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Showing papers on "Diffraction published in 2022"


Journal ArticleDOI
TL;DR: In this paper , a dual-polarized vortex beam generator based on metasurface and metagrating (MG) is proposed, where the phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells.
Abstract: Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems.

77 citations


Journal ArticleDOI
TL;DR: In this paper , the propagation characteristics and attenuation prediction equation of blast-induced vibration on closely spaced rock tunnels were discussed based on field monitoring and numerical simulation, and the applicability of some commonly used empirical equations to predict the particle peak velocity on lower bench and sidewall of closely spaced adjacent tunnel was discussed and compared.

45 citations


Journal ArticleDOI
TL;DR: In this article , the authors proposed a general method to perfectly control diffraction patterns based on a multi-beam PGM, which can be used to design multiple-beam antennas and that has significance in wireless communication applications.
Abstract: Phase-gradient metasurfaces (PGMs) constitute an efficient platform for deflection of a beam in a desired direction. According to the generalized Snell's law, the direction of the reflected/refracted wave can be tuned by the spatial phase function provided by the PGMs. However, most studies on PGM focus only on a single diffraction order, that is, the incident wave can be reflected or refracted to a single target direction. Even in the case of multiple beams pointing in different directions, the beams are still in the same order mode, and the energy carried by different beams cannot be controlled. In addition, the energy ratio of multiple beams is generally uncontrollable. Here, we propose a general method to perfectly control diffraction patterns based on a multi-beam PGM. An analytical solution for arbitrarily controlling diffraction beams is derived through which the generation and energy distribution in high-order diffraction beams can be achieved. Three metasurfaces with different diffraction orders and energy ratios are designed and fabricated to demonstrate the proposed method. The efficiencies of diffraction for the desired channels are close to 100%. The simulated and measured far-field patterns are in good agreement with theoretical predictions, validating the proposed method that provides a new way to design multi-beam antennas and that has significance in wireless communication applications.

43 citations


Journal ArticleDOI
TL;DR: In this paper , the implementation principles and related research progress of sub-wavelength focusing and super-resolution imaging based on artificial acoustic devices, including but not limited to phononic crystals (PCs) and acoustic metamaterials (AMMs), were systematically discussed.
Abstract: The effective operation of certain electronic, medical, industrial, and testing equipment relies on high-quality focusing and imaging capability, which also plays a vital role in the field of wave physics. Therefore, continuously improving the resolution capacity is essential. However, in a homogeneous medium dominated by the diffraction limit, the best resolution for wave focusing and imaging could only reach half the wavelength corresponding to the lowest operating frequency, significantly hindering the relevant application value. The development of phononic crystals (PCs) and acoustic metamaterials (AMMs) has realized sub-wavelength focusing and super-resolution imaging and attracted increasing research attention in physics, mechanics, engineering, and biomedical science. This Tutorial explained the basic principles and traditional methods of acoustic focusing and imaging. Then, the implementation principles and related research progress of sub-wavelength focusing and super-resolution imaging based on artificial acoustic devices, including but not limited to PCs and AMMs, were systematically discussed. Moreover, a method was introduced to realize sub-wavelength or sub-diffraction focusing by integrating these artificial devices into the time-reversal procedure. Finally, the potential development trends and practical application prospects were presented.

28 citations


Journal ArticleDOI
TL;DR: In this paper , a methodology was developed to enable experiments at static compression in the terapascal regime with laser heating, and it was applied to realize pressures of about 600 and 900 gigapascals in a laser-heated double-stage diamond anvil cell.
Abstract: Abstract Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions 1,2 . Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials analysis. Here we report on a methodology developed to enable experiments at static compression in the terapascal regime with laser heating. We apply this method to realize pressures of about 600 and 900 gigapascals in a laser-heated double-stage diamond anvil cell 3 , producing a rhenium–nitrogen alloy and achieving the synthesis of rhenium nitride Re 7 N 3 —which, as our theoretical analysis shows, is only stable under extreme compression. Full chemical and structural characterization of the materials, realized using synchrotron single-crystal X-ray diffraction on microcrystals in situ, demonstrates the capabilities of the methodology to extend high-pressure crystallography to the terapascal regime.

