Microstructure change of vanadium clusters in ZnO crystalline films by heat-treatment

Vanadium clusters with a size of several nanometres can be dispersively distributed in ZnO films by using co-deposition. EELS mapping of V-L-2,L-3, HRTEM images, SAD patterns and EELS are a good combination for characterizing nanometre-sized V clusters embedded in a ZnO system. There is no obvious orientation relationship between V and ZnO lattices due to a less good match between ZnO and V atomic planes. The ratio of the vanadium L-white lines of vanadium clusters embedded in ZnO becomes bigger than that of the bulk. The samples were observed in situ from 298 to 923 K with a heating holder so as to study the aggregation process of vanadium clusters in the ZnO crystalline matrix. First, the size of the ZnO crystal grains becomes bigger after the sample is heated at 623 K for an hour; second, the size of ZnO and vanadium particles grows bigger after the sample is heated at 723 K for half an hour, and another orientation relationship between ZnO and vanadium appears; third, after the sample is heated at 873 K for half an hour, the size of vanadium becomes smaller, while V particles and ZnO begin to react and form another phase; finally, Zn2VO7 phase is formed after the sample is heated at 923 K for half an hour.