Tuning the Limiting Thickness of a Thin Oxide Layer on Al(111) with Oxygen Gas Pressure

Abstract

We report an x-ray photoelectron spectroscopy study of the oxidation of Al(111) surfaces at room temperature, which reveals that the limiting thickness of an aluminum oxide film can be tuned by using oxygen pressure. This behavior is attributed to a strong dependence of the kinetic potential on the oxygen gas pressure. The coverage of oxygen anions on the surface of the oxide film depends on the gas pressure leading to a pressure dependence of the kinetic potential. Our results indicate that a significantly large oxygen pressure (>1 Torr) is required to develop the saturated surface coverage of oxygen ions, which results in the maximum kinetic potential and therefore the saturated limiting thickness of the oxide film.

Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum

“…Moreover, the magnitude of the Mott potential agrees with experimental estimates [2,5]. It is interesting to note that, although there is a slow decrease of the Gibbs free energy of the adsorbed oxygen molecule, the Mott potential does not display such behavior.…”

“…The calculated limiting thickness at 1 Torr is only slightly larger than the one recently measured by Zhou et al [5,6] The minor discrepancy (roughly one trilayer) can be attributed to the simplification of the structural models as well as to the well known overbinding of adsorption energies of O 2 predicted by the current version of DFT [16]. It should be noted that the initially formed oxide layers in the experiment appear to be disordered [5], which only gradually transform into crystalline α-Al 2 O 3 [29]. However, we have explicitly confirmed that our conclusions are not critically dependent on the chosen phase of alumina or the presence of defects in the film [30].…”

“…Whereas the CM model predicts an apparent limiting thickness due to slow kinetics, the present results uncover a real limiting thickness due to low O 2 adsorption energy. This is a completely new interpretation of the cause behind the observed limiting thickness on alumina and provides an explanation of the pressure dependence in film thickness recently observed experimentally [5].…”

“…To facilitate the comparison with experiments [5,6], the Gibbs free energy of O 2 adsorption at 1=9 coverage is shown as a function of pressure at room temperature in Fig. 2(g).…”

“…Recently, Zhou et al [5,6] showed that the thickness of the aluminum oxide on Al(111) can be tuned by the oxygen pressure. It was observed that the thickness of the alumina film increases with increasing oxygen pressure up FIG.…”