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 60 0 degrees c in a high-vacuum resistance heated evaporator, and anneale d at 300, 450, and 600 degrees C for 1 h in air, respectively. The gol d films with a cr adhesive layer exhibited improved adhesion of the fi lms to the substrate. Pull-off tests demonstrated that the adhesion of the Au/Cr films deposited at ambient temperature more than doubled af ter annealing at 600 degrees C. The surface morphology of the gold fil ms was observed using scanning electron microscopy. The sheet resistan ce of each layer was also investigated using a four-point probe method . finally, the sensing characteristics as exemplified by observed resi stance 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 sy stems have low sensitivity for H2S due to the interdiffusion between l ayers.