| 1. |
- Barillot, T., et al.
(författare)
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Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule
- 2021
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Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or hole) dynamics prior to significant structural change was first recognized more than 20 years ago and termed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specific hole within the molecule. We report an investigation of the dynamics of inner valence hole states in isopropanol where we use an x-ray pump-x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an ab initio theoretical treatment. We record the signature of transient hole dynamics and make the first tentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify that the effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localized in space and time in molecules and thus to charge transfer phenomena that are fundamental in chemical and material physics.
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| 2. |
- Cavalieri, A L, et al.
(författare)
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Clocking femtosecond X rays.
- 2005
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Ingår i: Phys Rev Lett. - 0031-9007. ; 94:11
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Tidskriftsartikel (refereegranskat)abstract
- Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of the x-ray pulse duration are hampered by the inability to precisely synchronize an external laser to the accelerator. At the Sub-Picosecond Pulse Source at the Stanford Linear-Accelerator Center we solved this problem by measuring the arrival time of each high energy electron bunch with electro-optic sampling. This measurement indirectly determined the arrival time of each x-ray pulse relative to an external pump laser pulse with a time resolution of better than 60 fs rms.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Gaffney, K J, et al.
(författare)
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Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb
- 2005
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 95:12
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Tidskriftsartikel (refereegranskat)abstract
- The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs. This structural anisotropy indicates that the initially generated fluid differs significantly from the equilibrium liquid.
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| 6. |
- Hillyard, P. B., et al.
(författare)
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Carrier-density-dependent lattice stability in InSb
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:12, s. 125501-
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast decay of the x-ray diffraction intensity following laser excitation of an InSb crystal has been utilized to observe carrier dependent changes in the potential energy surface. For the first time, an abrupt carrier dependent onset for potential energy surface softening and the appearance of accelerated atomic disordering for a very high average carrier density have been observed. Inertial dynamics dominate the early stages of crystal disordering for a wide range of carrier densities between the onset of crystal softening and the appearance of accelerated atomic disordering.
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| 7. |
- Cryan, James P., et al.
(författare)
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Auger Electron Angular Distribution of Double Core-Hole States in the Molecular Reference Frame
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:8, s. 083004-
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Tidskriftsartikel (refereegranskat)abstract
- The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×1011 photons in a ∼5 fs pulse, that can be focused to produce double core vacancies through rapid sequential ionization. This enables double core vacancy Auger electron spectroscopy, an entirely new way to study femtosecond chemical dynamics with Auger electrons that probe the local valence structure of molecules near a specific atomic core. Using 1.1 keV photons for sequential x-ray ionization of impulsively aligned molecular nitrogen, we observed a rich single-site double core vacancy Auger electron spectrum near 413 eV, in good agreement with ab initio calculations, and we measured the corresponding Auger electron angle dependence in the molecular frame.
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| 8. |
- Cryan, J P, et al.
(författare)
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Molecular frame Auger electron energy spectrum from N2
- 2012
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:5, s. 055601-
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the first angle-resolved, non-resonant (normal) Auger spectra for impulsively aligned nitrogen molecules. We have measured the angular pattern of Auger electron emission following K -shell photoionization by 1.1 keV photons from the Linac Coherent Light Source (LCLS). Using strong-field-induced molecular alignment to make molecular frame measurements is equally effective for both repulsive and quasi-bound final states. The capability to resolve Auger emission angular distributions in the molecular frame of reference provides a new tool for spectral assignments in congested Auger electron spectra that takes advantage of the symmetries of the final diction states. Based on our experimental results and theoretical predictions, we propose the assignment of the spectral features in the Auger electron spectrum.
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| 9. |
- Gabrysch, Markus, et al.
(författare)
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Formation of secondary electron cascades in single-crystalline plasma-deposited diamond upon exposure to femtosecond x-ray pulses
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:6
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Tidskriftsartikel (refereegranskat)abstract
- Secondary electron cascades were measured in high purity single-crystalline chemical vapor deposition (CVD) diamond, following exposure to ultrashort hard x-ray pulses (140 fs full width at half maximum, 8.9 keV energy) from the Sub-Picosecond Pulse Source at the Stanford Linear Accelerator Center. We report measurements of the pair creation energy and of drift mobility of carriers in two CVD diamond crystals. This was done for the first time using femtosecond x-ray excitation. Values for the average pair creation energy were found to be 12.17 +/- 0.57 and 11.81 +/- 0.59 eV for the two crystals, respectively. These values are in good agreement with recent theoretical predictions. The average drift mobility of carriers, obtained by the best fit to device simulations, was mu(h)= 2750 cm(2)/V s for holes and was mu(e)= 2760 cm(2) / V s for electrons. These mobility values represent lower bounds for charge mobilities due to possible polarization of the samples. The results demonstrate outstanding electric properties and the enormous potential of diamond in ultrafast x-ray detectors.
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| 10. |
- Pedersoli, E., et al.
(författare)
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Mesoscale morphology of airborne core-shell nanoparticle clusters : x-ray laser coherent diffraction imaging
- 2013
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16 SI, s. 164033-
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Tidskriftsartikel (refereegranskat)abstract
- Unraveling the complex morphology of functional materials like core-shell nanoparticles and its evolution in different environments is still a challenge. Only recently has the single-particle coherent diffraction imaging (CDI), enabled by the ultrabright femtosecond free-electron laser pulses, provided breakthroughs in understanding mesoscopic morphology of nanoparticulate matter. Here, we report the first CDI results for Co@SiO2 core-shell nanoparticles randomly clustered in large airborne aggregates, obtained using the x-ray free-electron laser at the Linac Coherent Light Source. Our experimental results compare favourably with simulated diffraction patterns for clustered Co@SiO2 nanoparticles with similar to 10 nm core diameter and similar to 30 nm shell outer diameter, which confirms the ability to resolve the mesoscale morphology of complex metastable structures. The findings in this first morphological study of core-shell nanomaterials are a solid base for future time-resolved studies of dynamic phenomena in complex nanoparticulate matter using x-ray lasers.
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