Showing papers on "Diffraction published in 2002"
TL;DR: It is demonstrated that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions.
Abstract: A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle--the so-called Wolf effect. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.
1,226 citations
TL;DR: In this article, the authors used synchrotron x-ray powder diffraction measurements to characterize the PMN-xPT phase diagram and to determine the stability region of the monoclinic phase, which extends from 31%$ to 37%$ at 20 K.
Abstract: Synchrotron x-ray powder diffraction measurements have been performed on unpoled ceramic samples of $(1\ensuremath{-}x)\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}$ (PMN-xPT) with $30%l~xl~39%$ as a function of temperature around the morphotropic phase boundary, which is the line separating the rhombohedral and tetragonal phases in the phase diagram. The experiments have revealed very interesting features previously unknown in this or related systems. The sharp and well-defined diffraction profiles observed at high and intermediate temperatures in the cubic and tetragonal phases, respectively, are in contrast to the broad features encountered at low temperatures. These peculiar characteristics, which are associated with the monoclinic phase of ${\mathrm{M}}_{C}$-type previously reported by Kiat et al. [Phys. Rev. B 65, 064106 (2000)] and Singh and Pandey [J. Phys. Condens Matter 13, L931 (2001)], can only be interpreted as multiple coexisting structures with ${\mathrm{M}}_{C}$ as the major component. An analysis of the diffraction profiles has allowed us to properly characterize the PMN-xPT phase diagram and to determine the stability region of the monoclinic phase, which extends from $x=31%$ to $x=37%$ at 20 K. The complex lansdcape of observed phases points to an energy balance between the different PMN-xPT phases which is intrinsically much more delicate than that of related systems such as ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ or $(1\ensuremath{-}x)\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{1/3}){\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}.$ These observations are in good accord with an optical study of $x=33%$ by Xu et al. [Phys. Rev. B 64, 020102 (2001)], who observed monoclinic domains with several different polar directions coexisting with rhombohedral domains, in the same single crystal.
741 citations
TL;DR: A theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.
Abstract: Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. We present a theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.
664 citations
TL;DR: A frequency‐space equation of diffraction tomography for the electric field vector is obtained within the first‐order Born approximation, using a simplified formalism resulting from using three‐dimensional spatial frequencies and replacing outgoing waves by linear combinations of homogeneous plane waves.
Abstract: We first obtain a frequency-space equation of diffraction tomography for the electric field vector, within the first-order Born approximation, using a simplified formalism resulting from using three-dimensional spatial frequencies and replacing outgoing waves by linear combinations of homogeneous plane waves. A coherent optical diffraction tomographic microscope is then described, in which a sample is successively illuminated by a series of plane waves having different directions, each scattered wave is recorded by phase-shifting interferometry, and the object is then reconstructed from these recorded waves. The measurement process in this device is analysed taking into account the illuminating wave, the wave scattered by the sample, the reference wave, and the phase relations between these waves. This analysis yields appropriate equations that take into account the characteristics of the reference wave and compensate random phase shifts. It makes it possible to obtain a high-resolution three-dimensional frequency representation in full conformity with theory. The experimentally obtained representations show index and absorptivity with a resolution limit of about a quarter of a wavelength, and have a depth of field of about 40 microm.
499 citations
TL;DR: A comprehensive chemical and structural analysis is made of a new type of trititanate nanotube, which is synthesized via the reaction of TiO(2) particles with NaOH aqueous solution.
Abstract: A comprehensive chemical and structural analysis is made of a new type of trititanate nanotube, which is synthesized via the reaction of TiO2 particles with NaOH aqueous solution. It is found that the trititanate nanotubes are multi-walled scroll nanotubes with an inter-shell spacing of about 0.78 nm and an average diameter of about 9 nm. An atomic model of the nanotube is derived based on information from powder X-ray diffraction, selective-area electron diffraction, high-resolution electron microscopy and structure simulations. A model nanotube may be constructed by wrapping a (100) sheet of H2Ti3O7 along [001] with the tube axis parallel to [010].
431 citations
Book•
18 Apr 2002
TL;DR: The theory of elasticity has been studied in the literature for tensors as discussed by the authors, where the theory of Elasticity is used to describe the properties of tensors in terms of their elasticity.
