silicon-based electronics is the conformal growth of ultrathin dielectric films, especially those with thicknesses lower than 5 nm, on chemically inert graphene surfaces. Here, we present physisorbed-precursor-assisted atomic layer deposition (pALD) as an extremely robust method for fabricating such films. Using atomic-scale characterisation, it is confirmed that conformal and intact ultrathin Al2O3 films can be synthesised on graphene by pALD. The mechanism underlying the pALD process is identified through first-principles calculations based on density functional theory. Further, this novel deposition technique is used to fabricate two types of wafer-scale devices. It is found that the incorporation of a 5 nm-thick pALD Al2O3 gate dielectric film improves the performance of metal-oxide-graphene field-effect transistors to a greater extent than does the incorporation of a conventional ALD Al2O3 film. We also employ a 5 nm-thick pALD HfO2 film as a highly scalable dielectric layer with a capacitance equivalent oxide thickness of 1 nm in graphene-based tunnelling field-effect transistors fabricated on a glass wafer and achieve a subthreshold swing of 30 mV/dec. This significant improvement in switching allows for the low-voltage operation of an inverter within 0.5 V of both the drain and the gate voltages, thus paving the way for low-power electronics.

  5. In situ imaging and control of layer-by-layer femtosecond laser thinning of graphene

    Science.gov (United States)

    Li, D. W.; Zhou, Y. S.; Huang, X.; Jiang, L.; Silvain, J.-F.; Lu, Y. F.

    2015-02-01

    Although existing methods (chemical vapor deposition, mechanical exfoliation, etc.) are available to produce graphene, the lack of thickness control limits further graphene applications. In this study, we demonstrate an approach to precisely thin graphene films to a specific thickness using femtosecond (fs) laser raster scanning. By using appropriate laser fluence and scanning times, graphene thinning with an atomic layer precision, namely layer-by-layer graphene removal, has been realized. The fs laser used was configured in a four-wave mixing (FWM) system which can be used to distinguish graphene layer thickness and count the number of layers using the linear relationship between the FWM signal intensity and the graphene thickness. Furthermore, FWM imaging has been successfully applied to achieve in situ, real-time monitoring of the fs laser graphene thinning process. This method can not only realize the large-scale thinning of graphene with atomic layer precision, but also provide in situ, rapid imaging capability of graphene for an accurate assessment of the number of layers.Although existing methods (chemical vapor deposition, mechanical exfoliation, etc.) are available to produce graphene, the lack of thickness control limits further graphene applications. In this study, we demonstrate an approach to precisely thin graphene films to a specific thickness using femtosecond (fs) laser raster scanning. By using appropriate laser fluence and scanning times, graphene thinning with an atomic layer precision, namely layer-by-layer graphene removal, has been realized. The fs laser used was configured in a four-wave mixing (FWM) system which can be used to distinguish graphene layer thickness and count the number of layers using the linear relationship between the FWM signal intensity and the graphene thickness. Furthermore, FWM imaging has been successfully applied to achieve in situ, real-time monitoring of the fs laser graphene thinning process. This method can not

  6. Ultimate permeation across atomically thin porous graphene.

    Science.gov (United States)

    Celebi, Kemal; Buchheim, Jakob; Wyss, Roman M; Droudian, Amirhossein; Gasser, Patrick; Shorubalko, Ivan; Kye, Jeong-Il; Lee, Changho; Park, Hyung Gyu

    2014-04-18

    A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer. The measured transport rates are in agreement with predictions of 2D transport theories. Attributed to its atomic thicknesses, these porous graphene membranes show permeances of gas, liquid, and water vapor far in excess of those shown by finite-thickness membranes, highlighting the ultimate permeation these 2D membranes can provide. PMID:24744372

  7. Atomic Layer Epitaxy of h-BN(0001) Multilayers on Co(0001) and Molecular Beam Epitaxy Growth of Graphene on h-BN(0001)/Co(0001).

    Science.gov (United States)

    Driver, M Sky; Beatty, John D; Olanipekun, Opeyemi; Reid, Kimberly; Rath, Ashutosh; Voyles, Paul M; Kelber, Jeffry A

    2016-03-22

    The direct growth of hexagonal boron nitride (h-BN) by industrially scalable methods is of broad interest for spintronic and nanoelectronic device applications. Such applications often require atomically precise control of film thickness and azimuthal registry between layers and substrate. We report the formation, by atomic layer epitaxy (ALE), of multilayer h-BN(0001) films (up to 7 monolayers) on Co(0001). The ALE process employs BCl3/NH3 cycles at 600 K substrate temperature. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) data show that this process yields an increase in h-BN average film thickness linearly proportional to the number of BCl3/NH3 cycles, with BN layers in azimuthal registry with each other and with the Co(0001) substrate. LEED diffraction spot profile data indicate an average BN domain size of at least 1900 Å. Optical microscopy data indicate the presence of some domains as large as ∼20 μm. Transmission electron microscopy (TEM) and ambient exposure studies demonstrate macroscopic and microscopic continuity of the h-BN film, with the h-BN film highly conformal to the Co substrate. Photoemission data show that the h-BN(0001) film is p-type, with band bending near the Co/h-BN interface. Growth of graphene by molecular beam epitaxy (MBE) is observed on the surface of multilayer h-BN(0001) at temperatures of 800 K. LEED data indicate azimuthal graphene alignment with the h-BN and Co(0001) lattices, with domain size similar to BN. The evidence of multilayer BN and graphene azimuthal alignment with the lattice of the Co(0001) substrate demonstrates that this procedure is suitable for scalable production of heterojunctions for spintronic applications. PMID:26940024

  8. Proximity effects in cold atom artificial graphene

    CERN Document Server

    Grass, Tobias; Tarruell, Leticia; Pellegrini, Vittorio; Lewenstein, Maciej

    2016-01-01

    Cold atoms in an optical lattice with brick-wall geometry have been used to mimic graphene, a two-dimensional material with characteristic Dirac excitations. Here we propose to bring such artificial graphene into the proximity of a second atomic layer with a square lattice geometry. For non-interacting fermions, we find that such bilayer system undergoes a phase transition from a graphene-like semi-metal phase, characterized by a band structure with Dirac points, to a gapped band insulator phase. In the presence of attractive interactions between fermions with pseudospin-1/2 degree of freedom, a competition between semi-metal and superfluid behavior is found at the mean-field level. Upon tuning the coupling between the layers, the system exhibits re-entrant superfluid phases. Using the quantum Monte Carlo method, we also investigate the case of strong repulsive interactions. In the Mott phase, each layer exhibits a different amount of long-range magnetic order. Upon coupling both layers, a valence-bond crysta...

  9. Imaging of few‐layer graphene flakes

    DEFF Research Database (Denmark)

    Eriksen, René Lynge; Albrektsen, Ole; Novikov, Sergey M.;

    (ORM), atomic force microscopy (AFM), and scanning confocal Raman microscopy. The thickness map, revealing distinct terraces separated by steps corresponding to mono‐ and bilayers of graphene, is extracted from a pixel‐to‐pixel fitting of ellipsometric spectra using optical constants derived by fitting...... slab model calculations to averaged spectra collected in large homogenous sample areas. An analysis of reflection spectra and contrast images acquired by ORM confirm the results by quantifying the number of graphene layers and retrieving the FLG optical constants using a simple Fresnel‐law‐based slab...

  10. Detection of gas atoms via vibration of graphenes

    International Nuclear Information System (INIS)

    The application of single-layered graphene sheets as mass sensors in detection of noble gases via a vibration analysis of graphenes is investigated using molecular dynamics simulations. An index based on frequency shifts of the graphenes attached by the distinct noble gas atoms is defined and examined to measure the sensitivity of the sensors. The dependence of number and location of gas atoms, size of graphene sheets, and type of restrained boundary of the sheets on the sensitivity is particularly studied. The simulation results indicate the resolution of a mass sensor made of a square graphene sheet with a size of 10 nm can achieve an order of 10-6 femtograms and the mass sensitivity can be enhanced with a decrease in sizes of graphenes. -- Highlights: → The potential application of graphenes as sensors in detection of gas atoms is revealed. → A resolution around 10-6 femtograms of gas atoms by graphene sensors is reported. → The sensitivity of the sensors is found to be increased with shorter graphenes with stiffer ends. → The random locations of gas atoms have less effect on the detection effect.

  11. Detection of gas atoms via vibration of graphenes

    Energy Technology Data Exchange (ETDEWEB)

    Arash, Behrouz [Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, Manitoba R3T 5V6 (Canada); Wang, Quan, E-mail: q_wang@umanitoba.ca [Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, Manitoba R3T 5V6 (Canada); Duan, Wen Hui [Department of Civil Engineering, Monash University, Clayton, VIC 3168 (Australia)

    2011-06-13

    The application of single-layered graphene sheets as mass sensors in detection of noble gases via a vibration analysis of graphenes is investigated using molecular dynamics simulations. An index based on frequency shifts of the graphenes attached by the distinct noble gas atoms is defined and examined to measure the sensitivity of the sensors. The dependence of number and location of gas atoms, size of graphene sheets, and type of restrained boundary of the sheets on the sensitivity is particularly studied. The simulation results indicate the resolution of a mass sensor made of a square graphene sheet with a size of 10 nm can achieve an order of 10{sup -6} femtograms and the mass sensitivity can be enhanced with a decrease in sizes of graphenes. -- Highlights: → The potential application of graphenes as sensors in detection of gas atoms is revealed. → A resolution around 10{sup -6} femtograms of gas atoms by graphene sensors is reported. → The sensitivity of the sensors is found to be increased with shorter graphenes with stiffer ends. → The random locations of gas atoms have less effect on the detection effect.

  12. Detection of gas atoms via vibration of graphenes

    Science.gov (United States)

    Arash, Behrouz; Wang, Quan; Duan, Wen Hui

    2011-06-01

    The application of single-layered graphene sheets as mass sensors in detection of noble gases via a vibration analysis of graphenes is investigated using molecular dynamics simulations. An index based on frequency shifts of the graphenes attached by the distinct noble gas atoms is defined and examined to measure the sensitivity of the sensors. The dependence of number and location of gas atoms, size of graphene sheets, and type of restrained boundary of the sheets on the sensitivity is particularly studied. The simulation results indicate the resolution of a mass sensor made of a square graphene sheet with a size of 10 nm can achieve an order of 10 femtograms and the mass sensitivity can be enhanced with a decrease in sizes of graphenes.

  13. Metal Oxide Nanoparticle Growth on Graphene via Chemical Activation with Atomic Oxygen

    OpenAIRE

    Johns, James E.; Alaboson, Justice M. P.; Patwardhan, Sameer; Ryder, Christopher R.; Schatz, George C.; Hersam, Mark C.

    2013-01-01

    Chemically interfacing the inert basal plane of graphene with other materials has limited the development of graphene-based catalysts, composite materials, and devices. Here, we overcome this limitation by chemically activating epitaxial graphene on SiC(0001) using atomic oxygen. Atomic oxygen produces epoxide groups on graphene, which act as reactive nucleation sites for zinc oxide nanoparticle growth using the atomic layer deposition precursor diethyl zinc. In particular, exposure of epoxid...

  14. Nano-soldering to single atomic layer

    Science.gov (United States)

    Girit, Caglar O.; Zettl, Alexander K.

    2011-10-11

    A simple technique to solder submicron sized, ohmic contacts to nanostructures has been disclosed. The technique has several advantages over standard electron beam lithography methods, which are complex, costly, and can contaminate samples. To demonstrate the soldering technique graphene, a single atomic layer of carbon, has been contacted, and low- and high-field electronic transport properties have been measured.

  15. Characterization of metal oxide layers grown on CVD graphene

    International Nuclear Information System (INIS)

    Growth of a fully oxidized aluminum oxide layer with low surface roughness on graphene grown by chemical vapor deposition is demonstrated. This is accomplished by the deposition of a 0.2 nm thick titanium seed layer on the graphene prior to the deposition of the aluminum under ultra high vacuum conditions, which was subsequently oxidized. The stoichiometry and surface roughness of the oxide layers were measured for a range of titanium and aluminum depositions utilizing ex situ x-ray photoelectron spectrometry and atomic force microscopy. These fully oxidized films are expected to produce good dielectric layers for use in graphene based electronic devices.

  16. Atomic bonding between metal and graphene

    KAUST Repository

    Wang, Hongtao

    2013-03-07

    To understand structural and chemical properties of metal-graphene composites, it is crucial to unveil the chemical bonding along the interface. We provide direct experimental evidence of atomic bonding between typical metal nano structures and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal atoms and clusters under electron irradiation. We demonstrate no electron-instigated interaction between Cr clusters and pristine graphene, though Cr has been reported to be highly reactive to graphene. The metal-mediated etching is a dynamic effect between metal clusters and pre-existing defects. The resolved atomic configurations of typical nano metal structures on graphene offer insight into modeling and simulations on properties of metal-decorated graphene for both catalysis and future carbon-based electronics. © 2013 American Chemical Society.

  17. Manipulation and Graphene local oxidation lithography using an Atomic Force Microscope

    International Nuclear Information System (INIS)

    in this work, SPM nano lithography in Atomic Force Microscope mode was used to etching and manipulate graphene films on a nanoscopic length scale in order to produce electronic nano structures. By means of local anodic oxidation with an Atomic Force Microscope which is an electrochemical process applying voltage between Atomic Force Microscope probe and graphene surface, we are able to structure isolating trenches into single-layer and few-layer graphene flakes. Trench sizes of less than 30 nm in width are attainable with this technique. Besides oxidation, the influence of mechanical peeling and scratching with an Atomic Force Microscope of few layer graphene sheets was investigated.

  18. Determination of graphene layer thickness using optical image processing

    Science.gov (United States)

    Cook, Monica; Mani, R. G.

    2015-03-01

    Graphene, a single atomic layer of carbon arranged in a hexagonal lattice structure, is a valuable material in a wide range of research. A significant impediment to graphene research is the need to manually characterize the thickness of high-quality graphene produced via mechanical exfoliation. Traditional methods of characterizing the layer thickness of graphene, including Raman spectroscopy and atomic force microscopy, require expensive equipment and can be damaging to the graphene sample. We examine here a known alternative method for quantitatively determining the layer thickness of graphene on SiO2/Si based on optical image processing, which is quick, inexpensive, and non-invasive. Using RGB images of a candidate graphene sample and a background image, taken with a simple optical microscope and charge-coupled device (CCD) camera, we process the images with an algorithm based on Fresnel's law to obtain the contrast spectrum. Each layer of graphene exhibits a unique contrast spectrum for its particular substrate, which is measured and used for accurate layer identification. We also discuss how this algorithm can be generalized to characterize the thickness of other promising two-dimensional materials as well as more complex structures on a variety of substrates.

  19. Engineering the strain in graphene layers with Au decoration

    Energy Technology Data Exchange (ETDEWEB)

    Pannu, Compesh, E-mail: compesh@gmail.com; Singh, Udai B.; Kumar, Sunil; Tripathi, A.; Kabiraj, D.; Avasthi, D.K., E-mail: dka4444@gmail.com

    2014-07-01

    Graphene sheets decorated with Au nanodots are synthesized by deposition of Au of three different thicknesses and subsequent annealing at 400 °C. Different thicknesses of Au film for the formation of Au nanodots on graphene are measured using Rutherford backscattering spectrometry and morphology is studied using scanning electron microscopy. Raman spectroscopy indicates 3–6-fold increase in I{sub D}/I{sub G} ratio depending on the content of Au deposited on graphene. The increase in disorder in Au decorated graphene layers is explained on the basis of interaction of Au atoms with Π bonds of graphene. The splitting and blueshift in G band signifies compressive strain in Au deposited graphene. X-ray diffraction studies using synchrotron radiation source confirm compressive strain in graphene, which increases with increase of Au film thickness.

  20. Layer-by-layer assembly of vertically conducting graphene devices.

    Science.gov (United States)

    Chen, Jing-Jing; Meng, Jie; Zhou, Yang-Bo; Wu, Han-Chun; Bie, Ya-Qing; Liao, Zhi-Min; Yu, Da-Peng

    2013-01-01

    Graphene has various potential applications owing to its unique electronic, optical, mechanical and chemical properties, which are primarily based on its two-dimensional nature. Graphene-based vertical devices can extend the investigations and potential applications range to three dimensions, while interfacial properties are crucial for the function and performance of such graphene vertical devices. Here we report a general method to construct graphene vertical devices with controllable functions via choosing different interfaces between graphene and other materials. Two types of vertically conducting devices are demonstrated: graphene stacks sandwiched between two Au micro-strips, and between two Co layers. The Au|graphene|Au junctions exhibit large magnetoresistance with ratios up to 400% at room temperature, which have potential applications in magnetic field sensors. The Co|graphene|Co junctions display a robust spin valve effect at room temperature. The layer-by-layer assembly of graphene offers a new route for graphene vertical structures. PMID:23715280

  1. Twisted bi-layer graphene: microscopic rainbows

    OpenAIRE

    Campos-Delgado, J.; Algara-Siller, G.; Santos, C. N.; Kaiser, U.; Raskin, J.-P.

    2013-01-01

    Twisted bi-layer graphene (tBLG) has recently attracted interest due to the peculiar electrical properties that arise from its random rotational configurations. Our experiments on CVD-grown graphene from Cu foil and transferred onto Si substrates, with an oxide layer of 100 nm, reveal naturally-produced bi-layer graphene patches which present different colorations when shined with white light. In particular yellow-, pink- and blue- colored areas are evidenced. Combining optical microscopy, Ra...

  2. Amorphous Ultrathin SnO2 Films by Atomic Layer Deposition on Graphene Network as Highly Stable Anodes for Lithium-Ion Batteries.

    Science.gov (United States)

    Xie, Ming; Sun, Xiang; George, Steven M; Zhou, Changgong; Lian, Jie; Zhou, Yun

    2015-12-23

    Amorphous SnO2 (a-SnO2) thin films were conformally coated onto the surface of reduced graphene oxide (G) using atomic layer deposition (ALD). The electrochemical characteristics of the a-SnO2/G nanocomposites were then determined using cyclic voltammetry and galvanostatic charge/discharge curves. Because the SnO2 ALD films were ultrathin and amorphous, the impact of the large volume expansion of SnO2 upon cycling was greatly reduced. With as few as five formation cycles best reported in the literature, a-SnO2/G nanocomposites reached stable capacities of 800 mAh g(-1) at 100 mA g(-1) and 450 mAh g(-1) at 1000 mA g(-1). The capacity from a-SnO2 is higher than the bulk theoretical values. The extra capacity is attributed to additional interfacial charge storage resulting from the high surface area of the a-SnO2/G nanocomposites. These results demonstrate that metal oxide ALD on high surface area conducting carbon substrates can be used to fabricate high power and high capacity electrode materials for lithium-ion batteries.

  3. Dimensional dependence of phonon transport in freestanding atomic layer systems

    Science.gov (United States)

    Kim, Duckjong; Hwangbo, Yun; Zhu, Lijing; Mag-Isa, Alexander E.; Kim, Kwang-Seop; Kim, Jae-Hyun

    2013-11-01

    Due to the fast development of nanotechnology, we have the capability of manipulating atomic layer systems such as graphene, hexagonal boron nitride and dichalcogenides. The major concern in the 2-dimensional nanostructures is how to preserve their exceptional single-layer properties in 3-dimensional bulk structures. In this study, we report that the extreme phonon transport in graphene is highly affected by the graphitic layer stacking based on experimental investigation of the thermal conduction in few-layer graphene, 1-7 layers thick, suspended over holes of various diameters. We fabricate freestanding axisymmetric graphene structures without any perturbing substrate, and measure the in-plane transport property in terms of thermal conduction by using Raman spectroscopy. From the difference in susceptibility to substrate effect, size effect on hot-spot temperature variation and layer number dependence of thermal conductivity, we show that the graphitic membranes with 2 or more layers have characteristics similar to 3-dimensional graphite, which are very different from those of 2-dimensional graphene membranes. This implies that the scattering of out-of-plane phonons by interlayer atomic coupling could be a key mechanism governing the intrinsic thermal property.Due to the fast development of nanotechnology, we have the capability of manipulating atomic layer systems such as graphene, hexagonal boron nitride and dichalcogenides. The major concern in the 2-dimensional nanostructures is how to preserve their exceptional single-layer properties in 3-dimensional bulk structures. In this study, we report that the extreme phonon transport in graphene is highly affected by the graphitic layer stacking based on experimental investigation of the thermal conduction in few-layer graphene, 1-7 layers thick, suspended over holes of various diameters. We fabricate freestanding axisymmetric graphene structures without any perturbing substrate, and measure the in-plane transport

  4. Single-layer behavior and its breakdown in twisted graphene layers

    Science.gov (United States)

    Luican-Mayer, Adina

    2013-03-01

    Stacking order plays a major role in the electronic properties of graphene layers because hopping between carbon atoms in neighboring layers is a key ingredient in their band structure. Twisting the layers away from the equilibrium Bernal stacking, which produces the superstructures known as Moiré patterns in scanning tunneling microscopy, decreases the overlap between atoms in adjacent layers and therefore significantly alters their electronic properties. Using scanning tunneling microscopy and spectroscopy, we obtained direct evidence for the electronic structure of twisted graphene layers.[2] The samples were membranes of CVD grown graphene and graphite crystals which contain areas with various twist angles. In topographic images the regions where layers are twisted away from Bernal stacking exhibit Moiré patterns with periods which depend on the twist angle. We find that the density of states on the twisted layers develops two Van Hove singularities that symmetrically flank the Dirac point at an energy that depends on the twist angle. High magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers reveal that for twist angles exceeding ~3 degrees the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20 degrees the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown of the carrier velocity which is strongly angle dependent.[3] These results are compared with theoretical predictions. DOE-FG02-99ER45742, NSF DMR 1207108, Alcatel-Lucent

  5. Drawing conclusions from graphene[Graphene: A sheet of crystalline carbon just one atom thick

    Energy Technology Data Exchange (ETDEWEB)

    Neto, A.C. [Boston University (United States)]. E-mail: neto@bu.edu; Guinea, F. [ICMM-CSIC (Spain); Peres, N.M. [Minho University (Portugal)

    2006-11-15

    In a time when cutting-edge scientific research is expensive and complex, it seems absurd that a breakthrough in physics could be achieved with simple adhesive tape. But in 2004, Andre Geim, Kostya Novoselov and co-workers at the University of Manchester in the UK did just that. By delicately cleaving a sample of graphite with sticky tape, they produced something that was long considered impossible: a sheet of crystalline carbon just one atom thick, known as graphene. The single-layered honeycomb structure of graphene makes it the 'mother' of all carbon-based systems: the graphite we find in our pencils is simply a stack of graphene layers; carbon nanotubes are made or rolled up sheets of graphene; and buckminsterfullerene molecules, or 'buckyballs' are nanometre-size spheres of wrapped-up graphene. These forms of carbon were isolated long before graphene and have been used in many applications, but their electric, magnetic and elastic properties all originate in the properties of graphene. In the November issue of Physics World, Antonio Castro Neto, Francisco Guinea and Nuno Miguel Peres explore the fascinating structure of graphene, which is so unique that it could allow scientists to observe strange relativistic effects at speeds much slower than the speed of light. (U.K.)

  6. Atomic layer epitaxy

    Science.gov (United States)

    Goodman, Colin H. L.; Pessa, Markus V.

    1986-08-01

    Atomic layer epitaxy (ALE) is not so much a new technique for the preparation of thin films as a novel modification to existing methods of vapor-phase epitaxy, whether physical [e.g., evaporation, at one limit molecular-beam epitaxy (MBE)] or chemical [e.g., chloride epitaxy or metalorganic chemical vapor deposition (MOCVD)]. It is a self-regulatory process which, in its simplest form, produces one complete molecular layer of a compound per operational cycle, with a greater thickness being obtained by repeated cycling. There is no growth rate in ALE as in other crystal growth processes. So far ALE has been applied to rather few materials, but, in principle, it could have a quite general application. It has been used to prepare single-crystal overlayers of CdTe, (Cd,Mn)Te, GaAs and AlAs, a number of polycrystalline films and highly efficient electroluminescent thin-film displays based on ZnS:Mn. It could also offer particular advantages for the preparation of ultrathin films of precisely controlled thickness in the nanometer range and thus may have a special value for growing low-dimensional structures.

  7. Recognizing nitrogen dopant atoms in graphene using atomic force microscopy

    Science.gov (United States)

    van der Heijden, Nadine J.; Smith, Daniël; Calogero, Gaetano; Koster, Rik S.; Vanmaekelbergh, Daniel; van Huis, Marijn A.; Swart, Ingmar

    2016-06-01

    Doping graphene by heteroatoms such as nitrogen presents an attractive route to control the position of the Fermi level in the material. We prepared N-doped graphene on Cu(111) and Ir(111) surfaces via chemical vapor deposition of two different molecules. Using scanning tunneling microscopy images as a benchmark, we show that the position of the dopant atoms can be determined using atomic force microscopy. Specifically, the frequency shift-distance curves Δ f (z ) acquired above a N atom are significantly different from the curves measured over a C atom. Similar behavior was found for N-doped graphene on Cu(111) and Ir(111). The results are corroborated by density functional theory calculations employing a van der Waals functional.

  8. Direct growth of multilayer graphene by precipitation using W capping layer

    Science.gov (United States)

    Yamada, Jumpei; Ueda, Yuki; Maruyama, Takahiro; Naritsuka, Shigeya

    2016-10-01

    In this study, the direct growth of multilayer graphene from amorphous carbon on a sapphire (0001) substrate by precipitation using a nickel catalyst layer and a tungsten capping layer was examined. The findings revealed that a tungsten carbide layer was formed on top of the catalyst, and this suppressed the diffusion of carbon atoms upwards towards the surface. This caused the graphene layer to precipitate below the catalyst layer rather than above it. Under optimized growth conditions, Raman spectroscopy indicated that a high-quality graphene layer was formed with a low D/G peak intensity ratio of 0.10.

  9. Graphene on SiC(0001 inspected by dynamic atomic force microscopy at room temperature

    Directory of Open Access Journals (Sweden)

    Mykola Telychko

    2015-04-01

    Full Text Available We investigated single-layer graphene on SiC(0001 by atomic force and tunneling current microscopy, to separate the topographic and electronic contributions from the overall landscape. The analysis revealed that the roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. We also observed that characteristic electron scattering effects on graphene edges and defects are not accompanied by any out-of-plane relaxations of carbon atoms.

  10. Atomically thin epitaxial template for organic crystal growth using graphene with controlled surface wettability.

    Science.gov (United States)

    Nguyen, Nguyen Ngan; Jo, Sae Byeok; Lee, Seong Kyu; Sin, Dong Hun; Kang, Boseok; Kim, Hyun Ho; Lee, Hansol; Cho, Kilwon

    2015-04-01

    A two-dimensional epitaxial growth template for organic semiconductors was developed using a new method for transferring clean graphene sheets onto a substrate with controlled surface wettability. The introduction of a sacrificial graphene layer between a patterned polymeric supporting layer and a monolayer graphene sheet enabled the crack-free and residue-free transfer of free-standing monolayer graphene onto arbitrary substrates. The clean graphene template clearly induced the quasi-epitaxial growth of crystalline organic semiconductors with lying-down molecular orientation while maintaining the "wetting transparency", which allowed the transmission of the interaction between organic molecules and the underlying substrate. Consequently, the growth mode and corresponding morphology of the organic semiconductors on graphene templates exhibited distinctive dependence on the substrate hydrophobicity with clear transition from lateral to vertical growth mode on hydrophilic substrates, which originated from the high surface energy of the exposed crystallographic planes of the organic semiconductors on graphene. The optical properties of the pentacene layer, especially the diffusion of the exciton, also showed a strong dependency on the corresponding morphological evolution. Furthermore, the effect of pentacene-substrate interaction was systematically investigated by gradually increasing the number of graphene layers. These results suggested that the combination of a clean graphene surface and a suitable underlying substrate could serve as an atomically thin growth template to engineer the interaction between organic molecules and aromatic graphene network, thereby paving the way for effectively and conveniently tuning the semiconductor layer morphologies in devices prepared using graphene. PMID:25798655

  11. Selective growth of Pb islands on graphene/SiC buffer layers

    International Nuclear Information System (INIS)

    Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√(3) reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Since Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode

  12. Protecting nickel with graphene spin-filtering membranes: A single layer is enough

    Energy Technology Data Exchange (ETDEWEB)

    Martin, M.-B.; Dlubak, B.; Piquemal-Banci, M.; Collin, S.; Petroff, F.; Anane, A.; Fert, A.; Seneor, P. [Unité Mixte de Physique CNRS/Thales, 1 Avenue Augustin Fresnel, 91767 Palaiseau, France and Université Paris Sud, 91405 Orsay (France); Weatherup, R. S.; Hofmann, S.; Robertson, J. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Yang, H. [IBS Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Department of Energy Science, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Blume, R. [Helmholtz-Zentrum Berlin fur Materialien und Energie, 12489 Berlin (Germany); Schloegl, R. [Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)

    2015-07-06

    We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.

  13. Protecting nickel with graphene spin-filtering membranes: A single layer is enough

    Science.gov (United States)

    Martin, M.-B.; Dlubak, B.; Weatherup, R. S.; Piquemal-Banci, M.; Yang, H.; Blume, R.; Schloegl, R.; Collin, S.; Petroff, F.; Hofmann, S.; Robertson, J.; Anane, A.; Fert, A.; Seneor, P.

    2015-07-01

    We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.

  14. Electrochemistry at the edge of a single graphene layer in a nanopore

    DEFF Research Database (Denmark)

    Banerjee, Sutanuka; Shim, Jeong; Rivera, J.;

    2013-01-01

    We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and AlO dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to a unique...... edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 10 A/cm. The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge......, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many...

  15. Crystallographic orientation dependent etching of graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Nemes-Incze, Peter; Biro, Laszlo Peter [Research Institute for Technical Physics and Materials Science, PO. Box 49, 1525 Budapest (Hungary); Magda, Gabor [Budapest University of Technology and Economics (BME), PO Box 91, 1521 Budapest (Hungary); Kamaras, Katalin [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, PO Box 49, 1525, Budapest (Hungary)

    2010-04-15

    Graphene has gripped the scientific community ever since its discovery in 2004, with very promising electronic properties and hopes to integrate graphene into nanoelectronic devices. For graphene to make its way into electronic devices, two major obstacles have to be overcome: reproducible preparation of large area graphene samples and patterning techniques to obtain functional components. In this paper we present a graphene etching technique, which is crystallographic orientation selective and allows for the patterning of graphene layers using a chemical reduction process. The process involves the reduction of the SiO{sub 2} support by the carbon in the graphene itself. This reaction only occurs at the sample edges and does not result in the degradation of the graphene crystal lattice itself. However, we have observed evidence of strong hole doping in our etched samples. This etching technique opens up new possibilities in graphene patterning and modification. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Atomic resolution of nitrogen-doped graphene on Cu foils

    Science.gov (United States)

    Wang, Chundong; Schouteden, Koen; Wu, Qi-Hui; Li, Zhe; Jiang, Jianjun; Van Haesendonck, Chris

    2016-09-01

    Atomic-level substitutional doping can significantly tune the electronic properties of graphene. Using low-temperature scanning tunneling microscopy and spectroscopy, the atomic-scale crystalline structure of graphene grown on polycrystalline Cu, the distribution of nitrogen dopants and their effect on the electronic properties of graphene were investigated. Both the graphene sheet growth and nitrogen doping were performed using microwave plasma-enhanced chemical vapor deposition. The results indicated that the nitrogen dopants preferentially sit at the grain boundaries of the graphene sheets and confirmed that plasma treatment is a potential method to incorporate foreign atoms into the graphene lattice to tailor the graphene’s electronic properties.

  17. Graphene mechanics: II. Atomic stress distribution during indentation until rupture.

    Science.gov (United States)

    Costescu, Bogdan I; Gräter, Frauke

    2014-06-28

    Previous Atomic Force Microscopy (AFM) experiments found single layers of defect-free graphene to rupture at unexpectedly high loads in the micronewton range. Using molecular dynamics simulations, we modeled an AFM spherical tip pressing on a circular graphene sheet and studied the stress distribution during the indentation process until rupture. We found the graphene rupture force to have no dependency on the sheet size and a very weak dependency on the indenter velocity, allowing a direct comparison to experiment. The deformation showed a non-linear elastic behavior, with a two-dimensional elastic modulus in good agreement with previous experimental and computational studies. In line with theoretical predictions for linearly elastic sheets, rupture forces of non-linearly elastic graphene are proportional to the tip radius. However, as a deviation from the theory, the atomic stress concentrates under the indenter tip more strongly than predicted and causes a high probability of bond breaking only in this area. In turn, stress levels decrease rapidly towards the edge of the sheet, most of which thus only serves the role of mechanical support for the region under the indenter. As a consequence, the high ratio between graphene sheets and sphere radii, hitherto supposed to be necessary for reliable deformation and rupture studies, could be reduced to a factor of only 5-10 without affecting the outcome. Our study suggests time-resolved analysis of forces at the atomic level as a valuable tool to predict and interpret the nano-scale response of stressed materials beyond graphene.

  18. 具有SiC缓冲层的Si衬底上直接沉积碳原子生长石墨烯%Direct Graphene Growth by Depositing Carbon Atoms on Si Substrate Covered by SiC Buffer Layers

    Institute of Scientific and Technical Information of China (English)

    唐军; 康朝阳; 李利民; 徐彭寿

    2011-01-01

    石墨烯是近年发现的一种新型多功能材料.在合适的衬底上制备石墨烯成为目前材料制备的一大挑战.本文利用分子束外延(MBE)设备,在Si 衬底上生长高质量的SiC 缓冲层,然后利用直接沉积C原子的方法生长石墨烯,并通过反射式高能电子衍射(RHEED)、拉曼(Raman)光谱和近边X 射线吸收精细结构谱(NEXAFS)等实验技术对不同衬底温度(800、900、1000、1100 °C)生长的薄膜进行结构表征.实验结果表明,在以上衬底温度下都能生长出具有乱层堆垛结构的石墨烯薄膜.当衬底温度升高时,碳原子的活性增强,其成键的能力也增大,从而使形成的石墨烯结晶质量提高.衬底温度为1000 °C时结晶质量最好.其原因可能是当衬底温度较低时,碳原子活性太低不足以形成有序的六方C-sp2环.但过高的衬底温度会使SiC 缓冲层的孔洞缺陷增加,衬底的Si 原子有可能获得足够的能量穿过SiC薄膜的孔洞扩散到衬底表面,与沉积的碳原子反应生成无序的SiC,这一方面会减弱石墨烯的生长,另一方面也会使石墨烯的结晶质量变差.%Graphene is a newly discovered material with many functions. The preparation of graphene on suitable substrates is a challenge in the material preparation field. In this paper, graphene thin films were grown on Si substrates covered with SiC buffer layers (SiC/Si) by the direct deposition of carbon atoms using molecular beam epitaxy (MBE) equipment. The structural properties of the samples produced at different substrate temperatures (800, 900, 1000, 1100 ° C) were investigated by reflection high energy electron diffraction (RHEED), Raman spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). The results indicate that the thin films grown at all temperatures exhibit the characteristics of graphene with a turbostratic stacking structure. As the substrate temperature increases the crystalline quality of the graphene

  19. Layered graphene structure of a hexagonal carbon

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Bin, E-mail: beenchang@nuaa.edu.cn

    2013-06-01

    Experiments show that there is a novel hexagonal carbon polymorph restricted to the space group of P-62c, but the detailed atomic structure is not determined. Here we set carbon atoms occupying P-62c 4f or P-62c 2c and 2d Wyckoff positions, and calculate the total energy of the different cell structures changing the internal parameter by first-principles calculations, which demonstrates that the stable structures in energy (at local minima) are hexagonal carbon (P-62c 2c and 2d) and hexagonal diamond (P-62c 4f, z=1/16). The calculated bulk modulus 437±16 GPa and interlayer distance 2.062 Å of the layered graphene structure P-62c 2c and 2d are in good agreement with those of the proposed new carbon, which indicates that P-62c 2c and 2d is a possible precursor or intermediate hard phase during the structural transformation of carbon.

  20. Layered graphene structure of a hexagonal carbon

    International Nuclear Information System (INIS)

    Experiments show that there is a novel hexagonal carbon polymorph restricted to the space group of P-62c, but the detailed atomic structure is not determined. Here we set carbon atoms occupying P-62c 4f or P-62c 2c and 2d Wyckoff positions, and calculate the total energy of the different cell structures changing the internal parameter by first-principles calculations, which demonstrates that the stable structures in energy (at local minima) are hexagonal carbon (P-62c 2c and 2d) and hexagonal diamond (P-62c 4f, z=1/16). The calculated bulk modulus 437±16 GPa and interlayer distance 2.062 Å of the layered graphene structure P-62c 2c and 2d are in good agreement with those of the proposed new carbon, which indicates that P-62c 2c and 2d is a possible precursor or intermediate hard phase during the structural transformation of carbon

  1. Electronic and phonon bandstructures of pristine few layer and metal doped graphene using first principles calculations

    Directory of Open Access Journals (Sweden)

    Sanjeev K. Gupta

    2013-03-01

    Full Text Available In the frame work of density functional theoretical calculations, the electronic and lattice dynamical properties of graphene (multilayers and supercell have been systematically investigated and analyzed using the plane wave pseudopotentials within the generalized gradient approximation and local density approximation functional. We have also studied the functionalization of graphene by adsorption and absorption of transition metals like Al and Ag. We find that the electronic properties exhibit large sensitivity to the number of layers and doping. The Al and Ag doped graphene exhibits peak at Fermi level in the density of states arising from the flat bands near Fermi level. The bonding of metal atoms and graphene leads to a charge transfer between them and consequently shift Fermi level with respect to the conical point at K-point. The adsorption of Ag/Al atoms suggests an effective interaction between the adatoms and graphene layers without disturbing the original graphene structure of lower graphene layers. Compared to single layer graphene, the optical phonon E2g mode and out of plane ZA mode at Γ-point splits in the bi-, tri- and four- layer graphene. We observe a shift for highest optical branch at Dirac K- point. We find that the different derivatives of graphene have different phonon dispersion relations. We demonstrate that there is removal of degeneracy of ZO/ZA modes at K- point with transition metal doping. The highest optical phonon branch becomes flat at Dirac point with doping of transition metals. Our study points that the substituted graphene sheets can have potential applications in ordered-disordered separated quantum films with two to four layers of atoms and new nano devices using graphene.

  2. Rapid growth of single-layer graphene on the insulating substrates by thermal CVD

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.Y. [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Dai, D.; Chen, G.X.; Yu, J.H. [Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Nishimura, K. [Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Advanced Nano-processing Engineering Lab, Mechanical Systems Engineering, Kogakuin University (Japan); Lin, C.-T. [Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Jiang, N., E-mail: jiangnan@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Zhan, Z.L., E-mail: zl_zhan@sohu.com [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

    2015-08-15

    Highlights: • A rapid thermal CVD process has been developed to directly grow graphene on the insulating substrates. • The treating time consumed is ≈25% compared to conventional CVD procedure. • Single-layer and few-layer graphene can be formed on quartz and SiO{sub 2}/Si substrates, respectively. • The formation of thinner graphene at the interface is due to the fast precipitation rate of carbon atoms during cooling. - Abstract: The advance of CVD technique to directly grow graphene on the insulating substrates is particularly significant for further device fabrication. As graphene is catalytically grown on metal foils, the degradation of the sample properties is unavoidable during transfer of graphene on the dielectric layer. Moreover, shortening the treatment time as possible, while achieving single-layer growth of graphene, is worthy to be investigated for promoting the efficiency of mass production. Here we performed a rapid heating/cooling process to grow graphene films directly on the insulating substrates by thermal CVD. The treating time consumed is ≈25% compared to conventional CVD procedure. In addition, we found that high-quality, single-layer graphene can be formed on quartz, but on SiO{sub 2}/Si substrate only few-layer graphene can be obtained. The pronounced substrate effect is attributed to the different dewetting behavior of Ni films on the both substrates at 950 °C.

  3. Hole-doping of mechanically exfoliated graphene by confined hydration layers

    NARCIS (Netherlands)

    Bollmann, T.R.J.; Antipina, L.Y.; Temmen, M.; Reichling, M.; Sorokin, P.B.

    2015-01-01

    By the use of non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM), we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CaF2(111). Hydration layers confined between the graphene and the Ca

  4. Fabrication and Characterization of Macroscopic Graphene Layers on Metallic Substrates

    OpenAIRE

    Freire Soler, Víctor Manuel

    2014-01-01

    In 2004 there were newly conditions for a scientific revolution, with very important technology implications and yet to be completely developed. It is the isolation of atomic carbon layers, better known as graphene, whose extreme mechanical and electronic properties stand out above all known materials: it presents the highest electron mobility, ambipolarity, it supports large current densities, the highest elastic modulus, increased thermal conductivity, it shows high impermeability, and reco...

  5. Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamide-urea-ammonium nitrate melt under ambient conditions

    Energy Technology Data Exchange (ETDEWEB)

    Dilimon, V.S.; Sampath, S., E-mail: sampath2562@gmail.co

    2011-01-31

    Electrochemical reduction of exfoliated graphene oxide, prepared from pre-exfoliated graphite, in acetamide-urea-ammonium nitrate ternary eutectic melt results in few layer-graphene thin films. Negatively charged exfoliated graphene oxide is attached to positively charged cystamine monolyer self-assembled on a gold surface. Electrochemical reduction of the oriented graphene oxide film is carried out in a room temperature, ternary molten electrolyte. The reduced film is characterized by atomic force microscopy (AFM), conductive AFM, Fourier-transform infrared spectroscopy and Raman spectroscopy. Ternary eutectic melt is found to be a suitable medium for the regulated reduction of graphene oxide to reduced graphene oxide-based sheets on conducting surfaces.

  6. Hole-doping of mechanically exfoliated graphene by confined hydration layers

    Institute of Scientific and Technical Information of China (English)

    Tjeerd R. J. Bollmann[1,2; Liubov Yu. Antipina[3,4; Matthias Temmen[2; Michael Reichling[2; Pavel B. Sorokin[5

    2015-01-01

    By the use of non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM), we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2(111). Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene's preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material's electron density transfers from graphene to the hydration layer. Density functional theory (DFT) calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.

  7. Specific heat of twisted bilayer graphene: Engineering phonons by atomic plane rotations

    Energy Technology Data Exchange (ETDEWEB)

    Nika, Denis L. [E. Pokatilov Laboratory of Physics and Engineering of Nanomaterials, Department of Physics and Engineering, Moldova State University, Chisinau MD-2009, Republic of Moldova (Moldova, Republic of); Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, Bourns College of Engineering, University of California—Riverside, Riverside, California, 92521 (United States); Cocemasov, Alexandr I. [E. Pokatilov Laboratory of Physics and Engineering of Nanomaterials, Department of Physics and Engineering, Moldova State University, Chisinau MD-2009, Republic of Moldova (Moldova, Republic of); Balandin, Alexander A., E-mail: balandin@ee.ucr.edu [Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, Bourns College of Engineering, University of California—Riverside, Riverside, California, 92521 (United States)

    2014-07-21

    We have studied the phonon specific heat in single-layer, bilayer, and twisted bilayer graphene. The calculations were performed using the Born-von Karman model of lattice dynamics for intralayer atomic interactions and spherically symmetric interatomic potential for interlayer interactions. We found that at temperature T < 15 K, specific heat varies with temperature as T{sup n}, where n = 1 for graphene, n = 1.6 for bilayer graphene, and n = 1.3 for the twisted bilayer graphene. The phonon specific heat reveals an intriguing dependence on the twist angle in bilayer graphene, which is particularly pronounced at low temperature. The results suggest a possibility of phonon engineering of thermal properties of layered materials by twisting the atomic planes.

  8. Doping monolayer graphene with single atom substitutions

    KAUST Repository

    Wang, Hongtao

    2012-01-11

    Functionalized graphene has been extensively studied with the aim of tailoring properties for gas sensors, superconductors, supercapacitors, nanoelectronics, and spintronics. A bottleneck is the capability to control the carrier type and density by doping. We demonstrate that a two-step process is an efficient way to dope graphene: create vacancies by high-energy atom/ion bombardment and fill these vacancies with desired dopants. Different elements (Pt, Co, and In) have been successfully doped in the single-atom form. The high binding energy of the metal-vacancy complex ensures its stability and is consistent with in situ observation by an aberration-corrected and monochromated transmission electron microscope. © 2011 American Chemical Society.

  9. Thermal conductivity of giant mono- to few-layered CVD graphene supported on an organic substrate

    Science.gov (United States)

    Liu, Jing; Wang, Tianyu; Xu, Shen; Yuan, Pengyu; Xu, Xu; Wang, Xinwei

    2016-05-01

    The thermal conductivity (k) of supported graphene is a critical property that reflects the graphene-substrate interaction, graphene structure quality, and is needed for thermal design of a graphene device. Yet the related k measurement has never been a trivial work and very few studies are reported to date, only at the μm level. In this work, for the first time, the k of giant chemical vapor decomposition (CVD) graphene supported on poly(methyl methacrylate) (PMMA) is characterized using our transient electro-thermal technique based on a differential concept. Our graphene size is ~mm, far above the samples studied in the past. This giant graphene measurement eliminates the thermal contact resistance problems and edge phonon scattering encountered in μm-scale graphene k measurement. Such mm-scale measurement is critical for device/system-level thermal design since it reflects the effect of abundant grains in graphene. The k of 1.33-layered, 1.53-layered, 2.74-layered and 5.2-layered supported graphene is measured as 365 W m-1 K-1, 359 W m-1 K-1, 273 W m-1 K-1 and 33.5 W m-1 K-1, respectively. These values are significantly lower than the k of supported graphene on SiO2, and are about one order of magnitude lower than the k of suspended graphene. We speculate that the abundant C atoms in the PMMA promote more ready energy and momentum exchange with the supported graphene, and give rise to more phonon scattering than the SiO2 substrate. This leads to a lower k of CVD graphene on PMMA than that on SiO2. We attribute the existence of disorder in the sp2 domain, graphene oxide (GO) and stratification in the 5.2-layered graphene to its more k reduction. The Raman linewidth (G peak) of the 5.2-layered graphene is also twice larger than that of the other three kinds of graphene, indicating the much more phonon scattering and shorter phonon lifetime in it. Also the electrical conductivity of the 5.2-layered graphene is about one-fifth of that for the other three. This

  10. Graphene and graphene-like layered transition metal dichalcogenides in energy conversion and storage.

    Science.gov (United States)

    Wang, Hua; Feng, Hongbin; Li, Jinghong

    2014-06-12

    Being confronted with the energy crisis and environmental problems, the exploration of clean and renewable energy materials as well as their devices are urgently demanded. Two-dimensional (2D) atomically-thick materials, graphene and grpahene-like layered transition metal dichalcogenides (TMDs), have showed vast potential as novel energy materials due to their unique physicochemical properties. In this Review, we outline the typical application of graphene and grpahene-like TMDs in energy conversion and storage fields, and hope to promote the development of 2D TMDs in this field through the analysis and comparisons with the relatively natural graphene. First, a brief introduction of electronic structures and basic properties of graphene and TMDs are presented. Then, we summarize the exciting progress of these materials made in both energy conversion and storage field including solar cells, electrocatalysis, supercapacitors and lithium ions batteries. Finally, the prospects and further developments in these exciting fields of graphene and graphene-like TMDs materials are also suggested.

  11. Raman Fingerprints of Atomically Precise Graphene Nanoribbons

    Science.gov (United States)

    Verzhbitskiy, Ivan A.; Corato, Marzio De; Ruini, Alice; Molinari, Elisa; Narita, Akimitsu; Hu, Yunbin; Schwab, Matthias G.; Bruna, Matteo; Yoon, Duhee; Milana, Silvia; Feng, Xinliang; Müllen, Klaus; Ferrari, Andrea C.; Casiraghi, Cinzia; Prezzi, Deborah

    2016-06-01

    Bottom-up approaches allow the production of ultra-narrow and atomically precise graphene nanoribbons (GNRs), with electronic and optical properties controlled by the specific atomic structure. Combining Raman spectroscopy and ab-initio simulations, we show that GNR width, edge geometry and functional groups all influence their Raman spectra. The low-energy spectral region below 1000 cm-1 is particularly sensitive to edge morphology and functionalization, while the D peak dispersion can be used to uniquely fingerprint the presence of GNRs, and differentiates them from other sp2 carbon nanostructures.

  12. Atomic Collapse in Graphene: Lost of Unitarity

    CERN Document Server

    Valenzuela, David; Loewe, Marcelo; Raya, Alfredo

    2016-01-01

    We explore the problem of atomic collapse in graphene by monopole impurities, both electric and magnetic, within the context of supersymmetric quantum mechanics. For electric impurities, upon factorizing the radial Dirac Hamiltonian and identifying the supercharges, existence of a critical charge that makes the ground state {\\em fall-into-the-center} translates into lost of unitarity for the corresponding Hamiltonian. For the problem of magnetic monopole impurities, preservation of unitarity for all values of the parameters of the corresponding potential translates into the absence of atomic collapse in this case.

  13. Electron properties of fluorinated single-layer graphene transistors

    OpenAIRE

    Withers, Freddie; Dubois, Marc; Savchenko, Alexander K.

    2010-01-01

    We have fabricated transistor structures using fluorinated single-layer graphene flakes and studied their electronic properties at different temperatures. Compared with pristine graphene, fluorinated graphene has very large and strongly temperature dependent resistance in the electro-neutrality region. We show that fluorination creates a mobility gap in graphene's spectrum where electron transport takes place via localised electron states.

  14. Layer resolved capacitive probing of graphene bilayers

    Science.gov (United States)

    Zibrov, Alexander; Parmentier, François; Li, Jia; Wang, Lei; Hunt, Benjamin; Dean, Cory; Hone, James; Taniguchi, Takashi; Watanabe, Kenji; Young, Andrea

    Compared to single layer graphene, graphene bilayers have an additional ``which-layer'' degree of freedom that can be controlled by an external electric field in a dual-gated device geometry. We describe capacitance measurements capable of directly probing this degree of freedom. By performing top gate, bottom gate, and penetration field capacitance measurements, we directly extract layer polarization of both Bernal and twisted bilayers. We will present measurements of hBN encapsulated bilayers at both zero and high magnetic field, focusing on the physics of the highly degenerate zero-energy Landau level in the high magnetic field limit where spin, valley, and layer degeneracy are all lifted by electronic interactions.

  15. Symmetry Breaking in Few Layer Graphene Films

    Energy Technology Data Exchange (ETDEWEB)

    Bostwick, A.; Ohta, T.; McChesney, J.L.; Emtsev, K.; Seyller,Th.; Horn, K.; Rotenberg, E.

    2007-05-25

    Recently, it was demonstrated that the quasiparticledynamics, the layer-dependent charge and potential, and the c-axisscreening coefficient could be extracted from measurements of thespectral function of few layer graphene films grown epitaxially on SiCusing angle-resolved photoemission spectroscopy (ARPES). In this articlewe review these findings, and present detailed methodology for extractingsuch parameters from ARPES. We also present detailed arguments againstthe possibility of an energy gap at the Dirac crossing ED.

  16. Spectroscopic characterization of ion-irradiated multi-layer graphenes

    Energy Technology Data Exchange (ETDEWEB)

    Tsukagoshi, Akira [Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280 (Japan); RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan); Honda, Shin-ichi, E-mail: s-honda@eng.u-hyogo.ac.jp [Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280 (Japan); RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan); Osugi, Ryo [Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280 (Japan); RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan); Okada, Hiraku [Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280 (Japan); Niibe, Masahito [Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Kamigori, Hyogo 678-1205 (Japan); Terasawa, Mititaka [Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Kamigori, Hyogo 678-1205 (Japan); RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan); Hirase, Ryuji; Izumi, Hirokazu; Yoshioka, Hideki [Hyogo Prefectural Institute of Technology, Kobe 654-0037 (Japan); Niwase, Keisuke [Hyogo University of Teacher Education, Kato, Hyogo 673-1494 (Japan); Taguchi, Eiji [Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Lee, Kuei-Yi [Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Oura, Masaki [RIKEN SPring-8 Center, Sayo, Hyogo 679-5148 (Japan)

    2013-11-15

    Low-energy Ar ions (0.5–2 keV) were irradiated to multi-layer graphenes and the damage process, the local electronic states, and the degree of alignment of the basal plane, and the oxidation process upon ion irradiation were investigated by Raman spectroscopy, soft X-ray absorption spectroscopy (XAS) and in situ X-ray photoelectron spectroscopy (XPS). By Raman spectroscopy, we observed two stages similar to the case of irradiated graphite, which should relate to the accumulations of vacancies and turbulence of the basal plane, respectively. XAS analysis indicated that the number of sp{sup 2}-hybridized carbon (sp{sup 2}-C) atoms decreased after ion irradiation. Angle-resolved XAS revealed that the orientation parameter (OP) decreased with increasing ion energy and fluence, reflecting the turbulence of the basal plane under irradiation. In situ XPS shows the oxidation of the irradiated multi-layer graphenes after air exposure.

