Matthieu Chollet

All Publications

• Excited State Covalency, Dynamics, and Photochemistry of Square Planar Ni-Thiolate Complexes Revealed by Ultrafast X-ray Absorption. Journal of the American Chemical Society Lim, H., Yang, X., Larsen, C. B., Ledbetter, K., Zoric, M. R., Raj, S. L., Kumar, G., Powers-Riggs, N., Hoffmann, M. C., Chollet, M., Gee, L. B., van Driel, T. B., Alonso-Mori, R., Kabanova, V., Kahraman, A., Johnson, P. J., Cirelli, C., Bacellar, C., Gaffney, K. J., Li, X., Cordones, A. A. 2025

  Abstract

  Highly covalent Ni bis(dithiolene) and related complexes provide an ideal platform for investigating the effects of metal-ligand orbital hybridization on excited state character and dynamics. In particular, we focus on the ligand field excited states that dominate the photophysics of first-row transition metal complexes. We investigate if they can be significantly delocalized off the metal center, possibly yielding photochemical reactivity more similar to charge transfer excited states than metal-centered ligand field excited states. Here, [Ni(mpo)2] (mpo = 2-mercaptopyridine-N-oxide) provides a representative example for the larger chemical class and is an active electro- and photocatalyst for proton reduction. A detailed characterization of the excited state electronic structure, dynamics, and photochemistry of [Ni(mpo)2] is presented based on ultrafast transient X-ray absorption spectroscopy at the Ni and S 1s core absorption K-edges. By comparing the ultrafast Ni K-edge absorption to ab initio calculations, we identify an excited state relaxation mechanism where an initial ligand-to-metal charge transfer excitation results in both excited state electron transfer (generating a catalytically relevant reduced photoproduct [Ni(mpo)2]-) and relaxation to a pseudotetrahedral triplet ligand field excited state. From the ultrafast S K-edge absorption, the ligand field excited state is found to be highly delocalized onto the thiolate ligands, and a tetrahedral structural distortion is shown to substantially influence the degree of delocalization. The results identify a significant structural coordinate to target when aiming to control the excited state covalency in square planar complexes.

  View details for DOI 10.1021/jacs.4c16212

  View details for PubMedID 39993950

• Hidden domain boundary dynamics toward crystalline perfection. Proceedings of the National Academy of Sciences of the United States of America Mangu, A., Stoica, V. A., Zheng, H., Yang, T., Zhang, M., Wang, H. H., Zu, R., Nguyen, Q. L., Song, S., Das, S., Meisenheimer, P., Donoway, E., Chollet, M., Sun, Y., Turner, J. J., Freeland, J. W., Wen, H., Martin, L. W., Chen, L. Q., Gopalan, V., Zhu, D., Cao, Y., Lindenberg, A. M. 2025; 122 (2): e2407772122

  Abstract

  A central paradigm of nonequilibrium physics concerns the dynamics of heterogeneity and disorder, impacting processes ranging from the behavior of glasses to the emergent functionality of active matter. Understanding these complex mesoscopic systems requires probing the microscopic trajectories associated with irreversible processes, the role of fluctuations and entropy growth, and the timescales on which nonequilibrium responses are ultimately maintained. Approaches that illuminate these processes in model systems may enable a more general understanding of other heterogeneous nonequilibrium phenomena, and potentially define ultimate speed and energy cost limits for information processing technologies. Here, we apply ultrafast single-shot X-ray photon correlation spectroscopy to resolve the nonequilibrium, heterogeneous, and irreversible mesoscale dynamics during a light-induced phase transition in a (PbTiO3)16/(SrTiO3)16 superlattice. Such ferroelectric superlattice systems are a useful platform to study phase transitions and topological dynamics due to their high degree of tunability. This provides an approach for capturing the nucleation of the light-induced phase, the formation of transient mesoscale defects at the boundaries of the nuclei, and the eventual annihilation of these defects, even in systems with complex polarization topologies. We identify a nonequilibrium correlation response spanning >10 orders of magnitude in timescales, with multistep behavior similar to the plateaus observed in supercooled liquids and glasses. We further show how the observed time-dependent long-time correlations can be understood in terms of stochastic and non-Markovian dynamics of domain walls, encoded in waiting-time distributions with power-law tails. This work defines possibilities for probing the nonequilibrium and correlated dynamics of disordered and heterogeneous media.

  View details for DOI 10.1073/pnas.2407772122

  View details for PubMedID 39773030

• The importance of shear on the collective charge transport in CDWs revealed by an XFEL source SCIENCE ADVANCES Le Bolloc'h, D., Bellec, E., Ghoneim, D., Gallo-Frantz, A., Wzietek, P., Ortega, L., Madsen, A., Monceau, P., Chollet, M., Gonzales-Vallejo, I., Jacques, V. R., Sinchenko, A. 2025; 11 (1): eadr6034

  Abstract

  Charge transport in materials has an impact on a wide range of devices based on semiconductor, battery, or superconductor technology. Charge transport in sliding charge density waves (CDW) differs from all others in that the atomic lattice is directly involved in the transport process. To obtain an overall picture of the structural changes associated to the collective transport, the large coherent x-ray beam generated by an x-ray free-electron laser (XFEL) source was used. The CDW phase can be retrieved over the entire sample from diffracted intensities using a genetic algorithm. For currents below threshold, increasing shear deformation is observed in the central part of the sample while longitudinal deformation appears above threshold when shear relaxes. Shear thus precedes longitudinal deformation, with relaxation of one leading to the appearance of the other. Moreover, strain accumulates on surface steps in the sliding regime, demonstrating the strong pinning character of these surface discontinuities. The sliding process of nanometric CDW involves macroscopic sample dimensions.

  View details for DOI 10.1126/sciadv.adr6034

  View details for Web of Science ID 001389489200003

  View details for PubMedID 39752497

  View details for PubMedCentralID PMC11698093

• Direct observation of ultrafast cluster dynamics in supercritical carbon dioxide using X-ray Photon Correlation Spectroscopy. Nature communications Majumdar, A., Li, H., Muhunthan, P., Späh, A., Song, S., Sun, Y., Chollet, M., Sokaras, D., Zhu, D., Ihme, M. 2024; 15 (1): 10540

  Abstract

  Supercritical fluids exhibit distinct thermodynamic and transport properties, making them of particular interest for a wide range of scientific and engineering applications. These anomalous properties emerge from structural heterogeneities due to the formation of molecular clusters at conditions above the critical point. While the static behavior of these clusters and their effects on the thermodynamic response functions have been recognized, the relation between the ultrafast cluster dynamics and transport properties remains elusive. By measuring the intermediate scattering function in carbon dioxide at conditions near the critical point with X-ray photon correlation spectroscopy, we directly capture the cross-over dynamics between 4 and 13 picoseconds, revealing the transition between ballistic and diffusive motion. Complementary analysis using large-scale molecular dynamics simulations reveals that this behavior arises from collisions between unbound molecules and clusters. This study provides direct evidence of the ultrafast momentum exchange between clusters, which has significant impact on transport properties, solvation processes, and reaction kinetics in supercritical fluids.

  View details for DOI 10.1038/s41467-024-54782-1

  View details for PubMedID 39627208

  View details for PubMedCentralID PMC11615208

• Strain-affected ferroelastic domain walls in RbMnFe charge-transfer materials undergoing collective Jahn-Teller distortion. RSC advances Herve, M., Akagi, S., Guerin, L., Gee, L. B., Ribson, R. D., Chollet, M., Cammarata, M., Nagashima, S., Ohkoshi, S., Tokoro, H., Collet, E. 2024; 14 (47): 35081-35089

  Abstract

  Many rubidium manganese hexacyanoferrate materials, with the general formula Rb x Mn[Fe(CN)6](x+2)/3·zH2O, exhibit diverse charge-transfer-based functionalities due to the bistability between a high temperature MnII(S = 5/2)FeIII(S = 1/2) cubic phase and a low-temperature MnIII(S = 2)FeII(S = 0) tetragonal phase. The collective Jahn-Teller distortion on the Mn sites is responsible for the cubic-to-tetragonal ferroelastic phase transition, which is associated with the appearance of ferroelastic domains. In this study, we use X-ray diffraction to reveal the coexistence of 3 types of ferroelastic tetragonal domains and estimate the spatial extension of the strain around the domain walls, which represents about 30% of the volume of the crystal.

