Atomic Simulations of Si@Ge and Ge@Si Nanowires for Mechanical and Thermal Properties

Abstract

Molecular dynamics simulations using Tersoff potential were performed in order to study the evolution of the atomic packing structures, loading states on the atoms, and tensile tests, as well as the thermal properties of Si/Ge core–shell nanowires with different core–shell structures and ratios at different temperatures. Potential energy and pair distribution functions indicate the structural features of these nanowires at different temperatures. During uniaxial tensile testing along the wire axis at different temperatures, different stages including elasticity, plasticity, necking, and fractures are characterized through stress–strain curves, and Young’s modulus, as well as tensile strength, are obtained. The packing patterns and Lode–Nadai parameters reveal the deformation evolution and different distributions of loading states at different strains and temperatures. The simulation results indicate that as the temperature increases, elasticity during the stretching process becomes less apparent. Young’s modulus of the Si/Ge core–shell nanowires at room temperature show differences with changing core–shell ratios. In addition, the Lode–Nadai parameters and atomic level pressures show the differences of these atoms under compression or tension. Temperature and strain significantly affects the pressure distribution in these nanowires. The phonon density of states, when varying the composition and strain, suggest different vibration modes at room temperature. The heat capacities of these nanowires were also determined.