Publications by authors named "Marcin Sikorski"

30 Publications

  • Page 1 of 1

Time-resolved in situ visualization of the structural response of zeolites during catalysis.

Nat Commun 2020 Nov 19;11(1):5901. Epub 2020 Nov 19.

Department of Physics, Sogang University, Seoul, 04107, Korea.

Zeolites are three-dimensional aluminosilicates having unique properties from the size and connectivity of their sub-nanometer pores, the Si/Al ratio of the anionic framework, and the charge-balancing cations. The inhomogeneous distribution of the cations affects their catalytic performances because it influences the intra-crystalline diffusion rates of the reactants and products. However, the structural deformation regarding inhomogeneous active regions during the catalysis is not yet observed by conventional analytical tools. Here we employ in situ X-ray free electron laser-based time-resolved coherent X-ray diffraction imaging to investigate the internal deformations originating from the inhomogeneous Cu ion distributions in Cu-exchanged ZSM-5 zeolite crystals during the deoxygenation of nitrogen oxides with propene. We show that the interactions between the reactants and the active sites lead to an unusual strain distribution, confirmed by density functional theory simulations. These observations provide insights into the role of structural inhomogeneity in zeolites during catalysis and will assist the future design of zeolites for their applications.
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http://dx.doi.org/10.1038/s41467-020-19728-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7677390PMC
November 2020

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy.

Sci Rep 2020 Oct 8;10(1):16837. Epub 2020 Oct 8.

SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 10 and 10 W cm. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted 'probe-before-destroy' measurement strategy can be adopted for electronic-structure related XFEL experiments.
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http://dx.doi.org/10.1038/s41598-020-74003-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7545180PMC
October 2020

Emergence of anomalous dynamics in soft matter probed at the European XFEL.

Proc Natl Acad Sci U S A 2020 09 15;117(39):24110-24116. Epub 2020 Sep 15.

Photon Science, Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany.

Dynamics and kinetics in soft matter physics, biology, and nanoscience frequently occur on fast (sub)microsecond but not ultrafast timescales which are difficult to probe experimentally. The European X-ray Free-Electron Laser (European XFEL), a megahertz hard X-ray Free-Electron Laser source, enables such experiments via taking series of diffraction patterns at repetition rates of up to 4.5 MHz. Here, we demonstrate X-ray photon correlation spectroscopy (XPCS) with submicrosecond time resolution of soft matter samples at the European XFEL. We show that the XFEL driven by a superconducting accelerator provides unprecedented beam stability within a pulse train. We performed microsecond sequential XPCS experiments probing equilibrium and nonequilibrium diffusion dynamics in water. We find nonlinear heating on microsecond timescales with dynamics beyond hot Brownian motion and superheated water states persisting up to 100 μs at high fluences. At short times up to 20 μs we observe that the dynamics do not obey the Stokes-Einstein predictions.
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http://dx.doi.org/10.1073/pnas.2003337117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7533660PMC
September 2020

Femtosecond laser produced periodic plasma in a colloidal crystal probed by XFEL radiation.

Sci Rep 2020 Jul 1;10(1):10780. Epub 2020 Jul 1.

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607, Hamburg, Germany.

With the rapid development of short-pulse intense laser sources, studies of matter under extreme irradiation conditions enter further unexplored regimes. In addition, an application of X-ray Free-Electron Lasers (XFELs) delivering intense femtosecond X-ray pulses, allows to investigate sample evolution in IR pump - X-ray probe experiments with an unprecedented time resolution. Here we present a detailed study of the periodic plasma created from the colloidal crystal. Both experimental data and theory modeling show that the periodicity in the sample survives to a large extent the extreme excitation and shock wave propagation inside the colloidal crystal. This feature enables probing the excited crystal, using the powerful Bragg peak analysis, in contrast to the conventional studies of dense plasma created from bulk samples for which probing with Bragg diffraction technique is not possible. X-ray diffraction measurements of excited colloidal crystals may then lead towards a better understanding of matter phase transitions under extreme irradiation conditions.
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http://dx.doi.org/10.1038/s41598-020-67214-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7329833PMC
July 2020

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay.

