Control of Polymorphic Properties of Multivalent Vanadium Oxide Thin Films

In this study, VxOy thin films were deposited on borosilicate glass substrates using direct current (DC) magnetron sputtering. The optoelectronic thermochromic properties of the resulting multiphase vanadium oxide thin films were investigated. As-deposited (at 280 °C) films were annealed at 350, 450, and 500 °C in an oxygen atmosphere for 30 min in a tube furnace to improve the crystallinity. Structural analysis indicated the formation of a mixed-phase vanadium oxide film consisting of VO2(B), V4O9, and V2O5 phases on the amorphous substrate after annealing above 350 °C. The results showed that the semiconductor-to-metallic phase transition temperature of the vanadium oxide film increased from 48 to 63 °C with increasing annealing temperatures. The sample annealed at 450 °C exhibited the highest variation in the infrared (IR) transmittance (ΔTIR = 28.42%) and the resistivity switch decreased by two orders of magnitude (1.4 × 10–1–2.3 × 10–3 Ω/cm). The thermal treatment temperature affected the width of the thermal hysteresis loop (HLW) and slope stiffness. A narrower HLW of 1.9 °C and a sharp slope stiffness of 8.74 were obtained for the sample annealed at 500 °C. The slope stiffness plays an important role in the fabrication of ultrafast tunable energy-saving smart windows and IR switches.

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