Structural studies of sub monolayer Sn/Cu(0 0 1) structures

Helium atom scattering (HAS) and scanning tunneling microscopy (STM) have been used to investigate five ordered phases formed by Sn-evaporation and deposition on room temperature Cu(0 0 1) surfaces. Complementary Auger (AES) and electron diffraction (LEED) studies have also been performed. Glide plane symmetry has been noted in a p(2 × 6) phase. The c(4 × 8), p(3√2 × √2), and c(4 × 4) phases exhibit measurable lateral relaxations. The c(4 × 8) and c(4 × 4) phases have Sn in distorted nearest-neighbor adsorption sites. New structural models are proposed for four Sn/Cu phases. Each of these models is discussed in light of the lateral stress relief mechanisms that are operative. STM topographic details are used to argue in favor of the prevalence of 2-D alloy-like structures in most phases. We speculate also on the necessity of subsurface vacancies in formation of the p2mg, p(2 × 6) ordered phase.