Peer-reviewed publications by year


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2021

Schematic of the laser pump--x-ray probe experiment on a thin SRO film and measured transient SRO strain below and above the magnetic phase transition.
Image: Maximilian Mattern

Mattern M., Pudell J.-E., Laskin G., von Reppert A., and Bargheer M.

Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3

Structural Dynamics 8, 024302 (2021).

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.

Schematic of the laser pump--x-ray probe experiment on a thin SRO film and measured transient SRO strain below and above the magnetic phase transition.
Image: Maximilian Mattern

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Layout of the KMC-3 XPP beamline
Image: Matthias Rössle

Rössle M., Leitenberger W., Reinhardt M., Koç A., Pudell J.-E., Kwamen C., and Bargheer M.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II

Journal of Synchrotron Radiation 28, 1 (2021).

The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.

Layout of the KMC-3 XPP beamline
Image: Matthias Rössle

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Sketch of the UXRD configuration with pump and probe pulses and external magnetic field perpendicular to the film
Image: Marwan Deb

Deb M., Popova E., Zeuschner S. P., Leitenberger W., Keller N., Rössle M., and Bargheer M.

Ultrafast control of lattice strain via magnetic circular dichroism

Physical Review B 103, 064301 (2021).

Using ultrafast x-ray diffraction, we directly monitor the lattice dynamics induced by femtosecond laser pulses in nanoscale thin films of bismuth iron garnet in external magnetic fields H_ext . We control the ultrafast laserinduced lattice strain amplitude by changing the laser pulse helicity. The strength of H_ext is used as an external parameter to switch the helicity dependence on and off, respectively. Based on magneto-optical spectroscopic measurements, we explain these phenomena by magnetic circular dichroism. Our findings highlight an important approach for ultrafast manipulation of lattice strain in magnetic materials, in particular insulators, and open exciting perspectives towards ultrafast control of lattice strain and heat-induced magnetization switching and spin waves in bismuth-substituted iron garnets using the polarization of light.
 

Sketch of the UXRD configuration with pump and probe pulses and external magnetic field perpendicular to the film
Image: Marwan Deb

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Layout of NanoGate setup
Image: Peter Gaal

Schmidt D., Bauer R., Chung S., Novikov D., Sander M., Pudell J.-E., Herzog M., Pfuetzenreuter D., Schwarzkopf J., Chernikov R., and Gaal P.

A new concept for temporal gating of synchrotron X-ray pulses

Journal of Synchrotron Radiation 28 (2021).

A new concept for temporal gating of synchrotron X-ray pulses based on laser-induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of >30% and 10^(−5), respectively. The full efficiency of the pulse picker has not been reached yet due to a long-range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.

Layout of NanoGate setup
Image: Peter Gaal

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Comparison of reciprocal space mappings recorded at the XPP beamline (BESSY II) and the PXS
Image: Steffen Zeuschner

Zeuschner S. P., Mattern M., Pudell J.-E., Reppert A. v., Rössle M., Leitenberger L., Schwarzkopf J., Boschker J. E., Herzog M., and Bargheer M.

Reciprocal space slicing: A time-efficient approach to femtosecond x-ray diffraction

Structural Dynamics 8, 014302 (2021).

An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.

Comparison of reciprocal space mappings recorded at the XPP beamline (BESSY II) and the PXS
Image: Steffen Zeuschner

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Sketch of multilayer sample where laser pulses excite and probe the triggered lattice and magnetization dynamics
Image: Marwan Deb/Steffen Zeuschner

Deb M., Popova E., Zeuschner S. P., Hehn M., Keller N., Mangin S., Malinowski G., and Bargheer M.

Generation of spin waves via spin-phonon interaction in a buried dielectric thin film

Physical Review B 103, 024411 (2021).

In this paper, we investigate the magnetic, optical, and lattice responses of a Pt/Cu/Bi1Y2Fe5O12/Gd3Ga5O12 heterostructure to femtosecond laser excitation of the opaque Pt/Cu metallic bilayer. The electronic excitation generates coherent and incoherent phonons, which trigger high-frequency standing spin waves (SWs) in the dielectric Bi1Y2Fe5O12 layer via a phonon-induced change of magnetic anisotropy. We find that the incoherent phonons (heat) can induce a fast (<1ps) and slow (>1000ps) decrease of the magnetic order by different spin-phonon interaction scenarios. These results open perspectives for generating high-frequency SWs in buried magnetic garnets.

Sketch of multilayer sample where laser pulses excite and probe the triggered lattice and magnetization dynamics
Image: Marwan Deb/Steffen Zeuschner

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2020

Transient absorption spectroscopy on TDBS-coated Gold nanorods
Image: Felix Stete

Stete F., Bargheer M., Koopman W.

Optical Non-linearities in Plasmon-Exciton Core-Shell Particles: the Role of Heat

arXiv:2009.00075

Strong coupling between plasmons and excitons gives rise to new hybrid polariton states with various fields of potential applications. Despite a plethora of research on plasmon--exciton systems, their transient behaviour is not yet fully understood. Besides Rabi oscillations in the first femtoseconds after an optical excitation, coupled systems show interesting non-linear features on the picosecond time scale. Here, we conclusively show that the source of these features is heat that is generated inside the particles. Until now, this hypothesis was only based on phenomenological arguments. We investigate the role of heat by recording transient spectra of plasmon--exciton core--shell nanoparticles with excitation off the polariton resonance. We present analytical simulations that precisely recreate the measurements solely by assuming an initial temperature rise of the electron gas inside the particles. The simulations combine established strategies for describing uncoupled plasmonic particles with a recently published model for static spectra. The simulations are consistent for various excitation powers confirming that indeed heating of the particles is the root of the changes in the transient signals.

Transient absorption spectroscopy on TDBS-coated Gold nanorods
Image: Felix Stete

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Influence of strong coupling on the extinction spectra of dye moleculeson plasmonic resonators
Image: Felix Stete

Stete F., Koopman W., Henkel C., Benson O., Kewes G., and Bargheer M.

Vacuum-Induced Saturation in Plasmonic Nanoparticles

arXiv:2008.09395

Vacuum fluctuations are a fundamental feature of quantized fields. It is usually assumed that observations connected to vacuum fluctuations require a system well isolated from other influences. In this work, we demonstrate that effects of the quantum vacuum can already occur in simple colloidal nano-assemblies prepared by wet chemistry. We claim that the electromagnetic field fluctuations at the zero-point level saturate the absorption of dye molecules self-assembled at the surface of plasmonic nano-resonators. For this effect to occur, reaching the strong coupling regime between the plasmons and excitons is not required. This intriguing effect of vacuum-induced saturation (VISA) is discussed within a simple quantum optics picture and demonstrated by comparing the optical spectra of hybrid gold-core dye-shell nanorods to electromagnetic simulations.

Influence of strong coupling on the extinction spectra of dye moleculeson plasmonic resonators
Image: Felix Stete

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Plasmon-catalyzed 4NTP to DMAB dimerization at Gold nanoparticle surfaces
Image: Felix Stete

Koopman W., Sarhan R. M., Stete F., Schmitt C. N. Z., and Bargheer M.

