Roles of a strain relaxation and an oxygen vacancy on nanoscale inhomogeneities in VO2 thin film

M.S. Kim, S.H. Park, S. Choi, J. Kim, K.H. Lee, S.Y. Noh, B.N. Chae, S. Lee, B.J. Kim, J.S. Lee

Current Applied Physics 46, 40 (2023)
We investigated structural and electronic inhomogeneities in a VO2 thin film grown on a (001)-oriented TiO2 substrate by exploiting nano-scale and macroscopic probing techniques. A compressive strain along the out-of-plane direction becomes additionally relaxed via microcracks which form a micron-sized rectangular pattern. A large inhomogeneity in the dielectric response is observed near the crack, and this signifies a strong coupling between electronic and lattice degrees of freedom. Interestingly, the strong inhomogeneity is observed also inside of the rectangular pattern, and it shows a gradient along one crystalline axis. We attribute such peculiar inhomogeneity observed in a relatively large length scale possibly to a combined effect of the strain relaxation and an oxygen vacancy distribution. As the nano-scale inhomogeneities in structural and electronic properties will eventually determine macroscopic responsivities, this work can be a good guide in designing VO2 thin films with appropriate controls of the strain and the chemical composition to realize better functionalities.