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We find that foreign adsorbates acting as local impurities can induce a metal-insulator transition by pinning a charge-density wave (CDW) on the quasi-1D metallic In/Si(111)-(4x1) chain system. Our scanning tunneling microscopy image clearly reveals the presence of a new local 4x2 structure nucleated by Na adatoms at room temperature, which turns out to be insulating with a doubled periodicity along the chains. We directly determine a CDW gap energy Delta = 105+/-8 meV by identifying a characteristic loss peak in our high-resolution electron-energy-loss spectra. We thus report the first observation of a local impurity-derived Peierls-like reconstruction of a quasi-1D system.

We investigated the initial stages of Ag growth on a Si(111)-4×1-In surface at room temperature (RT) and low temperatures (LT, 70∼120K) in situ by reflection-high-energy electron diffraction (RHEED), scanning tunnelling microscopy (STM) and electrical resistance measurements in ultrahigh vacuum, together with on a Si(111)-7 × 7 clean surface for comparison. It has been revealed that the 4×1-In surface actually acts as a highly anisotropic template for Ag growth at RT, but not at LT. The Ag islands grown on the wetting layers were elongated along the 4×1-stripe at RT, while they were isotropic and round in shape at LT. This is due to a difference in migration ability of the arriving Ag adatoms. The anisotropic growth has been found to affect the formation of percolation paths for electrical conduction among the Ag islands; the growth conditions (deposition rate and temperature) do not affect the critical coverage for percolation so much on the 4×1-In surface, compared with in the case of isotropic growth on the 7×7 surface. The initial deposition of submonolayer-thick wetting layers has been found to induce some structural changes of the substrate surface; at RT, the 4×1-In structure changes into a 4×'2' structure, while the 8×'2'-In structure at LT changes into a 4×1 structure. The former change induces a resistance increase, while the latter induces a resistance drop. These changes may be caused by the induced changes in surface states and band bending beneath the surface.