Surface Chemistry and Interfacial Bonding of Benzyl Isocyanide on Cu(111)

The adsorption, thermal chemistry and interfacial electronic structure of benzyl isocyanide (BzNC, C 6 H 5 CH 2 NC) dosed on Cu(111) at 160 K have been studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). During TPD, BzNC dissociates above 280 K, leading to desorption of C 6 H 5 CH 3, H 2, and HCN. Intact BzNC also desorbs with local rate maxima at four different temperatures 247, 285, 340, and 455 K denoted β 1 −β 4 . The major peak (β 1, 455 K) is present for all doses. The other three β peaks grow in together and appear as β 1 approaches saturation. The β 2 peak at 247 K is very narrow and is attributed to BzNC desorption from crowded 2D islands accompanied by a stabilizing rearrangement of the remaining BzNC. Reflecting a strong permanent dipole that is oriented perpendicular to the surface, adsorption of 1 monolayer (ML) of BzNC on Cu(111) lowers the work function by 2.35 eV. The XPS and UPS results for this saturation coverage at 160 K are interpreted in terms of an ensemble average structure dominated by BzNC bound to Cu through the terminal carbon and dominated by σ-donation to Cu and minimal π-back-donation of electron density from Cu to BzNC. At lower coverages, a second structure involving both σ-donation and π-back-donation, signaled by a UPS resonance at 3.8 eV BE, becomes important, and for the lowest coverages, this second structure dominates.