Size-dependent thermal expansion properties of Silicon nanowires

Based on the lattice dynamics theories, a size dependence model for the thermal expansion coefficient of [001] oriented Silicon nanowires has been developed. Keating model, as the interactional potential, has been adopted to describe the elastic strain energy of Silicon nanowires. The strained phonon dispersion relations of silicon lattice have been analyzed though the strained Si/Ge superlattices theory. It is found that the thermal expansion coefficient of Silicon nanowires with thickness smaller than about 20nm increase dramatically with decreasing size, and is significantly higher than that of bulk silicon. The value of α is 2.49×10^-6 K^-1 for bulk silicon, and 2.72×10^-6 K^-1 for Silicon nanowires with the thickness of 5nm at the room temperature.