Showing papers on "Diffraction published in 2012"
TL;DR: The method has the sensitivity to measure a 0.1 Å displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.
Abstract: Molecular structures are imaged with sub-angstrom precision and exposure times of a few femtoseconds. Molecular imaging, or the determination of the positions of atoms in molecules, is an important technique in the physical, chemical and biological sciences. But going beyond mere structure determination, recent technical developments offer the tantalizing prospect of access to ultrafast snapshots of biological molecules and condensed-phase systems undergoing structural changes. One approach uses laser-ionized bursts of coherent electron wave packets to self-interrogate the parent molecular structure. Here, Blaga et al. use this laser-induced electron diffraction (LIED) method to map the structural responses of oxygen and nitrogen molecules to ionization. By measuring a 0.1-angstrom displacement in the oxygen bond length occurring in a time interval of about 5 femtoseconds, the authors establish LIED as a promising approach for imaging of gas-phase molecules with unprecedented spatio-temporal resolution. Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-angstrom spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules1,2 and condensed-phase systems3,4,5,6 undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure7,8,9,10,11. Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction10 (LIED), to image molecular structures with sub-angstrom precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3 μm) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1 A displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.
498 citations
TL;DR: In this article, the authors review both theoretical and experimental advances in the recently emerged field of modulated photonic lattices and highlight a new type of modulation-induced light localization based on the defect-free surface waves.
401 citations
TL;DR: NHWAVE as mentioned in this paper is a shock-capturing non-hydrostatic model for simulating wave refraction, diffraction, shoaling, breaking and landslide-generated tsunami in finite water depth.
380 citations
TL;DR: In this article, a new form of low-energy transmission Kikuchi diffraction, performed in the SEM Transmission EBSD (t-EBSD) detector and software, has been proposed to capture and analyse the angular intensity variation in large-angle forward scattering of electrons in transmission.
Abstract: Summary
The spatial resolution of electron diffraction within the scanning electron microscope (SEM) has progressed from channelling methods capable of measuring crystallographic characteristics from 10 μm regions to electron backscatter diffraction (EBSD) methods capable of measuring 120 nm particles Here, we report a new form of low-energy transmission Kikuchi diffraction, performed in the SEM Transmission-EBSD (t-EBSD) makes use of an EBSD detector and software to capture and analyse the angular intensity variation in large-angle forward scattering of electrons in transmission, without postspecimen coils We collected t-EBSD patterns from Fe–Co nanoparticles of diameter 10 nm and from 40 nm-thick Ni films with in-plane grain size 15 nm The patterns exhibited contrast similar to that seen in EBSD, but are formed in transmission Monte Carlo scattering simulations showed that in addition to the order of magnitude improvement in spatial resolution from isolated particles, the energy width of the scattered electrons in t-EBSD is nearly two orders of magnitude narrower than that of conventional EBSD This new low-energy transmission diffraction approach builds upon recent progress in achieving unprecedented levels of imaging resolution for materials characterization in the SEM by adding high-spatial-resolution analytical capabilities
355 citations
TL;DR: An ultra-thin metamaterial constructed by an ensemble of the same type of anisotropic aperture antennas with phase discontinuity for wave front manipulation across the metammaterial enables effective wave front engineering within a subwavelength scale.
Abstract: We propose an ultra-thin metamaterial constructed by an ensemble of the same type of anisotropic aperture antennas with phase discontinuity for wave front manipulation across the metamaterial. A circularly polarized light is completely converted to the cross-polarized light which can either be bent or focused tightly near the diffraction limit. It depends on a precise control of the optical-axis profile of the antennas on a subwavelength scale, in which the rotation angle of the optical axis has a simple linear relationship to the phase discontinuity. Such an approach enables effective wave front engineering within a subwavelength scale.
320 citations
TL;DR: Measurements indicate that current X-ray free-electron laser technology should enable structural determination from submicrometre protein crystals with atomic resolution, and the shortest apparent pulse lengths occur at the highest resolution.
Abstract: Researchers describe a mechanism capable of compressing fast and intense X-ray pulses through the rapid loss of crystalline periodicity. It is hoped that this concept, combined with X-ray free-electron laser technology, will allow scientists to obtain structural information at atomic resolutions.
