Surface Phase Transitions and Surface Atomic Structures: Leed Studies.

The ordered phases and the atomic structures of Al, K and Cs adsorbates on the graphite (0001), Cu(111) and Cu(110) surfaces have been studied with Low Energy Electron Diffraction (LEED) within the temperature range between 80K and 400K. The deposition of aluminum onto the graphite surface resulted in the Volmer-Weber type island (3-D) growth at temperatures above 250K and an amorphous Al overlayer at T < 250K. The Cs deposition onto the graphite also resulted in island (2-D) growth before the appearance of a p(2 x 2)-Cs structure. The evaporation of K and of Cs onto the 80K Cu(111) surface resulted in the growth of orientationally ordered incommensurate structures of the alkali-metal overlayers. The order-disorder transition of the incommensurate phases was continuous and the transition temperature was a function of the overlayer lattice (or coverage). At a coverage of about 0.25, the incommensurate structures were locked into a p(2 x 2) structure, resulting in a specific heat critical exponent consistent with a 4-state Potts model. In addition, the ordered structures, such as (3/4 sqrt{3} x 3/4 sqrt {3}) R30^circ -K and (6 x 6)-Cs, were also observed on the Cu(111) surface. These are indicated in the phase diagrams. The evaporation of K and Cs onto the 80K Cu(110) surface resulted in the growth of quasi-hexagonally (QH) ordered overlayers with an observed continuous decrease of the overlayer alkali atom spacing proportional to coverage. The alkali-metal overlayers induced the Cu(110) substrate reconstruction at temperatures above 150K. Well-ordered (1 x 2) reconstructed structures and (1 x 3) reconstructed structure were observed as a function of temperature and coverage. The detail relationships of overlayer ordered phases and substrate reconstructions are compiled in phase diagrams for K and for Cs on the Cu(110) surface.