Showing papers on "Diffraction published in 2015"

3D intensity and phase imaging from light field measurements in an LED array microscope

Abstract: Realizing high resolution across large volumes is challenging for 3D imaging techniques with high-speed acquisition. Here, we describe a new method for 3D intensity and phase recovery from 4D light field measurements, achieving enhanced resolution via Fourier ptychography. Starting from geometric optics light field refocusing, we incorporate phase retrieval and correct diffraction artifacts. Further, we incorporate dark-field images to achieve lateral resolution beyond the diffraction limit of the objective (5× larger NA) and axial resolution better than the depth of field, using a low-magnification objective with a large field of view. Our iterative reconstruction algorithm uses a multislice coherent model to estimate the 3D complex transmittance function of the sample at multiple depths, without any weak or single-scattering approximations. Data are captured by an LED array microscope with computational illumination, which enables rapid scanning of angles for fast acquisition. We demonstrate the method with thick biological samples in a modified commercial microscope, indicating the technique’s versatility for a wide range of applications.

X-Ray Diffraction: Instrumentation and Applications

Abstract: X-ray diffraction (XRD) is a powerful nondestructive technique for characterizing crystalline materials. It provides information on structures, phases, preferred crystal orientations (texture), and other structural parameters, such as average grain size, crystallinity, strain, and crystal defects. X-ray diffraction peaks are produced by constructive interference of a monochromatic beam of X-rays scattered at specific angles from each set of lattice planes in a sample. The peak intensities are determined by the distribution of atoms within the lattice. Consequently, the X-ray diffraction pattern is the fingerprint of periodic atomic arrangements in a given material. This review summarizes the scientific trends associated with the rapid development of the technique of X-ray diffraction over the past five years pertaining to the fields of pharmaceuticals, forensic science, geological applications, microelectronics, and glass manufacturing, as well as in corrosion analysis.

Fabrication of ideal geometric-phase holograms with arbitrary wavefronts

Abstract: Throughout optics and photonics, phase is normally controlled via an optical path difference. Although much less common, an alternative means for phase control exists: a geometric phase (GP) shift occurring when a light wave is transformed through one parameter space, e.g., polarization, in such a way as to create a change in a second parameter, e.g., phase. In thin films and surfaces where only the GP varies spatially—which may be called GP holograms (GPHs)—the phase profile of nearly any (physical or virtual) object can in principle be embodied as an inhomogeneous anisotropy manifesting exceptional diffraction and polarization behavior. Pure GP elements have had poor efficiency and utility up to now, except in isolated cases, due to the lack of fabrication techniques producing elements with an arbitrary spatially varying GP shift at visible and near-infrared wavelengths. Here, we describe two methods to create high-fidelity GPHs, one interferometric and another direct-write, capable of recording the wavefront of nearly any physical or virtual object. We employ photoaligned liquid crystals to record the patterns as an inhomogeneous optical axis profile in thin films with a few μm thickness. We report on eight representative examples, including a GP lens with F/2.3 (at 633 nm) and 99% diffraction efficiency across visible wavelengths, and several GP vortex phase plates with excellent modal purity and remarkably small central defect size (e.g., 0.7 and 7 μm for topological charges of 1 and 8, respectively). We also report on a GP Fourier hologram, a fan-out grid with dozens of far-field spots, and an elaborate phase profile, which showed excellent fidelity and very low leakage wave transmittance and haze. Together, these techniques are the first practical bases for arbitrary GPHs with essentially no loss, high phase gradients (∼rad/μm), novel polarization functionality, and broadband behavior.

Three-dimensional reconstruction of the giant mimivirus particle with an X-ray free-electron laser

Abstract: We present a proof-of-concept three-dimensional reconstruction of the giant mimivirus particle from experimentally measured diffraction patterns from an x-ray free-electron laser. Three-dimensional imaging requires the assembly of many two-dimensional patterns into an internally consistent Fourier volume. Since each particle is randomly oriented when exposed to the x-ray pulse, relative orientations have to be retrieved from the diffraction data alone. We achieve this with a modified version of the expand, maximize and compress algorithm and validate our result using new methods.

Test of Equivalence Principle at 10(-8) Level by a Dual-Species Double-Diffraction Raman Atom Interferometer.

