@misc{BaerSchubertMarsenetal., author = {B{\"a}r, Marcus and Schubert, Bj{\"o}rn-Arvid and Marsen, Bj{\"o}rn and Wilks, Regan G. and Blum, M. and Krause, S. and Pookpanratana, Sujitra and Zhang, Y. and Unold, Thomas and Yang, W. and Weinhardt, Lothar and Heske, Clemens and Schock, Hans-Werner}, title = {Cu2ZnSnS4 thin-film solar cell absorbers illuminated by soft x-rays}, series = {Journal of Materials Research}, volume = {27}, journal = {Journal of Materials Research}, number = {8}, issn = {2044-5326}, doi = {10.1557/jmr.2012.59}, pages = {1097 -- 1104}, abstract = {In view of the complexity of thin-film solar cells, which are comprised of a multitude of layers, interfaces, surfaces, elements, impurities, etc., it is crucial to characterize and understand the chemical and electronic structure of these components. Because of the high complexity of the Cu2ZnSn(S,Se)4 compound semiconductor absorber material alone, this is particularly true for kesterite-based devices. Hence, this paper reviews our recent progress in the characterization of Cu2ZnSnS4 (CZTS) thin films. It is demonstrated that a combination of different soft x-ray spectroscopies is an extraordinarily powerful method for illuminating the chemical and electronic material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of these properties. The focus of the article will be on secondary impurity phases, electronic structure, native oxidation, and the CZTS surface composition.}, language = {en} } @misc{WeinhardtBenkertMeyeretal., author = {Weinhardt, Lothar and Benkert, Andreas and Meyer, Frank and Blum, Monika and Wilks, Regan G. and Yang, Wan Li and B{\"a}r, Marcus and Reinert, Friedrich and Heske, Clemens}, title = {Nuclear dynamics and spectator effects in resonant inelastic soft x-ray scattering of gas-phase water molecules}, series = {The journal of chemical physics}, volume = {136}, journal = {The journal of chemical physics}, number = {14}, issn = {1089-7690}, pages = {144311}, abstract = {The electronic structure of gas-phase H2O and D2O molecules has been investigated using resonant inelastic soft x-ray scattering (RIXS). We observe spectator shifts for all valence orbitals when exciting into the lowest three absorption resonances. Strong changes of the relative valence orbital emission intensities are found when exciting into the different absorption resonances, which can be related to the angular anisotropy of the RIXS process. Furthermore, excitation into the 4a1 resonance leads to nuclear dynamics on the time scale of the RIXS process; we find evidence for vibrational coupling and molecular dissociation in both, the spectator and the participant emission.}, language = {en} } @misc{BlumOdeliusWeinhardtetal., author = {Blum, M. and Odelius, Michael and Weinhardt, Lothar and Pookpanratana, Sujitra and B{\"a}r, Marcus and Zhang, Y. and Fuchs, Oliver and Yang, W. and Umbach, Eberhard and Heske, Clemens}, title = {Ultrafast Proton Dynamics in Aqueous Amino Acid Solutions Studied by Resonant Inelastic Soft X‑ray Scattering}, series = {The Journal of physical chemistry : B}, volume = {116}, journal = {The Journal of physical chemistry : B}, number = {46}, issn = {1520-5207}, pages = {13757 -- 13764}, abstract = {Resonant inelastic soft X-ray scattering (RIXS) has been used to study the electronic structure of glycine and lysine in aqueous solution. Upon variation of the pH value of the solution from acidic to basic, major changes of the nitrogen K edge RIXS data are observed for both amino acids, which are associated with the protonation and deprotonation of the amino groups. The experimental results are compared with simulations based on density functional theory, yielding a detailed understanding of the spectral changes, as well as insights into the ultrafast proton dynamics in the intermediate core-excited/ionized state of the RIXS process.}, language = {en} } @misc{HofmannYuFolseetal., author = {Hofmann, Timo and Yu, Ted H. and Folse, Michael and Weinhardt, Lothar and B{\"a}r, Marcus and Zhang, Yufeng and Merinov, Boris V. and Myers, Deborah J. and Goddard, William A. and Heske, Clemens}, title = {Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d‑Band Energies of Metals for Catalytic Applications}, series = {The Journal of Physical Chemistry : C}, volume = {116}, journal = {The Journal of Physical Chemistry : C}, number = {45}, issn = {1932-7455}, pages = {24016 -- 24026}, abstract = {The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, He II, and monochromatized Al Kα excitation. The influence of final states, photoionization cross-section, and adsorption of residual gas molecules in an ultrahigh vacuum environment are discussed in terms of their impact on the VBS. We find that VBSs recorded with monochromatized Al Kα radiation are most closely comparable to the ground state density of states (DOS) derived from quantum mechanics calculations. We use the Al Kα-excited PES measurements to correct the energy scale of the calculated ground-state DOS to approximate the "true" ground-state d-band structure. Finally, we use this data to test the d-band center model commonly used to predict the electronicproperty/ catalytic-activity relationship of metals. We find that a simple continuous dependence of activity on d-band center position is not supported by our results (both experimentally and computationally).}, language = {en} }