2009 Vol. 33, No. 11
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Time-resolved X-ray scattering was employed to in-situ monitor the epitaxial growth process of the thin films and multilayers of EuTiO3 and SrTiO3 during pulsed laser deposition. The temporal intensity oscillations of the reflected X-rays at anti-Bragg position and the transient processes following the flux pulses were observed. The temporal intensity oscillations were used to control the film thickness, and the reflectivity along the crystal truncation rod was used to measure both the film thickness and the surface/interface roughness. The primary features of the X-ray intensity oscillations were reproduced via simulating the experimental data using diffusive rate equation model. Several mechanisms of determining the X-ray intensity features were discerned.
Microstructure of NiO-containing Co/Cu/Co spin valves (CCC-SV) annealed at room temperature for nearly four years has been studied by synchrotron radiation X-ray diffraction. With the annealing time expanding, the thickness of each sub-layer remains nearly unchanged while the interface roughness varies obviously compared with that of samples without annealing. The roughness at the interface of NiO/Co decreases with the annealing time increasing for both of the samples with NiO layer on the top (TSV) and under the bottom (BSV) of CCC-SV. On the other hand, the roughness at Co/Cu interface increases with the annealing time expanding for BSV while it decreases for TSV. These results indicate that the structure of TSV is more stable than that of BSV.
SrTiO3 thin films are epitaxially grown on DyScO3, LaAlO3 substrates with/without buffer layers of DyScO3 and SrRuO3 using laser-MBE. X-ray diffraction methods, such as high resolution X-ray diffraction, grazing incident X-ray diffraction, and reciprocal space mapping are used to investigate the lattice structure, dislocation density, in-plane lattice strain distribution along film thickness. From the measurement results, the effects of substrate on film lattice quality and microstructure are discussed.
Two isolated pentagon rule satisfying isomers of C76 are optimized. And 1(D2 isomer is reconfirmed to be the relative more stable one. The X-ray absorption near-edge structure (XANES) spectra are theoretically characterized by the hybrid density functional theory (DFT) method in combination with the full core-hole potentials. Isomer identification of XANES spectra for C76 is found and XANES spectra dependence on local structure of fullerene is discussed.
In order to further understand the sources of PM2.5 in Shanghai air, the synchrotron X-ray fluorescence microprobe at the BL-4A Beamline of Photon Factory of High Energy Accelerator Research Organization, Japan, was applied to analyze the individual PM2.5 particles collected from Shanghai air in the winter of 2007. Eight categories of emission sources were recognized in these individual particles. The source identification shows that most of the analyzed PM2.5 particles are derived from vehicle exhaust and metallurgical emissions. This suggests that the important emission sources of PM2.5 in Shanghai air would be vehicle exhaust and metallurgical activities.
The sulfur species existing in different size aerosol particles were determined based on the `white line' energy shift and the features of post edge structure of sulfur K-edge XANES (X-ray Absorption Near Edge Structure). The results indicated that sulfates were dominant sulfur species in aerosol particles. However, small amount of reductive sulfur species were also found in the ultrafine aerosol particles(<0.1 μm). Sulfates in aerosols mostly exhibited as (NH4)2SO4 and gypsum. Most (NH4)2SO4 distributed in aerosol particles finer than 0.952 μm, while gypsum was the dominant sulfate in coarse aerosols.
X-ray diffraction enhanced imaging (DEI) is applied to inspect internal structures of weakly absorbing low-Z sample. How to extract phase information from raw images measured in different positions of rocking curve is the key problem of DEI. In this paper, we present an effective extraction method called polynomial curve fitting method, in order to extract accurate information angular in a fast speed. It is compared with the existing methods such as multiple-images statistical method and Gaussian curve fitting method. The experiments results on a plastic cylinder and a black ant at the Beijing Synchrotron Radiation Facility prove that the polynomial curve fitting method can obtain most approximate refraction-angle values and its computation speed is 10 times faster than the Gaussian curve fitting method.
