One-Dimensional Adsorbate Systems: Electronic, Dynamic, and Kinetic Features

Abstract

Anisotropic lateral interactions between adsorbate species on single crystal surfaces can lead to one-dimensional (1D) behavior of various physical properties not only on anisotropic substrates, but even on low index, high symmetry surfaces, for which symmetry breaking by the adsorbate-adsorbate interactions can occur. Examples for both cases are demonstrated here for three different physical properties of adsorbate layers: the electronic adsorbate band structure, the surface phonon bands, and the desorption kinetics. As examples of 1D electronic band structures we use the systems Xe on H-modified Pt(110), and C2H4 on single-domain Si(l00)-(2 × 1) surfaces; the reasons and some consequences of their behavior will be discussed, partly also in comparison to very similar 2D systems. ID-dispersion of extrinsic surface phonon bands is found in (2 × l)-row structures of adsorbed oxygen atoms as well as of (O+NO) coadsorbate layers on the hexagonal Ru(001) surface; comparison with dilute [(2 × 2)-O] and with dense adsorbate [(1 × l)-O] and coadsorbate [(2 × 2)-(NO+3O)] systems on the same surface clearly shows the effect of dimensionality on the vibrational coupling of adsorbates. Finally, the direct influence of reduced dimensionality of an adsorbate system on surface kinetics will be demonstrated for the case of Xe on flat and stepped Pt(111) surfaces. The distinct modification of desorption kinetics observed here can be well understood in terms of the statistical thermodynamics of the adlayer, in particular the critical temperatures of the adsorbate condensate phases and its dimensionality dependence. In all cases the lateral adsorbate-adsorbate coupling—though via quite different coupling mechanisms in the various cases—underlies the found behavior.