Preparation and characterization of Pd/Ni thin films for hydrogen sensing

To investigate a newly proposed hydrogen sensing method, Pd_100-xNi_x (x=8, 9, 12, 15) thin films are deposited on rough α-Al₂O₃ substrates by electron beam evaporation in ultrahigh vacuum. The structure and composition of the Pd/Ni films are studied by X-ray diffraction, electron probe microanalysis, and scanning electron microscopy. At 22°C, the electrical resistance increases with increasing hydrogen concentration and the steady-state response to hydrogen in the presence of nitrogen is significantly larger than that of Pd/Ni thin-film sensors reported in the literature. The sensor response time is typically several tens of seconds. The sensor can operate after exposure to air for more than half a year. Oxygen has little effect on sensor response time and steady-state response. Exposure to several percent of CO for several minutes can increase the sensor response time significantly. Several possible remedies for CO poisoning are proposed. The sensor sensitivity decreases with increasing temperature, rendering the sensor insensitive above 100°C.