Decoding the kinetic limitations of plasmon catalysis: the case of 4-nitrothiophenol dimerization

Nanoscale 12, 24411 (2020).

Plasmon-mediated chemistry presents an intriguing new approach to photocatalysis. However, the reaction enhancement mechanism is not well understood. In particular, the relative importance of plasmon-generated hot charges and photoheating is strongly debated. In this article, we evaluate the influence of microscopic photoheating on the kinetics of a model plasmon-catalyzed reaction: the light-induced 4-nitrothiophenol (4NTP) to 4,4′-dimercaptoazobenzene (DMAB) dimerization. Direct measurement of the reaction temperature by nanoparticle Raman-thermometry demonstrated that the thermal effect plays a dominant role in the kinetic limitations of this multistep reaction. At the same time, no reaction is possible by dark heating to the same temperature. This shows that plasmon nanoparticles have the unique ability to enhance several steps of complex tandem reactions simultaneously. These results provide insight into the role of hot electron and thermal effects in plasmonic catalysis of complex organic reactions, which is highly important for the ongoing development of plasmon based photosynthesis.

Plasmon-catalyzed 4NTP to DMAB dimerization at Gold nanoparticle surfaces
Image: Felix Stete

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Schematic of a resonant inelastic x-ray scattering (RIXS) experiment on Ta2NiSe5 and the recorded energy loss spectra
Image: Claude Monney

Monney C., Herzog M., Pulkkinen A., Huang Y., Pelliciari J., Olalde-Velasco P., Katayama N., Nohara M., Takagi H., Schmitt T., and Mizokawa T.

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

Physical Review B 102, 085148 (2020).

The transition metal chalcogenide Ta2NiSe5 undergoes a second-order phase transition at Tc=328K involving a small lattice distortion. Below Tc, a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta2NiSe5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L3 edge. In addition to a weak fluorescence response, we observe a collection of intense Raman-like peaks that we attribute to electron-hole excitations. Using density functional theory calculations of its electronic band structure, we identify the main Raman-like peaks as interband transitions between valence and conduction bands. By performing angle-dependent RIXS measurements, we uncover the dispersion of these electron-hole excitations that allows us to extract the low-energy boundary of the electron-hole continuum. From the dispersion of the valence band measured by angle-resolved photoemission spectroscopy, we derive the effective mass of the lowest unoccupied conduction band.

Schematic of a resonant inelastic x-ray scattering (RIXS) experiment on Ta2NiSe5 and the recorded energy loss spectra
Image: Claude Monney

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Artists view on the transport of hot electrons through a metal multilayer stack and the transient lattice temperature derived from the UXRD experiment
Image: Jan-Etienne Pudell

Pudell J.E., Mattern M., Hehn M., Malinowski G., Herzog M., and Bargheer M.

Heat Transport without Heating?—An Ultrafast X‐Ray Perspective into a Metal Heterostructure

Advanced Functional Materials 30, 2004555 (2020).

Rewarded as Inside Back Cover article:
Advanced Functional Materials 30, 2070304 (2020).

When the spatial dimensions of metallic heterostructures shrink below the mean free path of its conduction electrons, the transport of electrons and hence the transport of thermal energy by electrons continuously changes from diffusive to ballistic. Electron–phonon coupling sets the mean free path to the nanoscale and the time for equilibration of electron and lattice temperatures to the picosecond range. A particularly intriguing situation occurs in trilayer heterostructures combining metals with very different electron–phonon coupling strength: Heat energy deposited in few atomic layers of Pt is transported into a nanometric Ni film, which is heated more than the Cu film through which the heat is released. Femtosecond pump‐probe experiments with hard X‐ray pulses provide a layer‐specific probe of the heat energy. A purely diffusive two‐temperature model with increased thermal conductivity of hot electrons excellently reproduces the observed signals from all three layers. At the time when the Ni lattice is maximally heated, no significant heat has entered the Cu lattice. This phenomenon would be enhanced in thinner layers where ballistic transport dominates. In this context it is shown that purely diffusive transport can lead to a linear time‐to‐length dependence that must not be misinterpreted as ballistic transport.

Artists view on the transport of hot electrons through a metal multilayer stack and the transient lattice temperature derived from the UXRD experiment
Image: Jan-Etienne Pudell

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Layout of XRD probing of surface acoutic waves and the resuting satellite Bragg peaks
Image: Dmitry Roshchupkin

Roshchupkin D., Ortega L., Vadilonga S., Zizak I., Emelin E., Plotitcyna O., Thiaudière D., Leitenberger W., Formoso V., and Fettar F.

X-ray diffraction on La3Ga5SiO14 crystal modulated by SAW near the K absorption edge of Ga

Applied Physics Letters 116, 174101 (2020).

The process of x-ray diffraction on the La3Ga5SiO14 (LGS) crystal modulated by surface acoustic waves (SAWs) near the K absorption edge of Ga (E=10 367 eV) was studied. A redistribution of the diffracted x-ray intensity between the diffraction satellites occurs at the absorption edge due to the change in the x-ray penetration depth into the crystal and an effective change in the interaction of x-ray radiation with the near-surface crystal region modulated by SAW. The intensity distribution of the diffraction satellites starts to change smoothly immediately after the K absorption edge of Ga with a decrease in the x-ray penetration depth into the crystal.

Layout of XRD probing of surface acoutic waves and the resuting satellite Bragg peaks
Image: Dmitry Roshchupkin

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Sketch of the time-resolved x-ray diffraction experiment on nanogranular FePt samples
Image: Alexander von Reppert

Reppert A. v., Willig L., Pudell J.-E., Zeuschner S. P., Sellge G., Ganss F., Hellwig O., Arregi J. A., Uhlíř V., Crut A., and Bargheer M.

Spin stress contribution to the lattice dynamics of FePt

Science Advances 6, eaba1142 (2020)

Invar-behavior occurring in many magnetic materials has long been of interest to materials science. Here, we show not only invar behavior of a continuous film of FePt but also even negative thermal expansion of FePt nanograins upon equilibrium heating. Yet, both samples exhibit pronounced transient expansion upon laser heating in femtosecond x-ray diffraction experiments. We show that the granular microstructure is essential to support the contractive out-of-plane stresses originating from in-plane expansion via the Poisson effect that add to the uniaxial contractive stress driven by spin disorder. We prove the spin contribution by saturating the magnetic excitations with a first laser pulse and then detecting the purely expansive response to a second pulse. The contractive spin stress is reestablished on the same 100-ps time scale that we observe for the recovery of the ferromagnetic order. Finite-element modeling of the mechanical response of FePt nanosystems confirms the morphology dependence of the dynamics.

Sketch of the time-resolved x-ray diffraction experiment on nanogranular FePt samples
Image: Alexander von Reppert

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Schematic representing the unit cell expansion after single-photon and tw-photon absorption
Image: Steffen Zeuschner

Zeuschner S. P., Pudell J.-E., Reppert A. v., Deb M., Popova E., Keller N., Rössle M., Herzog M., and Bargheer M.