  17. Fluorinated graphene and hexagonal boron nitride as ALD seed layers for graphene-based van der Waals heterostructures

    International Nuclear Information System (INIS)

    Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H2O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics. (paper)

  18. Electronic properties of incommensurate atomic layers

    International Nuclear Information System (INIS)

    We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene–hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectroscopic features in zero magnetic field and also in strong magnetic field. (author)

  19. Graphene coated with controllable N-doped carbon layer by molecular layer deposition as electrode materials for supercapacitors

    Science.gov (United States)

    Chen, Yao; Gao, Zhe; Zhang, Bin; Zhao, Shichao; Qin, Yong

    2016-05-01

    In this work, graphene is coated with nitrogen-doped carbon layer, which is produced by a carbonization process of aromatic polyimide (PI) films deposited on the surfaces of graphene by molecular layer deposition (MLD). The utilization of MLD not only allows uniform coating of PI layers on the surfaces of pristine graphene without any surface treatment, but also enables homogenous dispersion of doped nitrogen atoms in the carbonized products. The as-prepared N-doped carbon layer coated graphene (NC-G) exhibited remarkable capacitance performance as electrode materials for supercapacitor, showing a high specific capacitance of 290.2 F g-1 at current density of 1 A g-1 in 6 M KOH aqueous electrolyte, meanwhile maintaining good rate performance and stable cycle capability. The NC-G synthesized by this way represents an alternative promising candidate as electrode material for supercapacitors.

  20. Electron diffraction studies on CVD grown bi-layered graphene

    Science.gov (United States)

    Lingam, Kiran; Karakaya, Mehmet; Podila, Ramakrishna; Quin, Haijun; Rao, Apparao; Dept. of Physics and Astronomy, Clemson University, Clemson, SC USA 29634. Team; Advanced Materials Research Laboratories, Clemson University, Anderson, SC USA 29625 Collaboration

    2013-03-01

    Graphene has generated enormous interest in the scientific community due to its peculiar properties like electron mobility, thermal conductivity etc. Several recent reports on exfoliated graphene emphasized the role of layer stacking on the electronic and optical properties of graphene in case of bi-layered and few layered graphene and several synthesis techniques like chemical vapor deposition (CVD) on Copper foils are employed to prepare graphene for applications at a large scale. However, a correlated study pertinent to the stacking order in CVD grown graphene is still unclear. In this work, using a combination of Raman spectroscopy and selected area electron diffraction analysis we analyzed the preferred misorientation angles in a CVD grown bi-layered graphene and also the role of Cu crystal facets on the graphene stacking order will be presented.

  1. Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate.

    Science.gov (United States)

    Lee, Jeong-Hoon; Song, Kwan-Woo; Park, Min-Ho; Kim, Hyung-Kyu; Yang, Cheol-Woong

    2011-07-01

    Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film. PMID:22121737

  2. One-Atom-Thick IR Metamaterials and Transformation Optics Using Graphene

    CERN Document Server

    Vakil, Ashkan

    2011-01-01

    Here we theoretically show, by designing and manipulating spatially inhomogeneous, non-uniform conductivity patterns across a single flake of graphene, that this single-atom-layered material can serve as a "one-atom-thick" platform for infrared metamaterials and transformation optical devices. It is known that by varying the chemical potential using gate electric and/or magnetic fields, the graphene conductivity in the THz and IR frequencies can be changed. This versatility provides the possibility that different "patches" on a single flake of graphene possess different conductivities, suggesting a mechanism to construct "single-atom-thick" IR metamaterials and transformation optical structures. Our computer simulation results pave the way for envisioning numerous IR photonic functions and metamaterial concepts-all on a "one-atom-thick" platform-of such we list a few here: edge waveguides, bent ribbon-like paths guiding light, photonic splitters and combiners, "one-atom-thick" IR scattering elements as buildi...

  3. Resistance and rupture analysis of single- and few-layer graphene nanosheets impacted by various projectiles

    Science.gov (United States)

    Sadeghzadeh, Sadegh; Liu, Ling

    2016-09-01

    In this paper, a quasi-classical model for the collision of various nanoparticles with single- and few-layer graphene nanosheets was introduced as a multi-scale approach that couples non-equilibrium molecular dynamics with the Finite Element Method. As a resistance criterion, it was observed that the coefficient of restitution and the induced stresses depend on the impact velocity of projectile. These parameters were evaluated computationally, and it was revealed that certain resulting behaviors differ from behaviors at the macro scale. By obtaining an out-of-plane yield stress limit of 1.0 TPa for graphene, the stress analysis of single- and multi-layer graphene sheets revealed that the limit projectile velocity needed for the yielding of graphene sheets increases with the increase in the number of layers. For aluminum nanoparticles, this increase is almost linear, and for other metals, it slightly deviates from the linear trend. It was also observed that the graphene sheets have a different rupture form when impacted by gaseous molecules than by metal particles. Considering the very high momentum of gas molecules and their shock-like behavior during high-speed collisions with a graphene sheet, pores with a size of one carbon atom can be created in graphene sheets. Since a single-layer graphene sheet can withstand a projectile which is 3.64 times larger than a projectile impacting a 20-layer graphene sheet, spaced graphene sheets seem to be more effective in absorbing the impact energy of projectiles than conventional few-layer graphene sheets.

  4. Benchmarking the penetration-resistance efficiency of multilayer graphene sheets due to spacing the graphene layers

    Science.gov (United States)

    Sadeghzadeh, S.

    2016-07-01

    In this paper, the penetration-resistance efficiency of single-layer and multilayer graphene sheets has been investigated by means of the multiscale approach. The employed multiscale approach has been implemented by establishing a direct correlation between the finite element method and the molecular dynamics approach and validated by comparing its results with those of the existing experimental works. Since by using numerous techniques, a new class of graphene sheets can be fabricated in which the graphene layers are spaced farther apart (more than the usual distance between layers), this paper has concentrated on the optimal spacing between graphene layers with the goal of improving the impact properties of graphene sheets as important candidates for novel impact-resistant panels. For this purpose, the relative protection (protection with respect to weight) values of graphene sheets were obtained, and it was observed that the relative protection of a single-layer graphene sheet is about 3.64 times that of a 20-layer graphene sheet. This study also showed that a spaced multilayer graphene sheet, with its inter-layer distance being 20 times the usual spacing between ordinary graphene layers, has an impact resistance which is about 20 % higher than that of an ordinary 20-layer graphene sheet. The findings of this paper can be appropriately used in the design and fabrication of future-generation impact-resistant protective panels.

  5. Growth of bi- and tri-layered graphene on silicon carbide substrate via molecular dynamics simulation

    Energy Technology Data Exchange (ETDEWEB)

    Min, Tjun Kit; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)

    2015-04-24

    Molecular dynamics (MD) simulation with simulated annealing method is used to study the growth process of bi- and tri-layered graphene on a 6H-SiC (0001) substrate via molecular dynamics simulation. Tersoff-Albe-Erhart (TEA) potential is used to describe the inter-atomic interactions among the atoms in the system. The formation temperature, averaged carbon-carbon bond length, pair correlation function, binding energy and the distance between the graphene formed and the SiC substrate are quantified. The growth mechanism, graphitization of graphene on the SiC substrate and characteristics of the surface morphology of the graphene sheet obtained in our MD simulation compare well to that observed in epitaxially grown graphene experiments and other simulation works.

  6. Optical and Electrical Characteristics of Graphene Double Layer Formed by a Double Transfer of Graphene Single Layers.

    Science.gov (United States)

    Kim, Young Jun; Bae, Gi Yoon; Chun, Sungwoo; Park, Wanjun

    2016-03-01

    We demonstrate formation of double layer graphene by means of a double transfer using two single graphene layers grown by a chemical vapor deposition method. It is observed that shiftiness and broadness in the double-resonance of Raman scattering are much weaker than those of bilayer graphene formed naturally. Transport characteristics examined from transmission line measurements and field effect transistors show the similar behavior with those of single layer graphene. It indicates that interlayer separation, in electrical view, is large enough to avoid correlation between layers for the double layer structure. It is also observed from a transistor with the double layer graphene that molecules adsorpted on two inner graphene surfaces in the double layered structure are isolated and conserved from ambient environment.

  7. Improving the electrical properties of graphene layers by chemical doping

    International Nuclear Information System (INIS)

    Although the electronic properties of graphene layers can be modulated by various doping techniques, most of doping methods cost degradation of structural uniqueness or electrical mobility. It is matter of huge concern to develop a technique to improve the electrical properties of graphene while sustaining its superior properties. Here, we report the modification of electrical properties of single- bi- and trilayer graphene by chemical reaction with potassium nitrate (KNO3) solution. Raman spectroscopy and electrical transport measurements showed the n-doping effect of graphene by KNO3. The effect was most dominant in single layer graphene, and the mobility of single layer graphene was improved by the factor of more than 3. The chemical doping by using KNO3 provides a facile approach to improve the electrical properties of graphene layers sustaining their unique characteristics. (paper)

  8. Symmetry breaking in few layer graphene films

    Energy Technology Data Exchange (ETDEWEB)

    Bostwick, Aaron [Advanced Light Source, E O Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Ohta, Taisuke [Advanced Light Source, E O Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); McChesney, Jessica L [Advanced Light Source, E O Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Emtsev, Konstantin V [Institut fuer Physik der Kondensierten Materie, Lehrstuhl fuer Technische Physik, Universitaet Erlangen-Nuernberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen (Germany); Seyller, Thomas [Institut fuer Physik der Kondensierten Materie, Lehrstuhl fuer Technische Physik, Universitaet Erlangen-Nuernberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen (Germany); Horn, Karsten [Department of Molecular Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Rotenberg, Eli [Advanced Light Source, E O Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2007-10-15

    Recently, it was demonstrated that the quasiparticle dynamics, the layer-dependent charge and potential, and the c-axis screening coefficient could be extracted from measurements of the spectral function of few layer graphene films grown epitaxially on SiC using angle-resolved photoemission spectroscopy (ARPES). In this paper we review these findings, and present detailed methodology for extracting such parameters from ARPES. We also present detailed arguments against the possibility of an energy gap at the Dirac crossing E{sub D}.

  9. Adsorption of monovalent metal atoms on graphene: a theoretical approach

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros, Paulo V C; De Brito Mota, F; De Castilho, Caio M C [Grupo de Fisica de Superficies e Materiais, Instituto de Fisica, Universidade Federal da Bahia, Campus Universitario da Federacao/Ondina, 40170-115, Salvador, Bahia (Brazil); Mascarenhas, Artur J S, E-mail: caio@ufba.br [Instituto Nacional de Ciencia e Tecnologia em Energia e Ambiente-INCT-E and A-CIENAM, Universidade Federal da Bahia, Salvador, Bahia (Brazil)

    2010-03-19

    This work investigates, using first-principles calculations, electronic and structural properties of hydrogen, lithium, sodium, potassium and rubidium that are adsorbed, in a regular pattern, on a graphene surface. The results for H-graphene (graphane) and Li-graphene were compared with previous calculations. The present results do not support previous claims that the Li-C bond in such a layer would result in an sp{sup 2} to an sp{sup 3} transition of carbon orbitals, being more compatible with some ionic character for the covalent bond and with lithium acting as an electron acceptor in a bridging environment. Calculations were also performed for the Na, K, and Rb-graphene systems, resulting in a similar electronic behaviour but with a more pronounced ionic character than for Li-graphene. Energy calculations indicate the possible stability of such ad-graphene layers, with only the Li-graphene being possible to be spontaneously obtained.

  10. Layer compression and enhanced optical properties of few-layer graphene nanosheets induced by ion irradiation

    CERN Document Server

    Tan, Yang; Akhmadaliev, Shavkat; Zhou, Shengqiang; Chen, Feng

    2016-01-01

    Graphene has been recognized as an attractive two-dimensional material for fundamental research and wide applications in electronic and photonic devices owing to its unique properties. The technologies to modulate the properties of graphene are of continuous interest to researchers in multidisciplinary areas. Herein, we report on the first experimental observation of the layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheets by applying the irradiation of energetic ion beams. After the irradiation, the space between the graphene layers was reduced, resulting in a tighter contact between the few-layer graphene nanosheet and the surface of the substrate. This processing also enhanced the interaction between the graphene nanosheets and the evanescent-field wave near the surface, thus reinforcing the polarization-dependent light absorption of the graphene layers (with 3-fold polarization extinction ratio increment). Utilizing the ion-irradiated graphene nanosheets as saturable...

  11. Exposure of epitaxial graphene on SiC(0001) to atomic hydrogen.

    Science.gov (United States)

    Guisinger, Nathan P; Rutter, Gregory M; Crain, Jason N; First, Phillip N; Stroscio, Joseph A

    2009-04-01

    Graphene films on SiC exhibit coherent transport properties that suggest the potential for novel carbon-based nanoelectronics applications. Recent studies suggest that the role of the interface between single layer graphene and silicon-terminated SiC can strongly influence the electronic properties of the graphene overlayer. In this study, we have exposed the graphitized SiC to atomic hydrogen in an effort to passivate dangling bonds at the interface, while investigating the results utilizing room temperature scanning tunneling microscopy.

  12. Isotropy of optical excitations in few-layer graphenes

    Energy Technology Data Exchange (ETDEWEB)

    Lee, S.H. [Department of Physics, National Cheng Kung University, 701 Tainan, Taiwan (China); Shyu, F.L. [Department of Physics, R.O.C. Military Academy, 830 Kaohsiung, Taiwan (China); Chiu, C.W., E-mail: giorgio@fonran.com.t [Department of Physics, National Cheng Kung University, 701 Tainan, Taiwan (China); Lin, M.F., E-mail: mflin@mail.ncku.edu.t [Department of Physics, National Cheng Kung University, 701 Tainan, Taiwan (China)

    2010-07-26

    The geometric and the most band structures of monolayer and AB-stacked bilayer graphenes exhibit strong anisotropy. Nevertheless, the absorption spectra are isotropic for the polarization vector on graphene plane. The velocity matrix elements dominate this property. These results suggest that AA- and AB-stacked few-layer graphenes and graphites manifest this feature.

  13. Atomic Structures of Graphene, Benzene and Methane with Bond Lengths as Sums of the Single, Double and Resonance Bond Radii of Carbon

    OpenAIRE

    Heyrovska, Raji

    2008-01-01

    Two dimensional layers of graphene are currently drawing a great attention in fundamental and applied nanoscience. Graphene consists of interconnected hexagons of carbon atoms as in graphite. This article presents for the first time the structures of graphene at the atomic level and shows how it differs from that of benzene, due to the difference in the double bond and resonance bond based radii of carbon. The carbon atom of an aliphatic compound such as methane has a longer covalent single b...

  14. Water desalination using nanoporous single-layer graphene.

    Science.gov (United States)

    Surwade, Sumedh P; Smirnov, Sergei N; Vlassiouk, Ivan V; Unocic, Raymond R; Veith, Gabriel M; Dai, Sheng; Mahurin, Shannon M

    2015-05-01

    By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 10(6) g m(-2) s(-1) at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m(-2) s(-1) atm(-1).

  15. Water desalination using nanoporous single-layer graphene

    Science.gov (United States)

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon M.

    2015-05-01

    By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 106 g m-2 s-1 at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m-2 s-1 atm-1.

  16. Electronic spin transport in bilayer and single layer graphene

    OpenAIRE

    Yang, Tsung-Yeh

    2011-01-01

    Graphene has drawn plenty of attention since its discovery in 2004. Due to its excellent properties, such as long spin relaxation length and gate-tunable spin transport, graphene is expected to be a potential candidate for spintronics applications. In this thesis, the systematic study of the spin relaxation mechanisms in bilayer and single layer graphene is presented. Graphene-based spin valve devices in four-terminal non-local geometry are fabricated for the investigation of the charge and s...

  17. Synthesis of few layer single crystal graphene grains on platinum by chemical vapour deposition

    Directory of Open Access Journals (Sweden)

    S. Karamat

    2015-08-01

    Full Text Available The present competition of graphene electronics demands an efficient route which produces high quality and large area graphene. Chemical vapour deposition technique, where hydrocarbons dissociate in to active carbon species and form graphene layer on the desired metal catalyst via nucleation is considered as the most suitable method. In this study, single layer graphene with the presence of few layer single crystal graphene grains were grown on Pt foil via chemical vapour deposition. The higher growth temperature changes the surface morphology of the Pt foil so a delicate process of hydrogen bubbling was used to peel off graphene from Pt foil samples with the mechanical support of photoresist and further transferred to SiO2/Si substrates for analysis. Optical microscopy of the graphene transferred samples showed the regions of single layer along with different oriented graphene domains. Two type of interlayer stacking sequences, Bernal and twisted, were observed in the graphene grains. The presence of different stacking sequences in the graphene layers influence the electronic and optical properties; in Bernal stacking the band gap can be tunable and in twisted stacking the overall sheet resistance can be reduced. Grain boundaries of Pt provides low energy sites to the carbon species, therefore the nucleation of grains are more at the boundaries. The stacking order and the number of layers in grains were seen more clearly with scanning electron microscopy. Raman spectroscopy showed high quality graphene samples due to very small D peak. 2D Raman peak for single layer graphene showed full width half maximum (FWHM value of 30 cm−1. At points A, B and C, Bernal stacked grain showed FWHM values of 51.22, 58.45 and 64.72 cm−1, while twisted stacked grain showed the FWHM values of 27.26, 28.83 and 20.99 cm−1, respectively. FWHM values of 2D peak of Bernal stacked grain showed an increase of 20–30 cm−1 as compare to single layer graphene

  18. Synthesis of few layer single crystal graphene grains on platinum by chemical vapour deposition

    Institute of Scientific and Technical Information of China (English)

    S. Karamat; S. Sonuşen; Ü. Çelik; Y. Uysallı; E. Özgönül; A. Oral

    2015-01-01

    The present competition of graphene electronics demands an efficient route which produces high quality and large area graphene. Chemical vapour deposition technique, where hydrocarbons dissociate in to active carbon species and form graphene layer on the desired metal catalyst via nucleation is considered as the most suitable method. In this study, single layer graphene with the presence of few layer single crystal graphene grains were grown on Pt foil via chemical vapour deposition. The higher growth temperature changes the surface morphology of the Pt foil so a delicate process of hydrogen bubbling was used to peel off graphene from Pt foil samples with the mechanical support of photoresist and further transferred to SiO2/Si substrates for analysis. Optical microscopy of the graphene transferred samples showed the regions of single layer along with different oriented graphene domains. Two type of interlayer stacking sequences, Bernal and twisted, were observed in the graphene grains. The presence of different stacking sequences in the graphene layers influence the electronic and optical properties;in Bernal stacking the band gap can be tunable and in twisted stacking the overall sheet resistance can be reduced. Grain boundaries of Pt provides low energy sites to the carbon species, therefore the nucleation of grains are more at the boundaries. The stacking order and the number of layers in grains were seen more clearly with scanning electron microscopy. Raman spectroscopy showed high quality graphene samples due to very small D peak. 2D Raman peak for single layer graphene showed full width half maximum (FWHM) value of 30 cm ? 1. At points A, B and C, Bernal stacked grain showed FWHM values of 51.22, 58.45 and 64.72 cm ? 1, while twisted stacked grain showed the FWHM values of 27.26, 28.83 and 20.99 cm ? 1, respectively. FWHM values of 2D peak of Bernal stacked grain showed an increase of 20–30 cm ? 1 as compare to single layer graphene which showed its

  19. Atomic level spatial variations of energy states along graphene edges.

    Science.gov (United States)

    Warner, Jamie H; Lin, Yung-Chang; He, Kuang; Koshino, Masanori; Suenaga, Kazu

    2014-11-12

    The local atomic bonding of carbon atoms around the edge of graphene is examined by aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). High-resolution 2D maps of the EELS combined with atomic resolution annular dark field STEM images enables correlations between the carbon K-edge EELS and the atomic structure. We show that energy states of graphene edges vary across individual atoms along the edge according to their specific C-C bonding, as well as perpendicular to the edge. Unique spectroscopic peaks from the EELS are assigned to specific C atoms, which enables unambiguous spectroscopic fingerprint identification for the atomic structure of graphene edges with unprecedented detail.

  20. Substrate-induced magnetism in epitaxial graphene buffer layers.

    Science.gov (United States)

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-01

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  1. Delaminated graphene at silicon carbide facets: atomic scale imaging and spectroscopy.

    Science.gov (United States)

    Nicotra, Giuseppe; Ramasse, Quentin M; Deretzis, Ioannis; La Magna, Antonino; Spinella, Corrado; Giannazzo, Filippo

    2013-04-23

    Atomic-resolution structural and spectroscopic characterization techniques (scanning transmission electron microscopy and electron energy loss spectroscopy) are combined with nanoscale electrical measurements (conductive atomic force microscopy) to study at the atomic scale the properties of graphene grown epitaxially through the controlled graphitization of a hexagonal SiC(0001) substrate by high temperature annealing. This growth technique is known to result in a pronounced electron-doping (∼10(13) cm(-2)) of graphene, which is thought to originate from an interface carbon buffer layer strongly bound to the substrate. The scanning transmission electron microscopy analysis, carried out at an energy below the knock-on threshold for carbon to ensure no damage is imparted to the film by the electron beam, demonstrates that the buffer layer present on the planar SiC(0001) face delaminates from it on the (112n) facets of SiC surface steps. In addition, electron energy loss spectroscopy reveals that the delaminated layer has a similar electronic configuration to purely sp2-hybridized graphene. These observations are used to explain the local increase of the graphene sheet resistance measured around the surface steps by conductive atomic force microscopy, which we suggest is due to significantly lower substrate-induced doping and a resonant scattering mechanism at the step regions. A first-principles-calibrated theoretical model is proposed to explain the structural instability of the buffer layer on the SiC facets and the resulting delamination.

  2. Detection of interlayer interaction in few-layer graphene

    Science.gov (United States)

    Wu, Zefei; Han, Yu; Lin, Jiangxiazi; Zhu, Wei; He, Mingquan; Xu, Shuigang; Chen, Xiaolong; Lu, Huanhuan; Ye, Weiguang; Han, Tianyi; Wu, Yingying; Long, Gen; Shen, Junying; Huang, Rui; Wang, Lin; He, Yuheng; Cai, Yuan; Lortz, Rolf; Su, Dangsheng; Wang, Ning

    2015-08-01

    Bernal-stacked few-layer graphene has been investigated by analyzing its Landau-level spectra through quantum capacitance measurements. We find that surface relaxation, which is insignificant in trilayer graphene, starts to manifest in Bernal-stacked tetralayer graphene. In trilayer graphene, the interlayer interaction parameters are generally similar to those of graphite. However, in tetralayer graphene, the hopping parameters of the two bulk layers are quite different from those of the two outer layers. This represents direct evidence of the surface relaxation phenomenon. Traditionally, the van der Waals interaction between the carbon layers is thought to be insignificant. However, we suggest that the interlayer interaction is an important factor in explaining the observed results, and the symmetry-breaking effects in graphene sublattice are not negligible.

  3. Critical Dispersion Distance of Silicon Nanoparticles Intercalated between Graphene Layers

    Directory of Open Access Journals (Sweden)

    Shuze Zhu

    2012-01-01

    Full Text Available Nanocomposites of silicon nanoparticles (Si NPs dispersed in between graphene layers emerge as potential anode materials of high-charge capacity for lithium-ion batteries. A key design requirement is to keep Si NPs dispersed without aggregation. Experimental design of the Si NP dispersion in graphene layers has remained largely empirical. Through extensive molecular dynamics simulations, we determine a critical NP dispersion distance as the function of NP size, below which Si NPs in between graphene layers evolve to bundle together. These results offer crucial and quantitative guidance for designing NP-graphene nanocomposite anode materials with high charge capacity.

  4. Controllable chemical vapor deposition growth of few layer graphene for electronic devices.

    Science.gov (United States)

    Wei, Dacheng; Wu, Bin; Guo, Yunlong; Yu, Gui; Liu, Yunqi

    2013-01-15

    Because of its atomic thickness, excellent properties, and widespread applications, graphene is regarded as one of the most promising candidate materials for nanoelectronics. The wider use of graphene will require processes that produce this material in a controllable manner. In this Account, we focus on our recent studies of the controllable chemical vapor deposition (CVD) growth of graphene, especially few-layer graphene (FLG), and the applications of this material in electronic devices. CVD provides various means of control over the morphologies of the produced graph ene. We studied several variables that can affect the CVD growth of graphene, including the catalyst, gas flow rate, growth time, and growth temperature and successfully achieved the controlled growth of hexagonal graphene crystals. Moreover, we developed several modified CVD methods for the controlled growth of FLGs. Patterned CVD produced FLGs with desired shapes in required areas. By introducing dopant precursor in the CVD process, we produced substitutionally doped FLGs, avoiding the typically complicated post-treatment processes for graphene doping. We developed a template CVD method to produce FLG ribbons with controllable morphologies on a large scale. An oxidation-activated surface facilitated the CVD growth of polycrystalline graphene without the use of a metal catalyst or a complicated postgrowth transfer process. In devices, CVD offers a controllable means to modulate the electronic properties of the graphene samples and to improve device performance. Using CVD-grown hexagonal graphene crystals as the channel materials in field-effect transistors (FETs), we improved carrier mobility. Substitutional doping of graphene in CVD opened a band gap for efficient FET operation and modulated the Fermi energy level for n-type or p-type features. The similarity between the chemical structure of graphene and organic semiconductors suggests potential applications of graphene in organic devices. We

  5. Graphene for Expandable Space Structures Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Graphene's tightly bonded impermeable single atomic layer of carbon offers unrivalled potential for lightweight flexible gas barrier applications. Graphene has been...

  6. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    Science.gov (United States)

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Schloegl, R.; Willinger, Marc-Georg

    2016-01-01

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene–graphene and graphene–substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite. PMID:27759024

  7. Time variant layer control in atmospheric pressure chemical vapor deposition based growth of graphene

    KAUST Repository

    Qaisi, Ramy M.

    2013-04-01

    Graphene is a semi-metallic, transparent, atomic crystal structure material which is promising for its high mobility, strength and transparency - potentially applicable for radio frequency (RF) circuitry and energy harvesting and storage applications. Uniform (same number of layers), continuous (not torn or discontinuous), large area (100 mm to 200 mm wafer scale), low-cost, reliable growth are the first hand challenges for its commercialization prospect. We show a time variant uniform (layer control) growth of bi- to multi-layer graphene using atmospheric chemical vapor deposition system. We use Raman spectroscopy for physical characterization supported by electrical property analysis. © 2013 IEEE.

  8. High quality reduced graphene oxide through repairing with multi-layered graphene ball nanostructures

    OpenAIRE

    Kyoung Hwan Kim; MinHo Yang; Kyeong Min Cho; Young-Si Jun; Sang Bok Lee; Hee-Tae Jung

    2013-01-01

    We present a simple and up-scalable method to produce highly repaired graphene oxide with a large surface area, by introducing spherical multi-layered graphene balls with empty interiors. These graphene balls are prepared via chemical vapor deposition (CVD) of Ni particles on the surface of the graphene oxides (GO). Transmission electron microscopy and Raman spectroscopy results reveal that defects in the GO surfaces are well repaired during the CVD process, with the help of nickel nanopartic...

  9. Atomic force spectroscopy and density-functional study of graphene corrugation on Ru(0001)

    Science.gov (United States)

    Voloshina, Elena; Dedkov, Yuriy

    2016-06-01

    Graphene, the thinnest material in the world, can form moiré structures on different substrates, including graphite, h -BN, or metal surfaces. In such systems, the structure of graphene, i.e., its corrugation, as well as its electronic and elastic properties, are defined by the combination of the system geometry and local interaction strength at the interface. The corrugation in such structures on metals is heavily extracted from diffraction or local probe microscopy experiments, and it can be obtained only via comparison with theoretical data, which usually simulate the experimental findings. Here we show that graphene corrugation on metals can be measured directly employing atomic force spectroscopy, and the obtained value coincides with state-of-the-art theoretical results. The presented results demonstrate an unexpected space selectivity for the Δ f (z ) signal in the atomic force spectroscopy in the moiré graphene lattice on Ru(0001), which is explained by the different response of the graphene layer on the indentation process. We also address the elastic reaction of the formed graphene nanodoms on the indentation process by the scanning tip that is important for the modeling and fabrication of graphene-based nanoresonators on the nanoscale.

  10. Direct observation of a long-lived single-atom catalyst chiseling atomic structures in graphene.

    Science.gov (United States)

    Wang, Wei Li; Santos, Elton J G; Jiang, Bin; Cubuk, Ekin Dogus; Ophus, Colin; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Ciston, Jim; Westervelt, Robert; Kaxiras, Efthimios

    2014-02-12

    Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.

  11. Selective growth of graphene in layer-by-layer via chemical vapor deposition

    Science.gov (United States)

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-07-01

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (~40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices.Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene

  12. Large-Area Quality Control of Atomically-Thin Layered Materials

    Science.gov (United States)

    Nolen, Craig Merten

    Fast progress in chemical vapor deposition of graphene and other quasi-two-dimensional layered materials such as topological insulators call for development of a reliable high-throughput method of layered materials identification and quality control. The number of atomic planes in graphene or other ultra-thin films has to be determined very fast and over large wafer-scale areas. The previously existed methods of accurate counting of the number of atomic planes in few-layer graphene were primarily based on micro-Raman spectroscopy. These methods were local, slow, and could not be scaled up to characterize the whole wafers. In this dissertation research I proposed and developed an automatic approach for graphene inspection over the wafer-size areas. The proposed method can be scaled up for industrial use. It is based on the image processing analysis of the pseudo-color contrasts uniquely assigned to each few-layer graphene region characterized by a specific number of atomic planes. The initial calibration of the technique is performed with the help of micro-Raman spectroscopy. The image processing is also used to account for the lighting non-uniformity of the samples. Implementation of the technique developed in this dissertation research reduces the cost and time required for graphene identification and quality assessment, and can become the next major impetus for practical applications of graphene, few-layer graphene and other atomically-thin films. The technique was tested on mechanically exfoliated graphene and then extended to the chemical-vapor-deposited graphene, and to bismuth telluride topological insulator thin films. The second part of the dissertation research deals with development of the electrostatic transfer process. The investigated approach allows one to transfer the patterned few-layer graphene films controllably to Si3N4 substrates compatible with other materials. The large-area quality control and graphene transfer techniques developed in this

  13. Nanosecond spin relaxation times in single layer graphene spin valves with hexagonal boron nitride tunnel barriers

    Science.gov (United States)

    Singh, Simranjeet; Katoch, Jyoti; Xu, Jinsong; Tan, Cheng; Zhu, Tiancong; Amamou, Walid; Hone, James; Kawakami, Roland

    2016-09-01

    We present an experimental study of spin transport in single layer graphene using atomic sheets of hexagonal boron nitride (h-BN) as a tunnel barrier for spin injection. While h-BN is expected to be favorable for spin injection, previous experimental studies have been unable to achieve spin relaxation times in the nanosecond regime, suggesting potential problems originating from the contacts. Here, we investigate spin relaxation in graphene spin valves with h-BN barriers and observe room temperature spin lifetimes in excess of a nanosecond, which provides experimental confirmation that h-BN is indeed a good barrier material for spin injection into graphene. By carrying out measurements with different thicknesses of h-BN, we show that few layer h-BN is a better choice than monolayer for achieving high non-local spin signals and longer spin relaxation times in graphene.

  14. Large changes of graphene conductance as a function of lattice orientation between stacked layers

    International Nuclear Information System (INIS)

    Using the conductive tip of an atomic force microscope as an electrode, we found that the electrical conductance of graphite terraces separated by steps can vary by large factors of up to 100, depending on the relative lattice orientation of the surface and subsurface layers. This effect can be attributed to interlayer interactions that, when stacked commensurately in a Bernal sequence (ABAB…), cause the band gap to open. Misaligned layers, on the other hand, behave like graphene. Angular misorientations of a few degrees were found to cause large increases in the conductance of the top layer, with the maximum occurring around 30°. These results suggest new applications for graphene multilayers by stacking layers at various angles to control the resistance of the connected graphene ribbons in devices. (paper)

  15. Multilayer films of cationic graphene-polyelectrolytes and anionic graphene-polyelectrolytes fabricated using layer-by-layer self-assembly

    International Nuclear Information System (INIS)

    Extremely thin sheets of carbon atoms called graphene have been predicted to possess excellent thermal properties, electrical conductivity, and mechanical stiffness. To harness such properties in composite materials for multifunctional applications, one would require the incorporation of graphene. In this study, new thin film composites were created using layer-by-layer (LBL) assembly of polymer-coated graphitic nanoplatelets. The positive and negative polyelectrolytes used to cover graphene sheets were poly allylamine hydrochloride (PAH) and poly sodium 4-styrenesulfonate (PSS). The synthesized poly allylamine hydrochloride-graphene (PAH-G) and poly sodium 4-styrenesulfonate-gaphene (PSS-G) were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and thermo gravimetric analysis (TGA). The multilayer films created by spontaneous sequential adsorption of PAH-G and PSS-G were characterized by ultra violet spectroscopy (UV-vis), scanning electron microscopy (SEM), and AFM. The electrical conductivity of the graphene/polyelectrolyte multilayer film composites measured by the four-point probe method was 0.2 S cm-1, which was sufficient for the construction of advanced electro-optical devices and sensors.

  16. Spotting 2D atomic layers on aluminum nitride thin films

    Science.gov (United States)

    Chandrasekar, Hareesh; Bharadwaj B, Krishna; Vaidyuala, Kranthi Kumar; Suran, Swathi; Bhat, Navakanta; Varma, Manoj; Raghavan, Srinivasan

    2015-10-01

    Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride (AIN) films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2″ Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS2 on AlN films as compared to the conventional SiO2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.

  17. Spotting 2D atomic layers on aluminum nitride thin films.

    Science.gov (United States)

    Chandrasekar, Hareesh; Bharadwaj B, Krishna; Vaidyuala, Kranthi Kumar; Suran, Swathi; Bhat, Navakanta; Varma, Manoj; Srinivasan Raghavan

    2015-10-23

    Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride (AIN) films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2″ Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS2 on AlN films as compared to the conventional SiO2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.

  18. Nanoscale imaging of freestanding nitrogen doped single layer graphene.

    Science.gov (United States)

    Iyer, Ganjigunte R S; Wang, Jian; Wells, Garth; Bradley, Michael P; Borondics, Ferenc

    2015-02-14

    Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale. PMID:25584935

  19. Nanoscale imaging of freestanding nitrogen doped single layer graphene.

    Science.gov (United States)

    Iyer, Ganjigunte R S; Wang, Jian; Wells, Garth; Bradley, Michael P; Borondics, Ferenc

    2015-02-14

    Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale.

  20. Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene.

    Science.gov (United States)

    Ko, Yong-Ho; Lee, Jong-Dae; Yoon, Taeshik; Lee, Chang-Woo; Kim, Taek-Soo

    2016-03-01

    The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface. PMID:26856638

  1. Atomic Scale Imaging of the Electronic Structure and Chemistry of Graphene and Its Precursors on Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, George W [Columbia University

    2015-02-16

    atom, provides information about the electronic structure of graphene and is particularly sensitive to the sign and magnitude of the charge transfer between graphene and any surface adsorbed species. Results: (A) Graphene on SiO2 In an effort designed to unravel aspects of the mechanisms for chemistry on graphene surfaces, STM and STS were employed to show that graphene on SiO2 is oxidized at lower temperatures than either graphite or multi-layer graphene. Two independent factors control this charge transfer: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. (B) Graphene on Copper In the case of graphene grown on copper surfaces, we found that the graphene grows primarily in registry with the underlying copper lattice for both Cu(111) and Cu(100). On Cu(111) the graphene has a hexagonal superstructure with a significant electronic component, whereas it has a linear superstructure on Cu(100). (C) Nitrogen Doped Graphene on Copper Using STM we have also studied the electronic structure and morphology of graphene films grown on a copper foil substrate in which N atoms substitute for carbon in the 2-D graphene lattice. The salient features of the results of this study were: (1) Nitrogen doped graphene on Cu foil exhibits a triangular structure with an “apparent” slight elevation of ~ 0.8 Å at N atom substitution sites; (2) Nitrogen doping results in ~0.4 electrons per N atom donated to the graphene lattice; (3) Typical N doping of graphene on Cu foil shows mostly single site Carbon atom displacement (~ 3N/1000C); (4) Some multi-site C atom displacement is observed (<10% of single site events). (D) Boron Doped Graphene on Copper We also used scanning tunneling microscopy and x-ray spectroscopy to characterize the atomic and electronic structure of boron-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice

  2. Nanoscale imaging of freestanding nitrogen doped single layer graphene

    Science.gov (United States)

    Iyer, Ganjigunte R. S.; Wang, Jian; Wells, Garth; Bradley, Michael P.; Borondics, Ferenc

    2015-01-01

    Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale.Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05385k

  3. High temperature and current density induced degradation of multi-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Baoming; Haque, M. A., E-mail: mah37@psu.edu [Mechanical and Nuclear Engineering, The Pennsylvania State University, 314, Leonhard Building, University Park, Pennsylvania 16802 (United States); Mag-isa, Alexander E.; Kim, Jae-Hyun [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Lee, Hak-Joo [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Center for Advanced Meta-Materials (CAMM), 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of)

    2015-10-19

    We present evidence of moderate current density, when accompanied with high temperature, promoting migration of foreign atoms on the surface of multi-layer graphene. Our in situ transmission electron microscope experiments show migration of silicon atoms at temperatures above 800 °C and current density around 4.2 × 10{sup 7} A/cm{sup 2}. Originating from the micro-machined silicon structures that clamp the freestanding specimen, the atoms are observed to react with the carbon atoms in the multi-layer graphene to produce silicon carbide at temperatures of 900–1000 °C. In the absence of electrical current, there is no migration of silicon and only pyrolysis of polymeric residue is observed.

  4. Electronic and Atomic-Scale Properties of Ultraflat CVD Graphene

    Science.gov (United States)

    Gutierrez, Christopher; Rosenthal, Ethan; Dadgar, Ali; Brown, Lola; Lochocki, Edward; Shen, Kyle; Park, Jiwoong; Pasupathy, Abhay

    2014-03-01

    Chemical vapor deposition (CVD) growth on copper foils has proven to be a reliable and cost-effective method for the production of graphene. However, most films grown by this method suffer from misoriented graphene grains as well as topographic roughness due to the polycrystallinity of the underlying copper foil substrate. Recent methods of copper foil treatment have allowed for the growth of graphene predominantly on large single crystal Cu(111) facets. In this talk we discuss scanning tunneling microscope (STM) measurements on such samples that reveal large terraces and atomically-resolved images that allow us to analyze the graphene-copper interaction during the growth. Scanning tunneling spectroscopy (STS) measurements and mapping are further employed to probe the electronic interaction between the graphene and copper substrate.

  5. Ultrahigh conductivity of large area suspended few layer graphene films

    Science.gov (United States)

    Rouhi, Nima; Wang, Yung Yu; Burke, Peter J.

    2012-12-01

    Room-temperature (atmospheric-pressure) electrical conductivity measurements of wafer-scale, large-area suspended (few layer) graphene membranes with areas up to 1000 μm2 (30 μm × 30 μm) are presented. Multiple devices on one wafer can be fabricated with high yield from the same chemical vapor deposition grown graphene sheet, transferred from a nickel growth substrate to large opening in a suspended silicon nitride support membrane. This represents areas two to orders of magnitude larger than prior transport studies on any suspended graphene device (single or few layer). We find a sheet conductivity of ˜2500 e2/h (or about 10 Ω/sq) of the suspended graphene, which is an order of magnitude higher than any previously reported sheet conductance of few layer graphene.

  6. Plasmon modes of circular cylindrical double-layer graphene.

    Science.gov (United States)

    Zhao, Tao; Hu, Min; Zhong, Renbin; Chen, Xiaoxing; Zhang, Ping; Gong, Sen; Zhang, Chao; Liu, Shenggang

    2016-09-01

    In this paper, a theoretical investigation on plasmon modes in a circular cylindrical double-layer graphene structure is presented. Due to the interlayer electromagnetic interaction, there exist two branches of plasmon modes, the optical plasmon mode and the acoustic plasmon mode. The characteristics of these two modes, such as mode pattern, effective mode index and propagation loss, are analyzed. The modal behaviors can be effectively tuned by changing the distance between two graphene layers, the chemical potential of graphene and the permittivity of interlayer dielectric. Importantly, the breakup of tradeoff between mode confinement and propagation loss is discovered in the distance-dependent modal behavior, which originates from the unique dispersion properties of a double-layer graphene system. As a consequence, both strong mode confinement and longer propagation length can be achieved. Our results may provide good opportunities for developing applications based on graphene plasmonics in circular cylindrical structure. PMID:27607651

  7. Surface stress of graphene layers supported on soft substrate

    Science.gov (United States)

    Du, Feng; Huang, Jianyong; Duan, Huiling; Xiong, Chunyang; Wang, Jianxiang

    2016-05-01

    We obtain the surface stress of a single layer and multilayers of graphene supported on silicone substrates by measuring the deformation of the graphene-covered substrates induced by the surface tension of liquid droplets together with the Neumann’s triangle concept. We find that the surface stress of the graphene-covered substrate is significant larger than that of the bare substrate, and it increases with increasing graphene layers, and finally reaches a constant value of about 120 mN/m on three and more layers of graphene. This work demonstrates that the apparent surface stress of graphene-substrate systems can be tuned by the substrate and the graphene layers. The surface stress and the tuning effect of the substrate on it may have applications in design and characterization of graphene-based ultra-sensitive sensors and other devices. Moreover, the method may also be used to measure the surface stress of other ultrathin films supported on soft substrates.

  8. Edge states of graphene wrinkles in single-layer graphene grown on Ni(111)

    Science.gov (United States)

    Liu, Liwei; Xiao, Wende; Wang, Dongfei; Yang, Kai; Tao, Lei; Gao, Hong-Jun

    2016-10-01

    As quasi-one-dimensional (1D) structures with characteristic widths of nanometer scale, graphene wrinkles (GWs) have been widely observed in graphene grown by chemical vapor deposition. Similar to conventional 1D graphene-based nanostructures, e.g., carbon nanotubes and graphene nanoribbons, 1D electron confinement has been observed in the GWs. However, it remains an open question whether the GWs have effective edges and exhibit corresponding edge states. Here, we report on the edge states of the GWs in single-layer graphene grown on Ni(111) by means of low temperature scanning tunneling microscopy and spectroscopy. We show that the GWs are decoupled from the substrate, while the surrounding planar graphene are strongly coupled with the substrate. The different graphene-substrate coupling leads to effective edges and 1D character of the GWs. The chiral edges of the GWs give rise to pronounced edge states around the Fermi level in the density of states.

  9. Atomic layer deposition of nanoporous biomaterials

    Directory of Open Access Journals (Sweden)

    Roger J Narayan

    2010-03-01

    Full Text Available Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.

  10. Growth and properties of few-layer graphene prepared by chemical vapor deposition

    OpenAIRE

    Park, Hye Jin; Meyer, Jannik; Roth, Siegmar; Skakalova, Viera

    2009-01-01

    The structure, and electrical, mechanical and optical properties of few-layer graphene (FLG) synthesized by chemical vapor deposition (CVD) on a Ni coated substrate were studied. Atomic resolution transmission electron microscope (TEM) images show highly crystalline single layer parts of the sample changing to multilayer domains where crystal boundaries are connected by chemical bonds. This suggests two different growth mechanisms. CVD and carbon segregation participate in the growth process ...

  11. Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Velez-Fort, E. [Laboratoire de Photonique et de Nanostructures (CNRS-LPN), Route de Nozay, 91460 Marcoussis (France); Institut de Minéralogie et de Physique des Milieux Condensés, CNRS–UMR7590, Sorbonne Universités-Pierre et Marie Curie, 4 Pl. Jussieu, 75005 Paris (France); Ouerghi, A. [Laboratoire de Photonique et de Nanostructures (CNRS-LPN), Route de Nozay, 91460 Marcoussis (France); Silly, M. G.; Sirtti, F. [Synchrotron-SOLEIL, Saint-Aubin, BP48, F91192 Gif sur Yvette Cedex (France); Eddrief, M.; Marangolo, M. [CNRS, UMR 7588, Institut des NanoSciences de Paris (INSP), F-75005 Paris (France); Sorbonne Universités, UPMC Univ. Paris 06, UMR 7588, INSP, F-75005 Paris (France); Shukla, A. [Institut de Minéralogie et de Physique des Milieux Condensés, CNRS–UMR7590, Sorbonne Universités-Pierre et Marie Curie, 4 Pl. Jussieu, 75005 Paris (France)

    2014-03-03

    Structural and electronic properties of epitaxial graphene on 4H-SiC were studied before and after an atomic oxidation process. X-ray photoemission spectroscopy indicates that oxygen penetrates into the substrate and decouples a part of the interface layer. Raman spectroscopy demonstrates the increase of defects due to the presence of oxygen. Interestingly, we observed on the near edge x-ray absorption fine structure spectra a splitting of the π* peak into two distinct resonances centered at 284.7 and 285.2 eV. This double structure smears out after the oxidation process and permits to probe the interface architecture between graphene and the substrate.

  12. Characterization of graphene and transition metal dichalcogenide at the atomic scale

    International Nuclear Information System (INIS)

    Edge structures and atomic defects are of fundamental importance since they can significantly affect the physical and chemical properties of low-dimensional materials, such as nanoribbons, and therefore merit thorough investigations at the atomic level. Recent developments of direct imaging and analytical techniques using an aberration-corrected scanning transmission electron microscope (STEM) have provided direct access to information on the local atomic structure and the chemical composition at the atomic scale. In this review, we report on the discrimination of single atoms including dopant atoms on a monolayered transition-metal dichalcogenide (TMD) nanoribbon and a single nitrogen adatom on graphene by time-resolved annular dark-field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS). We also show that in situ scanning transmission electron microscopy can be used to monitor the structural transformation between semiconducting (2H) and metallic (1T) phases in monolayer MoS2, and can enable direct observation of in-plane graphene growth at a step edge of a bi-layer graphene and domain boundary formation during growth with atomic-resolution. (author)

  13. Characterization of Graphene and Transition Metal Dichalcogenide at the Atomic Scale

    Science.gov (United States)

    Liu, Zheng; Lin, Yung-Chang; Warner, Jamie H.; Teng, Po-Yuan; Yeh, Chao-Hui; Chiu, Po-Wen; Iijima, Sumio; Suenga, Kazu

    2015-12-01

    Edge structures and atomic defects are of fundamental importance since they can significantly affect the physical and chemical properties of low-dimensional materials, such as nanoribbons, and therefore merit thorough investigations at the atomic level. Recent developments of direct imaging and analytical techniques using an aberration-corrected scanning transmission electron microscope (STEM) have provided direct access to information on the local atomic structure and the chemical composition at the atomic scale. In this review, we report on the discrimination of single atoms including dopant atoms on a monolayered transition-metal dichalcogenide (TMD) nanoribbon and a single nitrogen adatom on graphene by time-resolved annular dark-field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS). We also show that in situ scanning transmission electron microscopy can be used to monitor the structural transformation between semiconducting (2H) and metallic (1T) phases in monolayer MoS2, and can enable direct observation of in-plane graphene growth at a step edge of a bi-layer graphene and domain boundary formation during growth with atomic-resolution.

  14. Epitaxial few-layer graphene: towards single crystal growth

    Energy Technology Data Exchange (ETDEWEB)

    Hibino, H; Kageshima, H; Nagase, M, E-mail: hibino@will.brl.ntt.co.j [NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198 (Japan)

    2010-09-22

    We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

  15. Atomic resolution electrostatic potential mapping of graphene sheets by off-axis electron holography

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, David, E-mail: david.cooper@cea.fr [University Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054, Grenoble (France); Pan, Cheng-Ta; Haigh, Sarah [School of Materials, The University of Manchester, Manchester M13 9PL (United Kingdom)

    2014-06-21

    Off-axis electron holography has been performed at atomic resolution with the microscope operated at 80 kV to provide electrostatic potential maps from single, double, and triple layer graphene. These electron holograms have been reconstructed in order to obtain information about atomically resolved and mean inner potentials. We propose that off-axis electron holography can now be used to measure the electrical properties in a range of two-dimensional semiconductor materials and three dimensional devices comprising stacked layers of films to provide important information about their electrical properties.

  16. Ultraviolet laser deposition of graphene thin films without catalytic layers

    KAUST Repository

    Sarath Kumar, S. R.

    2013-01-09

    In this letter, the formation of nanostructured graphene by ultraviolet laser ablation of a highly ordered pyrolytic graphite target under optimized conditions is demonstrated, without a catalytic layer, and a model for the growth process is proposed. Previously, graphene film deposition by low-energy laser (2.3 eV) was explained by photo-thermal models, which implied that graphene films cannot be deposited by laser energies higher than the C-C bond energy in highly ordered pyrolytic graphite (3.7 eV). Here, we show that nanostructured graphene films can in fact be deposited using ultraviolet laser (5 eV) directly over different substrates, without a catalytic layer. The formation of graphene is explained by bond-breaking assisted by photoelectronic excitation leading to formation of carbon clusters at the target and annealing out of defects at the substrate.

  17. Raman and ellipsometry spectroscopic analysis of graphene films grown directly on Si substrate via CVD technique for estimating the graphene atomic planes number

    Science.gov (United States)

    Al-Hazmi, F. S.; Beall, Gary W.; Al-Ghamdi, A. A.; Alshahrie, Ahmed; Shokr, F. S.; Mahmoud, Waleed E.

    2016-08-01

    Two reliable approaches for estimating the number of atomic planes of graphene films grown on Si substrate were demonstrated by Raman and ellipsometry spectroscopies. The first approach depends on the measurement of the ratio of the integrated Raman scattering intensity of the graphene G band to the optical phonon band of Si substrate (IG/ISi). The second approach belongs to ellipsometry measurement of the ratio of the amplitude of the reflected polarized light from the surface of the graphene films to the amplitude of reflected polarized light from the surface of the Si substrate (ΨG/ΨSi). These two approaches could efficiently recognize the number of atomic planes in the graphene films (1 ≤ n ≤ 10). The results were compared with atomic force microscopy (AFM) measurement and showed a linear regression with slope of 0.36 ± 0.01 nm/graphene layer. The Two approaches will open a new avenue to efficiently count the number of graphene layers during the preparation process.

  18. Critical Dispersion Distance of Silicon Nanoparticles Intercalated between Graphene Layers

    OpenAIRE

    Shuze Zhu; Jason Galginaitis; Teng Li

    2012-01-01

    Nanocomposites of silicon nanoparticles (Si NPs) dispersed in between graphene layers emerge as potential anode materials of high-charge capacity for lithium-ion batteries. A key design requirement is to keep Si NPs dispersed without aggregation. Experimental design of the Si NP dispersion in graphene layers has remained largely empirical. Through extensive molecular dynamics simulations, we determine a critical NP dispersion distance as the function of NP size, below which Si NPs in between ...

  19. Atomic-Scale Sliding Friction on Graphene in Water.

    Science.gov (United States)

    Vilhena, J G; Pimentel, Carlos; Pedraz, Patricia; Luo, Feng; Serena, Pedro A; Pina, Carlos M; Gnecco, Enrico; Pérez, Rubén

    2016-04-26

    The sliding of a sharp nanotip on graphene completely immersed in water is investigated by molecular dynamics (MD) and atomic force microscopy. MD simulations predict that the atomic-scale stick-slip is almost identical to that found in ultrahigh vacuum. Furthermore, they show that water plays a purely stochastic role in sliding (solid-to-solid) friction. These observations are substantiated by friction measurements on graphene grown on Cu and Ni, where, oppositely of the operation in air, lattice resolution is readily achieved. Our results promote friction force microscopy in water as a robust alternative to ultra-high-vacuum measurements. PMID:26982997

  20. Ballistic electron propagation through periodic few-layer graphene nanostructures

    Science.gov (United States)

    Dragoman, Daniela; Mihalache, Iulia

    2016-10-01

    We have studied electron propagation in periodic structures containing mono- and few-layer graphene regions and/or semiconducting stripes. The calculation of the transmission coefficient in all cases has been performed using transfer matrices inside regions with the same material/potential energy, as well as interface matrices between regions in which the evolution laws of charge carriers differ. Numerical simulations of the transmission coefficient, as well as of the low-temperature conductance, suggest that different periodic structures modulate differently the electrical current. The obtained results can be used to model ballistic transport in all-graphene devices, in particular in few-layer graphene structures.

  1. Chemical storage of hydrogen in few-layer graphene.

    Science.gov (United States)

    Subrahmanyam, K S; Kumar, Prashant; Maitra, Urmimala; Govindaraj, A; Hembram, K P S S; Waghmare, Umesh V; Rao, C N R

    2011-02-15

    Birch reduction of few-layer graphene samples gives rise to hydrogenated samples containing up to 5 wt % of hydrogen. Spectroscopic studies reveal the presence of sp(3) C-H bonds in the hydrogenated graphenes. They, however, decompose readily on heating to 500 °C or on irradiation with UV or laser radiation releasing all the hydrogen, thereby demonstrating the possible use of few-layer graphene for chemical storage of hydrogen. First-principles calculations throw light on the mechanism of dehydrogenation that appears to involve a significant reconstruction and relaxation of the lattice. PMID:21282617

  2. Chemical storage of hydrogen in few-layer graphene

    OpenAIRE

    Subrahmanyam, K. S.; Kumar, Prashant; Maitra, Urmimala; Govindaraj, A.; Hembram, K.P.S.S.; Waghmare, Umesh V.; RAO, C. N. R.

    2011-01-01

    Birch reduction of few-layer graphene samples gives rise to hydrogenated samples containing up to 5 wt % of hydrogen. Spectroscopic studies reveal the presence of sp3 C-H bonds in the hydrogenated graphenes. They, however, decompose readily on heating to 500 °C or on irradiation with UV or laser radiation releasing all the hydrogen, thereby demonstrating the possible use of few-layer graphene for chemical storage of hydrogen. First-principles calculations throw light on the mechanism of dehyd...

