The sensing mechanism of metal insulator silicon-based field effect transistor devices (MISFET) for H 2 and NH 3 detection has been studied for Pt/SiO 2 and Ir/SiO 2 model sensors with in situ infrared spectroscopy and density functional theory calculations (DFT). The spectroscopy experiments showed reversible formation of isolated OH groups on the silica surface upon H 2 or NH 3 exposure. In addition, an intense broad band was observed around 3270 cm -1 . Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. These results strongly indicate that dissociation and spill-over of hydrogen occurs during exposure of Pt/SiO 2 and Ir/SiO 2 to H 2 or NH 3 . These results indicate a common sensing mechanism for hydrogen and ammonia.
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