TY - JOUR A1 - Toalá, Jesús Alberto A1 - Bowman, Dominic A1 - Van Reeth, Timothy A1 - Todt, Helge Tobias A1 - Dsilva, Karan A1 - Shenar, Tomer A1 - Koenigsberger, Gloria Suzanne A1 - Estrada-Dorado, Sandino A1 - Oskinova, Lidia M. A1 - Hamann, Wolf-Rainer T1 - Multiple variability time-scales of the early nitrogen-rich Wolf-Rayet star WR 7 JF - Monthly notices of the Royal Astronomical Society N2 - We present the analysis of the optical variability of the early, nitrogen-rich Wolf-Rayet (WR) star WR 7. The analysis of multisector Transiting Exoplanet Survey Satellite (TESS) light curves and high-resolution spectroscopic observations confirm multiperiodic variability that is modulated on time-scales of years. We detect a dominant period of 2.6433 +/- 0.0005 d in the TESS sectors 33 and 34 light curves in addition to the previously reported high-frequency features from sector 7. We discuss the plausible mechanisms that may be responsible for such variability in WR 7, including pulsations, binarity, co-rotating interaction regions (CIRs), and clumpy winds. Given the lack of strong evidence for the presence of a stellar or compact companion, we suggest that WR 7 may pulsate in quasi-coherent modes in addition to wind variability likely caused by CIRs on top of stochastic low-frequency variability. WR 7 is certainly a worthy target for future monitoring in both spectroscopy and photometry to sample both the short (less than or similar to 1 d) and long (greater than or similar to 1000 d) variability time-scales. KW - stars: atmospheres KW - stars: evolution KW - stars: individual: WR 7 KW - stars: winds KW - outflows KW - stars: Wolft-Rayet Y1 - 2022 U6 - https://doi.org/10.1093/mnras/stac1455 SN - 0035-8711 SN - 1365-2966 VL - 514 IS - 2 SP - 2269 EP - 2277 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Oskinova, Lidia M. A1 - Schaerer, Daniel T1 - Ionization of He II in star-forming galaxies by X-rays from cluster winds and superbubbles JF - Astronomy and astrophysics : an international weekly journal N2 - The nature of the sources powering nebular He II emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars. Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific He II ionizing flux produced by hot gas and show that if its temperature is not too high (less than or similar to 2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain He II ionization in galaxies. To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of He II ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. Furthermore, we show that ensembles of star clusters up to similar to 10-20 Myr old in galaxies can produce enough soft X-rays to induce nebular He II emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the He II nebula in this galaxy is powered by a hot superbubble. Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of He II ionizing flux in low-metallicity star-forming galaxies. KW - galaxies KW - ISM KW - high-redshift KW - bubbles KW - X-rays Y1 - 2022 U6 - https://doi.org/10.1051/0004-6361/202142520 SN - 0004-6361 SN - 1432-0746 VL - 661 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Tönjes, Ralf A1 - Kori, Hiroshi T1 - Phase and frequency linear response theory for hyperbolic chaotic oscillators JF - Chaos : an interdisciplinary journal of nonlinear science N2 - We formulate a linear phase and frequency response theory for hyperbolic flows, which generalizes phase response theory for autonomous limit cycle oscillators to hyperbolic chaotic dynamics. The theory is based on a shadowing conjecture, stating the existence of a perturbed trajectory shadowing every unperturbed trajectory on the system attractor for any small enough perturbation of arbitrary duration and a corresponding unique time isomorphism, which we identify as phase such that phase shifts between the unperturbed trajectory and its perturbed shadow are well defined. The phase sensitivity function is the solution of an adjoint linear equation and can be used to estimate the average change of phase velocity to small time dependent or independent perturbations. These changes in frequency are experimentally accessible, giving a convenient way to define and measure phase response curves for chaotic oscillators. The shadowing trajectory and the phase can be constructed explicitly in the tangent space of an unperturbed trajectory using co-variant Lyapunov vectors. It can also be used to identify the limits of the regime of linear response. Y1 - 2022 U6 - https://doi.org/10.1063/5.0064519 SN - 1054-1500 SN - 1089-7682 VL - 32 IS - 4 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Zheng, Chunming A1 - Tönjes, Ralf A1 - Pikovskij, Arkadij T1 - Transition to synchrony in a three-dimensional swarming model with helical trajectories JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We investigate the transition from incoherence to global collective motion in a three-dimensional swarming model of agents with helical trajectories, subject to noise and global coupling. Without noise this model was recently proposed as a generalization of the Kuramoto model and it was found that alignment of the velocities occurs discontinuously for arbitrarily small attractive coupling. Adding noise to the system resolves this singular limit and leads to a continuous transition, either to a directed collective motion or to center-of-mass rotations. Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevE.104.014216 SN - 2470-0045 SN - 2470-0053 VL - 104 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Tönjes, Ralf A1 - Pikovsky, Arkady T1 - Low-dimensional description for ensembles of identical phase oscillators subject to Cauchy noise JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We study ensembles of globally coupled or forced identical phase oscillators subject to independent white Cauchy noise. We demonstrate that if the oscillators are forced in several harmonics, stationary synchronous regimes can be exactly described with a finite number of complex order parameters. The corresponding distribution of phases is a product of wrapped Cauchy distributions. For sinusoidal forcing, the Ott-Antonsen low-dimensional reduction is recovered. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.102.052315 SN - 2470-0045 SN - 2470-0053 VL - 102 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Gong, Chen Chris A1 - Zheng, Chunming A1 - Tönjes, Ralf A1 - Pikovskij, Arkadij T1 - Repulsively coupled Kuramoto-Sakaguchi phase oscillators ensemble subject to common noise JF - Chaos : an interdisciplinary journal of nonlinear science N2 - We consider the Kuramoto-Sakaguchi model of identical coupled phase oscillators with a common noisy forcing. While common noise always tends to synchronize the oscillators, a strong repulsive coupling prevents the fully synchronous state and leads to a nontrivial distribution of oscillator phases. In previous numerical simulations, the formation of stable multicluster states has been observed in this regime. However, we argue here that because identical phase oscillators in the Kuramoto-Sakaguchi model form a partially integrable system according to the Watanabe-Strogatz theory, the formation of clusters is impossible. Integrating with various time steps reveals that clustering is a numerical artifact, explained by the existence of higher order Fourier terms in the errors of the employed numerical integration schemes. By monitoring the induced change in certain integrals of motion, we quantify these errors. We support these observations by showing, on the basis of the analysis of the corresponding Fokker-Planck equation, that two-cluster states are non-attractive. On the other hand, in ensembles of general limit cycle oscillators, such as Van der Pol oscillators, due to an anharmonic phase response function as well as additional amplitude dynamics, multiclusters can occur naturally. Published under license by AIP Publishing. Y1 - 2019 U6 - https://doi.org/10.1063/1.5084144 SN - 1054-1500 SN - 1089-7682 VL - 29 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Gong, Chen Chris A1 - Tönjes, Ralf A1 - Pikovsky, Arkady T1 - Coupled Möbius maps as a tool to model Kuramoto phase synchronization JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We propose Mobius maps as a tool to model synchronization phenomena in coupled phase oscillators. Not only does the map provide fast computation of phase synchronization, it also reflects the underlying group structure of the sinusoidally coupled continuous phase dynamics. We study map versions of various known continuous-time collective dynamics, such as the synchronization transition in the Kuramoto-Sakaguchi model of nonidentical oscillators, chimeras in two coupled populations of identical phase oscillators, and Kuramoto-Battogtokh chimeras on a ring, and demonstrate similarities and differences between the iterated map models and their known continuous-time counterparts. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.102.022206 SN - 2470-0045 SN - 2470-0053 SN - 1063-651X SN - 2470-0061 SN - 1550-2376 VL - 102 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Zheng, Chunming A1 - Tönjes, Ralf T1 - Noise-induced swarming of active particles JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We report on the effect of spatially correlated noise on the velocities of self-propelled particles. Correlations in the random forces acting on self-propelled particles can induce directed collective motion, i.e., swarming. Even with repulsive coupling in the velocity directions, which favors a disordered state, strong correlations in the fluctuations can align the velocities locally leading to a macroscopic, turbulent velocity field. On the other hand, while spatially correlated noise is aligning the velocities locally, the swarming transition to globally directed motion is inhibited when the correlation length of the noise is nonzero, but smaller than the system size. We analyze the swarming transition in d-dimensional space in a mean field model of globally coupled velocity vectors. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevE.106.064601 SN - 2470-0045 SN - 2470-0053 VL - 106 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pasechnik, Sergey V. A1 - Shmeleva, Dina A1 - Saidgaziev, Ayvr Sh. A1 - Kharlamov, Semen A1 - Vasilieva, Aleksandra A. A1 - Santer, Svetlana T1 - Shear flows induced by electro-osmotic pumps in optofluidic liquid crystal cell for modulation of visible light and THz irradiation JF - Liquid Crystals and their Application : Russian Journal N2 - The work is devoted to the use of electrokinetic phenomena in liquid crystals to create a new class of microfluidics devices - optofluidics, designed to control electromagnetic radiation, including the THz frequency range. To achieve the goal, an optical method is used to study changes in the orientational structure in LC layers caused by a shear flow generated by electroosmotic pumps. Simula-tion of LC behaviour in an experimental cell containing electroosmotic pumps and flat layers of a nematic liquid crystal is fulfilled. The experimental depend-ences of the intensity of polarized radiation passing through flat LC layers on the control voltage applied to the electroosmotic pump and the results of calcu-lations of the hydrodynamic and mechano-optical characteristics of the experi-mental LC cell are presented. The propagation of THz irradiation across the multilayer structure of the optofluidic cell is considered taking into account the minimum number of re-reflections of waves from different layers and the ab-sorption of THz irradiation in a propylene and a liquid crystal. N2 - Работа посвящена использованию электрокинетических явлений в жидких кристаллах для создания нового класса микрофлюидных устройств – опто- флюидики, предназначенных для управления электромагнитным излуче- нием, в том числе терагерцового диапазона частот. Для достижения цели оптическим методом исследуются изменения ориентационной структуры в слоях ЖК, вызванные сдвиговым течением, генерируемым электроосмоти- ческими насосами. Проведено моделирование поведения ЖК в эксперимен- тальной ячейке, содержащей электроосмотические насосы и плоские слои нематического жидкого кристалла. Представлены экспериментальные за- висимости интенсивности поляризованного излучения, проходящего через плоские слои ЖК, от управляющего напряжения, подаваемого на электро- осмотический насос, и результаты расчетов гидродинамических и механо- оптических характеристик экспериментальной ЖК-ячейки. Рассмотрено распространение ТГц излучения по многослойной структуре оптофлюид- ной ячейки с учетом минимального числа переотражений волн от разных слоев и поглощения ТГц излучения в пропилене и жидком кристалле. KW - nematic liquid crystal KW - terahertz range KW - electrokinetic phenomena KW - osmotic flow KW - director configuration KW - optical irradiation intensity KW - E7 KW - polypropylene Y1 - 2022 U6 - https://doi.org/10.18083/LCAppl.2022.3.49 SN - 1991-3966 SN - 2499–9644 VL - 22 IS - 3 SP - 49 EP - 57 PB - Nanomaterials Research Institute CY - Ivanovo ER - TY - JOUR A1 - Pick, Leonie A1 - Effenberger, Frederic A1 - Zhelavskaya, Irina A1 - Korte, Monika T1 - A Statistical Classifier for Historical Geomagnetic Storm Drivers Derived Solely From Ground-Based Magnetic Field Measurements JF - Earth and Space Science N2 - Solar wind observations show that geomagnetic storms are mainly driven by interplanetary coronal mass ejections (ICMEs) and corotating or stream interaction regions (C/SIRs). We present a binary classifier that assigns one of these drivers to 7,546 storms between 1930 and 2015 using ground‐based geomagnetic field observations only. The input data consists of the long‐term stable Hourly Magnetospheric Currents index alongside the corresponding midlatitude geomagnetic observatory time series. This data set provides comprehensive information on the global storm time magnetic disturbance field, particularly its spatial variability, over eight solar cycles. For the first time, we use this information statistically with regard to an automated storm driver identification. Our supervised classification model significantly outperforms unskilled baseline models (78% accuracy with 26[19]% misidentified interplanetary coronal mass ejections [corotating or stream interaction regions]) and delivers plausible driver occurrences with regard to storm intensity and solar cycle phase. Our results can readily be used to advance related studies fundamental to space weather research, for example, studies connecting galactic cosmic ray modulation and geomagnetic disturbances. They are fully reproducible by means of the underlying open‐source software (Pick, 2019, http://doi.org/10.5880/GFZ.2.3.2019.003) KW - geomagnetic observatory data KW - geomagnetic storm drivers KW - historical geomagnetic storms KW - supervised machine learning Y1 - 2019 U6 - https://doi.org/10.1029/2019EA000726 SN - 2333-5084 VL - 6 SP - 2000 EP - 2015 PB - American Geophysical Union CY - Malden, Mass. ER - TY - JOUR A1 - Karamzadeh Toularoud, Nasim A1 - Heimann, Sebastian A1 - Dahm, Torsten A1 - Krüger, Frank T1 - Application based seismological array design by seismicity scenario modelling JF - Geophysical journal international N2 - The design of an array configuration is an important task in array seismology during experiment planning. Often the array response function (ARF), which depends on the relative position of array stations and frequency content of the incoming signals, is used as the array design criterion. In practice, additional constraints and parameters have to be taken into account, for example, land ownership, site-specific noise levels or characteristics of the seismic sources under investigation. In this study, a flexible array design framework is introduced that implements a customizable scenario modelling and optimization scheme by making use of synthetic seismograms. Using synthetic seismograms to evaluate array performance makes it possible to consider additional constraints. We suggest to use synthetic array beamforming as an array design criterion instead of the ARF. The objective function of the optimization scheme is defined according to the monitoring goals, and may consist of a number of subfunctions. The array design framework is exemplified by designing a seven-station small-scale array to monitor earthquake swarm activity in Northwest Bohemia/Vogtland in central Europe. Two subfunctions are introduced to verify the accuracy of horizontal slowness estimation; one to suppress aliasing effects due to possible secondary lobes of synthetic array beamforming calculated in horizontal slowness space and the other to reduce the event’s mislocation caused by miscalculation of the horizontal slowness vector. Subsequently, a weighting technique is applied to combine the subfunctions into