Delay time and Hartman effect in strain engineered graphene

International Nuclear Information System (INIS)

Chen, Xi; Deng, Zhi-Yong; Ban, Yue

2014-01-01

Tunneling times, including group delay and dwell time, are studied for massless Dirac electrons transmitting through a one-dimensional barrier in strain-engineered graphene. The Hartman effect, the independence of group delay on barrier length, is induced by the strain effect, and associated with the transmission gap and the evanescent mode. The influence of barrier height/length and strain modulus/direction on the group delay is also discussed, which provides the flexibility to control the group delay with applications in graphene-based devices. The relationship between group delay and dwell time is finally derived to clarify the nature of the Hartman effect

Thickness-Dependent Strain Effect on the Deformation of the Graphene-Encapsulated Au Nanoparticles

Directory of Open Access Journals (Sweden)

Shuangli Ye

2014-01-01

Full Text Available The strain effect on graphene-encapsulated Au nanoparticles is investigated. A finite-element calculation is performed to simulate the strain distribution and morphology of the monolayer and multilayer graphene-encapsulated Au nanoparticles, respectively. It can be found that the inhomogeneous strain and deformation are enhanced with the increasing shrinkage of the graphene shell. Moreover, the strain distribution and deformation are very sensitive to the layer number of the graphene shell. Especially, the inhomogeneous strain at the interface between the graphene shell and encapsulated Au nanoparticles is strongly tuned by the graphene thickness. For the mono- and bilayer graphene-encapsulated Au nanoparticles, the dramatic shape transformation can be observed. However, with increasing the graphene thickness further, there is hardly deformation for the encapsulated Au nanoparticles. These simulated results indicate that the strain and deformation can be designed by the graphene layer thickness, which provides an opportunity to engineer the structure and morphology of the graphene-encapsulated nanoparticles.

Wrinkle-Free Single-Crystal Graphene Wafer Grown on Strain-Engineered Substrates.

Science.gov (United States)

Deng, Bing; Pang, Zhenqian; Chen, Shulin; Li, Xin; Meng, Caixia; Li, Jiayu; Liu, Mengxi; Wu, Juanxia; Qi, Yue; Dang, Wenhui; Yang, Hao; Zhang, Yanfeng; Zhang, Jin; Kang, Ning; Xu, Hongqi; Fu, Qiang; Qiu, Xiaohui; Gao, Peng; Wei, Yujie; Liu, Zhongfan; Peng, Hailin

2017-12-26

Wrinkles are ubiquitous for graphene films grown on various substrates by chemical vapor deposition at high temperature due to the strain induced by thermal mismatch between the graphene and substrates, which greatly degrades the extraordinary properties of graphene. Here we show that the wrinkle formation of graphene grown on Cu substrates is strongly dependent on the crystallographic orientations. Wrinkle-free single-crystal graphene was grown on a wafer-scale twin-boundary-free single-crystal Cu(111) thin film fabricated on sapphire substrate through strain engineering. The wrinkle-free feature of graphene originated from the relatively small thermal expansion of the Cu(111) thin film substrate and the relatively strong interfacial coupling between Cu(111) and graphene, based on the strain analyses as well as molecular dynamics simulations. Moreover, we demonstrated the transfer of an ultraflat graphene film onto target substrates from the reusable single-crystal Cu(111)/sapphire growth substrate. The wrinkle-free graphene shows enhanced electrical mobility compared to graphene with wrinkles.

Strain-tuning of edge magnetism in zigzag graphene nanoribbons.

Science.gov (United States)

Yang, Guang; Li, Baoyue; Zhang, Wei; Ye, Miao; Ma, Tianxing

2017-09-13

Using the determinant quantum Monte-Carlo method, we elucidate the strain tuning of edge magnetism in zigzag graphene nanoribbons. Our intensive numerical results show that a relatively weak Coulomb interaction may induce a ferromagnetic-like behaviour with a proper strain, and the edge magnetism can be enhanced greatly as the strain along the zigzag edge increases, which provides another way to control graphene magnetism even at room temperature.

Effects of strain on Goos-Hänchen-like shifts of graphene

International Nuclear Information System (INIS)

Cao Zhenzhou; Cheng Yanfu; Li Guanqiang

2012-01-01

We have studied the Goos-Hänchen-like (GHL) shifts for massless Dirac electrons passing across a potential barrier in strained graphene. The analytical solutions of the transmission coefficient and the GHL shifts are obtained. The GHL shifts as the function of the strain tensor and direction, the incidence angle and the barrier's width are discussed. We also explore how critical angles change as the strain tensor and incidence electron energy change. Finally, we make a proposal of experimental measurement of the GHL shifts. The study of the GHL shifts will make for applications in graphene-based nano-electronics.

Engineering the quantum anomalous Hall effect in graphene with uniaxial strains

Energy Technology Data Exchange (ETDEWEB)

Diniz, G. S., E-mail: ginetom@gmail.com; Guassi, M. R. [Institute of Physics, University of Brasília, 70919-970 Brasília-DF (Brazil); Qu, F. [Institute of Physics, University of Brasília, 70919-970 Brasília-DF (Brazil); Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States)

2013-12-28

We theoretically investigate the manipulation of the quantum anomalous Hall effect (QAHE) in graphene by means of the uniaxial strain. The values of Chern number and Hall conductance demonstrate that the strained graphene in presence of Rashba spin-orbit coupling and exchange field, for vanishing intrinsic spin-orbit coupling, possesses non-trivial topological phase, which is robust against the direction and modulus of the strain. Besides, we also find that the interplay between Rashba and intrinsic spin-orbit couplings results in a topological phase transition in the strained graphene. Remarkably, as the strain strength is increased beyond approximately 7%, the critical parameters of the exchange field for triggering the quantum anomalous Hall phase transition show distinct behaviors—decrease (increase) for strains along zigzag (armchair) direction. Our findings open up a new platform for manipulation of the QAHE by an experimentally accessible strain deformation of the graphene structure, with promising application on novel quantum electronic devices with high efficiency.

Engineering the quantum anomalous Hall effect in graphene with uniaxial strains

International Nuclear Information System (INIS)

Diniz, G. S.; Guassi, M. R.; Qu, F.

2013-01-01

We theoretically investigate the manipulation of the quantum anomalous Hall effect (QAHE) in graphene by means of the uniaxial strain. The values of Chern number and Hall conductance demonstrate that the strained graphene in presence of Rashba spin-orbit coupling and exchange field, for vanishing intrinsic spin-orbit coupling, possesses non-trivial topological phase, which is robust against the direction and modulus of the strain. Besides, we also find that the interplay between Rashba and intrinsic spin-orbit couplings results in a topological phase transition in the strained graphene. Remarkably, as the strain strength is increased beyond approximately 7%, the critical parameters of the exchange field for triggering the quantum anomalous Hall phase transition show distinct behaviors—decrease (increase) for strains along zigzag (armchair) direction. Our findings open up a new platform for manipulation of the QAHE by an experimentally accessible strain deformation of the graphene structure, with promising application on novel quantum electronic devices with high efficiency

Strain-activated edge reconstruction of graphene nanoribbons

KAUST Repository

Cheng, Yingchun

2012-02-17

The edge structure and width of graphene nanoribbons (GNRs) are crucial factors for the electronic properties. A combination of experiment and first-principles calculations allows us to determine the mechanism of the hexagon-hexagon to pentagon-heptagon transformation. GNRs thinner than 2 nm have been fabricated by bombardment of graphene with high-energetic Au clusters. The edges of the GNRs are modified in situ by electron irradiation. Tensile strain along the edge decreases the transformation energy barrier. Antiferromagnetism and a direct band gap are found for a zigzag GNR, while a fully reconstructed GNR shows an indirect band gap. A GNR reconstructed on only one edge exhibits ferromagnetism. We propose that strain is an effective method to tune the edge and, therefore, the electronic structure of thin GNRs for graphene-based electronics.

Strain-activated edge reconstruction of graphene nanoribbons

KAUST Repository

Cheng, Yingchun; Han, Yu; Schwingenschlö gl, Udo; Wang, H. T.; Zhang, Xixiang; Zhu, Y. H.; Zhu, Zhiyong

2012-01-01

The edge structure and width of graphene nanoribbons (GNRs) are crucial factors for the electronic properties. A combination of experiment and first-principles calculations allows us to determine the mechanism of the hexagon-hexagon to pentagon-heptagon transformation. GNRs thinner than 2 nm have been fabricated by bombardment of graphene with high-energetic Au clusters. The edges of the GNRs are modified in situ by electron irradiation. Tensile strain along the edge decreases the transformation energy barrier. Antiferromagnetism and a direct band gap are found for a zigzag GNR, while a fully reconstructed GNR shows an indirect band gap. A GNR reconstructed on only one edge exhibits ferromagnetism. We propose that strain is an effective method to tune the edge and, therefore, the electronic structure of thin GNRs for graphene-based electronics.

Creating periodic local strain in monolayer graphene with nanopillars patterned by self-assembled block copolymer

Energy Technology Data Exchange (ETDEWEB)

Mi, Hongyi; Mikael, Solomon; Seo, Jung-Hun; Gui, Gui; Ma, Alice L.; Ma, Zhenqiang, E-mail: nealey@uchicago.edu, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Liu, Chi-Chun; Nealey, Paul F., E-mail: nealey@uchicago.edu, E-mail: mazq@engr.wisc.edu [Department of Chemical and Biological Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States)

2015-10-05

A simple and viable method was developed to produce biaxial strain in monolayer graphene on an array of SiO{sub 2} nanopillars. The array of SiO{sub 2} nanopillars (1 cm{sup 2} in area, 80 nm in height, and 40 nm in pitch) was fabricated by employing self-assembled block copolymer through simple dry etching and deposition processes. According to high resolution micro-Raman spectroscopy and atomic force microscopy analyses, 0.9% of maximum biaxial tensile strain and 0.17% of averaged biaxial tensile strain in graphene were created. This technique provides a simple and viable method to form biaxial tensile strain in graphene and offers a practical platform for future studies in graphene strain engineering.

Effects of strain on the Schwinger pair creation in graphene

International Nuclear Information System (INIS)

Fanbanrai, P.; Hutem, A.; Boonchui, S.

2015-01-01

The effects of strain on mechanically deformed graphene are determined by looking at how the strain affects the amplitude of the Schwinger two particle pair state. The influences of the lattice distortions, such as isotropic tensile strain ϵ is , shear strain ϵ ss , uniaxial armchair strain ϵ as , and zigzag strain ϵ zs , on the photon emission spectrum have been analyzed. We find that the intensities of the emission increases or decreases when compared to those of the unstrained graphene, depending on the type of strain applied. Thus the structure of energy band, the frequencies of the photons and the emission spectrum can be controlled by use of the different strains

Changes in the vibrational properties of graphene and other related nanostructures under strain

International Nuclear Information System (INIS)

Codorniu Pujals, D.

2015-01-01

It is well known that the presence of strain in solids modifies their vibrational properties due to the variation of the atomic position and the changes of the interatomic distances. Monolayer graphene is especially sensible to the effects of strain, for example, to that produced by the curvature of some region of the graphene plane. These changes in the vibrational properties of graphene modifies in different way its Raman spectrum. In the case of other graphene-related materials as fullerenes, nano-onions and nano tubes, the curvature is always present, consequently, there is a modification of the vibrational properties in relation with those in graphene, due to the strain provoked by curvature. In this paper, the overall picture of the effect of strain on the vibrational properties of graphene and other carbon nanostructures is presented from a theoretical point of view and the main considerations are correlated with experimental results from Raman spectroscopy (Author)

Defect production in Ar irradiated graphene membranes under different initial applied strains

Energy Technology Data Exchange (ETDEWEB)

Martinez-Asencio, J., E-mail: jesusmartinez@ua.es [Dept. Física Aplicada, Facultad de Ciencias, Fase II, Universidad de Alicante, Alicante E-036090 (Spain); Ruestes, C.J.; Bringa, E. [CONICET and Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza 5500 (Argentina); Caturla, M.J. [Dept. Física Aplicada, Facultad de Ciencias, Fase II, Universidad de Alicante, Alicante E-036090 (Spain)

2017-02-15

Highlights: • Defects in graphene membranes are formed due to 140 eV Ar ions irradiation using MD. • Different initial strains are applied, which influence the type and number of defects. • Mono-vacancies, di-vacancies and tri-vacancies production behaves linearly with dose. • The total number of defects under compression is slightly higher than under tension. - Abstract: Irradiation with low energy Ar ions of graphene membranes gives rise to changes in the mechanical properties of this material. These changes have been associated to the production of defects, mostly isolated vacancies. However, the initial state of the graphene membrane can also affect its mechanical response. Using molecular dynamics simulations we have studied defect production in graphene membranes irradiated with 140 eV Ar ions up to a dose of 0.075 × 10{sup 14} ions/cm{sup 2} and different initial strains, from −0.25% (compressive strain) to 0.25% (tensile strain). For all strains, the number of defects increases linearly with dose with a defect production of about 80% (80 defects every 100 ions). Defects are mostly single vacancies and di-vacancies, although some higher order clusters are also observed. Two different types of di-vacancies have been identified, the most common one being two vacancies at first nearest neighbours distance. Differences in the total number of defects with the applied strain are observed which is related to the production of a higher number of di-vacancies under compressive strain compared to tensile strain. We attribute this effect to the larger out-of-plane deformations of compressed samples that could favor the production of defects in closer proximity to others.

Strain-Induced Pseudo--Magnetic Fields in Graphene: MegaGauss in Nanobubbles

Science.gov (United States)

Levy, Niv

2011-03-01

Recent theoretical proposals suggest that strain can be used to modify graphene electronic states through the creation of a pseudo--magnetic field. This effect is unique to graphene because of its massless Dirac fermion-like band structure and particular lattice symmetry (C3v). Scanning tunneling microscopy shows that graphene grown on a platinum (111) surface forms nanobubbles, which are highly strained due to thermal expansion mismatch between the film and the substrate. We find that scanning tunneling spectroscopy measurements of these nanobubbles exhibit Landau levels that form in the presence of strain-induced pseudo--magnetic fields greater than 300 Tesla. This demonstration of enormous pseudo--magnetic fields opens the door to both the study of charge carriers in previously inaccessible high magnetic field regimes and deliberate mechanical control over electronic structure in graphene or so-called ``strain engineering''. In collaboration with S. A. Burke ,2 , K. L. Meaker 2 , M. Panlasigui 2 , A. Zettl 2,3 , F. Guinea 4 , A. H. Castro Neto 5 and M. F. Crommie 2,3 . 1. Present address: Department of Physics and Astronomy and Department of Chemistry, University of British Columbia, Vancouver, BC V6T 121, Canada. 2. Department of Physics, University of California, Berkeley, CA 94720, USA. 3. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 4. Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid 28049, Spain. 5. Department of Physics, Boston University, Boston, MA 02215, USA.

Strain-induced friction anisotropy between graphene and molecular liquids

Science.gov (United States)

Liao, Meng; To, Quy-Dong; Léonard, Céline; Monchiet, Vincent; Vo, Van-Hoang

2017-01-01

In this paper, we study the friction behavior of molecular liquids with anisotropically strained graphene. Due to the changes of lattice and the potential energy surface, the friction is orientation dependent and can be computed by tensorial Green-Kubo formula. Simple quantitative estimations are also proposed for the zero-time response and agree reasonably well with the molecular dynamics results. From simulations, we can obtain the information of structures, dynamics of the system, and study the influence of strain and molecular shapes on the anisotropy degree. It is found that unilateral strain can increase friction in all directions but the strain direction is privileged. Numerical evidences also show that nonspherical molecules are more sensitive to strain and give rise to more pronounced anisotropy effects.

Strain-engineered band parameters of graphene-like SiC monolayer

International Nuclear Information System (INIS)

Behera, Harihar; Mukhopadhyay, Gautam

2014-01-01

Using full-potential density functional theory (DFT) calculations we show that the band gap and effective masses of charge carriers in SiC monolayer (ML-SiC) in graphene-like two-dimensional honeycomb structure are tunable by strain engineering. ML-SiC was found to preserve its flat 2D graphene-like structure under compressive strain up to 7%. A transition from indirect-to-direct gap-phase is predicted to occur for a strain value lying within the interval (1.11 %, 1.76%). In both gap-phases band gap decreases with increasing strain, although the rate of decrease is different in the two gap-phases. Effective mass of electrons show a non-linearly decreasing trend with increasing tensile strain in the direct gap-phase. The strain-sensitive properties of ML-SiC, may find applications in future strain-sensors, nanoelectromechanical systems (NEMS) and nano-optomechanical systems (NOMS) and other nano-devices

Valley Hall effect and Nernst effect in strain engineered graphene

Science.gov (United States)

Niu, Zhi Ping; Yao, Jian-ming

2018-04-01

We theoretically predict the existence of tunneling valley Hall effect and Nernst effect in the normal/strain/normal graphene junctions, where a strained graphene is sandwiched by two normal graphene electrodes. By applying an electric bias a pure transverse valley Hall current with longitudinal charge current is generated. If the system is driven by a temperature bias, a valley Nernst effect is observed, where a pure transverse valley current without charge current propagates. Furthermore, the transverse valley current can be modulated by the Fermi energy and crystallographic orientation. When the magnetic field is further considered, we obtain a fully valley-polarized current. It is expected these features may be helpful in the design of the controllable valleytronic devices.

Mechanical failure of zigzag graphene nanoribbons under tensile strain induced by edge reconstruction

KAUST Repository

Cheng, Yingchun

2012-10-01

The structural and mechanical properties of graphene nanoribbons (GNRs) under uniaxial tensile strain are studied by density functional theory. The ideal strength of a zigzag GNR (120 GPa) is close to that of pristine graphene. However, for a GNR with both edges reconstructed to pentagon–heptagon pairs (from hexagon–hexagon pairs) it decreases to 94 GPa and the maximum tensile strain is reduced to 15%. Our results constitute a comprehensive picture of the edge structure effect on the mechanical properties of GNRs.

Mechanical failure of zigzag graphene nanoribbons under tensile strain induced by edge reconstruction

KAUST Repository

Cheng, Yingchun; Schwingenschlö gl, Udo; Zhu, Zhiyong

2012-01-01

The structural and mechanical properties of graphene nanoribbons (GNRs) under uniaxial tensile strain are studied by density functional theory. The ideal strength of a zigzag GNR (120 GPa) is close to that of pristine graphene. However, for a GNR with both edges reconstructed to pentagon–heptagon pairs (from hexagon–hexagon pairs) it decreases to 94 GPa and the maximum tensile strain is reduced to 15%. Our results constitute a comprehensive picture of the edge structure effect on the mechanical properties of GNRs.

Strain-induced phase transition and electron spin-polarization in graphene spirals.

Science.gov (United States)

Zhang, Xiaoming; Zhao, Mingwen

2014-07-16

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices.

Strain and water effects on the electronic structure and chemical activity of in-plane graphene/silicene heterostructure

Science.gov (United States)

Kistanov, Andrey A.; Cai, Yongqing; Zhang, Yong-Wei; Dmitriev, Sergey V.; Zhou, Kun

2017-03-01

By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from  -7% (compression) to  +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the water molecule and the graphene/silicene sheet can be modulated by strain. Moreover, the presence of the boron-nitride (BN)-substrate significantly influences the chemical activity of the graphene/silicene heterostructure upon its interaction with the H2O molecule and may cause an increase/decrease of the charge transfer between the H2O molecule and the heterostructure. These findings provide insights into the modulation of electronic properties of the in-plane free-standing/substrate-supported graphene/silicene heterostructure, and render possible ways to control its electronic structure, carrier density and redox characteristics, which may be useful for its potential applications in nanoelectronics and gas sensors.

Strain and water effects on the electronic structure and chemical activity of in-plane graphene/silicene heterostructure

International Nuclear Information System (INIS)

Kistanov, Andrey A; Zhou, Kun; Cai, Yongqing; Zhang, Yong-Wei; Dmitriev, Sergey V

2017-01-01

By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from  −7% (compression) to  +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H 2 O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H 2 O compared with the adsorption on a planar surface, and the charge transfer between the water molecule and the graphene/silicene sheet can be modulated by strain. Moreover, the presence of the boron-nitride (BN)-substrate significantly influences the chemical activity of the graphene/silicene heterostructure upon its interaction with the H 2 O molecule and may cause an increase/decrease of the charge transfer between the H 2 O molecule and the heterostructure. These findings provide insights into the modulation of electronic properties of the in-plane free-standing/substrate-supported graphene/silicene heterostructure, and render possible ways to control its electronic structure, carrier density and redox characteristics, which may be useful for its potential applications in nanoelectronics and gas sensors. (paper)

Fundamental studies of graphene/graphite and graphene-based Schottky photovoltaic devices

Science.gov (United States)

Miao, Xiaochang

In the carbon allotropes family, graphene is one of the most versatile members and has been extensively studied since 2004. The goal of this dissertation is not only to investigate the novel fundamental science of graphene and its three-dimensional sibling, graphite, but also to explore graphene's promising potential in modern electronic and optoelectronic devices. The first two chapters provide a concise introduction to the fundamental solid state physics of graphene (as well as graphite) and the physics at the metal/semiconductor interfaces. In the third chapter, we demonstrate the formation of Schottky junctions at the interfaces of graphene (semimetal) and various inorganic semiconductors that play dominating roles in today's semiconductor technology, such as Si, SiC, GaAs and GaN. As shown from their current-voltage (I -V) and capacitance-voltage (C-V) characteristics, the interface physics can be well described within the framework of the Schottky-Mott model. The results are also well consist with that from our previous studies on graphite based Schottky diodes. In the fourth chapter, as an extension of graphene based Schottky work, we investigate the photovoltaic (PV) effect of graphene/Si junctions after chemically doped with an organic polymer (TFSA). The power conversion efficiency of the solar cell improves from 1.9% to 8.6% after TFSA doping, which is the record in all graphene based PVs. The I -V, C-V and external quantum efficiency measurements suggest 12 that such a significant enhancement in the device performance can be attributed to a doping-induced decrease in the series resistance and a simultaneous increase in the built-in potential. In the fifth chapter, we investigate for the first time the effect of uniaxial strains on magneto-transport properties of graphene. We find that low-temperature weak localization effect in monolayer graphene is gradually suppressed under increasing strains, which is due to a strain-induced decreased intervalley

The effect of strain-rate on the tensile and compressive behavior of graphene reinforced epoxy/nanocomposites

International Nuclear Information System (INIS)

Shadlou, Shahin; Ahmadi-Moghadam, Babak; Taheri, Farid

2014-01-01

Highlights: • The epoxy/graphene nanocomposites were studied at various strain rates. • The variations in constitutive stress–strain response were scrutinized. • Positive reinforcing attributes of graphene diminished at higher strain rates. • Graphene particles have higher efficiency under compression loading than tension. • A new modification factor for Halpin–Tsai model was proposed. - Abstract: The effect of strain rate on the mechanical behavior of epoxy reinforced with graphene nanoplatelets (GNPs) is investigated. Nanocomposites containing various amounts of GNP are prepared and tested at four different strain rates (0.01, 0.1, 1 and 10/s) under compressive and tensile loading regimes. The results show that incorporation of GNP highly affects the behavior of epoxy. The fracture surfaces of tensile specimens are also investigated using scanning electron microscopy (SEM) to discern the surface features and dispersion state of GNP. Finally, the predictive capability of some of the available models for evaluating the strength of nanocomposites are assessed and compared against the experimental results. Moreover, a modification factor to the widely used Halpin–Tsai model is proposed to improve the accuracy of the model when evaluating the Young’s modulus of nanocomposites at various strain rates

A comparative investigation on strain induced crystallization for graphene and carbon nanotubes filled natural rubber composites

Directory of Open Access Journals (Sweden)

D. H. Fu

2015-07-01

Full Text Available Natural rubber containing graphene and carbon nanotubes (CNTs composites were prepared by ultrasonicallyassisted latex mixing. Natural rubber filled by both graphene and CNTs show significant enhanced tensile strength, while graphene exhibits a better reinforcing effect than CNTs. Strain-induced crystallization in natural rubber composites during stretching was determined by synchrotron wide-angle X-ray diffraction. With the addition of CNTs or graphene, the crystallization for natural rubber occurs at a lower strain compared to unfilled natural rubber, and the strain amplification effects were observed. The incorporation of graphene results in a faster strain-induced crystallization rate and a higher crystallinity compared to CNTs. The entanglement-bound rubber tube model was used to analyze the chain network structure and determine the network parameters of composites. The results show that the addition of graphene or CNTs has an influence on the molecular network structure and improves the contribution of entanglement to the conformational constraint, while graphene has a more marked effect than CNTs.

Tuning the Schottky contacts in the phosphorene and graphene heterostructure by applying strain.

Science.gov (United States)

Liu, Biao; Wu, Li-Juan; Zhao, Yu-Qing; Wang, Lin-Zhi; Caii, Meng-Qiu

2016-07-20

The structures and electronic properties of the phosphorene and graphene heterostructure are investigated by density functional calculations using the hybrid Heyd-Scuseria-Ernzerhof (HSE) functional. The results show that the intrinsic properties of phosphorene and graphene are preserved due to the weak van der Waals contact. But the electronic properties of the Schottky contacts in the phosphorene and graphene heterostructure can be tuned from p-type to n-type by the in-plane compressive strains from -2% to -4%. After analyzing the total band structure and density of states of P atom orbitals, we find that the Schottky barrier height (SBH) is determined by the P-pz orbitals. What is more, the variation of the work function of the phosphorene monolayer and the graphene electrode and the Fermi level shift are the nature of the transition of Schottky barrier from n-type Schottky contact to p-type Schottky contact in the phosphorene and graphene heterostructure under different in-plane strains. We speculate that these are general results of tuning of the electronic properties of the Schottky contacts in the phosphorene and graphene heterostructure by controlling the in-plane compressive strains to obtain a promising method to design and fabricate a phosphorene-graphene based field effect transistor.

An atomistic investigation of the effect of strain on frictional properties of suspended graphene

Directory of Open Access Journals (Sweden)

Qingshun Bai

2016-05-01

Full Text Available We performed molecular dynamics (MD simulations of a diamond probe scanned on a suspended graphene to reveal the effect of strain on the frictional properties of suspended graphene. The graphene was subjected to some certain strain along the scanning direction. We compared the friction coefficient obtained from different normal loads and strain. The results show that the friction coefficient can be decreased about one order of magnitude with the increase of the strain. And that can be a result of the decreased asymmetry of the contact region which is caused by strain. The synthetic effect of potential energy and the fluctuation of contact region were found to be the main reason accounting for the fluctuation of the friction force. The strain can reduce the fluctuation of the contact region and improve the stability of friction.

Spin-dependent delay time and Hartman effect in asymmetrical graphene barrier under strain

Science.gov (United States)

Sattari, Farhad; Mirershadi, Soghra

2018-01-01

We study the spin-dependent tunneling time, including group delay and dwell time, in a graphene based asymmetrical barrier with Rashba spin-orbit interaction in the presence of strain, sandwiched between two normal leads. We find that the spin-dependent tunneling time can be efficiently tuned by the barrier width, and the bias voltage. Moreover, for the zigzag direction strain although the oscillation period of the dwell time does not change, the oscillation amplitude increases by increasing the incident electron angle. It is found that for the armchair direction strain unlike the zigzag direction the group delay time at the normal incidence depends on the spin state of electrons and Hartman effect can be observed. In addition, for the armchair direction strain the spin polarization increases with increasing the RSOI strength and the bias voltage. The magnitude and sign of spin polarization can be manipulated by strain. In particular, by applying an external electric field the efficiency of the spin polarization is improved significantly in strained graphene, and a fully spin-polarized current is generated.

Quantum transport in graphene in presence of strain-induced pseudo-Landau levels

DEFF Research Database (Denmark)

Settnes, Mikkel; Leconte, Nicolas; Barrios-Vargas, Jose E.

2016-01-01

We report on mesoscopic transport fingerprints in disordered graphene caused by strain-field induced pseudomagnetic Landau levels (pLLs). Efficient numerical real space calculations of the Kubo formula are performed for an ordered network of nanobubbles in graphene, creating pseudomagnetic fields...

Effect of strain on geometric and electronic structures of graphene on a Ru(0001) surface

Institute of Scientific and Technical Information of China (English)

Sun Jia-Tao; Du Shi-Xuan; Xiao Wen-De; Hu Hao; Zhang Yu-Yang; Li Guo; Gao Hong-Jun

2009-01-01

The atomic and electronic structures of a graphene monolayer on a Ru(0001) surface under compressive strain are investigated by using first-principles calculations. Three models of graphene monolayers with different carbon periodicities due to the lattice mismatch are proposed in the presence and the. absence of the Ru(0001) substrate separately. Considering the strain induced by the lattice mismatch, we optimize the atomic structures and investigate the electronic properties of the graphene. Our calculation results show that the graphene layers turn into periodic corrugations and there exist strong chemical bonds in the interface between the graphene N x N superlattice and the substrate. The strain does not induce significant changes in electronic structure. Furthermore, the results calculated in the local density approximation (LDA) are compared with those obtained in the generalized gradient approximation (GGA), showing that the LDA results are more reasonable than the GGA results when only two substrate layers are used in calculation.

Effect of uniaxial strain on the tunnel magnetoresistance of T-shaped graphene nanoribbon based spin-valve

Science.gov (United States)

Fouladi, A. Ahmadi

2016-07-01

We theoretically investigated the spin-dependent transport through a T-shaped graphene nanoribbon (TsGNR) based spin-valve consisting of armchair graphene sandwiched between two semi-infinite ferromagnetic armchair graphene nanoribbon leads in the presence of an applied uniaxial strain. Based on a tight-binding model and standard nonequilibrium Green's function technique, it is demonstrated that the tunnel magnetoresistance (TMR) for the system can be increased about 98% by tuning the uniaxial strain. Our results show that the absolute values of TMR around the zero bias voltage for compressive strain are larger than tensile strain. In addition, the TMR of the system can be nicely controlled by GNR width.

Strain-induced tunable negative differential resistance in triangle graphene spirals

Science.gov (United States)

Tan, Jie; Zhang, Xiaoming; Liu, Wenguan; He, Xiujie; Zhao, Mingwen

2018-05-01

Using non-equilibrium Green’s function formalism combined with density functional theory calculations, we investigate the significant changes in electronic and transport properties of triangle graphene spirals (TGSs) in response to external strain. Tunable negative differential resistance (NDR) behavior is predicted. The NDR bias region, NDR width, and peak-to-valley ratio can be well tuned by external strain. Further analysis shows that these peculiar properties can be attributed to the dispersion widths of the p z orbitals. Moreover, the conductance of TGSs is very sensitive to the applied stress, which is promising for applications in nanosensor devices. Our findings reveal a novel approach to produce tunable electronic devices based on graphene spirals.

An ultrasensitive strain sensor with a wide strain range based on graphene armour scales.

Science.gov (United States)

Yang, Yi-Fan; Tao, Lu-Qi; Pang, Yu; Tian, He; Ju, Zhen-Yi; Wu, Xiao-Ming; Yang, Yi; Ren, Tian-Ling

2018-06-12

An ultrasensitive strain sensor with a wide strain range based on graphene armour scales is demonstrated in this paper. The sensor shows an ultra-high gauge factor (GF, up to 1054) and a wide strain range (ε = 26%), both of which present an advantage compared to most other flexible sensors. Moreover, the sensor is developed by a simple fabrication process. Due to the excellent performance, this strain sensor can meet the demands of subtle, large and complex human motion monitoring, which indicates its tremendous application potential in health monitoring, mechanical control, real-time motion monitoring and so on.

New position of Dirac points in the strained graphene reciprocal lattice

Directory of Open Access Journals (Sweden)

Cui-Lian Li

2014-08-01

Full Text Available In the strained graphene, Fermi velocity shows space-dependent and it changes as the position of Dirac point shifts. In this paper, we apply the tight-binding approach within linear elasticity theory to investigate the shifting of Dirac points in the strained graphene reciprocal lattice space. Based on this, we derive the analytical expression on the new positions of the Dirac points as the strain parameter varies. Comparing the data from our analytical expression, ones from Eq. (20 in Phys. Rev. B 80, 045401 (2009, and those from numerical calculation, we find that our analytical expression raises the effective prediction range of the strain parameter from 3% to 15%. i.e., our analytical expression is practicable until the strain parameter is larger than 15%. This almost includes the whole range where the Dirac points present and the energy gap is zero. Moreover, we further calculate the energy gap by numerical method when the shear strain parameter varies from 0 to 20%, and find that the energy gap can not open until the strain parameter is larger than 16%. After this, the energy gap open and the Dirac points disappear.

Strain dependence of the heat transport properties of graphene nanoribbons

International Nuclear Information System (INIS)

Emmeline Yeo, Pei Shan; Loh, Kian Ping; Gan, Chee Kwan

2012-01-01

Using a combination of accurate density-functional theory and a nonequilibrium Green’s function method, we calculate the ballistic thermal conductance characteristics of tensile-strained armchair (AGNR) and zigzag (ZGNR) edge graphene nanoribbons, with widths between 3 and 50 Å. The optimized lateral lattice constants for AGNRs of different widths display a three-family behavior when the ribbons are grouped according to N modulo 3, where N represents the number of carbon atoms across the width of the ribbon. Two lowest-frequency out-of-plane acoustic modes play a decisive role in increasing the thermal conductance of AGNR-N at low temperatures. At high temperatures the effect of tensile strain is to reduce the thermal conductance of AGNR-N and ZGNR-N. These results could be explained by the changes in force constants in the in-plane and out-of-plane directions with the application of strain. This fundamental atomistic understanding of the heat transport in graphene nanoribbons paves a way to effect changes in their thermal properties via strain at various temperatures. (paper)

Measuring strain and rotation fields at the dislocation core in graphene

Science.gov (United States)

Bonilla, L. L.; Carpio, A.; Gong, C.; Warner, J. H.

2015-10-01

Strain fields, dislocations, and defects may be used to control electronic properties of graphene. By using advanced imaging techniques with high-resolution transmission electron microscopes, we have measured the strain and rotation fields about dislocations in monolayer graphene with single-atom sensitivity. These fields differ qualitatively from those given by conventional linear elasticity. However, atom positions calculated from two-dimensional (2D) discrete elasticity and three-dimensional discrete periodized Föppl-von Kármán equations (dpFvKEs) yield fields close to experiments when determined by geometric phase analysis. 2D theories produce symmetric fields whereas those from experiments exhibit asymmetries. Numerical solutions of dpFvKEs provide strain and rotation fields of dislocation dipoles and pairs that also exhibit asymmetries and, compared with experiments, may yield information on out-of-plane displacements of atoms. While discrete theories need to be solved numerically, analytical formulas for strains and rotation about dislocations can be obtained from 2D Mindlin's hyperstress theory. These formulas are very useful for fitting experimental data and provide a template to ascertain the importance of nonlinear and nonplanar effects. Measuring the parameters of this theory, we find two characteristic lengths between three and four times the lattice spacings that control dilatation and rotation about a dislocation. At larger distances from the dislocation core, the elastic fields decay to those of conventional elasticity. Our results may be relevant for strain engineering in graphene and other 2D materials of current interest.

Flexible, Highly Sensitive, and Wearable Pressure and Strain Sensors with Graphene Porous Network Structure.

Science.gov (United States)

Pang, Yu; Tian, He; Tao, Luqi; Li, Yuxing; Wang, Xuefeng; Deng, Ningqin; Yang, Yi; Ren, Tian-Ling

2016-10-03

A mechanical sensor with graphene porous network (GPN) combined with polydimethylsiloxane (PDMS) is demonstrated by the first time. Using the nickel foam as template and chemically etching method, the GPN can be created in the PDMS-nickel foam coated with graphene, which can achieve both pressure and strain sensing properties. Because of the pores in the GPN, the composite as pressure and strain sensor exhibit wide pressure sensing range and highest sensitivity among the graphene foam-based sensors, respectively. In addition, it shows potential applications in monitoring or even recognize the walking states, finger bending degree, and wrist blood pressure.

Electric-field and strain-tunable electronic properties of MoS2/h-BN/graphene vertical heterostructures.

Science.gov (United States)

Zan, Wenyan; Geng, Wei; Liu, Huanxiang; Yao, Xiaojun

2016-01-28

Vertical heterostructures of MoS2/h-BN/graphene have been successfully fabricated in recent experiments. Using first-principles analysis, we show that the structural and electronic properties of such vertical heterostructures are sensitive to applied vertical electric fields and strain. The applied electric field not only enhances the interlayer coupling but also linearly controls the charge transfer between graphene and MoS2 layers, leading to a tunable doping in graphene and controllable Schottky barrier height. Applied biaxial strain could weaken the interlayer coupling and results in a slight shift of graphene's Dirac point with respect to the Fermi level. It is of practical importance that the tunable electronic properties by strain and electric fields are immune to the presence of sulfur vacancies, the most common defect in MoS2.

Integration of graphene sensor with electrochromic device on modulus-gradient polymer for instantaneous strain visualization

Science.gov (United States)

Yang, Tingting; Zhong, Yujia; Tao, Dashuai; Li, Xinming; Zang, Xiaobei; Lin, Shuyuan; Jiang, Xin; Li, Zhihong; Zhu, Hongwei

2017-09-01

In nature, some animals change their deceptive coloration for camouflage, temperature preservation or communication. This astonishing function has inspired scientists to replicate the color changing abilities of animals with artificial skin. Recently, some studies have focused on the smart materials and devices with reversible color changing or light-emitting properties for instantaneous strain visualization. However, most of these works only show eye-detectable appearance change when subjected to large mechanical deformation (100%-500% strain), and conspicuous color change at small strain remains rarely explored. In the present study, we developed a user-interactive electronic skin with human-readable optical output by assembling a highly sensitive resistive strain sensor with a stretchable organic electrochromic device (ECD) together. We explored the substrate effect on the electromechanical behavior of graphene and designed a strategy of modulus-gradient structure to employ graphene as both the highly sensitive strain sensing element and the insensitive stretchable electrode of the ECD layer. Subtle strain (0-10%) was enough to evoke an obvious color change, and the RGB value of the color quantified the magnitude of the applied strain. Such high sensitivity to smaller strains (0-10%) with color changing capability will potentially enhance the function of wearable devices, robots and prosthetics in the future.

Self-adaptive strain-relaxation optimization for high-energy lithium storage material through crumpling of graphene.

Science.gov (United States)

Zhao, Yunlong; Feng, Jiangang; Liu, Xue; Wang, Fengchao; Wang, Lifen; Shi, Changwei; Huang, Lei; Feng, Xi; Chen, Xiyuan; Xu, Lin; Yan, Mengyu; Zhang, Qingjie; Bai, Xuedong; Wu, Hengan; Mai, Liqiang

2014-08-01

High-energy lithium battery materials based on conversion/alloying reactions have tremendous potential applications in new generation energy storage devices. However, these applications are limited by inherent large volume variations and sluggish kinetics. Here we report a self-adaptive strain-relaxed electrode through crumpling of graphene to serve as high-stretchy protective shells on metal framework, to overcome these limitations. The graphene sheets are self-assembled and deeply crumpled into pinecone-like structure through a contraction-strain-driven crumpling method. The as-prepared electrode exhibits high specific capacity (2,165 mAh g(-1)), fast charge-discharge rate (20 A g(-1)) with no capacity fading in 1,000 cycles. This kind of crumpled graphene has self-adaptive behaviour of spontaneous unfolding-folding synchronized with cyclic expansion-contraction volumetric variation of core materials, which can release strain and maintain good electric contact simultaneously. It is expected that such findings will facilitate the applications of crumpled graphene and the self-adaptive materials.

Self-adapted and tunable graphene strain sensors for detecting both subtle and large human motions.

Science.gov (United States)

Tao, Lu-Qi; Wang, Dan-Yang; Tian, He; Ju, Zhen-Yi; Liu, Ying; Pang, Yu; Chen, Yuan-Quan; Yang, Yi; Ren, Tian-Ling

2017-06-22

Conventional strain sensors rarely have both a high gauge factor and a large strain range simultaneously, so they can only be used in specific situations where only a high sensitivity or a large strain range is required. However, for detecting human motions that include both subtle and large motions, these strain sensors can't meet the diverse demands simultaneously. Here, we come up with laser patterned graphene strain sensors with self-adapted and tunable performance for the first time. A series of strain sensors with either an ultrahigh gauge factor or a preferable strain range can be fabricated simultaneously via one-step laser patterning, and are suitable for detecting all human motions. The strain sensors have a GF of up to 457 with a strain range of 35%, or have a strain range of up to 100% with a GF of 268. Most importantly, the performance of the strain sensors can be easily tuned by adjusting the patterns of the graphene, so that the sensors can meet diverse demands in both subtle and large motion situations. The graphene strain sensors show significant potential in applications such as wearable electronics, health monitoring and intelligent robots. Furthermore, the facile, fast and low-cost fabrication method will make them possible and practical to be used for commercial applications in the future.

Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

Science.gov (United States)

Abdelhafiz, Ali; Vitale, Adam; Joiner, Corey; Vogel, Eric; Alamgir, Faisal M

2015-03-25

In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

Graphene based strain sensor with LCP substrate

Science.gov (United States)

Nie, M.; Yang, H. S.; Xia, Y. H.

2018-02-01

A flexible strain sensor constructed by an efficient, low-cost fabrication strategy is presented in this paper. It is assembled by adhering grid-like graphene on LCP substrate. Kinds of measurement setup have been designed to verify that the proposed flexible sensor device is suitable to be used in health monitoring system. From the experiment results, it can be proved that the sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication. With the great performance of this flexible strain sensor, it is considered to play an important role in body monitoring, structural health monitoring system, fatigue detection and healthcare systems in the near future.

Flexible Strain Sensor Based on Layer-by-Layer Self-Assembled Graphene/Polymer Nanocomposite Membrane and Its Sensing Properties

Science.gov (United States)

Zhang, Dongzhi; Jiang, Chuanxing; Tong, Jun; Zong, Xiaoqi; Hu, Wei

2018-04-01

Graphene is a potential building block for next generation electronic devices including field-effect transistors, chemical sensors, and radio frequency switches. Investigations of strain application of graphene-based films have emerged in recent years, but the challenges in synthesis and processing achieving control over its fabrication constitute the main obstacles towards device applications. This work presents an alternative approach, layer-by-layer self-assembly, allowing a controllable fabrication of graphene/polymer film strain sensor on flexible substrates of polyimide with interdigital electrodes. Carboxylated graphene and poly (diallyldimethylammonium chloride) (PDDA) were exploited to form hierarchical nanostructure due to electrostatic action. The morphology and structure of the film were inspected by using scanning electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The strain-sensing properties of the graphene/PDDA film sensor were investigated through tuning micrometer caliper exertion and a PC-assisted piezoresistive measurement system. Experimental result shows that the sensor exhibited not only excellent response and reversibility behavior as a function of deflection, but also good repeatability and acceptable linearity. The strain-sensing mechanism of the proposed sensor was attributed to the electrical resistance change resulted from piezoresistive effect.

Mechanical properties of graphene nanoribbons under uniaxial tensile strain

Science.gov (United States)

Yoneyama, Kazufumi; Yamanaka, Ayaka; Okada, Susumu

2018-03-01

Based on the density functional theory with the generalized gradient approximation, we investigated the mechanical properties of graphene nanoribbons in terms of their edge shape under a uniaxial tensile strain. The nanoribbons with armchair and zigzag edges retain their structure under a large tensile strain, while the nanoribbons with chiral edges are fragile against the tensile strain compared with those with armchair and zigzag edges. The fracture started at the cove region, which corresponds to the border between the zigzag and armchair edges for the nanoribbons with chiral edges. For the nanoribbons with armchair edges, the fracture started at one of the cove regions at the edges. In contrast, the fracture started at the inner region of the nanoribbons with zigzag edges. The bond elongation under the tensile strain depends on the mutual arrangement of covalent bonds with respect to the strain direction.

Long-wavelength optical phonon behavior in uniaxial strained graphene: Role of electron-phonon interaction

Science.gov (United States)

Assili, M.; Haddad, S.

2014-09-01

We derive the frequency shifts and the broadening of Γ-point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic spectrum, induced by the strain, results in a polarization dependence of the LO and TO modes. This dependence is in agreement with the experimental results showing a periodic modulation of the Raman intensity of the split G peak. Moreover, the anomalous behavior of the frequency shift reported in undeformed graphene is found to be robust under strain.

Mechanical properties and failure behaviour of graphene/silicene/graphene heterostructures

International Nuclear Information System (INIS)

Chung, Jing-Yang; Sorkin, Viacheslav; Pei, Qing-Xiang; Zhang, Yong-Wei; Chiu, Cheng-Hsin

2017-01-01

Van der Waals heterostructures based on graphene and other 2D materials have attracted great attention recently. In this study, the mechanical properties and failure behaviour of a graphene/silicene/graphene heterostructure are investigated using molecular dynamics simulations. We find that by sandwiching silicene in-between two graphene layers, both ultimate tensile strength and Young’s modulus of the heterostructure increase approximately by a factor of 10 compared with those of stand-alone silicene. By examining the fracture process of the heterostructure, we find that graphene and silicene exhibit quite different fracture behaviour. While graphene undergoes cleavage through its zigzag edge only, silicene can cleave through both its zigzag and armchair edges. In addition, we study the effects of temperature and strain rate on the mechanical properties of the heterostructure and find that an increase in temperature results in a decrease in its mechanical strength and stiffness, while an increase in strain rate leads to an increase in its mechanical strength without significant changes in its stiffness. We further explore the failure mechanism and show that the temperature and strain-rate dependent fracture stress can be accurately described by the kinetic theory of fracture. Our findings provide a deep insight into the mechanical properties and failure mechanism of graphene/silicene heterostructures. (paper)

Grüneisen parameter of the G mode of strained monolayer graphene

KAUST Repository

Cheng, Yingchun

2011-03-28

We present a detailed analysis of the effects of uniaxial and biaxial strain on the frequencies of the G mode of monolayer graphene, using first principles calculations. Our results allow us to explain discrepancies in the experimentally determined values of the Grüneisen parameter. The direction and strength of the applied strain, Poisson\\'s ratio of the substrate, and the intrinsic strain in different experimental setups turn out to be important. A reliable determination of the Grüneisen parameter is a prerequisite of strain engineering.

