Spectroscopy and reactions of hydrazoic acid on silicon single crystal surfaces. III. HN₃ and DN₃ on Si(111)(7 × 7)

We have studied the thermal stability and spectroscopy of HN₃ on Si(111)(7 × 7) in the temperature range from 120 to 1350 K. The results are similar to those observed on other two low-index Si surfaces. HN₃ was found to molecularly adsorb on Si(111)(7 × 7) at 120 K, with the formation of dimers at higher dosages (≥ 2.0 L). At 270 K, HN₃ began to decompose into HN and N₂ species as indicated by the changes in the NH vibration mode in HREELS and the chemical shift of the N 1s XPS peak. Between 300 and 800 K, the NH species further decomposed into H and N on the surface, while N₂ desorbed molecularly. In this temperature range, the steady increase of the SiN_x and SiH peaks were noted and LEED exhibited a weak (1 × 1) pattern. When the surface was annealed at T_s > 800 K, H_(a) recombined to desorb, with N remaining as the only species on the surface. Further annealing at higher temperatures caused the gradual transformation of the SiN_x species into Si₃N₄, as confirmed by all the spectroscopic results, including LEED which showed an (8 × 8) pattern.