COMMENSURATE INCOMMENSURATE PHASE-TRANSITION BETWEEN 6X6 AND ROOT-3X-ROOT-3+ SATELLITE STRUCTURES OF THE AU/SI(111) SURFACE

Alternate annealing in the low- (less-than-or-equal-to 250-degrees-C) and high- ( > 400-degrees-C) temperature regimes of the Au/Si (111) surface at different Au coverages prepared by room-temperature deposition and isothermal annealing in the high-temperature regime at over-(ML) coverages have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). lt is found that the 6 X 6 pattern and the square-root 3 X square-root 3 + satellite pattern are formed at 0. 9-2.2 ML coverages by annealing for several minutes at 250 and 500-degrees-C, respectively, when there exist an Au surface peak and a diffusion tail extended towards the lower energy behind the Au peak and that the phase transition between both patterns is reversible by alternate annealing in two temperature regimes as long as the diffusion tail is not diminished. From this result, the 6 X 6 structure is ascribed to excess embedded Au atoms situated at the ordered sites and Au atoms constituting the square-root 3 X square-root 3 structure at the top surface. Moreover, it is found that the phase transition between the square-root 3 X square-root 3 structure and the mixed structure of square-root 3 X square-root 3 + 5 X 1 are also reversible by alternate annealing in the two temperature regimes at the actual coverages of 0.72-0.84 ML. Furthermore, from analysis of the isochronal annealing data at 1.7 ML, the activation energy of the diffusion of Au in Si is found to be 1.3 eV.