Vibrational analysis of H<inf>2</inf> and NH<inf>3</inf> adsorption on Pt/SiO<inf>2</inf> and Ir/SiO<inf>2</inf> model sensors

Abstract

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.

Vibrational Study of SOx Adsorption on Pt/SiO2

“…Previous studies, with integrated in situ diffuse reflectance infrared Fourier transformed spectroscopic (DRIFTS) measurements and theoretical modeling, show that the detection of hydrogen involves adsorption and subsequent dissociation of the hydrogen molecule on the catalytic metal gate, followed by diffusion of the hydrogen atoms/ions to the insulator. The latter create a polarized layer of hydroxyl groups and the resulting electric field changes the conductivity of the channel underneath the gate. , The formation of hydroxyl groups was revealed by vibrational frequency studies of the interaction of hydrogen-containing species on the Pt/SiO 2 system. , In these studies, a high-surface area silica impregnated with platinum was used as a model for the sensor surface(s) in order to facilitate a reasonable signal-to-noise ratio in the direct measurements of adsorbed species with DRIFTS.…”

“…1,12 The formation of hydroxyl groups was revealed by vibrational frequency studies of the interaction of hydrogen-containing species on the Pt/SiO 2 system. 13,14 In these studies highsurface area silica impregnated with platinum was used as a model for the sensor surface(s) in order to facilitate a reasonable signal-to-noise ratio in the direct measurements of adsorbed species with DRIFTS.…”

In Situ Investigations on the Facile Synthesis and Catalytic Performance of CeO2-Pt/Al2O3 Catalyst

“…The shoulder at 1533 cm −1 should be related with O-H bending mode in water [28]. The local peak centered at 1587 cm −1 corresponds to the bending mode of the Pt-NH 3 species [29]. Increasing temperature from 100 • C to 200 • C only led to a significant decrease in the intensity of the bending vibration hydroxyl group δ(OH) in water, which illustrates water loss in the catalyst sample.…”

Materials Design for the Improvement of SiC Field Effect Gas Sensor performance in High Temperature Process Control applications

“…Data collected from e.g., mass spectrometry measurements and Infra-Red (IR) spectroscopic characterizations of the metal and insulator surfaces during hydrogen exposure seems to support a mechanism whereby the hydrogen atoms reaching the metal/insulator interface can be transferred from the metal to oxygen atoms in the surface of the insulator under creation of so-called hydroxide (-OH) groups [209][210][211]. Since these -OH groups have a large dipole moment [209], their appearance at the interface introduces a fairly sharp potential step from the gate metal to the insulator surface, equivalent to the previously discussed internal gate voltage drop, VGS,int, or change in gate-to-substrate electric field.…”