Phase Transition of II−VI Semiconductor Nanocrystals

The phase transition is fundamental for understanding physical and chemical properties of materials. The phase transition at the nanometer scale is usually distinguished from that of the bulk counterpart. It is essential to pursue the basic physics involved in the phase transition on nanoscale for applications of nanomaterials. Herein, we have established an analytical thermodynamic model at the nanometer scale to study the phase transition of II−VI semiconductor nanocrystals, and revealed the size-dependent polymorphism behaviors of the phase transition. The physical origin of the size effects on the polymorphism behaviors of II−VI semiconductor nanocrystals was addressed on the basis of the contributions of surface energy and surface stress of nanocrystals to the total Gibbs free energy. It was found that the low surface energy and the small surface stress always predominate the thermal stability of nanostructures with the metastable phase. These results provided new insight into the fundamental understanding of the phase transition of II−VI semiconductor nanocrystals.