Direct Observation of Interactions between Individual Atoms on Tungsten Surfaces

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Abstract
Using the field ion microscope (FIM), it is possible to investigate the interactions between individual atoms on metal surfaces. The number of atoms participating in an experiment can be specified and controlled by successive depositions or field evaporations. It is found that the interaction potential between two atoms depends on the substrate surface structure. In agreement with other investigators, the binding energy is found to be not pairwise additive. The interatomic potential between two Re atoms on W (110) planes shows at least two minima and a maximum, suggesting an oscillatory structure similar to the well-known Friedel oscillation. Surface migration as well as structures of clusters with less than six atoms is also investigated. It is found that the equilibrium structures of the clusters depend very sensitively on surface temperature. It is also found that potential traps of ∼ 0.14 eV exist on crystal planes which otherwise appear to be perfectly regular in the FIM images.