Showing papers on "Diffraction published in 2003"
TL;DR: The scaling model presented here includes: scale and temperature factor per batch of data; temperature factor as a continuous function of the radiation dose; absorption in the crystal; uneven exposure within a single diffraction image; and corrections for phenomena that depend on the diffraction peak position on the detector.
Abstract: A novel and general approach to scaling diffraction intensities is presented. The method minimizes the disagreement among multiple measurements of symmetry-related reflections using a stable refinement procedure. The scale factors are described by a flexible exponential function that allows different scaling corrections to be chosen and combined according to the needs of the experiment. The scaling model presented here includes: scale and temperature factor per batch of data; temperature factor as a continuous function of the radiation dose; absorption in the crystal; uneven exposure within a single diffraction image; and corrections for phenomena that depend on the diffraction peak position on the detector. This scaling model can be extended to include additional corrections for various instrumental and data-collection problems.
660 citations
TL;DR: The x-ray diffraction pattern of the high-pressure form is consistent with a distorted graphite structure in which bridging carbon atoms between graphite layers pair and form σ-bonds, whereas the nonbridgingcarbon atoms remain unpaired with π-bond.
Abstract: Compressed under ambient temperature, graphite undergoes a transition at ∼17 gigapascals. The near K-edge spectroscopy of carbon using synchrotron x-ray inelastic scattering reveals that half of the π-bonds between graphite layers convert to σ-bonds, whereas the other half remain as π-bonds in the high-pressure form. The x-ray diffraction pattern of the high-pressure form is consistent with a distorted graphite structure in which bridging carbon atoms between graphite layers pair and form σ-bonds, whereas the nonbridging carbon atoms remain unpaired with π-bonds. The high-pressure form is superhard, capable of indenting cubic-diamond single crystals.
566 citations
TL;DR: In this article, the one-dimensional two-species quantum hydrodynamic model is considered in the limit of small mass ratio of the charge carriers, and the system is shown to support linear waves, which are described by a deformed Korteweg-de Vries equation.
Abstract: The one-dimensional two-species quantum hydrodynamic model is considered in the limit of small mass ratio of the charge carriers. Closure is obtained by adopting an equation of state pertaining to a zero-temperature Fermi gas for the electrons and by disregarding pressure effects for the ions. By an appropriate rescaling of the variables, a nondimensional parameter H, proportional to quantum diffraction effects, is identified. The system is then shown to support linear waves, which in the limit of small H resemble the classical ion-acoustic waves. In the weakly nonlinear limit, the quantum plasma is shown to support waves described by a deformed Korteweg–de Vries equation which depends in a nontrivial way on the quantum parameter H. In the fully nonlinear regime, the system also admits traveling waves which can exhibit periodic patterns. The quasineutral limit of the system is also discussed.
560 citations
TL;DR: Time-resolved X-ray diffraction measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition are reported, which leads to a subsequent loss of long-range order.
Abstract: The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10(-14) to 10(-12) s. Until recently, only optical techniques were capable of providing adequate time resolution, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-ray diffraction. However, the measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase, has to date remained obscure. Here we report time-resolved X-ray diffraction measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance-near the Lindemann limit-leads to a subsequent loss of long-range order, which is most probably due to melting of the material.
548 citations
TL;DR: In this paper, the internal strains within a polycrystalline magnesium alloy plate have been measured during tensile and compression testing in situ by neutron diffraction using an elasto-plastic self-consistent simulation code.
522 citations
TL;DR: In this paper, the dispersion relation and group velocities correlate remarkably well with predictions from a simple point-dipole model, and a change in particle shape to spheroidal particles shows up to a threefold increase in group velocity.
Abstract: Finite-difference time-domain simulations show direct evidence of optical pulse propagation below the diffraction limit of light along linear arrays of spherical noble metal nanoparticles with group velocities up to 0.06c. The calculated dispersion relation and group velocities correlate remarkably well with predictions from a simple point-dipole model. A change in particle shape to spheroidal particles shows up to a threefold increase in group velocity. Pulses with transverse polarization are shown to propagate with negative phase velocities antiparallel to the energy flow.
442 citations
TL;DR: In this paper, a dipole model for DESY HERA deep inelastic scattering data was developed, which incorporates the impact parameter distribution of the proton and showed that the t distributions are sensitive to saturation phenomena.
Abstract: We develop a dipole model for DESY HERA deep inelastic scattering data which incorporates the impact parameter distribution of the proton. The model describes the inclusive total ${\ensuremath{\gamma}}^{*}p$ cross sections as well as the diffractive $J/\ensuremath{\psi}$ differential cross sections. We compare the model with previous approaches and show that the t distributions are sensitive to saturation phenomena. We estimate the boundary of the saturation region and show that it dominates the data in the low-${Q}^{2}$ region where the total ${\ensuremath{\gamma}}^{*}p$ cross section exhibits the same universal rise as hadronic cross sections. The model is then extended to nuclei and shows good agreement with the nuclear shadowing data at small x. Finally, we estimate the saturation scale in nuclei.
