Asymmetric hysteresis in vanadium dioxide thin films

Vanadium dioxide is a material that undergoes phase changes and switches between metallic and insulating states, thereby producing dramatic changes in optical properties. This transition is a reversible but hysteretic process, which is investigated here as a function of atomic layer deposited film thickness. Increasing the thickness of vanadium dioxide films from 8.6 to 57 nm lead to an increase in hysteresis width. Thicker films develop two different slopes (steep and gradual) when cooling through the metal-insulator transition, where the steep transition matches that of the heating cycle of the transition. This asymmetry in the hysteresis is apparent and similar in both the electrical and optical measurements. Temperature-dependent Raman spectroscopy and temperature-dependent x-ray diffraction confirm the same anomaly suggesting a structural dependence on hysteretic shape. Transmission electron microscopy identifies texturing and faceting in-plane, especially along the surface of these films, and confirms the x-ray diffraction data. Identifying this facet texturing is valuable for film growth as well as for applications, such as logic and memory systems, that utilize the hysteretic nature of vanadium dioxide. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement