Theoretical investigation of size and shape effects on the melting temperature of ZnOnanostructures

Abstract

We report a theoretical investigation concerning the melting temperature,Tm, of ZnO and Zn nanoparticles (NPs), nanowires (NWs) and nanotubes (NTs). The shapesconsidered here for the zinc oxide low dimensional structures include sphericalNPs, NWs with circular, rectangular (nanobelts) and hexagonal sections andNTs with circular and hexagonal sections. A comparison between ZnO and Znnanostructures demonstrates a higher stability of ZnO for most size and shape rangesconsidered. Moreover, the size effect on the melting temperature for ZnO is found to bequite strong: for a spherical ZnO NP with a radius of 5 nm, the size effect onTm correspondsto a decrease of ∼36% relative to the bulk melting temperature, whereas the reductionfor the case of a metallic Zn NP with the same dimension is∼13%. Basedon Tm estimations as a function of size and shape, we predict that certain ZnO nanostructures, such as small(<10 nm) NTs, may not be viable for nanoelectronics or nanophotonic devices, sinceTm is too close to, or in some cases even below, room temperature. Theinfluence of the surface tension uncertainties on the calculated meltingtemperatures is also discussed. Finally, based on the determination ofTm at the nanoscale, the maximal intrinsic residual stress in ahexagonal ZnO NW and in a cylindrical Zn NW is estimated to be∼45 MPaand ∼1.9 GPa, respectively.