  3. Few-layer graphene growth from polystyrene as solid carbon source utilizing simple APCVD method

    Science.gov (United States)

    Ahmadi, Shahrokh; Afzalzadeh, Reza

    2016-07-01

    This research article presents development of an economical, simple, immune and environment friendly process to grow few-layer graphene by controlling evaporation rate of polystyrene on copper foil as catalyst and substrate utilizing atmospheric pressure chemical vapor deposition (APCVD) method. Evaporation rate of polystyrene depends on molecular structure, amount of used material and temperature. We have found controlling rate of evaporation of polystyrene by controlling the source temperature is easier than controlling the material weight. Atomic force microscopy (AFM) as well as Raman Spectroscopy has been used for characterization of the layers. The frequency of G‧ to G band ratio intensity in some samples varied between 0.8 and 1.6 corresponding to few-layer graphene. Topography characterization by atomic force microscopy confirmed Raman results.

  4. Atomic Structures of Graphene, Benzene and Methane with Bond Lengths as Sums of the Single, Double and Resonance Bond Radii of Carbon

    CERN Document Server

    Heyrovska, Raji

    2008-01-01

    Two dimensional layers of graphene are currently drawing a great attention in fundamental and applied nanoscience. Graphene consists of interconnected hexagons of carbon atoms as in graphite. This article presents for the first time the structures of graphene at the atomic level and shows how it differs from that of benzene, due to the difference in the double bond and resonance bond based radii of carbon. The carbon atom of an aliphatic compound such as methane has a longer covalent single bond radius as in diamond. All the atomic structures presented here have been drawn to scale.

  5. Addressing Raman features of individual layers in isotopically labeled Bernal stacked bilayer graphene

    Science.gov (United States)

    Costa, Sara D.; Weis, Johan Ek; Frank, Otakar; Fridrichová, Michaela; Kalbac, Martin

    2016-06-01

    In this report important Raman modes for the evaluation of strain in graphene (the 2D and 2D‧) are analyzed. The isotope labeling is used to disentangle contribution of individual graphene layers of graphene bilayer to the studied Raman modes. It is shown that for Bernal-stacked bilayers, the 2D and the 2D‧ Raman modes have three distinct components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The reported results thus enable addressing the properties of individual graphene layers in graphene bilayer by Raman spectroscopy.

  6. Atomic structure of epitaxial graphene sidewall nanoribbons: flat graphene, miniribbons, and the confinement gap.

    Science.gov (United States)

    Palacio, Irene; Celis, Arlensiú; Nair, Maya N; Gloter, Alexandre; Zobelli, Alberto; Sicot, Muriel; Malterre, Daniel; Nevius, Meredith S; de Heer, Walt A; Berger, Claire; Conrad, Edward H; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2015-01-14

    Graphene nanoribbons grown on sidewall facets of SiC have demonstrated exceptional quantized ballistic transport up to 15 μm at room temperature. Angular-resolved photoemission spectroscopy (ARPES) has shown that the ribbons have the band structure of charge neutral graphene, while bent regions of the ribbon develop a bandgap. We present scanning tunneling microscopy and transmission electron microscopy of armchair nanoribbons grown on recrystallized sidewall trenches etched in SiC. We show that the nanoribbons consist of a single graphene layer essentially decoupled from the facet surface. The nanoribbons are bordered by 1-2 nm wide bent miniribbons at both the top and bottom edges of the nanoribbons. We establish that nanoscale confinement in the graphene miniribbons is the origin of the local large band gap observed in ARPES. The structural results presented here show how this gap is formed and provide a framework to help understand ballistic transport in sidewall graphene.

  7. Antiferro quadrupolar ordering in Fe intercalated few layers graphene

    Directory of Open Access Journals (Sweden)

    Abu Jahid Akhtar

    2013-07-01

    Full Text Available The π electron cloud above and below the honeycomb structure of graphene causes each carbon atom to carry a permanent electric quadrupole moment which can attach any cation to impart interesting physical properties. We have synthesized Fe intercalated graphene structures to investigate tunable magnetic properties as a result of this chemical modification. An interesting antiferro quadrupolar ordering is observed which arises due to a coupling between magnetic dipole moment of Fe and electric quadrupole moment on graphene surface. In contrast to antiferromagnetic Neel temperature (TN, here the ordering temperature (TQ increases from 35.5 K to 47.5 K as the magnetic field is raised upto 1 Tesla.

  8. Pattern recognition approach to quantify the atomic structure of graphene

    DEFF Research Database (Denmark)

    Kling, Jens; Vestergaard, Jacob Schack; Dahl, Anders Bjorholm;

    2014-01-01

    We report a pattern recognition approach to detect the atomic structure in high-resolution transmission electron microscopy images of graphene. The approach provides quantitative information such as carbon-carbon bond lengths and bond length variations on a global and local scale alike. © 2014...

  9. Capacitance of Graphene Bilayer as a Which-Layer Probe

    OpenAIRE

    Young, Andrea F.; Levitov, Leonid S.

    2011-01-01

    The unique capabilities of capacitance measurements in bilayer graphene enable probing of layer-specific properties that are normally out of reach in transport measurements. Furthermore, capacitance measurements in the top-gate and penetration field geometries are sensitive to different physical quantities: the penetration field capacitance probes the two layers equally, whereas the top gate capacitance preferentially samples the near layer, resulting in the "near-layer capacitance enhancemen...

  10. Single-layer graphene on silicon nitride micromembrane resonators

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Silvan; Guillermo Villanueva, Luis; Amato, Bartolo; Boisen, Anja [Department of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, 2800 Kongens Lyngby (Denmark); Bagci, Tolga; Zeuthen, Emil; Sørensen, Anders S.; Usami, Koji; Polzik, Eugene S. [QUANTOP, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark); Taylor, Jacob M. [Joint Quantum Institute/NIST, College Park, Maryland 20899 (United States); Herring, Patrick K.; Cassidy, Maja C. [School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138 (United States); Marcus, Charles M. [Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen (Denmark); Cheol Shin, Yong; Kong, Jing [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2014-02-07

    Due to their low mass, high quality factor, and good optical properties, silicon nitride (SiN) micromembrane resonators are widely used in force and mass sensing applications, particularly in optomechanics. The metallization of such membranes would enable an electronic integration with the prospect for exciting new devices, such as optoelectromechanical transducers. Here, we add a single-layer graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling of graphene covered membranes is found to be equal to a perfectly conductive membrane, without significantly adding mass, decreasing the superior mechanical quality factor or affecting the optical properties of pure SiN micromembranes. The concept of graphene-SiN resonators allows a broad range of new experiments both in applied physics and fundamental basic research, e.g., for the mechanical, electrical, or optical characterization of graphene.

  11. Ultraviolet dielectric hyperlens with layered graphene and boron nitride

    CERN Document Server

    Wang, Junxia; Zhang, Baile

    2012-01-01

    The concept of hyperlens, as a novel transformation optics device, is a promising real-time super-resolution lens that can effectively transform evanescent waves into propagating waves and thus break the diffraction limit. However, previous hyperlens implementations usually adopted metal which would absorb most energy during light transmission and thus deteriorate imaging efficiency. Here we propose a novel hyperlens design based on dielectric layered graphene and h-boron nitride (h-BN) whose performance can surpass the counterpart design with metal. Our first-principle and Kramers-Kronig relation calculation shows that both layered graphene and layered h-BN exhibit strong anisotropic properties in ultraviolet spectrum regions, where their permittivity components perpendicular to the optic axis can be negative while the components parallel to the optic axis can be positive. Based on the anisotropic properties, flat and cylindrical hyperlenses are designed and numerically verified with layered graphene at 1200...

  12. Silicon nitride gate dielectrics and bandgap engineering in graphene layers

    OpenAIRE

    Zhu, Wenjuan; Neumayer, Deborah; Perebeinos, Vasili; Avouris, Phaedon

    2010-01-01

    We show that silicon nitride can provide uniform coverage of graphene in field-effect transistors while preserving the channel mobility. This insulator allowed us to study the maximum channel resistance at the Dirac (neutrality) point as a function of the strength of a perpendicular electric field in top-gated devices with different numbers of graphene layers. Using a simple model to account for surface potential variations (electron-hole puddles) near the Dirac point we estimate the field-in...

  13. Tunable hybrid surface waves supported by a graphene layer

    CERN Document Server

    Iorsh, Ivan; Belov, Pavel; Kivshar, Yuri

    2012-01-01

    We study surface waves localized near a surface of a semi-infinite dielectric medium covered by a layer of graphene in the presence of a strong external magnetic field. We demonstrate that both TE-TM hybrid surface plasmons can propagate along the graphene surface. We analyze the effect of the Hall conductivity on the disper- sion of hybrid surface waves and suggest a possibility to tune the plasmon dispersion by the magnetic field.

  14. Structure, stability and defects of single layer hexagonal BN in comparison to graphene

    International Nuclear Information System (INIS)

    We study by molecular dynamics the structural properties of single layer hexagonal boron nitride (h-BN) in comparison to graphene. We show that the Tersoff bond order potential developed for BN by Albe et al (1997 Radiat. Eff. Defects Solids 141 8597) gives a thermally stable hexagonal single layer with a bending constant κ = 0.54 eV at T = 0. We find that the non-monotonic behaviour of the lattice parameter, the expansion of the interatomic distance and the growth of the bending rigidity with temperature are qualitatively similar to those of graphene. Conversely, the energetics of point defects is extremely different: instead of StoneWales defects, the two lowest energy defects in h-BN involve either a broken bond or an out-of-plane displacement of a N atom to form a tetrahedron with three B atoms in the plane. We provide the formation energies and an estimate of the energy barriers.

  15. Complex Materials by Atomic Layer Deposition.

    Science.gov (United States)

    Schwartzberg, Adam M; Olynick, Deirdre

    2015-10-14

    Complex materials are defined as nanostructured materials with combinations of structure and/or composition that lead to performance surpassing the sum of their individual components. There are many methods that can create complex materials; however, atomic layer deposition (ALD) is uniquely suited to control composition and structural parameters at the atomic level. The use of ALD for creating complex insulators, semiconductors, and conductors is discussed, along with its use in novel structural applications.

  16. Electrochemical double layer near polar reduced graphene oxide electrode: Insights from molecular dynamic study

    International Nuclear Information System (INIS)

    Graphical abstract: Display Omitted - Highlights: • We have investigated the electrochemical double layer capacity of polar reduced graphene oxide electrode with aqueous solution by using molecular dynamic simulation, which is rare in previous studies currently. • The dipole orientation of water molecules near the polar reduced graphene oxide electrode will strongly depend on the polarity of functional group on reduced graphene oxide surface. The polarization interaction also restricts the rotation response of water molecules and weakens their mobility near the charged electrode, resulting in the decrease of integral capacitance value of reduced graphene oxide with increasing of functional groups concentration. • To obtain the accurate partial charge distribution of decorated functional group and corresponding surface polarization of reduced graphene oxide electrode, Bader charge analysis based on density functional theory calculations is used. - Abstract: Reduced graphene oxide (rGO) has emerged as an attractive choice for electrochemical double layer capacitors. Based on the accurate atomic partial charge distribution determined by density functional theory calculations, the electrochemical double layer structural and capacitive properties at the rGO/NaCl aqueous electrolyte interface are studied using the molecular dynamic simulations. Due to the charge redistribution mainly around oxygen functional groups, rGO will form a strong polar surface. It will significantly change the arrangement of surrounding water molecules through a hydrogen bond like interaction. The change of dipole orientation of water will induce corresponding net charge redistribution, leading to a change of potential of zero charge of rGO electrode. The polarization interaction also restricts the orientation of electrolyte molecules and weakens their mobility, resulting in the decrease of integral capacitance value of rGO with increasing of functional groups concentration. This work

  17. Elastic Buckling Behaviour of General Multi-Layered Graphene Sheets

    Directory of Open Access Journals (Sweden)

    Rong Ming Lin

    2015-04-01

    Full Text Available Elastic buckling behaviour of multi-layered graphene sheets is rigorously investigated. Van der Waals forces are modelled, to a first order approximation, as linear physical springs which connect the nodes between the layers. Critical buckling loads and their associated modes are established and analyzed under different boundary conditions, aspect ratios and compressive loading ratios in the case of graphene sheets compressed in two perpendicular directions. Various practically possible loading configurations are examined and their effect on buckling characteristics is assessed. To model more accurately the buckling behaviour of multi-layered graphene sheets, a physically more representative and realistic mixed boundary support concept is proposed and applied. For the fundamental buckling mode under mixed boundary support, the layers with different boundary supports deform similarly but non-identically, leading to resultant van der Waals bonding forces between the layers which in turn affect critical buckling load. Results are compared with existing known solutions to illustrate the excellent numerical accuracy of the proposed modelling approach. The buckling characteristics of graphene sheets presented in this paper form a comprehensive and wholesome study which can be used as potential structural design guideline when graphene sheets are employed for nano-scale sensing and actuation applications such as nano-electro-mechanical systems.

  18. Electronic Structure and Morphology of Graphene Layers on SiC

    Science.gov (United States)

    Ohta, Taisuke

    2008-03-01

    Recent years have witnessed the discovery and the unique electronic properties of graphene, a sheet of carbon atoms arranged in a honeycomb lattice. The unique linear dispersion relation of charge carriers near the Fermi level (``Dirac Fermions'') lead to exciting transport properties, such as an unusual quantum Hall effect, and have aroused scientific and technological interests. On the way towards graphene-based electronics, a knowledge of the electronic band structure and the morphology of epitaxial graphene films on silicon carbide substrates is imperative. We have studied the evolution of the occupied band structure and the morphology of graphene layers on silicon carbide by systematically increasing the layer thickness. Using angle-resolved photoemission spectroscopy (ARPES), we examine this unique 2D system in its development from single layer to multilayers, by characteristic changes in the π band, the highest occupied state, and the dispersion relation in the out-of-plane electron wave vector in particular. The evolution of the film morphology is evaluated by the combination of low-energy electron microscopy and ARPES. By exploiting the sensitivity of graphene's electronic states to the charge carrier concentration, changes in the on-site Coulomb potential leading to a change of π and π* bands can be examined using ARPES. We demonstrate that, in a graphene bilayer, the gap between π and π* bands can be controlled by selectively adjusting relative carrier concentrations, which suggests a possible application of the graphene bilayer for switching functions in electronic devices. This work was done in collaboration with A. Bostwick, J. L. McChesney, and E. Rotenberg at Advanced Light Source, Lawrence Berkeley National Laboratory, K. Horn at Fritz-Haber-Institut, K. V. Emtsev and Th. Seyller at Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, and F. El Gabaly and A. K. Schmid at National Center for Electron Microscopy, Lawrence Berkeley

  19. Perovskite thin films via atomic layer deposition.

    Science.gov (United States)

    Sutherland, Brandon R; Hoogland, Sjoerd; Adachi, Michael M; Kanjanaboos, Pongsakorn; Wong, Chris T O; McDowell, Jeffrey J; Xu, Jixian; Voznyy, Oleksandr; Ning, Zhijun; Houtepen, Arjan J; Sargent, Edward H

    2015-01-01

    A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3 NH3 PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm(-1) .

  20. Perovskite Thin Films via Atomic Layer Deposition

    KAUST Repository

    Sutherland, Brandon R.

    2014-10-30

    © 2014 Wiley-VCH Verlag GmbH & Co. KGaA. (Graph Presented) A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI2 and subsequently CH3NH3PbI3 perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm-1.

  1. Self-regulating homogenous growth of high-quality graphene on Co-Cu composite substrate for layer control

    Science.gov (United States)

    Lin, Tianquan; Huang, Fuqiang; Wan, Dongyun; Bi, Hui; Xie, Xiaoming; Jiang, Mianheng

    2013-06-01

    The composite substrate of Co and Cu was proposed to grow homogenous high quality wafer-size graphene films by an atmosphere pressure CVD method. The composite substrate consists of a moderate-carbon-solubility metal top (Co coating) as a C-dissolving layer and a low-carbon-solubility metal base (Cu foil) as a C-rejecting layer. During the CVD process, the interdiffusion of Co and Cu atoms occurs in the composite. With the dynamic control on Co and Cu alloying process to affect the carbon solubility, active carbon atoms captured by the Co layer were segregated to form spontaneously a high-quality graphene film on the top of Cu-Co substrate. The tunable layer-number of the graphene films can be precisely controlled by adjusting the thickness of the Co layer. High quality single-layered graphene films with a 98% yield were prepared on an 80 nm-Co-coated Cu foil and insensitive to growth temperature and time. More importantly, this type of composite substrate has also been developed to grow AB-stacked bilayers and three-layer graphene with 99% surface coverage and absence of defects. The approach is opening up a new avenue for high-quality graphene production with precise layer control through composite substrate design.The composite substrate of Co and Cu was proposed to grow homogenous high quality wafer-size graphene films by an atmosphere pressure CVD method. The composite substrate consists of a moderate-carbon-solubility metal top (Co coating) as a C-dissolving layer and a low-carbon-solubility metal base (Cu foil) as a C-rejecting layer. During the CVD process, the interdiffusion of Co and Cu atoms occurs in the composite. With the dynamic control on Co and Cu alloying process to affect the carbon solubility, active carbon atoms captured by the Co layer were segregated to form spontaneously a high-quality graphene film on the top of Cu-Co substrate. The tunable layer-number of the graphene films can be precisely controlled by adjusting the thickness of the Co

  2. Molecular Layer-seeded Ultra-thin Top-gate Dielectrics for High Transconductance Graphene Transistors

    Science.gov (United States)

    Sangwan, Vinod; Jariwala, Deep; Karmel, Hunter; Alaboson, Justice; Lauhon, Lincoln; Marks, Tobin; Hersam, Mark

    2012-02-01

    The potential of graphene in integrated analog and digital circuits can only be fully realized through incorporation of ultra-thin gate dielectrics to enable large-scale small-channel graphene field-effect transistors (GFETs). Atomic-layer deposition (ALD) is a viable technique to fabricate gate-dielectrics, however, it requires a seeding layer on otherwise inert graphene. Here, we demonstrate a single molecule thick perylene-3,4,9,10-tetracarboxylic dianhydride overlayer as an effective seeding layer to grow high-κ Al2O3 on mechanically exfoliated graphene for high-performance GFETs. Using an ultra-thin (films (5-10 nm), we demonstrate fabrication of the thinnest ALD-grown gate-dielectric (4 nm) reported to date in top-gated GFETs. This yields high performance GFETs with the intrinsic transconductance parameter approaching 2.4 mS and the field-effect mobility ˜3000 cm^2/Vs. We also demonstrate generalization of this molecular layer seeded-ALD growth method to higher- κ gate dielectrics, yielding further enhanced GFET transconductance for possible application to radio-frequency circuits.

  3. Giant edge state splitting at atomically precise graphene zigzag edges

    Science.gov (United States)

    Wang, Shiyong; Talirz, Leopold; Pignedoli, Carlo A.; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2016-05-01

    Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron-electron interactions in these localized states.

  4. Giant edge state splitting at atomically precise graphene zigzag edges.

    Science.gov (United States)

    Wang, Shiyong; Talirz, Leopold; Pignedoli, Carlo A; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2016-05-16

    Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron-electron interactions in these localized states.

  5. Two-dimensional carbon crystals. Electrical transport in single- and double-layer graphene; Zweidimensionale Kohlenstoffkristalle. Elektrischer Transport in Einzel- und Doppellagen-Graphen

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Hennrik

    2012-02-03

    In his work atomically thin layers of carbon, socalled graphene, are investigated. These systems exhibit outstanding electronic properties which are analysed using magnetotransport measurements. For this purpose, different types of samples are prepared, analysed and discussed. In addition to conventional single layer and single crystal bilayer systems, folded flakes with twisted planes are examined. Since monolayer graphene is a two dimensional crystal in which every atom sits at the surface, it is very sensitive to any type of perturbation. Three different cases are investigated: Firstly, dopants are removed from the surface and the change in transport properties is monitored. Secondly, the regime of small carrier concentrations is used to observe field induced recharging of inhomogeneities. Thirdly, an atomic force microscope is used to alter the graphene itself in a defined region. The implications of this modification are again investigated using magnetotransport measurements. The influence of one layer on another one is studied in decoupled two layer samples. A folded sample with separatly contacted layers is used to show transport through the folded region. For jointly contacted layers parallel transport measurements are performed to analyse screening effects of an applied electric field and substrate influence. The interaction of the two layers is shown by a significant reduction of the Fermivelocity.

  6. Layer Number Dependence of Li(+) Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution.

    Science.gov (United States)

    Hui, Jingshu; Burgess, Mark; Zhang, Jiarui; Rodríguez-López, Joaquín

    2016-04-26

    A fundamental question facing electrodes made out of few layers of graphene (FLG) is if they display chemical properties that are different to their bulk graphite counterpart. Here, we show evidence that suggests that lithium ion intercalation on FLG, as measured via stationary voltammetry, shows a strong dependence on the number of layers of graphene that compose the electrode. Despite its extreme thinness and turbostratic structure, Li ion intercalation into FLG still proceeds through a staging process, albeit with different signatures than bulk graphite or multilayer graphene. Single-layer graphene does not show any evidence of ion intercalation, while FLG with four graphene layers displays limited staging peaks, which broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate changes in the surface conductivity of FLG during SEI evolution. Observation of ion intercalation on large area FLG was conditioned to the fabrication of "ionic channels" on the electrode. SECM measurements using a recently developed Li-ion sensitive imaging technique evidenced the role of these channels in enabling Li-ion intercalation through localized flux measurements. This work highlights the impact of nanostructure and microstructure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using graphene, an atomically thin interface where surface and bulk reactivity converge. PMID:26943950

  7. Layered Atom Arrangements in Complex Materials

    Energy Technology Data Exchange (ETDEWEB)

    K.E. Sikafus; R.W.Grimes; S.M.Corish; A.R. Cleave; M.Tang; C.R.Stanek; B.P. Uberuaga; J.A.Valdez

    2005-04-15

    In this report, we develop an atom layer stacking model to describe systematically the crystal structures of complex materials. To illustrate the concepts, we consider a sequence of oxide compounds in which the metal cations progress in oxidation state from monovalent (M{sup 1+}) to tetravalent (M{sup 4+}). We use concepts relating to geometric subdivisions of a triangular atom net to describe the layered atom patterns in these compounds (concepts originally proposed by Shuichi Iida). We demonstrate that as a function of increasing oxidation state (from M{sup 1+} to M{sup 4+}), the layer stacking motifs used to generate each successive structure (specifically, motifs along a 3 symmetry axis), progress through the following sequence: MMO, MO, M{sub r}O, MO{sub r/s}O{sub u/v}, MOO (where M and O represent fully dense triangular atom nets and r/s and u/v are fractions used to describe partially filled triangular atom nets). We also develop complete crystallographic descriptions for the compounds in our oxidation sequence using trigonal space group R{bar 3}.

  8. Crystallographic growth and alignment of carbon nanotubes on few-layer graphene

    Science.gov (United States)

    Arash, Aram; Hunley, Patrick D.; Nasseri, Mohsen; Boland, Mathias J.; Sundararajan, Abhishek; Hudak, Bethany M.; Guiton, Beth S.; Strachan, Douglas R.

    2015-03-01

    Hybrid carbon nanotube and graphene structures are emerging as an exciting material system built from a common sp2 carbon backbone. Such hybrid systems have promise for use in improving the performance of energy storage and high-speed electronic applications. Towards the attainment of such hybrid materials, the catalytic growth and crystallographic alignment of these integrated structures are investigated along with the atomic-scale features of their interfaces. The catalytic activity of nanoparticles to form carbon nanotubes on the surface of few-layer graphene is tuned through precise feedstock application. Through careful materials synthesis, the interfaces of these hybrid carbon nanotube - graphene systems are investigated through ultra-high resolution electron microscopy.

  9. Fingerprints of Multiple Electron Scatterings in Single-Layer Graphene

    Science.gov (United States)

    Jung, Minbok; Sohn, So-Dam; Park, Jonghyun; Lee, Keun-U.; Shin, Hyung-Joon

    2016-03-01

    The electrons in graphene exhibit unusual behaviours, which can be described by massless Dirac quasiparticles. Understanding electron scattering in graphene has been of significant importance for its future application in electronic devices because electron scattering determines electrical properties such as resistivity and electron transport. There are two types of electron scatterings in graphene: intervalley scattering and intravalley scattering. In single-layer graphene, to date, it has been difficult to observe intravalley scattering because of the suppression of backscattering resulting from the chiral nature of the electrons in graphene. Here, we report the multiple electron scattering behaviours in single-layer graphene on a metallic substrate. By applying one- and two-dimensional Fourier transforms to maps of the local density of states, we can distinguish individual scattering processes from complex interference patterns. These techniques enable us to provide direct evidence of intravalley scattering, revealing a linear dispersion relation with a Fermi velocity of ~7.4 × 105 m/s.

  10. Topological properties of artificial graphene assembled by atom manipulation

    Science.gov (United States)

    Ko, Wonhee; Mar, Warren; Gomes, Kenjiro K.; Manoharan, Hari C.

    2011-03-01

    Graphene exhibits special electronic properties stemming from its two-dimensional (2D) structure and embedded relativistic Dirac cones. However, many proposed topologically ordered ground states remain elusive in conventional measurements due to the difficulty in arranging the necessary quantum textures into natural graphene. By exploiting atomic manipulation with a custom-built ultrastable scanning tunneling microscope, we have constructed graphene-like structures by arranging molecules to create a honeycomb lattice of electrons drawn from normal 2D surface states. Spectroscopy reveals a spectacular transformation of nonrelativistic massive 2D electrons into massless Dirac fermions carrying a chiral pseudospin symmetry. We demonstrate the tailoring of this new class of graphene to reveal signature topological properties: an energy gap and emergent mass created by breaking the pseudospin symmetry or changing the hopping term non-uniformly with a Kekulé bond distortion; gauge fields generated by applying atomically engineered strains; and the condensation of electrons into quantum Hall-like states and topologically confined phases. Supported by the DOE, Office of Basic Energy Sciences, Division of Material Science and Engineering under contract DE-AC02-76SF00515.

  11. Thermal Casimir-Polder interaction of different atoms with graphene

    CERN Document Server

    Chaichian, M; Mostepanenko, V M; Tureanu, A

    2012-01-01

    The thermal correction to the energy of Casimir-Polder interaction of atoms with a suspended graphene membrane described by the Dirac model is investigated. We show that a major impact on the thermal correction is made by the size of the gap in the energy spectrum of graphene quasiparticles. Specifically, if the temperature is much smaller than the gap parameter (alternatively, larger or of the order of the gap parameter), the thermal correction is shown to be relatively small (alternatively, large). We have calculated the free energy of the thermal Casimir-Polder interaction of atoms of He, Na, Rb, and Cs with graphene described by both the hydrodynamic and Dirac models. It is shown that in exact computations using the Dirac model, one should use the polarization operator at nonzero temperature. The computational results for the Casimir-Polder free energy obtained in the framework of hydrodynamic model of graphene are several times larger than in the Dirac model within the separation region below 2$\\mu$m. We...

  12. Dynamic negative compressibility of few-layer graphene, h-BN, and MoS2.

    Science.gov (United States)

    Barboza, Ana Paula M; Chacham, Helio; Oliveira, Camilla K; Fernandes, Thales F D; Ferreira, Erlon H Martins; Archanjo, Braulio S; Batista, Ronaldo J C; de Oliveira, Alan B; Neves, Bernardo R A

    2012-05-01

    We report a novel mechanical response of few-layer graphene, h-BN, and MoS(2) to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS(2)), but it is absent in single-layer graphene and in few-layer mica and Bi(2)Se(3). We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed. PMID:22468807

  13. Interfacial effect on the electrochemical properties of the layered graphene/metal sulfide composites as anode materials for Li-ion batteries

    Science.gov (United States)

    Lv, Yagang; Chen, Biao; Zhao, Naiqin; Shi, Chunsheng; He, Chunnian; Li, Jiajun; Liu, Enzuo

    2016-09-01

    The layered graphene/metal sulfide composites exhibit excellent electrochemical properties as anode materials for lithium ion battery, due to the synergistic effect between metal sulfide and graphene which still needs to be further understood. In this study, Li adsorption and diffusion on MoS2 and SnS2 monolayers and Li2S surface, as well as at their interfaces with graphene, are systematically investigated through first-principles calculations. The analysis of charge density difference, Bader charge, and density of states indicates that the adsorbed Li atoms interact with both the S atoms at metal sulfide surfaces and C atoms in graphene, resulting in larger Li adsorption energies at the interfaces compared with that on the corresponding surfaces, but with almost no enhancement of the energy barriers for Li atom diffusion. The enhanced Li adsorption capability at Li2S/G interface contributes to the extra storage capacity of graphene/metal sulfide composites. Furthermore, the synergistic mechanism between metal sulfide and graphene is revealed. Moreover, band structure analysis shows the electronic conductivity is enhanced with the incorporation of graphene. The results corroborate the interfacial pseudocapacity-like Li atom storage mechanism, and are helpful for the design of layered graphene/metal sulfide composites as anode materials for lithium ion batteries.

  14. Infrared dynamics of cold atoms on hot graphene membranes

    Science.gov (United States)

    Sengupta, Sanghita; Kotov, Valeri N.; Clougherty, Dennis P.

    2016-06-01

    We study the infrared dynamics of low-energy atoms interacting with a sample of suspended graphene at finite temperature. The dynamics exhibits severe infrared divergences order by order in perturbation theory as a result of the singular nature of low-energy flexural phonon emission. Our model can be viewed as a two-channel generalization of the independent boson model with asymmetric atom-phonon coupling. This allows us to take advantage of the exact nonperturbative solution of the independent boson model in the stronger channel while treating the weaker one perturbatively. In the low-energy limit, the exact solution can be viewed as a resummation (exponentiation) of the most divergent diagrams in the perturbative expansion. As a result of this procedure, we obtain the atom's Green function which we use to calculate the atom damping rate, a quantity equal to the quantum sticking rate. A characteristic feature of our results is that the Green's function retains a weak, infrared cutoff dependence that reflects the reduced dimensionality of the problem. As a consequence, we predict a measurable dependence of the sticking rate on graphene sample size. We provide detailed predictions for the sticking rate of atomic hydrogen as a function of temperature and sample size. The resummation yields an enhanced sticking rate relative to the conventional Fermi golden rule result (equivalent to the one-loop atom self-energy), as higher-order processes increase damping at finite temperature.

  15. Tribological characteristics of few-layer graphene over Ni grain and interface boundaries

    Science.gov (United States)

    Tripathi, Manoj; Awaja, Firas; Paolicelli, Guido; Bartali, Ruben; Iacob, Erica; Valeri, Sergio; Ryu, Seunghwa; Signetti, Stefano; Speranza, Giorgio; Pugno, Nicola Maria

    2016-03-01

    The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate via an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10-5 Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull-off adhesion forces were addressed in the course of friction measurements to explain the role of the out-of-plane deformation of graphene layer(s). Finite element simulations showed good agreement with experiments and led to a rationalization of the observations. Thus, with interfacial grain boundaries the FLG tribology can be effectively tuned.The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate via an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10-5 Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull

  16. Local, global, and nonlinear screening in twisted double-layer graphene

    Science.gov (United States)

    Lu, Chih-Pin; Rodriguez-Vega, Martin; Li, Guohong; Luican-Mayer, Adina; Watanabe, Kenji; Taniguchi, Takashi; Rossi, Enrico; Andrei, Eva Y.

    2016-06-01

    One-atom-thick crystalline layers and their vertical heterostructures carry the promise of designer electronic materials that are unattainable by standard growth techniques. To realize their potential it is necessary to isolate them from environmental disturbances, in particular those introduced by the substrate. However, finding and characterizing suitable substrates, and minimizing the random potential fluctuations they introduce, has been a persistent challenge in this emerging field. Here we show that Landau-level (LL) spectroscopy offers the unique capability to quantify both the reduction of the quasiparticles’ lifetime and the long-range inhomogeneity due to random potential fluctuations. Harnessing this technique together with direct scanning tunneling microscopy and numerical simulations we demonstrate that the insertion of a graphene buffer layer with a large twist angle is a very effective method to shield a 2D system from substrate interference that has the additional desirable property of preserving the electronic structure of the system under study. We further show that owing to its remarkable nonlinear screening capability a single graphene buffer layer provides better shielding than either increasing the distance to the substrate or doubling the carrier density and reduces the amplitude of the potential fluctuations in graphene to values even lower than the ones in AB-stacked bilayer graphene.

  17. Atomic layer deposition of nanoporous biomaterials.

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, R. J.; Adiga, S. P.; Pellin, M. J.; Curtiss, L. A.; Stafslien, S.; Chisholm, B.; Monteiro-Riviere, N. A.; Brigmon, R. L.; Elam, J. W.; Univ. of North Carolina; North Carolina State Univ.; Eastman Kodak Co.; North Dakota State Univ.; SRL

    2010-03-01

    Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials. Nanoporous alumina, also known as anodic aluminum oxide (AAO), is a nanomaterial that exhibits several unusual properties, including high pore densities, straight pores, small pore sizes, and uniform pore sizes. In 1953, Keller et al. showed that anodizing aluminum in acid electrolytes results in a thick layer of nearly cylindrical pores, which are arranged in a close-packed hexagonal cell structure. More recently, Matsuda & Fukuda demonstrated preparation of highly ordered platinum and gold nanohole arrays using a replication process. In this study, a negative structure of nanoporous alumina was initially fabricated and a positive structure of a nanoporous metal was subsequently fabricated. Over the past fifteen years, nanoporous alumina membranes have been used as templates for growth of a variety of nanostructured materials, including nanotubes, nanowires, nanorods, and nanoporous membranes.

  18. To the Question about Migration of Impurity Atoms in Graphene

    Directory of Open Access Journals (Sweden)

    A.S. Dolgov

    2013-10-01

    Full Text Available The uncorrelated accidental jumps of the migration subjects from the allowed positions to the identical immediate ones in the two-dimensional hexagonal structure, which simulates the graphene nodes distribution, are considered. The impurity atoms are placed in the interstitial positions between two atoms of each hexagon sides. The offered system corresponds to the sufficiently high temperatures, where the elementary migration act represents the classical over-barrier jump whose probability is defined by the temperature. The exact solution of the unlimited set of the migration microscopic equations is written in the generating function technique and the corresponding microscopic characteristics are found. The anisotropy of the early migration stage can act as an instrument of the matrix state diagnosis and also the formation of the specified impurity geometric structures which are jointed with graphene. The diffusive spread rate, which is compared with the rate of the cellular migration spread, is found. The evolution features of the macroscopic distribution picture of the impurity component on the graphene lattice which are designated by the microscopic geometry impurity atoms displacement are discussed.

  19. Electron tunneling in single layer graphene with an energy gap

    Institute of Scientific and Technical Information of China (English)

    Xu Xu-Guang; Zhang Chao; Xu Gong-Jie; Cao Jun-Cheng

    2011-01-01

    When a single layer graphene is epitaxially grown on silicon carbide, it will exhibit a finite energy gap like a conventional semiconductor, and its energy dispersion is no longer linear in momentum in the low energy regime. In this paper, we have investigated the tunneling characteristics through a two-dimensional barrier in a single layer graphene with an energy gap. It is found that when the electron is at a zero angle of incidence, the transmission probability as a function of incidence energy has a gap. Away from the gap the transmission coefficient oscillates with incidence energy which is analogous to that of a conventional semiconductor. The conductance under zero temperature has a gap. The properties of electron transmission may be useful for developing graphene-based nano-electronics.

  20. A graphene superficial layer for the advanced electroforming process

    Science.gov (United States)

    Rho, Hokyun; Park, Mina; Lee, Seungmin; Bae, Sukang; Kim, Tae-Wook; Ha, Jun-Seok; Lee, Sang Hyun

    2016-06-01

    Advances in electroplating technology facilitate the progress of modern electronic devices, including computers, microprocessors and other microelectronic devices. Metal layers with high electrical and thermal conductivities are essential for high speed and high power devices. In this paper, we report an effective route to fabricate free-standing metal films using graphene as a superficial layer in the electroforming process. Chemical vapor deposition (CVD) graphene grown on a Cu foil was used as a template, which provides high electrical conductivity and low adhesive force with the template, thus enabling an effective electroforming process. The required force for delamination of the electroplated Cu layer from graphene is more than one order smaller than the force required for removing graphene from the Cu foil. We also demonstrated that the electroformed free-standing Cu thin films could be utilized for patterning microstructures and incorporated onto a flexible substrate for LEDs. This innovative process could be beneficial for the advancement of flexible electronics and optoelectronics, which require a wide range of mechanical and physical properties.Advances in electroplating technology facilitate the progress of modern electronic devices, including computers, microprocessors and other microelectronic devices. Metal layers with high electrical and thermal conductivities are essential for high speed and high power devices. In this paper, we report an effective route to fabricate free-standing metal films using graphene as a superficial layer in the electroforming process. Chemical vapor deposition (CVD) graphene grown on a Cu foil was used as a template, which provides high electrical conductivity and low adhesive force with the template, thus enabling an effective electroforming process. The required force for delamination of the electroplated Cu layer from graphene is more than one order smaller than the force required for removing graphene from the Cu foil

  1. Spatial atomic layer deposition: a route towards further industrialization of atomic layer deposition

    NARCIS (Netherlands)

    Poodt, P.W.G.; Cameron, D.C.; Dickey, E.; George, S.M.; Kuznetsov, V.; Parsons, G.N.; Roozeboom, F.; Sundaram, G.; Vermeer, A.

    2012-01-01

    Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this

  2. Electronic properties of impurity-infected few-layer graphene nanoribbons

    International Nuclear Information System (INIS)

    Spurred by achievements in devising different multilayered graphene-based nano-systems, based on the random tight-binding Hamiltonian model and within the coherent potential approximation, the influence of varying the number of layers and the effect of doping by the boron and nitrogen impurities on the density of states of a mono- and few-layer armchair- and zigzag-edge graphene nanoribbons are theoretically investigated. When the nanoribbons are pristine, with increasing the number of layers the band gap of the armchair nanoribbons is decreased, yet the zigzag ribbons remain metallic and depending on the number of the layers few peaks are appeared around the zero-energy level. Moreover, in the presence of impurities, the band gap of the armchair nanoribbons is decreased for each number of layers. The Van-Hove singularities are steadily broadened and the density of states move to a higher (lower) value of the energy as a result of doping with boron (nitrogen) atoms. This study could provide with us to explore and devise new optoelectronic devices based on the impurity-infected graphene nanoribbons with tunable widths and edges

  3. Electronic properties of impurity-infected few-layer graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Mousavi, Hamze, E-mail: hamze.mousavi@gmail.com [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Nano Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Bagheri, Mehran [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Evin, Tehran 19835-63113 (Iran, Islamic Republic of)

    2015-02-01

    Spurred by achievements in devising different multilayered graphene-based nano-systems, based on the random tight-binding Hamiltonian model and within the coherent potential approximation, the influence of varying the number of layers and the effect of doping by the boron and nitrogen impurities on the density of states of a mono- and few-layer armchair- and zigzag-edge graphene nanoribbons are theoretically investigated. When the nanoribbons are pristine, with increasing the number of layers the band gap of the armchair nanoribbons is decreased, yet the zigzag ribbons remain metallic and depending on the number of the layers few peaks are appeared around the zero-energy level. Moreover, in the presence of impurities, the band gap of the armchair nanoribbons is decreased for each number of layers. The Van-Hove singularities are steadily broadened and the density of states move to a higher (lower) value of the energy as a result of doping with boron (nitrogen) atoms. This study could provide with us to explore and devise new optoelectronic devices based on the impurity-infected graphene nanoribbons with tunable widths and edges.

  4. Temperature- and thickness-dependent electrical conductivity of few-layer graphene and graphene nanosheets

    International Nuclear Information System (INIS)

    We established a calculation model of the conductivity of multilayer graphene based on Boltzmann transport equation and 2D electron gas theory. Numerical simulations show that the conductivities of few-layer graphene and graphene nanosheets are reduced when thickness is increased. The reduction rate decreases for micron-range thicknesses and remains constant thereafter. Moreover, the conductivity increases with the increase in temperature, in which the increase rate declines as temperature increases. Higher thickness exhibits a more obvious temperature effect on conductivity. Such effect also increases with the increase in temperature. - Highlights: • Two types of carrier transport channels, surface channel and interlayer channel, were advised. • Electron scattering mechanism in the surface channel and interlayer channel were investigated. • The calculation model of the conductivity of multilayer graphene was established. • Temperature- and thickness-dependent conductivity of FLG and GNs was simulated. • Numerical simulation results are consistent with the published experimental results

  5. Electron transport in molecular junctions with graphene as protecting layer

    Energy Technology Data Exchange (ETDEWEB)

    Hüser, Falco; Solomon, Gemma C., E-mail: gsolomon@nano.ku.dk [Nano-Science Center and Department of Chemistry, University of Copenhagen, 2100 København Ø (Denmark)

    2015-12-07

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  6. Graphene crystal growth by thermal precipitation of focused ion beam induced deposition of carbon precursor via patterned-iron thin layers

    Directory of Open Access Journals (Sweden)

    Rius Gemma

    2014-01-01

    Full Text Available Recently, relevant advances on graphene as a building block of integrated circuits (ICs have been demonstrated. Graphene growth and device fabrication related processing has been steadily and intensively powered due to commercial interest; however, there are many challenges associated with the incorporation of graphene into commercial applications which includes challenges associated with the synthesis of this material. Specifically, the controlled deposition of single layer large single crystal graphene on arbitrary supports, is particularly challenging. Previously, we have reported the first demonstration of the transformation of focused ion beam induced deposition of carbon (FIBID-C into patterned graphitic layers by metal-assisted thermal treatment (Ni foils. In this present work, we continue exploiting the FIBID-C approach as a route for graphene deposition. Here, thin patterned Fe layers are used for the catalysis of graphenization and graphitization. We demonstrate the formation of high quality single and few layer graphene, which evidences, the possibility of using Fe as a catalyst for graphene deposition. The mechanism is understood as the minute precipitation of atomic carbon after supersaturation of some iron carbides formed under a high temperature treatment. As a consequence of the complete wetting of FIBID-C and patterned Fe layers, which enable graphene growth, the as-deposited patterns do not preserve their original shape after the thermal treatment

  7. Angular Distribution of Electrons in Photoionization of Atoms Adsorbed on a Graphene Sheet

    CERN Document Server

    Baltenkov, A S

    2013-01-01

    Within the framework of a model representing the potential of a graphene sheet U(z) as an electro-neutral layer formed by smeared carbon atoms, the effect of this potential on spectral characteristics of atoms adsorbed on a graphene sheet has been studied. Since the distance between the adsorbed atom nucleus and sheet surface significantly exceeds the radii of inner atomic shells the potential U(z) makes influence on the continuum wave functions only. Their behavior in the upper semi-space (z>0) and in the lower one (z<0) where the adsorbed atom is located is defined by a jump of the logarithmic derivative of the wave function for z=0. The photoelectron angular distributions have been calculated for different mutual positions of the polarization vector e and the axis Z normal to the sheet surface. It has been shown that the existence of the electron waves reflected from the potential U(z) leads to evident asymmetry of the angular distribution relative to the plane z=0. The experimental observation of this ...

  8. Atomic Scale Imaging of the Electronic Structure and Chemistry of Graphene and Its Precursors on Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, George W [Columbia University

    2015-02-16

    atom, provides information about the electronic structure of graphene and is particularly sensitive to the sign and magnitude of the charge transfer between graphene and any surface adsorbed species. Results: (A) Graphene on SiO2 In an effort designed to unravel aspects of the mechanisms for chemistry on graphene surfaces, STM and STS were employed to show that graphene on SiO2 is oxidized at lower temperatures than either graphite or multi-layer graphene. Two independent factors control this charge transfer: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. (B) Graphene on Copper In the case of graphene grown on copper surfaces, we found that the graphene grows primarily in registry with the underlying copper lattice for both Cu(111) and Cu(100). On Cu(111) the graphene has a hexagonal superstructure with a significant electronic component, whereas it has a linear superstructure on Cu(100). (C) Nitrogen Doped Graphene on Copper Using STM we have also studied the electronic structure and morphology of graphene films grown on a copper foil substrate in which N atoms substitute for carbon in the 2-D graphene lattice. The salient features of the results of this study were: (1) Nitrogen doped graphene on Cu foil exhibits a triangular structure with an “apparent” slight elevation of ~ 0.8 Å at N atom substitution sites; (2) Nitrogen doping results in ~0.4 electrons per N atom donated to the graphene lattice; (3) Typical N doping of graphene on Cu foil shows mostly single site Carbon atom displacement (~ 3N/1000C); (4) Some multi-site C atom displacement is observed (<10% of single site events). (D) Boron Doped Graphene on Copper We also used scanning tunneling microscopy and x-ray spectroscopy to characterize the atomic and electronic structure of boron-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice

  9. Adsorption of two sodium atoms on graphene -- A first principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, Gagandeep, E-mail: gaganj1981@yahoo.com [Department of Physics & Centre of Advanced Studies in Physics, Panjab University, Chandigarh-160014 (India); Chandigarh Engineering College, Landran, Mohali, Punjab (India); Rani, Babita, E-mail: babitabaghla15@gmail.com [Department of Physics & Centre of Advanced Studies in Physics, Panjab University, Chandigarh-160014 (India); Department of Physics, Punjabi University Patiala-147002 (India); Gupta, Shuchi, E-mail: sgupta@pu.ac.in [University Institute of Engineering & Technology, Panjab University, Chandigarh -160014 (India); Dharamvir, Keya, E-mail: keya@pu.ac.in [Department of Physics & Centre of Advanced Studies in Physics, Panjab University, Chandigarh-160014 (India)

    2015-08-28

    We perform a systematic density functional theory (DFT) study of the adsorption of two sodium atoms on graphene using the SIESTA package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, magnetic moment and charge transfer of the Na{sub n}-graphene (n=1, 2) system are calculated. Three initial horizontal orientations of the pair of sodium atoms on graphene are studied. Our calculations reveal that sodium atoms bind weakly to the graphene surface which is in agreement with previous results. We also notice a charge transfer of 0.288e from a sodium adatom to the graphene sheet altering its magnetic moment (−0.318 µ{sub B}) that is reduced from the gas phase value of the isolated atom (1 µ{sub B}). The calculated adsorption energies suggest that clustering of Na atoms on graphene is energetically favorable.

  10. Structure and field emission of graphene layers on top of silicon nanowire arrays

    Science.gov (United States)

    Huang, Bohr-Ran; Chan, Hui-Wen; Jou, Shyankay; Chen, Guan-Yu; Kuo, Hsiu-An; Song, Wan-Jhen

    2016-01-01

    Monolayer graphene was grown on copper foils and then transferred on planar silicon substrates and on top of silicon nanowire (SiNW) arrays to form single- to quadruple-layer graphene films. The morphology, structure, and electron field emission (FE) of these graphene films were investigated. The graphene films on the planar silicon substrates were continuous. The single- to triple-layer graphene films on the SiNW arrays were discontinuous and while the quadruple-layer graphene film featured a mostly continuous area. The Raman spectra of the graphene films on the SiNW arrays showed G and Gʹ bands with a singular-Lorentzian shape together with a weak D band. The D band intensity decreased as the number of graphene layers increased. The FE efficiency of the graphene films on the planar silicon substrates and the SiNW arrays varied with the number of graphene layers. The turn-on field for the single- to quadruple-layer graphene films on planar silicon substrates were 4.3, 3.7, 3.5 and 3.4 V/μm, respectively. The turn-on field for the single- to quadruple-layer graphene films on SiNW arrays decreased to 3.9, 3.3, 3.0 and 3.3 V/μm, respectively. Correlation of the FE with structure and morphology of the graphene films is discussed.

  11. Development of the layer-by-layer biosensor using graphene films: application for cholesterol determination

    International Nuclear Information System (INIS)

    The preparation and characterization of graphene films for cholesterol determination are described. The graphene films were synthesized by thermal chemical vapor deposition (CVD) method. Methane gas (CH4) and copper tape were used as carbon source and catalyst in the graphene growth process, respectively. The intergrated array was fabricated by using micro-electro-mechanical systems (MEMS) technology in which Fe3O4-doped polyaniline (PANi) film was electropolymerized on Pt/Gr electrodes. The properties of the Pt/Gr/PANi/Fe3O4 films were investigated by field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and electrochemical techniques. Cholesterol oxidase (ChOx) has been immobilized onto the working electrode with glutaraldehyde agent. The cholesterol electrochemical biosensor shows high sensitivity (74 μA mM−1 cm−2) and fast response time (2) of 0.9986. This new layer-by-layer biosensor based on graphene films promises many practical applications. (paper)

  12. A graphene superficial layer for the advanced electroforming process.

    Science.gov (United States)

    Rho, Hokyun; Park, Mina; Lee, Seungmin; Bae, Sukang; Kim, Tae-Wook; Ha, Jun-Seok; Lee, Sang Hyun

    2016-07-01

    Advances in electroplating technology facilitate the progress of modern electronic devices, including computers, microprocessors and other microelectronic devices. Metal layers with high electrical and thermal conductivities are essential for high speed and high power devices. In this paper, we report an effective route to fabricate free-standing metal films using graphene as a superficial layer in the electroforming process. Chemical vapor deposition (CVD) graphene grown on a Cu foil was used as a template, which provides high electrical conductivity and low adhesive force with the template, thus enabling an effective electroforming process. The required force for delamination of the electroplated Cu layer from graphene is more than one order smaller than the force required for removing graphene from the Cu foil. We also demonstrated that the electroformed free-standing Cu thin films could be utilized for patterning microstructures and incorporated onto a flexible substrate for LEDs. This innovative process could be beneficial for the advancement of flexible electronics and optoelectronics, which require a wide range of mechanical and physical properties. PMID:26949072

  13. Fabrication of graphene thin films based on layer-by-layer self-assembly of functionalized graphene nanosheets.

    Science.gov (United States)

    Park, Je Seob; Cho, Sung Min; Kim, Woo-Jae; Park, Juhyun; Yoo, Pil J

    2011-02-01

    In this study, we present a facile means of fabricating graphene thin films via layer-by-layer (LbL) assembly of charged graphene nanosheets (GS) based on electrostatic interactions. To this end, graphite oxide (GO) obtained from graphite powder using Hummers method is chemically reduced to carboxylic acid-functionalized GS and amine-functionalized GS to perform an alternate LbL deposition between oppositely charged GSs. Specifically, for successful preparation of positively charged GS, GOs are treated with an intermediate acyl-chlorination reaction by thionyl chloride and a subsequent amidation reaction in pyridine, whereby a stable GO dispersibility can be maintained within the polar reaction solvent. As a result, without the aid of additional hybridization with charged nanomaterials or polyelectrolytes, the oppositely charged graphene nanosheets can be electrostatically assembled to form graphene thin films in an aqueous environment, while obtaining controllability over film thickness and transparency. Finally, the electrical property of the assembled graphene thin films can be enhanced through a thermal treatment process. Notably, the introduction of chloride functions during the acyl-chlorination reaction provides the p-doping effect for the assembled graphene thin films, yielding a sheet resistance of 1.4 kΩ/sq with a light transmittance of 80% after thermal treatment. Since the proposed method allows for large-scale production as well as elaborate manipulation of the physical properties of the graphene thin films, it can be potentially utilized in various applications, such as transparent electrodes, flexible displays and highly sensitive biosensors. PMID:21207942

  14. Plasmon resonance in single- and double-layer CVD graphene nanoribbons

    DEFF Research Database (Denmark)

    Wang, Di; Emani, Naresh K.; Chung, Ting Fung;

    2015-01-01

    Dynamic tunability of the plasmonic resonance in graphene nanoribbons is desirable in the near-infrared. We demonstrated a constant blue shift of plasmonic resonances in double-layer graphene nanoribbons with respect to single-layer graphene nanoribbons. © OSA 2015....

  15. Quantum confined electronic states in atomically well-defined graphene nanostructures

    OpenAIRE

    Hämäläinen, Sampsa; Sun, Zhixiang; Boneschanscher, Mark P.; Uppstu, Andreas; Ijäs, Mari; Harju, Ari; Vanmaekelbergh, Daniël; Liljeroth, Peter

    2011-01-01

    Despite the enormous interest in the properties of graphene and the potential of graphene nanostructures in electronic applications, the study of quantum confined states in atomically well-defined graphene nanostructures remains an experimental challenge. Here, we study graphene quantum dots (GQDs) with well-defined edges in the zigzag direction, grown by chemical vapor deposition (CVD) on an iridium(111) substrate, by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS)...