Sci Rep 2020 Mar 19;10(1):5054. Epub 2020 Mar 19.

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany.

The ability to deliver two coherent X-ray pulses with precise time-delays ranging from a few femtoseconds to nanoseconds enables critical capabilities of probing ultra-fast phenomena in condensed matter systems at X-ray free electron laser (FEL) sources. Recent progress made in the hard X-ray split-and-delay optics developments now brings a very promising prospect for resolving atomic-scale motions that were not accessible by previous time-resolved techniques. Here, we report on characterizing the spatial and temporal coherence properties of the hard X-ray FEL beam after propagating through split-and-delay optics. Speckle contrast analysis of small-angle scattering measurements from nanoparticles reveals well-preserved transverse coherence of the beam. Measuring intensity fluctuations from successive X-ray pulses also reveals that only single or double temporal modes remain in the transmitted beam, corresponding to nearly Fourier transform limited pulses.
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http://dx.doi.org/10.1038/s41598-020-61926-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7081363PMC
March 2020

Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering.

Nat Commun 2020 Jan 31;11(1):634. Epub 2020 Jan 31.

PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA, 94025, USA.

The non-equilibrium dynamics of electrons and nuclei govern the function of photoactive materials. Disentangling these dynamics remains a critical goal for understanding photoactive materials. Here we investigate the photoinduced dynamics of the [Fe(bmip)] photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simultaneous femtosecond-resolution Fe Kα and Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS). This measurement shows temporal oscillations in the XES and XSS difference signals with the same 278 fs period oscillation. These oscillations originate from an Fe-ligand stretching vibrational wavepacket on a triplet metal-centered (MC) excited state surface. This MC state is populated with a 110 fs time constant by 40% of the excited molecules while the rest relax to a MLCT excited state. The sensitivity of the Kα XES to molecular structure results from a 0.7% average Fe-ligand bond length shift between the 1 s and 2p core-ionized states surfaces.
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http://dx.doi.org/10.1038/s41467-020-14468-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6994595PMC
January 2020

Evaluation of serial crystallographic structure determination within megahertz pulse trains.

Struct Dyn 2019 Nov 4;6(6):064702. Epub 2019 Dec 4.

Center for Free-Electron Laser Science, Deutsches Elektronen Synchrotron, Notkestrasse 85, 22607 Hamburg, Germany.

The new European X-ray Free-Electron Laser (European XFEL) is the first X-ray free-electron laser capable of delivering intense X-ray pulses with a megahertz interpulse spacing in a wavelength range suitable for atomic resolution structure determination. An outstanding but crucial question is whether the use of a pulse repetition rate nearly four orders of magnitude higher than previously possible results in unwanted structural changes due to either radiation damage or systematic effects on data quality. Here, separate structures from the first and subsequent pulses in the European XFEL pulse train were determined, showing that there is essentially no difference between structures determined from different pulses under currently available operating conditions at the European XFEL.
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http://dx.doi.org/10.1063/1.5124387DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6892710PMC
November 2019

Hot Branching Dynamics in a Light-Harvesting Iron Carbene Complex Revealed by Ultrafast X-ray Emission Spectroscopy.

Angew Chem Int Ed Engl 2020 Jan 31;59(1):364-372. Epub 2019 Oct 31.

Division of Chemical Physics, Department of Chemistry, Lund University, Box 124, Lund, SE-22100, Sweden.

Iron N-heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub-ps X-ray spectroscopy study of an Fe NHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot MLCT state, from the initially excited MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the MC state, in competition with vibrational relaxation and cooling to the relaxed MLCT state. The relaxed MLCT state then decays much more slowly (7.6 ps) to the MC state. The MC state is rapidly (2.2 ps) deactivated to the ground state. The MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition-metal complexes for similar ultrafast decays to optimize photochemical performance.
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http://dx.doi.org/10.1002/anie.201908065DOI Listing
January 2020

Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy.