Measurement of transient strain induced by two-photon excitation

Physical Review Research 2, 022013(R) (2020).

By ultrafast x-ray diffraction we quantify the strain from coherent and incoherent phonons generated by one- and two-photon absorption. We investigated the ferrimagnetic insulator bismuth-doped yttrium iron garnet, which is a workhorse for laser-induced spin dynamics that may be excited indirectly via phonons. We identify the two-photon absorption by the quadratic intensity dependence of the transient strain and confirm a short lifetime of the intermediate state via the inverse proportional dependence on the pump-pulse duration. We determine the two-photon absorption coefficient using the linear relation between strain and absorbed energy density. For large intensities of about 1 TW/cm² considerable strain amplitudes of 0.1% are driven exclusively by two-photon absorption.

Schematic representing the unit cell expansion after single-photon and tw-photon absorption
Image: Steffen Zeuschner

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UXRD data recorded at various temperatures which evidence the generation of unconventional picosecond strain pulses
Image: Alexander von Reppert

Reppert A. v., Matter M., Pudell J.-E., Zeuschner S. P., Dumesnil K., and Bargheer M.

Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer

Structural Dynamics 7, 024303 (2020).

Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space-dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.

UXRD data recorded at various temperatures which evidence the generation of unconventional picosecond strain pulses
Image: Alexander von Reppert

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SEM images of spiked Gold nanotriangles and associated SERS spectra
Image: Radwan M. Sarhan

Liebig F., Sarhan R. M., Bargheer M., Schmitt C. N. Z., Poghosyan A. H., Shahinyan A. A., and Koetz J.

Spiked gold nanotriangles: formation, characterization and applications in surface-enhanced Raman spectroscopy and plasmon-enhanced catalysis

RCS Advances 10, 8152 (2020).

We show the formation of metallic spikes on the surface of gold nanotriangles (AuNTs) by using the same reduction process which has been used for the synthesis of gold nanostars. We confirm that silver nitrate operates as a shape-directing agent in combination with ascorbic acid as the reducing agent and investigate the mechanism by dissecting the contribution of each component, i.e., anionic surfactant dioctyl sodium sulfosuccinate (AOT), ascorbic acid (AA), and AgNO3. Molecular dynamics (MD) simulations show that AA attaches to the AOT bilayer of nanotriangles, and covers the surface of gold clusters, which is of special relevance for the spike formation process at the AuNT surface. The surface modification goes hand in hand with a change of the optical properties. The increased thickness of the triangles and a sizeable fraction of silver atoms covering the spikes lead to a blue-shift of the intense near infrared absorption of the AuNTs. The sponge-like spiky surface increases both the surface enhanced Raman scattering (SERS) cross section of the particles and the photo-catalytic activity in comparison with the unmodified triangles, which is exemplified by the plasmon-driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4′-dimercaptoazobenzene (DMAB).

SEM images of spiked Gold nanotriangles and associated SERS spectra
Image: Radwan M. Sarhan

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SEM images of differently prepared Gold nanotriangles
Image: Radwan M. Sarhan

Liebig F., Sarhan R. M., Schmitt C. N., Thünemann A., Prietzel C., Bargheer M., and Koetz J.

Gold Nanotriangles with Crumble Topping and their Influence on Catalysis and Surface-Enhanced Raman Spectroscopy

ChemPlusChem 85, 1 (2020).

By adding hyaluronic acid (HA) to dioctyl sodium sulfosuccinate (AOT)‐stabilized gold nanotriangles (AuNTs) with an average thickness of 7.5±1 nm and an edge length of about 175±17 nm, the AOT bilayer is replaced by a polymeric HA‐layer leading to biocompatible nanoplatelets. The subsequent reduction process of tetrachloroauric acid in the HA‐shell surrounding the AuNTs leads to the formation of spherical gold nanoparticles on the platelet surface. With increasing tetrachloroauric acid concentration, the decoration with gold nanoparticles can be tuned. SAXS measurements reveal an increase of the platelet thickness up to around 14.5 nm, twice the initial value of bare AuNTs. HRTEM micrographs show welding phenomena between densely packed particles on the platelet surface, leading to a crumble formation while preserving the original crystal structure. Crumbles crystallized on top of the platelets enhance the Raman signal by a factor of around 20, and intensify the plasmon‐driven dimerization of 4‐nitrothiophenol (4‐NTP) to 4,4′‐dimercaptoazobenzene in a yield of up to 50 %. The resulting crumbled nanotriangles, with a biopolymer shell and the absorption maximum in the second window for in vivo imaging, are promising candidates for biomedical sensing.

SEM images of differently prepared Gold nanotriangles
Image: Radwan M. Sarhan

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2019

Static and time-resolved MOKE data on continuous and granular FePt thin film samples
Image: Lisa Willig

Willig L., von Reppert A., Deb M., Ganss F., Hellwig O., and Bargheer M.

Finite-size effects in ultrafast remagnetization dynamics of FePt

Physical Review B 100, 224408 (2019).

We investigate the ultrafast magnetization dynamics of FePt in the L10 phase after an optical heating pulse, as used in heat-assisted magnetic recording. We compare continuous and nano-granular thin films and emphasize the impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantly with increasing external magnetic field only for the continuous film, where domain-wall motion governs the dynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transport in the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular film for all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heat transport properties in magnetic materials.

Static and time-resolved MOKE data on continuous and granular FePt thin film samples
Image: Lisa Willig

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Schematic representation of standing spin waves in Bi:YIG and their respective damping coefficients as determined from MOKE experiments
Image: Marwan Deb

Deb M., Popova E., Hehn M., Keller N., Petit-Watelot S., Bargheer M., Mangin S., Malinowski G.

Damping of Standing Spin Waves in Bismuth-Substituted Yttrium Iron Garnet as Seen via the Time-Resolved Magneto-Optical Kerr Effect

Physical Review Applied 12, 044006 (2019).

We investigate spin-wave resonance modes and their damping in insulating thin films of bismuth-substituted yttrium iron garnet by performing femtosecond magneto-optical pump-probe experiments. For large magnetic fields in the range below the magnetization saturation, we find that the damping of high-order standing spin-wave (SSW) modes is about 40 times lower than that for the fundamental one. The observed phenomenon can be explained by considering different features of magnetic anisotropy and exchange fields that, respectively, define the precession frequency for fundamental and high-order SSWs. These results provide further insight into SSWs in iron garnets and may be exploited in many new photomagnonic devices.

Schematic representation of standing spin waves in Bi:YIG and their respective damping coefficients as determined from MOKE experiments
Image: Marwan Deb

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Experimental results from time-resolved x-ray reflectivity/scattering on coherently amplified surface acoustic waves (SAW) and respective modelling
Image: Jan-Etienne Pudell

Pudell J.-E., Sander M., Bauer R., Bargheer M., Herzog M., and Gaal P.

Full Spatiotemporal Control of Laser-Excited Periodic Surface Deformations

Physical Review Applied 12, 024036 (2019).

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.

