ADHESION, SURFACE-MORPHOLOGY, AND GAS-SENSING CHARACTERISTICS OF THIN-GOLD-FILM CHEMICAL SENSORS

Thin films of the Au, Au/Ni/Cr, and Au/Pd/Cr systems were deposited on alumina substrates at ambient temperature and 250 degrees C in a high-vacuum resistance heated evaporator, and annealed at 300, 450, and 600 degrees c in a high-vacuum resistance heated evaporator, and annealed at 300, 450, and 600 degrees 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 degrees 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.