one single scalar objective function to use in the optimization process. KW - Array Seismology KW - Array design KW - Seismicity modelling Y1 - 2018 SN - 0956-540X SN - 1365-246X VL - 216 IS - 3 SP - 1711 EP - 1727 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Li, Tian-yi A1 - Benduhn, Johannes A1 - Qiao, Zhi A1 - Liu, Yuan A1 - Li, Yue A1 - Shivhare, Rishi A1 - Jaiser, Frank A1 - Wang, Pei A1 - Ma, Jie A1 - Zeika, Olaf A1 - Neher, Dieter A1 - Mannsfeld, Stefan C. B. A1 - Ma, Zaifei A1 - Vandewal, Koen A1 - Leo, Karl T1 - Effect of H- and J-Aggregation on the Photophysical and Voltage Loss of Boron Dipyrromethene Small Molecules in Vacuum-Deposited Organic Solar Cells JF - The journal of physical chemistry letters N2 - An understanding of the factors limiting the open-circuit voltage (V-oc) and related photon energy loss mechanisms is critical to increase the power conversion efficiency (PCE) of small-molecule organic solar cells (OSCs), especially those with near-infrared (NIR) absorbers. In this work, two NIR boron dipyrromethene (BODIPY) molecules are characterized for application in planar (PHJ) and bulk (BHJ) heterojunction OSCs. When two H atoms are substituted by F atoms on the peripheral phenyl rings of the molecules, the molecular aggregation type in the thin film changes from the H-type to J-type. For PHJ devices, the nonradiative voltage loss of 0.35 V in the J-aggregated BODIPY is lower than that of 0.49 V in the H-aggregated device. In BHJ devices with a nonradiative voltage loss of 0.35 V, a PCE of 5.5% is achieved with an external quantum efficiency (EQE) maximum of 68% at 700 nm. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpclett.9b01222 SN - 1948-7185 VL - 10 IS - 11 SP - 2684 EP - 2691 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Galbrecht, Frank A1 - Scherf, Ullrich T1 - Efficient polymer electrophosphoreseent devices with interfacial layers JF - Advanced functional materials N2 - It is shown that several polymers can form insoluble interfacial layers on a poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer after annealing of the double-layer structure. The thickness of the interlayer is dependent on the characteristics of the underlying PEDOT.PSS and the molecular weight of the polymers. It is further shown that the electronic structures of the interlayer polymers have a significant effect on the properties of red-light-emitting polymer-based electrophosphorescent devices. Upon increasing the highest occupied molecular orbital and lowest unoccupied molecular orbital positions, a significant increase in current density and device efficiency is observed. This is attributed to efficient blocking of electrons in combination with direct injection of holes from the interlayer to the phosphorescent dye. Upon proper choice of the interlayer polymer, efficient red, polymer-based electrophosphorescent devices with a peak luminance efficiency of 5.5 cd A(-1) (external quantum efficiency = 6 %) and a maximum power-conversion efficiency of 5 Im W-1 can be realized. Y1 - 2006 U6 - https://doi.org/10.1002/adfm.200500834 SN - 1616-301X SN - 1616-3028 VL - 16 IS - 16 SP - 2156 EP - 2162 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kurpiers, Jona A1 - Ferron, Thomas A1 - Roland, Steffen A1 - Jakoby, Marius A1 - Thiede, Tobias A1 - Jaiser, Frank A1 - Albrecht, Steve A1 - Janietz, Silvia A1 - Collins, Brian A. A1 - Howard, Ian A. A1 - Neher, Dieter T1 - Probing the pathways of free charge generation in organic bulk heterojunction solar cells JF - Nature Communications N2 - The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-04386-3 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Pudell, Jan-Etienne A1 - Stete, Felix A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Schmitt, Clemens Nikolaus Zeno A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - Scaling up nanoplasmon catalysis BT - the role of heat dissipation JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Nanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4′-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by one-dimensional heat transport. KW - Gold KW - Raman spectroscopy KW - Silicon KW - Irradiation KW - Lasers Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b12574 SN - 1932-7447 VL - 123 IS - 14 SP - 9352 EP - 9357 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sini, Gjergji A1 - Schubert, Marcel A1 - Risko, Chad A1 - Roland, Steffen A1 - Lee, Olivia P. A1 - Chen, Zhihua A1 - Richter, Thomas V. A1 - Dolfen, Daniel A1 - Coropceanu, Veaceslav A1 - Ludwigs, Sabine A1 - Scherf, Ullrich A1 - Facchetti, Antonio A1 - Frechet, Jean M. J. A1 - Neher, Dieter T1 - On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface JF - Advanced energy materials N2 - Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules. KW - donor-acceptor interfaces KW - energy gradients KW - geometrical deformations KW - nonfullerene acceptors KW - organic photovoltaics KW - photocurrent generation KW - polymer solar cells Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201702232 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 12 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ullbrich, Sascha A1 - Benduhn, Johannes A1 - Jia, Xiangkun A1 - Nikolis, Vasileios C. A1 - Tvingstedt, Kristofer A1 - Piersimoni, Fortunato A1 - Roland, Steffen A1 - Liu, Yuan A1 - Wu, Jinhan A1 - Fischer, Axel A1 - Neher, Dieter A1 - Reineke, Sebastian A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Emissive and charge-generating donor-acceptor interfaces for organic optoelectronics with low voltage losses JF - Nature materials N2 - Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes(1,2). Non-radiative charge-transfer state decay is dominant in state-of-the-art D-A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01-0.0001% range(3,4). In contrast, the electroluminescence external quantum yield reaches up to 16% in D-A-based organic light-emitting diodes(5-7). Here, we show that proper control of charge-transfer state properties allows simultaneous occurrence of a high photovoltaic and emission quantum yield within a single, visible-light-emitting D-A system. This leads to ultralow-emission turn-on voltages as well as significantly reduced voltage losses upon solar illumination. These results unify the description of the electro-optical properties of charge-transfer states in organic optoelectronic devices and foster the use of organic D-A blends in energy conversion applications involving visible and ultraviolet photons(8-11). KW - Electronics, photonics and device physics KW - Optoelectronic devices and components KW - Photonic devices KW - Solar energy and photovoltaic technology Y1 - 2019 U6 - https://doi.org/10.1038/s41563-019-0324-5 SN - 1476-1122 SN - 1476-4660 VL - 18 IS - 5 SP - 459 EP - 464 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Ran, Niva A. A1 - Love, John A. A1 - Heiber, Michael C. A1 - Jiao, Xuechen A1 - Hughes, Michael P. A1 - Karki, Akchheta A1 - Wang, Ming A1 - Brus, Viktor V. A1 - Wang, Hengbin A1 - Neher, Dieter A1 - Ade, Harald A1 - Bazan, Guillermo C. A1 - Thuc-Quyen Nguyen, T1 - Charge generation and recombination in an organic solar cell with low energetic offsets JF - dvanced energy materials N2 - Organic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short-circuit currents (J(SC)) and fill factors (FF). However, it is necessary to reduce the energetic offsets to achieve high open-circuit voltages (V-OC). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl-C61-butyric acid methyl ester (PC61BM), that achieves a high V-OC (0.9 V) with very low energy losses (E-loss = 0.52 eV) from the energy of absorbed photons, a respectable J(SC) (13 mA cm(-2)), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field-dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge-carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC61BM. These results hold promise that given the appropriate morphology, the J(SC), V-OC, and FF can all be improved, even with very low energetic offsets. KW - energetic offset KW - fill factor KW - morphology KW - organic solar cells KW - recombination Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201701073 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 5 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hosseini, Seyed Mehrdad A1 - Roland, Steffen A1 - Kurpiers, Jona A1 - Chen, Zhiming A1 - Zhang, Kai A1 - Huang, Fei A1 - Armin, Ardalan A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Impact of Bimolecular Recombination on the Fill Factor of Fullerene and Nonfullerene-Based Solar Cells BT - A Comparative Study of Charge Generation and Extraction JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Power conversion efficiencies of donor/acceptor organic solar cells utilizing nonfullerene acceptors have now increased beyond the record of their fullerene-based counterparts. There remain many fundamental questions regarding nanomorphology, interfacial states, charge generation and extraction, and losses in these systems. Herein, we present a comparative study of bulk heterojunction solar cells composed of a recently introduced naphthothiadiazole-based polymer (NT812) as the electron donor and two different acceptor molecules, namely, [6,6]-phenyl-C71-butyric acid methyl ester (PCBM)[70] and 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC). A comparison between the photovoltaic performance of these two types of solar cells reveals that the open-circuit voltage (Voc) of the NT812:ITIC-based solar cell is larger, but the fill factor (FF) is lower than that of the NT812:PCBM[70] device. We find the key reason behind this reduced FF in the ITIC-based device to be faster nongeminate recombination relative to the NT812:PCBM[70] system. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b11669 SN - 1932-7447 VL - 123 IS - 11 SP - 6823 EP - 6830 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Roland, Steffen A1 - Yan, Liang A1 - Zhang, Qianqian A1 - Jiao, Xuechen A1 - Hunt, Adrian A1 - Ghasemi, Masoud A1 - Ade, Harald A1 - You, Wei A1 - Neher, Dieter T1 - Charge Generation and Mobility-Limited Performance of Bulk Heterojunction Solar Cells with a Higher Adduct Fullerene JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Alternative electron acceptors are being actively explored in order to advance the development of bulk-heterojunction (BHJ) organic solar cells (OSCs). The indene-C-60 bisadduct (ICBA) has been regarded as a promising candidate, as it provides high open-circuit voltage in BHJ solar cells; however, the photovoltaic performance of such ICBA-based devices is often inferior when compared to cells with the omnipresent PCBM electron acceptor. Here, by pairing the high performance polymer (FTAZ) as the donor with either PCBM or ICBA as the acceptor, we explore the physical mechanism behind the reduced performance of the ICBA-based device. Time delayed collection field (TDCF) experiments reveal reduced, yet field-independent free charge generation in the FTAZ:ICBA system, explaining the overall lower photocurrent in its cells. Through the analysis of the photoluminescence, photogeneration, and electroluminescence, we find that the lower generation efficiency is neither caused by inefficient exciton splitting, nor do we find evidence for significant energy back-transfer from the CT state to singlet excitons. In fact, the increase in open circuit voltage when replacing PCBM by ICBA is entirely caused by the increase in the CT energy, related to the shift in the LUMO energy, while changes in the radiative and nonradiative recombination losses are nearly absent. On the other hand, space charge limited current (SCLC) and bias-assisted charge extraction (BACE) measurements consistently reveal a severely lower electron mobilitiy in the FTAZ:ICBA blend. Studies of the blends with resonant soft X-ray scattering (R-SoXS), grazing incident wide-angle X-ray scattering (GIWAXS), and scanning transmission X-ray microscopy (STXM) reveal very little differences in the mesoscopic morphology but significantly less nanoscale molecular ordering of the fullerene domains in the ICBA based blends, which we propose as the main cause for the lower generation efficiency and smaller electron mobility. Calculations of the JV curves with an analytical model, using measured values, show good agreement with the experimentally determined JV characteristics, proving that these devices suffer from slow carrier extraction, resulting in significant bimolecular recombination losses. Therefore, this study highlights the importance of high charge carrier mobility for newly synthesized acceptor materials, in addition to having suitable energy levels. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcc.7b02288 SN - 1932-7447 VL - 121 SP - 10305 EP - 10316 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Benduhn, Johannes A1 - Tvingstedt, Kristofer A1 - Piersimoni, Fortunato A1 - Ullbrich, Sascha A1 - Fan, Yeli A1 - Tropiano, Manuel A1 - McGarry, Kathryn A. A1 - Zeika, Olaf A1 - Riede, Moritz K. A1 - Douglas, Christopher J. A1 - Barlow, Stephen A1 - Marder, Seth R. A1 - Neher, Dieter A1 - Spoltore, Donato A1 - Vandewal, Koen T1 - Intrinsic non-radiative voltage losses in fullerene-based organic solar cells JF - Nature Energy N2 - Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to (1.45-1.65) eV, that is, (0.2-0.3) eV higher than for technologies with minimized non-radiative voltage losses. Y1 - 2017 U6 - https://doi.org/10.1038/nenergy.2017.53 SN - 2058-7546 VL - 2 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Hofacker, Andreas A1 - Neher, Dieter T1 - Dispersive and steady-state recombination in organic disordered semiconductors JF - Physical review : B, Condensed matter and materials physics N2 - Charge carrier recombination in organic disordered semiconductors is strongly influenced by the thermalization of charge carriers in the density of states (DOS). Measurements of recombination dynamics, conducted under transient or steady-state conditions, can easily be misinterpreted when a detailed understanding of the interplay of thermalization and recombination is missing. To enable adequate measurement analysis, we solve the multiple-trapping problem for recombining charge carriers and analyze it in the transient and steady excitation paradigm for different DOS distributions. We show that recombination rates measured after pulsed excitation are inherently time dependent since recombination gradually slows down as carriers relax in the DOS. When measuring the recombination order after pulsed excitation, this leads to an apparent high-order recombination at short times. As times goes on, the recombination order approaches an asymptotic value. For the Gaussian and the exponential DOS distributions, this asymptotic value equals the recombination order of the equilibrated system under steady excitation. For a more general DOS distribution, the recombination order can also depend on the carrier density, under both transient and steady-state conditions. We conclude that transient experiments can provide rich information about recombination in and out of equilibrium and the underlying DOS occupation provided that consistent modeling of the system is performed. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.245204 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Mechau, Norman A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Molecular tracer diffusion in thin azobenzene polymer layers JF - Applied physics letters N2 - Translational diffusion of fluorescent tracer molecules in azobenzene polymer layers is studied at different temperatures and under illumination using the method of fluorescence recovery after photobleaching. Diffusion is clearly observed in the dark above the glass transition temperature, while homogeneous illumination at 488 nm and 100 mW/cm(2) does not cause any detectable diffusion of the dye molecules within azobenzene layers. This implies that the viscosity of azobenzene layers remains nearly unchanged under illumination with visible light in the absence of internal or external forces. (c) 2006 American Institute of Physics. Y1 - 2006 U6 - https://doi.org/10.1063/1.2405853 SN - 0003-6951 VL - 89 IS - 25 PB - Elsevier CY - Melville ER - TY - JOUR A1 - Alqahtani, Obaid A1 - Babics, Maxime A1 - Gorenflot, Julien A1 - Savikhin, Victoria A1 - Ferron, Thomas A1 - Balawi, Ahmed H. A1 - Paulke, Andreas A1 - Kan, Zhipeng A1 - Pope, Michael A1 - Clulow, Andrew J. A1 - Wolf, Jannic A1 - Burn, Paul L. A1 - Gentle, Ian R. A1 - Neher, Dieter A1 - Toney, Michael F. A1 - Laquai, Frederic A1 - Beaujuge, Pierre M. A1 - Collins, Brian A. T1 - Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors JF - Advanced energy materials N2 - The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)(2), namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes. KW - charge transport KW - domain purity KW - microscopy KW - mixed domains KW - organic solar cells KW - photovoltaic devices KW - resonant X-ray scattering KW - small molecules KW - transient spectroscopy Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201702941 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 19 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Liu, Ji-Cai A1 - Ignatova, Nina A1 - Kimberg, Victor A1 - Krasnov, Pavel A1 - Föhlisch, Alexander A1 - Simon, Marc A1 - Gel'mukhanov, Faris T1 - Time-resolved study of recoil-induced rotation by X-ray pump - X-ray probe spectroscopy JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Modern stationary X-ray spectroscopy is unable to resolve rotational structure. In the present paper, we propose to use time-resolved two color X-ray pump-probe spectroscopy with picosecond resolution for real-time monitoring of the rotational dynamics induced by the recoil effect. The proposed technique consists of two steps. The first short pump X-ray pulse ionizes the valence electron, which transfers angular momentum to the molecule. The second time-delayed short probe X-ray pulse resonantly excites a 1s electron to the created valence hole. Due to the recoil-induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core-excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X-ray absorption as a function of the delay time between the pulses. We developed an accurate theory of the X-ray pump-probe spectroscopy of the recoil-induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time-dependent X-ray absorption using the CO molecule as a case-study. We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamics. Y1 - 2022 U6 - https://doi.org/10.1039/d1cp05000a SN - 1463-9076 SN - 1463-9084 VL - 24 IS - 11 SP - 6627 EP - 6638 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Voroshnin, Vladimir A1 - Tarasov, Artem V. A1 - Bokai, Kirill A. A1 - Chikina, Alla A1 - Senkovskiy, Boris V. A1 - Ehlen, Niels A1 - Usachov, Dmitry Yu. A1 - Gruneis, Alexander A1 - Krivenkov, Maxim A1 - Sanchez-Barriga, Jaime A1 - Fedorov, Alexander T1 - Direct spectroscopic evidence of magnetic proximity effect in MoS2 monolayer on graphene/Co JF - ACS nano N2 - A magnetic field modifies optical properties and provides valley splitting in a molybdenum disulfide (MoS2) monolayer. Here we demonstrate a scalable approach to the epitaxial synthesis of MoS2 monolayer on a magnetic graphene/Co system. Using spin- and angle-resolved photoemission spectroscopy we observe a magnetic proximity effect that causes a 20 meV spin-splitting at the (Gamma) over bar point and canting of spins at the (K) over bar point in the valence band toward the in-plane direction of cobalt magnetization. Our density functional theory calculations reveal that the in-plane spin component at (K) over bar is localized on Co atoms in the valence band, while in the conduction band it is localized on the MoS2 layer. The calculations also predict a 16 meV spin-splitting at the (Gamma) over bar point and 8 meV (K) over bar-(K) over bar' valley asymmetry for an out-of-plane magnetization. These findings suggest control over optical transitions in MoS2 via Co magnetization. Our estimations show that the magnetic proximity effect is equivalent to the action of the magnetic field as large as 100 T. KW - magnetic proximity effect KW - MoS2 KW - monolayer KW - graphene KW - spin-resolved KW - ARPES Y1 - 2022 U6 - https://doi.org/10.1021/acsnano.1c10391 SN - 1936-0851 SN - 1936-086X VL - 16 IS - 5 SP - 7448 EP - 7456 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Abiuso, Paolo A1 - Holubec, Viktor A1 - Anders, Janet A1 - Ye, Zhuolin A1 - Cerisola, Federico A1 - Perarnau-Llobet, Marti T1 - Thermodynamics and optimal protocols of multidimensional quadratic Brownian systems JF - Journal of physics communications N2 - We characterize finite-time thermodynamic processes of multidimensional quadratic overdamped systems. Analytic expressions are provided for heat, work, and dissipation for any evolution of the system covariance matrix. The Bures-Wasserstein metric between covariance matrices naturally emerges as the local quantifier of dissipation. General principles of how to apply these geometric tools to identify optimal protocols are discussed. Focusing on the relevant slow-driving limit, we show how these results can be used to analyze cases in which the experimental control over the system is partial. KW - stochastic thermodynamics KW - thermodynamic control KW - thermodynamic length KW - overdamped brownian systems Y1 - 2022 U6 - https://doi.org/10.1088/2399-6528/ac72f8 SN - 2399-6528 VL - 6 IS - 6 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Stojkoski, Viktor A1 - Sandev, Trifce A1 - Kocarev, Ljupco A1 - Pal, Arnab T1 - Autocorrelation functions and ergodicity in diffusion with stochastic resetting JF - Journal of physics : A, Mathematical and theoretical N2 - Diffusion with stochastic resetting is a paradigm of resetting processes. Standard renewal or master equation approach are typically used to study steady state and other transport properties such as average, mean squared displacement etc. What remains less explored is the two time point correlation functions whose evaluation is often daunting since it requires the implementation of the exact time dependent probability density functions of the resetting processes which are unknown for most of the problems. We adopt a different approach that allows us to write a stochastic solution for a single trajectory undergoing resetting. Moments and the autocorrelation functions between any two times along the trajectory can then be computed directly using the laws of total expectation. Estimation of autocorrelation functions turns out to be pivotal for investigating the ergodic properties of various observables for this canonical model. In particular, we investigate two observables (i) sample mean which is widely used in economics and (ii) time-averaged-mean-squared-displacement (TAMSD) which is of acute interest in physics. We find that both diffusion and drift-diffusion processes with resetting are ergodic at the mean level unlike their reset-free counterparts. In contrast, resetting renders ergodicity breaking in the TAMSD while both the stochastic processes are ergodic when resetting is absent. We quantify these behaviors with detailed analytical study and corroborate with extensive numerical simulations. Our results can be verified in experimental set-ups that can track single particle trajectories and thus have strong implications in understanding the physics of resetting. KW - autocorrelations KW - ergodicity KW - diffusion KW - stochastic resetting Y1 - 2022 U6 - https://doi.org/10.1088/1751-8121/ac4ce9 SN - 1751-8113 SN - 1751-8121 VL - 55 IS - 10 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kühn, Danilo A1 - Müller, Moritz A1 - Sorgenfrei, Nomi A1 - Giangrisostomi, Erika A1 - Jay, Raphael Martin A1 - Ovsyannikov, Ruslan A1 - Martensson, Nils A1 - Sanchez-Portal, Daniel A1 - Föhlisch, Alexander T1 - Directional sub-femtosecond charge transfer dynamics and the dimensionality of 1T-TaS2 JF - Scientific reports N2 - For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in-and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves. Y1 - 2019 U6 - https://doi.org/10.1038/s41598-018-36637-0 SN - 2045-2322 VL - 9 IS - 488 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Giangrisostomi, Erika A1 - Ovsyannikov, Ruslan A1 - Sorgenfrei, Nomi A1 - Zhang, Teng A1 - Lindblad, Andreas A1 - Sassa, Yasmine A1 - Cappel, Ute B. A1 - Leitner, Torsten A1 - Mitzner, Rolf A1 - Svensson, Svante A1 - Martensson, Nils A1 - Föhlisch, Alexander T1 - Low Dose Photoelectron Spectroscopy at BESSY II BT - electronic structure of matter in its native state JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - The implementation of a high-transmission, angular-resolved time-of-Right electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances. Y1 - 2018 U6 - https://doi.org/10.1016/j.elspec.2017.05.011 SN - 0368-2048 SN - 1873-2526 VL - 224 SP - 68 EP - 78 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Pontius, Niko A1 - Beye, Martin A1 - Trabant, Christoph A1 - Mitzner, Rolf A1 - Sorgenfrei, Nomi A1 - Kachel, Torsten A1 - Woestmann, Michael A1 - Roling, Sebastian A1 - Zacharias, Helmut A1 - Ivanov, Rosen A1 - Treusch, Rolf A1 - Buchholz, Marcel