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Nature photonics 14(6), 391 - 397 (2020). doi:10.1038/s41566-020-0607-z, The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created., Published by Nature Publ. Group, London [u.a.]

Defect structure of Czochralski grown (1 1 1) oriented silicon single crystals (Cz-Si), irradiated with fast neutrons (energy 5 MeV, dose 5×10 16 cm −2 ) and annealed at up to 1400 K, also under hydrostatic Ar pressure equal to 1.1 GPa, has been investigated by high-resolution X-ray diffraction and synchrotron topography at HASY Laboratory. The annealing, especially at 1270 and 1400 K, results in precipitation of interstitial oxygen and creation of extended defects. A thermally induced oxygen precipitation at high temperatures–pressures in neutron-irradiated Cz-Si reveals the irradiation-related history of investigated samples.

Samples cut out from different regions of SrLaGaO 4 (SLG) single crystal grown along [001]-direction were studied with a number of X-ray diffraction topographic methods exploring both conventional and synchrotron X-ray sources. The synchrotron investigation included in particular white beam projection transmission topography at ultra short wavelength and taking monochromatic beam topographs at different points of the rocking curves at different azimuths. The methods enabled the evaluation of the character of lattice deformation connected with the characteristic 'rod-like' defects observed in the core region of the crystal. A shrinkage of the material inside the defects was indicated.

Highly perfect (00.1) oriented 6H–SiC wafers were implanted with 2 MeV As + ions to a number of fluencies in the range from 5 × 10 12 cm −2 to 1 × 10 14 cm −2 and examined with synchrotron X-ray diffraction methods and RBS/channeling method. The X-ray methods included the investigation of rocking curves recorded with a small 50 × 50 μm 2 probe beam and white beam Bragg-Case section and projection topography. The implanted layers provided distinct interference maxima in the rocking curves and interference fringes in Bragg-Case section topographies (strain modulation fringes). A good visibility of interference maxima enabled effective evaluation of the strain profile by fitting the theoretical rocking curves to the experimental ones. The evaluated strain profiles approximated by browsed Gaussian curves were similar to the distribution of point defects calculated with SRIM 2008 code. The profiles were similar to the defect distribution determined from the channeling measurements.

Czochralski grown 1 1 1 oriented Si 0.986 Ge 0.014 and Si 0.974 Ge 0.026 samples, with interstitial oxygen concentration 8 × 10 17 cm −3 , were processed for 5 h at 1270/1400 K (HT), under Ar pressure 10 5 Pa or 1.1 GPa (HP). Defect structure of Si–Ge was determined by synchrotron topography, high resolution X-ray diffractometry, infrared spectrometry and photoluminescence (PL) measurements. Topography of Si–Ge reveals so-called striations, related to Ge segregation. X-ray diffuse scattering is most pronounced for processed Si 0.974 Ge 0.026 ; its intensity decreases with HT (HP). Processing, especially under HP, results in a changed lattice parameter, e.g. for Si 0.974 Ge 0.026 processed at 1270 K under 1.1 GPa, a = 0.543444(5) nm while equals to 0.543301(5) nm for the as-grown sample. Intensity of PL at about 1.07 eV, related to the presence of electron hole droplets (EHD), decreased after processing at HT-(HP), evidencing out-annealing of point-like defects. Defects created in Si–Ge are in part related to tiny precipitates of oxygen. Dislocations are practically absent in processed Si–Ge. One can hope to apply HT-HP processing to improve structural perfection of Si–Ge.

SrLaGaO4 single crystals are perspective substrate materials for high temperature superconductors thin films, elements of thermal radiation receivers and other electronic devices. The defect structure of the Czochralski grown SrLaGaO4 crystal was investigated by means of X-ray topography exploring both conventional and synchrotron sources. The crystal lattice defects in the core region of the crystal were investigated. The regular network of defects arranged in rows only in 〈100〉 direction was observed. Owing to high resolution of synchrotron radiation white beam back reflection topographs one can distinguish individual spots forming the lines of the rows. It can be supposed that these elongated rod-like volume defects are located in {100} lattice planes forming a kind of walls. They are built approximately of the same phase as crystal but crystallize at a different moment than a rest of the crystal due to the constitutional supercooling.

