OPTICAL PROPERTIES OF NIOBIUM- AND TANTALUM-DOPED VANADIUM DIOXIDE THIN FILMS
Ama Agyapong, Tanviben Patel, Victor Adedeji.
Elizabeth City State University, Elizabeth City, NC.
Prior research shows that vanadium dioxide (VO2) undergoes reversible structural changes causing it to be spectrally selective at around 68 °C. The purpose of this research is to explore the spectral selectiveness of VO2 by incorporating a small amount of niobium (Nb) and tantalum (Ta) in the samples. These transition metals are larger than the vanadium in VO2 thin films and influence the magnitude of the change during optical properties switching and the corresponding transition temperatures as well. The samples were prepared by DC magnetron sputtering of vanadium metal and RF co-sputtering of the transition metal impurities. The metals were deposited on quartz substrates and subsequently annealed at a temperature of 500 °C in a pure oxygen and nitrogen gas mixture for 4 hours at a pressure of 800 mTorr to produce VO2 with the impurities. The reflectance and transmittance data of the samples were acquired under varying sample temperatures: from room temperature to about 90 °C and back to room temperature. Results showing the variation of reflectance and transmittance with temperature are reported. SEM images show the surface morphology of the as-deposited samples and oxidized samples. EDX data gave the atomic composition of the films before and after oxidation. Surface chemical composition mapping indicates the uniformity of the samples.