Grüneisen parameter of the G mode of strained monolayer graphene

KAUST Repository

Cheng, Yingchun; Huang, Gaoshan; Schwingenschlö gl, Udo; Zhu, Zhiyong

2011-01-01

We present a detailed analysis of the effects of uniaxial and biaxial strain on the frequencies of the G mode of monolayer graphene, using first principles calculations. Our results allow us to explain discrepancies in the experimentally determined values of the Grüneisen parameter. The direction and strength of the applied strain, Poisson's ratio of the substrate, and the intrinsic strain in different experimental setups turn out to be important. A reliable determination of the Grüneisen parameter is a prerequisite of strain engineering.

A nonlocal strain gradient model for dynamic deformation of orthotropic viscoelastic graphene sheets under time harmonic thermal load

Science.gov (United States)

Radwan, Ahmed F.; Sobhy, Mohammed

2018-06-01

This work presents a nonlocal strain gradient theory for the dynamic deformation response of a single-layered graphene sheet (SLGS) on a viscoelastic foundation and subjected to a time harmonic thermal load for various boundary conditions. Material of graphene sheets is presumed to be orthotropic and viscoelastic. The viscoelastic foundation is modeled as Kelvin-Voigt's pattern. Based on the two-unknown plate theory, the motion equations are obtained from the dynamic version of the virtual work principle. The nonlocal strain gradient theory is established from Eringen nonlocal and strain gradient theories, therefore, it contains two material scale parameters, which are nonlocal parameter and gradient coefficient. These scale parameters have two different effects on the graphene sheets. The obtained deflection is compared with that predicted in the literature. Additional numerical examples are introduced to illustrate the influences of the two length scale coefficients and other parameters on the dynamic deformation of the viscoelastic graphene sheets.

Anisotropic mechanical properties and Stone-Wales defects in graphene monolayer: A theoretical study

International Nuclear Information System (INIS)

Fan, B.B.; Yang, X.B.; Zhang, R.

2010-01-01

We investigate the mechanical properties of graphene monolayer via the density functional theoretical (DFT) method. We find that the strain energies are anisotropic for the graphene under large strain. We attribute the anisotropic feature to the anisotropic sp 2 hybridization in the hexagonal lattice. We further identify that the formation energies of Stone-Wales (SW) defects in the graphene monolayer are determined by the defect concentration and also the direction of applied tensile strain, correlating with the anisotropic feature.

Characterization of Elastic Properties of Porous Graphene Using an Ab Initio Study

Directory of Open Access Journals (Sweden)

Reza Ansari

2016-12-01

Full Text Available Importance of covalent bonded two-dimensional monolayer nanostructures and also hydrocarbons is undeniably responsible for creation of new fascinating materials like polyphenylene polymer, a hydrocarbon super honeycomb network, so-called porous graphene. The mechanical properties of porous graphene such as its Young’s modulus, Poisson’s ratio and the bulk modulus as the determinative properties are calculated in this paper using ab initio calculations. To accomplish this aim, the density functional theory on the basis of generalized gradient approximation and the Perdew–Burke–Ernzerhof exchange correlation is employed. Density functional theory calculations are used to calculate strain energy of porous graphene with respect to applied strain. Selected numerical results are then presented to study the properties of porous graphene. Comparisons are made between the properties of porous graphene and those of other analogous nanostructures. The results demonstrated lower stiffness of porous graphene than those of graphene and graphyne, and higher stiffness than that of graphdyine and other graphyne families. Unlikely, Poisson’s ratio is observed to be more than that of graphene and also less than that of graphyne. It is further observed that the presence of porosity and also formation of C-H bond in the pore sites is responsible for these discrepancies. Porous graphene is found to behave as the isotropic material.

Engineering the work function of armchair graphene nanoribbons using strain and functional species: a first principles study

International Nuclear Information System (INIS)

Peng Xihong; Tang Fu; Copple, Andrew

2012-01-01

First principles density functional theory calculations were performed to study the effects of strain, edge passivation, and surface functional species on the structural and electronic properties of armchair graphene nanoribbons (AGNRs), with a particular focus on the work function. The work function was found to increase with uniaxial tensile strain and decrease with compression. The variation of the work function under strain is primarily due to the shift of the Fermi energy with strain. In addition, the relationship between the work function variation and the core level shift with strain is discussed. Distinct trends of the core level shift under tensile and compressive strain were discovered. For AGNRs with the edge carbon atoms passivated by oxygen, the work function is higher than for nanoribbons with the edge passivated by hydrogen under a moderate strain. The difference between the work functions in these two edge passivations is enlarged (reduced) under a sufficient tensile (compressive) strain. This has been correlated to a direct-indirect bandgap transition for tensile strains of about 4% and to a structural transformation for large compressive strains at about - 12%. Furthermore, the effect of the surface species decoration, such as H, F, or OH with different covering density, was investigated. It was found that the work function varies with the type and coverage of surface functional species. Decoration with F and OH increases the work function while H decreases it. The surface functional species were decorated on either one side or both sides of AGNRs. The difference in the work functions between one-sided and two-sided decorations was found to be relatively small, which may suggest an introduced surface dipole plays a minor role. (paper)

On the utility of vacancies and tensile strain-induced quality factor enhancement for mass sensing using graphene monolayers

International Nuclear Information System (INIS)

Kim, Sung Youb; Park, Harold S

2010-01-01

We have utilized classical molecular dynamics to investigate the mass sensing potential of graphene monolayers, using gold as the model adsorbed atom. In doing so, we report two key findings. First, we find that while perfect graphene monolayers are effective mass sensors at very low (T < 10 K) temperatures, their mass sensing capability is lost at higher temperatures due to diffusion of the adsorbed atom at elevated temperatures. We demonstrate that even if the quality (Q) factors are significantly elevated through the application of tensile mechanical strain, the mass sensing resolution is still lost at elevated temperatures, which demonstrates that high Q-factors alone are insufficient to ensure the mass sensing capability of graphene. Second, we find that while the introduction of single vacancies into the graphene monolayer prevents the diffusion of the adsorbed atom, the mass sensing resolution is still lost at higher temperatures, again due to Q-factor degradation. We finally demonstrate that if the Q-factors of the graphene monolayers with single vacancies are kept acceptably high through the application of tensile strain, then the high Q-factors, in conjunction with the single atom vacancies to stop the diffusion of the adsorbed atom, enable graphene to maintain its mass sensing capability across a range of technologically relevant operating temperatures.

Evaluating arbitrary strain configurations and doping in graphene with Raman spectroscopy

Czech Academy of Sciences Publication Activity Database

Mueller, N. S.; Heeg, S.; Peňa-Álvarez, Miriam; Kusch, P.; Wasserroth, S.; Clark, N.; Schedin, F.; Parthenios, J.; Papagelis, K.; Galiotis, C.; Kalbáč, Martin; Vijayaraghavan, A.; Huebner, U.; Gorbachev, R.; Frank, Otakar; Reich, S.

2018-01-01

Roč. 5, č. 1 (2018), č. článku 015016. ISSN 2053-1583 R&D Projects: GA ČR(CZ) GA17-18702S; GA MŠk LL1301 Institutional support: RVO:61388955 Keywords : graphene * Raman * strain * doping * correlation analysis * circular polarization Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 6.937, year: 2016

A valley-filtering switch based on strained graphene.

Science.gov (United States)

Zhai, Feng; Ma, Yanling; Zhang, Ying-Tao

2011-09-28

We investigate valley-dependent transport through a graphene sheet modulated by both the substrate strain and the fringe field of two parallel ferromagnetic metal (FM) stripes. When the magnetizations of the two FM stripes are switched from the parallel to the antiparallel alignment, the total conductance, valley polarization and valley conductance excess change greatly over a wide range of Fermi energy, which results from the dependence of the valley-related transmission suppression on the polarity configuration of inhomogeneous magnetic fields. Thus the proposed structure exhibits the significant features of a valley-filtering switch and a magnetoresistance device.

A valley-filtering switch based on strained graphene

International Nuclear Information System (INIS)

Zhai Feng; Ma Yanling; Zhang Yingtao

2011-01-01

We investigate valley-dependent transport through a graphene sheet modulated by both the substrate strain and the fringe field of two parallel ferromagnetic metal (FM) stripes. When the magnetizations of the two FM stripes are switched from the parallel to the antiparallel alignment, the total conductance, valley polarization and valley conductance excess change greatly over a wide range of Fermi energy, which results from the dependence of the valley-related transmission suppression on the polarity configuration of inhomogeneous magnetic fields. Thus the proposed structure exhibits the significant features of a valley-filtering switch and a magnetoresistance device. (paper)

Dominant phonon wave vectors and strain-induced splitting of the 2D Raman mode of graphene

Science.gov (United States)

Narula, Rohit; Bonini, Nicola; Marzari, Nicola; Reich, Stephanie

2012-03-01

The dominant phonon wave vectors q* probed by the 2D Raman mode of pristine and uniaxially strained graphene are determined via a combination of ab initio calculations and a full two-dimensional integration of the transition matrix. We show that q* are highly anisotropic and rotate about K with the polarizer and analyzer condition relative to the lattice. The corresponding phonon-mediated electronic transitions show a finite component along K-Γ that sensitively determines q*. We invalidate the notion of “inner” and “outer” processes. The characteristic splitting of the 2D mode of graphene under uniaxial tensile strain and given polarizer and analyzer setting is correctly predicted only if the strain-induced distortion and red-shift of the in-plane transverse optical (iTO) phonon dispersion as well as the changes in the electronic band structure are taken into account.

Uniaxial Drawing of Graphene-PVA Nanocomposites: Improvement in Mechanical Characteristics via Strain-Induced Exfoliation of Graphene

OpenAIRE

Jan, Rahim; Habib, Amir; Akram, Muhammad Aftab; Zia, Tanveer-ul-Haq; Khan, Ahmad Nawaz

2016-01-01

Polyvinyl alcohol (PVA)-stabilized graphene nanosheets (GNS) of lateral dimension (L) ~1??m are obtained via liquid phase exfoliation technique to prepare its composites in the PVA matrix. These composites show low levels of reinforcements due to poor alignment of GNS within the matrix as predicted by the modified Halpin-Tsai model. Drawing these composites up to 200?% strain, a significant improvement in mechanical properties is observed. Maximum values for Young?s modulus and strength are ~...

The generation of piezoelectricity and flexoelectricity in graphene by breaking the materials symmetries

Science.gov (United States)

Javvaji, Brahmanandam; He, Bo; Zhuang, Xiaoying

2018-06-01

Graphene is a non-piezoelectric material. Engineering the piezoelectricity in graphene is possible with the help of impurities, defects and structural modifications. This study reports the mechanism of strain induced polarization and the estimation of piezoelectric and flexoelectric coefficients for graphene system. The combination of charge-dipole potential and the strong many-body potential is employed for describing the inter-atomic interactions. The breaking of symmetry in graphene material is utilized to generate the polarization. Pristine graphene, graphene with circular defect, graphene with triangular defect and trapezium-shaped graphene are considered. Molecular dynamics simulations are performed for straining the graphene atomic systems. The optimization of charge-dipole potential functions measure the polarization for these systems. Pristine and circular defect graphene systems show a constant polarization with strain. The polarization is varying with strain for a triangular defected and trapezium-shaped graphene system. The local atomic deformation produces a change in polarization with respect to the strain gradient. Estimated piezo and flexo coefficients motivate the usage of graphene in electro-mechanical devices.

The generation of piezoelectricity and flexoelectricity in graphene by breaking the materials symmetries.

Science.gov (United States)

Javvaji, Brahmanandam; He, Bo; Zhuang, Xiaoying

2018-06-01

Graphene is a non-piezoelectric material. Engineering the piezoelectricity in graphene is possible with the help of impurities, defects and structural modifications. This study reports the mechanism of strain induced polarization and the estimation of piezoelectric and flexoelectric coefficients for graphene system. The combination of charge-dipole potential and the strong many-body potential is employed for describing the inter-atomic interactions. The breaking of symmetry in graphene material is utilized to generate the polarization. Pristine graphene, graphene with circular defect, graphene with triangular defect and trapezium-shaped graphene are considered. Molecular dynamics simulations are performed for straining the graphene atomic systems. The optimization of charge-dipole potential functions measure the polarization for these systems. Pristine and circular defect graphene systems show a constant polarization with strain. The polarization is varying with strain for a triangular defected and trapezium-shaped graphene system. The local atomic deformation produces a change in polarization with respect to the strain gradient. Estimated piezo and flexo coefficients motivate the usage of graphene in electro-mechanical devices.

Zero Modes and Global Antiferromagnetism in Strained Graphene

Directory of Open Access Journals (Sweden)

Bitan Roy

2014-05-01

Full Text Available A novel magnetic ground state is reported for the Hubbard Hamiltonian in strained graphene. When the chemical potential lies close to the Dirac point, the ground state exhibits locally both the Néel and ferromagnetic orders, even for weak Hubbard interaction. Whereas the Néel order parameter remains of the same sign in the entire system, the magnetization at the boundary takes the opposite sign from the bulk. The total magnetization vanishes this way, and the magnetic ground state is globally only an antiferromagnet. This peculiar ordering stems from the nature of the strain-induced single-particle zero-energy states, which have support on one sublattice of the honeycomb lattice in the bulk, and on the other sublattice near the boundary of a finite system. We support our claim with the self-consistent numerical calculation of the order parameters, as well as by the Monte Carlo simulations of the Hubbard model in both uniformly and nonuniformly strained honeycomb lattice. The present result is contrasted with the magnetic ground state of the same Hubbard model in the presence of a true magnetic field (and for vanishing Zeeman coupling, which is exclusively Néel ordered, with zero local magnetization everywhere in the system.

Structural and electronic properties of armchair graphene nanoribbons under uniaxial strain

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Qu, Li-Hua; Zhang, Jian-Min; Xu, Ke-Wei; Ji, Vincent

2014-02-01

We theoretically investigate the structures, relative stabilities and electronic properties of the armchair graphene nanoribbons (AGNRs) under uniaxial strain via first-principles calculations. The results show that, although each bond length decreases (increases) with increasing compression (tension) strain especially for the axial bonds a1, a4 and a7, the ribbon geometrical width d increases (decreases) with increasing compression (tension) strain due to the rotation of the zigzag bonds a2, a3, a5 and a6. For each nanoribbon, as expected, the lowest average energy corresponds to the unstrained state and the larger contract (elongate) deformation corresponds to the higher average energy. At a certain strain, the average energy increases with decreasing the ribbon width n. The average energy increases quadratically with the absolute value of the uniaxial strain, showing an elastic behavior. The dependence of the band gap on the strain is sensitive to the ribbon width n which can be classified into three distinct families n=3I, 3I+1 and 3I+2, where I is an integer. The ribbon width leads to oscillatory band gaps due to quantum confinement effect.

A large-strain, fast-response, and easy-to-manufacture electrothermal actuator based on laser-reduced graphene oxide

Science.gov (United States)

Zhang, Tian-Yu; Wang, Qian; Deng, Ning-Qin; Zhao, Hai-Ming; Wang, Dan-Yang; Yang, Zhen; Liu, Ying; Yang, Yi; Ren, Tian-Ling

2017-09-01

In this paper, we have developed a high-performance graphene electrothermal actuator (ETA). The fabrication method is easy, fast, environmentally friendly, and suitable for preparing both large-size and miniature graphene ETAs. When applied with the driving voltage of 65 V, the graphene ETA achieves a large bending angle of 270° with a fast response of 8 s and the recovery process costs 19 s. The large bending deformation is reversible and can be precisely controlled by the driving voltage. A simple robotic hand prepared by using a single graphene ETA can hold the object, which is more than ten times the weight of itself. By virtue of its large-strain, fast response, and easy-to-manufacture, we believe that the graphene ETA has tremendous potential in extensive applications involving biomimetic robotics, artificial muscles, switches, and microsensors in both macroscopic and microscopic fields.

Long-wavelength optical phonon behavior in uniaxial strained graphene: Role of electron-phonon interaction

OpenAIRE

Assili, Mohamed; Haddad, Sonia

2014-01-01

We derive the frequency shifts and the broadening of $\\Gamma$ point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic...

Uniaxial Drawing of Graphene-PVA Nanocomposites: Improvement in Mechanical Characteristics via Strain-Induced Exfoliation of Graphene

Science.gov (United States)

Jan, Rahim; Habib, Amir; Akram, Muhammad Aftab; Zia, Tanveer-ul-Haq; Khan, Ahmad Nawaz

2016-08-01

Polyvinyl alcohol (PVA)-stabilized graphene nanosheets (GNS) of lateral dimension ( L) ~1 μm are obtained via liquid phase exfoliation technique to prepare its composites in the PVA matrix. These composites show low levels of reinforcements due to poor alignment of GNS within the matrix as predicted by the modified Halpin-Tsai model. Drawing these composites up to 200 % strain, a significant improvement in mechanical properties is observed. Maximum values for Young's modulus and strength are ~×4 and ~×2 higher respectively than that of neat PVA. Moreover, the rate of increase of the modulus with GNS volume fraction is up to 700 GPa, higher than the values predicted using the Halpin-Tsai theory. However, alignment along with strain-induced de-aggregation of GNS within composites accounts well for the obtained results as confirmed by X-ray diffraction (XRD) characterization.

Hyperelastic tension of graphene

Energy Technology Data Exchange (ETDEWEB)

Saavedra Flores, E. I., E-mail: erick.saavedra@usach.cl [Departamento de Ingeniería en Obras Civiles, Universidad de Santiago de Chile, Av. Ecuador 3659, Santiago (Chile); Ajaj, R. M. [Aeronautics and Astronautics, University of Southampton, Southampton SO171BJ (United Kingdom); Adhikari, S.; Dayyani, I.; Friswell, M. I. [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Castro-Triguero, Rafael [Department of Mechanics, University of Cordoba, Campus de Rabanales, Cordoba CP 14071 (Spain)

2015-02-09

In this paper, we investigate the hyperelastic tensile behaviour of single layer graphene sheets (SLGSs). A one-term incompressible Ogden-type hyperelastic model is chosen to describe the mechanical response of C-C bonds. By establishing equality between the Ogden strain-energy and the variation of the Tersoff-Brenner interatomic potential, three different geometries of SLGSs are studied under tensile loading. We compute the Young's modulus, the finite-deformation Poisson's ratio, ultimate strains, total reactions, and the variation of the potential energy per carbon atom for large strains. Numerical simulations are compared with results obtained by molecular mechanics and molecular dynamics simulations, finite elements, continuum mechanics theory, and experiments. Our predictions are validated, revealing the potential predictive capabilities of the present hyperelastic framework for the analysis of graphene in the context of infinitesimal and large deformations. The good agreement found between our calculations and the published data suggests that graphene may be described as a hyperelastic material.

Flexible substrate based 2D ZnO (n)/graphene (p) rectifying junction as enhanced broadband photodetector using strain modulation

Science.gov (United States)

Sahatiya, Parikshit; Jones, S. Solomon; Thanga Gomathi, P.; Badhulika, Sushmee

2017-06-01

Strain modulation is considered to be an effective way to modulate the electronic structure and carrier behavior in flexible semiconductors heterojunctions. In this work, 2D Graphene (Gr)/ZnO junction was successfully fabricated on flexible eraser substrate using simple, low-cost solution processed hydrothermal method and has been utilized for broadband photodetection in the UV to visible range at room temperature. Optimization in terms of process parameters were done to obtain 2D ZnO over 2D graphene which shows decrease in bandgap and broad absorption range from UV to visible. Under compressive strain piezopotential induced by the atoms displacements in 2D ZnO, 87% enhanced photosensing for UV light was observed under 30% strain. This excellent performance improvement can be attributed to piezopotential induced under compressive strain in 2D ZnO which results in lowering of conduction band energy and raising the schottky barrier height thereby facilitating electron-hole pair separation in 2D Gr/ZnO junction. Detailed mechanism studies in terms of density of surface states and energy band diagram is presented to understand the proposed phenomena. Results provide an excellent approach for improving the optoelectronic performance of 2D Gr/ZnO interface which can also be applied to similar semiconductor heterojunctions.

Identifying suitable substrates for high-quality graphene-based heterostructures

Science.gov (United States)

Banszerus, L.; Janssen, H.; Otto, M.; Epping, A.; Taniguchi, T.; Watanabe, K.; Beschoten, B.; Neumaier, D.; Stampfer, C.

2017-06-01

We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphene-based heterostuctures on a large number of different substrate materials, including hexagonal boron nitride (hBN), transition metal dichalcogenides, silicon, different oxides and nitrides, as well as polymers. By applying a hBN-assisted, contamination free, dry transfer process for CVD graphene, high-quality heterostructures with low doping densities and low strain variations are assembled. The Raman spectra of these pristine heterostructures are sensitive to substrate-induced doping and strain variations and are thus used to probe the suitability of the substrate material for potential high-quality graphene devices. We find that the flatness of the substrate material is a key figure for gaining, or preserving high-quality graphene.

Reply to ``Comment on `Band structure engineering of graphene by strain: First-principles calculations' ''

Science.gov (United States)

Gui, Gui; Li, Jin; Zhong, Jianxin

2009-10-01

We reply to the Comment by Farjam and Rafii-Tabar [Phys. Rev. B 80, 167401 (2009)] on our paper [Phys. Rev. B 78, 075435 (2008)]. We show that the gap opening found in our paper is due to the use of a small number of k points in the calculation which prevents revealing the sharp contact of the two bands near K or R . Once a large number of k points is used, the density-functional theory (DFT) VASP codes give the same conclusion as obtained by Farjam and Rafii-Tabar by using the QUANTUM-ESPRESSO codes, namely, there is no gap opening in the band structure of graphene under small planar strain. We also point out that all other results in our paper remain correct, except for the conclusion of the gap opening. The results demonstrate the importance of using a large number of k points for determining the gap width of the band structure of graphene under strain as well as the validity of the DFT VASP codes for the system.

Graphene nanoribbon as an elastic damper

Science.gov (United States)

Evazzade, Iman; Lobzenko, Ivan P.; Saadatmand, Danial; Korznikova, Elena A.; Zhou, Kun; Liu, Bo; Dmitriev, Sergey V.

2018-05-01

Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.

Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

Energy Technology Data Exchange (ETDEWEB)

Lohrasbi, Elaheh [Department of Chemistry, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Javanbakht, Mehran, E-mail: mehranjavanbakht@gmail.com [Department of Chemistry, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Fuel and Solar Cell Lab, Renewable Energy Research Center, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Mozaffari, Sayed Ahmad [Fuel and Solar Cell Lab, Renewable Energy Research Center, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Thin Layer and Nanotechnology Laboratory, Department of Chemical Technology, Iranian Research Organization for Science and Technology (IROST), Tehran (Iran, Islamic Republic of)

2017-06-15

Highlights: • SO{sub 3}H-graphene supported PtFeCo alloy nanoparticles were prepared. • Co:Fe atomic ratio plays important role in the electrocatalytic performance. • PtCoFe/SG with 7:3 Co:Fe atomic ratio is optimized for PEMFCs. • Power density of 530 mW cm{sup −2} with 0.1 mg cm{sup −2} Pt loading was obtained at 75 °C. - Abstract: The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO{sub 3}− groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1 mg cm{sup −2} Pt) reaches to a maximum of 530 mW cm{sup −2} at 75 °C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

International Nuclear Information System (INIS)

Lohrasbi, Elaheh; Javanbakht, Mehran; Mozaffari, Sayed Ahmad

2017-01-01

Highlights: • SO_3H-graphene supported PtFeCo alloy nanoparticles were prepared. • Co:Fe atomic ratio plays important role in the electrocatalytic performance. • PtCoFe/SG with 7:3 Co:Fe atomic ratio is optimized for PEMFCs. • Power density of 530 mW cm"−"2 with 0.1 mg cm"−"2 Pt loading was obtained at 75 °C. - Abstract: The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO_3− groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1 mg cm"−"2 Pt) reaches to a maximum of 530 mW cm"−"2 at 75 °C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

International Nuclear Information System (INIS)

Izuani Che Rosid, N A; Ahmadi, M T; Ismail, Razali

2016-01-01

The effect of tensile uniaxial strain on the non-parabolic electronic band structure of armchair graphene nanoribbon (AGNR) is investigated. In addition, the density of states and the carrier statistic based on the tight-binding Hamiltonian are modeled analytically. It is found that the property of AGNR in the non-parabolic band region is varied by the strain. The tunable energy band gap in AGNR upon strain at the minimum energy is described for each of n-AGNR families in the non-parabolic approximation. The behavior of AGNR in the presence of strain is attributed to the breakable AGNR electronic band structure, which varies the physical properties from its normality. The linear relation between the energy gap and the electrical properties is featured to further explain the characteristic of the deformed AGNR upon strain. (paper)

Out-of-plane strain and electric field tunable electronic properties and Schottky contact of graphene/antimonene heterostructure

Science.gov (United States)

Phuc, Huynh V.; Hieu, Nguyen N.; Hoi, Bui D.; Phuong, Le T. T.; Hieu, Nguyen V.; Nguyen, Chuong V.

2017-12-01

In this paper, the electronic properties of graphene/monolayer antimonene (G/m-Sb) heterostructure have been studied using the density functional theory (DFT). The effects of out-of-plane strain (interlayer coupling) and electric field on the electronic properties and Schottky contact of the G/m-Sb heterostructure are also investigated. The results show that graphene is bound to m-Sb layer by a weak van-der-Waals interaction with the interlayer distance of 3.50 Å and the binding energy per carbon atom of -39.62 meV. We find that the n-type Schottky contact is formed at the G/m-Sb heterostructure with the Schottky barrier height (SBH) of 0.60 eV. By varying the interlayer distance between graphene and the m-Sb layer we can change the n-type and p-type SBH at the G/m-Sb heterostructure. Especially, we find the transformation from n-type to p-type Schottky contact with decreasing the interlayer distance. Furthermore, the SBH and the Schottky contact could be controlled by applying the perpendicular electric field. With the positive electric field, electrons can easily transfer from m-Sb to graphene layer, leading to the transition from n-type to p-type Schottky contact.

Study of magnetic properties of graphene nanostructures and graphene nanoribbons

Directory of Open Access Journals (Sweden)

F Fazileh

2012-03-01

Full Text Available The discovery of graphene and its remarkable electronic and magnetic properties has initiated great research interest in this material. Furthermore, there are many derivatives in these graphene related materials among which graphene nanoribbons and graphene nanofragments are candidates for future carbon-based nanoelectronics and spintronics. Theoretical studies have shown that magnetism can arise in various situations such as point defects, disorder and reduced dimensionality. Using a mean field Hubbard model, we studied the appearance of magnetic textures in zero-dimensional graphene nanofragments and one-dimensional graphene zigzag nanoribbons. Among nanofragments, triangular shape, bowtie and coronene were studied. We explain how the shape of these materials, the imbalance in the number of atoms belonging to the graphene sublattices, the existence of zero-energy states and the total and local magnetic moments were related. At the end, we focused on the effects of a model disorder potential (Anderson-type, and illustrate how density of states of zigzag nanoribbons was affected.

Interfacial thermal conductance in multilayer graphene/phosphorene heterostructure

International Nuclear Information System (INIS)

Zhang, Ying-Yan; Pei, Qing-Xiang; Mai, Yiu-Wing; Lai, Siu-Kai

2016-01-01

Vertical integration of 2D materials has recently appeared as an effective method for the design of novel nano-scale devices. Using non-equilibrium molecular dynamics simulations, we study the interfacial thermal transport property of graphene/phosphorene heterostructures where phosphorene is sandwiched in between graphene. Various modulation techniques are thoroughly explored. We found that the interfacial thermal conductance at the interface of graphene and phosphorene can be enhanced significantly by using vacancy defects, hydrogenation and cross-plane compressive strain. By contrast, the reduction in the interfacial thermal conductance can be achieved by using cross-plane tensile strain. Our results provide important guidelines for manipulating the thermal transport in graphene/phosphorene based-nano-devices. (paper)

Polycyclic Aromatic Hydrocarbons Adsorption onto Graphene: A DFT and AIMD Study

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Bing Li

2018-05-01

Full Text Available Density functional theory (DFT calculations and ab-initio molecular dynamics (AIMD simulations were performed to understand graphene and its interaction with polycyclic aromatic hydrocarbons (PAHs molecules. The adsorption energy was predicted to increase with the number of aromatic rings in the adsorbates, and linearly correlate with the hydrophobicity of PAHs. Additionally, the analysis of the electronic properties showed that PAHs behave as mild n-dopants and introduce electrons into graphene; but do not remarkably modify the band gap of graphene, indicating that the interaction between PAHs and graphene is physisorption. We have also discovered highly sensitive strain dependence on the adsorption strength of PAHs onto graphene surface. The AIMD simulation indicated that a sensitive and fast adsorption process of PAHs can be achieved by choosing graphene as the adsorbent. These findings are anticipated to shed light on the future development of graphene-based materials with potential applications in the capture and removal of persistent aromatic pollutants.

Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

Science.gov (United States)

Zhao, Yang; Dong, Shuhong; Yu, Peishi; Zhao, Junhua

2018-06-01

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

Stable configurations of graphene on silicon

Energy Technology Data Exchange (ETDEWEB)

Javvaji, Brahmanandam; Shenoy, Bhamy Maithry [Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560012 (India); Mahapatra, D. Roy, E-mail: droymahapatra@aero.iisc.ernet.in [Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560012 (India); Ravikumar, Abhilash [Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal 575025 (India); Hegde, G.M. [Center for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012 (India); Rizwan, M.R. [Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal 575025 (India)

2017-08-31

Highlights: • Simulations of epitaxial growth process for silicon–graphene system is performed. • Identified the most favourable orientation of graphene sheet on silicon substrate. • Atomic local strain due to the silicon–carbon bond formation is analyzed. - Abstract: Integration of graphene on silicon-based nanostructures is crucial in advancing graphene based nanoelectronic device technologies. The present paper provides a new insight on the combined effect of graphene structure and silicon (001) substrate on their two-dimensional anisotropic interface. Molecular dynamics simulations involving the sub-nanoscale interface reveal a most favourable set of temperature independent orientations of the monolayer graphene sheet with an angle of ∽15° between its armchair direction and [010] axis of the silicon substrate. While computing the favorable stable orientations, both the translation and the rotational vibrations of graphene are included. The possible interactions between the graphene atoms and the silicon atoms are identified from their coordination. Graphene sheet shows maximum bonding density with bond length 0.195 nm and minimum bond energy when interfaced with silicon substrate at 15° orientation. Local deformation analysis reveals probability distribution with maximum strain levels of 0.134, 0.047 and 0.029 for 900 K, 300 K and 100 K, respectively in silicon surface for 15° oriented graphene whereas the maximum probable strain in graphene is about 0.041 irrespective of temperature. Silicon–silicon dimer formation is changed due to silicon–carbon bonding. These results may help further in band structure engineering of silicon–graphene lattice.

Influence of temperature and free edges on the mechanical properties of graphene

International Nuclear Information System (INIS)

Dewapriya, M A N; Srikantha Phani, A; Rajapakse, R K N D

2013-01-01

A systematic molecular dynamics simulation study is performed to assess the effects of temperature and free edges on the ultimate tensile strength and Young's modulus of a single-layer graphene sheet. It is observed that graphene sheets at higher temperatures fail at lower strains, due to the high kinetic energy of atoms. A numerical model, based on kinetic analysis, is used to predict the ultimate strength of the graphene under various temperatures and strain rates. As the width of a graphene reduces, the excess edge energy associated with free edge atoms induces an initial strain on the relaxed configuration of the sheets. This initial strain has a greater influence on the Young's modulus of the zigzag sheet compared with that of the armchair sheets. The simulations reveal that the carbon–carbon bond length and amplitude of intrinsic ripples of the graphene increases with temperature. The initial out-of-plane displacement of carbon atoms is necessary to simulate the physical behaviour of a graphene when the Nosé–Hoover or Berendsen thermostat is used. (paper)

Nanoscale Mechanical Characterization of Graphene/Polymer Nanocomposites using Atomic Force Microscopy

Science.gov (United States)

Cai, Minzhen

Graphene materials, exhibiting outstanding mechanical properties, are excellent candidates as reinforcement in high-performance polymer nanocomposites. In this dissertation, advanced atomic force microscopy (AFM) techniques are applied to study the nanomechanics of graphene/polymer nanocomposites, specifically the graphene/polymer interfacial strength and the stress transfer at the interface. Two novel methods to directly characterize the interfacial strength between individual graphene sheets and polymers using AFM are presented and applied to a series of polymers and graphene sheets. The interfacial strength of graphene/polymer varies greatly for different combinations. The strongest interaction is found between graphene oxide (GO) and polyvinyl alcohol (PVA), a strongly polar, water-based polymer. On the other hand, polystyrene, a non polar polymer, has the weakest interaction with GO. The interfacial bond strength is attributed to hydrogen bonding and physical adsorption. Further, the stress transfer in GO/PVA nanocomposites is studied quantitatively by monitoring the strain in individual GO sheet inside the polymer via AFM and Raman spectroscopy. For the first time, the strains of individual GO sheets in nanocomposites are imaged and quantified as a function of the applied external strains. The matrix strain is directly transferred to GO sheets for strains up to 8%. At higher strain levels, the onset of the nanocomposite failure and a stick-slip behavior is observed. This study reveals that GO is superior to pure graphene as reinforcement in nanocomposites. These results also imply the potential to make a new generation of nanocomposites with exceptional high strength and toughness. In the second part of this dissertation, AFM is used to study the structure of silk proteins and the morphology of spider silks. For the first time, shear-induced self-assembly of native silk fibroin is observed. The morphology of the Brown Recluse spider silk is investigated and a

Atomistic simulation and continuum modeling of graphene nanoribbons under uniaxial tension

International Nuclear Information System (INIS)

Lu, Qiang; Gao, Wei; Huang, Rui

2011-01-01

Atomistic simulations are performed to study the nonlinear mechanical behavior of graphene nanoribbons under quasistatic uniaxial tension, emphasizing the effects of edge structures (armchair and zigzag, without and with hydrogen passivation) on elastic modulus and fracture strength. The numerical results are analyzed within a theoretical model of thermodynamics, which enables determination of the bulk strain energy density, the edge energy density and the hydrogen adsorption energy density as nonlinear functions of the applied strain based on static molecular mechanics simulations. These functions can be used to describe mechanical behavior of graphene nanoribbons from the initial linear elasticity to fracture. It is found that the initial Young's modulus of a graphene nanoribbon depends on the ribbon width and the edge chirality. Furthermore, it is found that the nominal strain to fracture is considerably lower for graphene nanoribbons with armchair edges than for ribbons with zigzag edges. Molecular dynamics simulations reveal two distinct fracture nucleation mechanisms: homogeneous nucleation for the zigzag-edged graphene nanoribbons and edge-controlled heterogeneous nucleation for the armchair-edged ribbons. The modeling and simulations in this study highlight the atomistic mechanisms for the nonlinear mechanical behavior of graphene nanoribbons with the edge effects, which is potentially important for developing integrated graphene-based devices

Relaxation of electron–hole spins in strained graphene nanoribbons

International Nuclear Information System (INIS)

Prabhakar, Sanjay; Melnik, Roderick

2015-01-01

We investigate the influence of magnetic field originating from the electromechanical effect on the spin-flip behaviors caused by electromagnetic field radiation in the strained graphene nanoribbons (GNRs). We show that the spin splitting energy difference (≈10 meV) due to pseudospin is much larger than the spin-orbit coupling effect (Balakrishnan et al 2013 Nat. Phys. 9 284) that might provide an evidence of broken symmetry of degeneracy. The induced spin splitting energy due to ripple waves can be further enhanced with increasing values of applied tensile edge stress for potential applications in straintronic devices. In particular, we show that the enhancement in the magnitude of the ripple waves due to externally applied tensile edge stress extends the tuning of spin-flip behaviors to larger widths of GNRs. (paper)

Electric field-induced valley degeneracy lifting in uniaxial strained graphene: Evidence from magnetophonon resonance

Science.gov (United States)

Assili, Mohamed; Haddad, Sonia; Kang, Woun

2015-03-01

A double peak structure in the magnetophonon resonance (MPR) spectrum of uniaxial strained graphene, under crossed electric and magnetic fields, is predicted. We focus on the Γ point optical phonon modes coupled to the inter-Landau level transitions 0 ⇆±1 where MPR is expected to be more pronounced at high magnetic field. We derive the frequency shifts and the broadenings of the longitudinal and transverse optical phonon modes taking into account the effect of the strain modified electronic spectrum on the electron-phonon coupling. We show that the MPR line for a given phonon mode acquires a double peak structure originating from the twofold valley degeneracy lifting. The latter is due to the different Landau level spacings in the two Dirac valleys resulting from the simultaneous action of the inplane electric field and the strain-induced Dirac cone tilt. We discuss the role of some key parameters such as disorder, strain, doping, and electric field amplitude on the emergence of the double peak structure.

Unified Drain Current Model of Armchair Graphene Nanoribbons with Uniaxial Strain and Quantum Effect

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EngSiew Kang

2014-01-01

Full Text Available A unified current-voltage I-V model of uniaxial strained armchair graphene nanoribbons (AGNRs incorporating quantum confinement effects is presented in this paper. The I-V model is enhanced by integrating both linear and saturation regions into a unified and precise model of AGNRs. The derivation originates from energy dispersion throughout the entire Brillouin zone of uniaxial strained AGNRs based on the tight-binding approximation. Our results reveal the modification of the energy band gap, carrier density, and drain current upon strain. The effects of quantum confinement were investigated in terms of the quantum capacitance calculated from the broadening density of states. The results show that quantum effect is greatly dependent on the magnitude of applied strain, gate voltage, channel length, and oxide thickness. The discrepancies between the classical calculation and quantum calculation were also measured and it has been found to be as high as 19% drive current loss due to the quantum confinement. Our finding which is in good agreement with the published data provides significant insight into the device performance of uniaxial strained AGNRs in nanoelectronic applications.

Topological defect clustering and plastic deformation mechanisms in functionalized graphene

Science.gov (United States)

Nunes, Ricardo; Araujo, Joice; Chacham, Helio

2011-03-01

We present ab initio results suggesting that strain plays a central role in the clustering of topological defects in strained and functionalized graphene models. We apply strain onto the topological-defect graphene networks from our previous work, and obtain topological-defect clustering patterns which are in excellent agreement with recent observations in samples of reduced graphene oxide. In our models, the graphene layer, containing an initial concentration of isolated topological defects, is covered by hydrogen or hydroxyl groups. Our results also suggest a rich variety of plastic deformation mechanism in functionalized graphene systems. We acknowledge support from the Brazilian agencies: CNPq, Fapemig, and INCT-Materiais de Carbono.

Effect of uniaxial stress on the electrochemical properties of graphene with point defects

Science.gov (United States)

Szroeder, Paweł; Sagalianov, Igor Yu.; Radchenko, Taras M.; Tatarenko, Valentyn A.; Prylutskyy, Yuriy I.; Strupiński, Włodzimierz

2018-06-01

We report a calculational study of electron states and the resulting electrochemical properties of uniaxially strained graphene with point defects. For this study the reduction of ferricyanide to ferrocyanide serves as a benchmark electrochemical reaction. We find that the heterogeneous electron transfer activity of the perfect graphene electrode rises under uniaxial strain. However, evolution of the cathodic reaction rate depends on the direction of strain. For moderate lattice deformations, the zigzag strain improves electrochemical performance better than the armchair strain. Standard rate constant increases by 50% at the zigzag strain of 10%. Vacancies, covalently bonded moieties, charged adatoms and substitutional impurities in the zigzag strained graphene induce changes in the shape of the curve of the cathodic reaction rate. However, this changes do not translate into the electrocatalytic activity. Vacancies and covalently bonded moieties at concentration of 0.1% do not affect the electrochemical performance. Charged adatoms and substitutional impurities give a slight increase in the standard rate constant by, respectively, 2.2% and 3.4%.

Tailoring the structural and electronic properties of a graphene-like ZnS monolayer using biaxial strain

International Nuclear Information System (INIS)

Behera, Harihar; Mukhopadhyay, Gautam

2014-01-01

Our first-principles full-potential density functional theory calculations show that a ZnS monolayer (ML-ZnS), which is predicted to adopt a graphene-like planar honeycomb structure with a direct band gap, undergoes strain-induced modifications in its structure and band gap when subjected to in-plane homogeneous biaxial strain (δ). ML-ZnS gets buckled for compressive strain greater than 0.92% ; the buckling parameter Δ(= 0.00 Å for planar ML-ZnS) linearly increases with increasing compressive strain (Δ = 0.435 Å at δ = −5.25%). A tensile strain of 2.91% turns the direct ML-ZnS band gap into indirect. Within our considered strain values of |δ| < 6%, the band gap shows linearly decreasing (non-linearly increasing as well as decreasing) variation with tensile (compressive) strain. These predictions (based on our calculations with two atoms per unit cell) may be exploited in future for potential applications in strain sensors and other nano-devices such as nano-electromechanical systems and nano-optomechanical systems. (paper)

Thermodynamics and kinetics of graphene chemistry: a graphene hydrogenation prototype study.

Science.gov (United States)

Pham, Buu Q; Gordon, Mark S

2016-12-07

The thermodynamic and kinetic controls of graphene chemistry are studied computationally using a graphene hydrogenation reaction and polyaromatic hydrocarbons to represent the graphene surface. Hydrogen atoms are concertedly chemisorped onto the surface of graphene models of different shapes (i.e., all-zigzag, all-armchair, zigzag-armchair mixed edges) and sizes (i.e., from 16-42 carbon atoms). The second-order Z-averaged perturbation theory (ZAPT2) method combined with Pople double and triple zeta basis sets are used for all calculations. It is found that both the net enthalpy change and the barrier height of graphene hydrogenation at graphene edges are lower than at their interior surfaces. While the thermodynamic product distribution is mainly determined by the remaining π-islands of functionalized graphenes (Phys. Chem. Chem. Phys., 2013, 15, 3725-3735), the kinetics of the reaction is primarily correlated with the localization of the electrostatic potential of the graphene surface.

FOCUS ON GRAPHENE

International Nuclear Information System (INIS)

Peres, N M R; Ribeiro, Ricardo M

2009-01-01

Graphene physics is currently one of the most active research areas in condensed matter physics. Countless theoretical and experimental studies have already been performed, targeting electronic, magnetic, thermal, optical, structural and vibrational properties. Also, studies that modify pristine graphene, aiming at finding new physics and possible new applications, have been considered. These include patterning nanoribbons and quantum dots, exposing graphene's surface to different chemical species, studying multilayer systems, and inducing strain and curvature (modifying in this way graphene's electronic properties). This focus issue includes many of the latest developments on graphene research. Focus on Graphene Contents The effect of sublattice symmetry breaking on the electronic properties of doped graphene A Qaiumzadeh and R Asgari Interfaces within graphene nanoribbons J Wurm, M Wimmer, I Adagideli, K Richter and H U Baranger Weak localization and transport gap in graphene antidot lattices J Eroms and D Weiss Electronic properties of graphene antidot lattices J A Fuerst, J G Pedersen, C Flindt, N A Mortensen, M Brandbyge, T G Pedersen and A-P Jauho Splitting of critical energies in the n=0 Landau level of graphene Ana L C Pereira Double-gated graphene-based devices S Russo, M F Craciun, M Yamamoto, S Tarucha and A F Morpurgo Pinning and switching of magnetic moments in bilayer graphene Eduardo V Castro, M P Lopez-Sancho and M A H Vozmediano Electronic transport properties of graphene nanoribbons Katsunori Wakabayashi, Yositake Takane, Masayuki Yamamoto and Manfred Sigrist Many-body effects on out-of-plane phonons in graphene J Gonzalez and E Perfetto Graphene zigzag ribbons, square lattice models and quantum spin chains Mahdi Zarea and Nancy Sandler On the universal ac optical background in graphene V P Gusynin, S G Sharapov and J P Carbotte Heat conduction in graphene: experimental study and theoretical interpretation S Ghosh, D L Nika, E P Pokatilov and A A

Electric field-induced valley degeneracy lifting in uniaxial strained graphene: evidence from magnetophonon resonance

OpenAIRE

Assili, Mohamed; Haddad, Sonia; Kang, Woun

2015-01-01

A double peak structure in the magneto-phonon resonance (MPR) spectrum of uniaxial strained graphene, under crossed electric and magnetic fields, is predicted. We focus on the $\\Gamma$ point optical phonon modes coupled to the inter-Landau level transitions $0 \\leftrightarrows \\pm 1$ where MPR is expected to be more pronounced at high magnetic field. We derive the frequency shifts and the broadenings of the longitudinal (LO) and transverse (TO) optical phonon modes taking into account the eff...

Low-voltage, large-strain soft electrothermal actuators based on laser-reduced graphene oxide/Ag particle composites

Science.gov (United States)

Wang, Qian; Li, Yu-Tao; Zhang, Tian-Yu; Wang, Dan-Yang; Tian, Ye; Yan, Jun-Chao; Tian, He; Yang, Yi; Yang, Fan; Ren, Tian-Ling

2018-03-01

In this paper, low-voltage, large-strain flexible electrothermal actuators (ETAs) based on laser-reduced graphene oxide (LRGO)/Ag particle composites were fabricated in a simple and cost-efficient process. By adding Ag particles to the LRGO, the sheet resistance decreased effectively. Under a driving voltage of 28 V, the actuator obtained a bending angle of 192° within 6 s. Besides, the bending deformation could be precisely controlled by the driving voltage ranging from 10° to 192°. Finally, a gripper composed of two actuators was demonstrated to manipulate a piece of polydimethylsiloxane block. With the advantages of low-voltage, fast-response, and easy-to-manufacture, the graphene based ETAs have a promising application in soft robotics and soft machines.

