Physikalisches Kolloquium

Physics Colloquium at The Faculty of Mathematics and Natural Sciences

Lectures on tuesdays 16:15pm in Hans-Geiger auditorium

Leibnizstr. 13, 24098 Kiel

 

Wintersemester 2019/2020

 

  • 15.10.2019

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  • 22.10.2019

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  • 29.10.2019: Prof. Dr. Nahid Talebi (IEAP, Universität Kiel)

    Titel: Nanooptics with Slow and Fast Electrons (Antrittsvorlesung)

    Abstract: Electron-light interactions and the various mechanisms lying within this context have been discussed from the very early days of the rise of quantum mechanics. Transition from classical concepts such as Thomson scattering to more advanced quantum mechanical counterparts like Compton scattering, photoelectric effect, and more recently free-electron lasers, opened the way towards designing precise accelerating mechanisms and radiation sources.

    Here, I first discuss electron-light interactions from the classical point of view. Mainly, inelastic interaction of electron beams with optical near-field distributions in nanostructures is considered. I show that near-field distributions can act as a mediator to transfer the energy between electron beams and light [1]. Moreover, based on the contribution of the electron-induced polarization to the radiation continuum, few-photon radiation sources are proposed and investigated [2]. Moreover, thin film electron-driven photon sources can be employed inside electron microscopes, for the purpose of spectral interferometry [3].

    In a second part of my talk, I discuss electron-light interactions from semi-classical standpoint. First, I investigate the free-space interaction and consider the generalization of Kapitza-Dirac effect (KDE) to address quantum-coherent phenomena which occur as a result of interference between ponderomotive and absorptive/emissive parts of the minimal coupling Hamiltonian [4]. Then, I talk about the interaction of point-projection slow-electron wavepackets with light and nanostructures [5]. It is shown that the coupling strength between electrons and near-field light is increased by decreasing the electron velocity; hence this fact demonstrates the sensitivity of slow electrons to the electromagnetic interactions, covering both elastic and inelastic scattering.

    References:
    [1] N Talebi, J. Opt. 19 (2017), 103001.
    [2] N Talebi, S Meuret, S Guo, M Hentschel, A Polman, H Giessen, et al., Nat. Commun. 10 (2019), 599.
    [3] N Talebi, Sci. Rep. 6 (2016), 33874.
    [4] N Talebi and C Lienau, "Interference between Quantum Paths in Coherent Kapitza-Dirac Effect," New J. Phys. 21 (2019), 093016
    [5] J Vogelsang, N Talebi, G Hergert, A Wöste, P Groß, A Hartschuh, et al., ACS Photon. 5 (2018), 3584.

    Gastgeber: Prof. Magnussen
  • 05.11.2019: (Fest-) Kolloquium Satellit Azur - Vortrag: Dr. Berndt Klecker, Max Planck Institut für extraterrestrische Physik, Garching

    Titel: Energiereiche Teilchen in der Magnetosphäre: Erkenntnisse von AZUR bis zu den Van Allen Probes

    Abstract: Vor nunmehr 50 Jahren, am 8. November 1969, wurde der erste deutsche Forschungssa-tellit (AZUR) gestartet. Etwa zehn Jahre vorher waren mit den ersten US amerikanischen Satelliten Explorer 1 und 3 (1958) energetische Teilchen in der Magnetosphäre der Erde entdeckt worden, und damit die Strahlungsgürtel der Erde, die später zu Ehren des Ent-deckers „Van Allen Strahlungsgürtel“ genannt wurden. Die Aufgabe von AZUR war es, mit einer Reihe von Sensoren (Magnetometer, Photometer, Teilchendetektoren) diese Strahlungsgürtel, sowie die Polarlichtzone und solare Teilchenereignisse näher zu er-kunden. Die Instrumentierung und der Satellit wurden in Zusammenarbeit mehrerer In-stitute in Deutschland (MPE, CAU, MPAe, TUB, DFVLR) und der Industrie (Hauptauf-tragnehmer Bölkow) entwickelt und mit einer Scout Rakete in Vandenberg (USA) gestartet.