Chem Sci 2019 Jun 22;10(22):5749-5760. Epub 2019 Apr 22.

PULSE Institute , SLAC National Accelerator Laboratory , Stanford University , Menlo Park , California 94025 , USA . Email: ; Email:

Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided significant insight into electronic excited state reaction dynamics, experimental approaches for identifying and characterizing intersections and seams between electronic states remain highly system dependent. Here we show that for 3d transition metal systems simultaneously recorded X-ray diffuse scattering and X-ray emission spectroscopy at sub-70 femtosecond time-resolution provide a solid experimental foundation for determining the mechanistic details of excited state reactions. In modeling the mechanistic information retrieved from such experiments, it becomes possible to identify the dominant trajectory followed during the excited state cascade and to determine the relevant loci of intersections between states. We illustrate our approach by explicitly mapping parts of the potential energy landscape dictating the light driven low-to-high spin-state transition (spin crossover) of [Fe(2,2'-bipyridine)], where the strongly coupled nuclear and electronic dynamics have been a source of interest and controversy. We anticipate that simultaneous X-ray diffuse scattering and X-ray emission spectroscopy will provide a valuable approach for mapping the reactive trajectories of light-triggered molecular systems involving 3d transition metals.
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http://dx.doi.org/10.1039/c8sc04023kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6568243PMC
June 2019

The Single Particles, Clusters and Biomolecules and Serial Femtosecond Crystallography instrument of the European XFEL: initial installation.

J Synchrotron Radiat 2019 May 12;26(Pt 3):660-676. Epub 2019 Apr 12.

European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany.

The European X-ray Free-Electron Laser (FEL) became the first operational high-repetition-rate hard X-ray FEL with first lasing in May 2017. Biological structure determination has already benefitted from the unique properties and capabilities of X-ray FELs, predominantly through the development and application of serial crystallography. The possibility of now performing such experiments at data rates more than an order of magnitude greater than previous X-ray FELs enables not only a higher rate of discovery but also new classes of experiments previously not feasible at lower data rates. One example is time-resolved experiments requiring a higher number of time steps for interpretation, or structure determination from samples with low hit rates in conventional X-ray FEL serial crystallography. Following first lasing at the European XFEL, initial commissioning and operation occurred at two scientific instruments, one of which is the Single Particles, Clusters and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument. This instrument provides a photon energy range, focal spot sizes and diagnostic tools necessary for structure determination of biological specimens. The instrumentation explicitly addresses serial crystallography and the developing single particle imaging method as well as other forward-scattering and diffraction techniques. This paper describes the major science cases of SPB/SFX and its initial instrumentation - in particular its optical systems, available sample delivery methods, 2D detectors, supporting optical laser systems and key diagnostic components. The present capabilities of the instrument will be reviewed and a brief outlook of its future capabilities is also described.
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http://dx.doi.org/10.1107/S1600577519003308DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510195PMC
May 2019

Initial observations of the femtosecond timing jitter at the European XFEL.

Opt Lett 2019 Apr;44(7):1650-1653

Intense, ultrashort, and high-repetition-rate X-ray pulses, combined with a femtosecond optical laser, allow pump-probe experiments with fast data acquisition and femtosecond time resolution. However, the relative timing of the X-ray pulses and the optical laser pulses can be controlled only to a level of the intrinsic error of the instrument which, without characterization, limits the time resolution of experiments. This limitation inevitably calls for a precise determination of the relative arrival time, which can be used after measurement for sorting and tagging the experimental data to a much finer resolution than it can be controlled to. The observed root-mean-square timing jitter between the X-ray and the optical laser at the SPB/SFX instrument at European XFEL was 308 fs. This first measurement of timing jitter at the European XFEL provides an important step in realizing ultrafast experiments at this novel X-ray source. A method for determining the change in the complex refractive index of samples is also presented.
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http://dx.doi.org/10.1364/OL.44.001650DOI Listing
April 2019

Measurement of the absolute number of photons of the hard X-ray beamline at the Linac Coherent Light Source.

