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Abstract: This paper describes fabrication methods used to demonstrate the advantages of nested or Montel optics for micro/nanofocusing of synchrotron X-ray beams. A standard Kirkpatrick-Baez (KB) mirror system uses two separated elliptical mirrors at glancing angles to the X-ray beam and sequentially arranged at 90° to each other to focus X-rays successively in the vertical and horizontal directions. A nested KB mirror system has the two mirrors positioned perpendicular and side-by-side to each other. Compared to a standard KB mirror system, Montel optics can focus a larger divergence and the mirrors can have a shorter focal length. As a result, nested mirrors can be fabricated with improved demagnification factor and ultimately smaller focal spot, than with a standard KB arrangement. The nested system is also more compact with an increased working distance, and is more stable, with reduced complexity of mirror stages. However, although Montel optics is commercially available for laboratory X-ray sources, due to technical difficulties they have not been used to microfocus synchrotron radiation X-rays, where ultra-precise mirror surfaces are essential. The main challenge in adapting nested optics for synchrotron microfocusing is to fabricate mirrors with a precise elliptical surface profile at the very edge where the two mirrors meet and where X-rays scatter. For example, in our application to achieve a sub-micron focus with high efficiency, a surface figure root-mean-square (rms) error on the order of 1nm is required in the useable area along the X-ray footprint with a ∼0.1mm-diameter cross section. In this paper we describe promising ways to fabricate precise nested KB mirrors using our profile coating technique and inexpensive flat Si substrates. [Copyright &y& Elsevier]

Abstract: A spatially resolved X-ray diffraction method – with a submicron 3D resolution together with SEM and OIM analysis are applied to understand the arrangements of voids, geometrically necessary dislocations and strain gradient distributions in samples of Al (123) and Cu (001) single crystals shocked to incipient spallation fracture. We describe how geometrically necessary dislocations and the effective strain gradient alter white beam Laue patterns of the shocked materials. Several distinct structural zones are observed at different depths under the impact surface. The density of geometrically necessary dislocations (GNDs) is extremely high near the impact and back surface of the shock recovered crystals. The spall region is characterized by a large density of mesoscale voids and GNDs. The spall region is separated from the impact and back surfaces by compressed regions with high total dislocation density but lower GNDs density. Self-organization of shear bands is observed in the shock recovered Cu single crystal. [Copyright &y& Elsevier]

Abstract: Timely development of materials for the demanding fusion energy environment requires a broad range of advanced scientific tools, including advanced structural characterization methods. The current state-of-the-art and emerging capabilities in electron microscopy, atom probe tomography, neutron scattering and X-ray scattering are reviewed with respect to potential applications in fusion materials research and development. Recent dramatic advances in capabilities in all four of these characterization tools are transforming the spatial precision and quantitative information that can be extracted during structural characterization. Examples include spectroscopic identification of single atoms in bulk materials, three-dimensional mapping of millimeter-scale volumes of materials with nanometer resolution, and high-resolution in situ measurements of internal stress and strain during mechanical testing. [Copyright &y& Elsevier]

Abstract: High-performance Kirkpatrick-Baez (KB) neutron supermirror optics can nondispersively image neutrons to small spots. Ray tracing finds that under many conditions, KB mirrors work near the theoretical limit set by source brilliance and can deliver orders of magnitude greater intensities than is possible with conventional (nonfocusing) neutron optics. In general, KB neutron supermirrors are preferred when the required beam size at the sample is small and when the distance between the optics and the sample is not small. Waveguides with beam definings slits are preferred for very short wavelengths, for big beams and when the slits can be placed very close to the sample. For example, for λ ∼0.1nm, if the distance from the last optical element to the sample is ∼100mm, almost two orders of magnitude greater intensity can be focused onto a 100μm spot with M =3KB supermirrors than with a beam guide and symmetric slits. This is independent of whether the beam guide collimates or condenses the beam so long as without slits the beam is larger than the acceptable beam size at the sample. We describe the ray tracing and phase space arguments that support the use of KB supermirrors for producing intense small beams and describe the performance of a prototype KB device which achieved a 89μm×90μm focus. We briefly describe even more advanced methods that can increase the beam divergence on the sample while maintaining a small beam. [Copyright &y& Elsevier]

Abstract: Polychromatic microdiffraction uses small X-ray beams to characterize the local crystallographic structure of materials. When combined with a depth resolving technique called differential aperture microscopy, the phase and local orientation of femto-liter volumes (0.5×0.5×0.7μm3) can be resolved beneath the surface of a sample. In addition, the local elastic strain and dislocation tensors can also be determined and the local dislocation type can be modeled. Here we present recent technical developments, including example applications and emerging research directions. [Copyright &y& Elsevier]

