Characterization of silicon thin overlayers on rutile \ce{TiO2} (110)-(1x1)

TL;DR

This study investigates silicon thin films on rutile TiO2(110)-(1x1), revealing strong Si/O interactions, formation of SiO2 and suboxides, and effects of annealing, supported by experimental spectroscopy and ab-initio calculations.

Contribution

It provides detailed experimental and theoretical insights into the structure and chemistry of silicon overlayers on TiO2(110), including interface bonding and surface modifications.

Findings

Strong Si/TiO2 interaction with Si oxidation to SiO2.

Formation of Ti-O-Si bonds at the interface.

Thermal annealing improves SiO2 stoichiometry but not surface order.

Abstract

Silicon thin films for coverages ($\theta$) between 0.3 and 3 monolayers have been grown on rutile \ce{TiO2}(110)-(1x1) at room temperature and studied by x-ray and ultra-violet photoelectron spectroscopies, Auger electron spectroscopy, and low energy electron diffraction (LEED). A clear evidence of a strong \ce{Si}/\ce{TiO2} interaction consistent with the high affinity of O for Si has been found. The Ti cations on the substrate are reduced, while the Si film is oxidized, yielding \ce{SiO2} and a mixture of silicon suboxides. Neutral Si atoms are observed at a coverage of 3 monolayers. At the interface region we observe the formation of cross-linking Ti-O-Si bonds. The thin Si overlayer strongly attenuates the $(1 \times 1)$ LEED pattern from the substrate. Finally, thermal annealing results in the improvement of the \ce{SiO2} stoichiometry, but the surface order is not recovered. Using ab-initio density functional theory we have obtained optimum geometrical configurations and corresponding density of states for 1/3 \le \theta \le 1$ monolayers of Si adsorbed on the $1 \times 1$ two-dimensional unit cell.