Properties Of Vanadium Dioxide Films Research Articles

Terahertz transmission properties of vanadium dioxide films deposited on gold grating structure with different periods

Vanadium dioxide (VO2) is a typical thermal induced phase transition material, exhibiting a transition from metallic phase at high temperature to insulating phase at low temperature, which is also accompanied by a conductivity change of over several orders of magnitude. The transition property makes VO2 prominent to achieve an effective degree of control of terahertz (THz) wave. In this paper, composite films consisting of metal grating with different periods and VO2 film were prepared by polymer assisted deposition method. Although the conductivity change of VO2 films deposited on gold grating structure across phase transition was declined to about two orders of magnitude, the amplitude modulation depth of THz of the composite films can still reach a high value. Furthermore, it was found that the THz modulation depth was related with the grating period. According to theoretical simulation, the fluctuation height of VO2 films, caused by metal grating structure during growth, can be used to regulate THz wave. These results demonstrate an economic and unsophisticated method to fabricate VO2 films with thickness fluctuation structure and then tune the THz waves.

New route for modification of thermochromic properties of vanadium dioxide films via high-energy X-ray irradiation

To study the effect of high-energy X-ray irradiation on the thermochromic properties of VO2 films, we prepared VO2 films on fused silica substrates by direct-current reactive magnetron sputtering and exposed them to X-ray irradiation at various doses in the range of 0–9000 Gy. X-ray diffraction analysis showed that an appropriate irradiation dose (1500 Gy) can enhance the crystallization of VO2 films, whereas a higher dose (9000 Gy) would reduce the crystallinity slightly. XPS measurement indicated that the VO2 film irradiated at 1500 Gy had the maximum V4+ content (71.64%) among the film samples. Moreover, atomic force microscopy and scanning electron microscopy measurements suggested that the VO2 film samples treated at 1500 Gy had higher surface roughness than other films, possibly owing to the localized annealing effect at lower doses. The visible and infrared transmittance of the irradiated and pristine samples were characterized and analyzed. The results demonstrated that high-energy X-ray irradiation strongly influenced the room-temperature infrared transmittance of the VO2 films, and the visible transmittance of the films decreased monotonously as the irradiation dose increased owing to the formation of color centers. In addition, the phase transition temperature of the VO2 film samples increased from 48 °C for the pristine sample to 53 °C for the sample irradiated at 1500 Gy, and then decreased continuously to 43 °C for the sample irradiated at 9000 Gy. These findings provided valuable insight into modification of the thermochromic properties of vanadium dioxide films by X-ray irradiation.

Semiconductor-metal phase transition properties and growth texture of vanadium dioxide films on Si3N4 layer

ABSTRACTDetailed investigation is carried out to study the thermal-resistance properties of vanadium dioxide films prepared on Si3N4 layer. The results demonstrate the films undergo the semiconductor to metal phase transition. The corresponding temperature of the maximum TCR value in cooling process is always lower than that in heating process for the same sample. Analysis reveals the thicker the film, the lower the corresponding temperature of the maximum TCR value in cooling process. The films’ dominant phase is VO2. As film thickness increases, (200) orientation is dominant and ratio of the grain length to width are 2: 1–3: 1.

Optical and electrical properties of vanadium dioxide films prepared under optimized RF sputtering conditions

Vanadium dioxide films were prepared by DC and rf reactive magnetron sputtering of a 99.7% pure vanadium target in an Ar+O 2 plasma with a well-controlled oxygen partial pressure. The films were deposited onto normal glass substrates at 400°C. The films showed a metal–semiconductor transition at the temperature, τ c =65–68°C. Optical and electrical properties of the films were investigated around the metal–semiconductor phase transition and found to be very sensitive to the oxygen flow rate. Sheet resistance of the films were recorded using a two-point probe over the temperature range 26⩽ τ⩽100°C. It was observed that the sheet resistance can change by three orders of magnitude when heating the films from room temperature to temperatures above the transition. Transmittance of the films was obtained in the 300⩽ λ⩽2500 nm wavelength range at two extreme temperatures (i.e. 26°C and 100°C). The luminous transmittance for the films was rather unaffected with heating, whereas near-infrared transmittance showed lower values. Optical constants, n and k were measured using ellipsometry. The semiconducting state optical constants were found to be 2.67 and 0.04 for n and k, respectively, while the metallic state values were 2.26 for refractive index and 0.3 for the extinction coefficient. The samples showed a slow deterioration when left in the laboratory for a period of one year.

Study of phase transition VO 2 thin film

Vanadium dioxide thin film that has semiconductor-to-metal phase transition has been obtained by either reactive evaporation or reactive ion assisted deposition with subsequent annealing processes. Various kinds of measurement methods have been developed in investigation of phase transition properties of vanadium dioxide films. It is observed that the performance of phase transition properties strongly depends upon the stoichiometric and crystalline characteristics of the thin film.

Effects of microstructure and nonstoichiometry on electrical properties of vanadium dioxide films

Voided growth structures of sputter-deposited films affect strongly their optical and electrical properties. Vanadium dioxide is an interesting material to study effects of film microstructure and nonstoichiometry on electrical properties because its phase transition makes it possible to investigate electrical behavior both in a semiconducting phase and in a metallic phase. We have deposited vanadium oxide films with different vanadium/oxygen ratios for substrate temperatures between 250 and 550 °C by dc reactive magnetron sputtering. The resistivity ratios between a semiconducting phase and a metallic phase are limited to 103 order by voided boundaries and oxygen vacancies. The voided boundaries are defined by columnar structure and agglomerated grain growth. The results emphasize the necessity of a combination of deposition to obtain the film with a favorable structure and postdeposition annealing to control the film stoichiometry.

Preparation and Properties of Vanadium Dioxide Films

Phase equilibria of the vanadium‐oxygen system have been restudied in the composition range in order to establish the conditions required for stable existence of the phase. Using this knowledge, it was possible to prepare films of exhibiting transition in conductivity between semiconducting and metallic states. Films of were first prepared by vapor deposition of vanadyl trichloride at temperatures below 127°C in 1 atm of . Reduction of these to was accomplished by heating in controlled atmospheres of appropriate partial oxygen pressure at temperatures between 500° and 550°C. The resulting thin film (0.1–1.0µ) exhibited a sharp drop (greater than two orders of magnitude) in resistance at the expected transition temperature, 67 °C.