X-ray diffraction enhanced imaging (DEI) has extremely high sensitivity for weakly absorbing low-Z samples in medical and biological fields. In this paper, we propose an Algebra Reconstruction Technique (ART) iterative reconstruction algorithm for computed tomography of diffraction enhanced imaging (DEI-CT). An Ordered Subsets (OS) technique is used to accelerate the ART reconstruction. Few-view reconstruction is also studied, and a partial differential equation (PDE) type filter which has the ability of edge-preserving and denoising is used to improve the image quality and eliminate the artifacts. The proposed algorithm is validated with both the numerical simulations and the experiment at the Beijing synchrotron radiation facility (BSRF).
Tomosynthesis is a three-dimension reconstruction method that can remove the effect of superimposition with limited angle projections. It is especially promising in mammography where radiation dose is concerned. In this paper, we propose a maximum likelihood tomosynthesis reconstruction algorithm (ML-TS) on the apparent absorption data of diffraction enhanced imaging (DEI). The motivation of this contribution is to develop a tomosynthesis algorithm in low-dose or noisy circumstances and make DEI get closer to clinic application. The theoretical statistical models of DEI data in physics are analyzed and the proposed algorithm is validated with the experimental data at the Beijing Synchrotron Radiation Facility (BSRF). The results of ML-TS have better contrast compared with the well known `shift-and-add' algorithm and FBP algorithm.
Neovascularization is correlative with many processes of diseases, especially for tumor growth, invasion, and metastasis. What is more, these tumor microvessels are totally different from normal vessels in morphology. Therefore, observation of the morphologic distribution of microvessels is one of the key points for many researchers in the field. Using diffraction enhanced imaging (DEI), we observed the mirocvessles with diameter of about 40 μm in mouse liver. Moreover, the refraction image obtained from DEI shows higher image contrast and exhibits potential use for medical applications.
The synchrotron radiation angle-resolved photoemission data of K3C60 single crystal film are analyzed, aiming at the photoionization cross-sections of the LUMO, HOMO and HOMO-1 bands in low photon energy region (14.5—27.5 eV). Many fine structures of the HOMO/HOMO-1 intensity ratios are observed, which support the general validity of a quantum chemistry model. However, the experimental data and the theoretical results have some disagreement in the energy positions and magnitudes of the fine structures, and the disagreement is more outstanding than the case of pure C60. So the photoemission data of K3C60 afford valuable experimental reference to further theoretical developments. The LUMO cross-section data, which cannot be discussed with the quantum chemistry description due to strong solid state effects, are also reported for further studies.
We have measured the synchrotron radiation photoelectron spectra of monolayer C60 on Ag(100). By calculating the intensity ratios between the LUMO bands and the two deeper bands (HOMO and HOMO-1), we estimate the amount of the charges transferred from Ag(100) to C60 within the range of 1 e to 1.8 e. The results dismay the expectation of surface superconductivity and afford a good reference for further studies of the monolayer C60/Ag(100) system.
Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy was employed to study the speciation of sulfur in raw coal, ash by-product and fine particulate matter from a small coal-burning boiler. By means of least square analysis of the XANES spectra, the major organic and inorganic sulfur forms were quantitatively determined. The results show that about 70% of the sulfur in raw coal is present as organic and a minor fraction of the sulfur occurs as other forms: 17% of pyrite and 13% of sulfate. While in bottom ash, fly ash, and PM2.5, the dominant form of sulfur is sulfate, with the percentage of 80,79 and 94, respectively. Moreover, a number of other reduced sulfur including thiophenic sulfur, element sulfur and pyrrhotite are also present. During coal combustion, most of organic sulfur and pyrite were oxidized and released into the atmosphere as SO2 gas, part of them was converted to sulfate existing in coal combustion by-products, and a small part of pyrite was probably reduced to elemental sulfur and pyrrhotite. The results may provide information for assessing the pollution caused by small boiler and developing new methods for the control of SO2 pollution.
The characteristics of daytime and nighttime suburbs PM2.5 in Shanghai were analyzed by synchrotron based X-ray fluorescence during the period of October, 2006 and November, 2007. The mass concentrations of nighttime PM2.5 was approximately two times that of daytime PM2.5. Some elements, such as Zn, Cu, Mn, Cl were found enriched at night. The local sources might have significant contribution to the nighttime PM2.5 pollutions.
