Anisotropic thermal displacements of adsorbed atoms and molecules on surfaces studied by low-energy electron diffraction

Abstract

We present a detailed account of the concept of ‘‘split positions’’ in low-energy electron diffraction (LEED). This allows us to study the dynamics of adsorbate particles on surfaces in addition to structural information usually provided by LEED. Enhanced lateral movements of adsorbed atoms and molecules are simulated by displacing them from their equilibrium position by an amount respresenting the mean-square deviation. Within the harmonic-oscillator approximation, the mean-square deviation is closely related to the eigenfrequencies of the vibrational modes which can be compared to values obtained by (standard) spectroscopic techniques. Several examples of adsorbate overlayers on metal and semiconductor surfaces will demonstrate the merits and potentiality of this approach.