On the conversion temperature of cleaved stepped Si(111) surfaces

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Abstract
The transition of the Si(111)-2*1 cleavage to the 7*7 structure sets in during annealing at 210 degrees C and may extend up to 400 degrees C, depending on the density of cleavage steps. In a simple model this conversion is described by activation-barrier-limited kinetics, and the experimental distribution of cleavage steps is approximated by a gaussian. The activation barrier, which is assumed for surface atoms to be a function of the distance on the terraces from the next riser, can then be evaluated from the experimentally determined mean angle of misorientation between the cleaved surface and the (111) plane. The dependence of the conversion temperature on the step density as calculated in the framework of this model agrees well with the experimental results. The resulting activation barrier shows the same dependence on the distance on the trends from the next riser as the image force of a charged particle in a right-angle corner of a conducting material. This finding supports the suggestion that the 7*7 structure contains charged vacancies.