309 citations
TL;DR: It is reported that rapid three-dimensional dynamics can be studied beyond the diffraction limit in thick or densely fluorescent living specimens over many time points by combining ultrathin planar illumination produced by scanned Bessel beams with super-resolution structured illumination microscopy.
301 citations
TL;DR: In this article, an allotrope of carbon with Cmmm symmetry was found to be more stable than graphite for pressures above 10 GPa, which is known as $Z$-carbon and is formed by pure $s{p}^{3}$ bonds.
Abstract: Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as $Z$-carbon, is formed by pure $s{p}^{3}$ bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to $Z$-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that $Z$-carbon is a transparent wide band-gap semiconductor with a hardness comparable to diamond.
275 citations
TL;DR: Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability, making the presented cell design suitable for a whole range of techniques from optical absorption to single-crystal X-ray diffraction studies, also in combination with external resistive or double-side laser heating.
Abstract: We present a new design of a universal diamond anvil cell, suitable for different kinds of experimental studies under high pressures. Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability, making the presented cell design suitable for a whole range of techniques from optical absorption to single-crystal X-ray diffraction studies, also in combination with external resistive or double-side laser heating. Three examples of the cell applications are provided: a Brillouin scattering of neon, single-crystal X-ray diffraction of α-Cr(2)O(3), and resistivity measurements on the (Mg(0.60)Fe(0.40))(Si(0.63)Al(0.37))O(3) silicate perovskite.
258 citations
01 Jan 2012
TL;DR: A remarkable development from this simple law was carried out by Pierre Fermat in 1657, which gave an alternative point of view to the phenomenon of refraction as discussed by the authors, which explained the reflection and refraction phenomena of light.
Abstract: Although the study of light began in ancient Greece in 500 BC, very few new contributions were proposed until Galileo (born in 1564), Willebrord Snell van Royen and Descartes (born in 1621) independently discovered the law of refraction. A remarkable development from this simple law was carried out by Pierre Fermat in 1657, which gave an alternative point of view to the phenomenon of refraction. In the same year that Galileo died (1642), Newton was born. This started a remarkably creative period in history of science. Newton did not have a particularly clear view about the nature of light. He believed that light was corpuscular in nature and that the particles traveled from the object to the eye as a stream of projectiles. These ideas reduced light propagation to processes of reflection and refraction of light to a collision problem [1]. Christian Huygens (in 1690) considered light to be a form of wave that travels from the source to the observer. His theory explained the reflection and refraction phenomena of light. It was then that the controversy between the wave and particle theories of light started. Newton recognized the difficulties in reconciling experimental data with some kind of corpuscular properties. He and some others anyway continued to believe in the corpuscular nature of light up to his death in 1727. Since then, other researchers such as Euler, Young, Fresnel, and Huygens suggested light as a wave in motion and developed a theory that explained the phenomena of optical interference and diffraction (late eighteenth and early nineteenth centuries). CONTENTS
249 citations
TL;DR: The total pair correlation function of the structural model shows good agreement with diffraction experiments performed on vitreous silica.
Abstract: Clear as glass: The atomic structure of a metal-supported vitreous thin silica film was resolved using low-temperature scanning tunneling microscopy (STM). Based on the STM image, a model was constructed and the atomic arrangement of the thin silica glass determined (see picture). The total pair correlation function of the structural model shows good agreement with diffraction experiments performed on vitreous silica.
TL;DR: In this article, the size and microstrain of NiO nanoparticles were calculated using Williamson-Hall plots and compared with the results obtained from the Scherrer equation, showing that the straight line obtained in the Williamson-hall plotting shows the homogeneity of the nanoparticles.
TL;DR: An optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner, and retrieving the absolute absorption cross section of light-absorbing structures is introduced.
Abstract: We introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker ...
TL;DR: In this paper, a formal equivalence between generalized refraction and blazed diffraction gratings was established, and the relative merits of the two approaches were discussed, as well as the relative importance of different approaches.
