Pub Date : 2024-01-31eCollection Date: 2024-01-01DOI: 10.1063/4.0000226
Duncan Burns, Nikolas Provatas, Martin Grant
In this article, we address the application of phase field crystal (PFC) theory, a hybrid atomistic-continuum approach, for modeling nanostructure kinetics encountered in laser deposition. We first provide an overview of the PFC methodology, highlighting recent advances to incorporate phononic and heat transport mechanisms. To simulate laser heating, energy is deposited onto a number of polycrystalline, two-dimensional samples through the application of initial stochastic fluctuations. We first demonstrate the ability of the model to simulate plasticity and recrystallization events that follow laser heating in the isothermal limit. Importantly, we also show that sufficient kinetic energy can cause voiding, which serves to suppress shock propagation. We subsequently employ a newly developed thermo-density PFC theory, coined thermal field crystal (TFC), to investigate laser heating of polycrystalline samples under non-isothermal conditions. We observe that the latent heat of transition associated with ordering can lead to long lasting metastable structures and defects, with a healing rate linked to the thermal diffusion. Finally, we illustrate that the lattice temperature simulated by the TFC model is in qualitative agreement with predictions of conventional electron-phonon two-temperature models. We expect that our new TFC formalism can be useful for predicting transient structures that result from rapid laser heating and re-solidification processes.
{"title":"Phase field crystal models with applications to laser deposition: A review.","authors":"Duncan Burns, Nikolas Provatas, Martin Grant","doi":"10.1063/4.0000226","DOIUrl":"10.1063/4.0000226","url":null,"abstract":"<p><p>In this article, we address the application of phase field crystal (PFC) theory, a hybrid atomistic-continuum approach, for modeling nanostructure kinetics encountered in laser deposition. We first provide an overview of the PFC methodology, highlighting recent advances to incorporate phononic and heat transport mechanisms. To simulate laser heating, energy is deposited onto a number of polycrystalline, two-dimensional samples through the application of initial stochastic fluctuations. We first demonstrate the ability of the model to simulate plasticity and recrystallization events that follow laser heating in the isothermal limit. Importantly, we also show that sufficient kinetic energy can cause voiding, which serves to suppress shock propagation. We subsequently employ a newly developed thermo-density PFC theory, coined thermal field crystal (TFC), to investigate laser heating of polycrystalline samples under non-isothermal conditions. We observe that the latent heat of transition associated with ordering can lead to long lasting metastable structures and defects, with a healing rate linked to the thermal diffusion. Finally, we illustrate that the lattice temperature simulated by the TFC model is in qualitative agreement with predictions of conventional electron-phonon two-temperature models. We expect that our new TFC formalism can be useful for predicting transient structures that result from rapid laser heating and re-solidification processes.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10869171/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139742323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-04eCollection Date: 2023-11-01DOI: 10.1063/4.0000203
K M Siddiqui, D B Durham, F Cropp, F Ji, S Paiagua, C Ophus, N C Andresen, L Jin, J Wu, S Wang, X Zhang, W You, M Murnane, M Centurion, X Wang, D S Slaughter, R A Kaindl, P Musumeci, A M Minor, D Filippetto
The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials science. The last couple of decades have witnessed ultrafast electron diffraction (UED) emerge as one of the forefront techniques with the sensitivity to resolve atomic motions. Increasingly sophisticated UED instruments are being developed that are aimed at increasing the beam brightness in order to observe structural signatures, but so far they have been limited to low average current beams. Here, we present the technical design and capabilities of the HiRES (High Repetition-rate Electron Scattering) instrument, which blends relativistic electrons and high repetition rates to achieve orders of magnitude improvement in average beam current compared to the existing state-of-the-art instruments. The setup utilizes a novel electron source to deliver femtosecond duration electron pulses at up to MHz repetition rates for UED experiments. Instrument response function of sub-500 fs is demonstrated with < 100 fs time resolution targeted in future. We provide example cases of diffraction measurements on solid-state and gas-phase samples, including both micro- and nanodiffraction (featuring 100 nm beam size) modes, which showcase the potential of the instrument for novel UED experiments.
