Crossover from metastable to unstable facet growth on Si(111)

Vicinal Si(111) surfaces misoriented towards the [2{}11] direction facet reversibly upon cooling through the (1×{}1) to (7×{}7) reconstructive phase transition. We have used low-energy electron microscopy to examine the kinetics of this phase separation. Nucleation and growth of facets occur when the surfaces are quenched just below the phase boundary. However, at lower temperatures we find evidence for the existence of a spinodal which divides the faceting kinetics into unstable and metastable regions. The location of the spinodal is consistent with previous measurements of Si(111) step energetics.