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Welcome to the research group on clusters and nanostructures!

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Recent Topics

Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters
In the strong-field photoemission from atoms, molecules, and surfaces, the fastest electrons emerge from tunneling and subsequent field-driven recollision, followed by elastic backscattering. This rescattering picture is central to attosecond science and enables control of the electron’s trajectory via the sub-cycle evolution of the laser electric field. Here we reveal a so far unexplored route for waveform-controlled electron acceleration emerging from forward rescattering in resonant plasmonic systems. We studied plasmon-enhanced photoemission from silver clusters and found that the directional acceleration can be controlled up to high kinetic energy with the relative phase of a two-color laser field. Our analysis reveals that the cluster’s plasmonic near-field establishes a sub-cycle directional gate that enables the selective acceleration. The identified generic mechanism offers robust attosecond control of the electron acceleration at plasmonic nanostructures, opening perspectives for laser-based sources of attosecond electron pulses.
J. Passig et al., Nature communications 8, 1181 (2017) 

Pressemeldung der Uni Rostock 

High performance charge-state resolving ion energy analyzer optimized for intense laser studies on low-density cluster targets
We report on a versatile ion analyzer which is capable to resolve ion charge states and energies with a resolution of E/ΔE = 100 at 75 keV/nucleon. Charge states are identified by their characteristic deflection in a magnetic field, whereas the ion energies are independently determined by a time-of-flight measurement. To monitor the signals a delay-line detector is used which records ion impact positions and times in each laser shot. Compared to conventional Thomson parabola spectrometers our instrument provides a low background measurement, hence a superior dynamic range. Further features are an improved energy resolution and a significantly increased transmission. We demonstrate the performance by showing charge-state resolved ion energy spectra from the Coulomb explosion of a low-density target, i.e., silver clusters exposed to intense femtosecond laser pulses.
D. Komar et al., Rev. Sci. Instrum. 87, 103110 (2016) 

Two-Color Strong-Field Photoelectron Spectroscopy and the Phase of the Phase
The presence of a weak second-harmonic field in an intense-laser ionization experiment affects the momentum-resolved electron yield, depending on the relative phase between the ω and the 2ω component. The proposed two-color “phase-of-the-phase spectroscopy” quantifies for each final electron momentum a relative-phase contrast (RPC) and a phase of the phase (PP) describing how much and with which phase lag, respectively, the yield changes as a function of the relative phase. Experimental results for RPC and PP spectra for rare gas atoms and CO2 are presented. The spectra demonstrate a rather universal structure that is analyzed with the help of a simple model based on electron trajectories, wave-packet spreading, and (multiple) rescattering. Details in the PP and RPC spectra are target sensitive and, thus, may be used to extract structural (or even dynamical) information with high accuracy.
S. Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2016) 

Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles
Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reactionspecific material transport with a size-dependent inner particle morphology.
S. Bartling et al., J. Phys. Chem. 143, 114301 (2015) 

Scattering image of an individual Ag nanoparticleThe 3D-architecture of individual free silver nanoparticles captured by X-ray scattering
Determining the three-dimensional shape of individual nanoparticles in flight is a challenging task. While for nanostructures at surfaces various tomographic methods exist free particles elude 3D experimental access because they cannot be immobilized without introducing additional interactions with the environment. Here we show that wide-angle soft x-ray scattering can be utilized for obtaining the full 3D morphology of individual silver nanoparticles in a single shot. Surprising geometries such as icosahedra and extremely flat particles are revealed in a so far unexplored size regime.
I. Barke et al.,Nature Communications 6, 6187 (2015) 

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