Oxygen and nitrogen interaction with rhodium single crystal surfaces

Abstract

Rhodium single crystals show a surprisingly wide range of reconstructions induced by light elements such as oxygen and nitrogen, as well a number of chemical reactions of fundamental chemical importance. In this review, we present and critically discuss the current state of knowledge of the interaction of oxygen, nitrogen and mixed O+N layers with such Rh surfaces, emphasising structural aspects and their impact on the surface reactivity. On the basis of the available experimental results we will elucidate some general trends, which shed light on the possible driving forces behind the diffusive and displacive reconstructions induced by adsorbed atomic oxygen and nitrogen. More attention will be paid to the reconstructive interactions on a Rh(1 1 0) surface. The following three topics are reviewed. The first concerns oxygen interaction with low and some high index Rh surfaces, covering oxygen coverages, adsorption sites, bond strength, ordered structures, sub-surface penetration and oxide formation, and observed by various surface sensitive techniques: X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) 3, high resolution electron energy loss spectroscopy (HREELS), ultraviolet photoemission spectroscopy (UPS), He scattering, scanning tunneling microscopy (STM), low energy electron diffraction (LEED), etc. They are summarised in a manner illustrating the similarities and differences in oxygen interaction with different Rh single crystal planes. The emphasis is on the reaction conditions when oxygen induces restructuring of the substrate surface. The variety of oxygen-induced (1 × n) missing/added row reconstructions on the Rh(1 1 0) surface is reviewed and discussed in some detail. Comparison will be made with (1 1 0) surfaces of other Group VIII/IB fcc metals Pd, Cu, Ni and Ag where missing/added row reconstructions are also observed. For Pd, the reconstruction seems similar, whereas for the other three metals it is in a direction orthogonal to that on Rh. In addition, the oxygen on Rh is co-ordinated to three substrate atoms, whereas on Cu, Ni and Ag it is co-ordinated to four atoms.