Ab initio studies of adsorption and diffusion processes on alpha-Al2O3 (0001) surfaces

• As one of the technologically most important ceramic materials, alumina (Al2O3) thin film growth has been studied extensively in the past. However, the mechanisms behind the formation of different phases and microstructures are still poorly understood, especially for physically vapor deposited films. An increased atomic scale understanding of alumina surface processes would thus be an important step towards a more complete understanding and control of the deposition process. In the present work, density functional theory based methods were used to study the adsorption of Al, O, AlO, and O2 on different terminations of alpha-alumina (0001) surfaces. The results show the existence of several metastable adsorption sites on the O-terminated surface and provide a possible explanation for the well-known difficulties in growing -Ñ-alumina at lower temperatures. Moreover, we demonstrate that Al adsorption in bulk positions is unstable, or considerably weaker, for completely hydrogenated surfaces, indicating that hydrogen stemming from residues in vacuum systems, might hinder the growth of crystalline alpha-alumina. Furthermore, nudged elastic band investigations of dynamic energy barriers for different surface diffusion processes show that Al diffusion, on the Al-terminated (0001) surface, requires only ~0.7 eV. This value is considerably lower than what is generally expected for the low temperature synthesis of alpha-alumina phase. These results add significantly to understanding the effects of several important factors on alumina growth, and their implication, on optimizing deposition processes for the synthesis of alumina films with desired properties, will be discussed.

Nyckelord

NATURAL SCIENCES

NATURVETENSKAP

Publikations- och innehållstyp

vet (ämneskategori)

kon (ämneskategori)