High-angular-resolution Fraunhofer diffraction data were collected from several samples with interfaces between dissimilar metals and an artificial crack in a metal foil using synchrotron x-radiation. The refractive index profile in the vicinity of the interface and crack of each sample was reconstructed with spatial resolution of about 40-60 nm by the Phase Retrieval X-Ray Diffractometry technique, using only limited a priori knowledge of the sample. These studies
have demonstrated the viability of the technique as an in-situ nondestructive method of characterization of internal interfaces within multiphase materials and crack developing under external force.
A novel approach to x-ray diffraction data analysis for non-destructive determination of the shape of nanoscale particles
and clusters in three-dimensions is illustrated with representative examples of composite nanostructures. The technique
is insensitive to the x-rays coherence, which allows 3D reconstruction of a modal image without tomographic synthesis
and in-situ analysis of large (over a several cubic millimeters) volume of material with a spatial resolution of few
nanometers, rendering the approach suitable for laboratory facilities.
We present the results of preliminary investigations determining the sensitivity and applicability of a novel x-ray
diffraction based nanoscale imaging technique, including simulations and experiments. The ultimate aim of this nascent
technique is non-destructive, bulk-material characterization on the nanometer scale, involving three dimensional image
reconstructions of embedded nanoparticles and in situ sample characterization. The approach is insensitive to x-ray
coherence, making it applicable to synchrotron and laboratory hard x-ray sources, opening the possibility of
unprecedented nanometer resolution with the latter. The technique is being developed with a focus on analyzing a
technologically important light metal alloy, Al-xCu (where x is 2.0-5.0 %wt). The mono- and polycrystalline samples
contain crystallographically oriented, weakly diffracting Al2Cu nanoprecipitates in a sparse, spatially random dispersion
within the Al matrix. By employing a triple-axis diffractometer in the non-dispersive setup we collected two-dimensional
reciprocal space maps of synchrotron x-rays diffracted from the Al2Cu nanoparticles. The intensity profiles of the
diffraction peaks confirmed the sensitivity of the technique to the presence and orientation of the nanoparticles. This is a
fundamental step towards in situ observation of such extremely sparse, weakly diffracting nanoprecipitates embedded in
light metal alloys at early stages of their growth.
X-ray phase-retrieval algorithms are widely exploited in contemporary diffraction techniques to image at the nanoscale.
Often reconstruction of the sample shape (image) suffices for the purpose of experiment. Identification of specimen
composition requires a quantitative profiling of the complex refractive index. We show that the diffraction effects from
the experimental setup and artifacts from the phase-retrieval algorithms themselves are comparable with the diffraction
contrast that is experimentally observable from thin specimens with very low electron density. We show that, based on
the analysis of application of the relevant phase-retrieval methods, there is a lower limit in optical density, which can be
reconstructed using the existing phase-retrieval methods. This limit appears to be imposed by real-life experimental
conditions and the intrinsic artifacts of the phase-retrieval techniques.
Gaussian-like shaping of the forward-diffracted intensity was observed from an initially rectangular cross-section of
coherent x-rays. The effect occurs when a wavelength inside a crystal exactly matches the period of atomic net planes
lying perpendicular to the incident beam. The transmitted peak intensity rose when the lateral width of the rectangular-shaped
incident beam increased. The transmitted intensity profile spatially was significantly narrower than that of the
incident beam size. The observations showed that, unlike in all other x-ray diffraction experiments, coherent and
incoherent x-rays produced different dependences of the peak intensity and its width on the incident beam size.
Experimental observations of synchrotron radiation diffraction from a thin surface layer at a 90-degree Bragg reflection are reported and discussed. The synchrotron experiments were performed using a bending magnet source at the European Synchrotron Radiation Facility (ESRF) in France and undulator sources at the Advanced Photon Source (APS) in the U.S. and SPring-8 in Japan. Thin (0.5, 1.0 and 1.5 micron) InGaAs films deposited on a GaAs (100) substrate were studied near the 90- degree using the GaAs (800) reflection. A slight, less than 0.1%, difference in the lattice spacing between the layer and the substrate is sufficient to allow a direct and exclusive observation of the diffraction profile from a thin layer as if it was a 'free-standing' thin crystal. This research opens new possibilities for x-ray optical schemes and the development of novel analytical techniques for surface/interface x-ray diffraction studies.
