Storage Ring BESSY Research Articles

The Materials Science Beamline EDDI for Energy-Dispersive Analysis of Subsurface Residual Stress Gradients

In April 2005 the materials science beamline EDDI (Energy Dispersive DIffraction), which the HMI operates at the Berlin synchrotron storage ring BESSY, started user service. The high energy white synchrotron beam up to about 150 keV used for the diffraction experiments is provided by a superconducting 7 Tesla multipole wiggler. Starting with some basic information on the technical parameters of the beamline, its set-up and measuring facilities, the paper focuses on the application of white beam diffraction to the analysis of residual stress fields in the near surface zone of polycrystalline materials. The concept of a program system is introduced, which we offer to our users for preparing and evaluating their measurements performed at the EDDI beamline.

Femtosecond Undulator Radiation from Sliced Electron Bunches

At the 1.7-GeV electron storage ring BESSY II, a first source of synchrotron radiation with 100 fs pulse duration, variable (linear and circular) polarization, tunable photon energy (300 to 1400 eV), and excellent signal-to-background ratio was constructed and is now in routine operation.

Calibration and characterization of semiconductor X-ray detectors with synchrotron radiation

Quantitative measurements of X-rays require absolutely calibrated detectors. In the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II in Berlin, X-ray detectors can be calibrated with low uncertainties. Two complementary approaches are realized for energy-dispersive detectors. One approach uses the storage ring as primary source standard and the detector response to the calculable spectral photon flux is measured in the undispersed synchrotron radiation. This requires the operation of the storage ring with only a few stored electrons. The other approach is the comparison to a primary detector standard, mainly a cryogenic electrical substitution radiometer. Here, monochromatized radiation of very high spectral purity has to be used which is available at different beamlines in the laboratory in the photon energy range from the UV up to about 120 keV. This method can also be applied for the calibration of non-energy-dispersive detectors. With monochromatized radiation, the response function of energy-dispersive detectors is recorded and compared to Monte Carlo simulations. A photon-energy-dependent parameterization of the response function allows deconvoluting the experimental spectra. The responsivity of Si photodiodes and the detection efficiency of Si(Li), HPGe and CdTe detectors are determined with low uncertainties in a broad spectral range.

Nitrogen and sulfur compounds in coastal Antarctic fine aerosol particles—an insight using non-destructive X-ray microanalytical methods

The capabilities of X-ray microanalytical methods, such as a near edge X-ray absorption fine structure (NEXAFS) investigation in conjunction with total reflection X-ray fluorescence (TXRF) analysis, as well as low- Z particle electron probe X-ray microanalysis (EPMA) to characterize fine Antarctic aerosol samples are demonstrated. Both techniques provided information on low- Z elements such as C, N and O. Size-segregated fine aerosol samples were collected at the Italian base at Terra Nova Bay (Antarctica) in February 2004. For comparative purposes, aerosol samples were also collected near the sea-shore in Alghero (Sardinia, Italy), in June 2004. The TXRF-NEXAFS measurements were carried out at the PGM monochromator beamline for undulator radiation in the PTB laboratory at the electron storage ring BESSY II. It was possible to quantify the molar ratio of ammonium and nitrate based on linear combinations of standard reference spectra of (NH 4) 2SO 4 and NaNO 3. Using TXRF-NEXAFS, the ammonium-to-nitrate ratio was determined in Antarctic fine aerosols collected from less than 2 m 3 of air, i.e. considerably lower than the sampling volumes usually used for ion chromatography analyses (30 m 3). This reduced sampling volume can enable the characterization of Antarctic aerosols to be done in higher temporal resolution. For Antarctic fine aerosols in the size range of 0.25–0.5 μm, nitrogen was observed to be present as almost entirely ammonium species. When the size of aerosol particles increases in the range of 0.25–2 μm, the content of ammonium decreases and yet the content of nitrate increases. An aerosol sample collected at Terra Nova Bay was investigated by the use of low- Z particle EPMA at a liquid nitrogen temperature in order to minimize beam damage of nitrogen-rich particles. Single-particle analytical results of 160 individual particles supported the TXRF-NEXAFS's observation that both ammonium-rich and nitrate-rich particles exist in the size range of 1–2 μm. Some particles were observed to contain both ammonium and nitrate species and yet pure ammonium nitrate particles were not encountered. The stoichiometry of the main chemical component of particles containing nitrogen and sulfur as major elements was found to be NH 4HSO 4.