A Ca 0.5 Sr 0.5 NdAlO 4 single crystal grown by the Czochralski method in the [1 0 0] direction was investigated by means of conventional projection X-ray topography, and by means of synchrotron white beam and monochromatic beam topography. The topographic investigation revealed growth striations with strong black diffraction contrasts distributed periodically in the form of concentric rings, and a significant number of resolved defects. Some of these defects seem to be associated with precipitates, while others form linear diffraction contrasts located perpendicularly to the striation stripes. The last category of defects can be somehow associated with dislocations, but provides much more intense and complex diffraction contrast that can be expected for individual dislocations. A significant lattice deformation associated with striation was revealed with some of the synchrotron topographic methods, particularly back-reflection white beam topography with fine mesh placed behind the crystal and transmission synchrotron section topography, where a characteristic bending of the section image was observed. The transmission section topographs provided also good visibility of segregation fringes in the plane intersected by the beam, corresponding to the subsequent positions of the growth surface.

The undoped Yb3Al5O12 (YbAG) single crystals and doped with 1.5, 10 and 30 at% erbium were grown by the Czochralski method. The YbAG crystals offer efficient emission of laser beam of 2.94 µm and 1.55 µm important for practical applications in communication and medicine. The crystals were investigated by various synchrotron X-ray diffraction methods including white beam topographic methods, monochromatic beam topography and recording of the rocking curves. The experiments were performed at E2 and F1 experimental stations in HASYLAB. The investigations proved a good crystallographic perfection of the crystals, in most cases revealing only segregation fringes and growth facets. The crystallographic identification of the facets was performed together with direct evaluation of growth front radius from the transmission section topographs. Relative lattice parameter changes connected with erbium segregation were found to be less than 2 × 10-5 inside the segregation fringes and 8 × 10-5 in the facets. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In x Ga 1− x As layers on InP substrate can be subjected to compressive or tensile strain due to lattice parameter differences depending on the alloy composition. In order to examine in details the strain of InGaAs/InP epiatxial layers and its evolution after subjecting the layers to annealing at high pressure, X-ray synchrotron topography, high resolution X-ray diffraction and atomic force microscopy have been employed. The data show that the changes of structural properties of the InGaAs layers subjected to high temperature–high pressure treatment at 670 K–1.2 Gpa, strongly depend on initial strain state and defect structure. The annealing of samples under high pressure results in change of strain in tensile layers only. The behaviour of observed defects is discussed.

The GdCa 4 O(BO 3 ) 3 single crystals of monoclinic structure grown by the Czochralski technique were investigated by the synchrotron radiation white beam (SRWB) and conventional X-ray topography. The samples cut out parallel to the crystal growth axis b have been investigated in order to reveal the distribution of defects along the growth axis. Dislocations bundles, correlated with periodical changes of crystal diameter and large volume defects have been observed. The white beam synchrotron projection topography allowed better recognition of many details of the defect structure.

Strontium lantanum gallate SrLaGaO 4 tetragonal single crystal was investigated by white beam synchrotron radiation topography. Projection and section topographs were taken in back reflection and transmission geometry. The central “core” crystal region was practically free of defects; only one extended “oval” defect with strong boundary contrast was observed. The strong white–black contrasts connected with elongated volume defects and cracks were observed in surrounding the “core” region.

The 001 oriented Cz-Si samples were implanted at room temperature with 200 keV deuterium ions to the dose 1.7 × 1017 cm–2 and treated at up to 950 °C under hydrostatic Ar pressure (HP) up to 11 kbar for up to 10 h. The sample properties were studied by means of monochromatic synchrotron X-ray diffraction topography as well as by rocking curve (RC) and photoluminescence (PL) measurements. The thermal annealing caused rapid disappearance of interference effects in RCs and topographs. This process was significantly moderated by HP providing the layers with spongy like structure owing the presence of deuterium - filled inclusions. In the last case the most significant contribution of the PL peaks attributed to dislocations was observed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates were studied with a number of X-ray diffraction methods exploring both synchrotron white and monochromatic beam. The observation of selective etching patterns was performed in neighbouring samples. White beam back-reflection projection topographs revealed only the segregation fringes around the central core and a delicate grain-like structure. The most important for verification of dislocation presence were the transmission projection and section topographs. These topographs also did not reveal any images of extended dislocation but only the growth bands and tiny grain-like structure. The section topographs provided some details of paroboloidal growth surface inside the crystal. It may be concluded that the investigated crystal probably contains small coherent inclusions responsible for the etch pits and the mentioned grain-like structure. The synchrotron rocking curves revealed a number of maxima, which might be attributed to the regions with different lattice parameter, connected with segregation fringes. The sequence of maxima was different for different regions of the sample. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Oxygen precipitation and creation of defects in Czochralski grown silicon (Cz-Si, with interstitial oxygen concentration 1.1 × 1018 cm–3) subjected to irradiation with neutrons (5 MeV, dose 1 × 1017 cm–2) and treated under atmospheric and high hydrostatic pressures (HP, up to 1.1 GPa) at 1270/1400 K are investigated by spectroscopic and X-Ray (synchrotron) methods. The presence of point defects created by neutron irradiation stimulates oxygen precipitation and creation of dislocations under HP, especially at 1270 K. The effect of pressure treatment is related to changes of concentration and mobility of silicon interstitials and vacancies as well as of the VO – type defects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The samples cut out from Si : Ge crystals with 3% and 1.2% of germanium were studied by means of synchrotron white beam Bragg-case section and projection topography as well as conventional transmission Lang topography. The obtained topographs revealed dominant contrast coming from the segregation of germanium. The use of Bragg-case section topography made possible to follow the shape of growth surfaces inside the crystal. The formation of contrast in Bragg-case section topographs for different orientation of growth surfaces with respect to the incident beam is discussed. The applied methods enabled also revealing growth surface instabilities occurring in some regions of Si : Ge crystals.