  View details for DOI 10.1039/d4ra06397j

  View details for PubMedID 39497769

• Ultrafast magnetostructural dynamics of MnAs PHYSICAL REVIEW B Vidal, F., Zheng, Y., Ferrari, E., Allaria, E., Spezzani, C., Laulhe, C., Popescu, H., Atkinson, P., Casaretto, N., Eddrief, M., Wang, H., Zhao, J., Seaberg, M., Alonso-Mori, R., Glownia, J. M., Chollet, M., Xu, H., Huang, X., Lima, F., Khakhulin, D., Macias, I., Vinci, D., Biednov, M., Jiang, Y., Uemura, Y., Ardana-Lamas, F., Zalden, P., Milne, C., Sacchi, M. 2024; 110 (14)

  View details for DOI 10.1103/PhysRevB.110.L140406

  View details for Web of Science ID 001343349000005

• Nanometer-Scale Acoustic Wave Packets Generated by Stochastic Core-Level Photoionization Events PHYSICAL REVIEW X Huang, Y., Sun, P., Teitelbaum, S. W., Li, H., Sun, Y., Wang, N., Song, S., Sato, T., Chollet, M., Osaka, T., Inoue, I., Duncan, R. A., Shin, H., Haber, J., Zhou, J., Bernardi, M., Gu, M., Rondinelli, J. M., Trigo, M., Yabashi, M., Maznev, A. A., Nelson, K. A., Zhu, D., Reis, D. A. 2024; 14 (4)

  View details for DOI 10.1103/PhysRevX.14.041010

  View details for Web of Science ID 001335434300002

• Dynamical decoding of the competition between charge density waves in a kagome superconductor. Nature communications Ning, H., Oh, K. H., Su, Y., von Hoegen, A., Porter, Z., Capa Salinas, A., Nguyen, Q. L., Chollet, M., Sato, T., Esposito, V., Hoffmann, M. C., White, A., Melendrez, C., Zhu, D., Wilson, S. D., Gedik, N. 2024; 15 (1): 7286

  Abstract

  The kagome superconductor CsV3Sb5 hosts a variety of charge density wave (CDW) phases, which play a fundamental role in the formation of other exotic electronic instabilities. However, identifying the precise structure of these CDW phases and their intricate relationships remain the subject of intense debate, due to the lack of static probes that can distinguish the CDW phases with identical spatial periodicity. Here, we unveil the out-of-equilibrium competition between two coexisting 2 × 2 × 2 CDWs in CsV3Sb5 harnessing time-resolved X-ray diffraction. By analyzing the light-induced changes in the intensity of CDW superlattice peaks, we demonstrate the presence of both phases, each displaying a significantly different amount of melting upon excitation. The anomalous light-induced sharpening of peak width further shows that the phase that is more resistant to photo-excitation exhibits an increase in domain size at the expense of the other, thereby showcasing a hallmark of phase competition. Our results not only shed light on the interplay between the multiple CDW phases in CsV3Sb5, but also establish a non-equilibrium framework for comprehending complex phase relationships that are challenging to disentangle using static techniques.

  View details for DOI 10.1038/s41467-024-51485-5

  View details for PubMedID 39179535

  View details for PubMedCentralID 9950456

• Time-Resolved X-ray Emission Spectroscopy and Synthetic High-Spin Model Complexes Resolve Ambiguities in Excited-State Assignments of Transition-Metal Chromophores: A Case Study of Fe-Amido Complexes. Journal of the American Chemical Society Reinhard, M. E., Sidhu, B. K., Lozada, I. B., Powers-Riggs, N., Ortiz, R. J., Lim, H., Nickel, R., Lierop, J. v., Alonso-Mori, R., Chollet, M., Gee, L. B., Kramer, P. L., Kroll, T., Raj, S. L., van Driel, T. B., Cordones, A. A., Sokaras, D., Herbert, D. E., Gaffney, K. J. 2024

  Abstract

  To fully harness the potential of abundant metal coordination complex photosensitizers, a detailed understanding of the molecular properties that dictate and control the electronic excited-state population dynamics initiated by light absorption is critical. In the absence of detectable luminescence, optical transient absorption (TA) spectroscopy is the most widely employed method for interpreting electron redistribution in such excited states, particularly for those with a charge-transfer character. The assignment of excited-state TA spectral features often relies on spectroelectrochemical measurements, where the transient absorption spectrum generated by a metal-to-ligand charge-transfer (MLCT) electronic excited state, for instance, can be approximated using steady-state spectra generated by electrochemical ligand reduction and metal oxidation and accounting for the loss of absorptions by the electronic ground state. However, the reliability of this approach can be clouded when multiple electronic configurations have similar optical signatures. Using a case study of Fe(II) complexes supported by benzannulated diarylamido ligands, we highlight an example of such an ambiguity and show how time-resolved X-ray emission spectroscopy (XES) measurements can reliably assign excited states from the perspective of the metal, particularly in conjunction with accurate synthetic models of ligand-field electronic excited states, leading to a reinterpretation of the long-lived excited state as a ligand-field metal-centered quintet state. A detailed analysis of the XES data on the long-lived excited state is presented, along with a discussion of the ultrafast dynamics following the photoexcitation of low-spin Fe(II)-Namido complexes using a high-spin ground-state analogue as a spectral model for the 5T2 excited state.

  View details for DOI 10.1021/jacs.4c02748

  View details for PubMedID 38889309

• Critical slowing of the spin and charge density wave order in thin film Cr following photoexcitation APL MATERIALS Patel, S. K., Gorobtsov, O., Cela, D., Hrkac, S. B., Hua, N., Medapalli, R., Shabalin, A. G., Wingert, J., Glownia, J. M., Zhu, D., Chollet, M., Shpyrko, O. G., Singer, A., Fullerton, E. E. 2024; 12 (6)

  View details for DOI 10.1063/5.0206207

  View details for Web of Science ID 001242304700002

• Characterization of Deformational Isomerization Potential and Interconversion Dynamics with Ultrafast X-ray Solution Scattering. Journal of the American Chemical Society Powers-Riggs, N. E., Birgisson, B. O., Raj, S. L., Biasin, E., Lenzen, P., Zederkof, D. B., Haubro, M., Tveiten, D. K., Hartsock, R. W., van Driel, T. B., Kunnus, K., Chollet, M., Robinson, J. S., Nelson, S., Forbes, R., Haldrup, K., Pedersen, K. S., Levi, G., Ougaard Dohn, A., Jonsson, H., Mo Ller, K. B., Natan, A., Nielsen, M. M., Gaffney, K. J. 2024

  Abstract

  Dimeric complexes composed of d8 square planar metal centers and rigid bridging ligands provide model systems to understand the interplay between attractive dispersion forces and steric strain in order to assist the development of reliable methods to model metal dimer complexes more broadly. [Ir2 (dimen)4]2+ (dimen = para-diisocyanomenthane) presents a unique case study for such phenomena, as distortions of the optimal structure of a ligand with limited conformational flexibility counteract the attractive dispersive forces from the metal and ligand to yield a complex with two ground state deformational isomers. Here, we use ultrafast X-ray solution scattering (XSS) and optical transient absorption spectroscopy (OTAS) to reveal the nature of the equilibrium distribution and the exchange rate between the deformational isomers. The two ground state isomers have spectrally distinct electronic excitations that enable the selective excitation of one isomer or the other using a femtosecond duration pulse of visible light. We then track the dynamics of the nonequilibrium depletion of the electronic ground state population─often termed the ground state hole─with ultrafast XSS and OTAS, revealing a restoration of the ground state equilibrium in 2.3 ps. This combined experimental and theoretical study provides a critical test of various density functional approximations in the description of bridged d8-d8 metal complexes. The results show that density functional theory calculations can reproduce the primary experimental observations if dispersion interactions are added, and a hybrid functional, which includes exact exchange, is used.

