Chemical and electronic characterization of methyl-terminated Si(111) surfaces by high-resolution synchrotron photoelectron spectroscopy

The chemical state, electronic properties, and geometric structure of methyl-terminated Si(111) surfaces prepared using a two-step chlorination/alkylation process were investigated using high-resolution synchrotron photoelectron spectroscopy and low-energy electron diffraction methods. The electron diffraction data indicated that the methylated Si surfaces maintained a (1×1) structure, where the dangling bonds of the silicon surface atoms were terminated by methyl groups. The surfaces were stable to annealing at 720 K. The high degree of ordering was reflected in a well-resolved vibrational fine structure of the carbon 1s photoelectron emission, with the fine structure arising from the excitation of C-H stretching vibrations having hnu=0.38±0.01 eV. The carbon-bonded surface Si atoms exhibited a well-defined x-ray photoelectron signal having a core level shift of 0.30±0.01 eV relative to bulk Si. Electronically, the Si surface was close to the flat-band condition. The methyl termination produced a surface dipole of –0.4 eV. Surface states related to piCH3 and sigmaSi-C bonding orbitals were identified at binding energies of 7.7 and 5.4 eV, respectively. Nearly ideal passivation of Si(111) surfaces can thus be achieved by methyl termination using the two-step chlorination/alkylation process

Organic layers at metal/electrolyte interfaces: molecular structure and reactivity of viologen monolayers

The adsorption of viologens (1,1′-disubstituted-4,4′-bipyridinium molecules) on a chloride-modified copper electrode has been studied using a combination of cyclic voltammetry (CV), in-situ scanning tunneling microscopy (STM) and ex-situ photoemission spectroscopy (XPS). Two prototypes of viologens could be identified with respect to their redox behavior upon adsorption, namely those which retain (non-reactive adsorption) and those which change their redox state (reactive adsorption) upon interaction with the chloride-modified copper surface at given potential. The first class of viologens represented by 1,1′-dibenzyl-4,4′-bipyridinium molecules (dibenzyl-viologens, abbreviated as DBV) can be adsorbed and stabilized on this electrode surface in their di-cationic state at potentials more positive than the reduction potential of the solution species. XPS N1s core level shifts verify that the adsorbed DBV molecules on the electrode are in their oxidized di-cationic state. Electrostatic attraction between the partially solvated viologen di-cations and the anionic chloride layer is discussed as the main driving force for the DBV stabilization on the electrode surface. Analysis of the N1s and O1s core level shifts points to a non-reactive DBV adsorption leaving the DBVads²⁺ solvation shell partly intact. The laterally ordered DBVads²⁺ monolayer turns out to be hydrophilic with at least four water molecules per viologen present within this cationic organic film. The analysis of the Cl2p core level reveals that no further chloride species are present at the surface besides those which are specifically adsorbed, i.e. which are in direct contact with the metallic copper surface underneath the organic layer. The reduction of these adsorbed DBVads²⁺ surface species takes place only in the same potential regime where the solvated DBVaq²⁺ bulk solution species react and is accompanied by a pronounced structural change from the di-cationic ‘cavitand’-structure to a ‘stripe’-structure of chains of π-stacked DBV•⁺ mono-cation radicals as verified by in-situ STM. The second class of viologens represented by 1,1′-diphenyl-4,4′-bipyridinium molecules (diphenyl-viologens, abbreviated as DPV) is much more reactive upon adsorption and cannot be stabilized on the electrode surface in a di-cationic state, at least within the narrow potential window of copper. The N1s core level binding energy indicates only the presence of the corresponding mono-reduced DPVads•⁺ species on the surface even at potentials more positive than the redox potential of the bulk solution species. This process leads to the formation of a hydrophobic viologen monolayer with stacked polymeric chains as the characteristic structural motif. The wet electrochemical reduction of viologens is further compared with a dry reduction under UHV conditions. The latter reaction inevitably affects the di-cationic viologen species in the course of the photoemission experiment. Slow photoelectrons and secondary electrons are assumed to transform the di-cationic viologens into the corresponding radical mono-cations upon irradiation

