The Experts below are selected from a list of 74412 Experts worldwide ranked by ideXlab platform
Jan Kern - One of the best experts on this subject based on the ideXlab platform.
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Jan Kern, Vittal K YachandraAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in si...
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Sheraz Gul, Jan KernAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in situ feedback system using Photosystem II as an example that catalyzes the oxidation of H2O to O2 at the Mn4CaO5 active site. We used the first moments of the Mn Kβ1,3 Emission spectra, which are sensitive to the oxidation state of Mn, as the primary diagnostics. This approach is applicable to different metalloproteins to determine the integrity of samples and follow changes in the chemical states of the reaction that can be initiated by light or activated by substrates and offers a metric for determining the diffraction images that are used for the final data sets.
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simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength dispersive x ray Emission Spectroscopy and in situ electrochemistry
Physical Chemistry Chemical Physics, 2015Co-Authors: Dimosthenis Sokaras, Roberto Alonsomori, Jan Kern, Benedikt Lassallekaiser, Sheraz Gul, Eitan Anzenberg, Yelena Gorlin, Tsuchien WengAbstract:Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-Ray Emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-Ray Emission Spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.
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simultaneous femtosecond x ray Spectroscopy and diffraction of photosystem ii at room temperature
Science, 2013Co-Authors: Jan Kern, Roberto Alonsomori, Richard J Gildea, Rosalie Tran, Johan Hattne, Hartawan Laksmono, Nathaniel Echols, Carina Glockner, Julia Hellmich, Raymond G SierraAbstract:Intense femtosecond X-Ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous X-Ray diffraction (XRD) and X-Ray Emission Spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
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simultaneous femtosecond x ray Spectroscopy and diffraction of photosystem ii at room temperature
Science, 2013Co-Authors: Roberto Alonsomori, Jan Kern, Richard J Gildea, Rosalie Tran, Johan Hattne, Nathaniel Echols, Carina Glockner, Julia Hellmich, Hartawan LaksmonoAbstract:Intense femtosecond X-Ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous X-Ray diffraction (XRD) and X-Ray Emission Spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
Dimosthenis Sokaras - One of the best experts on this subject based on the ideXlab platform.
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kβ x ray Emission Spectroscopy as a probe of cu i sites application to the cu i site in preprocessed galactose oxidase
Inorganic Chemistry, 2020Co-Authors: Hyeongtaek Lim, Michael L Baker, Ryan E Cowley, Sunghee Kim, Mayukh Bhadra, Maxime A Siegler, Thomas Kroll, Dimosthenis Sokaras, Tsuchien Weng, Dalia R BiswasAbstract:Cu(I) active sites in metalloproteins are involved in O2 activation, but their O2 reactivity is difficult to study due to the Cu(I) d10 closed shell which precludes the use of conventional spectroscopic methods. Kβ X-Ray Emission Spectroscopy (XES) is a promising technique for investigating Cu(I) sites as it detects photons emitted by electronic transitions from occupied orbitals. Here, we demonstrate the utility of Kβ XES in probing Cu(I) sites in model complexes and a metalloprotein. Using Cu(I)Cl, Emission features from double-ionization (DI) states are identified using varying incident X-Ray photon energies, and a reasonable method to correct the data to remove DI contributions is presented. Kβ XES spectra of Cu(I) model complexes, having biologically relevant N/S ligands and different coordination numbers, are compared and analyzed, with the aid of density functional theory (DFT) calculations, to evaluate the sensitivity of the spectral features to the ligand environment. While the low-energy Kβ2,5 Emission feature reflects the ionization energy of ligand np valence orbitals, the high-energy Kβ2,5 Emission feature corresponds to transitions from molecular orbitals (MOs) having mainly Cu 3d character with the intensities determined by ligand-mediated d-p mixing. A Kβ XES spectrum of the Cu(I) site in preprocessed galactose oxidase (GOpre) supports the 1Tyr/2His structural model that was determined by our previous X-Ray absorption Spectroscopy and DFT study. The high-energy Kβ2,5 Emission feature in the Cu(I)-GOpre data has information about the MO containing mostly Cu 3dx2-y2 character that is the frontier molecular orbital (FMO) for O2 activation, which shows the potential of Kβ XES in probing the Cu(I) FMO associated with small-molecule activation in metalloproteins.
