@article{FritzReisAdamsetal., author = {Fritz, D. M. and Reis, D. A. and Adams, B. and Akre, R. A. and Arthur, J. and Blome, Christian and Bucksbaum, P. H. and Cavalieri, A. L. and Engemann, S. and Fahy, S. and Falcone, R. W. and Fuoss, P. H. and Gaffney, K. J. and George, M. J. and Hajdu, J. and Hertlein, M. P. and Hillyard, P. B. and Horn-von Hoegen, Michael and Kammler, Martin and Kaspar, J. and Kienberger, R. and Krejcik, P. and Lee, S. H. and Lindenberg, A. M. and McFarland, B. and Meyer, D. and Montagne, T. and Murray, E. D. and Nelson, A. J. and Nicoul, Matthieu and Pahl, R. and Rudati, J. and Schlarb, H. and Siddons, D. P. and Sokolowski-Tinten, Klaus and Tschentscher, Th and von der Linde, D. and Hastings, J. B.}, title = {Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays}, series = {Science}, volume = {315}, journal = {Science}, number = {5812}, publisher = {AAAS}, doi = {10.1126/science.1135009}, pages = {633 -- 636}, abstract = {Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid.}, language = {en} } @article{HildSeifertKammleretal., author = {Hild, R. and Seifert, C. and Kammler, Martin and Meyer zu Heringdorf, Frank-Joachim and Horn-von Hoegen, Michael and Zhachuk, R.A and Olshanetsky, B.Z}, title = {Kinetics of Au induced faceting of vicinal Si(111)}, series = {Surface Science}, volume = {512}, journal = {Surface Science}, number = {1-2}, publisher = {Elsevier}, doi = {10.1016/S0039-6028(02)01666-7}, pages = {117 -- 127}, abstract = {Au induced faceting of vicinal Si(1 1 1) has been studied during adsorption at elevated temperature by spot profile analyzing of low energy electron diffraction and after quenching to room temperature by scanning tunneling microscopy. On the surfaces inclined towards five different types of facets form with increasing Au coverage at adsorption temperatures Tads below 800 °C. They are (4 4 3), (7 7 5), (5 5 3), a stepped (2 2 1), and the (3 3 1) facets. Atomic models for the (5 5 3) and (7 7 5) facet planes are proposed on the basis of high resolution STM images. At C we found the formation of an ordered step train which covers the entire surface. With further increasing Au coverage the stepped surface decomposes again into (1 1 1) terraces and step bunches. Driving force is the formation of the Si(1 1 1)-(5×2)-Au reconstruction.}, language = {en} } @inproceedings{SimonsohnDaviesKnorrWildBodeetal., author = {Simonsohn, Angelika and Davies-Knorr, Patricia and Wild-Bode, Christine and Zolyniak, Nicole and Bischoff, Thomas and Pfingsten, Andrea and Fischer, Martin R.}, title = {Entwicklung eines interprofessionellen Online-Kurses f{\"u}r Medizin- und Physiotherapiestudierende}, series = {Gemeinsame Jahrestagung der Gesellschaft f{\"u}r Medizinische Ausbildung (GMA), des Arbeitskreises zur Weiterentwicklung der Lehre in der Zahnmedizin (AKWLZ) und der Chirurgischen Arbeitsgemeinschaft Lehre (CAL), 25.09. - 28.09.2019, Frankfurt am Main}, booktitle = {Gemeinsame Jahrestagung der Gesellschaft f{\"u}r Medizinische Ausbildung (GMA), des Arbeitskreises zur Weiterentwicklung der Lehre in der Zahnmedizin (AKWLZ) und der Chirurgischen Arbeitsgemeinschaft Lehre (CAL), 25.09. - 28.09.2019, Frankfurt am Main}, publisher = {German Medical Science}, address = {D{\"u}sseldorf}, doi = {10.3205/19gma310}, url = {http://nbn-resolving.de/urn:nbn:de:0183-19gma3108}, abstract = {Das sich ver{\"a}ndernde Gesundheitssystem macht Anpassungen in der Ausbildung der Gesundheitsberufe notwendig. Dabei wird die St{\"a}rkung der Interprofessionalit{\"a}t besonders betont. Die Entwicklung und Implementierung von interprofessionellen Lernszenarien birgt jedoch oftmals organisatorisch-logistische Herausforderungen. Es fehlen derzeit noch orts- und zeitunabh{\"a}ngige Lernszenarien, die asynchrones interprofessionelles Lernen erm{\"o}glichen. Der neu entwickelte Online-Kurs „Medizin und Physiotherapie in der Rehabilitation" hat zum Ziel, zur Schließung dieser L{\"u}cke beizutragen. Die Kursentwicklung ist Teil eines Forschungsprojekts, das den Einfluss von interprofessionellem Online-Lernen auf die Kooperationskompetenz untersucht.