TY - JOUR A1 - Mattern, Maximilian A1 - Reppert, Alexander von A1 - Zeuschner, Steffen Peer A1 - Herzog, Marc A1 - Pudell, Jan-Etienne A1 - Bargheer, Matias T1 - Concepts and use cases for picosecond ultrasonics with x-rays JF - Photoacoustics N2 - This review discusses picosecond ultrasonics experiments using ultrashort hard x-ray probe pulses to extract the transient strain response of laser-excited nanoscopic structures from Bragg-peak shifts. This method provides direct, layer-specific, and quantitative information on the picosecond strain response for structures down to few-nm thickness. We model the transient strain using the elastic wave equation and express the driving stress using Gruneisen parameters stating that the laser-induced stress is proportional to energy density changes in the microscopic subsystems of the solid, i.e., electrons, phonons and spins. The laser-driven strain response can thus serve as an ultrafast proxy for local energy-density and temperature changes, but we emphasize the importance of the nanoscale morphology for an accurate interpretation due to the Poisson effect. The presented experimental use cases encompass ultrathin and opaque metal-heterostructures, continuous and granular nanolayers as well as negative thermal expansion materials, that each pose a challenge to established all-optical techniques. KW - Picosecond ultrasonics KW - Ultrafast x-ray diffraction KW - Ultrafast x-ray KW - scattering KW - Ultrafast photoacoustics KW - Nanoscale heat transfer KW - Negative KW - thermal expansion Y1 - 2023 U6 - https://doi.org/10.1016/j.pacs.2023.100503 SN - 2213-5979 VL - 31 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Dumesnil, Karine A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Towards shaping picosecond strain pulses via magnetostrictive transducers JF - Photoacoustics N2 - Using time-resolved x-ray diffraction, we demonstrate the manipulation of the picosecond strain response of a metallic heterostructure consisting of a dysprosium (Dy) transducer and a niobium (Nb) detection layer by an external magnetic field. We utilize the first-order ferromagnetic–antiferromagnetic phase transition of the Dy layer, which provides an additional large contractive stress upon laser excitation compared to its zerofield response. This enhances the laser-induced contraction of the transducer and changes the shape of the picosecond strain pulses driven in Dy and detected within the buried Nb layer. Based on our experiment with rare-earth metals we discuss required properties for functional transducers, which may allow for novel field-control of the emitted picosecond strain pulses. KW - picosecond ultrasonics KW - magnetostriction KW - ultrafast x-ray diffraction KW - ultrafast photoacoustics KW - nanoscale heat transfer KW - negative thermal expansion Y1 - 2023 U6 - https://doi.org/10.1016/j.pacs.2023.100463 SN - 2213-5979 VL - 30 PB - Elsevier CY - Amsterdam 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 - Mattern, Maximilian A1 - Reppert, Alexander von A1 - Zeuschner, Steffen Peer A1 - Pudell, Jan-Etienne A1 - Kühne, F. A1 - Diesing, Detlef A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics JF - Applied physics letters N2 - We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds. Y1 - 2022 U6 - https://doi.org/10.1063/5.0080378 SN - 0003-6951 SN - 1077-3118 VL - 120 IS - 9 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Shayduk, Roman A1 - Hallmann, Jörg A1 - Rodriguez-Fernandez, Angel A1 - Scholz, Markus A1 - Lu, Wei A1 - Bösenberg, Ulrike A1 - Möller, Johannes A1 - Zozulya, Alexey A1 - Jiang, Man A1 - Wegner, Ulrike A1 - Secareanu, Radu-Costin A1 - Palmer, Guido A1 - Emons, Moritz A1 - Lederer, Max A1 - Volkov, Sergey A1 - Lindfors-Vrejoiu, Ionela A1 - Schick, Daniel A1 - Herzog, Marc A1 - Bargheer, Matias A1 - Madsen, Anders T1 - Femtosecond x-ray diffraction study of multi-THz coherent phonons in SrTiO3 JF - Applied physics letters N2 - We report generation of ultra-broadband longitudinal acoustic coherent phonon wavepackets in SrTiO3 (STO) with frequency components extending throughout the first Brillouin zone. The wavepackets are efficiently generated in STO using femtosecond infrared laser excitation of an atomically flat 1.6 nm-thick epitaxial SrRuO3 film. We use femtosecond x-ray diffraction at the European X-Ray Free Electron Laser Facility to study the dispersion and damping of phonon wavepackets. The experimentally determined damping constants for multi-THz frequency phonons compare favorably to the extrapolation of a simple ultrasound damping model over several orders of magnitude. Y1 - 2022 U6 - https://doi.org/10.1063/5.0083256 SN - 0003-6951 SN - 1077-3118 VL - 120 IS - 20 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Jaffrès, Henri-Yves