Experimental results from time-resolved x-ray reflectivity/scattering on coherently amplified surface acoustic waves (SAW) and respective modelling
Image: Jan-Etienne Pudell

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SEM image and schematic of Gold nanostars with different surfactants
Image: Radwan. M. Sarhan

Liebig F., Henning R., Sarhan R. M., Prietzel C., Schmitt C. N. Z., Bargheer M., and Koetz J.

A simple one-step procedure to synthesise gold nanostars in concentrated aqueous surfactant solutions

RSC Advances 9, 23633 (2019).

Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag+ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption.

SEM image and schematic of Gold nanostars with different surfactants
Image: Radwan. M. Sarhan

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MOKE data on standing spin waves in iron garnet at various external magnetic fields
Image: Marwan Deb

Deb M., Popova E., Hehn M., Keller N., Petit-Watelot S., Bargheer M., Mangin S., and Malinowski G.

Femtosecond Laser-Excitation-Driven High Frequency Standing Spin Waves in Nanoscale Dielectric Thin Films of Iron Garnets

Physical Review Letters 123, 027202 (2019).

We demonstrate that femtosecond laser pulses allow triggering high-frequency standing spin-wave modes in nanoscale thin films of a bismuth-substituted yttrium iron garnet. By varying the strength of the external magnetic field, we prove that two distinct branches of the dispersion relation are excited for all the modes. This is reflected in particular at a very weak magnetic field (∼33  mT) by a spin dynamics with a frequency up to 15 GHz, which is 15 times higher than the one associated with the ferromagnetic resonance mode. We argue that this phenomenon is triggered by ultrafast changes of the magnetic anisotropy via laser excitation of incoherent and coherent phonons. These findings open exciting prospects for ultrafast photo magnonics.

MOKE data on standing spin waves in iron garnet at various external magnetic fields
Image: Marwan Deb

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Schematic and experimental data of electric and XRD probing of ferroelectic devices during its switching process
Image: Christelle Kwamen

Kwamen C., Rössle M., Leitenberger W., Alexe M., and Bargheer M.

Time-resolved X-ray diffraction study of the structural dynamics in an epitaxial ferroelectric thin Pb(Zr0.2Ti0.8)O3 film induced by sub-coercive fields

Applied Physics Letters 114, 162907 (2019).

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.

Schematic and experimental data of electric and XRD probing of ferroelectic devices during its switching process
Image: Christelle Kwamen

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UXRD data with extraction of Bragg peak shifts of individual layers in a giant magnetostriction thin film sample
Image: Steffen Zeuschner

Zeuschner, S. P., Parpiiev T., Pezeril T., Hillion A., Dumesnil K., Anane A., Pudell J.-E., Willig L., Rössle M., Herzog M., Reppert A. v., and Bargheer M.

Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction

Structural Dynamics 6, 024302 (2019).

We combine ultrafast X-ray diffraction (UXRD) and time-resolved Magneto-Optical Kerr Effect (MOKE) measurements to monitor the strain pulses in laser-excited TbFe2/Nb heterostructures. Spatial separation of the Nb detection layer from the laser excitation region allows for a background-free characterization of the laser-generated strain pulses. We clearly observe symmetric bipolar strain pulses if the excited TbFe2 surface terminates the sample and a decomposition of the strain wavepacket into an asymmetric bipolar and a unipolar pulse, if a SiO2 glass capping layer covers the excited TbFe2 layer. The inverse magnetostriction of the temporally separated unipolar strain pulses in this sample leads to a MOKE signal that linearly depends on the strain pulse amplitude measured through UXRD. Linear chain model simulations accurately predict the timing and shape of UXRD and MOKE signals that are caused by the strain reflections from multiple interfaces in the heterostructure.

UXRD data with extraction of Bragg peak shifts of individual layers in a giant magnetostriction thin film sample
Image: Steffen Zeuschner

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Spatiotemporal lattice dynamics in Holmium and corresponding transient Bragg peak shifts in its paramagnetic and antiferromagnetic phases
Image: Jan-Etienne Pudell

Pudell J.-E., Reppert A. v., Schick D., Zamponi F., Rössle M., Herzog M., Zabel H., and Bargheer M.

Ultrafast negative thermal expansion driven by spin disorder

Physical Review B 99, 094304 (2019).

We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium,
and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each
layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the
exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical
penetration depth. Below the Néel temperature of Ho, the optical excitation triggers negative thermal expansion,
which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution
increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho
[Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar
strain pulse with an inverted sign traveling through the heterostructure.

Spatiotemporal lattice dynamics in Holmium and corresponding transient Bragg peak shifts in its paramagnetic and antiferromagnetic phases
Image: Jan-Etienne Pudell

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Schematic of laser-induced plasmon-driven chemistry on Gold nanotriangles coated with molecules
Image: Radwan M. Sarhan

Sarhan R. M., Koopman W., Pudell J.-E., Stete F., Rössle M., Herzog M., Schmitt C. N. Z., Liebig F., Koetz J., and Bargheer M.

Scaling up Nanoplasmon Catalysis: The Role of Heat DIssipation

The Journal of Physical Chemistry C 123, 9352 (2019).

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.

Schematic of laser-induced plasmon-driven chemistry on Gold nanotriangles coated with molecules
Image: Radwan M. Sarhan

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Schematic representation of plasmon-driven photodimerization triggered by light or heat
Image: Radwan M. Sarhan

Sarhan R. M., Koopman W., Schuetz R., Schmid T., Liebig F., Koetz J., and Bargheer M.

The importance of plasmonic heating for the plasmon-driven photodimerization of 4-nitrothiophenol

Scientific Reports 9, 3060 (2019).

Metal nanoparticles form potent nanoreactors, driven by the optical generation of energetic electrons and nanoscale heat. The relative influence of these two factors on nanoscale chemistry is strongly debated. This article discusses the temperature dependence of the dimerization of 4-nitrothiophenol (4-NTP) into 4,4′-dimercaptoazobenzene (DMAB) adsorbed on gold nanoflowers by Surface-Enhanced Raman Scattering (SERS). Raman thermometry shows a significant optical heating of the particles. The ratio of the Stokes and the anti-Stokes Raman signal moreover demonstrates that the molecular temperature during the reaction rises beyond the average crystal lattice temperature of the plasmonic particles. The product bands have an even higher temperature than reactant bands, which suggests that the reaction proceeds preferentially at thermal hot spots. In addition, kinetic measurements of the reaction during external heating of the reaction environment yield a considerable rise of the reaction rate with temperature. Despite this significant heating effects, a comparison of SERS spectra recorded after heating the sample by an external heater to spectra recorded after prolonged illumination shows that the reaction is strictly photo-driven. While in both cases the temperature increase is comparable, the dimerization occurs only in the presence of light. Intensity dependent measurements at fixed temperatures confirm this finding.

Schematic representation of plasmon-driven photodimerization triggered by light or heat
Image: Radwan M. Sarhan

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2018

The different transient strain dynamics in continuous and granular FePt thin films (top) are connected to the their different morphological constraints (bottom).
Image: Alexander von Reppert

Reppert A. v., Willig L., Pudell J.-E., Rössle M., Leitenberger W., Herzog M., Ganss F., Hellwig O., and Bargheer M.