Abstract: We report an improved test of the weak equivalence principle by using a simultaneous Rb-85-Rb-87 dual-species atom interferometer We propose and implement a four-wave double-diffraction Raman transition scheme for the interferometer, and demonstrate its ability in suppressing common-mode phase noise of Raman lasers after their frequencies and intensity ratios are optimized The statistical uncertainty of the experimental data for Eotvos parameter is 08 x 10(-8) at 3200 s With various systematic errors corrected, the final value is eta = (28 +/- 30) x 10(-8) The major uncertainty is attributed to the Coriolis effect

Spatially resolved analysis of short-range structure perturbations in a plastically bent molecular crystal

Abstract: The exceptional mechanical flexibility observed with certain organic crystals defies the common perception of single crystals as brittle objects. Here, we describe the morphostructural consequences of plastic deformation in crystals of hexachlorobenzene that can be bent mechanically at multiple locations to 360° with retention of macroscopic integrity. This extraordinary plasticity proceeds by segregation of the bent section into flexible layers that slide on top of each other, thereby generating domains with slightly different lattice orientations. Microscopic, spectroscopic and diffraction analyses of the bent crystal showed that the preservation of crystal integrity when stress is applied on the (001) face requires sliding of layers by breaking and re-formation of halogen-halogen interactions. Application of stress on the (100) face, in the direction where π···π interactions dominate the packing, leads to immediate crystal disintegration. Within a broader perspective, this study highlights the yet unrecognized extraordinary malleability of molecular crystals with strongly anisotropic supramolecular interactions.

Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies.

Abstract: Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials. Here, we show that a simple confined self-assembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal's curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies--potentially as more efficient mimics of structural color as it occurs in nature.

Comparative study of the microstructures and mechanical properties of direct laser fabricated and arc-melted AlxCoCrFeNi high entropy alloys

Abstract: High entropy alloys (HEA) are a relatively new metal alloy system that have promising potential in high temperature applications. These multi-component alloys are typically produced by arc-melting, requiring several remelts to achieve chemical homogeneity. Direct laser fabrication (DLF) is a rapid prototyping technique, which produces complex components from alloy powder by selectively melting micron-sized powder in successive layers. However, studies of the fabrication of complex alloys from simple elemental powder blends are sparse. In this study, DLF was employed to fabricate bulk samples of three alloys based on the Al x CoCrFeNi HEA system, where x was 0.3, 0.6 and 0.85 M fraction of Al. This produced FCC, FCC/BCC and BCC crystal structures, respectively. Corresponding alloys were also produced by arc-melting, and all microstructures were characterised and compared longitudinal and transverse to the build/solidification direction by x-ray diffraction, glow discharge optical emission spectroscopy and scanning electron microscopy (EDX and EBSD). Strong similarities were observed between the single phase FCC and BCC alloys produced by both techniques, however the FCC/BCC structures differed significantly. This has been attributed to a difference in the solidification rate and thermal gradient in the melt pool between the two different techniques. Room temperature compression testing showed very similar mechanical behaviour and properties for the two different processing routes. DLF was concluded to be a successful technique to manufacture bulk HEA׳s.

Comprehensive Investigation of the Na3V2(PO4)2F3–NaV2(PO4)2F3 System by Operando High Resolution Synchrotron X-ray Diffraction

Abstract: Na3V2(PO4)2F3 is a positive electrode material for Na-ion batteries which is attracting strong interest due to its high capacity, rate capability, and long-term cycling stability. The sodium extraction mechanism from this material has been always described in the literature as a straightforward solid solution, but several hints point toward a more complicated phase diagram. In this work we performed high angular resolution synchrotron radiation diffraction measurements, realized operando on sodium batteries upon charge. We reveal an extremely interesting phase diagram, created by the successive crystallization of four intermediate phases before the end composition NaV2(PO4)2F3 is reached. Only one of these phases undergoes a solid solution reaction, in the interval between 1.8 and 1.3 Na per formula unit. The ability to resolve weak Bragg reflections allowed us to reveal differences in terms of symmetry among the phases, to determine their previously unknown space groups, and to correlate them with sodium...

Strain mapping at nanometer resolution using advanced nano-beam electron diffraction

Abstract: We report on the development of a nanometer scale strain mapping technique by means of scanning nano-beam electron diffraction. Only recently possible due to fast acquisition with a direct electron detector, this technique allows for strain mapping with a high precision of 0.1% at a lateral resolution of 1 nm for a large field of view reaching up to 1 μm. We demonstrate its application to a technologically relevant strain-engineered GaAs/GaAsP hetero-structure and show that the method can even be applied to highly defected regions with substantial changes in local crystal orientation. Strain maps derived from atomically resolved scanning transmission electron microscopy images were used to validate the accuracy, precision and resolution of this versatile technique.

