| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 95 === Nanostructured IrO2 crystals are grown on a gold-coated quartz substrate by metal organic chemical vapor deposition (MOCVD). The resultant quartz crystal microbalance (QCM) sensor shows a good gas sensitivity towards carboxylic acid and amine vapors at the ppm level.
When the oxide is heated at 450oC~600oC in high vacuum, the IrO2 is partially reduced by thermal decomposition. The composition and the morphology of the sample surface before and after reduction are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning electron microscopy (SEM). Molecular simulation is also used to explain the mechanism of adsorption and desorption.
From XPS analysis, we find that the sample surface composition is IrO2/IrO3/Ir(OH)x before reduction. Upon exposure to 1000 ppm of propanic acid vapors, the QCM frequency shift is found to be 160 Hz with 73% reversibility when desorbed; After a reduction at 450oC, the surface composition and the QCM frequency shift remain the same, while the reversibility becomes 88%; When the reduction is carried out at 550 oC, the surface is reduced to become Ir/IrO2, and the Ir/IrO2 sensor shows a higher gas sensitivity (~270 Hz) and better reversibility (~98%) as compared to the IrO2/IrO3/Ir(OH)x sensor.
When reduction temperature is further increased to 600oC, the sensor shows an even higher sensitivity (~320Hz) but lower reversibility (~32%). However, if a thin Ti layer onto the Au electrode before growing the IrO2 crystals, followed by the 600oC reduction treatment, then the reversibility of the sensor can be improved to about 80%.
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