Outcomes

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Publications view all
our research
Phys. Rev. B 99, 144305 (2019)
Single-shot time-resolved magnetic x-ray absorption at a free-electron laser
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Ultrafast dynamics are generally investigated using stroboscopic pump-probe measurements, which characterize the sample properties for a single, specific time delay. These measurements are then repeated for a series of discrete time delays to reconstruct the overall time trace of the process. As a consequence, this approach is limited to the investigation of fully reversible phenomena. We recently introduced an off-axis zone plate based x-ray streaking technique, which overcomes this limitation by sampling the relaxation dynamics with a single femtosecond x-ray pulse streaked over a picosecond long time window. In this article we show that the x-ray absorption cross section can be employed as the contrast mechanism in this novel technique. We show that changes of the absorption cross section on the percent level can be resolved with this method. To this end we measure the ultrafast magnetization dynamics in CoDy alloy films. Investigating different chemical compositions and infrared pump fluences, we demonstrate the routine applicability of this technique. Probing in transmission the average magnetization dynamics of the entire film, our experimental findings indicate that the demagnetization time is independent of the specific infrared laser pump fluence. These results pave the way for the investigation of irreversible phenomena in a wide variety of scientific areas.
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our research
Phys. Rev. Materials 3, 023001(R) (2019)
Segregation scheme of indium in AlGaInAs nanowire shells
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Quaternary alloys enable the independent optimization of different semiconductor properties, such as the separate tuning of the band gap and the lattice constant. Nanowire core-shell structures should allow a larger range of compositional tuning as strain can be accommodated in a more effective manner than in thin films. Still, the faceted structure of the nanowire may lead to local segregation effects. Here, we explore the incorporation of indium in AlGaAs shells up to 25%. In particular, we show the effect of In incorporation on the energy shift of the AlGaInAs single-photon emitters present in the shell. We observe a redshift up to 300 meV as a function of the group-III site fraction of In. We correlate the shift with segregation at the nanoscale. We find evidence of the segregation of the group-III elements at different positions in the nanowire, not observed before. We propose a model that takes into account the strain distribution in the nanowire shell and the adatom diffusion on the nanowire facets to explain the observations. This work provides novel insights on the segregation phenomena necessary to engineer the composition of multidinary alloys.
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our research
Solid State Ionics 330, 17 (2019)
Nano-scale oxide formation inside electrochemically-formed Pt blisters at a solid electrolyte interface
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We report on platinum oxide formation during electrochemical anodic polarization of a platinum film on yttria-stabilized zirconia (YSZ) under electrochemical oxygen potential control. The electrochemical potential drives oxygen through the YSZ electrolyte towards a nominally 175 nm thin Pt film, which we found to locally delaminate from the substrate by forming nano-scale blisters. High resolution scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) mapping of focused-ion beam (FIB)-prepared cross-sections of single bubbles of a few micrometers in diameter reveal them to be hollow and enclosed by a Pt outer and a few tens of nanometers thick PtOx inner shell. The oxide shell presumably formed due to the increase of local oxygen chemical activity under the applied process conditions (723 K, 500 mbar O2, bias voltage +100 mV). Interface X-ray diffraction indicates that the solid electrolyte surface morphology is largely unaffected by the process suggesting that the YSZ surface is stable on the atomic scale under application relevant oxygen transport conditions. Platinum is known to be rather stable towards oxidation, even at elevated oxygen pressure, leading to oxide-scale thicknesses of the order of 1 nm. Our results however indicate that many of the kinetic barriers for oxidation during the nano-confined blistering process are lowered. This may have implications in general for the mechanism how oxygen is stored in an electrode at such an internal metal - oxide/metal - gas interface, which is important for the functionality of many solid-state electrochemical and memresistive devices.
