Electronic Structure of Diamond Surfaces Functionalized by Ru(tpy)(2)

Highly doped diamond films are new candidates for electrodes in reactive environments, such as electrocatalytic interfaces. Here the electronic structure of such films is investigated by X-ray absorption spectroscopy at the C Is and B Is edges, combined with X-ray and ultraviolet photoelectron spectroscopy, as well as optical measurements. A diamond surface functionalized covalently with Ru(tpy)(2), a model complex similar to ruthenium-based molecules used in photocatalysis and photovoltaics, is compared to a hydrogen-terminated diamond surface as a reference. Bulk-sensitive absorption spectra with photon detection reveal diamond gap states, while surface-sensitive spectra with electron detection reveal the adsorbate states and pi-bonding at the diamond surface. The positions of the frontier orbitals of the dye relative to the band edges of diamond are inferred from the spectroscopic data. The implications of using diamond films as inert electron donors in photocatalysis and dye-sensitized solar cells are discussed.