It is a well-established fact that the illumination of a surface with light of sufficient photon energy results in the emission of electrons. But is the same also true if surface plasmon polaritons are used instead of the light? Surface plasmon polaritons are electron density modulations that can optically be exited at noble metal surfaces and that can propagate across the surface as a wave. The local variation in electron density of the plasmon is coupled to an electric field, so it sounds reasonable to assume that electron emission might be possible from a surface plasmon polariton. To experimentally verify this hypotheses, the TR-PEEM team around Prof. Frank Meyer zu Heringdorf used custom-tailored grating couplers to focus surface plasmon polaritons into a small spot. By employing femtosecond time-resolved microscopy, the team was able to separate light-induced effects from plasmon-induced effects in time and space and were able to unambiguously distinguish between the well-known photoemission and what the team coined “plasmoemission”. As the plasmon intensity is high in the focus spot, the team observed highly nonlinear emission behavior, i.e. processes, where five plasmon quanta were absorbed by one electron prior to emission from the solid.
It is not possible to focus light into an arbitrarily small spot. Even if one used enormously large lenses, a parallel beam of light would be focused into a “beam waist” instead of a point-like focal spot. The diameter of the beam waist depends on the wavelength of the light to be focused. In a collaboration with colleagues from Stuttgart and Haifa, the team of Prof. Dr. Frank-J. Meyer zu Heringdorf has now used a trick to nevertheless indirectly focus light into a small sport. The team used 800nm light to excite surface plasmon polaritons at the interface between an atomically smooth Gold platelet and a Silicon substrate. Such “short range” plasmons exhibit a wavelength of only 180nm. By forming a plasmonic focus and by using a transient standing wave field, the authors were able to create an electron-emission spot with a minimal dimension of only 60 nm.
Using ultrafast electron diffraction, the dynamics of a structural phase transition driven by femtosecond laser pulses could be observed with atomic spatial and femtosecond-temporal resolution. With a time resolution of less than 350 fs (10-15 s), Dr. Tim Frigge succeeded in tracing the movement of the atoms for the first time. These ground-breaking results have been published in Nature, supplemented by the work of the Bovensiepen group at the University of Duisburg-Essen and the work of the Schmidt group at the University of Paderborn.
You can read the paper here
You can read an article about it in Physics World here
You can read the University of Duisburg press release here: EnglishDeutsch
Read our Article in Science
In cooperation with scientists from the universities of Haifa (Israel), Kaiserslautern and Stuttgart, Professor Frank Meyer zu Heringdorf’s team published an article in Science magazine. Using time-resolved non-linear photoemission microscopy, surface plasmon polariton waves were observed with sub-femtosecond time-resolution to spiral to the center of an archimedean spiral. The spiral plasmon waves show an orbital angular momentum that was imprinted into the plasmon wave by using circularly polarized femtosecond laser pulses.
SPA-LEED Workshop 2016: A Great Success!
For almost two days, 50 participants presented and discussed their research results in the "Wolfsburg" in Mülheim an der Ruhr. Four high-ranking speakers (Claus Ropers (University of Göttingen), Stefan Kowarik (HU Berlin), Michael Tringides (Ames Lab, University of Iowa) and Michael Ramsey (University of Graz)). The workshop was financially supported by CENIDE, the SFB 1242, the FOR 1700 and the SPA-LEED manufacturer ScientaOmicron. The next SPA-LEED workshop will be organized by Professor Christian Kumpf of the Forschungszentrum Jülich in 2018.
DFG Information Meeting
At the next DFG information meeting, organized by the Science Support Center of the University of Duisburg Essen, Professor Michael Horn-von Hoegen will be giving advice for writing successful poposals. The meeting will be held at the Fraunhofer Haus 2 on November 15, 2016. After the general meeting, individual coaching will take place in workshops until 6 pm.
The Collaborative Research Centre 1242 Is Established
The DFG has established the SFB 1242, titled "Non-equilibrium dynamics of condensed matter in the time domain" in the Department of Physics. Starting on July 1, three projects in our workgroup will be funded with a total of four doctoral students and one postdoc, and these projects will examine the ultrafast structural and electronic dynamics of surfaces and thin films. In project C3 "Driven phase transitions on surfaces", a new apparatus for ultrafast electron diffraction will be built to break the current world record for the time resolution of 350 femtoseconds. With an improved time resolution of 200 femtoseconds the movement of atoms could be directly followed! In project B4, "Non-equilibrium dynamics of the phonon system", the generation, transformation and non-equilibrium of phonons in adsorbate systems and thin metal films is monitored by means of inelastic ultrafast electron diffraction after impulsive excitation. In project B6, the spatial-temporal separation of laser and plasmon pulses on the femtosecond time scale achieved in preliminary work is to be used in order to allow the targeted interaction of plasmon waves with one-particle electron excitations in nanostructures.
Humboldt Foundation Scholarship Awarded to Dr. Marin Petrovic
After completing his dissertation in Zagreb on the topic of graphene, Dr. Petrovic successfully competed for a coveted Alexander von Humboldt Foundation fellowship. In cooperation with his host, Professor Frank Meyer zu Heringdorf, Dr. Petrovic will use low-energy electron microscopy (LEEM) to examine the growth of hexabornite nitride (hBN) Layers on iridium as well as the formation of lateral graphene / hBN heterostructures (in-situ).
SPA-LEED Workshop 2016
Spot Profile Analysis Low Energy Electron Diffraction, i.e., SPA-LEED, was developed at the University of Hannover in the 1980s, and has since then acquired a dedicated group of researchers who have applied the technique to a variety of surface science problems. Researchers who work actively with SPA-LEED meet every 1-2 years for an informal exchange of their research and to discuss the future of the method.
The last meeting was in Hannover on the occasion of Professor Martin Henzler’s 80th birthday; the next SPA-LEED workshop will be hosted by Professor Michael Horn-von Hoegen and Professor Frank Meyer zu Heringdorf from the University of Duisburg-Essen, Germany.
Frank Meyer zu Heringdorf Appointed Associate Professor
Dr. Frank Meyer zu Heringdorf was appointed associated professor on August 12, 2015, with the three external experts on the recommendation panel praising his stellar performance in research and teaching. Professor Meyer zu Heringdorf will hold an introductary lecture addressing plasmon propagation in slow-motion as part of the physics colloquium on April 27th, 2016.
Tim Frigge Wins Award at Japanese Symposium
At the "9th International Symposium on Ultrafast Surface Dynamics" in Lake Biwa, Japan, Tim Frigge won the "Best Presentation Award for Young Scientists" award for his lecture "Ultrafast Structural Dynamics of Photo Induced Phase Transitions on Surfaces Observed by fs-RHEED."
DPG Spring Meeting
The following invited talk will be presented at the Spring Meeting of German Physical Society in Berlin:
"1D Metal Wires at Surfaces: Preparation, Phase Transitions, and Ultrafast non Equilibrium Dynamics"