Abstract
Nanoporous alumina structures were fabricated on quartz crystal microbalances (QCMs) by electrochemically anodizing aluminum electrodes which had a typical thickness of 13μm. By varying the temperature and voltage of anodization, the diameter of the cylindrical pores could be controlled in the range of 12–40nm. Properties of the porous films were determined from scanning electron microscopy images and by analyzing isotherms of nitrogen, propane, and water. The isotherms showed signatures of capillary condensation and hysteresis. The mass sensitivity of the QCMs with porous alumina electrodes was increased by a factor of up to 120 compared to conventional QCMs with flat electrodes. Measurements at atmospheric pressure and room temperature in which the relative humidity was varied showed that QCMs with porous alumina electrodes are very sensitive to the partial pressure of water, and can be used as humidity sensors.
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