A1 - Metcalf, Pete A1 - Schuessler-Langeheine, Christian A1 - Föhlisch, Alexander T1 - Probing the non-equilibrium transient state in magnetite by a jitter-free two-color X-ray pump and X-ray probe experiment JF - Structural dynamics N2 - We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 +/- 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices. (C) 2018 Author(s). Y1 - 2018 U6 - https://doi.org/10.1063/1.5042847 SN - 2329-7778 VL - 5 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Kühn, Danilo A1 - Giangrisostomi, Erika A1 - Jay, Raphael Martin A1 - Sorgenfrei, Nomi A1 - Föhlisch, Alexander T1 - The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission JF - New journal of physics : the open-access journal for physics N2 - Pump-probe photoelectron spectroscopy (PES) is a versatile tool to investigate the dynamics of transient states of excited matter. Vacuum space-charge effects can mask these dynamics and complicate the interpretation of electron spectra. Here we report on space-charge effects in Au 4f photoemission from a polycrystalline gold surface, excited with moderately intense 90 ps (FWHM) soft x-ray probe pulses, under the influence of the Coulomb forces exerted by a pump electron cloud, which was produced by intense 40 fs laser pulses. The experimentally observed kinetic energy shift and spectral broadening of the Au 4f lines, measured with highly-efficient time-of-flight spectroscopy, are in good agreement with simulations utilizing a mean-field model of the electrostatic pump electron potential. This confirms that the line broadening is predominantly caused by variations in the take-off time of the probe electrons without appreciable influence of local scattering events. Our findings might be of general interest for pump-probe PES with picosecond-pulse-length sources. KW - space-charge effects KW - mean-field model KW - x-ray photoemission KW - electron spectroscopy KW - pump-probe KW - ARTOF Y1 - 2019 U6 - https://doi.org/10.1088/1367-2630/ab2f5c SN - 1367-2630 VL - 21 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Li, Tian-yi A1 - Benduhn, Johannes A1 - Li, Yue A1 - Jaiser, Frank A1 - Spoltore, Donato A1 - Zeika, Olaf A1 - Ma, Zaifei A1 - Neher, Dieter A1 - Vandewal, Koen A1 - Leo, Karl T1 - Boron dipyrromethene (BODIPY) with meso-perfluorinated alkyl substituents as near infrared donors in organic solar cells JF - Journal of materials chemistry : A, Materials for energy and sustainability N2 - Three furan-fused BODIPYs were synthesized with perfluorinated methyl, ethyl and n-propyl groups on the meso-carbon. They were obtained with high yields by reacting the furan-fused 2-carboxylpyrrole in corresponding perfluorinated acid and anhydride. With the increase in perfluorinated alkyl chain length, the molecular packing in the single crystal is influenced, showing increasing stacking distance and decreasing slope angle. All the BODIPYs were characterized as intense absorbers in near infrared region in solid state, peaking at similar to 800 nm with absorption coefficient of over 280 000 cm(-1). Facilitated by high thermal stability, the furan-fused BODIPYs were employed in vacuum-deposited organic solar cells as electron donors. All devices exhibit PCE over 6.0% with the EQE maximum reaching 70% at similar to 790 nm. The chemical modification of the BODIPY donors have certain influence on the active layer morphology, and the highest PCE of 6.4% was obtained with a notably high jsc of 13.6 mA cm(-2). Sensitive EQE and electroluminance studies indicated that the energy losses generated by the formation of a charge transfer state and the radiative recombination at the donor-acceptor interface were comparable in the range of 0.14-0.19 V, while non-radiative recombination energy loss of 0.38 V was the main energy loss route resulting in the moderate V-oc of 0.76 V. Y1 - 2018 U6 - https://doi.org/10.1039/c8ta06261g SN - 2050-7488 SN - 2050-7496 VL - 6 IS - 38 SP - 18583 EP - 18591 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Thünemann, Andreas F. A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Undulated Gold Nanoplatelet Superstructures BT - In Situ Growth of Hemispherical Gold Nanoparticles onto the Surface of Gold Nanotriangles JF - Langmuir N2 - Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor. Y1 - 2018 U6 - https://doi.org/10.1021/acs.langmuir.7b02898 SN - 0743-7463 VL - 34 IS - 15 SP - 4584 EP - 4594 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Tchoumba Kwamen, Christelle Larodia A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Alexe, Marin A1 - Bargheer, Matias T1 - Time-resolved X-ray diffraction study of the structural dynamics in an epitaxial ferroelectric thin Pb(Zr0.2Ti0.8)O-3 film induced by sub-coercive fields JF - Applied physics letters N2 - The electric field-dependence of structural dynamics in a tetragonal ferroelectric lead zirconate titanate thin film is investigated under subcoercive and above-coercive fields using time-resolved X-ray diffraction. The domain nucleation and growth are monitored in real time during the application of an external field to the prepoled thin film capacitor. We propose the observed broadening of the in-plane peak width of the symmetric 002 Bragg reflection as an indicator of the domain disorder and discuss the processes that change the measured peak intensity. Subcoercive field switching results in remnant disordered domain configurations. Published under license by AIP Publishing. Y1 - 2019 U6 - https://doi.org/10.1063/1.5084104 SN - 0003-6951 SN - 1077-3118 VL - 114 IS - 16 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Stete, Felix A1 - Koopman, Wouter-Willem Adriaan A1 - Bargheer, Matias T1 - Signatures of strong coupling on nanoparticles BT - revealing absorption anticrossing by tuning the dielectric environment JF - ACS Photonics N2 - In the strong coupling regime, exciton and plasmon excitations are hybridized into combined system excitations. The correct identification of the coupling regime in these systems is currently debated, from both experimental and theoretical perspectives. In this article we show that the extinction spectra may show a large peak splitting, although the energy loss encoded in the absorption spectra clearly rules out the strong coupling regime. We investigate the coupling of J-aggregate excitons to the localized surface plasmon polaritons on gold nanospheres and nanorods by fine-tuning the plasmon resonance via layer-by-layer deposition of polyelectrolytes. While both structures show a characteristic anticrossing in extinction and scattering experiments, the careful assessment of the systems’ light absorption reveals that strong coupling of the plasmon to the exciton is not present in the nanosphere system. In a phenomenological model of two classical coupled oscillators, a Fano-like regime causes only the resonance of the light-driven oscillator to split up, while the other one still dissipates energy at its original frequency. Only in the strong-coupling limit do both oscillators split up the frequencies at which they dissipate energy, qualitatively explaining our experimental finding. KW - hybrid nanoparticles KW - exciton plasmon coupling KW - layer-by-layer deposition KW - strong coupling KW - absorption measurements Y1 - 2017 U6 - https://doi.org/10.1021/acsphotonics.7b00113 SN - 2330-4022 VL - 4 SP - 1669 EP - 1676 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Laskin, Gennadii A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3 JF - Structural dynamics N2 - We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Grüneisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime. KW - Thin films KW - Thermodynamic properties KW - Bragg peak KW - Ultrafast X-ray diffraction KW - Thermal effects KW - Phonons KW - Magnetism KW - Lattice dynamics KW - Lasers KW - Perovskites Y1 - 2020 U6 - https://doi.org/10.1063/4.0000072 SN - 2329-7778 VL - 8 IS - 2 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Zeuschner, Steffen Peer A1 - Wang, Xi-Guang A1 - Deb, Marwan A1 - Popova, Elena A1 - Malinowski, Gregory A1 - Hehn, Michel A1 - Keller, Niels A1 - Berakdar, Jamal A1 - Bargheer, Matias T1 - Standing spin wave excitation in Bi BT - YIG films via temperature-induced anisotropy changes and magneto-elastic coupling JF - Physical review : B, Condensed matter and materials physics N2 - Based on micromagnetic simulations and experimental observations of the magnetization and lattice dynamics after the direct optical excitation of the magnetic insulator Bi : YIG or indirect excitation via an optically opaque Pt/Cu double layer, we disentangle the dynamical effects of magnetic anisotropy and magneto-elastic coupling. The strain and temperature of the lattice are quantified via modeling ultrafast x-ray diffraction data. Measurements of the time-resolved magneto-optical Kerr effect agree well with the magnetization dynamics simulated according to the excitation via two mechanisms: the magneto-elastic coupling to the experimentally verified strain dynamics and the ultrafast temperature-induced transient change in the magnetic anisotropy. The numerical modeling proves that, for direct excitation, both mechanisms drive the fundamental mode with opposite phase. The relative ratio of standing spin wave amplitudes of higher-order modes indicates that both mechanisms are substantially active. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevB.106.134401 SN - 2469-9950 SN - 2469-9969 VL - 106 IS - 13 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Liebig, Ferenc A1 - Henning, Ricky A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - A new route to gold nanoflowers JF - Nanotechnology N2 - Catanionic vesicles spontaneously formed by mixing the anionic surfactant bis(2-ethylhexyl)sulfosuccinate sodium salt with the cationic surfactant cetyltrimethylammonium bromide were used as a reducing medium to produce gold clusters, which are embedded and well-ordered into the template phase. The gold clusters can be used as seeds in the growth process that follows by adding ascorbic acid as a mild reducing component. When the ascorbic acid was added very slowly in an ice bath round-edged gold nanoflowers were produced. When the same experiments were performed at room temperature in the presence of Ag+ ions, sharp-edged nanoflowers could be synthesized. The mechanism of nanoparticle formation can be understood to be a non-diffusion-limited Ostwald ripening process of preordered gold nanoparticles embedded in catanionic vesicle fragments. Surface-enhanced Raman scattering experiments show an excellent enhancement factor of 1.7 . 10(5) for the nanoflowers deposited on a silicon wafer. KW - catanionic vesicles KW - gold cluster KW - gold nanoflowers KW - crystal growth KW - HRTEM KW - SEM Y1 - 2018 U6 - https://doi.org/10.1088/1361-6528/aaaffd SN - 0957-4484 SN - 1361-6528 VL - 29 IS - 18 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - Sander, M. A1 - Bauer, R. A1 - Bargheer, Matias A1 - Herzog, Marc A1 - Gaál, Peter T1 - Full Spatiotemporal Control of Laser-Excited Periodic Surface Deformations JF - Physical review applied N2 - We demonstrate full control of acoustic and thermal periodic deformations at solid surfaces down to subnanosecond time scales and few-micrometer length scales via independent variation of the temporal and spatial phase of two optical transient grating (TG) excitations. For this purpose, we introduce an experimental setup that exerts control of the spatial phase of subsequent time-delayed TG excitations depending on their polarization state. Specific exemplary coherent control cases are discussed theoretically and corresponding experimental data are presented in which time-resolved x-ray reflectivity measures the spatiotemporal surface distortion of nanolayered heterostructures. Finally, we discuss examples where the application of our method may enable the control of functional material properties via tailored spatiotemporal strain fields. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.12.024036 SN - 2331-7019 VL - 12 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Stete, Felix A1 - Schossau, Phillip A1 - Bargheer, Matias A1 - Koopman, Wouter-Willem Adriaan T1 - Size-Dependent coupling of Hybrid Core-Shell Nanorods BT - Toward Single-Emitter Strong-Coupling JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Owing to their ability of concentrating electromagnetic fields to subwavelength mode volumes, plasmonic nanoparticles foster extremely high light-matter coupling strengths reaching far into the strong-coupling regime of light matter interaction. In this article, we present an experimental investigation on the dependence of coupling strength on the geometrical size of the nanoparticle. The coupling strength for differently sized hybrid plasmon-core exciton-shell nanorods was extracted from the typical resonance anticrossing of these systems, obtained by controlled modification of the environment permittivity using layer-by-layer deposition of polyelectrolytes. The observed size dependence of the coupling strength can be explained by a simple model approximating the electromagnetic mode volume by the geometrical volume of the particle. On the basis of this model, the coupling strength for particles of arbitrary size can be predicted, including the particle size necessary to support single-emitter strong coupling. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcc.8b04204 SN - 1932-7447 VL - 122 IS - 31 SP - 17976 EP - 17982 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Grothusheitkamp, Daniela A1 - Kunz, Thomas A1 - Methner, Frank-Jürgen T1 - Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry JF - Journal of mass spectrometr N2 - The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS. KW - APCI KW - fungus KW - gas chromatography KW - ion mobility spectrometry KW - mass KW - spectrometry KW - mold KW - soft X-ray Y1 - 2020 U6 - https://doi.org/10.1002/jms.4501 SN - 1076-5174 SN - 1096-9888 VL - 55 IS - 5 SP - 1 EP - 10 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Pranav, Manasi A1 - Hultzsch, Thomas A1 - Musiienko, Artem A1 - Sun, Bowen A1 - Shukla, Atul A1 - Jaiser, Frank A1 - Shoaee, Safa A1 - Neher, Dieter T1 - Anticorrelated photoluminescence and free charge generation proves field-assisted exciton dissociation in low-offset PM6:Y5 organic solar cells JF - APL materials : high impact open access journal in functional materials science N2 - Understanding the origin of inefficient photocurrent generation in organic solar cells with low energy offset remains key to realizing high-performance donor-acceptor systems. Here, we probe the origin of field-dependent free-charge generation and photoluminescence in wnon-fullereneacceptor (NFA)-based organic solar cells using the polymer PM6 and the NFA Y5-a non-halogenated sibling to Y6, with a smaller energetic offset to PM6. By performing time-delayed collection field (TDCF) measurements on a variety of samples with different electron transport layers and active layer thickness, we show that the fill factor and photocurrent are limited by field-dependent free charge generation in the bulk of the blend. We also introduce a new method of TDCF called m-TDCF to prove the absence of artifacts from non-geminate recombination of photogenerated and dark charge carriers near the electrodes. We then correlate free charge generation with steady-state photoluminescence intensity and find perfect anticorrelation between these two properties. Through this, we conclude that photocurrent generation in this low-offset system is entirely controlled by the field-dependent dissociation of local excitons into charge-transfer states. (c) 2023 Author(s). Y1 - 2023 U6 - https://doi.org/10.1063/5.0151580 SN - 2166-532X VL - 11 IS - 6 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Hovhannisyan, Karen V. A1 - Nemati, Somayyeh A1 - Henkel, Carsten A1 - Anders, Janet T1 - Long-time equilibration can determine transient thermality JF - PRX Quantum N2 - When two initially thermal many-body systems start to interact strongly, their transient states quickly become non-Gibbsian, even if the systems eventually equilibrate. To see beyond this apparent lack of structure during the transient regime, we use a refined notion of thermality, which we call g-local. A system is g-locally thermal if the states of all its small subsystems are marginals of global thermal states. We numerically demonstrate for two harmonic lattices that whenever the total system equilibrates in the long run, each lattice remains g-locally thermal at all times, including the transient regime. This is true even when the lattices have long-range interactions within them. In all cases, we find that the equilibrium is described by the generalized Gibbs ensemble, with three-dimensional lattices requiring special