Microstructure of orientation controlled VO2 thin films via ZnO buffer

B-axis preferential oriented VO2 thin films were prepared on glass substrates via ZnO buffers by pulsed laser deposition. In order to explore the relationship between the VO2 and ZnO layers, cross-sectional images of the orientation-controlled VO2 thin films were examined using a transmission electron microscope (TEM). As revealed by the TEM images, for the VO2 thin films deposited on a relatively thick ZnO buffer (~ 70 nm), an interface layer was formed between the VO2 and ZnO layers. The interface layer was identified as V3O5 based on X-ray photoelectron spectra (XPS) and high resolution TEM images. For the VO2 thin films deposited on a 5-nm thick ZnO buffer, only a b-axis oriented VO2 layer was observed. The b-axis oriented VO2 layer displayed a columnar structure, and the layer thickness was occupied by one grain. However, TEM images of the thicker VO2 thin films (~ 90 nm) deposited on 5-nm ZnO buffer revealed a VO2 (111) facet on the grain and amorphous residues of VO2. These results indicated that the grains of VO2 grew from the interface with the ZnO buffer, and the grain growth was slower than the speed of deposition.

► B-axis oriented VO2 thin films were prepared on glass on ZnO buffer layers.
► Transmission electron microscopy confirms the formation of an interface layer.
► X-ray photoelectron spectroscopy data reveal a V3O5 interface layer.
► VO2 (111) facet on grains and amorphous residues of VO2 were observed.
► The grain growth was slower than the rate of deposition.