Sang-Yong Yu

Control of phase transition in quasi-one-dimensional atomic wires by electron doping

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.

A New Period-Doubled Modulation on the In/Si(111)4 ×1 Surface Induced by Defects

We report observations of defect-induced period-doubled (×2) modulations in scanning tunneling microscopy images of the In/Si(111)4 ×1 surface at room temperature. The perturbation is one-dimensional, ranging up to ten lattice constants in the row direction. The modulation is attributed to a perturbation in electronic charge density rather than to a lattice distortion. The defect-induced ×2 structure differs from the low-temperature (LT) 4 ×2 observed for the defect-free surface. First-principle calculations found that the defects stabilize a hypothetical structure with small lattice distortions, whose calculated energy is lower than that of the large lattice-distorted structure proposed for the 4 ×2-LT phase. This symmetry-broken, defect-induced modulation is extraordinary in that it does not mimic the LT phase observed in the defect-free system.