(55) Making and Characterizing Vanadium (IV) Dioxide Thin Films

Vanadium (IV) dioxide (VO2) abruptly and reversibly changes its electronic and crystal structures at 68 °C (154 °F). At temperatures below 68 °C, VO2 exhibits properties of a semiconductor and the molecules are arranged in... [ view full abstract ]

Vanadium (IV) dioxide (VO₂) abruptly and reversibly changes its electronic and crystal structures at 68 °C (154 °F). At temperatures below 68 °C, VO₂ exhibits properties of a semiconductor and the molecules are arranged in a mono-clinic unit cell symmetry. Above 68 °C, VO₂ exhibits metallic properties and adopts tetragonal unit cell symmetry. In VO₂, the transition is best described as a first-order semiconductor-to-metal transition accompanied by a lattice distortion. With this phase transition, VO₂ experiences many drastic changes, such as a rapid decrease in optical transmittance in the near-Infra Red (IR), an increase in conductivity, and a change in the Raman spectrum. These properties allow the use of VO₂ optoelectronic switches, thermal sensors and coatings for energy-efficient windows.

At the nanoscale, this transition temperature is highly dependent on the size of the VO₂ nanoparticles. The change in transition temperature can be studied experimentally by examining the change in the Raman spectrum or by measuring the decrease in optical transmittance in the near-IR. This research aims to find a reliable way of producing vanadium dioxide (VO₂) thin films by depositing vanadium pent-oxide (V₂O₅) on substrates using physical vapor deposition (PVD) technique and then thermally decomposing it. The current Raman spectroscopy setup and IR optical transmittance setup at Sewanee has successfully detected the temperature at which semiconductor-to-metal transition occurs in VO₂. In the future, it will be possible to create different sizes of VO₂ nanoparticles and study how its size effects the transition temperature at which semiconductor-to-metal transition occurs.