Structure and one-dimensional metallicity of rare-earth silicide nanowires on Si(001)

Rare-earth deposition on Si(001) substrates and thermal treatment lead to the formation of metastable silicide nanowires with extremely high aspect ratios and quasi-one-dimensional metallicity. In this work, the prototypical erbium silicide nanowires are investigated theoretically by ab initio thermodynamics, considering a multitude of possible nanowire structures. The calculations indicate that the nanowires consist of hexagonal ErSi2 with two possible orientations with respect to the substrate, that they are partially buried into the substrate, and that they are electronically decoupled from the substrate. However, wires of finite width are predicted to be less favorable than planar silicide structures, demonstrating that the wires are metastable and suggesting that their formation is more governed by kinetic effects than by thermodynamics.