Abstract
New results are reported for the Extended X-ray Absorption Fine Structure (EXAFS) of oxygen on Al(111) at submonolayer coverages. The O-Al bond lengths are derived for both the chemisorbed phase characterized by a 1.4 eV chemical shift of the Al 2p level and the oxide-like phase formed upon heating and exhibiting a 2.7 eV shift. Comparison of the derived bond length of 1.75 ± 0.03 Å for the submonolayer oxide-like phase with those in amorphous alumina (1.85 – 1.88 Å) and bulk corundum (α − Al 2O 3) (1.92 Å) which all exhibit the same chemical shift leads to structural models for the progressive oxide formation. We show that for a predominantly ionic bond changes in bond length and coordination number are directly related. Such considerations lead to the conclusion that the short (1.76 ± 0.03 Å) bond in the chemisorbed phase must exhibit considerable covalent character.
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