COMMENSURATE PHASES AND PHASE-TRANSITIONS IN QUASI-COMPACT SUBMONOLAYERS OF PB/CU(110)

We report thermal energy atom scattering studies of two-dimensional Pb layers on Cu(110) and their transformations in the range of coverages between those of the p(4 x 1) structure THETA = 0.75) and of the p(5 x 1) structure (THETA = 0.80). At substrate temperatures from 50-degrees to 100-degrees-C, the increase of the layer coverage results in a series of commensurated structures with large unit cells built up of integer number of p(4 x 1) and p(5 x 1) unit cells. The transitions between these structures are of first order. The densest observed intermediate commensurate structure is the p(19 x 1) (THETA = 0.789). The further completion of the layer proceeds by random elimination of "light" domain walls and has a continuous character.