Abstract: Ultrasonics: An Overview Introduction Ultrasonics in Nature Historical Development Physical Acoustics Low-Frequency Bulk Acoustic Wave Applications Surface Acoustic Waves Piezoelectric Materials High-Power Ultrasonics Medical Ultrasonics Acousto-Optics Underwater Acoustics and Seismology Introduction to Vibrations and Waves Vibrations Wave Motion Bulk Waves in Fluids One-Dimensional Theory of Fluids Three-Dimensional Model Introduction to the Theory of Elasticity A Short Introduction to Tensors Strain Tensor Stress Tensor Thermodynamics of Deformation Hooke's Law Other Elastic Constants Bulk Acoustic Waves in Solids 1D Model of Solids Wave Equation in Three Dimensions Material Properties Viscoelastic Solids Finite Beams: Radiation, Diffraction, and Scattering Radiation Scattering Focused Acoustic Waves Radiation Pressure Doppler Effect Reflection and Transmission of Ultrasonic Waves at Interfaces Introduction Reflection and Transmission at Normal Incidence Oblique Incidence: Fluid-Fluid Interface Fluid-Solid Interface Solid-Solid Interface Rayleigh Waves Introduction Rayleigh Wave Propagation Fluid-Loaded Surface Lamb Waves Potential Method for Lamb Waves Fluid-Loading Effects Acoustic Waveguides Introduction: Partial Wave Analysis Waveguide Equation: SH Modes Lamb Waves Rayleigh Waves Layered Substrates Multilayer Structures Free Isotropic Cylinder Waveguide Configurations Crystal Acoustics Introduction Group Velocity and Characteristic Surfaces Piezoelectricity Cavitation and Sonoluminescence Bubble Dynamics Multibubble Sonoluminescence Single Bubble SL Bulk Acoustic Wave Transducers, Delay Lines, and Oscillators Bulk Acoustic Wave Transducers Bulk Acoustic Wave Delay Lines Quartz Crystal Resonators Silicon Oscillators Surface Acoustic Wave Transducers, Analog Signal Processing, and Mobile Applications Introduction Basic Components Materials and Technology Signal Processing Saw Applications Saw Wireless Communication to Coded Devices Microacoustics: RF MEMS, FBAR, and CMUT Introduction Overview of MEMS Technology Rf MEMS FBAR CMUT Capacitive Transducers Acoustic Sensors Thickness-Shear Mode Resonators Saw Sensors SH-Type Sensors Flexural Plate Wave Sensors CMUT Chem/Biosensor FBAR Liquid Sensors Thin-Rod Acoustic Sensors Gravimetric Sensitivity Analysis and Comparison Physical Sensing of Liquids Chemical Gas Sensors Taste Sensing: Electronic Tongue Biosensing Perspectives in Acoustic Sensors Focused Beam Acoustic Microscopy Introduction Resolution Acoustic Lens Design Contrast Mechanisms and Quantitative Measurements Applications of Acoustic Microscopy Near-Field Acoustic Microscopy Introduction Scanning Tunneling Microscope Atomic Force Microscope Ultrasonic AFM Contact Resonance Force Microscopy Mechanical Diode Effect Microscopy Acoustic Wave Probe Microscopy Other Probe Microscopies Perspectives Nondestructive Evaluation of Materials Introduction Surfaces Plates Layered Structures Adhesion Thickness Gauging Process Control Structural Health Monitoring Time Reversal Mirrors Non/Loosely Contacting NDE Techniques Laser Ultrasonics Electromagnetic Acoustic Transducers Air-Coupled Transducers Resonant Ultrasound Spectroscopy Appendix A: Bessel Functions Appendix B: Acoustic Properties of Materials Appendix C: Complementary Laboratory Experiments
414 citations
TL;DR: In this article, a dipole model for electromagnetic energy transfer below the diffraction limit along chains of closely spaced metal nanoparticles is presented, and the key parameters that govern the energy transport are determined for various interparticle spacings using measurements of the resonance frequencies of L and T modes, yielding a bandwidth of 1.4×10-14 rad/s and a maximum group velocity of vg=4.0×10^6 m/s for a 75 nm-spacing.