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Deliverables view all
WP6 - JRA1 – Research on In-Operando and high throughput methods
D6.8 - Realization 3D focusing mixer for X-ray and nanoanalytic applications
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Microfluidic mixers are useful instruments for the investigation of fast (bio)chemical reactions, as they allow time-resolved measurements using small sample volumes. Many reactions, especially those leading to nucleation and growth of nanoparticles, pose problems for microfluidic systems, as the reaction products have a tendency to aggregate and stick to the channel walls, known as the fouling of the reaction. Aggregates invalidate the gathered data and may clog the device by obstructing the channel. The goal of this project was to develop a mixer employing 3D-sheathing to prevent channel blockage, by inhibiting aggregation at the channel walls. We report here on the development of a micromixer geometry that would accomplish the 3Dsheathing behavior. Despite the ease in devising the necessary peripheral systems to perform experiments, the realization of the mixer itself proved to be more difficult. We found that both the correct design of the mixing part and the precision in the fabricated channels are crucial for this approach. We tested a number of materials and production methods to determine an optimal mixer geometry that should achieve the desired 3D-sheathing The precision of the channels we have produced thus far has inhibited the satisfactory function of the instrument. Measurements could be conducted with the prototype, but after some time the lacking precision still led to recirculation and agglomeration. We are currently working towards the improvement of the channels and the channel profile to resolve the remaining problems. Research performed as part of this project has been presented at the MNE2017 conference and the ÖPG Tagung 2018, and been published in Microelectronic Engineering. The development of the prototype itself has been presented on various occasions, e.g. SAXS Excites 2017, Nesy 2019.
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WP6 - JRA1 – Research on In-Operando and high throughput methods
D6.9 - Nanodrop cell for X-ray and nanoanalytic applications
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In today's competitive world of science efficient analysis tools are indispensable. The tools should be instruments providing measurements of small sample amounts, being both cost and time effective. Measurements should be not only easy and fast to execute, but also reliable and precise. Here we report on a new instrument, which enables measurements in a routine and automated way for the high throughput screening of liquid samples. The instrument is an automatic sample changer feeding a novel sample holder for volumes in the range of 5-20 μL. The general operating principle of the sample holder not only allows for precise measurements of very small volumes, but also the reduction of sample quality. High surface-tovolume effects easily occur in more conventional systems based on pumping the sample through tubing into capillaries. While avoiding such high surface-to-volume effects the automatic sample changer enables the measurement of hundreds of samples without requiring of manual intervention. We extensively tested the instrument and showed that it satisfies the initial specifications. It quickly provides reliable, high-quality data using minimal volumes of sample. This new instrument greatly simplifies and accelerates experiments, constituting therefore a valuable contribution for accessing large scale infrastructures. The prototype is already available for testing during general user access at the Austrian SAXS beamline at the Elettra-Sincrotrone Trieste (first experiments are scheduled within March and April 2019) and later on in the NFFA workpackage TNA4. The development of the instrument has been reported at several conferences, including MNE2017, OEPG 2018, NESY Winterschool 2017 and 2019. A publication concerning the system and its testing is currently in preparation.
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WP9 - JRA4 - Research on Time-resolved ultrafast probes on nanosystems
D9.4 - Setup for pump-probe small and wide angle scattering experiments
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With the drastic need for renewable energy sources, materials with solar harvesting capabilities receive increasingly attention for technological and scientific purposes. In such energy-conversion materials, the principal interaction between light and matter occurs on the nanometer level – a regime in which most properties of bulk-matter do not hold. A comprehensive understanding of these phenomena, particularly the structural material response within the first pico- and nanoseconds after the absorption of light, is critical for the design of novel nanomaterials with enhanced energy conversion efficiency. Deliverable 9.4 aims at building a time-resolved opticalpump X-Ray-probe setup, capable of studying the picosecond lattice dynamics of nanomaterials. This is achieved by installing an ultrafast high-repetition-rate laser at the AustroSAXS beamline of the Elettra synchrotron, where X-Ray scattering / diffraction patterns are taken before, during and after optical excitation. Pilot-experiments were successful, paving the way for accessibility by future NFFA-Europe users.
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Transnational Access Statistics
13 calls for access
424 proposals submitted
64% rate of acceptance
32% with Large Scale Facilities
13% with theory
9% with industry
~3 average users per proposal
51 countries applying
1176 lab sessions