Showing papers on "Synchrotron radiation published in 1991"
TL;DR: The problem of determining the three-dimensional structure of thousands of atoms is reduced to that of initially solving for a few anomalous scattering centers that can be used as a reference for developing the entire structure.
Abstract: Resonance between beams of x-ray waves and electronic transitions from bound atomic orbitals leads to a phenomenon known as anomalous scattering. This effect can be exploited in x-ray crystallographic studies on biological macromolecules by making diffraction measurements at selected wavelengths associated with a particular resonant transition. In this manner the problem of determining the three-dimensional structure of thousands of atoms is reduced to that of initially solving for a few anomalous scattering centers that can then be used as a reference for developing the entire structure. This method of multiwavelength anomalous diffraction has now been applied in a number of structure determinations. Optimal experiments require appropriate synchrotron instrumentation, careful experimental design, and sophisticated analytical procedures. There are rich opportunities for future applications.
1,113 citations
TL;DR: In this article, the structural and chemical changes that occur within the layered mineral aurichalchite (Cu5−xZnx(OH)6(CO3)
Abstract: EVER since X-ray sources first became available, the merit of deploying diffraction and absorption spectroscopic studies simultaneously has been acknowledged1. Information on oxidation states and local (~6-A radius) atomic environments is now obtained routinely from X-ray absorption measurements using synchrotron sources2–4. Synchrotron radiation is also used commonly for high-resolution powder diffraction crystallography. We report here an instrumental arrangement that has allowed us to extract quantitative short- and long-range structural information on samples undergoing chemical change by measuring X-ray absorption spectra and X-ray diffraction patterns in situ and within a few seconds of one another, using a synchrotron X-ray source. To illustrate the combination of these techniques, we have followed the structural and chemical changes that occur within the layered mineral aurichalchite (Cu5−xZnx(OH)6(CO3)2) when heated in dry air to ~ 450 °C. Despite marked changes in crystallinity, the local environment and electronic state of the Cu2+ ions remain unchanged, even when at ~ 450 °C the material is converted to a mixture of CuO and ZnO. Heating this mixture in H2/N2 produces an active catalyst for the water-gas shift reaction (CO2 + H2 → CO + H2O), which our studies show to consist of small particles of copper metal (with some zinc incorporated) supported on ZnO.
216 citations
TL;DR: The 5-meV bandwidth provided by a special silicon crystal monochromator obviates the need for a nuclear resonant filter and offers the possibility of performing a wide range of Mossbauer spectroscopy experiments using synchrotron radiation.
Abstract: Delayed coherent nuclear forward scattering of synchrotron radiation by polycrystalline Fe foils (both isotopically enriched and naturally abundant) has been measured. Quantum beats wre observed in the time spectra. With the chosen experimental conditions these can only arise from coherent scattering. The 5-meV bandwidth provided by a special silicon crystal monochromator obviates the need for a nuclear resonant filter. This direct approach offers the possibility of performing a wide range of M\"ossbauer spectroscopy experiments using synchrotron radiation.
192 citations
TL;DR: In this paper, the absolute molar extinction coefficients of benzene in jets have been determined by scaling measured free jet values to the known value in the vapor phase for a broadband at 200.1 nm in the S2 state.
Abstract: The direct absorption spectrum of benzene in a free jet has been measured in the 130–260 nm region (S1, S2, and S3 states, Rydberg series, and the first ionization limit) using synchrotron radiation as a light source. The absolute molar extinction coefficients (e) of benzene in jets have been determined by scaling measured free‐jet values to the known value in the vapor phase for a broadband at 200.1 nm in the S2 state. The vibrational temperature for ν16 mode was estimated to be 185 K. The maximum value of e of the S1 absorption system was found to be 1400 l mol−1 cm−1 (spectral bandwidth=0.065 nm). A shoulder observed at 205.45 nm in the S2 absorption system is assigned to the S2 origin, induced by pseudo‐Jahn–Teller distortion.
131 citations
TL;DR: X-ray scattering studies of the nematic to smectic-{ital A} transition in 4-cyano-4{prime}-octylbiphenyl under nonequilibrium shear-flow conditions demonstrate that, under flow, synchrotron x-ray-diffraction techniques provide a powerful structural probe of steady-state dynamical behavior.
