Bonding of nitrogen-containing organic molecules to the silicon(001) surface: The role of aromaticity

The adsorption of pyrrole, aniline, 3-pyrroline, and pyrrolidine on the Si( 001)-(2 x 1) surface has been studied using Fourier transform infrared (FTI R) spectroscopy and X-ray photoelectron spectroscopy (XPS). Both pyrrole an d aniline retain their aromatic character after bonding to the surface. Spe ctroscopic evidence indicates that each of these aromatic molecules can att ach to the Si(001) surface via cleavage of one N-H bond, linking the molecu le to the surface through a Si-N tether. Isotopic studies of pyrrole show e vidence for additional cleavage of C-H bonds. While strong selectivity favo ring bonding through the nitrogen atom is observed for the aromatic molecul es, the unsaturated molecule 3-pyrroline shows evidence for at least two bo nding configurations. XPS and FTIR data show that 3-pyrroline can bond eith er through the nitrogen atom with cleavage of an N-H bond, or through the C =C bond via the surface equivalent of a [2 + 2] cycloaddition reaction. Pyr rolidine appears to bond only through the nitrogen atom. Potential factors controlling the selectivity in bonding and the role of aromaticity in contr olling reaction pathways on silicon surfaces are discussed.