J Synchrotron Radiat 2019 Mar 11;26(Pt 2):320-327. Epub 2019 Feb 11.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

X-ray free-electron lasers provide intense pulses of coherent X-rays with a short pulse duration. These sources are chaotic by nature and therefore, to be used at their full potential, require that every X-ray pulse is characterized in terms of various relevant properties such as intensity, photon energy, position and timing. Diagnostics are for example installed on an X-ray beamline to specifically monitor the intensity of individual X-ray pulses. To date, these can however only provide a single-shot value of the relative number of photons per shot. Here are reported measurements made in January 2015 of the absolute number of photons in the hard X-ray regime at LCLS which is typically 3.5 × 10 photons shot between 6 and 9.5 keV at the X-ray Pump-Probe instrument. Moreover, an average transmission of ≉62% of the hard X-ray beamline over this energy range is measured and the third-harmonic content of ≉0.47% below 9 keV is characterized.
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http://dx.doi.org/10.1107/S1600577519000250DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6412180PMC
March 2019

Demonstration of femtosecond X-ray pump X-ray probe diffraction on protein crystals.

Struct Dyn 2018 Sep 1;5(5):054303. Epub 2018 Oct 1.

Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland.

The development of X-ray free-electron lasers (XFELs) has opened the possibility to investigate the ultrafast dynamics of biomacromolecules using X-ray diffraction. Whereas an increasing number of structures solved by means of serial femtosecond crystallography at XFELs is available, the effect of radiation damage on protein crystals during ultrafast exposures has remained an open question. We used a split-and-delay line based on diffractive X-ray optics at the Linac Coherent Light Source XFEL to investigate the time dependence of X-ray radiation damage to lysozyme crystals. For these tests, crystals were delivered to the X-ray beam using a fixed-target approach. The presented experiments provide probe signals at eight different delay times between 19 and 213 femtoseconds after a single pump event, thereby covering the time-scales relevant for femtosecond serial crystallography. Even though significant impact on the crystals was observed at long time scales after exposure with a single X-ray pulse, the collected diffraction data did not show significant signal reduction that could be assigned to beam damage on the crystals in the sampled time window and resolution range. This observation is in agreement with estimations of the applied radiation dose, which in our experiment was clearly below the values expected to cause damage on the femtosecond time scale. The experiments presented here demonstrate the feasibility of time-resolved pump-multiprobe X-ray diffraction experiments on protein crystals.
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http://dx.doi.org/10.1063/1.5050618DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6192410PMC
September 2018

Megahertz serial crystallography.