Abstract: We report on x-ray scattering studies of the nematic to smectic-A transition in 4-cyano-4'-octylbiphenyl under nonequilibrium shear-flow conditions. As the transition is approached, the interplay between the viscous frictional and the flow-induced-fluctuation forces on the nematic director leads to a series of regimes whose occurrence results from the divergence in one of the viscosities due to the critical slowing down of the smectic-A order-parameter fluctuations. The experiments demonstrate that, under flow, synchrotron x-ray-diffraction techniques provide a powerful structural probe of steady-state dynamical behavior.
128 citations
15 Jun 1991-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a method based on deep-etch lithography and subsequent replication processes was developed for fabricating microstructures with extreme structural heights, and a particularly high precision was achieved when the lithographic process is carried out by means of synchrotron radiation.
Abstract: For fabricating microstructures with extreme structural heights a technology has been developed which is based on deep-etch lithography and subsequent replication processes. A particularly high precision is achieved when the lithographic process is carried out by means of synchrotron radiation. Electroforming and molding processes are used for the replication of microstructures from a large variety of materials. The field of application comprises sensors, electrical and optical microconnectors, components for fluid technology, micromechanical components, microfiltration systems and novel composite materials.
126 citations
TL;DR: Monte Carlo calculations are used to verify the classical electrodynamics result describing the multiparticle coherent enhancement at long wavelengths for synchrotron-radiation emission and show the derivation of the result that, for a bunch of electrons in a storage ring, the synch rotations has a multiparticles coherent enhancement that is given by the square of the Fourier transform of the longitudinal spatial distribution function of the electrons.
Abstract: We have used Monte Carlo calculations to verify the classical electrodynamics result describing the multiparticle coherent enhancement at long wavelengths for synchrotron-radiation emission. In addition we show the derivation of the result that, for a bunch of electrons in a storage ring, the synchrotron-radiation emission has a multiparticle coherent enhancement that is given by the square of the Fourier transform of the longitudinal spatial distribution function of the electrons. The result has been verified for Gaussian and sinusoidal distributions. For a Gaussian distribution of particles in a bunch, this is seen to have an effect only at wavelengths close to the bunch length. For a sinusoidal distribution as in the transverse optical klystron, the enhancement can easily be seen to occur at one specific wavelength.
107 citations
Book•
01 Oct 1991
TL;DR: In this paper, Equations of Motion for Weak Focusing Mechanics of Trajectories Optical Elements with Static Magnetic Fields Strong Focusing Lattice Exercises Synchrotron Oscillations Synchoretron Radiation RF Linear Accelerators Resonances Space-charge Effects How to Baffle Liouville Spin Dynamics Topics in Instrumentation and Beam Measurements
Abstract: Introduction Equations of Motion for Weak Focusing Mechanics of Trajectories Optical Elements with Static Magnetic Fields Strong Focusing Lattice Exercises Synchrotron Oscillations Synchrotron Radiation RF Linear Accelerators Resonances Space-Charge Effects How to Baffle Liouville Spin Dynamics Topics in Instrumentation and Beam Measurements.
85 citations
TL;DR: In this article, a new process of preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations.
Abstract: A new process of the preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations. It is shown that the positrons form a nonthermal power-law-like energy distribution via their gyroresonant interaction with the extraordinary modes emitted by the ions. It is noted that this process may be of significance in connection with the shock excitation of nonthermal synchrotron radiation from astrophysical systems powered by relativistic outflows from compact central objects, e.g., supernova remnants powered by pulsars and jets from active galactic nuclei.
85 citations
TL;DR: In this article, the theory of low-emittance optics is presented, including some important examples of magnet lattices, and a significant increase of the photon density is achieved by inserting special wiggler and undulator magnets into a storage ring, providing very high intensities of coherent synchrotron radiation.
Abstract: A relativistic electron passing through a bending magnet emits electromagnetic radiation in the forward direction with an extremely narrow opening angle. The photon density of this 'so-called synchrotron' radiation is correspondingly high and has, in addition, a very broad radiation spectrum. Because of its outstanding properties, synchrotron radiation has become a very powerful tool in basic research and technical applications. The required relativistic electron beam is provided by utilizing modern particle accelerator techniques. Presently the most successful accelerator type used as a dedicated synchrotron radiation source is the storage ring. Very important for a high quality of radiation is strong focusing of the electron beam circulating in the accelerator. The theory of this low-emittance optics is presented, including some important examples of magnet lattices. Inserting special wiggler and undulator magnets into a storage ring gives a significant increase of the photon density. In particular, the undulator magnets provide very high intensities of coherent synchrotron radiation. A logical consequence of the coherent undulator radiation was the development of the free electron laser (FEL), which is described in the last section of this review.
