Structure of the Si(100)-(2×2)In surface

The question of whether the Si(100)-(2×{}2)In reconstruction consists of orthogonal or parallel In ad-dimers was answered by performing studies, using scanning tunneling microscopy and impact-collision ion-scattering spectrometry (ICISS), on low coverages of In adsorbed on a vicinal Si(100) surface. The formation of a predominantly single domain of the (2×{}2) phase on the vicinal surface allowed us to use the ICISS experiments to distinguish between the orthogonal and parallel ad-dimer geometries. Our results strongly support the model involving the parallel ad-dimer, in agreement with previous theoretical predictions.