Abstract: Variations in the local crystallographic orientation due to the presence of geometrically necessary dislocations and dislocation boundaries smear the distribution of intensity near Laue reflections. Here, some simple model distributions of geometrically necessary dislocations, GNDs, are used to estimate the dislocation tensor field from the intensity distribution of Laue peaks. Streaking of the Laue spots is found to be quantitatively and qualitatively distinct depending on the ratio between the absorption coefficient and the GND density gradient. In addition, different slip systems cause distinctly different Laue-pattern streaking. Experimental Laue patterns are therefore sensitive to stored dislocations and GNDs. As an example, white beam microdiffraction was applied to characterize the dislocation arrangement in a deformed polycrystalline Ni grain during in situ uniaxial tension. [Copyright &y& Elsevier]

Abstract: Three-dimensional (3D) measurements of strain tensor distributions with subgrain resolution are now possible due to an emerging class of instrumentation: the 3D X-ray crystal microscopes. These instruments combine ultra-intense synchrotron X-ray sources and advanced X-ray optics to probe polycrystalline materials with submicron spatial resolution. By employing polychromatic X-ray beams and a virtual pinhole camera method, called differential aperture microscopy, 3D distributions of the local crystalline phase, orientation (local texture) and elastic and plastic strain tensor distributions can be measured with resolution below the grain size of most materials. The elastic strain tensor elements can typically be determined with uncertainties less than 100ppm in brittle materials. Orientations can be quantified to ∼0.01° and the local unpaired dislocation density can be measured in ductile materials. Efforts are underway to improve the spatial resolution and increase the depth probed. Because the 3D X-ray crystal microscope is a penetrating nondestructive tool, it is ideal for studies of mesoscale structural evolution in materials. The unprecedented information that can be obtained with this new class of instrumentation is certain to advance our understanding of the materials physics underpinning the behavior of polycrystalline materials. [Copyright &y& Elsevier]

Abstract: Advanced polychromatic microdiffraction is sensitive to the organization of dislocations and other defects that rotate the lattice planes. Using ultra-brilliant third-generation synchrotron sources and non-dispersive X-ray focusing optics, it is now possible to analyze individual dislocation cells and walls at a submicron scale that cannot be probed by traditional methods. The method is applied to an Ir weld sample to illustrate how microdiffraction can be used to determine the locally active dislocation system. [Copyright &y& Elsevier]

Electromigration-induced failure in metal interconnect constitutes a major reliability problem in the semiconductor industry. Recently, experimental techniques capable of probing grain orientation and stress with a spatial resolution compatible with the dimensions of the lines have emerged. White beam X-ray microdiffraction is particularly well suited to the in situ study of electromigration. The technique was used to probe microstructure in interconnects and recently unambiguously unveiled the plastic nature of the deformation induced by mass transport during electromigration in Al(Cu) interconnect lines even before macroscopic damage. The aim of the present research is to understand the complex dislocation structure arising from electromigration-induced plastic deformation by simulating the shape of the reflections and comparing them with the shape observed in the experimental data. We provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during an in situ electromigration experiment. Custom software allows us to determine the orientation of the predominant dislocation network in each sample subgrain. [Copyright &y& Elsevier]

Abstract: We have developed software to accelerate the analysis of the diffuse scattering data and to recover the short-range-order (SRO) and other parameters. The software is applied to data collected from a Cu50Au50 single crystal. [Copyright &y& Elsevier]

Abstract: Nondispersive optics are essential for emerging microdiffraction and nanobeam research. Here we describe extensions to traditional Kirkpatrick–Baez optics required to develop nondispersive microdiffraction and nanoprobe optics with 1–10nm spatial resolution. [Copyright &y& Elsevier]

Abstract: This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence (μ-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation of complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent. [Copyright &y& Elsevier]

Abstract: X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with submicron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechancial Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2×1017 H+/cm2 protons. Preliminary results indicate that a measurable strain, on the order of 10−3, was introduced into the film near the End of Range (EOR) region of the protons. [Copyright &y& Elsevier]

Describes the three-dimensional X-ray microscopy technique using polychromatic synchrotron X-ray microbeams to probe local crystal structure. Application of the technique to single-crystal, composite and functionally graded materials; Development of X-ray microscopy technique; Extraction of complete Laue diffraction patterns by using the technique.

