Sub ppm Detection of Hydrogen

A light pulse technique and a field-effect device were used to detect small concentration steps of hydrogen in air. The detection limit was lower than 40 ppb, which is at least one order of magnitude lower than previously reported measurements (with field-effect devices) of hydrogen concentration in air. The device structure was a metal-insulator-semiconductor capacitor with a metal double layer with 17.5 nm Pd (upper layer) and 7.5 nm Pt on a SiO₂ insulator and a Si substrate.