  16. Redistribution of carbon atoms in Pt substrate for high quality monolayer graphene synthesis

    International Nuclear Information System (INIS)

    The two-dimensional material graphene shows its extraordinary potential in many application fields. As the most effective method to synthesize large-area monolayer graphene, chemical vapor deposition has been well developed; however, it still faces the challenge of a high occurrence of multilayer graphene, which causes the small effective area of monolayer graphene. This phenomenon limits its applications in which only a big size of monolayer graphene is needed. In this paper, by introducing a redistribution stage after the decomposition of carbon source gas to redistribute the carbon atoms dissolved in Pt foils, the number of multilayer flakes on the monolayer graphene decreases. The mean area of monolayer graphene can be extended to about 16 000 μm2, which is eight times larger than that of the graphene grown without the redistribution stage. A Raman spectrograph is used to demonstrate the high quality of the monolayer graphene grown by the improved process. (semiconductor materials)

  17. Single-Layer Graphene as a Barrier Layer for Intense UV Laser-Induced Damages for Silver Nanowire Network.

    Science.gov (United States)

    Das, Suprem R; Nian, Qiong; Saei, Mojib; Jin, Shengyu; Back, Doosan; Kumar, Prashant; Janes, David B; Alam, Muhammad A; Cheng, Gary J

    2015-11-24

    Single-layer graphene (SLG) has been proposed as the thinnest protective/barrier layer for wide applications involving resistance to oxidation, corrosion, atomic/molecular diffusion, electromagnetic interference, and bacterial contamination. Functional metallic nanostructures have lower thermal stability than their bulk forms and are therefore susceptible to high energy photons. Here, we demonstrate that SLG can shield metallic nanostructures from intense laser radiation that would otherwise ablate them. By irradiation via a UV laser beam with nanosecond pulse width and a range of laser intensities (in millions of watt per cm(2)) onto a silver nanowire network, and conformally wrapping SLG on top of the nanowire network, we demonstrate that graphene "extracts and spreads" most of the thermal energy away from nanowire, thereby keeping it damage-free. Without graphene wrapping, the radiation would fragment the wires into smaller pieces and even decompose them into droplets. A systematic molecular dynamics simulation confirms the mechanism of SLG shielding. Consequently, particular damage-free and ablation-free laser-based nanomanufacturing of hybrid nanostructures might be sparked off by application of SLG on functional surfaces and nanofeatures. PMID:26447828

  18. Tunable electronic properties of graphene through controlling bonding configurations of doped nitrogen atoms.

    Science.gov (United States)

    Zhang, Jia; Zhao, Chao; Liu, Na; Zhang, Huanxi; Liu, Jingjing; Fu, Yong Qing; Guo, Bin; Wang, Zhenlong; Lei, Shengbin; Hu, PingAn

    2016-01-01

    Single-layer and mono-component doped graphene is a crucial platform for a better understanding of the relationship between its intrinsic electronic properties and atomic bonding configurations. Large-scale doped graphene films dominated with graphitic nitrogen (GG) or pyrrolic nitrogen (PG) were synthesized on Cu foils via a free radical reaction at growth temperatures of 230-300 °C and 400-600 °C, respectively. The bonding configurations of N atoms in the graphene lattices were controlled through reaction temperature, and characterized using Raman spectroscopy, X-ray photoelectron spectroscopy and scanning tunneling microscope. The GG exhibited a strong n-type doping behavior, whereas the PG showed a weak n-type doping behavior. Electron mobilities of the GG and PG were in the range of 80.1-340 cm(2) V(-1)·s(-1) and 59.3-160.6 cm(2) V(-1)·s(-1), respectively. The enhanced doping effect caused by graphitic nitrogen in the GG produced an asymmetry electron-hole transport characteristic, indicating that the long-range scattering (ionized impurities) plays an important role in determining the carrier transport behavior. Analysis of temperature dependent conductance showed that the carrier transport mechanism in the GG was thermal excitation, whereas that in the PG, was a combination of thermal excitation and variable range hopping. PMID:27325386

  19. Drastic Minimization in the van der Waals Interaction with the Bottom Epitaxial Graphene Layer by the Diels-Alder Surface Chemistry of the Top Graphene Layer

    OpenAIRE

    Sarkar, Santanu

    2014-01-01

    The Diels-Alder surface modified top epitaxial graphene layer, with newly created pair of sp3 carbon centres, results in abrupt minimization of interlayer van der Waals interactions between two stacked graphene planes, and escapes the wafer during post-reaction manipulation stage, leaving the layer under it almost pristine-like. Above picture shows Diels-Alder functionalized sp2/sp3 graphene adduct leaves the parent wafer. In this communication we systematically address several fundamental qu...

  20. Plasmons in spatially separated double-layer graphene nanoribbons

    Science.gov (United States)

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-01

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  1. Texture of atomic layer deposited ruthenium

    OpenAIRE

    Musschoot, J.; Xie, Q; Deduytsche, D.; De Keyser, K; Longrie, D.; Haemers, J.; Van den Berghe, S.; Van Meirhaeghe, R. L.; D'Haen, Jan; Detavernier, C

    2010-01-01

    Ruthenium films were grown by plasma enhanced atomic layer deposition (ALD) on Si(1 0 0) and ALD TiN. X-ray diffraction (XRD) showed that the as-deposited films on Si(1 0 0) were polycrystalline, on TiN they were (0 0 2) oriented. After annealing at 800 degrees C for 60 s, all Ru films were strongly (0 0 2) textured and very smooth. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) demonstrated that the lateral grain size of the annealed films was several 100 ...

  2. Bioactive surfaces with atomic layer deposition

    OpenAIRE

    Kvalvik, Julie Nitsche

    2015-01-01

    The overall goal of this work has been to make bioactive surfaces with atomic layer deposition (ALD). To do this, a new ALD system with titanium tetraisopropoxide (TTIP) and lysine as precursors was developed with emphasis on studying the effects of pulsing times and deposition temperatures. TTIP was chosen as titanium is regarded to be biocompatible and lysine was chosen as poly-L-lysine is a part of the extra-cellular matrix (ECM) and hence affects cell adhesion. The effect of a water pulse...

  3. Atomic Layer Deposition from Dissolved Precursors.

    Science.gov (United States)

    Wu, Yanlin; Döhler, Dirk; Barr, Maïssa; Oks, Elina; Wolf, Marc; Santinacci, Lionel; Bachmann, Julien

    2015-10-14

    We establish a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD) known with gaseous precursors toward precursors dissolved in a liquid. An established ALD reaction behaves similarly when performed from solutions. "Solution ALD" (sALD) can coat deep pores in a conformal manner. sALD offers novel opportunities by overcoming the need for volatile and thermally robust precursors. We establish a MgO sALD procedure based on the hydrolysis of a Grignard reagent.

  4. Fabrication of patterned flexible graphene devices via facile direct transfer of as-grown bi-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Park, Heun; Kim, Kyung Hoon; Yoon, Jangyeol [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Kim, Kuk Ki; Park, Seung Min [Department of Chemistry, Kyung Hee University, Seoul 130-701 (Korea, Republic of); Ha, Jeong Sook, E-mail: jeongsha@korea.ac.kr [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of); KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701 (Korea, Republic of)

    2015-02-15

    Highlights: • Patterned bi-layer graphene was directly transferred onto various polymer substrates by using micro-contact printing technique. • Coating of dimethylformamide onto the polydimethylsiloxane (PDMS) stamp enhanced the adhesion between the bi-layer graphene and the PDMS stamp. • Patterned graphene devices showed mechanically stable electrical properties upon repeated bending cycles. - Abstract: We report on the fabrication of patterned flexible graphene devices via a facile direct transfer of bi-layer graphene grown on alumina (Al{sub 2}O{sub 3}) substrate, and the use of Ag nanowire stickers as flexible electrodes. Patterned polydimethylsiloxane (PDMS) stamps coated with vaporized dimethylformamide (DMF) are utilized to transfer as-grown graphene directly onto a flexible polyethylene terephthalate (PET) substrate. The facile direct transfer is attributed to the enhanced adhesion of the bi-layer graphene to PDMS, due to DMF-coating, as well as the weak adhesion between the bi-layer graphene and the Al{sub 2}O{sub 3} substrate. In this way, flexible patterned graphene devices have been fabricated with Ag nanowire stickers as electrodes. Stable electrical conduction characteristics were measured over repetitive bending with a bending radius down to 5 mm.

  5. Fabrication of patterned flexible graphene devices via facile direct transfer of as-grown bi-layer graphene

    International Nuclear Information System (INIS)

    Highlights: • Patterned bi-layer graphene was directly transferred onto various polymer substrates by using micro-contact printing technique. • Coating of dimethylformamide onto the polydimethylsiloxane (PDMS) stamp enhanced the adhesion between the bi-layer graphene and the PDMS stamp. • Patterned graphene devices showed mechanically stable electrical properties upon repeated bending cycles. - Abstract: We report on the fabrication of patterned flexible graphene devices via a facile direct transfer of bi-layer graphene grown on alumina (Al2O3) substrate, and the use of Ag nanowire stickers as flexible electrodes. Patterned polydimethylsiloxane (PDMS) stamps coated with vaporized dimethylformamide (DMF) are utilized to transfer as-grown graphene directly onto a flexible polyethylene terephthalate (PET) substrate. The facile direct transfer is attributed to the enhanced adhesion of the bi-layer graphene to PDMS, due to DMF-coating, as well as the weak adhesion between the bi-layer graphene and the Al2O3 substrate. In this way, flexible patterned graphene devices have been fabricated with Ag nanowire stickers as electrodes. Stable electrical conduction characteristics were measured over repetitive bending with a bending radius down to 5 mm

  6. Negative Differential Resistance in Atomic Carbon Chain-Graphene Junctions

    Institute of Scientific and Technical Information of China (English)

    安丽萍; 刘春梅; 刘念华

    2012-01-01

    We investigate the electronic transport properties of atomic carbon chain-graphene junctions by using the density-functionla theory combining with the non-equilibrium Green's functions. The results show that the transport properties are sensitively dependent on the contact geometry of carbon chain. From the calculated I-V curve we find negative differential resistance (NDR) in the two types of junctions. The NDR can be considered as a result of molecular orbitals moving related to the bias window.

  7. Touch stimulated pulse generation in biomimetic single-layer graphene

    Science.gov (United States)

    Sul, Onejae; Chun, Hyunsuk; Choi, Eunseok; Choi, Jungbong; Cho, Kyeongwon; Jang, Dongpyo; Chun, Sungwoo; Park, Wanjun; Lee, Seung-Beck

    2016-02-01

    Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac point in the graphene energy band, which generates a sharp peak in the measured resistance. We found that by changing the gate potential it was possible to modulate the threshold pressure and using a series of graphene channels, a train of pulses were generated during a transient pressurizing stimulus demonstrating biomimetic behaviour.Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac

  8. Kapitza Resistance between Few-Layer Graphene and Water: Liquid Layering Effects

    DEFF Research Database (Denmark)

    Alexeev, Dmitry; Chen, Jie; Walther, Jens Honore;

    2015-01-01

    The Kapitza resistance (RK) between few-layer graphene (FLG) and water was studied using molecular dynamics simulations. The RK was found to depend on the number of the layers in the FLG though, surprisingly, not on the water blockthickness. This distinct size dependence is attributed to the large...... between FLG and water. These findings suggest novel ways to engineer the thermal transport properties of solid−liquidinterfaces by controlling and regulating the liquid layering at the interface....

  9. Energetics of a Li Atom adsorbed on B/N doped graphene with monovacancy

    Science.gov (United States)

    Rani, Babita; Jindal, V. K.; Dharamvir, Keya

    2016-08-01

    We use density functional theory (DFT) to study the adsorption properties and diffusion of Li atom across B/N-pyridinic graphene. Regardless of the dopant type, B atoms of B-pyridinic graphene lose electron density. On the other hand, N atoms (p-type dopants) have tendency to gain electron density in N-pyridinic graphene. Higher chemical reactivity and electronic conductivity of B/N-pyridinic graphene are responsible for stronger binding of Li with the substrates as compared to pristine graphene. The binding energy of Li with B/N-pyridinic graphene exceeds the cohesive energy of bulk Li, making it energetically unfavourable for Li to form clusters on these substrates. Li atom gets better adsorbed on N-pyridinic graphene due to an additional p-p hybridization of the orbitals while Li on B-pyridinic prefers the ionic bonding. Also, significant distortion of N-pyridinic graphene upon Li adsorption is a consequence of the change in bonding mechanism between Li atom and the substrate. Our results show that bonding character and hence binding energies between Li and graphene can be tuned with the help of B/N doping of monovacancy defects. Further, the sites for most stable adsorption are different for the two types of doped and defective graphene, leading to greater Li uptake capacity of B-pyridinic graphene near the defect. In addition, B-pyridinic graphene offering lower diffusion barrier, ensures better Li kinetics. Thus, B-pyridinic graphene presents itself as a better anode material for LIBs as compared to N-pyridinic graphene.

  10. One-Pot Microwave-Assisted Synthesis of Graphene/Layered Double Hydroxide (LDH) Nanohybrids

    Institute of Scientific and Technical Information of China (English)

    Sunil P Lonkar; Jean-Marie Raquez; Philippe Dubois

    2015-01-01

    A facile and rapid method to synthesize graphene/layered double hydroxide (LDH) nanohybrids by a micro-wave technique is demonstrated. The synthesis procedure involves hydrothermal crystallization of Zn–Al LDH at the same time in situ reduction of graphene oxide (GO) to graphene. The microstructure, composition, and morphology of the resulting graphene/LDH nanohybrids were characterized. The results confirmed the formation of nanohybrids and the reduction of graphene oxide. The growth mechanism of LDH and in situ reduction of GO were discussed. The LDH sheet growth was found to prevent the scrolling of graphene layers in resulting hybrids. The electrochemical properties exhibit superior performance for graphene/Zn–Al LDH hybrids over pristine graphene. The present approach may open a strategy in hybridizing graphene with multimetallic nano-oxides and hydroxides using microwave method.

  11. Role of barrier layer on dielectric function of graphene double layer system at finite temperature

    Science.gov (United States)

    Patel, Digish K.; Ambavale, Sagar K.; Prajapati, Ketan; Sharma, A. C.

    2016-05-01

    We have theoretically investigated the static dielectric function of graphene double layer system (GDLS) at finite temperatures within the random phase approximation. GDLS has been suspended on a substrate and barrier layer of three different materials; h-BN, Al2O3 and HfO2 has been introduced between two graphene sheets of GDLS. We have reported dependence of the overall dielectric function of GDLS on interlayer distance and the effect of the dielectric environment at finite temperatures. Results show close relation between changing environment and behavior of dielectric constant of GDLS.

  12. Low-energy phase change memory with graphene confined layer

    Science.gov (United States)

    Zhu, Chengqiu; Ma, Jun; Ge, Xiaoming; Rao, Feng; Ding, Keyuan; Lv, Shilong; Wu, Liangcai; Song, Zhitang

    2016-06-01

    How to reduce the Reset operation energy is the key scientific and technological problem in the field of phase change memory (PCM). Here, we show in the Ge2Sb2Te5 based PCM cell, inserting an additional graphene monolayer in the Ge2Sb2Te5 layer can remarkably decrease both the Reset current and energy. Because of the small out-of-plane electrical and thermal conductivities of such monolayer graphene, the Set resistance and the heat dissipation towards top TiN electrode of the modified PCM cell are significantly increased and decreased, respectively. The mushroom-typed larger active phase transition volume thus can be confined inside the underlying thinner GST layer, resulting in the lower power consumption.

  13. Enhanced Performance of Dye-Sensitized Solar Cells with Nanostructure Graphene Electron Transfer Layer

    Directory of Open Access Journals (Sweden)

    Chih-Hung Hsu

    2014-01-01

    Full Text Available The utilization of nanostructure graphene thin films as electron transfer layer in dye-sensitized solar cells (DSSCs was demonstrated. The effect of a nanostructure graphene thin film in DSSC structure was examined. The nanostructure graphene thin films provides a great electron transfer channel for the photogenerated electrons from TiO2 to indium tin oxide (ITO glass. Obvious improvements in short-circuit current density of the DSSCs were observed by using the graphene electron transport layer modified photoelectrode. The graphene electron transport layer reduces effectively the back reaction in the interface between the ITO transparent conductive film and the electrolyte in the DSSC.

  14. Size-Selective Cu Nanocrystals Growth on Single and 2-3 Layers Graphene Films.

    Science.gov (United States)

    Gao, Hui; Li, Xiaolong; Wang, Yunfei; Guo, Haijie; Wang, Yuhua

    2015-09-01

    Cu nanoparticles decorated CVD growth single layer and 2-3 layers graphene films have been synthesized by sputtering deposition and annealing process. The wrinkles were observed on single layer graphene due to high annealing temperature (700 degrees C) and rapid cooling process, which were proved by HRSEM and Raman spectra. Smaller mean diameter and narrower size distribution of Cu nanoparticles were observed on 2-3 layers graphene film than that on single layer graphene. The large particles grow at the expense of small particles, and the particle growth was governed by the Ostwald ripening process. PMID:26716337

  15. Graphene-like single-layered covalent organic frameworks: synthesis strategies and application prospects.

    Science.gov (United States)

    Liu, Xuan-He; Guan, Cui-Zhong; Wang, Dong; Wan, Li-Jun

    2014-10-29

    Two-dimensional (2D) nanomaterials, such as graphene and transition metal chalcogenides, show many interesting dimension-related materials properties. Inspired by the development of 2D inorganic nanomaterials, single-layered covalent organic frameworks (sCOFs), featuring atom-thick sheets and crystalline extended organic structures with covalently bonded building blocks, have attracted great attention in recent years. With their unique graphene-like topological structure and the merit of structural diversity, sCOFs promise to possess novel and designable properties. However, the synthesis of sCOFs with well-defined structures remains a great challenge. Herein, the recent development of the bottom-up synthesis methods of 2D sCOFs, such as thermodynamic equilibrium control methods, growth-kinetics control methods, and surface-assisted covalent polymerization methods, are reviewed. Finally, some of the critical properties and application prospects of these materials are outlined.

  16. Negative magnetoresistance in a vertical single-layer graphene spin valve at room temperature.

    Science.gov (United States)

    Singh, Arun Kumar; Eom, Jonghwa

    2014-02-26

    Single-layer graphene (SLG) is an ideal material for spintronics because of its high charge-carrier mobility, long spin lifetime resulting from the small spin-orbit coupling, and hyperfine interactions of carbon atoms. Here, we report a vertical spin valve with SLG with device configuration Co/SLG/Al2O3/Ni. We observed negative magnetoresistance (-0.4%) for the Co/SLG/Al2O3/Ni junction at room temperature. However, the Co/Al2O3/Ni junction, which is without graphene, shows positive magnetoresistance. The current-voltage (I-V) characteristics of both Co/SLG/Al2O3/Ni and Co/Al2O3/Ni junctions are nonlinear, and this reveals that charge transport occurs by a tunneling mechanism. We have also explained the reason for negative magnetoresistance for the Co/SLG/Al2O3/Ni junction. PMID:24495123

  17. Initial evaluation and comparison of plasma damage to atomic layer carbon materials using conventional and low T{sub e} plasma sources

    Energy Technology Data Exchange (ETDEWEB)

    Jagtiani, Ashish V.; Miyazoe, Hiroyuki; Chang, Josephine; Farmer, Damon B.; Engel, Michael; Neumayer, Deborah; Han, Shu-Jen; Engelmann, Sebastian U., E-mail: suengelm@us.ibm.com; Joseph, Eric A. [IBM, T. J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Boris, David R.; Hernández, Sandra C.; Walton, Scott G. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States); Lock, Evgeniya H. [Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375 (United States)

    2016-01-15

    The ability to achieve atomic layer precision is the utmost goal in the implementation of atomic layer etch technology. Carbon-based materials such as carbon nanotubes (CNTs) and graphene are single atomic layers of carbon with unique properties and, as such, represent the ultimate candidates to study the ability to process with atomic layer precision and assess impact of plasma damage to atomic layer materials. In this work, the authors use these materials to evaluate the atomic layer processing capabilities of electron beam generated plasmas. First, the authors evaluate damage to semiconducting CNTs when exposed to beam-generated plasmas and compare these results against the results using typical plasma used in semiconductor processing. The authors find that the beam generated plasma resulted in significantly lower current degradation in comparison to typical plasmas. Next, the authors evaluated the use of electron beam generated plasmas to process graphene-based devices by functionalizing graphene with fluorine, nitrogen, or oxygen to facilitate atomic layer deposition (ALD). The authors found that all adsorbed species resulted in successful ALD with varying impact on the transconductance of the graphene. Furthermore, the authors compare the ability of both beam generated plasma as well as a conventional low ion energy inductively coupled plasma (ICP) to remove silicon nitride (SiN) deposited on top of the graphene films. Our results indicate that, while both systems can remove SiN, an increase in the D/G ratio from 0.08 for unprocessed graphene to 0.22 to 0.26 for the beam generated plasma, while the ICP yielded values from 0.52 to 1.78. Generally, while some plasma-induced damage was seen for both plasma sources, a much wider process window as well as far less damage to CNTs and graphene was observed when using electron beam generated plasmas.

  18. Graphene Oxide as a Monoatomic Blocking Layer

    DEFF Research Database (Denmark)

    Petersen, Søren; Glyvradal, Magni; Bøggild, Peter;

    2012-01-01

    covered by a compressed mosaic LB film of mGO flakes. These hybrid LB films were examined with atomic force microscopy (AFM) and X-ray reflectivity, both with and without the metal top electrodes. While the AFM enabled surface and morphology analysis, the X-ray reflectivity allowed for a detailed...

  19. CVD films of narrow atomically precise graphene nanoribbons

    Science.gov (United States)

    Shekhirev, Mikhail; Lipatov, Alexey; Harkleroad, Ashley; Sinitskii, Alexander

    Atomically precise graphene nanoribbons (GNRs) is a promising material for the next-generation electronics and optoelectronics. So far, solution-based and surface-assisted approaches have been the two main routes to synthesize GNRs with atomically smooth armchair edges. However, efficient processing of the resulting GNRs into uniform thin films to fabricate GNR-based functional devices remains a formidable challenge. In this presentation we will report the synthesis of narrow armchair GNRs using an alternative approach - a radical polymerization of rationally designed molecular precursors. The technique allows fabrication of thin, transparent and conductive films of GNRs on almost any substrate. Microscopic structure and electrical properties of the fabricated GNR films will also be discussed.

  20. Layer-by-layer polypyrrole coated graphite oxide and graphene nanosheets as catalyst support materials for fuel cells

    OpenAIRE

    Saner Okan, Burcu; Alkan Gürsel, Selmiye; Alkan Gursel, Selmiye; YÜRÜM, YUDA; Yurum, Yuda

    2013-01-01

    For the production of advanced type of catalyst support materials, the distinguished properties of graphene nanosheets were combined with the structural properties of conducting polypyrrole by the incorporation of graphene nanosheets into a polymer matrix by the proposed simple and low-cost fabrication technique. A precise tuning of electrical conductivity and thermal stability was also achieved by controlling the thickness of randomly dispersed graphene nanosheets by a layer-by-layer polymer...

  1. Free Energy Relationships in the Electrical Double Layer over Single-Layer Graphene

    Energy Technology Data Exchange (ETDEWEB)

    Achtyl, Jennifer L. [Northwestern University, Evanston; Vlassiouk, Ivan V [ORNL; Fulvio, Pasquale F [ORNL; Mahurin, Shannon Mark [ORNL; Dai, Sheng [ORNL; Geiger, Franz M. [Northwestern University, Evanston

    2013-01-01

    Fluid/solid interfaces containing singlelayer graphene are important in the areas of chemistry, physics, biology, and materials science, yet this environment is difficult to access with experimental methods, especially under flow conditions and in a label-free manner. Herein, we demonstrate the use of second harmonic generation to quantify the interfacial free energy at the fused silica/single-layer graphene/water interface at pH 7 and under conditions of flowing aqueous electrolyte solutions ranging in NaCl concentrations from 10 4 to 10 1 M. Our analysis reveals that single-layer graphene reduces the interfacial free energy density of the fused silica/water interface by a factor of up to 7, which is substantial given that many interfacial processes, including those that are electrochemical in nature, are exponentially sensitive to interfacial free energy density.

  2. Layer-by-layer assembly of thin films containing exfoliated pristine graphene nanosheets and polyethyleneimine.

    Science.gov (United States)

    Sham, Alison Y W; Notley, Shannon M

    2014-03-11

    A method for the modification of surface properties through the deposition of stabilized graphene nanosheets is described. Here, the thickness of the film is controlled through the use of the layer-by-layer technique, where the sequential adsorption of the cationic polyethyleneimine (PEI) is followed by the adsorption of anionic graphene sheets modified with layers of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) surfactants. The graphene particles were prepared using the surfactant-assisted liquid-phase exfoliation technique, with the low residual negative charge arising from edge defects. The buildup of the multilayer assembly through electrostatic interactions was strongly influenced by the solution conditions, including pH, ionic strength, and ionic species. Thereby, not only could the thickness of the film be tailored through the choice of the number of bilayers deposited but the viscoelastic properties of the film could also be modified by changing solution conditions at which the different species were deposited. The quartz crystal microbalance was used to measure the mass of graphene and polyelectrolyte immobilized at the interface as well as to probe the energy dissipated in the adsorbed layer.

  3. Atomic-layer deposition of silicon nitride

    CERN Document Server

    Yokoyama, S; Ooba, K

    1999-01-01

    Atomic-layer deposition (ALD) of silicon nitride has been investigated by means of plasma ALD in which a NH sub 3 plasma is used, catalytic ALD in which NH sub 3 is dissociated by thermal catalytic reaction on a W filament, and temperature-controlled ALD in which only a thermal reaction on the substrate is employed. The NH sub 3 and the silicon source gases (SiH sub 2 Cl sub 2 or SiCl sub 4) were alternately supplied. For all these methods, the film thickness per cycle was saturated at a certain value for a wide range of deposition conditions. In the catalytic ALD, the selective deposition of silicon nitride on hydrogen-terminated Si was achieved, but, it was limited to only a thin (2SiO (evaporative).

  4. Seeing graphene-based sheets

    OpenAIRE

    Jaemyung Kim; Franklin Kim; Jiaxing Huang

    2010-01-01

    Graphene-based sheets such as graphene, graphene oxide and reduced graphene oxide have stimulated great interest due to their promising electronic, mechanical and thermal properties. Microscopy imaging is indispensable for characterizing these single atomic layers, and oftentimes is the first measure of sample quality. This review provides an overview of current imaging techniques for graphene-based sheets and highlights a recently developed fluorescence quenching microscopy technique that al...

  5. A X-ray diffraction analysis on graphene layers of Assam coal

    Indian Academy of Sciences (India)

    Binoy K Saikia; Rajani K Boruah; Pradip K Gogoi

    2009-01-01

    The so-called turbostatic structure of carbons in coal with randomly oriented stacking of the lamellae (graphene) produces intense peaks, which are the dominant features in its X-ray diffraction profiles. The diffractogram may be conveniently divided into two regions of reciprocal space, the medium S region (1 < S < 3 Å) and a high S region (S > 3 Å) where = 4 -1 sin. To better understand the molecular level structure of high sulphur Assam coal, two coal samples (Tirap-1 and Tirap-2) from Tirap colliery of Makum coalfield, Assam (India) has been interpreted in this study by using the X-ray diffraction profiles. Random layered (graphene) structural parameters of these coals were determined by using X-ray diffraction technique, which showed that the and are 64.99 Å and 22.63 Å for Tirap-2 and 55.54 Å and 23.80 Å for that of Tirap-1 coals respectively. The position of band was found to be at 4.34 Å and 4.13 Å for Tirap-2 and Tirap-1 coals respectively. The number of layers and average number of carbon atoms (N) per aromatic graphene were found to be 21 and 8 for both the coal samples. Proximate, ultimate and ash analysis of the two coal samples were also carried out in this investigation.

  6. Effect of radial stretch on vibration characteristics of single-layered circular graphene sheets

    Science.gov (United States)

    Pahlani, Gunjan; Verma, Deepti; Gupta, Shakti

    Vibrations of single-layered circular graphene sheets are studied using molecular mechanics (MM) simulations. Interactions between bonded and non-bonded atoms are prescribed using MM3 potential. Frequencies of different modes of vibration are computed from the eigenvalues and eigen vectors of mass weighted Hessian of the system. This study is performed on graphene sheets of various diameters. A linear continuum membrane model for predicting vibrational frequencies is studied using finite element (FE) method. Frequencies for several modes computed from continuum and molecular model matched well for moderate values of radial stretch, however, with increased stretch those deviated from each other significantly. In particular for higher values of stretch the MM simulations predict considerably lower values of frequencies compared to that found from FE simulations. Also, at higher values of stretch the frequency vs. stretch curve obtained from MM simulations showed a hardening behavior which could not be captured by the linear continuum model. We have also found a similar behavior in two-layered graphene sheets using MM simulations.

  7. Examination of humidity effects on measured thickness and interfacial phenomena of exfoliated graphene on silicon dioxide via amplitude modulation atomic force microscopy

    International Nuclear Information System (INIS)

    The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO2) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO2. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO2 substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM

  8. Examination of humidity effects on measured thickness and interfacial phenomena of exfoliated graphene on silicon dioxide via amplitude modulation atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jinkins, K.; Farina, L.; Wu, Y., E-mail: wuy@uwplatt.edu [Engineering Physics Department, University of Wisconsin-Platteville, 1 University Plaza, Platteville, Wisconsin 53818 (United States); Camacho, J. [Mechanical Engineering Department, University of Wisconsin-Platteville, 1 University Plaza, Platteville, Wisconsin 53818 (United States)

    2015-12-14

    The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO{sub 2}) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO{sub 2}. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO{sub 2} substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM.

  9. Competition between plastic deformation and fracture processes in metal–graphene layered composites

    International Nuclear Information System (INIS)

    Competition between plastic deformation and fracture processes in metal–graphene layered composites is theoretically described. In the framework of the suggested approach, plastic deformation and fracture processes controlling the flow stress/strength of a metal–graphene layered composite are the transfer of plastic deformation across a graphene interface and the nanocrack formation initiated by stress fields of lattice dislocations stopped near a graphene interface. With these processes theoretically described, we reveal strength characteristics of metal–graphene layered composites as functions of their key structural parameters, including the metallic layer thickness λ and graphene layer thickness h. The results of our theoretical examination are consistent with the corresponding experimental data (Kim et al 2013 Nat. Commun. 4 2114). (paper)

  10. Chemical nature of boron and nitrogen dopant atoms in graphene strongly influences its electronic properties.

    Science.gov (United States)

    Lazar, Petr; Zbořil, Radek; Pumera, Martin; Otyepka, Michal

    2014-07-21

    Boron and nitrogen doped graphenes are highly promising materials for electrochemical applications, such as energy storage, generation and sensing. The doped graphenes can be prepared by a broad variety of chemical approaches. The substitution of a carbon atom should induce n-type behavior in the case of nitrogen and p-type behavior in the case of boron-doped graphene; however, the real situation is more complex. The electrochemical experiments show that boron-doped graphene prepared by hydroboration reaction exhibits similar properties as the nitrogen doped graphene; according to theory, the electrochemical behavior of B and N doped graphenes should be opposite. Here we analyze the electronic structure of N/B-doped graphene (at ∼5% coverage) by theoretical calculations. We consider graphene doped by both substitution and addition reactions. The density of states (DOS) plots show that graphene doped by substitution of the carbon atom by N/B behaves as expected, i.e., as an n/p-doped material. N-doped graphene also has a lower value of the workfunction (3.10 eV) with respect to that of the pristine graphene (4.31 eV), whereas the workfunction of B-doped graphene is increased to the value of 5.57 eV. On the other hand, the workfunctions of graphene doped by addition of -NH2 (4.77 eV) and -BH2 (4.54 eV) groups are both slightly increased and therefore the chemical nature of the dopant is less distinguishable. This shows that mode of doping depends significantly on the synthesis method used, as it leads to different types of behaviour, and, in turn, different electronic and electrochemical properties of doped graphene, as observed in electrocatalytic experiments. This study has a tremendous impact on the design of doped graphene systems from the point of view of synthetic chemistry.

  11. Graphene Layer Growth Chemistry: Five-Six-Ring Flip Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Whitesides, R.; Domin, D.; Salomon-Ferrer, R.; Lester Jr., W.A.; Frenklach, M.

    2007-12-01

    Reaction pathways are presented for hydrogen-mediated isomerization of a five and six member carbon ring complex on the zigzag edge of a graphene layer. A new reaction sequence that reverses orientation of the ring complex, or 'flips' it, was identified. Competition between the flip reaction and 'ring separation' was examined. Ring separation is the reverse of the five and six member ring complex formation reaction, previously reported as 'ring collision'. The elementary steps of the pathways were analyzed using density-functional theory (DFT). Rate coefficients were obtained by solution of the energy master equation and classical transition state theory utilizing the DFT energies, frequencies, and geometries. The results indicate that the flip reaction pathway dominates the separation reaction and should be competitive with other pathways important to the graphene zigzag edge growth in high temperature environments.

  12. First-principles study of hydrogen adsorption on titanium-decorated single-layer and bilayer graphenes

    Institute of Scientific and Technical Information of China (English)

    Pan Hong-Zhe; Wang Yong-Long; He Kai-Hua; Wei Ming-Zhen; Ouyang Yu; Chen Li

    2013-01-01

    The adsorption of hydrogen molecules on titanium-decorated (Ti-decorated) single-layer and bilayer graphenes is studied using density functional theory (DFT) with the relativistic effect.Both the local density approximation (LDA) and the generalized gradient approximation (GGA) are used for obtaining the region of the adsorption energy of H2 molecules on Ti-decorated graphene.We find that a graphene layer with titanium (Ti) atoms adsorbed on both sides can store hydrogen up to 9.51 wt% with average adsorption energy in a range from-0.170 eV to-0.518 eV.Based on the adsorption energy criterion,we find that chemisorption is predominant for H2 molecules when the concentration of H2 molecules absorbed is low while physisorption is predominant when the concentration is high.The computation results for the bilayer graphene decorated with Ti atoms show that the lower carbon layer makes no contribution to hydrogen adsorption.

  13. Enhanced Performance of Dye-Sensitized Solar Cells with Nanostructure Graphene Electron Transfer Layer

    OpenAIRE

    Chih-Hung Hsu; Jia-Ren Wu; Lung-Chien Chen; Po-Shun Chan; Cheng-Chiang Chen

    2014-01-01

    The utilization of nanostructure graphene thin films as electron transfer layer in dye-sensitized solar cells (DSSCs) was demonstrated. The effect of a nanostructure graphene thin film in DSSC structure was examined. The nanostructure graphene thin films provides a great electron transfer channel for the photogenerated electrons from TiO2 to indium tin oxide (ITO) glass. Obvious improvements in short-circuit current density of the DSSCs were observed by using the graphene electron transport l...

  14. An Analytical Model for Adsorption and Diffusion of Atoms/Ions on Graphene Surface

    Directory of Open Access Journals (Sweden)

    Yan-Zi Yu

    2015-01-01

    Full Text Available Theoretical investigations are made on adsorption and diffusion of atoms/ions on graphene surface based on an analytical continuous model. An atom/ion interacts with every carbon atom of graphene through a pairwise potential which can be approximated by the Lennard-Jones (L-J potential. Using the Fourier expansion of the interaction potential, the total interaction energy between the adsorption atom/ion and a monolayer graphene is derived. The energy-distance relationships in the normal and lateral directions for varied atoms/ions, including gold atom (Au, platinum atom (Pt, manganese ion (Mn2+, sodium ion (Na1+, and lithium-ion (Li1+, on monolayer graphene surface are analyzed. The equilibrium position and binding energy of the atoms/ions at three particular adsorption sites (hollow, bridge, and top are calculated, and the adsorption stability is discussed. The results show that H-site is the most stable adsorption site, which is in agreement with the results of other literatures. What is more, the periodic interaction energy and interaction forces of lithium-ion diffusing along specific paths on graphene surface are also obtained and analyzed. The minimum energy barrier for diffusion is calculated. The possible applications of present study include drug delivery system (DDS, atomic scale friction, rechargeable lithium-ion graphene battery, and energy storage in carbon materials.

  15. Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges.

    Science.gov (United States)

    Zhao, Jiong; Deng, Qingming; Avdoshenko, Stanislav M; Fu, Lei; Eckert, Jürgen; Rümmeli, Mark H

    2014-11-01

    Single-atom catalysts are of great interest because of their high efficiency. In the case of chemically deposited sp(2) carbon, the implementation of a single transition metal atom for growth can provide crucial insight into the formation mechanisms of graphene and carbon nanotubes. This knowledge is particularly important if we are to overcome fabrication difficulties in these materials and fully take advantage of their distinct band structures and physical properties. In this work, we present atomically resolved transmission EM in situ investigations of single Fe atoms at graphene edges. Our in situ observations show individual iron atoms diffusing along an edge either removing or adding carbon atoms (viz., catalytic action). The experimental observations of the catalytic behavior of a single Fe atom are in excellent agreement with supporting theoretical studies. In addition, the kinetics of Fe atoms at graphene edges are shown to exhibit anomalous diffusion, which again, is in agreement with our theoretical investigations.

  16. Layer-dependent supercapacitance of graphene films grown by chemical vapor deposition on nickel foam

    KAUST Repository

    Chen, Wei

    2013-03-01

    High-quality, large-area graphene films with few layers are synthesized on commercial nickel foams under optimal chemical vapor deposition conditions. The number of graphene layers is adjusted by varying the rate of the cooling process. It is found that the capacitive properties of graphene films are related to the number of graphene layers. Owing to the close attachment of graphene films on the nickel substrate and the low charge-transfer resistance, the specific capacitance of thinner graphene films is almost twice that of the thicker ones and remains stable up to 1000 cycles. These results illustrate the potential for developing high-performance graphene-based electrical energy storage devices. © 2012 Elsevier B.V. All rights reserved.

  17. Geometrical nonlinear free vibration of multi-layered graphene sheets

    Energy Technology Data Exchange (ETDEWEB)

    Wang Jinbao [School of Naval Architecture and Civil Engineering, Zhejiang Ocean University, Zhoushan 316000 (China); He Xiaoqiao; Kitipornchai, S [Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Zhang Hongwu, E-mail: bcxqhe@cityu.edu.hk [State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024 (China)

    2011-04-06

    A nonlinear continuum model is developed for the nonlinear vibration analysis of multi-layered graphene sheets (MLGSs), in which the nonlinear van der Waals (vdW) interaction between any two layers is formulated explicitly. The nonlinear equations of motion are studied by the harmonic-balance methods. Based on the present model, the nonlinear stiffened amplitude-frequency relations of double-layered graphene sheets (DLGSs) are investigated in the spectral neighbourhood of lower frequencies. The influence of the vdW interaction on the vibration properties of DLGSs is well illustrated by plotting the resulting modes' shapes, in which in-phase and anti-phase vibrations of DLGSs are studied. In particular, the large-amplitude vibration which associates with the anti-phase resonant frequencies, separating DLGS into single-layered GSs, is a promising application that needs to be explored further. In contrast, the vibration modes that are associated with the resonant frequencies are nonidentical and give various vibration patterns, which indicates that MLGSs are highly suited to being used as high-frequency resonators.

  18. Layered Chalcogenides beyond Graphene: from Electronic Structure Evolution to the Spin Transport

    Science.gov (United States)

    Yuan, Hongtao

    2014-03-01

    Recent efforts on graphene-like atomic layer materials, aiming at novel electronic properties and quantum phenomena beyond graphene, have attracted much attention for potential electronics/spintronics applications. Compared to the weak spin-orbit-interaction (SOI) in graphene, metal chalcogenides MX2 have heavy 4d/5d elements with strong atomic SOI, providing a unique way for generating spin polarization based on valleytronics physics. Indeed, such a spin-polarized band structure has been demonstrated theoretically and supported by optical investigations. However, despite these exciting progresses, following two important issues in MX2 community remain elusive: 1. the quantitative band structure of MX2 compounds (where are the valleys -band maxima/minima- locating in the BZ) have not been experimentally confirmed. Especially for those cleaved ultrathin mono- and bi-layer flakes hosting most of recently-reported exotic phenomena at the 2D limit, the direct detection for band dispersion becomes of great importance for valleytronics. 2. Spin transports have seldom been reported even though such a strong SOI system can serve as an ideal platform for the spin polarization and spin transport. In this work, we started from the basic electronic structures of representative MX2, obtained by ARPES, and investigated both the band variation between these compounds and their band evolution from bulk to the monolayer limit. After having a systematic understanding on band structures, we reported a giant Zeeman-type spin-polarization generated and modulated by an external electric field in WSe2 electric-double-layer transistors. The non-magnetic approach for realizing such an intriguing spin splitting not only keeps the system time-reversally invariant but also suggests a new paradigm for manipulating the spin-degrees of freedom of electrons. Acknowledge the support from DoE, BES, Division of MSE under contract DE-AC02-76SF00515.

  19. Substrate-Independent Growth of Atomically Precise Chiral Graphene Nanoribbons

    Science.gov (United States)

    2016-01-01

    Contributing to the need for new graphene nanoribbon (GNR) structures that can be synthesized with atomic precision, we have designed a reactant that renders chiral (3,1)-GNRs after a multistep reaction including Ullmann coupling and cyclodehydrogenation. The nanoribbon synthesis has been successfully proven on different coinage metals, and the formation process, together with the fingerprints associated with each reaction step, has been studied by combining scanning tunneling microscopy, core-level spectroscopy, and density functional calculations. In addition to the GNR’s chiral edge structure, the substantial GNR lengths achieved and the low processing temperature required to complete the reaction grant this reactant extremely interesting properties for potential applications. PMID:27548516

  20. Detecting single graphene layer by using fluorescence from high-speed Ar^7+ ion

    Science.gov (United States)

    Miyamoto, Yoshiyuki; Zhang, Hong

    2008-03-01

    A highly-charged-ion interacting with graphite causes structural change in nano-scales [1]. While when the ion's kinetic energy reaches few MeVs, the induced is not the structural change but electronic excitation. An experiment [2] showed fluorescence from Ar^7+ ions penetrating through carbon foil with kinetic energy of 2 MeV. Motivated by this experiment, we tested interaction between an Ar^7+ ion and a graphene sheet by the time-dependent density functional approach, and found that the electronic excitation in the Ar^ 7+ ion is also the case even when the incident kinetic energy is 500 KeV and the target thickness is only mono-atomic layer. This simulation suggests the possibility of detecting a suspended mono-atomic layer of graphene [3] by monitoring fluorescence from the penetrated Ar^7+ ions. We will discuss its importance for analyzing bombardment of solids by highly charged, high-speed ions and possible experiments according to the present result. References: [1] T. Meguro, et al., Appl. Phys. Lett 79, 3866 (2001). [2] S. Bashkin, H. Oona, E. Veje, Phys, Rev. A25, 417 (1982). [3] J. Mayer et al., Nature (London), 446, 60 (2007).

  1. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    Science.gov (United States)

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-08-01

    We report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of deposition show a strong dependence between the Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  2. Topological insulator Bi2Se3 thin films grown on double-layer graphene by molecular beam epitaxy

    OpenAIRE

    Song, Can-Li; Wang, Yi-Lin; Jiang, Ye-Ping; Zhang, Yi; Chang, Cui-Zu; Wang, Lili; He, Ke; Chen, Xi; Jia, Jin-Feng; Wang, Yayu; Fang, Zhong; Dai, Xi; Xie, Xin-Cheng; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2010-01-01

    Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0\\pm 0.2x1011/cm2, and become a bulk insulator at a ...

  3. Visualization of deuterium dead layer by atom probe tomography

    KAUST Repository

    Gemma, Ryota

    2012-12-01

    The first direct observation, by atom probe tomography, of a deuterium dead layer is reported for Fe/V multilayered film loaded with D solute atoms. The thickness of the dead layers was measured to be 0.4-0.5 nm. The dead layers could be distinguished from chemically intermixed layers. The results suggest that the dead layer effect occurs even near the interface of the mixing layers, supporting an interpretation that the dead layer effect cannot be explained solely by electronic charge transfer but also involves a modulation of rigidity. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  4. Gap opening and tuning in single-layer graphene with combined electric and magnetic field modulation

    Institute of Scientific and Technical Information of China (English)

    Lin Xin; Wang Hai-Long; Pan Hui; Xu Huai-Zhe

    2011-01-01

    The energy band structure of single-layer graphene under one-dimensional electric and magnetic field modulation is theoretically investigated. The criterion for bandgap opening at the Dirac point is analytically derived with a two-fold degeneracy second-order perturbation method. It is shown that a direct or an indirect bandgap semiconductor could be realized in a single-layer graphene under some specific configurations of the electric and magnetic field arrangement. Due to the bandgap generated in the single-layer graphene, the Klein tunneling observed in pristine graphene is completely suppressed.

  5. Quantum Dots and Andreev Reflections in Graphene

    NARCIS (Netherlands)

    Liu, X.L.

    2010-01-01

    Graphene is an exceptionally thin semiconductor that consists of only one atomic layer of carbon atoms. The electrons in graphene live in a strictly two-dimensional (2D) world. In addition to this remarkable 2Dness, it is also peculiar that the behavior of the electrons in graphene is governed by th

  6. Biomass derived solvents for the scalable production of single layered graphene from graphite.

    Science.gov (United States)

    Sharma, Mukesh; Mondal, Dibyendu; Singh, Nripat; Prasad, Kamalesh

    2016-07-12

    Among four different biomass derived green and sustainable solvents namely levulinic acid (LA), ethyl lactate (EL), γ-valerolactone (GVL) and formic acid (FA) only LA was found to exfoliate graphite to single and few layered graphene sheets. During exfoliation, the formation of LA crystals embedded with single layered graphene sheets was observed. The process is scalable and the solvent can be recovered and reused in five subsequent cycles of exfoliation for the large scale production of graphene sheets.

  7. Atomic Layer Thermopile Materials: Physics and Application

    Directory of Open Access Journals (Sweden)

    P. X. Zhang

    2008-01-01

    Full Text Available New types of thermoelectric materials characterized by highly anisotropic Fermi surfaces and thus anisotropic Seebeck coefficients are reviewed. Early studies revealed that there is an induced voltage in high TC oxide superconductors when the surface of the films is exposed to short light pulses. Subsequent investigations proved that the effect is due to anisotropic components of the Seebeck tensor, and the type of materials is referred to atomic layer thermopile (ALT. Our recent studies indicate that multilayer thin films at the nanoscale demonstrate enhanced ALT properties. This is in agreement with the prediction in seeking the larger figure of merit (ZT thermoelectric materials in nanostructures. The study of ALT materials provides both deep insight of anisotropic transport property of these materials and at the same time potential materials for applications, such as light detector and microcooler. By measuring the ALT properties under various perturbations, it is found that the information on anisotropic transport properties can be provided. The information sometimes is not easily obtained by other tools due to the nanoscale phase coexistence in these materials. Also, some remained open questions and future development in this research direction have been well discussed.

  8. The enhanced electrocatalytic activity of graphene co-doped with chlorine and fluorine atoms

    International Nuclear Information System (INIS)

    Graphene co-doped with fluorine and chlorine was prepared through a one-step synthesis to greatly enhance its electrocatalytic activity and stability for oxygen reduction reaction. - Highlights: • Developed a one-step synthesis of graphene co-doped with different halogen atoms. • The obtained graphene exhibits great electrocatalytic activity in the oxygen reduction reaction. • The chlorine–fluorine co-doped graphene has great stability in methanol crossover effect. • Experiments indicate that there are possible synergetic interactions between halogen dopants. - Abstract: Graphene co-doped with fluorine and chlorine heteroatoms was prepared through a one-step synthesis and was investigated as the oxygen reduction electrocatalysts. Voltammetric measurements show that fluorine and chlorine co-doped graphene has remarkable catalytic activity toward the electrochemical reduction of oxygen in alkaline solution. Besides having a high tolerance to methanol crossover effect, the co-doped graphene also showed a better stability than that of commercial Pt/C electrocatalysts and of the chlorine-doped graphene that was prepared by the same approach. The charge transfer resistance of the co-doped graphene was substantially lower than that of the chlorine-doped graphene, suggesting that there may exist a synergistic interaction between fluorine and chlorine dopants. The rapid synthetic method reported here provides an effective approach for future investigation of halogen (co-) doped graphene

  9. Fabrication of hybrid graphene oxide/polyelectrolyte capsules by means of layer-by-layer assembly on erythrocyte cell templates

    Directory of Open Access Journals (Sweden)

    Joseba Irigoyen

    2015-12-01

    Full Text Available A novel and facile method was developed to produce hybrid graphene oxide (GO–polyelectrolyte (PE capsules using erythrocyte cells as templates. The capsules are easily produced through the layer-by-layer technique using alternating polyelectrolyte layers and GO sheets. The amount of GO and therefore its coverage in the resulting capsules can be tuned by adjusting the concentration of the GO dispersion during the assembly. The capsules retain the approximate shape and size of the erythrocyte template after the latter is totally removed by oxidation with NaOCl in water. The PE/GO capsules maintain their integrity and can be placed or located on other surfaces such as in a device. When the capsules are dried in air, they collapse to form a film that is approximately twice the thickness of the capsule membrane. AFM images in the present study suggest a film thickness of approx. 30 nm for the capsules in the collapsed state implying a thickness of approx. 15 nm for the layers in the collapsed capsule membrane. The polyelectrolytes used in the present study were polyallylamine hydrochloride (PAH and polystyrenesulfonate sodium salt (PSS. Capsules where characterized by transmission electron microscopy (TEM, atomic force microscopy (AFM, dynamic light scattering (DLS and Raman microscopy, the constituent layers by zeta potential and GO by TEM, XRD, and Raman and FTIR spectroscopies.

  10. Enhanced memory effect with embedded graphene nanoplatelets in ZnO charge trapping layer

    Energy Technology Data Exchange (ETDEWEB)

    El-Atab, Nazek; Nayfeh, Ammar [Department of Electrical Engineering and Computer Science (EECS), Institute Center for Microsystems–iMicro, Masdar Institute of Science and Technology, Abu Dhabi (United Arab Emirates); Cimen, Furkan [Department of Electrical and Electronics Engineering, Bilkent University, Ankara 06800 (Turkey); Alkis, Sabri [UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800 (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey); Okyay, Ali K. [Department of Electrical and Electronics Engineering, Bilkent University, Ankara 06800 (Turkey); UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800 (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey)

    2014-07-21

    A charge trapping memory with graphene nanoplatelets embedded in atomic layer deposited ZnO (GNIZ) is demonstrated. The memory shows a large threshold voltage V{sub t} shift (4 V) at low operating voltage (6/−6 V), good retention (>10 yr), and good endurance characteristic (>10{sup 4} cycles). This memory performance is compared to control devices with graphene nanoplatelets (or ZnO) and a thicker tunnel oxide. These structures showed a reduced V{sub t} shift and retention characteristic. The GNIZ structure allows for scaling down the tunnel oxide thickness along with improving the memory window and retention of data. The larger V{sub t} shift indicates that the ZnO adds available trap states and enhances the emission and retention of charges. The charge emission mechanism in the memory structures with graphene nanoplatelets at an electric field E ≥ 5.57 MV/cm is found to be based on Fowler-Nordheim tunneling. The fabrication of this memory device is compatible with current semiconductor processing, therefore, has great potential in low-cost nano-memory applications.

  11. Quantum dynamics of hydrogen atoms on graphene. II. Sticking

    Energy Technology Data Exchange (ETDEWEB)

    Bonfanti, Matteo, E-mail: matteo.bonfanti@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Jackson, Bret [Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Hughes, Keith H. [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany); Martinazzo, Rocco, E-mail: rocco.martinazzo@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Richerche, v. Golgi 19, 20133 Milano (Italy)

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated.

  12. Quantum dynamics of hydrogen atoms on graphene. II. Sticking.

    Science.gov (United States)

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H; Burghardt, Irene; Martinazzo, Rocco

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated. PMID:26429029

  13. The stability and electronic structure of Fe atoms embedded in zigzag graphene nanoribbons

    International Nuclear Information System (INIS)

    The stability and electronic properties of the Fe atoms embedded in divacancy defects in graphene nanoribbons (GNR) with zigzag-shaped edges have been studied by first-principles calculations. When Fe is positioned in the middle of the ribbon, it has little effect on the edge C atoms, which reserves the flat edges of graphene nanoribbons. On the other hand, when Fe atom is near the edge, structural distortion takes place resulting in tilted-edge structure with low energies. This indicates that the Fe atoms prefer to occupy divacancy sites near the edges. This is also in consistent with the analyses of electronic structures. Meanwhile, our results reveal that embedding Fe atom in the graphene nanoribbons is an effective method to make the GNR possessing metallic properties.

  14. Growth of Large-Area Single- and Bi-Layer Graphene by Controlled Carbon Precipitation on Polycrystalline Ni Surfaces

    OpenAIRE

    Reina, Alfonso; Thiele, Stefan; Jia, Xiaoting; Bhaviripudi, Sreekar; Dresselhaus, Mildred S.; Schaefer, Juergen A.; Kong, Jing

    2009-01-01

    We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity. As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–...

  15. Strong THz and Infrared Optical Forces on a Suspended Single-Layer Graphene Sheet

    CERN Document Server

    Mousavi, S Hossein; Wang, Zheng

    2014-01-01

    Single-layer graphene exhibits exceptional mechanical properties attractive for optomechanics: it combines low mass density, large tensile modulus, and low bending stiffness. However, at visible wavelengths, graphene absorbs weakly and reflects even less, thereby inadequate to generate large optical forces needed in optomechanics. Here, we numerically show that a single-layer graphene sheet is sufficient to produce strong optical forces under terahertz or infrared illumination. For a system as simple as graphene suspended atop a uniform substrate, high reflectivity from the substrate is crucial in creating a standing-wave pattern, leading to a strong optical force on graphene. This force is readily tunable in amplitude and direction by adjusting the suspension height. In particular, repellent optical forces can levitate graphene to a series of stable equilibrium heights above the substrate. One of the key parameters to maximize the optical force is the excitation frequency: peak forces are found near the scat...

  16. Graphene-like two-dimensional layered nanomaterials: applications in biosensors and nanomedicine

    Science.gov (United States)

    Yang, Guohai; Zhu, Chengzhou; Du, Dan; Zhu, Junjie; Lin, Yuehe

    2015-08-01

    The development of nanotechnology provides promising opportunities for various important applications. The recent discovery of atomically-thick two-dimensional (2D) nanomaterials can offer manifold perspectives to construct versatile devices with high-performance to satisfy multiple requirements. Many studies directed at graphene have stimulated renewed interest on graphene-like 2D layered nanomaterials (GLNs). GLNs including boron nitride nanosheets, graphitic-carbon nitride nanosheets and transition metal dichalcogenides (e.g. MoS2 and WS2) have attracted significant interest in numerous research fields from physics and chemistry to biology and engineering, which has led to numerous interdisciplinary advances in nano science. Benefiting from the unique physical and chemical properties (e.g. strong mechanical strength, high surface area, unparalleled thermal conductivity, remarkable biocompatibility and ease of functionalization), these 2D layered nanomaterials have shown great potential in biochemistry and biomedicine. This review summarizes recent advances of GLNs in applications of biosensors and nanomedicine, including electrochemical biosensors, optical biosensors, bioimaging, drug delivery and cancer therapy. Current challenges and future perspectives in these rapidly developing areas are also outlined. It is expected that they will have great practical foundation in biomedical applications with future efforts.