    AZUR markiert somit den Beginn der Weltraumforschung in Deutschland, die in den folgenden Jahrzehnten einen stürmischen Aufschwung erlebte. Seither wurden weltweit zahlreiche wissenschaftliche Satelliten zur Erforschung der Magnetosphäre der Erde gestartet. Im ersten Teil des Vortrags werde ich zunächst einen Überblick über die Mission AZUR, deren Ergebnisse, sowie die Strahlungsgürtel der Erde geben. Im zweiten Teil folgt dann eine Übersicht der weiteren Entwicklung mit einigen Höhepunkten, die mit Missionen wie ISEE-1/2 (Start 1977), AMPTE (Start 1984), SAMPEX (Start 1992), Cluster (Start 2000) und van Allen Probes (Start 2012) verbunden sind.

    Gastgeber: Prof. Heber
  • 12.11.2019: Prof. Arutiun Ehiasarian (Sheffield Hallam Universiity, UK)

    Titel: High Power Impulse Magnetron Sputtering: The Age of Adolescence

    Abstract: High Power Impulse Magnetron Sputtering (HIPIMS) is a technology for the deposition of thin films using large volumes of dense plasma. The growth of films in such an environment benefits from a greatly enhanced degree of freedom of the system which diversifies the reactions in the plasma phase and opens unique pathways for film formation and tailor-ing film properties. To achieve this, plasma generation is carried out at significantly higher instantaneous power than conventional sputtering methods. The power is delivered in pulses on timescales that are sufficient to produce dense metal plasma of 1013 cm-3 whilst avoiding heat buildup and transitions from glow to arc discharge on the target. In par-ticular regimes, the plasma self-organises into waves which propagate in the E×B direction and build up localised plasma density spikes that shield the confining fields and increase pressure to generate intense particle emission in direction to the substrate.

    Metallic plasmas containing rare earth ions were used to produce an implantation zone of a few nanometres to seal and protect the surface of substrates against oxidation. They also served to promote adhesion by providing conditions for local epitaxial growth inducing a crystalline interface and chemistry for better wetting during film nucleation.

    For metallic films of Mo, the ratio of double- to single- charged metal ions could be varied in a wide range through the peak current and charge exchange reactions with the process gas. The ratio correlated with the grain size and im-proved smoothness of the films due to the additional energy gained by the higher charge states through the sheath. It also shifted the crystallographic orientation from a highly textured to a random mix. ErNi films have improved crystallin-ity and heat lift capacity at cryogenic temperatures whilst Nb films have better superconducting properties. Better coverage of meshes and high aspect ratio vias is achieved.

    In reactive sputtering conditions, the deposition flux comprises mainly ions of metal and dissociated nitrogen which change the dynamics of adatoms on the surface and promotes a (200) crystallographic texture which in turn sustains fully dense column boundaries in TiN monolithic films.

    Nanolayered CrN/NbN and CrAlN/CrN developed with low waviness and enhanced density making them suitable for corrosion, wear, biological and high-temperature oxidation environments. Nanocomposites of CrAlN-SiN can be pro-duced with different cluster size and corresponding hardness.

    The deposition of oxides has benefited from controlling the current in the discharge pulse to produce high density TiO2 films for architectural glass coatings and enabling the production of highly insulating materials such as SiO2 for the glass and semiconductor industries.

    Industrial uptake is rife in the fields of hard coatings and microelectronics with a number of vendors providing turn-key solutions.

    Gastgeber: Prof. Kersten
  • 19.11.2019: Dr. Jingnan Guo (Habilitationsvorlesung)

    Titel: Gravitational waves and how scientists found them
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    Originally proposed by Henri Poincaré in 1905 and pridicted by Albert Einstein in 1916 in his general theory of relativity, graviational waves are generated by some of the most violent and energetic processes in the Universe and spread like 'ripples' throughout space-time. Massive accelerating objects such as neutron stars and black holes orbiting and even colliding into each other disrupt space-time in such a way that these waves of distorted space-time would radiate outward from the source.  These ripples travel at the speed of light through the Universe, carrying with them information about their origins as well as clues to the nature of gravity itself. However, it took nearly a century until gravitational waves were first directly detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) in September of 2015. In this lecture, I will give an overview of the basic principle, challenge, and data processing for the detection of gravitational waves.

