Vorträge im WS 2009/2010

Dr. Michael Gausa, ALOMAR, Andøya Rocket Range

Research opportunities at the ALOMAR Observatory (69N 16E) and the Andøya Rocket Range (5. März 2010)

ALOMAR (the Arctic Lidar Observatory for Middle Atmosphere Research) has been in operation since about one and a half decades. ALOMAR is part of the Andøya Rocket Range, the northern most permanent launch site for scientific sounding rockets, which is organised as a public company. ALOMAR is a service provider for scientists investigating in atmospheric research. At ALOMAR scientific groups from Germany, Britain, France, Spain, USA, Canada, Japan and Norway are per- forming measurements in all atmospheric layers from the ground to the ionosphere. For investiga- tions in the upper atmosphere layers simultaneous observations with sounding rockets are fre- quently coordinated. The scientific fields where groups at ALOMAR are investigating in, cover all atmospheric layers and a broad spectrum of independent research questions. However, in several cases similarities are obvious. E.g. are various turbulence studies of interest in the boundary layer, close to the mesopause and in the ionosphere. Other examples are aerosols, which are investigated in the troposphere, in the stratosphere and close to the mesopause. In lower atmosphere layer the understanding of the aerosol and cirrus cloud radiative forcing in the arctic is relevant for climate models. Recently started programmes with lidars and sun photometers investigate in these questions at ALOMAR. In the height range of the ozone layer aerosols (stratospheric clouds) are forcing the ozone depletion, finally in the mesopause region the in depth knowledge of forming of meteor dust (smoke) in the lower thermosphere plays a major role in understanding the condensation processes of phenomena like Noctilucent Clouds and Polar Mesospheric Summer and Winter echoes. The present talk will give an overview over the scientific activities performed at ALOMAR.
Prof. Oleg Shpyrko, University of California, San Diego, USA

Structure and dynamics of condensed matter systems with coherent x-ray beams (16. Februar 2010)

My talk will discuss studies of nanoscale structure and dynamics of disordered materials using coherent x-ray synchrotron sources. Coherent x-rays scattering from random distribution of scatterers - for example irregular magnetic domains or rough surfaces, produce a random interference pattern known as "x-ray speckle". By studying temporal intensity fluctuations of the x-ray speckles, a technique known as X-ray Photon Correlation Spectroscopy (XPCS), one is able to probe nanoscale dynamics of a wide variety of disordered systems. I will demonstrate application of this XPCS technique to study fluctuations of spin- and charge- density wave domains in antiferromagnetic Chromium, as well examples of recent XPCS work on capillary dynamics of liquids in nanoscale confinement. I will also demonstrate how coherent x-ray diffraction (speckle) pattern can be inverted to provide a real-space image of the magnetic domains, using the so-called ptychographic lens-less imaging approach that allows successful recovery of phase information of diffraction pattern lost during measurements. Discussion of these results will be placed in a broader context of novel experimental approaches to studies of disordered, heterogeneous or non-equilibrium materials. Such new capabilities arise from fully coherent x-ray sources, such as X-ray Free Electron Laser facilities that are currently being actively developed and constructed in the United States, Europe and Asia.
Prof. Dr. Rolf Schuster, Institut für Physikalische Chemie, Universität Karlsruhe

Mikroelektrochemie (9. Februar 2010)

Metallabscheidung und Auflösung gehören zu den wichtigsten elektrochemischen Prozessen, die auch vielfältigen Eingang in technische Verfahren gefunden haben. Im Vortrag möchte ich über zwei Aspekte berichten, die wir hierzu in unserer Arbeitsgruppe bearbeiten: i) Die lokale Durchführung elektrochemischer Reaktionen zur Mikrostrukturierung elektrochemisch aktiver Materialien. Elektrochemische Reaktionen können durch Anwendung kurzer Spannungspul- se zwischen einer Werkzeugelektrode und einem Werkstück mit Genauigkeiten von bis zu ca. 20 nm lokalisiert werden. Dies erlaubt die Mikrobearbeitung verschiedener Metalle. Weiterhin werden Ergebnisse zur lokalen Abscheidung von Ag aus dünnen Elektrolytfilmen mittels des Elektronen- strahls eines Rasterelektronenmikroskops gezeigt. ii) Messung der Wärmetönung elektrochemischer Oberflächenreaktionen. Elektrochemische Reak- tionswärmen geben Aufschluss über die Reaktionsentropie der Oberflächenreaktion und damit über die an der Abscheidung beteiligten atomaren Prozesse. Wir konnten z.B. die Wärme messen, die bei der Abscheidung von wenigen Prozent einer Kupfermonolage freigesetzt wurde. Hierdurch ließen sich Anionenadsorptionsprozesse identifizieren, welche die Kupferabscheidung begleiten.
Prof. Dr. Andrea Cavalleri, Max Planck Research Department for Structural Dynamics Centre for Free Electron Laser Science – University of Hamburg