{"title":"Relativistic ultrafast electron diffraction at high repetition rates.","authors":"K M Siddiqui, D B Durham, F Cropp, F Ji, S Paiagua, C Ophus, N C Andresen, L Jin, J Wu, S Wang, X Zhang, W You, M Murnane, M Centurion, X Wang, D S Slaughter, R A Kaindl, P Musumeci, A M Minor, D Filippetto","doi":"10.1063/4.0000203","DOIUrl":"10.1063/4.0000203","url":null,"abstract":"<p><p>The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials science. The last couple of decades have witnessed ultrafast electron diffraction (UED) emerge as one of the forefront techniques with the sensitivity to resolve atomic motions. Increasingly sophisticated UED instruments are being developed that are aimed at increasing the beam brightness in order to observe structural signatures, but so far they have been limited to low average current beams. Here, we present the technical design and capabilities of the HiRES (High Repetition-rate Electron Scattering) instrument, which blends relativistic electrons and high repetition rates to achieve orders of magnitude improvement in average beam current compared to the existing state-of-the-art instruments. The setup utilizes a novel electron source to deliver femtosecond duration electron pulses at up to MHz repetition rates for UED experiments. Instrument response function of sub-500 fs is demonstrated with < 100 fs time resolution targeted in future. We provide example cases of diffraction measurements on solid-state and gas-phase samples, including both micro- and nanodiffraction (featuring 100 nm beam size) modes, which showcase the potential of the instrument for novel UED experiments.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10697722/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138499779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-06eCollection Date: 2023-11-01DOI: 10.1063/4.0000218
S T Kempers, S Borrelli, E R Kieft, H A van Doorn, P H A Mutsaers, O J Luiten
Pump-probe experiments in ultrafast electron microscopy require temporal overlap between the pump and probe pulses. Accurate measurements of the time delay between them allows for the determination of the time zero, the moment in time where both pulses perfectly overlap. In this work, we present the use of a photodiode-based alignment method for these time zero measurements. The cheap and easy-to-use device consists of a photodiode in a sample holder and enables us to temporally align individual, single-electron pulses with femtosecond laser pulses. In a first device, a temporal resolution of 24 ps is obtained, limited by the photodiode design. Future work will utilize a smaller photodiode with a lower capacitance, which will increase the temporal resolution and add spatial resolution as well. This upgrade will bring the method toward the micrometer and picosecond spatiotemporal resolution.
{"title":"Photodiode-based time zero determination for ultrafast electron microscopy.","authors":"S T Kempers, S Borrelli, E R Kieft, H A van Doorn, P H A Mutsaers, O J Luiten","doi":"10.1063/4.0000218","DOIUrl":"10.1063/4.0000218","url":null,"abstract":"<p><p>Pump-probe experiments in ultrafast electron microscopy require temporal overlap between the pump and probe pulses. Accurate measurements of the time delay between them allows for the determination of the time zero, the moment in time where both pulses perfectly overlap. In this work, we present the use of a photodiode-based alignment method for these time zero measurements. The cheap and easy-to-use device consists of a photodiode in a sample holder and enables us to temporally align individual, single-electron pulses with femtosecond laser pulses. In a first device, a temporal resolution of 24 ps is obtained, limited by the photodiode design. Future work will utilize a smaller photodiode with a lower capacitance, which will increase the temporal resolution and add spatial resolution as well. This upgrade will bring the method toward the micrometer and picosecond spatiotemporal resolution.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10629968/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71522981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-06eCollection Date: 2023-11-01DOI: 10.1063/4.0000215
Luke Watson, Thomas Pope, Raphael M Jay, Ambar Banerjee, Philippe Wernet, Thomas J Penfold
Accurate computations of experimental observables are essential for interpreting the high information content held within x-ray spectra. However, for complicated systems this can be difficult, a challenge compounded when dynamics becomes important owing to the large number of calculations required to capture the time-evolving observable. While machine learning architectures have been shown to represent a promising approach for rapidly predicting spectral lineshapes, achieving simultaneously accurate and sufficiently comprehensive training data is challenging. Herein, we introduce Δ-learning for x-ray spectroscopy. Instead of directly learning the structure-spectrum relationship, the Δ-model learns the structure dependent difference between a higher and lower level of theory. Consequently, once developed these models can be used to translate spectral shapes obtained from lower levels of theory to mimic those corresponding to higher levels of theory. Ultimately, this achieves accurate simulations with a much reduced computational burden as only the lower level of theory is computed, while the model can instantaneously transform this to a spectrum equivalent to a higher level of theory. Our present model, demonstrated herein, learns the difference between TDDFT(BLYP) and TDDFT(B3LYP) spectra. Its effectiveness is illustrated using simulations of Rh L3-edge spectra tracking the C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex.
