Measurement of Thermal Diffusivity of V2O5 Thin Films Using Nanosecond Thermoreflectance Techniqu

Nanosecond thermoreflectance technique is a very useful method to measure the thermophysical properties of thin films, because of rapid measurement of changed reflectance by generated heat in the thin film caused by nanosecond pulse laser. In this study, the nanosecond thermoreflectance system based on rear heatingfront detection technique using pulsed DPSS laser was composed, and the thermal diffusivity of vanadium pentoxide (V2O5) thin films was measured using this system. V2O5 thin films are applied as chemical sensor, thermometer or thermal imaging sensor since its outstanding chemical, electrical, and thermal properties. V2O5 is the most stable compound among the vanadium oxide systems and when V2O5 thin film is growing by sputtering, it is crystallized with orthorhombic structure at 773 K temperature. Crystallized V2O5 film shows metal-insulator transition (MIT) phenomenon near 550 K. The structural properties of V2O5 thin film samples with thickness of 200 and 244 nm grown by RF magnetron sputtering were verified using SEM, XRD and Raman spectrum. The thermal diffusivities of 200, 244 nm thickness samples were measured from 300 K to 680 K and the values at 300 K were 1.67×10-7 m2/s and 1.87×10-7 m2/s, respectively and they were not changed until to 590 K. However, at 620 K, the values suddenly increased to 7.33×10-7 m2/s and 13.2×10-7 m2/s, respectively. From this result, we think that the MIT of V2O5 thin films occurred at about 590 K.