Absolute measurement of F_2-laser power at 157 nm

We report a comparison of laser power measurements at the F2-laser wavelength of 157 nm made at two facilities of the Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute. At the PTB laboratory at the electron storage ring BESSY II in Berlin, the scale for laser power was directly traced to a cryogenic radiometer operating at 157 nm, whereas at the PTB laser radiometry facility in Braunschweig the calibration of transfer detectors was performed with a newly developed standard for laser power at 157 nm, which is traceable in several steps to a cryogenic radiometer operating at 633 nm. The comparison was performed under vacuum conditions with laser pulse energies of approximately 10 microJ, however with different average powers because different primary standard radiometers were used. The relative deviation for the responsivity of the transfer detector was 4.8% and thus within the combined standard uncertainty.

Detector Calibration and Measurement of Fundamental Parameters for X-Ray Spectrometry

Energy-dispersive X-ray spectrometry offers the opportunity for a fast and reliable determination of the composition of a specimen. For fundamental parameter based quantification, detailed knowledge of the X-ray generation cross sections and of the detection system’s efficiency is required. The detection efficiency is determined comparing the measured and calculated spectrum of undispersed synchrotron radiation (SR) from the electron storage ring BESSY II in the spectral range from 0.1 keV to 100 keV. Alternatively, monochromatized SR in the spectral range from 0.1 keV to 60 keV is used to determine the detection efficiency with a typical relative uncertainty of 1% to 2% by direct comparison with a reference detector. Employing well-calibrated detectors and monochromatized SR of well-known radiant power and high spectral purity, fluorescence yields have been investigated and resonant Raman scattering was studied as an example of a basic effect creating spectral background.

The PTB high-accuracy spectral responsivity scale in the VUV and x-ray range

At the electron storage ring BESSY II, the Physikalisch-Technische Bundesanstalt operates ten experimental stations at six synchrotron radiation beamlines for photon metrology in the spectral range from ultraviolet radiation to x-rays. Five of these beamlines are used to realize and disseminate a scale of spectral responsivity for photodetectors. Detector calibration is based on the use of cryogenic radiometers as primary detector standards. The current status of instrumentation and measurement capabilities is described. Best measurement capabilities (k = 2) for the calibration of photodiodes vary between 0.4% and 2.3%.

The EUV metrology program of PTB

The development of EUV lithography (EUVL) is critically based on the availability of a suitable metrology. The industrial demand for high accuracy characterization of EUV components is met at the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) operated at the electron storage ring BESSY II. Using stable and well-characterized synchrotron radiation, PTB performs – in cooperation with industry – the characterization of optical components (reflectometry), the calibration and characterization of EUV radiation detectors and sources and lifetime characterization of optics and sensors. Recent examples from either of these working areas are presented.

Femtosecond Terahertz Radiation from Femtoslicing at BESSY

Femtosecond far-infrared radiation pulses in the THz spectral range were observed as a consequence of the energy modulation of 1.7 GeV electrons by femtosecond laser pulses in the BESSY storage ring in order to generate femtosecond x-ray pulses ("femtoslicing"). In addition to being crucial for diagnostics of the laser-electron interaction, the THz radiation itself is useful for experiments where intense ultrashort THz pulses of well-defined temporal and spectral characteristics are required.

X-ray resonant Raman scattering on Ni employing polarized and unpolarized exciting radiation

The X-ray resonant Raman scattering effect on nickel was studied by means of monochromatic polarized and unpolarized exciting radiation, respectively. Experiments involving polarized exciting radiation were carried out at the four crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt for synchrotron radiation from 4 to 10 keV at the electron storage ring BESSY II. Resonant Raman spectra of thin Ni foils were recorded at the Cu-K α (8041 eV) exciting beam energy. In the Institute of Nuclear Physics of the N.C.S.R. Demokritos, the resonant Raman spectrum of a thick nickel target was also recorded for an unpolarized Cu-K α (8041 eV) exciting beam produced after the ionization of a thick Cu target by 1.7 MeV protons in a triaxial, orthogonal geometry. In the present work, the individual spectral characteristics and the methodological approaches adopted for the extraction of the Ni-RRS cross sections, with respect to each mode of excitation, are presented, compared and discussed. An excellent agreement was found between the Ni KL-RRS cross sections determined for polarized and unpolarized exciting radiation confirming the theoretical predictions within the experimental uncertainties achieved.

