Modifications in the phase transition properties of predeposited VO2 films

Abstract

Thin films of the phase transition material vanadium dioxide (VO2) were deposited by thermal oxidation of e-beam evaporated vanadium on a variety of bulk materials. Substrate effects on transition temperature are confirmed as being due to a mismatch between film and substrate thermal expansion coefficients. Decreasing tensile stress results in a lowering of VO2 transition temperature. Effects of low-energy Ar+ bombardment on the electrical and optical properties of these predeposited VO2 films were investigated. Bombardment energies in the range 138–500 eV at 1.0–1.3 mA/cm2 for 120–180 s were provided by a Commonwealth Millatron. The higher Ar+ energies resulted in collapse of the VO2 optical transmittance hysteresis loop, while low-energy Ar+ ions caused both a downward shift in the transition temperature and a decrease in hysteresis loop width, suggesting a dependence of these quantities on intrinsic stress. In addition, large decreases in cold-state resistivity are reported and attributed to a reduction of the surface oxide by the low energy argon beam.

Spectroscopic analysis of phase constitution of high quality VO2 thin film prepared by facile sol-gel method

“…17,21 The SMT temperature is suggested to be associated with internal stress, impurities and the stoichiometry. [5][6][7]19 In fact, the effects of the thermal stress on the shifting SMT temperature of VO 2 films on different types of substrates are confirmed. 7,44 The thermal stress produced in the film on cooling from the process temperature to room temperature due to the thermal expansion coefficient difference between the film and substrate.…”

“…[5][6][7]19 In fact, the effects of the thermal stress on the shifting SMT temperature of VO 2 films on different types of substrates are confirmed. 7,44 The thermal stress produced in the film on cooling from the process temperature to room temperature due to the thermal expansion coefficient difference between the film and substrate. Since both VO 2 (M1) films were formed on Al 2 O 3 substrates with the same annealing process in our study, the difference in thermal stress of both films derives from the difference in the thermal coefficients of Al 2 O 3 substrate along c axis and perpendicular to c axis.…”

“…In addition, the reduction of SMT temperature has been attributed to the intrinsic stress affected by the specific microstructure. 7,21 The microstructures for both films in SEM images show well-formed grains and no significant difference. So the difference in the intrinsic stress mainly comes from the difference in the stress induced by lattice mismatch between the film and substrate.…”

Effect of lattice misfit on the transition temperature of VO2 thin film

“…Although doping tungsten on VO 2 is known to be the most effective method to lower T c with a decreasing rate of approximately 25 K/% [7], in thin film, the T c of pure VO 2 can be changed by engineering the thermal stress applied to the VO 2 thin film. It was reported that thermal stress between the film and the substrate can affect T c of VO 2 , caused by the anisotropy in the thermal expansion of VO 2 [11]. Also, VO 2 thin films with less than 100 nm thickness can have lower T c compared to the bulk VO 2 [12].…”

Preparation of Vanadium Dioxide Thin Films with Adjustable Electric Field Intensity Transition Point

“…With the continuous research of vanadium dioxide in recent years, the control technology of vanadium dioxide phase transition temperature has been basically mature, mainly in the following three ways: adjust the applied stress [8][9], control the microstructure [10][11][12] and ion doping [13][14][15]. But the control of the phase change field strength was basically not studied, There were two main reasons for this.…”