Abstract: When an electromagnetic wave is obliquely incident on the interface between two homogeneous media with different refractive indices, the requirement of phase continuity across the interface generally leads to a shift in the trajectory of the wave. When a linearly position-dependent phase shift is imposed at the interface, the resulting refraction may be described using a generalized version of Snell's law. In this Letter, we establish a formal equivalence between generalized refraction and blazed diffraction gratings, further discussing the relative merits of the two approaches.
TL;DR: The generation of a new surface wave, the cosine-Gauss beam, is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings.
Abstract: A new surface wave is introduced, the cosine-Gauss beam, which does not diffract while it propagates in a straight line and tightly bound to the metallic surface for distances up to 80 mu m. The generation of this highly localized wave is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings. Cosine-Gauss beams have potential for applications in plasmonics, notably for efficient coupling to nanophotonic devices, opening up new design possibilities for next-generation optical interconnects.
TL;DR: Ab initio phasing of partially coherent diffraction patterns in three dimensions is demonstrated, while simultaneously determining the coherence properties of the illuminating wavefield.
Abstract: The wave properties of light, particularly its coherence, are responsible for interference effects, which can be exploited in powerful imaging applications. Coherent diffractive imaging relies heavily on coherence and has recently experienced rapid growth. Coherent diffractive imaging recovers an object from its diffraction pattern by computational phasing with the potential of wavelength-limited resolution. Diminished coherence results in reconstructions that suffer from artefacts or fail completely. Here we demonstrate ab initio phasing of partially coherent diffraction patterns in three dimensions, while simultaneously determining the coherence properties of the illuminating wavefield. Both the dramatic improvements in image interpretability and the three-dimensional evaluation of the coherence will have broad implications for quantitative imaging of nanostructures and wavefield characterization with X-rays and electrons.
TL;DR: In this paper, an extensive measurement campaign of the diffraction at objects like edges, wedges and cylinders for frequencies of 60 and 300 GHz is presented, where different materials, realistic antennas as well as transmission through the objects are taken into account.
Abstract: Current indoor wireless communication systems are shifting from classical microwave bands towards mm wave frequencies, whereas here the 60 GHz band is of special interest. Future systems are expected to work at even higher carrier frequencies in the sub-mm band beyond 300 GHz. In indoor wave propagation channels of such systems, diffraction occurs at a multitude of objects and hence must be considered for propagation simulations. Although the relevance of diffraction has been thouroughly studied at lower frequencies, it has not yet been analyzed methodically in the mm and sub-mm wave frequency range. This paper presents an extensive measurement campaign of the diffraction at objects like edges, wedges and cylinders for frequencies of 60 and 300 GHz. Different materials, realistic antennas as well as transmission through the objects are taken into account. Theoretical approaches are validated against the measurement results. Furthermore, shadowing of rays by persons is investigated and modeled with the help of diffraction. Finally, ray tracing is applied in an office scenario in order to evaluate the impact of diffraction on mm and sub-mm wave indoor channel characteristics.
TL;DR: The main physical effects of patterning are focused on, namely a reduction of reflection losses, diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.
Abstract: We theoretically investigate the light-trapping properties of one- and two-dimensional periodic patterns etched on the front surface of c-Si and a-Si thin film solar cells with a silver back reflector and an anti-reflection coating. For each active material and configuration, absorbance A and short-circuit current density Jsc are calculated by means of rigorous coupled wave analysis (RCWA), for different active materials thicknesses in the range of interest of thin film solar cells and in a wide range of geometrical parameters. The results are then compared with Lambertian limits to light-trapping for the case of zero absorption and for the general case of finite absorption in the active material. With a proper optimization, patterns can give substantial absorption enhancement, especially for 2D patterns and for thinner cells. The effects of the photonic patterns on light harvesting are investigated from the optical spectra of the optimized configurations. We focus on the main physical effects of patterning, namely a reduction of reflection losses (better impedance matching conditions), diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.
TL;DR: This paper explores methods of measuring elastic strain variations in the presence of larger lattice rotations using high resolution electron backscatter diffraction and demonstrates that accurate recovery of elastic strains requires accurate knowledge of the pattern centre if this remapping algorithm is used.