Abstract: Far-field polarization spectroscopy on chains of Au nanoparticles reveals the existence of longitudinal (L) and transverse (T) plasmon-polariton modes. The experimental results provide support for the validity of a recently published dipole model for electromagnetic energy transfer below the diffraction limit along chains of closely spaced metal nanoparticles. The key parameters that govern the energy transport are determined for various interparticle spacings using measurements of the resonance frequencies of L and T modes, yielding a bandwidth of 1.4×10^14 rad/s and a maximum group velocity of vg=4.0×10^6 m/s for a 75 nm-spacing.
404 citations
TL;DR: The phenomenon of super-resolution in time-reversal acoustics is analyzed theoretically and with numerical simulations and numerical simulations confirm the theory.
Abstract: The phenomenon of super-resolution in time-reversal acoustics is analyzed theoretically and with numerical simulations. A signal that is recorded and then retransmitted by an array of transducers, propagates back though the medium, and refocuses approximately on the source that emitted it. In a homogeneous medium, the refocusing resolution of the time-reversed signal is limited by diffraction. When the medium has random inhomogeneities the resolution of the refocused signal can in some circumstances beat the diffraction limit. This is super-resolution. A theoretical treatment of this phenomenon is given, and numerical simulations which confirm the theory are presented.
370 citations
TL;DR: Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented and spiral geometrical phases for infrared radiation at a wavelength of 10.6microm are demonstrated.
Abstract: Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented Such elements can be achieved by use of continuous computer-generated space-variant subwavelength dielectric gratings We present a theoretical analysis and experimentally demonstrate spiral geometrical phases for infrared radiation at a wavelength of 106microm
338 citations
TL;DR: For the first time, the 3D structure of a noncrystalline nanostructured material is experimentally determined at 50 nm resolution using coherent x-ray diffraction and the oversampling phasing method.
Abstract: We have imaged a 2D buried Ni nanostructure at 8 nm resolution using coherent x-ray diffraction and the oversampling phasing method. By employing a 3D imaging reconstruction algorithm, for the first time we have experimentally determined the 3D structure of a noncrystalline nanostructured material at 50 nm resolution. The 2D and 3D imaging resolution is currently limited by the exposure time and the computing power, while the ultimate resolution is limited by the x-ray wavelengths. We believe these results pave the way for the development of atomic resolution 3D x-ray diffraction microscopy.
328 citations
TL;DR: It is experimentally prove that light propagation in a discrete system, i.e., an array of coupled waveguides, exhibits striking anomalies and it is shown that refraction is restricted to a cone, irrespective of the initial tilt of the beam.
Abstract: We experimentally prove that light propagation in a discrete system, i.e., an array of coupled waveguides, exhibits striking anomalies. We show that refraction is restricted to a cone, irrespective of the initial tilt of the beam. Diffraction can be controlled in size and sign by the input conditions. Diffractive beam spreading can even be arrested and diverging light can be focused. The results can be thoroughly theoretically explained.
TL;DR: In this article, it was pointed out that the light transmission anomalies observed for thin-film metallic gratings can be explained entirely in terms of dynamical diffraction theory and that surface plasmons are an intrinsic component of the diffracted wave field and, as such, play no independent causal role in the anomalies.
Abstract: In this paper, it is pointed out that the light transmission anomalies observed for thin-film metallic gratings can be explained entirely in terms of dynamical diffraction theory. Surface plasmons are an intrinsic component of the diffracted wave field and, as such, play no independent causal role in the anomalies, as has been implied by others. The dynamical scattering matrix for the Bloch-wave modes of the diffracted photon wave field (E, H) is derived for a three-dimensionally periodic medium with arbitrary dielectric constant. A new theoretical treatment and numerical results are presented for a one-dimensional array of slits. In model metallic slit arrays, with negative dielectric constant, 100% and 0% transmission is possible at different wavelengths in the zero-order beam. In slit arrays, both propagating and evanescent modes (traditional surface plasmons) are strongly excited at both the peak and the minimum transmission conditions.