The MOCVD-grown epitaxial layers of AlxGa1−xAs with x=0.43 were implanted at room temperature with 1.5 MeV As ions to different doses in the range from 5×1013 to 5×1015 cm−2. The samples were studied with a number of X-ray diffraction methods using synchrotron radiation, in particular, recording of rocking curves with a very small 50×50 μm2 probe beam and with Bragg-case section topography. The strain profiles were determined by fitting the theoretical rocking curves obtained by numerical integration of the Takagi–Taupin equations. It was found that for the doses up to 1×1015 cm−2, the strain profiles were dominated by a component caused by introduced interstitial atoms with almost constant strain in the region close to the surface. A second strain component directly corresponding to the distribution of introduced As atoms was indicated for the higher doses. For the highest dose of 5×1015 cm−2, considerable lateral variations of introduced strain were detected by both Bragg-case topography and synchrotron reciprocal space mapping.

Silicon implanted with He+ at 150 keV to a dose 5×1016 cm−2 (Si:He) and treated at high temperature (up to 1270 K) and pressure (up to 1.2 GPa) was investigated using synchrotron X-ray topography, rocking curve and photoluminescence measurements. Rocking curves of as-implanted Si:He exhibit interference maxima related to strain resulting from the presence of He. Annealing at 720 K under 105 Pa for 1 h reduces the strain by about 1.5 while the treatment at 720 K–1.2 GPa affects it to a less degree. The pressure-moderated decrease of strain was observed also for the treatment at 870 K but not at 1270 K. The HP induced effects depend on retarded He diffusion and creation of specific defects at HP.

Silicon layered structures containing porous silicon modified with various thermal treatments and epitaxial layers deposited on porous layers were studied with a number of complementary X-ray diffraction methods using synchrotron source. The methods of characterisation included recording of rocking curves for reflections with various asymmetry as well as projection, section and micro-Laue topography. It was found that oxidising and sintering of porous silicon seriously modified the strains in the porous layer and in some cases even inverting the sense of strain with respect to that in initially formed porous layer. Consequently the deposited epitaxial layer usually was not laterally coherent with the substrate. Some of the investigated layers were not stable in time and after few months period exhibited significant lost of coherence of porous skeleton.

The effects of various high temperature-pressure treatments in Czochralski grown silicon (Cz-Si) implanted with 130 keV hydrogen to the dose of 4 × 10 1 6 cm - 2 were investigated using synchrotron X-ray topographic methods and rocking curve measurements. The high temperature-pressure processes included 10 h annealing at 450°C, 650°C, and 725°C at argon pressure 12 kbar and 1 bar. The topographic investigations were performed with projection and section methods in back-reflection and transmission geometry. It was found that annealing resulted in significantly reduced strain induced by the implantation, which became undetectable with presently used very sensitive synchrotron arrangement. A significant difference between the Cz-Si:H samples annealed at high and atmospheric pressure was observed. In the first case a distinct topographic contrast attributed to the formation of comparatively larger inclusions was observed. This effect was different at different temperatures. The samples annealed at enhanced pressure were more uniform and often produced significant interference effects.

An Si:Ge crystal with approximately 3% of germanium was studied with strongly collimated short-wavelength monochromatic synchrotron beam (beamline E2 at HASYLAB). The topographs obtained in the asymmetric 224 reflection revealed the presence of interference fringes related to growth bands caused by segregation of germanium. The fringes, observed for the first time, were strongly dependent on the angular setting and it was possible to distinguish at least three systems of fringes. A number of features of the existing strain field, which may be important for the formation of the fringes, was determined using other topographic methods, especially the Bragg-case section topography.

