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

• Published in: Journal of physical chemistry. C Vol. 123; no. 33; pp. 20434 - 20442
• Main Authors: Mohrhusen, Lars, Kräuter, Jessica, Willms, Michael, Al-Shamery, Katharina
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22-08-2019
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.9b05975

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 desorption of argon from the sample. Moreover, we present a systematic study of the incorporation of argon in the rutile crystal as well as the diffusion and desorption of argon from these samples. By following the temperature-dependent Ar 2p photoelectron spectra, the change of the electronic environment of embedded argon is elucidated, demonstrating the interaction with reduced Ti cations. Hence, residual argon (in case of Ar+) possibly acts as a strong oxidant or induces significant lattice distortions. Our results show that residual argon from the sample preparation is an important hidden dopant and needs to be considered in the evaluation of typical studies on oxide surfaces under UHV conditions in future work.