27 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated short-range order (SRO) solute clusters in the long-period stacking/order (LPSO) phases with an intrinsic-I (I1) type stacking faults (SFs), which have been uniquely formed in Mg-Co-Y alloys, based on atomic-resolution scanning transmission electron microscopy (STEM) combined with first-principles calculations.

26 citations


Journal ArticleDOI
TL;DR: In this article , the authors investigated short-range order (SRO) solute clusters in the long-period stacking/order (LPSO) phases with an intrinsic-I (I1) type stacking faults (SFs), which have been uniquely formed in Mg-Co-Y alloys, based on atomic-resolution scanning transmission electron microscopy (STEM) combined with first-principles calculations.

25 citations


Journal ArticleDOI
TL;DR: In this article , the authors evaluated subsurface defects of CaF2 single crystals induced by abrasive machining, the mappings between micro cracks and diffraction pattern curves, and the influence of micro cracks on lattice structures.

24 citations


Journal ArticleDOI
09 Jun 2022
TL;DR: In this article , the authors demonstrate a high efficiency hologram using a one-step nanomanufacturing method with a titanium dioxide nanoparticle-embedded-resin, allowing for high-throughput and low-cost fabrication.
Abstract: Metasurface holography, the reconstruction of holographic images by modulating the spatial amplitude and phase of light using metasurfaces, has emerged as a next-generation display technology. However, conventional fabrication techniques used to realize metaholograms are limited by their small patterning areas, high manufacturing costs, and low throughput, which hinder their practical use. Herein, we demonstrate a high efficiency hologram using a one-step nanomanufacturing method with a titanium dioxide nanoparticle-embedded-resin, allowing for high-throughput and low-cost fabrication. At a single wavelength, a record high 96.4% theoretical efficiency is demonstrated with an experimentally measured conversion efficiency of 90.6% and zero-order diffraction of 7.3% producing an ultrahigh-efficiency, twin-image free hologram, that can even be directly observed under ambient light conditions. Moreover, we design a broadband meta-atom with an average efficiency of 76.0% and experimentally demonstrate a metahologram with an average efficiency of 62.4% at visible wavelengths from 450 to 650 nm.

23 citations


Journal ArticleDOI
TL;DR: A systematic review of the various aspects of internal load transfer using different diffraction-based methods has been carried out in this work to strengthen the understanding of metal matrix composites (MMCs) and their micromechanics as discussed by the authors .
Abstract: A systematic review of the various aspects of internal load transfer using different diffraction-based methods has been carried out in this work to strengthen the understanding of metal matrix composites (MMCs) and their micromechanics. The load transfer from the softer and more compliant metallic matrix to the harder reinforcement plays a major role in conventional MMCs with a relatively high volume fraction of reinforcement particles. The mechanism of load transfer is dependent upon several factors, and a thorough understanding of them is important to design MMCs with optimum properties. Advanced diffraction-based techniques, such as neutron diffraction and synchrotron X-ray diffraction, have been applied successfully to study internal load transfer in MMCs by several authors. These techniques have allowed the measurement of elastic lattice strains in all crystallographic phases of a bulk MMC. The phase stress can then be calculated from the measured lattice strain using standard elasticity relations. Evolution of both the lattice microstrain and stress in each crystalline phase as a function of the applied stress yields information about the deformation and damage within the composite material. This review gives an overview of the studies carried out so far on internal load transfer in MMCs and the insights obtained this way.