  17. Layer-by-layer assembly of functionalized reduced graphene oxide for direct electrochemistry and glucose detection.

    Science.gov (United States)

    Mascagni, Daniela Branco Tavares; Miyazaki, Celina Massumi; da Cruz, Nilson Cristino; de Moraes, Marli Leite; Riul, Antonio; Ferreira, Marystela

    2016-11-01

    We report an electrochemical glucose biosensor made with layer-by-layer (LbL) films of functionalized reduced graphene oxide (rGO) and glucose oxidase (GOx). The LbL assembly using positively and negatively charged rGO multilayers represents a simple approach to develop enzymatic biosensors. The electron transport properties of graphene were combined with the specificity provided by the enzyme. rGO was obtained and functionalized using chemical methods, being positively charged with poly(diallyldimethylammonium chloride) to form GPDDA, and negatively charged with poly(styrene sulfonate) to form GPSS. Stable aqueous dispersions of GPDDA and GPSS are easily obtained, enabling the growth of LbL films on various solid supports. The use of graphene in the immobilization of GOx promoted Direct Electron Transfer, which was evaluated by Cyclic Voltammetry. Amperometric measurements indicated a detection limit of 13.4μmol·L(-1) and sensitivity of 2.47μA·cm(-2)·mmol(-1)·L for glucose with the (GPDDA/GPSS)1/(GPDDA/GOx)2 architecture, whose thickness was 19.80±0.28nm, as determined by Surface Plasmon Resonance (SPR). The sensor may be useful for clinical analysis since glucose could be detected even in the presence of typical interfering agents and in real samples of a lactose-free milk and an electrolyte solution to prevent dehydration. PMID:27524075

  18. Sprayable, Paintable Layer-by-Layer Polyaniline Nanofiber/Graphene Electrodes for Electrochemical Energy Storage

    Science.gov (United States)

    Kwon, Se Ra; Jeon, Ju-Won; Lutkenhus, Jodie

    2015-03-01

    Sprayable batteries are growing in interest for applications in structural energy storage and power or flexible power. Spray-assisted layer-by-layer (LbL) assembly, in which complementary species are alternately sprayed onto a surface, is particularly amenable toward this application. Here, we report on the fabrication of composite films containing polyaniline nanofibers (PANI NF) and graphene oxide (GO) sheets fabricated via spray-assisted LbL assembly. The resulting films are electrochemical reduced to yield PANI NF/electrochemically reduced graphene (ERGO) electrodes for use as a cathode in non-aqueous energy storage systems. Through the spray-assisted LbL process, the hybrid electrodes could be fabricated 74 times faster than competing dip-assisted LbL assembly. The resulting electrodes are highly porous (0.72 void fraction), and are comprised of 67 wt% PANI NF and 33 wt% ERGO. The sprayed electrodes showed better rate capability, higher specific power, as well as more stable cycle life than dip-assisted LbL electrodes. It is shown here that the spray-assisted LbL approach is well-suited towards the fabrication of paintable electrodes containing polyaniline nanofibers and electrochemically reduced graphene oxide sheets.

  19. Prediction of structural and mechanical properties of atom-decorated porous graphene via density functional calculations

    Science.gov (United States)

    Ansari, Reza; Ajori, Shahram; Malakpour, Sina

    2016-04-01

    The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption).

  20. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns

    Science.gov (United States)

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M.; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S.; Ma, Zhenqiang; Nealey, Paul F.

    2016-08-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces.

  1. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns.

    Science.gov (United States)

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S; Ma, Zhenqiang; Nealey, Paul F

    2016-01-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces. PMID:27528258

  2. Long-Term Passivation of Strongly Interacting Metals with Single-Layer Graphene

    OpenAIRE

    Weatherup, Robert S.; D’Arsié, Lorenzo; Cabrero-Vilatela, Andrea; Caneva, Sabina; Blume, Raoul; Robertson, John; Schloegl, Robert; Hofmann, Stephan

    2015-01-01

    The long-term (>18 months) protection of Ni surfaces against oxidation under atmospheric conditions is demonstrated by coverage with single-layer graphene, formed by chemical vapor deposition. In situ, depth-resolved X-ray photoelectron spectroscopy of various graphene-coated transition metals reveals that a strong graphene–metal interaction is of key importance in achieving this long-term protection. This strong interaction prevents the rapid intercalation of oxidizing species at the graphen...

  3. USE OF ATOMIC LAYER DEPOSITION OF FUNCTIONALIZATION OF NANOPOROUS BIOMATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    Brigmon, R.; Narayan, R.; Adiga, S.; Pellin, M.; Curtiss, L.; Stafslien, S.; Chisholm, B.; Monteiro-Riviere, N.; Elam, J.

    2010-02-08

    Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.

  4. Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

    Science.gov (United States)

    Ajlani, Hosni; Azizi, Mohamed Karim; Gharsallah, Ali; Oueslati, Meherzi

    2016-07-01

    Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.

  5. Designing nanoscale constructs from atomic thin sheets of graphene, boron nitride and gold nanoparticles for advanced material applications

    Science.gov (United States)

    Jasuja, Kabeer

    2011-12-01

    ' interaction with graphene, and applied to address the challenge of dispersing bare-surfaced GNPs for efficient liquid-phase catalysis. We also revisited the functionalization of graphene and present a non-invasive surface introduction of interfaceable moieties. Isostructural to graphene, ultrathin BN sheet is another atomic-thick nanomaterial possessing a highly diverse set of properties inconceivable from graphene. Exfoliating UTBNSs has been challenging due to their exceptional intersheet-bonding and chemical-inertness. To develop applications of BN monolayers and evolve research, a facile lab-scale approach was desired that can produce processable dispersions of BN monolayers. We demonstrated a novel chlorosulfonic acid based treatment that resulted in protonation assisted layer-by-layer exfoliation of BN monolayers with highest reported yields till date. Further, the BN monolayers exhibited extensively protonated N centers, which are utilized for chemically interfacing GNPs, demonstrating their ability to act as excellent nano-templates. The scientific details obtained from the research shown here will significantly support current research activities and greatly impact their future applications. Our research findings have been published in ACS Nano, Small, Journal of Physical Chemistry Letters, MRS Proceedings and have gathered >45 citations.

  6. Electrochemically Produced Graphene for Microporous Layers in Fuel Cells.

    Science.gov (United States)

    Najafabadi, Amin Taheri; Leeuwner, Magrieta J; Wilkinson, David P; Gyenge, Előd L

    2016-07-01

    The microporous layer (MPL) is a key cathodic component in proton exchange membrane fuel cells owing to its beneficial influence on two-phase mass transfer. However, its performance is highly dependent on material properties such as morphology, porous structure, and electrical resistance. To improve water management and performance, electrochemically exfoliated graphene (EGN) microsheets are considered as an alternative to the conventional carbon black (CB) MPLs. The EGN-based MPLs decrease the kinetic overpotential and the Ohmic potential loss, whereas the addition of CB to form a composite EGN+CB MPL improves the mass-transport limiting current density drastically. This is reflected by increases of approximately 30 and 70 % in peak power densities at 100 % relative humidity (RH) compared with those for CB- and EGN-only MPLs, respectively. The composite EGN+CB MPL also retains the superior performance at a cathode RH of 20 %, whereas the CB MPL shows significant performance loss.

  7. Multi-layer graphene membrane based memory cell

    Science.gov (United States)

    Siahlo, Andrei I.; Popov, Andrey M.; Poklonski, Nikolai A.; Lozovik, Yurii E.; Vyrko, Sergey A.; Ratkevich, Sergey V.

    2016-10-01

    The scheme and operational principles of the nanoelectromechanical memory cell based on the bending of a multi-layer graphene membrane by the electrostatic force are proposed. An analysis of the memory cell total energy as a function of the memory cell sizes is used to determine the sizes corresponding to a bistable memory cell with the conducting ON and non-conducting OFF states and to calculate the switching voltage between the OFF and ON states. It is shown that a potential barrier between the OFF and ON states is huge for practically all sizes of a bistable memory cell which excludes spontaneous switching and allows the proposed memory cell to be used for long-term archival storage.

  8. Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties.

    Science.gov (United States)

    Noroozi, Monir; Zakaria, Azmi; Radiman, Shahidan; Abdul Wahab, Zaidan

    2016-01-01

    In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene. PMID:27064575

  9. Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties.

    Science.gov (United States)

    Noroozi, Monir; Zakaria, Azmi; Radiman, Shahidan; Abdul Wahab, Zaidan

    2016-01-01

    In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene.

  10. Thinning and functionalization of few-layer graphene sheets by CF4 plasma treatment

    KAUST Repository

    Shen, Chao

    2012-05-24

    Structural changes of few-layer graphene sheets induced by CF4 plasma treatment are studied by optical microscopy and Raman spectroscopy, together with theoretical simulation. Experimental results suggest a thickness reduction of few-layer graphene sheets subjected to prolonged CF4 plasma treatment while plasma treatment with short time only leads to fluorine functionalization on the surface layer by formation of covalent bonds. Raman spectra reveal an increase in disorder by physical disruption of the graphene lattice as well as functionalization during the plasma treatment. The F/CF3 adsorption and the lattice distortion produced are proved by theoretical simulation using density functional theory, which also predicts p-type doping and Dirac cone splitting in CF4 plasma-treated graphene sheets that may have potential in future graphene-based micro/nanodevices.

  11. Facile Large Scale Production of Few-Layer Graphene Sheets by Shear Exfoliation in Volatile Solvent.

    Science.gov (United States)

    Akhtar, M Wasim; Park, Chan Woo; Kim, Youn Sop; Kim, Jong Seok

    2015-12-01

    Few layer graphene sheets were synthesized from natural graphite through mechanical shear mixer in 1-butanol as solvent. The liquid phase exfoliation of graphite through the shear mixer generated incising forces for 20 minutes which changed the large amount of graphite's flake into few layer graphene. The removal of solvent from the deposited dispersion was performed immediately by keeping at the room temperature. The deposited graphene thin films were characterized by AFM, HR-TEM, XRD, FT-IR and Raman Spectroscopy. The HR-TEM results showed the formation of few layers and well dispersed graphene. The Raman spectroscopy and XRD characterization confirmed the good quality and non-oxidized state of graphene. PMID:26682388

  12. Control of layer stacking in CVD graphene under quasi-static condition.

    Science.gov (United States)

    Subhedar, Kiran M; Sharma, Indu; Dhakate, Sanjay R

    2015-09-14

    The type of layer stacking in bilayer graphene has a significant influence on its electronic properties because of the contrast nature of layer coupling. Herein, different geometries of the reaction site for the growth of bilayer graphene by the chemical vapor deposition (CVD) technique and their effects on the nature of layer stacking are investigated. Micro-Raman mapping and curve fitting analysis confirmed the type of layer stacking for the CVD grown bilayer graphene. The samples grown with sandwiched structure such as quartz/Cu foil/quartz along with a spacer, between the two quartz plates to create a sealed space, resulted in Bernal or AB stacked bilayer graphene while the sample sandwiched without a spacer produced the twisted bilayer graphene. The contrast difference in the layer stacking is a consequence of the difference in the growth mechanism associated with different geometries of the reaction site. The diffusion dominated process under quasi-static control is responsible for the growth of twisted bilayer graphene in sandwiched geometry while surface controlled growth with ample and continual supply of carbon in sandwiched geometry along with a spacer, leads to AB stacked bilayer graphene. Through this new approach, an efficient technique is presented to control the nature of layer stacking. PMID:26245487

  13. Synthesis of ethanol-soluble few-layer graphene nanosheets for flexible and transparent conducting composite films

    International Nuclear Information System (INIS)

    We report a facile method of preparing few-layer graphene nanosheets (FLGs), which can be soluble in ethanol. Atomic force microscopy and high-resolution transmission electron microscopy studies reveal that FLGs have average thicknesses in the range of 2.6-2.8 nm, corresponding to 8-9 layers. A graphene/nafion composite film has a sheet resistance of 9.70 kΩ/sq at the transmittance of 74.5% (at 550 nm) while the nafion film on polyethylene terephthalate has a sheet resistance of 128 kΩ/sq at transmittance of 90.0%. For the cycling/bending test, almost no change in resistance was exhibited when the film was bent at an angle up to 1400, and no obvious deviation in resistance could be found after 100 bending cycles was applied. In addition, an FLGs-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite layer was demonstrated as the effective hole transporting layer to improve the hole transporting ability in an organic photovoltaic device, with which the power conversion efficiency was enhanced from 3.10% to 3.70%. The results demonstrated the promising applications of FLGs on graphene-based electronics, such as transparent electrode and flexible conducting film.

  14. A platform for large-scale graphene electronics--CVD growth of single-layer graphene on CVD-grown hexagonal boron nitride.

    Science.gov (United States)

    Wang, Min; Jang, Sung Kyu; Jang, Won-Jun; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Ruoff, Rodney S; Song, Young Jae; Lee, Sungjoo

    2013-05-21

    Direct chemical vapor deposition (CVD) growth of single-layer graphene on CVD-grown hexagonal boron nitride (h-BN) film can suggest a large-scale and high-quality graphene/h-BN film hybrid structure with a defect-free interface. This sequentially grown graphene/h-BN film shows better electronic properties than that of graphene/SiO2 or graphene transferred on h-BN film, and suggests a new promising template for graphene device fabrication. PMID:23576235

  15. Nanotribological properties of water films adsorbing atop, and absorbing below, graphene layers supported by metal substrates

    Science.gov (United States)

    Liu, Zijian; Curtis, C. K.; Stine, R.; Sheehan, P.; Krim, J.

    The tribological properties of graphite, a common lubricant with known sensitivity to the presence of water, have been studied extensively at the macroscopic and microscopic scales. Although far less attention has been devoted to the tribological properties of graphene, it has been established that the tribological response to the presence of water is dissimilar from that of graphite. We report here a quartz crystal microbalance study of the nanotribological properties of water films adsorbed/absorbed on graphene layers prepared by either chemical decomposition on nickel(111) substrates or transfer of freestanding graphene layers to aluminum substrates. Sliding friction levels of the water films were also measured for metal surfaces in the absence of a graphene layer. We observe very high friction levels for water adsorbed atop graphene on Ni(111) and very low levels for water on aluminum. For the case of graphene/aluminum, the data indicate that the water is absorbing between the graphene layer and the aluminum. Dissipation levels moreover indicate the presence of an interstitial water increases sliding friction between the graphene and the aluminum substrate Work supported by NSF and NRL.

  16. Synthesis of few layer graphene by non-transferred arc plasma system.

    Science.gov (United States)

    Baek, Jong-Jun; Kim, Tae-Hee; Park, Dong-Wha

    2013-11-01

    Graphene has recently been the focus of a great deal of attention owing to its outstanding properties, which include high mobility, high thermal conductivity and high structural stability. In this study, a few layer graphene was successfully synthesized from methane gas using a non-transferred direct current arc plasma system. Non-transferred thermal plasma offers high temperature, steep temperature gradient and high enthalpy to enhance the reaction kinetics of graphene synthesis. In order to prepare high quality few layer graphene, graphene products synthesized under several conditions was analyzed comparatively. Effects of gap distance between the plasma torch and graphite substrate, the flow rate of additional reactant gas, and different types of plasma forming gas on the synthesis of few layer graphene were investigated. Methane gas was injected into the plasma jet as a carbon source for the synthesis of graphene and a thermal plasma jet was generated by pure argon or a mixture of argon-hydrogen. The results revealed that hydrogen gas improved the quality of few layer graphene by inducing surface etching and increasing plasma power. PMID:24245266

  17. Electronic spin transport and spin precession in single graphene layers at room temperature

    NARCIS (Netherlands)

    Tombros, Nikolaos; Jozsa, Csaba; Popinciuc, Mihaita; Jonkman, Harry T.; van Wees, Bart J.

    2007-01-01

    Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic tra

  18. Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

    International Nuclear Information System (INIS)

    We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

  19. Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential.

    Science.gov (United States)

    Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

    2016-01-14

    To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. PMID:26658834

  20. Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential.

    Science.gov (United States)

    Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

    2016-01-14

    To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.

  1. A theoretical study of symmetry-breaking organic overlayers on single- and bi-layer graphene

    Science.gov (United States)

    Morales-Cifuentes, Josue; Einstein, T. L.

    2013-03-01

    An ``overlayer'' of molecules that breaks the AB symmetry of graphene can produce (modify) a band gap in single- (bi-) layer graphene.[2] Since the triangular shaped trimesic acid (TMA) molecule forms two familiar symmetry breaking configurations, we are motivated to model TMA physisorption on graphene surfaces in conjunction with experiments by Groce et al. at UMD. Using VASP, with ab initio van der Waals density functionals (vdW-DF), we simulate adsorption of TMA onto a graphene surface in several symmetry-breaking arrangements in order to predict/understand the effect of TMA adsorption on experimental observables. Supported by NSF-MRSEC Grant DMR 05-20471.

  2. Coatings of nanostructured pristine graphene-IrOx hybrids for neural electrodes: Layered stacking and the role of non-oxygenated graphene.

    Science.gov (United States)

    Pérez, E; Lichtenstein, M P; Suñol, C; Casañ-Pastor, N

    2015-10-01

    The need to enhance charge capacity in neural stimulation-electrodes is promoting the formation of new materials and coatings. Among all the possible types of graphene, pristine graphene prepared by graphite electrochemical exfoliation, is used in this work to form a new nanostructured IrOx-graphene hybrid (IrOx-eG). Graphene is stabilized in suspension by IrOx nanoparticles without surfactants. Anodic electrodeposition results in coatings with much smaller roughness than IrOx-graphene oxide. Exfoliated pristine graphene (eG), does not electrodeposit in absence of iridium, but IrOx-nanoparticle adhesion on graphene flakes drives the process. IrOx-eG has a significantly different electronic state than graphene oxide, and different coordination for carbon. Electron diffraction shows the reflection features expected for graphene. IrOx 1-2 nm cluster/nanoparticles are oxohydroxo-species and adhere to 10nm graphene platelets. eG induces charge storage capacity values five times larger than in pure IrOx, and if calculated per carbon atom, this enhancement is one order magnitude larger than the induced by graphene oxide. IrOx-eG coatings show optimal in vitro neural cell viability and function as cell culture substrates. The fully straightforward electrochemical exfoliation and electrodeposition constitutes a step towards the application of graphene in biomedical systems, expanding the knowledge of pristine graphene vs. graphene oxide, in bioelectrodes. PMID:26117758

  3. Coatings of nanostructured pristine graphene-IrOx hybrids for neural electrodes: Layered stacking and the role of non-oxygenated graphene

    International Nuclear Information System (INIS)

    The need to enhance charge capacity in neural stimulation-electrodes is promoting the formation of new materials and coatings. Among all the possible types of graphene, pristine graphene prepared by graphite electrochemical exfoliation, is used in this work to form a new nanostructured IrOx–graphene hybrid (IrOx–eG). Graphene is stabilized in suspension by IrOx nanoparticles without surfactants. Anodic electrodeposition results in coatings with much smaller roughness than IrOx–graphene oxide. Exfoliated pristine graphene (eG), does not electrodeposit in absence of iridium, but IrOx-nanoparticle adhesion on graphene flakes drives the process. IrOx–eG has a significantly different electronic state than graphene oxide, and different coordination for carbon. Electron diffraction shows the reflection features expected for graphene. IrOx 1–2 nm cluster/nanoparticles are oxohydroxo-species and adhere to 10 nm graphene platelets. eG induces charge storage capacity values five times larger than in pure IrOx, and if calculated per carbon atom, this enhancement is one order magnitude larger than the induced by graphene oxide. IrOx–eG coatings show optimal in vitro neural cell viability and function as cell culture substrates. The fully straightforward electrochemical exfoliation and electrodeposition constitutes a step towards the application of graphene in biomedical systems, expanding the knowledge of pristine graphene vs. graphene oxide, in bioelectrodes. - Highlights: • Pristine Graphene is incorporated in coatings as nanostructured IrOx–eG hybrid. • IrOx-nanoparticles drive the electrodeposition of graphene. • Hybrid CSC is one order of magnitude the charge capacity of IrOx. • Per carbon atom, the CSC increase is 35 times larger than for graphene oxide. • Neurons are fully functional on the coating

  4. Coatings of nanostructured pristine graphene-IrOx hybrids for neural electrodes: Layered stacking and the role of non-oxygenated graphene

    Energy Technology Data Exchange (ETDEWEB)

    Pérez, E. [Institut Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, E-08193, Bellaterra, Barcelona (Spain); Lichtenstein, M.P.; Suñol, C. [Institut d' Investigacions Biomèdiques de Barcelona (IIBB-CSIC), Institut d' Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), c/Rosselló 161, 08036 Barcelona (Spain); Casañ-Pastor, N., E-mail: nieves@icmab.es [Institut Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, E-08193, Bellaterra, Barcelona (Spain)

    2015-10-01

    The need to enhance charge capacity in neural stimulation-electrodes is promoting the formation of new materials and coatings. Among all the possible types of graphene, pristine graphene prepared by graphite electrochemical exfoliation, is used in this work to form a new nanostructured IrOx–graphene hybrid (IrOx–eG). Graphene is stabilized in suspension by IrOx nanoparticles without surfactants. Anodic electrodeposition results in coatings with much smaller roughness than IrOx–graphene oxide. Exfoliated pristine graphene (eG), does not electrodeposit in absence of iridium, but IrOx-nanoparticle adhesion on graphene flakes drives the process. IrOx–eG has a significantly different electronic state than graphene oxide, and different coordination for carbon. Electron diffraction shows the reflection features expected for graphene. IrOx 1–2 nm cluster/nanoparticles are oxohydroxo-species and adhere to 10 nm graphene platelets. eG induces charge storage capacity values five times larger than in pure IrOx, and if calculated per carbon atom, this enhancement is one order magnitude larger than the induced by graphene oxide. IrOx–eG coatings show optimal in vitro neural cell viability and function as cell culture substrates. The fully straightforward electrochemical exfoliation and electrodeposition constitutes a step towards the application of graphene in biomedical systems, expanding the knowledge of pristine graphene vs. graphene oxide, in bioelectrodes. - Highlights: • Pristine Graphene is incorporated in coatings as nanostructured IrOx–eG hybrid. • IrOx-nanoparticles drive the electrodeposition of graphene. • Hybrid CSC is one order of magnitude the charge capacity of IrOx. • Per carbon atom, the CSC increase is 35 times larger than for graphene oxide. • Neurons are fully functional on the coating.

  5. The Structural and Mechanical Properties of Graphene functionalized by Atomic Oxygen

    Directory of Open Access Journals (Sweden)

    I.K. Petrushenko

    2014-01-01

    Full Text Available In this paper, the structural and mechanical properties of graphene functionalized by atomic oxygen are investigated in the framework of the density functional theory. It was determined that the addition of oxygen leads to the deformation of the native graphene structure and reduction of its elastic properties. Here, a small functionalization leads to small structural changes, and, at the same time, to reduction of the Young's modulus of graphene. Larger functionalization causes structural deformation, with no significant changes of Young's modulus. It is shown that induced structural reorganization of the investigated models does not cause a rupture.

  6. Synthesis of Few-Layer Graphene Using DC PE-CVD

    Science.gov (United States)

    Kim, Jeong Hyuk; Castro, Edward Joseph D.; Hwang, Yong Gyoo; Lee, Choong Hun

    2011-12-01

    Few layer graphene (FLG) had been successfully grown on polycrystalline Ni films or foils on a large scale using DC Plasma Enhanced Chemical Vapor Deposition (DC PE-CVD) as a result of the Raman spectra drawn out of the sample. The size of graphene films is dependent on the area of the Ni film as well as the DC PE-CVD chamber size. Synthesis time has an effect on the quality of graphene produced. However, further analysis and experiments must be pursued to further identify the optimum settings and conditions of producing better quality graphene. Applied plasma voltage on the other hand, had an influence on the minimization of defects in the graphene grown. It has also presented a method of producing a free standing PMMA/graphene membrane on a FeCl3(aq) solution which could then be transferred to a desired substrate.

  7. Investigating change of properties in gallium ion irradiation patterned single-layer graphene

    Science.gov (United States)

    Wang, Quan; Dong, Jinyao; Bai, Bing; Xie, Guoxin

    2016-10-01

    Besides its excellent physical properties, graphene promises to play a significant role in electronics with superior properties, which requires patterning of graphene for device integration. Here, we presented the changes in properties of single-layer graphene before and after patterning using gallium ion beam. Combined with Raman spectra of graphene, the scanning capacitance microscopy (SCM) image confirmed that a metal-insulator transition occurred after large doses of gallium ion irradiation. The changes in work function and Raman spectra of graphene indicated that the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. The patterning width of graphene presented an increasing trend due to the scattering influence of the impurities and the substrate.

  8. Nanoscale strain engineering of graphene and graphene-based devices

    OpenAIRE

    Yeh, N. -C.; Hsu, C.-C.; Teague, M. L.; Wang, J.-Q.; Boyd, D A; Chen, C.-C.

    2016-01-01

    Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here, we describe the theoretical foundation f...

  9. Seeing graphene-based sheets

    Directory of Open Access Journals (Sweden)

    Jaemyung Kim

    2010-03-01

    Full Text Available Graphene-based sheets such as graphene, graphene oxide and reduced graphene oxide have stimulated great interest due to their promising electronic, mechanical and thermal properties. Microscopy imaging is indispensable for characterizing these single atomic layers, and oftentimes is the first measure of sample quality. This review provides an overview of current imaging techniques for graphene-based sheets and highlights a recently developed fluorescence quenching microscopy technique that allows high-throughput, high-contrast imaging of graphene-based sheets on arbitrary substrate and even in solution.

  10. Quantum transport in graphene

    NARCIS (Netherlands)

    Oostinga, J.B.

    2010-01-01

    After the experimental discovery of graphene -a single atomic layer of graphite- a scientific rush started to explore graphene’s electronic behaviour. Graphene is a fascinating two-dimensional electronic system, because its electrons behave as relativistic particles. Moreover, it is a promising mate

  11. Comparison of graphene oxide with reduced graphene oxide as hole extraction layer in organic photovoltaic cells.

    Science.gov (United States)

    Choi, Kyoung Soon; Park, Yensil; Kim, Soo Young

    2013-05-01

    A comparison was performed between the use of graphene oxide (GO) and reduced graphene oxide (rGO) as a hole extraction layer (HEL) in organic photovoltaic (OPV) cells with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester. Hydrazine hydrate (HYD) and the thermal method (Thermal) were adopted to change the GO to rGO. The GO HEL was deposited on an indium tin oxide electrode by spin coating, followed by the reduction process to form the rGO HELs. The success of the reduction processes was confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, transmittance, and 2-point probe method. The OPV cell with the GO (-3 nm) HEL exhibits an increased power conversion efficiency (PCE) as high as 2.5% under 100 mW/cm2 illumination under air mass conditions, which is higher than that of the OPV cell without HEL, viz. 1.78%. However, the PCE of the OPV cell with rGO HEL is not high as the values of 1.8% for the HYD-rGO and 1.9% for the Thermal-rGO. The ultraviolet photoemission spectroscopy results showed that the work function of GO was 4.7 eV, but those of HYD-rGO and Thermal-rGO were 4.2 eV and 4.5 eV, respectively. Therefore, it is considered that GO is adequate to extract the holes from the active layer, but HYD-rGO and Thermal-rGO are not appropriate to use as HELs in OPV cells from the viewpoint of the energy alignment.

  12. Graphene in silicon photovoltaic cells

    OpenAIRE

    Tap Béteille, Hélène; Caussat, Brigitte; Vergnes, Hugues; Trinsoutrot, Pierre; Conédéra, Véronique; Guerin, François; Gessinn, Frédéric; Grisolia, Jérémie; Launay, Jérôme; Arguel, Philippe

    2012-01-01

    Graphene is an allotrope of carbon. Its structure is one-atom-thick planar sheets of carbon atoms that are densely packed in a honeycomb crystal lattice [1]. The richness of optical and electronic properties of graphene attracts enormous interest. Its true potential seems to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited. The optical absorption of graphene layers is proportional to the number of lay...

  13. Nonlinear dynamics of bi-layered graphene sheet, double-walled carbon nanotube and nanotube bundle

    Science.gov (United States)

    Gajbhiye, Sachin O.; Singh, S. P.

    2016-05-01

    Due to strong van der Waals (vdW) interactions, the graphene sheets and nanotubes stick to each other and form clusters of these corresponding nanostructures, viz. bi-layered graphene sheet (BLGS), double-walled carbon nanotube (DWCNT) and nanotube bundle (NB) or ropes. This research work is concerned with the study of nonlinear dynamics of BLGS, DWCNT and NB due to nonlinear interlayer vdW forces using multiscale atomistic finite element method. The energy between two adjacent carbon atoms is represented by the multibody interatomic Tersoff-Brenner potential, whereas the nonlinear interlayer vdW forces are represented by Lennard-Jones 6-12 potential function. The equivalent nonlinear material model of carbon-carbon bond is used to model it based on its force-deflection relation. Newmark's algorithm is used to solve the nonlinear matrix equation governing the motion of the BLGS, DWCNT and NB. An impulse and harmonic excitations are used to excite these nanostructures under cantilevered, bridged and clamped boundary conditions. The frequency responses of these nanostructures are computed, and the dominant resonant frequencies are identified. Along with the forced vibration of these structures, the eigenvalue extraction problem of armchair and zigzag NB is also considered. The natural frequencies and corresponding mode shapes are extracted for the different length and boundary conditions of the nanotube bundle.

  14. 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

  15. Work function of few layer graphene covered nickel thin films measured with Kelvin probe force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Eren, B. [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland); Material Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Gysin, U.; Marot, L., E-mail: Laurent.marot@unibas.ch; Glatzel, Th.; Steiner, R.; Meyer, E. [Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)

    2016-01-25

    Few layer graphene and graphite are simultaneously grown on a ∼100 nm thick polycrystalline nickel film. The work function of few layer graphene/Ni is found to be 4.15 eV with a variation of 50 meV by local measurements with Kelvin probe force microscopy. This value is lower than the work function of free standing graphene due to peculiar electronic structure resulting from metal 3d-carbon 2p(π) hybridization.

  16. Tunable electromagnetic chirality induced by graphene inclusions in multi-layered metamaterials

    CERN Document Server

    Rizza, Carlo; Ciattoni, Alessandro

    2013-01-01

    We theoretically investigate the electromagnetic response of a novel class of multi-layered metamaterials obtained by alternating graphene sheets and dielectric layers, the whole structure not exhibiting a plane of reflection symmetry along the stacking direction. We show that the electromagnetic response of the structure is characterized by a magneto-electric coupling described by an effective chiral parameter. Exploiting the intrinsic tunability of the graphene-light coupling, we prove that one can tune both the dielectric and the chiral electromagnetic response by varying the graphene chemical potential through external voltage gating.

  17. Direct Measurement of the Fermi Energy in Graphene Using a Double Layer Structure

    OpenAIRE

    Kim, Seyoung; Jo, Insun; Dillen, D. C.; Ferrer, D. A.; Fallahazad, B.; Z. Yao; Banerjee, S K; Tutuc, E.

    2011-01-01

    We describe a technique which allows a direct measurement of the relative Fermi energy in an electron system using a double layer structure, where graphene is one of the two layers. We illustrate this method by probing the Fermi energy as a function of density in a graphene monolayer, at zero and in high magnetic fields. This technique allows us to determine the Fermi velocity, Landau level spacing, and Landau level broadening in graphene. We find that the N=0 Landau level broadening is large...

  18. Topological insulator Bi2Se3 thin films grown on double-layer graphene by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0±0.2x1011/cm2, and become a bulk insulator at a thickness of ten quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement.

  19. Correlating atomic structure and transport in suspended graphene nanoribbons.

    Science.gov (United States)

    Qi, Zhengqing John; Rodríguez-Manzo, Julio A; Botello-Méndez, Andrés R; Hong, Sung Ju; Stach, Eric A; Park, Yung Woo; Charlier, Jean-Christophe; Drndić, Marija; Johnson, A T Charlie

    2014-08-13

    Graphene nanoribbons (GNRs) are promising candidates for next generation integrated circuit (IC) components; this fact motivates exploration of the relationship between crystallographic structure and transport of graphene patterned at IC-relevant length scales (edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. Finally, we report on simulations of quantum transport in GNRs that are in qualitative agreement with the observations.

  20. Atomic-layer engineering of oxide superconductors

    Science.gov (United States)

    Bollinger, A. T.; Eckstein, J. N.; Dubuis, G.; Pavuna, D.; Božović, I.

    2012-02-01

    Molecular beam epitaxy technique has enabled synthesis of atomically smooth thin films, multilayers, and superlattices of cuprates and other complex oxides. Such heterostructures show high temperature superconductivity and enable novel experiments that probe the basic physics of this phenomenon. For example, it was established that high temperature superconductivity and anti-ferromagnetic phases separate on Ångström scale, while the pseudo-gap state apparently mixes with high temperature superconductivity over an anomalously large length scale (the "Giant Proximity Effect"). We review some recent experiments on such films and superlattices, including X-ray diffraction, atomic force microscopy, angle-resolved time of flight ion scattering and recoil spectroscopy, transport measurements, highresolution transmission electron microscopy, resonant X-ray scattering, low-energy muon spin resonance, and ultrafast photo-induced reflection high energy electron diffraction. The results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations, a discovery of interface high temperature superconductivity that occurs in a single CuO2 plane, evidence for local pairs, and establishing tight limits on the temperature range of superconducting fluctuations.

  1. Atomic-Layer Engineering of Oxide Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bozovic I.; Bollinger, A.T.; Eckstein, J.N.; Dubuis, G.; Pavuna, D.

    2012-03-01

    Molecular beam epitaxy technique has enabled synthesis of atomically smooth thin films, multilayers, and superlattices of cuprates and other complex oxides. Such heterostructures show high temperature superconductivity and enable novel experiments that probe the basic physics of this phenomenon. For example, it was established that high temperature superconductivity and anti-ferromagnetic phases separate on Angstrom scale, while the pseudo-gap state apparently mixes with high temperature superconductivity over an anomalously large length scale (the 'Giant Proximity Effect'). We review some recent experiments on such films and superlattices, including X-ray diffraction, atomic force microscopy, angle-resolved time of flight ion scattering and recoil spectroscopy, transport measurements, high resolution transmission electron microscopy, resonant X-ray scattering, low-energy muon spin resonance, and ultrafast photo-induced reflection high energy electron diffraction. The results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations, a discovery of interface high temperature superconductivity that occurs in a single CuO{sub 2} plane, evidence for local pairs, and establishing tight limits on the temperature range of superconducting fluctuations.

  2. Atomic Resolution Transmission Electron Microscopy of Defects in Hexagonal Boron Nitride and Graphene

    Science.gov (United States)

    Gibb, Ashley; Alem, Nasim; Song, Chengyu; Ciston, Jim; Zettl, Alex

    2014-03-01

    Monolayer sheets of sp2-bonded materials such as graphene and hexagonal boron nitride (h-BN) have been studied extensively due to their properties including high mechanical strength, thermal conductivity, stability, interesting electronic properties, and potential for integration into novel devices. Understanding the atomic scale structure of defects in these materials is important because defects can significantly affect the physical properties in these materials. In particular, understanding the dynamics of these defects explains much about the material's stability. We have synthesized h-BN and graphene using low pressure chemical vapor deposition and imaged defects using atomic resolution aberration corrected transmission electron microscopy.

  3. Numerical Investigation Of The Bombardment Of A Graphene Sheet By A Beam Of Carbon Atoms

    Directory of Open Access Journals (Sweden)

    O.V. Khomenko

    2009-01-01

    Full Text Available Classical molecular dynamics simulations of the bombardment of a graphene sheet by a beam of carbon atoms are carried out. Covalent bonds in the irradiated sample are described by the Brenner potential. The approximation of elastic balls interacting with graphene via the Lennard-Jones potential is used for particles in a beam. The influence of the energy and density of irradiating carbon atoms and of the presence of a thermostat on physical processes occurring during the collisions with the sample is investigated. Energy values of the particles in a beam, which are enough for the sample destruction, are defined.

  4. Absorption of THz electromagnetic wave in two mono-layers of graphene

    Science.gov (United States)

    Reynolds, Cole B.; Shoufie Ukhtary, M.; Saito, Riichiro

    2016-05-01

    Nearly 100% absorption of an electromagnetic (EM) wave in terahertz (THz) frequency is proposed for a system consisting of two mono-layers of graphene. Here, we demonstrate that the system can almost perfectly absorb an EM wave with frequency of 2 THz, even though we have a low electron mobility of roughly 1000 cm2  Vs‑1. The absorption probability is calculated by using the transfer matrix method. We show that the two mono-layers of the graphene system is needed to obtain nearly 100% absorption when the graphene has a relatively low Fermi energy. The absorption dependence on the distance between the graphene layers is also discussed.

  5. Deformation sensor based on polymer-supported discontinuous graphene multi-layer coatings

    Energy Technology Data Exchange (ETDEWEB)

    Carotenuto, G.; Schiavo, L.; Romeo, V.; Nicolais, L. [Institute for Composite and Biomedical Materials, National Research Council, Piazzale E. Fermi, 1, 80055 Portici (Italy)

    2014-05-15

    Graphene can be conveniently used in the modification of polymer surfaces. Graphene macromolecules are perfectly transparent to the visible light and electrically conductive, consequently these two properties can be simultaneously provided to polymeric substrates by surface coating with thin graphene layers. In addition, such coating process provides the substrates of: water-repellence, higher surface hardness, low-friction, self-lubrication, gas-barrier properties, and many other functionalities. Polyolefins have a non-polar nature and therefore graphene strongly sticks on their surface. Nano-crystalline graphite can be used as graphene precursor in some chemical processes (e.g., graphite oxide synthesis by the Hummer method), in addition it can be directly applied to the surface of a polyolefin substrate (e.g., polyethylene) to cover it by a thin graphene multilayer. In particular, the nano-crystalline graphite perfectly exfoliate under the application of a combination of shear and friction forces and the produced graphene single-layers perfectly spread and adhere on the polyethylene substrate surface. Such polymeric materials can be used as ITO (indium-tin oxide) substitute and in the fabrication of different electronic devices. Here the fabrication of transparent resistive deformation sensors based on low-density polyethylene films coated by graphene multilayers is described. Such devices are very sensible and show a high reversible and reproducible behavior.

  6. A further comparison of graphene and thin metal layers for plasmonics.

    Science.gov (United States)

    He, Xiaoyong; Gao, Pingqi; Shi, Wangzhou

    2016-05-21

    Which one is much more suitable for plasmonic materials, graphene or metal? To address this problem well, the plasmonic properties of thin metal sheets at different thicknesses have been investigated and compared with a graphene layer. As demonstration examples, the propagation properties of insulator-metal-insulator and metamaterials (MMs) structures are also shown. The results manifest that the plasmonic properties of the graphene layer are comparable to that of thin metal sheets with the thickness of tens of nanometers. For the graphene MMs structure, by using the periodic stack structure in the active region, the resonant transmission strength significantly improves. At the optimum period number, 3-5 periods of graphene/SiO2, the graphene MMs structure manifests good frequency and amplitude tunable properties simultaneously, and the resonant strength is also strong with large values of the Q-factor. Therefore, graphene is a good tunable plasmonic material. The results are very helpful to develop novel graphene plasmonic devices, such as modulators, antenna and filters.

  7. Deformation sensor based on polymer-supported discontinuous graphene multi-layer coatings

    International Nuclear Information System (INIS)

    Graphene can be conveniently used in the modification of polymer surfaces. Graphene macromolecules are perfectly transparent to the visible light and electrically conductive, consequently these two properties can be simultaneously provided to polymeric substrates by surface coating with thin graphene layers. In addition, such coating process provides the substrates of: water-repellence, higher surface hardness, low-friction, self-lubrication, gas-barrier properties, and many other functionalities. Polyolefins have a non-polar nature and therefore graphene strongly sticks on their surface. Nano-crystalline graphite can be used as graphene precursor in some chemical processes (e.g., graphite oxide synthesis by the Hummer method), in addition it can be directly applied to the surface of a polyolefin substrate (e.g., polyethylene) to cover it by a thin graphene multilayer. In particular, the nano-crystalline graphite perfectly exfoliate under the application of a combination of shear and friction forces and the produced graphene single-layers perfectly spread and adhere on the polyethylene substrate surface. Such polymeric materials can be used as ITO (indium-tin oxide) substitute and in the fabrication of different electronic devices. Here the fabrication of transparent resistive deformation sensors based on low-density polyethylene films coated by graphene multilayers is described. Such devices are very sensible and show a high reversible and reproducible behavior

  8. Deformation sensor based on polymer-supported discontinuous graphene multi-layer coatings

    Science.gov (United States)

    Carotenuto, G.; Schiavo, L.; Romeo, V.; Nicolais, L.

    2014-05-01

    Graphene can be conveniently used in the modification of polymer surfaces. Graphene macromolecules are perfectly transparent to the visible light and electrically conductive, consequently these two properties can be simultaneously provided to polymeric substrates by surface coating with thin graphene layers. In addition, such coating process provides the substrates of: water-repellence, higher surface hardness, low-friction, self-lubrication, gas-barrier properties, and many other functionalities. Polyolefins have a non-polar nature and therefore graphene strongly sticks on their surface. Nano-crystalline graphite can be used as graphene precursor in some chemical processes (e.g., graphite oxide synthesis by the Hummer method), in addition it can be directly applied to the surface of a polyolefin substrate (e.g., polyethylene) to cover it by a thin graphene multilayer. In particular, the nano-crystalline graphite perfectly exfoliate under the application of a combination of shear and friction forces and the produced graphene single-layers perfectly spread and adhere on the polyethylene substrate surface. Such polymeric materials can be used as ITO (indium-tin oxide) substitute and in the fabrication of different electronic devices. Here the fabrication of transparent resistive deformation sensors based on low-density polyethylene films coated by graphene multilayers is described. Such devices are very sensible and show a high reversible and reproducible behavior.

  9. Preparation and capacitance properties of graphene/NiAl layered double-hydroxide nanocomposite.

    Science.gov (United States)

    Wang, Zhuo; Zhang, Xin; Wang, Junhui; Zou, Linda; Liu, Zhaotie; Hao, Zhengping

    2013-04-15

    Graphene/NiAl layered double-hydroxide (LDH) composite with high capacitive properties has been prepared in a friendly one-step process. It is found that NiAl-LDH is formed in the addition of precipitator agent (NaOH and NaNO3) by hydrothermal method, at the same time graphene oxide (GO) is reduced to graphene. The morphology and structure of the obtained material are examined by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM) techniques. It is revealed that the NiAl-LDH disperses well on the surface of graphene and the formation of NiAl-LDH nanoparticles is beneficial to the peeling of graphene (RGO). More importantly, the addition of NiAl-LDH to graphene endows the materials with desirable specific surface areas and higher porosity. These structural advantages result in higher specific capacitance compared with pristine graphene. Electrochemical property investigations show that the graphene/NiAl-LDH had a higher specific capacitance than graphene. PMID:23411355

  10. Highly brilliant synchrotron radiation operando spectromicroscopy to bridge a gap between material electronic properties and device performances of 2D atomic layers

    International Nuclear Information System (INIS)

    Si-based electronics has reached an ultimate fabrication level (22 nm design rule), which makes further progress hardly achieved. Therefore, 2D atomic layers including graphene have been extensively studied as next-generation device materials to supplement device functions which Si-based electronics cannot serve. Unfortunately, however, there is a gap between material electronic properties and device performances in the researches on 2D atomic layers. We demonstrate soft x-ray operando spectromicroscopies, photoemission electron microscopy (PEEM) and 3D scanning photoelectron microscopy (3D nano-ESCA), in SPring-8 to bridge the gap in graphene research. The complementary use of these operando spectromicroscopies enables us to probe both valence band and conduction bands of graphene channels under operation, resulting in revealing the effects of the interfaces with contact metal and oxide. The significance of the operando spectromicroscopy is now recognized, resulting in the adoption as a major research target in NEDO academic-industrial alliance project. (author)

  11. Realization of a tunable artificial atom at a supercritically charged vacancy in graphene

    Science.gov (United States)

    Mao, Jinhai; Jiang, Yuhang; Moldovan, Dean; Li, Guohong; Watanabe, Kenji; Taniguchi, Takashi; Masir, Massoud Ramezani; Peeters, Francois M.; Andrei, Eva Y.

    2016-06-01

    Graphene's remarkable electronic properties have fuelled the vision of a graphene-based platform for lighter, faster and smarter electronics and computing applications. One of the challenges is to devise ways to tailor graphene's electronic properties and to control its charge carriers. Here we show that a single-atom vacancy in graphene can stably host a local charge and that this charge can be gradually built up by applying voltage pulses with the tip of a scanning tunnelling microscope. The response of the conduction electrons in graphene to the local charge is monitored with scanning tunnelling and Landau level spectroscopy, and compared to numerical simulations. As the charge is increased, its interaction with the conduction electrons undergoes a transition into a supercritical regime where itinerant electrons are trapped in a sequence of quasi-bound states which resemble an artificial atom. The quasi-bound electron states are detected by a strong enhancement of the density of states within a disc centred on the vacancy site which is surrounded by halo of hole states. We further show that the quasi-bound states at the vacancy site are gate tunable and that the trapping mechanism can be turned on and off, providing a mechanism to control and guide electrons in graphene.

  12. Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene

    Science.gov (United States)

    Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; Son, Young-Woo; Park, Yeonggu; Lee, Mi Jung; Byun, Ik-Su; Kim, Jin-Soo; Choi, Choon-Gi; Bostwick, Aaron; Rotenberg, Eli; Park, Bae Ho

    2014-01-01

    Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene. PMID:25434431

  13. Highly atom-economic synthesis of graphene/Mn₃O₄ hybrid composites for electrochemical supercapacitors.

    Science.gov (United States)

    Jiangying, Qu; Feng, Gao; Quan, Zhou; Zhiyu, Wang; Han, Hu; Beibei, Li; Wubo, Wan; Xuzhen, Wang; Jieshan, Qiu

    2013-04-01

    A highly atom-economic procedure for the preparation of reduced graphene oxide/Mn3O4 (rGO/Mn3O4) composites is reported. Pristine graphene oxide/manganese sulfate (GO/MnSO4) suspension produced by modified Hummers method is utilized with high efficiency, which has been in situ converted into GO/Mn3O4 hybrid composite by air oxidation, then into rGO/Mn3O4 composite by means of dielectric barrier discharge (DBD) plasma-assisted deoxygenation. The Mn3O4 content of the rGO/Mn3O4 composites can be readily tailored. It is observed that Mn3O4 nanoparticles of 15-24 nm are well-dispersed on graphene sheets with Mn3O4 loading as high as 90%. The specific capacitance of the as-prepared rGO/Mn3O4 hybrids with 90% Mn3O4 reaches 193 F g(-1) when employed as the electrode material in neutral Na2SO4 electrolyte solutions (76 F g(-1) for pristine graphene and 95 F g(-1) for pure Mn3O4), which indicates the positive synergetic effects from both graphene and attached Mn3O4. The method developed in this study should offer a new technique for the large scale and highly atom-economic production of graphene/MnOx composites for many applications. PMID:23459860

  14. Epitaxial B-Graphene: Large-Scale Growth and Atomic Structure.

    Science.gov (United States)

    Usachov, Dmitry Yu; Fedorov, Alexander V; Petukhov, Anatoly E; Vilkov, Oleg Yu; Rybkin, Artem G; Otrokov, Mikhail M; Arnau, Andrés; Chulkov, Evgueni V; Yashina, Lada V; Farjam, Mani; Adamchuk, Vera K; Senkovskiy, Boris V; Laubschat, Clemens; Vyalikh, Denis V

    2015-07-28

    Embedding foreign atoms or molecules in graphene has become the key approach in its functionalization and is intensively used for tuning its structural and electronic properties. Here, we present an efficient method based on chemical vapor deposition for large scale growth of boron-doped graphene (B-graphene) on Ni(111) and Co(0001) substrates using carborane molecules as the precursor. It is shown that up to 19 at. % of boron can be embedded in the graphene matrix and that a planar C-B sp(2) network is formed. It is resistant to air exposure and widely retains the electronic structure of graphene on metals. The large-scale and local structure of this material has been explored depending on boron content and substrate. By resolving individual impurities with scanning tunneling microscopy we have demonstrated the possibility for preferential substitution of carbon with boron in one of the graphene sublattices (unbalanced sublattice doping) at low doping level on the Ni(111) substrate. At high boron content the honeycomb lattice of B-graphene is strongly distorted, and therefore, it demonstrates no unballanced sublattice doping. PMID:26121999

  15. Morphology Control of Zinc Oxide Nanostructure on Single Layer Graphene.

    Science.gov (United States)

    Ahn, Seungbae; Vijayarangamuthu, K; Jeon, Ki-Jeon

    2016-05-01

    Various morphologies of zinc oxide (ZnO) nanostructures on single layer graphene were synthesized by electrodeposition method. The current density was utilized to control the morphology of the ZnO. The Scanning Electron Microscope (SEM) was used to examine the surface morphology of the samples. SEM analysis shows morphology changes to nanorod, flower, and flakes with increase in the current density from 0.1, 0.2, and 0.3 mA/cm(-1) respectively. The XRD, XPS, and Raman spectroscopy were adopted to characterize the ZnO nanostructure and to understand the formation of various morphologies. The Raman result clearly shows extra modes due to for flakes structure caused by c-axis orientation along the substrate direction. Further, XPS data also supports formation of ZnO without any other intermediate compound such as Zn(OH)2. The formation of various morphologies was correlated to the formation different ratio of Zn2+ and OH- ions and the change in growth direction due to various current densities. PMID:27483766

  16. Spectroscopic detection of atom-surface interactions in an atomic vapour layer with nanoscale thickness

    CERN Document Server

    Whittaker, K A; Hughes, I G; Sargsyan, A; Sarkisyan, D; Adams, C S

    2015-01-01

    We measure the resonance line shape of atomic vapor layers with nanoscale thickness confined between two sapphire windows. The measurement is performed by scanning a probe laser through resonance and collecting the scattered light. The line shape is dominated by the effects of Dicke narrowing, self-broadening, and atom-surface interactions. By fitting the measured line shape to a simple model we discuss the possibility to extract information about the atom-surface interaction.

  17. Vertically aligned GaAs nanowires on graphite and few-layer graphene: generic model and epitaxial growth.

    Science.gov (United States)

    Munshi, A Mazid; Dheeraj, Dasa L; Fauske, Vidar T; Kim, Dong-Chul; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

    2012-09-12

    By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells. PMID:22889019

  18. Mesoporous Few-Layer Graphene Platform for Affinity Biosensing Application.

    Science.gov (United States)

    Ali, Md Azahar; Singh, Chandan; Mondal, Kunal; Srivastava, Saurabh; Sharma, Ashutosh; Malhotra, Bansi D

    2016-03-30

    A label-free, highly reproducible, sensitive, and selective biosensor is proposed using antiapolipoprotein B 100 (AAB) functionalized mesoporous few-layer reduced graphene oxide and nickel oxide (rGO-NiO) nanocomposite for detection of low density lipoprotein (LDL) molecules. The formation of mesoporous rGO-NiO composite on indium tin oxide conductive electrode has been accomplished via electrophoretic technique using colloidal suspension of rGO sheets and NiO nanoparticles. This biosensor shows good stability obtained by surface conjugation of antibody AAB molecules with rGO-NiO matrix by EDC-NHS coupling chemistry. The defect-less few layer rGO sheets, NiO nanoparticles (nNiO) and formation of nanocomposite has been confirmed by Raman mapping, electron microscopic studies, X-ray diffraction, and electrochemical techniques. The synthesized rGO-NiO composite is mesoporous dominated with a small percentage of micro and macroporous structure as is evident by the results of Brunauer-Emmett-Teller experiment. Further, the bioconjugation of AAB with rGO-NiO has been investigated by Fourier transform-infrared spectroscopy studies. The kinetic studies for binding of antigen-antibody (LDL-AAB) and analytical performance of this biosensor have been evaluated by the impedance spectroscopic method. This biosensor exhibits an excellent sensitivity of 510 Ω (mg/dL)(-1) cm(-2) for detection of LDL molecules and is sensitive to 5 mg/dL concentration of LDL in a wide range of 0-130 mg/dL. Thus, this fabricated biosensor is an efficient and highly sensitive platform for the analysis of other antigen-antibody interactions and biomolecules detection. PMID:26950488

  19. Failure of multi-layer graphene coatings in acidic media

    DEFF Research Database (Denmark)

    Yu, Feng; Stoot, Adam Carsten; Bøggild, Peter;

    2016-01-01

    Being impermeable to all gases, graphene has been proposed as an effective ultrathin barrier film and protective coating. However, here it is shown how the gastight property of graphene-based coatings may indirectly lead to their catastrophic failure under certain conditions. When nickel coated w...

  20. Electrochemical atomic layer deposition of copper nanofilms on ruthenium

    Science.gov (United States)

    Gebregziabiher, Daniel K.; Kim, Youn-Geun; Thambidurai, Chandru; Ivanova, Valentina; Haumesser, Paul-Henri; Stickney, John L.