Abstract: We report on three-dimensional spatially resolved X-ray microdiffraction measurements of inhomogeneous deformation within individual polycrystalline grains. These measurements provide new insights into the role of grain boundaries. Particularly striking is the qualitatively different mechanical behavior of subgrain volumes near grain boundaries and triple junctions compared to bulk-grain mechanical behavior. These differences are studied by characterizing the evolution of the local orientation distribution in a polycrystalline Ni sample using polychromatic synchrotron X-ray microdiffraction. Dependence of deformation on grain boundary types and triple junctions is determined. Quantitative distinctions in deformation behavior between low-angle boundaries, special low-energy high-angle boundaries, general high-angle boundaries and triple junctions are characterized in terms of spatially resolved misorientation development and extensions of grain boundary effects. In general, larger lattice misorientations are observed near boundaries with higher grain boundary energy. Special high-coincidence grain boundaries exhibit smaller deformation misorientations than general high-angle grain boundaries. These observations are consistent with the observed increases in ductility in grain boundary engineered materials. [Copyright &y& Elsevier]

The depth-dependent strain gradients near buried interfaces in a model system of NiAl–Mo composite were nondestructively probed with 3-D X-ray microdiffraction. Coupled with micromechanical analysis, our study shows that the relaxation of the residual thermal strains in the NiAl–Mo composites results in the formation of a near-surface “slip zone” with large strain gradients in both the reinforcing Mo fibers and NiAl matrix. Based on these results an approach to calculate the fiber–matrix interface strength for composite materials is suggested. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional spatially resolved strains were mapped in a model NiAl/Mo composite after nanoindentation. The depth-dependent strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length scale using X-ray microdiffraction and compared with a detailed micromechanical stress analysis. It is shown that indentation-induced deformation in the composite material is distinct from deformation expected in a single-phase material. This difference arises in part from residual thermal strains in both phases of the composite in the as-grown state. Interplay between residual thermal strains and external mechanical strain results in a complex distribution of dilatational strain in the Mo fibers and NiAl matrix and is distinct in different locations within the indented area. Reversal of the strain sign (e.g., alternating tensile/compressive/tensile strain distribution) is observed in the NiAl matrix. Bending of the Mo fibers during indentation creates relatively large ∼1.5° misorientations between the different fibers and NiAl matrix. Compressive strain along the 〈001〉 direction reached −0.017 in the Mo fibers and −0.007 in the NiAl matrix. [ABSTRACT FROM AUTHOR]

Abstract: We compare experimental measurements of inhomogeneous plastic deformation in a Ni bicrystal with crystal plasticity simulations. Polychromatic X-ray microdiffraction, orientation imaging microscopy and scanning electron microscopy, were used to characterize the geometrically necessary dislocation distribution of the bicrystal after uniaxial tensile deformation. Changes in the local crystallographic orientations within the sample reflect its plastic response during the tensile test. Elastic strain in both grains increases near the grain boundary. Finite element simulations were used to understand the influence of initial grain orientation and structural inhomogeneities on the geometrically necessary dislocations arrangement and distribution and to understand the underlying materials physics. [Copyright &y& Elsevier]

Abstract: The availability of intense, focused synchrotron X-ray microbeams has enabled new techniques for materials investigations with sub-micron spatial resolution. The scanning microbeam setup we have developed at the XOR-UNI beamline at the Advanced Photon Source (APS) is versatile in that it provides 1D, 2D or 3D scans (including depth resolution), and can alternate between polychromatic- and monochromatic-beam modes. Focusing in both modes uses elliptical Kirkpatrick–Baez (K–B) reflecting mirrors. Beam diameters of ~500 nm FWHM are now routine, and 90 nm focus has been demonstrated. In white-beam mode, a CCD detector records a complete Laue diffraction pattern, which is analyzed with an automated indexing program. These X-ray diffraction patterns provide real-space maps of the local lattice structure, crystal orientation, grain morphology, and strain tensor. Spatially-resolved X-ray microdiffraction studies are now providing previously unavailable measurements of local microstructures. These measurements, in turn, yield new insights in several classic fields of materials science. This paper will illustrate the application of polychromatic scanning X-ray microscopy with examples from 1D, 2D and 3D materials systems. In 1D systems, we have mapped the structure and orientation of an individual ZnO nanorod along with the associated Ge catalyst particle used to control the nanocrystal growth. In 2D systems, X-ray microdiffraction studies have revealed the mechanisms for local crystallographic tilting in epitaxial oxide films grown on textured Ni substrates for superconducting applications. In 3D systems, X-ray microscopy investigations have included in-situ studies of microstructural evolution during thermal grain growth in polycrystalline aluminum. In general, these spatially-resolved measurements provide important new insights and are valuable as input for theoretical and computer modeling studies of a wide range of material processes. [Copyright &y& Elsevier]

