Synthesis and temperature dependent local structural and electrical properties of VO2 films
Abstract We examine the local structural and electrical properties of VO 2 films showing metal to insulator transition (MIT) by using in situ x ray absorption fine structure (XAFS) measurements at the V K edge and resistance measurements in the temperature range 20 120 degC. VO 2 films are synthesized on Al 2 O 3 (0001) substrates by DC magnetron sputtering deposition. X ray diffraction measurements show that the films have b oriented monoclinic phase crystals at room temperature. XAFS measurements reveal a local structural transition in the films from the monoclinic (M 1 to the rutile (R) phase at ~70 degC during their heating; further, temperature dependent resistance (R T) measurements showed a sharp MIT in the films at ~75 degC. Extended XAFS (EXAFS) measurements reveal non rigid changes of V O and V V bond lengths from the M 1 to the R phase via the M 2 phase. In situ EXAFS and R T measurements show that the synthesized VO 2 films act as Mott insulators and that their electrical property change is not proportional to their structural property change at their MIT temperature.