  View details for DOI 10.1021/jacs.4c00817

  View details for PubMedID 38727611

• Deciphering Charge Transfer Processes in Transition Metal Complexes from the Perspective of Ultrafast Electronic and Nuclear Motions. The journal of physical chemistry letters Mara, M. W., Weingartz, N. P., Leshchev, D., Hsu, D., Valentine, A., Mills, A., Roy, S., Chakraborty, A., Kim, P., Biasin, E., Haldrup, K., Kirschner, M. S., Rimmerman, D., Chollet, M., Glownia, J. M., van Driel, T. B., Castellano, F. N., Li, X., Chen, L. X. 2024: 5250-5258

  Abstract

  Chemical transformations in charge transfer states result from the interplay between electronic dynamics and nuclear reorganization along excited-state trajectories. Here, we investigate the ultrafast structural dynamics following photoinduced electron transfer from the metal-metal-to-ligand charge transfer state of an electron donor, a Pt dimer complex, to a covalently linked electron acceptor group using ultrafast time-resolved wide-angle X-ray scattering and optical transient absorption spectroscopy methods to disentangle the interdependence of the excited-state electronic and nuclear dynamics. Following photoexcitation, Pt-Pt bond formation and contraction takes up to 1 ps, much slower than the corresponding process in analogous complexes without electron acceptor groups. Because the Pt-Pt distance change is slow with respect to excited-state electron transfer, it can affect the rate of electron transfer. These results have potential impacts on controlling electron transfer rates via structural alterations to the electron donor group, tuning the charge transfer driving force.

  View details for DOI 10.1021/acs.jpclett.4c00735

  View details for PubMedID 38722188

• Ultrafast X-ray Absorption Spectroscopy Reveals Excited-State Dynamics of B12Coenzymes Controlled by the Axial Base. The journal of physical chemistry. B Chung, T., McClain, T. P., Alonso-Mori, R., Chollet, M., Deb, A., Garcia-Esparza, A. T., Huang Ze En, J., Lamb, R. M., Michocki, L. B., Reinhard, M., van Driel, T. B., Penner-Hahn, J. E., Sension, R. J. 2024

  Abstract

  Polarized time-resolved X-ray absorption spectroscopy at the Co K-edge is used to probe the excited-state dynamics and photolysis of base-off methylcobalamin and the excited-state structure of base-off adenosylcobalamin. For both molecules, the final excited-state minimum shows evidence for an expansion of the cavity around the Co ion by ca. 0.04 to 0.05 A. The 5-coordinate base-off cob(II)alamin that is formed following photodissociation has a structure similar to that of the 5-coordinate base-on cob(II)alamin, with a ring expansion of 0.03 to 0.04 A and a contraction of the lower axial bond length relative to that in the 6-coordinate ground state. These data provide insights into the role of the lower axial ligand in modulating the reactivity of B12 coenzymes.

  View details for DOI 10.1021/acs.jpcb.3c07779

  View details for PubMedID 38301132

• Ultrafast Measurements of Mode-Specific Deformation Potentials of Bi₂Te₃ and Bi₂Se₃ PHYSICAL REVIEW X Huang, Y., Querales-Flores, J. D., Teitelbaum, S. W., Cao, J., Henighan, T., Liu, H., Jiang, M., De la Pena, G., Krapivin, V., Haber, J., Sato, T., Chollet, M., Zhu, D., Katayama, T., Power, R., Allen, M., Rotundu, C. R., Bailey, T. P., Uher, C., Trigo, M., Kirchmann, P. S., Murray, E. D., Shen, Z., Savic, I., Fahy, S., Sobota, J. A., Reis, D. A. 2023; 13 (4)

  View details for DOI 10.1103/PhysRevX.13.041050

  View details for Web of Science ID 001405601100001

• Simultaneous bright- and dark-field X-ray microscopy at X-ray free electron lasers. Scientific reports Dresselhaus-Marais, L. E., Kozioziemski, B., Holstad, T. S., Ræder, T. M., Seaberg, M., Nam, D., Kim, S., Breckling, S., Choi, S., Chollet, M., Cook, P. K., Folsom, E., Galtier, E., Gonzalez, A., Gorkhover, T., Guillet, S., Haldrup, K., Howard, M., Katagiri, K., Kim, S., Kim, S., Kim, S., Kim, H., Knudsen, E. B., Kuschel, S., Lee, H. J., Lin, C., McWilliams, R. S., Nagler, B., Nielsen, M. M., Ozaki, N., Pal, D., Pablo Pedro, R., Saunders, A. M., Schoofs, F., Sekine, T., Simons, H., van Driel, T., Wang, B., Yang, W., Yildirim, C., Poulsen, H. F., Eggert, J. H. 2023; 13 (1): 17573

  Abstract

  The structures, strain fields, and defect distributions in solid materials underlie the mechanical and physical properties across numerous applications. Many modern microstructural microscopy tools characterize crystal grains, domains and defects required to map lattice distortions or deformation, but are limited to studies of the (near) surface. Generally speaking, such tools cannot probe the structural dynamics in a way that is representative of bulk behavior. Synchrotron X-ray diffraction based imaging has long mapped the deeply embedded structural elements, and with enhanced resolution, dark field X-ray microscopy (DFXM) can now map those features with the requisite nm-resolution. However, these techniques still suffer from the required integration times due to limitations from the source and optics. This work extends DFXM to X-ray free electron lasers, showing how the [Formula: see text] photons per pulse available at these sources offer structural characterization down to 100 fs resolution (orders of magnitude faster than current synchrotron images). We introduce the XFEL DFXM setup with simultaneous bright field microscopy to probe density changes within the same volume. This work presents a comprehensive guide to the multi-modal ultrafast high-resolution X-ray microscope that we constructed and tested at two XFELs, and shows initial data demonstrating two timing strategies to study associated reversible or irreversible lattice dynamics.

  View details for DOI 10.1038/s41598-023-35526-5

  View details for PubMedID 37845245

  View details for PubMedCentralID 8279502

• Nonthermal Bonding Origin of a Novel Photoexcited Lattice Instability in SnSe. Physical review letters Huang, Y., Teitelbaum, S., Yang, S., De la Peña, G., Sato, T., Chollet, M., Zhu, D., Niedziela, J. L., Bansal, D., May, A. F., Lindenberg, A. M., Delaire, O., Trigo, M., Reis, D. A. 2023; 131 (15): 156902

  Abstract

  Lattice dynamics measurements are often crucial tools for understanding how materials transform between different structures. We report time-resolved x-ray scattering-based measurements of the nonequilibrium lattice dynamics in SnSe, a monochalcogenide reported to host a novel photoinduced lattice instability. By fitting interatomic force models to the fluence dependent excited-state dispersion, we determine the nonthermal origin of the lattice instability to be dominated by changes of interatomic interactions along a bilayer-connecting bond, rather than of an intralayer bonding network that is of primary importance to the lattice instability in thermal equilibrium.

  View details for DOI 10.1103/PhysRevLett.131.156902

  View details for PubMedID 37897786

• Hard x-ray - optical four-wave mixing using a split-and-delay line OPTICS EXPRESS Peters, W. K., Feltman, J., Jones, T., Song, S., Chollet, M., Robinson, J., Padmanabhan, P., Foglia, L., Bencivenga, F., Coffee, R., Bowlan, P. 2023; 31 (19): 31410-31418

  View details for DOI 10.1364/OE.485287

  View details for Web of Science ID 001106628300001

• Ultrafast X-Ray Scattering Reveals Composite Amplitude Collective Mode in the Weyl Charge Density Wave Material (TaSe_{4})_{2}I. Physical review letters Nguyen, Q. L., Duncan, R. A., Orenstein, G., Huang, Y., Krapivin, V., de la Peña, G., Ornelas-Skarin, C., Reis, D. A., Abbamonte, P., Bettler, S., Chollet, M., Hoffmann, M. C., Hurley, M., Kim, S., Kirchmann, P. S., Kubota, Y., Mahmood, F., Miller, A., Osaka, T., Qu, K., Sato, T., Shoemaker, D. P., Sirica, N., Song, S., Stanton, J., Teitelbaum, S. W., Tilton, S. E., Togashi, T., Zhu, D., Trigo, M. 2023; 131 (7): 076901

  Abstract

  We report ultrafast x-ray scattering experiments of the quasi-1D charge density wave (CDW) material (TaSe_{4})_{2}I following ultrafast infrared photoexcitation. From the time-dependent diffraction signal at the CDW sidebands we identify a 0.11 THz amplitude mode derived primarily from a transverse acoustic mode of the high-symmetry structure. From our measurements we determine that this mode interacts with the valence charge indirectly through another collective mode, and that the CDW system in (TaSe_{4})_{2}I has a composite nature supporting multiple dynamically active structural degrees of freedom.