Graphene-based stretchable and transparent moisture barrier

Science.gov (United States)

Won, Sejeong; Van Lam, Do; Lee, Jin Young; Jung, Hyun-June; Hur, Min; Kim, Kwang-Seop; Lee, Hak-Joo; Kim, Jae-Hyun

2018-03-01

We propose an alumina-deposited double-layer graphene (2LG) as a transparent, scalable, and stretchable barrier against moisture; this barrier is indispensable for foldable or stretchable organic displays and electronics. Both the barrier property and stretchability were significantly enhanced through the introduction of 2LG between alumina and a polymeric substrate. 2LG with negligible polymeric residues was coated on the polymeric substrate via a scalable dry transfer method in a roll-to-roll manner; an alumina layer was deposited on the graphene via atomic layer deposition. The effect of the graphene layer on crack generation in the alumina layer was systematically studied under external strain using an in situ micro-tensile tester, and correlations between the deformation-induced defects and water vapor transmission rate were quantitatively analyzed. The enhanced stretchability of alumina-deposited 2LG originated from the interlayer sliding between the graphene layers, which resulted in the crack density of the alumina layer being reduced under external strain.

Haldane model under nonuniform strain

Science.gov (United States)

Ho, Yen-Hung; Castro, Eduardo V.; Cazalilla, Miguel A.

2017-10-01

We study the Haldane model under strain using a tight-binding approach, and compare the obtained results with the continuum-limit approximation. As in graphene, nonuniform strain leads to a time-reversal preserving pseudomagnetic field that induces (pseudo-)Landau levels. Unlike a real magnetic field, strain lifts the degeneracy of the zeroth pseudo-Landau levels at different valleys. Moreover, for the zigzag edge under uniaxial strain, strain removes the degeneracy within the pseudo-Landau levels by inducing a tilt in their energy dispersion. The latter arises from next-to-leading order corrections to the continuum-limit Hamiltonian, which are absent for a real magnetic field. We show that, for the lowest pseudo-Landau levels in the Haldane model, the dominant contribution to the tilt is different from graphene. In addition, although strain does not strongly modify the dispersion of the edge states, their interplay with the pseudo-Landau levels is different for the armchair and zigzag ribbons. Finally, we study the effect of strain in the band structure of the Haldane model at the critical point of the topological transition, thus shedding light on the interplay between nontrivial topology and strain in quantum anomalous Hall systems.

Green conversion of graphene oxide to graphene nanosheets and its biosafety study.

Directory of Open Access Journals (Sweden)

Adhiraj Dasgupta

Full Text Available Chemical reduction of graphene oxide (GO to graphene employs the use of toxic and environmentally harmful reducing agents, hindering mass production of graphene which is of tremendous technological importance. In this study we report a green approach to the synthesis of graphene, bio-reduced by crude polysaccharide. The polysaccharide reduces exfoliated GO to graphene at room temperature in an aqueous medium. Transmission electron microscopy image provides clear evidence for the formation of few layer graphene. Characterization of the resulting polysaccharide reduced GO by Raman spectroscopy, Fourier transform infrared spectroscopy and Energy dispersive X-ray analysis confirms reduction of GO to graphene. We also investigated the degree of biosafety of the reduced GO and found it to be safe under 100 μg/ml.

Size-dependent deformation behavior of nanocrystalline graphene sheets

Energy Technology Data Exchange (ETDEWEB)

Yang, Zhi [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Huang, Yuhong [College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, Shaanxi (China); Ma, Fei, E-mail: mafei@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Sun, Yunjin [Faculty of Food Science and Engineering, Beijing University of Agriculture, Beijing Key Laboratory of Agricultural Product Detection and Control of Spoilage Organisms and Pesticide Residue, Beijing Laboratory of Food Quality and Safety, Beijing 102206 (China); Xu, Kewei, E-mail: kwxu@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Opt-electronic Engineering, Xi’an University of Arts and Science, Xi’an 710065, Shaanxi (China); Chu, Paul K., E-mail: paul.chu@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

2015-08-15

Highlights: • MD simulation is conducted to study the deformation of nanocrystalline graphene. • Unexpectedly, the elastic modulus decreases with the grain size considerably. • But the fracture stress and strain are nearly insensitive to the grain size. • A composite model with grain domains and GBs as two components is suggested. - Abstract: Molecular dynamics (MD) simulation is conducted to study the deformation behavior of nanocrystalline graphene sheets. It is found that the graphene sheets have almost constant fracture stress and strain, but decreased elastic modulus with grain size. The results are different from the size-dependent strength observed in nanocrystalline metals. Structurally, the grain boundaries (GBs) become a principal component in two-dimensional materials with nano-grains and the bond length in GBs tends to be homogeneously distributed. This is almost the same for all the samples. Hence, the fracture stress and strain are almost size independent. As a low-elastic-modulus component, the GBs increase with reducing grain size and the elastic modulus decreases accordingly. A composite model is proposed to elucidate the deformation behavior.

Use of high energy ball milling to study the role of graphene nanoplatelets and carbon nanotubes reinforced magnesium alloy

Energy Technology Data Exchange (ETDEWEB)

Rashad, Muhammad, E-mail: rashadphy87@gmail.com [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Pan, Fusheng, E-mail: fspan@cqu.edu.cn [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Chongqing Academy of Science and Technology, Chongqing, Chongqing 401123 (China); Zhang, Jianyue [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Asif, Muhammad [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China)

2015-10-15

Graphene nanoplatelets (few layer graphene) and carbon nanotubes were used as reinforcement fillers to enhance the mechanical properties of AZ31 magnesium alloy through high energy ball milling, sintering, and hot extrusion techniques. Experimental results revealed that tensile fracture strain of AZ31 magnesium alloy was enhanced by +49.6% with 0.3 wt.% graphene nanoplatelets compared to −8.3% regression for 0.3 wt.% carbon nanotubes. The tensile strength of AZ31 magnesium alloy was decreased (−11.2%) with graphene nanoplatelets addition, while increased (+7.7%) with carbon nanotubes addition. Unlike tensile test, compression tests showed different trend. The compression strength of carbon nanotubes-AZ31 composite was +51.2% greater than AZ31 magnesium alloy as compared to +0.6% increase for graphene nanoplatelets. The compressive fracture strain of carbon nanotubes-AZ31 composite was decreased (−14.1%) while no significant change in fracture strain of graphene nanoplatelets-AZ31 composite was observed. The X-ray diffraction results revealed that addition of reinforcement particles weaken the basal textures which affect the composite's yield asymmetry. Microstructure evaluation revealed the absence of intermetallic phase formation between reinforcements and matrix. The carbon reinforcements in AZ31 magnesium alloy dissolve and isolate β phases throughout the matrix. The increased fracture strain and mechanical strength of graphene nanoplatelets and carbon nanotubes-AZ31 composites are attributed to large specific surface area of graphene nanoplatelets and stiffer nature of carbon nanotubes respectively. - Highlights: • Powder metallurgy method was used to fabricate magnesium composites. • The AZ31-carbon materials composite were blended using ball milling. • The reinforcement particles weaken the basal texture which affects yield asymmetry of composites. • AZ31-graphene nanoplatelets composite exhibited impressive increase in tensile elongation

Use of high energy ball milling to study the role of graphene nanoplatelets and carbon nanotubes reinforced magnesium alloy

International Nuclear Information System (INIS)

Rashad, Muhammad; Pan, Fusheng; Zhang, Jianyue; Asif, Muhammad

2015-01-01

Graphene nanoplatelets (few layer graphene) and carbon nanotubes were used as reinforcement fillers to enhance the mechanical properties of AZ31 magnesium alloy through high energy ball milling, sintering, and hot extrusion techniques. Experimental results revealed that tensile fracture strain of AZ31 magnesium alloy was enhanced by +49.6% with 0.3 wt.% graphene nanoplatelets compared to −8.3% regression for 0.3 wt.% carbon nanotubes. The tensile strength of AZ31 magnesium alloy was decreased (−11.2%) with graphene nanoplatelets addition, while increased (+7.7%) with carbon nanotubes addition. Unlike tensile test, compression tests showed different trend. The compression strength of carbon nanotubes-AZ31 composite was +51.2% greater than AZ31 magnesium alloy as compared to +0.6% increase for graphene nanoplatelets. The compressive fracture strain of carbon nanotubes-AZ31 composite was decreased (−14.1%) while no significant change in fracture strain of graphene nanoplatelets-AZ31 composite was observed. The X-ray diffraction results revealed that addition of reinforcement particles weaken the basal textures which affect the composite's yield asymmetry. Microstructure evaluation revealed the absence of intermetallic phase formation between reinforcements and matrix. The carbon reinforcements in AZ31 magnesium alloy dissolve and isolate β phases throughout the matrix. The increased fracture strain and mechanical strength of graphene nanoplatelets and carbon nanotubes-AZ31 composites are attributed to large specific surface area of graphene nanoplatelets and stiffer nature of carbon nanotubes respectively. - Highlights: • Powder metallurgy method was used to fabricate magnesium composites. • The AZ31-carbon materials composite were blended using ball milling. • The reinforcement particles weaken the basal texture which affects yield asymmetry of composites. • AZ31-graphene nanoplatelets composite exhibited impressive increase in tensile elongation

Buckling Behavior of Substrate Supported Graphene Sheets

Directory of Open Access Journals (Sweden)

Kuijian Yang

2016-01-01

Full Text Available The buckling of graphene sheets on substrates can significantly degrade their performance in materials and devices. Therefore, a systematic investigation on the buckling behavior of monolayer graphene sheet/substrate systems is carried out in this paper by both molecular mechanics simulations and theoretical analysis. From 70 simulation cases of simple-supported graphene sheets with different sizes under uniaxial compression, two different buckling modes are investigated and revealed to be dominated by the graphene size. Especially, for graphene sheets with length larger than 3 nm and width larger than 1.1 nm, the buckling mode depends only on the length/width ratio. Besides, it is revealed that the existence of graphene substrate can increase the critical buckling stress and strain to 4.39 N/m and 1.58%, respectively, which are about 10 times those for free-standing graphene sheets. Moreover, for graphene sheets with common size (longer than 20 nm, both theoretical and simulation results show that the critical buckling stress and strain are dominated only by the adhesive interactions with substrate and independent of the graphene size. Results in this work provide valuable insight and guidelines for the design and application of graphene-derived materials and nano-electromechanical systems.

Temperature-induced strain release via rugae on the nanometer and micrometer scale in graphene monolayer

Czech Academy of Sciences Publication Activity Database

Verhagen, Timotheus; Valeš, Václav; Frank, Otakar; Kalbáč, Martin; Vejpravová, Jana

2017-01-01

Roč. 119, Aug (2017), s. 483-491 ISSN 0008-6223 R&D Projects: GA ČR(CZ) GA15-01953S; GA MŠk LL1301 Institutional support: RVO:68378271 ; RVO:61388955 Keywords : graphene * wrinkle * low temperature Raman mapping * strain * doping * thermal expansion Subject RIV: BM - Solid Matter Physics ; Magnetism; CF - Physical ; Theoretical Chemistry (UFCH-W) OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.); Physical chemistry (UFCH-W) Impact factor: 6.337, year: 2016

Effect of initial strain and material nonlinearity on the nonlinear static and dynamic response of graphene sheets

Science.gov (United States)

Singh, Sandeep; Patel, B. P.

2018-06-01

Computationally efficient multiscale modelling based on Cauchy-Born rule in conjunction with finite element method is employed to study static and dynamic characteristics of graphene sheets, with/without considering initial strain, involving Green-Lagrange geometric and material nonlinearities. The strain energy density function at continuum level is established by coupling the deformation at continuum level to that at atomic level through Cauchy-Born rule. The atomic interactions between carbon atoms are modelled through Tersoff-Brenner potential. The governing equation of motion obtained using Hamilton's principle is solved through standard Newton-Raphson method for nonlinear static response and Newmark's time integration technique to obtain nonlinear transient response characteristics. Effect of initial strain on the linear free vibration frequencies, nonlinear static and dynamic response characteristics is investigated in detail. The present multiscale modelling based results are found to be in good agreement with those obtained through molecular mechanics simulation. Two different types of boundary constraints generally used in MM simulation are explored in detail and few interesting findings are brought out. The effect of initial strain is found to be greater in linear response when compared to that in nonlinear response.

Switchable Polarization in Mn Embedded Graphene.

Science.gov (United States)

Noor-A-Alam, Mohammad; Ullah, Hamid; Shin, Young-Han

2018-03-14

Graphene, despite its many unique properties, is neither intrinsically polar due to inversion symmetry nor magnetic. However, based on density functional theory, we find that Mn, one of transition metals, embedded in single or double vacancy (Mn@SV and Mn@DV) in a graphene monolayer induces a dipole moment perpendicular to the sheet, which can be switched from up to down by Mn penetration through the graphene. Such switching could be realized by an external stimuli introduced through the tip of a scanning probe microscope, as already utilized in the studies of molecular switches. We estimate the energy barriers for dipole switching, which are found to be 2.60 eV and 0.28 eV for Mn@SV and Mn@DV, respectively. However, by applying biaxial tensile strain, we propose a mechanism for tuning the barrier. We find that 10% biaxial tensile strain, which is already experimentally achievable in graphene-like two-dimensional materials, can significantly reduce the barrier to 0.16 eV in Mn@SV. Moreover, in agreement with previous studies, we find a high magnetic moment of 3 μ B for both Mn@SV and Mn@DV, promising the potential of these structures in spintronics as well as in nanoscale electro-mechanical or memory devices.

Strain effects on the optical conductivity of gapped graphene in the presence of Holstein phonons beyond the Dirac cone approximation

Energy Technology Data Exchange (ETDEWEB)

Yarmohammadi, Mohsen, E-mail: m.yarmohammadi69@gmail.com [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of)

2016-08-15

In this paper we study the optical conductivity and density of states (DOS) of doped gapped graphene beyond the Dirac cone approximation in the presence of electron-phonon (e-ph) interaction under strain, i.e., within the framework of a full π-band Holstein model, by using the Kubo linear response formalism that is established upon the retarded self-energy. A new peak in the optical conductivity for a large enough e-ph interaction strength is found which is associated to transitions between the midgap states and the Van Hove singularities of the main π-band. Optical conductivity decreases with strain and at large strains, the system has a zero optical conductivity at low energies due to optically inter-band excitations through the limit of zero doping. As a result, the Drude weight changes with e-ph interaction, temperature and strain. Consequently, DOS and optical conductivity remains stable with temperature at low e-ph coupling strengths.

Graphene-nanoplatelet-based photomechanical actuators

International Nuclear Information System (INIS)

Loomis, James; King, Ben; Burkhead, Tom; Xu Peng; Bessler, Nathan; Panchapakesan, Balaji; Terentjev, Eugene

2012-01-01

This paper reports large light-induced reversible and elastic responses of graphene nanoplatelet (GNP) polymer composites. Homogeneous mixtures of GNP/polydimethylsiloxane (PDMS) composites (0.1–5 wt%) were prepared and their infrared (IR) mechanical responses studied with increasing pre-strains. Using IR illumination, a photomechanically induced change in stress of four orders of magnitude as compared to pristine PDMS polymer was measured. The actuation responses of the graphene polymer composites depended on the applied pre-strains. At low levels of pre-strain (3–9%) the actuators showed reversible expansion while at high levels (15–40%) the actuators exhibited reversible contraction. The GNP/PDMS composites exhibited higher actuation stresses compared to other forms of nanostructured carbon/PDMS composites, including carbon nanotubes (CNTs), for the same fabrication method. An extraordinary optical-to-mechanical energy conversion factor (η M ) of 7–9 MPa W −1 for GNP-based polymer composite actuators is reported. (paper)

Probing the interaction of noble gases with pristine and nitrogen-doped graphene through Raman spectroscopy

Science.gov (United States)

Cunha, Renato; Perea-López, Néstor; Elías, Ana Laura; Fujisawa, Kazunori; Carozo, Victor; Feng, Simin; Lv, Ruitao; dos Santos, Maria Cristina; Terrones, Mauricio; Araujo, Paulo T.

2018-05-01

The interactions of adsorbates with graphene have received increasing attention due to its importance in the development of applications involving graphene-based coatings. Here, we present a study of the adsorption of noble gases on pristine and nitrogen-doped graphene. Single-layer graphene samples were synthesized by chemical vapor deposition (CVD) and transferred to transmission electron microscopy (TEM) grids. Several noble gases were allowed to adsorb on the suspended graphene substrate at very low temperatures. Raman spectra show distinct frequency blue shifts in both the 2D and G bands, which are induced by gas adsorption onto high quality single layer graphene (1LG). These shifts, which we associate with compressive biaxial strain in the graphene layers induced by the noble gases, are negligible for nitrogen-doped graphene. Additionally, a thermal depinning transition, which is related to the desorption of a noble gas layer from the graphene surface at low temperatures (ranging from 20 to 35 K), was also observed at different transition temperatures for different noble gases. These transition temperatures were found to be 25 K for argon and 35 K for xenon. Moreover, we were able to obtain values for the compressive biaxial strain in graphene induced by the adsorbed layer of noble gases, using Raman spectroscopy. Ab initio calculations confirmed the correlation between the noble gas-induced strain and the changes in the Raman features observed.

Study on the graphene/silicon Schottky diodes by transferring graphene transparent electrodes on silicon

International Nuclear Information System (INIS)

Wang, Xiaojuan; Li, Dong; Zhang, Qichong; Zou, Liping; Wang, Fengli; Zhou, Jun; Zhang, Zengxing

2015-01-01

Graphene/silicon heterostructures present a Schottky characteristic and have potential applications for solar cells and photodetectors. Here, we fabricated graphene/silicon heterostructures by using chemical vapor deposition derived graphene and n-type silicon, and studied the electronic and optoelectronic properties through varying their interface and silicon resistivity. The results exhibit that the properties of the fabricated configurations can be effectively modulated. The graphene/silicon heterostructures with a Si (111) interface and high resistivity show a better photovoltaic behavior and should be applied for high-performance photodetectors. With the combined atomic force microscopy and theoretical analysis, the possible origination is discussed. The work here should be helpful on exploring high-performance graphene/silicon photoelectronics. - Highlights: • Different graphene/silicon heterostructures were fabricated. • Electronic and optoelectronic properties of the heterostructures were studied. • Graphene/silicon heterostructures were further explored for photodetectors.

Study on the graphene/silicon Schottky diodes by transferring graphene transparent electrodes on silicon

Energy Technology Data Exchange (ETDEWEB)

Wang, Xiaojuan [MOE Key Laboratory of Advanced Micro-structured Materials & Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Li, Dong; Zhang, Qichong; Zou, Liping; Wang, Fengli [MOE Key Laboratory of Advanced Micro-structured Materials & Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Zhou, Jun, E-mail: zhoujunzhou@tongji.edu.cn [Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Zhang, Zengxing, E-mail: zhangzx@tongji.edu.cn [MOE Key Laboratory of Advanced Micro-structured Materials & Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China)

2015-10-01

Graphene/silicon heterostructures present a Schottky characteristic and have potential applications for solar cells and photodetectors. Here, we fabricated graphene/silicon heterostructures by using chemical vapor deposition derived graphene and n-type silicon, and studied the electronic and optoelectronic properties through varying their interface and silicon resistivity. The results exhibit that the properties of the fabricated configurations can be effectively modulated. The graphene/silicon heterostructures with a Si (111) interface and high resistivity show a better photovoltaic behavior and should be applied for high-performance photodetectors. With the combined atomic force microscopy and theoretical analysis, the possible origination is discussed. The work here should be helpful on exploring high-performance graphene/silicon photoelectronics. - Highlights: • Different graphene/silicon heterostructures were fabricated. • Electronic and optoelectronic properties of the heterostructures were studied. • Graphene/silicon heterostructures were further explored for photodetectors.

Determination of Young's Modulus of Graphene by Raman Spectroscopy

Science.gov (United States)

Lee, Jae-Ung; Yoon, Duhee; Cheong, Hyeonsik

2012-02-01

The mechanical properties of graphene are interesting research subjects because its Young's modulus and strength are extremely high. Values of ˜1 TPa for the Young's modulus have been reported [Lee et al. Science, 321, 385 (2008), Koenig et al. Nat. Nanotech. 6, 543 (2011)]. We made a graphene sample on a SiO2/Si substrate with closed-bottom holes by mechanical exfoliation. A pressure difference across the graphene membrane was applied by putting the sample in a vacuum chamber. This pressure difference makes the graphene membrane bulge upward like a balloon. By measuring the shifts of the Raman G and 2D bands, we estimated the amount of strain on the graphene membrane. By comparing the strain estimated from the Raman measurements with numerical simulations based on the finite element method, we obtained the Young's modulus of graphene.

Strain-tunable half-metallicity in hybrid graphene-hBN monolayer superlattices

International Nuclear Information System (INIS)

Meng, Fanchao; Zhang, Shiqi; Lee, In-Ho; Jun, Sukky; Ciobanu, Cristian V.

2016-01-01

Highlights: • Armchair superlattices have a bandgap modulated by the deformed domain widths. • Strain and domain width lead to novel spin-dependent behavior for zigzag boundaries. • Limits for spin-dependent bandgap and half-metallic behavior have been charted. - Abstract: As research in 2-D materials evolves toward combinations of different materials, interesting electronic and spintronic properties are revealed and may be exploited in future devices. A way to combine materials is the formation of spatially periodic domain boundaries in an atom-thick monolayer: as shown in recent reports, when these domains are made of graphene and hexagonal boron nitride, the resulting superlattice has half-metallic properties in which one spin component is (semi)metallic and the other is semiconductor. We explore here the range of spin-dependent electronic properties that such superlattices can develop for different type of domain boundaries, domain widths, and values of tensile strain applied to the monolayer. We show evidence of an interplay between strain and domain width in determining the electronic properties: while for armchair boundaries the bandgap is the same for both spin components, superlattices with zigzag boundaries exhibit rich spin-dependent behavior, including different bandgaps for each spin component, half-metallicity, and reversal of half-metallicity. These findings can lead to new ways of controlling the spintronic properties in hybrid-domain monolayers, which may be exploited in devices based on 2-D materials.

Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates.

Science.gov (United States)

da Cunha Rodrigues, Gonçalo; Zelenovskiy, Pavel; Romanyuk, Konstantin; Luchkin, Sergey; Kopelevich, Yakov; Kholkin, Andrei

2015-06-25

Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V(-1), that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

Institute of Scientific and Technical Information of China (English)

Yu-qing Song; Xiao-ping Wang

2017-01-01

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted,diminishing the influence induced by residue and transfer technology.It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate,compared to that coated with the bilayer graphene,which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene,respectively.We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection.Our finding indicates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects,depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.

Platinum adsorption onto graphene and oxidized graphene: A quantum mechanics study

Energy Technology Data Exchange (ETDEWEB)

Jafari, S.A.; Jahanshahi, M. [Nanotechnology Research Institute, School of Chemical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of); Ahangari, M. Ghorbanzadeh, E-mail: ghorbanzadeh.morteza@gmail.com [Department of Mechanical Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar (Iran, Islamic Republic of)

2017-04-01

Density functional theory based on first-principle calculations was used to examine platinum-supported oxidized graphene as a beneficial nanomaterial in terms of its catalytic activity and utility for contaminant removal and disinfecting polluted solutions in both domestic and industrial applications. The first step was to select the most appropriate available computing package to apply the supercell technique, which would provide a better representation of a large and real graphene slab. Using OpenMX was less time-consuming after we enforced a basis set for valence electrons to avoid an all-electron calculation, and this had very slight and negligible effect on the accuracy of the calculations. The OpenMX software was selected to perform forward steps of investigating changes in the properties such as adsorption energy and ground state structure of the complexes made by the adsorption of a platinum atom on the surface of pristine graphene (Pt/PG) and oxidized graphene (Pt/OG), which had the lowest adsorption energy of −5.28 eV. Moreover, we examined the effect of Pt atom adsorption on the surface and between two layers of graphene. Our results show that, there was no specific change observed in mentioned properties of Pt atom adsorption on bilayer graphene in comparison with single layer. - Highlights: • Pt adsorption on graphene and oxidized graphene was examined. • We have also considered the effect of the layered graphene on the Pt adsorption. • We first compared two different DFT calculation codes, SIESTA and OpenMX. • We then used ORCA to validate and select a suitable computation package for this study.

Etchant-free graphene transfer using facile intercalation of alkanethiol self-assembled molecules at graphene/metal interfaces.

Science.gov (United States)

Ohtomo, Manabu; Sekine, Yoshiaki; Wang, Shengnan; Hibino, Hiroki; Yamamoto, Hideki

2016-06-02

We report a novel etchant-free transfer method of graphene using the intercalation of alkanethiol self-assembled monolayers (SAMs) at the graphene/Cu interfaces. The early stage of intercalation proceeds through graphene grain boundaries or defects within a few seconds at room temperature until stable SAMs are formed after a few hours. The formation of SAMs releases the compressive strain of graphene induced by Cu substrates and make graphene slightly n-doped due to the formation of interface dipoles of the SAMs on metal surfaces. After SAM formation, the graphene is easily delaminated off from the metal substrates and transferred onto insulating substrates. The etchant-free process enables us to decrease the density of charged impurities and the magnitude of potential fluctuation in the transferred graphene, which suppress scattering of carriers. We also demonstrate the removal of alkanethiol SAMs and reuse the substrate. This method will dramatically reduce the cost of graphene transfer, which will benefit industrial applications such as of graphene transparent electrodes.

Raman spectra of bilayer graphene covered with Poly(methyl methacrylate) thin film

Energy Technology Data Exchange (ETDEWEB)

Xia Minggang [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Science, Xi' an Jiaotong University, 710049 (China); Center on Experimental Physics, School of Science, Xi' an Jiaotong University, 710049 (China); Su Zhidan; Zhang Shengli [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Science, Xi' an Jiaotong University, 710049 (China); Department of Applied Physics, School of Science, Xi' an Jiaotong University, 710049 (China)

2012-09-15

The Raman spectra of bilayer graphene covered with poly(methyl methacrylate) (PMMA) were investigated. Both the G and 2D peaks of PMMA-coated graphene were stiff and broad compared with those of uncovered graphene. This could be attributed to the residual strain induced by high-temperature baking during fabrication of the nanodevice. Furthermore, the two 2D peaks stiffened and broadened with increasing laser power, which is just the reverse to uncovered graphene. The stiffness is likely caused by graphene compression induced by the circular bubble of the thin PMMA film generated by laser irradiation. Our findings may contribute to the application of PMMA in the strain engineering of graphene nanodevices.

Raman spectra of bilayer graphene covered with Poly(methyl methacrylate thin film

Directory of Open Access Journals (Sweden)

Minggang Xia

2012-09-01

Full Text Available The Raman spectra of bilayer graphene covered with poly(methyl methacrylate (PMMA were investigated. Both the G and 2D peaks of PMMA-coated graphene were stiff and broad compared with those of uncovered graphene. This could be attributed to the residual strain induced by high-temperature baking during fabrication of the nanodevice. Furthermore, the two 2D peaks stiffened and broadened with increasing laser power, which is just the reverse to uncovered graphene. The stiffness is likely caused by graphene compression induced by the circular bubble of the thin PMMA film generated by laser irradiation. Our findings may contribute to the application of PMMA in the strain engineering of graphene nanodevices.

Performance of monolayer graphene nanomechanical resonators with electrical readout.

Science.gov (United States)

Chen, Changyao; Rosenblatt, Sami; Bolotin, Kirill I; Kalb, William; Kim, Philip; Kymissis, Ioannis; Stormer, Horst L; Heinz, Tony F; Hone, James

2009-12-01

The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical applications. Here, we demonstrate the fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the megahertz range, and the strong dependence of resonant frequency on applied gate voltage can be fitted to a membrane model to yield the mass density and built-in strain of the graphene. Following the removal and addition of mass, changes in both density and strain are observed, indicating that adsorbates impart tension to the graphene. On cooling, the frequency increases, and the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching approximately 1 x 10(4) at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, the groundwork for applications of these devices, including high-sensitivity mass detectors, is put in place.

Fabrication and transport studies of graphene-superconductor heterostructures

Science.gov (United States)

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

2014-03-01

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

Nanopatched Graphene with Molecular Self-Assembly Toward Graphene-Organic Hybrid Soft Electronics.

Science.gov (United States)

Kang, Boseok; Lee, Seong Kyu; Jung, Jaehyuck; Joe, Minwoong; Lee, Seon Baek; Kim, Jinsung; Lee, Changgu; Cho, Kilwon

2018-04-30

Increasing the mechanical durability of large-area polycrystalline single-atom-thick materials is a necessary step toward the development of practical and reliable soft electronics based on these materials. Here, it is shown that the surface assembly of organosilane by weak epitaxy forms nanometer-thick organic patches on a monolayer graphene surface and dramatically increases the material's resistance to harsh postprocessing environments, thereby increasing the number of ways in which graphene can be processed. The nanopatched graphene with the improved mechanical durability enables stable operation when used as transparent electrodes of wearable strain sensors. Also, the nanopatched graphene applied as an electrode modulates the molecular orientation of deposited organic semiconductor layers, and yields favorable nominal charge injection for organic transistors. These results demonstrate the potential for use of self-assembled organic nanopatches in graphene-based soft electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, characterization and applications of graphene architectures

Science.gov (United States)

Thomas, Abhay Varghese

to the heat transfer process. In Chapter 3, we explore the assembly of graphene papers by top down methods (i.e. exfoliation of bulk graphite). We then explore the use of such graphene papers as an anode material in Lithium--ion batteries. The morphologically novel electrode fabrication and its exceptional performance as a lithium ion battery anode were explored and an in--depth investigation was carried out to determine the precise reason for the enhanced anode performance. A modified thermal reduction technique of a stable graphene oxide paper was developed to create a novel, free standing, binder free, reduced graphene oxide architecture using the top--down synthesis approach. The process was optimized to maximize the capacity by varying temperature and time as the critical parameters for reduction. An in--depth study was undertaken using raman spectroscopy, computational modelling, scanning electron microscopy, x--ray diffraction and x--ray photoelectron spectroscopy to show that lithium metal was plated into the nano--pores of the anode and the defective nature of the graphene sheets acted as seed points for this plating. In Chapter 4 we focus on graphene oxide papers produced by top--down exfoliation methods. More specifically, controlled instabilities or wrinkles created on graphene oxide thin films were developed as a tunable optical transmission layer for use in dynamic glazing systems. Graphene oxide thin films, prepared using the top--down synthesis, were subjected to compressive strains in the uni--axial and bi--axial direction to create uniform wrinkling of the films. Scanning electron, optical and atomic force microscopy was used to image the wrinkling morphology to qualitatively understand the behavior of the films and delaminated buckling of the graphene oxide films was determined to be the cause of the wrinkling. UV--VIS--NIR transmission measurements were carried out to determine the average transmission of the films with uni-axial and bi

Densely Aligned Graphene Nanoribbon Arrays and Bandgap Engineering

Energy Technology Data Exchange (ETDEWEB)

Su, Justin [Stanford Univ., CA (United States); Chen, Changxin [Stanford Univ., CA (United States); Gong, Ming [Stanford Univ., CA (United States); Kenney, Michael [Stanford Univ., CA (United States)

2017-01-04

Graphene has attracted great interest for future electronics due to its high mobility and high thermal conductivity. However, a two-dimensional graphene sheet behaves like a metal, lacking a bandgap needed for the key devices components such as field effect transistors (FETs) in digital electronics. It has been shown that, partly due to quantum confinement, graphene nanoribbons (GNRs) with ~2 nm width can open up sufficient bandgaps and evolve into semiconductors to exhibit high on/off ratios useful for FETs. However, a challenging problem has been that, such ultra-narrow GNRs (~2 nm) are difficult to fabricate, especially for GNRs with smooth edges throughout the ribbon length. Despite high on/off ratios, these GNRs show very low mobility and low on-state conductance due to dominant scattering effects by imperfections and disorders at the edges. Wider GNRs (>5 nm) show higher mobility, higher conductance but smaller bandgaps and low on/off ratios undesirable for FET applications. It is highly desirable to open up bandgaps in graphene or increase the bandgaps in wide GNRs to afford graphene based semiconductors for high performance (high on-state current and high on/off ratio) electronics. Large scale ordering and dense packing of such GNRs in parallel are also needed for device integration but have also been challenging thus far. It has been shown theoretically that uniaxial strains can be applied to a GNR to engineer its bandgap. The underlying physics is that under uniaxial strain, the Dirac point moves due to stretched C-C bonds, leading to an increase in the bandgap of armchair GNRs by up to 50% of its original bandgap (i.e. bandgap at zero strain). For zigzag GNRs, due to the existence of the edge states, changes of bandgap are smaller under uniaxial strain and can be increased by ~30%. This work proposes a novel approach to the fabrication of densely aligned graphene nanoribbons with highly smooth edges afforded by anisotropic etching and uniaxial strain for

Rapid Evaporation of Water on Graphene/Graphene-Oxide: A Molecular Dynamics Study.

Science.gov (United States)

Li, Qibin; Xiao, Yitian; Shi, Xiaoyang; Song, Shufeng

2017-09-07

To reveal the mechanism of energy storage in the water/graphene system and water/grapheme-oxide system, the processes of rapid evaporation of water molecules on the sheets of graphene and graphene-oxide are investigated by molecular dynamics simulations. The results show that both the water/graphene and water/grapheme-oxide systems can store more energy than the pure water system during evaporation. The hydroxyl groups on the surface of graphene-oxide are able to reduce the attractive interactions between water molecules and the sheet of graphene-oxide. Also, the radial distribution function of the oxygen atom indicates that the hydroxyl groups affect the arrangement of water molecules at the water/graphene-oxide interface. Therefore, the capacity of thermal energy storage of the water/graphene-oxide system is lower than that of the water/graphene system, because of less desorption energy at the water/graphene-oxide interface. Also, the evaporation rate of water molecules on the graphene-oxide sheet is slower than that on the graphene sheet. The Leidenfrost phenomenon can be observed during the evaporation process in the water/grapheme-oxide system.

Graphene devices based on laser scribing technology

Science.gov (United States)

Qiao, Yan-Cong; Wei, Yu-Hong; Pang, Yu; Li, Yu-Xing; Wang, Dan-Yang; Li, Yu-Tao; Deng, Ning-Qin; Wang, Xue-Feng; Zhang, Hai-Nan; Wang, Qian; Yang, Zhen; Tao, Lu-Qi; Tian, He; Yang, Yi; Ren, Tian-Ling

2018-04-01

Graphene with excellent electronic, thermal, optical, and mechanical properties has great potential applications. The current devices based on graphene grown by micromechanical exfoliation, chemical vapor deposition (CVD), and thermal decomposition of silicon carbide are still expensive and inefficient. Laser scribing technology, a low-cost and time-efficient method of fabricating graphene, is introduced in this review. The patterning of graphene can be directly performed on solid and flexible substrates. Therefore, many novel devices such as strain sensors, acoustic devices, memory devices based on laser scribing graphene are fabricated. The outlook and challenges of laser scribing technology have also been discussed. Laser scribing may be a potential way of fabricating wearable and integrated graphene systems in the future.

Grain-boundary unzipping by oxidation in polycrystalline graphene

Science.gov (United States)

Alexandre, Simone; Lucio, Aline; Nunes, Ricardo

2011-03-01

The need for large-scale production of graphene will inevitably lead to synthesis of the polycrystalline material [1,2]. Understanding the chemical, mechanical, and electronic properties of grain boundaries in graphene polycrystals will be crucial for the development of graphene-based electronics. Oxidation of this material has been suggested to lead to graphene ribbons, by the oxygen-driven unzipping mechanism. A cooperative-strain mechanism, based on the formation of epoxy groups along lines of parallel bonds in the hexagons of graphene's honeycomb lattice, was proposed to explain the unzipping effect in bulk graphene In this work we employ ab initio calculations to study the oxidation of polycrystalline graphene by chemisorption of oxygen at the grain boundaries. Our results indicate that oxygen tends to segregate at the boundaries, and that the unzipping mechanism is also operative along the grain boundaries, despite the lack of the parallel bonds due to the presence of fivefold and sevenfold carbon rings along the boundary core. We acknowledge support from the Brazilian agencies: CNPq, Fapemig, and INCT-Materiais de Carbono.

Thermal conductivity of graphene nanoribbons under shear deformation: A molecular dynamics simulation

Science.gov (United States)

Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon

2017-01-01

Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12–16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications. PMID:28120921

Vacuum Technology in the study of Graphene

International Nuclear Information System (INIS)

Ghoshal, A K; Banerjee, S N; Chakraborty, D

2012-01-01

Graphene, an allotrope of carbon is a two-dimensional sheet of covalently bonded carbon atoms that has been attracting great attention in the field of electronics. In a recent review graphene is defined as a flat monolayer of carbon atoms tightly packed into a 2-D honeycomb lattice. A survey has been made of the production processes and instrumentation for characterization of graphene. In the production of graphene, the methods mainly used are Epitaxial growth, oxide reduction, growth from metal-carbon melts, growth from sugar. In the characterization of graphene, the instruments that are mainly used to study the atomic properties, electronic properties, optical properties, spin properties are Scanning Electron Microscopy, Transmission Electron Microscopy, Raman Spectroscopy. In all these instruments high or ultra-high vacuum is required. This paper attempts to correlate vacuum technology in the production and characterization of graphene.

Electronic transport in torsional strained Weyl semimetals

Science.gov (United States)

Soto-Garrido, Rodrigo; Muñoz, Enrique

2018-05-01

In a recent paper (Muñoz and Soto-Garrido 2017 J. Phys.: Condens. Matter 29 445302) we have studied the effects of mechanical strain and magnetic field on the electronic transport properties in graphene. In this article we extended our work to Weyl semimetals (WSM). We show that although the WSM are 3D materials, most of the analysis done for graphene (2D material) can be carried out. In particular, we studied the electronic transport through a cylindrical region submitted to torsional strain and external magnetic field. We provide exact analytical expressions for the scattering cross section and the transmitted electronic current. In addition, we show the node-polarization effect on the current and propose a recipe to measure the torsion angle from transmission experiments.

Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene nanoelectromechanical systems resonators

International Nuclear Information System (INIS)

Singh, Vibhor; Sengupta, Shamashis; Solanki, Hari S; Dhall, Rohan; Allain, Adrien; Dhara, Sajal; Deshmukh, Mandar M; Pant, Prita

2010-01-01

We use suspended graphene electromechanical resonators to study the variation of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300 to 30 K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that thermal expansion of graphene is negative for all temperatures between 300 and 30 K. We also study the dispersion, the variation of resonant frequency with DC gate voltage, of the electromechanical modes and find considerable tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With a lowering of temperature, we find that the positively dispersing electromechanical modes evolve into negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature-compensated sensors.

Incorporating 2D Materials with Micro-electromechanical Systems to Explore Strain Physics and Devices

Science.gov (United States)

Christopher, Jason; Vutukuru, Mounika; Kohler, Travis; Bishop, David; Swan, Anna; Goldberg, Bennett

2D materials can withstand an order of magnitude more strain than their bulk counterparts which can be used to dramatically change electrical, thermal and optical properties or even cause unconventional behavior such as generating pseudo-magnetic fields. Here we present micro-electromechanical systems (MEMS) as a platform for straining 2D materials to make such novel phenomena accessible. Unlike other strain techniques, MEMS are capable of precisely controlling the magnitude and orientation of the strain field and are readily integrated with current technology facilitating a path from lab bench to application. In this study, we use graphene as our prototypical 2D material, and determine strain via micro-Raman spectroscopy making extensive use of graphene's well-characterized phonon strain response. We report on the strength of various techniques for affixing graphene to MEMS, and investigate the role of surface morphology and chemistry in creating a high friction interface capable of inducing large strain. This work is supported by NSF DMR Grant 1411008, and author J. Christopher thanks the NDSEG program for its support.

First-principles studies on graphene-supported transition metal clusters

International Nuclear Information System (INIS)

Sahoo, Sanjubala; Khanna, Shiv N.; Gruner, Markus E.; Entel, Peter

2014-01-01

Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM 13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM 13 clusters, Co 13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe 13 and Ni 13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters

Computational Tools and Studies of Graphene Nanostructures

DEFF Research Database (Denmark)

Papior, Nick Rübner

require revised algorithms. Furthermore, the advent of 2D materials may prove prominent in future nanoelectronics for electronic and heat transport devices. Such materials include the Nobel Prize winning material, graphene which has unique properties. The main focus of the work presented in this thesis...... example is used to highlight the importance of the quantum capacitance that is evident in low density of states systems. Additionally the gating method was used in nonequilibrium to study the gate-bias dependence on graphene nano-constrictions. This indicated a pinning effect arising due to differences...... in coupling strength between the device and the two electrodes. Two studies are presented using the non-equilibrium method with Ne = 3. First, graphene T-junctions are studied to uncover potential interconnects in future graphene based devices. This T-junction is studied under two non-equilibrium situations...

Study of film graphene/graphene oxide obtained by partial reduction chemical of oxide graphite

International Nuclear Information System (INIS)

Gascho, J.L.S.; Costa, S.F.; Hoepfner, J.C.; Pezzin, S.H.

2014-01-01

This study investigated the morphology of graphene/graphene oxide film obtained by partial chemical reduction of graphite oxide (OG) as well as its resistance to solvents. Films of graphene/graphene oxide are great candidates for replacement of indium oxide doped with tin (ITO) in photoelectric devices. The OG was obtained from natural graphite, by Hummer's method modified, and its reduction is made by using sodium borohydride. Infrared spectroscopy analysis of Fourier transform (FTIR), Xray diffraction (XRD) and scanning electron microscopy, high-resolution (SEM/FEG) for the characterization of graphene/graphene oxide film obtained were performed. This film proved to be resilient, not dispersing in any of the various tested solvents (such as ethanol, acetone and THF), even under tip sonication, this resistance being an important property for the applications. Furthermore, the film had a morphology similar to that obtained by other preparation methods.(author)

Ultrafast Dynamic Pressure Sensors Based on Graphene Hybrid Structure.

Science.gov (United States)

Liu, Shanbiao; Wu, Xing; Zhang, Dongdong; Guo, Congwei; Wang, Peng; Hu, Weida; Li, Xinming; Zhou, Xiaofeng; Xu, Hejun; Luo, Chen; Zhang, Jian; Chu, Junhao

2017-07-19

Mechanical flexible electronic skin has been focused on sensing various physical parameters, such as pressure and temperature. The studies of material design and array-accessible devices are the building blocks of strain sensors for subtle pressure sensing. Here, we report a new and facile preparation of a graphene hybrid structure with an ultrafast dynamic pressure response. Graphene oxide nanosheets are used as a surfactant to prevent graphene restacking in aqueous solution. This graphene hybrid structure exhibits a frequency-independent pressure resistive sensing property. Exceeding natural skin, such pressure sensors, can provide transient responses from static up to 10 000 Hz dynamic frequencies. Integrated by the controlling system, the array-accessible sensors can manipulate a robot arm and self-rectify the temperature of a heating blanket. This may pave a path toward the future application of graphene-based wearable electronics.

Graphene as a flexible template for controlling magnetic interactions between metal atoms.

Science.gov (United States)

Lee, Sungwoo; Kim, Dongwook; Robertson, Alex W; Yoon, Euijoon; Hong, Suklyun; Ihm, Jisoon; Yu, Jaejun; Warner, Jamie H; Lee, Gun-Do

2017-03-01

Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between two substitutional Fe atoms covalently bonded in graphene to gradually increase and these results in the magnetic moment disappearing at a critical strain value. At the critical strain, a carbon atom can enter between the two Fe atoms and blocks the interaction between relevant orbitals of Fe atoms to quench the magnetic moment. The control of interactions between doped atoms by exploiting the mechanical flexibility of graphene is a unique approach to manipulating the magnetic properties and opens up new opportunities for mechanical-magnetic 2D device systems.

Surface adhesion properties of graphene and graphene oxide studied by colloid-probe atomic force microscopy

International Nuclear Information System (INIS)

Ding Yanhuai; Zhang Ping; Ren Huming; Zhuo Qin; Yang Zhongmei; Jiang Xu; Jiang Yong

2011-01-01

Surface adhesion properties are important to various applications of graphene-based materials. Atomic force microscopy is powerful to study the adhesion properties of samples by measuring the forces on the colloidal sphere tip as it approaches and retracts from the surface. In this paper we have measured the adhesion force between the colloid probe and the surface of graphene (graphene oxide) nanosheet. The results revealed that the adhesion force on graphene and graphene oxide surface were 66.3 and 170.6 nN, respectively. It was found the adhesion force was mainly determined by the water meniscus, which was related to the surface contact angle of samples.

Graphene Foam: Uniaxial Tension Behavior and Fracture Mode Based on a Mesoscopic Model.

Science.gov (United States)

Pan, Douxing; Wang, Chao; Wang, Tzu-Chiang; Yao, Yugui

2017-09-26

Because of the combined advantages of both porous materials and two-dimensional (2D) graphene sheets, superior mechanical properties of three-dimensional (3D) graphene foams have received much attention from material scientists and energy engineers. Here, a 2D mesoscopic graphene model (Modell. Simul. Mater. Sci. Eng. 2011, 19, 054003), was expanded into a 3D bonded graphene foam system by utilizing physical cross-links and van der Waals forces acting among different mesoscopic graphene flakes by considering the debonding behavior, to evaluate the uniaxial tension behavior and fracture mode based on in situ SEM tensile testing (Carbon 2015, 85, 299). We reasonably reproduced a multipeak stress-strain relationship including its obvious yielding plateau and a ductile fracture mode near 45° plane from the tensile direction including the corresponding fracture morphology. Then, a power scaling law of tensile elastic modulus with mass density and an anisotropic strain-dependent Poisson's ratio were both deduced. The mesoscopic physical mechanism of tensile deformation was clearly revealed through the local stress state and evolution of mesostructure. The fracture feature of bonded graphene foam and its thermodynamic state were directly navigated to the tearing pattern of mesoscopic graphene flakes. This study provides an effective way to understand the mesoscopic physical nature of 3D graphene foams, and hence it may contribute to the multiscale computations of micro/meso/macromechanical performances and optimal design of advanced graphene-foam-based materials.