    Gastgeber: Prof. Wimmer-Schweingruber
  • 26.11.2019: Prof. Dr. K.A.H. van Leeuwen (Eindhoven School of Education)

    Titel: New tools for electron microscopy

    Abstract: Electron microscopes have developed into extremely powerful and versatile tools for research in physics, chemistry, biology, and material science. Although around since 1931 and very well developed by now, efforts to extend the usability even further are still fierce and fast-progressing. Examples are the development of ultrafast electron microscopy, which allows the study of dynamical processes on a very short timescale, combining EELS (electron energy loss spectroscopy) with electron microscopy in order to image material composition, and extending phase-contrast (Zernike) microscopy to the electron domain, which enables the imaging of non-absorbing objects. In this talk I will discuss novel devices for electron microscopy based on microwave cavities as well as the ponderomotive interaction with pulsed laser beams. Microwave cavities allow extensive phase space manipulation of electron beams, with applications in ultrafast and in EELS microscopy. Using the ponderomotive interaction, the actual phase of the quantum mechanical electron wavefunction can be manipulated. The latter has a direct application as an (immaterial) phase plate for Zernike phase contrast microscopy, but also opens a wider range of options in diffractive and interferometric optics with electrons. The Eindhoven CQT group (headed by prof. Jom Luiten) collaborates with prof. Nahid Talebi in the ponderomotive project.

    Gastgeber: Prof. Talebi
  • 03.12.2019: Prof. Dr. Elke Scheer (Universität Konstanz)

    Titel: Visualization of spatial modulation and persistent response states of strongly-driven membrane resonators

    Abstract: Micro- and nano-scale mechanical resonators operated in the strongly nonlinear regime exhibit unusual dynamic behavior, including the phenomenon of persistent response, which denotes the development of a vibrating state with nearly constant and high amplitude over a wide frequency range. The origin of this persistent response state can be revealed for membrane resonators by optical profilometry. By applying a combination of temporally and spatially resolved methods we show that the rectangular membrane adopts a peculiar ring-shaped pattern I which different parts of the membrane oscillate at different frequencies, a phenomenon that we denote as spatial modulation [1]. At even larger driving strength, the persistent response arises as a signature of mode coupling between different flexural modes and their localized overtones.

    abstract_scheer_image

    Finally, we propose a phase diagram for the manifold vibrational states that the membrane can adopt and a model based on the coupling of nonlinear oscillators that qualitatively describes the experimental observations.

    [1] F. Yang et al., Phys. Rev. Lett. 122, 154301 (2019)

    Gastgeber: Prof. Berndt
  • 10.12.2019: Dr. Franko Greiner (IEAP)

    Titel: From dust in plasma to (nano) dusty plasma

    Abstract: The physics of dusty plasmas is a relatively new field of plasma physics. It has its origins in extra-terrestrial and plasma technological research. The research field of dusty plasmas grew significantly triggered by the first creation of dust crystals in the laboratory in the mid-nineties. After a first phase of discovery, a lot of initial adapted experimental techniques and accompanying theoretical models were developed. Since then research demanded more and more for high precision diagnostics and methods. Researchers of the plasma physics department at Kiel University have actively participated on this development from the very beginning including the analysis of dust crystals, single particles, particles as plasma probes, particle chains, Yukawa balls and microparticle clouds under microgravity conditions. Within the last years the fundamental physics of billions of nanoparticles produced and confined in a nano-dusty plasma (see figure) became a new hot topic in the field. This talk presents the current status and future perspectives of nanodust diagnostics with special emphasis on novel diagnostics like imaging Mie ellipsometry and dust density wave diagnostics.

    nanodustcloud

    Gastgeber: Prof. Benedikt
  • 17.12.2019: Dr. Dominik Kraus (Helmholtz-Zentrum Dresden-
    Rossendorf)

    Titel: Warm Dense Matter: From Giant Planets and Stars to Nanoparticles

    Abstract: The interiors of planets and stars exhibit extreme conditions: High temperatures and enormous pressures create environments which are not fully understood and hard to en-compass for state-of-the-art physics models. Applying the largest and most brilliant laser light sources, it is now possible to investigate such conditions in the laboratory. Recent efforts provide seminal insights into chemistry and phase transitions occurring deep in-side giant planets and elucidate the electronic structure of elements in the interiors of brown dwarfs and stars. At the same time, highly interesting materials can be formed via these conditions, such as nanodiamonds or hexagonal diamond, so-called lonsdaleite, which, in its pure form, is predicted to exceed the hardness of cubic diamond. Finally, the applied methods also allow for testing the response of materials at extreme conditions and ultrafast timescales. I will present a showcase of recent experiments investigating these topics and provide an outlook for future developments.

