Structure of ultrathin Ag films on the Al(100) surface

초록

The structure for submonolayer amounts of Ag deposited on the Al(100) surface at room temperature has been studied using low-energy electron diffraction (LEED) and low-energy ion-scattering spectroscopy (LEIS/ISS). The Ag coverage was determined using Rutherford backscattering spectroscopy. We conclude that the Ag atoms form two domains of a buckled, quasihexagonal coincident lattice structure on the Al(100) surface, having a repeat distance of 5 Al interatomic spacings in the [110] direction. The LEED pattern shows a double-domain (5x1) structure with additional intensity in those spots corresponding to a (111) close-packed hexagonal layer. The analysis of the ISS results suggests that the heights of the adsorbed Ag atoms above the Al surface are not all the same, leading to the proposed buckling model that is in agreement with recent scanning tunneling microscopy measurements. In addition, some Al atoms move from the substrate up into the Ag adlayer to form a surface alloy. Model calculations using the quantum approximate Bozzolo-Ferrante-Smith (BFS) method indicate that the hexagonal layer is energetically preferred as a result of increased nearest-neighbor coordination within the Ag layer.

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