Pathways of nitric oxide dissociation on Si(001) and subsequent atomistic processes: A first-principles molecular dynamics study

We present first-principles molecular dynamics (MD) simulations of the dissociation of a nitric oxide (NO) molecule on an Si(001) surface and subsequent incorporation of the nitrogen atom into the subsurface, which are important in the understanding of the synthesis of oxynitride thin films. The MD runs for different initial conditions revealed various dissociation pathways. In some, the dissociated N and O atoms bridge an Si dimer and substrate backbond. The dissociated nitrogen incorporates into the subsurface with the formation of N≡Si₃. The NO dissociates across two Si dimers. All the processes finish within a couple of picoseconds at all of the temperatures considered, implying that the corresponding energy barriers are quite small (≲ 0.2). Inclusion of the spin polarization increases only the energy barrier for the initial dissociation process from a molecular state, suggesting the existence of a molecular precursor state. The facile dissociation of the NO and incorporation of N are consistent with photoemission measurements.