Ultrafast laser generated strain in granular and continuous FePt thin films

Applied Physics Letters 113, 123101 (2019).

We employ ultrafast X-ray diffraction to compare the lattice dynamics of laser-excited continuous and granular FePt films on MgO (100) substrates. Contrary to recent results on free-standing granular films, we observe in both cases a pronounced and long-lasting out-of-plane expansion. We attribute this discrepancy to the in-plane expansion, which is suppressed by symmetry in continuous films. Granular films on substrates are less constrained and already show a reduced out-of-plane contraction. Via the Poisson effect, out-of-plane contractions drive in-plane expansion and vice versa. Consistently, the granular film exhibits a short-lived out-of-plane contraction driven by ultrafast demagnetization which is followed by a reduced and delayed expansion. From the acoustic reflections of the observed strain waves at the film-substrate interface, we extract a 13% reduction of the elastic constants in thin 10 nm FePt films compared to bulk-like samples.

The different transient strain dynamics in continuous and granular FePt thin films (top) are connected to the their different morphological constraints (bottom).
Image: Alexander von Reppert

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Schematic of the various energy flow channels in a Gold-Nickel bilayer sample.
Image: Jan-Etienne Pudell

Pudell J.-E., Maznev A. A., Herzog M., Kronseder M., Back C. H., Malinowski G., Reppert A. v., and Bargheer M.

Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction

Nature Communications 9, 3335 (2018).

Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron–phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities.

Schematic of the various energy flow channels in a Gold-Nickel bilayer sample.
Image: Jan-Etienne Pudell

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Dependence of extinction resonances exhibiting an "avoided crossing" on plasmon resonance energy realized by layer-ba-layer coating of the plasmonic nanoparticle.
Image: Felix Stete

Stete F., Schoßau P., Bargheer M., and Koopman W.

Size-Dependent Coupling of Hybrid Core–Shell Nanorods: Toward Single-Emitter Strong-Coupling

The Journal of Physical Chemistry C 122, 17976 (2018).

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.

Dependence of extinction resonances exhibiting an "avoided crossing" on plasmon resonance energy realized by layer-ba-layer coating of the plasmonic nanoparticle.
Image: Felix Stete

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Liebig F., Sarhan R. M., Prietzel C., Schmitt S. N. Z., Bargheer M., and Koetz J.
Tuned Surface-Enhanced Raman Scattering Performance of Undulated Au@Ag Triangles
ACS Applied Nano Materials 1, 1995 (2018).


Liebig F., Sarhan R. M., Prietzel C., Thünemann A. F., Bargheer M., and Koetz J.
Undulated Gold Nanoplatelet Superstructures: In Situ Growth of Hemispherical Gold Nanoparticles onto the Surface of Gold Nanotriangles
Langmuir 34, 4584 (2018).


Mor S., Herzog M., Noack J., Katayama N., Nohara M., Takagi H., Trunschke A., Mizokawa T., Monney C., and Stähler J.
Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta2NiSe5
Physical Revies B 97, 115154 (2018).


Liebig F., Henning R., Sarhan R. M., Prietzel C., Bargheer M., and Koetz J.
A new route to gold nanoflowers
Nanotechnology 29, 185603 (2018).

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2017

Sander M., Pudell J. -E., Herzog M., Bargheer M., Bauer R., Besse V., Temnov V., and Gaal P.
Quantitative disentanglement of coherent and incoherent laser-induced surface deformations by time-resolved x-ray reflectivity
Applied Physics Letters 111, 261903 (2017).


Kwamen C., Rössle M., Reinhardt M., Leitenberger W., Zamponi F., Alexe M., and Bargheer M.
Simultaneous dynamic characterization of charge and structural motion during ferroelectric switching
Physical Review B 96, 134105 (2017).


Lomazde N., Kopyshev A., Bargheer M., Wollgarten M., and Santer S.
Mass production of polymer nano-wires filled with metal nano-particles
Scientific Reports 7, 8506 (2017).


El Nagar G., Sarhan R. M., Ahbouserie A., Maticiuc N., Bargheer M., Lauermann I., and Roth Ch.
Efficient 3D-Silver Flower-like Microstructures for Non-Enzymatic Hydrogen Peroxide (H2O2) Amperometric Detection
Scientific Reports 7, 12181 (2017).


Mor S., Herzog M., Golez D., Werner P., Eckstein M., Katayama N., Nohara M., Takagi H., Mizokawa T., Monney C., and Stähler J.
Ultrafast Electronic Band Gap Control in an Excitonic Insulator
Physical Review Letters 119, 086401 (2017).


Stete F., Koopman W., and Bargheer M.
Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment
ACS Photonics 4, 1669 (2017).


Sander M., Herzog M., Pudell J.-E., Bargheer M., Weinkauf N., Pedersen M., Newby G., Sellmann J., Schwarzkopf J., Besse V., Temnov V. V., and Gaal P.
Spatiotemporal coherent control of thermal excitations in solids
Physical Review Letters 119, 075901 (2017).


Koc A., Reinhardt M., von Reppert A., Rössle M., Leitenberger W., Dumesnil K., Gaal P., Zamponi F., and Bargheer M.
Ultrafast X-ray Diffraction Thermometry Measures the Influence of Spin Excitations on the Heat Transport through nanolayers
Physical Review B 96, 014306 (2017).


Koc A., Reinhardt M., von Reppert A., Rössle M., Leitenberger W., Gleich M., Weinelt M., Zamponi F., and Bargheer M.
Grueneisen-approach for the experimental determination of transient spin and phonon energies from ultrafast x-ray diffraction data: gadolinium
Journal of Physics: Condensed Matter 29, 264001 (2017).


Liebig F., Sarhan R. M., Sander M., Koopman W., Schuetz R., Bargheer M., and Koetz J.
Deposition of gold nanotriangles in large scale close-packed monolayers for X-ray based temperature calibration and SERS monitoring of plasmon-driven catalytic reactions
ACS Applied Materials & Interfaces 9, 20247 (2017).

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2016

Liebig F., Sarhan R. M., Prietzel C., Reinecke A., and Koetz J.
“Green” gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering
RSC Advances 6, 33561 (2016).


Pavlenko E., Sander M., Cui Q., and Bargheer M.
Gold Nanorods Sense the Ultrafast Viscoelastic Deformation of Polymers upon Molecular Strain Actuation
The Journal of Physical Chemistry C 120, 24957 (2016).


von Reppert A., Sarhan R. M., Stete F., Pudell J.-E., Del Fatti N., Crut A., Koetz J., Liebig F., Prietzel C., and Bargheer M.
Watching the Vibration and Cooling of Ultrathin Gold Nanotriangles by Ultrafast X-ray Diffraction
The Journal of Physical Chemistry C 120, 28894 (2016).