  View details for DOI 10.1103/PhysRevLett.131.076901

  View details for PubMedID 37656841

• Revealing Excited-State Trajectories on Potential Energy Surfaces with Atomic Resolution in Real Time. Angewandte Chemie (International ed. in English) Leshchev, D., J S Valentine, A., Kim, P., Mills, A. W., Roy, S., Chakraborty, A., Biasin, E., Haldrup, K., Hsu, D. J., Kirschner, M. S., Rimmerman, D., Chollet, M., Glownia, J. M., van Driel, T. B., Castellano, F. N., Li, X., Chen, L. X. 2023: e202304615

  Abstract

  Photoexcited molecular trajectories on potential energy surfaces (PESs) prior to thermalization are intimately connected to the photochemical reaction outcome. The excited-state trajectories of a diplatinum complex featuring photo-activated metal-metal σ-bond formation and associated Pt-Pt stretching motions were detected in real time using femtosecond wide-angle X-ray solution scattering. The observed motions correspond well with coherent vibrational wavepacket motions detected by femtosecond optical transient absorption. Two key coordinates for intersystem crossing have been identified, the Pt-Pt bond length and the orientation of the ligands coordinated with the platinum centers, along which the excited-state trajectories can be projected onto the calculated PESs of the excited states. This investigation has gleaned novel insight into electronic transitions occurring on the time scales of vibrational motions measured in real time, revealing ultrafast nonadiabatic or non-equilibrium processes along excited-state trajectories involving multiple excited-state PESs.

  View details for DOI 10.1002/anie.202304615

  View details for PubMedID 37114904

• Influence of local symmetry on lattice dynamics coupled to topological surface states PHYSICAL REVIEW B Sobota, J. A., Teitelbaum, S. W., Huang, Y., Querales-Flores, J. D., Power, R., Allen, M., Rotundu, C. R., Bailey, T. P., Uher, C., Henighan, T., Jiang, M., Zhu, D., Chollet, M., Sato, T., Trigo, M., Murray, e. D., Savic, I., Kirchmann, P. S., Fahy, S., Reis, D. A., Shen, Z. 2023; 107 (1)

  View details for DOI 10.1103/PhysRevB.107.014305

  View details for Web of Science ID 000921610800004

• Observation of a Novel Lattice Instability in Ultrafast Photoexcited SnSe PHYSICAL REVIEW X Huang, Y., Yang, S., Teitelbaum, S., De la Pena, G., Sato, T., Chollet, M., Zhu, D., Niedziela, J. L., Bansal, D., May, A. F., Lindenberg, A. M., Delaire, O., Reis, D. A., Trigo, M. 2022; 12 (1)

  View details for DOI 10.1103/PhysRevX.12.011029

  View details for Web of Science ID 000761380600001

• Femtosecond X-ray Spectroscopy Directly Quantifies Transient Excited-State Mixed Valency. The journal of physical chemistry letters Liekhus-Schmaltz, C., Fox, Z. W., Andersen, A., Kjaer, K. S., Alonso-Mori, R., Biasin, E., Carlstad, J., Chollet, M., Gaynor, J. D., Glownia, J. M., Hong, K., Kroll, T., Lee, J. H., Poulter, B. I., Reinhard, M., Sokaras, D., Zhang, Y., Doumy, G., March, A. M., Southworth, S. H., Mukamel, S., Cordones, A. A., Schoenlein, R. W., Govind, N., Khalil, M. 1800: 378-386

  Abstract

  Quantifying charge delocalization associated with short-lived photoexcited states of molecular complexes in solution remains experimentally challenging, requiring local element specific femtosecond experimental probes of time-evolving electron transfer. In this study, we quantify the evolving valence hole charge distribution in the photoexcited charge transfer state of a prototypical mixed valence bimetallic iron-ruthenium complex, [(CN)5FeIICNRuIII(NH3)5]-, in water by combining femtosecond X-ray spectroscopy measurements with time-dependent density functional theory calculations of the excited-state dynamics. We estimate the valence hole charge that accumulated at the Fe atom to be 0.6 ± 0.2, resulting from excited-state metal-to-metal charge transfer, on an 60 fs time scale. Our combined experimental and computational approach provides a spectroscopic ruler for quantifying excited-state valency in solvated complexes.

  View details for DOI 10.1021/acs.jpclett.1c03613

  View details for PubMedID 34985900

• Testing the data framework for an AI algorithm in preparation for high data rate X-ray facilities Chen, H., Chitturi, S. R., Plumley, R., Shen, L., Drucker, N. C., Burdet, N., Peng, C., Mardanya, S., Ratner, D., Mishra, A., Yoon, C., Song, S., Chollet, M., Fabbris, G., Dunne, M., Nelson, S., Li, M., Lindenberg, A., Jia, C., Nashed, Y., Bansil, A., Chowdhury, S., Feiguin, A. E., Turner, J. J., Thayer, J. B., IEEE IEEE. 2022: 1-9

  View details for DOI 10.1109/XLOOP56614.2022.00006

  View details for Web of Science ID 000968746500001

• Measurements of nonequilibrium interatomic forces using time-domain x-ray scattering PHYSICAL REVIEW B Teitelbaum, S. W., Henighan, T. C., Liu, H., Jiang, M. P., Zhu, D., Chollet, M., Sato, T., Murray, E. D., Fahy, S., O'Mahony, S., Bailey, T. P., Uher, C., Trigo, M., Reis, D. A. 2021; 103 (18)

  View details for DOI 10.1103/PhysRevB.103.L180101

  View details for Web of Science ID 000655872300005

• Subterahertz collective dynamics of polar vortices. Nature Li, Q., Stoica, V. A., Pasciak, M., Zhu, Y., Yuan, Y., Yang, T., McCarter, M. R., Das, S., Yadav, A. K., Park, S., Dai, C., Lee, H. J., Ahn, Y., Marks, S. D., Yu, S., Kadlec, C., Sato, T., Hoffmann, M. C., Chollet, M., Kozina, M. E., Nelson, S., Zhu, D., Walko, D. A., Lindenberg, A. M., Evans, P. G., Chen, L., Ramesh, R., Martin, L. W., Gopalan, V., Freeland, J. W., Hlinka, J., Wen, H. 2021; 592 (7854): 376–80

  Abstract

  The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

  View details for DOI 10.1038/s41586-021-03342-4

  View details for PubMedID 33854251

• Author Correction: Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer. Nature chemistry Biasin, E., Fox, Z. W., Andersen, A., Ledbetter, K., Kjar, K. S., Alonso-Mori, R., Carlstad, J. M., Chollet, M., Gaynor, J. D., Glownia, J. M., Hong, K., Kroll, T., Lee, J. H., Liekhus-Schmaltz, C., Reinhard, M., Sokaras, D., Zhang, Y., Doumy, G., March, A. M., Southworth, S. H., Mukamel, S., Gaffney, K. J., Schoenlein, R. W., Govind, N., Cordones, A. A., Khalil, M. 2021

  View details for DOI 10.1038/s41557-021-00663-9

  View details for PubMedID 33627886

• Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer. Nature chemistry Biasin, E., Fox, Z. W., Andersen, A., Ledbetter, K., Kjar, K. S., Alonso-Mori, R., Carlstad, J. M., Chollet, M., Gaynor, J. D., Glownia, J. M., Hong, K., Kroll, T., Lee, J. H., Liekhus-Schmaltz, C., Reinhard, M., Sokaras, D., Zhang, Y., Doumy, G., March, A. M., Southworth, S. H., Mukamel, S., Gaffney, K. J., Schoenlein, R. W., Govind, N., Cordones, A. A., Khalil, M. 2021

  Abstract

  It is well known that the solvent plays a critical role in ultrafast electron-transfer reactions. However, solvent reorganization occurs on multiple length scales, and selectively measuring short-range solute-solvent interactions at the atomic level with femtosecond time resolution remains a challenge. Here we report femtosecond X-ray scattering and emission measurements following photoinduced charge-transfer excitation in a mixed-valence bimetallic (FeiiRuiii) complex in water, and their interpretation using non-equilibrium molecular dynamics simulations. Combined experimental and computational analysis reveals that the charge-transfer excited state has a lifetime of 62fs and that coherent translational motions of the first solvation shell are coupled to the back electron transfer. Our molecular dynamics simulations identify that the observed coherent translational motions arise from hydrogen bonding changes between the solute and nearby water molecules upon photoexcitation, and have an amplitude of tenths of angstroms, 120-200cm-1 frequency and ~100fs relaxation time. This study provides an atomistic view of coherent solvent reorganization mediating ultrafast intramolecular electron transfer.