Imaging single cells in a beam of live cyanobacteria with an X-ray laser

Abstract: There exists a conspicuous gap of knowledge about the organization of life at mesoscopic levels. Ultra-fast coherent diffractive imaging with X-ray free-electron lasers can probe structures at the relevant length scales and may reach sub-nanometer resolution on micron-sized living cells. Here we show that we can introduce a beam of aerosolised cyanobacteria into the focus of the Linac Coherent Light Source and record diffraction patterns from individual living cells at very low noise levels and at high hit ratios. We obtain two-dimensional projection images directly from the diffraction patterns, and present the results as synthetic X-ray Nomarski images calculated from the complex-valued reconstructions. We further demonstrate that it is possible to record diffraction data to nanometer resolution on live cells with X-ray lasers. Extension to sub-nanometer resolution is within reach, although improvements in pulse parameters and X-ray area detectors will be necessary to unlock this potential.

Optical investigation in shuttle like BaMoO4:Er3+–Yb3+ phosphor in display and temperature sensing

Abstract: The crystal structure of the Er 3+ –Yb 3+ codoped BaMoO 4 phosphors synthesized through co-precipitation method has been studied by using the X-ray diffraction analysis. The impurity contents and surface morphology have been examined by field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analysis respectively. The introduction of the Er 3+ /Yb 3+ did not change the crystal structure and morphology of the developed phosphor. The developed phosphor upon excitation at 980 nm diode laser radiation shows strong green, relatively weak red and near infrared upconversion emission bands. The codoping with Yb 3+ ions in the BaMoO 4 :Er 3+ phosphor enhanced the green emission intensity about ∼236-folds. The decay curve analysis and temperature dependence intensity variations for the most intense green bands arising from the 2 H 11/2 and 4 S 3/2 levels to the ground level ( 4 I 15/2 ) in Er 3+ ion have been performed. The pump power and temperature dependent study shows the feasibility of using the developed phosphor in display and temperature sensing devices.

Tuning the Kinetic Water Stability and Adsorption Interactions of Mg-MOF-74 by Partial Substitution with Co or Ni

Abstract: Varying amounts of Co and Ni were substituted into the metal–organic framework Mg-MOF-74 via a one-pot solvothermal reaction, and the effects of these substitutions on CO2 adsorption and kinetic water stability properties were examined. Based on elemental analyses, Co and Ni are more favorably incorporated into the MOF-74 framework from solution than Mg. In addition, reaction temperature more strongly impacts the final metal composition in these mixed-metal (MM) MOF-74 structures than does the reaction solvent composition. Single-component CO2 adsorption isotherms were measured for the MM-MOF-74 systems at 5, 25, and 45 °C, and isosteric heats of adsorption were calculated. These results suggest that CO2 adsorption properties can be adjusted by partial metal substitution. Water adsorption isotherms were also measured for the MM-MOF-74 samples, with powder X-ray diffraction patterns and Brunauer–Emmett–Teller surface areas measured both before and after water exposure. Results show that Mg-MOF-74 can gain ...

High-frequency scattering by an impenetrable sphere

Abstract: The scattering of a scalar plane wave by a totally reflecting sphere (hardcore potential) at high frequencies is treated by a modified Watson transformation. The behavior of the solution both in the near and far regions of space is discussed, as well as the accuracy and domain of applicability of the WKB approximation and classical diffraction theory. It is shown that different transformations are required in the forward and backward half-spaces, and corresponding integral representations for the primary wave are derived. The transformations are rigorously proved and the convergence of the residue series is discussed. In the shadow region, the physical interpretation of the complex angular momentum poles in terms of surface waves is in agreement with Keller's geometrical theory of diffraction. In the lit region, sufficiently far from the shadow boundary, the WKB expansion for the wave function is confirmed up to the second order. On the surface of the sphere, Kirchhoff's approximation is accurate, except in the penumbra region, where the behavior is described by Fock's function. The diffraction effects in the neighborhood of the shadow boundary are investigated and the corrections to classical diffraction theory are obtained. The shift of the shadow boundary is evaluated. The expression for the wave function in the Fresnel-Lommel region is derived and applied to the discussion of the Poisson spot and the behavior near the axis. The total scattering amplitude is evaluated for all angles, including the neighborhood of the forward and backward directions. The corrections to the forward diffraction peak and the transition to the region of geometrical reflection are discussed. The modified Watson transformation is also applied directly to the scattering amplitude. The connection between representations valid in different regions is established.

