Si(111)3×3-Al: An Adatom-Induced Reconstruction

First-principles pseudopotential total-energy and force calculations have been used to study the $\mathrm{Si}\mathrm{}\left(111\right)\mathrm{}\sqrt{3}\times \sqrt{3}$-Al surface. A new adatom model of this reconstruction is proposed wherein each Al adatom sits in a threefold-symmetric site with three first-layer Si neighbors and one second-layer Si neighbor directly below. For this model, the calculated dispersion of the adatom-induced surface states is in good agreement with experiment. A theory for the observed momentum distribution of adatom-induced surface states is proposed.