|
Gas sensors play an important role in detecting, monitoring and controlling the presence of hazardous and poisonous gases in the atmosphere at very low concentrations. The present work is aimed at developing acoustic sensors for registration of NH3 in the atmosphere. For that purpose, resonator structures are created by deposition of sorption TiO2 layers on quartz plates.
The TiO2 thin films were prepared by Liquid Phase Deposition (LPD) method, including reaction between metal fluorocomplex and boric acid in an aqueous solution. The films were then annealed at 500 K for an hour. The morphology and the chemical composition of the films were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).
The SEM study revealed that the TiO2 films are polycrystalline and uniform. XPS was used to probe the actual surface composition and the homogeneity of TiO2 layers in a depth of the films. The as-deposited films exhibited broad Ti2p photoelectron peaks, corresponding to a mixture of Ti3+ and Ti4+ oxidation states, indicating a sub-stoichiometric composition. Depth profiling of the as-deposited samples performed by Ar+ ion sputtering, established stoichiometry of TiO1.86. After annealing at 500 K, the binding energy and the shape of the Ti2p peaks became characteristic of Ti4+ oxidation state. The depth profiling revealed significant change in the thickness of the annealed film due to compression of the oxide layers.
Gas sensing properties were tested by measuring the mass loading when the films were exposed to 100 -500 ppm NH3 vapor .
|