Improvement of Sensor Sensitivity of Quartz Crystal Microbalance by Mechanical and Chemical Treatment∗

The influence of quartz plate roughening on the dynamic parameters of quartz resonators has been studied. For this aim AT-cut quartz plates with a diameter of 8 mm, after a standard technological cleaning, are subjected to treatment with abrasive of varying grain sizes: 3, 7, 14 and 20 μm. Piezoquartz resonators are fabricated on these plates with 4 mm Au electrodes. The alterations of resonators’ dynamic parameters are followed after mass loading with a sensitive magnetron sputtered WO3 layer, 200 nm thick. Quartz Crystal Microbalance (QCM) sorption properties are evaluated for 100 ppm NH3 concentration; the frequency shift from 20 to 120 Hz, are obtained when the grain sizes change from 3 to 20 μm. The measured average roughness by Atomic Force Microscopy (AFM) was 179 nm, 288 nm, 763 nm for 7 μm, 14 μm and 20 μm, respectively. The influence of the etching process of AT-cut quartz plates on the QCM parameters has been studied. Quartz wafers (100 μm thick, with a diameter of 8 mm), have been etched in [NH4]2 F2: H2O = 1:1 solution at temperature range from 70C to 90C. The influence of etch treatment on the quartz surface morphology has been estimated by AFM. Sorption properties of QCM-MoO3 are evaluated at NH3 concentrations in the interval from 100 ppm to 500 ppm. The increase of effective sorption surface, obtained by mechanical and chemical treatment, can be successfully used to realize high sensitive QCM-thin film structure. PACS codes: 07.07.-a