Direct comparison of the electrical, optical, and structural phase transitions of VO2 on ZnO nanostructures

We examined the temperature-dependent electrical, optical, and structural properties of VO2 on ZnO nanorods with different lengths in the temperature range from 30 to 100 degrees C. ZnO nanorods with a uniform length were grown on Al2O3 substrates using a metal organic chemical vapor deposition, and subsequently, VO2 was ex-situ deposited on ZnO nanorods/Al2O3 templates using a sputtering deposition. The optical properties of the VO2/ZnO nanorods were measured simultaneously with direct current (DC) resistance using the reflectivity of an infrared (IR) laser beam with a wavelength of 790 nm. The local structural properties around V atoms of VO2/ZnO nanorods were simultaneously measured with the DC resistance using x-ray absorption fine structure at the V K edge. Direct comparison of the temperature-dependent resistance, IR reflectivity, and local structure reveals that an optical phase transition first occurs, a structural phase transition follows, and an insulator-to-metal transition finally appears during heating.