TL;DR: In this paper, density functional theory and in situ surface X-ray diffraction are used to identify and characterize atomic sites yielding high methane conversion and reveal facile dissociation on either under-coordinated Pd sites in PdO(101) or metallic surfaces.
Abstract: The active phase of Pd during methane oxidation is a long-standing puzzle, which, if solved, could provide routes for design of improved catalysts. Here, density functional theory and in situ surface X-ray diffraction are used to identify and characterize atomic sites yielding high methane conversion. Calculations are performed for methane dissociation over a range of Pd and PdOx surfaces and reveal facile dissociation on either under-coordinated Pd sites in PdO(101) or metallic surfaces. The experiments show unambiguously that high methane conversion requires sufficiently thick PdO(101) films or metallic Pd, in full agreement with the calculations. The established link between high activity and atomic structure enables rational design of improved catalysts.
TL;DR: With appropriate calibration, FT-Raman spectroscopy is a promising tool for rapid determination of starch crystallinity and a strong linear correlation was found between crystallinities and integrated areas of the skeletal mode Raman band at 480cm-1.
TL;DR: Two-dimensional electronic spectroscopy allows fundamentally new insights into the structure and dynamics of multi-chromophore systems and the fact that it automatically measures absorptive spectra.
Abstract: We introduce the translating wedge-based identical pulses encoding system, a novel device for the generation of collinear, interferometrically locked ultrashort pulse pairs. By means of birefringent wedges, we are able to control the pulse delay with attosecond precision and stability better that λ/360, without affecting the pulse duration and in a spectral range that spans from UV to mid-IR. This device is expected to dramatically simplify two-dimensional spectroscopy experiments.
TL;DR: The design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry equipped with a segmented-type crystal for x-ray diffraction and an energy resolution in the order of 0.25 eV and 1 eV is reported.
Abstract: We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV-9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.
TL;DR: It is shown that new families of diffraction-free nonparaxial accelerating optical beams can be generated by considering the symmetries of the underlying vectorial Helmholtz equation, and fully vectorial self-similar accelerating optical wave solutions are obtained via oblate-prolate spheroidal wave functions.
Abstract: We show that new families of diffraction-free nonparaxial accelerating optical beams can be generated by considering the symmetries of the underlying vectorial Helmholtz equation. Both two-dimensional transverse electric and magnetic accelerating wave fronts are possible, capable of moving along elliptic trajectories. Experimental results corroborate these predictions when these waves are launched from either the major or minor axis of the ellipse. In addition, three-dimensional spherical nondiffracting field configurations are presented along with their evolution dynamics. Finally, fully vectorial self-similar accelerating optical wave solutions are obtained via oblate-prolate spheroidal wave functions. In all occasions, these effects are illustrated via pertinent examples.
TL;DR: In this article, a series of polished and unpolished nanographites obtained from pyrolysis of various precursor types have been systematically studied by both Raman spectroscopy and x-ray diffraction.
Abstract: A series of polished and unpolished $s{p}^{2}$-nanostructured carbons ``nanographites'' obtained from the pyrolysis of various precursor types have been systematically studied by both Raman spectroscopy and x-ray diffraction. The ratio between the intensities of the disorder-induced $D$ band and the first-order graphite $G$ band (${I}_{D}$/${I}_{G}$) commonly used up to now to estimate the ``crystallite'' diameter ${L}_{a}$ displays, in the case of polished graphitized $s{p}^{2}$ carbons, clear spatial heterogeneities and can lead to the overestimation of the intrinsic structural disorder. The full width at half maximum of the $G$ band, which is shown to be insensitive to the polishing process, exhibits a linear dependence on the mean ``crystallite'' diameter [FWHM($G$) $=$ 14 $+$ 430/${L}_{a}$] and therefore can be used for an accurate structural characterization of these nanographites.
TL;DR: The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.
