Metallic Character of the Al₂O₃(0001)-(√31 × √31)R ± 9° Surface Reconstruction

Abstract

The basal (0001) surface plane of R-Al 2 O 3 has been extensively studied both by experimental techniques and applications of theory. Although this surface is not easily created upon cleavage, it grows in during aluminum oxidation and has been shown to be one of the lowest energy surfaces of alumina. Upon heating under vacuum, this (0001) surface of R-Al 2 O 3 undergoes a series of reconstructions. The final structure obtained at ∼1700 K is an air-stable termination known as the ( 31 × 31)R ( 9°reconstruction. Alternatively, this reconstructed surface can also be obtained at lower temperatures by aluminum deposition on a clean Al 2 O 3 (1 × 1) basal plane surface. Applying density functional theory within the generalized gradient approximation to a model surface, we show that the transformation from the (1 × 1) termination to ( 31 × 31)R ( 9°is accompanied by a dramatic change in the band gap associated with the ceramic's surface. Specifically, the (1 × 1) termination is insulating for both surface and deeper "bulk-like" atoms, while the ( 31 × 31)R ( 9°termination results in a metallic surface aluminum coating that behaves very much like an aluminum (111) surface. Although some experimental evidence for the ( 31 × 31)R ( 9°metallic surface states exists, it has generally been ignored, and both the (1 × 1) and ( 31 × 31)R ( 9°terminations are commonly treated as insulating. The metallic surface character of the reconstructed basal plane of R-Al 2 O 3 may present interesting implications for future applications of heat-treated alumina surfaces. † Part of the special issue "John T. Yates, Jr., Festschrift".

Effects of Additives and Impurity on the Adhesive Behavior of the NiAl(110)/Al2O3 (0001) Interface: An Ab Initio Study

“…The periodic repetitions of the supercell geometry along the z-axis are separated by~12 Å of vacuum to eliminate interactions between periodic cells, and the Al 2 O 3 slab is cut to have an Al truncated surface since it was shown to be the most stable surface termination. [38,44,45] The calculated bulk NiAl lattice constant of 2.891 Å , which is in good agreement with the experimental value of 2.887 Å , yields a lattice misfit of 0.5 pct between NiAl and Al 2 O 3 surfaces, demonstrating a reasonable coherent interface model.…”

“…The recent ab initio DFT calculations, [44,45] however, demonstrated that the Al-terminated Al 2 O 3 (0001) surface is more stable than that with O as a termination layer. Therefore, it is essential to investigate the NiAl/Al 2 O 3 interface with Al-terminated layer, at which the highest work of separation can be achieved through examining various translations of NiAl (110) relative to the Al 2 O 3 .…”

Growth and characterization of thin epitaxial Co3O4(1Vaz1, Henrich2, Ahn3 et al. 2009Journal of Crystal Growth32150View full textAdd to dashboardCite

“…1a [25,26]; the Al termination yields non-polar surfaces. Experimentally, it is observed that ð0 0 0 1Þ surfaces prepared at temperatures below $1500 K show a stable ð1  1Þ surface, corresponding to the nonpolar Al-termination; this surface is also characterized by large inward relaxation of the Al atoms [27][28][29][30][31][32]. Annealing to higher temperatures produces a rotated ð ffiffiffiffiffiffi 31 p  ffiffiffiffiffiffi 31 p Þ surface reconstruction, associated with the Al-rich (Al-Al) surface [30,[33][34][35][36][37][38][39][40][41].…”

Adsorption of Cu and Pd on α-Al2O3(0001) surfaces with different stoichiometries

“…Fig 2͑b͔͒. The metallic-like character of the Al-rich surface of corundum has been reported previously. 33,34 For the reconstructed ͱ31ϫͱ31 surface we would expect the metallization to strongly influence the surface reactivity. For the oxygen terminated surface, on the other hand, the 2p shell could be unfilled.…”