A series of Ca-induced reconstructions on Si(1 1 1) surface

We have studied surface reconstructions induced by submonolayer Ca adsorption on a Si(1 1 1) surface using reflection-high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). With increase of Ca coverage at substrate temperatures above 550°C, the RHEED pattern changed successively: clean 7×7→3×1→5×1→7×1→2×1. The 3×1 pattern transformed into a 3 × “2” pattern including half-order streaks by cooling down to room temperature. The STM images of these reconstructions commonly showed striped structures with the periodicities corresponding to the RHEED patterns. Each stripe in the 3 × “2”, 5 × 1, 7 × 1, and 2×1 structures is composed of several rows. The twofold periodicity along the stripes of the 3 × “2” phase was observed in filled-state images as well as in empty-state ones; simple protrusions are arranged with the double periodicity in the empty-state image, while a dimerization of small protrusions occurs along the stripes in the filled-state image. From these results, atomic structure models for these Ca-induced reconstructions are suggested.