{"title":"A Δ-learning strategy for interpretation of spectroscopic observables.","authors":"Luke Watson, Thomas Pope, Raphael M Jay, Ambar Banerjee, Philippe Wernet, Thomas J Penfold","doi":"10.1063/4.0000215","DOIUrl":"10.1063/4.0000215","url":null,"abstract":"<p><p>Accurate computations of experimental observables are essential for interpreting the high information content held within x-ray spectra. However, for complicated systems this can be difficult, a challenge compounded when dynamics becomes important owing to the large number of calculations required to capture the time-evolving observable. While machine learning architectures have been shown to represent a promising approach for rapidly predicting spectral lineshapes, achieving simultaneously accurate and sufficiently comprehensive training data is challenging. Herein, we introduce Δ-learning for x-ray spectroscopy. Instead of directly learning the structure-spectrum relationship, the Δ-model learns the structure dependent difference between a higher and lower level of theory. Consequently, once developed these models can be used to translate spectral shapes obtained from lower levels of theory to mimic those corresponding to higher levels of theory. Ultimately, this achieves accurate simulations with a much reduced computational burden as only the lower level of theory is computed, while the model can instantaneously transform this to a spectrum equivalent to a higher level of theory. Our present model, demonstrated herein, learns the difference between TDDFT(BLYP) and TDDFT(B3LYP) spectra. Its effectiveness is illustrated using simulations of Rh L<sub>3</sub>-edge spectra tracking the C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10629969/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71522979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-03eCollection Date: 2023-11-01DOI: 10.1063/4.0000204
Christopher J Milne, Natalia Nagornova, Thomas Pope, Hui-Yuan Chen, Thomas Rossi, Jakub Szlachetko, Wojciech Gawelda, Alexander Britz, Tim B van Driel, Leonardo Sala, Simon Ebner, Tetsuo Katayama, Stephen H Southworth, Gilles Doumy, Anne Marie March, C Stefan Lehmann, Melanie Mucke, Denys Iablonskyi, Yoshiaki Kumagai, Gregor Knopp, Koji Motomura, Tadashi Togashi, Shigeki Owada, Makina Yabashi, Martin M Nielsen, Marek Pajek, Kiyoshi Ueda, Rafael Abela, Thomas J Penfold, Majed Chergui
The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy, and ab initio molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The x-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the x-ray absorption signal is found to rise in ∼1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of ∼100 cm-1, which corresponds to a phonon mode of the system involving the Zn sub-lattice.
