Charge Transfer between Isomer Domains on n+-Doped Si(111)-2x1: Energetic Stabilization
Domains of different surface reconstruction – negatively- or positively-buckled isomers – have been previously observed on highly n-doped Si(111)-2×1 surfaces by angle-resolved ultraviolet photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. At low temperature, separate domains of the two isomer types are apparent in the data. It was argued in the prior work that the negative isomers have lower energy of their empty surface states than the positive isomers, providing a driving force for the formation of the negative isomers. In this work we show that the relative abundance of these two isomers shows considerable variation from sample to sample, and it is argued that the size of isomer domains is likely related to this variation. A model is introduced in which the electrostatic effects of charge transfer between the domains is computed, yielding total energy differences between the two types of isomers. It is found that transfer of electrons from domains of positive isomers to negative ones leads to an energetic stabilization of the negative isomers. The model predicts a dependence of the isomer populations on doping that is in agreement with most experimental results. Furthermore, it accounts, at least qualitatively, for the marked lineshape variation from sample to sample observed in photoemission spectra.