}, language = {de} } @unpublished{CavalleriSidersTothetal., author = {Cavalleri, Andrea and Siders, Craig and Toth, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and von der Linde, Dietrich and Kammler, Martin and Horn- von Hoegen, Michael}, title = {Measurement of harmonic and anharmonic semi-conductor-lattice dynamics with ultrafast x-ray diffraction}, abstract = {Many fundamental processes in solids, such as heat transport and phase transitions involve atomic movement on ultrafast time-scales, but cannot be directly measured with visible light. Using ultrafast x-ray diffraction, atomic motion can be measured on its natural time-scale. Photo-excitation of bulk and layered semiconductors was achieved with 800-nm wavelength femtosecond laser pulses. Optical excitation triggers a chain of relaxation processes, causing rapid lattice heating, generation and propagation of stress/strain waves into the bulk and eventual anharmonic decay of coherent acoustic phonons into the thermal bath of the solid. While the first steps of carrier relaxation, excitation and decay of Raman-active optical phonons have been in the past characterized optically at surfaces, the bulk acoustic dynamics at longer times has not. We measure length scales of lattice excitation, thereby detecting ultrafast heat diffusion via fast electrons, coherent acoustic pulse propagation into the bulk or across buried interfaces and anharmonic damping of non-equilibrium acoustic phonons. The measurement is performed with sensitivity on lattice spacing of 10 femtometers (i.e., 3 nuclear diameters).}, language = {en} } @unpublished{SidersCavalleriTothetal., author = {Siders, Craig and Cavalleri, Andrea and Toth, Csaba and Squier Jeff A., and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and von der Linde, Dietrich and Kammler, Martin and Horn- von Hoegen, Michael}, title = {Ultrafast Nonthermal Melting of Femtosecond-laser-irradiated Germanium Measured by Ultrafast X-ray Diffraction}, abstract = {Many fundamental processes in nature, such as chemical reactions and phase transitions involve rearrangement of the constituent atoms. Such changes cannot be directly measured with visible light and occur transiently on time-scales comparable with the natural oscillation periods of atoms (femtoseconds to picoseconds). We present experiments on Ge-111 films irradiated with 100-fs 800-nm light pulses and probed by a time-delayed sub-ps x-ray pulse at 8 keV. After excitation of a dense electron-hole plasma within the 160-nm film, the ultrafast pathway of lattice disordering is measured as a function laser fluence. For close-to-threshold irradiation, inhomogeneous thermal melting, occurring via surface nucleation of the liquid phase and growth into the bulk determines the dynamics of the solid-to-liquid phase transition. For excitation at about twice the melting threshold, a nonthermal pathway, starting from a highly excited cold solid and relaxing into a hot liquid causes ultrafast melting. At long time delays, nearly perfect recrystallization of a (111) crystal is observed.}, language = {en} } @inproceedings{SidersCavalleriTothetal., author = {Siders, C. W. and Cavalleri, Andrea and T{\´o}th, Csaba and Wilson, K. R. and Squier, Jeff A. and Barty, C. P. J. and Kammler, Martin and Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D.}, title = {Femtosecond X-ray diffraction of short-pulse irradiated semiconductors}, series = {Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 24-24 May 2002, Long Beach, CA, USA}, booktitle = {Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 24-24 May 2002, Long Beach, CA, USA}, publisher = {IEEE}, doi = {10.1109/CLEO.2002.1033997}, pages = {297 -- 298}, abstract = {Summary form only given, as follow. Ultrafast optical-pump, X-ray diffraction probe experiments are providing new ways to study transient processes including the direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place. Current table-top-terawatt femtosecond laser systems provide an attractive source of few-hundred femtosecond duration bursts of angstrom-scale X-ray radiation with fluxes comparable to standard rotating anode sources. Their compact size enables time resolved structural dynamics to be studied in the small laboratory with temporal resolution better than typical molecular vibrational periods. Ultrafast structural dynamics in crystalline samples are readily studied with such systems and experiments to be discussed in this talk include ultrafast non-thermal solid-to-liquid transition in thin single-crystal Ge-111 films grown on Si-111 substrates; ultrafast non-thermal solid-to-solid transitions in bulk vanadium dioxide from a low temperature insulating phase to a high temperature metallic phase; and harmonic and anharmonic coherent acoustic dynamics in layered Ge-111/Si-111 and bulk GaAs-111 samples. Future improvements in high-average power short-pulse lasers will enable the study of a wider class of materials such as amorphous solids or liquid-phase dynamics of simple molecules, while proposed 4th generation light sources based upon single-pass X-ray free-electron lasers will permit singleshot structural determination of complex biomolecules.