Rapid Stencil Mask Fabrication Enabled One-Step Polymer-Free Graphene Patterning and Direct Transfer for Flexible Graphene Devices.

Science.gov (United States)

Yong, Keong; Ashraf, Ali; Kang, Pilgyu; Nam, SungWoo

2016-04-27

We report a one-step polymer-free approach to patterning graphene using a stencil mask and oxygen plasma reactive-ion etching, with a subsequent polymer-free direct transfer for flexible graphene devices. Our stencil mask is fabricated via a subtractive, laser cutting manufacturing technique, followed by lamination of stencil mask onto graphene grown on Cu foil for patterning. Subsequently, micro-sized graphene features of various shapes are patterned via reactive-ion etching. The integrity of our graphene after patterning is confirmed by Raman spectroscopy. We further demonstrate the rapid prototyping capability of a stretchable, crumpled graphene strain sensor and patterned graphene condensation channels for potential applications in sensing and heat transfer, respectively. We further demonstrate that the polymer-free approach for both patterning and transfer to flexible substrates allows the realization of cleaner graphene features as confirmed by water contact angle measurements. We believe that our new method promotes rapid, facile fabrication of cleaner graphene devices, and can be extended to other two dimensional materials in the future.

Tuning transport properties of graphene three-terminal structures by mechanical deformation

Science.gov (United States)

Torres, V.; Faria, D.; Latgé, A.

2018-04-01

Straintronic devices made of carbon-based materials have been pushed up due to the graphene high mechanical flexibility and the possibility of interesting changes in transport properties. Properly designed strained systems have been proposed to allow optimized transport responses that can be explored in experimental realizations. In multiterminal systems, comparisons between schemes with different geometries are important to characterize the modifications introduced by mechanical deformations, especially if the deformations are localized at a central part of the system or extended in a large region. Then, in the present analysis, we study the strain effects on the transport properties of triangular and hexagonal graphene flakes, with zigzag and armchair edges, connected to three electronic terminals, formed by semi-infinite graphene nanoribbons. Using the Green's function formalism with circular renormalization schemes, and a single band tight-binding approximation, we find that resonant tunneling transport becomes relevant and is more affected by localized deformations in the hexagonal graphene flakes. Moreover, triangular systems with deformation extended to the leads, like longitudinal three-folded type, are shown as an interesting scenario for building nanoscale waveguides for electronic current.

Bending sound in graphene: Origin and manifestation

Energy Technology Data Exchange (ETDEWEB)

Adamyan, V.M., E-mail: vadamyan@onu.edu.ua [Department of Theoretical Physics, Odessa I.I. Mechnikov National University, 2 Dvoryanska St., Odessa 65026 (Ukraine); Bondarev, V.N., E-mail: bondvic@onu.edu.ua [Department of Theoretical Physics, Odessa I.I. Mechnikov National University, 2 Dvoryanska St., Odessa 65026 (Ukraine); Zavalniuk, V.V., E-mail: vzavalnyuk@onu.edu.ua [Department of Theoretical Physics, Odessa I.I. Mechnikov National University, 2 Dvoryanska St., Odessa 65026 (Ukraine); Department of Fundamental Sciences, Odessa Military Academy, 10 Fontanska Road, Odessa 65009 (Ukraine)

2016-11-11

Highlights: • The origin of sound-like dispersion of graphene bending mode is disclosed. • The speed of graphene bending sound is determined. • The renormalized graphene bending rigidity is derived. • The intrinsic corrugations of graphene are estimated. - Abstract: It is proved that the acoustic-type dispersion of bending mode in graphene is generated by the fluctuation interaction between in-plane and out-of-plane terms in the free energy arising with account of non-linear components in the graphene strain tensor. In doing so we use an original adiabatic approximation based on the alleged (confirmed a posteriori) significant difference of sound speeds for in-plane and bending modes. The explicit expression for the bending sound speed depending only on the graphene mass density, in-plane elastic constants and temperature is deduced as well as the characteristics of the microscopic corrugations of graphene. The obtained results are in good quantitative agreement with the data of real experiments and computer simulations.

Bending sound in graphene: Origin and manifestation

International Nuclear Information System (INIS)

Adamyan, V.M.; Bondarev, V.N.; Zavalniuk, V.V.

2016-01-01

Highlights: • The origin of sound-like dispersion of graphene bending mode is disclosed. • The speed of graphene bending sound is determined. • The renormalized graphene bending rigidity is derived. • The intrinsic corrugations of graphene are estimated. - Abstract: It is proved that the acoustic-type dispersion of bending mode in graphene is generated by the fluctuation interaction between in-plane and out-of-plane terms in the free energy arising with account of non-linear components in the graphene strain tensor. In doing so we use an original adiabatic approximation based on the alleged (confirmed a posteriori) significant difference of sound speeds for in-plane and bending modes. The explicit expression for the bending sound speed depending only on the graphene mass density, in-plane elastic constants and temperature is deduced as well as the characteristics of the microscopic corrugations of graphene. The obtained results are in good quantitative agreement with the data of real experiments and computer simulations.

Raise and collapse of pseudo Landau levels in graphene

Science.gov (United States)

Castro, Eduardo V.; Cazalilla, Miguel A.; Vozmediano, María A. H.

2017-12-01

Lattice deformations couple to the low-energy electronic excitations of graphene as vector fields similar to the electromagnetic potential. The observation of strain-induced pseudo Landau levels with scanning tunnel microscopy experiments has been one of the most exciting events in the history of graphene. Nevertheless, the experimental observation presents some ambiguities. Similar strain patterns show different images that are sometimes difficult to interpret. In this Rapid Communication, we show that, for some strain configurations, the deformation potential acts as a parallel electric field able to destabilize the Landau level structure via a mechanism identical to that occurring for real electromagnetic fields. This effect also alters the estimations of the value of the pseudomagnetic field, which can be significantly bigger. The mechanism applies equally if the electric field has an external origin, which opens the door to an electric control of giant pseudomagnetic fields in graphene.

Improvement of the quality of graphene-capped InAs/GaAs quantum dots

Energy Technology Data Exchange (ETDEWEB)

Othmen, Riadh, E-mail: othmenriadh@yahoo.fr; Rezgui, Kamel; Ajlani, Hosni; Oueslati, Meherzi [Faculté des Sciences de Tunis, Université de Tunis El Manar, Campus, 2092 El Manar Tunis (Tunisia); Cavanna, Antonella; Madouri, Ali [CNRS/LPN, Route de Nozay, F-91460 Marcoussis (France); Arezki, Hakim; Gunes, Fethullah [Laboratoire de Génie Electrique de Paris, 11, rue Joliot Curie Plateau de Moulon, 91192 Gif sur Yvette (France)

2014-06-07

In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts Δω of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure graphene–InAs/GaAs QDs wherein the graphene plays a key role as a cap layer.

Preparation and study of properties of dispersed graphene oxide

Directory of Open Access Journals (Sweden)

Evgeniya Seliverstova

2015-09-01

Full Text Available Ability of graphene oxide to form stable dispersion in organic solvents was studied in this work. As it was shown, sonication of graphene leads to the decreas of the particle size. Stability of prepared graphene dispersions was studied upon measurements of distribution of number of the particles via size and change of optical density of the solutions with time. It was found that graphene oxide forms a more stable dispersion in tetrahydrofuran and dimethylformamide than in chloroform and acetone.

Effect of humid-thermal environment on wave dispersion characteristics of single-layered graphene sheets

Science.gov (United States)

Ebrahimi, Farzad; Dabbagh, Ali

2018-04-01

In the present article, the hygro-thermal wave propagation properties of single-layered graphene sheets (SLGSs) are investigated for the first time employing a nonlocal strain gradient theory. A refined higher-order two-variable plate theory is utilized to derive the kinematic relations of graphene sheets. Here, nonlocal strain gradient theory is used to achieve a more precise analysis of small-scale plates. In the framework of the Hamilton's principle, the final governing equations are developed. Moreover, these obtained equations are deemed to be solved analytically and the wave frequency values are achieved. Some parametric studies are organized to investigate the influence of different variants such as nonlocal parameter, length scale parameter, wave number, temperature gradient and moisture concentration on the wave frequency of graphene sheets.

Towards functionalization of graphene: in situ study of the nucleation of copper-phtalocyanine on graphene

Science.gov (United States)

Schwarz, Daniel; Henneke, Caroline; Kumpf, Christian

2016-02-01

Molecular films present an elegant way for the uniform functionalization or doping of graphene. Here, we present an in situ study on the initial growth of copper phthalocyanine (CuPc) on epitaxial graphene on Ir(111). We followed the growth up to a closed monolayer with low energy electron microscopy and selected area electron diffraction (μLEED). The molecules coexist on graphene in a disordered phase without long-range order and an ordered crystalline phase. The local topography of the graphene substrate plays an important role in the nucleation process of the crystalline phase. Graphene flakes on Ir(111) feature regions that are under more tensile stress than others. We observe that the CuPc molecules form ordered domains initially on those graphene regions that are closest to the fully relaxed lattice. We attribute this effect to a stronger influence of the underlying Ir(111) substrate for molecules adsorbed on those relaxed regions.

Towards functionalization of graphene: in situ study of the nucleation of copper-phtalocyanine on graphene

International Nuclear Information System (INIS)

Schwarz, Daniel; Henneke, Caroline; Kumpf, Christian

2016-01-01

Molecular films present an elegant way for the uniform functionalization or doping of graphene. Here, we present an in situ study on the initial growth of copper phthalocyanine (CuPc) on epitaxial graphene on Ir(111). We followed the growth up to a closed monolayer with low energy electron microscopy and selected area electron diffraction (μLEED). The molecules coexist on graphene in a disordered phase without long-range order and an ordered crystalline phase. The local topography of the graphene substrate plays an important role in the nucleation process of the crystalline phase. Graphene flakes on Ir(111) feature regions that are under more tensile stress than others. We observe that the CuPc molecules form ordered domains initially on those graphene regions that are closest to the fully relaxed lattice. We attribute this effect to a stronger influence of the underlying Ir(111) substrate for molecules adsorbed on those relaxed regions. (paper)

First principles investigation of nitrogenated holey graphene

Science.gov (United States)

Xu, Cui-Yan; Dong, Hai-Kuan; Shi, Li-Bin

2018-04-01

The zero band gap problem limits the application of graphene in the field of electronic devices. Opening the band gap of graphene has become a research issue. Nitrogenated holey graphene (NHG) has attracted much attention because of its semiconducting properties. However, the stacking orders and defect properties have not been investigated. In this letter, the structural and stacking properties of NHG are first investigated. We obtain the most stable stacking structure. Then, the band structures for bulk and multilayer NHG are studied. Impact of the strain on the band gaps and bond characteristics is discussed. In addition, we investigate formation mechanism of native defects of carbon vacancy (VC), carbon interstitial (Ci), nitrogen vacancy (VN), and nitrogen interstitial (Ni) in bulk NHG. Formation energies and transition levels of these native defects are assessed.

Bubbles in graphene

DEFF Research Database (Denmark)

Settnes, Mikkel; Power, Stephen; Lin, Jun

2015-01-01

Strain-induced deformations in graphene are predicted to give rise to large pseudomagnetic fields. We examine theoretically the case of gas-inflated bubbles to determine whether signatures of such fields are present in the local density of states. Sharp-edged bubbles are found to induce Friedel...

Empirical potential for molecular simulation of graphene nanoplatelets

Science.gov (United States)

Bourque, Alexander J.; Rutledge, Gregory C.

2018-04-01

A new empirical potential for layered graphitic materials is reported. Interatomic interactions within a single graphene sheet are modeled using a Stillinger-Weber potential. Interatomic interactions between atoms in different sheets of graphene in the nanoplatelet are modeled using a Lennard-Jones interaction potential. The potential is validated by comparing molecular dynamics simulations of tensile deformation with the reported elastic constants for graphite. The graphite is found to fracture into graphene nanoplatelets when subjected to ˜15% tensile strain normal to the basal surface of the graphene stack, with an ultimate stress of 2.0 GPa and toughness of 0.33 GPa. This force field is useful to model molecular interactions in an important class of composite systems comprising 2D materials like graphene and multi-layer graphene nanoplatelets.

Production of 3D-shaped graphene via transfer printing

International Nuclear Information System (INIS)

Winters, Sinead; Nolan, Hugo; Duesberg, Georg S.; Hallam, Toby

2012-01-01

We present the fabrication of three-dimensional graphene structures supported by a polymer scaffold. The structures are fabricated using transfer printing. The structures could have potential applications in electronics, sensing and electrochemical electrodes. Electrochemical measurements confirm an increase in surface area due to the folding of the graphene over the polymer scaffolding. Further, the production method opens the possibility for strain engineering in graphene, opening a wide range of potential novel effects in the physical and chemical properties of graphene. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Stretchable and High-Performance Supercapacitors with Crumpled Graphene Papers

Science.gov (United States)

Zang, Jianfeng; Cao, Changyong; Feng, Yaying; Liu, Jie; Zhao, Xuanhe

2014-01-01

Fabrication of unconventional energy storage devices with high stretchability and performance is challenging, but critical to practical operations of fully power-independent stretchable electronics. While supercapacitors represent a promising candidate for unconventional energy-storage devices, existing stretchable supercapacitors are limited by their low stretchability, complicated fabrication process, and high cost. Here, we report a simple and low-cost method to fabricate extremely stretchable and high-performance electrodes for supercapacitors based on new crumpled-graphene papers. Electrolyte-mediated-graphene paper bonded on a compliant substrate can be crumpled into self-organized patterns by harnessing mechanical instabilities in the graphene paper. As the substrate is stretched, the crumpled patterns unfold, maintaining high reliability of the graphene paper under multiple cycles of large deformation. Supercapacitor electrodes based on the crumpled graphene papers exhibit a unique combination of high stretchability (e.g., linear strain ~300%, areal strain ~800%), high electrochemical performance (e.g., specific capacitance ~196 F g−1), and high reliability (e.g., over 1000 stretch/relax cycles). An all-solid-state supercapacitor capable of large deformation is further fabricated to demonstrate practical applications of the crumpled-graphene-paper electrodes. Our method and design open a wide range of opportunities for manufacturing future energy-storage devices with desired deformability together with high performance. PMID:25270673

Stretchable and High-Performance Supercapacitors with Crumpled Graphene Papers

Science.gov (United States)

Zang, Jianfeng; Cao, Changyong; Feng, Yaying; Liu, Jie; Zhao, Xuanhe

2014-10-01

Fabrication of unconventional energy storage devices with high stretchability and performance is challenging, but critical to practical operations of fully power-independent stretchable electronics. While supercapacitors represent a promising candidate for unconventional energy-storage devices, existing stretchable supercapacitors are limited by their low stretchability, complicated fabrication process, and high cost. Here, we report a simple and low-cost method to fabricate extremely stretchable and high-performance electrodes for supercapacitors based on new crumpled-graphene papers. Electrolyte-mediated-graphene paper bonded on a compliant substrate can be crumpled into self-organized patterns by harnessing mechanical instabilities in the graphene paper. As the substrate is stretched, the crumpled patterns unfold, maintaining high reliability of the graphene paper under multiple cycles of large deformation. Supercapacitor electrodes based on the crumpled graphene papers exhibit a unique combination of high stretchability (e.g., linear strain ~300%, areal strain ~800%), high electrochemical performance (e.g., specific capacitance ~196 F g-1), and high reliability (e.g., over 1000 stretch/relax cycles). An all-solid-state supercapacitor capable of large deformation is further fabricated to demonstrate practical applications of the crumpled-graphene-paper electrodes. Our method and design open a wide range of opportunities for manufacturing future energy-storage devices with desired deformability together with high performance.

Coulomb Oscillations in a Gate-Controlled Few-Layer Graphene Quantum Dot.

Science.gov (United States)

Song, Yipu; Xiong, Haonan; Jiang, Wentao; Zhang, Hongyi; Xue, Xiao; Ma, Cheng; Ma, Yulin; Sun, Luyan; Wang, Haiyan; Duan, Luming

2016-10-12

Graphene quantum dots could be an ideal host for spin qubits and thus have been extensively investigated based on graphene nanoribbons and etched nanostructures; however, edge and substrate-induced disorders severely limit device functionality. Here, we report the confinement of quantum dots in few-layer graphene with tunable barriers, defined by local strain and electrostatic gating. Transport measurements unambiguously reveal that confinement barriers are formed by inducing a band gap via the electrostatic gating together with local strain induced constriction. Numerical simulations according to the local top-gate geometry confirm the band gap opening by a perpendicular electric field. We investigate the magnetic field dependence of the energy-level spectra in these graphene quantum dots. Experimental results reveal a complex evolution of Coulomb oscillations with the magnetic field, featuring kinks at level crossings. The simulation of energy spectrum shows that the kink features and the magnetic field dependence are consistent with experimental observations, implying the hybridized nature of energy-level spectrum of these graphene quantum dots.

Nanotoxicity of graphene and graphene oxide.

Science.gov (United States)

Seabra, Amedea B; Paula, Amauri J; de Lima, Renata; Alves, Oswaldo L; Durán, Nelson

2014-02-17

Graphene and its derivatives are promising candidates for important biomedical applications because of their versatility. The prospective use of graphene-based materials in a biological context requires a detailed comprehension of the toxicity of these materials. Moreover, due to the expanding applications of nanotechnology, human and environmental exposures to graphene-based nanomaterials are likely to increase in the future. Because of the potential risk factors associated with the manufacture and use of graphene-related materials, the number of nanotoxicological studies of these compounds has been increasing rapidly in the past decade. These studies have researched the effects of the nanostructural/biological interactions on different organizational levels of the living system, from biomolecules to animals. This review discusses recent results based on in vitro and in vivo cytotoxicity and genotoxicity studies of graphene-related materials and critically examines the methodologies employed to evaluate their toxicities. The environmental impact from the manipulation and application of graphene materials is also reported and discussed. Finally, this review presents mechanistic aspects of graphene toxicity in biological systems. More detailed studies aiming to investigate the toxicity of graphene-based materials and to properly associate the biological phenomenon with their chemical, structural, and morphological variations that result from several synthetic and processing possibilities are needed. Knowledge about graphene-based materials could ensure the safe application of this versatile material. Consequently, the focus of this review is to provide a source of inspiration for new nanotoxicological approaches for graphene-based materials.

An atomistic methodology of energy release rate for graphene at nanoscale

International Nuclear Information System (INIS)

Zhang, Zhen; Lee, James D.; Wang, Xianqiao

2014-01-01

Graphene is a single layer of carbon atoms packed into a honeycomb architecture, serving as a fundamental building block for electric devices. Understanding the fracture mechanism of graphene under various conditions is crucial for tailoring the electrical and mechanical properties of graphene-based devices at atomic scale. Although most of the fracture mechanics concepts, such as stress intensity factors, are not applicable in molecular dynamics simulation, energy release rate still remains to be a feasible and crucial physical quantity to characterize the fracture mechanical property of materials at nanoscale. This work introduces an atomistic simulation methodology, based on the energy release rate, as a tool to unveil the fracture mechanism of graphene at nanoscale. This methodology can be easily extended to any atomistic material system. We have investigated both opening mode and mixed mode at different temperatures. Simulation results show that the critical energy release rate of graphene is independent of initial crack length at low temperature. Graphene with inclined pre-crack possesses higher fracture strength and fracture deformation but smaller critical energy release rate compared with the graphene with vertical pre-crack. Owing to its anisotropy, graphene with armchair chirality always has greater critical energy release rate than graphene with zigzag chirality. The increase of temperature leads to the reduction of fracture strength, fracture deformation, and the critical energy release rate of graphene. Also, higher temperature brings higher randomness of energy release rate of graphene under a variety of predefined crack lengths. The energy release rate is independent of the strain rate as long as the strain rate is small enough

Nonlinear electro-magneto-mechanical constitutive modelling of monolayer graphene

Science.gov (United States)

Sfyris, D.; Sfyris, G. I.; Bustamante, R.

2016-04-01

Using the classical theory of invariants for the specific class of graphene's symmetry, we constitutively characterize electro-magneto-mechanical interactions of graphene at continuum level. Graphene's energy depends on five arguments: the Finger strain tensor, the curvature tensor, the shift vector, the effective electric field intensity and the effective magnetic induction. The Finger strain tensor describes in- surface phenomena, the curvature tensor is responsible for the out-of-surface motions, while the shift vector is used due to the fact that graphene is a multilattice. The electric and the magnetic fields are described by the effective electric field intensity and the effective magnetic induction, respectively. An energy with the above arguments that also respects graphene's symmetries is found to have 42 invariants. Using these invariants, we evaluate all relevant measures by finding derivatives of the energy with respect to the five arguments of the energy. We also lay down the field equations that should be satisfied. These are the Maxwell equations, the momentum equation, the moment of momentum equation and the equation ruling the shift vector. Our framework is general enough to capture fully coupled processes in the finite deformation regime.

Point defect weakened thermal contraction in monolayer graphene.

Science.gov (United States)

Zha, Xian-Hu; Zhang, Rui-Qin; Lin, Zijing

2014-08-14

We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitude and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.

Landau quantization of Dirac fermions in graphene and its multilayers

Science.gov (United States)

Yin, Long-Jing; Bai, Ke-Ke; Wang, Wen-Xiao; Li, Si-Yu; Zhang, Yu; He, Lin

2017-08-01

When electrons are confined in a two-dimensional (2D) system, typical quantum-mechanical phenomena such as Landau quantization can be detected. Graphene systems, including the single atomic layer and few-layer stacked crystals, are ideal 2D materials for studying a variety of quantum-mechanical problems. In this article, we review the experimental progress in the unusual Landau quantized behaviors of Dirac fermions in monolayer and multilayer graphene by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Through STS measurement of the strong magnetic fields, distinct Landau-level spectra and rich level-splitting phenomena are observed in different graphene layers. These unique properties provide an effective method for identifying the number of layers, as well as the stacking orders, and investigating the fundamentally physical phenomena of graphene. Moreover, in the presence of a strain and charged defects, the Landau quantization of graphene can be significantly modified, leading to unusual spectroscopic and electronic properties.

Towards functionalization of graphene: in situ study of the nucleation of copper-phtalocyanine on graphene

OpenAIRE

Schwarz, Daniel; Henneke, Caroline; Kumpf, Christian

2016-01-01

Molecular films present an elegant way for the uniform functionalization or doping of graphene. Here, we present an in situ study on the initial growth of copper phthalocyanine (CuPc) on epitaxial graphene on Ir(111). We followed the growth up to a closed monolayer with low energy electron microscopy and selected area electron diffraction (μLEED). The molecules coexist on graphene in a disordered phase without long-range order and an ordered crystalline phase. The local topography of the grap...

Simulation Study on the Controllable Dielectrophoresis Parameters of Graphene

Science.gov (United States)

Ji, Jian-Long; Liu, Ya-Li; Ge, Yang; Xie, Sheng-Dong; Zhang, Xi; Sang, Sheng-Bo; Jian, Ao-Qun; Duan, Qian-Qian; Zhang, Qiang; Zhang, Wen-Dong

2017-03-01

The method of using dielectrophoresis (DEP) to assemble graphene between micro-electrodes has been proven to be simple and efficient. We present an optimization method for the kinetic formula of graphene DEP, and discuss the simulation of the graphene assembly process based on the finite element method. The simulated results illustrate that the accelerated motion of graphene is in agreement with the distribution of the electric field squared gradient. We also conduct research on the controllable parameters of the DEP assembly such as the alternating current (AC) frequency, the shape of micro-electrodes, and the ratio of the gap between electrodes to the characteristic/geometric length of graphene (λ). The simulations based on the Clausius-Mossotti factor reveal that both graphene velocity and direction are influenced by the AC frequency. When graphene is close to the electrodes, the shape of micro-electrodes will exert great influence on the velocity of graphene. Also, λ has a great influence on the velocity of graphene. Generally, the velocity of graphene would be greater when λ is in the range of 0.4-0.6. The study is of a theoretical guiding significance in improving the precision and efficiency of the graphene DEP assembly. Supported by the Basic Research Project of Shanxi Province under Grant No 2015021092, the National Natural Science Foundation of China under Grant Nos 61471255, 61474079, 61501316, 51505324 and 51622507, and the National High-Technology Research and Development Program of China under Grant No 2015AA042601.

Adsorption of CO molecules on doped graphene: A first-principles study

Directory of Open Access Journals (Sweden)

Weidong Wang

2016-02-01

Full Text Available As a typical kinds of toxic gases, CO plays an important role in environmental monitoring, control of chemical processes, space missions, agricultural and medical applications. Graphene is considered a potential candidate of gases sensor, so the adsorption of CO molecules on various graphene, including pristine graphene, Nitrogen-doped graphene (N-doped graphene and Aluminum-doped graphene (Al-doped graphene, are studied by using first-principles calculations. The optimal configurations, adsorption energies, charge transfer, and electronic properties including band structures, density of states and differential charge density are obtained. The adsorption energies of CO molecules on pristine graphene and N-doped graphene are −0.01 eV, and −0.03 eV, respectively. In comparison, the adsorption energy of CO on Al-doped graphene is much larger, −2.69 eV. Our results also show that there occurs a large amount of charge transfer between CO molecules and graphene sheet after the adsorption, which suggests Al-doped graphene is more sensitive to the adsorption of CO than pristine graphene and N-doped graphene. Therefore, the sensitivity of gases on graphene can be drastically improved by introducing the suitable dopants.

Nitrotyrosine adsorption on defective graphene: A density functional theory study

Science.gov (United States)

Majidi, R.; Karami, A. R.

2015-06-01

We have applied density functional theory to study adsorption of nitrotyrosine on perfect and defective graphene sheets. The graphene sheets with Stone-Wales (SW) defect, pentagon-nonagon (5-9) single vacancy, and pentagon-octagon-pentagon (5-8-5) double vacancy were considered. The calculations of adsorption energy showed that nitrotyrosine presents a more strong interaction with defective graphene rather than with perfect graphene sheet. The order of interaction strength is: SW>5-9>5-8-5>perfect graphene. It is found that the electronic properties of perfect and defective graphene are sensitive to the presence of nitrotyrosine. Hence, graphene sheets can be considered as a good sensor for detection of nitrotyrosine molecule which is observed in connection with several human disorders, such as Parkinson's and Alzheimer's disease.

Graphene Thermal Properties: Applications in Thermal Management and Energy Storage

Directory of Open Access Journals (Sweden)

Jackie D. Renteria

2014-11-01

Full Text Available We review the thermal properties of graphene, few-layer graphene and graphene nanoribbons, and discuss practical applications of graphene in thermal management and energy storage. The first part of the review describes the state-of-the-art in the graphene thermal field focusing on recently reported experimental and theoretical data for heat conduction in graphene and graphene nanoribbons. The effects of the sample size, shape, quality, strain distribution, isotope composition, and point-defect concentration are included in the summary. The second part of the review outlines thermal properties of graphene-enhanced phase change materials used in energy storage. It is shown that the use of liquid-phase-exfoliated graphene as filler material in phase change materials is promising for thermal management of high-power-density battery parks. The reported experimental and modeling results indicate that graphene has the potential to outperform metal nanoparticles, carbon nanotubes, and other carbon allotropes as filler in thermal management materials.

Wet-Spun Superelastic Graphene Aerogel Millispheres with Group Effect.

Science.gov (United States)

Zhao, Xiaoli; Yao, Weiquan; Gao, Weiwei; Chen, Hao; Gao, Chao

2017-09-01

Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high-performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost-effective scalable fabrication and miniaturization with group effect. This study shows millimeter-scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core-shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure-elastic and adsorbing materials. The GS shows a press-fly behavior with an extremely high jump velocity up to 1.2 m s -1 . For the first time, both free and oil-adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of mechanism involved in synthesis of graphene oxide and reduced graphene oxide from graphene nanoplatelets

Science.gov (United States)

Sharma, Bhasha; Shekhar, Shashank; Malik, Parul; Jain, Purnima

2018-06-01

Graphene, a wonder material has inspired quest among researchers due to its numerous applications and exceptional properties. This paper highlights the mechanism and chemistry behind the fabrication of graphene oxide by using phosphoric acid. Chemical functionalization is of prime importance which avoids agglomeration of nanoparticles to attain inherent properties. As non-homogeneous dispersion limits its utilization due to interfacial interactions which restrict reactive sites to produce intercalated network. Thus, chemically functionalized graphene leads to stable dispersion and enhances thermal, mechanical and electrical properties of the resultant polymer composite materials. Solubility of graphene in aqueous solution is the major issue because graphene is hydrophobic, to rectify this oxygen containing hydrophilic groups must be introduced to make it compatible and this can be attained by covalent functionalization. Among all nanofiller GO has shown average particle size i.e. 95 nm and highest surface charge density. The characteristic changes were estimated using Raman spectra.

Strain Lattice Imprinting in Graphene by C60 Intercalation at the Graphene/Cu Interface

NARCIS (Netherlands)

Monazami, Ehsan; Bignardi, Luca; Rudolf, Petra; Reinke, Petra

2015-01-01

Intercalation of C60 molecules at the graphene-substrate interface by annealing leads to amorphous and crystalline intercalated structures. A comparison of topography and electronic structure with wrinkles and moiré patterns confirms intercalation. The intercalated molecules imprint a local

Chemical functionalization of graphene by carbene cycloaddition: A density functional theory study

International Nuclear Information System (INIS)

Zan, Wenyan

2014-01-01

Graphical abstract: - Highlights: • The reaction process of graphene functionalization with CCl 2 group in atomic scales was studied. • The potential candidate carbenes CR 2 (R = H, F, CN, NO 2 0 , NO 2 90 , CH 3 , OCH 3 , CCH, C 6 H 5 ) were separately combined with graphene. • The functionalization of graphene nanoribbon with dichlorocarbene group was investigated. • The electronic properties of graphene functionalized by carbene groups were discussed. - Abstract: In this work, we have systematically studied the structural, energetic and electronic properties of graphene functionalized with carbene groups by using density functional theory. Introducing a low concentration of CCl 2 group in graphene was studied in detail by DFT, and closed cyclopropane-like three-membered ring structure was formed, meanwhile, the potential candidate carbene groups CR 2 (R = H, F, CH 3 , CN, NO 2 , OCH 3 , CCH, C 6 H 5 ) were added to graphene sheet, and CR 2 (R = H, NO 2 , CH 3 ) groups were expected to be good reactive species to covalently modify graphene. The graphene functionalization with carbene groups above can open graphene's band gap. More CCl 2 molecules were added to graphene, and different concentrations of CCl 2 group can tune graphene's band gap. In addition, the addition of CCl 2 group to graphene edges was investigated, and the stronger binding energy was found. Multiple CCl 2 molecules preferred to be bound with the same edge of graphene nanoribbon. This work provides an insight into the detailed molecular mechanism of graphene functionalization with carbene groups

Thermal properties of graphene under tensile stress

Science.gov (United States)

Herrero, Carlos P.; Ramírez, Rafael

2018-05-01

Thermal properties of graphene display peculiar characteristics associated to the two-dimensional nature of this crystalline membrane. These properties can be changed and tuned in the presence of applied stresses, both tensile and compressive. Here, we study graphene monolayers under tensile stress by using path-integral molecular dynamics (PIMD) simulations, which allows one to take into account quantization of vibrational modes and analyze the effect of anharmonicity on physical observables. The influence of the elastic energy due to strain in the crystalline membrane is studied for increasing tensile stress and for rising temperature (thermal expansion). We analyze the internal energy, enthalpy, and specific heat of graphene, and compare the results obtained from PIMD simulations with those given by a harmonic approximation for the vibrational modes. This approximation turns out to be precise at low temperatures, and deteriorates as temperature and pressure are increased. At low temperature, the specific heat changes as cp˜T for stress-free graphene, and evolves to a dependence cp˜T2 as the tensile stress is increased. Structural and thermodynamic properties display non-negligible quantum effects, even at temperatures higher than 300 K. Moreover, differences in the behavior of the in-plane and real areas of graphene are discussed, along with their associated properties. These differences show up clearly in the corresponding compressibility and thermal expansion coefficient.

Interlayer shear of nanomaterials: Graphene-graphene, boron nitride-boron nitride and graphene-boron nitride

Institute of Scientific and Technical Information of China (English)

Yinfeng Li; Weiwei Zhang; Bill Guo; Dibakar Datta

2017-01-01

In this paper,the interlayer sliding between graphene and boron nitride (h-BN) is studied by molecular dynamics simulations.The interlayer shear force between h-BN/h-BN is found to be six times higher than that of graphene/graphene,while the interlayer shear between graphene/h-BN is approximate to that of graphene/graphene.The graphene/h-BN heterostructure shows several anomalous interlayer shear characteristics compared to its bilayer counterparts.For graphene/graphene and h-BN/h-BN,interlayer shears only exit along the sliding direction while interlayer shear for graphene/h-BN is observed along both the translocation and perpendicular directions.Our results provide significant insight into the interlayer shear characteristics of 2D nanomaterials.

Stability of germanene under tensile strain

KAUST Repository

Kaloni, Thaneshwor P.

2013-09-01

The stability of germanene under biaxial tensile strain and the accompanying modifications of the electronic properties are studied by density functional theory. The phonon spectrum shows that up to 16% strain the germanene lattice is stable, where the Dirac cone shifts towards higher energy and hole-doped Dirac states are achieved. The latter is due to weakening of the Ge-Ge bonds and reduction of the s-p hybridization. Our calculated Grüneisen parameter shows a similar dependence on the strain as reported for silicene (which is different from that of graphene). © 2013 Elsevier B.V. All rights reserved.

Stability of germanene under tensile strain

KAUST Repository

Kaloni, Thaneshwor P.; Schwingenschlö gl, Udo

2013-01-01

The stability of germanene under biaxial tensile strain and the accompanying modifications of the electronic properties are studied by density functional theory. The phonon spectrum shows that up to 16% strain the germanene lattice is stable, where the Dirac cone shifts towards higher energy and hole-doped Dirac states are achieved. The latter is due to weakening of the Ge-Ge bonds and reduction of the s-p hybridization. Our calculated Grüneisen parameter shows a similar dependence on the strain as reported for silicene (which is different from that of graphene). © 2013 Elsevier B.V. All rights reserved.

Raman Spectroscopic Study of As-Deposited and Exfoliated Defected Graphene Grown on (001 Si Substrates by CVD

Directory of Open Access Journals (Sweden)

T. I. Milenov

2017-01-01

Full Text Available We present here results on a Raman spectroscopic study of the deposited defected graphene on Si substrates by chemical vapor deposition (thermal decomposition of acetone. The graphene films are not deposited on the (001 Si substrate directly but on two types of interlayers of mixed phases unintentionally deposited on the substrates: а diamond-like carbon (designated here as DLC and amorphous carbon (designated here as αC are dominated ones. The performed thorough Raman spectroscopic study of as-deposited as well as exfoliated specimens by two different techniques using different excitation wavelengths (488, 514, and 613 nm as well as polarized Raman spectroscopy establishes that the composition of the designated DLC layers varies with depth: the initial layers on the Si substrate consist of DLC, nanodiamond species, and C70 fullerenes while the upper ones are dominated by DLC with an occasional presence of C70 fullerenes. The αC interlayer is dominated by turbostratic graphite and contains a larger quantity of C70 than the DLC-designated interlayers. The results of polarized and unpolarized Raman spectroscopic studies of as-grown and exfoliated graphene films tend to assume that single- to three-layered defected graphene is deposited on the interlayers. It can be concluded that the observed slight upshift of the 2D band as well as the broadening of 2D band should be related to the strain and doping.

Pressure-mediated doping in graphene.

Science.gov (United States)

Nicolle, Jimmy; Machon, Denis; Poncharal, Philippe; Pierre-Louis, Olivier; San-Miguel, Alfonso

2011-09-14

Exfoliated graphene and few layer graphene samples supported on SiO(2) have been studied by Raman spectroscopy at high pressure. For samples immersed on a alcohol mixture, an electron transfer of ∂n/∂P ∼ 8 × 10(12) cm(-2) GPa(-1) is observed for monolayer and bilayer graphene, leading to giant doping values of n ∼ 6 × 10(13) cm(-2) at the maximum pressure of 7 GPa. Three independent and consistent proofs of the doping process are obtained from (i) the evolution of the Raman G-band to 2D-band intensity ratio, (ii) the pressure coefficient of the G-band frequency, and (iii) the 2D band components splitting in the case of the bilayer sample. The charge transfer phenomena is absent for trilayer samples and for samples immersed in argon or nitrogen. We also show that a phase transition from a 2D biaxial strain response, resulting from the substrate drag upon volume reduction, to a 3D hydrostatic compression takes place when going from the bilayer to the trilayer sample. By model calculations we relate this transition to the unbinding of the graphene-SiO(2) system when increasing the number of graphene layers and as function of the surface roughness parameters. We propose that the formation of silanol groups on the SiO(2) substrate allows for a capacitance-induced substrate-mediated charge transfer.

Mechanical Stability of Flexible Graphene-Based Displays.

Science.gov (United States)

Anagnostopoulos, George; Pappas, Panagiotis-Nektarios; Li, Zheling; Kinloch, Ian A; Young, Robert J; Novoselov, Kostya S; Lu, Ching Yu; Pugno, Nicola; Parthenios, John; Galiotis, Costas; Papagelis, Konstantinos

2016-08-31

The mechanical behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the "island-like" microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behavior of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the maximum temperature gradient developed at the point of "finger" contact after 80 000 cycles does not exceed the glass transition temperature of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays are discussed.

Scalable Production of Graphene-Based Wearable E-Textiles.

Science.gov (United States)

Karim, Nazmul; Afroj, Shaila; Tan, Sirui; He, Pei; Fernando, Anura; Carr, Chris; Novoselov, Kostya S

2017-12-26

Graphene-based wearable e-textiles are considered to be promising due to their advantages over traditional metal-based technology. However, the manufacturing process is complex and currently not suitable for industrial scale application. Here we report a simple, scalable, and cost-effective method of producing graphene-based wearable e-textiles through the chemical reduction of graphene oxide (GO) to make stable reduced graphene oxide (rGO) dispersion which can then be applied to the textile fabric using a simple pad-dry technique. This application method allows the potential manufacture of conductive graphene e-textiles at commercial production rates of ∼150 m/min. The graphene e-textile materials produced are durable and washable with acceptable softness/hand feel. The rGO coating enhanced the tensile strength of cotton fabric and also the flexibility due to the increase in strain% at maximum load. We demonstrate the potential application of these graphene e-textiles for wearable electronics with activity monitoring sensor. This could potentially lead to a multifunctional single graphene e-textile garment that can act both as sensors and flexible heating elements powered by the energy stored in graphene textile supercapacitors.

Wrinkling of graphene membranes supported by silica nanoparticles on substrates

Science.gov (United States)

Yamamoto, Mahito; Cullen, William; Fuhrer, Michael; Einstein, Theodore; Department of Physics, University of Maryland Team

2011-03-01

The challenging endeavor of modulating the morphology of graphene via a patterned substrate to produce a controlled deformation has great potential importance for strain engineering the electronic properties of graphene. An essential step in this direction is to understand the response of graphene to substrate features of known geometry. Here we employ silica nanoparticles with a diameter of 10-100 nm to uniformly decorate Si O2 and mica substrates before depositing graphene, to promote nanoscale modulation of graphene geometry. The morphology of graphene on this modified substrate is then characterized by atomic force spectroscopy. We find that graphene on the substrate is locally raised by the supporting nanoparticles, and wrinkling propagates radially from the protrusions to form a ridge network which links the protrusions. We discuss the dependence of the wrinkled morphology on nanoparticle diameter and graphene thickness in terms of graphene elasticity and adhesion energy. Supported by NSF-MRSEC, Grant DMR 05-20471

Strain engineering of van der Waals heterostructures

NARCIS (Netherlands)

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

2018-01-01

Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS2, and Bi2Te3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals

Size Effect of Defects on the Mechanical Properties of Graphene

Science.gov (United States)

Park, Youngho; Hyun, Sangil

2018-03-01

Graphene, a two-dimensional material, has been studied and utilized for its excellent material properties. In reality, achieving a pure single-crystalline structure in graphene is difficult, so usually graphene may have various types of defects in it. Vacancies, Stone-Wales defects, and grain boundaries can drastically change the material properties of graphene. Graphene with vacancy defects has been of interest because it is a two-dimensional analogy of three-dimensional porous materials. It has efficient material properties, and can function as a part of modern devices. The mechanical properties have been studied by using molecular dynamics for either a single vacancy defect with various sizes or multiple vacancy defects with same defect ratios. However, it is not clear which one has more influence on the mechanical properties between the size of the defects and the defect ratio. Therefore, we investigated the hole-size effect on the mechanical properties of single-crystalline graphene at various defect ratios. A void defect with large size can have a rather high tensile modulus with a low fracture strain compared to a void defect with small size. We numerically found that the tensile properties of scattered single vacancies is similar to that of amorphous graphene. We suspect that this is due to the local orbital change of the carbon atoms near the boundary of the void defects, so-called the interfacial phase.

Effects of interfacial alignments on the stability of graphene on Ru(0001) substrate

Energy Technology Data Exchange (ETDEWEB)

Gao, Lei; Liu, Yanmin; Ma, Tianbao, E-mail: mtb@mail.tsinghua.edu.cn; Shi, Ruoyu; Hu, Yuanzhong; Luo, Jianbin, E-mail: luojb@mail.tsinghua.edu.cn [State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China)

2016-06-27

Structure and electronic properties of two-dimensional materials could be tuned by interfacial misfit or orientation angles. However, graphene grown on Ru(0001) substrate usually shows stable moiré superlattice with a periodicity of 3.0 nm indicating an aligned geometry. The reason for the absence of misaligned structure is still unknown. We have performed first-principles calculation to investigate the microstructure and morphology of graphene on Ru(0001) substrate in both aligned and misaligned geometries with rotation angles of 0°, 7.6°, and 23.4°, respectively. Our results indicate that both the graphene corrugation and moiré superlattice periodicity decrease as the rotation angle increases. Meanwhile the interaction energy between graphene and Ru(0001) substrate also becomes weakened with the rotation angle, as the decrease and discretization of intense charge transfer sites at the graphene/Ru interface, which is closely related to the interface stacking structure. Counterintuitively, the strain energy in graphene also increases anomalously with the rotation angle, which is attributed to the highly distorted local deformation of graphene due to the strong but discrete covalent bonding with Ru substrate. The simultaneous increase in both the interaction energy and strain energy in graphene/Ru(0001) heterostructure with rotation angle contributes to the preferred configuration in the aligned state.

Wrinkling instability in graphene supported on nanoparticle-patterned SiO2

Science.gov (United States)

Cullen, William; Yamamoto, Mahito; Pierre-Louis, Olivier; Einstein, Theodore; Fuhrer, Michael

2012-02-01

Atomically-thin graphene is arguably the thinnest possible mechanical membrane: graphene's effective thickness (the thickness of an isotropic continuum slab which would have the same elastic and bending stiffness) is significantly less than 1 å, indicating that graphene can distort out-of-plane to conform to sub-nanometer features. Here we study the elastic response of graphene supported on a SiO2 substrate covered with SiO2 nanoparticles. At a low density of nanoparticles, graphene is largely pinned to the substrate due to adhesive interaction. However, with increasing nanoparticle density, graphene's elasticity dominates adhesion and strain is relieved by the formation of wrinkles which connect peaks introduced by the supporting nanoparticles. At a critical density, the wrinkles percolate, resulting in a wrinkle network. We develop a simple elastic model allowing for adhesion which accurately predicts the critical spacing between nanoparticles for wrinkle formation. This work has been supported by the University of Maryland NSF-MRSEC under Grant No. DMR 05-20471 with supplemental funding from NRI, and NSF-DMR 08-04976.

Graphene Synthesis & Graphene/Polymer Nanocomposites

Science.gov (United States)

Liao, Ken-Hsuan

-layered free standing TRG. This indicates TRG is mono-layer-dispersed in the matrix polymer. How graphene/polymer nanocomposite glass transition temperatures ( Tg) vary was investigated in this study. We measured Tg in PMMA. We used isotactic PMMA (i-PMMA) and syndiotactic-rich atactic PMMA (a-PMMA) to make TRG/PMMA nanocomposites using solvent blending and in situ polymerization in order to investigate the stereo-regularity and processing effects on the Tg. A T g increase was found in i-PMMA and in situ PMMA but not in a-PMMA. The results can be explained by the thin film confinement effect of polymer. We attribute the Tg increase to both a higher interaction density and a stronger hydrogen bonding at the interfaces. We have studied the elastic modulus of graphene oxide with various oxygen content. We used in situ AFM nano-indentation to measure the influence of oxygen on the elastic modulus of graphene oxide with various carbon/oxygen (C/O) ratios. The results show that chemical reduction (lower oxygen contents) decreases the elastic modulus of graphene oxide. We speculate that chemical reduction of oxygen atoms of epoxy groups on graphene oxide surface removes the bridging effect between carbon atoms, which leads to more flexible sheets. (Abstract shortened by UMI.).

