Characterization of the atomic-level structure of γ-alumina and (111) Pt/γ-alumina interfaces

The atomic-level structure of platinum/gamma-alumina interfaces is characterized in a model system of dense gamma-alumina embedded with faceted Pt NPs produced by implantation of platinum ions into sapphire followed by thermal annealing in air at 800 degrees C. Aberration-corrected scanning transmission electron microscopy (STEM) was used to collect atomic-resolution images, which are compared to STEM image simulations of two experimentally-based bulk models of gamma-alumina by Smrcok et al. and Zhou and Snyder. A density functional theory (DFT) based model of (111) interfaces with different chemical terminations (O, Al-1, Al-2) of the gamma-alumina developed by Oware Sarfo et al. is also compared to experimental STEM data from Pt/gamma-alumina interfaces. The Smrcok gamma-alumina model provides a better fit than the Zhou structure to the bulk of the gamma-alumina. The oxygen-terminated Oware Sarfo model best fits the experimental data and is a very good model close to the interface. However, the fit of the interface model to the experimental data is poorer beyond the third atomic layer in the gamma-alumina. This is attributed to compromises required in the design of the model to limit the cell size and computational time for DFT calculations. Understanding the accuracy and limits of the structural models of gamma-alumina and Pt/gamma-alumina interfaces is important to further the understanding of the structure/property relationships in this system.