Authors:
Max O Wiedorn Dominik Oberthür Richard Bean Robin Schubert Nadine Werner Brian Abbey Martin Aepfelbacher Luigi Adriano Aschkan Allahgholi Nasser Al-Qudami Jakob Andreasson Steve Aplin Salah Awel Kartik Ayyer Saša Bajt Imrich Barák Sadia Bari Johan Bielecki Sabine Botha Djelloul Boukhelef Wolfgang Brehm Sandor Brockhauser Igor Cheviakov Matthew A Coleman Francisco Cruz-Mazo Cyril Danilevski Connie Darmanin R Bruce Doak Martin Domaracky Katerina Dörner Yang Du Hans Fangohr Holger Fleckenstein Matthias Frank Petra Fromme Alfonso M Gañán-Calvo Yaroslav Gevorkov Klaus Giewekemeyer Helen Mary Ginn Heinz Graafsma Rita Graceffa Dominic Greiffenberg Lars Gumprecht Peter Göttlicher Janos Hajdu Steffen Hauf Michael Heymann Susannah Holmes Daniel A Horke Mark S Hunter Siegfried Imlau Alexander Kaukher Yoonhee Kim Alexander Klyuev Juraj Knoška Bostjan Kobe Manuela Kuhn Christopher Kupitz Jochen Küpper Janine Mia Lahey-Rudolph Torsten Laurus Karoline Le Cong Romain Letrun P Lourdu Xavier Luis Maia Filipe R N C Maia Valerio Mariani Marc Messerschmidt Markus Metz Davide Mezza Thomas Michelat Grant Mills Diana C F Monteiro Andrew Morgan Kerstin Mühlig Anna Munke Astrid Münnich Julia Nette Keith A Nugent Theresa Nuguid Allen M Orville Suraj Pandey Gisel Pena Pablo Villanueva-Perez Jennifer Poehlsen Gianpietro Previtali Lars Redecke Winnie Maria Riekehr Holger Rohde Adam Round Tatiana Safenreiter Iosifina Sarrou Tokushi Sato Marius Schmidt Bernd Schmitt Robert Schönherr Joachim Schulz Jonas A Sellberg M Marvin Seibert Carolin Seuring Megan L Shelby Robert L Shoeman Marcin Sikorski Alessandro Silenzi Claudiu A Stan Xintian Shi Stephan Stern Jola Sztuk-Dambietz Janusz Szuba Aleksandra Tolstikova Martin Trebbin Ulrich Trunk Patrik Vagovic Thomas Ve Britta Weinhausen Thomas A White Krzysztof Wrona Chen Xu Oleksandr Yefanov Nadia Zatsepin Jiaguo Zhang Markus Perbandt Adrian P Mancuso Christian Betzel Henry Chapman Anton Barty

Nat Commun 2018 10 2;9(1):4025. Epub 2018 Oct 2.

Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607, Hamburg, Germany.

The new European X-ray Free-Electron Laser is the first X-ray free-electron laser capable of delivering X-ray pulses with a megahertz inter-pulse spacing, more than four orders of magnitude higher than previously possible. However, to date, it has been unclear whether it would indeed be possible to measure high-quality diffraction data at megahertz pulse repetition rates. Here, we show that high-quality structures can indeed be obtained using currently available operating conditions at the European XFEL. We present two complete data sets, one from the well-known model system lysozyme and the other from a so far unknown complex of a β-lactamase from K. pneumoniae involved in antibiotic resistance. This result opens up megahertz serial femtosecond crystallography (SFX) as a tool for reliable structure determination, substrate screening and the efficient measurement of the evolution and dynamics of molecular structures using megahertz repetition rate pulses available at this new class of X-ray laser source.
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http://dx.doi.org/10.1038/s41467-018-06156-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6168542PMC
October 2018

Nonequilibrium Phase Precursors during a Photoexcited Insulator-to-Metal Transition in V_{2}O_{3}.

Phys Rev Lett 2018 May;120(20):207601

Department of Physics and Center for Advanced Nanoscience, University of California San Diego, La Jolla, California 92093, USA.

Here, we photoinduce and directly observe with x-ray scattering an ultrafast enhancement of the structural long-range order in the archetypal Mott system V_{2}O_{3}. Despite the ultrafast increase in crystal symmetry, the change of unit cell volume occurs an order of magnitude slower and coincides with the insulator-to-metal transition. The decoupling between the two structural responses in the time domain highlights the existence of a transient photoinduced precursor phase, which is distinct from the two structural phases present in equilibrium. X-ray nanoscopy reveals that acoustic phonons trapped in nanoscale twin domains govern the dynamics of the ultrafast transition into the precursor phase, while nucleation and growth of metallic domains dictate the duration of the slower transition into the metallic phase. The enhancement of the long-range order before completion of the electronic transition demonstrates the critical role the nonequilibrium structural phases play during electronic phase transitions in correlated electrons systems.
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http://dx.doi.org/10.1103/PhysRevLett.120.207601DOI Listing
May 2018

Ultrafast X-ray Absorption Near Edge Structure Reveals Ballistic Excited State Structural Dynamics.

