Defect-induced period-doubling perturbation on Si(111)4x1-In

We investigated using STM and LEED the influence of defects at room temperature on the quasi-one dimensional Si(111)4$\times $1-In surface which changes into a 4$\times $2 (or 8$\times $2) phase below 120 K. Various types of defects (vacancy, step edge, and phase shift boundary) and adatoms (H$_{2}$, O$_{2}$, and In) were found to induce local period-doubling ($\times $2) modulations at room temperature. The $\times $2 modulated region shows metallic $I-V$ characteristics, having little change from that of the defect-free 4$\times $1 region despite the difference in topology in the image. Therefore, the defect-induced $\times $2 modulation is discriminated from the low-temperature phase that was reported to be insulating. Using the first-principles calculations, the $\times $2 modulation is found to originate from a different 4$\times $2 structure of the clean surface that is stabilized by the presence of defects. The nature of the phase transition of this In/Si(111) system and the influence of the defects will be discussed.