Long-Range Atomic Order on Double-Stepped Al₂O₃(0001) Surfaces.

Abstract

The deterministic preparation of highly ordered single-crystalline surfaces is a key step for studying and utilizing the physical properties of various advanced materials. This paper presents the fast and straightforward preparation of vicinal Al₂O₃(0001) surfaces with micrometer-scale atomic order. Crisp electron-diffraction spots up to at least 20^th order evidence atomic coherence on terraces with widths exceeding 1 μm. The unique combination of three properties of Al₂O₃(0001) underlie this remarkable coherence: its high-temperature stability; the differences in the ionic bonding systems of the surface as compared to the bulk; and the fact that the terraces are non-polar whereas the step edges have a polar character. The step edges are furthermore found to have alternating configurations, which drive a step-doubling transition. On double-stepped surfaces, the Al-rich <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mo>(</mo> <msqrt><mn>31</mn></msqrt> <mo>×</mo> <msqrt><mn>31</mn></msqrt> <mo>)</mo> <mi>R</mi> <mo>±</mo> <mn>9</mn></mrow> <annotation>$(\sqrt {31}\times \sqrt {31})\textrm {R}\pm 9$</annotation></semantics> </math> ° surface reconstruction attains a singular in-plane orientation. These results set a benchmark for high-quality surface preparation and thus expand the scope for both fundamental studies on and the technological utilization of exciting material systems.