Structure and morphology of aluminium-oxide films formed by thermal oxidation of aluminium

The structure and morphology of thin aluminium-oxide films grown by the dry, thermal oxidation of a bare Al(4 3 1) substrate at a partial oxygen pressure of 1.33x10-4 Pa in the temperature range of 373-773 K were studied using X-ray photoelectron spectroscopy and high resolution electron microscopy. The initial oxidation of the bare Al substrate proceeds by an island-by-layer growth mechanism, involving the lateral diffusion over the bare Al substrate surface of mobile oxygen species. At low temperatures (T≤573 K), the mobility of the oxygen species is very low, and an amorphous oxide film of relatively uniform, limiting thickness develops. X-ray photoelectron spectroscopic analysis established the occurrence of a surface-oxide species at the very surface of these films. At higher temperatures (T>573 K) an initially amorphous oxide film of less uniform thickness develops that gradually transforms into crystalline γ-Al2O3. At these temperatures an amorphous-to-γ-Al2O3 transition oxide phase occurs