J Phys Chem A 2018 Jun 25;122(22):4963-4971. Epub 2018 May 25.

Department of Chemistry , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States.

Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B, cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 Å is followed by significant elongation of the axial bonds (>0.25 Å) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S excited state structure within 500 fs of excitation.
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http://dx.doi.org/10.1021/acs.jpca.8b04223DOI Listing
June 2018

Coherent X-rays reveal the influence of cage effects on ultrafast water dynamics.

Nat Commun 2018 05 15;9(1):1917. Epub 2018 May 15.

Department of Physics, AlbaNova University Center, Stockholm University, S-106 91, Stockholm, Sweden.

The dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.
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http://dx.doi.org/10.1038/s41467-018-04330-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5953967PMC
May 2018

Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2'-bipyridine)(CN)].

Phys Chem Chem Phys 2018 Feb;20(6):4238-4249

PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, USA.

The excited state dynamics of solvated [Fe(bpy)(CN)], where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)] has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile. In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)] in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (MC) character, unlike other reported six-coordinate Fe(ii)-centered coordination compounds, which form MC quintet (MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)] allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated MC intermediate provides a strong foundation for identifying MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.
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http://dx.doi.org/10.1039/c7cp07838bDOI Listing
February 2018

Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B.

J Am Chem Soc 2017 02 30;139(5):1894-1899. Epub 2017 Jan 30.

Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV-visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co-CN bond and Co-N bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. These observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.
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http://dx.doi.org/10.1021/jacs.6b11295DOI Listing
February 2017

Structure of photosystem II and substrate binding at room temperature.

Nature 2016 12 21;540(7633):453-457. Epub 2016 Nov 21.

Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the MnCaO cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S to S), in which S is the dark-stable state and S is the last semi-stable state before O-O bond formation and O evolution. A detailed understanding of the O-O bond formation mechanism remains a challenge, and will require elucidation of both the structures of the OEC in the different S-states and the binding of the two substrate waters to the catalytic site. Here we report the use of femtosecond pulses from an X-ray free electron laser (XFEL) to obtain damage-free, room temperature structures of dark-adapted (S), two-flash illuminated (2F; S-enriched), and ammonia-bound two-flash illuminated (2F-NH; S-enriched) PS II. Although the recent 1.95 Å resolution structure of PS II at cryogenic temperature using an XFEL provided a damage-free view of the S state, measurements at room temperature are required to study the structural landscape of proteins under functional conditions, and also for in situ advancement of the S-states. To investigate the water-binding site(s), ammonia, a water analogue, has been used as a marker, as it binds to the MnCaO cluster in the S and S states. Since the ammonia-bound OEC is active, the ammonia-binding Mn site is not a substrate water site. This approach, together with a comparison of the native dark and 2F states, is used to discriminate between proposed O-O bond formation mechanisms.
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http://dx.doi.org/10.1038/nature20161DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5201176PMC
December 2016

Application of an ePix100 detector for coherent scattering using a hard X-ray free-electron laser.

J Synchrotron Radiat 2016 09 4;23(Pt 5):1171-9. Epub 2016 Aug 4.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

A prototype ePix100 detector was used in small-angle scattering geometry to capture speckle patterns from a static sample using the Linac Coherent Light Source (LCLS) hard X-ray free-electron laser at 8.34 keV. The average number of detected photons per pixel per pulse was varied over three orders of magnitude from about 23 down to 0.01 to test the detector performance. At high average photon count rates, the speckle contrast was evaluated by analyzing the probability distribution of the pixel counts at a constant scattering vector for single frames. For very low average photon counts of less than 0.2 per pixel, the `droplet algorithm' was first applied to the patterns for correcting the effect of charge sharing, and then the pixel count statistics of multiple frames were analyzed collectively to extract the speckle contrast. Results obtained using both methods agree within the uncertainty intervals, providing strong experimental evidence for the validity of the statistical analysis. More importantly it confirms the suitability of the ePix100 detector for X-ray coherent scattering experiments, especially at very low count rates with performances surpassing those of previously available LCLS detectors.
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http://dx.doi.org/10.1107/S1600577516010869DOI Listing
September 2016

Sequential Single Shot X-ray Photon Correlation Spectroscopy at the SACLA Free Electron Laser.