Hydrogen molecule on lithium adsorbed graphene: A DFT study

International Nuclear Information System (INIS)

Kaur, Gagandeep; Gupta, Shuchi; Gaganpreet; Dharamvir, Keya

2016-01-01

Electronic structure calculations for the adsorption of molecular hydrogen on lithium (Li) decorated and pristine graphene have been studied systematically using SIESTA code [1] within the framework of the first-principle DFT under the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)[2], including spin polarization. The energy of adsorption of hydrogen molecule on graphene is always enhanced by the presence of co-adsorbed lithium. The most efficient adsorption configuration is when H 2 is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

EDITORIAL: Epitaxial graphene Epitaxial graphene

Science.gov (United States)

de Heer, Walt A.; Berger, Claire

2012-04-01

Graphene is widely regarded as an important new electronic material with interesting two-dimensional electron gas properties. Not only that, but graphene is widely considered to be an important new material for large-scale integrated electronic devices that may eventually even succeed silicon. In fact, there are countless publications that demonstrate the amazing applications potential of graphene. In order to realize graphene electronics, a platform is required that is compatible with large-scale electronics processing methods. It was clear from the outset that graphene grown epitaxially on silicon carbide substrates was exceptionally well suited as a platform for graphene-based electronics, not only because the graphene sheets are grown directly on electronics-grade silicon carbide (an important semiconductor in its own right), but also because these sheets are oriented with respect to the semiconductor. Moreover, the extremely high temperatures involved in production assure essentially defect-free and contamination-free materials with well-defined interfaces. Epitaxial graphene on silicon carbide is not a unique material, but actually a class of materials. It is a complex structure consisting of a reconstructed silicon carbide surface, which, for planar hexagonal silicon carbide, is either the silicon- or the carbon-terminated face, an interfacial carbon rich layer, followed by one or more graphene layers. Consequently, the structure of graphene films on silicon carbide turns out to be a rich surface-science puzzle that has been intensively studied and systematically unravelled with a wide variety of surface science probes. Moreover, the graphene films produced on the carbon-terminated face turn out to be rotationally stacked, resulting in unique and important structural and electronic properties. Finally, in contrast to essentially all other graphene production methods, epitaxial graphene can be grown on structured silicon carbide surfaces to produce graphene

The mechanical design of hybrid graphene/boron nitride nanotransistors: Geometry and interface effects

Science.gov (United States)

Einalipour Eshkalak, Kasra; Sadeghzadeh, Sadegh; Jalaly, Maisam

2018-02-01

From electronic point of view, graphene resembles a metal or semi-metal and boron nitride is a dielectric material (band gap = 5.9 eV). Hybridization of these two materials opens band gap of the graphene which has expansive applications in field-effect graphene transistors. In this paper, the effect of the interface structure on the mechanical properties of a hybrid graphene/boron nitride was studied. Young's modulus, fracture strain and tensile strength of the models were simulated. Three likely types (hexagonal, octagonal and decagonal) were found for the interface of hybrid sheet after relaxation. Although Csbnd B bonds at the interface were indicated to result in more promising electrical properties, nitrogen atoms are better choice for bonding to carbon for mechanical applications.

Materials science. Dynamic mechanical behavior of multilayer graphene via supersonic projectile penetration.

Science.gov (United States)

Lee, Jae-Hwang; Loya, Phillip E; Lou, Jun; Thomas, Edwin L

2014-11-28

Multilayer graphene is an exceptional anisotropic material due to its layered structure composed of two-dimensional carbon lattices. Although the intrinsic mechanical properties of graphene have been investigated at quasi-static conditions, its behavior under extreme dynamic conditions has not yet been studied. We report the high-strain-rate behavior of multilayer graphene over a range of thicknesses from 10 to 100 nanometers by using miniaturized ballistic tests. Tensile stretching of the membrane into a cone shape is followed by initiation of radial cracks that approximately follow crystallographic directions and extend outward well beyond the impact area. The specific penetration energy for multilayer graphene is ~10 times more than literature values for macroscopic steel sheets at 600 meters per second. Copyright © 2014, American Association for the Advancement of Science.

Mechanical Stability of Flexible Graphene-Based Displays

Science.gov (United States)

2016-01-01

The mechanical behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the “island-like” microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene “islands” but also on the yielding behavior of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the maximum temperature gradient developed at the point of “finger” contact after 80 000 cycles does not exceed the glass transition temperature of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays are discussed. PMID:27494211

High Temperature Growth of Graphene from Cobalt Volume: Effect on Structural Properties

Directory of Open Access Journals (Sweden)

Giampiero Amato

2018-02-01

Full Text Available Several transition metals other than the largely used Cu and Ni can be, in principle, employed to catalyze carbon precursors for the chemical vapor deposition of graphene, because the thermodynamics of their alloying with carbon is well known. For example, the wealth of information in the Co-C phase diagram can be used to predict the properties of graphene grown in this way. It is, in fact, expected that growth occurs at a temperature higher than in Ni, with beneficial consequences to the mechanical and electronic properties of the final product. In this work, the growth of graphene onto Co film is presented together with an extensive Raman characterization of the structural properties of the material so far obtained. Previous results reporting the full coverage with negligible defective areas, in spite of discontinuities in the underlying metal, are confirmed, together with the occurrence of strain in the graphene sheet. Strain is deeply investigated in this work, in view of possible employment in engineering the material properties. The observed strain is ascribed to the high thermal mismatch with the substrate, even if an effect of the crystallographic transition of Co cannot be excluded.

Evaluation of H2S sensing characteristics of metals-doped graphene and metals-decorated graphene: Insights from DFT study

Science.gov (United States)

Khodadadi, Zahra

2018-05-01

The high tendency of graphene to adsorb H2S gas has made it a good choice for the purpose of separating H2S gas from industrial waste streams, and it can also be used as a good H2S sensor. In this research, the adsorption of H2S molecule on pristine, transition metal (Ni, Cu and Zn)-doped graphene and metal-decorated graphene nanosheets have been investigated via first-principles approach based on Density Functional Theory (DFT). The most stable adsorption geometry, rate of adsorption energy and charge transfer of H2S molecule on pristine, metal-doped, and metal-decorated graphene nanosheets have been discussed. The adsorption of H2S gas on several kinds of graphene nanosheets was studied by three different models. As H2S molecule adsorbed on metal-doped graphene nanosheets, we found that the configuration with two hydrogen atoms towards the metal-doped graphene nanosheet as most desirable situation. Moreover, the calculations show that the adsorption energy of H2S on Cu-doped graphene nanosheet is the highest among all the other metal-doped graphene nanosheet systems. We also investigated the H2S capability to bind to Ni, Cu and Zn-decorated graphene nanosheets. It was found that after adsorption, the configuration of the sulfur atom, which was located close to the metal-decorated graphene nanosheets was stable thermodynamically. The Ni-decorated graphene nanosheet with large adsorption energy and short binding distance is suitable for chemisorptions. The unfilled d-shells Ni-decorated graphene nanosheets are primarily responsible for increase in the reactivity.

Surface modification of multilayer graphene using Ga ion irradiation

Energy Technology Data Exchange (ETDEWEB)

Wang, Quan, E-mail: wangq@mail.ujs.edu.cn [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Shao, Ying; Ge, Daohan; Ren, Naifei [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); Yang, Qizhi [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); State key laboratory of Robotics, Chinese Academy of Sciences, Shengyang 110000 (China)

2015-04-28

The effect of Ga ion irradiation intensity on the surface of multilayer graphene was examined. Using Raman spectroscopy, we determined that the irradiation caused defects in the crystal structure of graphene. The density of defects increased with the increase in dwell times. Furthermore, the strain induced by the irradiation changed the crystallite size and the distance between defects. These defects had the effect of doping the multilayer graphene and increasing its work function. The increase in work function was determined using contact potential difference measurements. The surface morphology of the multilayer graphene changed following irradiation as determined by atomic force microscopy. Additionally, the adhesion between the atomic force microscopy tip and sample increased further indicating that the irradiation had caused surface modification, important for devices that incorporate graphene.

Graphene-Vertically Aligned Carbon Nanotube Hybrid on PDMS as Stretchable Electrodes.

Science.gov (United States)

Ding, Junjun; Fu, Shichen; Zhang, Runzhi; Boon, Eric Peter; Lee, Woo; Fisher, Frank T; Yang, Eui-Hyeok

2017-09-11

Stretchable electrodes are a critical component for flexible electronics such as displays, energy devices, and wearable sensors. Carbon nanotubes (CNTs) and graphene have been considered for flexible electrode applications, due to their mechanical strength, high carrier mobility, and excellent thermal conductivity. Vertically aligned carbon nanotubes (VACNTs) provide the possibility to serve as interconnects to graphene sheets as stretchable electrodes that could maintain high electrical conductivity under large tensile strain. In this work, a graphene oxide (GO) -VACNT hybrid on a PDMS substrate was demonstrated. Here, 50 μm long VACNTs were grown on a Si/SiO2 wafer substrate via atmospheric pressure chemical vapor deposition (APCVD). VACNTs were directly transferred by delamination from the Si/SiO2 to a semi-cured PDMS substrate, ensuring strong adhesion between VACNTs and PDMS upon full curing of the PDMS. GO ink was then printed on the surface of the VACNT carpet and thermally reduced to reduced graphene oxide (rGO). The sheet resistance of the rGO-VACNT hybrid was measured under uniaxial tensile strains up to 300% applied to the substrate. Under applied strain, the rGO-VACNT hybrid maintained a sheet resistant of 386±55 Ω/sq. Cyclic stretching of the rGO-VACNT hybrid was performed with up to 50 cycles at 100% maximum tensile strain, showing no increase in sheet resistance. These results demonstrate promising performance of the rGO-VACNT hybrid for flexible electronics applications. © 2017 IOP Publishing Ltd.

Graphene oxide and adsorption of chloroform: A density functional study

Energy Technology Data Exchange (ETDEWEB)

Kuisma, Elena; Hansson, C. Fredrik; Lindberg, Th. Benjamin; Gillberg, Christoffer A.; Idh, Sebastian; Schröder, Elsebeth, E-mail: schroder@chalmers.se [Quantum Device Physics Laboratory, Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-412 96 Göteborg (Sweden)

2016-05-14

Chlorinated hydrocarbon compounds are of environmental concerns, since they are toxic to humans and other mammals, and are widespread, and exposure is hard to avoid. Understanding and improving methods to reduce the amount of the substances are important. We present an atomic-scale calculational study of the adsorption of chlorine-based substance chloroform (CHCl{sub 3}) on graphene oxide, as a step in estimating the capacity of graphene oxide for filtering out such substances, e.g., from drinking water. The calculations are based on density functional theory, and the recently developed consistent-exchange functional for the van der Waals density-functional method is employed. We obtain values of the chloroform adsorption energy varying from roughly 0.2 to 0.4 eV per molecule. This is comparable to previously found results for chloroform adsorbed directly on clean graphene, using similar calculations. In a wet environment, like filters for drinking water, the graphene will not stay clean and will likely oxidize, and thus adsorption onto graphene oxide, rather than clean graphene, is a more relevant process to study.

External-strain-induced semimetallic and metallic phase of chlorographene

Science.gov (United States)

Puri, Shivam; Bhowmick, Somnath

2018-04-01

To overcome the limitations of graphene due to lack of intrinsic band gap, it is generally functionalized with hydrogen or halogen atoms such as fluorine and chlorine. Generally, such functionalization yields a moderate- to high-band-gap material in case of 100% coverage, for example ≈1.5 eV in graphene functionalized with chlorine atoms or chlorographene. In this paper, using ab initio calculations, we report very interesting transformations observed in chlorographene under external strain, driving it to a state with nearly vanishing band gap (under tensile strain) and even converting it to a metal (under compressive strain). We also show the importance of spin-orbit coupling, responsible for the few meV band gap of chlorographene observed under high tensile strain, which would have been a gapless semimetal otherwise.

Graphene oxide and reduced graphene oxide studied by the XRD, TEM and electron spectroscopy methods

International Nuclear Information System (INIS)

Stobinski, L.; Lesiak, B.; Malolepszy, A.; Mazurkiewicz, M.; Mierzwa, B.; Zemek, J.; Jiricek, P.; Bieloshapka, I.

2014-01-01

Highlights: • Graphene oxide (FL-GOc) and reduced graphene oxide (FL-RGOc): XRD, TEM, XPS, REELS. • FL-GOc: stacking nanostructure—22 × 6 nm (DxH), 0.9 nm layers separation (XRD). • FL-RGOc: stacking nanostructure—8 × 1 nm (DxH), 0.4 nm layers separation (XRD). • Reduction: oxygen group degradation, decreasing distance between graphene layers. • Number of graphene layers in stacking nanostructure: 6–7 (FL-GOc), 2–3 (FL-RGOc). - Abstract: The commercial and synthesised few-layer graphene oxide, prepared using oxidation reactions, and few-layer reduced graphene oxide samples were structurally and chemically investigated by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron spectroscopy methods, i.e. X-ray photoelectron spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). The commercial graphene oxide (FL-GOc) shows a stacking nanostructure of about 22 × 6 nm average diameter by height with the distance of 0.9 nm between 6-7 graphene layers, whereas the respective reduced graphene oxide (FL-RGOc)—about 8 × 1 nm average diameter by height stacking nanostructure with the distance of 0.4 nm between 2-3 graphene layers (XRD). The REELS results are consistent with those by the XRD indicating 8 (FL-GOc) and 4 layers (FL-RGOc). In graphene oxide and reduced graphene oxide prepared from the graphite the REELS indicates 8–11 and 7–10 layers. All graphene oxide samples show the C/O ratio of 2.1–2.3, 26.5–32.1 at% of C sp 3 bonds and high content of functional oxygen groups (hydroxyl—C-OH, epoxy—C-O-C, carbonyl—C=O, carboxyl—C-OOH, water) (XPS). Reduction increases the C/O ratio to 2.8–10.3, decreases C sp 3 content to 11.4–20.3 at% and also the content of C-O-C and C=O groups, accompanied by increasing content of C-OH and C-OOH groups. Formation of additional amount of water due to functional oxygen group reduction leads to layer delamination. Removing of functional oxygen groups

Bilayer graphene quantum dot defined by topgates

Energy Technology Data Exchange (ETDEWEB)

Müller, André; Kaestner, Bernd; Hohls, Frank; Weimann, Thomas; Pierz, Klaus; Schumacher, Hans W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

2014-06-21

We investigate the application of nanoscale topgates on exfoliated bilayer graphene to define quantum dot devices. At temperatures below 500 mK, the conductance underneath the grounded gates is suppressed, which we attribute to nearest neighbour hopping and strain-induced piezoelectric fields. The gate-layout can thus be used to define resistive regions by tuning into the corresponding temperature range. We use this method to define a quantum dot structure in bilayer graphene showing Coulomb blockade oscillations consistent with the gate layout.

Graphene and graphene oxide: biofunctionalization and applications in biotechnology.

Science.gov (United States)

Wang, Ying; Li, Zhaohui; Wang, Jun; Li, Jinghong; Lin, Yuehe

2011-05-01

Graphene is the basic building block of 0D fullerene, 1D carbon nanotubes, and 3D graphite. Graphene has a unique planar structure, as well as novel electronic properties, which have attracted great interests from scientists. This review selectively analyzes current advances in the field of graphene bioapplications. In particular, the biofunctionalization of graphene for biological applications, fluorescence-resonance-energy-transfer-based biosensor development by using graphene or graphene-based nanomaterials, and the investigation of graphene or graphene-based nanomaterials for living cell studies are summarized in more detail. Future perspectives and possible challenges in this rapidly developing area are also discussed. Copyright © 2011 Elsevier Ltd. All rights reserved.

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.

2013-03-11

The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.; Cheng, Yingchun; Schwingenschlö gl, Udo

2013-01-01

The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

Ab initio study of friction of graphene flake on graphene/graphite or SiC surface

Science.gov (United States)

Gulseren, Oguz; Tayran, Ceren; Sayin, Ceren Sibel

Recently, the rich dynamics of graphene flake on graphite or SiC surfaces are revealed from atomic force microcopy experiments. The studies toward to the understanding of microscopic origin of friction are getting a lot of attention. Despite the several studies of these systems using molecular dynamics methods, density functional theory based investigations are limited because of the huge system sizes. In this study, we investigated the frictional force on graphene flake on graphite or SiC surfaces from pseudopotential planewave calculations based on density functional theory. In both cases, graphene flake (24 C) on graphite or SiC surface, bilayer flake is introduced by freezing the top layer as well as the bottom layer of the surface slab. After fixing the load with these frozen layers, we checked the relative motion of the flake over the surface. A minimum energy is reached when the flake is moved on graphene to attain AB stacking. We also conclude that edge reconstruction because of the finite size of the flake is very critical for frictional properties of the flake; therefore the saturation of dangling bonds with hydrogen is also addressed. Not only the symmetric configurations remaining parameter space is extensively studied. Supported by TUBITAK Project No: 114F162. This work is supported by TUBITAK Project No: 114F162.

Raman spectroscopy of boron-doped single-layer graphene.

Science.gov (United States)

Kim, Yoong Ahm; Fujisawa, Kazunori; Muramatsu, Hiroyuki; Hayashi, Takuya; Endo, Morinobu; Fujimori, Toshihiko; Kaneko, Katsumi; Terrones, Mauricio; Behrends, Jan; Eckmann, Axel; Casiraghi, Cinzia; Novoselov, Kostya S; Saito, Riichiro; Dresselhaus, Mildred S

2012-07-24

The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

Electronic Properties of Graphene-PtSe2 Contacts.

Science.gov (United States)

Sattar, Shahid; Schwingenschlögl, Udo

2017-05-10

In this article, we study the electronic properties of graphene in contact with monolayer and bilayer PtSe 2 using first-principles calculations. It turns out that there is no charge transfer between the components because of the weak van der Waals interaction. We calculate the work functions of monolayer and bilayer PtSe 2 and analyze the band bending at the contact with graphene. The formation of an n-type Schottky contact with monolayer PtSe 2 and a p-type Schottky contact with bilayer PtSe 2 is demonstrated. The Schottky barrier height is very low in the bilayer case and can be reduced to zero by 0.8% biaxial tensile strain.

First-principles study on silicon atom doped monolayer graphene

Science.gov (United States)

Rafique, Muhammad; Shuai, Yong; Hussain, Nayyar

2018-01-01

This paper illustrates the structural, electronic and optical properties of individual silicon (Si) atom-doped single layer graphene using density functional theory method. Si atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si atoms from 3.125% to 9.37% (i.e. From one to three Si atoms in 4 × 4 pure graphene supercell containing 32 carbon atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K-point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si atoms present in graphene lattice. Upon analyzing the optical properties of Si atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.

Anisotropic mechanical properties of graphene sheets from molecular dynamics

International Nuclear Information System (INIS)

Ni Zhonghua; Bu Hao; Zou Min; Yi Hong; Bi Kedong; Chen Yunfei

2010-01-01

Anisotropic mechanical properties are observed for a sheet of graphene along different load directions. The anisotropic mechanical properties are attributed to the hexagonal structure of the unit cells of the graphene. Under the same tensile loads, the edge bonds bear larger load in the longitudinal mode (LM) than in the transverse mode (TM), which causes fracture sooner in LM than in TM. The Young's modulus and the third order elastic modulus for the LM are slightly larger than that for the TM. Simulation also demonstrates that, for both LM and TM, the loading and unloading stress-strain response curves overlap as long as the graphene is unloaded before the fracture point. This confirms that graphene sustains complete elastic and reversible deformation in the elongation process.

An Oxygen Reduction Study of Graphene-Based Nanomaterials of Different Origin

Directory of Open Access Journals (Sweden)

Jaana Lilloja

2016-07-01

Full Text Available The aim of this study is to compare the electrochemical behaviour of graphene-based materials of different origin, e.g., commercially available graphene nanosheets from two producers and reduced graphene oxide (rGO towards the oxygen reduction reaction (ORR using linear sweep voltammetry, rotating disc electrode and rotating ring-disc electrode methods. We also investigate the effect of catalyst ink preparation using two different solvents (2-propanol containing OH− ionomer or N,N-dimethylformamide on the ORR. The graphene-based materials are characterised by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Clearly, the catalytic effect depends on the origin of graphene material and, interestingly, the electrocatalytic activity of the catalyst material for ORR is lower when using the OH− ionomer in electrode modification. The graphene electrodes fabricated with commercial graphene show better ORR performance than rGO in alkaline solution.

Stress and charge transfer in uniaxially strained CVD graphene

Czech Academy of Sciences Publication Activity Database

Bouša, Milan; Anagnostopoulos, G. C.; del Corro, Elena; Drogowska, Karolina; Pekárek, J.; Kalbáč, Martin; Parthenios, J.; Papagelis, K.; Galiotis, C.; Frank, Otakar

2016-01-01

Roč. 253, č. 12 (2016), s. 2355-2361 ISSN 0370-1972 R&D Projects: GA ČR GA14-15357S; GA MŠk LL1301 Institutional support: RVO:61388955 Keywords : chemical vapour deposition * graphene * Raman spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.674, year: 2016

Stacking order dependent mechanical properties of graphene/MoS{sub 2} bilayer and trilayer heterostructures

Energy Technology Data Exchange (ETDEWEB)

Elder, Robert M., E-mail: robert.elder26.ctr@mail.mil, E-mail: mahesh.neupane.ctr@mail.mil; Neupane, Mahesh R., E-mail: robert.elder26.ctr@mail.mil, E-mail: mahesh.neupane.ctr@mail.mil; Chantawansri, Tanya L. [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)

2015-08-17

Transition metal dichalcogenides (TMDC) such as molybdenum disulfide (MoS{sub 2}) are two-dimensional materials that show promise for flexible electronics and piezoelectric applications, but their weak mechanical strength is a barrier to practical use. In this work, we perform nanoindentation simulations using atomistic molecular dynamics to study the mechanical properties of heterostructures formed by combining MoS{sub 2} with graphene. We consider both bi- and tri-layer heterostructures formed with MoS{sub 2} either supported or encapsulated by graphene. Mechanical properties, such as Young's modulus, bending modulus, ultimate tensile strength, and fracture strain, are extracted from nanoindentation simulations and compared to the monolayer and homogeneous bilayer systems. We observed that the heterostructures, regardless of the stacking order, are mechanically more robust than the mono- and bi-layer MoS{sub 2}, mainly due to the mechanical reinforcement provided by the graphene layer. The magnitudes of ultimate strength and fracture strain are similar for both the bi- and tri-layer heterostructures, but substantially larger than either the mono- and bi-layer MoS{sub 2}. Our results demonstrate the potential of graphene-based heterostructures to improve the mechanical properties of TMDC materials.

Development of graphene nanoplatelet embedded polymer microcantilever for vapour phase explosive detection applications

International Nuclear Information System (INIS)

Ray, Prasenjit; Pandey, Swapnil; Ramgopal Rao, V.

2014-01-01

In this work, a graphene based strain sensor has been reported for explosive vapour detection applications by exploiting the piezoresistive property of graphene. Instead of silicon based cantilevers, a low cost polymeric micro-cantilever platform has been used to fabricate this strain sensor by embedding the graphene nanoplatelet layer inside the beam. The fabricated devices were characterized for their mechanical and electromechanical behaviour. This device shows a very high gauge factor which is around ∼144. Also the resonant frequency of these cantilevers is high enough such that the measurements are not affected by environmental noise. These devices have been used in this work for reliable detection of explosive vapours such as 2,4,6-Trinitrotoluene down to parts-per-billion concentrations in ambient conditions.

A new loss mechanism in graphene nanoresonators due to the synthetic electric fields caused by inherent out-of-plane membrane corrugations

International Nuclear Information System (INIS)

Firsova, N E; Firsov, Yu A

2012-01-01

For the first time the influence of out-of-plane deformations, which always exist in graphene, on the non-stationary processes is considered for the case of a monolayer graphene nanoresonator. A new loss mechanism for this device caused by dissipative intra-valley currents stipulated by synthetic electric fields is studied. These fields are generated by time-dependent gauge fields arising in a graphene membrane due to its intrinsic out-of-plane distortions and the influence of the external periodic electromotive force. The corresponding formula for the quality factor has a quantum mechanical origin and includes quantum mechanical parameters. This loss mechanism accounts for an essential part (about 40%) of losses in a graphene nanoresonator and it is specific just for graphene. The ways of minimization of this kind of dissipation (an increase in the quality factor of the electromechanical system) are discussed. It is explained why one can enhance the quality factor by correctly choosing a combination of strains (by strain engineering). In addition, it is shown that the quality factor can be increased by switching on a magnetic field perpendicular to the graphene membrane.

Heat conduction in graphene: experimental study and theoretical interpretation

International Nuclear Information System (INIS)

Ghosh, S; Nika, D L; Pokatilov, E P; Balandin, A A

2009-01-01

We review the results of our experimental investigation of heat conduction in suspended graphene and offer a theoretical interpretation of its extremely high thermal conductivity. The direct measurements of the thermal conductivity of graphene were performed using a non-contact optical technique and special calibration procedure with bulk graphite. The measured values were in the range of ∼3000-5300 W mK -1 near room temperature and depended on the lateral dimensions of graphene flakes. We explain the enhanced thermal conductivity of graphene as compared to that of bulk graphite basal planes by the two-dimensional nature of heat conduction in graphene over the whole range of phonon frequencies. Our calculations show that the intrinsic Umklapp-limited thermal conductivity of graphene grows with the increasing dimensions of graphene flakes and can exceed that of bulk graphite when the flake size is on the order of a few micrometers. The detailed theory, which includes the phonon-mode-dependent Gruneisen parameter and takes into account phonon scattering on graphene edges and point defects, gives numerical results that are in excellent agreement with the measurements for suspended graphene. Superior thermal properties of graphene are beneficial for all proposed graphene device applications.

Experimental Study on Characteristics of Grinded Graphene Nanofluids with Surfactants

Directory of Open Access Journals (Sweden)

HeonJin Seong

2018-06-01

Full Text Available In earlier studies, much research has focused on increasing the efficiency of heat exchanger fields. Therefore, in this study, graphene nanofluid was fabricated for use as a heat transfer medium for a heat exchanger. Graphene has excellent electrical conductivity, mechanical properties, and heat transfer properties. It is expected that the heat transfer efficiency will be improved by fabricating the nanofluid. However, graphene is prone to sedimentation, because of its cohesion due to van der Waals binding force. In this experiment, a nanofluid was fabricated with enhanced dispersibility by surfactant and the ball-milling process. The zeta potential, absorbance, and thermal conductivity of the nanofluid were measured. As a result, when using the ratio of 2:1 (graphene:sodium dodecyl sulfate (SDS, a higher thermal conductivity was obtained than in other conditions.

In situ observation of stress relaxation in epitaxial graphene

International Nuclear Information System (INIS)

N'Diaye, Alpha T; Coraux, Johann; Busse, Carsten; Michely, Thomas; Gastel, Raoul van; Poelsema, Bene; MartInez-Galera, Antonio J; Gomez-RodrIguez, Jose M; Hattab, Hichem; Wall, Dirk; Heringdorf, Frank-J Meyer zu; Hoegen, Michael Horn-von

2009-01-01

Upon cooling, branched line defects develop in epitaxial graphene grown at high temperature on Pt(111) and Ir(111). Using atomically resolved scanning tunneling microscopy, we demonstrate that these defects are wrinkles in the graphene layer, i.e. stripes of partially delaminated graphene. With low energy electron microscopy (LEEM), we investigate the wrinkling phenomenon in situ. Upon temperature cycling, we observe hysteresis in the appearance and disappearance of the wrinkles. Simultaneously with wrinkle formation a change in bright field imaging intensity of adjacent areas and a shift in the moire spot positions for micro diffraction of such areas takes place. The stress relieved by wrinkle formation results from the mismatch in thermal expansion coefficients of graphene and the substrate. A simple one-dimensional model taking into account the energies related to strain, delamination and bending of graphene is in qualitative agreement with our observations.

Multi-scale graphene patterns on arbitrary substrates via laser-assisted transfer-printing process

KAUST Repository

Park, J. B.

2012-01-01

A laser-assisted transfer-printing process is developed for multi-scale graphene patterns on arbitrary substrates using femtosecond laser scanning on a graphene/metal substrate and transfer techniques without using multi-step patterning processes. The short pulse nature of a femtosecond laser on a graphene/copper sheet enables fabrication of high-resolution graphene patterns. Thanks to the scale up, fast, direct writing, multi-scale with high resolution, and reliable process characteristics, it can be an alternative pathway to the multi-step photolithography methods for printing arbitrary graphene patterns on desired substrates. We also demonstrate transparent strain devices without expensive photomasks and multi-step patterning process. © 2012 American Institute of Physics.

Effect of e-beam irradiation on graphene layer grown by chemical vapor deposition

International Nuclear Information System (INIS)

Iqbal, M. Z.; Kumar Singh, Arun; Iqbal, M. W.; Seo, Sunae; Eom, Jonghwa

2012-01-01

We have grown graphene by chemical vapor deposition (CVD) and transferred it onto Si/SiO 2 substrates to make tens of micron scale devices for Raman spectroscopy study. The effect of electron beam (e-beam) irradiation of various doses (600 to 12 000 μC/cm 2 ) on CVD grown graphene has been examined by using Raman spectroscopy. It is found that the radiation exposures result in the appearance of the strong disorder D band attributed the damage to the lattice. The evolution of peak frequencies, intensities, and widths of the main Raman bands of CVD graphene is analyzed as a function of defect created by e-beam irradiation. Especially, the D and G peak evolution with increasing radiation dose follows the amorphization trajectory, which suggests transformation of graphene to the nanocrystalline and then to amorphous form. We have also estimated the strain induced by e-beam irradiation in CVD graphene. These results obtained for CVD graphene are in line with previous findings reported for the mechanically exfoliated graphene [D. Teweldebrhan and A. A. Balandin, Appl. Phys. Lett. 94, 013101 (2009)]. The results have important implications for CVD graphene characterization and device fabrication, which rely on the electron microscopy.

Looking behind the scenes: Raman spectroscopy of top-gated epitaxial graphene through the substrate

International Nuclear Information System (INIS)

Fromm, F; Wehrfritz, P; Seyller, Th; Hundhausen, M

2013-01-01

Raman spectroscopy is frequently used to study the properties of epitaxial graphene grown on silicon carbide (SiC). In this work, we present a confocal micro-Raman study of epitaxial graphene on SiC(0001) in top-down geometry, i.e. in a geometry where both the primary laser light beam as well as the back-scattered light is guided through the SiC substrate. Compared to the conventional top-up configuration, in which confocal micro-Raman spectra are measured from the air side, we observe a significant intensity enhancement in top-down configuration, indicating that most of the Raman-scattered light is emitted into the SiC substrate. The intensity enhancement is explained in terms of dipole radiation at a dielectric surface. The new technique opens the possibility to probe graphene layers in devices where the graphene layer is covered by non-transparent materials. We demonstrate this by measuring gate-modulated Raman spectra of a top-gated epitaxial graphene field effect device. Moreover, we show that these measurements enable us to disentangle the effects of strain and charge on the positions of the prominent Raman lines in epitaxial graphene on SiC. (paper)

Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators

Directory of Open Access Journals (Sweden)

wang K.-L.

2012-03-01

Full Text Available We report novel properties derived from scanning tunnelling spectroscopic (STS studies of Dirac fermions in graphene and the surface state (SS of a strong topological insulator (STI, Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD, strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by the alternating anti-localization and localization spectra associated with the zero-mode of two sublattices while global time-reversal symmetry is preserved under the presence of pseudo-magnetic fields. For Bi2Se3 epitaxial films grown on Si(111 by molecular beam epitaxy (MBE, spatially localized unitary impurity resonances with sensitive dependence on the energy difference between the Fermi level and the Dirac point are observed for samples thicker than 6 quintuple layers (QL. These findings are characteristic of the SS of a STI and are direct manifestation of strong topological protection against impurities. For samples thinner than 6-QL, STS studies reveal the openup of an energy gap in the SS due to overlaps of wave functions between the surface and interface layers. Additionally, spin-preserving quasiparticle interference wave-vectors are observed, which are consistent with the Rashba-like spin-orbit splitting.

Structural and electronic transformation in low-angle twisted bilayer graphene

Science.gov (United States)

Gargiulo, Fernando; Yazyev, Oleg V.

2018-01-01

Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moiré pattern inherent to twisted bilayer graphene taking place at twist angles θ below a crossover angle θ\\star=1.2\\circ . The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network.

First-principles study of Cu adsorption on vacancy-defected/Au-doped graphene

Science.gov (United States)

Liu, Yang; An, Libao; Gong, Liang

2018-04-01

To enhance the interaction between Cu and graphene in graphene reinforced Cu matrix composites, the first principles calculation was carried out to study the adsorption of Cu atoms on graphene. P-type doping and n-type doping were formed, respectively, on vacancy-defected and Au-doped graphene based on band structure analysis, and this was verified by subsequent investigation on density of states. A computation on charge transfer confirmed that p-type doping could promote the electron transport between Cu and graphene, while n-type doping would prevent it. In addition, adsorption energy and Mulliken population analysis revealed that both vacancy defects and Au doping could improve the stability of the Cu-graphene system. The research conducted in this paper provides useful guidance for the preparation of Cu/graphene composites.

Toward intrinsic graphene surfaces: a systematic study on thermal annealing and wet-chemical treatment of SiO2-supported graphene devices.

Science.gov (United States)

Cheng, Zengguang; Zhou, Qiaoyu; Wang, Chenxuan; Li, Qiang; Wang, Chen; Fang, Ying

2011-02-09

By combining atomic force microscopy and trans-port measurements, we systematically investigated effects of thermal annealing on surface morphologies and electrical properties of single-layer graphene devices fabricated by electron beam lithography on silicon oxide (SiO(2)) substrates. Thermal treatment above 300 °C in vacuum was required to effectively remove resist residues on graphene surfaces. However, annealing at high temperature was found to concomitantly bring graphene in close contact with SiO(2) substrates and induce increased coupling between them, which leads to heavy hole doping and severe degradation of mobilities in graphene devices. To address this problem, a wet-chemical approach employing chloroform was developed in our study, which was shown to enable both intrinsic surfaces and enhanced electrical properties of graphene devices. Upon the recovery of intrinsic surfaces of graphene, the adsorption and assisted fibrillation of amyloid β-peptide (Aβ1-42) on graphene were electrically measured in real time.

First-principles study of the alkali earth metal atoms adsorption on graphene

International Nuclear Information System (INIS)

Sun, Minglei; Tang, Wencheng; Ren, Qingqiang; Wang, Sake; JinYu; Du, Yanhui; Zhang, Yajun

2015-01-01

Graphical abstract: - Highlights: • The adsorption of Be and Mg adatoms on graphene is physisorption. • Ca, Sr, and Ba adatoms bond ionically to graphene and the most stable adsorption site for them is hollow site. • The zero band gap semiconductor graphene becomes metallic and magnetic after the adsorption of Ca, Sr, and Ba adatoms. - Abstract: Geometries, electronic structures, and magnetic properties for alkali earth metal atoms absorbed graphene have been studied by first-principle calculations. For Be and Mg atoms, the interactions between the adatom and graphene are weak van der Waals interactions. In comparison, Ca, Sr and Ba atoms adsorption on graphene exhibits strong ionic bonding with graphene. We found that these atoms bond to graphene at the hollow site with a significant binding energy and large electron transfer. It is intriguing that these adatoms may induce important changes in both the electronic and magnetic properties of graphene. Semimetal graphene becomes metallic and magnetic due to n-type doping. Detailed analysis shows that the s orbitals of these adatoms should be responsible for the arising of the magnetic moment. We believe that our results are suitable for experimental exploration and useful for graphene-based nanoelectronic and data storage.

First-principles study of the alkali earth metal atoms adsorption on graphene

Energy Technology Data Exchange (ETDEWEB)

Sun, Minglei [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Tang, Wencheng, E-mail: 101000185@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Ren, Qingqiang [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan (China); Wang, Sake [Department of Physics, Southeast University, Nanjing 210096, Jiangsu (China); JinYu [School of Materials Science and Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189, Jiangsu (China); Du, Yanhui [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Zhang, Yajun [Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, Zhejiang (China)

2015-11-30

Graphical abstract: - Highlights: • The adsorption of Be and Mg adatoms on graphene is physisorption. • Ca, Sr, and Ba adatoms bond ionically to graphene and the most stable adsorption site for them is hollow site. • The zero band gap semiconductor graphene becomes metallic and magnetic after the adsorption of Ca, Sr, and Ba adatoms. - Abstract: Geometries, electronic structures, and magnetic properties for alkali earth metal atoms absorbed graphene have been studied by first-principle calculations. For Be and Mg atoms, the interactions between the adatom and graphene are weak van der Waals interactions. In comparison, Ca, Sr and Ba atoms adsorption on graphene exhibits strong ionic bonding with graphene. We found that these atoms bond to graphene at the hollow site with a significant binding energy and large electron transfer. It is intriguing that these adatoms may induce important changes in both the electronic and magnetic properties of graphene. Semimetal graphene becomes metallic and magnetic due to n-type doping. Detailed analysis shows that the s orbitals of these adatoms should be responsible for the arising of the magnetic moment. We believe that our results are suitable for experimental exploration and useful for graphene-based nanoelectronic and data storage.

Terahertz carrier dynamics in graphene and graphene nanostructures

DEFF Research Database (Denmark)

Jensen, Søren A.; Turchinovich, Dmitry; Tielrooij, Klaas Jan

2014-01-01

Photoexcited charge carriers in 2D graphene and in 1D graphene nanostructures were studied with optical pump-THz probe spectroscopy. We find efficient hot-carrier multiplication in 2D graphene, and predominantly free carrier early time response in 1D nanostructures. © 2014 OSA....

Porous graphene for high capacity lithium ion battery anode material

Energy Technology Data Exchange (ETDEWEB)

Wang, Yusheng, E-mail: xxwysheng@163.com [College of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Zhang, Qiaoli; Jia, Min; Yang, Dapeng [College of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); Wang, Jianjun; Li, Meng [College of Science, Zhongyuan University of Technology, Zhengzhou 450007 (China); Zhang, Jing [College of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); Sun, Qiang [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Jia, Yu, E-mail: jiayu@zzu.edu.cn [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China)

2016-02-15

Graphical abstract: - Highlights: • Porous graphene sheet as Li storage media. • Excellent mobility both along in-plane and out-plane directions. • The interactions can be easily tuned by an applied strain. - Abstract: Based on density functional theory calculations, we studied the Li dispersed on porous graphene (PG) for its application as Li ion battery anode material. The hybridization of Li atoms and the carbon atoms enhanced the interaction between Li atoms and the PG. With holes of specific size, the PG can provide excellent mobility with moderate barriers of 0.37–0.39 eV. The highest Li storage composite can be LiC{sub 0.75}H{sub 0.38} which corresponds to a specific capacity of 2857.7 mA h/g. Both specific capacity and binding energy are significantly larger than the corresponding value of graphite, this makes PG a promising candidate for the anode material in battery applications. The interactions between the Li atoms and PG can be easily tuned by an applied strain. Under biaxial strain of 16%, the binding energy of Li to PG is increased by 17% compared to its unstrained state.

Metal-doped graphene layers composed with boron nitride-graphene as an insulator: a nano-capacitor.

Science.gov (United States)

Monajjemi, Majid

2014-11-01

A model of a nanoscale dielectric capacitor composed of a few dopants has been investigated in this study. This capacitor includes metallic graphene layers which are separated by an insulating medium containing a few h-BN layers. It has been observed that the elements from group IIIA of the periodic table are more suitable as dopants for hetero-structures of the {metallic graphene/hBN/metallic graphene} capacitors compared to those from groups IA or IIA. In this study, we have specifically focused on the dielectric properties of different graphene/h-BN/graphene including their hetero-structure counterparts, i.e., Boron-graphene/h-BN/Boron-graphene, Al-graphene/h-BN/Al-graphene, Mg-graphene/h-BN/Mg-graphene, and Be-graphene/h-BN/Be-graphene stacks for monolayer form of dielectrics. Moreover, we studied the multi dielectric properties of different (h-BN)n/graphene hetero-structures of Boron-graphene/(h-BN)n/Boron-graphene.

Promising applications of graphene and graphene-based nanostructures

Science.gov (United States)

Nguyen, Bich Ha; Hieu Nguyen, Van

2016-06-01

The present article is a review of research works on promising applications of graphene and graphene-based nanostructures. It contains five main scientific subjects. The first one is the research on graphene-based transparent and flexible conductive films for displays and electrodes: efficient method ensuring uniform and controllable deposition of reduced graphene oxide thin films over large areas, large-scale pattern growth of graphene films for stretchble transparent electrodes, utilization of graphene-based transparent conducting films and graphene oxide-based ones in many photonic and optoelectronic devices and equipments such as the window electrodes of inorganic, organic and dye-sensitized solar cells, organic light-emitting diodes, light-emitting electrochemical cells, touch screens, flexible smart windows, graphene-based saturated absorbers in laser cavities for ultrafast generations, graphene-based flexible, transparent heaters in automobile defogging/deicing systems, heatable smart windows, graphene electrodes for high-performance organic field-effect transistors, flexible and transparent acoustic actuators and nanogenerators etc. The second scientific subject is the research on conductive inks for printed electronics to revolutionize the electronic industry by producing cost-effective electronic circuits and sensors in very large quantities: preparing high mobility printable semiconductors, low sintering temperature conducting inks, graphene-based ink by liquid phase exfoliation of graphite in organic solutions, and developing inkjet printing technique for mass production of high-quality graphene patterns with high resolution and for fabricating a variety of good-performance electronic devices, including transparent conductors, embedded resistors, thin-film transistors and micro supercapacitors. The third scientific subject is the research on graphene-based separation membranes: molecular dynamics simulation study on the mechanisms of the transport of

Non-monotonic piezoresistive behaviour of graphene nanoplatelet (GNP-polymer composite flexible films prepared by solvent casting

Directory of Open Access Journals (Sweden)

S. Makireddi

2017-07-01

Full Text Available Graphene-polymer nanocomposite films show good piezoresistive behaviour and it is reported that the sensitivity increases either with the increased sheet resistance or decreased number density of the graphene fillers. A little is known about this behaviour near the percolation region. In this study, graphene nanoplatelet (GNP/poly (methyl methacrylate (PMMA flexible films are fabricated via solution casting process at varying weight percent of GNP. Electrical and piezoresistive behaviour of these films is studied as a function of GNP concentration. Piezoresistive strain sensitivity of the films is measured by affixing the film to an aluminium specimen which is subjected to monotonic uniaxial tensile load. The change in resistance of the film with strain is monitored using a four probe. An electrical percolation threshold at 3 weight percent of GNP is observed. We report non-monotonic piezoresistive behaviour of these films as a function GNP concentration. We observe an increase in gauge factor (GF with unstrained resistance of the films up to a critical resistance corresponding to percolation threshold. Beyond this limit the GF decreases with unstrained resistance.

Field Emission of Wet Transferred Suspended Graphene Fabricated on Interdigitated Electrodes.

Science.gov (United States)

Xu, Ji; Wang, Qilong; Tao, Zhi; Qi, Zhiyang; Zhai, Yusheng; Wu, Shengqi; Zhang, Xiaobing; Lei, Wei

2016-02-10

Suspended graphene (SG) membranes could enable strain-engineering of ballistic Dirac fermion transport and eliminate the extrinsic bulk disorder by annealing. When freely suspended without contact to any substrates, graphene could be considered as the ultimate two-dimensional (2D) morphology, leading to special field characteristics with the 2D geometrical effect and effectively utilized as an outstanding structure to explore the fundamental electronic or optoelectronic mechanism. In this paper, we report field emission characterization on an individual suspended few-layer graphene. A controllable wet transfer method is used to obtain the continuous and suspended graphene membrane on interdigitated gold electrodes. This suspended structure displays an overall field emission from the entirely surface, except for the variation in the emitting positions, acquiring a better enhancement than the exfoliated graphene on the conventional flat substrate. We also observe the transition process from space charge flow at low bias to the Fowler-Nordheim theory at high current emission regime. It could enable theoretical and experimental investigation of the typical electron emission properties of the 2D regime. Numerical simulations are also carried out to study the electrical properties of the suspended structure. Further improvement on the fabrication would realize low disorder, high quality, and large-scale suspended graphene devices.

Photoluminescence study in diaminobenzene functionalized graphene oxide

Energy Technology Data Exchange (ETDEWEB)

Gupta, Abhisek, E-mail: guptaabhisek017@gmail.com, E-mail: cnssks@iacs.res.in; Saha, Shyamal K., E-mail: guptaabhisek017@gmail.com, E-mail: cnssks@iacs.res.in [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

2014-10-15

Being an excellent electronic material graphene is a very poor candidate for optoelectronic applications. One of the major strategies to develop the optical property in GO is the functionalization of graphene oxide (GO). In the present work GO sheets are functionalized by o-phenylenediamine to achieve diaminobenzene functionalized GO composite (DAB-GO). Formation of DAB-GO composite is further characterized by FTIR, UV, Raman studies. Excellent photoluminescence is observed in DAB-GO composite via passivation of the surface reactive sites by ring-opening amination of epoxides of GO.

Small gold clusters on graphene, their mobility and clustering: a DFT study

International Nuclear Information System (INIS)

Amft, Martin; Sanyal, Biplab; Eriksson, Olle; Skorodumova, Natalia V

2011-01-01

Motivated by the experimentally observed high mobility of gold atoms on graphene and their tendency to form nanometer-sized clusters, we present a density functional theory study of the ground state structures of small gold clusters on graphene, their mobility and clustering. Our detailed analysis of the electronic structures identifies the opportunity to form strong gold-gold bonds and the graphene-mediated interaction of the pre-adsorbed fragments as the driving forces behind gold's tendency to aggregate on graphene. While clusters containing up to three gold atoms have one unambiguous ground state structure, both gas phase isomers of a cluster with four gold atoms can be found on graphene. In the gas phase the diamond-shaped Au 4 D cluster is the ground state structure, whereas the Y-shaped Au 4 Y becomes the actual ground state when adsorbed on graphene. As we show, both clusters can be produced on graphene by two distinct clustering processes. We also studied in detail the stepwise formation of a gold dimer out of two pre-adsorbed adatoms, as well as the formation of Au 3 . All reactions are exothermic and no further activation barriers, apart from the diffusion barriers, were found. The diffusion barriers of all studied clusters range from 4 to 36 meV only, and are substantially exceeded by the adsorption energies of - 0.1 to - 0.59 eV. This explains the high mobility of Au 1-4 on graphene along the C-C bonds.

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...

