From the TU Wien press release:
Aluminum oxide (Al2O3), also known as alumina, corundum, sapphire, or ruby, is one of the best insulators used in a wide range of applications: in electronic components, as a support material for catalysts, or as a chemically resistant ceramic, to name a few. Knowledge of the precise arrangement of the surface atoms is key to understanding how chemical reactions occur on this material, such as those in catalytic processes. Atoms inside the material follow a fixed arrangement, giving rise to the characteristic shapes of crystals. On the surface, however, the structure deviates from that inside the crystal. The strongly insulating nature of alumina hindered experimental studies, and the surface structure evaded precise determination for more than half a century. Researchers at TU Wien and the University of Vienna have now solved the complex structure of the Al2O3 surface, a puzzle listed in 1997 as one of the “Three mysteries of surface science”. The research group led by Jan Balajka and Ulrike Diebold recently published their findings in the prestigious journal Science.
Here, you can find the full TU Wien press statement.
Abstract:
Macroscopic properties of materials stem from fundamental atomic-scale details, yet for insulators, resolving surface structures remains a challenge. We imaged the basal (0001) plane of α–aluminum oxide (α-Al2O3) using noncontact atomic force microscopy with an atomically defined tip apex. The surface formed a complex (√31×√31)R±9° reconstruction. The lateral positions of the individual oxygen and aluminum surface atoms come directly from experiment; we determined with computational modeling how these connect to the underlying crystal bulk. Before the restructuring, the surface Al atoms assume an unfavorable, threefold planar coordination; the reconstruction allows a rehybridization with subsurface O that leads to a substantial energy gain. The reconstructed surface remains stoichiometric, Al2O3.
Reconstructed Al2O3 surface
© Science
Authors:
Johanna I. Hütner, Andrea Conti, David Kugler, Florian Mittendorfer, Georg Kresse, Michael Schmid, Ulrike Diebold, and Jan Balajka
Subprojects:
P02 – Surface structure and reactivity of multi-component oxides at the atomic scale
P03 – Bayesian regression for multi-level machine-learned potentials