Si:Ge crystals with approximately 3% of germanium were studied with various topographic methods using both conventional and synchrotron sources of X-rays. The present investigation included various types of white beam synchrotron topography and conventional Lang topographic methods. The topographic results obtained with various methods were dominated by strong contrast coming from growth bands. The Bragg-case section topographs with the beam front limited to 5 μm revealed the distribution of growth bands inside the crystals. Thanks to the low glancing angle the section topographs provided many information about the shape of growth surface despite small thickness of investigated wafers. Additionally taking the topographs at very large film-to-crystal distances it was possible to reveal the character of lattice deformation across the striations and to draw information about germanium distribution.

MOCVD grown AlxGa1−xAs epitaxial layers with x=0.45 and GaAs single crystals with an initial dislocation density less than 103/cm2 were implanted with different doses of 1.5 MeV Se+ and 1.0 MeV Si+ ions and 170 keV protons at room (RT) and liquid nitrogen temperatures (LNT). In all cases the ion range was close to 1 μm. The samples were studied with a number of complementary X-ray methods, most of them with synchrotron radiation. The synchrotron methods revealed many interference phenomena which were used for the strain profile analysis based on fitting the simulated rocking curves and Bragg-case section topographs. It was found that the amorphisation of Al0.45Ga0.55As took place only after implantation at LNT. Upon implantation at RT an increase of the lattice parameter was observed that eventually saturated with an increasing ion dose. Also the flattening of the strain profile close to the surface was observed. Most of the observed strain effects were attributed to the point defects in the matrix crystal. For the highest doses the second strain component corresponding to the distribution of introduced ions was revealed.

Simultaneous analysis of strain modulation fringes in synchrotron Bragg-case section patterns and rocking curves recorded with a very narrow probe beam was used for the determination of strain profiles in GaAs implanted with high doses of 1.5 MeV Se ions. The existence of two components of the strain was revealed: the first is due to the introduced interstitial defects of the matrix crystal and the second is directly connected with introduced Se ions. These two components significantly differed in their depth profiles and their behaviour upon thermal annealing.

Defect structure of Czochralski-grown oxygen-containing silicon–germanium (Si–Ge) samples with Ge content 1.5×10 18 cm −3 , subjected to processing for 5 h at up to 1400 K under hydrostatic Ar pressure up to 1.1 GPa, has been investigated by synchrotron topography (at HASYLAB), high-resolution X-ray diffraction, photoluminescence and related methods. Ge admixture prevents formation of extended defects at processing done under 10 5 Pa. Such defects are created, however, in Si–Ge processed at 1400 K under high pressure (1.1 GPa).

A special arrangement of Bonse–Hart X-ray interferometers, which uses the Bragg geometry of X-ray diffraction for the beam splitter, mirrors and the analyser (so-called BBB interferometers), has been designed and characterized both computationally and experimentally in different versions. The design includes wavelength-dependent optimization of transmission through the lamella, which is used both for beam splitting and for recombination. For characterization of the function of the instrument, interference patterns were evaluated from BBB interferograms, as well as from LLL (employing the Laue geometry for coherent beam splitting, reflecting and analysing) topograms and from interferograms resulting from a new combined geometrical layout. The influence of gravitation on the horizontally running diffraction planes was visible as a system of fringes in the interferograms, resulting from bending of the lamella under its own weight.

Various types of layer structures obtained by direct bonding of oxidised silicon wafers were studied by means of different X-ray topographic methods using white synchrotron beam and the observation of selective etching pattern using scanning electron microscopy and optical microscopy with Nomarski contrast. In the present investigation the particularly important results were obtained with synchrotron section topography, which revealed different defects caused by bonding of thick wafers, in particular the dislocations and microcracks. The different situation was observed in the case of bonding with a very thin layer separated from a silicon substrate by high dose proton implantation. In this case a thin layer accommodated practically all induced strain and the bonded oxidised thick substrate remained defect-free in its inner volume.

The MOCVD grown Al 0.45 Ga 0.55 As epitaxial layers with low dislocation density, implanted with 1.5 MeV Se + ions to the doses 6×10 13 -4×10 14 ions/cm 2 , were studied using a multicrystal arrangement and applying synchrotron X-ray radiation. A very small size of the probe beam close to 30 μm was used to obtain a good resolution of interference maxima and to study the changes of the rocking curves in different regions of the sample. Due to the curvature of the samples, the interference maxima were revealed in plane wave topographs as interference fringes and the high intensity of the source enabled studying of the fringes also in these regions of the curve where the reflected intensity is very low. The continuity of the fringes across the boundary of implanted region was observed for the high angle side of the maximum due to epitaxial layer. A good approximation of experimental rocking curves and fringe pattern in the plane-wave topographs was obtained by numerical integration of the Takagi-Taupin equations assuming a strain profile with almost constant lattice parameter in a relatively thick layer close to the surface.