20 citations


Journal ArticleDOI
TL;DR: In this article , the structural and mechanical properties of nanoporous (NP) carbon materials by extensive atomistic machine-learning (ML) driven molecular dynamics (MD) simulations are studied.
Abstract: We study the structural and mechanical properties of nanoporous (NP) carbon materials by extensive atomistic machine-learning (ML) driven molecular dynamics (MD) simulations. To this end, we retrain a ML Gaussian approximation potential (GAP) for carbon by recalculating the a-C structural database of Deringer and Csányi adding van der Waals interactions. Our GAP enables a notable speedup and improves the accuracy of energy and force predictions. We use the GAP to thoroughly study the atomistic structure and pore-size distribution in computational NP carbon samples. These samples are generated by a melt-graphitization-quench MD procedure over a wide range of densities (from 0.5 to 1.7 g/cm3) with structures containing 131 072 atoms. Our results are in good agreement with experimental data for the available observables and provide a comprehensive account of structural (radial and angular distribution functions, motif and ring counts, X-ray diffraction patterns, pore characterization) and mechanical (elastic moduli and their evolution with density) properties. Our results show relatively narrow pore-size distributions, where the peak position and width of the distributions are dictated by the mass density of the materials. Our data allow further work on computational characterization of NP carbon materials, in particular for energy-storage applications, as well as suggest future experimental characterization of NP carbon-based materials.

Journal ArticleDOI
TL;DR: In this paper , the performance of a symmetric two-dimensional electromagnetically induced grating produced in a four-level $N$-type atomic scheme was investigated, which interacts with a weak probe field and two simultaneous coupling fields: a 2D standing wave and a composite optical vortex beam.
Abstract: We investigate the performance of a symmetrical two-dimensional electromagnetically induced grating produced in a four-level $N$-type atomic scheme, which interacts with a weak probe field and two simultaneous coupling fields: a two-dimensional standing wave and a composite optical vortex beam. Based on the Maxwell wave equation, we study numerically the behavior of the amplitude, the phase modulations, as well as the probe field diffraction intensities of different order under various conditions for the coupling field detunings and the orbital angular momentum of the Laguerre-Gaussian field. The different orders of diffraction are altered when the azimuthal angle of the composite vortex light changes, thus producing a two-dimensional symmetric grating which transfers the probe energy to higher orders of diffraction. A detailed analysis of the probe field energy transfer to these different orders proves the possibility for direct control over the performance of the grating.

Journal ArticleDOI
TL;DR: ReciPro as mentioned in this paper is a comprehensive multipurpose crystallographic program equipped with an intuitive graphical user interface (GUI), and it can smoothly and quantitatively simulate not only single-crystal and/or polycrystalline (powder) diffraction patterns of X-ray, electron and neutron diffraction of a selected crystal model, based on the kinematic scattering theory, but also various electron diffraction images and high-resolution transmission electron microscopy (TEM) images based on dynamical scattering theory.
Abstract: ReciPro is a comprehensive multipurpose crystallographic program equipped with an intuitive graphical user interface (GUI), and it is completely free and open source. This software has a built-in crystal database consisting of over 20 000 crystal models, and the visualization system can seamlessly display a specified crystal model as an attractive three-dimensional graphic. The comprehensive features are not confined to these crystal model databases and viewers. It can smoothly and quantitatively simulate not only single-crystal and/or polycrystalline (powder) diffraction patterns of X-ray, electron and neutron diffraction of a selected crystal model, based on the kinematic scattering theory, but also various electron diffraction patterns and high-resolution transmission electron microscopy (TEM) images, based on the dynamical scattering theory. The features of stereographic projection of crystal planes/axes to explore crystal orientation relationships and the semi-automatic diffraction spot indexing function for experimental diffraction patterns assist diffraction experiments and analyses. These features are linked through a user-friendly GUI, and the results can be synchronously displayed almost in real time. ReciPro will assist a wide range of crystallographers (including beginners) using X-ray, electron and neutron diffraction crystallography and TEM.

