Optical and dielectric properties of a nanostructured NbO2 thin film prepared by thermal oxidation

Nanostructured NbO2 films have been prepared on Si (001) substrates by thermally oxidizing a spiral niobium coil in a vacuum of the order of 10(-2) Torr. The film consists of single-crystalline NbO2 nanoslices (several tens of nanometres thick) that are aligned with each other. When excited with 512 nm light, the NbO2 film showed room-temperature photoluminescence around 700 and 825 nm. It also exhibits, interestingly, excellent dielectric properties in the frequency range from 1 kHz to 10 MHz. It has a dielectric constant comparable to that of SiO2 and Si3N4, is independent of the frequency applied, and has a dielectric loss of less than 1% in the measured frequency range, making NbO2 a potential material for applications into MOS devices. The Raman spectrum of the NbO2 phase, for the first time, is also reported.