Dissociative adsorption of NF3 on Si(001)-(2 x 1)

Using the first-principles pseudopotential-generalized gradient approximati on (GGA) approach, we have performed an accurate determination of the atomi c and electronic structure of the dissociative adsorption for nitrogen trif luoride on Si(001)-(2 x 1). The chemisorbed system is energetically favoura ble and occurs in a very similar way to that found for the ammonia molecule : the NF3 molecule dissociates with the formation of Si-NF2 and Si-F bonds. We find that the system is characterized by elongated (around 6%) and symm etric silicon dimers (the tilt angle is just 1.5 degrees), and by the fact that the Si-NF2 group retains the pyramidal geometry of the nitrogen triflu oride molecule. We also observe that the Si-N bond is inclined at almost 8. 6 degrees with respect to the surface normal. The N-Si bond length is 1.85 Angstrom and the N-F bond length is 1.47 Angstrom. Finally, our electronic structure calculations suggest that the adsorption of NF3 molecules almost completely passivates the silicon surface. (C) 2000 Elsevier Science B.V. A ll rights reserved.