82 citations
01 May 1991-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a novel capillary optics technique for focusing synchrotron X-ray beams has been applied in an experiment performed at the DORIS storage ring at HASYLAB.
Abstract: A novel capillary optics technique for focusing synchrotron X-ray beams has been applied in an experiment performed at the DORIS storage ring at HASYLAB. This new technique, which utilizes the total reflection properties of X-rays inside small capillaries, has recently been applied to generate beams of X-rays, with a beam size down to about 10 μm using conventional X-ray tubes. The result from our recent experiment shows that capillary optics can also be used to generate a submicron beam of X-rays from a synchrotron light source. A description of the capillary unit, and the alignment procedure is given. The influence of the thermal load on the device caused by the intense flux of synchrotron radiation will be discussed. Future perspectives of the capillary technique as applied to synchrotron radiation will be discussed.
TL;DR: The observation of effects due to spin-orbit interaction in angle-resolved photoemission from an itinerant ferromagnet (fcc cobalt) using circularly polarized vuv synchrotron radiation is reported, which may be understood as a form of magnetic circular dichroism appearing in the uv photomission regime.
Abstract: We report the observation of effects due to spin-orbit interaction in angle-resolved photoemission from an itinerant ferromagnet (fcc cobalt) using circularly polarized vuv synchrotron radiation. The photoelectron spectra of the Co 3d-band region are found to depend on the relative orientation of the sample magnetization and the photon spin. This effect may be understood as a form of magnetic circular dichroism appearing in the uv photomission regime. It may be used to investigate magnetic phenomena in ferromagnets without performing an explicit spin-polarization analysis.
TL;DR: In this paper, the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR) was performed, where contamination free thin films were grown at room temperature using decaborane (B10H14) as the source gas.
Abstract: We have performed the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR). Contamination‐free thin films were grown at room temperature using decaborane (B10H14) as the source gas. After deposition the films were examined using photoelectron microscopy, which showed that film growth was limited to the region illuminated by SR. The temperature of the substrate rose less than 10 K. These results indicate that gas‐phase excitations are not important and that the films are deposited by a nonthermal, photoinduced mechanism. Masked exposures demonstrate the potential of this technique for patterned deposition.
TL;DR: In this paper, the effect of thermal annealing and irradiation in an intense white synchrotron x-ray beam on the xray reflectance of tungsten/carbon and tungststen/silicon multilayers is reported.
Abstract: The effect of thermal annealing and irradiation in an intense white synchrotron x‐ray beam on the x‐ray reflectance of tungsten/carbon and tungsten/silicon multilayers is reported. Thermal annealing at 400 °C for two hours produces larger effects than irradiation of cooled multilayers in the white beam of a 20‐pole hard x‐ray wiggler with 0.94‐T peak field on the storage ring DORIS operating at 5.42 GeV and electron currents of 20–36 mA for 40 h. Thermal annealing caused the period and first order reflectance of a W/Si sample to decrease, in contrast to a W/C sample whose period and reflectance increased on annealing. Of five actively cooled samples irradiated, one W/C sample showed significant change in reflectance. Preannealing of this multilayer stabilized it to radiation‐induced changes. Irradiation effects also depend on multilayer period and constituent materials. Implications of these results for models describing multilayer reflectance and for multilayer applications in the new generation of synchrotron radiation sources are discussed.
TL;DR: In this paper, the authors used a synchrotron source of X-rays to obtain high-resoultion small-angle X-ray scattering (SAXS) patterns from commercial poly( p -phenylene terephthalamide) (Kevlar) fibres.
TL;DR: In this paper, high-resolution radio observations from 1982 and 1987 were used to measure the expansion of the synchrotron component of the Crab Nebula, including a measurement of the nebula's outer edge.