    2010-04-01

    As ULSI scales to smaller and smaller dimensions, it has become necessary to form layers of materials only a few nm thick. In addition, trenches are now being incorporated in ULSI formation which require conformal coating and will not be amenable to CMP. Atomic layer deposition (ALD) is being developed to address such issues. ALD is the formation of materials layer by layer using self-limiting reactions. This article describes the formation of Cu seed layers (for the Cu damascene process) on a Ru barrier layer. The deposit was formed by the electrochemical analog of ALD, using electrochemical self-limiting reactions which are referred to as underpotential deposition (UPD). Monolayer restricted galvanic displacement was used to form atomic layers of Cu. First Pb UPD was deposited, forming a sacrificial layer, and then a Cu +2 solution was flushed into the cell and Pb was exchanged for Cu. A linear dependence was shown for Cu growth over 8 ALD cycles, and STM showed a conformal deposition, as expected for an ALD process. Relative Cu coverages were determined using Auger electron spectroscopy, while absolute Cu coverages were obtained from coulometry during oxidative stripping of the deposits. Use of a Cl - containing electrolyte results in Cu deposits covered with an atomic layer of Cl atoms, which have been shown to protect the surfaced from oxidation during various stages of the deposition process. The 10 nm thick Ru substrates were formed on Si(1 0 0) wafers, and were partially oxidized upon receipt. Electrochemical reduction, prior to Cu deposition, removed the oxygen and some traces of carbon, the result of transport. Ion bombardment proved to clean all oxygen and carbon traces from the surface.

  1. An Introduction to Atomic Layer Deposition with Thermal Applications

    Science.gov (United States)

    Dwivedi, Vivek H.

    2015-01-01

    Atomic Layer Deposition (ALD) is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment. Through the introduction of paired precursor gases thin films can be deposited on a myriad of substrates ranging from glass, polymers, aerogels, and metals to high aspect ratio geometries. This talk will focus on the utilization of ALD for engineering applications.

  2. Dissipative optomechanics of a single-layer graphene in a microcavity

    CERN Document Server

    Xiao, Lin-Da; Liu, Yong-Chun; Yan, Meng-Yuan; Xiao, Yun-Feng

    2014-01-01

    We study the optomechanical coupling of a single-layer graphene with a high-Q Fabry-P?erot microcavity in the membrane-in-the-middle configuration. In ordinary dissipative coupling systems, mechanical oscillators modulate the loss associated with the input coupling of the cavity mode; while in our system, the graphene oscillator couples dissipatively with the cavity mode through modulating its absorption loss. By analyzing the effects of the interband transition of a graphene suspended near the node of the cavity field, we obtain strong and tunable dissipative coupling without excessively reducing the optical quality factor. Finally, it is found that the exural mode of the graphene could be cooled down to its ground state in the present coupling system. This study provides new insights for graphene optomechanics in the visible range.

  3. Preservation of the Pt(100) surface reconstruction after growth of a continuous layer of graphene

    DEFF Research Database (Denmark)

    Nilsson, Louis; Andersen, Mie; Bjerre, Jacob;

    2012-01-01

    Scanning tunneling microscopy shows that a layer of graphene can be grown on the hex-reconstructed Pt(100) surface and that the reconstruction is preserved after growth. A continuous sheet of graphene can be grown across domain boundaries and step edges without loss of periodicity or change...... to accommodation of edge dislocations. The defect formation energy and the induced buckling of the graphene have been characterized by DFT calculations....... in direction. Density functional theory calculations on a simple model system support the observation that the graphene can have different rotation angles relative to the hex-reconstructed Pt surface. The graphene sheet direction can be changed by incorporating pentagon-heptagon defects giving rise...

  4. Iridium wire grid polarizer fabricated using atomic layer deposition

    Directory of Open Access Journals (Sweden)

    Knez Mato

    2011-01-01

    Full Text Available Abstract In this work, an effective multistep process toward fabrication of an iridium wire grid polarizer for UV applications involving a frequency doubling process based on ultrafast electron beam lithography and atomic layer deposition is presented. The choice of iridium as grating material is based on its good optical properties and a superior oxidation resistance. Furthermore, atomic layer deposition of iridium allows a precise adjustment of the structural parameters of the grating much better than other deposition techniques like sputtering for example. At the target wavelength of 250 nm, a transmission of about 45% and an extinction ratio of 87 are achieved.

  5. A Study on Field Emission Characteristics of Planar Graphene Layers Obtained from a Highly Oriented Pyrolyzed Graphite Block.

    KAUST Repository

    Lee, Seok Woo

    2009-07-12

    This paper describes an experimental study on field emission characteristics of individual graphene layers for vacuum nanoelectronics. Graphene layers were prepared by mechanical exfoliation from a highly oriented pyrolyzed graphite block and placed on an insulating substrate, with the resulting field emission behavior investigated using a nanomanipulator operating inside a scanning electron microscope. A pair of tungsten tips controlled by the nanomanipulator enabled electric connection with the graphene layers without postfabrication. The maximum emitted current from the graphene layers was 170 nA and the turn-on voltage was 12.1 V.

  6. Atomically-Smooth MgO films grown on Epitaxial Graphene by Pulsed Laser Deposition

    Science.gov (United States)

    Stuart, Sean; Sandin, Andreas; Rowe, Jack; Dougherty, Dan; Ulrich, Marc

    2013-03-01

    The growth of high quality insulating films on graphene is a crucial materials science task for graphene electronic and spintronic applications. It has been demonstrated that direct spin injection from a magnetic electrode to graphene is possible using MgO tunnel barriers of sufficient quality. We have used pulsed laser deposition (PLD) to grow thin magnesium oxide films directly on epitaxial graphene on SiC(0001). We observe very smooth film morphologies (typical rms roughness of ~ 0.4 nm) that are nearly independent of film thickness and conform to the substrate surface which had ~ 0.2 nm rms roughness. Surface roughness of 0.04 nm have been recorded for ~ 1nm films with no pinholes seen by AFM. XPS and XRD data show non crystalline, hydroxylated MgO films with uniform coverage. This work shows that PLD is a good technique to produce graphene-oxide interfaces without pre-deposition of an adhesion layer or graphene functionalization. The details and kinetics of the deposition process will be described with comparisons being made to other dielectric-on-graphene deposition approaches. Funded by ARO Staff Research Contract # W911NF.

  7. Coherent nonlinear electromagnetic response in twisted bilayer and few-layer graphene

    Indian Academy of Sciences (India)

    Vipin Kumar; Enamullah; Upendra Kumar; Girish S Setlur

    2014-10-01

    The phenomenon of Rabi oscillations far from resonance is described in bilayer and few-layer graphene. These oscillations in the population and polarization at the Dirac point in -layer graphene are seen in the nth harmonic termin the external driving frequency. The underlying reason behind these oscillations is attributable to the pseudospin degree of freedom possessed by all these systems. Conventional Rabi oscillations, which occur only near resonance, are seen in multiple harmonics in multilayer graphene. However, the experimentally measurable current density exhibits anomalous behaviour only in the first harmonic in all the graphene systems. A fully numerical solution of the optical Bloch equations is in complete agreement with the analytical results, thereby justifying the approximation schemes used in the latter. The same phenomena are also described in twisted bilayer graphene with and without an electric potential difference between the layers. It is found that the anomalous Rabi frequency is strongly dependent on twist angle for weak applied fields – a feature absent in single-layer graphene, whereas the conventional Rabi frequency is relatively independent of the twist angle.

  8. Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit

    Energy Technology Data Exchange (ETDEWEB)

    Fakih, Ibrahim, E-mail: ibrahim.fakih@mail.mcgill.ca; Sabri, Shadi; Szkopek, Thomas, E-mail: thomas.szkopek@mcgill.ca [Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec H3A 2A7 (Canada); Mahvash, Farzaneh [Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec H3A 2A7 (Canada); Département de Chimie et Biochimie, Universite du Québec à Montréal, Montreal, Quebec H3C 3P8 (Canada); Nannini, Matthieu [McGill Nanotools Microfab, McGill University, Montreal, Quebec H3A 2A7 (Canada); Siaj, Mohamed [Département de Chimie et Biochimie, Universite du Québec à Montréal, Montreal, Quebec H3C 3P8 (Canada)

    2014-08-25

    We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying the Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 10{sup 14} sites/cm{sup 2}. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.

  9. Few layers isolated graphene domains grown on copper foils by microwave surface wave plasma CVD using camphor as a precursor

    Science.gov (United States)

    Ram Aryal, Hare; Adhikari, Sudip; Uchida, Hideo; Wakita, Koichi; Umeno, Masayoshi

    2016-03-01

    Few layers isolated graphene domains were grown by microwave surface wave plasma CVD technique using camphor at low temperature. Graphene nucleation centers were suppressed on pre-annealed copper foils by supplying low dissociation energy. Scanning electron microscopy study of time dependent growth reveals that graphene nucleation centers were preciously suppressed, which indicates the possibility of controlled growth of large area single crystal graphene domains by plasma processing. Raman spectroscopy revealed that the graphene domains are few layered which consist of relatively low defects.

  10. Near-field microwave microscopy of high-κ oxides grown on graphene with an organic seeding layer

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander, E-mail: tseleva@ornl.gov; Kalinin, Sergei V. [Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge, Tennessee 37831 (United States); Sangwan, Vinod K.; Jariwala, Deep; Lauhon, Lincoln J. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Marks, Tobin J.; Hersam, Mark C. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Department of Chemistry, Northwestern University, Evanston, Illinois 60208 (United States)

    2013-12-09

    Near-field scanning microwave microscopy (SMM) is used for non-destructive nanoscale characterization of Al{sub 2}O{sub 3} and HfO{sub 2} films grown on epitaxial graphene on SiC by atomic layer deposition using a self-assembled perylene-3,4,9,10-tetracarboxylic dianhydride seeding layer. SMM allows imaging of buried inhomogeneities in the dielectric layer with a spatial resolution close to 100 nm. The results indicate that, while topographic features on the substrate surface cannot be eliminated as possible sites of defect nucleation, the use of a vertically heterogeneous Al{sub 2}O{sub 3}/HfO{sub 2} stack suppresses formation of large outgrowth defects in the oxide film, ultimately improving lateral uniformity of the dielectric film.

  11. Raman enhancement effect on two-dimensional layered materials: graphene, h-BN and MoS2.

    Science.gov (United States)

    Ling, Xi; Fang, Wenjing; Lee, Yi-Hsien; Araujo, Paulo T; Zhang, Xu; Rodriguez-Nieva, Joaquin F; Lin, Yuxuan; Zhang, Jin; Kong, Jing; Dresselhaus, Mildred S

    2014-06-11

    Realizing Raman enhancement on a flat surface has become increasingly attractive after the discovery of graphene-enhanced Raman scattering (GERS). Two-dimensional (2D) layered materials, exhibiting a flat surface without dangling bonds, were thought to be strong candidates for both fundamental studies of this Raman enhancement effect and its extension to meet practical applications requirements. Here, we study the Raman enhancement effect on graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2), by using the copper phthalocyanine (CuPc) molecule as a probe. This molecule can sit on these layered materials in a face-on configuration. However, it is found that the Raman enhancement effect, which is observable on graphene, hBN, and MoS2, has different enhancement factors for the different vibrational modes of CuPc, depending strongly on the surfaces. Higher-frequency phonon modes of CuPc (such as those at 1342, 1452, 1531 cm(-1)) are enhanced more strongly on graphene than that on h-BN, while the lower frequency phonon modes of CuPc (such as those at 682, 749, 1142, 1185 cm(-1)) are enhanced more strongly on h-BN than that on graphene. MoS2 demonstrated the weakest Raman enhancement effect as a substrate among these three 2D materials. These differences are attributed to the different enhancement mechanisms related to the different electronic properties and chemical bonds exhibited by the three substrates: (1) graphene is zero-gap semiconductor and has a nonpolar C-C bond, which induces charge transfer (2) h-BN is insulating and has a strong B-N bond, while (3) MoS2 is semiconducting with the sulfur atoms on the surface and has a polar covalent bond (Mo-S) with the polarity in the vertical direction to the surface. Therefore, the different Raman enhancement mechanisms differ for each material: (1) charge transfer may occur for graphene; (2) strong dipole-dipole coupling may occur for h-BN, and (3) both charge transfer and dipole-dipole coupling may

  12. High-yield synthesis of few-layer graphene flakes through electrochemical expansion of graphite in propylene carbonate electrolyte.

    Science.gov (United States)

    Wang, Junzhong; Manga, Kiran Kumar; Bao, Qiaoliang; Loh, Kian Ping

    2011-06-15

    High-yield production of few-layer graphene flakes from graphite is important for the scalable synthesis and industrial application of graphene. However, high-yield exfoliation of graphite to form graphene sheets without using any oxidation process or super-strong acid is challenging. Here we demonstrate a solution route inspired by the lithium rechargeable battery for the high-yield (>70%) exfoliation of graphite into highly conductive few-layer graphene flakes (average thickness salts and organic solvents under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The dispersible graphene can be ink-brushed to form highly conformal coatings of conductive films (15 ohm/square at a graphene loading of <1 mg/cm(2)) on commercial paper. PMID:21557613

  13. Large networks of vertical multi-layer graphenes with morphology-tunable magnetoresistance.

    Science.gov (United States)

    Yue, Zengji; Levchenko, Igor; Kumar, Shailesh; Seo, Donghan; Wang, Xiaolin; Dou, Shixue; Ostrikov, Kostya Ken

    2013-10-01

    We report on the comparative study of magnetotransport properties of large-area vertical few-layer graphene networks with different morphologies, measured in a strong (up to 10 T) magnetic field over a wide temperature range. The petal-like and tree-like graphene networks grown by a plasma enhanced CVD process on a thin (500 nm) silicon oxide layer supported by a silicon wafer demonstrate a significant difference in the resistance-magnetic field dependencies at temperatures ranging from 2 to 200 K. This behaviour is explained in terms of the effect of electron scattering at ultra-long reactive edges and ultra-dense boundaries of the graphene nanowalls. Our results pave a way towards three-dimensional vertical graphene-based magnetoelectronic nanodevices with morphology-tuneable anisotropic magnetic properties. PMID:23603856

  14. A highly sensitive pressure sensor using a double-layered graphene structure for tactile sensing.

    Science.gov (United States)

    Chun, Sungwoo; Kim, Youngjun; Oh, Hyeong-Sik; Bae, Giyeol; Park, Wanjun

    2015-07-21

    In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (-0.24 kPa(-1)) and high pressure (0.039 kPa(-1)) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures.

  15. The effect of gamma-irradiation on few-layered graphene materials

    Energy Technology Data Exchange (ETDEWEB)

    Ansón-Casaos, A., E-mail: alanson@icb.csic.es [Instituto de Carboquímica, ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza (Spain); Puértolas, J.A. [Department of Materials Science and Technology-EINA, Instituto de Investigación en Ingeniería de Aragón, I3A, Universidad de Zaragoza, E-50018 Zaragoza (Spain); Pascual, F.J. [Department of Materials Science and Technology-EINA, Instituto de Investigación en Ingeniería de Aragón, I3A, Universidad de Zaragoza, E-50018 Zaragoza (Spain); Centro Universitario de la Defensa de Zaragoza, Academia General Militar, Carretera de Huesca s/n, E-50090 Zaragoza (Spain); Hernández-Ferrer, J. [Instituto de Carboquímica, ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza (Spain); Castell, P. [AITIIP Technological Center, Polígono Industrial Empresarium, C/Romero 12, 50720 Zaragoza (Spain); Benito, A.M.; Maser, W.K.; Martínez, M.T. [Instituto de Carboquímica, ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza (Spain)

    2014-05-01

    Highlights: • The effect of γ-irradiation was studied on two graphene materials. • Both graphene materials were examined in their oxidized and post-reduced forms. • We comparatively characterized γ-irradiation and chemical reduction effects. • Irradiation caused modifications in the graphene carbon lattice. • Small changes in the oxygen content occurred during irradiation. - Abstract: The effect of γ-irradiation on the structure and composition of chemically synthesized few-layered graphene materials was studied. Fully oxidized graphene oxide and graphene nanoribbons, as well as their respective chemically post-reduced forms, were treated under γ-irradiation in an air-sealed environment. Three different irradiation doses of 60, 90 and 150 kGy were applied. Structure and composition of the irradiated materials were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The XRD patterns were not affected by γ-irradiation, and small changes were observed in the FTIR and TGA results. However, significant modifications were detected by Raman spectroscopy and XPS, particularly in the Raman G/D band intensity ratios and in the C 1s XPS profiles. Comparatively, the changes in Raman and XPS spectra after γ-irradiation were even greater than those occurring during the chemical reduction of graphene oxides. Our results indicate that the graphene carbon lattice was strongly affected by γ-irradiation, but the materials experienced small variations in their oxygen content.

  16. Electrical characterization of graphene oxide and organic dielectric layers based on thin film transistor

    International Nuclear Information System (INIS)

    Highlights: • We report the synthesis of graphene oxide nanosheets and electrical characterization of graphene oxide based thin film transistor. • Graphene oxide (GO) nanosheets were prepared by using modified Hummers method. • We used insulator layers which are polymethylmethacrylate (PMMA) and polyvinyl phenol (PVP) for graphene oxide based thin flim transistor. - Abstract: We have studied the electrical characteristics of graphene oxide based thin flim transistor with the polymer insulators such as polymethyl methacrylate (PMMA) and poly-4-vinylphenol (PVP). Graphene oxide (GO) nanosheets were prepared by using modified Hummers method. The structural properties of GO nanosheets were characterized with Ultraviolet Visible (UV–vis), FT-IR spectroscopy and X-rays diffraction (XRD). Graphene oxide based thin flim transistor (GO-TFT) was prepared by a spin-coating and thermal evaporation technique. The electrical characterization of GO-TFT was analyzed by output and transfer characteristics by using Keithley-4200 semiconductor characterization system (SCS). The graphene oxide based thin flim transistor devices show p-type semiconducting behavior. The mobility, threshold voltage, sub-threshold swing value and Ion/Ioff of GO-TFT were found to be 0.105 cm2 V−1 s−1, −8.7 V, 4.03 V/decade and 10, respectively

  17. Basics of quantum field theory of electromagnetic interaction processes in single-layer graphene

    Science.gov (United States)

    Hieu Nguyen, Van

    2016-09-01

    The content of this work is the study of electromagnetic interaction in single-layer graphene by means of the perturbation theory. The interaction of electromagnetic field with Dirac fermions in single-layer graphene has a peculiarity: Dirac fermions in graphene interact not only with the electromagnetic wave propagating within the graphene sheet, but also with electromagnetic field propagating from a location outside the graphene sheet and illuminating this sheet. The interaction Hamiltonian of the system comprising electromagnetic field and Dirac fermions fields contains the limits at graphene plane of electromagnetic field vector and scalar potentials which can be shortly called boundary electromagnetic field. The study of S-matrix requires knowing the limits at graphene plane of 2-point Green functions of electromagnetic field which also can be shortly called boundary 2-point Green functions of electromagnetic field. As the first example of the application of perturbation theory, the second order terms in the perturbative expansions of boundary 2-point Green functions of electromagnetic field as well as of 2-point Green functions of Dirac fermion fields are explicitly derived. Further extension of the application of perturbation theory is also discussed.

  18. In situ formation of graphene layers on graphite surfaces for efficient anodes of microbial fuel cells.

    Science.gov (United States)

    Tang, Jiahuan; Chen, Shanshan; Yuan, Yong; Cai, Xixi; Zhou, Shungui

    2015-09-15

    Graphene can be used to improve the performance of the anode in a microbial fuel cell (MFC) due to its good biocompatibility, high electrical conductivity and large surface area. However, the chemical production and modification of the graphene on the anode are environmentally hazardous because of the use of various harmful chemicals. This study reports a novel method based on the electrochemical exfoliation of a graphite plate (GP) for the in situ formation of graphene layers on the surface of a graphite electrode. When the resultant graphene-layer-based graphite plate electrode (GL/GP) was used as an anode in an MFC, a maximum power density of 0.67 ± 0.034 W/m(2) was achieved. This value corresponds to 1.72-, 1.56- and 1.26-times the maximum power densities of the original GP, exfoliated-graphene-modified GP (EG/GP) and chemically-reduced-graphene-modified GP (rGO/GP) anodes, respectively. Electrochemical measurements revealed that the high performance of the GL/GP anode was attributable to its macroporous structure, improved electron transfer and high electrochemical capacitance. The results demonstrated that the proposed method is a facile and environmentally friendly synthesis technique for the fabrication of high-performance graphene-based electrodes for use in microbial energy harvesting. PMID:25950933

  19. Thermal van der Waals Interaction between Graphene Layers

    OpenAIRE

    Gómez-Santos, G.

    2009-01-01

    The van de Waals interaction between two graphene sheets is studied at finite temperatures. Graphene's thermal length $(\\xi_T = \\hbar v / k_B T)$ controls the force versus distance $(z)$ as a crossover from the zero temperature results for $z\\ll \\xi_T$, to a linear-in-temperature, universal regime for $z\\gg \\xi_T$. The large separation regime is shown to be a consequence of the classical behavior of graphene's plasmons at finite temperature. Retardation effects are largely irrelevant, both in...

  20. Electronic structures of single- and multi-layer epitaxial graphene on SiC (0001)

    Science.gov (United States)

    Kim, Seungchul; Ihm, Jisoon; Son, Young-Woo

    2009-03-01

    The electronic structures of single- and multi-layered epitaxial graphene on silicon carbide (0001) surface are studied theoretically. To calculate energy bands of the systems, we construct the simple Hamiltonian with tight-binding approximations. We confirm that the present simple model do give identical electronic structure to the previous ab-initio study on the single layer case [1]. We extend the model up to four epitaxial graphene layers to explain various interesting experimental findings. The roles of the coupling between graphenes and the buffer layer, and their large scale reconstructions to the electronic structures are also investigated. [1] S. Kim, J. Ihm, H. J. Choi, Y.-W. Son, Phys. Rev. Lett. 100, 176802 (2008).

  1. NO2 and Humidity Sensing Characteristics of Few-layer Graphene

    CERN Document Server

    Ghosh, Anupama; Panchakarla, L S; Govindaraj, A; Rao, C N R

    2009-01-01

    Sensing characteristics of few-layer graphenes for NO2 and humidity have been investigated with graphene samples prepared by the thermal exfoliation of graphitic oxide (EG), conversion of nanodiamond (DG) and arc-discharge of graphite in hydrogen (HG). The sensitivity for NO2 is found to be highest with DG. Nitrogen-doped HG (n-type) shows increased sensitivity for NO2 compared to pure HG. The highest sensitivity for humidity is observed with HG. The sensing characteristics of graphene have been examined for different aliphatic alcohols and the sensitivity is found to vary with the chain length and branching.

  2. Large networks of vertical multi-layer graphenes with morphology-tunable magnetoresistance

    Science.gov (United States)

    Yue, Zengji; Levchenko, Igor; Kumar, Shailesh; Seo, Donghan; Wang, Xiaolin; Dou, Shixue; Ostrikov, Kostya (Ken)

    2013-09-01

    We report on the comparative study of magnetotransport properties of large-area vertical few-layer graphene networks with different morphologies, measured in a strong (up to 10 T) magnetic field over a wide temperature range. The petal-like and tree-like graphene networks grown by a plasma enhanced CVD process on a thin (500 nm) silicon oxide layer supported by a silicon wafer demonstrate a significant difference in the resistance-magnetic field dependencies at temperatures ranging from 2 to 200 K. This behaviour is explained in terms of the effect of electron scattering at ultra-long reactive edges and ultra-dense boundaries of the graphene nanowalls. Our results pave a way towards three-dimensional vertical graphene-based magnetoelectronic nanodevices with morphology-tuneable anisotropic magnetic properties.We report on the comparative study of magnetotransport properties of large-area vertical few-layer graphene networks with different morphologies, measured in a strong (up to 10 T) magnetic field over a wide temperature range. The petal-like and tree-like graphene networks grown by a plasma enhanced CVD process on a thin (500 nm) silicon oxide layer supported by a silicon wafer demonstrate a significant difference in the resistance-magnetic field dependencies at temperatures ranging from 2 to 200 K. This behaviour is explained in terms of the effect of electron scattering at ultra-long reactive edges and ultra-dense boundaries of the graphene nanowalls. Our results pave a way towards three-dimensional vertical graphene-based magnetoelectronic nanodevices with morphology-tuneable anisotropic magnetic properties. Electronic supplementary information (ESI) available: Fig. S1-S6, a schematic of the experimental setup, SEM and TEM characterizations, and details of electrical measurements. See DOI: 10.1039/c3nr00550j

  3. Bio-inspired two-dimensional nanofluidic generators based on a layered graphene hydrogel membrane.

    Science.gov (United States)

    Guo, Wei; Cheng, Chi; Wu, Yanzhe; Jiang, Yanan; Gao, Jun; Li, Dan; Jiang, Lei

    2013-11-13

    An electrogenetic layered graphene hydrogel membrane (GHM) possesses ultra-large interlayer spacing of about 10 nm, forming charged 2D nanocapillaries between graphene sheets that selectively permeate counter-ions and exclude co-ions. When an electrolyte flow goes through the GHM, it functions as an integrated 2D nanofluidic generator converting hydraulic motion into electricity. The maximum streaming conductance density approaches 16.8 μA cm(-2) bar(-1) . PMID:23900945

  4. Role of metallic substrate on the plasmon modes in double-layer graphene structures

    Science.gov (United States)

    Cruz, G. Gonzalez de la

    2015-07-01

    Novel heterostructures combining different layered materials offer new opportunities for applications and fundamental studies of collective excitations driven by interlayer Coulomb interactions. In this work, we have investigated the influence of the metallic-like substrate on the plasmon spectrum of a double layer graphene system and a structure consisting of conventional two-dimensional electron gas (2DEG) immersed in a semiconductor quantum well and a graphene sheet with an interlayer separation of d. Long-range Coulomb interactions between substrate and graphene layered systems lead a new set of spectrum plasmons. At long wavelengths (q→0) the acoustic modes (ω~q) depend, besides on the carrier density in each layer, on the distance between the first carrier layer and the substrate in both structures. Furthermore, in the relativistic/nonrelativistic layered structure an undamped acoustic mode emerges for a certain interlayer critical distance dc. On the other hand, the optical plasmon modes emerging from the coupling of the double-layer systems and the substrate, both start at finite frequency at q=0 in contrast to the collective excitation spectrum ω~q1/2 reported in the literature for double-layer graphene structures.

  5. A graphene meta-interface for enhancing the stretchability of brittle oxide layers

    Science.gov (United States)

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-02-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers.Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05412e

  6. A Review of Atomic Layer Deposition for Nanoscale Devices

    Directory of Open Access Journals (Sweden)

    Edy Riyanto

    2012-12-01

    Full Text Available Atomic layer deposition (ALD is a thin film growth technique that utilizes alternating, self-saturation chemical reactions between gaseous precursors to achieve a deposited nanoscale layers. It has recently become a subject of great interest for ultrathin film deposition in many various applications such as microelectronics, photovoltaic, dynamic random access memory (DRAM, and microelectromechanic system (MEMS. By using ALD, the conformability and extreme uniformity of layers can be achieved in low temperature process. It facilitates to be deposited onto the surface in many variety substrates that have low melting temperature. Eventually it has advantages on the contribution to the wider nanodevices.

  7. Method and apparatus for depositing atomic layers on a substrate

    NARCIS (Netherlands)

    Vermeer, A.J.P.M.; Roozeboom, F.; Deelen, J. van

    2016-01-01

    Method of depositing an atomic layer on a substrate. The method comprises supplying a precursor gas from a precursor-gas supply of a deposition head that may be part of a rotatable drum. The precursor gas is provided from the precursor-gas supply towards the substrate. The method further comprises m

  8. Silicon protected with atomic layer deposited TiO2

    DEFF Research Database (Denmark)

    Seger, Brian; Tilley, David S.; Pedersen, Thomas;

    2013-01-01

    The semiconducting materials used for photoelectrochemical (PEC) water splitting must withstand the corrosive nature of the aqueous electrolyte over long time scales in order to be a viable option for large scale solar energy conversion. Here we demonstrate that atomic layer deposited titanium...

  9. Cost-Effective Systems for Atomic Layer Deposition

    Science.gov (United States)

    Lubitz, Michael; Medina, Phillip A., IV; Antic, Aleks; Rosin, Joseph T.; Fahlman, Bradley D.

    2014-01-01

    Herein, we describe the design and testing of two different home-built atomic layer deposition (ALD) systems for the growth of thin films with sub-monolayer control over film thickness. The first reactor is a horizontally aligned hot-walled reactor with a vacuum purging system. The second reactor is a vertically aligned cold-walled reactor with a…

  10. Stable aqueous dispersions of functionalized multi-layer graphene by pulsed underwater plasma exfoliation of graphite

    Science.gov (United States)

    Meyer-Plath, Asmus; Beckert, Fabian; Tölle, Folke J.; Sturm, Heinz; Mülhaupt, Rolf

    2016-02-01

    A process was developed for graphite particle exfoliation in water to stably dispersed multi-layer graphene. It uses electrohydraulic shockwaves and the functionalizing effect of solution plasma discharges in water. The discharges were excited by 100 ns high voltage pulsing of graphite particle chains that bridge an electrode gap. The underwater discharges allow simultaneous exfoliation and chemical functionalization of graphite particles to partially oxidized multi-layer graphene. Exfoliation is caused by shockwaves that result from rapid evaporation of carbon and water to plasma-excited gas species. Depending on discharge energy and locus of ignition, the shockwaves cause stirring, erosion, exfoliation and/or expansion of graphite flakes. The process was optimized to produce long-term stable aqueous dispersions of multi-layer graphene from graphite in a single process step without requiring addition of intercalants, surfactants, binders or special solvents. A setup was developed that allows continuous production of aqueous dispersions of flake size-selected multi-layer graphenes. Due to the well-preserved sp2-carbon structure, thin films made from the dispersed graphene exhibited high electrical conductivity. Underwater plasma discharge processing exhibits high innovation potential for morphological and chemical modifications of carbonaceous materials and surfaces, especially for the generation of stable dispersions of two-dimensional, layered materials.

  11. Graphene as a Buffer Layer for Silicon Carbide-on-Insulator Structures

    Directory of Open Access Journals (Sweden)

    Kanji Yasui

    2012-11-01

    Full Text Available We report an innovative technique for growing the silicon carbide-on-insulator (SiCOI structure by utilizing polycrystalline single layer graphene (SLG as a buffer layer. The epitaxial growth was carried out using a hot-mesh chemical vapor deposition (HM-CVD technique. Cubic SiC (3C-SiC thin film in (111 domain was realized at relatively low substrate temperature of 750 °C. 3C-SiC energy bandgap of 2.2 eV was confirmed. The Si-O absorption band observed in the grown film can be caused by the out-diffusion of the oxygen atom from SiO2 substrate or oxygen doping during the cleaning process. Further experimental works by optimizing the cleaning process, growth parameters of the present growth method, or by using other growth methods, as well, are expected to realize a high quality SiCOI structure, thereby opening up the way for a breakthrough in the development of advanced ULSIs with multifunctionalities.

  12. Ultrafast non-thermal electron dynamics in single layer graphene

    OpenAIRE

    Novoselov K.S.; Geim A.K.; Nair R.R.; Polini M.; Tomadin A.; Cerullo G.; Manzoni C.; Brida D.; Milana S.; Lombardo A.; Ferrari A.C.

    2012-01-01

    We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.

  13. Stepwise Reduction of Immobilized Mono layer Graphene Oxides

    DEFF Research Database (Denmark)

    Petersen, Søren; He, Yudong; Lang, Jiang;

    2013-01-01

    Chemically converted graphene is highly relevant for transparent conducting film applications such as display and photovoltaic uses. So far, the major obstacle for realizing the potential has been to fully reduce/deoxygenate the graphene oxide (GO), which is challenging in part due...... to the pronounced aggregation that accompanies deoxygenation of GO in solution. Surface immobilization of monolayered graphene oxide (mGO) in Langmuir-Blodgett (LB) films was investigated as a method to circumvent this problem. Two types of LB films with different density of mGO flakes were prepared, i.e., diluted...... spectroscopy (XPS) along with electrical characterization. XPS measurements confirmed a full conversion into virtually oxygen-free chemically converted graphene. The electrical characterization revealed large variations in the conductivity for single sheets in the diluted LB films, with an average conductivity...

  14. Femtosecond laser induced periodic surface structures on multi-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Beltaos, Angela, E-mail: abeltaos@ualberta.ca; Kovačević, Aleksander G.; Matković, Aleksandar; Ralević, Uroš; Savić-Šević, Svetlana; Jovanović, Djordje; Jelenković, Branislav M.; Gajić, Radoš [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia)

    2014-11-28

    In this work, we present an observation of laser induced periodic surface structures (LIPSS) on graphene. LIPSS on other materials have been observed for nearly 50 years, but until now, not on graphene. Our findings for LIPSS on multi-layer graphene were consistent with previous reports of LIPSS on other materials, thus classifying them as high spatial frequency LIPSS. LIPSS on multi-layer graphene were generated in an air environment by a linearly polarized femtosecond laser with excitation wavelength λ of 840 nm, pulse duration τ of ∼150 fs, and a fluence F of ∼4.3–4.4 mJ/cm{sup 2}. The observed LIPSS were perpendicular to the laser polarization and had dimensions of width w of ∼30–40 nm and length l of ∼0.5–1.5 μm, and spatial periods Λ of ∼70–100 nm (∼λ/8–λ/12), amongst the smallest of spatial periods reported for LIPSS on other materials. The spatial period and width of the LIPSS were shown to decrease for an increased number of laser shots. The experimental results support the leading theory behind high spatial frequency LIPSS formation, implying the involvement of surface plasmon polaritons. This work demonstrates a new way to pattern multi-layer graphene in a controllable manner, promising for a variety of emerging graphene/LIPSS applications.

  15. Nanoscale Dielectric Capacitors Composed of Graphene and Boron Nitride Layers: A First Principles Study of High-Capacitance at Nanoscale

    OpenAIRE

    Özçelik, V. Ongun; Ciraci, S.

    2013-01-01

    We investigate a nanoscale dielectric capacitor model consisting of two-dimensional, hexagonal h-BN layers placed between two commensurate and metallic graphene layers using self-consistent field density functional theory. The separation of equal amounts of electric charge of different sign in different graphene layers is achieved by applying electric field perpendicular to the layers. The stored charge, energy, and the electric potential difference generated between the metallic layers are c...

  16. The Atomic-scale Growth of Large-Area Monolayer Graphene on Single-Crystal Copper Substrates

    OpenAIRE

    Zhao, L; Rim, K. T.; Zhou, H.; He, R.; Heinz, T. F.; Pinczuk, A.; Flynn, G. W.; Pasupathy, A. N.

    2010-01-01

    We study the growth and microscopic structure of large-area graphene monolayers, grown on copper single crystals by chemical vapor deposition (CVD) in ultra-high vacuum (UHV). Using atomic-resolution scanning tunneling microscopy (STM), we find that graphene grows primarily in registry with the underlying copper lattice for both Cu(111) and Cu(100). The graphene has a hexagonal superstructure on Cu(111) with a significant electronic component, whereas it has a linear superstructure on Cu(100)...

  17. CMUTs with High-K Atomic Layer Deposition Dielectric Material Insulation Layer

    OpenAIRE

    Xu, Toby; Tekes, Coskun; Degertekin, F. Levent

    2014-01-01

    Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especiall...

  18. Microwave-Assisted Synthesis of Highly-Crumpled, Few-Layered Graphene and Nitrogen-Doped Graphene for Use as High-Performance Electrodes in Capacitive Deionization

    OpenAIRE

    Ahmad Amiri; Goodarz Ahmadi; Mehdi Shanbedi; Maryam Savari; Kazi, S. N.; B. T. Chew

    2015-01-01

    Capacitive deionization (CDI) is a promising procedure for removing various charged ionic species from brackish water. The performance of graphene-based material in capacitive deionization is lower than the expectation of the industry, so highly-crumpled, few-layered graphene (HCG) and highly-crumpled nitrogen-doped graphene (HCNDG) with high surface area have been introduced as promising candidates for CDI electrodes. Thus, HCG and HCNDG were prepared by exfoliation of graphite in the presen...

  19. Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

    Science.gov (United States)

    Berner, Nina C.; Winters, Sinéad; Backes, Claudia; Yim, Chanyoung; Dümbgen, Kim C.; Kaminska, Izabela; Mackowski, Sebastian; Cafolla, Attilio A.; Hirsch, Andreas; Duesberg, Georg S.

    2015-10-01

    The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated π-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale.The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated π-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale. Electronic supplementary information (ESI) available

  20. One-Minute Room-Temperature Transfer-Free Production of Mono- and Few-Layer Polycrystalline Graphene on Various Substrates

    Science.gov (United States)

    Jiang, Shenglin; Zeng, Yike; Zhou, Wenli; Miao, Xiangshui; Yu, Yan

    2016-01-01

    Graphene deposited on various substrates has attracted the attention of the scientific and technical communities for use in a wide range of applications. Graphene on substrates is commonly produced by two types of methods, namely, methods that require a transfer step and transfer-free methods. Compared with methods that require a transfer step, transfer-free methods have a simpler procedure and a lower cost. Thus, transfer-free methods have considerable potential to meet the industrial and commercial demands of production methods. However, some limitations of the current transfer-free methods must be overcome, such as the high temperatures encountered during production, the relatively long manufacturing times, incompatibilities for both rigid and flexible substrates, and an inability to extend the process to other two-dimensional (2-D) atomic crystals. In this work, a room-temperature rubbing method is developed for the rapid transfer-free production of defect-free polycrystalline graphene on rigid and flexible substrates. Starting with inexpensive commercially obtained graphite powder, mono- and few-layer graphene can be fabricated directly on various substrates, with an average production time of less than one minute (from raw graphite to graphene on the substrate). Importantly, this method can be extended to other 2-D atomic crystals.

  1. One-Minute Room-Temperature Transfer-Free Production of Mono- and Few-Layer Polycrystalline Graphene on Various Substrates.

    Science.gov (United States)

    Jiang, Shenglin; Zeng, Yike; Zhou, Wenli; Miao, Xiangshui; Yu, Yan

    2016-01-01

    Graphene deposited on various substrates has attracted the attention of the scientific and technical communities for use in a wide range of applications. Graphene on substrates is commonly produced by two types of methods, namely, methods that require a transfer step and transfer-free methods. Compared with methods that require a transfer step, transfer-free methods have a simpler procedure and a lower cost. Thus, transfer-free methods have considerable potential to meet the industrial and commercial demands of production methods. However, some limitations of the current transfer-free methods must be overcome, such as the high temperatures encountered during production, the relatively long manufacturing times, incompatibilities for both rigid and flexible substrates, and an inability to extend the process to other two-dimensional (2-D) atomic crystals. In this work, a room-temperature rubbing method is developed for the rapid transfer-free production of defect-free polycrystalline graphene on rigid and flexible substrates. Starting with inexpensive commercially obtained graphite powder, mono- and few-layer graphene can be fabricated directly on various substrates, with an average production time of less than one minute (from raw graphite to graphene on the substrate). Importantly, this method can be extended to other 2-D atomic crystals. PMID:26763292

  2. Atomic and molecular layer deposition for surface modification

    Energy Technology Data Exchange (ETDEWEB)

    Vähä-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.fi [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland); Sievänen, Jenni; Salo, Erkki; Heikkilä, Pirjo; Kenttä, Eija [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland); Johansson, Leena-Sisko, E-mail: leena-sisko.johansson@aalto.fi [Aalto University, School of Chemical Technology, Department of Forest Products Technology, PO Box 16100, FI‐00076 AALTO (Finland); Koskinen, Jorma T.; Harlin, Ali [VTT Technical Research Centre of Finland, PO Box 1000, FI‐02044 VTT (Finland)

    2014-06-01

    Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are based on repeated cycles of gas–solid surface reactions. A partial monolayer of atoms or molecules is deposited to the surface during a single deposition cycle, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. Typically ALD/MLD has been used for applications where uniform and pinhole free thin film is a necessity even on 3D surfaces. However, thin – even non-uniform – atomic and molecular deposited layers can also be used to tailor the surface characteristics of different non-ideal substrates. For example, print quality of inkjet printing on polymer films and penetration of water into porous nonwovens can be adjusted with low-temperature deposited metal oxide. In addition, adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a hybrid layer based on lactic acid. - Graphical abstract: Print quality of a polylactide film surface modified with atomic layer deposition prior to inkjet printing (360 dpi) with an aqueous ink. Number of printed dots illustrated as a function of 0, 5, 15 and 25 deposition cycles of trimethylaluminum and water. - Highlights: • ALD/MLD can be used to adjust surface characteristics of films and fiber materials. • Hydrophobicity after few deposition cycles of Al{sub 2}O{sub 3} due to e.g. complex formation. • Same effect on cellulosic fabrics observed with low temperature deposited TiO{sub 2}. • Different film growth and oxidation potential with different precursors. • Hybrid layer on inorganic layer can be used to improve adhesion of polymer melt.

  3. Reducing interface recombination for Cu(In,Ga)Se2 by atomic layer deposited buffer layers

    International Nuclear Information System (INIS)

    Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide

  4. Introduction to Graphene

    OpenAIRE

    Bjarni Hannesson 1993

    2016-01-01

    In this report some properties of graphene, a single atomic layer of carbon, are outlined. The structure of graphene is reviewed and its dispersion relation within the tight-binding approximation and the effective mass approximation. The observed half-integer quantum Hall effect in graphene is illustrated and finally bilayer graphene is discussed briefly. Í þessari ritgerð verður fjallað um grafín sem er einnar frumeindar þykkt lag af kolefni. Frumeindirnar í grafíni mynda tvívíða sexhyrni...

  5. On the hydrogen-graphene layers interactions, relevance to the onboard storage problem.

    Science.gov (United States)

    Nechaev, Y S; Ochsner, A

    2012-10-01

    Empirical evaluations of fundamental characteristics of the physical and chemical interaction of hydrogen with graphene layers in different kinds of graphite and novel carbonaceous nanomaterials of graphene layer structure have been carried out. This was done by using the approaches of the thermodynamics of reversible and irreversible processes for analysis of the adsorption, absorption, diffusion, the temperature-programmed desorption (TPD) and other experimental data and comparing such analytical results with first-principles calculations. Such an analysis of a number of the known experimental and theoretical data has shown a real possibility of the multilayer specific adsorption (intercalation) of hydrogen between graphene layers in novel carbonaceous nanomaterials. This is of relevance for solving the bottle-neck problem of the hydrogen on-board storage in fuel-cell-powered vehicles, and other technical applications. PMID:23421196

  6. On the hydrogen-graphene layers interactions, relevance to the onboard storage problem.

    Science.gov (United States)

    Nechaev, Y S; Ochsner, A

    2012-10-01

    Empirical evaluations of fundamental characteristics of the physical and chemical interaction of hydrogen with graphene layers in different kinds of graphite and novel carbonaceous nanomaterials of graphene layer structure have been carried out. This was done by using the approaches of the thermodynamics of reversible and irreversible processes for analysis of the adsorption, absorption, diffusion, the temperature-programmed desorption (TPD) and other experimental data and comparing such analytical results with first-principles calculations. Such an analysis of a number of the known experimental and theoretical data has shown a real possibility of the multilayer specific adsorption (intercalation) of hydrogen between graphene layers in novel carbonaceous nanomaterials. This is of relevance for solving the bottle-neck problem of the hydrogen on-board storage in fuel-cell-powered vehicles, and other technical applications.

  7. Chemical-Vapor-Deposited Graphene as Charge Storage Layer in Flash Memory Device

    Directory of Open Access Journals (Sweden)

    W. J. Liu

    2016-01-01

    Full Text Available We demonstrated a flash memory device with chemical-vapor-deposited graphene as a charge trapping layer. It was found that the average RMS roughness of block oxide on graphene storage layer can be significantly reduced from 5.9 nm to 0.5 nm by inserting a seed metal layer, which was verified by AFM measurements. The memory window is 5.6 V for a dual sweep of ±12 V at room temperature. Moreover, a reduced hysteresis at the low temperature was observed, indicative of water molecules or −OH groups between graphene and dielectric playing an important role in memory windows.

  8. Screening properties of graphene layers studied by Kelvin Probe Force Microscopy and Landau Level Spectroscopy

    Science.gov (United States)

    Vetick, John; Lu, Chih-Pin; Altvater, Michael; Duan, Junxi; Li, Guohong; Andrei, Eva Y.

    2015-03-01

    Graphene is one of the best conductors known, but due to its two dimensional structure and the need to support it on insulating substrates, its electronic properties are often masked by substrate-induced random potential fluctuations. In order to realize graphene's full potential for electronic application it is therefore important to understand its screening properties and to find ways to minimize substrate invasiveness. We employed Kelvin Probe Force microscopy (KPFM) to investigate the screening properties of CVD grown graphene crystals as a function of layer number and substrate material using a gated device geometry. The KPFM study was complemented by low temperature scanning tunneling microscopy and Landau level spectroscopy in similar samples and device configurations. Measurements were carried out on single layer, bilayer, trilayer and twisted bilayer samples deposited on SiO2 and hBN substrates. Our findings show that twisted graphene layers provide superior screening of charged impurities and random potentials while at the same time preserving the unique electronic band structure of single layer graphene. Work Supported by DOE-FG02-99ER45742 and NSF DMR 1207108.

  9. Interaction between single gold atom and the graphene edge: A study via aberration-corrected transmission electron microscopy

    KAUST Repository

    Wang, Hongtao

    2012-01-01

    Interaction between single noble metal atoms and graphene edges has been investigated via aberration-corrected and monochromated transmission electron microscopy. A collective motion of the Au atom and the nearby carbon atoms is observed in transition between energy-favorable configurations. Most trapping and detrapping processes are assisted by the dangling carbon atoms, which are more susceptible to knock-on displacements by electron irradiation. Thermal energy is lower than the activation barriers in transition among different energy-favorable configurations, which suggests electron-beam irradiation can be an efficient way of engineering the graphene edge with metal atoms. © 2012 The Royal Society of Chemistry.

  10. Graphene on a metal surface with an h-BN buffer layer: gap opening and N-doping

    Science.gov (United States)

    Wang, Tao; Lu, Yunhao; Feng, Y. P.

    2016-04-01

    Graphene grown on a metal surface, Cu(111), with a boron-nitride (h-BN) buffer layer is studied. Our first-principles calculations reveal that charge is transferred from the copper substrate to graphene through the h-BN buffer layer which results in n-doped graphene in the absence of a gate voltage. More importantly, a gap of 0.2 eV, which is comparable to that of a typical narrow gap semiconductor, opens just 0.5 eV below the Fermi level at the Dirac point. The Fermi level can be easily shifted inside this gap to make graphene a semiconductor, which is crucial for graphene-based electronic devices. A graphene-based p-n junction can be realized with graphene eptaxially grown on a metal surface.

  11. Substrate effect modulates adhesion and proliferation of fibroblast on graphene layer.

    Science.gov (United States)

    Lin, Feng; Du, Feng; Huang, Jianyong; Chau, Alicia; Zhou, Yongsheng; Duan, Huiling; Wang, Jianxiang; Xiong, Chunyang

    2016-10-01

    Graphene is an emerging candidate for biomedical applications, including biosensor, drug delivery and scaffold biomaterials. Cellular functions and behaviors on different graphene-coated substrates, however, still remain elusive to a great extent. This paper explored the functional responses of cells such as adhesion and proliferation, to different kinds of substrates including coverslips, silicone, polydimethylsiloxane (PDMS) with different curing ratios, PDMS treated with oxygen plasma, and their counterparts coated with single layer graphene (SLG). Specifically, adherent cell number, spreading area and cytoskeleton configuration were exploited to characterize cell-substrate adhesion ability, while MTT assay was employed to test the proliferation capability of fibroblasts. Experimental outcome demonstrated graphene coating had excellent cytocompatibility, which could lead to an increase in early adhesion, spreading, proliferation, and remodeling of cytoskeletons of fibroblast cells. Notably, it was found that the underlying substrate effect, e.g., stiffness of substrate materials, could essentially regulate the adhesion and proliferation of cells cultured on graphene. The stiffer the substrates were, the stronger the abilities of adhesion and proliferation of fibroblasts were. This study not only deepens our understanding of substrate-modulated interfacial interactions between live cells and graphene, but also provides a valuable guidance for the design and application of graphene-based biomaterials in biomedical engineering. PMID:27451366

  12. Thermal transport across graphene and single layer hexagonal boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jingchao, E-mail: zhang@unl.edu, E-mail: yyue@whu.edu.cn [Holland Computing Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 (United States); Hong, Yang [Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 (United States); Yue, Yanan, E-mail: zhang@unl.edu, E-mail: yyue@whu.edu.cn [School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072 (China)

    2015-04-07

    As the dimensions of nanocircuits and nanoelectronics shrink, thermal energies are being generated in more confined spaces, making it extremely important and urgent to explore for efficient heat dissipation pathways. In this work, the phonon energy transport across graphene and hexagonal boron-nitride (h-BN) interface is studied using classic molecular dynamics simulations. Effects of temperature, interatomic bond strength, heat flux direction, and functionalization on interfacial thermal transport are investigated. It is found out that by hydrogenating graphene in the hybrid structure, the interfacial thermal resistance (R) between graphene and h-BN can be reduced by 76.3%, indicating an effective approach to manipulate the interfacial thermal transport. Improved in-plane/out-of-plane phonon couplings and broadened phonon channels are observed in the hydrogenated graphene system by analyzing its phonon power spectra. The reported R results monotonically decrease with temperature and interatomic bond strengths. No thermal rectification phenomenon is observed in this interfacial thermal transport. Results reported in this work give the fundamental knowledge on graphene and h-BN thermal transport and provide rational guidelines for next generation thermal interface material designs.

  13. Interface engineering of layer-by-Layer stacked graphene anodes for high-performance organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu; Tong, Shi Wun; Loh, Kian Ping [Department of Chemistry, National University of Singapore (Singapore); Xu, Xiang Fan; Oezyilmaz, Barbaros [Department of Physics, National University of Singapore (Singapore)

    2011-04-05

    An interface engineering process to deploy graphene film as the anode in poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM)-based polymer solar cells is demonstrated. By modifying the interface between the graphene anode and the photoactive layer with MoO{sub 3} and poly(3,4-ethylenedioythiophene):poly(styrenesulfonate) (PEDOT:PSS), the power conversion efficiency of the solar cells reaches {approx}83.3% of control devices that use an indium tin oxide (ITO) anode. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Flexible bactericidal graphene oxide–chitosan layers for stem cell proliferation

    Energy Technology Data Exchange (ETDEWEB)

    Mazaheri, M. [Department of Materials Science and Engineering, Sharif University of Technology, PO Box 11365-9466, Tehran (Iran, Islamic Republic of); Akhavan, O., E-mail: oakhavan@sharif.edu [Department of Physics, Sharif University of Technology, PO Box 11155-9161, Tehran (Iran, Islamic Republic of); Institute for Nanoscience and Nanotechnology, Sharif University of Technology, PO Box 14588-89694, Tehran (Iran, Islamic Republic of); Simchi, A. [Department of Materials Science and Engineering, Sharif University of Technology, PO Box 11365-9466, Tehran (Iran, Islamic Republic of); Institute for Nanoscience and Nanotechnology, Sharif University of Technology, PO Box 14588-89694, Tehran (Iran, Islamic Republic of)

    2014-05-01

    Highlights: • Fabrication of flexible graphene oxide–chitosan nanocomposite layers was reported. • The flexibility of the chitosan layers were improved by adding graphene oxide sheets. • The nanocomposite layers with 1.5 wt% graphene oxide content showed yielded flexible and antibacterial surfaces for stem cell proliferation. - Abstract: Graphene oxide (GO)–chitosan composite layers with stacked layer structures were synthesized using chemically exfoliated GO sheets (with lateral dimensions of ∼1 μm and thickness of ∼1 nm), and applied as antibacterial and flexible nanostructured templates for stem cell proliferation. By increasing the GO content from zero to 6 wt%, the strength and elastic modulus of the layers increased ∼80% and 45%, respectively. Similar to the chitosan layer, the GO–chitosan composite layers showed significant antibacterial activity (>77% inactivation after only 3 h) against Staphylococcus aureus bacteria. Surface density of the actin cytoskeleton fibers of human mesenchymal stem cells (hMSCs) cultured on the chitosan and GO(1.5 wt%)–chitosan composite layers was found nearly the same, while it significantly decreased by increasing the GO content to 3 and 6 wt%. Our results indicated that although a high concentration of GO in the chitosan layer (here, 6 wt%) could decelerate the proliferation of the hMSCs on the flexible layer, a low concentration of GO (i.e., 1.5 wt%) not only resulted in biocompatibility but also kept the mechanical flexibility of the self-sterilized layers for high proliferation of hMSCs.

  15. Optical Band Gap and Thermal Diffusivity of Polypyrrole-Nanoparticles Decorated Reduced Graphene Oxide Nanocomposite Layer

    OpenAIRE

    Amir Reza Sadrolhosseini; Suraya Abdul Rashid; Noor, A. S. M.; Alireza Kharazmi; Lim, H. N.; Mohd Adzir Mahdi

    2016-01-01

    A polypyrrole-nanoparticles reduced graphene oxide nanocomposite layer was prepared using electrochemical method. The prepared samples were characterized using Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and UV-visible spectroscopy. The band gap of nanocomposite layers was calculated from UV-visible spectra and the thermal diffusivity of layers was measured using a photoacoustic technique. As experimental results, the optical band gap was in the range...

