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SUMMARYCRISPR-Cas systems provide their prokaryotic hosts with acquired immunity against viruses and other foreign genetic elements, but how these systems are regulated to prevent auto-immunity is poorly understood. In type II CRISPR-Cas systems, a transactivating CRISPR RNA (tracrRNA) scaffold functions together with a CRISPR RNA (crRNA) guide to program Cas9 for the recognition and cleavage of foreign DNA targets. Here, we show that a long-form tracrRNA performs an unexpected second function by folding into a natural single guide that directs Cas9 to transcriptionally repress its own promoter. Further, we demonstrate that Pcas9 serves as a critical regulatory node; de-repression causes a dramatic induction of Cas genes, crRNAs and tracrRNAs resulting in a 3,000-fold increase in immunization rates against unrecognized viruses. Heightened immunity comes at the cost of increased auto-immune toxicity, demonstrating the critical importance of the controller. Using a bioinformatic analysis, we provide evidence that tracrRNA-mediated autoregulation is widespread in type II CRISPR-Cas systems. Collectively, we unveil a new paradigm for the intrinsic regulation of CRISPR-Cas systems by natural single guides, which may facilitate the frequent horizontal transfer of these systems into new hosts that have not yet evolved their own regulatory strategies.

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.]

Knowledge on the defect and electronic structure allows for improved modeling of material properties. A short literature review has shown that the information on defect structure of rare earth orthovanadate single crystals is limited. In this paper, defect and electronic structure of a needle-shaped Yb:LuVO 4 single crystal grown by the slow cooling method have been studied by means of X-ray diffraction topography employing white synchrotron beam, high-resolution diffraction (HRD) and photoelectron spectroscopy (XPS) techniques. Topographic investigations show that the crystal is composed of two blocks disoriented by about 1.5° and separated by a narrow deformed region. Some contrasts observed within the crystal volume may be attributed to glide bands and sector boundaries. The contrasts appearing in the vicinity of the surface may be interpreted as due to the presence of small inclusions. The HRD study indicates, in particular, that among point defects, the vacancy type defects dominate and that the density of other defects is small in comparison. The XPS measurements enabled, despite highly insulating properties of the studied crystal, an analysis of its bulk electronic structure, including the main core-levels (O 1 s , V 2 p , Lu 4 f ) as well as the valence band range.

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.

GaAs crystals and Al0.43Ga0.57As epitaxial layers of low dislocation density were implanted with 146 keV, 100 keV and 60 keV H+ ions and studied by recording of rocking curves, reciprocal space mapping and Bragg-type section topography. The X-ray investigation were performed also in the case of GaAs double implanted with 146 keV and 60 keV protons with doses of 6 × 1015 cm–2 and 4.2 × 1015 cm–2, with penetration ranges differing by a factor 2. The rocking curves and Bragg-type section patterns for single implantation were readily explainable by approximating the strain profiles by the point-defect distribution calculated with the TRIM95 program. In the case of double implantation with hydrogen ions the rocking curve contained much narrower interference maxima than the curves for single implantation. The experimental curve was well approximated by the theoretical one obtained by numerical integration of the Takagi–Taupin equations. The strain profile in this calculation was a sum of strain profiles of single implantations. The narrow interference maxima were most probably caused by beating of the radiation, reflected by two strain maxima located at different depths in the implanted crystal. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

In x Al 1 − x As layers on InP substrate can be subjected to compressive as well as tensile strain due to lattice parameter differences induced by suitable alloy composition changes. The 2 μm thick In x Al 1 − x As (0.50 ≤ x ≤ 0.53) layers were grown on the (0 0 1) oriented InP substrates by molecular beam epitaxy (MBE). They were investigated using X-ray diffraction and chemical etching. X-ray studies were performed applying high-resolution diffractometry in the double (DAD) and triple (TAD) axis configuration. It was found that the In 0.53 Al 0.47 As/InP layer under compressive strain relaxes partially along two 〈1 1 0〉 directions. On the other hand, the In 0.50 Al 0.50 As/InP layers, being under tensile strain, consist of two sub-layers; the first one, adjacent to the substrate is pseudomorphic whereas the upper sub-layer is partially relaxed and the relaxation is anisotropic. The upper sub-layer is fully strained in the [1 1 0] direction while partially relaxed in the [−1 1 0] one.