  View details for DOI 10.1038/s41557-020-00629-3

  View details for PubMedID 33589787

• Short-lived metal-centered excited state initiates iron-methionine photodissociation in ferrous cytochrome c. Nature communications Reinhard, M. E., Mara, M. W., Kroll, T., Lim, H., Hadt, R. G., Alonso-Mori, R., Chollet, M., Glownia, J. M., Nelson, S., Sokaras, D., Kunnus, K., Driel, T. B., Hartsock, R. W., Kjaer, K. S., Weninger, C., Biasin, E., Gee, L. B., Hodgson, K. O., Hedman, B., Bergmann, U., Solomon, E. I., Gaffney, K. J. 2021; 12 (1): 1086

  Abstract

  The dynamics of photodissociation and recombination in heme proteins represent an archetypical photochemical reaction widely used to understand the interplay between chemical dynamics and reaction environment. We report a study of the photodissociation mechanism for the Fe(II)-S bond between the heme iron and methionine sulfur of ferrous cytochrome c. This bond dissociation is an essential step in the conversion of cytochrome c from an electron transfer protein to a peroxidase enzyme. We use ultrafast X-ray solution scattering to follow the dynamics of Fe(II)-S bond dissociation and 1s3p (Kbeta) X-ray emission spectroscopy to follow the dynamics of the iron charge and spin multiplicity during bond dissociation. From these measurements, we conclude that the formation of a triplet metal-centered excited state with anti-bonding Fe(II)-S interactions triggers the bond dissociation and precedes the formation of the metastable Fe high-spin quintet state.

  View details for DOI 10.1038/s41467-021-21423-w

  View details for PubMedID 33597529

• Wavefront preserving and high efficiency diamond grating beam splitter for x-ray free electron laser OPTICS EXPRESS Li, K., Liu, Y., Seaberg, M., Chollet, M., Weiss, T. M., Sakdinawat, A. 2020; 28 (8): 10939-10950

  Abstract

  X-ray free electron lasers (XFELs) provide femtosecond high-power x-ray beams with high spatial coherence, resulting in numerous influential discoveries. Diffractive optics allow for the easy manipulation and measurement of an x-ray beam's wavefront and enable the realization of complex designed properties and specifications. For example, phase gratings can be used as x-ray beam splitters to enable beam sharing by multiple end stations or in-situ beam monitoring, including spectrum and wavefront measurements. Wavefront preservation and high efficiency and survivability under high power are requirements for such beam splitters. Diamond is the most suitable choice for phase grating fabrication, due to its high thermal conductivity that enables it to survive high average power XFEL beams. We have fabricated a large area (2×2 mm2) high aspect ratio (13:1) diamond grating on a diamond plate. Testing was performed at 9.5 keV and resulted in a high splitting efficiency (30%). Tunable efficiency was obtained via tilting the grating with respect to the x-ray beam. Wavefront fidelity of the split beams were measured to less than λ/100 using a Talbot wavefront sensor.

  View details for DOI 10.1364/OE.380534

  View details for Web of Science ID 000526518300020

  View details for PubMedID 32403615

• Speckle correlation as a monitor of X-ray free-electron laser induced crystal lattice deformation. Journal of synchrotron radiation Plumley, R. n., Sun, Y. n., Teitelbaum, S. n., Song, S. n., Sato, T. n., Chollet, M. n., Nelson, S. n., Wang, N. n., Sun, P. n., Robert, A. n., Fuoss, P. n., Sutton, M. n., Zhu, D. n. 2020; 27 (Pt 6): 1470–76

  Abstract

  X-ray free-electron lasers (X-FELs) present new opportunities to study ultrafast lattice dynamics in complex materials. While the unprecedented source brilliance enables high fidelity measurement of structural dynamics, it also raises experimental challenges related to the understanding and control of beam-induced irreversible structural changes in samples that can ultimately impact the interpretation of experimental results. This is also important for designing reliable high performance X-ray optical components. In this work, X-FEL beam-induced lattice alterations are investigated by measuring the shot-to-shot evolution of near-Bragg coherent scattering from a single crystalline germanium sample. It is shown that X-ray photon correlation analysis of sequential speckle patterns measurements can be used to monitor the nature and extent of lattice rearrangements. Abrupt, irreversible changes are observed following intermittent high-fluence monochromatic X-ray pulses, thus revealing the existence of a threshold response to X-FEL pulse intensity.

  View details for DOI 10.1107/S1600577520011509

  View details for PubMedID 33147171

• Compact hard x-ray split-delay system based on variable-gap channel-cut crystals OPTICS LETTERS Sun, Y., Wang, N., Song, S., Sun, P., Chollet, M., Sato, T., van Driel, T. B., Nelson, S., Plumley, R., Montana-Lopez, J., Teitelbaum, S. W., Haber, J., Hastings, J. B., Baron, A. R., Sutton, M., Fuoss, P. H., Robert, A., Zhu, D. 2019; 44 (10): 2582–85

  Abstract

  We present the concept and a prototypical implementation of a compact x-ray split-delay system that is capable of performing continuous on-the-fly delay scans over a range of ∼10  ps with sub-100 nanoradian pointing stability. The system consists of four channel-cut silicon crystals, two of which have gradually varying gap sizes from intentional 5 deg asymmetric cuts. The delay adjustment is realized by linear motions of these two monolithic varying-gap channel cuts, where the x-ray beam experiences pairs of anti-parallel reflections, and thus becomes less sensitive in output beam pointing to motion imperfections of the translation stages. The beam splitting is accomplished by polished crystal edges. A high degree of mutual coherence between the two branches at the focus is observed by analyzing small-angle coherent x-ray scattering patterns. We envision a wide range of applications including single-shot x-ray pulse temporal diagnostics, studies of high-intensity x-ray-matter interactions, as well as measurement of dynamics in disordered material systems using split-pulse x-ray photon correlation spectroscopy.

  View details for DOI 10.1364/OL.44.002582

  View details for Web of Science ID 000467906400050

  View details for PubMedID 31090737

• Pump-probe experimental methodology at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Glownia, J. M., Gumerlock, K., Lemke, H. T., Sato, T., Zhu, D., Chollet, M. 2019; 26: 685–91

  View details for DOI 10.1107/S160057751900225X

  View details for Web of Science ID 000467526100009

• The Macromolecular Femtosecond Crystallography Instrument at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Sierra, R. G., Batyuk, A., Sun, Z., Aquila, A., Hunter, M. S., Lane, T. J., Liang, M., Yoon, C., Alonso-Mori, R., Armenta, R., Castagna, J., Hollenbeck, M., Osier, T. O., Hayes, M., Aldrich, J., Curtis, R., Koglin, J. E., Rendahl, T., Rodriguez, E., Carbajo, S., Guillet, S., Paul, R., Hart, P., Nakahara, K., Carini, G., DeMirci, H., Dao, E., Hayes, B. M., Rao, Y. P., Chollet, M., Feng, Y., Fuller, F. D., Kupitz, C., Sato, T., Seaberg, M. H., Song, S., van Driel, T. B., Yavas, H., Zhu, D., Cohen, A. E., Wakatsuki, S., Boutet, S. 2019; 26: 346–57

  View details for DOI 10.1107/S1600577519001577

  View details for Web of Science ID 000460859600007

• The Macromolecular Femtosecond Crystallography Instrument at the Linac Coherent Light Source. Journal of synchrotron radiation Sierra, R. G., Batyuk, A. n., Sun, Z. n., Aquila, A. n., Hunter, M. S., Lane, T. J., Liang, M. n., Yoon, C. H., Alonso-Mori, R. n., Armenta, R. n., Castagna, J. C., Hollenbeck, M. n., Osier, T. O., Hayes, M. n., Aldrich, J. n., Curtis, R. n., Koglin, J. E., Rendahl, T. n., Rodriguez, E. n., Carbajo, S. n., Guillet, S. n., Paul, R. n., Hart, P. n., Nakahara, K. n., Carini, G. n., DeMirci, H. n., Dao, E. H., Hayes, B. M., Rao, Y. P., Chollet, M. n., Feng, Y. n., Fuller, F. D., Kupitz, C. n., Sato, T. n., Seaberg, M. H., Song, S. n., van Driel, T. B., Yavas, H. n., Zhu, D. n., Cohen, A. E., Wakatsuki, S. n., Boutet, S. n. 2019; 26 (Pt 2): 346–57

  Abstract

  The Macromolecular Femtosecond Crystallography (MFX) instrument at the Linac Coherent Light Source (LCLS) is the seventh and newest instrument at the world's first hard X-ray free-electron laser. It was designed with a primary focus on structural biology, employing the ultrafast pulses of X-rays from LCLS at atmospheric conditions to overcome radiation damage limitations in biological measurements. It is also capable of performing various time-resolved measurements. The MFX design consists of a versatile base system capable of supporting multiple methods, techniques and experimental endstations. The primary techniques supported are forward scattering and crystallography, with capabilities for various spectroscopic methods and time-resolved measurements. The location of the MFX instrument allows for utilization of multiplexing methods, increasing user access to LCLS by running multiple experiments simultaneously.

