Pulsed Laser Deposited Nanostructured Vanadium Oxide Thin Films Characterized as Ammonia Sensors

Vanadium oxide thin films were fabricated by pulsed laser deposition. The microstructure and crystal symmetry of the deposited films were studied with X-ray diffraction, scanning electron microscopy (SEM), and Raman spectroscopy, respectively. The films surface morphology was examined by atomic force microscopy. Raman spectroscopy and XRD results showed that the thin film phase-structure was composed of pure orthorhombic V2O5 phase, or they had a mixed phase structure of orthorhombic V2O5 and triclinic V7O16. Surface morphology of the films consisted of nanosized particles, although in pure V2O5 films some bigger agglomerates and flakes were also seen. The conductivity based gas sensing measurements showed a clear response already at ppb-levels of NH3 and strong selectivity to ammonia was found when compared to NO and CO gases. Also, the films showed promising gas sensing behavior in cross-sensitivity measurements between NO and NH3, being able to sense ammonia even in the presence of NO. This is an important property when considering possible sensing applications to control Selective Catalytic Reduction processes, e.g. in diesel engine exhausts, where introduced ammonia, or urea, transforms nitrogen oxide gases in a catalytic converter to nitrogen and water.