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Jan Kern, Vittal K YachandraAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in si...
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Sheraz Gul, Jan KernAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in situ feedback system using Photosystem II as an example that catalyzes the oxidation of H2O to O2 at the Mn4CaO5 active site. We used the first moments of the Mn Kβ1,3 Emission spectra, which are sensitive to the oxidation state of Mn, as the primary diagnostics. This approach is applicable to different metalloproteins to determine the integrity of samples and follow changes in the chemical states of the reaction that can be initiated by light or activated by substrates and offers a metric for determining the diffraction images that are used for the final data sets.
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probing 5 f state configurations in uru 2 si 2 with u l iii edge resonant x ray Emission Spectroscopy
Physical Review B, 2016Co-Authors: C H Booth, Dimosthenis Sokaras, Scott Medling, J G Tobin, R E Baumbach, E D Bauer, Dennis Nordlund, T C WengAbstract:Author(s): Booth, CH; Medling, SA; Tobin, JG; Baumbach, RE; Bauer, ED; Sokaras, D; Nordlund, D; Weng, TC | Abstract: © 2016 American Physical Society. Resonant X-Ray Emission Spectroscopy (RXES) was employed at the U LIII absorption edge and the Lα1 Emission line to explore the 5f occupancy, nf, and the degree of 5f-orbital delocalization in the hidden-order compound URu2Si2. By comparing to suitable reference materials such as UF4, UCd11, and α-U, we conclude that the 5f orbital in URu2Si2 is at least partially delocalized with nf=2.87±0.08, and does not change with temperature down to 10 K within the estimated error. These results place further constraints on theoretical explanations of the hidden order, especially those requiring a localized f2 ground state.
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simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength dispersive x ray Emission Spectroscopy and in situ electrochemistry
Physical Chemistry Chemical Physics, 2015Co-Authors: Dimosthenis Sokaras, Roberto Alonsomori, Jan Kern, Benedikt Lassallekaiser, Sheraz Gul, Eitan Anzenberg, Yelena Gorlin, Tsuchien WengAbstract:Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-Ray Emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-Ray Emission Spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.
Serena Debeer - One of the best experts on this subject based on the ideXlab platform.
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probing physical oxidation state by resonant x ray Emission Spectroscopy applications to iron model complexes and nitrogenase
Angewandte Chemie, 2021Co-Authors: Rebeca G Castillo, Anselm W Hahn, Benjamin E Van Kuiken, Justin T Henthorn, Jeremy Mcgale, Serena DebeerAbstract:The ability of resonant X-Ray Emission Spectroscopy (XES) to recover physical oxidation state information, which may often be ambiguous in conventional X-Ray Spectroscopy, is demonstrated. By combining Kβ XES with resonant excitation in the XAS pre-edge region, resonant Kβ XES (or 1s3p RXES) data are obtained, which probe the 3dn+1 final-state configuration. Comparison of the non-resonant and resonant XES for a series of high-spin ferrous and ferric complexes shows that oxidation state assignments that were previously unclear are now easily made. The present study spans iron tetrachlorides, iron sulfur clusters, and the MoFe protein of nitrogenase. While 1s3p RXES studies have previously been reported, to our knowledge, 1s3p RXES has not been previously utilized to resolve questions of metal valency in highly covalent systems. As such, the approach presented herein provides chemists with means to more rigorously and quantitatively address challenging electronic-structure questions.
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calcium valence to core x ray Emission Spectroscopy a sensitive probe of oxo protonation in structural models of the oxygen evolving complex
Inorganic Chemistry, 2019Co-Authors: Zachary Mathe, Benjamin E Van Kuiken, Dimitrios A Pantazis, Heui Beom Lee, Richard Gnewkow, Theodor Agapie, Serena DebeerAbstract:Calcium is an abundant, nontoxic metal that finds many roles in synthetic and biological systems including the oxygen-evolving complex (OEC) of photosystem II. Characterization methods for calcium centers, however, are underdeveloped compared to those available for transition metals. Valence-to-core X-Ray Emission Spectroscopy (VtC XES) selectively probes the electronic structure of an element's chemical environment, providing insight that complements the geometric information available from other techniques. Here, the utility of calcium VtC XES is established using an in-house dispersive spectrometer in combination with density functional theory. Spectral trends are rationalized within a molecular orbital framework, and Kβ2,5 transitions, derived from molecular orbitals with primarily ligand p character, are found to be a promising probe of the calcium coordination environment. In particular, it is shown that calcium VtC XES is sensitive to the electronic structure changes that accompany oxo protonation in Mn3CaO4-based molecular mimics of the OEC. Through correlation to calculations, the potential of calcium VtC XES to address unresolved questions regarding the mechanism of biological water oxidation is highlighted.