    Gastgeber: Prof. Bonitz
  • 07.01.2020: Dr. Sophie Meuret (CNRS France)

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    Gastgeber: Prof. Talebi
  • 14.01.2020: Prof. Antti-Pekka Jauho (DTU Copenhagen)

    Titel: Quantum transport in nanostructured graphene

    Abstract: Ballistic and quantum effects are often suppressed in nanostructured graphene due to disorder effects. With careful sample preparation, however, spectacular effects can be observed and modelled with quantita-tive agreement. In this talk, I describe three such cases. The first one is a theoretical prediction – yet to be realized, but the next two are jointly carried out be experimentalists and theorists, and a very satisfactory agreement is achieved between theory and experiment. (1) A nonplanar sheet of graphene may exhibit “pseudomagnetic” fields. The two inequivalent valleys in the band structure of graphene couple differently to a pseudomagnetic field suggesting the possibility of manipulating the valley index (valleytronics) with the pseudomagnetic fields. I describe a recent suggestion utilizing these ideas based on bubbles in a graphene sheet [1]. (2) Graphene nanowires, formed at the step edges of a SiC crystal, can display exceptional ballis-tic transport [2]. In recent experiments, in a multiprobe STM setup, spatially resolved measurements can probe the details of the conductance channels, thus putting these useful theoretical concepts on a firm ex-perimental basis. I describe these measurements, and their detailed modelling, which agree in quantitative detail [3]. (3) Commensurality oscillations may occur in magnetotransport in periodically modulated two-dimensional systems. The challenge for graphene based systems has been the fabrication of sufficiently tight and regular superlattices. Recently it has been realized that encapsulating the graphene layer between hBN layers first, and only subsequently applying the ebeam-assisted etching to fabricate the periodic lat-tice, leads to sufficiently regular structures where these quantum effects can be observed [4].

    The work at CNG is supported by Danish National Research Foundation, Project DNRF103.

    [1] M. Settnes et al., “Graphene nanobubbles as valley filters and beam splitters”, Phys. Rev. Lett. 117, 276801 (2016)
    [2] J. Baringhaus et al., “Exceptional ballistic transport in epitaxial graphene nanoribbons”, Nature 506, 349 (2014)
    [3] J. Aprojanz et al., “Ballistic tracks in graphene nanoribbons”, Nature Communications 9, 4426 (2018)
    [4] B. S. Jessen et al., “Lithographic band structure engineering of graphene”, Nature Nanotechnology 14, 340 (2019)

    Gastgeber: Prof. Bonitz
  • 21.01.2020: Prof. Dr. Harald Brune (EPFL, Lausanne)

    Titel: The Magnetism of Single Surface Adsorbed Atoms – Recent Achievements and Future Perspectives

    Abstract: The ultimate size limit of a magnetic bit is a single atom. Despite long lasting research efforts of several groups, and despite the spectacularly large orbital moments and anisotropy energies reported on single surface adsorbed atoms, all investigated systems were paramagnetic down to lowest temperatures. This changed in 2016, where two systems with magnetic remanence were identified. We report on these systems where indeed single atoms are stable magnets. We show how their magnetization can be read and written and we elaborate on the mechanisms that limit their stability. These involve electron and phonon scattering, but also the interaction between electron and nuclear spins. Our results show that single atom magnetic information storage is feasible with coercitive fields and temperatures that outperform the best molecular magnets. We discuss the features that need to be met for single atom magnetic quantum bits, i.e., for single atoms that enable coherent manipulation of the wave function describing their magnetic quantum state.

