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 Nanoscale Research Letters , 2011, Abstract: The mechanical behavior of graphene under various indentation depths, velocities, and temperatures is studied using molecular dynamics analysis. The results show that the load, elastic and plastic energies, and relaxation force increased with increasing indentation depth and velocity. Nanoindentation induced pile ups and corrugations of the graphene. Resistance to deformation decreased at higher temperature. Strong adhesion caused topological defects and vacancies during the unloading process.
 Physics , 2009, DOI: 10.1103/PhysRevB.80.121405 Abstract: Structure and thermodynamics of crystalline membranes are characterized by the long wavelength behavior of the normal-normal correlation function G(q). We calculate G(q) by Monte Carlo and Molecular Dynamics simulations for a quasi-harmonic model potential and for a realistic potential for graphene. To access the long wavelength limit for finite-size systems (up to 40000 atoms) we introduce a Monte Carlo sampling based on collective atomic moves (wave moves). We find a power-law behaviour $G(q)\propto q^{-2+\eta}$ with the same exponent $\eta \approx 0.85$ for both potentials. This finding supports, from the microscopic side, the adequacy of the scaling theory of membranes in the continuum medium approach, even for an extremely rigid material like graphene.
 Physics , 2012, DOI: 10.1063/1.4726053 Abstract: As impermeable to gas molecules and at the same time transparent to high-energy ions, graphene has been suggested as a window material for separating a high-vacuum ion beam system from targets kept at ambient conditions. However, accumulation of irradiation-induced damage in the graphene membrane may give rise to its mechanical failure. Using atomistic simulations, we demonstrate that irradiated graphene even with a high vacancy concentration does not show signs of such instability, indicating a considerable robustness of graphene windows. We further show that upper and lower estimates for the irradiation damage in graphene can be set using a simple model.
 Physics , 2011, DOI: 10.1103/PhysRevB.83.115424 Abstract: By combining classical molecular dynamics simulations and density functional theory total energy calculations, we study the possibility of doping graphene with B/N atoms using low-energy ion irradiation. Our simulations show that the optimum irradiation energy is 50 eV with substitution probabilities of 55% for N and 40% for B. We further estimate probabilities for different defect configurations to appear under B/N ion irradiation. We analyze the processes responsible for defect production and report an effective swift chemical sputtering mechanism for N irradiation at low energies (~125 eV) which leads to production of single vacancies. Our results show that ion irradiation is a promising method for creating hybrid C-B/N structures for future applications in the realm of nanoelectronics.
 Physics , 2012, Abstract: We provide a comprehensive picture of magnetotransport in graphene monolayers in the limit of non-quantizing magnetic fields. We discuss the effects of two carrier transport, weak localization, weak anti-localization, and strong localization for graphene devices of various mobilities, through theory, experiments and numerical simulations. In particular, we observe the weak localization of the localization length, which allows us to make the connection between weak and strong localization. It provides a unified framework for both localizations, which explains the observed experimental features. We compare these results to numerical simulation and find a remarkable agreement between theory, experiment and numerics. Various graphene devices were used in this study, including graphene on different substrates, such as glass and silicon, as well as low and high mobility devices.
 Physics , 2009, DOI: 10.1103/PhysRevB.79.165425 Abstract: We discuss the Monte Carlo method of simulating lattice field theories as a means of studying the low-energy effective theory of graphene. We also report on simulational results obtained using the Metropolis and Hybrid Monte Carlo methods for the chiral condensate, which is the order parameter for the semimetal-insulator transition in graphene, induced by the Coulomb interaction between the massless electronic quasiparticles. The critical coupling and the associated exponents of this transition are determined by means of the logarithmic derivative of the chiral condensate and an equation-of-state analysis. A thorough discussion of finite-size effects is given, along with several tests of our calculational framework. These results strengthen the case for an insulating phase in suspended graphene, and indicate that the semimetal-insulator transition is likely to be of second order, though exhibiting neither classical critical exponents, nor the predicted phenomenon of Miransky scaling.
 Physics , 2011, Abstract: In this paper we demonstrate the direct evidence of solitons in graphene by means of molecular dynamics simulations and mathematical analysis. It shows various solitons emerge in the graphene flakes with two different chiralities by cooling procedures. They are in-plane longitudinal and transverse solitons. Their propagations and collisions are studied in details. A soliton solution is derived by making several valid simplifications. We hope it shed light on understanding the unusual thermal properties of graphene.
 Physics , 2010, DOI: 10.1103/PhysRevB.81.235439 Abstract: We study the structural and thermodynamic properties of bilayer graphene, a prototype two-layer membrane, by means of Monte Carlo simulations based on the empirical bond order potential LCBOPII. We present the temperature dependence of lattice parameter, bending rigidity and high temperature heat capacity as well as the correlation function of out-of-plane atomic displacements. The thermal expansion coefficient changes sign from negative to positive above $\approx 400$ K, which is lower than previously found for single layer graphene and close to the experimental value of bulk graphite. The bending rigidity is twice as large than for single layer graphene, making the out-of-plane fluctuations smaller. The crossover from correlated to uncorrelated out-of-plane fluctuations of the two carbon planes occurs for wavevectors shorter than $\approx 3$ nm$^{-1}$
 Physics , 2012, DOI: 10.1039/C2SM26476E Abstract: Graphene nanopore based sensor devices are exhibiting the great potential for the detection of DNA. To understand the fundamental aspects of DNA translocating through a graphene nanopore, in this work, molecular dynamics (MD) simulations and potential of mean force (PMF) calculations were carried out to investigate the layer impact of small graphene nanopore (2 nm-3 nm) to DNA translocation. It was observed that the ionic conductance was sensitive to graphene layer of open-nanopores, the probability for DNA translocation through graphene nanopore was related with the thickness of graphene nanopores. MD simulations showed that DNA translocation time was most sensitive to the thickness of graphene nanopore for a 2.4 nm aperture, and the observed free energy barrier of PMFs and the profile change revealed the increased retardation of DNA translocation through bilayer graphene nanopore as compared to monolayer graphene nanopore.
 Physics , 2012, DOI: 10.1088/0957-4484/23/47/475501 Abstract: We perform classical molecular dynamics simulations to investigate the enhancement of the mass sensitivity and resonant frequency of graphene nanomechanical resonators that is achieved by driving them into the nonlinear oscillation regime. The mass sensitivity as measured by the resonant frequency shift is found to triple if the actuation energy is about 2.5 times the initial kinetic energy of the nanoresonator. The mechanism underlying the enhanced mass sensitivity is found to be the effective strain that is induced in the nanoresonator due to the nonlinear oscillations, where we obtain an analytic relationship between the induced effective strain and the actuation energy that is applied to the graphene nanoresonator. An important implication of this work is that there is no need for experimentalists to apply tensile strain to the resonators before actuation in order to enhance the mass sensitivity. Instead, enhanced mass sensitivity can be obtained by the far simpler technique of actuating nonlinear oscillations of an existing graphene nanoresonator.
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