The synchrotron Laue method with a beam limited by a pin hole was applied for studying the implanted layers in silicon and in A III B V multicompound epitaxial layers. A significant difference between the micro-Laue patterns in case of heavy and light ion implantation was observed. In the first case the pin-hole pattern contained spots coming from different layers mutually displaced due to lattice deformation. In the case of light ion implantation into silicon the lattice deformation effects were revealed in strongly overexposed patterns by activation of forbidden reflections due to lattice tetragonalization. It was found that all interference fringes connected with the spherical wave diffraction contributed to a long tail corresponding to the plane of diffraction. The possibility of observation of asymptotic distortion scattering due to dislocation was also proved.

Silicon crystals implanted with 1 and 1.6 MeV protons were studied by means of conventional source double-crystal and synchrotron multi-crystal arrangements. Both the rocking curves and series of topographs were recorded in different parallel settings employing different reflections and wavelengths of radiation. A comparison of rocking curves in different regions of implanted areas was performed in synchrotron multi-crystal arrangement with a beam of a very small diameter. The rocking curves exhibited subsidiary interference maxima with increasing periodicity on the low angle side. The plane wave topographs taken at different angular setting revealed characteristic fringes whose number decreased with increasing distance from the main maximum. The fringe pattern did not depend on the direction of the diffraction vector. The number of fringes for equivalent angular distance from the maximum was larger for higher order of reflection. The shape of the rocking curve and other diffraction patterns were reasonably explained assuming the lattice parameter change depth distribution proportional to the profile obtained from the Biersack-Ziegler theory and lateral non-uniformity of ion dose. A good approximation of the experimental results was obtained using numerical integration of the Takagi-Taupin equations.

AlxGa1−xAs epitaxial layers grown on semi-insulating GaAs (SI-GaAs) substrates with x = 0.25 and on in-doped GaAs with x = 0.45 were implanted at room temperature with 1.5 MeV Se ions to fluences ranging from 0.6 × 1014 to 4 × 1014at/cm2. Implanted crystals were analyzed with 1.8 MeV 4He ions using the RBS/channeling technique. In order to determine the defect structure and their depth profiles measurements were carried out at two different temperatures: 295 and 105 K. XRD with synchrotron beams was used for structural analysis. White beam topography was used to detect lattice deformation and strain relaxation. The lattice parameters were determined by rocking curve measurements with a monochromatic beam. For all samples a significant tetragonalization of the implanted region was observed. For the layers grown on SI-GaAs the lattice distortion increases with increasing ion dose until a critical lattice strain is attained. At that point the complete relaxation of the epitaxial layer occurs. In contrast, no relaxation was observed for layers grown on practically defect free in-doped substrates. The mechanism of this transformation is attributed to the much higher dislocation density in the SI-GaAs substrate. Nucleation of new dislocations at defects produced by ion implantation and their interaction with threading dislocations leads to the strain relaxation by plastic deformation of epitaxial layers.

Back-reflection section topography using white-beam synchrotron radiation has been applied for the investigation of silicon implanted with 1 and 1.6 MeV protons and 4.8 MeV α particles. The beam width was limited to 5 μm, and a series of spots in the vicinity of a centrally adjusted reflection were indexed and analysed. The back-reflection section pattern of implanted crystals usually exhibits fringes corresponding to the reflection from the surface and a series of fringes corresponding to the rear region of the shot-through layer, the destroyed layer and the bulk. The patterns were used for direct evaluation of ion ranges and thicknesses of the shot-through layer. The overall characteristics of the obtained patterns were successfully reproduced in simulations based on numerical integration of the Takagi-Taupin equations. The agreement between the simulation and experiment proves that the lattice-parameter depth-distribution profiles can be assumed to be proportional to interstitial-vacancy distributions obtained using the Monte Carlo method from the Biersack-Ziegler theory. The simulation also reproduced interference tails observed in some section patterns. It was found that these tails are caused by the ion-dose change along the beam and they were probably formed due to the interference between the radiation reflected from the bulk and those rays reflected by the rear region of the shot-through layer.