{"title":"Disentangling the evolution of electrons and holes in photoexcited ZnO nanoparticles.","authors":"Christopher J Milne, Natalia Nagornova, Thomas Pope, Hui-Yuan Chen, Thomas Rossi, Jakub Szlachetko, Wojciech Gawelda, Alexander Britz, Tim B van Driel, Leonardo Sala, Simon Ebner, Tetsuo Katayama, Stephen H Southworth, Gilles Doumy, Anne Marie March, C Stefan Lehmann, Melanie Mucke, Denys Iablonskyi, Yoshiaki Kumagai, Gregor Knopp, Koji Motomura, Tadashi Togashi, Shigeki Owada, Makina Yabashi, Martin M Nielsen, Marek Pajek, Kiyoshi Ueda, Rafael Abela, Thomas J Penfold, Majed Chergui","doi":"10.1063/4.0000204","DOIUrl":"10.1063/4.0000204","url":null,"abstract":"<p><p>The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy, and <i>ab initio</i> molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The x-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the x-ray absorption signal is found to rise in ∼1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of ∼100 cm<sup>-1</sup>, which corresponds to a phonon mode of the system involving the Zn sub-lattice.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10628992/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71522980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-27eCollection Date: 2023-09-01DOI: 10.1063/4.0000193
Philip Heimann, Nicholas J Hartley, Ichiro Inoue, Victor Tkachenko, Andre Antoine, Fabien Dorchies, Roger Falcone, Jérôme Gaudin, Hauke Höppner, Yuichi Inubushi, Konrad J Kapcia, Hae Ja Lee, Vladimir Lipp, Paloma Martinez, Nikita Medvedev, Franz Tavella, Sven Toleikis, Makina Yabashi, Toshinori Yabuuchi, Jumpei Yamada, Beata Ziaja
Intense x-ray pulses can cause the non-thermal structural transformation of diamond. At the SACLA XFEL facility, pump x-ray pulses triggered this phase transition, and probe x-ray pulses produced diffraction patterns. Time delays were observed from 0 to 250 fs, and the x-ray dose varied from 0.9 to 8.0 eV/atom. The intensity of the (111), (220), and (311) diffraction peaks decreased with time, indicating a disordering of the crystal lattice. From a Debye-Waller analysis, the rms atomic displacements perpendicular to the (111) planes were observed to be significantly larger than those perpendicular to the (220) or (311) planes. At a long time delay of 33 ms, graphite (002) diffraction indicates that graphitization did occur above a threshold dose of 1.2 eV/atom. These experimental results are in qualitative agreement with XTANT+ simulations using a hybrid model based on density-functional tight-binding molecular dynamics.
{"title":"Non-thermal structural transformation of diamond driven by x-rays.","authors":"Philip Heimann, Nicholas J Hartley, Ichiro Inoue, Victor Tkachenko, Andre Antoine, Fabien Dorchies, Roger Falcone, Jérôme Gaudin, Hauke Höppner, Yuichi Inubushi, Konrad J Kapcia, Hae Ja Lee, Vladimir Lipp, Paloma Martinez, Nikita Medvedev, Franz Tavella, Sven Toleikis, Makina Yabashi, Toshinori Yabuuchi, Jumpei Yamada, Beata Ziaja","doi":"10.1063/4.0000193","DOIUrl":"https://doi.org/10.1063/4.0000193","url":null,"abstract":"<p><p>Intense x-ray pulses can cause the non-thermal structural transformation of diamond. At the SACLA XFEL facility, pump x-ray pulses triggered this phase transition, and probe x-ray pulses produced diffraction patterns. Time delays were observed from 0 to 250 fs, and the x-ray dose varied from 0.9 to 8.0 eV/atom. The intensity of the (111), (220), and (311) diffraction peaks decreased with time, indicating a disordering of the crystal lattice. From a Debye-Waller analysis, the rms atomic displacements perpendicular to the (111) planes were observed to be significantly larger than those perpendicular to the (220) or (311) planes. At a long time delay of 33 ms, graphite (002) diffraction indicates that graphitization did occur above a threshold dose of 1.2 eV/atom. These experimental results are in qualitative agreement with XTANT+ simulations using a hybrid model based on density-functional tight-binding molecular dynamics.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10613085/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71414817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-27eCollection Date: 2023-09-01DOI: 10.1063/4.0000207
Marco Reinhard, Dean Skoien, Jacob A Spies, Angel T Garcia-Esparza, Benjamin D Matson, Jeff Corbett, Kai Tian, James Safranek, Eduardo Granados, Matthew Strader, Kelly J Gaffney, Roberto Alonso-Mori, Thomas Kroll, Dimosthenis Sokaras
We present a dedicated end-station for solution phase high repetition rate (MHz) picosecond hard x-ray spectroscopy at beamline 15-2 of the Stanford Synchrotron Radiation Lightsource. A high-power ultrafast ytterbium-doped fiber laser is used to photoexcite the samples at a repetition rate of 640 kHz, while the data acquisition operates at the 1.28 MHz repetition rate of the storage ring recording data in an alternating on-off mode. The time-resolved x-ray measurements are enabled via gating the x-ray detectors with the 20 mA/70 ps camshaft bunch of SPEAR3, a mode available during the routine operations of the Stanford Synchrotron Radiation Lightsource. As a benchmark study, aiming to demonstrate the advantageous capabilities of this end-station, we have conducted picosecond Fe K-edge x-ray absorption spectroscopy on aqueous [FeII(phen)3]2+, a prototypical spin crossover complex that undergoes light-induced excited spin state trapping forming an electronic excited state with a 0.6-0.7 ns lifetime. In addition, we report transient Fe Kβ main line and valence-to-core x-ray emission spectra, showing a unique detection sensitivity and an excellent agreement with model spectra and density functional theory calculations, respectively. Notably, the achieved signal-to-noise ratio, the overall performance, and the routine availability of the developed end-station have enabled a systematic time-resolved science program using the monochromatic beam at the Stanford Synchrotron Radiation Lightsource.
