Effect of steps on structural phase transitions of Si(111) 7×7 surfaces

The effect of steps on the structural phase transition for the Si(111) 7×7 structure dimer-adatom-stacking fault (DAS) structure is investigated using a cell model. This model describes the state of the Si(111) surface in units of 7×7 triangular halves. In the previous work, the subject of which was an infinite terrace, the result calculated for the temperature dependence of the DAS order parameter exhibited much larger hysteresis than in the experiments, although the main features of the phase transition were consistent with experiments. The presence of steps is expected to suppress hysteresis. Calculations for the temperature dependence of the order parameter are performed using a Monte Carlo simulation in the presence of steps. By assuming reasonable values of the formation energy of the DAS cell at the step edges and the intervals between the steps, the calculated result agrees with the experimental results in terms of hysteresis.