  View details for PubMedID 30855242

• Higher-order modes at FELs: a machine interpretation Sun, P., Sun, Y., Zhu, D., Song, S., Li, H., Chollet, M., Seaberg, M., Hastings, J. B., Robert, A., Sutton, M., Feng, Y., Tschentscher, T., Patthey, L., Tiedtke, K., Zangrando, M. SPIE-INT SOC OPTICAL ENGINEERING. 2019

  View details for DOI 10.1117/12.2522912

  View details for Web of Science ID 000502119600001

• Femtosecond x-ray diffraction reveals a liquid-liquid phase transition in phase-change materials. Science (New York, N.Y.) Zalden, P. n., Quirin, F. n., Schumacher, M. n., Siegel, J. n., Wei, S. n., Koc, A. n., Nicoul, M. n., Trigo, M. n., Andreasson, P. n., Enquist, H. n., Shu, M. J., Pardini, T. n., Chollet, M. n., Zhu, D. n., Lemke, H. n., Ronneberger, I. n., Larsson, J. n., Lindenberg, A. M., Fischer, H. E., Hau-Riege, S. n., Reis, D. A., Mazzarello, R. n., Wuttig, M. n., Sokolowski-Tinten, K. n. 2019; 364 (6445): 1062–67

  Abstract

  In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid-liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics.

  View details for DOI 10.1126/science.aaw1773

  View details for PubMedID 31197008

• Ultrafast disordering of vanadium dimers in photoexcited VO2 SCIENCE Wall, S., Yang, S., Vidas, L., Chollet, M., Glownia, J. M., Kozina, M., Katayama, T., Henighan, T., Jiang, M., Miller, T. A., Reis, D. A., Boatner, L. A., Delaire, O., Trigo, M. 2018; 362 (6414): 572-+

  View details for DOI 10.1126/science.aau3873

  View details for Web of Science ID 000450460000043

• Frequency-selective excitation of high-wavevector phonons APPLIED PHYSICS LETTERS Teitelbaum, S. W., Henighan, T., Liu, H., Jiang, M. P., Kozina, M., Zhu, D., Chollet, M., Sato, T., Glownia, J. M., Trigo, M., Reis, D. A. 2018; 113 (17)

  View details for DOI 10.1063/1.5047447

  View details for Web of Science ID 000449145700017

• Direct Measurement of Anharmonic Decay Channels of a Coherent Phonon. Physical review letters Teitelbaum, S. W., Henighan, T., Huang, Y., Liu, H., Jiang, M. P., Zhu, D., Chollet, M., Sato, T., Murray, É. D., Fahy, S., O'Mahony, S., Bailey, T. P., Uher, C., Trigo, M., Reis, D. A. 2018; 121 (12): 125901

  Abstract

  We report channel-resolved measurements of the anharmonic coupling of the coherent A_{1g} phonon in photoexcited bismuth to pairs of high wave vector acoustic phonons. The decay of a coherent phonon can be understood as a parametric resonance process whereby the atomic displacement periodically modulates the frequency of a broad continuum of modes. This coupling drives temporal oscillations in the phonon mean-square displacements at the A_{1g} frequency that are observed across the Brillouin zone by femtosecond x-ray diffuse scattering. We extract anharmonic coupling constants between the A_{1g} and several representative decay channels that are within an order of magnitude of density functional perturbation theory calculations.

  View details for DOI 10.1103/PhysRevLett.121.125901

  View details for PubMedID 30296113

• Direct Measurement of Anharmonic Decay Channels of a Coherent Phonon PHYSICAL REVIEW LETTERS Teitelbaum, S. W., Henighan, T., Huang, Y., Liu, H., Jiang, M. P., Zhu, D., Chollet, M., Sato, T., Murray, E. D., Fahy, S., O'Mahony, S., Bailey, T. P., Uher, C., Trigo, M., Reis, D. A. 2018; 121 (12)

  View details for DOI 10.1103/PhysRevLett.121.125901

  View details for Web of Science ID 000445177300013

• Ultrafast disordering of vanadium dimers in photoexcited VO2. Science (New York, N.Y.) Wall, S., Yang, S., Vidas, L., Chollet, M., Glownia, J. M., Kozina, M., Katayama, T., Henighan, T., Jiang, M., Miller, T. A., Reis, D. A., Boatner, L. A., Delaire, O., Trigo, M. 2018; 362 (6414): 572–76

  Abstract

  Many ultrafast solid phase transitions are treated as chemical reactions that transform the structures between two different unit cells along a reaction coordinate, but this neglects the role of disorder. Although ultrafast diffraction provides insights into atomic dynamics during such transformations, diffraction alone probes an averaged unit cell and is less sensitive to randomness in the transition pathway. Using total scattering of femtosecond x-ray pulses, we show that atomic disordering in photoexcited vanadium dioxide (VO2) is central to the transition mechanism and that, after photoexcitation, the system explores a large volume of phase space on a time scale comparable to that of a single phonon oscillation. These results overturn the current understanding of an archetypal ultrafast phase transition and provide new microscopic insights into rapid evolution toward equilibrium in photoexcited matter.

  View details for PubMedID 30385575

• Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2 '- bipyridine)(2)(CN)(2)] STRUCTURAL DYNAMICS Kjaer, K. S., Zhang, W., Alonso-Mori, R., Bergmann, U., Chollet, M., Hadt, R. G., Hartsock, R. W., Harlang, T., Kroll, T., Kubicek, K., Lemke, H. T., Liang, H. W., Liu, Y., Nielsen, M. M., Robinson, J. S., Solomon, E. I., Sokaras, D., van Driel, T. B., Weng, T., Zhu, D., Persson, P., Warnmark, K., Sundstrom, V., Gaffney, K. J. 2017; 4 (4): 044030

  Abstract

  We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2'-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2'-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2- in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy)N(CN)6-2N]2N-4, where N = 1-3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

  View details for PubMedID 28653021

• Metalloprotein entatic control of ligand-metal bonds quantified by ultrafast x-ray spectroscopy SCIENCE Mara, M. W., Hadt, R. G., Reinhard, M., Kroll, T., Lim, H., Hartsock, R. W., Alonso-Mori, R., Chollet, M., Glownia, J. M., Nelson, S., Sokaras, D., Kunnus, K., Hodgson, K. O., Hedman, B., Bergmann, U., Gaffney, K. J., Solomon, E. I. 2017; 356 (6344): 1276-+

  Abstract

  The multifunctional protein cytochrome c (cyt c) plays key roles in electron transport and apoptosis, switching function by modulating bonding between a heme iron and the sulfur in a methionine residue. This Fe-S(Met) bond is too weak to persist in the absence of protein constraints. We ruptured the bond in ferrous cyt c using an optical laser pulse and monitored the bond reformation within the protein active site using ultrafast x-ray pulses from an x-ray free-electron laser, determining that the Fe-S(Met) bond enthalpy is ~4 kcal/mol stronger than in the absence of protein constraints. The 4 kcal/mol is comparable with calculations of stabilization effects in other systems, demonstrating how biological systems use an entatic state for modest yet accessible energetics to modulate chemical function.

  View details for PubMedID 28642436

  View details for PubMedCentralID PMC5706643

• Coherent structural trapping through wave packet dispersion during photoinduced spin state switching NATURE COMMUNICATIONS Lemke, H. T., Kjaer, K. S., Hartsock, R., van Driel, T. B., Chollet, M., Glownia, J. M., Song, S., Zhu, D., Pace, E., Matar, S. F., Nielsen, M. M., Benfatto, M., Gaffney, K. J., Collet, E., Cammarata, M. 2017; 8

  Abstract

  The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born-Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3](2+) compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.

