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Structural Dynamics (Melville, N.Y.)

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https://www.readbyqxmd.com/read/28503632/ultrafast-x-ray-diffraction-probe-of-terahertz-field-driven-soft-mode-dynamics-in-srtio3
#1
M Kozina, T van Driel, M Chollet, T Sato, J M Glownia, S Wandel, M Radovic, U Staub, M C Hoffmann
We use ultrafast X-ray pulses to characterize the lattice response of SrTiO3 when driven by strong terahertz fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO3. The lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28529964/ultrafast-electron-microscopy-integrated-with-a-direct-electron-detection-camera
#2
Young Min Lee, Young Jae Kim, Ye-Jin Kim, Oh-Hoon Kwon
In the past decade, we have witnessed the rapid growth of the field of ultrafast electron microscopy (UEM), which provides intuitive means to watch atomic and molecular motions of matter. Yet, because of the limited current of the pulsed electron beam resulting from space-charge effects, observations have been mainly made to periodic motions of the crystalline structure of hundreds of nanometers or higher by stroboscopic imaging at high repetition rates. Here, we develop an advanced UEM with robust capabilities for circumventing the present limitations by integrating a direct electron detection camera for the first time which allows for imaging at low repetition rates...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28529963/high-current-table-top-setup-for-femtosecond-gas-electron-diffraction
#3
Omid Zandi, Kyle J Wilkin, Yanwei Xiong, Martin Centurion
We have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28529962/picosecond-sulfur-k-edge-x-ray-absorption-spectroscopy-with-applications-to-excited-state-proton-transfer
#4
Benjamin E Van Kuiken, Matthew R Ross, Matthew L Strader, Amy A Cordones, Hana Cho, Jae Hyuk Lee, Robert W Schoenlein, Munira Khalil
Picosecond X-ray absorption (XA) spectroscopy at the S K-edge (∼2.4 keV) is demonstrated and used to monitor excited state dynamics in a small organosulfur molecule (2-Thiopyridone, 2TP) following optical excitation. Multiple studies have reported that the thione (2TP) is converted into the thiol (2-Mercaptopyridine, 2MP) following photoexcitation. However, the timescale and photochemical pathway of this reaction remain uncertain. In this work, time-resolved XA spectroscopy at the S K-edge is used to monitor the formation and decay of two transient species following 400 nm excitation of 2TP dissolved in acetonitrile...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28503631/stacking-order-dynamics-in-the-quasi-two-dimensional-dichalcogenide-1t-tas2-probed-with-mev-ultrafast-electron-diffraction
#5
L Le Guyader, T Chase, A H Reid, R K Li, D Svetin, X Shen, T Vecchione, X J Wang, D Mihailovic, H A Dürr
Transitions between different charge density wave (CDW) states in quasi-two-dimensional materials may be accompanied also by changes in the inter-layer stacking of the CDW. Using MeV ultrafast electron diffraction, the out-of-plane stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 is investigated for the first time. From the intensity of the CDW satellites aligned around the commensurate l = 1/6 characteristic stacking order, it is found out that this phase disappears with a 0...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28503630/defect-mediated-phonon-dynamics-in-tas2-and-wse2
#6
Daniel R Cremons, Dayne A Plemmons, David J Flannigan
We report correlative crystallographic and morphological studies of defect-dependent phonon dynamics in single flakes of 1T-TaS2 and 2H-WSe2 using selected-area diffraction and bright-field imaging in an ultrafast electron microscope. In both materials, we observe in-plane speed-of-sound acoustic-phonon wave trains, the dynamics of which (i.e., emergence, propagation, and interference) are strongly dependent upon discrete interfacial features (e.g., vacuum/crystal and crystal/crystal interfaces). In TaS2, we observe cross-propagating in-plane acoustic-phonon wave trains of differing frequencies that undergo coherent interference approximately 200 ps after initial emergence from distinct interfacial regions...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28470026/perspective-structure-and-ultrafast-dynamics-of-biomolecular-hydration-shells
#7
Damien Laage, Thomas Elsaesser, James T Hynes
The structure and function of biomolecules can be strongly influenced by their hydration shells. A key challenge is thus to determine the extent to which these shells differ from bulk water, since the structural fluctuations and molecular excitations of hydrating water molecules within these shells can cover a broad range in both space and time. Recent progress in theory, molecular dynamics simulations, and ultrafast vibrational spectroscopy has led to new and detailed insight into the fluctuations of water structure, elementary water motions, and electric fields at hydrated biointerfaces...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28470025/dynamic-diffraction-effects-and-coherent-breathing-oscillations-in-ultrafast-electron-diffraction-in-layered-1t-tasete
#8
Linlin Wei, Shuaishuai Sun, Cong Guo, Zhongwen Li, Kai Sun, Yu Liu, Wenjian Lu, Yuping Sun, Huanfang Tian, Huaixin Yang, Jianqi Li
