@misc{PudellMaznevHerzogetal.2018, author = {Pudell, Jan-Etienne and Maznev, Alexei and Herzog, Marc and Kronseder, M. and Back, Christian and Malinowski, Gregory and von Reppert, Alexander and Bargheer, Matias}, title = {Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {797}, issn = {1866-8372}, doi = {10.25932/publishup-42623}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426233}, pages = {7}, year = {2018}, abstract = {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.}, language = {en} } @misc{ZeuschnerParpiievPezeriletal.2019, author = {Zeuschner, Steffen and Parpiiev, Tymur and Pezeril, Thomas and Hillion, Arnaud and Dumesnil, Karine and Anane, Abdelmadjid and Pudell, Jan-Etienne and Willig, Lisa and R{\"o}ssle, Matthias and Herzog, Marc and von Reppert, Alexander and Bargheer, Matias}, title = {Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-naturwissenschaftliche Reihe}, number = {706}, issn = {1866-8372}, doi = {10.25932/publishup-42845}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-428457}, pages = {9}, year = {2019}, abstract = {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.}, language = {en} } @misc{LiebigSarhanBargheeretal.2020, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Bargheer, Matias and Schmitt, Clemens Nikolaus Zeno and Poghosyan, Armen H. and Shahinyanf, Aram A. and Koetz, Joachim}, title = {Spiked gold nanotriangles}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {829}, issn = {1866-8372}, doi = {10.25932/publishup-44556}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445568}, pages = {11}, year = {2020}, abstract = {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).}, language = {en} } @misc{vonReppertMatternPudelletal.2020, author = {von Reppert, Alexander and Mattern, Maximilian and Pudell, Jan-Etienne and Zeuschner, Steffen Peer and Dumesnil, Karine and Bargheer, Matias}, title = {Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {899}, issn = {1866-8372}, doi = {10.25932/publishup-46935}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469350}, pages = {15}, year = {2020}, abstract = {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.}, language = {en} }