Adhesion, surface morphology, and gas sensing characteristics of thin-gold-film chemical sensors

Abstract

Thin films of the Au, Au/Cr, Au/Ni/Cr, and Au/Pd/Cr systems were deposited on alumina substrates at ambient temperature and 250 °C in a high-vacuum resistance heated evaporator, and annealed at 300, 450, and 600 °C for 1 h in air, respectively. The gold films with a Cr adhesive layer exhibited improved adhesion of the films to the substrate. Pull-off tests demonstrated that the adhesion of the Au/Cr films deposited at ambient temperature more than doubled after annealing at 600 °C. The surface morphology of the gold films was observed using scanning electron microscopy. The sheet resistance of each layer was also investigated using a four-point probe method. Finally, the sensing characteristics as exemplified by observed resistance changes during exposure of the films to a gas were measured at room temperature for hydrogen sulfide (H2S). The sensitivity of the Au/Cr system for H2S is the highest of the four systems. As a result of the Auger-electron spectroscopy analysis, the Au/Ni/Cr and Au/Pd/Cr systems have low sensitivity for H2S due to the interdiffusion between layers.