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Eggenstein-Leopoldshafen, Germany

Seiler A.,Institute for Photon Science and Synchrotron Radiation | Seiler A.,Laboratory for Applications of Synchrotron Radiation | Ibrahimkutty S.,Institute for Photon Science and Synchrotron Radiation | Ibrahimkutty S.,Laboratory for Applications of Synchrotron Radiation | And 14 more authors.
Journal of Physical Chemistry C | Year: 2016

The thermal stability of parallel, high aspect ratio DySi2 nanowires and nanoislands self-organized on vicinal Si(001) is investigated as a function of the annealing temperature from room temperature up to 760 °C by in situ grazing incidence small-angle X-ray scattering (GISAXS). A transformation of the nanoobjects has been observed above a temperature of 500 °C. The nanowires collapse forming small islands, while the nanoislands grow in size due to Ostwald ripening. The formation of facets is observed during annealing. A comprehensive understanding of the surface morphology changes is obtained by complementing the in situ GISAXS experiment with atomic force microscopy measurements. © 2016 American Chemical Society. Source


Bar M.,Helmholtz Center Berlin | Bar M.,University of Nevada, Las Vegas | Starr D.E.,TU Brandenburg | Lambertz A.,Institute for Energy Research of Germany | And 12 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Hydrogenated microcrystalline silicon oxide (μc-SiOx:H) layers are one alternative approach to ensure sufficient interlayer charge transport while maintaining high transparency and good passivation in Si-based solar cells. We have used a combination of complementary x-ray and electron spectroscopies to study the chemical and electronic structure of the μc-SiOx:H material system. With these techniques, we monitor the transition from a purely Si-based crystalline bonding network to a silicon oxide dominated environment, coinciding with a significant decrease of the material's conductivity. Most Si-based solar cell structures contain emitter/contact/passivation layers. Ideally, these layers fulfill their desired task (i.e., induce a sufficiently high internal electric field, ensure a good electric contact, and passivate the interfaces of the absorber) without absorbing light. Usually this leads to a trade-off in which a higher transparency can only be realized at the expense of the layer's ability to properly fulfill its task. One alternative approach is to use hydrogenated microcrystalline silicon oxide (μc-SiOx:H), a mixture of microcrystalline silicon and amorphous silicon (sub)oxide. The crystalline Si regions allow charge transport, while the oxide matrix maintains a high transparency. To date, it is still unclear how in detail the oxygen content influences the electronic structure of the μc-SiOx:H mixed phase material. To address this question, we have studied the chemical and electronic structure of the μc-SiOx:H (0 ≤x = O/Si ≤1) system with a combination of complementary x-ray and electron spectroscopies. The different surface sensitivities of the employed techniques help to reduce the impact of surface oxides on the spectral interpretation. For all samples, we find the valence band maximum to be located at a similar energy with respect to the Fermi energy. However, for x > 0.5, we observe a pronounced decrease of Si 3s - Si 3p hybridization in favor of Si 3p - O 2p hybridization in the upper valence band. This coincides with a significant increase of the material's resistivity, possibly indicating the breakdown of the conducting crystalline Si network. © 2014 SPIE. Source


Blum M.,University of Nevada, Las Vegas | Blum M.,Lawrence Berkeley National Laboratory | Blum M.,University of Wurzburg | Odelius M.,Albanova University Center | And 14 more authors.
Journal of Physical Chemistry B | Year: 2012

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. © 2012 American Chemical Society. Source


Weinhardt L.,Institute for Photon Science and Synchrotron Radiation | Weinhardt L.,University of Wurzburg | Weinhardt L.,University of Nevada, Las Vegas | Blumc M.,University of Nevada, Las Vegas | And 14 more authors.
Journal of Electron Spectroscopy and Related Phenomena | Year: 2013

We summarize our development of instrumentation for the study of liquids, aqueous solutions, and liquid/solid interfaces using resonant inelastic soft X-ray scattering (RIXS) and illustrate the value of the experimental approach with a few instructional examples. Using a high-transmission, high-resolution soft X-ray spectrometer, we are able to measure complete RIXS maps, i.e., record the soft X-ray emission intensity as a function of emission and absorption energy. As a first example, we show that a comparison of RIXS maps of "normal" and deuterated liquid and gas-phase water allows us to identify dissociation processes on the time scale of the oxygen 1 s core-hole lifetime. Similar dissociation effects are found for aqueous solutions of ammonia and amino acids. For the latter, the pH value has a strong influence on the nitrogen K emission spectra, which can thus be used to identify protonation and deprotonation processes in the solution. Finally, we review the investigation of the interface between liquid water and a CuIn(S,Se)2 thin-film solar cell absorber, demonstrating the power of the technique to study liquid-solid interfaces in real-world systems. Under X-ray irradiation, the formation of sulfate on the absorber surface can be found. © 2012 Elsevier B.V. All rights reserved. Source

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