Ronald Frahm

BAMline: the first hard X-ray beamline at BESSY II

The first hard X-ray beamline at BESSY II will be installed by BAM and PTB at a superconducting 7 T wavelength shifter. The main optical elements of the beamline are a Double-Multilayer-Monochromator and a Double-Crystal-Monochromator. The two devices can be used separately or in-line. Main applications of monochromatic radiation with photon energies up to 50 keV are X-ray fluorescence analysis, micro-computed tomography, X-ray topography, detector calibration and reflectometry. Calculable undispersed radiation up to 200 keV will be available for radiometric applications.

Generating Highly Active Partially Oxidized Platinum during Oxidation of Carbon Monoxide over Pt/Al2O3: In Situ, Time-Resolved, and High-Energy-Resolution X-Ray Absorption Spectroscopy

High activity is generated by sudden formation of disordered oxidic platinum over a platinum catalyst supported on alumina (see picture). High temperature and low concentration of carbon monoxide are required to generate high activity.

Determination of secondary phases in kesterite Cu2ZnSnS4 thin films by x-ray absorption near edge structure analysis

Secondary phases in Cu2ZnSnS4 (CZTS) are investigated by x-ray absorption spectroscopy. Evaluating the x-ray absorption near edge structure at the sulfur K-edge, we show that secondary phases exhibit sufficiently distinct features to allow their quantitative determination with high accuracy. We are able to quantify the ZnS fraction with an absolute accuracy of ±3%, by applying linear combination analysis using reference spectra. We find that even in CZTS thin films with [Sn]/[Zn] ≈ 1, a significant amount of ZnS can be present. A strong correlation of the ZnS-content with the degradation of the electrical performance of solar cells is observed.

Mapping the chemical states of an element inside a sample using tomographic x-ray absorption spectroscopy

Hard x-ray absorption spectroscopy is combined with scanning microtomography to reconstruct full near-edge spectra of an elemental species at each location on an arbitrary virtual section through a sample. These spectra reveal the local concentrations of different chemical compounds of the absorbing element inside the sample and give insight into the oxidation state, the local atomic structure, and the local projected free density of states. The method is implemented by combining a quick scanning monochromator and data acquisition system with a scanning microprobe setup based on refractive x-ray lenses.

X-RAY UNDULATOR BEAMLINE BW1 AT DORIS III

The BW1 x‐ray undulator beamline at HASYLAB offers high intensity for a wide variety of diffraction and absorption experiments. The x‐ray undulator is a 4‐m‐long device with 127 periods. At 4.5 GeV energy of the positron storage ring DORIS III it can be tuned in its 3rd harmonic to photon energies from 9 to 15 keV. The basis for such a beamline is a high precision monochromator which has to be able to cope with high heat loads from the insertion device. There are four operating modes: (i) focused white beam using two mirrors with a cutoff energy of approximately 11 keV, (ii) focused monochromatic beam using both mirrors with a cutoff energy of ≊12 keV and a double‐crystal monochromator, (iii) unfocused monochromatic beam using the monochromator without mirrors, and (iv) focused monochromatic beam using the monochromator without mirrors but with a sagittally focusing second crystal. Currently, a horizontal diffractometer for the investigation of liquid surfaces, an ultrahigh vacuum chamber for standing wav...

Investigation of Room Temperature Oxidation of Cu in Air by Yoneda‐XAFS

The structure of thin copper oxide layers which are formed on metallic Cu due to the exposure to air are investigated with Yoneda‐XAFS and ReflEXAFS. The measured Yoneda‐XAFS data were compared to quantitative model calculations in the framework of the distorted wave Born approximation (DWBA) assuming different model structures for the oxide layer. Yoneda‐XAFS fine structure spectra measured for various different grazing angles show that the experimental data are best described by a model structure consisting of a duplex type oxide layer with an outer layer of CuO (tenorite) in direct contact with the gas atmosphere and an inner Cu2O (cuprite) layer at the interface to the underlying Cu metal.

Quick-EXAFS setup at the SuperXAS beamline for in situ X-ray absorption spectroscopy with 10 ms time resolution

A new quick-scanning EXAFS (QEXAFS) monochromator, ionization chambers and data acquisition system have been developed and installed at the SuperXAS beamline at the Swiss Light Source to reach a temporal resolution of 10 ms.

Piezo-QEXAFS: advances in time-resolved X-ray absorption spectroscopy.

The Piezo-QEXAFS technique is a novel tool for time-resolved X-ray absorption spectroscopy in the hard X-ray range. Monochromator components consisting of specialized tilt stages to perform fast energy scans, lightweight crystal holders, bending mechanics, and control electronics are being installed and commissioned. It is planned to perform fast EXAFS scans with time resolution in the millisecond range. With Piezo-QEXAFS all typical X-ray absorption experiments will be possible as it retains the standard linear geometry. The achieved time resolution opens interesting insights into the dynamics of phase transitions and chemical reactions.

Novel angular encoder for a quick-extended x-ray absorption fine structure monochromator.

New concepts for time-resolved x-ray absorption spectroscopy using the quick-extended x-ray absorption fine structure (QEXAFS) method are presented. QEXAFS is a powerful tool to gain structural information about, e.g., fast chemical reactions or phase transitions on a subsecond scale. This can be achieved with a monochromator design that employs a channel-cut crystal on a cam driven tilt table for rapid angular oscillations of the Bragg angle. A new angular encoder system and a new data acquisition were described and characterized that were applied to a QEXAFS monochromator to get spectra with a directly measured accurate energy scale. New electronics were designed to allow a fast acquisition of the Bragg angle values and the absorption data during the measurements simultaneously.

Hydrothermal Synthesis of Bi6S2O15 Nanowires: Structural, in situ EXAFS, and Humidity‐Sensing Studies

J. Stötzel, Prof. R. Frahm Department of Physics, University of Wuppertal 42097 Wuppertal (Germany) [ ] We gratefully acknowledge the Swiss Light Source (SLS, Villigen, Switzerland) for providing beam time at the superXAS beamline for QEXAFS experiments. We are grateful to M. J. Beier for help and J.D.G. to DANSCATT for financial support. The support of the Electron Microscopy ETH Zurich, EMEZ, and Center for Microscopy and Image Analysis, University of Zurich, is acknowledged. We are grateful to Prof. W. Bensch and Dr. N. Pienack (University of Kiel, Germany) for in situ EDXRD experiments and to HASYLAB (DESY, Hamburg, Germany) for providing beam time at beamline F3. Financial support from the Sino Swiss Science and Technology Cooperation (SSSTC, project no. EG05-092008) is gratefully acknowledged. We thank the Swiss National Science Foundation (SNF Professorship PP002 114711/1) and the University of Zurich for financial support. : Supporting Information is available on the WWW under http:// www.small-journal.com or from the author.