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Effects of graphene coating on the plastic deformation of single crystal copper nano-cuboid under different nanoindentation modes
摘要： Molecular dynamic simulations of nanoindentation were performed to investigate the effects of graphene coatings on the plastic deformation of copper (Cu) under different indentation conditions. The results show that the graphene coating can dramatically strengthen the load bearing capability of Cu substrate for the displacement-controlled indentation, which is proportional to the number of graphene layers increasing from single to triple. And the load force also increases with the rising indentation speed, causing larger and rapider plastic deformation. For the load-controlled indentation, the graphene coating can protect the Cu substrate from being damaged by the external force. The protection capability of graphene increases as the layers growing to triple at the same loading. What's more, the larger load force can facilitate the increase in penetration depth at the equilibrium state. Our observation provide a better understanding of mechanism of plastic deformation under the effect of graphene covering.
关键词： Plastic deformation,Nanoindentation,Molecular dynamic simulations,Graphene coating
更新于2025-09-23 15:23:52
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Role of carbon-rings in polycrystalline GeSb2Te4 phase-change material
摘要： Carbon (C) is used to increase the overall performance of Ge-Sb-Te (GST) phase-change memory material. Yet the C configuration in polycrystalline GST and its microscopic role is unclear. Using the well-studied GeSb2Te4 as an example, this work unravels the microscopic C doping role based on ab initio calculations. Our results reveal that carbon prefers occupying the interstitials at very low C concentrations, while with a roughly critical C concentration of over 2%, carbon atoms will cluster at the grain boundaries, with very few carbon atoms might exist at the interstitials. With further increasing the C concentrations, C atoms tend to form ring-like configurations in the grain boundaries rather than chain-like configurations. This is due to that the covalent bonds in ring-like configurations are stronger than that in chain-like configurations. Further analysis on the lone-pair electrons and electronic densities of states show that C dopants significantly change the number of lone-pair electrons of surrounding atoms, thus affecting the electronic structure. Finally, the diffusion coefficient of C is estimated to be of the order of 10^-13 m^2/s at 400 K, indicating the good stability of C dopants in GeSb2Te4. Our work provides fundamental understanding on the microscopic role of C doping in GST phase-change materials and benefits for improving the properties of the recording materials by controlling the doping concentration.
关键词： Ab initio molecular dynamic simulations,Ab initio calculations,Phase-change materials,Grain boundary,GeSb2Te4,Carbon doping
更新于2025-09-23 15:23:52
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Molecular Simulations of Laser Spike Annealing of Block-Copolymer Lamellar Thin-Films
摘要： We use molecular dynamic simulations to study the phase behavior of a coarse-grained lamella-forming A-b-B di-block copolymer under thin-film soft confinement for different heating cycle lengths, film thicknesses, and substrate-polymer affinities. This model describes the effect on thin-film morphology with a free surface (air-polymer interface) and a solid substrate. Our simulation results were first validated by showing that they capture changes for the order-disorder transition temperature with annealing conditions consistent with those found in laser spike annealing experiments, when the vertical lamella phase formed on neutral substrates. In addition, simulations with a substrate selective for a particular block revealed the formation of other phases including a mixed vertical-horizontal lamella and a metastable island phase having horizontal but incomplete lamella layers. The nanoscale roughness features of this island phase, and hence its surface wettability, can be tuned with suitable choices of chemistry and annealing conditions.
关键词： thin-film,nanoscale roughness,order-disorder transition,phase behavior,laser spike annealing,molecular dynamic simulations,block copolymer
更新于2025-09-23 15:21:01
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Oxygen vacancy-assisted high ionic conductivity in perovskite LaCoO3? (δ?=?1/3) thin film: A first-principles-based study
摘要： Synthesising a solid state material with high oxygen-ionic conductivity is a challenge. In this work, an integrated method of density functional theory and first-principles molecular dynamics (FPMD) simulations has been performed to investigate the oxygen-ionic conductivity in the LaCoO3?δ films. We demonstrated that, in the strained epitaxial LaCoO3?δ films, O vacancy superstructures release strain and produce the high oxygen-ionic conductivity with an activation barrier of 0.65 ± 0.1 eV. We found that the oxygen hopping occurs in the oxygen-deficient regions of CoO mainly. We proposed a possible oxygen-ionic diffusion highway with an energy barrier of 0.55 eV by using the transition state calculations. Thus, the oxygen-deficient regions are the keys to the high oxygen-ionic conductivity in the LaCoO3?δ thin films.
关键词： Oxygen mobility,First-principles computations,Perovskite LaCoO3,Molecular dynamic simulations,Defects
更新于2025-09-11 14:15:04