  16. Flexible bactericidal graphene oxide–chitosan layers for stem cell proliferation

    International Nuclear Information System (INIS)

    Highlights: • Fabrication of flexible graphene oxide–chitosan nanocomposite layers was reported. • The flexibility of the chitosan layers were improved by adding graphene oxide sheets. • The nanocomposite layers with 1.5 wt% graphene oxide content showed yielded flexible and antibacterial surfaces for stem cell proliferation. - Abstract: Graphene oxide (GO)–chitosan composite layers with stacked layer structures were synthesized using chemically exfoliated GO sheets (with lateral dimensions of ∼1 μm and thickness of ∼1 nm), and applied as antibacterial and flexible nanostructured templates for stem cell proliferation. By increasing the GO content from zero to 6 wt%, the strength and elastic modulus of the layers increased ∼80% and 45%, respectively. Similar to the chitosan layer, the GO–chitosan composite layers showed significant antibacterial activity (>77% inactivation after only 3 h) against Staphylococcus aureus bacteria. Surface density of the actin cytoskeleton fibers of human mesenchymal stem cells (hMSCs) cultured on the chitosan and GO(1.5 wt%)–chitosan composite layers was found nearly the same, while it significantly decreased by increasing the GO content to 3 and 6 wt%. Our results indicated that although a high concentration of GO in the chitosan layer (here, 6 wt%) could decelerate the proliferation of the hMSCs on the flexible layer, a low concentration of GO (i.e., 1.5 wt%) not only resulted in biocompatibility but also kept the mechanical flexibility of the self-sterilized layers for high proliferation of hMSCs

  17. Band gap engineering for single-layer graphene by using slow Li+ ions

    Science.gov (United States)

    Ryu, Mintae; Lee, Paengro; Kim, Jingul; Park, Heemin; Chung, Jinwook

    2016-08-01

    In order to utilize the superb electronic properties of graphene in future electronic nano-devices, a dependable means of controlling the transport properties of its Dirac electrons has to be devised by forming a tunable band gap. We report on the ion-induced modification of the electronic properties of single-layer graphene (SLG) grown on a SiC(0001) substrate by doping low-energy (5 eV) Li+ ions. We find the opening of a sizable and tunable band gap up to 0.85 eV, which depends on the Li+ ion dose as well as the following thermal treatment, and is the largest band gap in the π-band of SLG by any means reported so far. Our Li 1s core-level data together with the valence band suggest that Li+ ions do not intercalate below the topmost graphene layer, but cause a significant charge asymmetry between the carbon sublattices of SLG to drive the opening of the band gap. We thus provide a route to producing a tunable graphene band gap by doping Li+ ions, which may play a pivotal role in the utilization of graphene in future graphene-based electronic nano-devices.

  18. Band gap engineering for single-layer graphene by using slow Li(+) ions.

    Science.gov (United States)

    Ryu, Mintae; Lee, Paengro; Kim, Jingul; Park, Heemin; Chung, Jinwook

    2016-08-01

    In order to utilize the superb electronic properties of graphene in future electronic nano-devices, a dependable means of controlling the transport properties of its Dirac electrons has to be devised by forming a tunable band gap. We report on the ion-induced modification of the electronic properties of single-layer graphene (SLG) grown on a SiC(0001) substrate by doping low-energy (5 eV) Li(+) ions. We find the opening of a sizable and tunable band gap up to 0.85 eV, which depends on the Li(+) ion dose as well as the following thermal treatment, and is the largest band gap in the π-band of SLG by any means reported so far. Our Li 1s core-level data together with the valence band suggest that Li(+) ions do not intercalate below the topmost graphene layer, but cause a significant charge asymmetry between the carbon sublattices of SLG to drive the opening of the band gap. We thus provide a route to producing a tunable graphene band gap by doping Li(+) ions, which may play a pivotal role in the utilization of graphene in future graphene-based electronic nano-devices. PMID:27345294

  19. Biomolecules Electrochemical Sensing Properties of a PMo11V@N-Doped Few Layer Graphene Nanocomposite

    OpenAIRE

    Diana M. Fernandes; Marta Nunes; de Carvalho, Ricardo J.; Revathi Bacsa; Israel-Martyr Mbomekalle; Philippe Serp; Pedro Oliveira; Cristina Freire

    2015-01-01

    A novel hybrid nanocomposite, PMo11V@N-doped few layer graphene, was prepared by a one-step protocol through direct immobilization of the tetrabutylammonium salt of a vanadium-substituted phosphomolybdate (PMo11V) onto N-doped few layer graphene (N-FLG). The nanocomposite characterization by FTIR and XPS confirmed its successful synthesis. Glassy carbon modified electrodes with PMo11V and PMo11V@N-FLG showed cyclic voltammograms consistent with surface-confined redox processes attributed to M...

  20. Quantifying defects in N-layer graphene via a phenomenological model of Raman spectroscopy

    Science.gov (United States)

    Giro, Ronaldo; Archanjo, Braulio S.; Martins Ferreira, Erlon H.; Capaz, Rodrigo B.; Jorio, Ado; Achete, Carlos A.

    2014-01-01

    We construct a model to obtain the density of point defects in N-layer graphene by combining Raman spectroscopy and the TRIM (Transport Range of Ions in Matter) simulation package. The model relates the intensity (or area) ratio of graphene's D and G bands to the defect density on each layer due to Ar+ bombardment. Our method is effective for ion fluences ranging from 1011 to ∼1014 Ar+/cm-2 and it should be in principle extendable to any kind of ion and energy.

  1. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    Science.gov (United States)

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-07-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid.

  2. An iron-based green approach to 1-h production of single-layer graphene oxide

    Science.gov (United States)

    Peng, Li; Xu, Zhen; Liu, Zheng; Wei, Yangyang; Sun, Haiyan; Li, Zheng; Zhao, Xiaoli; Gao, Chao

    2015-01-01

    As a reliable and scalable precursor of graphene, graphene oxide (GO) is of great importance. However, the environmentally hazardous heavy metals and poisonous gases, explosion risk and long reaction times involved in the current synthesis methods of GO increase the production costs and hinder its real applications. Here we report an iron-based green strategy for the production of single-layer GO in 1 h. Using the strong oxidant K2FeO4, our approach not only avoids the introduction of polluting heavy metals and toxic gases in preparation and products but also enables the recycling of sulphuric acid, eliminating pollution. Our dried GO powder is highly soluble in water, in which it forms liquid crystals capable of being processed into macroscopic graphene fibres, films and aerogels. This green, safe, highly efficient and ultralow-cost approach paves the way to large-scale commercial applications of graphene.

  3. Atomic layer deposition of alternative glass microchannel plates

    International Nuclear Information System (INIS)

    The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm2). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm−2 s−1), and low gain variation (±5%)

  4. Photoenhanced atomic layer epitaxy. Hikari reiki genshiso epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mashita, M.; Kawakyu, Y. (Toshiba corp., Tokyo (Japan))

    1991-10-01

    The growth temperature range was greatly expanded of atomic layer epitaxy (ALE) expected as the growth process of ultra-thin stacks. Ga layers and As layers were formed one after the other on a GaAs substrate in the atmosphere of trimethylgallium (TMG) or AsH{sub 2} supplied alternately, by KrF excimer laser irradiation normal to the substrate. As a result, the growth temperature range was 460-540{degree}C nearly 10 times that of 500 {plus minus} several degrees centigrade in conventional thermal growth method. Based on the experimental result where light absorption of source molecules adsorbed on a substrate surface was larger than that under gaseous phase condition, new adsorbed layer enhancement model was proposed to explain above irradiation effect verifying it by experiments. As this photoenhancement technique is applied to other materials, possible fabrication of new crystal structures as a super lattice with ultra-thin stacks of single atomic layers is expected because of a larger freedom in material combination for hetero-ALE. 11 refs., 7 figs.

  5. Graphene functionalization by single atoms doping - a theoretical study

    Science.gov (United States)

    Natan, Amir; Segev, Elad; Hersam, Mark; Seideman, Tamar

    2014-03-01

    We present first principles results and analysis for the electronic structure of chemically modified graphene. We analyze the cases of fluorine adsorption and nitrogen substitution and show that a simple analytical model can describe the doping level as a function of dopant concentration for both cases. We show the relationship between different physical parameters and the electronic band structure of the modified material and its doping level. Finally, we discuss the possible effects of substrate and of different dopant patterns on the band structure and possible applications. amirnatan@post.tau.ac.il

  6. Electrochemical properties of CVD grown pristine graphene: monolayer- vs. quasi-graphene.

    Science.gov (United States)

    Brownson, Dale A C; Varey, Sarah A; Hussain, Fiazal; Haigh, Sarah J; Banks, Craig E

    2014-01-01

    We report the electrochemical properties of pristine monolayer, double layer and few-layer (termed quasi-) graphene grown via CVD and transferred using PMMA onto an insulating substrate (silicon dioxide wafers). Characterisation has been performed by Raman spectroscopy, optical spectroscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy, revealing 'true' pristine single-layer graphene (O/C of 0.05) at the former and pristine quasi-graphene at the latter (O/C of 0.07); the term "quasi-graphene" is coined due to the surface comprising on average 4-graphene-layers. The graphene electrodes are electrochemically characterised using both inner-sphere and outer-sphere redox probes with electrochemical performances of the graphene electrodes compared to other available graphitic electrodes, namely that of basal- and edge- plane pyrolytic graphite electrodes constructed from Highly Ordered Pyrolytic Graphite (HOPG), with information on heterogeneous rate constants (k(o)) obtained. The electrochemical rate constants are predominantly influenced by the electronic properties of the graphene surfaces. Monolayer graphene is found to exhibit slow heterogeneous electron transfer (HET) kinetics towards the redox probes studied, with HET rates ca. 2 and 8 times faster at quasi-graphene and HOPG respectively, relative to that of the monolayer graphene electrode. Critically contrasting the performance of monolayer graphene to quasi-graphene and HOPG electrodes reveals that increasing the number of graphene layers results in improved electrochemical properties, where in terms of the electrochemical reversibility of the probes studied: monolayer-graphene graphene electron transfer kinetics at graphitic materials, the slow HET rates at pristine single-layer graphene electrodes are likely due to graphene's fundamental geometry, which comprises a small edge plane and large basal plane contribution. In the case of quasi-graphene and HOPG, they possess increasing global

  7. Local atomic and electronic structure of boron chemical doping in monolayer graphene.

    Science.gov (United States)

    Zhao, Liuyan; Levendorf, Mark; Goncher, Scott; Schiros, Theanne; Pálová, Lucia; Zabet-Khosousi, Amir; Rim, Kwang Taeg; Gutiérrez, Christopher; Nordlund, Dennis; Jaye, Cherno; Hybertsen, Mark; Reichman, David; Flynn, George W; Park, Jiwoong; Pasupathy, Abhay N

    2013-10-01

    We use scanning tunneling microscopy and X-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ~0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying copper substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film. PMID:24032458

  8. Adsorption of metal atoms at a buckled graphene grain boundary using model potentials

    Energy Technology Data Exchange (ETDEWEB)

    Helgee, Edit E.; Isacsson, Andreas [Department of Applied Physics, Chalmers University of Technology, SE-412 96, Göteborg (Sweden)

    2016-01-15

    Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.

  9. Friction and conductance imaging of sp2- and sp3-hybridized subdomains on single-layer graphene oxide

    Science.gov (United States)

    Lee, Hyunsoo; Son, Narae; Jeong, Hu Young; Kim, Tae Gun; Bang, Gyeong Sook; Kim, Jong Yun; Shim, Gi Woong; Goddeti, Kalyan C.; Kim, Jong Hun; Kim, Namdong; Shin, Hyun-Joon; Kim, Wondong; Kim, Sehun; Choi, Sung-Yool; Park, Jeong Young

    2016-02-01

    We investigated the subdomain structures of single-layer graphene oxide (GO) by characterizing local friction and conductance using conductive atomic force microscopy. Friction and conductance mapping showed that a single-layer GO flake has subdomains several tens to a few hundreds of nanometers in lateral size. The GO subdomains exhibited low friction (high conductance) in the sp2-rich phase and high friction (low conductance) in the sp3-rich phase. Current-voltage spectroscopy revealed that the local current flow in single-layer GO depends on the quantity of hydroxyl and carboxyl groups, and epoxy bridges within the 2-dimensional carbon layer. The presence of subdomains with different sp2/sp3 carbon ratios on a GO flake was also confirmed by chemical mapping using scanning transmission X-ray microscopy. These results suggest that spatial mapping of the friction and conductance can be used to rapidly identify the composition of heterogeneous single-layer GO at nanometer scale, which is essential for understanding charge transport in nanoelectronic devices.We investigated the subdomain structures of single-layer graphene oxide (GO) by characterizing local friction and conductance using conductive atomic force microscopy. Friction and conductance mapping showed that a single-layer GO flake has subdomains several tens to a few hundreds of nanometers in lateral size. The GO subdomains exhibited low friction (high conductance) in the sp2-rich phase and high friction (low conductance) in the sp3-rich phase. Current-voltage spectroscopy revealed that the local current flow in single-layer GO depends on the quantity of hydroxyl and carboxyl groups, and epoxy bridges within the 2-dimensional carbon layer. The presence of subdomains with different sp2/sp3 carbon ratios on a GO flake was also confirmed by chemical mapping using scanning transmission X-ray microscopy. These results suggest that spatial mapping of the friction and conductance can be used to rapidly identify

  10. Graphene-Tapered ZnO Nanorods Array as a Flexible Antireflection Layer

    Directory of Open Access Journals (Sweden)

    Taeseup Song

    2015-01-01

    Full Text Available Flexible solar cells have drawn a great deal of attention due to their various advantages including deformable and wearable characteristics. In the solar cells, the antireflection layer plays an important role in the improvement in the conversion efficiency by increasing the light transmission and suppressing the Fresnel refraction. For the successful implantation of the antireflection layer into the flexible solar cells, the flexible mechanical property of the antireflection layer is also necessary. However, the study on flexible antireflection layer for the flexible solar cells or optoelectronics is still lacking. In this study, we report the graphene-tapered ZnO nanorods array as a flexible antireflection layer for the application in flexible solar cells. Flexible two-dimensional graphene sheet and the tapered morphology of ZnO nanorods enable conformal coverage on the flexible substrate with curved surface and significant improvements in antireflection properties, respectively.

  11. Graphene and Graphene Nanomesh Spintronics

    Directory of Open Access Journals (Sweden)

    Junji Haruyama

    2013-12-01

    Full Text Available Spintronics, which manipulate spins but not electron charge, are highly valued as energy and thermal dissipationless systems. A variety of materials are challenging the realization of spintronic devices. Among those, graphene, a carbon mono-atomic layer, is very promising for efficient spin manipulation and the creation of a full spectrum of beyond-CMOS spin-based nano-devices. In the present article, the recent advancements in graphene spintronics are reviewed, introducing the observation of spin coherence and the spin Hall effect. Some research has reported the strong spin coherence of graphene. Avoiding undesirable influences from the substrate are crucial. Magnetism and spintronics arising from graphene edges are reviewed based on my previous results. In spite of carbon-based material with only sp2 bonds, the zigzag-type atomic structure of graphene edges theoretically produces spontaneous spin polarization of electrons due to mutual Coulomb interaction of extremely high electron density of states (edge states localizing at the flat energy band. We fabricate honeycomb-like arrays of low-defect hexagonal nanopores (graphene nanomeshes; GNMs on graphenes, which produce a large amount of zigzag pore edges, by using a nonlithographic method (nanoporous alumina templates and critical temperature annealing under high vacuum and hydrogen atmosphere. We observe large-magnitude ferromagnetism, which arises from polarized spins localizing at the hydrogen-terminated zigzag-nanopore edges of the GNMs, even at room temperature. Moreover, spin pumping effects are found for magnetic fields applied in parallel with the few-layer GNM planes. Strong spin coherence and spontaneously polarized edge spins of graphene can be expected to lead to novel spintronics with invisible, flexible, and ultra-light (wearable features.

  12. Atomic layer deposited aluminum oxide barrier coatings for packaging materials

    Energy Technology Data Exchange (ETDEWEB)

    Hirvikorpi, Terhi, E-mail: terhi.hirvikorpi@vtt.f [Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), P.O. Box 70, FI-02151 Espoo (Finland); Vaehae-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.f [Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), P.O. Box 70, FI-02151 Espoo (Finland); Mustonen, Tuomas, E-mail: tuomas.mustonen@vtt.f [Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), P.O. Box 70, FI-02151 Espoo (Finland); Iiskola, Eero, E-mail: eero.iiskola@kcl.f [Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), P.O. Box 70, FI-02151 Espoo (Finland); Karppinen, Maarit, E-mail: maarit.karppinen@tkk.f [Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, P.O. Box 6100, FI-02015 TKK (Finland)

    2010-03-01

    Thin aluminum oxide coatings have been deposited at a low temperature of 80 {sup o}C on various uncoated papers, polymer-coated papers and boards and plain polymer films using the atomic layer deposition (ALD) technique. The work demonstrates that such ALD-grown Al{sub 2}O{sub 3} coatings efficiently enhance the gas-diffusion barrier performance of the studied porous and non-porous materials towards oxygen, water vapor and aromas.

  13. Suppressing unstable deformation of nanocolloidal crystals with atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Di [Department of Mechanical Engineering, Villanova University, Villanova, PA 19085 (United States); Zhang, Lei; Lee, Daeyeon [Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104 (United States); Cheng, Xuemei [Department of Physics, Bryn Mawr College, Bryn Mawr, PA 19010 (United States); Feng, Gang, E-mail: gang.feng@villanova.edu [Department of Mechanical Engineering, Villanova University, Villanova, PA 19085 (United States)

    2015-07-15

    Despite their useful photonic properties, poor mechanical robustness hinders the application of nanocolloidal crystals (NCCs). Understanding the mechanical behavior of NCCs is critical to propose effective reinforcement techniques. We find that as-assembled NCCs exhibit unstable deformation, manifested as pop-ins upon nanoindentation. By deepening indentation, the unstable deformation mode transitions from NC dislodging to shear band (SB) formation. We find that alumina atomic layer deposition (ALD) significantly suppresses NC dislodging and SB formations in NCCs by increasing interparticle bonding.

  14. Silicon protected with atomic layer deposited TiO2

    DEFF Research Database (Denmark)

    Seger, Brian; Tilley, S. David; Pedersen, Thomas;

    2013-01-01

    of atomic layer deposited TiO2 increased the donor density from an as-deposited value of 1.3 × 1019 cm -3 to 2.2 × 1020 cm-3 following the annealing step. Using an Fe(ii)/Fe(iii) redox couple it was shown that the lower dopant density only allows electron transfer through TiO2 under conditions of weak band...

  15. Growth and optical characteristics of high-quality ZnO thin films on graphene layers

    Directory of Open Access Journals (Sweden)

    Suk In Park

    2015-01-01

    Full Text Available We report the growth of high-quality, smooth, and flat ZnO thin films on graphene layers and their photoluminescence (PL characteristics. For the growth of high-quality ZnO thin films on graphene layers, ZnO nanowalls were grown using metal-organic vapor-phase epitaxy on oxygen-plasma treated graphene layers as an intermediate layer. PL measurements were conducted at low temperatures to examine strong near-band-edge emission peaks. The full-width-at-half-maximum value of the dominant PL emission peak was as narrow as 4 meV at T = 11 K, comparable to that of the best-quality films reported previously. Furthermore, the stimulated emission of ZnO thin films on the graphene layers was observed at the low excitation energy of 180 kW/cm2 at room temperature. Their structural and optical characteristics were investigated using X-ray diffraction, transmission electron microscopy, and PL spectroscopy.

  16. Growth and optical characteristics of high-quality ZnO thin films on graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Park, Suk In; Tchoe, Youngbin; Baek, Hyeonjun; Hyun, Jerome K.; Yi, Gyu-Chul, E-mail: njkim36@gmail.com, E-mail: gcyi@snu.ac.kr [Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 151-747 (Korea, Republic of); Heo, Jaehyuk [Advanced Development Team, LED Business, Samsung Electronics Co., Ltd., San#24 Nongseo-Dong, Giheung-Gu, Yongin-City, Gyeonggi-Do 446–711 (Korea, Republic of); Jo, Janghyun; Kim, Miyoung [Department of Materials Science and Engineering, Seoul National University, Seoul 151–744 (Korea, Republic of); Kim, Nam-Jung, E-mail: njkim36@gmail.com, E-mail: gcyi@snu.ac.kr [Department of Physics and Chemistry, Korea Military Academy, Seoul (Korea, Republic of)

    2015-01-01

    We report the growth of high-quality, smooth, and flat ZnO thin films on graphene layers and their photoluminescence (PL) characteristics. For the growth of high-quality ZnO thin films on graphene layers, ZnO nanowalls were grown using metal-organic vapor-phase epitaxy on oxygen-plasma treated graphene layers as an intermediate layer. PL measurements were conducted at low temperatures to examine strong near-band-edge emission peaks. The full-width-at-half-maximum value of the dominant PL emission peak was as narrow as 4 meV at T = 11 K, comparable to that of the best-quality films reported previously. Furthermore, the stimulated emission of ZnO thin films on the graphene layers was observed at the low excitation energy of 180 kW/cm{sup 2} at room temperature. Their structural and optical characteristics were investigated using X-ray diffraction, transmission electron microscopy, and PL spectroscopy.

  17. Channel cracks in atomic-layer and molecular-layer deposited multilayer thin film coatings

    International Nuclear Information System (INIS)

    Metal oxide thin film coatings produced by atomic layer deposition have been shown to be an effective permeation barrier. The primary failure mode of such coatings under tensile loads is the propagation of channel cracks that penetrate vertically into the coating films. Recently, multi-layer structures that combine the metal oxide material with relatively soft polymeric layers produced by molecular layer deposition have been proposed to create composite thin films with desired properties, including potentially enhanced resistance to fracture. In this paper, we study the effects of layer geometry and material properties on the critical strain for channel crack propagation in the multi-layer composite films. Using finite element simulations and a thin-film fracture mechanics formalism, we show that if the fracture energy of the polymeric layer is lower than that of the metal oxide layer, the channel crack tends to penetrate through the entire composite film, and dividing the metal oxide and polymeric materials into thinner layers leads to a smaller critical strain. However, if the fracture energy of the polymeric material is high so that cracks only run through the metal oxide layers, more layers can result in a larger critical strain. For intermediate fracture energy of the polymer material, we developed a design map that identifies the optimal structure for given fracture energies and thicknesses of the metal oxide and polymeric layers. These results can facilitate the design of mechanically robust permeation barriers, an important component for the development of flexible electronics.

  18. Optical properties of spray coated layers with carbon nanotubes and graphene nanoplatelets

    Science.gov (United States)

    Lorenc, Zofia; Krzeminski, Jakub; Wroblewski, Grzegorz; Salbut, Leszek

    2016-04-01

    Carbon nanotubes as well as graphene are allotropic forms of carbon. Graphene is a two dimensional (2D) form of atomic-scale, hexagonal lattice, while carbon nanotube is a cylindrical nanostructure composed of a rolled sheet of graphene lattice at specific and discrete angles. Both of discussed materials have a high potential for modern engineering, especially in organic and printed electronics. High transparency in the visible part of the electromagnetic spectrum and low electrical resistance are desirable features in various applications and may be fulfilled with studied carbon nanomaterials. They have chances to become an important technological improvement in customers electronic devices by applying them to electrodes production in flexible screens and light sources. Graphene end carbon nanotubes are conceptually similar. However, characteristic properties of these two substances are different. In the article authors present the results of the transmission in visible electromagnetic spectrum characteristics of different samples. This parameter and the resistance of electrodes are tested, analysed and compared. Characteristics of optical transmittance against resistance with the optimal point of that relationship are presented in paper. Moreover, dependency of graphene nanoplatelets agglomerates arrangement against type of nano-fillers is shown. Two groups of tested inks contain graphene nanoplatelets with different fillers diameters. The third group contains carbon nanotubes. Described parameters are important for production process and results of analysis can be used by technologists working with elastic electronics.

  19. Overview of atomic layer etching in the semiconductor industry

    Energy Technology Data Exchange (ETDEWEB)

    Kanarik, Keren J., E-mail: keren.kanarik@lamresearch.com; Lill, Thorsten; Hudson, Eric A.; Sriraman, Saravanapriyan; Tan, Samantha; Marks, Jeffrey; Vahedi, Vahid; Gottscho, Richard A. [Lam Research Corporation, 4400 Cushing Parkway, Fremont, California 94538 (United States)

    2015-03-15

    Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting. ALE has been studied in the laboratory for more than 25 years. Today, it is being driven by the semiconductor industry as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition. As we enter the era of atomic-scale dimensions, there is need to unify the ALE field through increased effectiveness of collaboration between academia and industry, and to help enable the transition from lab to fab. With this in mind, this article provides defining criteria for ALE, along with clarification of some of the terminology and assumptions of this field. To increase understanding of the process, the mechanistic understanding is described for the silicon ALE case study, including the advantages of plasma-assisted processing. A historical overview spanning more than 25 years is provided for silicon, as well as ALE studies on oxides, III–V compounds, and other materials. Together, these processes encompass a variety of implementations, all following the same ALE principles. While the focus is on directional etching, isotropic ALE is also included. As part of this review, the authors also address the role of power pulsing as a predecessor to ALE and examine the outlook of ALE in the manufacturing of advanced semiconductor devices.

  20. Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils

    Science.gov (United States)

    Chung, Ting Fung; Shen, Tian; Cao, Helin; Jauregui, Luis A.; Wu, Wei; Yu, Qingkai; Newell, David; Chen, Yong P.

    2013-04-01

    The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interest. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapor deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this paper, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapor deposition. We also discuss potential applications of such large-scale synthetic graphene.

  1. Ultrafast Non-Thermal Electron Dynamics in Single Layer Graphene

    Directory of Open Access Journals (Sweden)

    Novoselov K.S.

    2013-03-01

    Full Text Available We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.

  2. Blending effect of 6,13-bis(triisopropylsilylethynyl) pentacene–graphene composite layers for flexible thin film transistors with a polymer gate dielectric

    International Nuclear Information System (INIS)

    Solution processible poly(4-vinylphenol) is employed as a transistor dielectric material for low cost processing on flexible substrates at low temperatures. A 6,13-bis (triisopropylsilylethynyl) (TIPS) pentacene–graphene hybrid semiconductor is drop cast to fabricate bottom-gate and bottom-contact field-effect transistor devices on flexible and glass substrates under an ambient air environment. A few layers of graphene flakes increase the area in the conduction channel, and form bridge connections between the crystalline regions of the semiconductor layer which can change the surface morphology of TIPS pentacene films. The TIPS pentacene–graphene hybrid semiconductor-based organic thin film transistors (OTFTs) cross-linked with a poly(4-vinylphenol) gate dielectric exhibit an effective field-effect mobility of 0.076 cm2 V−1 s−1 and a threshold voltage of −0.7 V at V gs = −40 V. By contrast, typical TIPS pentacene shows four times lower mobility of 0.019 cm2 V−1 s−1 and a threshold voltage of 5 V. The graphene/TIPS pentacene hybrids presented in this paper can enhance the electrical characteristics of OTFTs due to their high crystallinity, uniform large-grain distribution, and effective reduction of crystal misorientation of the organic semiconductor layer, as confirmed by x-ray diffraction spectroscopy, atomic force microscopy, and optical microscopy studies. (paper)

  3. Blending effect of 6,13-bis(triisopropylsilylethynyl) pentacene-graphene composite layers for flexible thin film transistors with a polymer gate dielectric.

    Science.gov (United States)

    Basu, Sarbani; Adriyanto, Feri; Wang, Yeong-Her

    2014-02-28

    Solution processible poly(4-vinylphenol) is employed as a transistor dielectric material for low cost processing on flexible substrates at low temperatures. A 6,13-bis (triisopropylsilylethynyl) (TIPS) pentacene-graphene hybrid semiconductor is drop cast to fabricate bottom-gate and bottom-contact field-effect transistor devices on flexible and glass substrates under an ambient air environment. A few layers of graphene flakes increase the area in the conduction channel, and form bridge connections between the crystalline regions of the semiconductor layer which can change the surface morphology of TIPS pentacene films. The TIPS pentacene-graphene hybrid semiconductor-based organic thin film transistors (OTFTs) cross-linked with a poly(4-vinylphenol) gate dielectric exhibit an effective field-effect mobility of 0.076 cm(2) V(-1) s(-1) and a threshold voltage of -0.7 V at V(gs) = -40 V. By contrast, typical TIPS pentacene shows four times lower mobility of 0.019 cm(2) V(-1) s(-1) and a threshold voltage of 5 V. The graphene/TIPS pentacene hybrids presented in this paper can enhance the electrical characteristics of OTFTs due to their high crystallinity, uniform large-grain distribution, and effective reduction of crystal misorientation of the organic semiconductor layer, as confirmed by x-ray diffraction spectroscopy, atomic force microscopy, and optical microscopy studies. PMID:24492205

  4. Double-sided F and Cl adsorptions on graphene at various atomic ratios: Geometric, orientation and electronic structure aspects

    Science.gov (United States)

    Widjaja, Hantarto; Jiang, Zhong-Tao; Altarawneh, Mohammednoor; Yin, Chun-Yang; Goh, Bee-Min; Mondinos, Nicholas; Amri, Amun; Dlugogorski, Bogdan Z.

    2016-06-01

    Elemental adsorption on graphene offers an effective procedure in fine-tuning electronic and mechanical properties of graphene. The effects of dopants depend on adsorption site, the degree of coverage as well as on the configuration of the deployed supercell. In this contribution, the density functional theory (DFT) calculations were performed to investigate the electronic structures of F and Cl adsorption (double-sided, top site) on graphene in terms of adsorption orientation, atomic ratios, i.e., from C:F/Cl = 18:2 to C:F/Cl = 2:2. Despite being members of the halogens group, F- and Cl-adsorbed on graphene show contrasting trends. F is adsorbed to graphene more strongly than Cl. F favours full and 25% adsorption coverage, while Cl favours 25% coverage. Both F and Cl cases open band gap (at Fermi energy) at certain atomic concentration coverage, but none creates magnetization.

  5. Passivation effects of atomic-layer-deposited aluminum oxide

    Directory of Open Access Journals (Sweden)

    Kotipalli R.

    2013-09-01

    Full Text Available Atomic-layer-deposited (ALD aluminum oxide (Al2O3 has recently demonstrated an excellent surface passivation for both n- and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Qf ~ 1012−1013 cm-2 in combination with a low density of interface states (Dit. This paper investigates the passivation quality of thin (15 nm Al2O3 films deposited by two different techniques: plasma-enhanced atomic layer deposition (PE-ALD and Thermal atomic layer deposition (T-ALD. Other dielectric materials taken into account for comparison include: thermally-grown silicon dioxide (SiO2 (20 nm, SiO2 (20 nm deposited by plasma-enhanced chemical vapour deposition (PECVD and hydrogenated amorphous silicon nitride (a-SiNx:H (20 nm also deposited by PECVD. With the above-mentioned dielectric layers, Metal Insulator Semiconductor (MIS capacitors were fabricated for Qf and Dit extraction through Capacitance-Voltage-Conductance (C-V-G measurements. In addition, lifetime measurements were carried out to evaluate the effective surface recombination velocity (SRV. The influence of extracted C-V-G parameters (Qf,Dit on the injection dependent lifetime measurements τ(Δn, and the dominant passivation mechanism involved have been discussed. Furthermore we have also studied the influence of the SiO2 interfacial layer thickness between the Al2O3 and silicon surface on the field-effect passivation mechanism. It is shown that the field effect passivation in accumulation mode is more predominant when compared to surface defect passivation.

  6. Thermal transport in low-dimensional systems: the case of Graphene and single layer Boron Nitride

    Science.gov (United States)

    Pereira, Luiz Felipe; Donadio, Davide

    2013-03-01

    Low-dimensional systems present unusual transport properties in comparison to bulk materials. In contrast with the three-dimensional case, in one- and two-dimensions heat transport models predict a divergence of the thermal conductivity with system size. In reality, in a low-dimensional system the mean-free-path of heat carriers (phonons) becomes comparable to the micrometer size of experimental samples. Recent developments in nanostructure fabrication allow a direct comparison between theory and experiments for such low-dimensional systems. We perform extensive molecular dynamics simulations of heat transport in graphene and single layer BN, in order to clarify the behavior of the thermal conductivity in realistic low-dimensional systems. In particular, we address the influence of system size on the simulation results. Equilibrium molecular dynamics predicts a convergence of the thermal conductivity with system size, even for systems with less than one hundred nanometers and thousands of atoms. Meanwhile, large scale non-equilibrium molecular dynamics shows a divergence of the thermal conductivity with system size up to the micrometer scale. We analyse the discrepancy between methods in terms of perturbations in phonon populations induced by the non-equilibrium regime.

  7. High-Surface-Area Nitrogen-Doped Reduced Graphene Oxide for Electric Double-Layer Capacitors.

    Science.gov (United States)

    Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; Jaye, Cherno; Fischer, Daniel A; Lee, Chang-Wook; Yang, Xiao-Qing; Roh, Kwang Chul; Kim, Kwang-Bum

    2015-06-01

    A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2)  g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content. PMID:25916491

  8. Catching the bound states in the continuum of a phantom atom in graphene

    Science.gov (United States)

    Guessi, L. H.; Machado, R. S.; Marques, Y.; Ricco, L. S.; Kristinsson, K.; Yoshida, M.; Shelykh, I. A.; de Souza, M.; Seridonio, A. C.

    2015-07-01

    We explore theoretically the formation of bound states in the continuum (BICs) in graphene hosting two collinear adatoms situated at different sides of the sheet and at the center of the hexagonal cell, where a phantom atom of a fictitious lattice emulates the six carbons of the cell. We verify that in this configuration the local density of states near the Dirac points exhibits two characteristic features: (i) a cubic dependence on energy instead of a linear one for graphene as found in New J. Phys. 16, 013045 (2014), 10.1088/1367-2630/16/1/013045, and (ii) the formation of BICs as an aftermath of a Fano destructive interference assisted by the Coulomb correlations in the adatoms. For the geometry where adatoms are collinear to carbon atoms, we report an absence of BICs.

  9. Transport properties of zigzag graphene nanoribbons adsorbed with single iron atom

    Institute of Scientific and Technical Information of China (English)

    杨玉娥; 肖杨; 颜晓红; 戴昌杰

    2015-01-01

    We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon (ZGNR) adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsorbed on the edge and on the interior of the nanoribbon. The results show that the transport features of the two configurations are similar. However, the transport properties are modified due to the scattering effects induced by coupling of the ZGNR band states to the localized 3d-orbital state of the iron atom. More importantly, one can find that several dips appear in the transmission curve, which is closely related to the above mentioned coupling. We expect that our results will have potential applications in graphene-based spintronic devices.

  10. Fabrication of graphene-nanoflake/poly(4-vinylphenol) polymer nanocomposite thin film by electrohydrodynamic atomization and its application as flexible resistive switching device

    Science.gov (United States)

    Choi, Kyung Hyun; Ali, Junaid; Na, Kyoung-Hoan

    2015-10-01

    This paper describes synthesis of graphene/poly(4-vinylphenol) (PVP) nanocomposite and deposition of thin film by electrohydrodynamic atomization (EHDA) for fabrication flexible resistive switching device. EHDA technique proved its viability for thin film deposition after surface morphology analyses by field emission scanning electron microscope (FESEM) and non-destructive 3D Nano-profilometry, as the deposited films were, devoid of abnormalities. The commercially available graphene micro-flakes were exfoliated and broken down to ultra-small (20 nm-200 nm) nano-flakes by ultra-sonication in presence of N-methyl-pyrrolidone (NMP). These graphene nanoflakes with PVP nanocomposite, were successfully deposited as thin films (thickness ~140±7 nm, Ra=2.59 nm) on indium-tin-oxide (ITO) coated polyethylene terephthalate (PET) substrate. Transmittance data revealed that thin films are up to ~87% transparent in visible and NIR region. Resistive switching behaviour of graphene/PVP nanocomposite thin film was studied by using the nanocomposite as active layer in Ag/active layer/ITO sandwich structure. The resistive switching devices thus fabricated, showed characteristic OFF to ON (high resistance to low resistance) transition at low voltages, when operated between ±3 V, characterized at 10 nA compliance currents. The devices fabricated by this approach exhibited a stable room temperature, low power current-voltage hysteresis and well over 1 h retentivity, and ROFF/RON≈35:1. The device showed stable flexibility up to a minimum bending diameter of 1.8 cm.

  11. Photocatalytic Nanostructuring of Graphene Guided by Block Copolymer Self-Assembly

    DEFF Research Database (Denmark)

    Wang, Zhongli; Li, Tao; Schulte, Lars;

    2016-01-01

    graphene nanomesh was fabricated by photocatalysis of single-layer graphene suspended on top of TiO2-covered nanopillars, which were produced by combining block copolymer nanolithography with atomic layer deposition. Graphene nanoribbons were also prepared by the same method applied to a line-forming block...

  12. Highly conductive epitaxial ZnO layers deposited by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Baji, Zs., E-mail: baji.zsofia@ttk.mta.hu [Research Centre for Natural Sciences Institute for Technical Physics and Materials Science, Konkoly Thege M. út 29-33, H-1121 Budapest (Hungary); Lábadi, Z.; Molnár, Gy.; Pécz, B. [Research Centre for Natural Sciences Institute for Technical Physics and Materials Science, Konkoly Thege M. út 29-33, H-1121 Budapest (Hungary); Vad, K. [Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), P.O. Box 51, H-4001, Debrecen (Hungary); Horváth, Z.E. [Research Centre for Natural Sciences Institute for Technical Physics and Materials Science, Konkoly Thege M. út 29-33, H-1121 Budapest (Hungary); Szabó, P.J. [Budapest University of Technology and Economics, Műegyetem rkp. 3-9. H-1111 Budapest (Hungary); Nagata, T. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Volk, J. [Research Centre for Natural Sciences Institute for Technical Physics and Materials Science, Konkoly Thege M. út 29-33, H-1121 Budapest (Hungary)

    2014-07-01

    The possibility of depositing conductive epitaxial layers with atomic layer deposition has been examined. Epitaxial ZnO layers were grown on GaN and doped with Al. The resistivity of the epitaxial layers is between 0.6 and 2 * 10{sup −4} Ω cm with both the mobilities and the carrier concentrations being very high. The source of the high carrier concentration was found to be a combination of Al and Ga doping, the latter resulted by Ga atoms diffusing into the ZnO from the GaN substrate. - Highlights: • High-quality epitaxial ZnO layers were deposited with ALD on GaN above 270 °C. • In the Al-doped layers, domains with different orientations also appear. • Lower-temperature epitaxy is possible with an epitaxial seed layer. • The conductivity of the epitaxial layers is between 0.6 and 2 * 10{sup −4} Ω cm. • The high carrier concentration is resulted by the Ga and Al doping.

  13. The role of atomic vacancies and boundary conditions on ballistic thermal transport in graphene nanoribbons

    OpenAIRE

    Scuracchio, P.; Costamagna, S.; Peeters, F. M; Dobry, A.

    2014-01-01

    Quantum thermal transport in armchair and zig-zag graphene nanoribbons are investigated in the presence of single atomic vacancies and subject to different boundary conditions. We start with a full comparison of the phonon polarizations and energy dispersions as given by a fifth-nearest-neighbor force-constant model (5NNFCM) and by elasticity theory of continuum membranes (ETCM). For free-edges ribbons we discuss the behavior of an additional acoustic edge-localized flexural mode, known as fo...

  14. Highly efficient hydrogen evolution reaction using crystalline layered three-dimensional molybdenum disulfides grown on graphene film.

    Energy Technology Data Exchange (ETDEWEB)

    Behranginia, Amirhossein; Asadi, Mohammad; Liu, Cong; Yasaei, Poya; Kumar, Bijandra; Phillips, Patrick; Foroozan, Tara; Waranius, Joseph C.; Kim, Kibum; Abiade, Jeremiah; Klie, Robert F.; Curtiss, Larry A.; Salehi-Khojin, Amin

    2016-01-26

    Electrochemistry is central to applications in the field of energy storage and generation. However, it has advanced far more slowly over the last two decades, mainly because of a lack of suitable and affordable catalysts. Here, we report the synthesis of highly crystalline layered three-dimensional (3D) molybdenum disulfide (MoS2) catalysts with bare Mo-edge atoms and demonstrate their remarkable performance for the hydrogen evolution reaction (HER). We found that Mo-edge-terminated 3D MoS2 directly grown on graphene film exhibits a remarkable exchange current density (18.2 mu A cm(-2)) and turnover frequency (>4 S-1) for HER. The obtained exchange current density is 15.2 and 2.3 times higher than that of MoS2/graphene and MoS2/Au catalysts, respectively, both with sulfided Mo-edge atoms. An easily scalable and robust growth process on a wide variety of substrates, along with prolonged stability, suggests that this material is a promising catalyst in energy-related applications.

  15. Nanostructure templating using low temperature atomic layer deposition

    Science.gov (United States)

    Grubbs, Robert K.; Bogart, Gregory R.; Rogers, John A.

    2011-12-20

    Methods are described for making nanostructures that are mechanically, chemically and thermally stable at desired elevated temperatures, from nanostructure templates having a stability temperature that is less than the desired elevated temperature. The methods comprise depositing by atomic layer deposition (ALD) structural layers that are stable at the desired elevated temperatures, onto a template employing a graded temperature deposition scheme. At least one structural layer is deposited at an initial temperature that is less than or equal to the stability temperature of the template, and subsequent depositions made at incrementally increased deposition temperatures until the desired elevated temperature stability is achieved. Nanostructure templates include three dimensional (3D) polymeric templates having features on the order of 100 nm fabricated by proximity field nanopatterning (PnP) methods.

  16. Nonstationary structure of atomic and molecular layers in electrothermal. Atomic absorption spectrometry: formation of atomic and molecular absorbing layers of gallium and indium

    International Nuclear Information System (INIS)

    The dynamics of the formation of absorbing layers of gallium and indium atoms and their compounds in a graphite tubular atomizer was investigated by the shadow spectral filming method. These compounds are localozed in the central part of the furnace over the platform and dissapear ay the hotter walls. It the case of gallium and indium atomization, the effects of chemical reactions between the vapor and the walls of the furnace on the formation of absorbing layers are stronger than that of diffusion and convective mass-transfer processes, which are common to all of the elements. Atom propagation from the center to the stomizer ends proceeds through the cascade mechanism because of its relatively low rate of warming up and strong longitudinal anisothermicity

  17. Interferometric Motion Detection in Atomic Layer 2D Nanostructures: Visualizing Signal Transduction Efficiency and Optimization Pathways

    Science.gov (United States)

    Wang, Zenghui; Feng, Philip X.-L.

    2016-07-01

    Atomic layer crystals are emerging building blocks for enabling new two-dimensional (2D) nanomechanical systems, whose motions can be coupled to other attractive physical properties in such 2D systems. Optical interferometry has been very effective in reading out the infinitesimal motions of these 2D structures and spatially resolving different modes. To quantitatively understand the detection efficiency and its dependence on the device parameters and interferometric conditions, here we present a systematic study of the intrinsic motion responsivity in 2D nanomechanical systems using a Fresnel-law-based model. We find that in monolayer to 14-layer structures, MoS2 offers the highest responsivity among graphene, h-BN, and MoS2 devices and for the three commonly used visible laser wavelengths (633, 532, and 405 nm). We also find that the vacuum gap resulting from the widely used 300 nm-oxide substrate in making 2D devices, fortunately, leads to close-to-optimal responsivity for a wide range of 2D flakes. Our results elucidate and graphically visualize the dependence of motion transduction responsivity upon 2D material type and number of layers, vacuum gap, oxide thickness, and detecting wavelength, thus providing design guidelines for constructing 2D nanomechanical systems with optimal optical motion readout.

  18. Atomically thin two-dimensional materials as hole extraction layers in organolead halide perovskite photovoltaic cells

    Science.gov (United States)

    Kim, Yu Geun; Kwon, Ki Chang; Le, Quyet Van; Hong, Kootak; Jang, Ho Won; Kim, Soo Young

    2016-07-01

    Atomically thin two-dimensional materials such as MoS2, WS2, and graphene oxide (GO) are used as hole extraction layers (HEL) in organolead halide perovskites solar cells (PSCs) instead of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HEL. MoS2 and WS2 layers with a polycrystalline structure were synthesized by a chemical deposition method using a uniformly spin-coated (NH4)MoS4 and (NH4)WS4 precursor solution. GO was synthesized by the oxidation of natural graphite powder using Hummers' method. The work functions of MoS2, WS2, and GO are measured to be 5.0, 4.95, and 5.1 eV, respectively. The X-ray diffraction spectrum indicated that the synthesized perovskite material is CH3NH3PbI3-xClx. The PSCs with the p-n junction structure were fabricated based on the CH3NH3PbI3-xClx perovskite layer. The power conversion efficiencies of the MoS2, WS2, and GO-based PSCs were 9.53%, 8.02%, and 9.62%, respectively, which are comparable to those obtained from PEDOT:PSS-based devices (9.93%). These results suggest that two-dimensional materials such as MoS2, WS2, and GO can be promising candidates for the formation of HELs in the PSCs.

  19. Examining the impact of multi-layer graphene using cellular and amphibian models

    Science.gov (United States)

    Muzi, Laura; Mouchet, Florence; Cadarsi, Stéphanie; Janowska, Izabela; Russier, Julie; Ménard-Moyon, Cécilia; Risuleo, Gianfranco; Soula, Brigitte; Galibert, Anne-Marie; Flahaut, Emmanuel; Pinelli, Eric; Gauthier, Laury; Bianco, Alberto

    2016-06-01

    In the last few years, graphene has been defined as the revolutionary material showing an incredible expansion in industrial applications. Different graphene forms have been applied in several contexts, spreading from energy technologies and electronics to food and agriculture technologies. Graphene showed promises also in the biomedical field. Hopeful results have been already obtained in diagnostic, drug delivery, tissue regeneration and photothermal cancer ablation. In view of the enormous development of graphene-based technologies, a careful assessment of its impact on health and environment is demanded. It is evident how investigating the graphene toxicity is of fundamental importance in the context of medical purposes. On the other hand, the nanomaterial present in the environment, likely to be generated all along the industrial life-cycle, may have harmful effects on living organisms. In the present work, an important contribution on the impact of multi-layer graphene (MLG) on health and environment is given by using a multifaceted approach. For the first purpose, the effect of the material on two mammalian cell models was assessed. Key cytotoxicity parameters were considered such as cell viability and inflammatory response induction. This was combined with an evaluation of MLG toxicity towards Xenopus laevis, used as both in vivo and environmental model organism.

  20. Electrical DNA sequencing by graphene edges functionalized with H or N atoms

    Science.gov (United States)

    Amorim, Rodrigo G.; Scheicheir, Ralph H.

    2014-03-01

    The current technology of DNA sequencing needs to be revolutionized in order to be sufficiently cost-efficient for widespread application in healthcare and genomic research. One of the most promising proposals is to use a solid-state nanodevice based on graphene due to its atomically thin edges which would readily enable single-nucleobase resolution in transverse conductance measurements. We used ab initio calculations based on Density Functional Theory combined with the non-equilibrium Green's function method to study how the capability of a graphene nanogap to electrically sense the four nucleobases (Adenine, Cytosine, Guanine and Thymine) is affected by different passivation (H or N) of the graphene edges. We will show how, for the same nucleobase, the zero bias conductance can be increased by five orders of magnitude when N atoms are chosen for functionalization over H atoms. Other aspects investigated by us concern the translational process of nucleobases through the nanogap and the corresponding spatial resolution due to diminishing transmittance as the nucleobase moves out of the gap.

  1. Ultra-Short Optical Pulse Generation with Single-Layer Graphene

    CERN Document Server

    Lee, C -C; Bunch, J S; Schibli, T R

    2010-01-01

    Pulses as short as 260 fs have been generated in a diode-pumped low-gain Er:Yb:glass laser by exploiting the nonlinear optical response of single-layer graphene. The application of this novel material to solid-state bulk lasers opens up a way to compact and robust lasers with ultrahigh repetition rates.

  2. Wavevector filtering through single-layer and bilayer graphene with magnetic barrier structures

    Science.gov (United States)

    Masir, M. Ramezani; Vasilopoulos, P.; Peeters, F. M.

    2008-12-01

    We show that the angular range of the transmission through magnetic barrier structures can be efficiently controlled in single-layer and bilayer graphenes and this renders the structure's efficient wavevector filters. As the number of magnetic barriers increases, this range shrinks, the gaps in the transmission versus energy become wider, and the conductance oscillates with the Fermi energy.

  3. A Simple Road for the Transformation of Few-Layer Graphene into MWNTs

    NARCIS (Netherlands)

    Quintana, Mildred; Grzelczak, Marek; Spyrou, Konstantinos; Calvaresi, Matteo; Bals, Sara; Kooi, Bart; Van Tendeloo, Gustaaf; Rudolf, Petra; Zerbetto, Francesco; Prato, Maurizio

    2012-01-01

    We report the direct formation of multiwalled carbon nanotubes (MWNT) by ultrasonication of graphite in dimethylformamide (DMF) upon addition of ferrocene aldehyde (Fc-CHO). The tubular structures appear exclusively at the edges of graphene layers and contain Fe clusters. Pc in conjunction with benz

  4. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene

    Science.gov (United States)

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  5. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene.

    Science.gov (United States)

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  6. Properties of Ultra-Thin Hafnium Oxide and Interfacial Layer Deposited by Atomic Layer Deposition

    Institute of Scientific and Technical Information of China (English)

    Taeho Lee; Young-Bae Kim; Kyung-Il Hong; Duck-Kyun Choi; Jinho Ahn

    2004-01-01

    Ultra-thin hafnium-oxide gate dielectric films deposited by atomic layer deposition technique using HfCl4 and H2O precursor on a hydrogen-terminated Si substrate were investigated. X-ray photoelectron spectroscopy indicates that the interface layer is Hf-silicate rather than phase separated Hf-silicide and silicon oxide structure. The Hf-silicate interfacial layer partially changes into SiOx after high temperature annealing, resulting in a complex HfO2-silicate-SiOx dielectric structure. Electrical measurements confirms that HfO2 on Si is stable up to 700 ℃ for 30 s under N2 ambient.

  7. Controlled surface oxidation of multi-layered graphene anode to increase hole injection efficiency in organic electronic devices

    Science.gov (United States)

    Han, Tae-Hee; Kwon, Sung-Joo; Seo, Hong-Kyu; Lee, Tae-Woo

    2016-03-01

    Ultraviolet ozone (UVO) surface treatment of graphene changes its sp2-hybridized carbons to sp3-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to ∼5.2 eV and improves the hole injection efficiency (η) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organic layers. By controlling the conditions of the UVO treatment, the electrical properties of the graphene can be tuned to improve η. This controlled surface modification of the graphene will provide a way to achieve efficient and stable flexible displays and solid-state lighting.

  8. Nano-scale strain engineering of graphene and graphene-based devices

    OpenAIRE

    Yeh, N. -C.; Hsu, C.-C.; Teague, M. L.; Wang, J.-Q.; Boyd, D A; Chen, C.-C.

    2015-01-01

    Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here we describe the theoretical foundation fo...

  9. Schottky barrier contrasts in single and bi-layer graphene contacts for MoS2 field-effect transistors

    Science.gov (United States)

    Du, Hyewon; Kim, Taekwang; Shin, Somyeong; Kim, Dahye; Kim, Hakseong; Sung, Ji Ho; Lee, Myoung Jae; Seo, David H.; Lee, Sang Wook; Jo, Moon-Ho; Seo, Sunae

    2015-12-01

    We have investigated single- and bi-layer graphene as source-drain electrodes for n-type MoS2 transistors. Ti-MoS2-graphene heterojunction transistors using both single-layer MoS2 (1M) and 4-layer MoS2 (4M) were fabricated in order to compare graphene electrodes with commonly used Ti electrodes. MoS2-graphene Schottky barrier provided electron injection efficiency up to 130 times higher in the subthreshold regime when compared with MoS2-Ti, which resulted in VDS polarity dependence of device parameters such as threshold voltage (VTH) and subthreshold swing (SS). Comparing single-layer graphene (SG) with bi-layer graphene (BG) in 4M devices, SG electrodes exhibited enhanced device performance with higher on/off ratio and increased field-effect mobility (μFE) due to more sensitive Fermi level shift by gate voltage. Meanwhile, in the strongly accumulated regime, we observed opposing behavior depending on MoS2 thickness for both SG and BG contacts. Differential conductance (σd) of 1M increases with VDS irrespective of VDS polarity, while σd of 4M ceases monotonic growth at positive VDS values transitioning to ohmic-like contact formation. Nevertheless, the low absolute value of σd saturation of the 4M-graphene junction demonstrates that graphene electrode could be unfavorable for high current carrying transistors.

  10. Schottky barrier contrasts in single and bi-layer graphene contacts for MoS2 field-effect transistors

    International Nuclear Information System (INIS)

    We have investigated single- and bi-layer graphene as source-drain electrodes for n-type MoS2 transistors. Ti-MoS2-graphene heterojunction transistors using both single-layer MoS2 (1M) and 4-layer MoS2 (4M) were fabricated in order to compare graphene electrodes with commonly used Ti electrodes. MoS2-graphene Schottky barrier provided electron injection efficiency up to 130 times higher in the subthreshold regime when compared with MoS2-Ti, which resulted in VDS polarity dependence of device parameters such as threshold voltage (VTH) and subthreshold swing (SS). Comparing single-layer graphene (SG) with bi-layer graphene (BG) in 4M devices, SG electrodes exhibited enhanced device performance with higher on/off ratio and increased field-effect mobility (μFE) due to more sensitive Fermi level shift by gate voltage. Meanwhile, in the strongly accumulated regime, we observed opposing behavior depending on MoS2 thickness for both SG and BG contacts. Differential conductance (σd) of 1M increases with VDS irrespective of VDS polarity, while σd of 4M ceases monotonic growth at positive VDS values transitioning to ohmic-like contact formation. Nevertheless, the low absolute value of σd saturation of the 4M-graphene junction demonstrates that graphene electrode could be unfavorable for high current carrying transistors

  11. Van der Waals forces and electron-electron interactions in two strained graphene layers

    OpenAIRE

    Sharma, Anand; Harnish, Peter; Sylvester, Alexander; Kotov, Valeri N.; Neto, A. H. Castro

    2014-01-01

    We evaluate the van der Waals (vdW) interaction energy at zero temperature between two undoped strained graphene layers separated by a finite distance. We consider the following three models for the anisotropic case: (a) where one of the two layers is uniaxially strained, (b) the two layers are strained in the same direction, and (c) one of the layers is strained in the perpendicular direction with respect to the other. We find that for all three models and given value of the electron-electro...

