In a new publication in Nature Communications, scientists of project P02 reveal the unreconstructed alumina surface.
Why do certain surfaces behave very differently from what theoretical calculations suggest? Scientists long assumed that the aluminum oxide (Al2O3) surface should be highly reactive and capable of splitting water molecules. In experiments, however, this behavior is barely observed.
TACO researchers from subproject P02 have now found an answer that may also help explain the behavior of many other materials: At the atomic scale, the surface looks completely different from what had been assumed, based on theoretical expectations. Instead of a smooth and regularly ordered surface, the outermost atoms are arranged in an irregular way, which dramatically changes the chemical properties of the surface. The scientists published their findings in the article “AFM imaging reveals the unreconstructed α‑Al2O3(0001) surface to be inhomogeneous and rough”, which appeared in the journal Nature Communications.
Abstract:
Alumina (Al2O3) is a key material for thin-film growth and heterogeneous catalysis, where the atomic surface structure critically impacts performance. Using noncontact atomic force microscopy (nc-AFM) combined with density functional theory (DFT) calculations, we challenge the common assumption that the unreconstructed α-Al2O3(0001) surface is atomically flat and uniformly Al-terminated. This widely accepted bulk termination satisfies polarity compensation requirements but results in highly undercoordinated Al cations at the surface. Despite substantial inward relaxation of these Al cations, we find that the (1 × 1) surface remains inherently metastable, relative to the thermodynamically stable (√31 × √31) R ± 9° surface reconstruction that forms at high temperatures above 1000 °C. Nc-AFM imaging of the unreconstructed surface reveals a rough and disordered morphology, with only nanometer-scale regions exhibiting the ordered Al-terminated (1 × 1) structure. Our results show that the unreconstructed Al2O3(0001) surface is intrinsically inhomogeneous, reconciling conflicting experimental observations and challenging the validity of commonly used atomistic models.
The full article can be found here.
The article was also featured in a TU Wien press release.
Authors:
Johanna I. Hütner-Reisch, Andrea Conti, David Kugler, Florian Mittendorfer, Michael Schmid, Ulrike Diebold & Jan Balajka
Subprojects:
P02 – Surface structure and reactivity of multi-component oxides at the atomic scale
