First-principles study of NH3 exposed Si(001)2x1: Relation between N 1s core-level shifts and atomic structure

Using a first-principles approach, we assign N 1s core-level shifts at ammo nium exposed Si(001)2x1 surfaces to definite bonding configurations of N at oms. Model structures are obtained by fully relaxing the atomic positions o f N atoms in different bonding configurations. Calculated values of N 1s co re-level shifts of N-Si-3, N-Si2H, and N-SiH2 structural units show a linea r dependence on the number of nearest-neighbor H atoms, in good agreement w ith data from photoemission experiments. Our results support the picture in which NH3 is adsorbed dissociatively as NH2 and H. (C) 2000 American Insti tute of Physics. [S0003-6951(00)00305-3].