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valence to core x ray Emission Spectroscopy as a probe of o o bond activation in cu2o2 complexes
Angewandte Chemie, 2019Co-Authors: George E Cutsail, Nicole L Gagnon, Andrew D Spaeth, William B Tolman, Serena DebeerAbstract:Valence-to-Core (VtC) X-Ray Emission Spectroscopy (XES) was used to directly detect the presence of an O-O bond in a complex comprising the [CuII 2 (μ-η2 :η2 -O2 )]2+ core relative to its isomer with a cleaved O-O bond having a [CuIII 2 (μ-O)2 ]2+ unit. The experimental studies are complemented by DFT calculations, which show that the unique VtC XES feature of the [CuII 2 (μ-η2 :η2 -O2 )]2+ core corresponds to the copper stabilized in-plane 2p π peroxo molecular orbital. These calculations illustrate the sensitivity of VtC XES for probing the extent of O-O bond activation in μ-η2 :η2 -O2 species and highlight the potential of this method for time-resolved studies of reaction mechanisms.
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comparative electronic structures of nitrogenase femoco and fevco
Dalton Transactions, 2017Co-Authors: Julian A Rees, Joanna K. Kowalska, Ragnar Bjornsson, Julia Schlesier, Daniel Sippel, Oliver Einsle, Frederico A Lima, Thomas Weyhermuller, Julie A Kovacs, Serena DebeerAbstract:An investigation of the active site cofactors of the molybdenum and vanadium nitrogenases (FeMoco and FeVco) was performed using high-resolution X-Ray Spectroscopy. Synthetic heterometallic iron–sulfur cluster models and density functional theory calculations complement the study of the MoFe and VFe holoproteins using both non-resonant and resonant X-Ray Emission Spectroscopy. Spectroscopic data show the presence of direct iron–heterometal bonds, which are found to be weaker in FeVco. Furthermore, the interstitial carbide is found to perturb the electronic structures of the cofactors through highly covalent Fe–C bonding. The implications of these conclusions are discussed in light of the differential reactivity of the molybdenum and vanadium nitrogenases towards various substrates. Possible functional roles for both the heterometal and the interstitial carbide are detailed.
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the fe v cofactor of vanadium nitrogenase contains an interstitial carbon atom
Angewandte Chemie, 2015Co-Authors: Serena Debeer, Julian A Rees, Ragnar Bjornsson, Julia Schlesier, Daniel Sippel, Oliver EinsleAbstract:The first direct evidence is provided for the presence of an interstitial carbide in the FeV cofactor of Azotobacter vinelandii vanadium nitrogenase. As for our identification of the central carbide in the FeMo cofactor, we employed Fe Kβ valence-to-core X-Ray Emission Spectroscopy and density functional theory calculations, and herein report the highly similar spectra of both variants of the cofactor-containing protein. The identification of an analogous carbide, and thus an atomically homologous active site in vanadium nitrogenase, highlights the importance and influence of both the interstitial carbide and the identity of the heteroatom on the electronic structure and catalytic activity of the enzyme.
C Heske - One of the best experts on this subject based on the ideXlab platform.