Journal ArticleDOI
TL;DR: In this article , a particular disposition of light illumination and collection paths is proposed to free optical imaging from the restrictions imposed by diffraction, which decouples lateral resolution from depth-of-focus by establishing a one-toone correspondence along a focal line between the incident and collected light.
Abstract: Microscopic imaging in three dimensions enables numerous biological and clinical applications. However, high-resolution optical imaging preserved in a relatively large depth range is hampered by the rapid spread of tightly confined light due to diffraction. Here, we show that a particular disposition of light illumination and collection paths liberates optical imaging from the restrictions imposed by diffraction. This arrangement, realized by metasurfaces, decouples lateral resolution from depth-of-focus by establishing a one-to-one correspondence (bijection) along a focal line between the incident and collected light. Implementing this approach in optical coherence tomography, we demonstrate tissue imaging at 1.3 μm wavelength with ~ 3.2 μm lateral resolution, maintained nearly intact over 1.25 mm depth-of-focus, with no additional acquisition or computation burden. This method, termed bijective illumination collection imaging, is general and might be adapted across various existing imaging modalities.

Journal ArticleDOI
TL;DR: In this article , the authors demonstrate the first live, autonomous control over neutron diffraction experiments by developing and deploying ANDiE, which is a simulator that can dynamically steer the sequence of measurements to determine the magnetic ordering transition of both MnO and Fe 1.09 Te.
Abstract: We demonstrate the first live, autonomous control over neutron diffraction experiments by developing and deploying ANDiE: the autonomous neutron diffraction explorer. Neutron scattering is a unique and versatile characterization technique for probing the magnetic structure and behavior of materials. However, instruments at neutron scattering facilities in the world is limited, and instruments at such facilities are perennially oversubscribed. We demonstrate a significant reduction in experimental time required for neutron diffraction experiments by implementation of autonomous navigation of measurement parameter space through machine learning. Prior scientific knowledge and Bayesian active learning are used to dynamically steer the sequence of measurements. We show that ANDiE can experimentally determine the magnetic ordering transition of both MnO and Fe 1.09 Te all while providing a fivefold enhancement in measurement efficiency. Furthermore, in a hypothesis testing post-processing step, ANDiE can determine transition behavior from a set of possible physical models. ANDiE's active learning approach is broadly applicable to a variety of neutron-based experiments and can open the door for neutron scattering as a tool of accelerated materials discovery.

Journal ArticleDOI
TL;DR: In this article , small-molecule serial femtosecond X-ray crystallography (smSFX) was used for the determination of material crystal structures from microcrystals.
Abstract: Abstract Inorganic–organic hybrid materials represent a large share of newly reported structures, owing to their simple synthetic routes and customizable properties 1 . This proliferation has led to a characterization bottleneck: many hybrid materials are obligate microcrystals with low symmetry and severe radiation sensitivity, interfering with the standard techniques of single-crystal X-ray diffraction 2,3 and electron microdiffraction 4–11 . Here we demonstrate small-molecule serial femtosecond X-ray crystallography (smSFX) for the determination of material crystal structures from microcrystals. We subjected microcrystalline suspensions to X-ray free-electron laser radiation 12,13 and obtained thousands of randomly oriented diffraction patterns. We determined unit cells by aggregating spot-finding results into high-resolution powder diffractograms. After indexing the sparse serial patterns by a graph theory approach 14 , the resulting datasets can be solved and refined using standard tools for single-crystal diffraction data 15–17 . We describe the ab initio structure solutions of mithrene (AgSePh) 18–20 , thiorene (AgSPh) and tethrene (AgTePh), of which the latter two were previously unknown structures. In thiorene, we identify a geometric change in the silver–silver bonding network that is linked to its divergent optoelectronic properties 20 . We demonstrate that smSFX can be applied as a general technique for structure determination of beam-sensitive microcrystalline materials at near-ambient temperature and pressure.