437 citations
TL;DR: In this article, a quantized Pancharatnam-berry phase diffractive optics using computer-generated space-variant subwavelength dielectric grating is presented.
Abstract: Quantized Pancharatnam–Berry phase diffractive optics using computer-generated space-variant subwavelength dielectric grating is presented. The formation of the geometrical phase is done by discrete orientation of the local subwavelength grating. We discuss a theoretical analysis and experimentally demonstrate a quantized geometrical blazed phase of polarization diffraction grating, as well as polarization dependent focusing lens for infrared radiation at wavelength 10.6 μm.
395 citations
TL;DR: A novel method, based on the angular spectrum of plane waves and coordinate rotation in the Fourier domain, removes geometric limitations posed by conventional propagation calculation and enables us to calculate complex amplitudes of diffracted waves on a plane not parallel to the aperture.
Abstract: A novel method for simulating field propagation is presented. The method, based on the angular spectrum of plane waves and coordinate rotation in the Fourier domain, removes geometric limitations posed by conventional propagation calculation and enables us to calculate complex amplitudes of diffracted waves on a plane not parallel to the aperture. This method can be implemented by using the fast Fourier transformation twice and a spectrum interpolation. It features computation time that is comparable with that of standard calculation methods for diffraction or propagation between parallel planes. To demonstrate the method, numerical results as well as a general formulation are reported for a single-axis rotation.
344 citations
TL;DR: In this paper, the mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters was studied using high-resolution x-ray diffraction.
Abstract: The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy.
333 citations
TL;DR: Three-dimensional images of the interiors of Au nanocrystals that show 50 nm wide bands of contrast with [111] orientation that probably arise from internal twinning by dynamic recrystallization during their formation at high temperature are obtained.
Abstract: X-ray diffraction using a coherent beam involves the mutual interference among all the extremities of small crystals. The continuous diffraction pattern so produced can be phased because it can be oversampled. We have thus obtained three-dimensional images of the interiors of Au nanocrystals that show 50 nm wide bands of contrast with ${111}$ orientation that probably arise from internal twinning by dynamic recrystallization during their formation at high temperature.
TL;DR: In this article, a statistical analysis of shape strains produced by the martensitic??? transformation in pure titanium indicates that there are three likely slip systems which could operate to give the complementary shear.
TL;DR: The successful recording and reconstruction of diffraction patterns from biological samples reported here represent an important step toward the potential of imaging single biomolecules at near-atomic resolution by combining single-particle diffraction with x-ray free electron lasers.
Abstract: We report the first experimental recording, to our knowledge, of the diffraction pattern from intact Escherichia coli bacteria using coherent x-rays with a wavelength of 2 A. By using the oversampling phasing method, a real space image at a resolution of 30 nm was directly reconstructed from the diffraction pattern. An R factor used for characterizing the quality of the reconstruction was in the range of 5%, which demonstrated the reliability of the reconstruction process. The distribution of proteins inside the bacteria labeled with manganese oxide has been identified and this distribution confirmed by fluorescence microscopy images. Compared with lens-based microscopy, this diffraction-based imaging approach can examine thicker samples, such as whole cultured cells, in three dimensions with resolution limited only by radiation damage. Looking forward, the successful recording and reconstruction of diffraction patterns from biological samples reported here represent an important step toward the potential of imaging single biomolecules at near-atomic resolution by combining single-particle diffraction with x-ray free electron lasers.
TL;DR: In this article, superlattice reflections at 12{hkl}p positions were observed in some electron diffraction patterns, which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c.
Abstract: X-ray diffraction and transmission electron microscopy have been performed on samples in the solid solution series (BiFeO3)x–(PbTiO3)1−x in which a morphotropic phase boundary occurs at x≈0.7. BiFeO3 exhibits superlattice reflections at 12{hkl}p positions in some electron diffraction patterns, the distribution of which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c. The amplitude of the rotations decreases in the R phase as PbTiO3 content increases and superlattice reflections are absent in electron diffraction patterns from the tetragonal (T) phase (x=0.6), indicating that it is untilted with space group P4mm. Electron diffraction patterns from samples where x=0.7 reveal superlattice reflections not associated with octahedral rotations and consistent with an intermediate phase with lower symmetry than T and R.
TL;DR: The characteristics of a singularity in a nondiffracting Bessel beam is explored experimentally by use of a programmable spatial light modulator with 64-level phase holograms and the diffraction efficiency is greatly improved.
Abstract: A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.
TL;DR: A unique C-shaped aperture is discovered that provides approximately 3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of approximately 0.1 lambda.
Abstract: Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides ~3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of ~0.1λ Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture—or one of the related shapes—is linked to both a propagation mode in the aperture and local surface plasmons.
TL;DR: In this paper, the results of an investigation aiming at finding what affects the grain size of nano-TiO2 powder during synthesis were reported, which showed that the different preparation conditions such as concentration, pH value, calcination time and calcination temperature have a lot of influences upon the properties of nano TiO2 powders.
