TY  - JOUR
A1  - Abboud, Ali
A1  - Send, Sebastian
A1  - Pashniak, N.
A1  - Leitenberger, Wolfram
A1  - Ihle, Sebastian
A1  - Huth, M.
A1  - Hartmann, Robert
A1  - Strüder, Lothar
A1  - Pietsch, Ullrich
T1  - Sub-pixel resolution of a pnCCD for X-ray white beam applications
JF  - Journal of instrumentation
N2  - A new approach to achieve sub-pixel spatial resolution in a pnCCD detector with 75 x 75 mu m(2) pixel size is proposed for X-ray applications in single photon counting mode. The approach considers the energy dependence of the charge cloud created by a single photon and its split probabilities between neighboring pixels of the detector based on a rectangular model for the charge cloud density. For cases where the charge of this cloud becomes distributed over three or four pixels the center position of photon impact can be reconstructed with a precision better than 2 mu m. The predicted charge cloud sizes are tested at selected X-ray fluorescence lines emitting energies between 6.4 keV and 17.4 keV and forming charge clouds with size (rms) varying between 8 mu m and 10 mu m respectively. The 2 mu m enhanced spatial resolution of the pnCCD is verified by means of an x-ray transmission experiment throughout an optical grating.
KW  - Solid state detectors
KW  - Interaction of radiation with matter
KW  - Detector modelling and simulations II (electric fields, charge transport, multiplication and induction, pulse formation, electron emission, etc)
Y1  - 2013
U6  - https://doi.org/10.1088/1748-0221/8/05/P05005
SN  - 1748-0221
VL  - 8
IS  - 3
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Bojahr, Andre
A1  - Gohlke, Matthias
A1  - Leitenberger, Wolfram
A1  - Pudell, Jan-Etienne
A1  - Reinhardt, Matthias
A1  - von Reppert, Alexander
A1  - Rössle, Matthias
A1  - Sander, Mathias
A1  - Gaal, Peter
A1  - Bargheer, Matias
T1  - Second Harmonic Generation of Nanoscale Phonon Wave Packets
JF  - Physical review letters
N2  - Phonons are often regarded as delocalized quasiparticles with certain energy and momentum. The anharmonic interaction of phonons determines macroscopic properties of the solid, such as thermal expansion or thermal conductivity, and a detailed understanding becomes increasingly important for functional nanostructures. Although phonon-phonon scattering processes depicted in simple wave-vector diagrams are the basis of theories describing these macroscopic phenomena, experiments directly accessing these coupling channels are scarce. We synthesize monochromatic acoustic phonon wave packets with only a few cycles to introduce nonlinear phononics as the acoustic counterpart to nonlinear optics. Control of the wave vector, bandwidth, and consequently spatial extent of the phonon wave packets allows us to observe nonlinear phonon interaction, in particular, second harmonic generation, in real time by wave-vector-sensitive Brillouin scattering with x-rays and optical photons.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.115.195502
SN  - 0031-9007
SN  - 1079-7114
VL  - 115
IS  - 19
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Bojahr, Andre
A1  - Herzog, Marc
A1  - Mitzscherling, Steffen
A1  - Maerten, Lena
A1  - Schick, Daniel
A1  - Goldshteyn, J.
A1  - Leitenberger, Wolfram
A1  - Shayduk, R.
A1  - Gaal, P.
A1  - Bargheer, Matias
T1  - Brillouin scattering of visible and hard X-ray photons from optically synthesized phonon wavepackets
JF  - Optics express : the international electronic journal of optics
N2  - We monitor how destructive interference of undesired phonon frequency components shapes a quasi-monochromatic hypersound wavepacket spectrum during its local real-time preparation by a nanometric transducer and follow the subsequent decay by nonlinear coupling. We prove each frequency component of an optical supercontinuum probe to be sensitive to one particular phonon wavevector in bulk material and cross-check this by ultrafast x-ray diffraction experiments with direct access to the lattice dynamics. Establishing reliable experimental techniques with direct access to the transient spectrum of the excitation is crucial for the interpretation in strongly nonlinear regimes, such as soliton formation.
