A series of Ca-induced reconstructions on Si(111) surface

We have studied surface reconstructions induced by submonolayer Ca adsorption on a Si(111) surface using reflection-high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). With increase of Ca coverage at substrate temperatures above 550 degreesC, the RHEED pattern changed successively: clean 7 x 7 --> 3 x 1 --> 5 x 1 --> 7 x 1 --> 2 x 1. The 3 x 1 pattern transformed into a 3 x 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 x 2, 5 x 1, 7 x 1, and 2 x I structures is composed of several rows. The twofold periodicity along the stripes of the 3 x 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. (C) 2001 Elsevier Science B.V. All rights reserved.