Tunable nonlinear refractive index of two-dimensional MoS 2 , WS 2 , and MoSe 2 nanosheet dispersions [Invited]

Abstract: Liquid-phase-exfoliation technology was utilized to prepare layered MoS2, WS2, and MoSe2 nanosheets in cyclohexylpyrrolidone. The nonlinear optical response of these nanosheets in dispersions was investigated by observing spatial self-phase modulation (SSPM) using a 488 nm continuous wave laser beam. The diffraction ring patterns of SSPM were found to be distorted along the vertical direction right after the laser traversing the nanosheet dispersions. The nonlinear refractive index of the three transition metal dichalcogenides dispersions n2 was measured to be ∼10−7 cm2 W−1, and the third-order nonlinear susceptibility χ(3)∼10−9 esu. The relative change of effective nonlinear refractive index Δn2e/n2e of the MoS2, WS2, and MoSe2 dispersions can be modulated 0.012–0.240, 0.029–0.154, and 0.091–0.304, respectively, by changing the incident intensities. Our experimental results imply novel potential application of two-dimensional transition metal dichalcogenides in nonlinear phase modulation devices.

Transmission properties of slanted annular aperture arrays. Giant energy deviation over sub-wavelength distance.

Abstract: This paper is devoted to the study of the transmission properties of Slanted Annular Aperture Arrays made in perfectly conducting metal. More precisely, we consider the transmission based on the excitation of the cutoff-less guided mode, namely the TEM mode. We numerically and analytically demonstrate some intrinsic properties of the structure showing a transmission coefficient of at least 50% of an unpolarized incident beam independently of the illumination configuration (angle and plane of incidence). The central symmetry exhibited by the structure is analytically exploited to demonstrate the existence of a polarization state for which all the incident energy is transmitted through the sub-wavelength apertures when the eigenmode is excited, whatever are the illumination and the geometrical parameters. For this state of polarization, the laminar flow of the energy through the structure can exhibit giant deviation over very small distances. An example of energy flow deviation of 220° per wavelength is presented for illustration. The results presented in this paper could be considered as an important contribution to the understanding of the enhanced transmission phenomenon based on the excitation of guided modes.

Magnetic assembly and field-tuning of ellipsoidal-nanoparticle-based colloidal photonic crystals.

Abstract: Anisotropic nanostructures provide an additional degree of freedom for tailoring the collective properties of their ensembles. Using Fe@SiO2 nanoellipsoids as anisotropic building blocks, herein we demonstrate a new class of magnetically responsive photonic structures whose photonic properties can be dynamically tuned by controlling the direction of the magnetic fields they are exposed to. These novel photonic structures diffract at a minimum wavelength when the field direction is perpendicular to the incident angle, and a maximum wavelength when the field is switched to parallel direction; and the diffraction intensity reaches maximum values when the fields are either parallel or perpendicular to the incident light, and decreases when the field direction is moved off-angle.

Hidden topological order and its correlation with glass-forming ability in metallic glasses

Abstract: Unlike the well-defined long-range periodic order that characterizes crystals, so far the inherent atomic packing mode in glassy solids remains mysterious. Based on molecular dynamics simulations, here we find medium-range atomic packing orders in metallic glasses, which are hidden in the diffraction data in terms of structure factors or pair correlation functions. The analysis of the hidden orders in various metallic glasses indicates that the glassy and crystalline solids share a nontrivial structural homology in short-to-medium range, and the hidden orders are formulated by inheriting partial crystalline orders during glass formation. As the number of chemical components increases, more hidden orders are often developed in a metallic glass and entangled topologically. We use this phenomenon to explain the geometric frustration in glass formation and the glass-forming ability of metallic alloys.

High-resolution characterization of the forbidden Si 200 and Si 222 reflections

Abstract: The occurrence of the basis-forbidden Si 200 and Si 222 reflections in specular X-ray diffraction ω–2Θ scans is investigated in detail as a function of the in-plane sample orientation Φ. This is done for two different diffractometer types with low and high angular divergence perpendicular to the diffraction plane. It is shown that the reflections appear for well defined conditions as a result of multiple diffraction, and not only do the obtained peaks vary in intensity but additional features like shoulders or even subpeaks may occur within a 2Θ range of about ±2.5°. This has important consequences for the detection and verification of layer peaks in the corresponding angular range.

Structure refinement using precession electron diffraction tomography and dynamical diffraction: theory and implementation.

Abstract: Accurate structure refinement from electron-diffraction data is not possible without taking the dynamical-diffraction effects into account. A complete three-dimensional model of the structure can be obtained only from a sufficiently complete three-dimensional data set. In this work a method is presented for crystal structure refinement from the data obtained by electron diffraction tomography, possibly combined with precession electron diffraction. The principle of the method is identical to that used in X-ray crystallography: data are collected in a series of small tilt steps around a rotation axis, then intensities are integrated and the structure is optimized by least-squares refinement against the integrated intensities. In the dynamical theory of diffraction, the reflection intensities exhibit a complicated relationship to the orientation and thickness of the crystal as well as to structure factors of other reflections. This complication requires the introduction of several special parameters in the procedure. The method was implemented in the freely available crystallographic computing system Jana2006.