Thickness determination for Cu and Ni nanolayers: Comparison of completely reference-free fundamental parameter-based X-ray fluorescence analysis and X-ray reflectometry

Monochromatized synchrotron radiation of the electron storage ring BESSY II has been used for the non-destructive thickness determination of nanolayered materials by two different methods. The aim of these investigations was the comparison of completely reference-free fundamental parameter-based X-ray fluorescence analysis with X-ray reflectometry to validate the quantification of X-ray fluorescence analysis as an absolute method. For this purpose, Cu and Ni layers with a thickness varying between 5 nm and 50 nm as well as double layers of both metals deposited on Si have been studied. In X-ray reflectometry characterization experiments, the tunability of the photon energy allows the determination of not only the total layer thickness but also the individual layer thicknesses of the Cu/Ni double-layer systems. Reference-free X-ray fluorescence analysis involves both the fundamental parameter approach and the knowledge of all relevant experimental parameters obtained by instrumentation calibrated absolutely. The layer thickness determined by both methods agreed within their combined uncertainties. In view of the limits of X-ray reflectometry for very thin layers, laterally inhomogeneous samples, and multi-elemental layer compositions, reference-free X-ray fluorescence analysis offers the potential for the thickness determination of such samples.

Stability of vacuum-ultraviolet radiometric transfer standards: Electron cyclotron resonance versus hollow cathode source

Established transfer standards such as Penning and hollow cathode discharge sources suffer from limited spectral range and, in particular, a limited lifetime and stability due to electrode erosion. The development of a vacuum-ultraviolet radiation source based on an electron cyclotron resonance (ECR)-created plasma might overcome these limitations. To test such a source with regard to its usefulness as radiometric transfer standard, the emission intensity of a Ne plasma was monitored over an operation period of 180 days, with regard to stability and reproducibility in the 50–75 nm wavelength range. For comparison and calibration, a hollow cathode was used as transfer standard traceable to the electron storage ring BESSY II as primary standard. It was found that the ECR source exceeded the lifetime of the hollow cathode source by far, offering a more balanced spectral emission line variety with similar stability.

PIN diamond detector development for LYRA, the solar VUV radiometer on board PROBA II

LYRA (the LYman-alpha RAdiometer onboard PROBA-2) will use diamond detectors for the first time in space solar physics. A set of measurement campaigns was designed to obtain the EUV-to-VIS characterization of the diamond detectors and knowledge of their modes of operation. The outputs of this campaign provide the reference data needed for the optimization of the detectors, and for the LYRA channels definition. The measurements of responsivity in EUV and VUV spectral ranges have been carried out by the Physkalisch-Technische Bundesanstalt (PTB) in Germany at the electron storage ring BESSY II. The detectors spectral responsivity measurements R(λ) was done for the following wavelength ranges: 40 to 80 nm, 80 to 120 nm and 120 to 240 nm. The longer wavelength range from 210 nm to 827 nm was measured with the monochromatic light by using a Xe-lamp at IMO-IMOMEC. The diodes exhibit high photoresponse in the deep UV region and over five orders of magnitude in discrimination between deep UV (200 nm) and visible light (550 nm). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of an Nb/Al/AlO x/Al/Nb superconducting tunnel junction detector with a very high spatial resolution in the soft X-ray range

A cryogenic superconducting tunnel junction (STJ) detector device was characterized and evaluated. It consists of an Nb/Al/AlO x /Al/Nb layered structure and contains four STJs with sizes between 70×70 μm 2 and 200×200 μm 2. For dedicated characterization experiments we employed monochromatized undulator radiation of high spectral purity, which is available at the PTB Radiometry laboratory at the electron storage ring BESSY II. We investigated the STJ energy resolution at various photon energies below 1500 eV with respect to the detector area, the illuminated area, the incident photon energy and the count rate while recording the detector response. Applying a 50 μm-aperture to collimate the incident beam, we achieved an energy resolution of less than 10 eV at a photon energy of up to 900 eV for the 141×141 μm 2-sized STJ. When a 5 μm-pinhole was employed approximately 25 mm in front of the STJ for the beam collimation, the energy resolution was independent of the detector size — between 5 and 9 eV for energies between 0.3 and 1.5 keV. Furthermore, we scanned both the effective detector area and the adjacent regions with a beam defined by a 5 μm-pinhole offering a beam width smaller than 18 μm. In this scan, both the energy resolution and the pulse height scale changed strongly within the central area of the STJ. These effects and those originating from the leads and edges are discussed. In addition, these findings contribute to understanding the decreasing energy resolution for increasing effective detector areas. We expect that such spatially resolved measurements will prove to be a proper method for detector evaluation and contribute to improving the detector layouts.

