Effect of porous morphology on phase transition in vanadium dioxide thin films

Vanadium oxide (VO₂) thin films were prepared on Si (100) substrates by direct current magnetron sputtering at room temperature, and then, postannealing was conducted at 450°C for 2h in vacuum. Structural characterizations demonstrated that the thin films exhibited porous morphology upon thermal annealing and the porosity and pore size depended on the oxygen flow rate in the process of film fabrication. Raman spectra were measured in the temperature range of 303-343K, and resistance measurement was conducted in the temperature range of 293-363K, to study the influence of porous morphology on the phase transition in VO₂ thin films. It was illustrated that the porous morphology could provide a free space to release the stress induced in the monoclinic-to-tetragonal phase transition of VO₂, and lower the transition temperature to a certain degree.