Abstract: The nature of residual damage from atomic displacement cascades in iron has been investigated by diffuse X-ray scattering. A single crystal iron sample was irradiated at ∼60°C in the High Flux Isotope Reactor at the Oak Ridge National Laboratory to a fluence of 1×1023 n/m2 (E >0.1MeV), or ∼0.01 dpa. Diffuse X-ray scattering measurements were carried out at the Advanced Photon Source at the Argonne National Laboratory on three specimens: unirradiated, as-irradiated, and irradiated and annealed for one hour at 450°C (IA). The specimens were cooled to ∼40K to minimize thermal diffuse scattering. Subsequent measurements of the specimen lattice parameter were completed at ORNL. The diffuse scattering in the as-irradiated specimen was dominated by interstitial defect clusters exhibiting a tetragonal distortion consistent with a 〈100〉 type defect. Substantial recovery of this defect component was observed following the anneal at 450°C. A lattice parameter increase was observed following irradiation, which is also consistent with a substantial population of interstitial type defects. A net lattice parameter decrease was observed in the IA specimen, indicating loss of the interstitial defects with a residual population of vacancy-type defects. [Copyright &y& Elsevier]

A recently developed differential-aperture X-ray microscopy (DAXM) technique provides local structure and crystallographic orientation with submicron spatial resolution in three-dimensions; it further provides angular precision of ∼0.01° and local elastic strain with an accuracy of ∼1.0×10−4 using microbeams from high brilliance third generation synchrotron X-ray sources. DAXM is a powerful tool for inter- and intra-granular studies of lattice distortions and lattice rotations on mesoscopic length scales of tenths of microns to hundreds of microns that are largely above the range of traditional electron microscopy probes. Nondestructive, point-to-point, spatially resolved measurements of local lattice orientations in bulk materials provide direct information on geometrically necessary dislocation density distributions through measurements of the lattice curvature in plastically deformed materials. This paper reviews the DAXM measurement technique and discusses recent demonstrations of DAXM capabilities for measurements of microtexture, local elastic strain, and plastic deformation microstructure. [Copyright &y& Elsevier]

X-ray microbeams have been used to perform nondestructive measurements of the local orientations and microstructure in single-crystal and grain-boundary regions in a columnar Al (0.2 wt.% Mg) tri-crystal deformed 20% in plane-strain. The measurements were made using a recently developed differential-aperture X-ray microscopy (DAXM) technique providing high angular resolution determinations of local orientations with micron 3-D spatial resolution using focused microbeams. The X-ray microbeam technique is described, three-dimensional spatially resolved pole-figures and lattice rotation distributions in single-crystal and grain-boundary regions are presented, and the potential of micron resolution 3-D X-ray structural microscopy for plastic deformation investigations is discussed. [Copyright &y& Elsevier]

X-ray fluorescence microtomography has been used to measure the trace element spatial distribution in a TRISO SiC shell after exposure to 1.9×1025 neutrons/m2. The bare SiC shell was prepared by laser drilling the TRISO particle and leaching away the core and C. The exposed shell was measured with an X-ray probe having a size of approximately 1×3 μm2 on beamline 2-ID at the Advanced Photon Source. The trace element distribution in the SiC shell was reconstructed after correcting the data for artifacts arising from absorption and experimental restrictions. The trace elements were found in small (<2 μm) regions through the SiC shell and appear to have been introduced during fabrication. X-ray fluorescence microtomography is an ideal tool for this work because it is a penetrating non-destructive probe with good sensitivity to high Z trace elements in a low Z matrix and because it provides a picture of the elemental distribution in the shell. [Copyright &y& Elsevier]

Abstract: Differential-aperture X-ray microscopy (DAXM) is a powerful approach to 3D tomography with particular relevance to X-ray microdiffraction. With DAXM, scattering from submicron volumes can be resolved. However, the method is intrinsically a scanning technique where every resolved volume element (voxel) requires at least one area-detector readout. Previous applications of DAXM have used a single wire for knife-edge step profiling. Here, we demonstrate a way to accelerate DAXM measurements using multiple wires. A proof-of-principle experiment with a three-wire prototype showed that the speed of measurements can be tripled, but careful calibrations of wires will be required to maintain the spatial accuracy. In addition, related possibilities for accelerating measurements are briefly discussed. [Copyright &y& Elsevier]