Adsorption and interaction of Sm on GaAs(110) studied by scanning tunneling microscopy

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Abstract
Scanning-tunneling-microscopy studies of the interactions of Sm with GaAs(110) at 300 K show two growth structures. Low density zigzag chains form by 0.01 monolayer (ML) with (divalent) Sm atoms bound to Ga surface atoms along the [11¯0] direction (Sm-Sm distances 6.9 and 7.9 Å). These zigzag chains are limited in length but bridge two or three substrate rows. Higher-density linear chains of (divalent) Sm atoms form at the expense of the zigzag chains with increased deposition, and the adatoms are bonded beside two Ga atoms near an As atom (Sm-Sm distance ∼4 Å). Only short single chains are observed, and they convert to reacted (trivalent) clusters that bridge substrate rows at higher coverage. By ∼0.33 ML, the surface structure is composed of linear chains and reacted clusters with a small number of residual zigzag chains. Synchrotron-radiation photoemission results provide a correlation of structure with Sm valence. Comparison to Cs/GaAs(110) offers insight into low-coverage nucleation.