Optical anisotropy of pristine and reduced V₂O₅(010)

The optical anisotropy of pristine and reduced single crystalline (010) orientated [Formula: see text] is presented. The reduction of [Formula: see text] is complex due to the abundance of V-O phases, strong dependence on the reducing conditions and multitude of reduction pathways. Different phases close in stoichiometry can exhibit drastically different electronic and optical properties. Reflectance anisotropy spectroscopy (RAS) provides a non-destructive optical probe that can be employed in real-time to monitor changes in thin films. Pristine [Formula: see text](010) exhibits strong anisotropy with significant features beyond the optical bandgap of 2.5 eV. Axially resolved optical constants, extracted using ellipsometry, facilitate the calculation of the RAS which is in excellent agreement with the experimental data. Vacuum annealing has been performed at four different temperatures and X-ray Diffraction and RAS have been conducted after each anneal. Depending on the anneal temperature, different phases are introduced into the [Formula: see text] crystal including [Formula: see text], [Formula: see text] and [Formula: see text]. Spectral features of each of these phases are identified. [Formula: see text] is understood in terms of the axially resolved optical constants from the literature, while isotropic [Formula: see text] modifies the total reflection once it undergoes its semiconductor-to-metal phase transition at 340 K. This understanding of the optical response of the ideal single crystal facilitates applying RAS to monitor the growth and changes of [Formula: see text] thin films in real time.