共查询到20条相似文献,搜索用时 31 毫秒
1.
Hongxin Wang Anthony T. Young Jinghua Guo Stephen P. Cramer Stephan Friedrich Artur Braun Weiwei Gu 《Journal of synchrotron radiation》2013,20(4):614-619
X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M2,3‐edge RIXS on NiO, NiF2 and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed. 相似文献
2.
A novel method for resonant inelastic soft X‐ray scattering via photoelectron spectroscopy detection
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Georgi L. Dakovski Ming-Fu Lin Daniel S. Damiani William F. Schlotter Joshua J. Turner Dennis Nordlund Hirohito Ogasawara 《Journal of synchrotron radiation》2017,24(6):1180-1186
A method for measuring resonant inelastic X‐ray scattering based on the conversion of X‐ray photons into photoelectrons is presented. The setup is compact, relies on commercially available detectors, and offers significant flexibility. This method is demonstrated at the Linac Coherent Light Source with ~0.5 eV resolution at the cobalt L3‐edge, with signal rates comparable with traditional grating spectrometers. 相似文献
3.
S. R. Andrews 《Phase Transitions》2013,86(1-4):181-201
High‐resolution X-ray scattering measurements of the antiferrodistortive phase transitions in the perovskites SrTiO3, RbCaF3 and KMnF3 have recently revealed the existence of two length scales in the critical scattering above Te . Here we review these observations and discuss how they might be related to the well known existence of two time scales (the "central peak" problem) in the critical dynamic response function above Te . We reach the tentative conclusion that within a few degrees of Te both the time and length scales of the fluctuations are strongly influenced by defects and that the intrinsic critical behaviour is swamped by these effects in most crystals. 相似文献
4.
Upgrade of MacCHESS facility for X‐ray scattering of biological macromolecules in solution
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Alvin Samuel Acerbo Michael J. Cook Richard Edward Gillilan 《Journal of synchrotron radiation》2015,22(1):180-186
X‐ray scattering of biological macromolecules in solution is an increasingly popular tool for structural biology and benefits greatly from modern high‐brightness synchrotron sources. The upgraded MacCHESS BioSAXS station is now located at the 49‐pole wiggler beamline G1. The 20‐fold improved flux over the previous beamline F2 provides higher sample throughput and autonomous X‐ray scattering data collection using a unique SAXS/WAXS dual detectors configuration. This setup achieves a combined q‐range from 0.007 to 0.7 Å?1, enabling better characterization of smaller molecules, while opening opportunities for emerging wide‐angle scattering methods. In addition, a facility upgrade of the positron storage ring to continuous top‐up mode has improved beam stability and eliminated beam drift over the course of typical BioSAXS experiments. Single exposure times have been reduced to 2 s for 3.560 mg ml?1 lysozyme with an average quality factor I/σ of 20 in the Guinier region. A novel disposable plastic sample cell design that incorporates lower background X‐ray window material provides users with a more pristine sample environment than previously available. Systematic comparisons of common X‐ray window materials bonded to the cell have also been extended to the wide‐angle regime, offering new insight into best choices for various q‐space ranges. In addition, a quantitative assessment of signal‐to‐noise levels has been performed on the station to allow users to estimate necessary exposure times for obtaining usable signals in the Guinier regime. Users also have access to a new BioSAXS sample preparation laboratory which houses essential wet‐chemistry equipment and biophysical instrumentation. User experiments at the upgraded BioSAXS station have been on‐going since commissioning of the beamline in Summer 2013. A planned upgrade of the G1 insertion device to an undulator for the Winter 2014 cycle is expected to further improve flux by an order of magnitude. 相似文献
5.
