Conti, A., Hütner, J. I., Mittendorfer, F., Schmid, M., Diebold, U., & Balajka, J. (2024, September 23). Metastable termination of the unreconstructed Al₂O₃(0001)-(1×1) surface [Poster Presentation]. 3rd TACO Workshop 2024, Frankenfels/NÖ, Austria.
Aluminum oxide (α-Al²O³) - also known as alumina, corundum, or sapphire - is a material with excellent mechanical, electrical, optical, and chemical properties used as an inert ceramic support for heterogeneous catalysis. Despite its widespread use, the atomic surface structure has not been conclusively established. The commonly assumed bulk-truncated termination of the unreconstructed (1×1) surface is non-polar, but contains highly unfavorable threefold-coordinated Al cations. To increase their coordination, the surface Al ions relax strongly into the underlying O plane. The Al relaxation, however, is not sufficient to yield a stable structure. The metastable surface exhibits small islands of the (1×1) structure within otherwise rough and disordered morphology. The Al²O³ (0001) surface is only stabilized through the formation of the complex (√31×√31)±9° reconstruction [8], formed at high temperatures (>1000°C). The mostly disordered unreconstructed surface may explain why theoretical predictions assuming a perfectly ordered and flat (1×1) surface do not agree with experimental results [1].
