Binding and Structure of Acetonitrile on Si(111)-7 × 7

Abstract

The covalent binding and structure of acetonitrile on Si(111)-7 × 7 have been investigated to provide information on the interaction of π electrons of the C⋮N group with the dangling bonds of Si(111)-7 × 7. Vibrational features of chemisorbed acetonitrile and acetonitrile-d3 unambiguously show the absence of C⋮N stretching mode around 2232 cm-1 coupled with the appearance of CN stretching mode at 1663 cm-1. Both C 1s and N 1s core levels of chemisorbed acetonitrile display large chemical shifts of 2.2 and 1.3 eV, respectively, compared with those of physisorbed molecules. In addition, the photoemission from πCN was observed to be weakened upon chemisorption. These results clearly suggest that the cyano group directly participates in the interaction with Si surface dangling bonds. Scanning tunneling microscopy images reveal that the cyano groups selectively bind to adatom−rest atom pairs on Si(111)-7 × 7. Density functional theory calculations indicate that the C and N atoms of the cyano group favorably link with the adatom and rest atom, respectively, forming C−Si and N−Si bonds.