Adsorbate-induced Surface Stiffening: Surface Lattice Dynamics of Ru(001)-(1x1)-O

TL;DR

This study combines experimental and theoretical methods to reveal how oxygen adsorption on Ru(001) surface causes unexpected surface stiffening and new phonon modes, challenging existing models of surface lattice dynamics.

Contribution

It provides new insights into surface lattice dynamics by showing adsorbate-induced stiffening effects that are not captured by traditional models.

Findings

Discovery of Rayleigh phonon mode stiffening due to adsorbate effects

Identification of a new high energy in-plane phonon mode

Contradiction of previous models assuming simple surface relaxation

Abstract

The dynamical properties of the high-density Ru(001)-(1$\times$1)-O phase has been investigated by a combined high-resolution electron energy loss spectroscopy and density functional theory study. Due to a strong static outward relaxation of the first Ru layer a soft Rayleigh phonon mode is expected. However, a Rayleigh mode stiffening together with a new high energy in-plane phonon mode above the bulk bands is found which is related to a strong adsorbate-induced intralayer force constant stiffening which counteracts an interlayer softening. This structurally rather simple system with one surface atom per (1$\times$1) unit cell demonstrates the limited applicability of previously adopted models.