Journal ArticleDOI
TL;DR: In this article , a comparative analysis of crystallite sizes of the prepared powders was carried out by different methods (models) such as the Scherrer, Williamson-Hall (W-H), Halder-Wagner (H-W), and size-strain plot (SSP) method.
Abstract: In this study, SrFe12-xNdxO19, where x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5, was prepared using high-energy ball milling. The prepared samples were characterized by X-ray diffraction (XRD). Using the XRD results, a comparative analysis of crystallite sizes of the prepared powders was carried out by different methods (models) such as the Scherrer, Williamson–Hall (W–H), Halder–Wagner (H–W), and size-strain plot (SSP) method. All the studied methods prove that the average nanocrystallite size of the prepared samples increases by increasing the Nd concentration. The H–W and SSP methods are more accurate than the Scherer or W–H methods, suggesting that these methods are more suitable for analyzing the XRD spectra obtained in this study. The specific saturation magnetization (σs), the effective anisotropy constant (Keff), the field of magnetocrystalline anisotropy (Ha), and the field of shape anisotropy (Hd) for SrFe12-xNdxO19 (0 ≤ x ≤ 0.5) powders were calculated. The coercivity (Hc) increases (about 9% at x = 0.4) with an increasing degree of substitution of Fe3+ by Nd3+, which is one of the main parameters for manufacturing permanent magnets.

Journal ArticleDOI
TL;DR: In this paper , the DCRFoam solver is used to simulate the reflection and diffraction processes that occur when detonation waves collide with various objects, including cylindrical, square, triangular, and inverted triangular obstacles.

Journal ArticleDOI
TL;DR: In this paper , small-molecule serial femtosecond X-ray crystallography (smSFX) was used for the determination of material crystal structures from microcrystals.
Abstract: Abstract Inorganic–organic hybrid materials represent a large share of newly reported structures, owing to their simple synthetic routes and customizable properties 1 . This proliferation has led to a characterization bottleneck: many hybrid materials are obligate microcrystals with low symmetry and severe radiation sensitivity, interfering with the standard techniques of single-crystal X-ray diffraction 2,3 and electron microdiffraction 4–11 . Here we demonstrate small-molecule serial femtosecond X-ray crystallography (smSFX) for the determination of material crystal structures from microcrystals. We subjected microcrystalline suspensions to X-ray free-electron laser radiation 12,13 and obtained thousands of randomly oriented diffraction patterns. We determined unit cells by aggregating spot-finding results into high-resolution powder diffractograms. After indexing the sparse serial patterns by a graph theory approach 14 , the resulting datasets can be solved and refined using standard tools for single-crystal diffraction data 15–17 . We describe the ab initio structure solutions of mithrene (AgSePh) 18–20 , thiorene (AgSPh) and tethrene (AgTePh), of which the latter two were previously unknown structures. In thiorene, we identify a geometric change in the silver–silver bonding network that is linked to its divergent optoelectronic properties 20 . We demonstrate that smSFX can be applied as a general technique for structure determination of beam-sensitive microcrystalline materials at near-ambient temperature and pressure.

Journal ArticleDOI
06 Mar 2022
TL;DR: In this article , a metagrating around BICs and EPs is proposed to achieve an extreme degree of control over coupling to different diffraction orders, such as weak to strong coupling.
Abstract: Coupled resonances in non-Hermitian systems can lead to exotic optical features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been recently emerged as powerful tools to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineer spatial wavefronts have remained elusive. Here, it is shown that, by operating a metagrating around BICs and EPs, it is possible to achieve an extreme degree of control over coupling to different diffraction orders. Subwavelength metallic slit arrays stacked on a metal-insulator-metal waveguide, enabling a careful control of the coupling between localized and guided modes are explored. By tuning the coupling strength from weak to strong, the overall spectral response can be tailored and the emergence of singular features, like BICs and EPs can be enabled. Perfect unitary diffraction efficiency with large spectrum selectivity is achieved around these singular features, with promising applications for selective wavefront shaping, filtering, and sensing.

