Effect of a noble metal coating on a natural aluminum oxide film.

The effect of a noble metal (silver or copper) island film on the vibration al spectrum of a natural aluminum oxide nlm was studied using the reflectio n-absorption spectroscopy technique. It was found that the intensity of the absorption band of aluminum oxide near 950 cm(-1) changes drastically afte r the deposition of the metal overlayer. This band intensity increases rapi dly with increasing of the silver film thickness more than twice. reaching the maximal value at the silver thickness 0.2 nm. then the band does not ch ange up to the thickness similar to 2 nm. Such behavior takes place only in the presence of aluminum under oxide film. We suggest that this: increase of the absorption band intensity is due to the increase of the aluminum oxi de film thickness, caused by an electrochemical reaction resulting in alumi num anodic oxidation. For thicker silver films the intensity of the aluminu m oxide band falls down slowly due to a metal screening effect. (C) 1999 El sevier Science S.A. All rights reserved.