High-resolution low-energy electron-diffraction study of the phase diagram of vicinal Si(111) surfaces

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Abstract
High-resolution low-energy electron-diffraction measurements of the temperature dependence of the behavior of vicinal surfaces of Si(111) misoriented towards the [2¯11] and [11¯0] directions by 1° are presented. Consistent with previous studies on Si surfaces misoriented by more than 4° from the (111) plane, both of these types of surfaces are observed to facet, or phase separate, reversibly as the temperature is lowered through the (1×1) to (7×7) transition. A recently proposed model for the observed faceting of Si predicts that the temperature-orientation phase diagram for this faceting is governed by the same critical exponent which governs the way equilibrium crystal shapes curve away from facets at nonzero temperatures. Measurements on the 1° misoriented samples allow better comparison with this theory: the measured phase diagram for surfaces misoriented towards the high-symmetry [2¯11] direction is consistent with the exponent prediction. Surfaces with reduced coherence lengths have a quantitatively different phase diagram. Changing the direction of the misorientation towards the low-symmetry [11¯0] direction gives a phase diagram inconsistent with universal behavior.