Utilization of an Si(331) beam conditioner together with an Si(111) double‐crystal monochromator (DCM) enables the angular resolution of synchrotron X‐ray topography to be increased by an order of ...magnitude compared with grazing‐incidence topography or back‐reflection topography conducted with the DCM alone. This improved technique with extremely small beam divergence is referred to as synchrotron X‐ray plane‐wave topography (SXPWT). This study demonstrates that the rocking curve width of 4H‐SiC 0008 in PWT is only 2.5′′ and thus the lattice distortion at the scale of 1′′ will significantly affect the diffracted intensity. This work reports the ultra‐high angular resolution in SXPWT which enables detailed probing of the lattice distortion outside the dislocation core in 4H‐SiC, where the sign of the Burgers vector can be readily determined through comparison with ray‐tracing simulations.
Minute lattice misorientation away from the dislocation core was revealed in rocking curve topography as the angular resolution was significantly increased. The contrast of the dislocation images can be calculated using ray‐tracing simulations
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The contrast of dislocations in 4H‐SiC crystals shows distinctive features on grazing‐incidence X‐ray topographs for diffraction at different positions on the operative rocking curve. Ray‐tracing ...simulations have previously been successfully applied to describe the dislocation contrast at the peak of a rocking curve.The present work shows that the dislocation images observed under weak diffraction conditions can also be simulated using the ray‐tracing method. These simulations indicate that the contrast of the dislocations is dominated by orientation contrast. Analysis of the effective misorientation reveals that the dislocation contrast in weak‐beam topography is more sensitive to the local lattice distortion, consequently enabling information to be obtained on the dislocation sense which cannot be obtained from the peak.
The contrast of dislocations in 4H‐SiC crystals shows distinctive features on grazing‐incidence X‐ray topographs for diffraction at different positions on the operative rocking curve. A misorientation model together with a ray‐tracing simulation effectively interpret the features on X‐ray topographs under weak diffraction conditions.
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On the basis of rigorous dynamical‐theory calculations, a complete X‐ray polarization‐switch effect of silicon crystals at the exact multiple‐beam diffraction condition is demonstrated. The ...underlying physical mechanism of this unique phenomenon can be revealed using a simple multiple‐wave propagation and interference model. The constructive and destructive interference of the multiple detoured‐diffraction beams along the direction of the primary diffracted beam directly leads to the complete polarization switch. This phenomenon can be realized using both synchrotron and laboratory X‐ray sources at many discrete wavelengths, and used to design a novel crystal‐based polarizer to achieve a 90° polarization rotation.
A complete X‐ray polarization‐switch effect of silicon crystals at the exact multiple‐beam diffraction geometry is reported. It will be very helpful for designing novel crystal‐based polarizers to achieve a 90° polarization rotation of incident X‐rays.
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Measured diffuse X‐ray scattering data for a `smooth' as well as for a `rough' silicon sample were fit to theoretical expressions within the distorted wave Born approximation (DWBA). Data for the ...power spectral density (PSD) for both samples were also obtained by means of atomic force microscopy and optical interferometry. The Fourier transforms of trial correlation functions were fit to the PSD data and then applied to the DWBA formalism. The net correlation functions needed to fit the PSD data for each sample comprised the sum of two terms with different cutoff lengths and different self‐affine fractal exponents. At zero distance these correlation functions added up to yield net values of σ2 = (2)2 and (71)2 Å2 for the smooth and rough samples, respectively. X‐ray scattering data were obtained at beamline 1‐BM of the Advanced Photon Source. Data and fits at values of qz = 0.05 and 0.10 Å−1 for the smooth sample are reported. Good fits for the smooth sample were obtained at both qz values simultaneously, that is, identical fitting parameters were applied at both values of qz. The smooth sample also exhibited weak Yoneda wings and a clear distinction between the strong specular scattering and the weak diffuse scattering. Data for the rough sample were qualitatively different and exhibited very weak scattering at the specular condition in contrast to extremely large Yoneda wings. Fits for the rough sample are reported for qz = 0.04, 0.05, and 0.06 Å−1. Although the large Yoneda wings could be fit quite well in both position and amplitude, scattering near the specular condition could not be equally well fit by applying the same fitting parameters at all values of qz. Albeit imperfect, best‐fitting results at the specular condition were obtained by invoking only diffuse scattering, that is, without including a separate theoretical expression for specular scattering.