Abstract: Using high-resolution radio observations from 1982 and 1987 the expansion of the synchrotron component of the Crab Nebula was measured, including a measurement of the expansion of the nebula's outer edge. The measurements show a rate of expansion similar to that obtained from optical data for the line-emitting filaments. It is shown that the synchrotron component of the Crab expands homologously and that its rate of expansion has accelerated since the supernova explosion. The data further suggest that the acceleration of the synchrotron component may be larger than that of the emission-line filaments which, if confirmed by future observations, implies that the relativistic gas is currently bursting through the net of filaments. The absence of deceleration allows the establishment of stringent upper limits on the density of gas into which the observed nebula is expanding. 19 refs.
TL;DR: It is found that, under optimum deposition conditions, the ML structures exhibit smooth and compositionally abrupt interfaces, with a normal-incidence reflectivity as high as 20% at 7.2 nm.
Abstract: Multilayer (ML) structures composed of alternating, ultrathin layers of Ru and B4C have been grown by dc magnetron sputtering. The ML microstructure has been characterized using x-ray diffraction and high-resolution transmission electron microscopy, and the normal-incidence reflectivity has been measured using synchrotron radiation. It is found that, under optimum deposition conditions, the ML structures exhibit smooth and compositionally abrupt interfaces, with a normal-incidence reflectivity as high as 20% at 7.2 nm. The reflectivity decreases when the ML structures are annealed at 500°C owing to interdiffusion and compound formation at the interfaces.
TL;DR: In this article, the authors presented the first results of high-spatial resolution x-ray imaging studies with an upgraded version of the scanning photoemission multiple application undulator microscope, which is a multilayer coated Schwarzschild objective that focuses undulator radiation onto the sample.
Abstract: We present the first results of high‐spatial resolution x‐ray imaging studies with an upgraded version of the scanning photoemission multiple application x‐ray imaging undulator microscope. The microscope is a multilayer coated Schwarzschild objective that focuses undulator radiation onto the sample. The recent upgrade improved the spatial resolution by a factor six reaching a full width at half maximum value of 0.5 μm. Highly polished mirrors reduced the diffuse background by almost two orders of magnitude and drastically improved the contrast. The improved microscope was used to perform a series of tests on microgrids and reverse Fresnel zone plates. The microscope capability to detect chemical and topological contrast was verified by using patterned metal overlayers on Si and GaAs substrates. Further improvements to increase the flux and the spatial resolution are underway; this includes the installation of a new undulator beamline.
TL;DR: The first measurement of photoelectron spectra emitted in the photoionization of a singly charged-ion beam by synchrotron radiation is reported, and the values observed for the kinetic energy and for the intensity of the photoelectrons line are in good agreement with the predicted values.
Abstract: The first measurement of photoelectron spectra emitted in the photoionization of a singly charged-ion beam by synchrotron radiation is reported. A Ca + -ion beam is resonantly photoionized by the monochromatized photon beam of the SU6 undulator of the SuperACO Storage Ring at 33.20 eV photon energy. The values observed for the kinetic energy and for the intensity of the photoelectron line are in good agreement with the predicted values. The success of this feasibility experiment opens up wide opportunities for similar photoionization and Auger studies on multiply charged ions
TL;DR: A spectrum of coherent synchrotron radiation emitted from a bunch train of relativistic electrons accelerated by the Tohoku 300-MeV linear accelerator (linac) has been observed in the wavelength range from 0.16 to 3.5 mm, and the intensity decreases sharply towards shorter wavelengths.
Abstract: A spectrum of coherent synchrotron radiation emitted from a bunch train of relativistic electrons accelerated by the Tohoku 300-MeV linear accelerator (linac) has been observed in the wavelength range from 0.16 to 3.5 mm. The energy of the electrons and the longitudinal bunch length are 150 MeV and about 2 mm. The observed spectrum has a broad peak at {lambda}{congruent}1.5 mm, and the intensity decreases sharply towards shorter wavelengths. The peak intensity is enhanced by a factor of 5{times}10{sup 6} in comparison with ordinary incoherent synchrotron radiation; the enhancement factor is comparable with the average number of electrons in the bunch. The electron distribution in the bunch is derived from the observed spectrum, and the bunch length (full width at half maximum) is obtained to be 0.25 mm. This bunch length is shorter than that estimated from the characteristics of the linac. The relation between the spectrum and the distribution of electrons in the bunch is discussed.
TL;DR: In this article, the surface of the as-grown film exhibits a 2×1 reconstruction reflection high-energy electron diffraction pattern, indicating two-dimensional growth, indicating that SR irradiation enhances the dynamic surface reactions, such as desorption of hydrogen and surface migration of adsorbed species.
