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A one-step electrochemical grafting process using Grignard reagents has been performed to achieve a complete monolayer methyl-terminated Si(111) surfaces. Anodic treatment (0.5 mA/cm2 for 300 s) ha...

This study seeks to explore the effects of the electronic structure of Pt/Ru alloy nanoparticles on reactivity of small organic molecules of relevance to fuel cell applications through the combined use of synchrotron radiation photoelectron spectroscopy and electrochemistry. Platinum core-level binding energies were found to increase linearly with the addition of ruthenium. This effect is a product of lattice strain and charge transfer, and is explained in terms of the d-band center theory proposed by Norskov and co-workers (Hammer, B.; Norskov, J. K. Surf. Sci. 1995, 343, 211). In the course of the study of electrooxidation of methanol we have found that it is very difficult, if not impossible, to separate the effects of the bifunctional mechanism and the electronic structure effects that might play a role in the activity. However, data for electrooxidation of formic acid, when studied at a short reaction time (where the indirect reaction pathways and poisoning intermediates are assumed to play a negligi...

The relative coverage, thermal stability, and electronic properties of CH_(3-) and C_2H_(5-)functionalized Si(111) surfaces prepared by a two-step chlorination/alkylation procedure have been compared using high-resolution synchrotron photoemission spectroscopy. Whereas the CH_(3-) terminated Si(111) surface showed only one C 2s peak for the occupied σ orbitals, the C 2s spectra of C_2H_(5-)terminated Si(111) surfaces showed a symmetric splitting of the occupied σ orbitals, as expected for an ethyl moiety bonded to the surface. The C_2H_5 termination resulted in an unpinning of the Si surface Fermi level, with a band bending of ∼0.2 eV, and produced a surface dipole potential step of −0.23(15) eV. The observed close-to-flat-band condition is similar to that of CH_3−Si(111) and is consistent with H termination of the non-alkylated Si atop sites in the two-step chlorination/alkylation process. The C_2H_(5-)functionalized Si(111) surfaces decomposed at temperatures >300 °C, whereas CH_3−Si(111) surfaces were stable up to at least 440 °C. The data clearly highlight the similarities and identify some significant differences between the behavior of the CH_3- and C_2H_(5-)functionalized Si(111) surfaces.

The initial stage of oxidative CuI film formation on Cu(111) has been studied in an electrochemical environment by means of cyclic voltammetry (CV), in situ scanning tunneling microscopy (STM) and ex situ synchrotron X-ray photoemission spectroscopy (SXPS). Cyclic voltammetric studies indicate a significant acceleration of copper oxidation in the presence of iodide. The reason for that is the iodide-mediated stabilization of cuprous species resulting in a downward shift of the onset potential for copper oxidation. Reactive sites for the copper oxidation followed by iodide complexation are exclusively defects such as substrate step edges. It is the surface-confined supersaturation of mobile CuI species that leads to the two-dimensional (2D) CuI film formation via nucleation and growth of a Cu/I bilayer on top of the preadsorbed iodide phase. In an advanced stage of copper oxidation, however, terraces are directly transformed into the 2D CuI film at the reactive boundary between metallic copper and the grow...

The adsorption of Ru dye N3 [RuII(2,2‘-bipyridyl-4,4‘-dicarboxylate)2(NCS)2] from ethanol solution and gas-phase adsorption and coadsorption of the solvent acetonitrile on liquid nitrogen cooled nanocrystalline (nc) TiO2 films have been investigated using highly surface sensitive synchrotron-induced photoelectron spectroscopy. Resonantly excited Ti3+-related band gap states form a peak 2.2 eV above the leading edge of the valence band, and additional states up to the Fermi level are found. The intensities of the gap states and related Ti3+ 2p emissions of pristine samples depend strongly on sample preparation and history. Gap-state-related emissions are partially quenched by dye as well as acetonitrile adsorption. Quenching of gap states due to acetonitrile is reversible. The maximum of the highest occupied molecular orbital (HOMO) emission of the dye is found 1.6 eV above the leading edge of the nc-TiO2 valence band. The binding energies of dye orbitals are increased upon acetonitrile coadsorption. The H...

The properties of Si(111) surfaces grafted with benzene derivatives were investigated using ultraviolet photoemission spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The investigated materials were nitro-, bromo-, and methoxybenzene layers (-C(6)H(4)-X, with X = NO(2), Br, O-CH(3)) deposited from diazonium salt solutions in a potentiostatic electrochemical process. The UPS spectra of the valence band region are governed by the molecular orbital density of states of the adsorbates, which is modified from the isolated state in the gas phase due to molecule-molecule and molecule-substrate interaction. Depending on the adsorbate, clearly different emission features are observed. The analysis of XPS intensities clearly proves multilayer formation for bromo- and nitrobenzene in agreement with the amount of charge transferred during the grafting process. Methoxybenzene forms only a sub-monolayer coverage. The detailed analysis of binding energy shifts of the XPS emissions for determining the band bending and the secondary electron onset in UPS spectra for determining the work function allow one to discriminate between surface dipole layers--changing the electron affinity--and band bending, affecting only the work function. Thus, complete energy band diagrams of the grafted Si(111) surfaces can be constructed. It was found that silicon surface engineering can be accomplished by the electrochemical grafting process using nitrobenzene and bromobenzene: silicon-derived interface gap states are chemically passivated, and the adsorbate-related surface dipole effects an increase of the electron affinity.