Active modulation of the optical absorption coefficient of sputtered VO2 nanostructure by external temperature stimuli

The development of materials that respond to a stimulus and whose mechanisms are based on phase transitions have enabled progress towards the engineering of the tunable optoelectronic devices, active plasmonic devices and tunable infrared active metamaterials. Vanadium dioxide (VO2) is a promising candidate that exhibits a sharp metal-insulator phase transition at ultrafast timescales, which is accompanied by a significant and reversible variation of the refractive index and optical absorption coefficient. Here we report on the modulation of the absorption coefficient of sputtered VO2 nanostructure via the external temperature stimuli. The absorption coefficient at low and high photon energies experiences an abrupt change and show sharp hysteresis near the critical temperature of 70 °C. Temperature dependence of the insulating VO2 optical band-gap energy shows a significant decrease from 0.74 to 0.41 eV with increasing the external temperature stimuli from 35 to 65 °C. Conductive atomic force microscopy reveals an island-like growth with well-defined columnar structure and also coexistence of insulating and metallic domains.