摘要:

This report is focused on the control of the plasma sputtering process used for the synthesis of multilayer mirrors for extreme UV and soft X‐ray optical devices. The case of a‐Si/Mo and of a‐Si(H)/Mo multilayers will be discussed, with emphasis on the study of the basic parameters that control the growth of the single Mo and a‐Si(H) layers. The deposition apparatus will be described. The effects of the plasma composition and of the bombardment of the growing layers by Ar+ions and electrons on the properties of the layers are reported. The hydrogen concentration can be varied up to about 30 at&percent; in the a‐Si(H) layers: the hydrogen incorporation leads to a decrease of the material density. The accurate control of the plasma density and of the electron temperature and plasma potential is accomplished through the Langmuir probe method, that permits the accurate measurement of the energy of the Ar+ions and of their fluence. The possibility of using the present apparatus for the synthesis of a class of ML designed for smaller wavelength applications (down to the water window spectral region) is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536366

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

X‐ray computer microtomography using synchrotron light (SR&mgr;CT) has proven to be a highly powerful method in many fields of modern research as medicine, biology and material science. Presently used instruments, however, are limited to about 1&mgr;m resolution at a total efficiency of a few percent, due to the properties of the scintillator, the optical light transfer, and the CCD granularity. To overcome these limitations we have realized a novel approach based on extremely asymmetrical Bragg reflection. Our instrument, the “Bragg Magnifier” combines two asymmetrically cut Si crystals, mounted close to each other on two rotation and adjustment units. It is installed at the Materials Science Beamline of the Swiss Light Source (SLS). It operates at favorably high energies between 21 keV and 23 keV. In a first experiment using a human bone trabecula a two‐dimensional magnification factor of 100×100 was achieved yielding a spatial resolution of 140nm. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536367

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present the analysis of double photoionization and of ionization accompanied by excitation of the helium atom and helium‐like ions. The high‐energy limit corresponding to the ultrarelativistic energies transferred to the atom is considered. The cross‐sections ratios are expressed through certain integral parameters of the wave function of the initial state. The calculations with the wave function obtained earlier by Correlation Function Hyperspherical Harmonic Method are carried out. The dependence of the relative role of the quasifree mechanism on the nuclear chargeZin ionization of the ground state and of the excitedn′s states is analyzed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536368

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The high‐energy electron beam ion trap SuperEBIT at the Lawrence Livermore National Laboratory allows the study of the x‐ray emission from highly charged ions interacting with electrons with energy in excess of 200 keV. Radiation from ions as highly charged as Cf96+has been produced this way. The facility is being used to investigate the contributions from quantum electrodynamics in heavy ions. Here the focus is lithiumlike ions, especially U89+, which provide the opportunity for the most accurate test of QED in highly charged ions. We have also used the facility to measure the degree of x‐ray line polarization as a function of the energy of the electron collision energy. For example, we have studied the linear polarization of the K‐shell emission lines of Fe24+for electron‐impact energies high as 120 keV. A new area of research is the investigation of nuclear excitation by electronic transitions. This is the inverse process of internal conversion, where an atomic x ray is absorbed by the nucleus resulting in an excited nuclear state. We are planning to study this process in189Os using 217 keV atomic x rays generated in the interaction with a 196 keV electron beam. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536369

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In this paper, we present the results of our investigation on the photoionization of the O3+ion in the 1s22s22p2P ground state and the 1s22s2p24P metastable states. The experimental results are compared to a 72‐states Multi Configurational Dirac Fock (MCDF) calculation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536370

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Results of the nondipolar angular distribution parameter &ggr; are presented for two cases of photoionization with substantially different photon energies, Kr 1s in the hard x‐ray regime, and He 1s in the vuv regime. The nondipolar asymmetries are apparent even at low energies. The presence of dipole and quadrupole resonances strongly modifies the energy dependence of the nondipolar asymmetry parameter &ggr;. Measurements of &ggr; can be used as a spectroscopic tool to characterize quadrupole resonances that are not accessible in photoabsorption measurements. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536371

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The 2p photoionization of free atoms of the late transition metals cobalt and nickel has been investigated using synchrotron radiation and is compared to CI calculations. Good agreement is found between experiment and theory. Furthermore a remarkable agreement between the atomic nickel 2p photoemission and recent data on nickel compounds is found. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536372

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

X‐ray absorption and emission features arising from the inner‐shell transitions in iron are of practical importance in astrophysics due to the Fe cosmic abundance and to the absence of traits from other elements in the nearby spectrum. As a result, the strengths and energies of such features can constrain the ionization stage, elemental abundance, and column density of the gas in the vicinity of the exotic cosmic objects, e.g. active galactic nuclei (AGN) and galactic black hole candidates. Although the observational technology in X‐ray astronomy is still evolving and currently lacks high spectroscopic resolution, the astrophysical models have been based on atomic calculations that predict a sudden and high step‐like increase of the cross section at the K‐shell threshold (see for instance Ref. [1]). New Breit‐Pauli R‐matrix calculations of the photoionization cross section of the ground states of Fexviiin the region near the K threshold are presented. They strongly support the view that the previously assumed sharp edge behaviour is not correct. The latter has been caused by the neglect of spectator Auger channels in the decay of the resonances converging to the K threshold. These decay channels include the dominant KLL channels and give rise to constant widths (independent of n). As a consequence, these series display damped Lorentzian components that rapidly blend to impose continuity at threshold, thus reformatting the previously held picture of the edge. Apparent broadened iron edges detected in the spectra of AGN and galactic black hole candidates seem [2, 3] to indicate that these quantum effects may be at least partially responsible for the observed broadening. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536373

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Updated recommended data for absolute photoionization cross sections of Kr and Xe with uncertainties of ± 3 &percent; are presented. The data are the result of a comprehensive analysis of reliable experimental measurements in absolute terms taking preceding recommendations into account. Significant corrections of the cross section values for certain photon‐energy regimes have been derived from the comparison of gas ionization by photons and electrons using a new experimental approach. The values presented serve as a background for new techniques to be used for the quantitative characterization of VUV‐FEL photon beams. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536374

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Recent studies on dynamics of photoexcitation and photoionization of molecules probed by multiple coincidence momentum imaging technique are reviewed. This technique consists of electron and ion time‐of‐flight analyzers with multi‐hit two‐dimensional position sensitive detectors and a supersonic jet. As specific examples we discuss nuclear motion caused by the C 1s→ 2&pgr;uexcitation in CO2and the C 1sphotoelectron angular distributions from fixed‐in‐space CO2. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536375

出版商:AIP    

年代:1903

数据来源: AIP