Surface phase separation of vicinal Si(111)

Abstract

The structure of a vicinal Si(111) surface, misoriented by 6° toward the [11¯0] direction, has been measured as a function of temperature. At T≳810°C the surface steps have short-range order with an average step-step spacing of 28.4±1.6 Å. Upon cooling through the temperature where the 7×7 reconstruction appears, the spacing begins to decrease although the step height remains the same. This corresponds to clustering of the steps to form a new face whose misorientation changes continuously and reversibly from 6.3°±0.4° at high temperature to 17.0°±3.0° at low temperature. The transition can be described in terms of changes in the equilibrium crystal shape of Si induced by the formation of the 7×7 reconstruction.