{"title":"Solution phase high repetition rate laser pump x-ray probe picosecond hard x-ray spectroscopy at the Stanford Synchrotron Radiation Lightsource.","authors":"Marco Reinhard, Dean Skoien, Jacob A Spies, Angel T Garcia-Esparza, Benjamin D Matson, Jeff Corbett, Kai Tian, James Safranek, Eduardo Granados, Matthew Strader, Kelly J Gaffney, Roberto Alonso-Mori, Thomas Kroll, Dimosthenis Sokaras","doi":"10.1063/4.0000207","DOIUrl":"10.1063/4.0000207","url":null,"abstract":"<p><p>We present a dedicated end-station for solution phase high repetition rate (MHz) picosecond hard x-ray spectroscopy at beamline 15-2 of the Stanford Synchrotron Radiation Lightsource. A high-power ultrafast ytterbium-doped fiber laser is used to photoexcite the samples at a repetition rate of 640 kHz, while the data acquisition operates at the 1.28 MHz repetition rate of the storage ring recording data in an alternating on-off mode. The time-resolved x-ray measurements are enabled via gating the x-ray detectors with the 20 mA/70 ps camshaft bunch of SPEAR3, a mode available during the routine operations of the Stanford Synchrotron Radiation Lightsource. As a benchmark study, aiming to demonstrate the advantageous capabilities of this end-station, we have conducted picosecond Fe K-edge x-ray absorption spectroscopy on aqueous [Fe<sup>II</sup>(phen)<sub>3</sub>]<sup>2+</sup>, a prototypical spin crossover complex that undergoes light-induced excited spin state trapping forming an electronic excited state with a 0.6-0.7 ns lifetime. In addition, we report transient Fe Kβ main line and valence-to-core x-ray emission spectra, showing a unique detection sensitivity and an excellent agreement with model spectra and density functional theory calculations, respectively. Notably, the achieved signal-to-noise ratio, the overall performance, and the routine availability of the developed end-station have enabled a systematic time-resolved science program using the monochromatic beam at the Stanford Synchrotron Radiation Lightsource.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10613086/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71414818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-11eCollection Date: 2023-09-01DOI: 10.1063/4.0000206
Robin Y Engel, Oliver Alexander, Kaan Atak, Uwe Bovensiepen, Jens Buck, Robert Carley, Michele Cascella, Valentin Chardonnet, Gheorghe Sorin Chiuzbaian, Christian David, Florian Döring, Andrea Eschenlohr, Natalia Gerasimova, Frank de Groot, Loïc Le Guyader, Oliver S Humphries, Manuel Izquierdo, Emmanuelle Jal, Adam Kubec, Tim Laarmann, Charles-Henri Lambert, Jan Lüning, Jonathan P Marangos, Laurent Mercadier, Giuseppe Mercurio, Piter S Miedema, Katharina Ollefs, Bastian Pfau, Benedikt Rösner, Kai Rossnagel, Nico Rothenbach, Andreas Scherz, Justine Schlappa, Markus Scholz, Jan O Schunck, Kiana Setoodehnia, Christian Stamm, Simone Techert, Sam M Vinko, Heiko Wende, Alexander A Yaroslavtsev, Zhong Yin, Martin Beye
Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray-matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the -edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale.
