Obergfell, Manuel


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Energy scales and dynamics of electronic excitations in functionalized gold nanoparticles measured at the single particle level

2019-07-07, Basu, Tuhin Shuvra, Diesch, Simon, Obergfell, Manuel, Demsar, Jure, Scheer, Elke

The knowledge of the electronic structure and dynamics of nanoparticles is a prerequisite to develop miniaturized single-electron devices based on nanoparticles. Low-temperature transport measurements of individual stable metallic nanoparticles enable unravelling the system specific electronic structure while ultrafast optical spectroscopy gives access to the electron dynamics. In this work, we investigate bare and thiol-functionalized gold nanoparticles. For the latter, we employ a fast and low-cost fabrication technique which yields nanoparticles with narrow size distribution. Using relatively long thiol-ended alkane chains for the functionalization modifies the electronic density of states of the nanoparticles. The study of decay dynamics of surface-plasmon-related hot electrons reveals the presence of electronic states at the interface which serve as a fast decay channel for electronic relaxation. By low-temperature scanning tunnelling microscopy we precisely investigate the energy scales and electronic interactions relevant for the tunnel charge transport through this system. We observe that the interaction between the functional ligand and the substrate on which the nanoparticles reside also influences the electronic transport. The procedure that we employ can be easily adapted to other metallic nanoparticles. Our findings are therefore important for incorporating them into single-electron devices.

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Cooperative atomic motion probed by ultrafast transmission electron diffraction

2015, Eichberger, Maximilian, Liebermann, S., Klose, Carolin, Obergfell, Manuel, Birmuske, Reinhard, Sutter, Johannes, Demsar, Jure

In numerous solids exhibiting broken symmetry ground states, changes in electronic (spin) structure are accompanied by structural changes. Femtosecond time-resolved techniques recently contributed many important insights into the origin of their ground states by tracking dynamics of the electronic subsystem with femtosecond light pulses. Moreover, several studies of structural dynamics in systems with periodic lattice modulation (PLD) were performed. Since intensities of the super-lattice diffraction peaks are in the first approximation proportional to the square of the PLD amplitude, their temporal dynamics provides access to cooperative atomic motion. This process takes place on a fraction of a period of the corresponding lattice vibration (typically 100 fs timescale). However, since energy transfer from the excited electronic system to the lattice takes place on a comparable timescale, contribution of the incoherent lattice motion on diffraction intensities has to be taken into account. Furthermore we demonstrate an ultrafast transmission electron diffraction set-up, where relative changes in individual diffraction peaks of less than 1% can be studied. Here we show, that by simultaneously tracking the dynamics of intensities in super-lattice peaks, lattice peaks and in the incoherent background over multiple diffraction orders the two processes can be effectively disentangled.

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Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85 Ce0.15CuO4−δ

2017, Beck, Matthias, Klammer, Maximilian, Rousseau, Ian, Obergfell, Manuel, Leiderer, Paul, Helm, Manfred, Kabanov, Viktor V., Diamant, Itay, Rabinowicz, Alon, Dagan, Yoram, Demsar, Jure


Manipulation of charge transfer and transport in plasmonic-ferroelectric hybrids for photoelectrochemical applications

2016, Wang, Zhijie, Cao, Dawei, Wen, Liaoyong, Xu, Rui, Obergfell, Manuel, Mi, Yan, Zhan, Zhibing, Nasori, Nasori, Demsar, Jure, Lei, Yong

Utilizing plasmonic nanostructures for efficient and flexible conversion of solar energy into electricity or fuel presents a new paradigm in photovoltaics and photoelectrochemistry research. In a conventional photoelectrochemical cell, consisting of a plasmonic structure in contact with a semiconductor, the type of photoelectrochemical reaction is determined by the band bending at the semiconductor/electrolyte interface. The nature of the reaction is thus hard to tune. Here instead of using a semiconductor, we employed a ferroelectric material, Pb(Zr,Ti)O3 (PZT). By depositing gold nanoparticle arrays and PZT films on ITO substrates, and studying the photocurrent as well as the femtosecond transient absorbance in different configurations, we demonstrate an effective charge transfer between the nanoparticle array and PZT. Most importantly, we show that the photocurrent can be tuned by nearly an order of magnitude when changing the ferroelectric polarization in PZT, demonstrating a versatile and tunable system for energy harvesting.