Epitaxial growth and defect microstructures of vanadium dioxide thin filmson sapphire substrates

Vanadium dioxide thin films have been deposited on sapphire substrates with different orientations by pulsed laser ablation. The samples are analyzed by x-ray diffraction and pole figures to determine epitaxial relationship. The crystal quality is evaluated by RBS/Channeling techniques. The results has shown that the growth of VO2 has a strong substrate dependence, the fil m on (0001) sapphire substrate exhibits better crystal quality than that on (11 (2) under bar0) and (01 (1) under bar2) sapphire substrates. The epitax y can be divided into two processes, the first is surface symmetry determin ed oriented growth, and tire second is in-plane oriented growth dominated b y the minimization of in-plane lattice mismatch. More over, different subst rates result in different defect microstructures, 120 degrees twin is obser ved in VO2 film on (0001) substrate while 180 degrees on (11 (2) under bar0 ) and no twin on (01 (1) under bar2), which also reflects the surface symme tries of the substrates.