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Atoms wandering on surfaces lead complex lives. For example, they face many restrictions on their freedom to move. High walls sometimes leave only one road open, and that road may have checkpoints. Such walls and checkpoints are a consequence of the crystal structure of the surface and the interaction between the surface atoms and the wandering atom. The crystal structure in turn is controlled by the nature of the bonding—metallic, covalent, ionic—between atoms in the crystal.
M. G. Lagally (Mon,) studied this question.