| 1. |
- Fritz, D. M., et al.
(författare)
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Ultrafast bond softening in bismuth : Mapping a solid's interatomic potential with X-rays
- 2007
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 315:5812, s. 633-636
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Daranciang, Dan, et al.
(författare)
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Ultrafast Photovoltaic Response in Ferroelectric Nanolayers
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 108:8
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Tidskriftsartikel (refereegranskat)abstract
- We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.
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| 3. |
- Lindenberg, A. M., et al.
(författare)
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X-ray diffuse scattering measurements of nucleation dynamics at femtosecond resolution.
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100:13, s. 135502-1-135502-5
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Tidskriftsartikel (refereegranskat)abstract
- Femtosecond time-resolved small and wide angle x-ray diffuse scattering techniques are applied to investigate the ultrafast nucleation processes that occur during the ablation process in semiconducting materials. Following intense optical excitation, a transient liquid state of high compressibility characterized by large-amplitude density fluctuations is observed and the buildup of these fluctuations is measured in real time. Small-angle scattering measurements reveal snapshots of the spontaneous nucleation of nanoscale voids within a metastable liquid and support theoretical predictions of the ablation process.
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| 4. |
- Zalden, Peter, et al.
(författare)
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Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials
- 2019
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Ingår i: Science. - Washington, DC : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6445, s. 1062-1067
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Tidskriftsartikel (refereegranskat)abstract
- In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics.
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