TL;DR: Dielectric periodic media can possess a complex photonic band structure with allowed bands displaying strong dispersion and anisotropy, and it is shown that for some frequencies the form of iso-frequency contours mimics theform of the first Brillouin zone of the crystal.
Abstract: Dielectric periodic media can possess a complex photonic band structure with allowed bands displaying strong dispersion and anisotropy. We show that for some frequencies the form of iso-frequency contours mimics the form of the first Brillouin zone of the crystal. A wide angular range of flat dispersion exists for such frequencies. The regions of iso-frequency contours with near-zero curvature cancel out diffraction of the light beam, leading to a self-guided beam.
TL;DR: In this paper, the authors used the Pascal programming language for the calculation of diffraction contrast factors of dislocations in elastically anisotropic cubic, hexagonal and trigonal crystals.
Abstract: The computer program ANIZC has been developed using the Pascal programming language for the calculation of diffraction contrast factors of dislocations in elastically anisotropic cubic, hexagonal and trigonal crystals. The contrast factor is obtained numerically by integrating the angular part of the distortion tensor in the slip plane. The distortion tensor is calculated by solving the sextic equation provided by the mechanical equilibrium of a single dislocation in an infinite anisotropic medium. The contrast factors can be used for the interpretation of strain anisotropy as obtained from peak profile measurements made on either single crystals, textured polycrystals or powders.
TL;DR: In this article, the authors describe an approach for recording 3D periodic structures in a photosensitive polymer using a single diffraction element mask with a central opening surrounded by three diffraction gratings oriented 120° relative to one another such that the three first order diffracted beams and the non-differentiated laser beam give a 3D spatial light intensity pattern.
Abstract: This letter describes an approach for recording three-dimensional (3D) periodic structures in a photosensitive polymer using a single diffraction element mask. The mask has a central opening surrounded by three diffraction gratings oriented 120° relative to one another such that the three first order diffracted beams and the nondiffracted laser beam give a 3D spatial light intensity pattern. Structures patterned in this polymer using 1.0 and 0.56 μm grating periods have hexagonal symmetry with micron- to submicron-periodicity over large substrate area. Band structure calculations of these low index contrast materials predict photonic gaps in certain high symmetry directions.
TL;DR: In this article, the theoretical X-ray scattering intensities of carbons with AB-stacking and turbostratic stacking structures were simulated as a function of lattice constants and crystallite sizes using the Debye and Warren-Bodenstein equations, and the scale factor, K of the Scherrerr equation was also estimated.
TL;DR: In this paper, a phase-decoupled refraction-diffraction approximation is proposed to accommodate diffraction in spectral wave models, which is expressed in terms of the directional turning rate of the individual wave components in the two-dimensional wave spectrum.
TL;DR: It is shown explicitly how mixed dynamic form factors for incoherent scattering should be taken into account for annular dark field or backscattered electron detectors, as well as for characteristic losses detected by X-ray emissions or by electron energy loss spectroscopy.
TL;DR: In this paper, a saturable optical molecular transition with a spatial intensity distribution featuring a local minimum allows the fundamental breaking of the diffraction barrier both in microscopy and in material structuring.
Abstract: Effecting a saturable optical molecular transition with a spatial intensity distribution featuring a local minimum allows the fundamental breaking of the diffraction barrier both in microscopy and in material structuring. If the transition can be repeatedly reverted, as in switchable fluorescent proteins and photochromic compounds, fluorescence imaging and writing is possible with spatial resolution down to the molecular scale.
TL;DR: In this paper, the structural and electronic properties of CeO2 and Ce1-xZrxO2 nanoparticles were investigated using time-resolved X-ray diffraction, Xray absorption near-edge spectroscopy (XANES) and X-Ray absorption nearedge spectrograms.
Abstract: In this article the structural and electronic properties of CeO2 and Ce1-xZrxO2 nanoparticles are investigated using time-resolved X-ray diffraction, X-ray absorption near-edge spectroscopy (XANES)...
TL;DR: In this article, the photoluminescence properties of SnO2 thin films grown by thermal chemical vapor deposition were investigated with different substrate temperatures and X-ray diffraction showed that the crystallinity of the grown thin films increased with increasing substrate temperature.
TL;DR: In this article, a number of optical elements with subwavelength structured surfaces have been developed, where the structures are equivalent to refractive index materials with form birefringence, and many new optical elements are realized using the artificial refractive indices of these sub-wavelength structures.
Abstract: Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.
TL;DR: In this article, a short fatigue crack in a cast Al alloy was visualized using a selective contrast agent, and the intricate three-dimensional shape of the fatigue crack, as well as the crack stops observed on the sample surface, were correlated to the grain structure of the material.
TL;DR: The results are surprising in that they show that classification can be done with less than one photon per pixel in the limiting resolution shell, assuming Poisson-type photon noise in the image.
TL;DR: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, this paper fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress.
Abstract: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, we fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress. The reflection spectrum for a single crystal grain was measured by applying microspectroscopy under compression. The photonic band gap wavelength shifted linearly and reversibly over almost the entire visible light wavelength region (460−810 nm).