Electronic states of vicinal surfaces

Abstract

Vicinal surfaces are crystal planes oriented a few degrees off from a high symmetry direction. Such a small deviation (called miscut) from a high symmetry axis leads to a characteristic periodic roughness at the nanoscale, namely atom-height step arrays that separate atomically-flat terraces. The alternating series of “terraces” and “steps” makes electronic properties of vicinal surfaces very peculiar, distinct from those of atomically-flat surfaces. On the one hand, terraces and steps feature atoms with distinct coordination and complex and varied elastic relaxations, influencing their core-level energies. We show how core levels at a vicinal surface exhibit a miscut-dependent stress release, as well as fine structural relaxations, such as faceting. On the other hand, atomic steps create a periodic modulation of the crystal potential, affecting two-dimensional (2-D) surface states of metals. This leads to Bloch scattering of surface electrons by the step lattice, and eventually, to one-dimensional (1-D) quantization by confinement at terraces or step edges. We discuss the occurrence and observation of superlattice scattering and 1"​ D confinement at a vicinal surface, the importance of the atomic nature of the surface state wave function, the dependence on the lattice constant of the step array, and the rich scattering phenomenon that arises in faceted structures and spin-textured bands.