A1 - Keller, Niels A1 - Bargheer, Matias T1 - Polarization-dependent subpicosecond demagnetization in iron garnets JF - Physical review : B, covering condensed matter and materials physics N2 - Controlling the magnetization dynamics at the fastest speed is a major issue of fundamental condensed matter physics and its applications for data storage and processing technologies. It requires a deep understanding of the interactions between the degrees of freedom in solids, such as spin, electron, and lattice as well as their responses to external stimuli. In this paper, we systematically investigate the fluence dependence of ultrafast magnetization dynamics induced by below-bandgap ultrashort laser pulses in the ferrimagnetic insulators BixY3-xFe5O12 with 1 xBi 3. We demonstrate subpicosecond demagnetization dynamics in this material followed by a very slow remagnetization process. We prove that this demagnetization results from an ultrafast heating of iron garnets by two-photon absorption (TPA), suggesting a phonon-magnon thermalization time of 0.6 ps. We explain the slow remagnetization timescale by the low phonon heat conductivity in garnets. Additionally, we show that the amplitudes of the demagnetization, optical change, and lattice strain can be manipulated by changing the ellipticity of the pump pulses. We explain this phenomenon considering the TPA circular dichroism. These findings open exciting prospects for ultrafast manipulation of spin, charge, and lattice dynamics in magnetic insulators by ultrafast nonlinear optics. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevB.106.184416 SN - 2469-9950 SN - 2469-9969 VL - 106 IS - 18 PB - American Institute of Physics, American Physical Society CY - Woodbury, NY ER - TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Jaffrès, Henri-Yves A1 - Keller, Niels A1 - Bargheer, Matias T1 - Controlling high-frequency spin-wave dynamics using double-pulse laser excitation JF - Physical review applied N2 - Manipulating spin waves is highly required for the development of innovative data transport and processing technologies. Recently, the possibility of triggering high-frequency standing spin waves in magnetic insulators using femtosecond laser pulses was discovered, raising the question about how one can manipulate their dynamics. Here we explore this question by investigating the ultrafast magnetiza-tion and spin-wave dynamics induced by double-pulse laser excitation. We demonstrate a suppression or enhancement of the amplitudes of the standing spin waves by precisely tuning the time delay between the two pulses. The results can be understood as the constructive or destructive interference of the spin waves induced by the first and second laser pulses. Our findings open exciting perspectives towards generating single-mode standing spin waves that combine high frequency with large amplitude and low magnetic damping. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevApplied.18.044001 SN - 2331-7019 VL - 18 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Herzog, Marc A1 - Reppert, Alexander von A1 - Pudell, Jan-Etienne A1 - Henkel, Carsten A1 - Kronseder, Matthias A1 - Back, Christian H. A1 - Maznev, Alexei A. A1 - Bargheer, Matias T1 - Phonon-dominated energy transport in purely metallic heterostructures JF - Advanced functional materials N2 - Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers. Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface. Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au. KW - heterostructures KW - nanoscale energy transports KW - non-equilibrium KW - thermal KW - transports KW - ultrafast phenomena Y1 - 2022 U6 - https://doi.org/10.1002/adfm.202206179 SN - 1616-301X SN - 1616-3028 VL - 32 IS - 41 PB - Wiley-VCH CY - Weinheim 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 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Schwarzkopf, Jutta A1 - Boschker, Jos A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Reciprocal space slicing BT - a time-efficient approach to femtosecond x-ray diffraction JF - Structural dynamics N2 - 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. Y1 - 2020 U6 - https://doi.org/10.1063/4.0000040 SN - 2329-7778 VL - 8 IS - 1 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Schmitt, Clemens Nikolaus Zeno A1 - Thünemann, Andreas F. A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Gold nanotriangles with crumble topping and their influence on catalysis and surface-enhanced raman spectroscopy JF - ChemPlusChem N2 - 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. KW - gold nanostructures KW - HRTEM KW - hyaluronic acid KW - monolayer formation KW - SERS Y1 - 2020 U6 - https://doi.org/10.1002/cplu.201900745 SN - 2192-6506 VL - 85 IS - 3 SP - 519 EP - 526 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Bargheer, Matias A1 - Schmitt, Clemens Nikolaus Zeno A1 - Poghosyan, Armen H. A1 - Shahinyanf, Aram A. A1 - Koetz, Joachim T1 - Spiked gold nanotriangles BT - Formation, characterization and applications in surface-enhanced Raman spectroscopy and plasmon-enhanced catalysis JF - RSC Advances N2 - 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). Y1 - 2020 U6 - https://doi.org/10.1039/d0ra00729c SN - 2046-2069 VL - 10 IS - 14 SP - 8152 EP - 8160 PB - RSC Publishing CY - London ER - TY - JOUR A1 - Reppert, Alexander von A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Zeuschner, Steffen Peer A1 - Dumesnil, Karine A1 - Bargheer, Matias T1 - Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer JF - Structural Dynamics N2 - 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. KW - Strain measurement KW - Photoexcitations KW - Crystal lattices KW - Femtosecond lasers KW - Thermal effects KW - Heterostructures KW - Ultrafast X-rays KW - Phonons Y1 - 2020 U6 - https://doi.org/10.1063/1.5145315 SN - 2329-7778 VL - 7 IS - 024303 PB - AIP Publishing LLC CY - Melville, NY 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 - Liebig, Ferenc A1 - Henning, Ricky A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Schmitt, Clemens Nikolaus Zeno A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - A simple one-step procedure to synthesise gold nanostars in concentrated aqueous surfactant solutions JF - RSC Advances N2 - 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. KW - optical-properties KW - nanoparticles KW - sers KW - ultrafast KW - size KW - nanotriangles KW - nanoflowers KW - wavelength Y1 - 2019 U6 - https://doi.org/10.1039/C9RA02384D SN - 2046-2069 VL - 9 SP - 23633 EP - 23641 PB - RSC Publishing CY - London 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 - 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 - Pudell, Jan-Etienne A1 - Reppert, Alexander von A1 - Schick, D. A1 - Zamponi, F. A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Zabel, Hartmut A1 - Bargheer, Matias T1 - Ultrafast negative thermal expansion driven by spin disorder JF - Physical review : B, Condensed matter and materials physics N2 - 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 Neel 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. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.99.094304 SN - 2469-9950 SN - 2469-9969 VL - 99 IS - 9 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Hehn, Michel A1 - Keller, Niels A1 - Petit-Watelot, Sebastien A1 - Bargheer, Matias A1 - Mangin, Stephane A1 - Malinowski, Gregory T1 - Femtosecond Laser-Excitation-Driven High Frequency Standing Spin Waves in Nanoscale Dielectric Thin Films of Iron Garnets JF - Physical review letters N2 - 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 (similar to 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. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevLett.123.027202 SN - 0031-9007 SN - 1079-7114 VL - 123 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Schuetz, Roman A1 - Schmid, Thomas A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - The importance of plasmonic heating for the plasmondriven photodimerization of 4-nitrothiophenol JF - Scientific Reports N2 - 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. KW - enhanced raman-scattering KW - charge-transfer KW - metal KW - nanoparticles KW - catalysis KW - AU KW - 4-nitrobenzenethiol KW - aminothiophenol KW - photocatalysis KW - wavelength Y1 - 2019 U6 - https://doi.org/10.1038/s41598-019-38627-2 SN - 2045-2322 VL - 9 PB - Macmillan Publishers Limited CY - London ER - TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Hehn, Michel A1 - Keller, Niels A1 - Petit-Watelot, Sebastien A1 - Bargheer, Matias A1 - Mangin, Stephane A1 - Malinowski, Gregory T1 - Damping of Standing Spin Waves in Bismuth-Substituted Yttrium Iron Garnet as Seen via the Time-Resolved Magneto-Optical Kerr Effect JF - Physical review applied N2 - 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. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.12.044006 SN - 2331-7019 VL - 12 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Zeuschner, Steffen Peer A1 - Parpiiev, Tymur A1 - Pezeril, Thomas A1 - Hillion, Arnaud A1 - Dumesnil, Karine A1 - Anane, Abdelmadjid A1 - Pudell, Jan-Etienne A1 - Willig, Lisa A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction JF - Structural Dynamics N2 - 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. KW - Heterostructures KW - Magnetooptical effects KW - Metal oxides KW - Crystal lattices KW - Transition metals KW - Magnetism KW - Ultrafast X-ray diffraction KW - Lasers KW - Bragg peak KW - Phonons Y1 - 2019 U6 - https://doi.org/10.1063/1.5084140 SN - 2329-7778 VL - 6 IS - 2 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Willig, Lisa A1 - Reppert, Alexander von A1 - Deb, Marwan A1 - Ganss, F. A1 - Hellwig, O. A1 - Bargheer, Matias T1 - Finite-size effects in ultrafast remagnetization dynamics of FePt JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the ultrafast magnetization dynamics of FePt in the L1(0) 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. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.100.224408 SN - 2469-9950 SN - 2469-9969 VL - 100 IS - 22 PB - American Physical Society CY - College Park 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 - 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 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Schmitt, Clemens Nikolaus Zeno A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Tuned Surface-Enhanced raman scattering performance of undulated Au@Ag triangles JF - ACS applied nano materials N2 - Negatively charged ultraflat gold nanotriangles (AuNTs) stabilized by the anionic surfactant dioctyl sodium sulfosuccinate (AOT) were reloaded with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC). Because of the spontaneous formation of a catanionic AOT micelle/BDAC bilayer onto the surface of the reloaded AuNTs, a reduction of Ag+ ions leads to the formation of spherical silver nanoparticles (AgNPs). With increasing concentration of AgNPs on the AuNTs, the localized surface plasmon resonance (LSPR) is shifted stepwise from 1300 to 800 nm. The tunable LSPR enables to shift the extinction maximum to the wavelength of the excitation laser of the Raman microscope at 785 nm. Surface-enhanced Raman scattering (SERS) experiments performed under resonance conditions show an SERS enhancement factor of the analyte molecule rhodamine RG6 of 5.1 X 10(5), which can be related to the silver hot spots at the periphery of the undulated gold nanoplatelets. KW - gold nanotriangles KW - catanionic surfactant bilayer KW - undulated nanoplatelets KW - SERS KW - LSPR Y1 - 2018 U6 - https://doi.org/10.1021/acsanm.8b00570 SN - 2574-0970 VL - 1 IS - 4 SP - 1995 EP - 2003 PB - American Chemical Society CY - Washington 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 - Reppert, Alexander von A1 - Willig, Lisa A1 - Pudell, Jan-Etienne A1 - Roessle, M. A1 - Leitenberger, Wolfram A1 - Herzog, Marc A1 - Ganss, F. A1 - Hellwig, O. A1 - Bargheer, Matias T1 - Ultrafast laser generated strain in granular and continuous FePt thin films JF - Applied physics letters N2 - 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. (C) 2018 Author(s). Y1 - 2018 U6 - https://doi.org/10.1063/1.5050234 SN - 0003-6951 SN - 1077-3118 VL - 113 IS - 12 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - Maznev, A. A. A1 - Herzog, Marc A1 - Kronseder, M. A1 - Back, Christian H. A1 - Malinowski, Gregory A1 - Reppert, Alexander von A1 - Bargheer, Matias T1 - Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction JF - Nature Communications N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-05693-5 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - GEN 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 T2 - Quantum Nano-Photonics N2 - The electromagnetic coupling of molecular excitations to plasmonic nanoparticles offers a promising method to manipulate the light-matter interaction at the nanoscale. Plasmonic nanoparticles foster exceptionally high coupling strengths, due to their capacity to strongly concentrate the light-field to sub-wavelength mode volumes. A particularly interesting coupling regime occurs, if the coupling increases to a level such that the coupling strength surpasses all damping rates in the system. In this so-called strong-coupling regime hybrid light-matter states emerge, which can no more be divided into separate light and matter components. These hybrids unite the features of the original components and possess new resonances whose positions are separated by the Rabi splitting energy h Omega. Detuning the resonance of one of the components leads to an anticrossing of the two arising branches of the new resonances omega(+) and omega(-) with a minimal separation of Omega = omega(+) - omega(-). Y1 - 2018 SN - 978-94-024-1546-9 SN - 978-94-024-1544-5 SN - 978-94-024-1543-8 U6 - https://doi.org/10.1007/978-94-024-1544-5_53 SN - 1871-465X SP - 445 EP - 447 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Stete, Felix A1 - Schossau, Phillip Gerald A1 - Koopman, Wouter-Willem Adriaan A1 - Bargheer, Matias T1 - Size Dependence of the Coupling Strength in Plasmon-Exciton Nanoparticles T2 - Quantum Nano-Photonics N2 - The coupling between molecular excitations and nanoparticles leads to promising