    Gastgeber: Prof. Berndt
  • 28.01.2020: Prof. Dr. Edvin Lundgren (Lund University)

    Titel: Operando high energy surface x-ray diffraction studies of model catalysts and electrodes

    Abstract: Catalysis is an important process and is widely applied on an industrial scale for a large number of applications in either gas or in liquid phase. Industrial catalysts are complex materials, and as a consequence the gas/liquid-surface interaction between simplified single crystal surfaces and molecules in controlled environments has been studied for decades. We have in recent years explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at elevated pressures and in an electrolyte. In this contribution, recent results using High Energy Surface X-Ray Diffraction (HESXRD) [1] combined with other in situ techniques [2-4] will be presented. Armed with structural knowledge from ultra-high vacuum experiments, the gas or electrolyte induced structures can be identified, and related to changes in the reactivity. The strength and weaknesses of the experimental techniques will be discussed.

    [1] J. Gustafson et al; Science 343 (2014) 758.
    [2] S. Blomberg et al; Phys. Rev. Lett. 110 (2013) 117601.
    [3] J. Zetterberg et al; Nat. Comm. 6 (2015) 7076.
    [4] W. Linpé et al; Submitted

    Image Lundgren

    Bio:
    Edvin Lundgren is a professor at the physics institute at Lund University, Sweden. Lundgren received his PhD at Lund University 1996 and spent 2 years at the ESRF, France and 3 years at TU-Wien, Austria before returning to Lund. His research is focused on surface structures on the atomic scale and applying in situ synchrotron-based techniques to material systems under working conditions. The research has led to the discovery of a new set of ultrathin oxides on late transition metals, atomic scale views on nano structures such as quantum dot and nanowire surfaces and novel work on in situ studies of model catalysts and electrodes at work.

    Gastgeber: Prof. Magnussen
  • 04.02.2020: Prof. Dr. Beatriz Roldán Cuenya (Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin)

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    Gastgeber: Prof. Magnussen
  • 11.02.2020: Dr. rer. nat. Eike Hentschel (Universitätsbibliothek Kiel)

    Titel: Zentrale Finanzierung von Open Access in Zeitschriften über DEAL und Publikationsfonds der CAU

    Abstract: An der CAU stehen mittlerweile 3 Säulen zur zentralen Finanzierung von Publikationsgebühren für Open Access-Artikel in Zeitschriften zur Verfügung:

    1. Im Rahmen der DEAL-Verträge der CAU aktuell mit Wiley und voraussichtlich ab Januar 2020 mit SpringerNature können alle Wissenschaftler*innen der CAU ihre Artikel als corresponding authors in den meisten Zeitschriften dieser Verlage (Subskriptionszeitschriften und originäre OA-Zeitschriften) ohne eigene Kosten Open Access veröffentlichen. Dazu kann die Autorin / der Autor im Publikationsprozess bei einer Wiley- (und später SpringerNature-) Zeitschrift einfach die unter Hinweis auf DEAL angebotene Open Access-Option auswählen. Ein DEAL-Vertrag mit Elsevier wird weiterhin angestrebt, ist aber aktuell noch nicht in Sicht.
    2. Ebenfalls für alle Wissenschaftler*innen der CAU steht außerdem ab 2020 ein DFG-finanzierter Publikationsfonds bereit, um Publikationsgebühren bis zu 2.000 EUR für ihre Artikel als corresponding authors in originären Open Access-Zeitschriften außerhalb von Wiley und SpringerNature zu finanzieren.
    3. Darüber hinaus steht speziell für Nachwuchswissenschaftler*innen der CAU ein weiterer Publikationsfonds des Landes zur Verfügung, um Publikationsgebühren bis zu 2.000 EUR für ihre Artikel als corresponding authors in originären Open Access-Zeitschriften außerhalb von Wiley und SpringerNature zu finanzieren. Anträge für beide Fonds können über Web-Formulare bei der UB eingereicht werden.

    Weitere Informationen finden Sie unter: https://www.ub.uni-kiel.de/de/publizieren/open-access (unter dem Punkt Finanzierung)

    Gastgeber: Prof. Magnussen
  • 18.02.2020: Prof. van de Sanden (Direktor von DIFFER (Dutch Institute for Fundamental Energy Research), Eindhoven, NL)

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    Gastgeber: Prof. Benedikt