Control of Polymorphic Properties of Multivalent Vanadium Oxide Thin Films

Abstract

In this study, V x O y 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 (ΔT IR = 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 (H LW) and slope stiffness. A narrower H LW 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.

Metal–Insulator Transition Detection of Vanadium Dioxide Thin Films by Visible Light Reflection

“…Here, a few possible factors behind the reduction of T c , such as over-stoichiometry, crystal defects, grain size, and tensile stress, can be suggested. 21,[25][26][27]48 On the other hand, we inferred that the use of reflectivity is a more suitable method for evaluating the phase transition of multivalent VO 2 thin films compared to using electrical resistivity. Further, the detailed reflectivity in the wavelength range 400−750 nm was measured and investigated in detail at 20 and 120 °C, as shown in Figure 3c.…”

“…In addition, a Δ R lower by 1 order of magnitude, from 55 to 2.5 Ω·cm, was observed. The reason for the low electrical switch can be explained by unwanted phase concentrations in the multiphase VO 2 thin films, which are known to occur when the films are deposited on oxidized silicon or amorphous glass substrates Figure b shows the temperature-dependent normalized transmittance variation (Δ Tr ) in the visible-light range, i.e., from 400 to 750 nm.…”

“…The reason for the low electrical switch can be explained by unwanted phase concentrations in the multiphase VO 2 thin films, which are known to occur when the films are deposited on oxidized silicon or amorphous glass substrates. 48 Figure 1b shows the temperature-dependent normalized transmittance variation (ΔTr) in the visible-light range, i.e., from 400 to 750 nm. The transmittance spectra were recorded every 5 °C during the heating (red circle right solid) and cooling (blue circle left solid) cycles from 20 to 120 °C.…”

VO2-Based Infrared Radiation Regulator with Excellent Dynamic Thermal Management Performance

“…The synthesis of the high-quality stoichiometric VO 2 films is challenging due to the multiple stoichiometries of vanadium oxides with multivalent vanadium cations. , Therefore, the chemical bonding of the V and W element in the regulators was investigated by XPS analysis (Figure c,d), and the C 1s signal at 284.6 eV was used as a binding energy reference. The main fitting peak of the V 2p 3/2 center at 516.1 eV can be attributed to V 4+ , and no fitting peaks of V 5+ are observed. , W element exists as W 6+ with the bonding energies W 4f 5/2 (38.4 eV) and W 4f 7/2 (35.8 eV). , By calculating the peak areas of V 2p 3/2 and W 4f, we determined that the ratio of V atom to W atom is about 98:2.…”

“…The main fitting peak of the V 2p 3/2 center at 516.1 eV can be attributed to V 4+ , and no fitting peaks of V 5+ are observed. 42,43 W element exists as W 6+ with the bonding energies W 4f 5/2 (38.4 eV) and W 4f 7/2 (35.8 eV). 18,44 By calculating the peak areas of V 2p 3/2 and W 4f, we determined that the ratio of V atom to W atom is about 98:2.…”