Photomodulated thermoreflectance detection of hydrogen gas using optically thin palladium film on silicon oxide

The sensitivity various thicknesses of optically thin film palladium layers evaporated onto silicon oxide substrate is investigated in the presence of a hydrogen/air atmosphere at room temperature. The magnitude of the resulting reflectivity change is measured using an excite-probe technique, through laser excited photothermal modulation of a probe beam. This allows for the recovery of information from both the amplitude and phase channels of the hydrogen sensor output. Data indicates that concentrations of 0.1% hydrogen in the presence of a balanced air mixture and room temperature may be measured with an 8 nm palladium film. The presence of inhomogeneities the palladium layers leads to anomalous behavior. (C) 1998 American Institute of Physics.