Silicon crystals implanted with 9 MeV protons to the dose of 5x 10 17 cm-2 were studied with X-ray topographic methods using both conventional and synchrotron radiation sources. After the implantation the crystals were thermally and electron annealed. The implantation produced large 600 pm thick shot-through layer while the total thickness of the samples was 1.6 mm. It was confirmed by means of double crystal topography that the whole crystal was elastically bent. The transmission section patterns revealed both parts of the implanted crystal separated by strong contrasts coming from the most damaged layer and distinct interference fringes which appeared on one side of the topograph only. The location of the fringes changed when the beam entered the other side of the sample. The mechanism of fringe formation was studied with numerical integration of the Takagi—Taupin equations, especially studying the intensity distribution in the diffraction plane. The simulations reproduced the location of the fringes in different geometries and indicate that they can be caused both by variable crystal curvature and variable ion dose. PACS numbers: 61.10.—i, 61.80.—x

A series of samples cut out from different types of gallium arsenide crystals with low dislocation density were studied by means of white beam synchrotron topography. The investigation was performed with transmission and back-reflection projection methods and transmission section method. Some of the topography in transmission geometry provided a very high sensitivity suitable for revealing small precipitates. The transmission section images significantly differed depending on the wavelength and absorption. In some cases a distinct Pendellosung fringes and fine details of dislocation and precipitates images were observed. It was possible to reproduce the character of these images by means of numerical simulation based on integration of Takagi-Taupin equations. Due to more convenient choice of radiation, synchrotron back-reflection projection topography provided much better visibility of dislocations than analogous methods realized with conventional X-ray sources.

White-beam synchrotron section topography was applied to a silicon crystal implanted with 4.8 MeV α-particles elastically bent with the radius of curvature close to 100 m. A number of section patterns corresponding to different reflections was analysed. It was found that the section pattern in the bent sample was drastically different from those observed in a flat sample. The difference consists in the occurrence of the sets of additional interference fringes covering a long distance up to several millimetres behind the main diffraction maximum. It was possible to reproduce some characteristic features of the fringes both in the implanted and non-implanted region by numerical integration of the Takagi-Taupin equation.

The formation of misfit dislocation was studied in GaAs homoepitaxial layers on the substrates containing considerable amount of isoelectronic indium. The layers were grown with metal-oxide chemical vapour deposition and chemical vapour deposition methods including low temperature process with tertiarbutylarsine arsenic source. The critical conditions of misfit dislocation formation were exceeded up to 5 x. The samples were examined before and after epitaxial process with a number of different X-ray topographic and diffractometric methods, including high resolution synchrotron white beam topography. The crystalIographic identification of the defects was supported by the numerical simulation of topographic images. It was found that a number of threading dislocations, continuing in the epitaxial layer from those existing in the substrate, did not take part in the formation of misfit dislocations despite a suitable slip system. On the other hand, the formation of misfit dislocations from small imperfections of epitaxial deposit was proved in many cases. A reasonable good quality of the 1ayers was confirmed by the resolution of individual defects and only smalI broadening of rocking curves. PACS numbers: 61.10.—i

Worldwide several systems for Digital Subtraction Angiography in energy subtraction mode (dichromography) with synchrotron radiation are developed. Two of the systems–the system NIKOS in the Hamburger Synchrotronstrahlungslabor HASYLAB in Hamburg and the system in Brookhaven–allow investigations of patients. The aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass density of 1 mg/cm2, thus allowing non-invasive investigations by intravenous application of the contrast medium. The two images for subtraction are simultaneously taken with photon energies just below and above the iodine K-edge (33.17 keV) in a line scan mode. In principle the system NIKOS consists of six main parts: A 20-pole wiggler with a total length of 2.4 m and a field of 1.26 T is installed in the storage ring DORIS at DESY in Hamburg. In a two beam monochromator two bent perfect Si(111) crystals in Laue geometry are used for filtering the quasi-monochromatic beams with a bandwidth of 180 eV out of the white synchrotron radiation beam. In a safety system three independent very fast beam shutters are installed which close within less than 10 ms at any malfunction of the system. Because the line scan mode is used a scanning device moves the patient with up to 50 cm/s through the two monochromatic beams. As a detector a two-line ionization chamber with a spatial resolution of 0.4 mm is installed. The chamber has a dynamic range of 39,000:1 and reads a line within 0.73 ms. The quantum efficiency for 33 keV photons is 85%. The computer system is used for control of the system, data acquisition, image processing and presentation. Since 1990 thirty patients were studied with the system NIKOS. In all cases follow-up investigations after interventions like bypass surgery, angioplasty or rotablation were performed. Intravenous angiograms from investigations with version III of the system are presented.

