Morphology and electronic structure of the Ca/Si(1 1 1) system

The Ca/Si(1 1 1) 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×1 (n=3,5,7,…) reconstructions that culminate with a 2×1 phase at 0.5 ML. Our results indicate that the honeycomb-chain-channel (HCC) model accounts well for the observed data from the 3×1 surface. We propose a model for the 2×1 phase based upon π-bonded Seiwatz Si chains, and explain the intermediate odd-order phases as appropriate combinations of the 2×1 Seiwatz chains and 3×1 HCC chains. Calculated surface energies based on this model correctly predict that for increasing Ca coverage, the 3×1, 5×1, and 2×1 phases will each appear as stable phases. Simulated STM images are in excellent agreement with experiment. The Ca 3×1 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.