2-DIMENSIONAL ADATOM GAS ON THE SI(111)-(ROOT-3X-ROOT-3)-AG SURFACE DETECTED THROUGH CHANGES IN ELECTRICAL-CONDUCTION

When Ag adatoms were deposited on top of the Si(111)-root 3 x root 3-A g surface at room temperature with less than a critical coverage Theta (C) (similar to 0.03 atomic layer), they were found to exist as a supe rsaturated metastable two-dimensional gas phase, which made the surfac e electrical conductance extremely high. With the coverage beyond Thet a(C), the gas phase began to nucleate into three-dimensional microcrys tals, leading to a steep reduction in the electrical conductance. A ki netic overshoot beyond the critical supersaturation for nucleation was also detected in in situ conductance measurements during the Ag depos ition.