  View details for DOI 10.1038/ncomms15342

  View details for Web of Science ID 000401959300001

  View details for PubMedID 28537270

• Drop-on-demand sample delivery for studying biocatalysts in action at X-ray free-electron lasers. Nature methods Fuller, F. D., Gul, S., Chatterjee, R., Burgie, E. S., Young, I. D., Lebrette, H., Srinivas, V., Brewster, A. S., Michels-Clark, T., Clinger, J. A., Andi, B., Ibrahim, M., Pastor, E., de Lichtenberg, C., Hussein, R., Pollock, C. J., Zhang, M., Stan, C. A., Kroll, T., Fransson, T., Weninger, C., Kubin, M., Aller, P., Lassalle, L., Bräuer, P., Miller, M. D., Amin, M., Koroidov, S., Roessler, C. G., Allaire, M., Sierra, R. G., Docker, P. T., Glownia, J. M., Nelson, S., Koglin, J. E., Zhu, D., Chollet, M., Song, S., Lemke, H., Liang, M., Sokaras, D., Alonso-Mori, R., Zouni, A., Messinger, J., Bergmann, U., Boal, A. K., Bollinger, J. M., Krebs, C., Högbom, M., Phillips, G. N., Vierstra, R. D., Sauter, N. K., Orville, A. M., Kern, J., Yachandra, V. K., Yano, J. 2017

  Abstract

  X-ray crystallography at X-ray free-electron laser sources is a powerful method for studying macromolecules at biologically relevant temperatures. Moreover, when combined with complementary techniques like X-ray emission spectroscopy, both global structures and chemical properties of metalloenzymes can be obtained concurrently, providing insights into the interplay between the protein structure and dynamics and the chemistry at an active site. The implementation of such a multimodal approach can be compromised by conflicting requirements to optimize each individual method. In particular, the method used for sample delivery greatly affects the data quality. We present here a robust way of delivering controlled sample amounts on demand using acoustic droplet ejection coupled with a conveyor belt drive that is optimized for crystallography and spectroscopy measurements of photochemical and chemical reactions over a wide range of time scales. Studies with photosystem II, the phytochrome photoreceptor, and ribonucleotide reductase R2 illustrate the power and versatility of this method.

  View details for DOI 10.1038/nmeth.4195

  View details for PubMedID 28250468

  View details for PubMedCentralID PMC5376230

• Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution CHEMICAL SCIENCE Zhang, W., Kjaer, K. S., Alonso-Mori, R., Bergmann, U., Chollet, M., Fredin, L. A., Hadt, R. G., Hartsock, R. W., Harlang, T., Kroll, T., Kubicek, K., Lemke, H. T., Liang, H. W., Liu, Y., Nielsen, M. M., Persson, P., Robinson, J. S., Solomon, E. I., Sun, Z., Sokaras, D., van Driel, T. B., Weng, T., Zhu, D., Warnmark, K., Sundstromb, V., Gaffney, K. J. 2017; 8 (1): 515-523

  Abstract

  Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover - the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN-) ligands and one 2,2'-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2-. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. We conclude that the MLCT excited state of [Fe(CN)4(bpy)]2- decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine)3]2+ by more than two orders of magnitude.

  View details for DOI 10.1039/c6sc03070j

  View details for Web of Science ID 000391454500060

  View details for PubMedCentralID PMC5341207

• Atomistic characterization of the active-site solvation dynamics of a model photocatalyst NATURE COMMUNICATIONS van Driel, T. B., Kjaer, K. S., Hartsock, R. W., Dohn, A. O., Harlang, T., Chollet, M., Christensen, M., Gawelda, W., Henriksen, N. E., Kim, J. G., Haldrup, K., Kim, K. H., Ihee, H., Kim, J., Lemke, H., Sun, Z., Sundstrom, V., Zhang, W., Zhu, D., Moller, K. B., Nielsen, M. M., Gaffney, K. J. 2016; 7

  Abstract

  The interactions between the reactive excited state of molecular photocatalysts and surrounding solvent dictate reaction mechanisms and pathways, but are not readily accessible to conventional optical spectroscopic techniques. Here we report an investigation of the structural and solvation dynamics following excitation of a model photocatalytic molecular system [Ir2(dimen)4](2+), where dimen is para-diisocyanomenthane. The time-dependent structural changes in this model photocatalyst, as well as the changes in the solvation shell structure, have been measured with ultrafast diffuse X-ray scattering and simulated with Born-Oppenheimer Molecular Dynamics. Both methods provide direct access to the solute-solvent pair distribution function, enabling the solvation dynamics around the catalytically active iridium sites to be robustly characterized. Our results provide evidence for the coordination of the iridium atoms by the acetonitrile solvent and demonstrate the viability of using diffuse X-ray scattering at free-electron laser sources for studying the dynamics of photocatalysis.

  View details for DOI 10.1038/ncomms13678

  View details for Web of Science ID 000388643800001

  View details for PubMedID 27892472

  View details for PubMedCentralID PMC5133712

• Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Shelby, M. L., Lestrange, P. J., Jackson, N. E., Haldrup, K., Mara, M. W., Stickrath, A. B., Zhu, D., Lemke, H. T., Chollet, M., Hoffman, B. M., Li, X., Chen, L. X. 2016; 138 (28): 8752-8764

  Abstract

  Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.

  View details for DOI 10.1021/jacs.6b02176

  View details for Web of Science ID 000380295600022

  View details for PubMedID 27286410

  View details for PubMedCentralID PMC5074555

• Architecture of the synaptotagmin-SNARE machinery for neuronal exocytosis NATURE Zhou, Q., Lai, Y., Bacaj, T., Zhao, M., Lyubimov, A. Y., Uervirojnangkoorn, M., Zeldin, O. B., Brewster, A. S., Sauter, N. K., Cohen, A. E., Soltis, S. M., Alonso-Mori, R., Chollet, M., Lemke, H. T., Pfuetzner, R. A., Choi, U. B., Weis, W. I., Diao, J., Suedhof, T. C., Brunger, A. T. 2015; 525 (7567): 62-?

  Abstract

  Synaptotagmin-1 and neuronal SNARE proteins have central roles in evoked synchronous neurotransmitter release; however, it is unknown how they cooperate to trigger synaptic vesicle fusion. Here we report atomic-resolution crystal structures of Ca(2+)- and Mg(2+)-bound complexes between synaptotagmin-1 and the neuronal SNARE complex, one of which was determined with diffraction data from an X-ray free-electron laser, leading to an atomic-resolution structure with accurate rotamer assignments for many side chains. The structures reveal several interfaces, including a large, specific, Ca(2+)-independent and conserved interface. Tests of this interface by mutagenesis suggest that it is essential for Ca(2+)-triggered neurotransmitter release in mouse hippocampal neuronal synapses and for Ca(2+)-triggered vesicle fusion in a reconstituted system. We propose that this interface forms before Ca(2+) triggering, moves en bloc as Ca(2+) influx promotes the interactions between synaptotagmin-1 and the plasma membrane, and consequently remodels the membrane to promote fusion, possibly in conjunction with other interfaces.

  View details for DOI 10.1038/nature14975

  View details for Web of Science ID 000360594100025

• Phonon spectroscopy with sub-meV resolution by femtosecond x-ray diffuse scattering PHYSICAL REVIEW B Zhu, D., Robert, A., Henighan, T., Lemke, H. T., Chollet, M., Glownia, J. M., Reis, D. A., Trigo, M. 2015; 92 (5)

  View details for DOI 10.1103/PhysRevB.92.054303

  View details for Web of Science ID 000359343600001

• Imaging transient melting of a nanocrystal using an X-ray laser PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Clark, J. N., Beitra, L., Xiong, G., Fritz, D. M., Lemke, H. T., Zhu, D., Chollet, M., Williams, G. J., Messerschmidt, M. M., Abbey, B., Harder, R. J., Korsunsky, A. M., Wark, J. S., Reis, D. A., Robinson, I. K. 2015; 112 (24): 7444-7448

  Abstract

  There is a fundamental interest in studying photoinduced dynamics in nanoparticles and nanostructures as it provides insight into their mechanical and thermal properties out of equilibrium and during phase transitions. Nanoparticles can display significantly different properties from the bulk, which is due to the interplay between their size, morphology, crystallinity, defect concentration, and surface properties. Particularly interesting scenarios arise when nanoparticles undergo phase transitions, such as melting induced by an optical laser. Current theoretical evidence suggests that nanoparticles can undergo reversible nonhomogenous melting with the formation of a core-shell structure consisting of a liquid outer layer. To date, studies from ensembles of nanoparticles have tentatively suggested that such mechanisms are present. Here we demonstrate imaging transient melting and softening of the acoustic phonon modes of an individual gold nanocrystal, using an X-ray free electron laser. The results demonstrate that the transient melting is reversible and nonhomogenous, consistent with a core-shell model of melting. The results have implications for understanding transient processes in nanoparticles and determining their elastic properties as they undergo phase transitions.

