Dissociation of NO on Si(001) and incorporation of N into the subsurface

We present our first-principles calculation on NO (nitric oxide) dissociation on the Si(001) surface and subsequent nitrogen incorporation into the subsurface. NO adsorbs on the surface as a molecular form parallel or perpendicular to a Si dimer, but its dissociated structures are much more stable than the molecular forms. In the dissociated configurations, nitrogen or oxygen tends to incorporate into the subsurface to saturate its dangling bonds. Investigation of the elementary processes using a nudged elastic band method reveals that the energy barrier for NO dissociation is nearly absent (~0.02 eV) for the parallel configuration and is 0.07 eV for the vertical configuration, suggesting that NO can dissociate at very low substrate temperatures. The subsequent stabilization processes lead to the structures with O bridging a Si dimer and subsurface atoms or with N incorporation into the subsurface. The resulting energy barriers are 0.16 eV for both cases. The dissociation across two dimers is also possible. The present findings are consistent with experimental studies reporting low-temperature NO dissociation and N≡Si₃ formation.