Sang-Wook Han
Jeonbuk National University, Korea
Title: Growth, structural and electrical properties of VO2/ZnO nanostructures
Biography
Biography: Sang-Wook Han
Abstract
VO2 is a typical metal-insulator-transition(MIT) material with the bandgap of ~0.7 eV and the Tc of ~ 70oC. VO2 is transparent and dark below and above the Tc, so that it can be applicable for smart windows by controlling the temperature. VO2 nanoparticles in a metallic phase block and scatter sunlight. The scattered sunlight by VO2 nanoparticles can be used in solar cells. We examined the local structural and electrical properties from VO2/ ZnO nanostructures by using the simultaneous measurements of x-ray absorption fine structure(XAFS) and resistance. The structural and electrical properties of VO2 depend on the length of ZnO nanorods underneath VO2. Direct comparison of simultaneously-measured resistance and XAFS from the VO2 demonstrates that the transitions of structures, local density of the V 3d orbital states, and resistance occurred in sequence during heating, whereas the properties changed simultaneously during cooling. XAFS reveals a substantial increase of Debye-Waller factors, particularly, V-V pairs along the {111} direction in the metallic phase. XAFS results indicate that soft phonon above Tc plays a critical role in the collapse of a small band gap of VO2. The local structural and the electrical properties of VO2/ZnO nanorods are considerably sensitive to the interface of VO2/ZnO as well as the length of ZnO nanorods. The interface properties of VO2 hetero-structures of should be taken into account for its applications to smart windows and solar cells.