A MOLECULAR-BEAM STUDY OF THE REACTION OF N-2 AT CLEAN AND SODIUM COVERED SI(100) SURFACES

Auger electron spectroscopy has been used to monitor the uptake of nit rogen at both clean and sodium covered Si(100) surfaces after exposure to helium seeded and unseeded beams of nitrogen. Nitridation of the c lean Si(100) surface occurs only at surface temperatures in excess of 450 K and the rate of reaction then shows a strong dependence on the t ranslational energy of the incident N-2 molecule. By contrast nitrogen reacts with a sodium covered surface at 300 K to form both a nitride, SiNx, and a nitrogen surface complex which partly converts to nitride on heating. Scattering of nitrogen from the clean (sodium-free) silic on surface occurs as a broad, specular lobe but, when sodium is presen t, there is additional diffuse scattering which is thought to arise fr om a weakly held NaN3 complex which readily desorbs at 300 K.