applications. It is for example used to enhance the optical cross-section of molecules in surface enhanced Raman scattering, Purcell enhancement or plasmon enhanced dye lasers. In a coupled system new resonances emerge resulting from the original plasmon (ωpl) and exciton (ωex) resonances as ω±=12(ωpl+ωex)±14(ωpl−ωex)2+g2−−−−−−−−−−−−−−−√, (1) where g is the coupling parameter. Hence, the new resonances show a separation of Δ = ω+ − ω− from which the coupling strength can be deduced from the minimum distance between the two resonances, Ω = Δ(ω+ = ω−). Y1 - 2018 SN - 978-94-024-1546-9 SN - 978-94-024-1544-5 SN - 978-94-024-1543-8 U6 - https://doi.org/10.1007/978-94-024-1544-5_26 SN - 1871-465X SP - 381 EP - 383 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Sander, Mathias A1 - Herzog, Marc A1 - Pudell, Jan-Etienne A1 - Bargheer, Matias A1 - Weinkauf, N. A1 - Pedersen, M. A1 - Newby, G. A1 - Sellmann, J. A1 - Schwarzkopf, J. A1 - Besse, V. A1 - Temnov, V. V. A1 - Gaal, P. T1 - Spatiotemporal Coherent Control of Thermal Excitations in Solids JF - Physical review letters N2 - X-ray reflectivity measurements of femtosecond laser-induced transient gratings (TG) are applied to demonstrate the spatiotemporal coherent control of thermally induced surface deformations on ultrafast time scales. Using grazing incidence x-ray diffraction we unambiguously measure the amplitude of transient surface deformations with sub-angstrom resolution. Understanding the dynamics of femtosecond TG excitations in terms of superposition of acoustic and thermal gratings makes it possible to develop new ways of coherent control in x-ray diffraction experiments. Being the dominant source of TG signal, the long-living thermal grating with spatial period. can be canceled by a second, time-delayed TG excitation shifted by Lambda/2. The ultimate speed limits of such an ultrafast x-ray shutter are inferred from the detailed analysis of thermal and acoustic dynamics in TG experiments. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevLett.119.075901 SN - 0031-9007 SN - 1079-7114 VL - 119 SP - 102 EP - 110 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Sander, Mathias A1 - Pudell, Jan-Etienne A1 - Herzog, Marc A1 - Bargheer, Matias A1 - Bauer, R. A1 - Besse, V. A1 - Temnov, V. A1 - Gaal, P. T1 - Quantitative disentanglement of coherent and incoherent laser-induced surface deformations by time-resolved x-ray reflectivity JF - Applied physics letters N2 - We present time-resolved x-ray reflectivity measurements on laser excited coherent and incoherent surface deformations of thin metallic films. Based on a kinematical diffraction model, we derive the surface amplitude from the diffracted x-ray intensity and resolve transient surface excursions with sub-angstrom spatial precision and 70 ps temporal resolution. The analysis allows for decomposition of the surface amplitude into multiple coherent acoustic modes and a substantial contribution from incoherent phonons which constitute the sample heating. Published by AIP Publishing. Y1 - 2017 U6 - https://doi.org/10.1063/1.5004522 SN - 0003-6951 SN - 1077-3118 VL - 111 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Sander, Mathias A1 - Koopman, Wouter-Willem Adriaan A1 - Schuetz, Roman A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Deposition of Gold Nanotriangles in Large Scale Close-Packed Monolayers for X-ray-Based Temperature Calibration and SERS Monitoring of Plasmon-Driven Catalytic Reactions JF - ACS applied materials & interfaces KW - gold nanotriangles KW - monolayer formation KW - SERS KW - dimerization KW - heat measurement Y1 - 2017 U6 - https://doi.org/10.1021/acsami.7b07231 SN - 1944-8244 VL - 9 SP - 20247 EP - 20253 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kwamen, C. A1 - Rössle, Matthias A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Zamponi, Flavio A1 - Alexe, Marin A1 - Bargheer, Matias T1 - Simultaneous dynamic characterization of charge and structural motion during ferroelectric switching JF - Physical review : B, Condensed matter and materials physics N2 - Monitoring structural changes in ferroelectric thin films during electric field induced polarization switching is important for a full microscopic understanding of the coupled motion of charges, atoms, and domainwalls in ferroelectric nanostructures. We combine standard ferroelectric test sequences of switching and nonswitching electrical pulses with time-resolved x-ray diffraction to investigate the structural response of a nanoscale Pb(Zr0.2Ti0.8)O-3 ferroelectric oxide capacitor upon charging, discharging, and polarization reversal. We observe that a nonlinear piezoelectric response of the ferroelectric layer develops on a much longer time scale than the RC time constant of the device. The complex atomic motion during the ferroelectric polarization reversal starts with a contraction of the lattice, whereas the expansive piezoelectric response sets in after considerable charge flow due to the applied voltage pulses on the electrodes of the capacitor. Our simultaneous measurements on a working device elucidate and visualize the complex interplay of charge flow and structural motion and challenges theoretical modeling. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.134105 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park 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 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Bargheer, Matias A1 - Wollgarten, Markus A1 - Santer, Svetlana T1 - Mass production of polymer nano-wires filled with metal nano-particles JF - Scientific reports N2 - Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro-or macroscale elements is hampered by the lack of structural components that have both, nano-and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-08153-0 SN - 2045-2322 VL - 7 SP - 3759 EP - 3764 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Bargheer, Matias A1 - Wollgarten, Markus A1 - Santer, Svetlana T1 - Mass production of polymer nanowires filled with metal nanoparticles JF - Scientific reports N2 - Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-08153-0 SN - 2045-2322 VL - 7 PB - Springer Nature CY - London ER - TY - JOUR A1 - El-Nagar, Gumaa A. A1 - Sarhan, Radwan Mohamed A1 - Abouserie, Ahed A1 - Maticiuc, Natalia A1 - Bargheer, Matias A1 - Lauermann, Iver A1 - Roth, Christina T1 - Efficient 3D-Silver Flower-like Microstructures for Non-Enzymatic Hydrogen Peroxide (H2O2) Amperometric Detection JF - Scientific reports Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-11965-9 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Koc, Azize A1 - Reinhardt, M. A1 - Reppert, Alexander von A1 - Roessle, Matthias A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Gaal, Peter A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the heat transport through a rare earth multilayer system composed of yttrium (Y), dysprosium (Dy), and niobium (Nb) by ultrafast x-ray diffraction. This is an example of a complex heat flow problem on the nanoscale, where several different quasiparticles carry the heat and conserve a nonequilibrium for more than 10 ns. The Bragg peak positions of each layer represent layer-specific thermometers that measure the energy flow through the sample after excitation of the Y top layer with fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium heat transport problem, we derive the individual contributions of the spins and the coupled electron-lattice system to the heat conduction. The full characterization of the spatiotemporal energy flow at different starting temperatures reveals that the spin excitations of antiferromagnetic Dy speed up the heat transport into the Dy layer at low temperatures, whereas the heat transport through this layer and further into the Y and Nb layers underneath is slowed down. The experimental findings are compared to the solution of the heat equation using macroscopic temperature-dependent material parameters without separation of spin and phonon contributions to the heat. We explain why the simulated energy density matches our experiment-based derivation of the heat transport, although the simulated thermoelastic strain in this simulation is not even in qualitative agreement. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevB.96.014306 SN - 2469-9950 SN - 2469-9969 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Koc, A. A1 - Reinhardt, M. A1 - Reppert, Alexander von A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Gleich, M. A1 - Weinelt, M. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Grueneisen-approach for the experimental determination of transient spin and phonon energies from ultrafast x-ray diffraction data: gadolinium JF - Journal of physics : Condensed matter N2 - We study gadolinium thin films as a model system for ferromagnets with negative thermal expansion. Ultrashort laser pulses heat up the electronic subsystem and we follow the transient strain via ultrafast x-ray diffraction. In terms of a simple Grueneisen approach, the strain is decomposed into two contributions proportional to the thermal energy of spin and phonon subsystems. Our analysis reveals that upon femtosecond laser excitation, phonons and spins can be driven out of thermal equilibrium for several nanoseconds. KW - ultrafast KW - x-ray diffraction KW - magnetostriction KW - nonequilibrium KW - spin KW - phonon KW - rare earth Y1 - 2017 U6 - https://doi.org/10.1088/1361-648X/aa7187 SN - 0953-8984 SN - 1361-648X VL - 29 SP - 5884 EP - 5891 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pavlenko, Elena S. A1 - Sander, Mathias A1 - Cui, Q. A1 - Bargheer, Matias T1 - Gold Nanorods Sense the Ultrafast Viscoelastic Deformation of Polymers upon Molecular Strain Actuation JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - On the basis of the layer-by-layer deposition of polyelectrolytes, we have designed hybrid nanolayer composites for integrated optoacoustic experiments. The femtosecond-laser-excitation of an Azo functionalized film launches nanoscale strain waves at GHz frequencies into a transparent polymer layer. Gold nanorods deposited on the surface sense the arrival of these hyper-sound-waves on the picosecond time scale via a modification of their longitudinal plasmon resonance. We simulated the strain waves using a simple linear masses-and-springs model, which yields good agreement with the observed time scales associated with the nanolayer thicknesses of the constituent materials. From systematic experiments with calibrated strain amplitudes we conclude that reversible viscoelastic deformations of the polyelectrolyte multilayers are triggered by ultrashort pressure transients of about 4 MPa. Our experiments show that strain-mediated interactions in nanoarchitectures composed of molecular photoswitches and plasmonic particles may be used to design new functionalities. The approach combines the highly flexible and cost-effective preparation of polyelectrolyte multilayers with ultrafast molecular strain actuation and plasmonic sensing. Although we use simple flat layered structures for demonstration, this new concept can be used for three-dimensional nanoassemblies with different functionalities. The ultrafast and reversible nature of the response is highly desirable, and the short wavelength associated with the high frequency of the hyper-sound-waves connecting photoactive molecules and nanoparticles inherently gives spectroscopic access to the nanoscale. High-frequency elastic moduli are derived from the ultrafast spectroscopy of the hypersonic response in polyelectrolyte multilayers. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcc.6b06915 SN - 1932-7447 VL - 120 SP - 24957 EP - 24964 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Pavlenko, Elena S. A1 - Sander, Mathias A1 - Mitzscherling, S. A1 - Pudell, Jan-Etienne A1 - Zamponi, Flavio A1 - Roessle, M. A1 - Bojahr, Andre A1 - Bargheer, Matias T1 - Azobenzene - functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers JF - Nanoscale N2 - We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain epsilon similar to 5 x 10(-4) is calibrated by ultrafast X-ray diffraction. Y1 - 2016 U6 - https://doi.org/10.1039/c6nr01448h SN - 2040-3364 SN - 2040-3372 VL - 8 SP - 13297 EP - 13302 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Reppert, Alexander von A1 - Sarhan, Radwan Mohamed A1 - Stete, Felix A1 - Pudell, Jan-Etienne A1 - Del Fatti, N. A1 - Crut, A. A1 - Koetz, Joachim A1 - Liebig, Ferenc A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias T1 - Watching the Vibration and Cooling of Ultrathin Gold Nanotriangles by Ultrafast X-ray Diffraction JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We study the vibrations of ultrathin gold nanotriangles upon optical excitation of the electron gas by ultrafast X-ray diffraction. We quantitatively measure the strain evolution in these highly asymmetric nano-objects, providing a direct estimation of the amplitude and phase of the excited vibrational motion. The maximal strain value is well reproduced by calculations addressing pump absorption by the nanotriangles and their resulting thermal expansion. The amplitude and phase of the out-of-plane vibration mode with 3.6 ps period dominating the observed oscillations are related to two distinct excitation mechanisms. Electronic and phonon pressures impose stresses with different time dependences. The nanosecond relaxation of the expansion yields a direct temperature sensing of the nano-object. The presence of a thin organic molecular layer at the nanotriangle/substrate interfaces drastically reduces the thermal conductance to the substrate. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcc.6b11651 SN - 1932-7447 VL - 120 SP - 28894 EP - 28899 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Reppert, Alexander von A1 - Pudell, Jan-Etienne A1 - Koc, A. A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet JF - Structural dynamics N2 - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Neel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. (C) 2016 Author(s). Y1 - 2016 U6 - https://doi.org/10.1063/1.4961253 SN - 2329-7778 VL - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Reppert, Alexander von A1 - Puddell, J. A1 - Koc, A. A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet JF - Structural dynamics N2 - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. Y1 - 2016 U6 - https://doi.org/10.1063/1.4961253 SN - 2329-7778 VL - 3 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Sander, Mathias A1 - Koc, A. A1 - Kwamen, C. T. A1 - Michaels, H. A1 - Reppert, Alexander von A1 - Pudell, Jan-Etienne A1 - Zamponi, Flavio A1 - Bargheer, Matias A1 - Sellmann, J. A1 - Schwarzkopf, J. A1 - Gaal, P. T1 - Characterization of an ultrafast Bragg-Switch for shortening hard x-ray pulses JF - Journal of applied physics N2 - We present a nanostructured device that functions as photoacoustic hard x-ray switch. The device is triggered by femtosecond laser pulses and allows for temporal gating of hard x-rays on picosecond (ps) timescales. It may be used for pulse picking or even pulse shortening in 3rd generation synchrotron sources. Previous approaches mainly suffered from insufficient switching contrasts due to excitation-induced thermal distortions. We present a new approach where thermal distortions are spatially separated from the functional switching layers in the structure. Our measurements yield a switching contrast of 14, which is sufficient for efficient hard x-ray pulse shortening. The optimized structure also allows for utilizing the switch at high repetition rates of up to 208 kHz. Published by AIP Publishing. Y1 - 2016 U6 - https://doi.org/10.1063/1.4967835 SN - 0021-8979 SN - 1089-7550 VL - 120 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Iurchuk, V. A1 - Schick, D. A1 - Bran, J. A1 - Colson, D. A1 - Forget, A. A1 - Halley, D. A1 - Koc, Azize A1 - Reinhardt, Mathias A1 - Kwamen, C. A1 - Morley, N. A. A1 - Bargheer, Matias A1 - Viret, M. A1 - Gumeniuk, R. A1 - Schmerber, G. A1 - Doudin, B. A1 - Kundys, B. T1 - Optical Writing of Magnetic Properties by Remanent Photostriction JF - Physical review letters N2 - We present an optically induced remanent photostriction in BiFeO3, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO3/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO3. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications. Y1 - 2016 U6 - https://doi.org/10.1103/PhysRevLett.117.107403 SN - 0031-9007 SN - 1079-7114 VL - 117 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Reinhardt, Matthias A1 - Koc, Azize A1 - Leitenberger, Wolfram A1 - Gaal, Peter A1 - Bargheer, Matias T1 - Optimized spatial overlap in optical pump-X-ray probe experiments with high repetition rate using laser-induced surface distortions JF - Journal of synchrotron radiation N2 - Ultrafast X-ray diffraction experiments require careful adjustment of the spatial overlap between the optical excitation and the X-ray probe pulse. This is especially challenging at high laser repetition rates. Sample distortions caused by the large heat load on the sample and the relatively low optical energy per pulse lead to only tiny signal changes. In consequence, this results in small footprints of the optical excitation on the sample, which turns the adjustment of the overlap difficult. Here a method for reliable overlap adjustment based on reciprocal space mapping of a laser excited thin film is presented. KW - ultrafast X-ray diffraction KW - nanostructures KW - surface deformation KW - heat diffusion KW - optical pump Y1 - 2016 U6 - https://doi.org/10.1107/S1600577515024443 SN - 1600-5775 VL - 23 SP - 474 EP - 479 PB - International Union of Crystallography CY - Chester ER - TY - JOUR A1 - Cui, Qianling A1 - Xia, Bihua A1 - Mitzscherling, Steffen A1 - Masic, Admir A1 - Li, Lidong A1 - Bargheer, Matias A1 - Moehwald, Helmuth T1 - Preparation of gold nanostars and their study in selective catalytic reactions JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - In this work, gold nanostars (AuNSs) with size around 90 nm were prepared through an easy one-step method. They show excellent catalytic activity and large surface-enhanced Raman scattering (SERS) activity at the same time. Surprisingly, they exhibited different catalytic performance on the reduction of aromatic nitro compounds with different substituents on the para position. To understand such a difference, the SERS spectra were recorded, showing that the molecular orientation of reactants on the gold surface were different. We anticipate that this research will help to understand the relationship of the molecular orientation with the catalytic activity of gold nanoparticles. KW - Nanoparticles KW - Gold KW - Catalytic reaction KW - Surface enhanced Raman scattering (SERS) KW - Molecular orientation Y1 - 2015 U6 - https://doi.org/10.1016/j.colsurfa.2014.10.028 SN - 0927-7757 SN - 1873-4359 VL - 465 SP - 20 EP - 25 PB - Elsevier CY - Amsterdam ER -