Worldwide at many synchrotron radiation laboratories different systems have been developed for digital subtraction angiography (DSA) in energy subtraction mode (dichromography). Aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass density of 1 mg/cm2, thus allowing non-invasive investigations by intravenous application of the contrast agent. The two images for subtraction are simultaneously taken with photon energies just below and above the iodine K-edge (33.17 keV) in a line scan mode. In the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY the system NIKOS II (NIKOS =Nicht-invasive Koronarangiographie mit Synchrotronstrahlung) consists of six main parts: the 20 pole wiggler HARWI, a two beam monochromator, a safety system, a fast scanning device, a fast low-noise two-line detector, and a computer system. In 1990 the first patients were investigated with the system NIKOS II. 30 ml of contrast medium were injected within 2 s into the vena cava superior. The scan velocity was 9 cm/s corresponding to 5.6 ms per line. The resulting images have a size of 10.0 cm (horizontal) × 12.3 cm (vertical). The pixel size in the images is 0.5 × 0.5 mm2. The radiation dose per scan (two energy images) was 25 mGy on the average. There are two main problems with the intravenous investigations using DSA in energy subtraction mode for visualization of coronary arteries: • The correct time T from the injection of the contrast material up to the beginning of the scan depends on the individual circulation time of the patient. • In intravenous investigations the small structures of interest (coronary arteries) can be superimposed by large structures (aorta, left atrium and ventricle). The images from the investigations are compared to angiograms, conventionally obtained. They have not yet the quality necessary for clinical routine but show the potential of the method if the system is optimized.

Drawbacks of white beam topography with synchrotron radiation, such as intense fluorescence background, thermal strain, and radiation damage, can be avoided by filtering the beam with an oscillating perfect crystal monochromator. The advantage of the white beam technique, namely the imaging of a sample of poor quality, is maintained. The image contrast is even improved due to the suppression of higher harmonics. Topographs of a LiF crystal demonstrate the feasibility of the method.

SiC crystals of high structural perfection were investigated with several methods of X-ray diffraction topography in Bragg-case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 103 cm-2. Most of them cannot be interpreted as hollow core dislocations (micro- or nano-pipes). The concentration of the latter was lower than 102 cm-2. The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg-case multi-crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw-type dislocations in the investigated crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A position sensitive one‐dimensional x‐ray detector with a large dynamic range (≳214:1) for high photon fluxes with fast image recording sequence (300 ms per frame) has been developed for transvenous coronary angiography with synchrotron radiation. A position resolution of 1 LP/mm and a detection quantum efficiency (DQE) of at least 58% (for 11 000 photons per pixel) has been achieved for 33 keV photons in a Xe‐CO2 gas mixture at 20 bars. The use of Kr‐CO2 as conversion gas provides a better contrast of the weak iodine signal than Xe‐CO2 or Si, respectively, for a fraction of 2% of the second harmonics of the synchrotron beam used.

High photon fluxes are crucial in dichromatic digital subtraction angiography with line scan systems to allow for adequate image quality. To obtain images wide enough and with sufficient vertical resolution, each of the two beams used has to be at least 100 mm wide but not more than 0.5 mm high at the patient’s heart with the beam energies bracketing the iodine‐K edge at 33.17 keV. A new monochromator in Laue transmission geometry has been developed, successfully tested at beamline ID11 of the European Synchrotron Radiation Facility (ESRF) and is now in use at the angiography wiggler beamline W2 at HASYLAB. The monochromator consists of two almost identical goniometer heads which are independently controlled. Within each head a bent silicon single crystal extracts a quasimonochromatic beam and focuses it vertically to the patient thus also increasing intensity compared to an unbent crystal. With a storage ring current of 50 mA the new monochromator provides 0.8×1011 photons/mm2/s in front of the patient w...

Al(x)Ga(1-x)As epitaxic layers, with x = 0.43 and GaAs single crystals implanted with various doses of high-energy Se and Si ions, and silicon single crystals implanted with high-energy light ions were studied by means of different X-ray diffraction methods employing either a strongly limited white beam or a highly collimated monochromatic beam. The methods provided complementary characterization of lattice parameter changes and lattice deformation in the implanted layers. The synchrotron rocking curves recorded with a small-diameter beam provided a very good separation of interference maxima and enabled determination of the strain profile. A characteristic difference in strain depth distributions between the implanted A(III)B(V) compounds and silicon was noticed. Ion implantation in A(III)B(V) compounds produced a relatively thick layer with an almost constant and distinctly increased lattice parameter in regions close to the surface, whereas, in the case of silicon, shot-through layers with almost unchanged lattice spacing were observed. Other important information obtained from the synchrotron micro-Laue pattern was that the interference fringes caused by crystal curvature or strain gradient are located in the plane of diffraction, while parts of the Laue spot corresponding to the deformed regions are usually displaced.