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isotope and temperature effects in liquid water probed by x ray absorption and resonant x ray Emission Spectroscopy
Physical Review Letters, 2008Co-Authors: O Fuchs, L Weinhardt, Michael Zharnikov, M Blum, Markus Weigand, Yan V Zubavichus, M Bar, Florian Maier, J D Denlinger, C HeskeAbstract: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 1b 1 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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surface modifications of cu in ga s2 thin film solar cell absorbers by kcn and h2o2 h2so4 treatments
Journal of Applied Physics, 2006Co-Authors: L Weinhardt, E Umbach, C Heske, O Fuchs, D Gros, Neelkanth G Dhere, Ankur A Kadam, Sachin S KulkarniAbstract:KCN etching of the CuxS surface layer formed during the production process of Cu(In,Ga)S2 thin film solar cell absorbers as well as subsequent H2O2∕H2SO4 etching of the Cu(In,Ga)S2 surface have been investigated using X-Ray photoelectron Spectroscopy, X-Ray excited Auger electron Spectroscopy, and X-Ray Emission Spectroscopy. We find that the KCN etching removes the CuxS layer—being identified as Cu2S—and that there is K deposited during this step, which is removed by the subsequent H2O2∕H2SO4 oxidation treatment. When a CdS buffer layer is deposited on the absorber directly after KCN etching, a K compound (KCO3) is observed at the CdS surface.
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self limitation of na content at the cds cu in ga se2 solar cell heterojunction
Thin Solid Films, 2000Co-Authors: C Heske, E Umbach, D Eich, R Fink, Christoph Bostedt, L J Terminello, U Groh, T Van Buuren, N Franco, M M GrushAbstract:Abstract The localization of Na impurities at the buried heterojunction of CdS/Cu(In,Ga)Se2 thin film solar cells has been studied by photoelectron Spectroscopy and X-Ray Emission Spectroscopy. This combination of a surface- and a bulk-sensitive technique allows to identify the localization of impurities at a buried interface in a non-destructive, semi-quantitative, and element-specific way. We compare samples with increasing CdS-overlayer thickness on (a) a CIGS film with nominal Na content and (b) a Na-rich CIGS film. The data clearly indicate a self-limitation of the Na content at this interface. The consequences are discussed in view of the possibility to tailor the electronic structure of the buried heterojunction by controlling the nominal Na content in the CIGS film.
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observation of intermixing at the buried cds cu in ga se2 thin film solar cell heterojunction
Applied Physics Letters, 1999Co-Authors: C Heske, E Umbach, D Eich, R Fink, T Van Buuren, Christoph Bostedt, L J Terminello, S Kakar, M M Grush, T A CallcottAbstract:A combination of X-Ray Emission Spectroscopy and X-Ray photoelectron Spectroscopy using high brightness synchrotron radiation has been employed to investigate the electronic and chemical structure of the buried CdS/Cu(In, Ga)Se2 interface, which is the active interface in highly efficient thin film solar cells. In contrast to the conventional model of an abrupt interface, intermixing processes involving the elements S, Se, and In have been identified. The results shed light on the electronic structure and interface formation processes of semiconductor heterojunctions and demonstrate a powerful tool for investigating buried interfaces in general.
Uwe Bergmann - One of the best experts on this subject based on the ideXlab platform.
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double core hole valence to core x ray Emission Spectroscopy a theoretical exploration using time dependent density functional theory
Journal of Chemical Physics, 2019Co-Authors: Yu Zhang, Uwe Bergmann, R W Schoenlein, Munira Khalil, Niranjan GovindAbstract:With the help of newly developed X-Ray free-electron laser (XFEL) sources, creating double core holes (DCHs) simultaneously at the same or different atomic sites in a molecule has now become possible. DCH X-Ray Emission is a new form of X-Ray nonlinear Spectroscopy that can be studied with a XFEL. Here, we computationally explore the metal K-edge valence-to-core (VtC) X-Ray Emission Spectroscopy (XES) of metal/metal and metal/ligand DCH states in a series of transition metal complexes with time-dependent density functional theory. The simulated DCH VtC-XES signals are compared with conventional single core hole (SCH) XES signals. The energy shifts and intensity changes of the DCH Emission lines with respect to the corresponding SCH-XES features are fingerprints of the coupling between the second core hole and the occupied orbitals around the DCHs that contain important chemical bonding information of the complex. The difference between delocalized/localized core hole models on DCH VtC-XES is also briefly discussed. We theoretically demonstrate that DCH XES provides subtle information on the local electronic structure around metal centers in transition metal complexes beyond conventional linear XES. Our predicted changes from calculations between SCH-XES and DCH-XES features should be detectable with modern XFEL sources.
