Controlling Size-Induced Phase Transformations Using Chemically Designed Nanolaminates

摘要

Since the initial observation of melting-point reduction with size for gold nanoparticles the relative stability of crystalline phases has also been demonstrated to be size-dependent in a number of technologically important materials, including CdSe and CdS, A12O3, and various other metal oxides and chalcogenides. As the surface free energy contribution to the total free energy becomes increasingly important as the size of a system is decreased, a crystalline phase with lower surface free energy may be favored with respect to the thermodynamically stable bulk phase when the crystallite size is smaller than a critical value in one or more dimensions. The role of size as an effective thermodynamic parameter is of fundamental importance, but also provides a mechanism for controlling the crystal structure of a material, and therefore its properties.