Abstract: Silicon photoepitaxy excited by synchrotron radiation (SR) has been observed for the first time. The epitaxial growth is observed even at lower than a 400 °C substrate temperature. The surface of the as‐grown film exhibits a 2×1 reconstruction reflection high‐energy electron diffraction pattern, indicating two‐dimensional growth. At lower than 600 °C, the SR‐irradiation growth rate is larger than that of thermal growth. This result suggests that SR irradiation enhances the dynamic surface reactions, such as desorption of hydrogen and surface migration of adsorbed species.
01 Oct 1991-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The behavior of the far infrared radiation produced by the passage of a mm long bunch of electrons through a vertical 0.44 T magnetic field is studied in this paper, where it is shown that the behavior of a single electron passing through a magnetic field can be described as follows:
Abstract: The behavior of the far infrared radiation produced by the passage of a mm long bunch of electrons through a vertical 0.44 T magnetic field is found to
TL;DR: In this article, the authors show that the radiation produced by the scattering of energetic electron streams in regions of plasma turbulence can be more efficient than synchroton emission, and that the minimum impact parameter is the scale size of the soliton, assumed to be many Debye lengths.
Abstract: Radiation produced by the scattering of energetic electron streams in regions of plasma turbulence can be more efficient than synchroton emission. Plasma instability occurs naturally due to counterstreaming plasmas in the environment of galactic jets, and saturates in a turbulent state of intense localized regions of electrostatic field. Energetic electrons accelerate while traversing soliton-like electric field structures. Their radiation is extremely broad-band in frequency, a bremsstrahlung type spectrum in which the minimum impact parameter is the scale size of the soliton, assumed to be a many Debye lengths.
TL;DR: In this article, the inner-valence electron states of the methane molecule have been studied by means of x-ray, synchrotron radiation, and UV-photoelectron spectroscopy.
Abstract: The inner‐valence electron states of the methane molecule have been studied by means of x‐ray, synchrotron radiation, and UV‐photoelectron spectroscopy. Five correlation satellites have been identified and a detailed study has been carried out of the 2a−11 single hole state. For this state a Franck–Condon analysis has been performed, suggesting an equilibrium bond distance of 1.279 A. The vibrational lines have a Lorentzian shape and the linewidth increases gradually with the vibrational quantum number. This probably indicates a reduction of the lifetime of the vibrational states due to predissociation. A discussion of the potential curves related to the correlation satellites is included.
TL;DR: In this paper, the PEPIPICO technique was used in conjunction with a source of continuum (synchrotron radiation) in order to determine the thresholds for fragmentation of CF4 into CF3++F+ (37.6 eV), CF2++F+, CF++F+.
Abstract: The PEPIPICO technique has been used in conjunction with a source of continuum (synchrotron radiation) in order to determine the thresholds for fragmentation of CF4 into CF3++F+ (37.6 eV), CF2++F+ (42.4 eV), CF++F+ (47.5 eV) and C++F+ (62.0 eV). These thresholds are tentatively correlated with specific double-hole states of CF4.
TL;DR: In this article, an ellipsoidal mirror was used as the synchrotron radiation focusing element combined with a double-crystal monochromator to realize an energy tunable intense small x-ray beam, and the distortion was significantly reduced with the small takeoff angle detection geometry.
Abstract: X‐ray absorption fine structure (XAFS) measurements in regions less than 20 μm in diameter were realized using an x‐ray microprobe employing the fluorescence detection method. To realize an energy tunable intense small x‐ray beam, an ellipsoidal mirror was used as the synchrotron radiation focusing element combined with a double‐crystal monochromator. Distortion of a XAFS spectrum due to the self‐absorption effect is discussed in detail. The degree of the distortion was experimentally evaluated from the measurement of the x‐ray fluorescence intensity as a function of takeoff angle, and the distortion was significantly reduced with the small takeoff angle detection geometry. Utilizing this technique, reliable XAFS spectra were obtained from a rock sample containing several minerals.
TL;DR: In this paper, the chemistry of the S/GaAs system was studied using synchrotron radiation photoemission spectroscopy, and it was found that the Ga-S bonding formation is the key for passivating GaAs surfaces for both sulfur-chemisorbed and (NH 4 ) 2 S x -treated GaAs.