The impact of coal-burning emission on sulfur in camphor leaves was investigated using Proton Induced X-ray Emission (PIXE) and synchrotron radiation technique X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The PIXE results show that the sulfur concentrations in the leaves collected at the polluted site are significantly higher than those in controls. The Sulfur XANES spectra show the presence of organic (disulfides, thiols, thioethers, sulfonates and sulfoxides) and inorganic sulfur (sulfates) in the leaves. The inorganic sulfur in the leaves of camphor tree polluted by coal combustion is 15% more than that of the control site. The results suggest that the long-term coal-burning pollution resulted in an enhanced content of the total sulfur and sulfate in the leaves, and the uptake of sulfur by leaves had exceeded the metabolic requirement of plants and the excess of sulfur was stored as SO42－. It can monitor the sulfur pollution in atmosphere.
The monodisperse polystyrene spheres are assembled into the colloidal crystal on the glass substrate by vertical deposition method, which is aimed at the so-called photonic crystal applications. The structural information of the bulk colloidal crystal is crucial for understanding the crystal growth mechanism and developing the various applications of colloidal crystal. Small-angle X-ray scattering (SAXS) technique was used to obtain the bulk structure of the colloidal crystal at Beamline 1W2A of BSRF. It is found that the SAXS pattern is sensitive to the relative orientation between the colloidal sample and the incident X-ray direction. The crystal lattice was well distinguished and determined by the SAXS data.
The spectra of RE-doped YPO4 (RE=Ce3+, Pr3+ or Nd3+) have been measured. The spectroscopic and decay kinetics properties of pure host YPO4 were also studied at 8 K and 300 K, which indicated the host had taken part in the luminescent processes of activators. Under the excitation over the bandgap of the host, the electron could relax to the activators. Through the comparison of spectra and decay time, Nd3+ doped YPO4 had better scinillation properties than Ce3+ or Pr3+ inYPO4.
The in-situ high-pressure structures of wulfenite have been investigated by means of angular dispersive X-ray diffraction with diamond anvil cell and synchrotron radiation. In the pressure up to 22.9 GPa, a pressure-induced scheelite-to-fergusonite transition is observed at about 10.6 GPa. The pressure dependence for the lattice parameters of wulfenite is reported, and the axial compression coefficients Ka0=－1.36×10－3 GPa－1 and Kc0= －2.78×10－3 GPa－1 are given. The room-temperature isothermal bulk modulus is also obtained by fitting the P-V data using the Murnaghan equation of state.
The compression behavior of the heavy RE-based BMG Gd40Y16Al24Co20 under high pressure has been investigated by in situ high pressure angle dispersive X-ray diffraction measurements using synchrotron radiation in the pressure range of 0~33.42 GPa at room temperature. By fitting the static equation of state at room temperature, we find the value of bulk modulus B is 61.27±4 GPa which is in good agreement with the experimental study by pulse-echo techniques of 58 GPa. The results show that the amorphous structure in the heavy RE-based BMG Gd40Y16Al24Co20 keeps quite stable up to 33.42 GPa although its compressibility is as large as about 33%. The coexistence of normal local structure similar to that of other BMGs and covalent bond structure similar to those of oxide glasses may be the reason for the anomalous property under high pressure of the Gd40Y16Al24Co20 BMG.
The China Spallation Neutron Source (CSNS) is an accelerator-based multidisciplinary user facility to be constructed in Dongguan, Guangdong, China. The CSNS complex consists of an H－ linear accelerator, a rapid cycling synchrotron accelerating the beam to 1.6 GeV, a solid-tungsten target station, and instruments for spallation neutron applications. The facility operates at 25 Hz repetition rate with an initial design beam power of 120 kW and is
upgradeable to 500 kW. Construction of the CSNS project will lay the foundation of a leading national research center based on advanced proton-accelerator technology, pulsed neutron-scattering technology, and related programs including muon, fast neutron, and proton applications as well as medical therapy and accelerator-driven subcritical reactor (ADS) applications to serve China's strategic needs in scientific research and technological innovation for the next 30 plus years.
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