R. N. Kyutt 《Physics of the Solid State》1997,39(7):1052-1056
Double-and triple-crystal diffractometry have been used to study structural perfection of a ∼1 μm-thick Ga1−x
InxSb1−y
Asy epitaxial film (x=0.9, y=0.8) on GaSb. It is shown that scattering from samples of this system can be divided into coherent and diffuse. The arrangement
of reciprocal-lattice points of the film and substrate in the two-dimensional intensity distribution for asymmetrical reflections
argues for the absence of elastic-strain relaxation. No dislocation networks are formed, and the diffuse scattering is produced
by Coulomb-type defects. Localization of diffuse scattering in reciprocal space suggests that these defects reside in the
epitaxial film. The diffuse-scattering distribution in asymmetrical reflections is shown to be anomalous; namely, it extends
in a direction parallel to the surface and is split into two maxima. Schemes have been proposed and realized for measuring
integral distributions of diffracted intensity along the surface and perpendicular to it, and their potential for studying
diffuse scattering from defects is explored.
Fiz. Tverd. Tela (St. Petersburg) 39, 1188–1193 (July 1997) 相似文献
6.
Xiaming Zhu Huizhen Wu Zijian Yuan Jinfang Kong Wenzhong Shen 《Journal of Raman spectroscopy : JRS》2009,40(12):2155-2161
Multiphonon resonant Raman scattering in N‐doped ZnO films was studied, and an enhancement of the resonant Raman scattering process as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed at room temperature. The resonant Raman scattering intensity of the 1LO phonon in N‐doped ZnO appears three times as strong as that of undoped ZnO, which mainly arises from the defect‐induced Raman scattering caused by N‐doping. The nature of the 1LO phonon at 578 cm−1 is interpreted as a quasimode with mixed A1 and E1 symmetry because of the defects formed in the ZnO lattice. In addition, the previously neglected impurity‐induced two‐LO‐phonon scattering process was clearly observed in N‐doped ZnO. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
Wolfram Leitenberger Robert Hartmann Ullrich Pietsch Robert Andritschke Ines Starke Lothar Strüder 《Journal of synchrotron radiation》2008,15(5):449-457
The first application of a pnCCD detector for X‐ray scattering experiments using white synchrotron radiation at BESSY II is presented. A Cd arachidate multilayer was investigated in reflection geometry within the energy range 7 keV < E < 35 keV. At fixed angle of incidence the two‐dimensional diffraction pattern containing several multilayer Bragg peaks and respective diffuse‐resonant Bragg sheets were observed. Since every pixel of the detector is able to determine the energy of every incoming photon with a resolution ΔE/E? 10?2, a three‐dimensional dataset is finally obtained. In order to achieve this energy resolution the detector was operated in the so‐called single‐photon‐counting mode. A full dataset was evaluated taking into account all photons recorded within 105 detector frames at a readout rate of 200 Hz. By representing the data in reciprocal‐space coordinates, it becomes obvious that this experiment with the pnCCD detector provides the same information as that obtained by combining a large number of monochromatic scattering experiments using conventional area detectors. 相似文献
8.
Harish Kumar Yadav R. S. Katiyar Vinay Gupta 《Journal of Raman spectroscopy : JRS》2011,42(12):2126-2131
The cascade model of inelastic resonant Raman scattering considers real electronic states in the conduction band (CB) as intermediaries to explain multiple longitudinal optical (LO) Stokes‐shifted lines in the emission spectra. In this study, we report modification in the cascade model under conditions where the scattered photons after multiple transitions have energy lower than the bandgap (Eg) and give rise to higher order n‐LO lines. The higher order n‐LO lines involve electron transition between the trap levels, which are created by impurities or defects in the forbidden energy gap, and are analogous to the real electronic states in CB, depending on the density of defects or impurities in the lattice. The presence of traps in the forbidden gap (1) acts as virtual intermediate states giving rise to higher order n‐LO modes and (2) tends to decrease the radiative recombination probability leading to quenching of the luminescence emission and line width (full‐width at half‐maximum) broadening. Ultraviolet Raman scattering in Mn‐doped ZnO (Zn1−xMnxO) thin films were investigated and the experimental observations analyzed in the domain of the modified cascade model. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
9.