Structures of Pt clusters on graphene doped with nitrogen, boron, and silicon: a theoretical study

Institute of Scientific and Technical Information of China (English)

Dai Xian-Qi; Tang Ya-Nan; Dai Ya-Wei; Li Yan-Hui; Zhao Jian-Hua; Zhao Bao; Yang Zong-Xian

2011-01-01

The structures of Pt clusters on nitrogen-, boron-, silicon- doped graphenes are theoretically studied using densityfunctional theory. These dopants (nitrogen, boron and silicon) each do not induce a local curvature in the graphene and the doped graphenes all retain their planar form. The formation energy of the silicon-graphene system is lower than those of the nitrogen-, boron-doped graphenes, indicating that the silicon atom is easier to incorporate into the graphene.All the substitutional impurities enhance the interaction between the Pt atom and the graphene. The adsorption energy of a Pt adsorbed on the silicon-doped graphene is much higher than those on the nitrogen- and boron-doped graphenes.The doped silicon atom can provide more charges to enhance the Pt-graphene interaction and the formation of Pt clusters each with a large size. The stable structures of Pt clusters on the doped-graphenes are dimeric, triangle and tetrahedron with the increase of the Pt coverage. Of all the studied structures, the tetrahedron is the most stable cluster which has the least influence on the planar surface of doped-graphene.

Piezoelectric Phenomenon of Fullerene-Graphene Bonded Structure

Directory of Open Access Journals (Sweden)

Lu Aijiang

2014-01-01

Full Text Available The adsorption of a C60 molecule on the graphene revealed the contribution of a conductor-semiconductor transition, based on a theoretical calculation. A stress or a strain was predicted as a possible reason to tune the transition backwards.

Three-dimensional graphene-polypyrrole hybrid electrochemical actuator

Science.gov (United States)

Liu, Jia; Wang, Zhi; Zhao, Yang; Cheng, Huhu; Hu, Chuangang; Jiang, Lan; Qu, Liangti

2012-11-01

The advancement of mechanical actuators benefits from the development of new structural materials with prominent properties. A novel three-dimensional (3D) hydrothermally converted graphene and polypyrrole (G-PPy) hybrid electrochemical actuator is presented, which is prepared via a convenient hydrothermal process, followed by in situ electropolymerization of pyrrole. The 3D pore-interconnected G-PPy pillar exhibits strong actuation responses superior to pure graphene and PPy film. In response to the low potentials of +/-0.8 V, the saturated strain of 3D G-PPy pillar can reach a record of 2.5%, which is more than 10 times higher than that of carbon nanotube film and about 3 times that of unitary graphene film under an applied potential of +/-1.2 V. Also, the 3D G-PPy actuator exhibits high actuation durability with high operating load as demonstrated by an 11 day continuous measurement. Finally, a proof-of-concept application of 3D G-PPy as smart filler for on/off switch is also demonstrated, which indicates the great potential of the 3D G-PPy structure developed in this study for advanced actuator systems.The advancement of mechanical actuators benefits from the development of new structural materials with prominent properties. A novel three-dimensional (3D) hydrothermally converted graphene and polypyrrole (G-PPy) hybrid electrochemical actuator is presented, which is prepared via a convenient hydrothermal process, followed by in situ electropolymerization of pyrrole. The 3D pore-interconnected G-PPy pillar exhibits strong actuation responses superior to pure graphene and PPy film. In response to the low potentials of +/-0.8 V, the saturated strain of 3D G-PPy pillar can reach a record of 2.5%, which is more than 10 times higher than that of carbon nanotube film and about 3 times that of unitary graphene film under an applied potential of +/-1.2 V. Also, the 3D G-PPy actuator exhibits high actuation durability with high operating load as demonstrated by an 11 day

Superlubric sliding of graphene nanoflakes on graphene.

Science.gov (United States)

Feng, Xiaofeng; Kwon, Sangku; Park, Jeong Young; Salmeron, Miquel

2013-02-26

The lubricating properties of graphite and graphene have been intensely studied by sliding a frictional force microscope tip against them to understand the origin of the observed low friction. In contrast, the relative motion of free graphene layers remains poorly understood. Here we report a study of the sliding behavior of graphene nanoflakes (GNFs) on a graphene surface. Using scanning tunneling microscopy, we found that the GNFs show facile translational and rotational motions between commensurate initial and final states at temperatures as low as 5 K. The motion is initiated by a tip-induced transition of the flakes from a commensurate to an incommensurate registry with the underlying graphene layer (the superlubric state), followed by rapid sliding until another commensurate position is reached. Counterintuitively, the average sliding distance of the flakes is larger at 5 K than at 77 K, indicating that thermal fluctuations are likely to trigger their transitions from superlubric back to commensurate ground states.

A molecular dynamics study on the interaction between epoxy and functionalized graphene sheets

DEFF Research Database (Denmark)

Melro, Liliana Sofia S. F. P.; Pyrz, Ryszard; Jensen, Lars Rosgaard

2016-01-01

The interaction between graphene and epoxy resin was studied using molecular dynamics simulations. The interfacial shear strength and pull out force were calculated for functionalised graphene layers (carboxyl, carbonyl, and hydroxyl) and epoxy composites interfaces. The influence of functional...... groups, as well as their distribution and coverage density on the graphene sheets were also analysed through the determination of the Young's modulus. Functionalisation proved to be detrimental to the mechanical properties, nonetheless according to interfacial studies the interaction between graphene...

Intrinsic structure and friction properties of graphene and graphene

Indian Academy of Sciences (India)

In this paper, atomic structure of single-layered graphene oxide (GO) and chemically reduced graphene oxide (CRGO) nanosheets was investigated using atomic force microscopy and scanning tunnelingmicroscopy (AFM and STM). Furthermore, friction properties of the graphene and GO nanosheets were studied by ...

Shear deformation-induced anisotropic thermal conductivity of graphene.

Science.gov (United States)

Cui, Liu; Shi, Sanqiang; Wei, Gaosheng; Du, Xiaoze

2018-01-03

Graphene-based materials exhibit intriguing phononic and thermal properties. In this paper, we have investigated the heat conductance in graphene sheets under shear-strain-induced wrinkling deformation, using equilibrium molecular dynamics simulations. A significant orientation dependence of the thermal conductivity of graphene wrinkles (GWs) is observed. The directional dependence of the thermal conductivity of GWs stems from the anisotropy of phonon group velocities as revealed by the G-band broadening of the phonon density of states (DOS), the anisotropy of thermal resistance as evidenced by the G-band peak mismatch of the phonon DOS, and the anisotropy of phonon relaxation times as a direct result of the double-exponential-fitting of the heat current autocorrelation function. By analyzing the relative contributions of different lattice vibrations to the heat flux, we have shown that the contributions of different lattice vibrations to the heat flux of GWs are sensitive to the heat flux direction, which further indicates the orientation-dependent thermal conductivity of GWs. Moreover, we have found that, in the strain range of 0-0.1, the anisotropy ratio of GWs increases monotonously with increasing shear strain. This is induced by the change in the number of wrinkles, which is more influential in the direction perpendicular to the wrinkle texture. The findings elucidated here emphasize the utility of wrinkle engineering for manipulation of nanoscale heat transport, which offers opportunities for the development of thermal channeling devices.

Ultralow friction of ink-jet printed graphene flakes.

Science.gov (United States)

Buzio, R; Gerbi, A; Uttiya, S; Bernini, C; Del Rio Castillo, A E; Palazon, F; Siri, A S; Pellegrini, V; Pellegrino, L; Bonaccorso, F

2017-06-08

We report the frictional response of few-layer graphene (FLG) flakes obtained by the liquid phase exfoliation (LPE) of pristine graphite. To this end, we inkjet print FLG on bare and hexamethyldisilazane-terminated SiO 2 substrates, producing micrometric patterns with nanoscopic roughness that are investigated by atomic force microscopy. Normal force spectroscopy and atomically-resolved morphologies indicate reduced surface contamination by solvents after a vacuum annealing process. Notably, the printed FLG flakes show ultralow friction comparable to that of micromechanically exfoliated graphene flakes. Lubricity is retained on flakes with a lateral size of a few tens of nanometres, and with a thickness as small as ∼2 nm, confirming the high crystalline quality and low defects density in the FLG basal plane. Surface exposed step edges exhibit the highest friction values, representing the preferential sites for the origin of the secondary dissipative processes related to edge straining, wear or lateral displacement of the flakes. Our work demonstrates that LPE enables fundamental studies on graphene friction to the single-flake level. The capability to deliver ultralow-friction-graphene over technologically relevant substrates, using a scalable production route and a high-throughput, large-area printing technique, may also open up new opportunities in the lubrication of micro- and nano-electromechanical systems.

Graphene for amino acid biosensing: Theoretical study of the electronic transport

Science.gov (United States)

Rodríguez, S. J.; Makinistian, L.; Albanesi, E. A.

2017-10-01

The study of biosensors based on graphene has increased in the last years, the combination of excellent electrical properties and low noise makes graphene a material for next generation electronic devices. This work discusses the application of a graphene-based biosensor for the detection of amino acids histidine (His), alanine (Ala), aspartic acid (Asp), and tyrosine (Tyr). First, we present the results of modeling from first principles the adsorption of the four amino acids on a graphene sheet, we calculate adsorption energy, substrate-adsorbate distance, equilibrium geometrical configurations (upon relaxation) and densities of states (DOS) for each biomolecule adsorbed. Furthermore, in order to evaluate the effects of amino acid adsorption on the electronic transport of graphene, we modeled a device using first-principles calculations with a combination of Density Functional Theory (DFT) and Nonequilibrium Greens Functions (NEGF). We provide with a detailed discussion in terms of transmission, current-voltage curves, and charge transfer. We found evidence of differences in the electronic transport through the graphene sheet due to amino acid adsorption, reinforcing the possibility of graphene-based sensors for amino acid sequencing of proteins.

Electromechanics of graphene spirals

Energy Technology Data Exchange (ETDEWEB)

Korhonen, Topi; Koskinen, Pekka, E-mail: pekka.koskinen@iki.fi [NanoScience Center, Department of Physics, University of Jyväskylä, 40014 Jyväskylä (Finland)

2014-12-15

Among the most fascinating nanostructure morphologies are spirals, hybrids of somewhat obscure topology and dimensionality with technologically attractive properties. Here, we investigate mechanical and electromechanical properties of graphene spirals upon elongation by using density-functional tight-binding, continuum elasticity theory, and classical force field molecular dynamics. It turns out that electronic properties are governed by interlayer interactions as opposed to strain effects. The structural behavior is governed by van der Waals interaction: in its absence spirals unfold with equidistant layer spacings, ripple formation at spiral perimeter, and steadily increasing axial force; in its presence, on the contrary, spirals unfold via smooth local peeling, complex geometries, and nearly constant axial force. These electromechanical trends ought to provide useful guidelines not only for additional theoretical investigations but also for forthcoming experiments on graphene spirals.

Chirality-dependent anisotropic elastic properties of a monolayer graphene nanosheet.

Science.gov (United States)

Guo, Jian-Gang; Zhou, Li-Jun; Kang, Yi-Lan

2012-04-01

An analytical approach is presented to predict the elastic properties of a monolayer graphene nanosheet based on interatomic potential energy and continuum mechanics. The elastic extension and torsional springs are utilized to simulate the stretching and angle variation of carbon-carbon bond, respectively. The constitutive equation of the graphene nanosheet is derived by using the strain energy density, and the analytical formulations for nonzero elastic constants are obtained. The in-plane elastic properties of the monolayer graphene nanosheet are proved to be anisotropic. In addition, Young's moduli, Poisson's ratios and shear modulus of the monolayer graphene nanosheet are calculated according to the force constants derived from Morse potential and AMBER force field, respectively, and they were proved to be chirality-dependent. The comparison with experimental results shows a very agreement.

Monitoring Deformation in Graphene Through Hyperspectral Synchrotron Spectroscopy to Inform Fabrication

Energy Technology Data Exchange (ETDEWEB)

Winter, Allen Douglas [School; Rojas, Wudmir Y. [School; Williams, Adrienne D. [Materials; Kim, Steve S. [Materials; Ouchen, Fahima [Materials; Fischer, Daniel A. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States; Weiland, Conan [Synchrotron Research Inc., Melbourne, Florida 32901, United States; Principe, Edward [Synchrotron Research Inc., Melbourne, Florida 32901, United States; Banerjee, Sarbajit [Department; amp,M University, College Station, Texas 77840, United States; Huynh, Chuong [Carl Zeiss Microscopy, LLC, One Corporation Way, Peabody, Massachusetts 01960, United States; Naik, Rajesh R. [Materials; Liu, Yijin [Stanford; Mehta, Apurva [Stanford; Grote, James [Materials; Prendergast, David [Molecular; Campo, Eva M. [School; Department

2017-07-13

The promise from graphene to produce devices with high mobilities and detectors with fast response times is truncated in practice by strain and deformation originating during growth and subsequent processing. This work describes effects from graphene growth, multiple layer transfer, and substrate termination on out of plane deformation, critical to device performance. Synchrotron spectroscopy data was acquired with a state-of-the-art hyperspectral large-area detector to describe growth and processing with molecular sensitivity at wafer length scales. A study of methodologies used in data analysis discouraged dichroic ratio approaches in favor of orbital vector approximations and data mining algorithms. Orbital vector methods provide a physical insight into mobility-detrimental rippling by identifying ripple frequency as main actor, rather than intensity; which was confirmed by data mining algorithms, and in good agreement with electron scattering theories of corrugation in graphene. This work paves the way to efficient information from mechanical properties in graphene in a high throughput mode throughout growth and processing in a materials by design approach.

Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

KAUST Repository

Nagaraju, Doddahalli H.

2014-12-01

Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl2. X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells. © 2014 Elsevier Ltd.

``The Princess and the Pea'' at the Nanoscale: Wrinkling and Delamination of Graphene on Nanoparticles

Science.gov (United States)

Yamamoto, Mahito; Pierre-Louis, Olivier; Huang, Jia; Fuhrer, Michael S.; Einstein, Theodore L.; Cullen, William G.

2012-10-01

Thin membranes exhibit complex responses to external forces or geometrical constraints. A familiar example is the wrinkling, exhibited by human skin, plant leaves, and fabrics, that results from the relative ease of bending versus stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest known membrane, deposited on a silica substrate decorated with silica nanoparticles. At small nanoparticle density, monolayer graphene adheres to the substrate, detached only in small regions around the nanoparticles. With increasing nanoparticle density, we observe the formation of wrinkles which connect nanoparticles. Above a critical nanoparticle density, the wrinkles form a percolating network through the sample. As the graphene membrane is made thicker, global delamination from the substrate is observed. The observations can be well understood within a continuum-elastic model and have important implications for strain-engineering the electronic properties of graphene.

Raman Spectroscopy Study of Annealing-Induced Effects on Graphene Prepared by Micromechanical Exfoliation

International Nuclear Information System (INIS)

Song, Ji Eun; Ko, Taeg Yeoung; Ryu, Sun Min

2010-01-01

Raman spectroscopy was combined with AFM to investigate the effects of thermal annealing on the graphene samples prepared by the widely used micromechanical exfoliation method. Following annealing cycles, adhesive residues were shown to contaminate graphene sheets with thin molecular layers in their close vicinity causing several new intense Raman bands. Detailed investigation shows that the Raman scattering is very strong and may be enhanced by the interaction with graphene. Although the current study does not pinpoint detailed origins for the new Raman bands, the presented results stress that graphene prepared by the above method may require extra cautions when treated with heat or possibly solvents. Since its isolation from graphite, graphene has drawn a lot of experimental and theoretical research. These efforts have been mostly in pursuit of various applications such as electronics, sensors, stretchable transparent electrodes, and various composite materials. To accomplish such graphene-based applications, understanding chemical interactions of this new material with environments during various processing treatments will become more important. Since thermal annealing is widely used in various research of graphene for varying purposes such as cleaning, nanostructuring, reactions, etc., understanding annealing-induced effects is prerequisite to many fundamental studies of graphene. In this regard, it is to be noted that there has been a controversy on the cause of the annealing-induced hole doping in graphene

A DFT study of Cu nanoparticles adsorbed on defective graphene

International Nuclear Information System (INIS)

García-Rodríguez, D.E.; Mendoza-Huizar, L.H.; Díaz, C.

2017-01-01

Highlights: • Cu_n supported on graphene may be a promising electrode material for DBFC's cells. • Cu_n/graphene interaction is rather local and size independent. • Cu_1_3 anchors strongly to defects in graphene, while keeping its gas-phase properties. - Abstract: Metal nanoparticles adsorbed on graphene are systems of interest for processes relative to catalytic reactions and alternative energy production. Graphene decorated with Cu-nanoparticles, in particular, could be a good alternative material for electrodes in direct borohydride fuel cells. However our knowledge of this system is still very limited. Based on density functional theory, we have analyzed the interaction of Cu_n nanoparticles (n = 4, 5, 6, 7, 13) with pristine and defective-graphene. We have considered two types of defects, a single vacancy (SV), and an extended lineal structural defect (ELSD), formed by heptagon-pentagon pairs. Our analysis has revealed the covalent character of the Cu_n-graphene interaction for pristine- and ELSD-graphene, and a more ionic-like interaction for SV-graphene. Furthermore, our analysis shows that the interaction between the nanoparticles and the graphene is rather local, i.e., only the nanoparticle atoms close to the contact region are involved in the interaction, being the electronic contact region much higher for defective-graphene than for pristine-graphene. Thus, the higher the particle the lower its average electronic and structural distortion.

Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

Energy Technology Data Exchange (ETDEWEB)

Nagaraju, D.H., E-mail: dhnagu@gmail.com [Department of Mechanical Engineering, 117 576 (Singapore); Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 (Saudi Arabia); Devaraj, S. [Department of Mechanical Engineering, 117 576 (Singapore); School of Chemical and Biotechnology, SASTRA University, Thanjavur, 613 401 (India); Balaya, P., E-mail: mpepb@nus.edu.sg [Department of Mechanical Engineering, 117 576 (Singapore); Engineering Science Program, National University of Singapore, 117 576 (Singapore)

2014-12-15

Highlights: • Palladium nanoparticles decorated graphene is synthesized in a single step. • Electro-catalytic activity of Gra/Pd toward alcohol oxidation is evaluated. • 1:1 Gra/Pd exhibits good electro-catalytic activity and efficient electron transfer. - Abstract: Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd{sup 2+} ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl{sub 2}. X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells.

Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

International Nuclear Information System (INIS)

Nagaraju, D.H.; Devaraj, S.; Balaya, P.

2014-01-01

Highlights: • Palladium nanoparticles decorated graphene is synthesized in a single step. • Electro-catalytic activity of Gra/Pd toward alcohol oxidation is evaluated. • 1:1 Gra/Pd exhibits good electro-catalytic activity and efficient electron transfer. - Abstract: Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd 2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl 2 . X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells

Enhance wastewater biological treatment through the bacteria induced graphene oxide hydrogel.

Science.gov (United States)

Shen, Liang; Jin, Ziheng; Wang, Dian; Wang, Yuanpeng; Lu, Yinghua

2018-01-01

The interaction between bacteria and graphene-family materials like pristine graphene, graphene oxide (GO) and reduced graphene oxide (rGO) is such an elusive issue that its implication in environmental biotechnology is unclear. Herein, two kinds of self-assembled bio-rGO-hydrogels (BGHs) were prepared by cultivating specific Shewanella sp. strains with GO solution for the first time. The microscopic examination by SEM, TEM and CLSM indicated a porous 3D structure of BGHs, in which live bacteria firmly anchored and extracellular polymeric substances (EPS) abundantly distributed. Spectra of XRD, FTIR, XPS and Raman further proved that GO was reduced to rGO by bacteria along with the gelation process, which suggests a potential green technique to produce graphene. Based on the characterization results, four mechanisms for the BGH formation were proposed, i.e., stacking, bridging, rolling and cross-linking of rGO sheets, through the synergistic effect of activities and EPS from special bacteria. More importantly, the BGHs obtained in this study were found able to achieve unique cleanup performance that the counterpart free bacteria could not fulfill, as exemplified in Congo red decolorization and Cr(VI) bioreduction. These findings therefore enlighten a prospective application of graphene materials for the biological treatment of wastewaters in the future. Copyright © 2017 Elsevier Ltd. All rights reserved.

First-principles study of the interaction and charge transfer between graphene and metals

NARCIS (Netherlands)

Khomyakov, Petr; Giovannetti, G.; Rusu, P.C.; Brocks, G.; van den Brink, J.; Kelly, Paul J.

2009-01-01

Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au,

Strain Assessment in Graphene Through the Raman 2D′ Mode

Czech Academy of Sciences Publication Activity Database

del Corro, Elena; Kavan, Ladislav; Kalbáč, Martin; Frank, Otakar

2015-01-01

Roč. 119, č. 45 (2015), s. 25651-25656 ISSN 1932-7447 R&D Projects: GA ČR GA14-15357S; GA MŠk LL1301 Institutional support: RVO:61388955 Keywords : Charge transfer doping * graphene * Charge transfer Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.509, year: 2015

A DFT study on the effect of supporting titania on silica graphene epoxy graphene and carbon nanotubes - Interfacial properties and optical response

CSIR Research Space (South Africa)

Kiarii, EM

2017-08-01

Full Text Available A first principles study of the Titania is done as used in photo-catalysis to generate charge carries. Models of titania, silica, graphene, epoxy graphene monoxide, single wall Carbon nanotubes and their respective layer were studied in order...

A systematic study of atmospheric pressure chemical vapor deposition growth of large-area monolayer graphene.

Science.gov (United States)

Liu, Lixin; Zhou, Hailong; Cheng, Rui; Chen, Yu; Lin, Yung-Chen; Qu, Yongquan; Bai, Jingwei; Ivanov, Ivan A; Liu, Gang; Huang, Yu; Duan, Xiangfeng

2012-01-28

Graphene has attracted considerable interest as a potential material for future electronics. Although mechanical peel is known to produce high quality graphene flakes, practical applications require continuous graphene layers over a large area. The catalyst-assisted chemical vapor deposition (CVD) is a promising synthetic method to deliver wafer-sized graphene. Here we present a systematic study on the nucleation and growth of crystallized graphene domains in an atmospheric pressure chemical vapor deposition (APCVD) process. Parametric studies show that the mean size of the graphene domains increases with increasing growth temperature and CH 4 partial pressure, while the density of domains decreases with increasing growth temperature and is independent of the CH 4 partial pressure. Our studies show that nucleation of graphene domains on copper substrate is highly dependent on the initial annealing temperature. A two-step synthetic process with higher initial annealing temperature but lower growth temperature is developed to reduce domain density and achieve high quality full-surface coverage of monolayer graphene films. Electrical transport measurements demonstrate that the resulting graphene exhibits a high carrier mobility of up to 3000 cm 2 V -1 s -1 at room temperature.

Surface study of platinum decorated graphene towards adsorption of NH_3 and CH_4

International Nuclear Information System (INIS)

Rad, Ali Shokuhi; Pazoki, Hossein; Mohseni, Soheil; Zareyee, Daryoush; Peyravi, Majid

2016-01-01

To distinguish the potential of graphene sensors, there is a need to recognize the interaction between graphene sheet and adsorbing molecules. We used density functional theory (DFT) calculations to study the properties of pristine as well as Pt-decorated graphene sheet upon adsorption of NH_3 and CH_4 on its surface to exploit its potential to be as gas sensors for them. We found much higher adsorption, higher charge transfer, lower intermolecular distance, and higher orbital hybridizing upon adsorption of NH_3 and CH_4 gas molecules on Pt-decorated graphene compared to pristine graphene. Also our calculations reveal that the adsorption energies on Pt-decorated graphene sheet are in order of NH_3 >CH_4 which could be corresponded to the order of their sensitivity on this modified surface. We used orbital analysis including density of states as well as frontier molecular orbital study for all analyte-surface systems to more understanding the kind of interaction (physisorption or chemisorption). Consequently, the Pt-decorated graphene can transform the existence of NH_3 and CH_4 molecules into electrical signal and it may be potentially used as an ideal sensor for detection of NH_3 and CH_4 in ambient situation. - Highlights: • Pt-decorated graphene was investigated as an adsorbent for NH_3 and CH_4. • Much higher adsorption of NH_3 and CH_4 on Pt-decorated graphene than pristine graphene. • Higher adsorption of NH_3 compared to CH_4 on Pt-decorated graphene. • Pt influences the electronic structure of graphene.

A DFT study of Cu nanoparticles adsorbed on defective graphene

Energy Technology Data Exchange (ETDEWEB)

García-Rodríguez, D.E. [Universidad Politécnica de Aguascalientes, Calle Paseo San Gerardo No. 297 Fracc. San Gerardo, 20342 Aguascalientes, Ags. (Mexico); Mendoza-Huizar, L.H. [Universidad Autónoma del Estado de Hidalgo, Área Académica de Química, Ciudad del Conocimiento. Carretera Pachuca-Tulancigo Km. 4.5 Mineral de la Reforma, 42186 Hidalgo (Mexico); Díaz, C., E-mail: cristina.diaz@uam.es [Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid (Spain); Institute for Advanced Research in Chemical Science (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid (Spain)

2017-08-01

Highlights: • Cu{sub n} supported on graphene may be a promising electrode material for DBFC's cells. • Cu{sub n}/graphene interaction is rather local and size independent. • Cu{sub 13} anchors strongly to defects in graphene, while keeping its gas-phase properties. - Abstract: Metal nanoparticles adsorbed on graphene are systems of interest for processes relative to catalytic reactions and alternative energy production. Graphene decorated with Cu-nanoparticles, in particular, could be a good alternative material for electrodes in direct borohydride fuel cells. However our knowledge of this system is still very limited. Based on density functional theory, we have analyzed the interaction of Cu{sub n} nanoparticles (n = 4, 5, 6, 7, 13) with pristine and defective-graphene. We have considered two types of defects, a single vacancy (SV), and an extended lineal structural defect (ELSD), formed by heptagon-pentagon pairs. Our analysis has revealed the covalent character of the Cu{sub n}-graphene interaction for pristine- and ELSD-graphene, and a more ionic-like interaction for SV-graphene. Furthermore, our analysis shows that the interaction between the nanoparticles and the graphene is rather local, i.e., only the nanoparticle atoms close to the contact region are involved in the interaction, being the electronic contact region much higher for defective-graphene than for pristine-graphene. Thus, the higher the particle the lower its average electronic and structural distortion.

Study on IR Properties of Reduced Graphene Oxide

Science.gov (United States)

Ma, Deyue; Li, Xiaoxia; Guo, Yuxiang; Zeng, Yurun

2018-01-01

Firstly, the reduced graphene oxide was prepared by modified hummer method and characterized. Then, the complex refractive index of reduced graphene oxide in IR band was tested and its IR absorption and radiation properties were researched by correlated calculation. The results show that reduced graphene oxide prepared by hummer method are multilayered graphene with defects and functional groups on its surface. Its absorption in near and far IR bands is strong, but it’s weaker in middle IR band. At the IR atmosphere Window, its normal spectral emissivity decreases with wavelength increasing, and its total normal spectral emissivity in 3 ∼ 5μm and 8 ∼ 14μm are 0.75 and 0.625, respectively. Therefore, reduced graphene oxide can be used as IR absorption and coating materials and have a great potential in microwave and infrared compatible materials.

Elastic properties of graphene: A pseudo-beam model with modified internal bending moment and its application

Science.gov (United States)

Xia, Z. M.; Wang, C. G.; Tan, H. F.

2018-04-01

A pseudo-beam model with modified internal bending moment is presented to predict elastic properties of graphene, including the Young's modulus and Poisson's ratio. In order to overcome a drawback in existing molecular structural mechanics models, which only account for pure bending (constant bending moment), the presented model accounts for linear bending moments deduced from the balance equations. Based on this pseudo-beam model, an analytical prediction is accomplished to predict the Young's modulus and Poisson's ratio of graphene based on the equation of the strain energies by using Castigliano second theorem. Then, the elastic properties of graphene are calculated compared with results available in literature, which verifies the feasibility of the pseudo-beam model. Finally, the pseudo-beam model is utilized to study the twisting wrinkling characteristics of annular graphene. Due to modifications of the internal bending moment, the wrinkling behaviors of graphene sheet are predicted accurately. The obtained results show that the pseudo-beam model has a good ability to predict the elastic properties of graphene accurately, especially the out-of-plane deformation behavior.

A flexible and transparent graphene/ZnO nanorod hybrid structure fabricated by exfoliating a graphite substrate

Science.gov (United States)

Nam, Gwang-Hee; Baek, Seong-Ho; Cho, Chang-Hee; Park, Il-Kyu

2014-09-01

We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain. The I-V characteristics of the graphene/ZnO NR hybrid structure show current flow through the graphene layer, while no current flow is observed on the ZnO NR/polydimethylsiloxane (PDMS) composite without graphene, thereby indicating that the few-layer graphene was successfully transferred onto the hybrid structure. A piezoelectric nanogenerator is demonstrated by using the fabricated graphene/ZnO NR hybrid structure. The nanogenerator exhibits stable output voltage up to 3.04 V with alternating current output characteristics.We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain. The I-V characteristics of the graphene/ZnO NR hybrid structure show current flow through the graphene layer, while no current flow is observed on the ZnO NR/polydimethylsiloxane (PDMS) composite without graphene, thereby indicating that the few-layer graphene was successfully transferred onto the hybrid structure. A piezoelectric nanogenerator is demonstrated by using the fabricated graphene/ZnO NR hybrid structure. The nanogenerator

Computational study of ammonia adsorption on the perfect and rippled graphene sheet

International Nuclear Information System (INIS)

Seyed-Talebi, Seyedeh Mozhgan; Beheshtian, Javad

2013-01-01

Adsorption of an ammonia molecule onto perfect and rippled graphene is studied using molecular mechanics calculations. The most stable orientation of an ammonia molecule and equilibrium distance of this molecule over graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined using DFT calculation. This result is in agreement with the predicted molecular mechanics calculation result. It also has been found that (i) the ammonia molecule is weakly adsorbed onto the graphene sheet; (ii) the periodic nature of the potential energy stored between ammonia and perfect graphene is altered due to the sinusoidal ripples; and (iii) the effect of amplitude and wavelength of the one-dimensional created ripple on different energy modes is reported

Computational study of ammonia adsorption on the perfect and rippled graphene sheet

Energy Technology Data Exchange (ETDEWEB)

Seyed-Talebi, Seyedeh Mozhgan [Department of Physics, Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Beheshtian, Javad, E-mail: J.Beheshtian@Srttu.edu [Department of Chemistry, Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of)

2013-11-15

Adsorption of an ammonia molecule onto perfect and rippled graphene is studied using molecular mechanics calculations. The most stable orientation of an ammonia molecule and equilibrium distance of this molecule over graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined using DFT calculation. This result is in agreement with the predicted molecular mechanics calculation result. It also has been found that (i) the ammonia molecule is weakly adsorbed onto the graphene sheet; (ii) the periodic nature of the potential energy stored between ammonia and perfect graphene is altered due to the sinusoidal ripples; and (iii) the effect of amplitude and wavelength of the one-dimensional created ripple on different energy modes is reported.

Polyurethane Nanocomposites Containing Reduced Graphene Oxide, FTIR, Raman, and XRD Studies

Directory of Open Access Journals (Sweden)

Michał Strankowski

2016-01-01

Full Text Available Recently, graphene and other graphene-based materials have become an essential part of composite science and technology. Their unique properties are not only restricted to graphene but also shared with derivative compounds like graphene oxide, reduced graphene oxide, functionalized graphene, and so forth. One of the most structurally important materials, graphene oxide (GO, is prepared by the oxidation of graphite. Though removal of the oxide groups can create vacancies and structural defects, reduced graphene oxide (rGO is used in composites as effective filler similar to GO. Authors developed a new polyurethane nanocomposite using a derivative of grapheme, thermally reduced graphene oxide (rGO, to modify the matrix of polyurethane elastomers, by rGO.

Electronic properties and optical absorption of graphene-polyvinylidene fluoride nanocomposites: A theoretical study

Energy Technology Data Exchange (ETDEWEB)

Chopra, Siddheshwar, E-mail: schopra1@amity.edu

2017-01-15

Graphene/polyvinylidene fluoride (graphene/PVDF) nanocomposites were studied using Density functional theory (DFT)/Time dependent density functional theory (TDDFT) calculations. Five nanocomposite configurations were constructed. Electronic properties like binding energy, electronic gap and work function were calculated. The most stable structure was determined. The electronic gap of graphene shifts from semiconducting to conducting, on nanocomposite formation. Workfunction of the most stable nanocomposite was 4.34eV ± 0.05eV, close to that of the pristine graphene (4.33eV ± 0.05eV). Thermochemical analysis showed that the adsorption is spontaneous above ∼870 K, and endothermic in nature. TDDFT calculations were performed for B3LYP, LSDA, BHHLYP and PBE0 functionals. B3LYP and PBE0 are suitable in describing optical absorption. Optical gap of graphene shrinks, and light absorption gets enhanced on nanocomposite formation. - Highlights: • Various properties of graphene-PVDF nanocomposites were studied theoretically. • Electronic gap of graphene shifts to conducting nature, on composite formation. • Adsorption is spontaneous above ∼870 K, and endothermic in nature. • B3LYP and PBE0 functionals are suitable in describing absorption. • Optical absorption gets enhanced on nanocomposite formation.

Electronic properties and optical absorption of graphene-polyvinylidene fluoride nanocomposites: A theoretical study

International Nuclear Information System (INIS)

Chopra, Siddheshwar

2017-01-01

Graphene/polyvinylidene fluoride (graphene/PVDF) nanocomposites were studied using Density functional theory (DFT)/Time dependent density functional theory (TDDFT) calculations. Five nanocomposite configurations were constructed. Electronic properties like binding energy, electronic gap and work function were calculated. The most stable structure was determined. The electronic gap of graphene shifts from semiconducting to conducting, on nanocomposite formation. Workfunction of the most stable nanocomposite was 4.34eV ± 0.05eV, close to that of the pristine graphene (4.33eV ± 0.05eV). Thermochemical analysis showed that the adsorption is spontaneous above ∼870 K, and endothermic in nature. TDDFT calculations were performed for B3LYP, LSDA, BHHLYP and PBE0 functionals. B3LYP and PBE0 are suitable in describing optical absorption. Optical gap of graphene shrinks, and light absorption gets enhanced on nanocomposite formation. - Highlights: • Various properties of graphene-PVDF nanocomposites were studied theoretically. • Electronic gap of graphene shifts to conducting nature, on composite formation. • Adsorption is spontaneous above ∼870 K, and endothermic in nature. • B3LYP and PBE0 functionals are suitable in describing absorption. • Optical absorption gets enhanced on nanocomposite formation.

Superlubricating graphene and graphene oxide films

Science.gov (United States)

Sumant, Anirudha V.; Erdemir, Ali; Choi, Junho; Berman, Diana

2018-02-13

A system and method for forming at least one of graphene and graphene oxide on a substrate and an opposed wear member. The system includes graphene and graphene oxide formed by an exfoliation process or solution processing method to dispose graphene and/or graphene oxide onto a substrate. The system further includes an opposing wear member disposed on another substrate and a gas atmosphere of an inert gas like N2, ambient, a humid atmosphere and a water solution.

Experimental and modeling study on charge storage/transfer mechanism of graphene-based supercapacitors

Science.gov (United States)

Ban, Shuai; Jing, Xie; Zhou, Hongjun; Zhang, Lei; Zhang, Jiujun

2014-12-01

A symmetrical graphene-based supercapacitor is constructed for studying the charge-transfer mechanism within the graphene-based electrodes using both experiment measurements and molecular simulation. The in-house synthesized graphene is characterized by XRD, SEM and BET measurements for morphology and surface area. It is observed that the electric capacity of graphene electrode can be reduced by both high internal resistance and limited mass transfer. Computer modeling is conducted at the molecular level to characterize the diffusion behavior of electrolyte ions to the interior of electrode with emphasis on the unique 2D confinement imposed by graphene layers. Although graphene powder poses a moderate internal surface of 400 m2 g-1, the capacitance performance of graphene electrode can be as good as that of commercial activated carbon which has an overwhelming surface area of 1700 m2 g-1. An explanation to this abnormal correlation is that graphene material has an intrinsic capability of adaptively reorganizing its microporous structure in response to intercalation of ions and immergence of electrolyte solvent. The accessible surface of graphene is believed to be dramatically enlarged for ion adsorption during the charging process of capacitor.

Flexural phonon limited phonon drag thermopower in bilayer graphene

Science.gov (United States)

Ansari, Mohd Meenhaz; Ashraf, SSZ

2018-05-01

We investigate the phonon drag thermopower from flexural phonons as a function of electron temperature and carrier concentration in the Bloch-Gruneisen regime in non-strained bilayer graphene using Boltzmann transport equation approach. The flexural phonons are expected to be the major source of intrinsic scattering mechanism in unstrained bilayer graphene due to their large density. The flexural phonon modes dispersion relation is quadratic so these low energy flexural phonons abound at room temperature and as a result deform the bilayer graphene sheet in the out of plane direction and affects the transport properties. We also produce analytical result for phonon-drag thermopower from flexural phonons and find that phonon-drag thermopower depicts T2 dependence on temperature and n-1 on carrier concentration.

“The Princess and the Pea” at the Nanoscale: Wrinkling and Delamination of Graphene on Nanoparticles

Directory of Open Access Journals (Sweden)

Mahito Yamamoto

2012-12-01

Full Text Available Thin membranes exhibit complex responses to external forces or geometrical constraints. A familiar example is the wrinkling, exhibited by human skin, plant leaves, and fabrics, that results from the relative ease of bending versus stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest known membrane, deposited on a silica substrate decorated with silica nanoparticles. At small nanoparticle density, monolayer graphene adheres to the substrate, detached only in small regions around the nanoparticles. With increasing nanoparticle density, we observe the formation of wrinkles which connect nanoparticles. Above a critical nanoparticle density, the wrinkles form a percolating network through the sample. As the graphene membrane is made thicker, global delamination from the substrate is observed. The observations can be well understood within a continuum-elastic model and have important implications for strain-engineering the electronic properties of graphene.

Tunneling Spectroscopy Studies of Epitaxial Graphene on Silicon Carbide(0001) and Its Interfaces

Science.gov (United States)

Sandin, Andreas Axel Tomas

A two dimensional network of sp2 bonded carbon atoms is defined as graphene. This novel material possesses remarkable electronic properties due to its unique band structure at the vicinity of the Fermi energy. The toughest challenge to bring use of graphene electronic properties in device geometries is that graphene is exceptionally sensitive to its electrical environment for integration into macroscopic system of electrical contacts and substrates. One of the most promising substrates for graphene is the polar surfaces of SiC for the reason it can be grown epitaxially by sublimating Si from the top-most SiC atomic layers. In this work, the interfaces of graphene grown on the Si-terminated polar surface SiC(0001) is studied in UHV using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), low energy electron diffraction (LEED) and auger electron Spectroscopy (AES). STM is used image the graphene surface and interfaces with the capability of atomic resolution. LEED is used to study surface atomic reciprocal ordering and AES is used to determine surface atomic composition during the graphene formation. Interfacial layer (Buffer layer), Single layer graphene and bilayer graphene are identified electronically by means of probing the first member of the image potential derived state. This state is found by dZ/dV spectroscopy in the high energy unoccupied states and is exceptionally sensitive to electrostatic changes to the surface which is detected by energy shifts of image potential states (IPS). This sensitivity is utilized to probe the graphene screening of external electric fields by varying the electric field in the tunneling junction and addresses the fact that charged impurity scattering is likely to be crucial for epitaxial graphene on SiC(0001) when it comes to transport parameters. Shifts of IPS energy position has also been used verify work function changes for identification of several Sodium Intercalation structures of epitaxial

First principles study of edge carboxylated graphene quantum dots

Science.gov (United States)

Abdelsalam, Hazem; Elhaes, Hanan; Ibrahim, Medhat A.

2018-05-01

The structure stability and electronic properties of edge carboxylated hexagonal and triangular graphene quantum dots are investigated using density functional theory. The calculated binding energies show that the hexagonal clusters with armchair edges have the highest stability among all the quantum dots. The binding energy of carboxylated graphene quantum dots increases by increasing the number of carboxyl groups. Our study shows that the total dipole moment significantly increases by adding COOH with the highest value observed in triangular clusters. The edge states in triangular graphene quantum dots with zigzag edges produce completely different energy spectrum from other dots: (a) the energy gap in triangular zigzag is very small as compared to other clusters and (b) the highest occupied molecular orbital is localized at the edges which is in contrast to other clusters where it is distributed over the cluster surface. The enhanced reactivity and the controllable energy gap by shape and edge termination make graphene quantum dots ideal for various nanodevice applications such as sensors. The infrared spectra are presented to confirm the stability of the quantum dots.

Anomalous friction of graphene nanoribbons on waved graphenes

Directory of Open Access Journals (Sweden)

Jun Fang

2015-11-01

Full Text Available Friction plays a critical role in the function and maintenance of small-scale structures, where the conventional Coulomb friction law often fails. To probe the friction at small scales, here we present a molecular dynamics study on the process of dragging graphene nanoribbons on waved graphene substrates. The simulation shows that the induced friction on graphene with zero waviness is ultra-low and closely related to the surface energy barrier. On waved graphenes, the friction generally increases with the amplitude of the wave at a fixed period, but anomalously increases and then decreases with the period at a fixed amplitude. These findings provide insights into the ultra-low friction at small scales, as well as some guidelines into the fabrication of graphene-based nano-composites with high performance.

Extrinsic morphology of graphene

International Nuclear Information System (INIS)

Li, Teng

2011-01-01

Graphene is intrinsically non-flat and corrugates randomly. Since the corrugating physics of atomically thin graphene is strongly tied to its electronics properties, randomly corrugating morphology of graphene poses a significant challenge to its application in nanoelectronic devices for which precise (digital) control is the key. Recent studies revealed that the morphology of substrate-supported graphene is regulated by the graphene–substrate interaction, thus is distinct from the random intrinsic morphology of freestanding graphene. The regulated extrinsic morphology of graphene sheds light on new pathways to fine tune the properties of graphene. To guide further research to explore these fertile opportunities, this paper reviews recent progress on modeling and experimental studies of the extrinsic morphology of graphene under a wide range of external regulation, including two-dimensional and one-dimensional substrate surface features and one-dimensional and zero-dimensional nanoscale scaffolds (e.g. nanowires and nanoparticles)

Spectroscopic studies of the physical origin of environmental aging effects on doped graphene

International Nuclear Information System (INIS)

Chang, J.-K.; Hsu, C.-C.; Liu, S.-Y.; Wu, C.-I.; Gharib, M.; Yeh, N.-C.

2016-01-01

The environmental aging effect of doped graphene is investigated as a function of the organic doping species, humidity, and the number of graphene layers adjacent to the dopant by studies of the Raman spectroscopy, x-ray and ultraviolet photoelectron spectroscopy, scanning electron microscopy, infrared spectroscopy, and electrical transport measurements. It is found that higher humidity and structural defects induce faster degradation in doped graphene. Detailed analysis of the spectroscopic data suggest that the physical origin of the aging effect is associated with the continuing reaction of H_2O molecules with the hygroscopic organic dopants, which leads to formation of excess chemical bonds, reduction in the doped graphene carrier density, and proliferation of damages from the graphene grain boundaries. These environmental aging effects are further shown to be significantly mitigated by added graphene layers.

Large-Scale Molecular Simulations on the Mechanical Response and Failure Behavior of a defective Graphene: Cases of 5-8-5 Defects

Science.gov (United States)

Wang, Shuaiwei; Yang, Baocheng; Yuan, Jinyun; Si, Yubing; Chen, Houyang

2015-10-01

Understanding the effect of defects on mechanical responses and failure behaviors of a graphene membrane is important for its applications. As examples, in this paper, a family of graphene with various 5-8-5 defects are designed and their mechanical responses are investigated by employing molecular dynamics simulations. The dependence of fracture strength and strain as well as Young’s moduli on the nearest neighbor distance and defect types is examined. By introducing the 5-8-5 defects into graphene, the fracture strength and strain become smaller. However, the Young’s moduli of DL (Linear arrangement of repeat unit 5-8-5 defect along zigzag-direction of graphene), DS (a Slope angle between repeat unit 5-8-5 defect and zigzag direction of graphene) and DZ (Zigzag-like 5-8-5 defects) defects in the zigzag direction become larger than those in the pristine graphene in the same direction. A maximum increase of 11.8% of Young’s modulus is obtained. Furthermore, the brittle cracking mechanism is proposed for the graphene with 5-8-5 defects. The present work may provide insights in controlling the mechanical properties by preparing defects in the graphene, and give a full picture for the applications of graphene with defects in flexible electronics and nanodevices.

Spin-valley splitting of electron beam in graphene

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Yu Song

2016-11-01

Full Text Available We study spatial separation of the four degenerate spin-valley components of an electron beam in a EuO-induced and top-gated ferromagnetic/pristine/strained graphene structure. We show that, in a full resonant tunneling regime for all beam components, the formation of standing waves can lead sudden phase jumps ∼−π and giant lateral Goos-Hänchen shifts as large as the transverse beam width, while the interplay of the spin and valley imaginary wave vectors in the modulated regions can lead differences of resonant angles for the four spin-valley flavors, manifesting a spin-valley beam splitting effect. The splitting effect is found to be controllable by the gating and strain.

EDITORIAL: Special issue on Graphene Special issue on Graphene

Science.gov (United States)

Morpurgo, Alberto F.; Trauzettel, Björn

2010-03-01

and effectively reflect the status of different areas of graphene research. The excitonic condensation in a double graphene system is discussed by Kharitonov and Efetov. Borca et al report on a method to fabricate and characterize graphene monolayers epitaxially grown on Ru(0001). Furthermore, the energy and transport gaps in etched graphene nanoribbons are analyzed experimentally by Molitor et al. Mucha-Kruczyński et al review the tight-binding model of bilayer graphene, whereas Wurm et al focus on a theoretical description of the Aharonov-Bohm effect in monolayer graphene rings. Screening effects and collective excitations are studied by Roldán et al. Subsequently, Palacios et al review the electronic and magnetic structures of graphene nanoribbons, a problem that is highly relevant for graphene-based transistors. Klein tunneling in single and multiple barriers in graphene is the topic of the review article by Pereira Jr et al, while De Martino and Egger discuss the spectrum of a magnetic quantum dot in graphene. Titov et al study the effect of resonant scatterers on the local density of states in a rectangular graphene setup with metallic leads. Finally, the resistance modulation of multilayer graphene controlled by gate electric fields is experimentally analyzed by Miyazaki et al. We would like to thank all the authors for their contributions, which combine new results and pedagogical discussions of the state-of-the-art in different areas: it is this combination that most often adds to the value of topical issues. Special thanks also goes to the staff of Institute of Physics Publishing for contributing to the success of this effort.

