No abstract available

No abstract available

[en] The phenomenon of the solution of liquid hydrogen and deuterium is investigated in the temperature range 19-23 K. The thermal effect of solution is established: while adding deuterium the temperature of the isotope mixture falls, adding hydrogen - rises. The estimation of the value of the solution heat effect is made. (author)

[en] Inner-shell excitation and associated decay spectroscopies are site specific probes of electronic and geometrical structure and photoionization dynamics. X-ray absorption probes the geometric and electronic structure, while time-of-flight mass spectrometry with multi-coincidence detection provides information on the photofragmentation dynamics of the initially produced inner-shell state. Auger decay of inner-shell excited and ionised states is an efficient source of multiply charged ions. The charge separation and fragmentation of these species, studied by photoelectron-photoion-photoion coincidence (also called charge separation mass spectrometry) gives insights into bonding and electronic structure. In molecules, the dependence of the fragmentation process on the X-ray energy can reveal cases of site and/or state selective fragmentation. At the ALS the authors have examined the soft X-ray spectroscopy and ionic fragmentation of a number of molecules, including carboranes, silylenes, phosphorus halides, SF₆ and CO₂. Their work is illustrated using results from the carborane and PF₃ studies

[en] In recent years silicon nanostructures have gained great interest because of their optical luminescence, which immediately suggests several applications, e.g., in optoelectronic devices. Nanostructures are also investigated because of the fundamental physics involved in the underlying luminescence mechanism, especially attention has been drawn to the influence of the reduced dimensions on the electronic structure. The forming of stable and well-defined nanostructured materials is one goal of cluster physics. For silicon nanostructures this goal has so far not been reached, but various indirect methods have been established, all having the problem of producing less well defined and/or unstable nanostructures. Ion implantation and subsequent annealing is a promising new technique to overcome some of these difficulties. In this experiment the authors investigate the electronic structure of ion-implanted silicon nanoparticles buried in a stabilizing SiO₂ substrate. Soft X-ray emission (SXE) spectroscopy features the appropriate information depth to investigate such buried structures. SXE spectra to a good approximation map the local partial density of occupied states (LPDOS) in broad band materials like Si. The use of monochromatized synchrotron radiation (MSR) allows for selective excitation of silicon atoms in different chemical environments. Thus, the emission from Si atom sites in the buried structure can be separated from contributions from the SiO₂ substrate. In this preliminary study strong size dependent effects are found, and the electronic structure of the ion-implanted nanoparticles is shown to be qualitatively different from porous silicon. The results can be interpreted in terms of quantum confinement and chemical shifts due to neighboring oxygen atoms at the interface to SiO₂

[en] Total reflection X-Ray Fluorescence (TXRF) is a widely used technique in which the normal trace element detection capability of hard x-ray fluorescence (XRF) is enhanced by use of an x-ray reflective substrate. TXRF is more sensitive than normal photon induced XRF due to the reduction of the substrate scattering and fluorescence signals. This reduction comes about because in total external reflection, the photon field only penetrates about 20 angstrom into the surface, instead of typically 50 μm for a silicon substrate at normal incidence for 10 KeV photons. The technique is used in many fields of trace element analysis, and is widely used in the determination of metal impurity concentrations on and in the surface of silicon wafers. The Semiconductor Industry Association roadmap (SIA) indicates a need for wafer contamination detection at the 10⁷atoms/cm² level in the next few years. Current commercial systems using rotating anode x-ray sources presently routinely operate with a sensitivity level of around 10¹⁰ atoms/cm² and this has led to interest in the use of synchrotron radiation to extend the sensitivity by three orders of magnitude. The pioneering work of Pianetta and co-workers at SSRL has clearly shown that this should be possible, using a fully optimized source and detector. The purpose of this work is to determine whether ALS would be a suitable source for this type of highly sensitive wafer TXRF. At first look it appears improbable as the SSRL work used a high flux multipole wiggler source, and it is clear that the detected fluorescence for relevant concentrations is small. In addition, SSRL operates at 3.0 GeV rather than 1.9 GeV, and is therefore more naturally suited to hard x-ray experiments. The aim of this work was therefore to establish a theoretical model for the scattering and fluorescence processes, so that one could predict the differences between alternative geometries and select an optimum configuration

[en] The 2s2p²²S₁₂ and ²P_1/2 levels in the boronlike ions are strongly affected by spin-orbit interaction, which leads to intermediate coupling, and the degree of the deviation from pure LS coupling varies with the nuclear charge of the ions. We have measured the relative intensities of the decays from the nominal 2s2p²²S_1/2 level to the 2s²2p ²P⁰_1/2,3/2 fine structure levels of the ground term, for all elements from O to Cl. This ratio would be 1 / 2 for pure LS states, but it clearly deviates from this value in the range of our study. We also discuss the measured relative intensities of the 2s2p²²P_1/2,3/2 decays. We compare our results with predictions from various calculations involving configuration mixing with electrons up to the n = 3 shell. Our own MCHF calculations indicate that an additional inclusion of n = 4 electrons has no significant effect on the transitions of interest. (orig.)

[en] In this work, the authors resolved the electronic absorption spectra of three tetraazaannulenes of different symmetry measured in solution at 298 and 77 K. The results obtained allowed assignation of the bands observed in the visible region to n → π* transitions and to vibronic components of two π → π* transitions. The efficiency of vibronic interaction is shown to depend on the molecular symmetry and reflects synchronized-desynchronized exchange of hydrogen atoms between nitrogen atoms in a macrocycle. 20 refs., 3 figs., 1 tab

[en] Studies are reported of visible anti-Stokes luminescence of one of most efficient IR image converters, the oxysulphide Ln₂O₂S (Ln=Y, Gd, La), mono- and codoped by trivalent rare-earth ions. Studies of these anti-Stokes luminophores involving also visual observations are performed in triplexes under low-intensity (compared with previous studies) excitation, 10-300 mW/cm²; λ=0.93 and 1.06 μm, produced by various infrared sources. Mechanisms of anti-Stokes luminescence are examined. Experimental results allow us to explain the effects of technological (powder structure of the polycrystalline anti-Stokes luminophore, details of triplex preparation) and of physico-chemical factors on the quantum yield of anti-Stokes luminescence of (Ln_0.86Y_0.08Er_0.06)₂O₂S. 39 refs., 3 figs., 2 tabs

[en] Effective spin-dependent operators are introduced for parametrization of the 5d⁹6p levels in the spectra of Tl IV-Bi VI ions. The wave functions of the intermediate-coupling and the Hartree-Fock radial functions obtained here are used for calculating the probabilities of the 5d⁹60 → 5d⁹6s and 5d⁹6p → 5d¹⁰ transitions and the radiative lifetimes of the 5d⁹6p levels. The dispersions of the radiation constants are found to estimate the precision of their calculation. 8 refs., 5 tabs