Tantalum pentoxide-based quartz crystal microbalance for NH3 detection

This work presents the abilities of a thin Ta2O5 film coated QCM's (Quartz Crystal Microbalance) to detect NH3 concentrations in a range 10 to 10000 ppm. The active layers of Ta2O5 (86 and 286 nm) are deposited by e-beam evaporation. The morphology of the Ta2O5 films is studied by Transmission Electron Microscopy. The chemical compositions of the evaporated source material and obtained films are investigated in details by X-ray Photoelectron Spectroscopy. The Ta:O ratio is approximately 1:3 in the source material as well as in the films. This ratio shows a negligible change for different film thicknesses. The dielectric properties of Ta2O5 are obtained from volt-capacity and ellipsometric measurements. The sorption abilities of QCMs with thin Ta2O5 are determined by measuring the resonance frequency shifts of the QCM over aqueous solutions of NH3 with different concentrations. The maximum response of the QCM increases when the film thickness and NH3 concentration rise. The minimal detectible concentration is found to be 10ppm NH3. The character of the sorption process is defined as physical. Based on experimental results, the sorbed mass of NH3 is calculated for the whole investigated interval. The investigations present the possibility to monitor NH3 by a QCM with Ta2O5.