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)

GaAs crystals with dislocation density smaller than 103 cm−2 were implanted at room temperature with 1.5 MeV Se+ ions with doses ranging from 3 × 1 0 12 to 3 × 1 0 15 cm - 2 . The samples were studied with a number of X-ray diffraction methods realized using synchrotron radiation, in particular recording of rocking curves with 50 × 100 μ m 2 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. The investigation revealed two different components of ion-induced strain. For doses up to 3 × 1 0 14 cm - 2 the strain profiles were dominated by a component caused by interstitial atoms with almost constant strain close to the surface. A second component directly corresponding to the depth distribution of implanted Se atoms was observed for the higher ion doses. Crystal amorphization was not yet observed for all applied doses. The comparative studies of similarly implanted Ge crystals did not exhibit the saturation of implantation induced strain. The amorphization of Ge crystals took place for relatively small dose of 6 × 1 0 13 cm - 2 . This difference is most probably caused by increased mobility of point defects observed close to 300 K.

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 investigations of GdCa 4 O(BO 3 ) 3 single crystals grown by the Czochralski technique were performed by conventional and synchrotron radiation (SR) monochromatic wave topography mainly in back reflection geometry. It was found that back reflection topography is effectively able to reveal the dislocation structure even in thin samples. Different distribution of defects was observed in samples cut off from the top, middle and end part of the “as-grown” crystal. SR monochromatic wave topographs taken for two flanks of the rocking curve show the characteristic inversion of diffraction contrast. Both monochromatic wave and projection Lang topographs did not reveal any segregation fringes proving high homogeneity of the chemical composition of the examined crystal.

A slab formed sample cut out from low doped Czochralski-grown silicon crystal was implanted with 117 MeV (3 MeV/nucleon) Ar ions to the dose 5 × 10 14 cm −2 and thermally annealed at 400 and 700 °C. The crystal was characterized with a number of complementary X-ray diffraction methods. The annealing did not completely remove the lattice strain induced by the implantation. The residual strain caused the series of interference maxima on the low angle side of the substrate maximum in the rocking curves. The rocking curves were different in different regions of the implanted area and characteristic fringes in plane wave topographs were observed. The analysis of rocking curves including the numerical simulation pointed to the existence of a local strain profile maximum situated below the shot-through layer with a relatively small deformation. The Bragg-case section topography experiment indicated a layer containing non-resolvable defects situated at the depths corresponding to the average ion range.

(111) oriented Fz-Si crystals were implanted with N+ or Si+ at 150 keV energy to a dose of 2×1016 cm−2. After implantation the samples were treated at a high temperature (up to 1400 K) under hydrostatic argon pressure (up to 1.1 GPa) for 1–5 h. Structural properties of Si:N and Si:Si before and after the treatment were investigated by high-resolution X-ray diffraction, synchrotron topography, transmission electron microscopy and photoluminescence methods. The structural properties of Si:N and Si:Si treated under hydrostatic pressure at 1270 K are different. A buried layer of uniform thickness with smooth interface was formed in Si:N under HP=1.1 GPa; the buried layer/Si interface becomes less smooth with rising treatment time. The shape of interference fringes and their changing distance at rocking curves are explained as an effect of nitrogen diffusion to the buried layer during the treatment. For the treated Si:Si samples, the observed strain changes are related to the out-diffusion of interstitial silicon atoms from the implanted layer to the sample surface and to creation of numerous extended defects near the implanted atoms range. Prolonged treatment (for 5 h) at 1.1 GPa and 1400 K results in creation of dislocations for Si:N while for Si:Si samples the structure of treated samples is more complex, involving also creation of amorphous-like surface film.