What causes hidradenitis suppurativa? - 15 years after

The 14 authors of the first review article on hidradenitis suppurativa (HS) pathogenesis published 2008 in EXPERIMENTAL DERMATOLOGY cumulating from the 1st International Hidradenitis Suppurativa Research Symposium held March 30?April 2, 2006 in Dessau, Germany with 33 participants were prophetic when they wrote "Hopefully, this heralds a welcome new tradition: to get to the molecular heart of HS pathogenesis, which can only be achieved by a renaissance of solid basic HS research, as the key to developing more effective HS therapy." (Kurzen et al. What causes hidradenitis suppurativa? Exp Dermatol 2008;17:455). Fifteen years later, there is no doubt that the desired renaissance of solid basic HS research is progressing with rapid steps and that HS has developed deep roots among inflammatory diseases in Dermatology and beyond, recognized as ?the only inflammatory skin disease than can be healed?. This anniversary article of 43 research-performing authors from all around the globe in the official journal of the European Hidradenitis Suppurativa Foundation e.V. (EHSF e.V.) and the Hidradenitis Suppurativa Foundation, Inc (HSF USA) summarizes the evidence of the intense HS clinical and experimental research during the last 15 years in all aspects of the disease and provides information of the developments to come in the near future

What causes hidradenitis suppurativa ?—15 years after

The 14 authors of the first review article on hidradenitis suppurativa (HS) pathogenesis published 2008 in EXPERIMENTAL DERMATOLOGY cumulating from the 1st International Hidradenitis Suppurativa Research Symposium held March 30–April 2, 2006 in Dessau, Germany with 33 participants were prophetic when they wrote “Hopefully, this heralds a welcome new tradition: to get to the molecular heart of HS pathogenesis, which can only be achieved by a renaissance of solid basic HS research, as the key to developing more effective HS therapy.” (Kurzen et al. What causes hidradenitis suppurativa? Exp Dermatol 2008;17:455). Fifteen years later, th

In Situ Synchrotron Photoemission Analysis of Semiconductor / Electrolyte Interfaces by the Frozen Electrolyte Approach: Interaction of HCl in Isopropanol with GaAs(100)

Abstract not Available.</jats:p

Chemical and Electronic Structure of the Solid-liquid Interface of Dye Sensitized Solar Cells - Application of Synchrotron Induced Photoelectron Spectroscopy

Abstract not Available.</jats:p

Photoelectron Spectroscopy at the Solid–Liquid Interface of Dye–Sensitized Solar Cells: Unique Experiments with the Solid–Liquid Interface Analysis System SoLiAS at BESSY

At the synchrotron BESSY we run the experimental station SoLiAS, dedicated to solid–liquid interface analysis with soft X-ray induced photoelectron spectroscopy (SXPS). SoLiAS allows wet chemically prepared surfaces to be transferred to the ultra high vacuum without contact with ambient air. In addition in situ (co)adsorption of volatile solvent species onto liquid nitrogen cooled samples is possible. SoLiAS proves to be very useful in analyzing the chemical and electronic structure at the solid–liquid interface of dye–sensitized solar cells. The standard dye RuII(2,2?-bipyridil-4,4?-dicarboxylate)2(NCS)2 was adsorbed from ethanol solution under clean N2 atmosphere in an UHV-integrated electrochemical cell (EC). The standard solvent acetonitrile was adsorbed in situ from the gas phase. For comparison also the nonpolar solvent benzene was adsorbed. Ex situ sintered nanocrystalline anatase substrates as well as in situ deposited polycrystalline TiO2 samples were used, which show a similar distribution of two types of occupied surface states. Distinct reversible changes occur in synchrotron-induced photoelectron valence band and core level spectra when the solvent acetonitrile is adsorbed to pristine and dye-covered TiO2 substrates. TiO2 surface states are quenched and the line width of the dye S2p emission decreases strongly. Based on the experimental results the alignment of the photovoltaic relevant electronic states and a model on the dye–solvent interaction can be deduced that points to the promotion of vectorial charge transfer by increased dye orientation due to solvation