Surface sensitive spectroscopic study of the interaction of oxygen with Al(111) - low temperature chemisorption and oxidation

Abstract

The interaction of an atomically clean Al(111) surface with O 2 has been studied using a combination of electron energy loss spectroscopy (EELS) and Auger spectroscopy (AES). Oxygen dissociatively adsorbs and occupies both surface and subsurface binding sites under all exposure conditions in the temperature range 122–700 K. Surface sites are preferentially occupied at low exposures, while higher exposures increasingly favor population of subsurface sites. Studies of O 2 adsorption at temperatures as low as 131 K have shown that formation of Al 2O 3 occurs at high oxygen exposures. The Al 2O 3 produced exhibits a 54 eV Auger transition and a characteristic vibrational spectrum with loss features at 430, 645, and 880 cm −1. Argon ion bombardment of thin monolayer level Al 2O 3 layers leads to preferential loss of Al 2O 3 and a reduction in the subsurface-to-surface oxygen ratio. Electron bombardment of similar, thin Al 2O 3 layers is ineffective in inducing desorption of surface species, whereas thick Al 2O 3 layers are strongly influenced by electron bombardment, as judged from AES behavior. Qualitative models for O 2 adsorption, oxidative annealing, and damage by ion and electron bombardment are given.