Experimental observations of refraction/small angle scattering of synchrotron radiation from non-crystalline materials are reported and discussed. This technique constitutes a further application of an experimental-analytical x-ray phase retrieval technique previously utilized for Bragg diffraction data. The recent impetus for these studies arose from high resolution measurements of x-ray refraction phenomena from a narrow aperture performed in the laboratory, which suggested that the phase retrieval formalism could also be applied to non-crystalline materials. The experiments were performed using bending magnet sources at the European Synchrotron Radiation Facility (ESRF) in France, and the Photon Factory, Japan. Refraction/small-angle scattering data was collected from thin (20 - 125 micrometer) filaments of optical fiber (silica), copper, nylon6, kapton and human hair. The experimental results obtained are in close agreement with theoretical simulations. Successful application of the phase retrieval formalism to this data will establish a basis for a novel materials characterization technique.
An experimental-analytical technique for x-ray phase retrieval and consequent crystal structure-factor determination is tested and discussed in the cases of high- (rotating anode or synchrotron radiation) or low-flux (fixed anode x-ray tubes) radiation sources. Experimentally measurable reflectivity magnitudes, using a rotating anode or conventional x-ray tube source, affect the directly reconstructed profile of the complex crystal structure-factor. Thermal and point defect diffuse scattering contaminates the tails of the Bragg diffracted intensity. A numerical procedure developed for the regularization of the directly reconstructed complex structure-factor allows the elimination of parasitic fringes in the resulting crystal-lattice strain profiles. In addition, replacement of plus/minus infinity limits in a mathematical formalism of the reconstruction procedure by actually measured experimental values of the scattering vector in practice affects the resulting profile of the complex crystal structure factor.
A highly advanced experimental-analytical x-ray diffraction technique for the unique determination of material structure is discussed with respect to its possible application for the characterization of materials used in photonic space devices. The PRXRD technique allows one to determine, in great detail--at the level of a few angstrom, the physical dimensions and fine structure of crystalline materials. During the recent years the technique has been used successfully to determine the defects and fine structure of 1- and 2-D crystal-lattice strain distributions in SiGe- and GaAs-based heterostructures and in silicon crystals implanted with high-energy ions. There are materials that presently used in design of semiconductor lasers, detectors and ultra-high frequency telecommunication devices suitable for space applications. Recent atomic spatial resolution studies have allowed, for the first time, observation and preliminary analysis of surface and interface nano-scale sub-layers, where the crystal structure-factor may noticeably differ from the bulk material.
An experimental set-up for the observation of intensity fringes of x-rays propagating in vacuum between two separated crystals is reported. In this experiment a Bragg reflection near 90 degrees was used to observe the oscillations of the measured intensity between the monochromator and mirror crystals. The x-ray intensity profiles; were collected as a function of the angular position of the crystal-mirror in the vicinity of a Si(800) reflection at a synchrotron radiation energy of about 9.1344 keV. Interference contrast in the experimentally observed intensity profiles proves the phase-sensitive nature of the intensity fringes. Novel approach to interpretation of synchrotron radiation coherence is discussed. The experimental observations open new possibilities for novel applications in high-energy radiation optics.
A new nondestructive method for structural imaging is proposed. The method is based on direct measurements of phase and amplitude changes in a 2D x-ray image. A standing wave is formed between two separated crystals allowing high- resolution imaging of the complex refractive index. A comprehensive analysis of the amplitude-phase contrast is possible because of the precisely controlled variation of the phases between the reference and reflected beams from a crystalline mirror.
X-ray focusing using square channel capillary arrays is reviewed. We review our theoretical understanding of these devices and go on to examine their potential in the context of x-ray astronomy as an approach to the construction of a lobster-eye telescope. We show that a reasonably small device has the potential, in principle, to improve the sensitivity of wide field of view x-ray telescopes by an order of magnitude. We go on to briefly review our experimental work and indicate that these devices are getting close to realizing their theoretical potential.
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