Novel mechanism for the formation of chemisorption phases: The (2×1)O-Cu(110) ‘‘added row’’ reconstruction

Scanning tunneling microscopy investigations on nucleation and growth of the (2×1)O-Cu(110) structure revealed that the new phase is formed by condensation of mobile chemisorbed O atoms with Cu adatoms evaporating from steps and diffusing across the terraces of the substrate surface. This process can be regarded as two-dimensional precipitation from a dilute mixed fluid into a solid phase rather than a solid-solid transformation. The resulting structure is more appropriately described to be of ‘‘added-row’’ rather than of ‘‘missing-row’’ type.