Showing papers by "Joachim Schulz published in 2002"

Multiple ionization of atom clusters by intense soft X-rays from a free-electron laser.

Abstract: Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion.

A MS-Windows simulation tool for synchrotron X-ray exposure and subsequent development

Abstract: A prerequisite for the commercialization of the LIGA process (from the German Lithographie=Lithography, Galvanoformung=electroforming and Abformung=moulding) for the fabrication of microstructures is the availability of a simulation tool which allows the simulation of the complete lithographic process, including synchrotron source, exposure parameters and subsequent development method. The program must be highly flexible and allow for the simulation of different sources, chosen beam-line components, exposure parameters and development method independently. A simulation tool, meeting the discussed requirements, is being developed at IMT/FZK in close collaboration with LURE. For user-friendliness, a GUI (Graphical User Interface) working in a MS-Windows environment has been built, which consists of main and sub work sheets (Fig. 1). In each sub work sheet, one “set of parameters” can be defined, e.g. the development method. In this paper, we will provide a general overview of the possibilities the program offers to the user.

Linear dichroism in the 4d photoionization of atomic europium

Abstract: The dichroism in the 4d photoelectron spectra of laser polarized Eu atoms has been determined with linearly polarized soft x-ray radiation. The results are discussed in comparison with the predictions by the LS-coupling model and by configuration interaction Hartree-Fock calculations, thereby demonstrating the strong influence of valence electron correlations. The interpretation of the dichroism in the 4d photoelectron spectra of solid Gd in terms of an ionic model is corroborated by the close similarity of the Gd solid and the Eu atom spectra.

Core-hole-induced degeneracy of the valence subshells in the 5p photoemission of atomic europium

Abstract: The $5p$ photoemission spectrum of atomic europium has been analyzed using high-resolution photoelectron spectroscopy. In contrast to the expected simple multiplet structure of a ${5p}^{\ensuremath{-}1}{4f}^{7}{(}^{8}S)$ configuration with six main lines, the observed Eu $5p$ photoemission shows a very complex spectrum. Configuration-interaction calculations reveal that the $5p$ core hole gives rise to a near degeneracy of the valence subshells in the final ionic states, so that the main multiplet structure of the spectrum can only be described by a strong mixture of the configurations ${6s}^{2},$ $6s5d,$ ${5d}^{2},$ and ${6p}^{2}.$ This mixing also results in a strong broadening of the lines at higher binding energy.

Combining high-resolution photoelectron spectroscopy and laser polarization for a study of the 4f and 5p photoionization of atomic thulium

Abstract: The 4f and 5p subvalence photoionization of atomic Tm has been investigated by combining high-resolution photoelectron spectroscopy and dichroism measurements of the laser-polarized atoms The experimental results are compared to Hartree–Fock calculations The Tm 5p photoelectron spectrum is dominated by spin–orbit splitting whereas mixing of the final ionic states strongly influences the Tm 4f photoionization Intermediate coupling is appropriate for the explanation of the complex Tm 4f multiplet structure, though some lines are well described within LS coupling This suggests a partial breakdown of the LS-coupling approximation for Tm 4f photoionization In comparison to the corresponding spectra of Eu the Tm spectra are much less affected by the admixture of 6s5d and 5d2 valence electron configurations

Lithographische Verfahren zur Mustererzeugung in der Mikrosystemtechnik

Abstract: griff Lithographie: „Geschliffener Solnhofener Schiefer, mit Fettkreide beschrieben und mit saurer Gummiarabicum-Lösung geätzt, nimmt nur an den beschriebenen Stellen die Druckfarbe an (lithos = stein; graphein = schreiben, zeichnen)“. Erfunden wurde die Lithographie von Alois Senefelder, Autor von Komödien und Liedern, im Jahr 1789, der nach einer Technik suchte, seine Stücke zu kopieren. Er handelte schon damals so, wie es heute von uns angewandten Wissenschaftlern verlangt wird: er erkannte die kommerziellen Chancen des Verfahrens und meldete es zum Patent an (1799). Die Anwendung des Verfahrens im Bereich der Kunst ließ nicht lange auf sich warten, wurde aber lange Zeit nicht so recht als eigenständige Kunstform akzeptiert. Dies änderte sich spätestens mit den Lithographien von Henri de Toulouse-Lautrec. Die Weiterentwicklung im Bereich der Massenreproduktion führte zum heutigen Offset-Druck.