We report on the controlled change in the phase transition in In atomic chains on a Si(111) surface by introducing Na as impurity atoms. The Na-induced changes in the transition temperature (Tc) from a metallic room-temperature 4×1 structure into an insulating low-temperature 8×2 structure were determined by using low-energy electron diffraction. The Tc decreased almost linearly when the amount of deposited Na atoms was increased. The decrease in Tc with the increase in the amount of adsorbed Na atoms is suggested to be due to the doping of electrons from adsorbate to the substrate.

The influences of surface defects created by hydrogen and oxygen adsorption on the ͑4 ϫ 1͒ → ͑8 ϫ 2͒ structural phase transition in an In/Si͑111͒ system have been studied using low-energy electron diffraction. The transition temperature ͑T c ͒ decreased with the hydrogen exposure as compared to the clean surface, whereas it increased with the oxygen exposure. The H-induced decrease in the T c is expected and explainable by the general destructive role of defects as random disorders in the transition. In contrast, the O-induced increase of the T c is rather unusual. Mobile defects or doping effects may account for the assisting role of the O-induced defects in the condensation of the ͑8 ϫ 2͒ low-temperature phase.

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The role of defects in the metal-insulator transition of a quasi-one-dimensional metallic surface Si͑111͒4 ϫ 1-In, is investigated by temperature-dependent reflection high-energy electron diffraction ͑RHEED͒ spot analysis and microfour-point-probe ͑MFPP͒ surface conductivity measurements. In the RHEED spot intensity analysis, we found that adsorption of hydrogen or indium decreases the structural transition temperature into the 8 ϫ 2 phase whereas it increases in the case of oxygen adsorption. In the MFPP, however, the metalinsulator transition temperature increased compared to that of the pristine surface universally irrespective of the additional atoms adsorbed as defects. The discrepancy between the two methods is discussed in terms of how the defects influence the metallic percolation path and formation of long-range order across the onedimensional chains. Our results indicate that proper care should be taken concerning what each experimental method monitors when discussing phase transition phenomenon with various techniques.

Controlled fabrication of lead halide-based perovskite (LHP) nanostructures provides a new methodology for exploiting the excellent optoelectronic properties of the material. Here, we report the vapor–liquid–solid (VLS) growth of a highly uniform and dense array of [0001]-oriented PbI2 nanowires using PbI2 thin film as the epitaxial substrate layer. We show that reducing the lattice mismatch of the van der Waals epitaxial PbI2 substrate layer is necessary to accommodate the aligned nanowire growth. Our proposed layer growth model suggests that the nanowire growth is stabilized by maintaining the {0001} liquid–solid interface, which stems from the nucleation on the PbI2 substrate layer. We also demonstrate that the strain-induced nanowire deflection after conversion into CH3NH3PbI3 depends on the transfer sequence and conversion time. These findings provide a general opportunity to design and fabricate nanostructures, such as heterojunctions or superstructures for future device applications, rationally based on lead halide or LHP nanowires.