  View details for DOI 10.1073/pnas.1417678112

  View details for Web of Science ID 000356251800042

  View details for PubMedID 26034277

  View details for PubMedCentralID PMC4475963

• Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis JOURNAL OF SYNCHROTRON RADIATION Sikorski, M., Song, S., Schropp, A., Seiboth, F., Feng, Y., Alonso-Mori, R., Chollet, M., Lemke, H. T., Sokaras, D., Weng, T., Zhang, W., Robert, A., Zhu, D. 2015; 22: 599-605

  Abstract

  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.

  View details for DOI 10.1107/S1600577515004361

  View details for Web of Science ID 000353920300021

  View details for PubMedID 25931074

  View details for PubMedCentralID PMC4416675

• Visualization of nanocrystal breathing modes at extreme strains NATURE COMMUNICATIONS Szilagyi, E., Wittenberg, J. S., Miller, T. A., Lutker, K., Quirin, F., Lemke, H., Zhu, D., Chollet, M., Robinson, J., Wen, H., Sokolowski-Tinten, K., Lindenberg, A. M. 2015; 6

  Abstract

  Nanoscale dimensions in materials lead to unique electronic and structural properties with applications ranging from site-specific drug delivery to anodes for lithium-ion batteries. These functional properties often involve large-amplitude strains and structural modifications, and thus require an understanding of the dynamics of these processes. Here we use femtosecond X-ray scattering techniques to visualize, in real time and with atomic-scale resolution, light-induced anisotropic strains in nanocrystal spheres and rods. Strains at the percent level are observed in CdS and CdSe samples, associated with a rapid expansion followed by contraction along the nanosphere or nanorod radial direction driven by a transient carrier-induced stress. These morphological changes occur simultaneously with the first steps in the melting transition on hundreds of femtosecond timescales. This work represents the first direct real-time probe of the dynamics of these large-amplitude strains and shape changes in few-nanometre-scale particles.

  View details for DOI 10.1038/ncomms7577

  View details for Web of Science ID 000352720700012

  View details for PubMedID 25762350

• Goniometer-based femtosecond crystallography with X-ray free electron lasers PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Cohen, A. E., Soltis, S. M., Gonzalez, A., Aguila, L., Alonso-Mori, R., Barnes, C. O., Baxter, E. L., Brehmer, W., Brewster, A. S., Brunger, A. T., Calero, G., Chang, J. F., Chollet, M., Ehrensberger, P., Eriksson, T. L., Feng, Y., Hattne, J., Hedman, B., Hollenbeck, M., Holton, J. M., Keable, S., Kobilka, B. K., Kovaleva, E. G., Kruse, A. C., Lemke, H. T., Lin, G., Lyubimov, A. Y., Manglik, A., Mathews, I. I., McPhillips, S. E., Nelson, S., Peters, J. W., Sauter, N. K., Smith, C. A., Song, J., Stevenson, H. P., Tsai, Y., Uervirojnangkoorn, M., Vinetsky, V., Wakatsuki, S., Weis, W. I., Zadvornyy, O. A., Zeldin, O. B., Zhu, D., Hodgson, K. O. 2014; 111 (48): 17122-17127

  Abstract

  The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-Å resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β2-adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.

  View details for DOI 10.1073/pnas.1418733111

  View details for Web of Science ID 000345920800042

  View details for PubMedID 25362050

  View details for PubMedCentralID PMC4260607

• Tracking excited-state charge and spin dynamics in iron coordination complexes. Nature Zhang, W., Alonso-Mori, R., Bergmann, U., Bressler, C., Chollet, M., Galler, A., Gawelda, W., Hadt, R. G., Hartsock, R. W., Kroll, T., Kjær, K. S., Kubicek, K., Lemke, H. T., Liang, H. W., Meyer, D. A., Nielsen, M. M., Purser, C., Robinson, J. S., Solomon, E. I., Sun, Z., Sokaras, D., van Driel, T. B., Vankó, G., Weng, T., Zhu, D., Gaffney, K. J. 2014; 509 (7500): 345-348

  Abstract

  Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3](2+), where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes.

  View details for DOI 10.1038/nature13252

  View details for PubMedID 24805234

• Tracking excited-state charge and spin dynamics in iron coordination complexes. Nature Zhang, W., Alonso-Mori, R., Bergmann, U., Bressler, C., Chollet, M., Galler, A., Gawelda, W., Hadt, R. G., Hartsock, R. W., Kroll, T., Kjær, K. S., Kubicek, K., Lemke, H. T., Liang, H. W., Meyer, D. A., Nielsen, M. M., Purser, C., Robinson, J. S., Solomon, E. I., Sun, Z., Sokaras, D., van Driel, T. B., Vankó, G., Weng, T., Zhu, D., Gaffney, K. J. 2014; 509 (7500): 345-348

  Abstract

  Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3](2+), where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes.

  View details for DOI 10.1038/nature13252

  View details for PubMedID 24805234

• Real-time visualization of nanocrystal solid-solid transformation pathways. Nano letters Wittenberg, J. S., Miller, T. A., Szilagyi, E., Lutker, K., Quirin, F., Lu, W., Lemke, H., Zhu, D., Chollet, M., Robinson, J., Wen, H., Sokolowski-Tinten, K., Alivisatos, A. P., Lindenberg, A. M. 2014; 14 (4): 1995-1999

  Abstract

  Measurement and understanding of the microscopic pathways materials follow as they transform is crucial for the design and synthesis of new metastable phases of matter. Here we employ femtosecond single-shot X-ray diffraction techniques to measure the pathways underlying solid-solid phase transitions in cadmium sulfide nanorods, a model system for a general class of martensitic transformations. Using picosecond rise-time laser-generated shocks to trigger the transformation, we directly observe the transition state dynamics associated with the wurtzite-to-rocksalt structural phase transformation in cadmium sulfide with atomic-scale resolution. A stress-dependent transition path is observed. At high peak stresses, the majority of the sample is converted directly into the rocksalt phase with no evidence of an intermediate prior to rocksalt formation. At lower peak stresses, a transient five-coordinated intermediate structure is observed consistent with previous first principles modeling.

  View details for DOI 10.1021/nl500043c

  View details for PubMedID 24588125

• Invited Article: A test-facility for large-area microchannel plate detector assemblies using a pulsed sub-picosecond laser REVIEW OF SCIENTIFIC INSTRUMENTS Adams, B., Chollet, M., Elagin, A., Oberla, E., Vostrikov, A., Wetstein, M., Obaid, R., Webster, P. 2013; 84 (6)

  Abstract

  The Large Area Picosecond Photodetector Collaboration is developing large-area fast photodetectors with time resolution

  View details for DOI 10.1063/1.4810018

  View details for Web of Science ID 000321273500001

  View details for PubMedID 23822326

• Spectral encoding based measurement of x-ray/optical relative delay to similar to 10 fs rms Conference on X-Ray Free-Electron Lasers - Beam Diagnostics, Beamline Instrumentation, and Applications Bionta, M. R., French, D., Cryan, J. P., Glownia, J. M., Hartmann, N., Nicholson, D. J., Baker, K., Bostedt, C., Cammarrata, M., Chollet, M., Ding, Y., Fritz, D. M., Durbin, S. M., Feng, Y., Harmand, M., Fry, A. R., Kane, D. J., Krzywinski, J., Lemke, H. T., Messerschmidt, M., Ratner, D. F., Schorb, S., Toleikis, S., Zhu, D., White, W. E., Coffee, R. N. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.929097

  View details for Web of Science ID 000311837900014