Hexagonal ZnO/SnO2 core–shell micropyramids: epitaxial growth-based synthesis, chemical conversion, and cathodoluminescence

Abstract

In this paper, ZnO/SnO₂ core–shell micropyramids were successfully prepared via a chemical vapor deposition process that is based on the epitaxial growth of SnO₂ on the surface of ZnO hexagonal micropyramids. Upon controlling appropriate deposition times and flow rates of the precursor, two epitaxial growth modes of SnO₂, i.e. a continuous thick film and well-arranged one-dimensional nanostructures were observed in the ZnO/SnO₂ core–shell micropyramids. Taking advantages of the difference in acid resistance between ZnO and SnO₂, the as-prepared ZnO/SnO₂ micropyramids were further converted into SnO₂ hollow micropyramids with a facile acid-etching treatment. Structural analysis revealed that the lattice mismatch degree between epitaxial planes determines the preferential growth direction of the SnO₂ epitaxial layer on the ZnO surface. Compared to the pristine ZnO template, interestingly, the ZnO/SnO₂ core–shell micropyramids exhibited very strong green emission around 504 nm. Such enhanced green emission should be induced by high-density structural defects generated in the interfacial area during the epitaxial growth.