Polycrystalline WO3 thin films for photoelectrochemical hydrogen production were investigated using photoelectron spectroscopy and inverse photoemission. First, we report on a careful study to ...minimize X-ray and electron beam-induced degradation. Second, we combined ultraviolet photoelectron spectroscopy and inverse photoemission to determine the surface positions of the valence and conduction band edges, respectively, and the work function (i.e., the position of the vacuum level). This allows us to paint a completely experiment-based picture of the WO3 surface level positions, which are of central relevance for the photoelectrochemical activity of such surfaces. We find the WO3 surface to be wide gap 3.28 (±0.14) eV and n-type, with the conduction band minimum 0.39 (±0.10) eV above the Fermi level and 0.31 (±0.11) eV above the H+/H2 reduction potential. The valence band maximum is 2.89 (±0.10) eV below the Fermi level and 1.74 (±0.11) eV below the H2O/O2 oxidation potential.
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The occupied and unoccupied electronic structure of imidazole (C
N
H
) and imidazolium (C
N
H
) in aqueous solutions is studied by X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray ...scattering (RIXS). Both systems show distinct RIXS fingerprints with strong resonant effects. A comparison with calculated X-ray emission spectra of isolated imidazole and imidazolium suggests only a small influence of hydrogen bonding in the aqueous solution on the electronic structure of imidazole and imidazolium, and allows the attribution of specific spectral features to the non-equivalent nitrogen and carbon atoms in the molecules. In the case of nitrogen, this can also be achieved by site-selective resonant excitation. Furthermore, we find spectator shifts and symmetry selectivity in the RIXS spectra, as well as indications for rapid proton dynamics on the femtosecond timescale of the RIXS process, and derive the HOMO-LUMO gaps for the two molecules in aqueous solution.
High-resolution x-ray absorption and emission spectra of liquid water exhibit a strong isotope effect. Further, the emission spectra show a splitting of the 1b1 emission line, a weak temperature ...effect, and a pronounced excitation-energy dependence. They can be described as a superposition of two independent contributions. By comparing with gas phase, ice, and NaOH/NaOD, we propose that the two components are governed by the initial state hydrogen bonding configuration and ultrafast dissociation on the time scale of the O 1s core hole decay.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Understanding the molecular structure of the hydration shells and their impact on the hydrogen bond (HB) network of water in aqueous salt solutions is a fundamentally important and technically ...relevant question. In the present work, such hydration effects were studied for a series of representative salt solutions (NaCl, KCl, CaCl2, MgCl2, and KBr) by soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). The oxygen K-edge XES spectra could be described with three components, attributed to initial state HB configurations in pure water, water molecules that have undergone an ultrafast dissociation initiated by the X-ray excitation, and water molecules in contact with salt ions. The behavior of the individual components, as well as the spectral shape of the latter component, has been analyzed in detail. In view of the role of ions in such effects as protein denaturation (i.e., the Hofmeister series), we discuss the ion-specific nature of the hydration shells and find that the results point to a predominant role of anions as compared to cations. Furthermore, we observe a concentration-dependent suppression of ultrafast dissociation in all salt solutions, associated with a significant distortion of intact HB configurations of water molecules facilitating such a dissociation.
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This study examined whether HIV counseling and testing leads to reductions in sexual risk behavior.
The meta-analysis included 27 published studies that provided sexual behavior outcome data, ...assessed behavior before and after counseling and testing, and provided details sufficient for the calculation of effect sizes. The studies involved 19,597 participants.
After counseling and testing, HIV-positive participants and HIV-serodiscordant couples reduced unprotected intercourse and increased condom use more than HIV-negative and untested participants. HIV-negative participants did not modify their behavior more than untested participants. Participants' age, volition for testing, and injection drug use treatment status, as well as the sample seroprevalence and length of the follow-up, explained the variance in results.
HIV counseling and testing appears to provide an effective means of secondary prevention for HIV-positive individuals but, as conducted in the reviewed studies, is not an effective primary prevention strategy for uninfected participants. Theory-driven research with attention given to the context of testing is needed to further explicate the determinants of behavior change resulting from HIV counseling and testing, and the effectiveness of specific counseling approaches.