Pulse energy measurements of extreme ultraviolet undulator radiation

A detector system based on the photoionization of rare gases at low particle densities hasbeen developed for absolute photon flux measurements of highly intense andextremely pulsed radiation in the VUV and EUV spectral range. Due to its widedynamic range, the device can be calibrated with spectrally dispersed synchrotronradiation at low photon intensities but applied with high power sources. Thedetector is free of degradation and almost transparent, and therefore suitable forintensity monitoring. We describe here the application of the detector for fluxmeasurements at a beamline for undispersed deflected undulator radiation in the PTBRadiometry Laboratory at the electron storage ring BESSY II. In the single-bunchoperation mode of BESSY II, measurements of the pulse energy down to 3 nJfor single EUV pulses have been performed. This demonstrates the capabilityof the gas detector for a broad range of applications with pulsed EUV sources.

Analysis of organic contaminants on Si wafers with TXRF-NEXAFS

Organic contamination is starting to play an important role in the production and quality control of Si wafers. For the traceability of the source of contamination, information on the chemical binding conditions is very valuable. A near edge X-ray absorption fine structure (NEXAFS) investigation is the natural development of total reflection X-ray fluorescence (TXRF) analysis of the wafer surfaces able to solve the problem of speciation. The plane grating monochromator beamline for undulator radiation of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II, which provides photon energies between 30 eV and 1.9 keV for the specimen excitation, is an ideal excitation source for TXRF-NEXAFS experiments that require a high resolving power and a sufficient photon flux for trace analysis of low Z elements. The contaminants have been diluted and deposited as droplets on wafer pieces thoroughly cleaned after the cutting. The K edges of C, N, O have been examined. Some discrepancies have been found in the analysis of the same compounds in two different beamtimes; molecular orientation is pointed to as the cause for the difference in magnitude of the resonances. The unintentional contamination has been identified as mainly composed of aliphatic chains.

Solar-Blind Diamond Detectors for Lyra, the Solar VUV Radiometer on Board Proba II

Fabrication, packaging and experimental results on the calibration of metal-semiconductor-metal (MSM) photodetectors made on diamond are reported. LYRA (Lyman-α RAdiometer onboard PROBA-2) will use diamond detectors for the first time in space for a solar physics instrument. A set of measurement campaigns was designed to obtain the XUV-to-VIS responsivity of the devices and other characterizations. The measurements of responsivity in EUV and VUV spectral ranges (40–240 nm) have been carried out by the Physkalisch-Technische Bundesanstalt (PTB) in Germany at the electron storage ring BESSY II. The longer wavelength range from 210 to 1127 nm was measured with monochromatic light by using a Xe-lamp at IMO-IMOMEC. The diamond detectors exhibit a photoresponse which lie in the 35–65 mA/W range at 200 nm (corresponding to an external quantum efficiency of 20–40%) and indicate a visible rejection ratio (200–500 nm) higher than four orders of magnitude.

Double pinhole diffraction of white synchrotron radiation

The spatial coherence of hard X-rays provided by a bending magnet of the storage ring BESSY II was investigated by performing Young's interference experiment. The interference pattern was created by the diffraction of two 2 μm pinholes drilled into a thin tantalum foil by focused ion sputtering. Using an energy-dispersive detector with an energy resolution of 200 eV the interference patterns were detected simultaneously between 5 keV< E<16 keV scanning a 5 μm pinhole through the detector window. The set-up is suitable to characterize the coherence properties of the beamline in a simple manner, i.e. to deduce parameters as the effective source size, the coherence length and the visibility. For the present case the visibility was close to 100% at 5 keV and decreased to 20% at 16 keV.

Facilities and Methods for the High‐Throughput Crystal Structural Analysis of Human Proteins

AbstractFor Abstract see ChemInform Abstract in Full Text.

Investigation of high-resolution superconducting tunnel junction detectors for low-energy X-ray fluorescence analysis

The energy resolution of conventional semiconductor detectors is insufficient for simultaneously separating the leading fluorescence lines of low Z and medium Z materials in the soft X-ray regime. It is therefore important to investigate alternative detection instruments offering higher energy resolution and evaluate their applicability to soft X-ray fluorescence (XRF) analysis. In this paper, various results of the characterization and evaluation of a cryogenic superconducting tunnel junction (STJ) detector, which was provided to the Physikalisch-Technische Bundesanstalt (PTB) by the Lawrence Livermore National Laboratory, are given with respect to both detector response functions and XRF. For this investigation, monochromatized undulator radiation of high spectral purity, available to the PTB X-ray radiometry laboratory at the electron storage ring BESSY II, was employed, by which it was possible to record the STJ response functions at various photon energies of interest ranging from 180 to 1600 eV. By scanning the effective detector area and the adjacent substrate and leads, relevant artefacts of the detector response were identified.