TL;DR: In this paper, diffraction patterns with rectangular unit cells revealed the diselenide as the most distorted from the hexagonal structures of the parent materials, with the Mo atoms forming a ''zigzag'' structure which is also corrugated perpendicular to the layers.
Abstract: Single layers of the transition-metal dichalcogenides ${\mathrm{WS}}_{2},$ ${\mathrm{MoS}}_{2},$ and ${\mathrm{MoSe}}_{2}$ were formed as aqueous suspensions by lithium intercalation and exfoliation of crystalline powders and examined by x-ray diffraction and x-ray absorption fine structure (XAFS) spectroscopy. The two-dimensional characteristics of these systems were readily apparent through the absence of any (hkl) peaks $(l\ensuremath{
e}0)$ and in the strong asymmetry of the $(\mathrm{hk}0)$ peaks in the diffraction patterns. Indexing the diffraction patterns with rectangular unit cells revealed the diselenide as the most distorted from the hexagonal structures of the parent materials, with the Mo atoms forming a ``zigzag'' structure which is also corrugated perpendicular to the layers. Mo K-edge and W L3-edge XAFS analysis using ${\mathrm{WTe}}_{2}$-related structural models enabled the determination of the short, intermediate, and long metal-metal near-neighbor distances with the shortest metal-metal distances contracted approximately 0.4 \AA{} compared to parent reference materials. Shifts in the Mo K-absorption-edge energy in ${\mathrm{MoSe}}_{2}$ correlated with changing Se-Se interactions. Combining the XAFS and diffraction results enabled an estimation of the layer puckering and atomic positions in three-dimensional models of the unit cells. Selenium K-edge XAFS also identified two selenium-oxygen scattering paths from water or ${\mathrm{OH}}^{\ensuremath{-}}$ ions coordinating the layers of exfoliated ${\mathrm{MoSe}}_{2}.$
TL;DR: In this article, high-temperature aging of a metal−surfactant complex followed by mild oxidation was used to produce high-dimensional assembly of cobalt ferrite nanocrystals.
Abstract: Highly crystalline and monodisperse cobalt ferrite nanocrystals were fabricated by the high-temperature aging of a metal−surfactant complex followed by mild oxidation. Particle sizes were varied from 4 to 9 nm by changing the experimental conditions. Transmission electron microscopic (TEM) images of the particles showed two- and three-dimensional assembly of the particles, demonstrating the uniformity of the nanocrystals. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic images of the nanocrystals confirmed the highly crystalline nature of the cobalt ferrite structure. The elemental analysis confirmed the stoichiometry of cobalt ferrite, despite some variations in the relative atomic composition of nanocrystals. The nanocrystals were found to have typical behaviors of magnetic nanocrystals and the narrow energy barrier distributions of magnetic anisotropy, implying that the nanocrystals obtained are very uniform.
TL;DR: This work reports the first experimental result obtained with an acoustic sink where a focal spot size of less than 1/14th of one wavelength is recorded.
Abstract: In recent years, time-reversal (TR) mirrors have been developed that create TR waves for ultrasonic transient fields propagating through complex media. A TR wave back propagates and refocuses exactly at its initial source. However, because of diffraction, even if the source is pointlike the wave refocuses on a spot size that cannot be smaller than half a wavelength. Here, by using a TR interpretation of this limit, we show that this latter limitation can be overcome if the source is replaced by its TR image. This new device acts as an acoustic sink that absorbs the TR wave. Here we report the first experimental result obtained with an acoustic sink where a focal spot size of less than 1/14th of one wavelength is recorded.
Book•
26 Feb 2002
TL;DR: In this article, the Pomeron in QCD and the Sudakov Parametrization are discussed, as well as the notion of hard diffraction in the context of QCD.
Abstract: 1. Introduction.- 2. Preliminaries.- 3. Kinematics.- 4. The Relativistic S-Matrix.- 5. Regge Theory.- 6. Geometrical and s-Channel Models.- 7. Soft Diffraction: a Phenomenological Survey.- 8. The Pomeron in QCD.- 9. Deep Inelastic Scattering.- 10. Phenomenology of Hard Diffraction.- 11. Hard Diffraction in QCD.- A. Conventions.- A.1 Four-Vectors.- A.2 Sudakov Parametrization.- A.3 Reference Frames.- A.4 Fermionic States.- B. Mellin Transforms.- C. QCD Formulas.- C.2 Feynman Rules for QCD.- References.