Abstract: The highly transient nature of shock loading and pronounced microstructure effects on dynamic materials response call for {\it in situ}, temporally and spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction under dynamic loading, due to their high photon energy, high photon fluxes, high coherency, and high pulse repetition rates. The feasibility of bulk-scale gas gun shock experiments with dynamic x-ray PCI and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source. The x-ray beam characteristics, experimental setup, x-ray diagnostics, and static and dynamic test results are described. We demonstrate ultrafast, multiframe, single-pulse PCI measurements with unprecedented temporal ($<$100 ps) and spatial ($\sim$2 $\mu$m) resolutions for bulk-scale shock experiments, as well as single-pulse dynamic Laue diffraction. The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.
TL;DR: In this paper, the feasibility of bulk-scale gas gun shock experiments with dynamic x-ray phase contrast imaging (PCI) and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source.
Abstract: The highly transient nature of shock loading and pronounced microstructure effects on dynamic materials response call for in situ, temporally and spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction under dynamic loading, due to their high photon fluxes, high coherency, and high pulse repetition rates. The feasibility of bulk-scale gas gun shock experiments with dynamic x-ray PCI and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source. The x-ray beam characteristics, experimental setup, x-ray diagnostics, and static and dynamic test results are described. We demonstrate ultrafast, multiframe, single-pulse PCI measurements with unprecedented temporal (<100 ps) and spatial (∼2 μm) resolutions for bulk-scale shock experiments, as well as single-pulse dynamic Laue diffraction. The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.
TL;DR: In this article, a modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions.
Abstract: Different procedures for analysis of particle sizes by the X-ray diffraction method are compared by the example of nanoparticles of nickel and iron(3+) oxide (Fe2O3). A modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions, and the efficiency of the method is shown. The analysis within the frame-work of the Warren-Averbach method makes it possible to restore the distribution function of nanoparticles (crystallites) over true diameters, which satisfactorily correlates with electron microscopy data. The applicability of the Warren-Averbach method to the estimation of crystallite sizes by the analysis of a single diffraction line is substantiated. The range of the applicability of the Scherrer, Williamson-Hall, Warren-Averbach, and modified Warren-Averbach methods to the substructure analysis by the X-ray diffraction is determined as depending on the method of nanostructure formation.
TL;DR: In this paper, the authors discuss the principle of coherent diffraction imaging, present various implementation schemes of this imaging modality, and illustrate its broad applications in materials science, nanoscience, and biology.
Abstract: For centuries, lens-based microscopy, such as optical, phase-contrast, fluorescence, confocal, and electron microscopy, has played an important role in the evolution of modern science and technology. In 1999, a novel form of microscopy, i.e., coherent diffraction imaging (also termed coherent diffraction microscopy or lensless imaging), was developed and transformed our conventional view of microscopy, in which the diffraction pattern of a noncrystalline specimen or a nanocrystal was first measured and then directly phased to obtain a high-resolution image. The well-known phase problem was solved by combining the oversampling method with iterative algorithms. In this paper, we will briefly discuss the principle of coherent diffraction imaging, present various implementation schemes of this imaging modality, and illustrate its broad applications in materials science, nanoscience, and biology. As coherent X-ray sources such as high harmonic generation and X-ray free-electron lasers are presently under rapid development worldwide, coherent diffraction imaging can potentially be applied to perform high-resolution imaging of materials/nanoscience and biological specimens at the femtosecond time scale.
TL;DR: In this paper, a review of the field is provided, with a viewpoint from materials science, based on the use of highly penetrating hard X-rays from a synchrotron source and the application of tomographic reconstruction algorithms for the analysis of the diffraction data.
Abstract: Three-dimensional X-ray diffraction microscopy is a fast and nondestructive structural characterization technique aimed at studies of the individual crystalline elements (grains or subgrains) within millimetre-sized polycrystalline specimens. It is based on two principles: the use of highly penetrating hard X-rays from a synchrotron source and the application of `tomographic' reconstruction algorithms for the analysis of the diffraction data. In favourable cases, the position, morphology, phase and crystallographic orientation can be derived for up to 1000 elements simultaneously. For each grain its average strain tensor may also be derived, from which the type II stresses can be inferred. Furthermore, the dynamics of the individual elements can be monitored during typical processes such as deformation or annealing. A review of the field is provided, with a viewpoint from materials science.