The reciprocal space maps around the 400 reciprocal space point were collected for a number of different implantations in GaAs and Al x Ga 1− x As including high dose implantations (∼10 16 ions/cm 2 ) with 1.5 MeV Se + and As + ions. We also studied the effect of high pressure annealing in GaAs implanted with 170 keV protons. The maps were recorded from an area of 50×100 μm 2 with a very good resolution of details. The maps usually revealed the same sequence of interference maxima as the double crystal rocking curves recorded with a widely open detector slit. This series of maxima was also well reproduced in numerically calculated theoretical rocking curves. The maxima were usually located exactly along the central θ /2 θ scan. In one case we observed a deviation of the interference maxima from the θ /2 θ direction, connected with lateral strain changes and consequent tilt deformation of the lattice. The maps for as implanted layers did not reveal significant diffuse scattering. A significant increase of diffuse scattering was present in proton implanted GaAs after thermal annealing performed at 450 °C under 11 kbar of argon pressure for a sample implanted with 170 keV protons with a dose 2·10 16 cm −2 .

Oxygen precipitates in samples of Czochralski grown silicon crystal annealed at various temperatures from 750 to 1100 °C were studied with X-ray methods realized both with white and monochromatic synchrotron radiation, particularly Bragg-case section topography. The samples were additionally controlled by observation of selective etching pattern, infrared, Fourier spectroscopy and laser scattering tomography. The visibility of oxygen precipitates in synchrotron topographic methods was strongly dependent on annealing temperature and time. For annealing performed at 750 °C the effect was relatively weak and consisted of small irregularities of Pendellosung fringes. The back reflection section topographs usually revealed fringes characteristic for bent crystals with some irregularities caused by oxygen precipitates. The significant effect was observed with X-ray diffraction methods for 3-h annealing at 1100 °C, when the individual precipitates were resolved in the topographs. In case of longer combined annealing cycles including annealing at 1050 °C, an irresolvable quantity of defects and complete dampening of interference fringes were observed The concentration of precipitates strongly increased along some striations while in other parts of the crystal the interference fringes were present.

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.

Synchrotron white beam with a wavefront limited by a 5 µm slit was used for obtaining the Bragg-case section patterns in silicon substrates and epitaxial layers. The section images contained various interference fringes, such as the Uragami fringes and fringes caused by crystal curvature. The system of fringes connected with individual defects was also observed. The experimental images were compared with simulated theoretical images obtained by numerical integration of the Takagi-Taupin equations. A reasonably good correspondence was obtained for dislocations inclined to the surface and misfit dislocations. The elements of the image were analysed using the visualization of |D h |2 and |D o |2 intensities in the plane of diffraction, where an additional amount of transmitted wave intensity indicated the decomposition of wavefields or the reflection of the redirected waves from the surfaces. Comparative studies of simulated precipitation images and modification of dislocation images caused by curvature and by the diffusion of an epitaxial junction were also performed.

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.

A comparison of two different multi-channel line detectors utilized in transvenous coronary angiography was performed. An Li+ drifted silicon strip detector (SSD) was tested at the SMERF facility X17B2 at the National Synchrotron Light Source (NSLS). An ionization chamber (IC) was tested at the W2 beamline at HASYLAB. Both detectors were operated in the charge-integrating mode. The main purpose was to measure and compare the Modulation Transfer Function (MTF( f )), Noise Power Spectrum (NPS( f )), Detective Quantum Efficiency (DQE( f )) in terms of spatial frequencies and the dynamic range of both detector systems. It turned out that the IC is superior to the SSD in time resolution and dynamic range at a single gain setting and has a slight advantage in the transmission of high spatial frequencies. Although for high photon flux the DQE values of the IC exceed those of the SSD, it is the reverse for low photon flux caused by a higher noise floor of the read-out electronics. This makes the SSD superior to the IC since the incident flux is limited by the tolerable entry dose to the patients. For the comparison other criteria like price, reliability, maintenance, etc., are not taken into consideration.

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.