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CEKLJ, DOBA, FSPLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
An efficient surface defect passivation is observed by reacting clean Si in a dilute hydrogen sulfide-argon gas mixture (< 5% H2S in Ar) for both n-type and p-type Si wafers with planar and textured ...surfaces. Surface recombination velocities of 1.5 and 8 cm/s are achieved on n-type and p-type Si wafers, respectively, at an optimum reaction temperature of 550oC that are comparable to the best surface passivation quality used in high efficiency Si solar cells. Surface chemical analysis using x-ray photoelectron spectroscopy shows that sulfur is primarily bonded in a sulfide environment, and synchrotron-based soft x-ray emission spectroscopy of the adsorbed sulfur atoms suggests the formation of S-Si bonds. Furthermore, the sulfur surface passivation layer is unstable in air, attributed to surface oxide formation and a simultaneous decrease of sulfide bonds. However, the passivation can be stabilized by a low-temperature (300oC) deposited amorphous silicon nitride (a-Si:NX:H) capping layer.
Nonresonant N K, O K, C K, and S L2,3 X-ray emission spectra of the 20 most common proteinogenic amino acids in their solid zwitterionic form are reported. They represent a comprehensive database ...that can serve as a reliable basis for the X-ray absorption spectroscopy (XES) studies of peptides and proteins. At the most important N and O K edges, clear similarities and differences between the spectra of certain amino acids are observed and associated with the specific chemical structure of these molecules and their functional groups. Analysis of these spectra allows the generation of spectral fingerprints of the protonated amino group, the deprotonated carboxylic group, and, using a building block approach, the specific nitrogen- and oxygen-containing functional groups in the side chains of the amino acids. Some of these fingerprints are compared to the spectra of reference compounds with the respective functional groups; they exhibit reasonable similarity, underlining the validity of the spectral fingerprint approach. The C K and S L2,3 XES spectra are found to be specific for each amino acid, in accordance with the different local environments of the involved C and S atoms, respectively.
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The electronic structure of gas-phase methanol molecules (H3COH, H3COD, and D3COD) at atmospheric pressure was investigated using resonant inelastic soft X-ray scattering (RIXS) at the O K and C K ...edges. We observe strong changes of the relative emission intensities of all valence orbitals as a function of excitation energy, which can be related to the symmetries of the involved orbitals causing an angularly anisotropic RIXS intensity. Furthermore, all observed emission lines are subject to strong spectator shifts of up to −0.9 eV at the O K edge and up to −0.3 eV at the C K edge. At the lowest O K resonance, we find clear evidence for dissociation of the methanol molecule on the time scale of the RIXS process, which is illustrated by comparing X-ray emission spectra of regular and deuterated methanol.
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•The effect of NaCl ink additive on indium oxide nanoparticle thin films is analyzed.•NaCl changes the thin film morphology and its chemical structure.•NaCl decomposes the ...nanoparticle shell leading to lower charge transport barriers.•Explanation of the increase in field effect mobility from 1 to >12cm2/Vs.•Understanding of the ink drying process and the nanoparticle agglomeration behavior.
One of the major challenges in flexible electronics industry is the fabrication of high-mobility field-effect transistors (FETs) at ambient conditions and on inexpensive polymer substrates compatible with roll-to-roll printing technology. In this context, a novel and general route towards room-temperature fabrication of printed FETs with remarkably high field-effect mobility (μFET) above 12cm2/Vs has recently been developed. A detailed understanding of the chemical structure of the involved nanoparticle (NP) thin films, prepared by chemical flocculation, is essential for further optimization of the charge transport properties of such devices. In this study, we thus analyze indium oxide NP thin films with and without NaCl additive using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). It is demonstrated that the introduction of a sodium chloride additive to the ink leads to a strongly altered film morphology and a modification of the NP shell. The results suggest that, as a consequence of the additive, the charge-transport barriers between individual indium oxide NPs are lowered, facilitating long-range charge percolation paths despite the presence of a significant concentration of carbonaceous residues.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The local valence orbital structure of solid glycine, diglycine, and triglycine is studied using soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS) maps, and ...spectra calculations based on density-functional theory. Using a building block approach, the contributions of the different functional groups of the peptides are separated. Cuts through the RIXS maps furthermore allow monitoring selective excitations of the amino and peptide functional units, leading to a modification of the currently established assignment of spectral contributions. The results thus paint a new-and-improved picture of the peptide bond, enhance the understanding of larger molecules with peptide bonds, and simplify the investigation of such molecules in aqueous environment.
Soft X-ray emission spectroscopy and RIXS are used to determine the local electronic structure of the peptide bond.
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