Direct observation of mobility and interactions of oxygen molecules chemisorbed on the Ag(110) surface

Abstract

The energetics of thermal motions and interactions of oxygen molecules chemisorbed on a Ag(110) surface were investigated by scanning tunneling microscopy at 60–100 K. Surface mobility is anisotropic, preferably in the [11-bar0] direction with an activation energy of 0.22±0.05 eV and a preexponential factor of 1×${10}^{13\pm 3}$ ${\mathrm{s}}^{\mathrm{-}1}$. Along the [11-bar0] direction a repulsive interaction between nearest neighbors of about 0.02 eV and an attraction of 0.04±0.01 eV between next nearest neighbors were derived. Along [001] appreciable repulsion exists between nearest neighbors, while a ``diagonal'' arrangement of molecules is associated with an attraction of 0.02±0.01 eV. The data are indicative for the operation of indirect, substrate-mediated molecule-molecule interactions.