The present work studies the size-dependent surface stress, surface stiffness, and Young's modulus of a prism crystalline nanowire, which is theoretically treated to be composed of a hypothetical nanowire phase, a true two-dimensional geometric surface phase, and a true one-dimensional geometric edge phase. The hypothetical nanowire phase could be elastically deformed due to relaxation of a free-standing nanowire, without any applied load, with respect to its bulk counterpart. The initially deformed nanowire phase is taken as reference in the present work in the determination of excess surface and edge energies. The theoretical results indicate that the edge phase causes the nominal specific surface energy, surface stress, and surface stiffness to be size dependent, and the surface phase and the edge phase make the nominal Young's modulus size dependent. The edge and surface effects are more significant as the cross-sectional area of a nanowire becomes smaller. Molecular dynamics simulations on hexagonal prism ͓111͔ ␤-SiC nanowires were conducted and the results verified the theoretical approach and illustrated the intrinsic mechanism of the size-dependent surface properties and Young's modulus of nanowires. The theoretical analysis and methodology are universal when the continuum concepts of surface energy, surface stress, and Young's modulus are used to characterize mechanical properties of nanowires.

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