Measurements of diffuse X‐ray scattering from polished silicon were fit. The fits employed autocorrelation functions obtained from direct metrology of the surface roughness.
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Rigorous dynamical theory calculations show that four‐beam diffraction (4BD) can be activated only by a unique photon energy and a unique incidence direction. Thus, 4BD may be used to precisely ...calibrate X‐ray photon energies and beam positions. Based on the principles that the forbidden‐reflection 4BD pattern, which is typically an X‐shaped cross, can be generated by instant imaging using the divergent beam from a point source without rocking the crystal, a detailed real‐time high‐resolution beam (and source) position monitoring scheme is illustrated for monitoring two‐dimensional beam positions and directions of modern synchrotron light sources, X‐ray free‐electron lasers and nano‐focused X‐ray sources.
A novel scheme based on four‐beam diffraction is illustrated for accurate calibration of X‐ray photon energies and real‐time monitoring of two‐dimensional beam positions of modern synchrotron light sources.
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The results are reported of an X‐ray diffraction study of an Si crystal designed and fabricated for very asymmetric diffraction from the 333 reflection for X‐ray energies of 8.100 and 8.200 keV. A ...crystal with an asymmetry angle of 46 ± 0.1° between the surface and the (111) planes was studied. The grazing angles of incidence were near 1.08 and 0.33° for these two energies, respectively. Features arising from surface undulations were not observed at 8.100 keV, but were observed at 8.200 keV. The results at 8.100 keV allow an alternative explanation based on strain near the surface to be ruled out. Topographic images were obtained as a function of rocking angle, and in the case of 8.200 keV the surface morphology is evident. The results are found to be in agreement with dynamical X‐ray diffraction calculations made with the Takagi–Taupin equations specialized to a surface having convex or concave features, as reported in the accompanying paper Macrander (2020). J. Appl. Cryst.53, https://doi.org/10.1107/S1600576720005178.
Very asymmetric crystal diffraction was obtained from a finely polished silicon crystal set to reflect in Bragg diffraction at grazing incidence for the 333 reflection. The angle of incidence to achieve Bragg diffraction was varied between 1.08 and 0.33° by changing the X‐ray energy from 8.100 to 8.200 keV. The effects of surface undulations were identified, and the results are compared with dynamical X‐ray diffraction calculations.
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Abstract
We report on a comprehensive experimental study of the impacts of the quality and stability of optical components on the transverse coherence of the 33-ID beamline at the Advanced Photon ...Source. More specifIcally, this study, carried out using grating interferometry, shows how the quality of two of the beamline’s key components, namely, the monochromator and the beryllium window, affects the beam transverse coherence and demonstrates that the decoherence effects of each optical component can be measured quantitatively, thus providing critical information for subsequent improvements to the beamline. The technique and analysis used in this work can be adapted to any coherence-oriented beamlines.
Coherent X-ray imaging is an active field at synchrotron sources. The images rely on the available coherent flux over a limited field of view. At many synchrotron beamlines a double-crystal ...monochromator (DCM) is employed in a standard nondispersive arrangement. For coherent diffraction imaging it is advantageous to increase the available field of view by increasing the spatial coherence length (SCL) of a beam exiting such a DCM. Here, Talbot interferometry data together with ray-tracing simulations for a (+ - - +) four-reflection experimental arrangement are presented, wherein the first two reflections are in the DCM and the final fourth reflection is asymmetric at grazing exit. Analyses of the interferometry data combined with the simulations show that compared with the beam exiting the DCM a gain of 76% in the SCL was achieved, albeit with a factor of 20 reduction in flux density, which may not be a severe penalty at a synchrotron beamline. Previous efforts reported in the literature to increase the SCL that employed asymmetric crystal diffraction at grazing incidence are also discussed. A much reduced SCL is found presently in simulations wherein the same asymmetric crystal is set for grazing incidence instead of grazing exit. In addition, the present study is compared and contrasted with two other means of increasing the SCL. These are (i) focusing the beam onto an aperture to act as a secondary source, and (ii) allowing the beam to propagate in vacuum an additional distance along the beamline.
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