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  • 1
    ISSN: 1434-6079
    Keywords: 3280F ; 3280D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spin- and angle-resolved photoelectron spectroscopy with elliptically polarized radiation has been used to fully characterize the dynamics of photoelectron emission from free Xe atoms in the 5p-autoionization and continuum region. An advantageous reaction geometry and its experimental realization at the storage ring BESSY are discussed. The three independent experimental parameters which characterize the angular dependence of the photoelectron spin-polarization vector are reported for the wavelength range from 100nm to 40 nm. The results are compared with theoretical predictions based on RRPA-, RPAE- and semiempirical MQDT-calculations. The combination of existing data for the differential photoionization cross section with the spinpolarization parameters is used to completely decouple the photoionization channels: The transition matrix elements and their relative phases are determined separately for every single dissociation channel. The results are discussed in the context of the MQDT. Correlation effects and the influence of spin-orbit interaction on the continuum states most clearly show up when the Dill-Fano angular-momentum-transfer formalism is applied.
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  • 2
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Parameters describing electron spin polarization in Hg 5d 10 subshell photoionization have been measured at rare-gas resonance wavelengths between 73.59 nm and 30.38 nm. The spin parameters as well as asymmetry parameters β of a recent measurement are discussed in comparison with both nonrelativistic and relativistic ab initio calculations of several authors. The importance of many-electron correlations and spin-orbit coupling effects is considered.
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  • 3
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the spin polarization of photoelectrons in the autoionization region of the Hg 6s 2-subshell using circularly polarized synchrotron radiation and using unpolarized light from rare gas discharge lamps are reported. The results obtained show a pronounced structure across the resonances. Together with data of the cross section and its angular distribution these data from a complete parameter set for the determination of the transition matrix elements and the phase difference of the continuum wavefunctions. Evidences for strong configuration interaction and channel mixing between the open and closed channels were found. The matrix elements and their ratio vary strongly across the resonances and the relative phase shows some changes of sign. A change of the relative phase by π across an autoionization resonance, predicted by Fano, has been verified experimentally for the triplet resonance.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2432-2434 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic domains on an Fe(100) surface have been imaged by means of energy-resolved photoemission microscopy. We excited the photoelectrons with circularly polarized synchrotron radiation in the soft x-ray region, and employed the effect of magnetic circular dichroism in the emitted photoelectrons in order to obtain contrast between differently oriented magnetic domains. This new approach offers a surface sensitive way to combine chemical and magnetic information on a microscopic scale.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During the past few years the magnetic circular dichroism effect (MCD) has become an increasingly important tool for studying magnetic materials and their surfaces. The employment of MCD is based on the use of circularly polarized soft x rays, which can be obtained from electron storage rings. Circularly polarized x rays appear either as off-plane bending magnet radiation or radiation from special undulator devices, e.g., crossed or helical ones. However, an unsolved problem has been the independent and simple measurement of the polarization of this radiation. At BESSY, we have developed a new compact polarimeter. The instrument consists of four major elements. There are (i) a pinhole to select the desired part of the photon emission cone and (ii) a 100-period Cr/C multilayer to serve as a monochromator with a spectral resolution power of 50. The angle of incidence is set to 15.9° to meet 718 eV photon energy that corresponds to a maximum MCD effect close to the Fe 2p threshold excitation energy. There are also (iii) a 50 nm Fe film on 3 μm Mylar foil to show the MCD effect in photon transmission (the foil is mounted under 45° to the photon beam and can be magnetized in the plane of the Fe film) and (iv) a Si-pin diode to measure the transmitted photon flux. The assembly fulfills the following requirements: (1) insensitive to linearly polarized and unpolarized light, (2) performance at high heat load, (3) reliability and long term stability also in air, (4) wavelength sensitivity, and (5) fast readout capability. In future work the polarimeter can be employed for the characterization of helical undulators such as the BESSY II UE56, which cover the range of the Fe 2p threshold. With foils of other transition metal or rare-earth materials, the sensitive photon energy range can be extended.© 1997 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multilayer transmission filter with 100 periods Cr/C has been produced in order to achieve a significant phase retardation for photon energies just below the carbon K edge. The phase retardation of this device was characterized and despite being smaller than expected the filter was suitable for the polarization characterization of a soft x-ray beamline with a primary standard. Neither the filter nor the beamline were found to change their characteristics in the course of seven months. Considering the state of the art of multilayer coatings additional model calculations show that these transmission filters can be applied also at 400 eV photon energy with an upper limit at 500 eV. © 1995 American Institute of Physics.
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The loss of transmission of optical elements by irradiation is a big problem of all synchrotron radiation laboratories. A major reason for the reduced transmission is the contamination with graphitic carbon that is due to adsorbed and cracked hydrocarbons. In accordance with earlier experiments at other storage rings, a cleaning procedure was developed at BESSY which consists of an oxygen discharge suspended by an rf cavity. The atomic oxygen that is created in the plasma reacts with the carbon to CO and CO2 and dissolves from the surface. The investigations focused on the items: (a) influence of the cleaning procedure on the reflectivity, (b) its influence on the surface roughness of the optical element, and (c) transfer of the procedure to other elements (e.g., vacuum ultraviolet detectors, diodes, different substrates). For an in-situ check of the cleaning efficiency, the reflectivity of gold-and carbon-coated test samples was measured before and after cleaning using the BESSY HE-TGM 2 beamline. The microroughness was investigated employing different surface sensitive techniques like scanning electron microscopy, scanning tunneling microscopy, and interferometry.
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Characteristics of Ti/Be multilayers deposited by laser sputtering were investigated by grazing incidence x-ray reflection. The reflectivity of mirrors was explained using exponential variation of dielectric function, the validity of scattering model was confirmed by synchrotron radiation reflectivity measurements at 1200 eV. The observed quasi-Bragg peaks were interpreted in terms of nonspecular scattering from interfacial roughness.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; End-sealing technique for static coating ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 10
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: YB66, a complex boron-rich man-made crystal, has been singled out as a potential monochromator material to disperse synchrotron soft X-rays in the 1–2 keV region. Results of a series of systematic property characterizations pertinent for this application are presented in this paper. These include Laue diffraction patterns and high-precision lattice-constant determination, etch rate, stoichiometry, thermal expansion, soft X-ray reflectivity and rocking-curve measurements, thermal load effects on monochromator performance, nature of intrinsic positive glitches and their reduction. The 004 reflection of YB66 has a reflectance of ∼3% in this spectral region. The width of the rocking curve varies from 0.25 eV at 1.1 keV to 1.0 eV at 2 keV, which is a factor of two better than that of beryl(1010) in the same energy range, and enables measurements of high-resolution XANES spectra at the Mg, Al and Si K-edges. The thermal bump on the first crystal arising from the low thermal conductivity of YB66 causes an energy drift of a few eVs with storage-ring current and necessitates periodic energy calibration with metal foils. The positive glitches in the transmission function just above the Mg K-edge have substantially been reduced using an Si or SiC mirror which suppresses the sharp reflectivity increases associated with anomalous scattering for the YB66 006 reflection at the Y L3- and L2-edges. Continual operation over the past five years of a YB66 double-crystal monochromator installed on the JUMBO beamline at Stanford Synchrotron Radiation Laboratory (SSRL) indeed proves the long-term stability of this material in synchrotron radiation under ultrahigh vacuum conditions as indicated by the invariance in rocking-curve characteristics after being exposed to an accumulative power level of ∼3 × 108 J over this period of time.Part I. Wong et al. (1990).
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