A. Tomás S. Aune T. Dafni G. Fanourakis E. Ferrer‐Ribas J. Galán A. Gardikiotis J. A. García T. Geralis I. Giomataris H. Gómez F. J. Iguaz I. G. Irastorza G. Luzón T. Papaevangelou A. Rodríguez J. Ruz L. Seguí T. Vafeiadis S. C. Yildz 《X射线光谱测定》2011,40(4):240-246
The last generation of micromegas, called microbulk, are ahead of classical gas detectors (or even other kind of micro‐pattern gas detectors) in gain stability, efficiency (by operation at high pressure), simplicity, robustness, energy resolution, readout features and radiopurity. This makes them a competent solution in the field of Rare Event Searches, a field where low background is the most appreciated feature of a detector. The CAST (CERN Axion Solar Telescope) experiment is the best example of their application in the X‐rays range. In CAST, these detectors have achieved background rates as low as 6 × 10?6 counts keV?1 cm?2 s?1. Beyond this nominal operation, there have been several periods where the background has been reduced to a level of 2 × 10?7 counts keV?1 cm?2 s?1, due to reasons which are under investigation. The CAST experiment will be presented, paying special attention to their microbulk micromegas, as well as the procedures to achieve low background. Latest news about the operation of these kinds of detectors for the first time in underground conditions will be advanced here. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
Non‐degenerate second‐order scattering due to interaction of infrared and ultraviolet pulses is observed in picosecond infrared‐pump/anti‐Stokes Raman‐probe experiments under electronic resonance conditions. We detected resonance hyper‐Rayleigh scattering at the sum frequency of the pulses as well as the corresponding frequency‐down‐shifted resonance hyper‐Raman lines. Nearly coinciding resonance hyper‐Raman and one‐photon resonance Raman spectra indicate conditions of A‐term resonance Raman scattering. Second‐order scattering is distinguished from transient anti‐Stokes Raman scattering of v = 1 to v = 0 transitions and v = 1 to v′ = 1 combination transitions by taking into account their different spectral and temporal behaviour. Separating these processes is essential for a proper analysis of transient vibrational populations. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
Bekir Salgin Dirk Vogel Diego Pontoni Heiko Schröder Bernd Schönberger Martin Stratmann Harald Reichert Michael Rohwerder 《Journal of synchrotron radiation》2012,19(1):48-53
A wide range of high‐performance X‐ray surface/interface characterization techniques are implemented nowadays at every synchrotron radiation source. However, these techniques are not always `non‐destructive' because possible beam‐induced electronic or structural changes may occur during X‐ray irradiation. As these changes may be at least partially reversible, an in situ technique is required for assessing their extent. Here the integration of a scanning Kelvin probe (SKP) set‐up with a synchrotron hard X‐ray interface scattering instrument for the in situ detection of work function variations resulting from X‐ray irradiation is reported. First results, obtained on bare sapphire and sapphire covered by a room‐temperature ionic liquid, are presented. In both cases a potential change was detected, which decayed and vanished after switching off the X‐ray beam. This demonstrates the usefulness of a SKP for in situ monitoring of surface/interface potentials during X‐ray materials characterization experiments. 相似文献
12.
Some methods have been recently developed to investigate the distribution of implanted ions in semiconductors, especially into silicon. Generally, these techniques are not valid for boron due to the absence of convenient radioactive isotopes, or to a too small sensitivity when the lower part of the distribution is of interest. This corresponds to our problem, since boron implanted nuclear particle detectors prepared with high resistivity material (up to 50,000 ω.cm) are needed. The properties of these P-N junctions depend in a certain amount on the impurity distribution existing several orders of magnitude below the top of the distribution. Therefore, only the junction location method can be employed. In this method a series of N-type silicon samples, differing each from the other by an increase in resistivity are implanted with boron. The depth of the P-N junction corresponds to the point of the profile where the concentration NA is equal to that of the substrate ND (i.e. this latter being well known from the resistivity of the starting material). If the location of the junction can be measured, the profile can then be constructed point by point. The junction location is visualized generally by copper staining. Roosild,(1) Kleinfelder,(2) Fairfield(3) and D. E. Davies(4) have used this procedure for boron implantations at energies higher than 50 keV. There is a problem due to the small penetration of the boron ion, and, for high resistivity materials, it is difficult to know the true limits of the zones stained with copper. In our problem, when heavy particle detectors are desired, it is necessary to implant at lower energies than those indicated previously (< 20 keV). We have developed a new technique derived from the junction depth method, which is useful even at very low implant energy (≈ 10 keV). It consists in measuring the energy loss by 100 keV protons when crossing the entrance window of the P-N junctions used as detectors. In the first part of this paper the method is described and the possible errors are analyzed and evaluated. In the second part, the distribution of 15 keV boron ions implanted under several experimental conditions is studied. Emphasis is given to the defects resulting from the silicon bombardment. 相似文献
13.
