Phase diagrams and rotated incommensurate phases of K, Rb, and Cs adsorbed on Ag(III)

Submonolayers of potassium, rubidium, and cesium on AE(111) form hexagonal overlayers which increase in density uniformly as coverage is increased. There are no indications that these overlayers form condensed (island) structures at any submonolayer coverages. The stability of the overlayers increases with coverage, with melting temperatures changing from about 40 K at 0.11 coverage to 250 K at 0.33 coverage for potassium, with somewhat higher temperatures for Rb and Cs. The overlayers are in general incommensurate, but at certain coverages form structures which are commensurate with the substrate. The commensurate structures formed at temperatures down to 35 K are the (2 root 3X2 root 3)R30 degrees structure for Cs and Rb, and the p(3X3), (root 7x root 7)R19.1 degrees, p(2x2), and (root 3x root 3)R30 degrees structures for K, Rb, and Cs. At certain densities the hexagonal overlayer structures are rotated with respect to the substrate. The rotation behavior at 35 K follows a general trend which is largely consistent with various models of epitaxial rotation. The rotation angles are temperature dependent, usually rotating toward alignment with the substrate (0 degrees) as the temperature is increased. Some of the data are consistent with the mean-field theory describing rotational epitaxy.