Due to its remarkable switching effect in electrical and optical properties, VO${}_2$ is a promising material for several applications. However, the stoichiometry control of multivalent vanadium oxides, especially with a rational deposition technique, is still challenging. Here, we propose and optimize a simple fabrication method for VO${}_2$ rich layers by the oxidation of metallic vanadium in atmospheric air. It was shown that a sufficiently broad annealing time window of 3.0–3.5 h can be obtained at an optimal oxidation temperature of 400 °C. The presence of VO${}_2$ was detected by selected area diffraction in a transmission electron microscope. According to the temperature dependent electrical measurements, the resistance contrast (R_{30 °C}/R_{100 °C}) varied between 44 and 68, whereas the optical switching was confirmed using in situ spectroscopic ellipsometric measurement by monitoring the complex refractive indices. The obtained phase transition temperature, both for the electrical resistance and for the ellipsometric angles, was found to be 49 ± 7 °C, i.e., significantly lower than that of the bulk VO₂ of 68 ± 6 °C.

Gradient a-Si_1−xGe_x layers have been deposited by ”one-sample concept” combinatorial direct current (DC) magnetron sputtering onto one-inch-long Si slabs. Characterizations by electron microscopy, ion beam analysis and ellipsometry show that the layers are amorphous with a uniform thickness, small roughness and compositions from $x=0$ to $x=1$ changing linearly with the lateral position. By focused-beam mapping ellipsometry, we show that the optical constants also vary linearly with the lateral position, implying that the optical constants are linear functions of the composition. Both the refractive index and the extinction coefficient can be varied in a broad range for a large spectral region. The precise control and the knowledge of layer properties as a function of composition is of primary importance in many applications from solar cells to sensors.