Controlling the Properties of Complex Solids with Light (2. Februar 2010)

Solids with “strongly” correlated electrons are those in which Coulomb interaction between charges exceeds their individual kinetic energy and sometimes even their coupling to the lattice. These sys- tems have been at the forefront of condensed matter research for nearly eighty years. On the one side, their physical properties, such as conductivities, magnetism and response to various perturba- tions cannot be discussed in terms of band theory, which has instead been spectacularly successful in semiconductors and metals. Yet, they exhibit a bewildering variety of interesting properties, both in terms of fundamental interest and of potential applications. In this talk, I will discuss our quest to understand dynamic properties of strongly correlated systems, with an eye toward the possibility of controlling them with light. How can light be used to manipu- late electrical and optical properties? Can light be used to control their magnetic properties? Can light be used to induce superconducting properties? This field is undergoing a revolution, primarily due to the spectacular developments that coherent light sources have had in the past two decades. It is now possible to generate spatially and tempo- rally coherent, ultrafast light pulses from THz frequencies all the way to hard x-ray wavelengths. This enables us to manipulate and interrogate time dependent microscopic properties in new ways. In the talk, I will cover our progress so far, balancing methodological and scientific advances.
Dr. Dirk Gericke, Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom

Theorie & Simulationen für Warme Dichte Materie (26. Januar 2010)

Die Beschreibung von Materie ist immer dann besonders erfolgreich, wenn eine Störungsrechnung angewandt werden kann. Für einige, sehr interessante, Probleme der modernen Physik ist das nicht der Fall. Warme dichte Materie, mit Dichten vergleichbar mit denen von Festkörpern und Temperaturen von einigen Elektronenvolt, ist so ein Zustand. Hier liegen die Fermienergie der Elektronen, die Korrelationsenergie der Ionen und auch die Ionisationsenergie im Bereich der thermischen Anregungen. Ein Verständnis warmer dichter Materie als ein hochkorrelierter Quantenzustand ist zur Zeit nur in ersten Ansätzen vorhanden. Nichtsdestoweniger hat warme dichte Materie wichtige Anwendungen bei der Inertialfusion und in der Astrophysik. Nach einer kurzen Einleitung zur Bedeutung warmer dichter Materie bei der Kernfusion und in der Planetenphysik werden die Probleme bei der theoretischen und experimentellen Untersuchung sowie die Grenzen von Konzepten der Festkörper- und Plasmaphysik aufgezeigt. Weiterhin werden direkte Quantensimulationen, basierend auf der Dichtefunktionaltheorie, als eine Möglichkeit zur Beschreibung diskutiert. Theorie und Simulationen werden dann auf die Streuung von Röntgenstrahlung an dichter Materie angewendet. Solche Streuexperimente sind eine der wenigen Diagnos- tikmethoden im Bereich der warmen dichten Materie und stellen weiterhin ein interessantes Prob- lem zum Test für eine theoretische Beschreibung dar. Am Beispiel der Röntgenstreuung wird dann gezeigt, wie ein Zusammenspiel von Experimenten, Theorie und Simulationen unser Verständnis von dichter Materie erweitern kann. Den Abschluss bildet ein Ausblick auf zukünftige Untersuchungen zu Mixturen und hoch angeregten Festkörpern.
Prof. Dr. Colin Carlile, University of Lund

The European Spallation Source - a new Materials Science facility in Northern Europe (12. Januar 2010)

After almost two decades of preparation, a site has been chosen for ESS. It will be constructed in Lund in southern Sweden. The ESS will be the world‘s premier neutron facility when it is fully commissioned in 2025. In order to realise this, a significant international effort will take place in- volving, at the time of writing, 13 countries. Links to XFEL are strong and the two facilities being located so close and connected by the Fehmarn bridge will create high visibility and huge opportu- nities for our region. This is expressed by the Science Corridor, whose backbone runs from Oslo to Hamburg, and the north Germany-Sweden Science Region, recently ratified by Research Ministers. An overview of the coming task to build ESS will be given with an insight into the science pro- gramme and the novel energy strategy which ESS will pursue.
Prof. Dr. Michael Drewsen, University of Aarhus, Department of Physics and Astronomy

