Phase separation and step roughening of vicinal Si(111): An x-ray-scattering study

We present a high-resolution x-ray-scattering study of the temperature-dependent structure of Si(111) vicinally miscut by 4°along the 110 direction. At temperatures below 1159 K, the surface phase separates into flat 7×7 terraces and densely stepped regions, in agreement with previous reports. The angle between the phase-separated regions shows a temperature dependence consistent with both entropic and strain-induced step-step repulsive interactions. At temperatures above 1159 K, the surface is shown to exist as a single, logarithmically rough phase; the observed scattering line shapes demonstrate the presence of a long-range step-step repulsion of a magnitude comparable to the entropic repulsion. © 1995 The American Physical Society.