The Phase Diagram of Vicinal Si(111) Surfaces Misoriented Toward the [110] Direction: Fid-Bau Portal

The Phase Diagram of Vicinal Si(111) Surfaces Misoriented Toward the [110] Direction

Phaneuf, R. J. / Williams, E. D.

Abstract The stable surface orientations of a crystal are specified by its equilibrium crystal shape [1]. In principle, attempts to prepare surfaces which are not stable, that is surfaces which have orientations which fall on sharp edges or sharp corners of the crystal shape, result in the breakup of the surface into coexisting stable orientations. As this “faceting” requires atomic transport over large distances it is not obvious that it will be observable on liboratory time scales. However, we have found evidence for phase separation on Si surfaces misoriented from 4 to 12° from the (111) plane towards the [1 $$ \bar {1} $$ 0] direction. As we describe in more detail below, this evidence comes from the study of the temperature and energy dependence of low energy electron diffraction patterns. At high temperature (above 900° C) we find that the surfaces have a uniform density of steps. As the temperature is lowered the surfaces reversibly phase separate into a phase which is unstepped with (7×7) reconstruction and a phase which is stepped [2]. Terming the observed behavior phase separation is justified by the observation that the angle of the stepped coexisting phase is independent of the initial orientation; it depends only upon temperature. We thus can present the temperature-orientation phase diagram. This phase diagram evidently implies that a sharp edge in the equilibrium crystal shape forms at the temperature of the (7×7) to (1×1) transition on the unstepped Si(111) surface.