Argon Embedded by Ion Bombardment: Relevance of Hidden Dopants in Rutile TiO2

To obtain a mechanistic understanding of occurring processes on oxide surfaces at the atomic level, systematic studies under ultra-high vacuum (UHV) conditions on single crystalline surfaces are commonly used. Usually, the sample preparation protocol for these surfaces includes argon-ion bombardment followed by annealing at elevated temperatures. For reduceable metal oxides, this leads to a significant reduction of the surface. Up to now, the particular role of the remaining argon in the subsequent formation of clean surfaces and the possible incorporation of argon into the crystal lattice as a dopant are typically neglected or remain unclear. This work presents combined, temperature-dependent X-ray photoelectron spectroscopy and a low-energy electron diffraction study under UHV conditions of the bulk-assisted reoxidation and restructuring of the rutile TiO2(110) single crystal surface after argon-ion bombardment. The formation of an ordered and reoxidized (110)(1 × 1) surface is accompanied by a stepwise...