Detection of dilute organic acids in water by inelastic tunneling spectroscopy

Abstract

Oxidized aluminum films; exposed to acetic, formic, and cynoacetic acid and covered with a lead film; form junctions which carry electrical current by electron tunneling. The technique of inelastic electron tunneling spectroscopy, which reveals the characteristic vibration spectra of the molecules adsorbed on the oxide surface, has been used to detect the presence of the organic molecules in the parts per million range. The intensity of the spectral lines, which depends upon the competition between water and the organic molecules for the adsorption sites on the alumina surface, appears to saturate in the 10 to 1000 ppm range. From the spectra obtained one can distinguish between different molecules with similar structure and between different surface bonding configurations. The method should be applicable to the detection of low concentrations of other, similar organic molecules that adsorb readily on the alumina surface.