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double core hole valence to core x ray Emission Spectroscopy a theoretical exploration using time dependent density functional theory
arXiv: Chemical Physics, 2019Co-Authors: Yu Zhang, Uwe Bergmann, R W Schoenlein, Munira Khalil, Niranjan GovindAbstract:With the help of newly developed X-Ray free-electron laser (XFEL) sources, creating double core holes simultaneously at the same or different atomic sites in a molecule has now become possible. Double core hole (DCH) X-Ray Emission is a new form of X-Ray nonlinear Spectroscopy that can be studied with a XFEL. Here we computationally explore the metal K-edge valence-to-core (VtC) X-Ray Emission Spectroscopy (XES) of metal/metal and metal/ligand double core hole states in a series of transition metal complexes with time-dependent density functional theory. The simulated DCH VtC-XES signals are compared with conventional single core hole (SCH) XES signals. The energy shifts and intensity changes of the DCH Emission lines with respect to the corresponding SCH-XES features are fingerprints of the coupling between the second core hole and the occupied orbitals around the DCHs that contain important chemical bonding information of the complex. The core hole localization effect on DCH VtC-XES is also briefly discussed. We theoretically demonstrate that DCH XES provides subtle information on the local electronic structure around metal centers in transition metal complexes beyond conventional linear XES. Our predicted changes from calculations between SCH-XES and DCH-XES features should be detectable with modern XFEL sources.
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Jan Kern, Vittal K YachandraAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in si...
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x ray Emission Spectroscopy as an in situ diagnostic tool for x ray crystallography of metalloproteins using an x ray free electron laser
Biochemistry, 2018Co-Authors: Thomas Fransson, Thomas Kroll, Dimosthenis Sokaras, Uwe Bergmann, Ruchira Chatterjee, Franklin D Fuller, Clemens Weninger, Roberto Alonsomori, Sheraz Gul, Jan KernAbstract:Serial femtosecond crystallography (SFX) using the ultrashort X-Ray pulses from a X-Ray free-electron laser (XFEL) provides a new way of collecting structural data at room temperature that allows for following the reaction in real time after initiation. XFEL experiments are conducted in a shot-by-shot mode as the sample is destroyed and replenished after each X-Ray pulse, and therefore, monitoring and controlling the data quality by using in situ diagnostic tools is critical. To study metalloenzymes, we developed the use of simultaneous collection of X-Ray diffraction of crystals along with X-Ray Emission Spectroscopy (XES) data that is used as a diagnostic tool for crystallography, by monitoring the chemical state of the metal catalytic center. We have optimized data analysis methods and sample delivery techniques for fast and active feedback to ensure the quality of each batch of samples and the turnover of the catalytic reaction caused by reaction triggering methods. Here, we describe this active in situ feedback system using Photosystem II as an example that catalyzes the oxidation of H2O to O2 at the Mn4CaO5 active site. We used the first moments of the Mn Kβ1,3 Emission spectra, which are sensitive to the oxidation state of Mn, as the primary diagnostics. This approach is applicable to different metalloproteins to determine the integrity of samples and follow changes in the chemical states of the reaction that can be initiated by light or activated by substrates and offers a metric for determining the diffraction images that are used for the final data sets.
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x ray Emission Spectroscopy evidences a central carbon in the nitrogenase iron molybdenum cofactor
Science, 2011Co-Authors: Kyle M Lancaster, Serena Debeer, Uwe Bergmann, Michael Roemelt, Patrick Ettenhuber, Markus W Ribbe, Frank NeeseAbstract:Nitrogenase is a complex enzyme that catalyzes the reduction of dinitrogen to ammonia. Despite insight from structural and biochemical studies, its structure and mechanism await full characterization. An iron-molybdenum cofactor (FeMoco) is thought to be the site of dinitrogen reduction, but the identity of a central atom in this cofactor remains unknown. Fe Kβ X-Ray Emission Spectroscopy (XES) of intact nitrogenase MoFe protein, isolated FeMoco, and the FeMoco-deficient ∆nifB protein indicates that among the candidate atoms oxygen, nitrogen, and carbon, it is carbon that best fits the XES data. The experimental XES is supported by computational efforts, which show that oxidation and spin states do not affect the assignment of the central atom to C4–. Identification of the central atom will drive further studies on its role in catalysis.
