A new period-doubled modulation on the In/Si(111)4 × 1 surface induced by defects

We report observations of defect-induced period-doubled (x2) 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 x2 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. © 2006 The Japan Society of Applied Physics.