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- ItemTime-resolved structural evolution during the collapse of responsive hydrogels: The microgel-to-particle transition(Washington, DC [u.a.] : Assoc., 2018) Keidel, Rico; Ghavami, Ali; Lugo, Dersy M.; Lotze, Gudrun; Virtanen, Otto; Beumers, Peter; Pedersen, Jan Skov; Bardow, Andre; Winkler, Roland G.; Richtering, WalterAdaptive hydrogels, often termed smart materials, are macromolecules whose structure adjusts to external stimuli. Responsive micro- and nanogels are particularly interesting because the small length scale enables very fast response times. Chemical cross-links provide topological constraints and define the three-dimensional structure of the microgels, whereas their porous structure permits fast mass transfer, enabling very rapid structural adaption of the microgel to the environment. The change of microgel structure involves a unique transition from a flexible, swollen finite-size macromolecular network, characterized by a fuzzy surface, to a colloidal particle with homogeneous density and a sharp surface. In this contribution, we determine, for the first time, the structural evolution during the microgel-to-particle transition. Time-resolved small-angle x-ray scattering experiments and computer simulations unambiguously reveal a two-stage process: In a first, very fast process, collapsed clusters form at the periphery, leading to an intermediate, hollowish core-shell structure that slowly transforms to a globule. This structural evolution is independent of the type of stimulus and thus applies to instantaneous transitions as in a temperature jump or to slower stimuli that rely on the uptake of active molecules from and/or exchange with the environment. The fast transitions of size and shape provide unique opportunities for various applications as, for example, in uptake and release, catalysis, or sensing.
- ItemIn situ single-shot diffractive fluence mapping for X-ray free-electron laser pulses([London] : Nature Publishing Group UK, 2018) Schneider, Michael; GĂĽnther, Christian M.; Pfau, Bastian; Capotondi, Flavio; Manfredda, Michele; Zangrando, Marco; Mahne, Nicola; Raimondi, Lorenzo; Pedersoli, Emanuele; Naumenko, Denys; Eisebitt, StefanFree-electron lasers (FELs) in the extreme ultraviolet (XUV) and X-ray regime opened up the possibility for experiments at high power densities, in particular allowing for fluence-dependent absorption and scattering experiments to reveal non-linear light-matter interactions at ever shorter wavelengths. Findings of such non-linear effects are met with tremendous interest, but prove difficult to understand and model due to the inherent shot-to-shot fluctuations in photon intensity and the often structured, non-Gaussian spatial intensity profile of a focused FEL beam. Presently, the focused beam is characterized and optimized separately from the actual experiment. Here, we present the simultaneous measurement of XUV diffraction signals from solid samples in tandem with the corresponding single-shot spatial fluence distribution on the actual sample. Our in situ characterization scheme enables direct monitoring of the sample illumination, providing a basis to optimize and quantitatively understand FEL experiments.
- ItemCompetition between proton transfer and intermolecular Coulombic decay in water([London] : Nature Publishing Group UK, 2018) Richter, Clemens; Hollas, Daniel; Saak, Clara-Magdalena; Förstel, Marko; Miteva, Tsveta; Mucke, Melanie; Björneholm, Olle; Sisourat, Nicolas; SlavĂÄŤek, Petr; Hergenhahn, UweIntermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron–electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a1 ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40–50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12–52 fs for small water clusters.
- ItemTheoretical analysis of hard x-ray generation by nonperturbative interaction of ultrashort light pulses with a metal(Melville, NY : AIP Publishing LLC, 2015) Weisshaupt, Jannick; Juvé, Vincent; Holtz, Marcel; Woerner, Michael; Elsaesser, ThomasThe interaction of intense femtosecond pulses with metals allows for generating ultrashort hard x-rays. In contrast to plasma theories, tunneling from the target into vacuum is introduced as electron generation step, followed by vacuum acceleration in the laser field and re-entrance into the target to generate characteristic x-rays and Bremsstrahlung. For negligible space charge in vacuum, the Kα flux is proportional to the incident intensity and the wavelength squared, suggesting a strong enhancement of the x-ray flux by mid-infrared driving pulses. This prediction is in quantitative agreement with experiments on femtosecond Cu Kα generation.
- ItemPrograming stimuli-responsiveness of gelatin with electron beams: Basic effects and development of a hydration-controlled biocompatible demonstrator(London : Nature Publishing Group, 2017) Riedel, Stefanie; Heyart, Benedikt; Apel, Katharina S.; Mayr, Stefan G.Biomimetic materials with programmable stimuli responsiveness constitute a highly attractive material class for building bioactuators, sensors and active control elements in future biomedical applications. With this background, we demonstrate how energetic electron beams can be utilized to construct tailored stimuli responsive actuators for biomedical applications. Composed of collagen-derived gelatin, they reveal a mechanical response to hydration and changes in pH-value and ion concentration, while maintaining their excellent biocompatibility and biodegradability. While this is explicitly demonstrated by systematic characterizing an electron-beam synthesized gelatin-based actuator of cantilever geometry, the underlying materials processes are also discussed, based on the fundamental physical and chemical principles. When applied within classical electron beam lithography systems, these findings pave the way for a novel class of highly versatile integrated bioactuators from micro-to macroscales.