{"title":"Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser.","authors":"Robin Y Engel, Oliver Alexander, Kaan Atak, Uwe Bovensiepen, Jens Buck, Robert Carley, Michele Cascella, Valentin Chardonnet, Gheorghe Sorin Chiuzbaian, Christian David, Florian Döring, Andrea Eschenlohr, Natalia Gerasimova, Frank de Groot, Loïc Le Guyader, Oliver S Humphries, Manuel Izquierdo, Emmanuelle Jal, Adam Kubec, Tim Laarmann, Charles-Henri Lambert, Jan Lüning, Jonathan P Marangos, Laurent Mercadier, Giuseppe Mercurio, Piter S Miedema, Katharina Ollefs, Bastian Pfau, Benedikt Rösner, Kai Rossnagel, Nico Rothenbach, Andreas Scherz, Justine Schlappa, Markus Scholz, Jan O Schunck, Kiana Setoodehnia, Christian Stamm, Simone Techert, Sam M Vinko, Heiko Wende, Alexander A Yaroslavtsev, Zhong Yin, Martin Beye","doi":"10.1063/4.0000206","DOIUrl":"10.1063/4.0000206","url":null,"abstract":"<p><p>Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray-matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the <math><mrow><msub><mi>L</mi><mn>3</mn></msub></mrow></math>-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm<sup>2</sup>. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10576398/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41242005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-03eCollection Date: 2023-09-01DOI: 10.1063/4.0000197
R Guillemin, L Inhester, M Ilchen, T Mazza, R Boll, Th Weber, S Eckart, P Grychtol, N Rennhack, T Marchenko, N Velasquez, O Travnikova, I Ismail, J Niskanen, E Kukk, F Trinter, M Gisselbrecht, R Feifel, G Sansone, D Rolles, M Martins, M Meyer, M Simon, R Santra, T Pfeifer, T Jahnke, M N Piancastelli
Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H2O2+, D2O2+, and HDO2+, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.
{"title":"Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser.","authors":"R Guillemin, L Inhester, M Ilchen, T Mazza, R Boll, Th Weber, S Eckart, P Grychtol, N Rennhack, T Marchenko, N Velasquez, O Travnikova, I Ismail, J Niskanen, E Kukk, F Trinter, M Gisselbrecht, R Feifel, G Sansone, D Rolles, M Martins, M Meyer, M Simon, R Santra, T Pfeifer, T Jahnke, M N Piancastelli","doi":"10.1063/4.0000197","DOIUrl":"10.1063/4.0000197","url":null,"abstract":"<p><p>Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H<sub>2</sub>O<sup>2+</sup>, D<sub>2</sub>O<sup>2+</sup>, and HDO<sup>2+</sup>, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10550338/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41159729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-03eCollection Date: 2023-09-01DOI: 10.1063/4.0000200
D F J Nijhof, T C H de Raadt, J V Huijts, J G H Franssen, P H A Mutsaers, O J Luiten
The ultrafast and ultracold electron source, based on laser cooling and trapping of atomic gas and its subsequent near-threshold two-step photoionization, is capable of generating electron bunches with a high transverse brightness at energies of roughly 10 keV. This paper investigates the possibility of increasing the range of applications of this source by accelerating the bunch using radio frequency electromagnetic fields. Bunch energies up to 35 keV are measured by analyzing the diffraction patterns generated from a mono-crystalline gold sample. It is found that the normalized transverse emittance is largely preserved during acceleration.
{"title":"RF acceleration of ultracold electron bunches.","authors":"D F J Nijhof, T C H de Raadt, J V Huijts, J G H Franssen, P H A Mutsaers, O J Luiten","doi":"10.1063/4.0000200","DOIUrl":"10.1063/4.0000200","url":null,"abstract":"<p><p>The ultrafast and ultracold electron source, based on laser cooling and trapping of atomic gas and its subsequent near-threshold two-step photoionization, is capable of generating electron bunches with a high transverse brightness at energies of roughly 10 keV. This paper investigates the possibility of increasing the range of applications of this source by accelerating the bunch using radio frequency electromagnetic fields. Bunch energies up to 35 keV are measured by analyzing the diffraction patterns generated from a mono-crystalline gold sample. It is found that the normalized transverse emittance is largely preserved during acceleration.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10550337/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41143102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}