Journal ArticleDOI
TL;DR: In this article , the vertical distribution of light-matter interactions at 1 nm spatial resolution by coupling A excitons of MoS 2 and gap-mode plasmonic nanocavities was demonstrated.
Abstract: Abstract The light-matter interaction between plasmonic nanocavity and exciton at the sub-diffraction limit is a central research field in nanophotonics. Here, we demonstrated the vertical distribution of the light-matter interactions at ~1 nm spatial resolution by coupling A excitons of MoS 2 and gap-mode plasmonic nanocavities. Moreover, we observed the significant photoluminescence (PL) enhancement factor reaching up to 2800 times, which is attributed to the Purcell effect and large local density of states in gap-mode plasmonic nanocavities. Meanwhile, the theoretical calculations are well reproduced and support the experimental results.

Journal ArticleDOI
TL;DR: In this paper , a time-domain version of Young's double-slit experiment is presented, where a beam of light twice gated in time produces an interference in the frequency spectrum.
Abstract: Double-slit experiments—where a wave is transmitted through a thin double aperture in space—have confirmed the wave–particle duality of quantum objects, such as single photons, electrons, neutrons, atoms and large molecules. Yet, the temporal counterpart of Young’s double-slit experiment—a wave interacting with a double temporal modulation of an interface—remains elusive. Here we report such a time-domain version of the classic Young’s double-slit experiment: a beam of light twice gated in time produces an interference in the frequency spectrum. The ‘time slits’, narrow enough to produce diffraction at optical frequencies, are generated from the optical excitation of a thin film of indium tin oxide near its epsilon-near-zero point. The separation between time slits determines the period of oscillations in the frequency spectrum, whereas the decay of fringe visibility in frequency reveals the shape of the time slits. Surprisingly, many more oscillations are visible than expected from existing theory, implying a rise time that approaches an optical cycle. This result enables the further exploration of time-varying physics, towards the spectral synthesis of waves and applications such as signal processing and neuromorphic computation. A temporal version of Young’s double-slit experiment shows characteristic interference in the frequency domain when light interacts with time slits produced by ultrafast changes in the refractive index of an epsilon-near-zero material.

Journal ArticleDOI
TL;DR: A physical mechanism to improve the light absorption efficiency of graphene monolayer from the universal value of 2.3% to about 30% in the visible and near-infrared wavelength range is investigated.
Abstract: In this study, we investigate a physical mechanism to improve the light absorption efficiency of graphene monolayer from the universal value of 2.3% to about 30% in the visible and near-infrared wavelength range. The physical mechanism is based on the diffraction coupling of surface plasmon polariton resonances in the periodic array of metal nanoparticles. Through the physical mechanism, the electric fields on the surface of graphene monolayer are considerably enhanced. Therefore, the light absorption efficiency of graphene monolayer is greatly improved. To further confirm the physical mechanism, we use an interaction model of double oscillators to explain the positions of the absorption peaks for different array periods. Furthermore, we discuss in detail the emerging conditions of the diffraction coupling of surface plasmon polariton resonances. The results will be beneficial for the design of graphene-based photoelectric devices.

Journal ArticleDOI
TL;DR: In this paper , the structure of two globular proteins was determined ab initio using microcrystal electron diffraction (MicroED) data that were collected on a direct electron detector in counting mode.
Abstract: Abstract Structures of two globular proteins were determined ab initio using microcrystal electron diffraction (MicroED) data that were collected on a direct electron detector in counting mode. Microcrystals were identified using a scanning electron microscope (SEM) and thinned with a focused ion beam (FIB) to produce crystalline lamellae of ideal thickness. Continuous-rotation data were collected using an ultra-low exposure rate to enable electron counting in diffraction. For the first sample, triclinic lysozyme extending to a resolution of 0.87 Å, an ideal helical fragment of only three alanine residues provided initial phases. These phases were improved using density modification, allowing the entire atomic structure to be built automatically. A similar approach was successful on a second macromolecular sample, proteinase K, which is much larger and diffracted to a resolution of 1.5 Å. These results demonstrate that macromolecules can be determined to sub-ångström resolution by MicroED and that ab initio phasing can be successfully applied to counting data.

