Photoemission studies of the reactions of ammonia and N atoms with Si(100)-(2×1) and Si(111)-(7×7) surfaces

We present results of detailed x-ray photoemission and ultraviolet photoemission spectroscopic studies of the reactions of silicon with ammonia and atomic nitrogen. We show that both Si(100)-(2×{}1) and Si(111)-(7×{}7) surfaces are very reactive towards ammonia, which adsorbs dissociatively even at 100 K. The extent of dissociation and the dissociation products are different on the two surfaces. On Si(100) the ammonia dissociates to NH while on Si(111) it dissociates to NH₂. On the Si(100) surface the NH species has a lower thermal stability, starting to dissociate at around 500 K. The NH₂ species on Si(111) is stable up to {~}700 K. We explain the above general features in terms of the dangling-bond structure of Si(100)-(2×{}1) and Si(111)-(7×{}7) surfaces.