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

Abstract

Vanadium clusters with a size of several nanometres can be dispersivelydistributed in ZnO films by using co-deposition. EELS mapping ofV-L2,3, HRTEM images, SAD patterns and EELS are a good combination for characterizingnanometre-sized V clusters embedded in a ZnO system. There is no obvious orientationrelationship between V and ZnO lattices due to a less good match between ZnO and Vatomic planes. The ratio of the vanadium L-white lines of vanadium clusters embedded inZnO becomes bigger than that of the bulk. The samples were observed in situ from 298 to923 K with a heating holder so as to study the aggregation process of vanadium clusters inthe ZnO crystalline matrix. First, the size of the ZnO crystal grains becomes bigger afterthe sample is heated at 623 K for an hour; second, the size of ZnO and vanadiumparticles grows bigger after the sample is heated at 723 K for half an hour, andanother orientation relationship between ZnO and vanadium appears; third, afterthe sample is heated at 873 K for half an hour, the size of vanadium becomessmaller, while V particles and ZnO begin to react and form another phase; finally,Zn2V O7 phase is formed after the sample is heated at 923 K for half an hour.