TL;DR: Cuprous oxide quantum particles as small as 2 nm (comparable to the Bohr exciton radius) were synthesized using an electrochemical route Quantum confinement effects are evident from a blueshift in the optical absorption as discussed by the authors.
Abstract: Cuprous oxide quantum particles as small as 2 nm (comparable to the Bohr exciton radius) were synthesized using an electrochemical route Quantum confinement effects are evident from a blueshift in the optical absorption The optical absorption spectra of Cu2O nanoparticles of different sizes are discussed Structural analysis by x-ray diffraction as well as electron diffraction shows the nanoparticles to be cubic and single phased Cu2O X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface of Cu2O core nanoparticles
Patent•
12 Feb 2002
TL;DR: In this article, an alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested.
Abstract: Alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested. An optical instrument illuminates all or part of the target area and measures the optical response. The instrument can measure transmission, reflectance, and/or ellipsometric parameters as a function of wavelength, polar angle of incidence, azimuthal angle of incidence, and/or polarization of the illumination and detected light. Overlay error or offset between those layers containing the test gratings is determined by a processor programmed to calculate an optical response for a set of parameters that include overlay error, using a model that accounts for diffraction by the gratings and interaction of the gratings with each others' diffracted field. The model parameters might also take account of manufactured asymmetries. The calculation may involve interpolation of pre-computed entries from a database accessible to the processor. The calculated and measured responses are iteratively compared and the model parameters changed to minimize the difference.
TL;DR: In this paper, the lasing mode of a 2D photonic crystal laser with in-plane multidirectionally distributed feedback effect is analyzed theoretically and experimentally, and the results indicate that 2D coherent lasing oscillation does not occur due to the multi-directional coupling effect in the 2D photon crystal.
Abstract: The lasing mode of a two-dimensional (2D) photonic crystal laser with in-plane multidirectionally distributed feedback effect is analyzed theoretically and experimentally. From an investigation of the Bragg diffraction conditions at several points in the photonic band diagram where lasing is expected, we identify a particular \ensuremath{\Gamma} point at which lasing occurs due to the coupling of lightwaves propagating in six equivalent \ensuremath{\Gamma}-X directions and diffraction normal to the substrate surface. In order to investigate the lasing mode in detail, the distribution of the electromagnetic field at the band edges at the \ensuremath{\Gamma} point is calculated, and each band edge is found to have a different field pattern. The lasing characteristics of the 2D photonic crystal laser at the lasing wavelength corresponding to the \ensuremath{\Gamma} point are measured. Single-mode lasing over a broad circular area is observed by microelectroluminescence measurements under pulsed conditions at room temperature. We also demonstrate the correspondence between the measured lasing wavelengths and calculated band edges by comparing the polarization characteristics with the calculated distribution of the electromagnetic field. The results indicate that 2D coherent lasing oscillation does, in fact, occur due to the multidirectional coupling effect in the 2D photonic crystal. From the theoretical calculation, we show that the polarization patterns of the lasers can be controlled by introducing artificial lattice defects.
TL;DR: In this article, metal nanowires sustaining collective electron oscillations (surface plasmon polaritons) can be used as optical waveguides to overcome the limitations of miniaturization imposed on conventional dielectric waveguide due to diffraction.
Abstract: We show that metal nanowires sustaining collective electron oscillations (surface plasmon polaritons) can be used as optical waveguides. Thereby, the use of a metal allows to overcome the limitations of miniaturization imposed on conventional dielectric waveguides due to diffraction. To demonstrate this effect we investigate a 200 nm wide and 50 nm high gold nanowire locally excited at a light wavelength of 800 nm. By direct imaging the optical near-field with subwavelength-resolution photon scanning tunneling microscopy we observe light transport along the nanowire over a distance of a few μm. Besides the realization of unprecedented integration densities of photonic devices, metal nanowires could be effectively used to optically address individual nanostructures or molecules.