}, language = {en} } @article{SokolowskiTintenHornvonHoegenvonderLindeetal., author = {Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Kammler, Martin}, title = {Transient lattice dynamics in fs-laser-excited semiconductors probed by ultrafast X-ray diffraction}, series = {Journal de Physique IV}, volume = {11}, journal = {Journal de Physique IV}, number = {Pr2}, publisher = {EDP}, doi = {10.1051/jp4:2001290}, pages = {473 -- 477}, abstract = {A study of lattice dynamics in fs-laser-excited crystalline bulk Ge and Ge/Si-heterostructures, using time-resolved x-ray diffraction, was presented. Fast energy transport deep into the bulk of the material, coherent acoustic phonon dynamics, lattice anharmonicity, and vibrational transport across a buried interfaces were observed. Graphs showing time-dependent shifts of the centroid of the measured rocking curves in the Ge-overlayer and in the Si-substrate for different fluences, were presented.}, language = {en} } @article{SokolowskiTintenCavalleriSidersetal., author = {Sokolowski-Tinten, Klaus and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, D. and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R.}, title = {Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures}, series = {Chemical Physics}, volume = {66}, journal = {Chemical Physics}, publisher = {Springer}, doi = {10.1007/978-3-642-56546-5_81}, pages = {281 -- 283}, abstract = {Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed.}, language = {en} } @unpublished{TringidesConradMenzeletal.2002, author = {Tringides, Michael C. and Conrad, E. H. and Menzel, Andreas and Voss, Neil R. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Dynamics of atomic steps on Si(001) studied by temporal LEED spectroscopy [Poster]}, year = {2002}, abstract = {While surface kinetics measurements for single atom diffusion have proliferated, little work exists attempting to measure surface dynamics under equilibrium conditions. We will present our recent work on developing Temporal LEED Spectroscopy (TLS) as a dynamic probe of surfaces capable of kinetics measurements at both high temperatures and surface coverages. By tuning the diffraction to specific structural entities such as steps, islands, etc., and monitoring the diffracted signal as a function of time, dynamics information about these structures can be obtained. As an example we will present TLS results for the dynamics of step fluctuations on Si(001) [1]. We have measured activation energies and identified step-edge diffusion as the rate limiting process for 950K < T < 1130K. Although this result is in apparent disagreement with earlier work, a careful analysis, considering crossover temperatures between different microscopic processes, can reconcile the differences. 1. M. Kammler, et al., Phys. Rev. B (in press).}, language = {en} } @article{HornvonHoegenMeyerzuHeringdorfKammleretal., author = {Horn-von Hoegen, Michael and Meyer zu Heringdorf, Frank-Joachim and Kammler, Martin and Schaeffer, C. and Reinking, D. and Hofmann, K. R.}, title = {Bi surfactant mediated epitaxy of Ge on Si(111)}, series = {Thin Solid Films}, volume = {343-344}, journal = {Thin Solid Films}, publisher = {Elsevier}, doi = {10.1016/S0040-6090(98)01659-9}, pages = {579 -- 582}, abstract = {We have tested Bi for the surfactant mediated epitaxy of Ge on Si(111). Islanding of Ge is prevented and a 2D layer growth of smooth and continuous Ge films is observed. The lattice mismatch is accommodated by a periodic array of dislocations confined to the Si/Ge interface. The large covalent radius of Bi reduces the binding energy, allowing Very efficient segregation and low doping levels even at low growth temperatures. Unfortunately, this results also in a high Bi desorption flux limiting the possible growth temperatures below 600 degrees C. Consequently the Ge films show a high defect density in the order of 10(8) cm(-2) for stacking faults and 10(9) cm(-2) for dislocations which limit electron Hall mobility to values below 700 cm(2)/V s at room temperature.}, language = {en} }