Sander M., Koc A., Kwamen C. T., Michaels H., von Reppert A., Pudell J.-E., Zamponi F., Bargheer M., Sellmann J., Schwarzkopf J., and Gaal P.
Characterization of an ultrafast Bragg-Switch for shortening hard x-ray pulses
Journal of Applied Physics 120, 193101 (2016).


von Reppert A., Pudell J.-E., Koc A., Reinhardt M., Leitenberger W., Dumesnil K., Zamponi F., and Bargheer M.
Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet
Structural Dynamics 3, 054302 (2016).


Iurchuk V., Schick D., Bran J., Colson D., Forget A., Halley D., Koc A., Reinhardt M., Kwamen C., Morley N. A., Bargheer M., Viret M., Gumeniuk R., Schmerber G., Doudin B., and Kundys B.
Optical Writing of Magnetic Properties by Remanent Photostriction
Physical Review Letters 117, 107403 (2016).


Reinhardt M., Koc A., Leitenberger W., Gaal P., and Bargheer M.
Optimized spatial overlap in optical pump--X-ray probe experiments with high repetition rate using laser-induced surface distortions
Journal of Synchrotron Radiation 23, 474 (2016.)


Pavlenko E., Sander M., Mitzscherling S., Pudell J.-E., Zamponi F., Rössle M., Bojahr A., and Bargheer M.
Azobenzene-functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers
Nanoscale 8, 13297 (2016).

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2015

Mitzscherling S., Cui Q., Koopman W., and Bargheer M.
Dielectric function of two-phase colloid--polymer nanocomposite
Physical Chemistry Chemical Physics 17, 29465 (2015).


Cui Q., Yashchenok A., Li L., Möhwald H., and Bargheer M.
Mechanistic study on reduction reaction of nitro compounds catalyzed by gold nanoparticles using in situ SERS monitoring
Colloids and Surfaces A: Physicochemical and Engineering Aspects 470, 108 (2015).


Bojahr A., Gohlke M., Leitenberger W., Pudell J.-E., Reinhardt M., von Reppert A., Rössle M., Sander M., Gaal P., and Bargheer M.
Second Harmonic Generation of Nanoscale Phonon Wave Packets
Physical Review Letters 115, 195502 (2015).


Maerten L., Bojahr A., Gohlke M., Rössle M., and Bargheer M.
Coupling of GHz Phonons to Ferroelastic Domain Walls in SrTiO3
Physical Review Letters 114, 047401 (2015).


Cui Q., Xia B., Mitzscherling S., Masic A., Li L., Bargheer M., and Möhwald H.
Preparation of gold nanostars and their study in selective catalytic reactions
Colloids and Surfaces A: Physicochemical and Engineering Aspects 465, 20 (2015).


Maerten L., Bojahr A., and Bargheer M.
Observing backfolded and unfolded acoustic phonons by broadband optical light scattering
Ultrasonics 56, 148 (2015).

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2014

Cui Q., Shen G., Yan X., Li L., Möhwald H., and Bargheer M.
Fabrication of Au@Pt Multibranched Nanoparticles and Their Application to In Situ SERS Monitoring
ACS Applied Materials & Interfaces 6, 17075 (2014).


Goldshteyn J., Bojahr A., Gaal P., Schick D., and Bargheer M.
Selective preparation and detection of phonon polariton wavepackets by stimulated Raman scattering
physica status solidi (b) 251, 821 (2014).


Cui Q., Yashchenok A., Zhang L., Li L., Masic A., Wienskol G., Möhwald H., and Bargheer
Fabrication of Bifunctional Gold/Gelatin Hybrid Nanocomposites and Their Application
ACS Applied Material Interfaces 6, 1999 (2014).


Gaal P., Schick D., Herzog M., Bojahr A., Shayduk R., Goldshteyn J., Navirian H. A., Leitenberger W., Vrejoiu I., Khakhulin D., Wulff M., and Bargheer M.
Ultrafast Switching of hard X-rays
Journal of Synchrotron Radiation 21, 380 (2014).


Navirian H. A., Schick D., Gaal P., Leitenberger W., Shayduk R., and Bargheer M.
Thermoelastic study of nanolayered structures using time-resolved x-ray diffraction at high repetition rate
Applied Physics Letters 104, 021906 (2014).


Schick D., Herzog M., Wen H., Chen P., Adamo C., Gaal P., Schlom D. G., Evans P. G., Li Y., and Bargheer M.
Localized excited charge carriers generate ultrafast inhomogeneous strain in the multiferroic BiFeO3
Physical Review Letters 112, 097602 (2014).


Schick D., Bojahr A., Herzog M., von Korff Schmising C., Shayduk R., and Bargheer M.
udkm1Dsim - A Simulation Toolkit for 1D Ultrafast Dynamics in Condensed Matter
Computer Physics Communication 185, 651 (2014).


Schick D., Herzog M., Bojahr A., Leitenberger W., Hertwig A., Shayduk R., and Bargheer M.
Ultrafast lattice response of photoexcited thin films studied by X-ray diffraction
Structural Dynamics 1, 064501 (2014).

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2013

Abboud A., Send S., Pashniak N., Leitenberger W., Ihle S., Huth M., Hartmann R., Strüder L., and Pietsch U.
Sub-pixel resolution of a pnCCD for X-ray white beam applications
Journal of Instrumentation 8, P05005 (2013).


Bojahr A., Herzog M., Mitzscherling S., Maerten L., Schick D., Goldshteyn J., Leitenberger W., Shayduk R., Gaal P., and Bargheer M.
Brillouin scattering of visible and hard X-ray photons from optically synthesized phonon wavepackets
Optics Express 21, 21188 (2013).


Schick D., Shayduk R., Bojahr A., Herzog M., von Korff Schmising C.,  Gaal P., and Bargheer M.
Ultrafast reciprocal-space mapping with a convergent beam
Journal of Applied Crystallography 46, 1372 (2013).


Send S., Abboud A., Hartmann R., Huth M., Leitenberger W., Pashniak N., Schmidt J., Strüder L., and Pietsch U.
Characterization of a pnCCD for applications with synchrotron radiation
Nuclear Instruments and Methods A 711, 132 (2013).


Schick D., Bojahr A., Herzog M., Gaal P., Vrejoiu I., and Bargheer M.
Following Strain-Induced Mosaicity Changes of Ferroelectric Thin Films by Ultrafast Reciprocal Space Mapping
Physical Review Letters 110, 095502 (2013).


Shayduk R., Herzog M., Bojahr A., Schick D., Gaal P., Leitenberger W., Navirian H., Sander M., Goldshteyn J., Vrejoiu I., and Bargheer M.
Direct time-domain sampling of subterahertz coherent acoustic phonon spectra in SrTiO3 using ultrafast x-ray diffraction
Physical Review B 87, 184301 (2013).

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2012

Gaal P., Schick D., Herzog M., Bojahr A., Shayduk R., Goldshteyn J., Navirian H. A., Leitenberger W., Vrejoiu I., Khakhulin D., Wulff M., and Bargheer M.
Time-domain sampling of x-ray pulses using an ultrafast sample response
Applied Physics Letters 101, 243106 (2012).


