THE CHEMISORPTION OF NH3 ON THE SI(100) SURFACE

In this paper we report the results of calculations of the chemisorption of ammonia onto the Si(100)2 x 1 surface using the SLAB-MINDO molecular orbital method. Consistent with the latest experimental data, the ammonia molecules are assumed to dissociate into the species NH2 and H which then attach themselves to the dangling bond orbitals of the surface silicon atoms of the 2 x 1 dimer reconstruction. The optimum topology appropriate to a uniform monolayer coverage has then determined by minimizing the total energy with respect to the coordinates of all the atoms lying above the fifth substrate layer. The Si-H bonds are found to be virtually identical to those determined previously for the Si(100)2 x 1 monohydride system. The Si-NH2 configuration, on the other hand, is predicted to be almost planar in direct contrast to the trigonal pyramidal geometry proposed previously. Local density of states curves corresponding to the surface N, Si and H atoms are also presented and correlated with the experimental data.