- ItemCoherent diffractive imaging of single helium nanodroplets with a high harmonic generation source([London] : Nature Publishing Group UK, 2017) Rupp, Daniela; Monserud, Nils; Langbehn, Bruno; Sauppe, Mario; Zimmermann, Julian; Ovcharenko, Yevheniy; Möller, Thomas; Frassetto, Fabio; Poletto, Luca; Trabattoni, Andrea; Calegari, Francesca; Nisoli, Mauro; Sander, Katharina; Peltz, Christian; J. Vrakking, Marc; Fennel, Thomas; Rouzée, ArnaudCoherent diffractive imaging of individual free nanoparticles has opened routes for the in situ analysis of their transient structural, optical, and electronic properties. So far, single-shot single-particle diffraction was assumed to be feasible only at extreme ultraviolet and X-ray free-electron lasers, restricting this research field to large-scale facilities. Here we demonstrate single-shot imaging of isolated helium nanodroplets using extreme ultraviolet pulses from a femtosecond-laser-driven high harmonic source. We obtain bright wide-Angle scattering patterns, that allow us to uniquely identify hitherto unresolved prolate shapes of superfluid helium droplets. Our results mark the advent of single-shot gas-phase nanoscopy with lab-based short-wavelength pulses and pave the way to ultrafast coherent diffractive imaging with phase-controlled multicolor fields and attosecond pulses.
- ItemCommunication: X-ray coherent diffractive imaging by immersion in nanodroplets(Melville, NY : AIP Publishing LLC, 2015) Tanyag, Rico Mayro P.; Bernando, Charles; Jones, Curtis F.; Bacellar, Camila; Ferguson, Ken R.; Anielski, Denis; Boll, Rebecca; Carron, Sebastian; Cryan, James P.; Englert, Lars; Epp, Sascha W.; Erk, Benjamin; Foucar, Lutz; Gomez, Luis F.; Hartmann, Robert; Neumark, Daniel M.; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Siefermann, Katrin R.; Ullrich, Joachim; Weise, Fabian; Bostedt, Christoph; Gessner, Oliver; Vilesov, Andrey F.Lensless x-ray microscopy requires the recovery of the phase of the radiation scattered from a specimen. Here, we demonstrate a de novo phase retrieval technique by encapsulating an object in a superfluid helium nanodroplet, which provides both a physical support and an approximate scattering phase for the iterative image reconstruction. The technique is robust, fast-converging, and yields the complex density of the immersed object. Images of xenon clusters embedded in superfluid helium droplets reveal transient configurations of quantum vortices in this fragile system.
- ItemPublisher Correction: Coherent diffractive imaging of single helium nanodroplets with a high harmonic generation source (Nature communications (2017) 8 1 (493))([London] : Nature Publishing Group UK, 2018) Rupp, Daniela; Monserud, Nils; Langbehn, Bruno; Sauppe, Mario; Zimmermann, Julian; Ovcharenko, Yevheniy; Möller, Thomas; Frassetto, Fabio; Poletto, Luca; Trabattoni, Andrea; Calegari, Francesca; Nisoli, Mauro; Sander, Katharina; Peltz, Christian; Vrakking, Marc J.; Fennel, Thomas; Rouzée, ArnaudIn the original version of this Article, the affiliation for Luca Poletto was incorrectly given as 'European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Hamburg, Germany', instead of the correct 'CNR, Istituto di Fotonica e Nanotecnologie Padova, Via Trasea 7, 35131 Padova, Italy'. This has now been corrected in both the PDF and HTML versions of the Article.
- ItemPublisher Correction: Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters (Nature communications (2017) 8 1 (1181))([London] : Nature Publishing Group UK, 2018) Passig, Johannes; Zherebtsov, Sergey; Irsig, Robert; Arbeiter, Mathias; Peltz, Christian; Göde, Sebastian; Skruszewicz, Slawomir; Meiwes-Broer, Karl-Heinz; Tiggesbäumker, Josef; Kling, Matthias F.; Fennel, ThomasThe original PDF version of this Article contained an error in Equation 1. The original HTML version of this Article contained errors in Equation 2 and Equation 4. These errors have now been corrected in both the PDF and the HTML versions of the Article. The original PDF version of this Article contained an error in Equation 1. A dot over the first occurrence of the variable ri was missing, and incorrectly read: (Formula Presented). The correct form of Equation 1 is as follows: (Formula Presented). This has now been corrected in the PDF version of the Article. The HTML version was correct from the time of publication. The original HTML version of this Article contained errors in Equation 2 and Equation 4. In Equation 2, a circle over the first occurrence of the variable ri replaced the intended dot, and incorrectly read: (Formula Presented). The correct form of Equation 2 is as follows: (Formula Presented). In Equation 4, circles over the first and fifth occurrences of the variable ri replaced the intended dots, and incorrectly read: (Formula Presented). The correct form of Equation 4 is as follows: (Formula Presented). This has now been corrected in the HTML version of the Article. The PDF version was correct from the time of publication.
- ItemFew-femtosecond passage of conical intersections in the benzene cation([London] : Nature Publishing Group UK, 2017) Galbraith, M.C.E.; Scheit, S.; Golubev, N.V.; Reitsma, G.; Zhavoronkov, N.; Despré, V.; Lépine, F.; Kuleff, A.I.; Vrakking, M.J.J.; Kornilov, O.; Köppel, H.; Mikosch, J.Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in the femtochemistry toolkit. Such dynamics are now within reach with the instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess the ultrafast nonadiabatic vibronic processes in a prototypical complex system - the excited benzene cation. We use few-femtosecond duration extreme ultraviolet and visible/near-infrared laser pulses to prepare and probe excited cationic states and observe two relaxation timescales of 11 ± 3 fs and 110 ± 20 fs. These are interpreted in terms of population transfer via two sequential conical intersections. The experimental results are quantitatively compared with state-of-the-art multi-configuration time-dependent Hartree calculations showing convincing agreement in the timescales. By characterising one of the fastest internal conversion processes studied to date, we enter an extreme regime of ultrafast molecular dynamics, paving the way to tracking and controlling purely electronic dynamics in complex molecules.