By measuring the temperature dependence of the superlattice-spot intensity in reflection high-energy electron diffraction from a clean Si(111) surface during the phase transition between 7×7 and 1×1 structures, a hysteresis was found with a temperature difference of 5 °C between heating and cooling processes. We conclude that a first-order phase transition is present. Hysteresis was barely observed for the (5×2 or √3 × √3 )-1×1 phase transitions of Au-induced superstructures.

• Received 4 January 1993

DOI:https://doi.org/10.1103/PhysRevB.47.9903