The use of auger electron spectroscopy for the characterisation of the surfaces of spherical gold electrodes

Abstract

Gold spheres (1.5 mm diameter) were obtained from wires of different purities by melting under various conditions (nature and pressure of the atmosphere used, sputtering and transfer conditions to the Auger spectroscope). Their surfaces were analysed by Auger electron spectroscopy (AES) as regards conditions of preparation. The main impurities detected were sulphur, carbon and oxygen, the latter appeared to be bonded to oxidizable elements such as silicon, calcium or even iron for the less pure samples. The origin of the surface contaminants has been investigated (bulk metal impurities, air pollutants, emission from the inner surface of pyrex tube used for melting, annealing and sputtering). Spheres of known surface condition were used as electrodes. The shape of differential capacity-potential curves obtained just after the electrode was dipped into the electrolyte was in good agreement with expectation based on previous AES analysis. Other gold electrodes were analysed by AES after various electrochemical treatments. Oxygen appeared to be stable under AES vacuum conditions on the surface of an electrochemically oxidized electrode. Such oxidized gold surfaces did not adsorb carbon compounds and sulphur unlike those which were reduced. Metallic impurities were not detected by AES on electrochemically reduced gold electrodes which did not retain oxygen from previous electro-oxidizing treatments. In this case oxygen traces observed by AES which amounted to random values according to the electrochemical treatment, seemed to be assignable to cumulative contribution of oxidized impurities not detected individually by AES.