Mechanical and Thermal Properties of Metallic and Semiconductive Nanostructures

Using a top-down approach, we report a theoretical investigation of the melting temperature at the nanoscale, Tm, for different shapes of 'free-standing' nanostructures. To easily calculate the nanoscale melting temperature for a wide range of metals and semiconductors, a convenient shape parameter called ashape is defined. Considering this parameter, we argue why smaller size effects are observed in high bulk melting temperature materials. Using Tm, a phase transition stress model is proposed to evaluate the intrinsic strain and stress during the first steps of solidification. Then, the size effect on the Thornton & Hoffman's criterion at the nanoscale is discussed and the intrinsic residual stress determination in nanostructures is found to be essential for sizes below 100 nm. Furthermore, the inverse Hall-Petch effect, for sizes below 15 nm, can be understood by this model. Finally, the residual strain in hexagonal zinc oxide nanowires is calculated as a function of the wire dimensions.