On the role of mobile nanoclusters in 2D island nucleation on Si(111)-(7x7) surface

Two-dimensional (2D) Si island nucleation has been studied by in situ reflection electron microscopy within a wide temperature range (650-1090 degrees C) on large-scale (similar to 10-100 mu m) terraces to exclude the impact of step permeability and adatom sink to steps. The dependence of 2D island concentration N-2D on substrate temperature T and Si deposition rate R displays N-2D alpha R(chi)exp(E-2D/kT) scaling which parameters change from chi approximate to 0.81, E-2D approximate to 1.02eV to chi approximate to 0.5, E-2D approximate to 1.8eV when Si(111) surface converts from (1x1) structure to (7x7) reconstruction. We propose that this strong E-2D rise accompanied by chi reduction is caused by the change of dominating diffusing particles from adatoms to reconstruction induced nanodusters. Using a rate-equation model developed to account the dynamics of both diffusing species on the Si(111)-(7x7) surface, we show that a stable nucleus of a 2D island appears when two mobile nanoclusters merge together while nucleation kinetics is limited by their attachment to island edges. (c) 2017 Elsevier B.V. All rights reserved.