Vacancy-enhanced submonolayer nucleation of Si on Si(1 1 1)

Scanning tunneling microscopy (STM) and high-resolution low-energy electron diffraction techniques are used to determine the characteristics of the two-dimensional Si island distribution on defect-free and imperfect Si(1 1 1) surfaces in real space and reciprocal space. The surface power spectra of STM and modeling of diffraction profiles give consistent island separation. Unlike the submonolayer nucleation of silicon islands on a defect-free Si(1 1 1) surface, it is shown that the island size distribution of Si, nucleated on a Si(1 1 1) surface having a high density of vacancy defects, does not exhibit a preferred characteristic island size. The process is interpreted as defect-induced nucleation with the critical island size equal to zero, for which there is no free energy barrier for nucleation. The results are qualitatively consistent with recent computer simulations, and are compared with other recent experimental work.