Dichromography represents a digital subtraction angiography mode based on energy substraction which allows imaging of fast moving subjects like the heart. For logarithmic subtraction 2 images with X-rays just below and above the iodine K-edge (33.17 keV) are simultaneously obtained in a line scan mode. Monochromatic X-rays of sufficient intensity to visualize coronary arteries of 1 mm diameter with extremely low iodine concentrations (1 mg/cm2) after venous injection is only provided by synchrotron radiation. The system NIKOS (non-invasive coronary arteriography with synchrotron radiation) at the Deutsches Elektronen Synchrotron (DESY) consists of 6 components: a wiggler, a monochromator, a safety system, a scanning device, a detector and a computer system. After experimental studies in dogs patients are imaged since 1990. Initial results demonstrate feasibility and safety of synchrotron radiation coronary angiography. Large scale studies are designed to further evaluate sensitivity and specificity. When compact synchrotron radiation sources become available, this technique could be used for follow-up studies and for evaluation of certain high coronary risk populations.

Worldwide several systems for Digital Subtraction Angiography in energy subtraction mode (dichromography) are developed. One of the systems which allows investigations of patients - the system NIKOS in the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY is described. The system consists out of six main parts : The 20 pole wiggler HARWI in the beamline W2 of the storage ring DORIS, the two beam monochromator for the two 12.5 cm wide monochromatic X-ray beams, the safety system, the fast scanning device, the fast low-noise two-line ionization chamber and the computer system. Since 1990 patients were investigated with the system NIKOS. Aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass density of 1 mg/cm2, thus allowing non-invasive investigations by intravenous application of the contrast medium. The two images for subtraction are simultaneously taken with photon energies just below and above the iodine K-edge (33.17 keV) in a line scan mode. Intravenous angiograms from investigations with version III of the system NIKOS are presented and the next steps for getting an increased image quality are described.

This contribution describes the development of a fast two line scan detector for digital subtraction angiography (DSA). For each line an input phosphor screen, an image intensifier and a photodiode array are successively coupled by a special fiber optic. A line comprises 250 pixels having a size of 0.5 .0.5mm 2 each. The vertical center to center distance of the two input lines is 2mm. Different materials for the phosphor lines such as Gd 2 O 2 S : Tb and CdWO 4 were tested. The 3 stage proximity focusing image intensifiers have a light intensity amplification of 120W/W. Fast readout electronics enable a minimum integration time of 2ms for the photodiode array. For this time the measured dynamic range of the detector is 3000. It can be improved by increasing the readout time. Details of the existing detector will be given. The tested detector was optimized for the application in non-invasive coronary angiography with synchrotron radiation (System NIKOS II). However, its modular design permits an optimization for other applications as well. By individual selection of the detector components, for example the spatial resolution and the shape of the input line can be adapted to specific problems.

It is demonstrated experimentally that the well known spin-selective deflection of neutrons transmitted through a static magnetic field region with triangular geometric boundaries combined with the high angular resolution of a non-dispersive double-crystal arrangement can be used to polarize a thermal neutron beam to a degree close to unity at reasonably low laboratory fields of 1.0 to 1.5 T.

A new type of crystal monochromator is presented which facilitates the selection of a precisely fixed wavelength λ0 from a continuum at an intermediate bandwidth Δλ/λ of typically 10−3. Its essential feature is consecutive Bragg reflections from two crystals with slightly different Bragg-plane spacings glued rigidly together at near-parallel orientation. The bicrystal effectively manifests a wavelength standard the exact value of which is determined by the angle β of misorientation of the two crystals. The application of a germanium–silicon version of the new device to neutron interferometry is described. The influence of ray geometry on the values of λ0 and Δλ is discussed.

A fast, low‐noise line scan detector (NIKOS) for digital radiography has been developed. It consists of an input x‐ray phosphor screen that is coupled to a modified Reticon photodiode array by means of fiber optics with incorporated image intensifier. In its current version the detector can be operated with a maximum 500 Hz image acquisition rate for interlaced readout of two lines of 128 pixels each. Using a Gd2O2S:Tb x‐ray input phosphor, an afterglow of 25% in the first subsequent readout was observed. We also conducted afterglow measurements on several other powder and single‐crystal phosphors and the photodiode array. Using CdWO4, the afterglow of the detector is limited by the lag of the photodiode array of 4.5%. By modifying the readout electronics the noise of the photodiode array was reduced to below 1 Graylevel, corresponding to a signal‐to‐noise ratio of 5200. The detective quantum efficiency (DQE) of the detector ranged from 0.18 to 0.4 for typical signal levels. The sensitivity was 10% saturation per 1.9 mR entrance dose. The modular design of the NIKOS detector allows for individual selection of each component to optimize performance for a given application.