| AVS 59th Annual International Symposium and Exhibition | |
| Advanced Surface Engineering | Monday Sessions |
| Session SE+NS-MoM |
| Session: | Nanostructured Thin Films and Coatings I: Interface Aspects |
| Presenter: | J.M. Schneider, RWTH Aachen University, Germany |
| Authors: | F. Nahif, RWTH Aachen University, Germany H. Bolvardi, RWTH Aachen University, Germany D. Music, RWTH Aachen University, Germany S. Mráz, RWTH Aachen University, Germany J.M. Schneider, RWTH Aachen University, Germany |
| Correspondent: | Click to Email |
Charge state resolved ion energy distribution functions (IEDFs) of Al+, Al2+ and Al3+ were measured as a function of Ar
pressure in the range from 5.7 × 10−5 to 2.13 Pa (0.01 to 256 Pa cm). A close to monoenergetic beam of Al+ ions was obtained in an Ar/O2 mixture at 128 Pa cm. Al2O3 films are deposited employing this monoenergetic Al+ beam using a substrate bias potential to increase the ion energy. A critical Al+ ion energy of 40 eV for the formation of the α-Al2O3 phase at a substrate temperature of 720 °C is determined. This energy is used as input for classical molecular dynamics and Monte-Carlo based simulations of the growth process, as well as ab initio calculations. The combination of theory and experiment indicates that in addition to the well known surface diffusion the previously non considered diffusion in sub-surface regions is an important atomistic mechanism in the phase formation of Al2O3. Using density functional theory and cathodic arc deposition experiments the effect of Si and Y addition on the stability of γ- and α-Al2O3 has been investigated. Si additives clearly shift the relative stability towards the γ-phase which can be understood based on the electronic structure. As the additive concentration increases, strong silicon-oxygen bonds are formed giving rise to the observed stabilization of the γ-phase.