Bojahr A., Herzog M., Schick D., Vrejoiu I., and Bargheer M.
Calibrated real-time detection of nonlinearly propagating strain waves
Physical Review B 86, 144306 (2012).


Weber C., Frank C., Bommel S., Rukat T., Leitenberger W., Schaefer P., Schreiber F., and Kowarik S.
Chain-length dependent growth dynamics of n-alkanes on silica investigated by energy-dispersive x-ray reflectivity in situ and in real-time
Journal of Chemical Physics 136, 20 (2012):


Navirian H., Shayduk R., Leitenberger W., Goldshteyn J., Gaal P., and Bargheer M.
Synchrotron-based ultrafast x-ray diffraction at high repetition rates
Review of Scientfic Instruments 83, 063303 (2012).


Bojahr A., Schick D., Maerten L., Herzog M., Vrejoiu I., von Korff Schmising C., Milne C. J., Johnson S. L., and Bargheer M.
Comparing the oscillation phase in optical pump-probe spectra to ultrafast x-ray diffraction in the metal-dielectric SrRuO3/SrTiO3 superlattice
Physical Review B 85, 224302 (2012).


Send S., Abboud A., Leitenberger W., Weiss M. S., Hartmann R., Strüder L., and Pietsch U
Analysis of polycrystallinity in hen egg-white lysozyme using a pnCCD
Journal of Applied Crystallography 45, 517 (2012).


Mihoc C., Schick D., Lütgens M., Lathe C., and Burkel E.
Formation of Al67Cu23Fe10 quasicrystals by microwave heating
International Journal of Materials Research 103, 1340 (2012).


Kiel M., Klötzer M., Mitzscherling S., and Bargheer M.
Measuring the Range of Plasmonic Interaction
Langmuir 28, 4800 (2012).


Herzog M., Bojahr A., Goldshteyn J., Leitenberger W., Vrejoiu I., Khakhulin D., Wulff M., Shayduk R., Gaal P., and Bargheer M.
Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction
Applied Physics Letters 100, 094101 (2012).


Gupta R., Gupta A., Leitenberger W., and Rüffer R.
Mechanism of stress relaxation in nanocrystalline Fe-N thin films
Physical Review B 85, 075401 (2012).


Schick D., Bojahr A., Herzog M., von Korff Schmising C., Shayduk R., Leitenberger W., Gaal P., and Bargheer M.
Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source
Review of Scientific Instruments 83, 025104 (2012).

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2011

W. Gruber, S. Chakravarty, C. Baehtz, W. Leitenberger, M. Braun, A. Kobler, C. Kübel and H. Schmidt.
Strain Relaxation and Vacancy Creation in Thin Platinum Films  
Physical Review Letters 107, 265501 (2011).


M. Kiel, H. Möhwald and M. Bargheer.
Broadband measurements of the transient optical complex dielectric function of a nanoparticle/polymer composite upon ultrafast excitation 
Physical Review B 84, 165121 (2011).


R. Shayduk, H. A. Navirian, W. Leitenberger, J. Goldshteyn, I. Vrejoiu, M. Weinelt, P. Gaal, M. Herzog, C. von Korff Schmising and M. Bargheer .
Nanoscale heat transport studied by high-resolution time-resolved x-ray diffraction 
New Journal of Physics 13, 093032 (2011).


H. A. Navirian, M. Herzog, J. Goldshteyn, W. Leitenberger, I. Vrejoiu, D. Khakhulin, M. Wulff, R. Shayduk, P. Gaal and M. Bargheer.
Shortening x-ray pulses for pump-probe experiments at synchrotrons 
Journal of Applied Physics 109, 126104 (2011).

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2010

C. von Korff Schmising, Anders Harpoeth, Nicolai Zhavoronkov, Michael Woerner, T. Elsaesser, M. Bargheer, Martin Schmidbauer, I. Vrejoiu, Dietrich Hesse and M. Alexe.
Femtosecond X-ray diffraction from nanolayered oxides 
Physics Procedia 3, 333 (2010).


H. Enquist, H. Navirian, R. Nueske, C. von Korff Schmising, A. Jurgilaitis, M. Herzog, M. Bargheer, P. Sondhauss and J. Larsson
Subpicosecond hard x-ray streak camera using single-photon counting 
Optics Letters 35, 3219 (2010).


M. Kiel, S. Mitzscherling, W. Leitenberger, S. Santer, B. Tiersch, T. K. Sievers, H. Möhwald and M. Bargheer
Structural Characterization of a Spin-Assisted Colloid-Polyelectrolyte Assembly: Stratified Multilayer Thin Films
Langmuir 26, 18499 (2010).


M. Herzog, W. Leitenberger, R. Shayduk, Renske van der Veen, C. J. Milne, S. L. Johnson, I. Vrejoiu, M. Alexe, D. Hesse and M. Bargheer
Ultrafast manipulation of hard x-rays by efficient Bragg switches
Applied Physics Letters 96, 161906 (2010).

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2009

M. Woerner, C. von Korff Schmising, M. Bargheer, N. Zhavoronkov, I. Vrejoiu, D. Hesse, M. Alexe and T. Elsaesser
Ultrafast structural dynamics of perovskite superlattices 
Applied Physics A: Materials Science & Processing 96, 83 (2009).


M. Braun, C. Root, F. J. Lederer, T. E. Schrader, W. Zinth, C. von Korff Schmising, M. Bargheer, T. Elsaesser and M. Woerner.
Ultrafast X-ray experiments on structural changes in single crystals of polar molecules 
Applied Physics A: Materials Science & Processing 96, 107 (2009).


F. Zamponi, Z. Ansari, C. von Korff Schmising, P. Rothhardt, N. Zhavoronkov, M. Woerner, T. Elsaesser, M. Bargheer, T. Trobitzsch-Ryll and M. Haschke
Femtosecond hard X-ray plasma sources with a kilohertz repetition rate 
Applied Physics A 96, 51 (2009).

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2008

C. von Korff Schmising, M. Bargheer, M. Woerner and T. Elsaesser.
Real-time studies of reversible lattice dynamics by femtosecond X-ray diffraction 
Oldenbourg 223, 283 (2008).


C. von Korff Schmising, A. Harpoeth, N. Zhavoronkov, Z. Ansari, C. Aku-Leh, M. Woerner, T. Elsaesser, M. Bargheer, M. Schmidbauer, I. Vrejoiu, D. Hesse and M. Alexe.
Ultrafast magnetostriction and phonon-mediated stress in a photoexcited ferromagnet 
Physical Review B 78, 060404 (2008).


M. Fushitani, M. Bargheer, M. Gühr, H. Ibrahim and N. Schwentner.
Control of chromophore-to-bath coupling by interferometry: Cl2 vibrational wave packets in solid Ar
Journal of Physics B: Atomic, Molecular and Optical Physics 41, 074013 (2008).

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2007

M. Gühr, M. Bargheer, M. Fushitani, T. Kiljunen and N. Schwentner.
Ultrafast dynamics of halogens in rare gas solids 
2007, Physical Chemistry Chemical Physics, Phys. Chem. Chem. Phys., 9, 7, 779--801


C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse and M. Alexe
Ultrafast structure and polarization dynamics in nanolayered perovskites studied by femtosecond X-ray diffraction
Journal of Physics: Conference Series 92, 012177 (2007).


