Molecular and dissociative bonding of amines with the Si(111)-(7 x 7) surface

The interaction of trimethylamine (TMA) and dimethylamine (DMA) with the Si(111)-(7 x 7) surface has been studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS). STM data for TMA at low coverage show molecular features exhibiting a strong preference for bonding at the center adatom sites. XPS data show that at low coverage the majority of molecules form a highly ionic dative-bonded molecular adduct in which the N atom donates electron density to the surface, leading to a very high N(1s) binding energy of 402.4 eV. UPS data show that the interaction of TMA with the Si(111)-(7 x 7) surface also involves the restatom, suggesting that formation of dative bonds may also alter the restatom state. At very high exposures, a new, dissociative pathway becomes important, leading to dissociation and the appearance of new fragments with lower N(1s) binding energies of 399.1 eV. Corresponding studies for DMA only show dissociative bonding on Si(111), forming H atoms and N(CH3)(2) species. While the N(CH3)(2) species bonds primarily to the adatoms, the H atoms can bond to either adatoms or restatoms. Possible reaction mechanism and the reactivity of the different types of surface silicon atoms are discussed. (C) 2002 Published by Elsevier Science B.V.