First principles total energy calculations of the surface atomic structure of yttrium disilicide on Si(1 1 1)

We perform first principles total energy calculations to investigate the adsorption of yttrium silicide on Si. Our studies apply the density functional theory, and use the exchange and correlation potential energies according to the generalized gradient approximation within the Perdew, Burke, Ernzerhof parametrization. We study the formation of a two-dimensional (2D) structure of YSi2 and the arrangement of a few layers of YSi1.7 on Si(1 1 1). One monolayer of YSi2 on Si(1 1 1) assembles in a 2D phase with (1 × 1) periodicity, which is composed of a layer of yttrium atoms on T4 sites and a silicon bilayer on top. Similar to the structure of rare earth and ScSi2 structures on Si(1 1 1), this bilayer of Si atoms resembles the ideal Si(1 1 1)-(1 × 1) surface, but rotated 180° with respect to the rest of the crystal. Additional layers of yttrium silicide on Si(1 1 1) build a hexagonal geometry similar to bulk YSi2: graphite-like Si planes (with vacancies) intercalated with Y planes, and yielding a (3×3) periodicity with a YSi1.7 stoichiometry. As in the formation of a single layer of YSi2, the surface is terminated by a Si bilayer similar to those of bulk Si along the (1 1 1) direction, but rotated 180°.