Instability of the distribution of atomic steps on Si(111) upon submonolayer gold adsorption at high temperatures

The gold adsorption effect on the distribution of monatomic steps on the (111) silicon surface is studied in situ by ultrahigh vacuum reflection electron microscopy at temperatures of $850$–$1260^\circ$C. A new effect of the instability of silicon surface morphology has been detected. This effect leads to the redistribution of regular steps (RSs) to step bunches (STs) and vice versa on a surface covered with a gold submonolayer. For the crystal heated by directly passing an electric current, the behavior of the RS $\Leftrightarrow$ SB morphological transitions on the silicon surface is investigated as a function of the gold coverage and the direction of the heating current. Thus, isothermal annealing at $900^\circ$C is accompanied by the following transitions on the silicon surface with predeposited 0.75 monolayer gold coverage: RS (0.72) $\Rightarrow$ SB (0.42) $\Rightarrow$ RS (0.24) $\Rightarrow$ SB (0.07) RS $\Rightarrow$ (0). The numbers given in parentheses are estimated values of the critical gold coverage measured in the monolayers at which the morphological transitions are observed. A change in the direction of the electric current used to heat the crystal leads to the reversible changes RS $\Rightarrow$ SB and SB $\Rightarrow$ RS at the same values of the critical gold coverage.