Journal ArticleDOI
TL;DR: In this paper , single-crystal diffraction studies in laser-heated diamond-anvil cells were conducted to show that Ca2CO4 orthocarbonate, which contains CO44− tetrahedra, can be formed already at 20 GPa at 1830 K, i.e., at much lower pressures than other carbonates with sp3-hybridized carbon.
Abstract: Abstract We show, by single-crystal diffraction studies in laser-heated diamond-anvil cells, that Ca2CO4 orthocarbonate, which contains CO44− tetrahedra, can be formed already at ~20 GPa at ~1830 K, i.e., at much lower pressures than other carbonates with sp3-hybridized carbon. Ca2CO4 can also be formed at ~89 GPa and ~2500 K. This very broad P-T range suggests the possible existence of Ca2CO4 in the Earth’s transition zone and in most of the lower mantle. Raman spectroscopy shows the typical bands associated with tetrahedral CO44−-groups. DFT-theory based calculations reproduce the experimental Raman spectra and indicate that at least in the athermal limit the phase assemblage of Ca2CO4 + 2SiO2 is more stable than 2CaSiO3 + CO2 at high pressures.

Journal ArticleDOI
TL;DR: In this paper , the authors showed that a much larger elastic-like strain of more than 4% can be achieved in a tweed textured Fe-Pd single crystal under a compressive stress of 300 MPa.

Journal ArticleDOI
TL;DR: In this paper , the structure elucidation of indomethacin by 3D electron diffraction was reported and revealed the truth that melt-and solution-crystallized and solution-decompositioned versions of the drug are in fact two polymorphs with different crystal structures.
Abstract: Indomethacin is a clinically classical non-steroidal anti-inflammatory drug that has been marketed since 1965. The third polymorph, Form δ, was discovered by both melt and solution crystallization in 1974. δ-indomethacin cannot be cultivated as large single crystals suitable for X-ray crystallography and, therefore, its crystal structure has not yet been determined. Here, we report the structure elucidation of δ-indomethacin by 3D electron diffraction and reveal the truth that melt-crystallized and solution-crystallized δ-indomethacin are in fact two polymorphs with different crystal structures. We propose to keep the solution-crystallized polymorph as Form δ and name the melt-crystallized polymorph as Form θ. Intriguingly, both structures display plastic flexibility based on a slippage mechanism, making indomethacin the first drug to have two plastic polymorphs. This discovery and correction of a 47-year-old misunderstanding signify that 3D electron diffraction has become a powerful tool for polymorphic structural studies.

Journal ArticleDOI
TL;DR: In this paper, the authors showed that a much larger elastic-like strain of more than 4% can be achieved in a tweed textured Fe-Pd single crystal under a compressive stress of 300 MPa.

Journal ArticleDOI
TL;DR: In this paper , a method for calculating the point scattering function (PSF) of an Offner imaging hyperspectrometer with a diffraction grating in the approximation of scalar diffraction theory is proposed.
Abstract: We propose a method for calculating the point scattering function (PSF) of an Offner imaging hyperspectrometer with a diffraction grating in the approximation of scalar diffraction theory. The method consistently takes into account limitations and diffraction of a light beam by elements of the hyperspectrometer system in accordance with the physics of image formation. The PSF of the Offner imaging hyperspectrometer is numerically simulated at various beam parameters and wavelengths. The simulation results are verified using analytical relationships, a geometrical optics approach, as well as a comparison with the related works of other researchers.