Ion Coulomb crystal based cavity quantum electrodynamics: Applications in quantum information science and plasma physics (15. Dezember 2009)

Cavity Quantum ElectroDynamics (CQED) is a research field which focuses on understanding the interactions between matter and the electromagnetic field in cavities at the quantum level. Cur- rently, CQED is a very active research field due to the prospect of creating efficient light-matter quantum interfaces at the single photon level for quantum information science. Ion Coulomb crys- tals have a series of properties of particular interest for CQED studies, as demonstrated in recent CQED experiments. Since the coupling strength between ions in the crystals and photons in the cavity strongly depend on the motion of the ions due to the Doppler-effect, the CQED signals can as well be exploited to learn about the temperature of ion Coulomb crystals and excitations of these crystals plasma modes.
Prof. Dr. Markus Drescher, Universität Hamburg, Institut für Experimentalphysik

Dynamik-Experimente mit ultrakurzen Röntgenpulsen am FLASH: Des Widerspenstigen Zähmung (8. Dezember 2009)

Die neue Generation von Röntgenquellen auf der Basis von Freie-Elektronen-Lasern (FEL) versorgen die Nutzer mit ultrakurzen Pulsen bislang nicht gekannter Intensität in diesem Wellenlängenbereich. Für die effiziente Nutzung dieser Pulse bei der Untersuchung extrem schnell ablaufender elektronischer oder molekularer Prozesse müssen allerdings wichtige methodische "Hausaufgaben" gemacht werden. Obwohl die Bandbreite des FEL Pulsdauern von wenigen Femtosekunden - für härtere Strahlung sogar sub-Femtosekunden - unterstützt, führt das hier verwendete Prinzip der self-amplified spontaneous emission (SASE) zu komplizierten Amplituden- und Phasenverläufen, die überdies von Schuß zu Schuß stark variieren. Methoden, die wir ursprünglich für die Attosekundenphysik entwickelt haben, erweisen sich als sehr wirksam, um diesen Herausforderungen zu begegnen. Ein starkes Terahertz Feld wird für die Realisierung einer Wechselfeld-Streak-Kamera genutzt, um die Pulse des Freie-Elektronen-Lasers "FLASH" am DESY, zeitlich zu charakterisieren. Ein neuartiger Kreuzkorrelator ermöglicht die Korrektur von statistischen Schwankungen des relativen Timings zwischen Laser- und Röntgenpulsen. Die Leistungsfähigkeit dieser neuen diagnostischen Werkzeuge wird anhand von Messungen zur Dynamik der Innerschalenanregung von Atomen bzw. zur Photodissoziation von Molekülen demonstriert.
Prof. Dr. Eric Becklin, University of California

Stratospheric Observatory for Infrared Astronomy (SOFIA) (1. Dezember 2009

The joint U.S. and German SOFIA project to develop and operate a 2.5-meter infrared airborne telescope in a Boeing 747-SP is in its final stages of development. Flying in the stratosphere, SOFIA allows observations throughout the infrared and submillimeter region, with an average transmission of greater than 80%. SOFIA has a wide instrument complement including broadband imagers, moderate resolution spectrographs capable of resolving broad features due to dust and large molecules, and high resolution spectrometers suitable for kinematic studies of molecular and atomic gas lines at km/s resolution. These instruments will enable SOFIA to make unique contributions to a broad array of science topics. First science flights will begin in 2010, and the observatory is expected to operate for more than 20 years. The sensitivity, characteristics, science instrument complement, future instrument opportunities and examples of first light science will be discussed. Also some of the latest results from the UCLA Galactic Center group will be discussed, especially in relationship to future SOFIA observing.
Prof. Dr. Uwe Czarnetzki, Ruhr-Universität Bochum, Fakultät für Physik und Astronomie, Institut für Plasma und Atomphysik

Phase und Symmetrie: Ein neuer Weg zur Kontrolle von Plasmen (24. November 2009)