Sci Rep 2015 Nov 27;5:17193. Epub 2015 Nov 27.

Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.

Hard X-ray free electron lasers allow for the first time to access dynamics of condensed matter samples ranging from femtoseconds to several hundred seconds. In particular, the exceptional large transverse coherence of the X-ray pulses and the high time-averaged flux promises to reach time and length scales that have not been accessible up to now with storage ring based sources. However, due to the fluctuations originating from the stochastic nature of the self-amplified spontaneous emission (SASE) process the application of well established techniques such as X-ray photon correlation spectroscopy (XPCS) is challenging. Here we demonstrate a single-shot based sequential XPCS study on a colloidal suspension with a relaxation time comparable to the SACLA free-electron laser pulse repetition rate. High quality correlation functions could be extracted without any indications for sample damage. This opens the way for systematic sequential XPCS experiments at FEL sources.
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http://dx.doi.org/10.1038/srep17193DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4661692PMC
November 2015

Photon-in photon-out hard X-ray spectroscopy at the Linac Coherent Light Source.

J Synchrotron Radiat 2015 May 15;22(3):612-20. Epub 2015 Apr 15.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

X-ray free-electron lasers (FELs) have opened unprecedented possibilities to study the structure and dynamics of matter at an atomic level and ultra-fast timescale. Many of the techniques routinely used at storage ring facilities are being adapted for experiments conducted at FELs. In order to take full advantage of these new sources several challenges have to be overcome. They are related to the very different source characteristics and its resulting impact on sample delivery, X-ray optics, X-ray detection and data acquisition. Here it is described how photon-in photon-out hard X-ray spectroscopy techniques can be applied to study the electronic structure and its dynamics of transition metal systems with ultra-bright and ultra-short FEL X-ray pulses. In particular, some of the experimental details that are different compared with synchrotron-based setups are discussed and illustrated by recent measurements performed at the Linac Coherent Light Source.
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http://dx.doi.org/10.1107/S1600577515004488DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4416677PMC
May 2015

Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis.

J Synchrotron Radiat 2015 May 14;22(3):599-605. Epub 2015 Apr 14.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus' location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging.
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http://dx.doi.org/10.1107/S1600577515004361DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4416675PMC
May 2015

The X-ray Correlation Spectroscopy instrument at the Linac Coherent Light Source.

J Synchrotron Radiat 2015 May 14;22(3):508-13. Epub 2015 Apr 14.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

The X-ray Correlation Spectroscopy instrument is dedicated to the study of dynamics in condensed matter systems using the unique coherence properties of free-electron lasers. It covers a photon energy range of 4-25 keV. The intrinsic temporal characteristics of the Linac Coherent Light Source, in particular the 120 Hz repetition rate, allow for the investigation of slow dynamics (milliseconds) by means of X-ray photon correlation spectroscopy. Double-pulse schemes could probe dynamics on the picosecond timescale. A description of the instrument capabilities and recent achievements is presented.
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http://dx.doi.org/10.1107/S1600577515004397DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4416668PMC
May 2015

The X-ray Pump-Probe instrument at the Linac Coherent Light Source.

J Synchrotron Radiat 2015 May 21;22(3):503-7. Epub 2015 Apr 21.

Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.

The X-ray Pump-Probe instrument achieves femtosecond time-resolution with hard X-ray methods using a free-electron laser source. It covers a photon energy range of 4-24 keV. A femtosecond optical laser system is available across a broad spectrum of wavelengths for generating transient states of matter. The instrument is designed to emphasize versatility and the scientific goals encompass ultrafast physical, chemical and biological processes involved in the transformation of matter and transfer of energy at the atomic scale.
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http://dx.doi.org/10.1107/S1600577515005135DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4416667PMC
May 2015

Demonstration of feasibility of X-ray free electron laser studies of dynamics of nanoparticles in entangled polymer melts.

