Photochemical Grafting of Alkenes onto Carbon Surfaces: Identifying the Roles of Electrons and Holes

We report a mechanistic investigation of the charge transfer processes that Occur during photochemical grafting of liquid alkenes to H-terminated surfaces of diamond and amorphous carbon. Spectrally resolved photoelectron yield experiments were performed to directly characterize the photoemission of electrons from the hydrogen-terminated Surfaces into liquid alkenes, using trifluoroacetamide-protected 1-aminodec-l-ene (TFAAD) and 10-N-Boc-aminodec-l-ene (tBoc) as model alkenes having different terminal acceptor groups; 1-dodecene Was also used as a control. Corresponding X-ray and ultraviolet photoelectron spectroscopy measurements (XPS, UPS) establish a clear correlation between the photoelectron yield, the grafting efficiency at different wavelengths, and the valence electronic structure Of the Substrate and of the reactant molecule. Direct imaging of the Molecular layers via scanning electron microscopy shows that there are substantial differences ill the sharpness of molecular patterns that can be produced on single-crystal type Ib (low-mobility) and type IIb (high-mobility) diamond samples. Our results demonstrate that electrons and holes both play important and distinct roles in the photochemical grafting of alkenes to diamond and amorphous carbon surfaces.