Initial Nitridation of the Ge(100)-2 × 1 Surface by Ammonia

Abstract

The reaction of ammonia (NH₃) on the Ge(100)-2 × 1 surface is investigated using density functional theory (DFT). We find that NH₃ adsorbs molecularly onto Ge(100)-2 × 1 via the formation of a dative bond. The calculations also show that, unlike Si(100)-2 × 1, the activation barrier for subsequent dissociation of NH₃ adsorbed on Ge(100)-2 × 1 is higher than that of reversible desorption, which indicates that NH₃ has a low reactive sticking probability on the Ge(100)-2 × 1 surface. We also predict that nitrogen insertion into the Ge−Ge dimer requires NH₃ overexposure because the activation barrier for NH₂ insertion into the Ge−Ge dimer is significantly above the entrance channel. The nitridation reaction pathway results in the N−H bridge-bonded state, which is found to be 17.4 kcal/mol more stable than the reactants. We find that the reactions of NH₃ on the Ge(100)-2 × 1 surface generally involve higher activation barriers and less stable intermediates than the analogous reactions on the Si(100)-2 × 1 surface.