Morphology and electronic structure of the Ca/Si(111) system

The Ca/Si(111) system has been studied using reflection high-energy electron diffraction,, scanning tunneling microscopy (STM), synchrotron radiation photoemission, and first-principles total-energy calculations, This system forms a series of odd-order n x 1 (n = 3, 5, 7,...) reconstructions that culminate with a 2 x 1 phase at 0.5 ML. Our results indicate that the honeycomb-chain-channel (HCC) model accounts well for the observed data from the 3 x 1 surface. We propose a model for the 2 x 1 phase based upon pi -bonded Seiwatz Si chains, and explain the intermediate odd-order phases as appropriate combinations of the 2 x 1 Seiwatz chains and 3 x 1 HCC chains. Calculated surface energies based on this model correctly predict that for increasing Ca coverage, the 3 x 1, 5 x 1, and 2 x 1 phases will each appear as stable phases. Simulated STM images are in excellent agreement with experiment. The Ca 3 x 1 phase exhibits a suppression of emission at the Fermi level and a local 2a (a = 0.38 nm) corrugation along the rows in STM images, both of which are consistent with the formation of either a charge-density wave or a one-dimensional correlated insulator. (C) 2001 Elsevier Science B.V. All rights reserved.