Baochang Cheng Wei Sun Jin Jiao Baixiang Tian Yanhe Xiao Shuijin Lei 《Journal of Raman spectroscopy : JRS》2010,41(10):1221-1226
In Dy3+ and Li+ codoped ZnO nanowires, the additives accumulate preferentially in {0001} planes, resulting in serious breakdown of the translational symmetry in ab plane and modification of the phonon oscillation field. Not only acoustic overtones, silent optical modes, surface optical (SO) phonon modes, and multi‐phonon processes can be effectively observed in the nonresonant Raman scattering (RS) and the Fourier‐transform infrared (FTIR) spectra, but the quasi‐LO and TO modes of mixed A1 and E1 symmetry also show a noticeable red shift from E1 symmetry (in ab plane) to A1 symmetry (along c axis). The presence of dislocations and internal strain at the surface layer rich in additives, coming from the segregation of additives, forms a quasi‐bilayer system, resulting in the appearance and enhancement of SO phonon modes in RS and FTIR spectra. The Fano interference, originating from the interaction between the discrete scattering from phonons and the continuum scattering from laser‐induced electrons in the doped nanostructures, leads to typical asymmetric lineshapes on the lower wavenumber sides. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
Karl Ludwig 《Journal of synchrotron radiation》2012,19(1):66-73
Successful X‐ray photon correlation spectroscopy studies often require that signals be optimized while minimizing power density in the sample to decrease radiation damage and, at free‐electron laser sources, thermal impact. This suggests exploration of scattering outside the Fraunhofer far‐field diffraction limit d2/λR, where d is the incident beam size, λ is the photon wavelength and R is the sample‐to‐detector distance. Here it is shown that, in an intermediate regime d2/λ > Rdξ/λ, where ξ is the structural correlation length in the material, the ensemble averages of the scattered intensity and of the structure factor are equal. Similarly, in the regime d2/λ > Rdξ(τ)/λ, where ξ(τ) is a time‐dependent dynamics length scale of interest, the ensemble‐averaged correlation functions g1(τ) and g2(τ) of the scattered electric field are also equal to their values in the far‐field limit. This broadens the parameter space for X‐ray photon correlation spectroscopy experiments, but detectors with smaller pixel size and variable focusing are required to more fully exploit the potential for such studies. 相似文献
15.
Typically, X‐ray absorption near‐edge structure measurements aim to probe the linear attenuation coefficient. These measurements are often carried out using partial fluorescence yield techniques that rely on detectors having photon energy discrimination improving the sensitivity and the signal‐to‐background ratio of the measured spectra. However, measuring the partial fluorescence yield in the soft X‐ray regime with reasonable efficiency requires solid‐state detectors, which have limitations due to the inherent dead‐time while measuring. Alternatively, many of the available detectors that are not energy dispersive do not suffer from photon count rate limitations. A filter placed in front of one of these detectors will make the energy‐dependent efficiency non‐linear, thereby changing the responsivity of the detector. It is shown that using an array of filtered X‐ray detectors is a viable method for measuring soft X‐ray partial fluorescence yield spectra without dead‐time. The feasibility of this technique is further demonstrated using α‐Fe2O3 as an example and it is shown that this detector technology could vastly improve the photon collection efficiency at synchrotrons and that these detectors will allow experiments to be completed with a much lower photon flux reducing X‐ray‐induced damage. 相似文献
16.
