Modifying ultrafast optical response of sputtered VOX nanostructures in a broad spectral range by altering post annealing atmosphere

Nanostructured VOX thin films were grown in a dc magnetron sputter system under two different Ar:O-2 gas flow ratios. The films were annealed under vacuum and various ratios of O-2/N-2 atmospheres. The insulator-to-metal transition properties of the thin films were investigated by temperature dependent resistance measurement. Photo induced insulator-to-metal transition properties were investigated by Z-scan and ultrafast white light continuum pump probe spectroscopy measurements. Experiments showed that not only insulator-to-metal transition, but also wavelength dependence (from NIR to VIS) and time scale (from ns to ultrafast) of nonlinear optical response of the VOX thin films could be fine tuned by carefully adjusting post annealing atmosphere despite different initial oxygen content in the production. Fabricated VO2 thin films showed reflection change in the visible region due to photo induced phase transition. The results have general implications for easy and more effective fabrication of the nanostructured oxide systems with controllable electrical, optical, and ultrafast optical responses.