Two-dimensional adatom gas on the Si(111)-(√3×√3)-Ag surface detected through changes in electrical conduction

When Ag adatoms were deposited on top of the Si(111)-√3×√3-Ag surface at room temperature with less than a critical coverage Θ_C (~0.03 atomic layer), they were found to exist as a supersaturated metastable two-dimensional gas phase, which made the surface electrical conductance extremely high. With the coverage beyond Θ_C, the gas phase began to nucleate into three-dimensional microcrystals, leading to a steep reduction in the electrical conductance. A kinetic overshoot beyond the critical supersaturation for nucleation was also detected in in situ conductance measurements during the Ag deposition.