The electron‐density distribution and the contribution to anomalous scattering factors for Fe ions in magnetite have been analyzed by X‐ray resonant scattering at the pre‐edge of Fe K absorption. Synchrotron X‐ray experiments were carried out using a conventional four‐circle diffractometer in the right‐handed circular polarization. Difference‐Fourier synthesis was applied with a difference in structure factors measured on and off the pre‐edge (Eon = 7.1082 keV, Eoff = 7.1051 keV). Electron‐density peaks due to X‐ray resonant scattering were clearly observed for both A and B sites. The real part of the anomalous scattering factor f′ has been determined site‐independently, based on the crystal‐structure refinements, to minimize the squared residuals at the Fe K pre‐edge. The f′ values obtained at Eon and Eoff are ?7.063 and ?6.682 for the A site and ?6.971 and ?6.709 for the B site, which are significantly smaller than the values of ?6.206 and ?5.844, respectively, estimated from the Kramers–Kronig transform. The f′ values at Eon are reasonably smaller than those at Eoff. Our results using a symmetry‐based consideration suggest that the origin of the pre‐edge peak is Fe ions occupying both A and B sites, where p–d mixing is needed with hybridized electrons of Fe in both sites overlapping the neighbouring O atoms. 相似文献
17.
X-ray scattering techniques have been used to study the diffuse scattering from a single crystal of Rb1–x(ND4)xD2PO4 withx=0.65. This system has a structural glass phase at low temperatures resulting from the competing ferroelectric interactions of RbD2PO4 and antiferroelectric interactions of (ND4)D2PO4. The diffuse scattering shows a broad peak with a maximum occurring at a wavevector of about 0.3a
*, and the intensity of these peaks is surprisingly different for wavevectorsq on opposite sides of the Bragg reflections. A model of the D bonding is developed which suggests that the diffuse scattering arises from the interaction between ferroelectric displacements alongc, ferroelectric displacements alongb, and transverse acoustic modes polarized alongb andc. The model accounts for the incommensurate wavevector and, qualitatively, for the intensity of the diffuse scattering around different Bragg reflections. The temperature dependence of the scattering is also measured. 相似文献
18.
Kurt Schroeder 《Zeitschrift für Physik B Condensed Matter》1976,25(1):91-95
We present a phenomenological model describing the trapping and release of mobile defects at random inhomogeneities. The traps are characterized by two parameters, the capture radiusR
t, describing the range of the interaction and the binding energyE
b describing the escape. We give an integral representation of the correlation function of the mobile particles in the presence of traps. For large distances the correlation function can be described by a simple diffusional process with an effective diffusion constant. Finally we discuss the neutron scattering by mobile defects resulting from this trapping model. 相似文献
19.
R. A. Ryutin 《Physics of Atomic Nuclei》2010,73(11):1956-1962
An experiment aimed at studying leading neutrons at LHC with the aid of the CMS detectors is proposed. Data of this experiments
can be used to extract cross sections for π
+
p and π
+
π
+ scattering. Numerical estimates are presented for the proposed measurements. 相似文献
20.
Fabrication of polycrystalline silicon films by Al‐induced crystallization of silicon‐rich oxide films
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Jong‐Hwan Yoon 《固体物理学:研究快报》2016,10(9):668-672
Polycrystalline silicon (poly‐Si) films were fabricated by aluminum (Al)‐induced crystallization of Si‐rich oxide (SiOx) films. The fabrication was achieved by thermal annealing of SiOx /Al bilayers below the eutectic temperature of the Al–Si alloy. The poly‐Si film resulting from SiO1.45 exhibited good crystallinity with highly preferential (111) orientation, as deduced from Raman scattering, X‐ray diffraction, and transmission electron microscopy measurements. The poly‐Si film is probably formed by the Al‐induced layer exchange mechanism, which is mediated by Al oxide. 相似文献