Steps on Si(001) vicinal surfaces tilted by various angles in the [11̄0]-[100]- and [21̄0]-zones, investigated by high-resolution LEED

Abstract

Abstract The kind and distribution of atomic steps in the vicinity of Si(001), clean and after exposure to water, was investigated by high-resolution spot-profile-analysis LEED. The sample was spherically shaped with Si(001) in its center so that a continuous tilt angle range 0° ⩽ γ ⩽ 13.5° was accessible. In the [1 1 0]-zone, single layer steps are found with a tendency for step pairing with narrower A- and wider B-terraces. Beyond γ = 1.5°, the A-terrace width locally becomes zero so that paired single steps and true D B -type double steps coexist, probably stabilized by kinks. Kinked D B -steps cause a correlated lateral shift of dimer rows across steps. Only beyond γ ≈ 8°, the clean surface is completely D B -stepped. Water adsorption reduces the pairing tendency. The pairing mechanism is based on the different contribution of S A - and S B -type single steps to surface strain. A mean terrace inclination decreasing with increasing terrace width is observed which is compatible with a constant edge depression. For γ > 9°, the special stability of the (117) orientation causes separation into (117) facets ( γ = 11.4°) and less tilted stepped domains. The step topography is similar in the [2 1 0]-zone. The steps there can be considered as strongly kinked [1 1 0]-type steps. In the [100]-zone, only single steps without pairing are observed up to γ = 6° which agrees with the equivalency of both sublattices with respect to the edge direction.