TL;DR: In this paper, a variational approximation and direct simulations are performed to show that stable quasi-stationary (2+1)-dimensional soliton beams exist in these media (direct simulations demonstrate stable propagation over a distance exceeding 100 diffraction lengths of the beam).
Abstract: Transverse beam propagation is considered in a layered structure in which Kerr nonlinearity alternates between self-focusing and self-defocusing, which makes it possible to prevent collapse. A structure composed of alternating self-focusing layers with strongly different values of the Kerr coefficient is considered too. By means of both a variational approximation (which is implemented in a completely analytical form, including the stability analysis) and direct simulations, it is demonstrated that stable quasi-stationary (2+1)-dimensional soliton beams exist in these media (direct simulations demonstrate stable propagation over a distance exceeding 100 diffraction lengths of the beam). Quasi-stationary cylindrical solitons with intrinsic vorticity exist too, but they all are unstable, splitting into separating zero-vorticity beams.
TL;DR: In this paper, it was found from x-ray diffraction measurements that the ferroelectric polarization originates from the tilting of polyhedra and buckling of R layers, which persists up to 1000 K.
Abstract: A ferroelectricity-magnetism-coexisting system, hexagonal $R{\mathrm{MnO}}_{3}(R=\mathrm{Y},$ Lu, and Sc), has been investigated by synchrotron x-ray and neutron powder diffraction measurements. It is found from x-ray diffraction measurements that the ferroelectric polarization originates from the tilting of ${\mathrm{MnO}}_{5}$ polyhedra and the buckling of R layers, which persists up to 1000 K. Neutron diffraction measurements have revealed the reduction of ordered moments from the expected value, as well as strong magnetic diffuse scattering existing far above ${T}_{\mathrm{N}},$ both of which are caused by geometrical frustration of the triangular lattice of Mn ions. We have also investigated the effects of Zr doping into the R site and have found that Zr doping drastically suppresses both ferroelectric distortion and magnetic ordering.
TL;DR: In this paper, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin c method, and the proposed method utilizes an asymmetrical diffraction geometry for which the Xray beam is incident at a grazing angle g to the sample surface.
TL;DR: The use of microbes as producers of semiconductor nanocrystals is demonstrated in this paper, where torulopsis yeast is challenged with lead, and it builds intracellular spherical crystallites of PbS, 2-5 nm in diameter and pure by X-ray diffraction.
Abstract: The use of microbes as producers of semiconductor nanocrystals is demonstrated When torulopsis yeast is challenged with lead, it builds intracellular spherical crystallites of PbS, 2-5 nm in diameter (see Figure for an HR-TEM image) and pure by X-ray diffraction The crystals, which can be isolated by freeze-thawing, show a sharp absorption maximum at 330 nm, corresponding to a bandgap of 375 eV
TL;DR: In this paper, a simplified version of the scattering sensitivity kernels that emerge from the Born or Rytov approximations in which surface wave travel times are a weighted average of phase or group slowness over the first Fresnel zone of the wave was described.
Abstract: [1] We determine the effect of replacing geometrical ray theory in surface wave tomography with scattering theory. We describe a tomographic method based on a simplified version of the scattering sensitivity kernels that emerge from the Born or Rytov approximations in which surface wave travel times are a weighted average of phase or group slowness over the first Fresnel zone of the wave. We apply this “diffraction tomography” to Rayleigh and Love wave group velocity measurements to produce group velocity maps from 20 to 150 s period on a 2° × 2° grid globally. Using identical data and damping parameters, we also produce maps using “Gaussian tomography” which is based on ray theory with intuitive Gaussian smoothing constraints. Significant differences in the amplitude and geometry of the imaged features appear primarily at long periods but exist even in the short-period maps in regions where average path lengths are large. Diffraction tomography, therefore, is significant in most oceanic regions at all periods, but it is also important on continents at long periods at least. On average, diffraction tomography produces larger velocity anomalies in a period-dependent band of spherical harmonic degrees, and diffraction and Gaussian tomography maps decorrelate past a critical spherical harmonic degree that also depends on period. The widths of resolving kernels that emerge from diffraction tomography are systematically larger than those from Gaussian tomography. Finally, mantle features inferred from diffraction tomography tend to have larger amplitudes and extend deeper than those from Gaussian tomography.