C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse and M. Alexe
Coupled Ultrafast Lattice and Polarization Dynamics in Ferroelectric Nanolayers 
2007, Phys. Rev. Lett., 98, 25, 257601


C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse and M. Alexe.
Accurate time delay determination for femtosecond X-ray diffraction experiments 
2007, Appl. Phys. B, 88, 1, 1-4


M. Bargheer.
Atombewegung im Röntgenkino - Die Femtosekunden-Röntgenbeugung entschlüsselt ultraschnelle Gitterdynamik
Physik Journal 8/9, 67 (2007).


M. Braun, C. von Korff Schmising, M. Kiel, N. Zhavoronkov, J. Dreyer, M. Bargheer, T. Elsaesser, C. Root, T. E. Schrader, P. Gilch, W. Zinth and M. Woerner
Ultrafast Changes of Molecular Crystal Structure Induced by Dipole Solvation 
2007, Phys. Rev. Lett., 98, 24, 248301


M. Bargheer, A. Cohen, R. B. Gerber, M. Gühr, M. V. Korolkov, J. Manz, M. Y. Niv, M. Schröder and N. Schwentner.
Dynamics of Electronic States and Spin-Flip for Photodissociation of Dihalogens in Matrices: Experiment and Semiclassical Surface-Hopping and Quantum Model Simulations for F2 and ClF in Solid Ar 
2007, The Journal of Physical Chemistry A, 111, 38, 9573--9585

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2006

C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse and M. Alexe
Strain propagation in nanolayered perovskites probed by ultrafast x-ray diffraction 
2006, Physical Review B (Condensed Matter and Materials Physics), 73, 21, 212202


M. Bargheer, N. Zhavoronkov, M. Woerner and T. Elsaesser.
Recent Progress in Ultrafast X-ray Diffraction 
2006, ChemPhysChem, 7, 4, 783-792


M. Bargheer, J. C. Woo, N. Zhavoronkov, D. S. Kim, M. Woerner and T. Elsaesser
Excitation mechanisms of coherent phonons unravelled by femtosecond X-ray diffraction 
2006, phys. stat. sol. (b), 243, 10, 2389-2396

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2005

N. Zhavoronkov, Y. Gritsai, M. Bargheer, M. Woerner, T. Elsaesser, F. Zamponi, I. Uschmann and E. Forster.
Microfocus Cu Ka source for femtosecond x-ray science
Optics Letters 30, 1737 (2005).


M. Fushitani, M. Bargheer, M. Gühr and N. Schwentner.
Pump–probe spectroscopy with phase-locked pulses in the condensed phase: decoherence and control of vibrational wavepackets
2005, Phys. Chem. Chem. Phys., 7, 3143-3149


M. Bargheer, N. Zhavoronkov, R. Bruch, H. Legall, H. Stiel, M. Woerner and T. Elsaesser.
Comparison of focusing optics for femtosecond X-ray diffraction
2005, Applied Physics B: Lasers and Optics, 80, 6, 715--719


N. Zhavoronkov, Y. Gritsai, M. Bargheer, M. Woerner and T. Elsaesser
Generation of ultrashort K-alpha radiation from quasipoint interaction area of femtosecond pulses with thin foils
2005, Applied Physics Letters, 86, 24, 244107

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2004

T. Kiljunen, M. Bargheer, M. Gühr and N. Schwentner
A potential energy surface and a trajectory study of photodynamics and strong-field alignment of ClF molecule in rare gas (Ar,Kr) solids
 2004, Phys. Chem. Chem. Phys., 6, 2185-2197


T. Kiljunen, M. Bargheer, M. Gühr, N. Schwentner and B. Schmidt.
Photodynamics and ground state librational states of ClF molecule in solid Ar. Comparison of experiment and theory
2004, Phys. Chem. Chem. Phys., 6, 2932 - 2939


M. Bargheer, N. Zhavoronkov, Y. Gritsai, J. C. Woo, D. S. Kim, M. Woerner and T. Elsaesser.
Coherent Atomic Motions in a Nanostructure Studied by Femtosecond X-ray Diffraction
 2004, Science, 306, 5702, 1771-1773


M. Bargheer, M. Gühr and N. Schwentner.
Collisions transfer coherence
Israel Journal of Chemistry 44, 9 (2004).

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2003

M. Bargheer and N. Schwentner.
Particle transport phenomena in low-temperature solids (Review) 
2003, Low Temperature Physics, 29, 3, 165-173


M. Gühr, M. Bargheer and N. Schwentner
Generation of Coherent Zone Boundary Phonons by Impulsive Excitation of Molecules
2003, Phys. Rev. Lett., 91, 8, 085504

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2002

M. Bargheer, R. B. Gerber, M. V. Korolkov, O. Kühn, J. Manz, M. Schröder and N. Schwentner
Subpicosecond spin-flip induced by the photodissociation dynamics of ClF in an Ar matrix
2002, Phys. Chem. Chem. Phys, 4, 5554 - 5562


M. Bargheer, M. Y. Niv, R. B. Gerber and N. Schwentner
Ultrafast Solvent-Induced Spin-Flip and Nonadiabatic Coupling: ClF in Argon Solids
2002, Phys. Rev. Lett., 89, 10, 108301


M. Bargheer, M. Gühr, P. Dietrich and N. Schwentner
Femtosecond spectroscopy of fragment–cage dynamics: I2 in Kr
2002, Phys. Chem. Chem. Phys., 4, 75-81


M. Gühr, M. Bargheer, P. Dietrich and N. Schwentner.
Predissociation and Vibrational Relaxation in the B state of I2 in Kr Matrix
Journal of Physical Chemistry A 106, 12002 (2002).


M. Bargheer, M. Gühr and N. Schwentner
Depolarization as a probe for ultrafast reorientation of diatomics in condensed phase: ClF versus I[sub 2] in rare gas solids
2002, The Journal of Chemical Physics, 117, 1, 5-8

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2001

M. Bargheer, P. Dietrich and N. Schwentner.
Spectroscopy and photodissociation of ClF in rare gas solids
 2001, The Journal of Chemical Physics, 115, 1, 149-157


M. Bargheer, J. Pietzner, P. Dietrich and N. Schwentner.
Ultrafast laser control of ionic-bond formation: ClF in argon solids
2001, The Journal of Chemical Physics, 115, 21, 9827-9834

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2000

M. Y. Niv, M. Bargheer and R. B. Gerber.
Photodissociation and recombination of F[sub 2] molecule in Ar[sub 54] cluster: Nonadiabatic molecular dynamics simulations
2000, The Journal of Chemical Physics, 113, 16, 6660-6672

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1999

M. Bargheer, P. Dietrich, K. Donovang and N. Schwentner.
Extraction of potentials and dynamics from condensed phase pump--probe spectra: Application to I[sub 2] in Kr matrices
1999, The Journal of Chemical Physics, 111, 18, 8556-8564

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