Influence of adsorbed oxygen on the tunnel current from an Al(111) surface

SUMMARY The tunnel current from an Al(111) surface with an adsorbed oxygen atom into a tungsten tip has been calculated. The tip is represented by a single tungsten atom adsorbed on a flat W(110) surface. The evaluation of the tunnel current is based on the generalized Ehrenfest theorem. The wave functions are obtained as self-consistent solutions of a model Hamiltonian. The lines of constant tunnel current are similar to those of constant charge density at the Fermi level, but the latter shows fine details which are not discernible in the tunnel current. The main feature is an oxygen induced protrusion of about 0·3 A height and 5 A width. The height of the protrusion is nearly unchanged over the investigated range of tip-sample separations. This contrasts the behaviour of the tunnel current found in a former investigation of the system O/Ni(100), where the oxygen-induced feature in the contours of constant tunnel current revealed a strong distance dependence. This difference is discussed in terms of the closer equilibrium distance and different screening behaviour for oxygen on Al(111).