Computational chemistry study on initial stages of nitridation of silicon surfaces

We performed computational studies on the change in enthalpy during incorporation of one nitrogen atom into bare silicon surfaces, and proposed six possible nitrided structures for the Si(100) surface and five for Si(111). The results indicated that the topmost silicon atoms on Si(111) surfaces were favorably nitrided as compared with the inner silicon atoms while both the topmost and the second layer of Si(100) were nitrided. To account for this tendency, the changes in enthalpy during nitridation were divided into the energy of deformation of the Si lattice (ΔE_def) and the energy of bond formation (ΔE_bond) between N and Si atoms. The heat of bond formation during nitridation on Si(111) was almost independent of nitridation sites. Therefore, differences in the enthalpy of nitridation between the outer surface and inner atoms resulted from Δ E_def. No distinct relationship was observed between the two energies, ΔE_def and ΔE_bond for Si(100).