Technische Plasmen werden häufig über die Einkopplung von Radiofrequenzfeldern im MHz- Bereich erzeugt. Anwendungen reichen z.B. von der Halbleiterproduktion über die Herstellung großflächiger Solarzellen bis zur Abscheidung bio-kompatibler Schichten. Die Oberflächenprozesse hängen dabei kritisch von Energie und Fluss der auftreffenden Ionen ab. Eine unabhängige Kontrolle dieser Parameter wird daher als Ideal angestrebt, ist in der Praxis aber bisher bestenfalls ansatzweise realisiert. Hier wird ein neuartiges Verfahren vorgestellt, dass über die relative Phase zweier harmonischer Frequenzen eine solche unabhängige Kontrolle erstmals ermöglicht. Darüber hinaus kann in geometrisch symmetrischen Entladungen die Symmetrie über die Phase gebrochen werden. Dies hat nicht nur große technische Vorteile, sondern führt auch zu einer hoch interessanten Dynamik der Ionen und Elektronen. Die Physik des sich daraus ergebenden nichtlinearen Systems lässt sich auf einige wenige Grundprinzipien zurückführen. Vorhersagen eines analytischen Modells werden mit Ergebnissen aus Particle-in-Cell/Monte-Carlo Simulationen und Experimenten verglichen. Trotz der Komplexität des Gesamtsystems zeigt sich eine weitgehende Übereinstimmung zwischen allen drei Ansätzen, woraus letztlich ein detailliertes Verständnis der Dynamik folgt.
Prof. Dr. Jose Ignacio Pascual, Institut für Experimentalphysik, Freie Universität Berlin

Vibrational Kondo effect in charge-transfer organic layers (10. November 2009)

The charge transfer salt TTF-TCNQ is an organic metal with one-dimensional band structure and a rich low temperature phenomenology in bulk crystals. These properties change completely when ultra-thin layers of TTF-TCNQ are grown on a Au(111). Using a low temperature scanning microscope we find that the electronic structure of the TTF-TCNQ/Au(111) interface is characterized by a metal-organic hybrid electronic band. Our results suggest that mixing of metal and organic states can build bands localized at the organicmetal interface having both molecular character and metallic-like mobility. The donor-acceptor electron transfer crucially determines the molecular properties at the metal-organic interface. A Kondo resonance has been observed on TCNQ molecules of the film, revealing that this specie lies in an anionic radical state, with a spin 1/2 ground state, due to the localization of an unpaired electron in the conjugated lowest unoccupied molecular orbital. This represents the realization of molecular magnetic materials using metal-free organic molecules. Furthermore, due to the ð character of this singlyoccupied molecular state, the unpaired electron is strongly coupled to molecular vibrations, leading to the split of the Kondo resonance in vibrational sidebands.
Prof. Marco Velli, Dipartimento di Astronomia Universit di Firenze

Solar Orbiter and Solar Probe Plus, the next decade in Heliophysics (3. November 2009)

ESA‘ s Solar Orbiter will provide the first opportunity of returning to the inner heliosphere after Helios, decreasing the previous closest perihelion to 0.21 AU, and coming on the shoulders of the success of not only Helios but also Ulysses, SOHO and many other investigations of the solar atmosphere and interplanetary medium. Solar Orbiter‘s goal is to understand the connection between the sun, the solar wind by clarifying how magnetic fields structure and dynamically defining the interplanetary medium and its connection to the sun. The four top-level scientific questions being addressed by Solar Orbiter are:
  • How and where do the solar wind plasma and magnetic field originate in the corona?
  • How do solar transients drive heliospheric variability?
  • How do solar eruptions produce energetic particle radiation that fills the heliosphere?
  • How does the solar dynamo work and drive connections between the Sun and the heliosphere?
Solar Orbiter also has important synergies with NASA’s Solar Probe Plus mission, and coordinated observations are expected to enhance greatly the scientific return of both. This talk is devoted to discussing the scientific basis and expected return of Solar Orbiter, both in itself and in conjunction with Solar Probe Plus.
Prof. Jacek Lipkowski, Department of Chemistry, University of Guelph, Guelph,Ontario

Building a Biomimetic Membrane at an Electrode Surface (27. Oktober 2009)

I will describe several years of our efforts to build a model biological membrane at a surface of a gold electrode. In this architecture, the membrane may be exposed to static electric fields on the order of 107 to 108V/m. These fields are comparable in magnitude to the static electric field acting on a natural biological membrane. The field may be conveniently used to manipulate organic molecules within the membrane. By turning a knob on the control instrument one can force phase transitions in the film of organic molecules or force them to disperse or to aggregate at the surface. We use electrochemical techniques to control the physical state of the film while the photon polarization infrared reflection absorption spectroscopy (PMIRRAS), surface imaging by STM and AFM and neutron scattering techniques are employed to study conformational changes of organic molecules and their ordering within the membrane. I will show examples of a membrane build of a simple zwitterionic phospholipid such as DMPC and a mixed membrane composed of DMPC and cholesterol. Our results will illustrate a tremendous effect of cholesterol on the membrane structure. I will also compare two methods of membrane deposition at the electrode surface, namely by unilamellar vesicles fusion and using the Langmuir-Blodgett technique.