Comparative gas sensor response of SnO2, SnO and Sn3O4 nanobelts to NO2 and potential interferents

Abstract: The gas sensor performance of single crystalline tin oxide nanobelts in different oxidation states (SnO 2 , SnO and Sn 3 O 4 ), synthesized by a carbothermal reduction method, is reported. The synthesized materials were characterized by X-ray diffraction, electron microscopy and nitrogen adsorption/desorption experiments. Gas sensor measurements showed that the sensor based on Sn 3 O 4 nanobelts exhibits the highest sensor response to 50 ppm NO 2 at 200 °C with an approximately 155-fold increase in electrical resistance. Moreover, at this operating temperature, Sn 3 O 4 nanobelts were found to display the highest selectivity to NO 2 relative to CO while SnO nanobelts exhibited the highest selectivity to NO 2 relative to H 2 and CH 4 . These results show that tin oxide semiconducting nanomaterials, with the unusual oxidation states of SnO and Sn 3 O 4 , show great promise as alternatives to SnO 2 for use in high performance gas sensor devices.

Controllable synthesis of CeO2/g-C3N4 composites and their applications in the environment

Abstract: This research has developed a photocatalytic reactor that includes circulating water, light, and a temperature control system. CeO2/g-C3N4 composites with high photocatalytic activity and stability were synthesized by a simple and facile hydrothermal method. The obtained photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that in the CeO2/g-C3N4 composites, the CeO2 nanoparticles were homogeneously cubic in shape (from 3 to 10 nm) and were evenly dispersed on the surface of the g-C3N4. At constant temperature (30 °C), 5% CeO2/g-C3N4 photocatalyst showed the best photocatalytic activity for degrading organic dye methylene blue (MB) under visible light irradiation. The photocatalytic reaction for degrading MB followed first-order kinetics and 5% CeO2/g-C3N4 exhibited a higher apparent rate of 1.2686 min−1, 7.8 times higher than that of the pure g-C3N4 (0.1621 min−1). In addition, it was found that 5% CeO2/g-C3N4 had a new property that it could be used as a sensor for the determination of trace amounts of Cu2+. Such unique design and one-step synthesis, with an exposed high-activity surface, are important for both technical applications and theoretical investigations.

Fast Printing and In Situ Morphology Observation of Organic Photovoltaics Using Slot‐Die Coating

Abstract: The mini-slot-die coater offers a simple, convenient, materials-efficient route to print bulk-heterojunction (BHJ) organic photovoltaics (OPVs) that show efficiencies similar to spin-coating. Grazing-incidence X-ray diffraction (GIXD) and GI small-angle X-ray scattering (GISAXS) methods are used in real time to characterize the active-layer formation during printing. A polymer-aggregation-phase-separation-crystallization mechanism for the evolution of the morphology describes the observations.

A new LEED Instrument for Quantitative Spot Profile Analysis

Abstract: A new instrument for spot profile analysis of electron diffraction - SPA-LEED - has been set up. The instrument works either with a transparent phosphor screen for visual inspection of the pattern or in its main mode with a channeltron for the measurement of the intensity. The diffraction pattern is recorded with a fixed channeltron position by scanning the beam over the channeltron aperture using two sets of electrostatic deflection plates. The scanning range covers about 30{\deg}. The intensity may vary over five orders of magnitude. The SPA-LEED system was checked with the Si 111 7 x 7 surface. A full width at half maximum of 0.3% of the normal reflex distance corresponding to a transfer width of 110 nm is reproducibly obtained. Under optimum conditions the transfer width rose up to about 200 nm. Initial high resolution measurements have been performed on the system Pb on Cu 111. The results demonstrate the possibilities of the new instrument for qualitative and quantitative analysis.

Propagation of sharply autofocused ring Airy Gaussian vortex beams

Abstract: Controlling the focal length and the intensity of the optical focus in the media is an important task. Here we investigate the propagation properties of the sharply autofocused ring Airy Gaussian vortex beams numerically and some numerical experiments are performed. We introduce the distribution factor b into the initial beams, and discuss the influences for the beams. With controlling the factor b, the beams that tend to a ring Airy vortex beam with the smaller value, or a hollow Gaussian vortex beam with the larger one. By a choice of initial launch condition, we find that the number of topological charge of the incident beams, as well as its size, greatly affect the focal intensity and the focal length of the autofocused ring Airy Gaussian vortex beams. Furthermore, we show that the off-axis autofocused ring Airy Gaussian beams with vortex pairs can be implemented.