Sci Rep 2014 Aug 11;4:6017. Epub 2014 Aug 11.

Department of Physics, Sogang University, Seoul 121-742, Korea.

The recent advent of hard x-ray free electron lasers (XFELs) opens new areas of science due to their exceptional brightness, coherence, and time structure. In principle, such sources enable studies of dynamics of condensed matter systems over times ranging from femtoseconds to seconds. However, the studies of "slow" dynamics in polymeric materials still remain in question due to the characteristics of the XFEL beam and concerns about sample damage. Here we demonstrate the feasibility of measuring the relaxation dynamics of gold nanoparticles suspended in polymer melts using X-ray photon correlation spectroscopy (XPCS), while also monitoring eventual X-ray induced damage. In spite of inherently large pulse-to-pulse intensity and position variations of the XFEL beam, measurements can be realized at slow time scales. The X-ray induced damage and heating are less than initially expected for soft matter materials.
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http://dx.doi.org/10.1038/srep06017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4127496PMC
August 2014

Performance of a beam-multiplexing diamond crystal monochromator at the Linac Coherent Light Source.

Rev Sci Instrum 2014 Jun;85(6):063106

Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.

A double-crystal diamond monochromator was recently implemented at the Linac Coherent Light Source. It enables splitting pulses generated by the free electron laser in the hard x-ray regime and thus allows the simultaneous operations of two instruments. Both monochromator crystals are High-Pressure High-Temperature grown type-IIa diamond crystal plates with the (111) orientation. The first crystal has a thickness of ~100 μm to allow high reflectivity within the Bragg bandwidth and good transmission for the other wavelengths for downstream use. The second crystal is about 300 μm thick and makes the exit beam of the monochromator parallel to the incoming beam with an offset of 600 mm. Here we present details on the monochromator design and its performance.
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http://dx.doi.org/10.1063/1.4880724DOI Listing
June 2014

Single shot coherence properties of the free-electron laser SACLA in the hard X-ray regime.

Sci Rep 2014 Jun 10;4:5234. Epub 2014 Jun 10.

1] Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany [2] The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany.

We measured the coherence properties of the free-electron laser SACLA on a single shot basis at an X-ray energy of 8 keV. By analysing small-angle X-ray scattering speckle patterns from colloidal dispersions we found a degree of transverse coherence of βt = 0.79 ± 0.09. Taking detector properties into account, we developed a simulation model in oder to determine the degree of coherence from intensity histograms. Finally we calculated a coherence time of τc = 0.1 fs and a pulse duration of 5.2 fs which corresponds with previous predictions.
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http://dx.doi.org/10.1038/srep05234DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4050387PMC
June 2014

X-ray photon correlation spectroscopy during homogenous shear flow.

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Feb 3;85(2 Pt 1):021402. Epub 2012 Feb 3.

Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA.

We report x-ray photon correlation spectroscopy measurements of advective and diffusive dynamics in a dispersion of colloidal particles subjected to homogeneous shear flow in a rotating-disk shear cell. Intensity autocorrelation functions from scattering data collected using homodyne detection respond to the variation in velocity across the scattering volume when the scattering vector has a component parallel to the flow direction. Theoretical expressions for the impact of homogenous shear flow on the correlation function provide a quantitative prediction of the dependence of correlation functions on the scattering vector and shear rate. Under most circumstances, the applied shear deformation dominates the decay of the intensity correlation function. When scattering data are collected perpendicular to the flow direction, it is possible to measure the diffusive dynamics of the particles free from effects of the superimposed shear flow; however, this approach only works below some upper shear rate limit, beyond which data are affected either by shear effects (caused by the finite width of the detector) or by particle transit through the scattering volume.
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http://dx.doi.org/10.1103/PhysRevE.85.021402DOI Listing
February 2012