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  - 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  - 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  -