treatment due to their extended set of conserved charges. We compare our findings with the well-known two-temperature model. While its standard form is not valid beyond weak coupling, we show that at strong coupling it can be partially salvaged by adopting the concept of a g-local temperature. Y1 - 2023 U6 - https://doi.org/10.1103/PRXQuantum.4.030321 SN - 2691-3399 VL - 4 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Chen, Junchao A1 - Lange, Thomas A1 - Andjelkovic, Milos A1 - Simevski, Aleksandar A1 - Krstić, Miloš T1 - Prediction of solar particle events with SRAM-based soft error rate monitor and supervised machine learning JF - Microelectronics reliability N2 - This work introduces an embedded approach for the prediction of Solar Particle Events (SPEs) in space applications by combining the real-time Soft Error Rate (SER) measurement with SRAM-based detector and the offline trained machine learning model. The proposed approach is intended for the self-adaptive fault-tolerant multiprocessing systems employed in space applications. With respect to the state-of-the-art, our solution allows for predicting the SER 1 h in advance and fine-grained hourly tracking of SER variations during SPEs as well as under normal conditions. Therefore, the target system can activate the appropriate mechanisms for radiation hardening before the onset of high radiation levels. Based on the comparison of five different machine learning algorithms trained with the public space flux database, the preliminary results indicate that the best prediction accuracy is achieved with the recurrent neural network (RNN) with long short-term memory (LSTM). Y1 - 2020 U6 - https://doi.org/10.1016/j.microrel.2020.113799 SN - 0026-2714 VL - 114 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Davidzon, Iary A1 - Ilbert, Olivier A1 - Faisst, Andreas L. A1 - Sparre, Martin A1 - Capak, Peter L. T1 - An Alternate Approach to Measure Specific Star Formation Rates at 2 < z < 7 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We trace the specific star formation rate (sSFR) of massive star-forming galaxies (greater than or similar to 10(10)M(circle dot)) from z similar to 2 to 7. Our method is substantially different from previous analyses, as it does not rely on direct estimates of star formation rate, but on the differential evolution of the galaxy stellar mass function (SMF). We show the reliability of this approach by means of semianalytical and hydrodynamical cosmological simulations. We then apply it to real data, using the SMFs derived in the COSMOS and CANDELS fields. We find that the sSFR is proportional to (1 + z)(1.1) (+/-) (0.2) at z > 2, in agreement with other observations but in tension with the steeper evolution predicted by simulations from z similar to 4 to 2. We investigate the impact of several sources of observational bias, which, however, cannot account for this discrepancy. Although the SMF of high-redshift galaxies is still affected by significant errors, we show that future large-area surveys will substantially reduce them, making our method an effective tool to probe the massive end of the main sequence of star-forming galaxies. KW - galaxies: evolution KW - galaxies: high-redshift KW - galaxies: star formation Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aaa19e SN - 0004-637X SN - 1538-4357 VL - 852 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Padash, Amin A1 - Aghion, Erez A1 - Schulz, Alexander A1 - Barkai, Eli A1 - Chechkin, Aleksei V. A1 - Metzler, Ralf A1 - Kantz, Holger T1 - Local equilibrium properties of ultraslow diffusion in the Sinai model JF - New journal of physics N2 - We perform numerical studies of a thermally driven, overdamped particle in a random quenched force field, known as the Sinai model. We compare the unbounded motion on an infinite 1-dimensional domain to the motion in bounded domains with reflecting boundaries and show that the unbounded motion is at every time close to the equilibrium state of a finite system of growing size. This is due to time scale separation: inside wells of the random potential, there is relatively fast equilibration, while the motion across major potential barriers is ultraslow. Quantities studied by us are the time dependent mean squared displacement, the time dependent mean energy of an ensemble of particles, and the time dependent entropy of the probability distribution. Using a very fast numerical algorithm, we can explore times up top 10(17) steps and thereby also study finite-time crossover phenomena. KW - Sinai diffusion KW - clustering KW - local equilibrium Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/ac7df8 SN - 1367-2630 VL - 24 IS - 7 PB - IOP Publishing CY - Bristol ER - TY - JOUR A1 - McKenna, Russell A1 - Pfenninger, Stefan A1 - Heinrichs, Heidi A1 - Schmidt, Johannes A1 - Staffell, Iain A1 - Bauer, Christian A1 - Gruber, Katharina A1 - Hahmann, Andrea N. A1 - Jansen, Malte A1 - Klingler, Michael A1 - Landwehr, Natascha A1 - Larsén, Xiaoli Guo A1 - Lilliestam, Johan A1 - Pickering, Bryn A1 - Robinius, Martin A1 - Tröndle, Tim A1 - Turkovska, Olga A1 - Wehrle, Sebastian A1 - Weinand, Jann Michael A1 - Wohland, Jan T1 - High-resolution large-scale onshore wind energy assessments BT - a review of potential definitions, methodologies and future research needs JF - Renewable energy N2 - The rapid uptake of renewable energy technologies in recent decades has increased the demand of energy researchers, policymakers and energy planners for reliable data on the spatial distribution of their costs and potentials. For onshore wind energy this has resulted in an active research field devoted to analysing these resources for regions, countries or globally. A particular thread of this research attempts to go beyond purely technical or spatial restrictions and determine the realistic, feasible or actual potential for wind energy. Motivated by these developments, this paper reviews methods and assumptions for analysing geographical, technical, economic and, finally, feasible onshore wind potentials. We address each of these potentials in turn, including aspects related to land eligibility criteria, energy meteorology, and technical developments of wind turbine characteristics such as power density, specific rotor power and spacing aspects. Economic aspects of potential assessments are central to future deployment and are discussed on a turbine and system level covering levelized costs depending on locations, and the system integration costs which are often overlooked in such analyses. Non-technical approaches include scenicness assessments of the landscape, constraints due to regulation or public opposition, expert and stakeholder workshops, willingness to pay/accept elicitations and socioeconomic cost-benefit studies. For each of these different potential estimations, the state of the art is critically discussed, with an attempt to derive best practice recommendations and highlight avenues for future research. KW - onshore wind KW - resource assessments KW - social acceptance KW - planning constraints KW - research priorities Y1 - 2022 U6 - https://doi.org/10.1016/j.renene.2021.10.027 SN - 0960-1481 VL - 182 SP - 659 EP - 684 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre BT - simple means to characterize the electron distribution of carbenes JF - Magnetic resonance in chemistry N2 - Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures). KW - C-13 chemical shift KW - carbenes KW - zwitterions KW - carbene electron deficiency KW - nucleus-independent chemical shifts (NICS) KW - through space NMR shieldings KW - (TSNMRS) Y1 - 2019 U6 - https://doi.org/10.1002/mrc.4979 SN - 0749-1581 SN - 1097-458X VL - 58 IS - 3 SP - 280 EP - 292 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Quantification of sigma-acceptor and pi-donor stabilization in O, S and Hal analogues of N-heterocyclic carbenes (NHCs) on the magnetic criterion JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (NHCs) have been calculated using the GIAO perturbation method employing the nucleus-independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes <-> ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and C-13 chemical shifts of the electron-deficient carbon centers. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpca.1c05257 SN - 1089-5639 SN - 1520-5215 VL - 125 IS - 33 SP - 7235 EP - 7245 PB - American Chemical Society CY - Washington ER -