Structural Characterization of Atomic Layer Deposited Vanadium Dioxide

Vanadium dioxide (VO2) is a promising smart material particularly appealing for added functionality in both electronic and optical applications. We investigate the structure of VO2 films fabricated using atomic layer deposition (ALD) on c-Al2O3 substrates and the structure of the same VO2 films after an optimized anneal for 2 h at 585 degrees C in 10(-5) Torr O-2. Synchrotron-based grazing incidence X-ray diffraction (GIXRD) measurements revealed that the as-deposited ALD. VO2 contains small crystalline inclusions of both V2O5 and VO. Ex situ annealing of the ALD VO2 film results in formation of mixed phase VO2 (predominantly M1 with indications of a: small amount of M-2), with a twinned monoclinic structure that is highly oriented and lattice matched to the c-Al2O3 substrate. Using in situ temperature-dependent measurements, the M1 and M-2 components were shown to transition across different temperature ranges, which could account for the hysteretic behavior seen in these VO2 thin films. Additionally, these high-quality crystalline VO2 films exhibit a 50% transmission modulation at a wavelength of 2 mu m, with only a 35 nm thick VO2 film.