X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites.

Science.gov (United States)

Gandhiraman, Ram P; Nordlund, Dennis; Javier, Cristina; Koehne, Jessica E; Chen, Bin; Meyyappan, M

2014-08-14

The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide-metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the π network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp 2 -derived unoccupied states π* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network.

Graphene-Molybdenum Disulfide-Graphene Tunneling Junctions with Large-Area Synthesized Materials.

Science.gov (United States)

Joiner, Corey A; Campbell, Philip M; Tarasov, Alexey A; Beatty, Brian R; Perini, Chris J; Tsai, Meng-Yen; Ready, William J; Vogel, Eric M

2016-04-06

Tunneling devices based on vertical heterostructures of graphene and other 2D materials can overcome the low on-off ratios typically observed in planar graphene field-effect transistors. This study addresses the impact of processing conditions on two-dimensional materials in a fully integrated heterostructure device fabrication process. In this paper, graphene-molybdenum disulfide-graphene tunneling heterostructures were fabricated using only large-area synthesized materials, unlike previous studies that used small exfoliated flakes. The MoS2 tunneling barrier is either synthesized on a sacrificial substrate and transferred to the bottom-layer graphene or synthesized directly on CVD graphene. The presence of graphene was shown to have no impact on the quality of the grown MoS2. The thickness uniformity of MoS2 grown on graphene and SiO2 was found to be 1.8 ± 0.22 nm. XPS and Raman spectroscopy are used to show how the MoS2 synthesis process introduces defects into the graphene structure by incorporating sulfur into the graphene. The incorporation of sulfur was shown to be greatly reduced in the absence of molybdenum suggesting molybdenum acts as a catalyst for sulfur incorporation. Tunneling simulations based on the Bardeen transfer Hamiltonian were performed and compared to the experimental tunneling results. The simulations show the use of MoS2 as a tunneling barrier suppresses contributions to the tunneling current from the conduction band. This is a result of the observed reduction of electron conduction within the graphene sheets.

Si clusters/defective graphene composites as Li-ion batteries anode materials: A density functional study

International Nuclear Information System (INIS)

Li, Meng; Liu, Yue-Jie; Zhao, Jing-xiang; Wang, Xiao-guang

2015-01-01

Highlights: • We study the interaction between Si clusters with pristine and defective graphene. • We find that the binding strength of Si clusters on graphene can be enhanced to different degrees after introducing various defects. • It is found that both graphene and Si cluster in the Si/graphene composites can preserve their Li uptake ability. - Abstract: Recently, the Si/graphene hybrid composites have attracted considerable attention due to their potential application for Li-ion batteries. How to effectively anchor Si clusters to graphene substrates to ensure their stability is an important factor to determine their performance for Li-ion batteries. In the present work, we have performed comprehensive density functional theory (DFT) calculations to investigate the geometric structures, stability, and electronic properties of the deposited Si clusters on defective graphenes as well as their potential applications for Li-ion batteries. The results indicate that the interfacial bonding between these Si clusters with the pristine graphene is quietly weak with a small adsorption energy (<−0.21 eV). Due to the presence of vacancy site, the binding strength of Si clusters on defective graphene is much stronger than that of pristine one, accompanying with a certain amount of charge transfer from Si clusters to graphene substrates. Moreover, the ability of Si/graphene hybrids for Li uptake is studied by calculating the adsorption of Li atoms. We find that both graphenes and Si clusters in the Si/graphene composites preserve their Li uptake ability, indicating that graphenes not only server as buffer materials for accommodating the expansion of Si cluster, but also provide additional intercalation sites for Li

Study of graphene growth on copper foil by pulsed laser deposition at reduced temperature

Science.gov (United States)

Abd Elhamid, Abd Elhamid M.; Hafez, Mohamed A.; Aboulfotouh, Abdelnaser M.; Azzouz, Iftitan M.

2017-01-01

Graphene has been successfully grown on commercial copper foil at low temperature of 500 °C by pulsed laser deposition (PLD). X-ray diffraction patterns showed that films have been grown in the presence of Cu(111) and Cu(200) facets. Raman spectroscopy was utilized to study the effects of temperature, surface structure, and cooling rate on the graphene growth. Raman spectra indicate that the synthesis of graphene layers rely on the surface quality of the Cu substrate together with the proper cooling profile coupled with graphene growth temperature. PLD-grown graphene film on Cu has been verified by transmission electron microscopy. Surface mediated growth of graphene on Cu foil substrate revealed to have a favorable catalytic effect. High growth rate of graphene and less defects can be derived using fast cooling rate.

Electronic properties of T graphene-like C-BN sheets: A density functional theory study

Science.gov (United States)

Majidi, R.

2015-11-01

We have used density functional theory to study the electronic properties of T graphene-like C, C-BN and BN sheets. The planar T graphene with metallic property has been considered. The results show that the presence of BN has a considerable effect on the electronic properties of T graphene. The T graphene-like C-BN and BN sheets show semiconducting properties. The energy band gap is increased by enhancing the number of BN units. The possibility of opening and controlling band gap opens the door for T graphene in switchable electronic devices.

Evolution of temperature-induced strain and doping of double-layer graphene: an in situ Raman spectral mapping study

Czech Academy of Sciences Publication Activity Database

Verhagen, Timotheus; Valeš, Václav; Kalbáč, Martin; Vejpravová, Jana

2015-01-01

Roč. 252, č. 11 (2015), s. 2401-2406 ISSN 0370-1972 R&D Projects: GA ČR(CZ) GA15-01953S Institutional support: RVO:68378271 ; RVO:61388955 Keywords : graphene * isotope labelling * low temperature * Raman spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.522, year: 2015

DFT study of adsorption and dissociation behavior of H2S on Fe-doped graphene

International Nuclear Information System (INIS)

Zhang, Hong-ping; Luo, Xue-gang; Song, Hong-tao; Lin, Xiao-yan; Lu, Xiong; Tang, Youhong

2014-01-01

Highlights: • Fe-doped and Pt-doped graphene can significantly improve the interactions between H 2 S and graphene. • The location of S had an important role in the interactions between H 2 S and Fe-doped graphene. • The influence of Fe-S distance can be very weak in a certain range and H 2 S can be dissociated into S and H 2 . - Abstracts: Understanding the interaction mechanisms of hydrogen sulfide (H 2 S) with graphene is important in developing graphene-based sensors for gas detection and removal. In this study, the effects of doped Fe atom on interaction of H 2 S with graphene were investigated by density functional theory calculations. Analyses of adsorption energy, electron density difference, and density of states indicated that the doped Fe atom can significantly improve the interaction of H 2 S gas molecules with graphene, as well as Pt-doped graphene. The location of the sulfur atom is important in the interactions between H 2 S and Fe-doped graphene. The influence of the Fe-S distance can be very weak within a certain distance, as simulated in this study

Equilibrium, kinetic and thermodynamic studies on the adsorption of phenol onto graphene

Energy Technology Data Exchange (ETDEWEB)

Li, Yanhui, E-mail: liyanhui@tsinghua.org.cn [Laboratory of Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, College of Electromechanical Engineering, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Du, Qiuju; Liu, Tonghao; Sun, Jiankun; Jiao, Yuqin [Laboratory of Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, College of Electromechanical Engineering, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Xia, Yanzhi, E-mail: xiayzh@qdu.edu.cn [Laboratory of Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, College of Electromechanical Engineering, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Xia, Linhua; Wang, Zonghua [Laboratory of Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, College of Electromechanical Engineering, Qingdao University, 308 Ningxia Road, Qingdao 266071 (China); Zhang, Wei; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai [Key Laboratory for Advanced Manufacturing by Material Processing Technology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)

2012-08-15

Graphical abstract: The effect of temperature on phenol adsorbed by graphene shows that the equilibrium adsorption capacity of phenol increases with the increase in temperature from 285 to 333 K. Increasing adsorption capacities with temperature indicates that the adsorption of phenol is controlled by an endothermic reaction. Highlights: ► The graphene has high phenol adsorption capacity. ► The graphene has a high specific surface area of 305 m{sup 2}/g. ► The adsorption capacity is high at acidic pH range. ► The graphene has rapid phenol adsorption rate. ► Phenol adsorption is a spontaneous and endothermic process. -- Abstract: Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.

Equilibrium, kinetic and thermodynamic studies on the adsorption of phenol onto graphene

International Nuclear Information System (INIS)

Li, Yanhui; Du, Qiuju; Liu, Tonghao; Sun, Jiankun; Jiao, Yuqin; Xia, Yanzhi; Xia, Linhua; Wang, Zonghua; Zhang, Wei; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai

2012-01-01

Graphical abstract: The effect of temperature on phenol adsorbed by graphene shows that the equilibrium adsorption capacity of phenol increases with the increase in temperature from 285 to 333 K. Increasing adsorption capacities with temperature indicates that the adsorption of phenol is controlled by an endothermic reaction. Highlights: ► The graphene has high phenol adsorption capacity. ► The graphene has a high specific surface area of 305 m 2 /g. ► The adsorption capacity is high at acidic pH range. ► The graphene has rapid phenol adsorption rate. ► Phenol adsorption is a spontaneous and endothermic process. -- Abstract: Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.

Study of EUV induced defects on few-layer graphene

NARCIS (Netherlands)

Gao, An; Rizo, P.J.; Zoethout, E.; Scaccabarozzi, L.; Lee, Christopher James; Banine, V.; Bijkerk, Frederik

2012-01-01

Defects in graphene greatly affect its properties1-3. Radiation induced-defects may reduce the long-term survivability of graphene-based nano-devices. Here, we expose few-layer graphene to extreme ultraviolet (EUV, 13.5nm) radiation and show there is a power-dependent increase in defect density. We

Transfer printing of graphene strip from the graphene grown on copper wires

International Nuclear Information System (INIS)

Su, Ching-Yuan; Fu Dongliang; Lu, Ang-Yu; Liu, Keng-Ku; Xu Yanping; Juang, Zhen-Yu; Li, Lain-Jong

2011-01-01

A simple, cost-effective and lithography-free fabrication of graphene strips for device applications is demonstrated. The graphene thin layers were directly grown on Cu wires, followed by Cu etching and transfer printing to arbitrary substrates by a PDMS stamp. The Cu wires can be arranged on the PDMS stamp in a desired pattern; hence, the substrates can receive graphene strips with the same pattern. Moreover, the preparation of graphene strips does not involve conventional lithography; therefore, the surface of the graphene strip is free of residual photoresists, which may be useful for studies requiring clean graphene surfaces.

Graphene device and method of using graphene device

Science.gov (United States)

Bouchiat, Vincent; Girit, Caglar; Kessler, Brian; Zettl, Alexander K.

2015-08-11

An embodiment of a graphene device includes a layered structure, first and second electrodes, and a dopant island. The layered structure includes a conductive layer, an insulating layer, and a graphene layer. The electrodes are coupled to the graphene layer. The dopant island is coupled to an exposed surface of the graphene layer between the electrodes. An embodiment of a method of using a graphene device includes providing the graphene device. A voltage is applied to the conductive layer of the graphene device. Another embodiment of a method of using a graphene device includes providing the graphene device without the dopant island. A dopant island is placed on an exposed surface of the graphene layer between the electrodes. A voltage is applied to the conductive layer of the graphene device. A response of the dopant island to the voltage is observed.

Mechanical and electro-mechanical properties of three-dimensional nanoporous graphene-poly(vinylidene fluoride composites

Directory of Open Access Journals (Sweden)

G. P. Zheng

2016-09-01

Full Text Available Three-dimensional nanoporous graphene monoliths are utilized to prepare graphene-poly(vinylidene fluoride nanocomposites with enhanced mechanical and electro-mechanical properties. Pre-treatment of the polymer (poly(vinylidene fluoride, PVDF with graphene oxides (GOs facilitates the formation of uniform and thin PVDF films with a typical thickness below 100 nm well coated at the graphene nano-sheets. Besides their excellent compressibility, ductility and mechanical strength, the nanoporous graphene-PVDF nanocomposites are found to possess high sensitivity in strain-dependent electrical conductivity. The improved mechanical and electro-mechanical properties are ascribed to the enhanced crystalline β phase in PVDF which possesses piezoelectricity. The mechanical relaxation analyses on the interfaces between graphene and PVDF reveal that the improved mechanical and electro-mechanical properties could result from the interaction between the –C=O groups in the nanoporous graphene and the –CF2 groups in PVDF, which also explains the important role of GOs in the preparation of the graphene-polymer nanocomposites with superior combined mechanical and electro-mechanical properties.

Graphene field-effect devices

Science.gov (United States)

Echtermeyer, T. J.; Lemme, M. C.; Bolten, J.; Baus, M.; Ramsteiner, M.; Kurz, H.

2007-09-01

In this article, graphene is investigated with respect to its electronic properties when introduced into field effect devices (FED). With the exception of manual graphene deposition, conventional top-down CMOS-compatible processes are applied. Few and monolayer graphene sheets are characterized by scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The electrical properties of monolayer graphene sandwiched between two silicon dioxide films are studied. Carrier mobilities in graphene pseudo-MOS structures are compared to those obtained from double-gated Graphene-FEDs and silicon metal-oxide-semiconductor field-effect-transistors (MOSFETs).

Buckled graphene: A model study based on density functional theory

KAUST Repository

Khan, Yasser

2010-09-01

We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet. © 2010 Elsevier B.V. All rights reserved.

Buckled graphene: A model study based on density functional theory

KAUST Repository

Khan, Yasser; Mukaddam, Mohsin Ahmed; Schwingenschlö gl, Udo

2010-01-01

We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet. © 2010 Elsevier B.V. All rights reserved.

Prediction of hydrogen storage on Y-decorated graphene: A density functional theory study

International Nuclear Information System (INIS)

Liu, Wenbo; Liu, Yang; Wang, Rongguo

2014-01-01

Highlight: • Rare earth metal Y has an excellent performance on hydrogen storage. • After decoration, each Y can attach six hydrogen molecules without dissociation. • The Y atoms disperse uniformly and stably on B/graphene. • The enhancement of H binding is caused by hybridization and electrostatic attraction. - Abstract: Yttrium decorated graphene has been investigated as a potential carrier for high density hydrogen storage. The adsorption energy and optimized geometry for yttrium on pristine and boron doped graphene have been studied by DFT calculations. The clustering and stability of isolated yttrium atoms on graphene has also been considered. For yttrium decorated boron doped graphene, each yttrium can attach six hydrogen molecules with average adsorption energy of −0.568 eV per hydrogen molecule and the hydrogen storage capacity of this material is 5.78 wt.%, indicating yttrium decorated boron doped graphene as a promising hydrogen storage candidate

First principles study the effects of alkali metal and chorine adatoms on the opposite surface of graphene

Science.gov (United States)

Xinxiang, Song; Guang, Yuan; Meifeng, Dong; Mimura, Hidenori; Chun, Li; Mang, Niu

2018-02-01

Study of the adsorption properties of graphene has great significance for expanding its application. So far, few studies have analyzed the effects of adatoms on opposite sides of graphene. We use density functional theory to report the effects of chlorine and alkali metal adatoms on the other side of graphene. Although there is an obvious charge transfer between the adatom and graphene, the interaction between the adatoms is shielded by the large π bonds of graphene and therefore the effects of the adatom on the other side of graphene are very weak.

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Science.gov (United States)

Jung, Han Sae; Tsai, Hsin-Zon; Wong, Dillon; Germany, Chad; Kahn, Salman; Kim, Youngkyou; Aikawa, Andrew S.; Desai, Dhruv K.; Rodgers, Griffin F.; Bradley, Aaron J.; Velasco, Jairo; Watanabe, Kenji; Taniguchi, Takashi; Wang, Feng; Zettl, Alex; Crommie, Michael F.

2015-01-01

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene’s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene’s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices. PMID:26273961

Electron scattering in graphene with adsorbed NaCl nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Drabińska, Aneta, E-mail: Aneta.Drabinska@fuw.edu.pl; Kaźmierczak, Piotr; Bożek, Rafał; Karpierz, Ewelina; Wysmołek, Andrzej; Kamińska, Maria [Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw (Poland); Wołoś, Agnieszka [Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw (Poland); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Pasternak, Iwona; Strupiński, Włodek [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); Krajewska, Aleksandra [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); Institute of Optoelectronics, Military University of Technology, Kaliskiego 2, 00-908 Warsaw (Poland)

2015-01-07

In this work, the results of contactless magnetoconductance and Raman spectroscopy measurements performed for a graphene sample after its immersion in NaCl solution were presented. The properties of the immersed sample were compared with those of a non-immersed reference sample. Atomic force microscopy and electron spin resonance experiments confirmed the deposition of NaCl nanoparticles on the graphene surface. A weak localization signal observed using contactless magnetoconductance showed the reduction of the coherence length after NaCl treatment of graphene. Temperature dependence of the coherence length indicated a change from ballistic to diffusive regime in electron transport after NaCl treatment. The main inelastic scattering process was of the electron-electron type but the major reason for the reduction of the coherence length at low temperatures was additional, temperature independent, inelastic scattering. We associate it with spin flip scattering, caused by NaCl nanoparticles present on the graphene surface. Raman spectroscopy showed an increase in the D and D′ bands intensities for graphene after its immersion in NaCl solution. An analysis of the D, D′, and G bands intensities proved that this additional scattering is related to the decoration of vacancies and grain boundaries with NaCl nanoparticles, as well as generation of new on-site defects as a result of the decoration of the graphene surface with NaCl nanoparticles. The observed energy shifts of 2D and G bands indicated that NaCl deposition on the graphene surface did not change carrier concentration, but reduced compressive biaxial strain in the graphene layer.

Electron scattering in graphene with adsorbed NaCl nanoparticles

International Nuclear Information System (INIS)

Drabińska, Aneta; Kaźmierczak, Piotr; Bożek, Rafał; Karpierz, Ewelina; Wysmołek, Andrzej; Kamińska, Maria; Wołoś, Agnieszka; Pasternak, Iwona; Strupiński, Włodek; Krajewska, Aleksandra

2015-01-01

In this work, the results of contactless magnetoconductance and Raman spectroscopy measurements performed for a graphene sample after its immersion in NaCl solution were presented. The properties of the immersed sample were compared with those of a non-immersed reference sample. Atomic force microscopy and electron spin resonance experiments confirmed the deposition of NaCl nanoparticles on the graphene surface. A weak localization signal observed using contactless magnetoconductance showed the reduction of the coherence length after NaCl treatment of graphene. Temperature dependence of the coherence length indicated a change from ballistic to diffusive regime in electron transport after NaCl treatment. The main inelastic scattering process was of the electron-electron type but the major reason for the reduction of the coherence length at low temperatures was additional, temperature independent, inelastic scattering. We associate it with spin flip scattering, caused by NaCl nanoparticles present on the graphene surface. Raman spectroscopy showed an increase in the D and D′ bands intensities for graphene after its immersion in NaCl solution. An analysis of the D, D′, and G bands intensities proved that this additional scattering is related to the decoration of vacancies and grain boundaries with NaCl nanoparticles, as well as generation of new on-site defects as a result of the decoration of the graphene surface with NaCl nanoparticles. The observed energy shifts of 2D and G bands indicated that NaCl deposition on the graphene surface did not change carrier concentration, but reduced compressive biaxial strain in the graphene layer

Optimization of Graphene Conductive Ink with 73 wt% Graphene Contents.

Science.gov (United States)

Xu, Chang-Yan; Shi, Xiao-Mei; Guo, Lu; Wang, Xi; Wang, Xin-Yi; Li, Jian-Yu

2018-06-01

With the pace of development accelerating in printed electronics, the fabrication and application of conductive ink have been brought into sharp focus in recent years. The discovery of graphene also unfolded a vigorous research campaign. In this paper, we prepared graphene conductive ink and explored the feasibility of applying the ink to flexible paper-based circuit. Since experimental study concentrating upon ink formulation was insufficient, orthogonal test design was used in the optimization of preparation formula of conductive ink for the first time. The purpose of this study was to determine the effect of constituent dosage on conductivity of graphene conductive ink, so as to obtain the optimized formula and prepare graphene conductive ink with good conductivity. Characterization of optimized graphene conductive ink we fabricated showed good adhesion to substrate and good resistance to acid and water. The graphene concentration of the optimized ink reached 73.17 wt% solid content. Particle size distribution of graphene conductive ink was uniform, which was about 1940 nm. Static surface tension was 28.9 mN/m and equilibrium contact angle was 23°, demonstrating that conductive ink had good wettability. Scanning Electron Microscope (SEM) analysis was also investigated, moreover, the feasibility of lightening a light-emitting diode (LED) light was verified. The graphene conductive ink with optimized formula can be stored for almost eight months, which had potential applications in flexible paper-based circuit in the future.

Thermal vibration of a rectangular single-layered graphene sheet with quantum effects

International Nuclear Information System (INIS)

Wang, Lifeng; Hu, Haiyan

2014-01-01

The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.

Aromatic graphene

Energy Technology Data Exchange (ETDEWEB)

Das, D. K., E-mail: gour.netai@gmail.com [Department of Metallurgical and Material Science Engineering, National Institute of Technology Durgapur-713209, West Bengal (India); Sahoo, S., E-mail: sukadevsahoo@yahoo.com [Department of Physics, National Institute of Technology Durgapur-713209, West Bengal (India)

2016-04-13

In recent years graphene attracts the scientific and engineering communities due to its outstanding electronic, thermal, mechanical and optical properties and many potential applications. Recently, Popov et al. [1] have studied the properties of graphene and proved that it is aromatic but without fragrance. In this paper, we present a theory to prepare graphene with fragrance. This can be used as scented pencils, perfumes, room and car fresheners, cosmetics and many other useful household substances.

Aromatic graphene

International Nuclear Information System (INIS)

Das, D. K.; Sahoo, S.

2016-01-01

In recent years graphene attracts the scientific and engineering communities due to its outstanding electronic, thermal, mechanical and optical properties and many potential applications. Recently, Popov et al. [1] have studied the properties of graphene and proved that it is aromatic but without fragrance. In this paper, we present a theory to prepare graphene with fragrance. This can be used as scented pencils, perfumes, room and car fresheners, cosmetics and many other useful household substances.

Mechanical and electromechanical properties of graphene and their potential application in MEMS

International Nuclear Information System (INIS)

Khan, Zulfiqar H; Kermany, Atieh R; Iacopi, Francesca; Öchsner, Andreas

2017-01-01

Graphene-based micro-electromechanical systems (MEMS) are very promising candidates for next generation miniaturized, lightweight, and ultra-sensitive devices. In this review, we review the progress to date of the assessment of the mechanical, electromechanical, and thermomechanical properties of graphene for application in graphene-based MEMS. Graphene possesses a plethora of outstanding properties—such as a 1 TPa Young’s modulus, exceptionally high 2D failure strength that stems from its sp 2 hybridization, and strong sigma bonding between carbon atoms. Such exceptional mechanical properties can enable, for example, graphene-based sound sources capable of generating sound beyond the audible range. The recently engineered piezoelectric properties of atomic force microscope tip-pressed graphene membranes or supported graphene on SiO 2 substrates, have paved the way in fabricating graphene-based nano-generators and actuators. On the other hand, graphene’s piezoresistive properties have enabled miniaturized pressure and strain sensors. 2D graphene nano-mechanical resonators can potentially measure ultralow forces, charges and potentially detect single atomic masses. The exceptional tribology of graphene can play a significant role in achieving superlubricity. In addition, the highest reported thermal conductivity of graphene is amenable for use in chips and providing better performing MEMS, as heat is efficiently dissipated. On top of that, graphene membranes could be nano-perforated to realize specialized applications like DNA translocation and desalination. Finally, to ensure stability and reliability of the graphene-based MEMS, adhesion is an important mechanical property that should be considered. In general, graphene could be used as a structural material in resonators, sensors, actuators and nano-generators with better performance and sensitivity than conventional MEMS. (topical review)

Basal-plane dislocations in bilayer graphene - Peculiarities in a quasi-2D material

Science.gov (United States)

Butz, Benjamin

2015-03-01

Dislocations represent one of the most fascinating and fundamental concepts in materials science. First and foremost, they are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly alter the local electronic or optical properties of semiconductors and ionic crystals. In layered crystals like graphite dislocation movement is restricted to the basal plane. Thus, those basal-plane dislocations cannot escape enabling their confinement in between only two atomic layers of the material. So-called bilayer graphene is the thinnest imaginable quasi-2D crystal to explore the nature and behavior of dislocations under such extreme boundary conditions. Robust graphene membranes derived from epitaxial graphene on SiC provide an ideal platform for their investigation. The presentation will give an insight in the direct observation of basal-plane partial dislocations by transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. The investigation reveals striking size effects. First, the absence of stacking fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern, which corresponds to an alternating AB BA change of the stacking order. Most importantly, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane, which directly results from accommodation of strain. In fact, the buckling completely changes the strain state of the bilayer graphene and is of key importance for its electronic/spin transport properties. Due to the high degree of disorder in our quasi-2D material it is one of the very few examples for a perfect linear magnetoresistance, i.e. the linear dependency of the in-plane electrical resistance on a magnetic field applied perpendicular to the graphene sheet up to field strengths of more than 60 T. This research is financed by the German Research Foundation

A comparative density functional study on electrical properties of layered penta-graphene

Energy Technology Data Exchange (ETDEWEB)

Yu, Zhi Gen, E-mail: yuzg@ihpc.a-star.edu.sg; Zhang, Yong-Wei, E-mail: zhangyw@ihpc.a-star.edu.sg [Institute of High Performance Computing, Singapore 138632 (Singapore)

2015-10-28

We present a comparative study of the influence of the number of layers, the biaxial strain in the range of −3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of p{sub z} orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN and ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.

Epitaxial-graphene/graphene-oxide junction: an essential step towards epitaxial graphene electronics.

Science.gov (United States)

Wu, Xiaosong; Sprinkle, Mike; Li, Xuebin; Ming, Fan; Berger, Claire; de Heer, Walt A

2008-07-11

Graphene-oxide (GO) flakes have been deposited to bridge the gap between two epitaxial-graphene electrodes to produce all-graphene devices. Electrical measurements indicate the presence of Schottky barriers at the graphene/graphene-oxide junctions, as a consequence of the band gap in GO. The barrier height is found to be about 0.7 eV, and is reduced after annealing at 180 degrees C, implying that the gap can be tuned by changing the degree of oxidation. A lower limit of the GO mobility was found to be 850 cm2/V s, rivaling silicon. In situ local oxidation of patterned epitaxial graphene has been achieved.

Hidden Area and Mechanical Nonlinearities in Freestanding Graphene

Science.gov (United States)

Nicholl, Ryan J. T.; Lavrik, Nickolay V.; Vlassiouk, Ivan; Srijanto, Bernadeta R.; Bolotin, Kirill I.

2017-06-01

We investigated the effect of out-of-plane crumpling on the mechanical response of graphene membranes. In our experiments, stress was applied to graphene membranes using pressurized gas while the strain state was monitored through two complementary techniques: interferometric profilometry and Raman spectroscopy. By comparing the data obtained through these two techniques, we determined the geometric hidden area which quantifies the crumpling strength. While the devices with hidden area ˜0 % obeyed linear mechanics with biaxial stiffness 428 ±10 N /m , specimens with hidden area in the range 0.5%-1.0% were found to obey an anomalous nonlinear Hooke's law with an exponent ˜0.1 .

Molecular dynamics simulation on double-elastic deformation of zigzag graphene nanoribbons at low temperature

International Nuclear Information System (INIS)

Sun, Y.J.; Huang, Y.H.; Ma, F.; Ma, D.Y.; Hu, T.W.; Xu, K.W.

2014-01-01

Highlights: • Molecular dynamics simulation was performed to study the deformation behaviors of Zigzag Graphene Nano-Ribbons (ZGNRs). • The “phase transformation” from hexagonal to quasi-rectangular and the subsequent second elastic deformation were observed. • Related thermal effects model was built to predict fracture strain of ZGNRs, and was consistent with simulation results. -- Abstract: Molecular dynamics simulation was performed to study the deformation behaviors of Zigzag Graphene Nano-Ribbons (ZGNRs) 150 Å × 150 Å in size, and double-elastic deformation was observed at temperatures lower than 90 K. Essentially, at such a low temperature, the lattice vibration was significantly weakened and thus the lifetime of C-C bonds was prolonged considerably. Moreover, it was difficult for broken bonds to accumulate and resulted in the destructive fracture of ZGNRs at low temperature. As a result, the “phase transformation” from hexagonal to quasi-rectangular and subsequently the second elastic deformation took place. However, at higher temperatures, says, 300 K, brittle fracture was observed and the fracture strength decreased with temperature, which was consistent with previously reported results. Additionally at higher strain rate, the atoms could not respond to the external loading in time, the fracture strain and fracture strength were enhanced

Theoretical study of optical conductivity of graphene with magnetic and nonmagnetic adatoms

Science.gov (United States)

Majidi, Muhammad Aziz; Siregar, Syahril; Rusydi, Andrivo

2014-11-01

We present a theoretical study of the optical conductivity of graphene with magnetic and nonmagnetic adatoms. First, by introducing an alternating potential in a pure graphene, we demonstrate a gap formation in the density of states and the corresponding optical conductivity. We highlight the distinction between such a gap formation and the so-called Pauli blocking effect. Next, we apply this idea to graphene with adatoms by introducing magnetic interactions between the carrier spins and the spins of the adatoms. Exploring various possible ground-state spin configurations of the adatoms, we find that the antiferromagnetic configuration yields the lowest total electronic energy and is the only configuration that forms a gap. Furthermore, we analyze four different circumstances leading to similar gaplike structures and propose a means to interpret the magneticity and the possible orderings of the adatoms on graphene solely from the optical conductivity data. We apply this analysis to the recently reported experimental data of oxygenated graphene.

Graphene Schottky diodes: An experimental review of the rectifying graphene/semiconductor heterojunction

International Nuclear Information System (INIS)

Di Bartolomeo, Antonio

2016-01-01

In the past decade graphene has been one of the most studied materials for several unique and excellent properties. Due to its two dimensional nature, physical and chemical properties and ease of manipulation, graphene offers the possibility of integration with the existing semiconductor technology for next-generation electronic and sensing devices. In this context, the understanding of the graphene/semiconductor interface is of great importance since it can constitute a versatile standalone device as well as the building-block of more advanced electronic systems. Since graphene was brought to the attention of the scientific community in 2004, the device research has been focused on the more complex graphene transistors, while the graphene/semiconductor junction, despite its importance, has started to be the subject of systematic investigation only recently. As a result, a thorough understanding of the physics and the potentialities of this device is still missing. The studies of the past few years have demonstrated that graphene can form junctions with 3D or 2D semiconducting materials which have rectifying characteristics and behave as excellent Schottky diodes. The main novelty of these devices is the tunable Schottky barrier height, a feature which makes the graphene/semiconductor junction a great platform for the study of interface transport mechanisms as well as for applications in photo-detection, high-speed communications, solar cells, chemical and biological sensing, etc. In this paper, we review the state-of-the art of the research on graphene/semiconductor junctions, the attempts towards a modeling and the most promising applications.

Graphene: corrosion-inhibiting coating.

Science.gov (United States)

Prasai, Dhiraj; Tuberquia, Juan Carlos; Harl, Robert R; Jennings, G Kane; Rogers, Bridget R; Bolotin, Kirill I

2012-02-28

We report the use of atomically thin layers of graphene as a protective coating that inhibits corrosion of underlying metals. Here, we employ electrochemical methods to study the corrosion inhibition of copper and nickel by either growing graphene on these metals, or by mechanically transferring multilayer graphene onto them. Cyclic voltammetry measurements reveal that the graphene coating effectively suppresses metal oxidation and oxygen reduction. Electrochemical impedance spectroscopy measurements suggest that while graphene itself is not damaged, the metal under it is corroded at cracks in the graphene film. Finally, we use Tafel analysis to quantify the corrosion rates of samples with and without graphene coatings. These results indicate that copper films coated with graphene grown via chemical vapor deposition are corroded 7 times slower in an aerated Na(2)SO(4) solution as compared to the corrosion rate of bare copper. Tafel analysis reveals that nickel with a multilayer graphene film grown on it corrodes 20 times slower while nickel surfaces coated with four layers of mechanically transferred graphene corrode 4 times slower than bare nickel. These findings establish graphene as the thinnest known corrosion-protecting coating.

Controlling the number of graphene sheets exfoliated from graphite by designed normal loading and frictional motion

International Nuclear Information System (INIS)

Lee, Seungjun; Lu, Wei

2014-01-01

We use molecular dynamics to study the exfoliation of patterned nanometer-sized graphite under various normal loading conditions for friction-induced exfoliation. Using highly ordered pyrolytic graphite (HOPG) as well as both amorphous and crystalline SiO 2 substrate as example systems, we show that the exfoliation process is attributed to the corrugation of the HOPG surface and the atomistic roughness of the substrate when they contact under normal loading. The critical normal strain, at which the exfoliation occurs, is higher on a crystalline substrate than on an amorphous substrate. This effect is related to the atomistic flatness and stiffness of the crystalline surface. We observe that an increase of the van der Waals interaction between the graphite and the substrate results in a decrease of the critical normal strain for exfoliation. We find that the magnitude of the normal strain can effectively control the number of exfoliated graphene layers. This mechanism suggests a promising approach of applying designed normal loading while sliding to pattern controlled number of graphene layers or other two-dimensional materials on a substrate surface.

Stretchable and Hydrophobic Electrochromic Devices Using Wrinkled Graphene and PEDOT:PSS

Directory of Open Access Journals (Sweden)

Srinivasa Kartik Nemani

2018-01-01

Full Text Available We present an electrochromic device (ECD fabricated using PEDOT:PSS and graphene as active conductive electrode films and a flexible compliant polyurethane substrate with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonylimide (EMI-TSFI additive, as ionic medium. This device with a docile, elastic intermediate substrate along with a transparency controlled PEDOT:PSS film provides a wide color contrast and fast switching rate. We harness wrinkling instability of graphene to achieve a hydrophobic nature without compromising transparency of the ECD. This mechanical self-assembly approach helps in controlling the wavelength of wrinkles generated by inducing measured prestrain conditions and regulating the modulus contrast by selection of underlying materials used, hereby controlling the extent of transparency. The reduction and oxidation switching times for the device were analyzed to be 5.76 s and 5.34 s for a 90% transmittance change at an operating DC voltage of 15 ± 0.1 V. Strain dependent studies show that the performance was robust with the device retaining switching contrasts even at 15% uniaxial strain conditions. Our device also exhibits superior antiwetting properties with an average water contact angle of 110°  ± 2° at an induced radial prestrain of 30% in the graphene film. A wide range color contrast, flexibility, and antiwetting nature of the device envision its uses in smart windows, visors, and other wearable equipment where these functionalities are of outmost importance for developing new generation of smart interactive devices.

Hybrid zinc oxide/graphene electrodes for depleted heterojunction colloidal quantum-dot solar cells.

Science.gov (United States)

Tavakoli, Mohammad Mahdi; Aashuri, Hossein; Simchi, Abdolreza; Fan, Zhiyong

2015-10-07

Recently, hybrid nanocomposites consisting of graphene/nanomaterial heterostructures have emerged as promising candidates for the fabrication of optoelectronic devices. In this work, we have employed a facile and in situ solution-based process to prepare zinc oxide/graphene quantum dots (ZnO/G QDs) in a hybrid structure. The prepared hybrid dots are composed of a ZnO core, with an average size of 5 nm, warped with graphene nanosheets. Spectroscopic studies show that the graphene shell quenches the photoluminescence intensity of the ZnO nanocrystals by about 72%, primarily due to charge transfer reactions and static quenching. A red shift in the absorption peak is also observed. Raman spectroscopy determines G-band splitting of the graphene shell into two separated sub-bands (G(+), G(-)) caused by the strain induced symmetry breaking. It is shown that the hybrid ZnO/G QDs can be used as a counter-electrode for heterojunction colloidal quantum-dot solar cells for efficient charge-carrier collection, as evidenced by the external quantum efficiency measurement. Under the solar simulated spectrum (AM 1.5G), we report enhanced power conversion efficiency (35%) with higher short current circuit (80%) for lead sulfide-based solar cells as compared to devices prepared by pristine ZnO nanocrystals.

A mesoporous WO3−X/graphene composite as a high-performance Li-ion battery anode

International Nuclear Information System (INIS)

Liu, Fei; Kim, Jong Gu; Lee, Chul Wee; Im, Ji Sun

2014-01-01

Graphical abstract: The highly flexible and conductive graphene layer can enhance electron transfer, protect metal oxides against disintegration and aggregation and buffer the strain induced by volume expansion during cycles. The mesoporous surface layer provides an open network for Li+ diffusion. - Highlights: • Novel cocktail effects of 2D mesoporous WO 3−X /graphene for lithium ion battery. • New approach for lithium ion battery by easy and unique synthesis method. • Mechanism study with proper data for understanding a reaction on anode surface. - Abstract: A novel mesoporous WO 3−X /graphene composite was developed. This material allowed rapid electron and Li + ion diffusion when used as a Li-ion battery (LIB) anode material. Remarkably, the graphene support protected WO 3−X from changing volume during the electrochemical cycling process; this process generally induces capacity loss. The current work describes a high-performance anode material for LIB that has highly dense WO 3−X , as well as high capacity, rate capability and stability

Giant valley drifts in uniaxially strained monolayer MoS2

KAUST Repository

Zhang, Qingyun

2013-12-30

Using first-principles calculations, we study the electronic structure of monolayer MoS2 under uniaxial strain. We show that the energy valleys drift far off the corners of the Brillouin zone (K points), about 12 times the amount observed in graphene. Therefore, it is essential to take this effect into consideration for a correct identification of the band gap. The system remains a direct band gap semiconductor up to 4% uniaxial strain, while the size of the band gap decreases from 1.73 to 1.54 eV. We also demonstrate that the splitting of the valence bands due to inversion symmetry breaking and spin-orbit coupling is not sensitive to strain.

Hydrogenation of graphene nanoflakes and C-H bond dissociation of hydrogenated graphene nanoflakes: a density functional theory study

Institute of Scientific and Technical Information of China (English)

Sheng Tao; Hui-Ting Liu; Liu-Ming Yan; Bao-Hua Yue; Ai-Jun Li

2017-01-01

The Gibbs free energy change for the hydrogenation of graphene nanoflakes Cn (n =24,28,30 and 32) and the C-H bond dissociation energy of hydrogenated graphene nanoflakes CnHm (n =24,28,30 and 32;and m =1,2 and 3) are evaluated using density functional theory calculations.It is concluded that the graphene nanoflakes and hydrogenated graphene nanoflakes accept the ortharyne structure with peripheral carbon atoms bonded via the most triple bonds and leaving the least unpaired dangling electrons.Five-membered rings are formed at the deep bay sites attributing to the stabilization effect from the pairing of dangling electrons.The hydrogenation reactions which eliminate one unpaired dangling electron and thus decrease the overall multiplicity of the graphene nanoflakes or hydrogenated graphene nanoflakes are spontaneous with negative or near zero Gibbs free energy change.And the resulting C-H bonds are stable with bond dissociation energy in the same range as those of aromatic compounds.The other C-H bonds are not as stable attributing to the excessive unpaired dangling electrons being filled into the C-H anti-bond orbital.

A comparison study between ZnO nanorods coated with graphene oxide and reduced graphene oxide

International Nuclear Information System (INIS)

Ding, Jijun; Wang, Minqiang; Deng, Jianping; Gao, Weiyin; Yang, Zhi; Ran, Chenxin; Zhang, Xiangyu

2014-01-01

Highlights: • Optical properties between ZnO-GO and ZnO-RGO composites were compared. • Photoluminescence quenching was observed in ZnO-GO composites. • We obtained enhanced photoluminescence in ZnO-RGO composites. -- Abstract: ZnO nanorods (ZnO NRs) coated with graphene oxide (ZnO-GO) and reduced graphene oxide sheets (ZnO-RGO) were prepared on indium tin oxide (ITO) substrates. The crystal structures, morphology and optical properties were analyzed by using X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM) images, absorption spectra and photoluminescence (PL) spectra, respectively. A comparison between PL properties from ZnO-GO and ZnO-RGO were studied. Results indicated that the peak at 442 nm and a broad band at 450–600 nm of ZnO NRs show PL quenching after coating with GO sheets. As coating with RGO sheets, the extent of PL quenching increases. It is interesting to note that as ZnO NRs coated with RGO sheets, the intensity of PL peak at 390 nm significantly increased. The enhanced PL emission research in ZnO-RGO is directed toward development of the “nextgeneration” optoelectronics devices related with graphene materials

Graphene-based structure, method of suspending graphene membrane, and method of depositing material onto graphene membrane

Science.gov (United States)

Zettl, Alexander K.; Meyer, Jannik Christian

2013-04-02

An embodiment of a method of suspending a graphene membrane across a gap in a support structure includes attaching graphene to a substrate. A pre-fabricated support structure having the gap is attached to the graphene. The graphene and the pre-fabricated support structure are then separated from the substrate which leaves the graphene membrane suspended across the gap in the pre-fabricated support structure. An embodiment of a method of depositing material includes placing a support structure having a graphene membrane suspended across a gap under vacuum. A precursor is adsorbed to a surface of the graphene membrane. A portion of the graphene membrane is exposed to a focused electron beam which deposits a material from the precursor onto the graphene membrane. An embodiment of a graphene-based structure includes a support structure having a gap, a graphene membrane suspended across the gap, and a material deposited in a pattern on the graphene membrane.

Local organization of graphene network inside graphene / polymer composites

NARCIS (Netherlands)

Alekseev, A.; Chen, D.; Tkalya, E.; Gomes Ghislandi, M.; Syurik, Y.V.; Ageev, O.A.; Loos, J.; With, de G.

2012-01-01

The local electrical properties of a conductive graphene/polystyrene (PS) composite sample are studied by scanning probe microscopy (SPM) applying various methods for electrical properties investigation. We show that the conductive graphene network can be separated from electrically isolated

Theoretical study of Ag doping-induced vacancies defects in armchair graphene

Science.gov (United States)

Benchallal, L.; Haffad, S.; Lamiri, L.; Boubenider, F.; Zitoune, H.; Kahouadji, B.; Samah, M.

2018-06-01

We have performed a density functional theory (DFT) study of the absorption of silver atoms (Ag,Ag2 and Ag3) in graphene using SIESTA code, in the generalized gradient approximation (GGA). The absorption energy, geometry, magnetic moments and charge transfer of Ag clusters-graphene system are calculated. The minimum energy configuration demonstrates that all structures remain planar and silver atoms fit into this plane. The charge transfer between the silver clusters and carbon atoms constituting the graphene surface is an indicative of a strong bond. The structure doped with a single silver atom has a magnetic moment and the two other are nonmagnetic.

Thermal properties of graphite oxide, thermally reduced graphene and chemically reduced graphene

Science.gov (United States)

Jankovský, Ondřej; Sedmidubský, David; Lojka, Michal; Sofer, Zdeněk

2017-07-01

We compared thermal behavior and other properties of graphite oxide, thermally reduced graphene and chemically reduced graphene. Graphite was oxidized according to the Hofmann method using potassium chlorate as oxidizing agent in strongly acidic environment. In the next step, the formed graphite oxide was chemically or thermally reduced yielding graphene. The mechanism of thermal reduction was studied using STA-MS. Graphite oxide and both thermally and chemically reduced graphenes were analysed by SEM, EDS, elemental combustion analysis, XPS, Raman spectroscopy, XRD and BET. These findings will help for the large scale production of graphene with appropriate chemical composition.

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.

Structures and Properties of Polyacrylonitrile/Graphene Composite Nanofiber Yarns Prepared by Multi-Needle Electrospinning Device with an Auxiliary Electrode.

Science.gov (United States)

Yan, Tao; Pan, Zhi-Juan

2018-06-01

In this paper, polyacrylonitrile/graphene composite nanofiber filaments were manufactured continuously by a homemade eight-needle electrospinning device with an auxiliary electrode. The polyacrylonitrile/graphene composite nanofiber yarns were obtained continuously by plying and twisting the composite nanofiber filaments. The structures and properties of the composite nanofiber filaments with different GP mass fractions and yarns were investigated. The results demonstrated that the maximum alignment degree of the composite nanofibers along the filament axis could reach 74.3% with 1%, and the alignment degree decreased with increasing graphene mass fraction. The diameters of the composite nanofibers were considerably smaller than those of the pure polyacrylonitrile nanofiber, and the minimum diameter was 156 nm for 1%. The conductivity of the composite nanofiber filaments was significantly enhanced by seven orders of magnitude compared with that of the pure polyacrylonitrile nanofiber filament, and the maximum value was 3.73×10-7 S/cm for 1.5%. Due to graphene agglomeration, the conductivity decreased when the mass fraction was more than 1.5%. The different number of filaments and twists were examined in detail to improve the poor mechanical properties of the nanofiber filaments. With an increase in twists, the breaking stress and strain increased initially and later decreased, and the maximum breaking stress and strain were 16.54 MPa and 26.42%, respectively. This study demonstrates the possibility of continuously and stably manufacturing polyacrylonitrile/graphene composite nanofiber yarns.

