Surface reactions of 3-butenenitrile on the Si(001)-2 × 1 surface at room temperature

Using a combination of local-scanning tunneling microscopy-and spatially integrated, but chemically sensitive probes-X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy-we have examined how 3-butenenitrile reacts with the Si(001)-2 × 1 surface at room temperature. Electron spectroscopies indicate three different nitrogen chemical bonds: a Si-C=N-Si bond, a C=C=N cumulative double bond, and a C≡N moiety datively bonded to a silicon atom. All molecular imprints detected by scanning tunneling microscopy (STM) involve two adjacent silicon dimers in the same row. The three geometries we propose-a double di-σ bonding via the C≡N and the C=C, a cumulative double bond formation associated with αC-H bond dissociation, and a di-σ vinyl bonding plus a C?≡N datively bonded to a silicon atom-are all compatible with electron spectroscopies and data. Real-time Auger yield kinetic measurements show that the double di-σ bonding geometry is unstable when exposed to a continuous flux of 3-butenenitrile molecules, as the Si-C=N-Si unit transforms into a C≡N moiety. A model is proposed to explain this observation.