Y1  - 2013
U6  - https://doi.org/10.1364/OE.21.021188
SN  - 1094-4087
VL  - 21
IS  - 18
SP  - 21188
EP  - 21197
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - JOUR
A1  - Brajpuriya, Ranjeet
A1  - Tripathi, Sumit
A1  - Sharma, Abhishek
A1  - Chaudhari, S.M.
A1  - Phase, D.M.
A1  - Gupta, Ajay
A1  - Shripathi, Thoudinja
A1  - Leitenberger, Wolfram
A1  - Pietsch, Ullrich
A1  - Laxmi, N.
T1  - Temperature dependent energy-dispersive X-ray diffraction and magnetic study of Fe/Al interface
N2  - In situ temperature dependent energy-dispersive structural and magnetic study of electron beam evaporated Fe/Al multilayer sample (MLS) has been investigated. The structural studies show the formation of an intermixed FeAl transition layer of a few nanometers thick at the interface during deposition, which on annealing at 300 degrees C transforms to B2FeAl intermetallic phase. Magnetization decreases with increase in temperature and drops to minimum above 300 degrees C due to increase in anti-ferromagnetic interlayer coupling and formation of nonmagnetic FeAl phase at the interface. The Curie temperature (T-c) is found to be 288 degrees C and is much less than that of bulk bcc Fe.
Y1  - 2007
UR  - http://www.sciencedirect.com/science/journal/01694332
U6  - https://doi.org/10.1016/j.apsusc.2007.04.069
SN  - 0169-4332
ER  - 
TY  - JOUR
A1  - Gaal, P.
A1  - Schick, Daniel
A1  - Herzog, Marc
A1  - Bojahr, Andre
A1  - Shayduk, Roman
A1  - Goldshteyn, J.
A1  - Navirian, Hengameh A.
A1  - Leitenberger, Wolfram
A1  - Vrejoiu, Ionela
A1  - Khakhulin, D.
A1  - Wulff, M.
A1  - Bargheer, Matias
T1  - Time-domain sampling of x-ray pulses using an ultrafast sample response
JF  - Applied physics letters
N2  - We employ the ultrafast response of a 15.4 nm thin SrRuO3 layer grown epitaxially on a SrTiO3 substrate to perform time-domain sampling of an x-ray pulse emitted from a synchrotron storage ring. Excitation of the sample with an ultrashort laser pulse triggers coherent expansion and compression waves in the thin layer, which turn the diffraction efficiency on and off at a fixed Bragg angle during 5 ps. This is significantly shorter than the duration of the synchrotron x-ray pulse of 100 ps. Cross-correlation measurements of the ultrafast sample response and the synchrotron x-ray pulse allow to reconstruct the x-ray pulse shape.
Y1  - 2012
U6  - https://doi.org/10.1063/1.4769828
SN  - 0003-6951
VL  - 101
IS  - 24
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Gaal, Peter
A1  - Schick, Daniel
A1  - Herzog, Marc
A1  - Bojahr, Andre
A1  - Shayduk, Roman
A1  - Goldshteyn, Jevgeni
A1  - Leitenberger, Wolfram
A1  - Vrejoiu, Ionela
A1  - Khakhulin, Dmitry
A1  - Wulff, Michael
A1  - Bargheer, Matias
T1  - Ultrafast switching of hard X-rays
JF  - Journal of synchrotron radiation
N2  - A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of <= 5 ps and a peak reflectivity of similar to 10(-3). The device is tested in a real synchrotron-based pump-probe experiment and reveals features of coherent phonon propagation in a second thin film sample, thus demonstrating the potential to significantly improve the temporal resolution at existing synchrotron facilities.