Pt-decorated graphene as superior media for H2S adsorption: A first-principles study

International Nuclear Information System (INIS)

Ganji, Masoud Darvish; Sharifi, Narges; Ardjmand, Mahdi; Ahangari, Morteza Ghorbanzadeh

2012-01-01

Highlights: ► We report the first DFT study in the H 2 S/Pt–graphene system. ► The adsorption properties of H 2 S at different possible site on the surface of pristine graphene are slightly stable presenting energies from 0.02 to 0.06 eV. ► When Pt decorates the graphene sheet on the single and double sides the H 2 S adsorption energy increase to −3.2 eV. ► A single Pt atom can locate up to seven H 2 S molecules stably binded with energies from −6.73 to −0.95 eV. ► The DOS plot indicates strong hybridization between H 2 S molecules and Pt–graphene sheet. - Abstract: The adsorption mechanism of hydrogen sulfide (H 2 S) molecules on pristine and Pt-decorated graphene sheets was studied using density functional theory calculations based on local density approximation and generalized gradient approximation methods. Our calculations show that a Pt-decorated graphene system has much higher binding energy, higher net charge transfer values and shorter connecting distances than pristine graphene due to chemisorption of the H 2 S molecule. Furthermore, the calculated density of states show that orbital hybridization is visible between the H 2 S and Pt-decorated graphene sheets, while there is no evidence for hybridization between the H 2 S molecule and the pristine graphene sheet. Interestingly, we find that up to seven H 2 S molecules can stably bind to a Pt atom on each side of the graphene sheet with desirable binding energy.

Graphene interfaced perovskite solar cells: Role of graphene flake size

Science.gov (United States)

Sakorikar, Tushar; Kavitha, M. K.; Tong, Shi Wun; Vayalamkuzhi, Pramitha; Loh, Kian Ping; Jaiswal, Manu

2018-04-01

Graphene interfaced inverted planar heterojunction perovskite solar cells are fabricated by facile solution method and studied its potential as hole conducting layer. Reduced graphene oxide (rGO) with small and large flake size and Polyethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) are utilized as hole conducting layers in different devices. For the solar cell employing PEDOT:PSS as hole conducting layer, 3.8 % photoconversion efficiency is achieved. In case of solar cells fabricated with rGO as hole conducting layer, the efficiency of the device is strongly dependent on flake size. With all other fabrication conditions kept constant, the efficiency of graphene-interfaced solar cell improves by a factor of 6, by changing the flake size of graphene oxide. We attribute this effect to uniform coverage of graphene layer and improved electrical percolation network.

Surface study of gallium- and aluminum- doped graphenes upon adsorption of cytosine: DFT calculations

International Nuclear Information System (INIS)

Shokuhi Rad, Ali; Zareyee, Daryoush; Peyravi, Majid; Jahanshahi, Mohsen

2016-01-01

Highlights: • P1 and P4 are the most stable adsorption configurations for cytosine. • NBO analysis show n-type semiconductor property for both Al- and Ga-doped graphenes. • Important changes in the HOMO and LUMO of doped graphene upon adsorption of cytosine. • Increase in the conductivity of system when cytosine is adsorbed on doped graphenes. - Abstract: The adsorption of cytosine molecule on Al- and Ga- doped graphenes is studied using first-principles density functional theory (DFT) calculations. The energetically most stable geometries of cytosine on both Al- and Ga- doped graphenes are determined and the adsorption energies are calculated. The net charge of transfer as well as local charge of doped atoms upon adsorption of cytosine are studied by natural bond orbitals (NBO) analysis. Orbital hybridizing of complexes was searched by frontier molecular orbital theory (FMO), and density of states (DOS). Depending on the side of cytosine, there are four possible sites for its adsorption on doped graphene; denoted as P1, P2, P3, and P4, respectively. The order of binding energy in the case of Al-doped graphene is found as P1 > P4 > P3 > P2. Interestingly, the order in the case of Ga-doped graphene changes to: P4 ∼ P1 > P3 > P2. Both surfaces show superior adsorbent property, resulting chemisorption of cytosine, especially at P1 and P4 position configurations. The NBO charge analysis reveals that the charge transfers from Al- and Ga- doped graphene sheets to cytosine. The electronic properties of both surfaces undertake important changes after cytosine adsorption, which indicates notable change in its electrical conductivity.

Surface study of gallium- and aluminum- doped graphenes upon adsorption of cytosine: DFT calculations

Energy Technology Data Exchange (ETDEWEB)

Shokuhi Rad, Ali, E-mail: a.shokuhi@gmail.com [Department of Chemical Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Zareyee, Daryoush [Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Peyravi, Majid; Jahanshahi, Mohsen [Faculty of Chemical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of)

2016-12-30

Highlights: • P1 and P4 are the most stable adsorption configurations for cytosine. • NBO analysis show n-type semiconductor property for both Al- and Ga-doped graphenes. • Important changes in the HOMO and LUMO of doped graphene upon adsorption of cytosine. • Increase in the conductivity of system when cytosine is adsorbed on doped graphenes. - Abstract: The adsorption of cytosine molecule on Al- and Ga- doped graphenes is studied using first-principles density functional theory (DFT) calculations. The energetically most stable geometries of cytosine on both Al- and Ga- doped graphenes are determined and the adsorption energies are calculated. The net charge of transfer as well as local charge of doped atoms upon adsorption of cytosine are studied by natural bond orbitals (NBO) analysis. Orbital hybridizing of complexes was searched by frontier molecular orbital theory (FMO), and density of states (DOS). Depending on the side of cytosine, there are four possible sites for its adsorption on doped graphene; denoted as P1, P2, P3, and P4, respectively. The order of binding energy in the case of Al-doped graphene is found as P1 > P4 > P3 > P2. Interestingly, the order in the case of Ga-doped graphene changes to: P4 ∼ P1 > P3 > P2. Both surfaces show superior adsorbent property, resulting chemisorption of cytosine, especially at P1 and P4 position configurations. The NBO charge analysis reveals that the charge transfers from Al- and Ga- doped graphene sheets to cytosine. The electronic properties of both surfaces undertake important changes after cytosine adsorption, which indicates notable change in its electrical conductivity.

Graphene Electrodes

DEFF Research Database (Denmark)

Pizzocchero, Filippo

The production of graphene and the other 2D materials is presented in the beginning of this thesis. Micromechanical exfoliation is the best method for obtaining relatively small and top quality samples. The invention of Graphene Finder simplifies the procedure of finding the exfoliated flakes...... in copper thin films is studied and found to be detrimental for the growth of graphene. The modified synthesis of rGO is introduced, as rGO represents a cheap alternative to CVD for large scale production of graphene. The transfer of flakes is performed by several methods, such as with PVA/PMMA support, CAB...... wedging and the pick-up technique with hBN. Several important improvements of the pick-up technique are introduced. These allowed us to transfer any 2D crystals and patterned graphene flakes with PMMA residues. We also developed the drop-down technique, which is used to release any crystal on the surface...

Graphene transfer process and optimization of graphene coverage

OpenAIRE

Sabki Syarifah Norfaezah; Shamsuri Shafiq Hafly; Fauzi Siti Fazlina; Chon-Ki Meghashama Lim; Othman Noraini

2017-01-01

Graphene grown on transition metal is known to be high in quality due to its controlled amount of defects and potentially used for many electronic applications. The transfer process of graphene grown on transition metal to a new substrate requires optimization in order to ensure that high graphene coverage can be obtained. In this work, an improvement in the graphene transfer process is performed from graphene grown on copper foil. It has been observed that the graphene coverage is affected b...

Graphene-aluminum nanocomposites

International Nuclear Information System (INIS)

Bartolucci, Stephen F.; Paras, Joseph; Rafiee, Mohammad A.; Rafiee, Javad; Lee, Sabrina; Kapoor, Deepak; Koratkar, Nikhil

2011-01-01

Highlights: → We investigated the mechanical properties of aluminum and aluminum nanocomposites. → Graphene composite had lower strength and hardness compared to nanotube reinforcement. → Processing causes aluminum carbide formation at graphene defects. → The carbides in between grains is a source of weakness and lowers tensile strength. - Abstract: Composites of graphene platelets and powdered aluminum were made using ball milling, hot isostatic pressing and extrusion. The mechanical properties and microstructure were studied using hardness and tensile tests, as well as electron microscopy, X-ray diffraction and differential scanning calorimetry. Compared to the pure aluminum and multi-walled carbon nanotube composites, the graphene-aluminum composite showed decreased strength and hardness. This is explained in the context of enhanced aluminum carbide formation with the graphene filler.

Modal analysis of graphene-based structures for large deformations, contact and material nonlinearities

Science.gov (United States)

Ghaffari, Reza; Sauer, Roger A.

2018-06-01

The nonlinear frequencies of pre-stressed graphene-based structures, such as flat graphene sheets and carbon nanotubes, are calculated. These structures are modeled with a nonlinear hyperelastic shell model. The model is calibrated with quantum mechanics data and is valid for high strains. Analytical solutions of the natural frequencies of various plates are obtained for the Canham bending model by assuming infinitesimal strains. These solutions are used for the verification of the numerical results. The performance of the model is illustrated by means of several examples. Modal analysis is performed for square plates under pure dilatation or uniaxial stretch, circular plates under pure dilatation or under the effects of an adhesive substrate, and carbon nanotubes under uniaxial compression or stretch. The adhesive substrate is modeled with van der Waals interaction (based on the Lennard-Jones potential) and a coarse grained contact model. It is shown that the analytical natural frequencies underestimate the real ones, and this should be considered in the design of devices based on graphene structures.

Graphene: from functionalization to devices

Science.gov (United States)

Tejeda, Antonio; Soukiassian, Patrick G.

2014-03-01

The year 2014 marks the first decade of the rise of graphene. Graphene, a single atomic layer of carbon atoms in sp2 bonding configuration having a honeycomb structure, has now become a well-known and well-established material. Among some of its many outstanding fundamental properties, one can mention a very high carrier mobility, a very large spin diffusion length, unsurpassed mechanical properties as graphene is the strongest material ever measured and an exceptional thermal conductivity scaling more than one order of magnitude above that of copper. After the first years of the graphene rush, graphene growth is now well controlled using various methods like epitaxial growth on silicon carbide substrate, chemical vapour deposition (CVD) or plasma techniques on metal, insulator or semiconductor substrates. More applied research is now taking over the initial studies on graphene production. Indeed, graphene is a promising material for many advanced applications such as, but not limited to, electronic, spintronics, sensors, photonics, micro/nano-electromechanical (MEMS/NEMS) systems, super-capacitors or touch-screen technologies. In this context, this Special Issue of the Journal of Physics D: Applied Physics on graphene reviews some of the recent achievements, progress and prospects in this field. It includes a collection of seventeen invited articles covering the current status and future prospects of some selected topics of strong current interest. This Special Issue is organized in four sections. The first section is dedicated to graphene devices, and opens with an article by de Heer et al on an investigation of integrating graphene devices with silicon complementary metal-oxide-semiconductor (CMOS) technology. Then, a study by Svintsov et al proposes a lateral all-graphene tunnel field-effect transistor (FET) with a high on/off current switching ratio. Next, Tsukagoshi et al present how a band-gap opening occurs in a graphene bilayer by using a perpendicular

Hydrogen atom addition to the surface of graphene nanoflakes: A density functional theory study

Energy Technology Data Exchange (ETDEWEB)

Tachikawa, Hiroto, E-mail: hiroto@eng.hokudai.ac.jp

2017-02-28

Highlights: • The reaction pathway of the hydrogen addition to graphene surface was determined by the DFT method. • Binding energies of atomic hydrogen to graphene surface were determined. • Absorption spectrum of hydrogenated graphene was theoretically predicted. • Hyperfine coupling constant of hydrogenated graphene was theoretically predicted. - Abstract: Polycyclic aromatic hydrocarbons (PAHs) provide a 2-dimensional (2D) reaction surface in 3-dimensional (3D) interstellar space and have been utilized as a model of graphene surfaces. In the present study, the reaction of PAHs with atomic hydrogen was investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of atomic hydrogen to graphene nanoflakes. PAHs with n = 4–37 were chosen, where n indicates the number of benzene rings. Activation energies of hydrogen addition to the graphene surface were calculated to be 5.2–7.0 kcal/mol at the CAM-B3LYP/6-311G(d,p) level, which is almost constant for all PAHs. The binding energies of hydrogen atom were slightly dependent on the size (n): 14.8–28.5 kcal/mol. The absorption spectra showed that a long tail is generated at the low-energy region after hydrogen addition to the graphene surface. The electronic states of hydrogenated graphenes were discussed on the basis of theoretical results.

Surface study of platinum decorated graphene towards adsorption of NH{sub 3} and CH{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Rad, Ali Shokuhi, E-mail: a.shokuhi@gmail.com [Department of Chemical Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Pazoki, Hossein; Mohseni, Soheil [Department of Chemical Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Zareyee, Daryoush [Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Peyravi, Majid [Faculty of Chemical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of)

2016-10-01

To distinguish the potential of graphene sensors, there is a need to recognize the interaction between graphene sheet and adsorbing molecules. We used density functional theory (DFT) calculations to study the properties of pristine as well as Pt-decorated graphene sheet upon adsorption of NH{sub 3} and CH{sub 4} on its surface to exploit its potential to be as gas sensors for them. We found much higher adsorption, higher charge transfer, lower intermolecular distance, and higher orbital hybridizing upon adsorption of NH{sub 3} and CH{sub 4} gas molecules on Pt-decorated graphene compared to pristine graphene. Also our calculations reveal that the adsorption energies on Pt-decorated graphene sheet are in order of NH{sub 3} >CH{sub 4} which could be corresponded to the order of their sensitivity on this modified surface. We used orbital analysis including density of states as well as frontier molecular orbital study for all analyte-surface systems to more understanding the kind of interaction (physisorption or chemisorption). Consequently, the Pt-decorated graphene can transform the existence of NH{sub 3} and CH{sub 4} molecules into electrical signal and it may be potentially used as an ideal sensor for detection of NH{sub 3} and CH{sub 4} in ambient situation. - Highlights: • Pt-decorated graphene was investigated as an adsorbent for NH{sub 3} and CH{sub 4}. • Much higher adsorption of NH{sub 3} and CH{sub 4} on Pt-decorated graphene than pristine graphene. • Higher adsorption of NH{sub 3} compared to CH{sub 4} on Pt-decorated graphene. • Pt influences the electronic structure of graphene.

Graphene and Graphene Metamaterials for Terahertz Absorbers

DEFF Research Database (Denmark)

Andryieuski, Andrei; Pizzocchero, Filippo; Booth, Tim

2013-01-01

Graphene, due to the possibility to tune its conductivity, is the promising material for a range of the terahertz (THz) applications, such as tunable reflectors, absorbers, modulators, filters and polarization converters. Subwavelength structuring of graphene in order to form metamaterials allows...... for even more control over the THz waves. In this poster presentation I will show an elegant way to describe the graphene metamaterials and the design of graphene based absorbers. I will also present our recent experimental results on the graphene absorbers characterization....

Plasmon mediated inverse Faraday effect in a graphene-dielectric-metal structure.

Science.gov (United States)

Bychkov, Igor V; Kuzmin, Dmitry A; Tolkachev, Valentine A; Plaksin, Pavel S; Shavrov, Vladimir G

2018-01-01

This Letter shows the features of inverse Faraday effect (IFE) in a graphene-dielectric-metal (GDM) structure. The constants of propagation and attenuation of the surface plasmon-polariton modes are calculated. The effective magnetic field induced by surface plasmon modes in the dielectric due to the IFE is estimated to reach above 1 tesla. The possibility to control the distribution of the magnetic field by chemical potential of graphene is shown. The concept of strain-driven control of the IFE in the structure has been proposed and investigated.

Raman spectroscopy in graphene

International Nuclear Information System (INIS)

Malard, L.M.; Pimenta, M.A.; Dresselhaus, G.; Dresselhaus, M.S.

2009-01-01

Recent Raman scattering studies in different types of graphene samples are reviewed here. We first discuss the first-order and the double resonance Raman scattering mechanisms in graphene, which give rise to the most prominent Raman features. The determination of the number of layers in few-layer graphene is discussed, giving special emphasis to the possibility of using Raman spectroscopy to distinguish a monolayer from few-layer graphene stacked in the Bernal (AB) configuration. Different types of graphene samples produced both by exfoliation and using epitaxial methods are described and their Raman spectra are compared with those of 3D crystalline graphite and turbostratic graphite, in which the layers are stacked with rotational disorder. We show that Resonance Raman studies, where the energy of the excitation laser line can be tuned continuously, can be used to probe electrons and phonons near the Dirac point of graphene and, in particular allowing a determination to be made of the tight-binding parameters for bilayer graphene. The special process of electron-phonon interaction that renormalizes the phonon energy giving rise to the Kohn anomaly is discussed, and is illustrated by gated experiments where the position of the Fermi level can be changed experimentally. Finally, we discuss the ability of distinguishing armchair and zig-zag edges by Raman spectroscopy and studies in graphene nanoribbons in which the Raman signal is enhanced due to resonance with singularities in the density of electronic states.

Electronic Properties of Corrugated Graphene, the Heisenberg Principle and Wormhole Geometry in Solid State

International Nuclear Information System (INIS)

Atanasov, Victor; Saxena, Avadh

2010-12-01

Adopting a purely two dimensional relativistic equation for graphene's carriers contradicts the Heisenberg uncertainty principle since it requires setting off-the-surface coordinate of a three-dimensional wavefunction to zero. Here we present a theoretical framework for describing graphene's massless relativistic carriers in accordance with this most fundamental of all quantum principles. A gradual confining procedure is used to restrict the dynamics onto a surface and in the process the embedding of this surface into the three dimensional world is accounted for. As a result an invariant geometric potential arises which scales linearly with the Mean curvature and shifts the Fermi energy of the material proportional to bending. Strain induced modification of the electronic properties or 'straintronics' is clearly an important field of study in graphene. This opens a venue to producing electronic devices, MEMS and NEMS where the electronic properties are controlled by geometric means and no additional alteration of graphene is necessary. The appearance of this geometric potential also provides us with clues as to how quantum dynamics looks like in the curved space-time of general relativity. In this context, we explore a two-dimensional cross-section of the wormhole geometry realized with graphene as a solid state thought experiment. (author)

Micro-patterned graphene-based sensing skins for human physiological monitoring

Science.gov (United States)

Wang, Long; Loh, Kenneth J.; Chiang, Wei-Hung; Manna, Kausik

2018-03-01

Ultrathin, flexible, conformal, and skin-like electronic transducers are emerging as promising candidates for noninvasive and nonintrusive human health monitoring. In this work, a wearable sensing membrane is developed by patterning a graphene-based solution onto ultrathin medical tape, which can then be attached to the skin for monitoring human physiological parameters and physical activity. Here, the sensor is validated for monitoring finger bending/movements and for recognizing hand motion patterns, thereby demonstrating its future potential for evaluating athletic performance, physical therapy, and designing next-generation human-machine interfaces. Furthermore, this study also quantifies the sensor’s ability to monitor eye blinking and radial pulse in real-time, which can find broader applications for the healthcare sector. Overall, the printed graphene-based sensing skin is highly conformable, flexible, lightweight, nonintrusive, mechanically robust, and is characterized by high strain sensitivity.

Facet-dependent study of efficient growth of graphene on copper

Indian Academy of Sciences (India)

The growth of graphene by chemical vapour deposition (CVD) on copper is the most promising scalable method for high-quality graphene. The use of ethanol, an economic and safe precursor, for the fast growth of graphene on copper by a home-built CVD set-up was analysed. Full coverage of uniform single-layer ...

Giant valley drifts in uniaxially strained monolayer MoS{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Schwingenschloegl, Udo; Zhang, Qingyun; Cheng, Yingchun; Gan, Li-Yong [PSE Division, KAUST, Thuwal 23955 (Saudi Arabia)

2016-07-01

Using first-principles calculations, we study the electronic structure of monolayer MoS{sub 2} under uniaxial strain. We show that the energy valleys drift far off the corners of the Brillouin zone (K points), about 12 times the amount observed in graphene. Therefore, it is essential to take this effect into consideration for a correct identification of the band gap. The system remains a direct band gap semiconductor up to 4% uniaxial strain, while the size of the band gap decreases from 1.73 to 1.54 eV. We also demonstrate that the splitting of the valence bands due to inversion symmetry breaking and spin-orbit coupling is not sensitive to strain.

Comparative study of synthesis and reduction methods for graphene oxide

KAUST Repository

Alazmi, Amira; Rasul, Shahid; Patole, Shashikant P.; Da Costa, Pedro M. F. J.

2016-01-01

Graphene oxide (GO) and reduced graphene oxide (rGO) have congregated much interest as promising active materials for a variety of applications such as electrodes for supercapacitors. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these materials. In this work, the effect of using different graphene oxidation-reduction strategies in the structure and chemistry of rGOs is systematically discussed. Two of the most popular oxidation routes in the literature were used to obtain GO. Subsequently, two sets of rGO powders were synthesised employing three different reduction routes, totalling six separate products. It is shown that the extension of the structural rearrangement in rGOs is not just dependent on the reduction step but also on the approach followed for the initial graphite oxidation.

Comparative study of synthesis and reduction methods for graphene oxide

KAUST Repository

Alazmi, Amira

2016-05-14

Graphene oxide (GO) and reduced graphene oxide (rGO) have congregated much interest as promising active materials for a variety of applications such as electrodes for supercapacitors. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these materials. In this work, the effect of using different graphene oxidation-reduction strategies in the structure and chemistry of rGOs is systematically discussed. Two of the most popular oxidation routes in the literature were used to obtain GO. Subsequently, two sets of rGO powders were synthesised employing three different reduction routes, totalling six separate products. It is shown that the extension of the structural rearrangement in rGOs is not just dependent on the reduction step but also on the approach followed for the initial graphite oxidation.

Exfoliation of graphene flake from SiC substrate using hydrogen injection; a first-principle study

Science.gov (United States)

Lee, Bora; Han, Seungwu; Kim, Yong-Sung

2009-03-01

Recently there is an immense interest in studying graphene for investigating its unique electronic properties as well as practical applications to nanoscale devices. Up to now there are two methods to obtain graphene layers. The first one is a mechanical method in which the single graphene sheet is split off the bulk graphite crystals using adhesives. The other method is graphitization of SiC surfaces by annealing at elevated temperatures. Even though the latter approach can provide a graphene layer in a more controlled way, the exfoliation of the graphene layer still poses a big challenge. In this presentation, based on the first-principles results, we propose a novel exfoliation method using hydrogen. As a model system, the 6H-SiC(0001) 4x4 cell is used, which corresponds to the 3x3 graphene cell. We calculate the binding energy of single hydrogen atom in various places; above and below graphene surface and inside the first SiC layer. The binding energies of hydrogen are calculated for different coverages. It is found that at high coverages, the hydrogen atoms prefer to bind below the graphene surface, cutting the graphene-SiC bonds. This means that the graphene can be exfoliated in the hydrogen-rich environment. The detailed analysis including the electronic structures will be presented.

Structural and optical studies on spin coated ZnO-graphene conjugated thin films

Science.gov (United States)

Srinatha, N.; Angadi, Basavaraj; Son, D. I.; Choi, W. K.

2018-05-01

ZnO-Graphene conjugated thin films were prepared using spin coating technique for different spin rates. Prior to the deposition, ZnO-Graphene nanoparticles were synthesized and their particle size and conjugation was studied through Transmission electron microscope (TEM). The deposited films were characterized using grazing incidence x-ray diffractometer (GIXRD), atomic force microscope (AFM) and UV-Visible spectrometer for their crystallinity, surface topographic features and optical properties. GIXRD patterns confirms the presence of both ZnO and Graphene related crystalline peaks supports the TEM results, which shows the quasi core-shell type conjugation of ZnO-Graphene particles. The crystallinity as well as thickness of the films found to decrease with increase of spin rate. AFM results reveal the uniform, smooth and homogeneity of films and also good adhesivity of ZnO-Graphene with glass substrates. No significant change in the transmittance and absorption with spin rate is observed, while the band gap energy found to decrease due to the reduction in the thickness of the films and conjugation of ZnO-Graphene. All films exhibit˜90 % transmittance in the visible wavelength region, could be potential candidates for optoelectronics and transparent conducting oxide (TCO) applications.

Tuning the tunneling magnetoresistance by using fluorinated graphene in graphene based magnetic junctions

Directory of Open Access Journals (Sweden)

Shweta Meena

2017-12-01

Full Text Available Spin polarized properties of fluorinated graphene as tunnel barrier with CrO2 as two HMF electrodes are studied using first principle methods based on density functional theory. Fluorinated graphene with different fluorine coverages is explored as tunnel barriers in magnetic tunnel junctions. Density functional computation for different fluorine coverages imply that with increase in fluorine coverages, there is increase in band gap (Eg of graphene, Eg ∼ 3.466 e V was observed when graphene sheet is fluorine adsorbed on both-side with 100% coverage (CF. The results of CF graphene are compared with C4F (fluorination on one-side of graphene sheet with 25% coverage and out-of-plane graphene based magnetic tunnel junctions. On comparison of the results it is observed that CF graphene based structure offers high TMR ∼100%, and the transport of carrier is through tunneling as there are no transmission states near Fermi level. This suggests that graphene sheet with both-side fluorination with 100% coverages acts as a perfect insulator and hence a better barrier to the carriers which is due to negligible spin down current (I↓ in both Parallel Configuration (PC and Antiparallel Configuration (APC.

Dry-cleaning of graphene

International Nuclear Information System (INIS)

Algara-Siller, Gerardo; Lehtinen, Ossi; Kaiser, Ute; Turchanin, Andrey

2014-01-01

Studies of the structural and electronic properties of graphene in its pristine state are hindered by hydrocarbon contamination on the surfaces. Also, in many applications, contamination reduces the performance of graphene. Contamination is introduced during sample preparation and is adsorbed also directly from air. Here, we report on the development of a simple dry-cleaning method for producing large atomically clean areas in free-standing graphene. The cleanness of graphene is proven using aberration-corrected high-resolution transmission electron microscopy and electron spectroscopy

Dry-cleaning of graphene

Energy Technology Data Exchange (ETDEWEB)

Algara-Siller, Gerardo [Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, Albert-Einstein-Allee 11, Ulm 89081 (Germany); Department of Chemistry, Technical University Ilmenau, Weimarer Strasse 25, Ilmenau 98693 (Germany); Lehtinen, Ossi; Kaiser, Ute, E-mail: ute.kaiser@uni-ulm.de [Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, Albert-Einstein-Allee 11, Ulm 89081 (Germany); Turchanin, Andrey [Faculty of Physics, University of Bielefeld, Universitätsstr. 25, Bielefeld 33615 (Germany)

2014-04-14

Studies of the structural and electronic properties of graphene in its pristine state are hindered by hydrocarbon contamination on the surfaces. Also, in many applications, contamination reduces the performance of graphene. Contamination is introduced during sample preparation and is adsorbed also directly from air. Here, we report on the development of a simple dry-cleaning method for producing large atomically clean areas in free-standing graphene. The cleanness of graphene is proven using aberration-corrected high-resolution transmission electron microscopy and electron spectroscopy.

An investigation into graphene exfoliation and potential graphene application in MEMS devices

Science.gov (United States)

Fercana, George; Kletetschka, Gunther; Mikula, Vilem; Li, Mary

2011-02-01

The design of microelectromecanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) are often materials-limited with respect to the efficiency and capability of the material. Graphene, a one atom thick honeycomb lattice of carbon, is a highly desired material for MEMS applications. Relevant properties of graphene include the material's optical transparency, mechanical strength, energy efficiency, and electrical and thermal conductivity due to its electron mobility. Aforementioned properties make graphene a strong candidate to supplant existing transparent electrode technology and replace the conventionally used material, indium-tin oxide. In this paper we present preliminary results on work toward integration of graphene with MEMS structures. We are studying mechanical exfoliation of highly ordered pyrolytic graphite (HOPG) crystals by repeatedly applying and separating adhesive materials from the HOPG surface. The resulting graphene sheets are then transferred to silicon oxide substrate using the previously applied adhesive material. We explored different adhesive options, particularly the use of Kapton tape, to improve the yield of graphene isolation along with chemical cross-linking agents which operate on a mechanism of photoinsertion of disassociated nitrene groups. These perfluorophenyl nitrenes participate in C=C addition reactions with graphene monolayers creating a covalent binding between the substrate and graphene. We are focusing on maximizing the size of isolated graphene sheets and comparing to conventional exfoliation. Preliminary results allow isolation of few layer graphene (FLG) sheets (ntechnology to be used in future deep space telescopes.

Failure criterion for graphene in biaxial loading—a molecular dynamics study

International Nuclear Information System (INIS)

Yazdani, Hessam; Hatami, Kianoosh

2015-01-01

Molecular dynamics simulations are carried out in order to develop a failure criterion for infinite/bulk graphene in biaxial tension. Stresses along the principal edge configurations of graphene (i.e. armchair and zigzag directions) are normalized to the corresponding uniaxial ultimate strength values. The combinations of normalized stresses resulting in the failure of graphene are used to define failure envelopes (limiting stress ratio surfaces). Results indicate that a bilinear failure envelope can be used to represent the tensile strength of graphene in biaxial loading at different temperatures with reasonable accuracy. A circular failure envelope is also introduced for practical applications. Both failure envelopes define temperature-independent upper limits for the feasible combinations of normalized stresses for a graphene sheet in biaxial loading. Predicted failure modes of graphene under biaxial loading are also shown and discussed. (paper)

Charge transfer at junctions of a single layer of graphene and a metallic single walled carbon nanotube.

Science.gov (United States)

Paulus, Geraldine L C; Wang, Qing Hua; Ulissi, Zachary W; McNicholas, Thomas P; Vijayaraghavan, Aravind; Shih, Chih-Jen; Jin, Zhong; Strano, Michael S

2013-06-10

Junctions between a single walled carbon nanotube (SWNT) and a monolayer of graphene are fabricated and studied for the first time. A single layer graphene (SLG) sheet grown by chemical vapor deposition (CVD) is transferred onto a SiO₂/Si wafer with aligned CVD-grown SWNTs. Raman spectroscopy is used to identify metallic-SWNT/SLG junctions, and a method for spectroscopic deconvolution of the overlapping G peaks of the SWNT and the SLG is reported, making use of the polarization dependence of the SWNT. A comparison of the Raman peak positions and intensities of the individual SWNT and graphene to those of the SWNT-graphene junction indicates an electron transfer of 1.12 × 10¹³ cm⁻² from the SWNT to the graphene. This direction of charge transfer is in agreement with the work functions of the SWNT and graphene. The compression of the SWNT by the graphene increases the broadening of the radial breathing mode (RBM) peak from 3.6 ± 0.3 to 4.6 ± 0.5 cm⁻¹ and of the G peak from 13 ± 1 to 18 ± 1 cm⁻¹, in reasonable agreement with molecular dynamics simulations. However, the RBM and G peak position shifts are primarily due to charge transfer with minimal contributions from strain. With this method, the ability to dope graphene with nanometer resolution is demonstrated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

Science.gov (United States)

Sharma, Venus; Srivastava, Sunita

2018-04-01

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Wettability Investigations and Wet Transfer Enhancement of Large-Area CVD-Graphene on Aluminum Nitride.

Science.gov (United States)

Knapp, Marius; Hoffmann, René; Cimalla, Volker; Ambacher, Oliver

2017-08-18

The two-dimensional and virtually massless character of graphene attracts great interest for radio frequency devices, such as surface and bulk acoustic wave resonators. Due to its good electric conductivity, graphene might be an alternative as a virtually massless electrode by improving resonator performance regarding mass-loading effects . We report on an optimization of the commonly used wet transfer technique for large-area graphene, grown via chemical vapor deposition, onto aluminum nitride (AlN), which is mainly used as an active, piezoelectric material for acoustic devices. Today, graphene wet transfer is well-engineered for silicon dioxide (SiO₂). Investigations on AlN substrates reveal highly different surface properties compared to SiO₂ regarding wettability, which strongly influences the quality of transferred graphene monolayers. Both physical and chemical effects of a plasma treatment of AlN surfaces change wettability and avoid large-scale cracks in the transferred graphene sheet during desiccation. Spatially-resolved Raman spectroscopy reveals a strong strain and doping dependence on AlN plasma pretreatments correlating with the electrical conductivity of graphene. In our work, we achieved transferred crack-free large-area (40 × 40 mm²) graphene monolayers with sheet resistances down to 350 Ω/sq. These achievements make graphene more powerful as an eco-friendly and cheaper replacement for conventional electrode materials used in radio frequency resonator devices.

Fluorescent biosensors enabled by graphene and graphene oxide.

Science.gov (United States)

Zhang, Huan; Zhang, Honglu; Aldalbahi, Ali; Zuo, Xiaolei; Fan, Chunhai; Mi, Xianqiang

2017-03-15

During the past few years, graphene and graphene oxide (GO) have attracted numerous attentions for the potential applications in various fields from energy technology, biosensing to biomedical diagnosis and therapy due to their various functionalization, high volume surface ratio, unique physical and electrical properties. Among which, graphene and graphene oxide based fluorescent biosensors enabled by their fluorescence-quenching properties have attracted great interests. The fluorescence of fluorophore or dye labeled on probes (such as molecular beacon, aptamer, DNAzymes and so on) was quenched after adsorbed on to the surface of graphene. While in the present of the targets, due to the strong interactions between probes and targets, the probes were detached from the surface of graphene, generating dramatic fluorescence, which could be used as signals for detection of the targets. This strategy was simple and economy, together with great programmable abilities of probes; we could realize detection of different kinds of species. In this review, we first briefly introduced the history of graphene and graphene oxide, and then summarized the fluorescent biosensors enabled by graphene and GO, with a detailed account of the design mechanism and comparison with other nanomaterials (e.g. carbon nanotubes and gold nanoparticles). Following that, different sensing platforms for detection of DNAs, ions, biomolecules and pathogens or cells as well as the cytotoxicity issue of graphene and GO based in vivo biosensing were further discussed. We hope that this review would do some help to researchers who are interested in graphene related biosening research work. Copyright © 2016 Elsevier B.V. All rights reserved.

Adsorption of gas molecules on Ga-doped graphene and effect of applied electric field: A DFT study

Energy Technology Data Exchange (ETDEWEB)

Liang, Xiong-Yi [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Ding, Ning [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Key Laboratory for Applied Technology of Sophisticated Analytical Instruments, Shandong Academy of Sciences, Jinan 250014 (China); Ng, Siu-Pang [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Wu, Chi-Man Lawrence, E-mail: lawrence.wu@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Key Laboratory for Applied Technology of Sophisticated Analytical Instruments, Shandong Academy of Sciences, Jinan 250014 (China)

2017-07-31

Highlights: • H{sub 2}O, NH{sub 3}, CO, NO{sub 2} and NO are physically adsorbed on pristine graphene. • The adsorption energies of all gas molecules on graphene are increased after doping with Ga. • NO{sub 2} shows the strongest affinity to Ga-doped graphene. • The electronic properties and adsorption of NO{sub 2} on graphene and can be effectively tuned using an external electric field. - Abstract: Density functional theory calculations have been carried out to study the adsorption of varous gas molecules (H{sub 2}O, NH{sub 3}, CO, NO{sub 2} and NO) on pristine graphene and Ga-doped graphene in order to explore the feasibility of Ga-doped graphene based gas sensor. For each gas molecule, various adsorption positions and orientations were considered. The most stable configuration was determined and the adsorption energies with van der Waals interactions were calculated. Further, electronic properties such as electron density, density of states, charge transfer and band structure were investigated to understand the mechanism of adsorption. The results showed that the gas molecules studied were only weakly adsorbed on pristine graphene with small adsorption energies. On the other hand, the adsorption energies of all gas molecules on Ga-doped graphene increased by various amounts. Adsorption of gas molecules on Ga-doped graphene can open a relatively large band gap ranging from 0.267 to 0.397 eV. NO{sub 2} was found to be very sensitive to Ga-doped graphene with adsorption energy of −1.928 eV due to strong orbital hybridization and large charge transfer. Furthermore, our study suggests that the affinity and electronic properties of NO{sub 2} on Ga-doped graphene can be dramatically changed by an external electric field. A negative electric field enhances the adsorption of NO{sub 2} on Ga-doped graphene as reflected in the increase in adsorption energy. In contrast, the interaction will be weakened under a positive electric field. The results of the DFT

Adsorption of gas molecules on Ga-doped graphene and effect of applied electric field: A DFT study

International Nuclear Information System (INIS)

Liang, Xiong-Yi; Ding, Ning; Ng, Siu-Pang; Wu, Chi-Man Lawrence

2017-01-01

Highlights: • H_2O, NH_3, CO, NO_2 and NO are physically adsorbed on pristine graphene. • The adsorption energies of all gas molecules on graphene are increased after doping with Ga. • NO_2 shows the strongest affinity to Ga-doped graphene. • The electronic properties and adsorption of NO_2 on graphene and can be effectively tuned using an external electric field. - Abstract: Density functional theory calculations have been carried out to study the adsorption of varous gas molecules (H_2O, NH_3, CO, NO_2 and NO) on pristine graphene and Ga-doped graphene in order to explore the feasibility of Ga-doped graphene based gas sensor. For each gas molecule, various adsorption positions and orientations were considered. The most stable configuration was determined and the adsorption energies with van der Waals interactions were calculated. Further, electronic properties such as electron density, density of states, charge transfer and band structure were investigated to understand the mechanism of adsorption. The results showed that the gas molecules studied were only weakly adsorbed on pristine graphene with small adsorption energies. On the other hand, the adsorption energies of all gas molecules on Ga-doped graphene increased by various amounts. Adsorption of gas molecules on Ga-doped graphene can open a relatively large band gap ranging from 0.267 to 0.397 eV. NO_2 was found to be very sensitive to Ga-doped graphene with adsorption energy of −1.928 eV due to strong orbital hybridization and large charge transfer. Furthermore, our study suggests that the affinity and electronic properties of NO_2 on Ga-doped graphene can be dramatically changed by an external electric field. A negative electric field enhances the adsorption of NO_2 on Ga-doped graphene as reflected in the increase in adsorption energy. In contrast, the interaction will be weakened under a positive electric field. The results of the DFT calculation indicates the potential application of Ga

Wettability of graphene-laminated micropillar structures

International Nuclear Information System (INIS)

Bong, Jihye; Seo, Keumyoung; Ju, Sanghyun; Park, Ji-Hoon; Ahn, Joung Real

2014-01-01

The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues

Diffusive charge transport in graphene

Science.gov (United States)

Chen, Jianhao

The physical mechanisms limiting the mobility of graphene on SiO 2 are studied and printed graphene devices on a flexible substrate are realized. Intentional addition of charged scattering impurities is used to study the effects of charged impurities. Atomic-scale defects are created by noble-gas ions irradiation to study the effect of unitary scatterers. The results show that charged impurities and atomic-scale defects both lead to conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates. While charged impurities cause intravalley scattering and induce a small change in the minimum conductivity, defects in graphene scatter electrons between the valleys and suppress the minimum conductivity below the metallic limit. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a small resistivity which is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity. Graphene is also made into high mobility transparent and flexible field effect device via the transfer-printing method. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime, and show the promise of graphene as a novel electronic material that have potential applications not only on conventional inorganic substrates, but also on flexible substrates.

An Introduction to Graphene Plasmonics

DEFF Research Database (Denmark)

Gonçalves, P.A.D.; Peres, N. M. R.

This book is meant as an introduction to graphene plasmonics and aims at the advanced undergraduate and graduate students entering the field of plasmonics in graphene. In it different theoretical methods are introduced, starting with an elementary description of graphene plasmonics and evolving...... the chapters to get acquainted with the field of plasmonics in graphene or reading the chapters and studying the appendices to get a working knowledge of the topic. The study of the material in this book will bring the students to the forefront of the research in this field....

Stability of Ptn cluster on free/defective graphene: A first-principles study

International Nuclear Information System (INIS)

Yang, G.M.; Fan, X.F.; Shi, S.; Huang, H.H.; Zheng, W.T.

2017-01-01

Highlights: • The single-vacancy can enhance obviously the adsorption of Pt cluster on graphene. • Pt clusters on defected graphene prefer to adopt the close-packed model, except Pt 13 . • The contact way of Pt n clusters on single-vacancy changes with the size increasing. - Abstract: With first-principles methods, we investigate the stability of isolated Pt n clusters from Sutton-Chen model and close-packed model, and their adsorption on defected graphene. The single-vacancy in graphene is found to enhance obviously the adsorption energy of Pt cluster on graphene due to the introduction of localized states near Fermi level. It is found that the close-packed model is more stable than Sutton-Chen model for the adsorption of Pt n cluster on single-vacancy graphene, except the magic number n = 13. The cluster Pt 13 may be the richest one for small Pt clusters on defected graphene due to the strong adsorption on single-vacancy. The larger cluster adsorbed on defected graphene is predicted with the close-packed crystal structure. The charge is found to transfer from the Pt atom/cluster to graphene with the charge accumulation at the interface and the charge polarization on Pt cluster. The strong interaction between Pt cluster and single vacancy can anchor effectively the Pt nanoparticles on graphene and is also expected that the new states introduced near Fermi level can enhance the catalytic characteristic of Pt cluster.

Graphene Coatings

DEFF Research Database (Denmark)

Stoot, Adam Carsten; Camilli, Luca; Bøggild, Peter

2014-01-01

Owing to its remarkable electrical and mechanical properties, graphene has been attracting tremendous interest in materials science. In particular, its chemical stability and impermeability make it a promising protective membrane. However, recent investigations reveal that single layer graphene...... cannot be used as a barrier in the long run, due to galvanic corrosion phenomena arising when oxygen or water penetrate through graphene cracks or domain boundaries. Here, we overcome this issue by using a multilayered (ML) graphene coating. Our lab- as well as industrial-scale tests demonstrate that ML...... graphene can effectively protect Ni in harsh environments, even after long term exposure. This is made possible by the presence of a high number of graphene layers, which can efficiently mask the cracks and domain boundaries defects found in individual layers of graphene. Our findings thus show...

Two-dimensional collagen-graphene as colloidal templates for biocompatible inorganic nanomaterial synthesis

Science.gov (United States)

Kumari, Divya; Sheikh, Lubna; Bhattacharya, Soumya; Webster, Thomas J; Nayar, Suprabha

2017-01-01

In this study, natural graphite was first converted to collagen-graphene composites and then used as templates for the synthesis of nanoparticles of silver, iron oxide, and hydroxyapatite. X-ray diffraction did not show any diffraction peaks of graphene in the composites after inorganic nucleation, compared to the naked composite which showed (002) and (004) peaks. Scanning electron micrographs showed lateral gluing/docking of these composites, possibly driven by an electrostatic attraction between the positive layers of one stack and negative layers of another, which became distorted after inorganic nucleation. Docking resulted in single layer-like characteristics in certain places, as seen under transmission electron microscopy, but sp2/sp3 ratios from Raman analysis inferred three-layer composite formation. Strain-induced folding of these layers into uniform clusters at the point of critical nucleation, revealed beautiful microstructures under scanning electron microscopy. Lastly, cell viability studies using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays showed the highest cell viability for the collagen-graphene-hydroxyapatite composites. In this manner, this study provided – to the field of nanomedicine – a new process for the synthesis of several nanoparticles (with low toxicity) of high interest for numerous medical applications. PMID:28553102

Adsorption properties of fission gases Xe and Kr on pristine and doped graphene: A first principle DFT study

Energy Technology Data Exchange (ETDEWEB)

Vazhappilly, Tijo, E-mail: tijoj@barc.gov.in [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Ghanty, Tapan K., E-mail: tapang@barc.gov.in [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094 (India); Jagatap, B.N. [Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085 (India)

2017-07-15

Graphene has excellent adsorption properties due to large surface area and has been used in applications related to gas sorption and separation. The separation of radioactive noble gases using graphene is an interesting area of research relevant to nuclear waste management. Radioactive noble gases Xe and Kr are present in the off-gas streams from nuclear fission reactors and spent nuclear fuel reprocessing plants. The entrapment of these volatile fission gases is important in the context of nuclear safety. The separation of Xe from Kr is extremely difficult, and energy intensive cryogenic distillation is generally employed. Physisorption based separation techniques using porous materials is a cost effective alternative to expensive cryogenic distillation. Thus, adsorption of noble gases on graphene is relevant for fundamental understanding of physisorption process. The properties of graphene can be tuned by doping and incorporation of defects. In this regard, we study the binding affinity of Xe and Kr in pristine and doped graphene sheets. We employ first principle calculations using density functional theory, corrected for dispersion interactions. The structural parameters obtained from the current study show excellent agreement with the available theoretical and experimental observations on similar systems. Noble gas adsorption energies on pristine graphene match very well with the available literature. Our results show that the binding energy of fission gases Xe and Kr on graphene can be considerably improved through doping the lattice with a heteroatom. - Graphical abstract: The adsorption of radioactive fission gases Xe and Kr on pristine/doped graphene is an interesting topic in the context of nuclear waste management. Previous experimental and computational studies about Xe/Kr adsorption on graphene were limited to only on pristine graphene. The doping by hetero atom changes the electronic properties of graphene and creates active sites in the lattice. Based

Reduction of Graphene Oxide to Graphene by Using Gamma Irradiation

International Nuclear Information System (INIS)

Shamellia Sharin; Irman Abdul Rahman; Ainee Fatimah Ahmad

2015-01-01

This research aims to gauge the ability of gamma radiation to induce the reduction of graphene oxide to graphene. Graphene oxide powders were dispersed into a mixture of alcohol and deionized water, and the mixture was then irradiated with a "6"0Co source using a GammaCell 220 Excel irradiator at absorbed doses of 0, 5, 15, 20 and 35 kGy. According to characterization using Fourier Transformed Infrared Spectroscopy (FTIR), it can be seen that almost every oxygen-containing functional group has been removed after irradiation of the graphene oxide mixture. Reduction of graphene oxide was also proven from the characterization using UV-Vis Spectroscopy, in which the wavelength of graphene oxide at 237 nm was red-shifted to 277 nm after being irradiated and the peak at 292 nm, (indicating the carboxyl group) disappears in the UV-Vis spectrum of reduced graphene oxide. Morphology of graphene oxide also changed from a smooth and flat surface to crumpled. The ratio of carbon/ oxygen in the graphene oxide was lower than the carbon/ oxygen of reduced graphene oxide. At the end of the experiment, it can be deduced that graphene oxide underwent reduction, characterized before and after irradiation using Emission Scanned Electron Microscopy and Energy Dispersive X-ray, Fourier Transformed Infrared Spectroscopy and UV-Vis Spectroscopy. Therefore, we postulate that the irradiation technique that induces reduction, can be used to obtain reduced graphene oxide from graphene oxide. (author)