  12. Quantifying the growth of individual graphene layers by in situ environmental transmission electron microscopy

    DEFF Research Database (Denmark)

    Kling, Jens; Hansen, Thomas Willum; Wagner, Jakob Birkedal

    2016-01-01

    The growth dynamics of layered carbon is studied by means of in situ transmission electron microscopy in order to obtain a deeper insight into the growth by chemical vapor deposition, which at present is the technique of choice for growing layered carbon. In situ growth of layered carbon structures...... on nickel using acetylene as carbon precursor gas is studied in the electron microscope at various gas pressures. By following the growth of individual graphene layers on the Ni surface, local growth rates are determined as a function of precursor pressure. Two growth regimes are identified, an initial...

  13. Film-coupled nanoparticles by atomic layer deposition: Comparison with organic spacing layers

    Energy Technology Data Exchange (ETDEWEB)

    Ciracì, Cristian, E-mail: cristian.ciraci@duke.edu; Mock, Jack J.; McGuire, Felicia; Liu, Xiaojun; Smith, David R. [Center for Metamaterials and Integrated Plasmonics and Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 (United States); Chen, Xiaoshu; Oh, Sang-Hyun [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2014-01-13

    Film-coupled nanoparticle systems have proven a reliable platform for exploring the field enhancement associated with sub-nanometer sized gaps between plasmonic nanostructures. In this Letter, we present a side-by-side comparison of the spectral properties of film-coupled plasmon-resonant, gold nanoparticles, with dielectric spacer layers fabricated either using atomic layer deposition or using organic layers (polyelectrolytes or self-assembled monolayers of molecules). In either case, large area, uniform spacer layers with sub-nanometer thicknesses can be accurately deposited, allowing extreme coupling regimes to be probed. The observed spectral shifts of the nanoparticles as a function of spacer layer thickness are similar for the organic and inorganic films and are consistent with numerical calculations taking into account the nonlocal response of the metal.

  14. Damage on multi-layer graphene by femtosecond laserablation%多层石墨烯在飞秒激光作用下的损伤

    Institute of Scientific and Technical Information of China (English)

    裴家云; 吴鑫; 严冬; 赵海燕

    2015-01-01

    Multi-layer graphene generated by chemical vapor deposition (CVD)was ablated by femtosecond laser,and the obtained single-pulse ablation threshold of multi-layer graphene was 0.22 mW.The samples before and after processing were characterized by optical microscopy,atomic force microscope (AFM),and Raman spectroscopy,and the damage effects of femtosecond laser ablation on multi-layer graphene were demonstrated.The results show that femtosecond laser remains potential advantagesin gra-phene micro pattern processing with the precision of sub-micro meter;meanwhile,thinning phenomenonfor multi-layer graphene occurs at the edge of ablation area.%使用飞秒激光对化学气相沉积(CVD)法制备的多层石墨烯进行辐照,得到了多层石墨烯的单脉冲破坏阈值为0.22 mW;利用光学显微镜、原子力显微镜(AFM)和拉曼光谱对加工前、后的试样进行表征,阐述了飞秒激光对多层石墨烯的烧蚀损伤效应,发现飞秒激光在石墨烯微图案化加工方面具有潜在的优势,能够达到亚微米级的加工精度;同时在烧蚀边缘区域,多层石墨烯出现减薄现象。

  15. Enhanced photocurrent density in graphene/Si based solar cell (GSSC) by optimizing active layer thickness

    Energy Technology Data Exchange (ETDEWEB)

    Rosikhin, Ahmad, E-mail: a.rosikhin86@yahoo.co.id; Hidayat, Aulia Fikri; Syuhada, Ibnu; Winata, Toto, E-mail: toto@fi.itb.ac.id [Department of physics, physics of electronic materials research division Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jl. Ganesha 10, Bandung 40132, Jawa Barat – Indonesia (Indonesia)

    2015-12-29

    Thickness dependent photocurrent density in active layer of graphene/Si based solar cell has been investigated via analytical – simulation study. This report is a preliminary comparison of experimental and analytical investigation of graphene/Si based solar cell. Graphene sheet was interfaced with Si thin film forming heterojunction solar cell that was treated as a device model for photocurrent generator. Such current can be enhanced by optimizing active layer thickness and involving metal oxide as supporting layer to shift photons absorption. In this case there are two type of devices model with and without TiO{sub 2} in which the silicon thickness varied at 20 – 100 nm. All of them have examined and also compared with each other to obtain an optimum value. From this calculation it found that generated currents almost linear with thickness but there are saturated conditions that no more enhancements will be achieved. Furthermore TiO{sub 2} layer is effectively increases photon absorption but reducing device stability, maximum current is fluctuates enough. This may caused by the disturbance of excitons diffusion and resistivity inside each layer. Finally by controlling active layer thickness, it is quite useful to estimate optimization in order to develop the next solar cell devices.

  16. Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation

    Science.gov (United States)

    Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn

    2016-03-01

    Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.

  17. Atomic Layer Deposition Films as Diffusion Barriers for Silver Artifacts

    Science.gov (United States)

    Marquardt, Amy; Breitung, Eric; Drayman-Weisser, Terry; Gates, Glenn; Rubloff, Gary W.; Phaneuf, Ray J.

    2012-02-01

    Atomic layer deposition (ALD) was investigated as a means to create transparent oxide diffusion barrier coatings to reduce the rate of tarnishing for silver objects in museum collections. Accelerated aging by heating various thicknesses (5 to 100nm) of ALD alumina (Al2O3) thin films on sterling and fine silver was used to determine the effectiveness of alumina as a barrier to silver oxidation. The effect of aging temperature on the thickness of the tarnish layer (Ag2S) created at the interface of the ALD coating and the bulk silver substrate was determined by reflectance spectroscopy and X-Ray Photoelectric Spectroscopy (XPS). Reflectance spectroscopy was an effective rapid screening tool to determine tarnishing rates and the coating's visual impact. X-Ray Photoelectric Spectroscopy (XPS), and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) analysis showed a phase transformation in the Ag2S tarnish layer at 177 C and saturation in the thickness of the silver sulfide layer, indicating possible self-passivation of the tarnish layer.

  18. Atomic-Scale Characterization and Manipulation of Freestanding Graphene Using Adapted Capabilities of a Scanning Tunneling Microscope

    Science.gov (United States)

    Barber, Steven

    Graphene was the first two-dimensional material ever discovered, and it exhibits many unusual phenomena important to both pure and applied physics. To ensure the purest electronic structure, or to study graphene's elastic properties, it is often suspended over holes or trenches in a substrate. The aim of the research presented in this dissertation was to develop methods for characterizing and manipulating freestanding graphene on the atomic scale using a scanning tunneling microscope (STM). Conventional microscopy and spectroscopy techniques must be carefully reconsidered to account for movement of the extremely flexible sample. First, the acquisition of atomic-scale images of freestanding graphene using the STM and the ability to pull the graphene perpendicular to its plane by applying an electrostatic force with the STM tip are demonstrated. The atomic-scale images contained surprisingly large corrugations due to the electrostatic attractive force varying in registry with the local density of states. Meanwhile, a large range of control over the graphene height at a point was obtained by varying the tip bias voltage, and the application to strain engineering of graphene's so-called pseudomagnetic field is examined. Next, the effect of the tunneling current was investigated. With increasing current, the graphene sample moves away from the tip rather than toward it. It was determined that this must be due to local heating by the electric current, causing the graphene to contract because it has a negative coefficient of thermal expansion. Finally, by imaging a very small area, the STM can monitor the height of one location over long time intervals. Results sometimes exhibit periodic behavior, with a frequency and amplitude that depend on the tunneling current. These fluctuations are interpreted as low-frequency flexural phonon modes within elasticity theory. All of these findings set the foundation for employing a STM in the study of freestanding graphene.

  19. Broadband electromagnetic response and ultrafast dynamics of few-layer epitaxial graphene

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Hyunyong; Borondics, Ferenc; Siegel, David A.; Zhou, Shuyun Y.; Martin, Michael C.; Lanzara, Alessandra; Kaindl, Robert A.

    2009-03-26

    We study the broadband optical conductivity and ultrafast carrier dynamics of epitaxial graphene in the few-layer limit. Equilibrium spectra of nominally buffer, monolayer, and multilayer graphene exhibit significant terahertz and near-infrared absorption, consistent with a model of intra- and interband transitions in a dense Dirac electron plasma. Non-equilibrium terahertz transmission changes after photoexcitation are shown to be dominated by excess hole carriers, with a 1.2-ps mono-exponential decay that refects the minority-carrier recombination time.

  20. Friction and conductance imaging of sp(2)- and sp(3)-hybridized subdomains on single-layer graphene oxide.

    Science.gov (United States)

    Lee, Hyunsoo; Son, Narae; Jeong, Hu Young; Kim, Tae Gun; Bang, Gyeong Sook; Kim, Jong Yun; Shim, Gi Woong; Goddeti, Kalyan C; Kim, Jong Hun; Kim, Namdong; Shin, Hyun-Joon; Kim, Wondong; Kim, Sehun; Choi, Sung-Yool; Park, Jeong Young

    2016-02-21

    We investigated the subdomain structures of single-layer graphene oxide (GO) by characterizing local friction and conductance using conductive atomic force microscopy. Friction and conductance mapping showed that a single-layer GO flake has subdomains several tens to a few hundreds of nanometers in lateral size. The GO subdomains exhibited low friction (high conductance) in the sp(2)-rich phase and high friction (low conductance) in the sp(3)-rich phase. Current-voltage spectroscopy revealed that the local current flow in single-layer GO depends on the quantity of hydroxyl and carboxyl groups, and epoxy bridges within the 2-dimensional carbon layer. The presence of subdomains with different sp(2)/sp(3) carbon ratios on a GO flake was also confirmed by chemical mapping using scanning transmission X-ray microscopy. These results suggest that spatial mapping of the friction and conductance can be used to rapidly identify the composition of heterogeneous single-layer GO at nanometer scale, which is essential for understanding charge transport in nanoelectronic devices. PMID:26819189

  1. Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.

    Science.gov (United States)

    Sobel, Nicolas; Hess, Christian

    2015-12-01

    Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy.

  2. Nanoscale strain engineering of graphene and graphene-based devices

    Science.gov (United States)

    Yeh, N.-C.; Hsu, C.-C.; Teague, M. L.; Wang, J.-Q.; Boyd, D. A.; Chen, C.-C.

    2016-06-01

    Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here, we describe the theoretical foundation for strain-engineering of the electronic properties of graphene, and then provide experimental evidence for strain-induced pseudo-magnetic fields and charging effects in monolayer graphene. We further demonstrate the feasibility of nano-scale strain engineering for graphene-based devices by means of theoretical simulations and nano-fabrication technology.

  3. Nanoscale strain engineering of graphene and graphene-based devices

    Institute of Scientific and Technical Information of China (English)

    N-C Yeh; C-C Hsu; M L Teague; J-Q Wang; D A Boyd; C-C Chen

    2016-01-01

    Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here, we describe the theoretical foundation for strain-engineering of the electronic properties of graphene, and then provide experimental evidence for strain-induced pseudo-magnetic fields and charging effects in monolayer graphene. We further demonstrate the feasibility of nano-scale strain engineering for graphene-based devices by means of theoretical simula-tions and nano-fabrication technology.

  4. Atomic Layer Deposited Catalysts for Fuel Cell Applications

    DEFF Research Database (Denmark)

    Johansson, Anne-Charlotte Elisabeth Birgitta

    layer deposition (ALD), on the other hand, is a highly suitable and still relatively unexplored approach for the synthesis of noble metal catalysts. It is a vapor phase growth method, primarily used to deposit thin lms. ALD is based on self-limiting chemical reactions of alternately injected precursors...... for the realization of such tiny devices. It is a mature technology, suitable for mass production, where versatile structuring is available at the micro and nano regime. Carbon black supported catalysts synthesized by wet chemistry methods are not readily applicable for standard microfabrication techniques. Atomic...

  5. Single-Layer Graphene Enhances the Osteogenic Differentiation of Human Mesenchymal Stem Cells In Vitro and In Vivo.

    Science.gov (United States)

    Liu, Yunsong; Chen, Tong; Du, Feng; Gu, Ming; Zhang, Ping; Zhang, Xiao; Liu, Jianzhang; Lv, Longwei; Xiong, Chunyang; Zhou, Yongsheng

    2016-06-01

    In recent years, although several studies have demonstrated the potential of graphene-coated substrates in promoting attachment, proliferation and differentiation of osteoblasts and mesenchymal stem cells (MSCs), the effects of single-layer graphene on the osteogenic differentiation of human MSCs (hMSCs) remains unclear, especially in vivo. In this study, we transferred chemical vapor deposition (CVD) grown single-layer graphene to glass slides and observed its effects on adhesion, proliferation and osteogenic differentiation of human adipose-derived stem cells (hASCs) and human bone marrow mesenchymal stem cells (hBMMSCs) in vitro. Then, in vivo, we incubated hASCs and hBMMSCs on single-layer graphene-coated smooth titanium (Ti) disks before implanting them into the back subcutaneous area of nude mice. We found that single-layer graphene accelerated cell adhesion to the substrate without influencing cell proliferation of hMSCs. Moreover, we present the first study that explores the epigenetic role of single-layer graphene in determining stem cell fate. By utilizing epigenetic approaches, we reveal that single-layer graphene promotes osteogenic differentiation of hMSCs both in vitro and in vivo, potentially by upregulating methylation of H3K4 at the promoter regions of osteogenesis-associated genes. Overall, our results highlight the potential of this material in implants and injured tissues in clinical applications. PMID:27319220

  6. Single-Layer Graphene Enhances the Osteogenic Differentiation of Human Mesenchymal Stem Cells In Vitro and In Vivo.

    Science.gov (United States)

    Liu, Yunsong; Chen, Tong; Du, Feng; Gu, Ming; Zhang, Ping; Zhang, Xiao; Liu, Jianzhang; Lv, Longwei; Xiong, Chunyang; Zhou, Yongsheng

    2016-06-01

    In recent years, although several studies have demonstrated the potential of graphene-coated substrates in promoting attachment, proliferation and differentiation of osteoblasts and mesenchymal stem cells (MSCs), the effects of single-layer graphene on the osteogenic differentiation of human MSCs (hMSCs) remains unclear, especially in vivo. In this study, we transferred chemical vapor deposition (CVD) grown single-layer graphene to glass slides and observed its effects on adhesion, proliferation and osteogenic differentiation of human adipose-derived stem cells (hASCs) and human bone marrow mesenchymal stem cells (hBMMSCs) in vitro. Then, in vivo, we incubated hASCs and hBMMSCs on single-layer graphene-coated smooth titanium (Ti) disks before implanting them into the back subcutaneous area of nude mice. We found that single-layer graphene accelerated cell adhesion to the substrate without influencing cell proliferation of hMSCs. Moreover, we present the first study that explores the epigenetic role of single-layer graphene in determining stem cell fate. By utilizing epigenetic approaches, we reveal that single-layer graphene promotes osteogenic differentiation of hMSCs both in vitro and in vivo, potentially by upregulating methylation of H3K4 at the promoter regions of osteogenesis-associated genes. Overall, our results highlight the potential of this material in implants and injured tissues in clinical applications.

  7. Stanene: Atomically Thick Free-standing Layer of 2D Hexagonal Tin.

    Science.gov (United States)

    Saxena, Sumit; Chaudhary, Raghvendra Pratap; Shukla, Shobha

    2016-01-01

    Stanene is one of most important of 2D materials due to its potential to demonstrate room temperature topological effects due to opening of spin-orbit gap. In this pursuit we report synthesis and investigation of optical properties of stanene up to few layers, a two-dimensional hexagonal structural analogue of graphene. Atomic scale morphological and elemental characterization using HRTEM equipped with SAED and EDAX detectors confirm the presence of hexagonal lattice of Sn atoms. The position of Raman peak along with the inter-planar 'd' spacing obtained from SAED for prepared samples are in good agreement with that obtained from first principles calculations and confirm that the sheets are not (111) α-Sn sheets. Further, the optical signature calculated using density functional theory at ~191 nm and ~233 nm for low buckled stanene are in qualitative agreement with the measured UV-Vis absorption spectrum. AFM measurements suggest interlayer spacing of ~0.33 nm in good agreement with that reported for epitaxial stanene sheets. No traces of oxygen were observed in the EDAX spectrum suggesting the absence of any oxidized phases. This is also confirmed by Raman measurements by comparing with oxidized stanene sheets. PMID:27492139

  8. Blistering during the atomic layer deposition of iridium

    Energy Technology Data Exchange (ETDEWEB)

    Genevée, Pascal, E-mail: pascal-genevee@chimie-paristech.fr, E-mail: a.szeghalmi@uni-jena.de; Ahiavi, Ernest; Janunts, Norik; Pertsch, Thomas; Kley, Ernst-Bernhard; Szeghalmi, Adriana, E-mail: pascal-genevee@chimie-paristech.fr, E-mail: a.szeghalmi@uni-jena.de [Institut für Angewandte Physik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Oliva, Maria [Fraunhofer IOF, Albert-Einstein-Strasse 7, 07743 Jena (Germany)

    2016-01-15

    The authors report on the formation of blisters during the atomic layer deposition of iridium using iridium acetylacetonate and oxygen precursors. Films deposited on fused silica substrates led to sparsely distributed large blisters while in the case of silicon with native oxide additional small blisters with a high density was observed. It is found that the formation of blisters is favored by a higher deposition temperature and a larger layer thickness. Postdeposition annealing did not have a significant effect on the formation of blisters. Finally, changing purge duration during the film growth allowed us to avoid blistering and evidenced that impurities released from the film in gas phase were responsible for the formation of blisters.

  9. Reusable urine glucose sensor based on functionalized graphene oxide conjugated Au electrode with protective layers

    Directory of Open Access Journals (Sweden)

    Hye Youn Kim

    2014-09-01

    Full Text Available An electrochemical based system with multiple layers coated on a functionalized graphene oxide Au electrode was developed to measure glucose concentration in urine in a more stable way. Two types of gold printed circuit boards were fabricated and graphene oxide was immobilized on their surface by chemical adsorption. Multiple layers, composed of a couple of polymers, were uniformly coated on the surface electrode. This device exhibited higher electrochemical responses against glucose, a greater resistivity in the presence of interferential substances in urine, and durable stabilities for longer periods of time than conventional units. The efficiency in current level according to the order and ratio of solution was evaluated during the immobilization of the layer. The fabricated electrodes were then also evaluated using hyperglycemic clinical samples and compared with the patterns of blood glucose measured with commercially available glucose meters. Our findings show that not only was their pattern similar but this similarity is well correlated.

  10. Quantum dynamics of hydrogen atoms on graphene. I. System-bath modeling

    International Nuclear Information System (INIS)

    An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics

  11. Quantum dynamics of hydrogen atoms on graphene. I. System-bath modeling

    Energy Technology Data Exchange (ETDEWEB)

    Bonfanti, Matteo, E-mail: matteo.bonfanti@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Jackson, Bret [Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Hughes, Keith H. [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany); Martinazzo, Rocco, E-mail: rocco.martinazzo@unimi.it [Dipartimento di Chimica, Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Richerche, v. Golgi 19, 20133 Milano (Italy)

    2015-09-28

    An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics.

  12. Rice husk-derived graphene with nano-sized domains and clean edges.

    Science.gov (United States)

    Muramatsu, Hiroyuki; Kim, Yoong Ahm; Yang, Kap-Seung; Cruz-Silva, Rodolfo; Toda, Ikumi; Yamada, Takumi; Terrones, Mauricio; Endo, Morinobu; Hayashi, Takuya; Saitoh, Hidetoshi

    2014-07-23

    A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.

  13. Electrochemical Reaction in Single Layer MoS2: Nanopores Opened Atom by Atom.

    Science.gov (United States)

    Feng, J; Liu, K; Graf, M; Lihter, M; Bulushev, R D; Dumcenco, D; Alexander, D T L; Krasnozhon, D; Vuletic, T; Kis, A; Radenovic, A

    2015-05-13

    Ultrathin nanopore membranes based on 2D materials have demonstrated ultimate resolution toward DNA sequencing. Among them, molybdenum disulfide (MoS2) shows long-term stability as well as superior sensitivity enabling high throughput performance. The traditional method of fabricating nanopores with nanometer precision is based on the use of focused electron beams in transmission electron microscope (TEM). This nanopore fabrication process is time-consuming, expensive, not scalable, and hard to control below 1 nm. Here, we exploited the electrochemical activity of MoS2 and developed a convenient and scalable method to controllably make nanopores in single-layer MoS2 with subnanometer precision using electrochemical reaction (ECR). The electrochemical reaction on the surface of single-layer MoS2 is initiated at the location of defects or single atom vacancy, followed by the successive removals of individual atoms or unit cells from single-layer MoS2 lattice and finally formation of a nanopore. Step-like features in the ionic current through the growing nanopore provide direct feedback on the nanopore size inferred from a widely used conductance vs pore size model. Furthermore, DNA translocations can be detected in situ when as-fabricated MoS2 nanopores are used. The atomic resolution and accessibility of this approach paves the way for mass production of nanopores in 2D membranes for potential solid-state nanopore sequencing. PMID:25928894

  14. Atomic layer deposition of alternative glass microchannel plates

    Energy Technology Data Exchange (ETDEWEB)

    O' Mahony, Aileen, E-mail: aom@incomusa.com; Craven, Christopher A.; Minot, Michael J.; Popecki, Mark A.; Renaud, Joseph M.; Bennis, Daniel C.; Bond, Justin L.; Stochaj, Michael E.; Foley, Michael R.; Adams, Bernhard W. [Incom, Inc., 294 Southbridge Road, Charlton, Massachusetts 01507 (United States); Mane, Anil U.; Elam, Jeffrey W. [Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439 (United States); Ertley, Camden; Siegmund, Oswald H. W. [Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, California 94720 (United States)

    2016-01-15

    The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm{sup 2}). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm{sup −2} s{sup −1}), and low gain variation (±5%)

  15. Atomically-thin molecular layers for electrode modification of organic transistors.

    Science.gov (United States)

    Gim, Yuseong; Kang, Boseok; Kim, BongSoo; Kim, Sun-Guk; Lee, Joong-Hee; Cho, Kilwon; Ku, Bon-Cheol; Cho, Jeong Ho

    2015-09-01

    Atomically-thin molecular layers of aryl-functionalized graphene oxides (GOs) were used to modify the surface characteristics of source-drain electrodes to improve the performances of organic field-effect transistor (OFET) devices. The GOs were functionalized with various aryl diazonium salts, including 4-nitroaniline, 4-fluoroaniline, or 4-methoxyaniline, to produce several types of GOs with different surface functional groups (NO2-Ph-GO, F-Ph-GO, or CH3O-Ph-GO, respectively). The deposition of aryl-functionalized GOs or their reduced derivatives onto metal electrode surfaces dramatically enhanced the electrical performances of both p-type and n-type OFETs relative to the performances of OFETs prepared without the GO modification layer. Among the functionalized rGOs, CH3O-Ph-rGO yielded the highest hole mobility of 0.55 cm(2) V(-1) s(-1) and electron mobility of 0.17 cm(2) V(-1) s(-1) in p-type and n-type FETs, respectively. Two governing factors: (1) the work function of the modified electrodes and (2) the crystalline microstructures of the benchmark semiconductors grown on the modified electrode surface were systematically investigated to reveal the origin of the performance improvements. Our simple, inexpensive, and scalable electrode modification technique provides a significant step toward optimizing the device performance by engineering the semiconductor-electrode interfaces in OFETs.

  16. Chemical Vapor Deposited Few-Layer Graphene as an Electron Field Emitter.

    Science.gov (United States)

    Behural, Sanjay K; Nayak, Sasmita; Yang, Qiaoqin; Hirose, Akira; Janil, Omkar

    2016-01-01

    Chemical vapor deposition (CVD) growth of graphene on polycrystalline copper (Cu) foil in a low pressure conditions has been presented, aiming to achieve the highest quality with large-scale fabrications, which requires comprehensive understanding and effective controlling of the growth process. Herein, few-layer graphene (FLG) films with large-domain sizes were grown on Cu metal catalyst substrates using a vertical mass-flow hot-filament CVD reactor, with the intention of large scale production, by optimizing the CVD system and three of the process parameters: (i) gas flow compositions, (ii) substrate annealing time and (iii) graphene deposition time. The detailed scanning electron microscope and Raman spectroscopy analysis indicate that all the above mentioned process parameters affect growth of FLG film on Cu substrate. The presence of two intense peaks, G and 2D-band at 1583.6 and 2702.6 cm⁻¹ for synthesized sample at optimized conditions (H₂/CH₄ ratio of 50:1 at graphene deposition time of 10 minutes and substrate annealed time for 20 minutes) revealed the formation of FLG films with large domain size. These graphene films on Cu have shown the room temperature field electron emission characteristics, hence appears to be prospective candidate for vacuum nanoelectronics. PMID:27398456

  17. A theoretical study of pump–probe experiment in single-layer, bilayer and multilayer graphene

    Indian Academy of Sciences (India)

    Enamullah; Vipin Kumar; Upendra Kumar; Girish S Setlur

    2014-06-01

    The pump–probe experiment is typically used to study relaxation phenomena in nonlinear optical systems. Here we use it as a tool to study the phenomenon of anomalous Rabi oscillations in graphene that was predicted recently in single-layer graphene. Unlike conventional Rabi oscillations, anomalous Rabi oscillations are unique to graphene (and possibly to surface states of topological insulators (TIs)), attributable to the pseudospin (conventional spin for TI) degree of freedom and Dirac-fermion character of the graphene system. A pump pulse of a finite duration long enough to contain a large number of cycles induces a current density that oscillates with the frequency of the pump pulse. The amplitude associated with these fast oscillations is seen to exhibit much slower oscillations with a frequency given by $2^2_R/$–the anomalous Rabi frequency, where $_R$ is the conventional Rabi frequency and is the frequency of the external pump field. This effect is easily probed by a probe pulse subsequent to the pump, where it manifests itself as periodic oscillations of the probe susceptibility as a function of pump duration at each probe frequency. Alternatively, it is also seen as an oscillatory function of the pump–probe delay with other variables remaining fixed. This period corresponds to the anomalous Rabi frequency. An analysis of the previously reported experimental data confirms the presence of anomalous Rabi oscillations in graphene.

  18. Vertex-Atom-Dependent Rectification in Triangular h-BNC/Triangular Graphene Heterojunctions

    Science.gov (United States)

    Wang, Lihua; Zhao, Jianguo; Zhang, Zizhen; Ding, Bingjun; Guo, Yong

    2016-08-01

    First-principles calculations have shown dramatically unexpected rectifying regularities in particular heterojunction configurations with triangular hexagonal boron-nitride-carbon ( h-BNC) and triangular graphene (TG) sandwiched between two armchair graphene nanoribbon electrodes. When the triangular h-BNC and TG are linked by vertex atoms of nitrogen and carbon (boron and carbon), forward (reverse) rectifying performance can be observed. Moreover, for a certain linking mode, the larger the elemental proportion p (where p = N_{{{boron}} + {{nitrogen}}} /N_{{{boron}} + {{nitrogen}} + {{carbon}}} ) in the h-BNC, the larger the ratio for forward (reverse) rectification. A mechanism for these rectification behaviors is suggested. The findings provide insights into control of rectification behaviors in TG-based nanodevices.

  19. An Atomically Layered InSe Avalanche Photodetector.

    Science.gov (United States)

    Lei, Sidong; Wen, Fangfang; Ge, Liehui; Najmaei, Sina; George, Antony; Gong, Yongji; Gao, Weilu; Jin, Zehua; Li, Bo; Lou, Jun; Kono, Junichiro; Vajtai, Robert; Ajayan, Pulickel; Halas, Naomi J

    2015-05-13

    Atomically thin photodetectors based on 2D materials have attracted great interest due to their potential as highly energy-efficient integrated devices. However, photoinduced carrier generation in these media is relatively poor due to low optical absorption, limiting device performance. Current methods for overcoming this problem, such as reducing contact resistances or back gating, tend to increase dark current and suffer slow response times. Here, we realize the avalanche effect in a 2D material-based photodetector and show that avalanche multiplication can greatly enhance the device response of an ultrathin InSe-based photodetector. This is achieved by exploiting the large Schottky barrier formed between InSe and Al electrodes, enabling the application of a large bias voltage. Plasmonic enhancement of the photosensitivity, achieved by patterning arrays of Al nanodisks onto the InSe layer, further improves device efficiency. With an external quantum efficiency approaching 866%, a dark current in the picoamp range, and a fast response time of 87 μs, this atomic layer device exhibits multiple significant advances in overall performance for this class of devices.

  20. Atomic layer deposition of superparamagnetic and ferrimagnetic magnetite thin films

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yijun; Liu, Ming, E-mail: mingliu@mail.xjtu.edu.cn, E-mail: wren@mail.xjtu.edu.cn, E-mail: zye@sfu.ca; Ren, Wei, E-mail: mingliu@mail.xjtu.edu.cn, E-mail: wren@mail.xjtu.edu.cn, E-mail: zye@sfu.ca [Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi' an Jiaotong University, Xi' an 710049 (China); Zhang, Yuepeng; Chen, Xing [Energy Systems Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States); Ye, Zuo-Guang, E-mail: mingliu@mail.xjtu.edu.cn, E-mail: wren@mail.xjtu.edu.cn, E-mail: zye@sfu.ca [Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi' an Jiaotong University, Xi' an 710049 (China); Department of Chemistry and 4D LABS, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada)

    2015-05-07

    One of the key challenges in realizing superparamagnetism in magnetic thin films lies in finding a low-energy growth way to create sufficiently small grains and magnetic domains which allow the magnetization to randomly and rapidly reverse. In this work, well-defined superparamagnetic and ferrimagnetic Fe{sub 3}O{sub 4} thin films are successfully prepared using atomic layer deposition technique by finely controlling the growth condition and post-annealing process. As-grown Fe{sub 3}O{sub 4} thin films exhibit a conformal surface and poly-crystalline nature with an average grain size of 7 nm, resulting in a superparamagnetic behavior with a blocking temperature of 210 K. After post-annealing in H{sub 2}/Ar at 400 °C, the as-grown α−Fe{sub 2}O{sub 3} sample is reduced to Fe{sub 3}O{sub 4} phase, exhibiting a ferrimagnetic ordering and distinct magnetic shape anisotropy. Atomic layer deposition of magnetite thin films with well-controlled morphology and magnetic properties provides great opportunities for integrating with other order parameters to realize magnetic nano-devices with potential applications in spintronics, electronics, and bio-applications.

  1. Catalytically active single-atom niobium in graphitic layers.

    Science.gov (United States)

    Zhang, Xuefeng; Guo, Junjie; Guan, Pengfei; Liu, Chunjing; Huang, Hao; Xue, Fanghong; Dong, Xinglong; Pennycook, Stephen J; Chisholm, Matthew F

    2013-01-01

    Carbides of groups IV through VI (Ti, V and Cr groups) have long been proposed as substitutes for noble metal-based electrocatalysts in polymer electrolyte fuel cells. However, their catalytic activity has been extremely limited because of the low density and stability of catalytically active sites. Here we report the excellent performance of a niobium-carbon structure for catalysing the cathodic oxygen reduction reaction. A large number of single niobium atoms and ultra small clusters trapped in graphitic layers are directly identified using state-of-the-art aberration-corrected scanning transmission electron microscopy. This structure not only enhances the overall conductivity for accelerating the exchange of ions and electrons, but it suppresses the chemical/thermal coarsening of the active particles. Experimental results coupled with theory calculations reveal that the single niobium atoms incorporated within the graphitic layers produce a redistribution of d-band electrons and become surprisingly active for O2 adsorption and dissociation, and also exhibit high stability. PMID:23715283

  2. Plasma enhanced atomic layer deposition of silicon nitride using neopentasilane

    Energy Technology Data Exchange (ETDEWEB)

    Weeks, Stephen, E-mail: Stephen.Weeks@intermolecular.com; Nowling, Greg; Fuchigami, Nobi; Bowes, Michael; Littau, Karl [Intermolecular, 3011 North 1st Street, San Jose, California 95134 (United States)

    2016-01-15

    Progress in transistor scaling has increased the demands on the material properties of silicon nitride (SiN{sub x}) thin films used in device fabrication and at the same time placed stringent restrictions on the deposition conditions employed. Recently, low temperature plasma enhanced atomic layer deposition has emerged as a viable technique for depositing these films with a thermal budget compatible with semiconductor processing at sub-32 nm technology nodes. For these depositions, it is desirable to use precursors that are free from carbon and halogens that can incorporate into the film. Beyond this, it is necessary to develop processing schemes that minimize the wet etch rate of the film as it will be subjected to wet chemical processing in subsequent fabrication steps. In this work, the authors introduce low temperature deposition of SiN{sub x} using neopentasilane [NPS, (SiH{sub 3}){sub 4}Si] in a plasma enhanced atomic layer deposition process with a direct N{sub 2} plasma. The growth with NPS is compared to a more common precursor, trisilylamine [TSA, (SiH{sub 3}){sub 3 }N] at identical process conditions. The wet etch rates of the films deposited with NPS are characterized at different plasma conditions and the impact of ion energy is discussed.

  3. Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils

    OpenAIRE

    Chung, Ting Fung; Shen, Tian; Cao, Helin; Jauregui, Luis A.; Wu, Wei; Yu, Qingkai; Newell, David; Chen, Yong P.

    2013-01-01

    The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interests. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapour deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality compar...

  4. Few layer graphene synthesis via SiC decomposition at low temperature and low vacuum

    Science.gov (United States)

    Kayali, Emre; Mercan, Elif; Emre Oren, Ersin; Cambaz Buke, Goknur

    2016-04-01

    Based on the large-scale availability and good electrical properties, the epitaxial graphene (EG) on SiC exhibits a big potential for future electronic devices. However, it is still necessary to work continuously on lowering the formation temperature and vacuum values of EG while improving the quality and increasing the lateral size to fabricate high-performance electronic devices at reduced processing costs. In this study, we investigated the effect of the presence of Mo plate and hydrogen atmosphere as well as the vacuum annealing durations on SiC decomposition. Our studies showed that the graphene layers can be produced at lower annealing temperatures (1200 °C) and vacuum values (10-4 Torr) in the presence of Mo plate and hydrogen. For high quality continuous graphene formation, Mo plate should be in contact with SiC. If there is a gap between Mo and SiC, non-wetting oxide droplets on few layer graphene (FLG) are recorded. Moreover, it is found that the morphology of these islands can be controlled by changing the annealing time and atmosphere conditions, and applying external disturbances such as vibration.

  5. Modification of SnO2 Anodes by Atomic Layer Deposition for High Performance Lithium Ion Batteries

    KAUST Repository

    Yesibolati, Nulati

    2013-05-01

    Tin dioxide (SnO2) is considered one of the most promising anode materials for Lithium ion batteries (LIBs), due to its large theoretical capacity and natural abundance. However, its low electronic/ionic conductivities, large volume change during lithiation/delithiation and agglomeration prevent it from further commercial applications. In this thesis, we investigate modified SnO2 as a high energy density anode material for LIBs. Specifically two approaches are presented to improve battery performances. Firstly, SnO2 electrochemical performances were improved by surface modification using Atomic Layer Deposition (ALD). Ultrathin Al2O3 or HfO2 were coated on SnO2 electrodes. It was found that electrochemical performances had been enhanced after ALD deposition. In a second approach, we implemented a layer-by-layer (LBL) assembled graphene/carbon-coated hollow SnO2 spheres as anode material for LIBs. Our results indicated that the LBL assembled electrodes had high reversible lithium storage capacities even at high current densities. These superior electrochemical performances are attributed to the enhanced electronic conductivity and effective lithium diffusion, because of the interconnected graphene/carbon networks among nanoparticles of the hollow SnO2 spheres.

  6. Graphene on graphene antidot lattices

    DEFF Research Database (Denmark)

    Gregersen, Søren Schou; Pedersen, Jesper Goor; Power, Stephen;

    2015-01-01

    Graphene bilayer systems are known to exhibit a band gap when the layer symmetry is broken by applying a perpendicular electric field. The resulting band structure resembles that of a conventional semiconductor with a parabolic dispersion. Here, we introduce a bilayer graphene heterostructure......, where single-layer graphene is placed on top of another layer of graphene with a regular lattice of antidots. We dub this class of graphene systems GOAL: graphene on graphene antidot lattice. By varying the structure geometry, band-structure engineering can be performed to obtain linearly dispersing...

  7. Coupled TM surface plasmon features of graphene-metal layered structure in the sub-THz frequency range

    International Nuclear Information System (INIS)

    TM surface plasmon (SP) characteristics of a four-layer structure, consisting of air as the superstrate, a monolayer of graphene, a dielectric buffer layer and metal as the substrate are analyzed at sub-THz frequencies. TM SPs in such case are represented by metal-like and graphene-like branches. For small frequencies the metal-like plasmon splits up into two branches depending on the graphene electron concentration; one of the branches goes into cutoff at the point where the branch features Brewster-type characteristics. Graphene-like plasmon modes are converted into short-range modes for small buffer thicknesses. Brewster-type SP modes can be effectively modulated in the vicinity of their cutoff thicknesses by means of the graphene electron concentration. (paper)

  8. Cyclododecane as support material for clean and facile transfer of large-area few-layer graphene

    International Nuclear Information System (INIS)

    The transfer of chemical vapor deposited graphene is a crucial process, which can affect the quality of the transferred films and compromise their application in devices. Finding a robust and intrinsically clean material capable of easing the transfer of graphene without interfering with its properties remains a challenge. We here propose the use of an organic compound, cyclododecane, as a transfer material. This material can be easily spin coated on graphene and assist the transfer, leaving no residues and requiring no further removal processes. The effectiveness of this transfer method for few-layer graphene on a large area was evaluated and confirmed by microscopy, Raman spectroscopy, x-ray photoemission spectroscopy, and four-point probe measurements. Schottky-barrier solar cells with few-layer graphene were fabricated on silicon wafers by using the cyclododecane transfer method and outperformed reference cells made by standard methods.

  9. The diversity of friction behavior between bi-layer graphenes

    International Nuclear Information System (INIS)

    For relative sliding between two rigid graphene sheets that are interacted on by a van der Waals force, we show that the friction behavior is significantly dependent on the interlayer separation distance h. Around the equilibrium interlayer distance he, the friction behavior exactly obeys a linear law. When h is far smaller than he, the linear friction behavior transforms to over-linear behavior. On the other hand, when h is larger than he, there is another critical value of the interlayer distance, hc; when h is larger than he and smaller than hc, the friction behavior transforms from linear to sub-linear behavior; however, when h is larger than hc, the coefficient of friction becomes negative. Further, the different friction behaviors are found to be well described by a universal power law, τ = μ∗(σ + σ0)n. (paper)

  10. Three-dimensional graphene-polyaniline hybrid hollow spheres by layer-by-layer assembly for application in supercapacitor

    International Nuclear Information System (INIS)

    Highlights: •A graphene-polyaniline (GR-PANI) hybrid hollow sphere is fabricated by layer-by-layer (LBL) assembly technique. •The GR-PANI hollow sphere has higher specific capacitance than stacked GR-PANI LBL film. •64% of its initial capacitance is maintained with the current density increased from 0.5 to 20 A g−1. •A high capacity retention rate of 83% after 1000 cycles can be achieved. -- Abstract: A novel kind of three-dimensional graphene-polyaniline hybrid hollow sphere (RGO-PANI HS) has been prepared via layer-by-layer (LBL) assembly of negatively-charged reduced graphene oxide (RGO) and positively charged polyaniline (PANI) on polystyrene (PS) microsphere, followed by the removal of the PS template. The hollow structure of the obtained RGO-PANI HS is confirmed by transmission electron microscopy (TEM). When used as the electrode materials for supercapacitor, the specific capacitance of the RGO-PANI HS reaches 381 F/g at a current density of 4.0 A/g, which is much higher than 251 F/g of the stacked RGO-PANI LBL film. The higher specific capacitance of RGO-PANI HS should be attributed to its unique hollow structure which provides a larger accessible surface area and facilitate the charge and ion transport. In addition, its specific capacitance can be facilely tailored by changing the assembly cycle number. Furthermore, good cycling stability is also demonstrated with 83% of the original capacitance value maintained after 1000 charging/discharging cycles

  11. Electrochemical properties of CVD grown pristine graphene: monolayer- vs. quasi-graphene

    Science.gov (United States)

    Brownson, Dale A. C.; Varey, Sarah A.; Hussain, Fiazal; Haigh, Sarah J.; Banks, Craig E.

    2014-01-01

    We report the electrochemical properties of pristine monolayer, double layer and few-layer (termed quasi-) graphene grown via CVD and transferred using PMMA onto an insulating substrate (silicon dioxide wafers). Characterisation has been performed by Raman spectroscopy, optical spectroscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy, revealing `true' pristine single-layer graphene (O/C of 0.05) at the former and pristine quasi-graphene at the latter (O/C of 0.07); the term ``quasi-graphene'' is coined due to the surface comprising on average 4-graphene-layers. The graphene electrodes are electrochemically characterised using both inner-sphere and outer-sphere redox probes with electrochemical performances of the graphene electrodes compared to other available graphitic electrodes, namely that of basal- and edge- plane pyrolytic graphite electrodes constructed from Highly Ordered Pyrolytic Graphite (HOPG), with information on heterogeneous rate constants (ko) obtained. The electrochemical rate constants are predominantly influenced by the electronic properties of the graphene surfaces. Monolayer graphene is found to exhibit slow heterogeneous electron transfer (HET) kinetics towards the redox probes studied, with HET rates ca. 2 and 8 times faster at quasi-graphene and HOPG respectively, relative to that of the monolayer graphene electrode. Critically contrasting the performance of monolayer graphene to quasi-graphene and HOPG electrodes reveals that increasing the number of graphene layers results in improved electrochemical properties, where in terms of the electrochemical reversibility of the probes studied: monolayer-graphene graphene electron transfer kinetics at graphitic materials, the slow HET rates at pristine single-layer graphene electrodes are likely due to graphene's fundamental geometry, which comprises a small edge plane and large basal plane contribution. In the case of quasi-graphene and HOPG, they possess increasing global

  12. Spontaneous and strong multi-layer graphene n-doping on soda-lime glass and its application in graphene-semiconductor junctions

    Science.gov (United States)

    Dissanayake, D. M. N. M.; Ashraf, A.; Dwyer, D.; Kisslinger, K.; Zhang, L.; Pang, Y.; Efstathiadis, H.; Eisaman, M. D.

    2016-02-01

    Scalable and low-cost doping of graphene could improve technologies in a wide range of fields such as microelectronics, optoelectronics, and energy storage. While achieving strong p-doping is relatively straightforward, non-electrostatic approaches to n-dope graphene, such as chemical doping, have yielded electron densities of 9.5 × 1012 e/cm2 or below. Furthermore, chemical doping is susceptible to degradation and can adversely affect intrinsic graphene’s properties. Here we demonstrate strong (1.33 × 1013 e/cm2), robust, and spontaneous graphene n-doping on a soda-lime-glass substrate via surface-transfer doping from Na without any external chemical, high-temperature, or vacuum processes. Remarkably, the n-doping reaches 2.11 × 1013 e/cm2 when graphene is transferred onto a p-type copper indium gallium diselenide (CIGS) semiconductor that itself has been deposited onto soda-lime-glass, via surface-transfer doping from Na atoms that diffuse to the CIGS surface. Using this effect, we demonstrate an n-graphene/p-semiconductor Schottky junction with ideality factor of 1.21 and strong photo-response. The ability to achieve strong and persistent graphene n-doping on low-cost, industry-standard materials paves the way toward an entirely new class of graphene-based devices such as photodetectors, photovoltaics, sensors, batteries, and supercapacitors.

  13. Spontaneous and strong multi-layer graphene n-doping on soda-lime glass and its application in graphene-semiconductor junctions

    Science.gov (United States)

    Dissanayake, D. M. N. M.; Ashraf, A.; Dwyer, D.; Kisslinger, K.; Zhang, L.; Pang, Y.; Efstathiadis, H.; Eisaman, M. D.

    2016-01-01

    Scalable and low-cost doping of graphene could improve technologies in a wide range of fields such as microelectronics, optoelectronics, and energy storage. While achieving strong p-doping is relatively straightforward, non-electrostatic approaches to n-dope graphene, such as chemical doping, have yielded electron densities of 9.5 × 1012 e/cm2 or below. Furthermore, chemical doping is susceptible to degradation and can adversely affect intrinsic graphene’s properties. Here we demonstrate strong (1.33 × 1013 e/cm2), robust, and spontaneous graphene n-doping on a soda-lime-glass substrate via surface-transfer doping from Na without any external chemical, high-temperature, or vacuum processes. Remarkably, the n-doping reaches 2.11 × 1013 e/cm2 when graphene is transferred onto a p-type copper indium gallium diselenide (CIGS) semiconductor that itself has been deposited onto soda-lime-glass, via surface-transfer doping from Na atoms that diffuse to the CIGS surface. Using this effect, we demonstrate an n-graphene/p-semiconductor Schottky junction with ideality factor of 1.21 and strong photo-response. The ability to achieve strong and persistent graphene n-doping on low-cost, industry-standard materials paves the way toward an entirely new class of graphene-based devices such as photodetectors, photovoltaics, sensors, batteries, and supercapacitors. PMID:26867673

  14. Single layered flexible photo-detector based on perylene/graphene composite through printed technology

    Science.gov (United States)

    Ali, Shawkat; Bae, Jinho; Lee, Chong Hyun

    2015-07-01

    In this paper, a single layered passive photo sensor based on perylene/graphene composite is proposed, which is deposited in comb type silver electrodes separated as 50 μm spacing. To increase an electrical conductivity of the proposed sensor, perylene and graphene are blended. Photo sensing layer (120nm thick) and Silver electrodes (50 μm width, 350 nm thick) are deposited on poly(ethylene terephthalate) (PET) substrate through electro-hydrodynamic (EHD) system. The proposed photo sensor detects a terminal resistance inversely varied by an incident light in the range between 78 GΩ in dark and 25 GΩ at light intensity of 400lux. The device response is maximum at 465 nm ~ 535 nm wavelength range at blue light. The device exhibited bendability up to 4mm diameter for 1000 endurance cycles. The surface morphology analysis is carried out with FE-SEM and microscope.

  15. Tunable photoresponse with small drain voltage in few-layer graphene-WSe2 heterostructures

    Science.gov (United States)

    Luo, Wei; Qin, Shiqiao; Long, Mingsheng; Liu, Erfu; Fu, Yajun; Zhou, Wei; Miao, Feng; Zhang, Sen; Zhang, Renyan; Zhang, Xue-Ao

    2016-07-01

    Two-dimensional layered heterostructures show great potential to develop optoelectronic systems. Here, we have investigated the photoresponse properties of two contact interfaces in few-layer graphene-WSe2 heterostructures. The photoresponsivity of graphene-WSe2 contact interface is about 2.67 mA/W, and the photoresponsivity of WSe2-metal contact interface is about 0.2 mA/W. Photocurrent images show that the two contact interfaces behave differently under drain voltage from - 0.5 V to 0.5 V. The photoresponsivity of one contact interface increases with the drain voltage, and that of the other decreases with the drain voltage. Experimental results and band diagram studies prove that the photoresponse properties of contact interfaces are tuned by small drain voltage. This study will be beneficial for understanding the effect of drain voltage on the heterostructures.

  16. Molecular dynamics simulation for interlayer interactions of graphene nanoribbons with multiple layers

    Science.gov (United States)

    Nazemnezhad, Reza; Zare, Mojtaba; Hosseini-Hashemi, Shahrokh; Shokrollahi, Hassan

    2016-10-01

    A new study is conducted with the aid of molecular dynamics (MD) simulation to investigate the effect of shear modulus value of the interlayer van der Waals (vdWs) interactions on free vibration of cantilever multi-layer graphene nanoribbons (MLGNRs). The corresponding calibrated nonlocal parameters of the nonlocal model are obtained accordingly. The vdWs interactions are treated as the cores between every two adjacent graphene layers and their equivalent shear modulus is calculated using MD simulation. The obtained resonant frequencies via the nonlocal sandwich model are compared to the MD simulation results to calibrate the nonlocal parameter. Results reveal a strong conclusion that the calibrated nonlocal parameter is dependent on the values of interlayer shear modulus.

  17. Electrostatically transparent graphene quantum-dot trap layers for efficient nonvolatile memory

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Rae; Jo, Yong Eun; Sung, Yeo Hyun; Won, Ui Yeon [Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Shin, Yong Seon; Kang, Won Tae; Yu, Woo Jong, E-mail: leeyoung@skku.edu, E-mail: micco21@skku.edu [Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Lee, Young Hee, E-mail: leeyoung@skku.edu, E-mail: micco21@skku.edu [Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Department of Energy Science, BK21 Physics Division, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2015-03-09

    In this study, we have demonstrated nonvolatile memory devices using graphene quantum-dots (GQDs) trap layers with indium zinc oxide (IZO) semiconductor channel. The Fermi-level of GQD was effectively modulated by tunneling electrons near the Dirac point because of limited density of states and weak electrostatic screening in monolayer graphene. As a result, large gate modulation was driven in IZO channel to achieve a subthreshold swing of 5.21 V/dec (300 nm SiO{sub 2} gate insulator), while Au quantum-dots memory shows 15.52 V/dec because of strong electrostatic screening in metal quantum-dots. Together, discrete charge traps of GQDs enable stable performance in the endurance test beyond 800 cycles of programming and erasing. Our study suggests the exciting potential of GQD trap layers to be used for a highly promising material in non-volatile memory devices.

  18. The over-step coalescence of carbon atoms on copper surface in the CVD growth of graphene: density functional calculations

    Directory of Open Access Journals (Sweden)

    Yingfeng Li

    2013-05-01

    Full Text Available The ways in which carbon atoms coalesce over the steps on copper (111 surface are ascertained by density functional theory (DFT calculations in the context of chemical vapor deposition (CVD growth of graphene. Two strategies, (1 by putting carbon atoms on and under the steps separately and (2 by importing additional carbon atoms between the ones separated by the steps, have been attempted to investigate if an over-step coalescence of carbon atoms could take place. Based on analyses about the optimized configurations and adsorption energies of carbon atoms nearby the steps, as well as the energy evolution curve of the system throughout the geometry optimizations process, we determined the main way in which graphene grows over the steps continuously: the carbon atoms, adsorbed additionally on the locations between the already existing ones which are separated by the steps, link them (these carbon atoms separated by the steps together. The direct over-step coalescence of the carbon atoms separated by the steps is very difficult, although the energy barrier preventing their coalescence can be weakened by importing carbon atoms on and under the steps gradually. Our results imply potential applications in directing the fabrication of graphene with particular structure by controlling the surface topography of copper substrate.

  19. Theoretical study of the dynamics of atomic hydrogen adsorbed on graphene multilayers

    Science.gov (United States)

    Moaied, Mohammed; Moreno, J. A.; Caturla, M. J.; Ynduráin, Félix; Palacios, J. J.

    2015-04-01

    We present a theoretical study of the dynamics of H atoms adsorbed on graphene bilayers with Bernal stacking. First, through extensive density functional theory calculations, including van der Waals interactions, we obtain the activation barriers involved in the desorption and migration processes of a single H atom. These barriers, along with attempt rates and the energetics of H pairs, are used as input parameters in kinetic Monte Carlo simulations to study the time evolution of an initial random distribution of adsorbed H atoms. The simulations reveal that, at room temperature, H atoms occupy only one sublattice before they completely desorb or form clusters. This sublattice selectivity in the distribution of H atoms may last for sufficiently long periods of time upon lowering the temperature down to 0 ∘C . The final fate of the H atoms, namely, desorption or cluster formation, depends on the actual relative values of the activation barriers which can be tuned by doping. In some cases, a sublattice selectivity can be obtained for periods of time experimentally relevant even at room temperature. This result shows the possibility for observation and applications of the ferromagnetic state associated with such distribution.

  20. Graphene-like optical light field and its interaction with two-level atoms

    Science.gov (United States)

    Lembessis, V. E.; Courtial, Johannes; Radwell, N.; Selyem, A.; Franke-Arnold, S.; Aldossary, O. M.; Babiker, M.

    2015-12-01

    The theoretical basis leading to the creation of a light field with a hexagonal honeycomb structure resembling graphene is considered along with its experimental realization and its interaction with atoms. It is argued that associated with such a light field is an optical dipole potential which leads to the diffraction of the atoms, but the details depend on whether the transverse spread of the atomic wave packet is larger than the transverse dimensions of the optical lattice (resonant Kapitza-Dirac effect) or smaller (optical Stern-Gerlach effect). Another effect in this context involves the creation of gauge fields due to the Berry phase acquired by the atom moving in the light field. The experimental realization of the light field with a honeycomb hexagonal structure is described using holographic methods and we proceed to explore the atom diffraction in the Kapitza-Dirac regime as well as the optical Stern-Gerlach regime, leading to momentum distributions with characteristic but different hexagonal structures. The artificial gauge fields too are shown to have the same hexagonal spatial structure and their magnitude can be significantly large. The effects are discussed with reference to typical parameters for the atoms and the fields.