KW  - ultrafast X-ray diffraction
KW  - thin film
KW  - coherent phonons
KW  - X-ray switching
KW  - pulse shortening
KW  - optical pump X-ray probe
KW  - time-resolved
Y1  - 2014
U6  - https://doi.org/10.1107/S1600577513031949
SN  - 0909-0495
SN  - 1600-5775
VL  - 21
SP  - 380
EP  - 385
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Gruber, W.
A1  - Chakravarty, S.
A1  - Baehtz, C.
A1  - Leitenberger, Wolfram
A1  - Bruns, M.
A1  - Kobler, A.
A1  - Kübel, Christian
A1  - Schmidt, H.
T1  - Strain relaxation and vacancy creation in thin platinum films
JF  - Physical review letters
N2  - Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 degrees C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.107.265501
SN  - 0031-9007
VL  - 107
IS  - 26
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Gupta, Ranjeeta
A1  - Gupta, Ajay
A1  - Leitenberger, Wolfram
A1  - Rüffer, R.
T1  - Mechanism of stress relaxation in nanocrystalline Fe-N thin films
JF  - Physical review : B, Condensed matter and materials physics
N2  - The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-deposited film possesses a strong in-plane compressive stress which relaxes with thermal annealing. Precise diffusion measurements using nuclear resonance reflectivity show that stress relaxation does not involve any long-range diffusion of Fe atoms. Rather, a redistribution of nitrogen atoms at various interstitial sites, as evidenced by conversion electron Mossbauer spectroscopy, is responsible for the relaxation of internal stresses. On the other hand, formation of the. gamma'-Fe4N phase at temperatures above 523 K involves long-range rearrangement of Fe atoms. The activation energy for Fe self-diffusion is found to be 0.38 +/- 0.04 eV.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevB.85.075401
SN  - 1098-0121
VL  - 85
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Herzog, Marc
A1  - Bojahr, Andre
A1  - Goldshteyn, J.
A1  - Leitenberger, Wolfram
A1  - Vrejoiu, I.
A1  - Khakhulin, D.
A1  - Wulff, M.
A1  - Shayduk, Roman
A1  - Gaal, P.
A1  - Bargheer, Matias
T1  - Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction
JF  - Applied physics letters
N2  - We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory.
KW  - acoustic waves
KW  - epitaxial layers
KW  - phonon dispersion relations
KW  - terahertz waves
KW  - thin film devices
KW  - X-ray diffraction
Y1  - 2012
U6  - https://doi.org/10.1063/1.3688492
SN  - 0003-6951
VL  - 100
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Herzog, Marc
A1  - Leitenberger, Wolfram
A1  - Shayduk, Roman
A1  - van der Veen, Renske Marjan
A1  - Milne, Chris J.
A1  - Johnson, Steven Lee
A1  - Vrejoiu, Ionela
A1  - Alexe, Marin
A1  - Hesse, Dietrich
A1  - Bargheer, Matias
T1  - Ultrafast manipulation of hard x-rays by efficient Bragg switches
N2  - We experimentally demonstrate efficient switching of the hard x-ray Bragg reflectivity of a SrRuO3 /SrTiO3 superlattice by optical excitation of large-amplitude coherent acoustic superlattice phonons. The rocking curve changes drastically on a 1 ps timescale. The (0 0 116) reflection is almost extinguished (Delta R/R-0=-0.91), while the (0 0 118) reflection increases by more than an order of magnitude (Delta R/R-0=24.1). The change of the x-ray structure factor depends nonlinearly on the phonon amplitude, allowing manipulation of the x-ray response on a timescale considerably shorter than the phonon period. Numerical simulations for a superlattice with slightly changed geometry and realistic parameters predict a switching-contrast ratio Delta R/R-0 of 700 with high reflectivity.
Y1  - 2010
UR  - http://apl.aip.org/
U6  - https://doi.org/10.1063/1.3402773
SN  - 0003-6951
ER  -