TL;DR: The availability of high brilliance third generation synchrotron sources together with progress in achromatic focusing optics allows us to add submicron spatial resolution to the conventional century-old x-ray diffraction technique as discussed by the authors.
Abstract: The availability of high brilliance third generation synchrotron sources together with progress in achromatic focusing optics allows us to add submicron spatial resolution to the conventional century-old x-ray diffraction technique. The new capabilities include the possibility to map in situ, grain orientations, crystalline phase distribution, and full strain/stress tensors at a very local level, by combining white and monochromatic x-ray microbeam diffraction. This is particularly relevant for high technology industry where the understanding of material properties at a microstructural level becomes increasingly important. After describing the latest advances in the submicron x-ray diffraction techniques at the Advanced Light Source, we will give some examples of its application in material science for the measurement of strain/stress in metallic thin films and interconnects. Its use in the field of environmental science will also be discussed.
TL;DR: In this paper, carbon onions prepared by high temperature annealing of ultradispersed diamond nanoparticles of about 5 nm in average diameter have been studied by X-ray diffraction using synchrotron radiation.
TL;DR: The forward and backward scattering parts (phase II) of the new neutron spectrometer, TOSCA, replacing the old TFXA, have been successfully installed at the ISIS pulsed neutron source as mentioned in this paper.
Abstract: The forward and backward scattering parts (phase II) of the new neutron spectrometer, TOSCA, replacing the old TFXA and TOSCA (phase I), have been successfully installed at the ISIS pulsed neutron source. The results show a significant enhancement in the counting rate due to the larger detector area. The improved resolution (to 1.5–3% of the energy transfer) as compared with the previous instruments (TXFA: 2.5–3.5%; TOSCA-I: 2–3.5%) has been achieved by increasing the primary flight path from 12 m to 17 m. A chopper has been added in order to avoid neutron frame overlap and to reduce the fast neutron background. Additional diffraction capability will be installed in the near future. An example of the high resolution that is routinely available is provided by the spectrum of potassium hydrogen phtalate at 20 K.
TL;DR: In this paper, the authors studied the optical properties of ZnO on (0001) Al2O3 grown by pulsed-laser deposition and found that the transition energies increase with increasing strain and eventually they are resolved into two well-defined bands at the strain of 1.63%.
Abstract: The mosacity and optical properties of ZnO on (0001) Al2O3 grown by pulsed-laser deposition have been studied by x-ray diffraction and spectroscopic ellipsometry. Strong dependence has been found between the grain size and the residual strain along the c axis, ezz, as well as the film texture. In general, strain relieves and texture improves at larger grain size regardless of the growth conditions. The excitonic transition energies are also found to vary in the presence of strain field. It is observed that the transition energies increase with increasing strain and eventually they are resolved into two well-defined bands at the strain of 1.63%. By taking into account of the biaxial strain, the theoretical band structure of ZnO has been considered by solving the Luttinger–Kohn Hamiltonian. Reasonable agreement is found between the theory and experiment.
TL;DR: In this paper, the size and lattice strain of the biological apatite were calculated by Fourier analysis and approximation with threefold convolution of X-ray lines. But this method is not suitable for oriented specimens.
Abstract: Diffraction line broadening observed for the biological apatite is ascribed to small crystallite dimensions and lattice imperfections. However, it is rather difficult to separate the individual contribution of each factor. Therefore in numerous works a total inverse width of a diffraction peak is only used as a size/strain parameter. Several authors determine the bioapatite crystallite size ignoring the lattice strain. As is shown in the present paper, this problem can be resolved for oriented specimens. The crystallite size and lattice strain were calculated by two independent methods: Fourier analysis and approximation with threefold convolution of X-ray lines. The approach proposed can be useful in the investigations into structural aspects of the bone apatite and its synthetic analogues as the crystal size is related to surface defects and the lattice strain to lattice imperfections.