Vibrational analysis of H2 and NH3 adsorption on Pt/SiO2 and Ir/SiO2 model sensors

The sensing mechanism of metal insulator silicon-based field effect transistor devices (MISFET) for H₂ and NH₃ detection has been studied for Pt/SiO₂ and Ir/SiO₂ 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 H₂ or NH₃ 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/SiO₂ and Ir/SiO₂ to H₂ or NH₃. These results indicate a common sensing mechanism for hydrogen and ammonia.