Oxygen adsorption on the Ru (10 bar 1 0) surface: Anomalous coverage dependence

TL;DR

This study investigates oxygen adsorption on Ru (10 bar 1 0) surface, revealing two ordered overlayers with coverage-dependent properties analyzed through LEED, DFT, and spectroscopy, highlighting anomalous bond length behavior.

Contribution

It provides detailed structural, vibrational, and energetic analysis of oxygen overlayers on Ru (10 bar 1 0), combining experimental and theoretical methods to uncover coverage-dependent phenomena.

Findings

Two ordered oxygen overlayers identified: c(2x4)-2O and (2x1)-2O.

Oxygen occupies threefold sites forming zigzag chains.

Experimental bond lengths shorten with coverage, contrary to DFT predictions.

Abstract

Oxygen adsorption onto Ru (10 bar 1 0) results in the formation of two ordered overlayers, i.e. a c(2 times 4)-2O and a (2 times 1)pg-2O phase, which were analyzed by low-energy electron diffraction (LEED) and density functional theory (DFT) calculation. In addition, the vibrational properties of these overlayers were studied by high-resolution electron loss spectroscopy. In both phases, oxygen occupies the threefold coordinated hcp site along the densely packed rows on an otherwise unreconstructed surface, i.e. the O atoms are attached to two atoms in the first Ru layer Ru(1) and to one Ru atom in the second layer Ru(2), forming zigzag chains along the troughs. While in the low-coverage c(2 times 4)-O phase, the bond lengths of O to Ru(1) and Ru(2) are 2.08 A and 2.03 A, respectively, corresponding bond lengths in the high-coverage (2 times 1)-2O phase are 2.01 A and 2.04 A (LEED). Although the adsorption energy decreases by 220 meV with O coverage (DFT calculations), we observe experimentally a shortening of the Ru(1)-O bond length with O coverage. This effect could not be reconciled with the present DFT-GGA calculations. The nu(Ru-O) stretch mode is found at 67 meV [c(2 times 4)-2O] and 64 meV [(2 times 1)pg-2O].