RESUMO
Using scanning tunnelling microscopy we have investigated the formation of low dimensional Fe-Si structures on Au covered Si(111) surfaces. The ultrathin Au layer induces a variety of surface reconstructions, depending on the coverage and temperature: Si(111)-5 x 2, [alpha-squareroot 3 x squareroot 3,beta-squareroot 3 x squareroot 3], and 6 x 6-Au. The subsequent deposition of 0.28 ML (monolayers) of Fe at 400 degrees C results in the formation of Fe-Si nanostructures whose morphological properties critically depend on the underlying surface. All Au induced reconstructions give rise to an increase in diffusion length as compared to the bare Si(111)-7 x 7 surface, thereby allowing the growth of well-separated nanostructures at considerably lower temperatures. Ultimately, the decoupling of surface diffusion and temperature, induced by the Au layer, can be exploited to tailor the island dimensions and density. With an appropriate choice of substrate, passivating layer and deposited material, nanostructures with the desired properties can be grown in a controlled way.
RESUMO
Using scanning tunneling microscopy, the influence of a thin Au layer on the diffusion of Fe adatoms and the subsequent island nucleation on a Si(111) surface is investigated. The adsorbate induces the Si(111)-â3×â3-Au structure that increases the surface mobility of subsequently deposited Fe atoms, resulting in the formation well-defined nanoclusters. Surprisingly, the domain walls-inherent to the â3×â3-Au reconstruction-do not influence the surface diffusion, which demonstrates that the passivation is of much more importance for the self-assembly than the surface corrugation. Using the decoupling of the diffusion and nucleation on the surface and the reaction with the surface and conventional nucleation theory, the activation energy for surface diffusion E(d) = 0.61 eV and the critical cluster size i = 3 are determined, which reveal the microscopic details of the diffusion and nucleation processes.