Anisotropic lattice movements due to the difference between intralayer and interlayer bonding are observed in the layered transition-metal dichalcogenide 1T-TaSeTe following femtosecond laser pulse excitation. Our ultrafast electron diffraction investigations using 4D-transmission electron microscopy (4D-TEM) clearly reveal that the intensity of Bragg reflection spots often changes remarkably due to the dynamic diffraction effects and anisotropic lattice movement. Importantly, the temporal diffracted intensity from a specific crystallographic plane depends on the deviation parameter s, which is commonly used in the theoretical study of diffraction intensity...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28428974/perspective-a-toolbox-for-protein-structure-determination-in-physiological-environment-through-oriented-2d-ordered-site-specific-immobilization
#9
M Altissimo, M Kiskinova, R Mincigrucci, L Vaccari, C Guarnaccia, C Masciovecchio
Revealing the structure of complex biological macromolecules, such as proteins, is an essential step for understanding the chemical mechanisms that determine the diversity of their functions. Synchrotron based X-ray crystallography and cryo-electron microscopy have made major contributions in determining thousands of protein structures even from micro-sized crystals. They suffer from some limitations that have not been overcome, such as radiation damage, the natural inability to crystallize a number of proteins, and experimental conditions for structure determination that are incompatible with the physiological environment...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28428973/compression-of-high-density-0-16-pc-electron-bunches-through-high-field-gradients-for-ultrafast-single-shot-electron-diffraction-the-compact-rf-gun
#10
Hazem Daoud, Klaus Floettmann, R J Dwayne Miller
We present an RF gun design for single shot ultrafast electron diffraction experiments that can produce sub-100 fs high-charge electron bunches in the 130 keV energy range. Our simulations show that our proposed half-cell RF cavity is capable of producing 137 keV, 27 fs rms (60 fs FWHM), 10(6) electron bunches with an rms spot size of 276 μm and a transverse coherence length of 2.0 nm. The required operation power is 9.2 kW, significantly lower than conventional rf cavity designs and a key design feature...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28405593/molecular-couplings-and-energy-exchange-between-dna-and-water-mapped-by-femtosecond-infrared-spectroscopy-of-backbone-vibrations
#11
Yingliang Liu, Biswajit Guchhait, Torsten Siebert, Benjamin P Fingerhut, Thomas Elsaesser
Molecular couplings between DNA and water together with the accompanying processes of energy exchange are mapped via the ultrafast response of DNA backbone vibrations after OH stretch excitation of the water shell. Native salmon testes DNA is studied in femtosecond pump-probe experiments under conditions of full hydration and at a reduced hydration level with two water layers around the double helix. Independent of their local hydration patterns, all backbone vibrations in the frequency range from 940 to 1120 cm(-1) display a quasi-instantaneous reshaping of the spectral envelopes of their fundamental absorption bands upon excitation of the water shell...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28405592/angle-resolved-photoemission-spectroscopy-of-liquid-water-at-29-5%C3%A2-ev
#12
Junichi Nishitani, Christopher W West, Toshinori Suzuki
Angle-resolved photoemission spectroscopy of liquid water was performed using extreme ultraviolet radiation at 29.5 eV and a time-of-flight photoelectron spectrometer. SiC/Mg coated mirrors were employed to select the single-order 19th harmonic from laser high harmonics, which provided a constant photon flux for different laser polarizations. The instrument was tested by measuring photoemission anisotropy for rare gases and water molecules and applied to a microjet of an aqueous NaI solution. The solute concentration was adjusted to eliminate an electric field gradient around the microjet...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28405591/svd-aided-pseudo-principal-component-analysis-a-new-method-to-speed-up-and-improve-determination-of-the-optimum-kinetic-model-from-time-resolved-data
#13
Key Young Oang, Cheolhee Yang, Srinivasan Muniyappan, Jeongho Kim, Hyotcherl Ihee
Determination of the optimum kinetic model is an essential prerequisite for characterizing dynamics and mechanism of a reaction. Here, we propose a simple method, termed as singular value decomposition-aided pseudo principal-component analysis (SAPPA), to facilitate determination of the optimum kinetic model from time-resolved data by bypassing any need to examine candidate kinetic models. We demonstrate the wide applicability of SAPPA by examining three different sets of experimental time-resolved data and show that SAPPA can efficiently determine the optimum kinetic model...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28396880/beating-darwin-bragg-losses-in-lab-based-ultrafast-x-ray-experiments
#14
Wilfred K Fullagar, Jens Uhlig, Ujjwal Mandal, Dharmalingam Kurunthu, Amal El Nahhas, Hideyuki Tatsuno, Alireza Honarfar, Fredrik Parnefjord Gustafsson, Villy Sundström, Mikko R J Palosaari, Kimmo M Kinnunen, Ilari J Maasilta, Luis Miaja-Avila, Galen C O'Neil, Young Il Joe, Daniel S Swetz, Joel N Ullom
The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this work.
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28396879/pulse-length-of-ultracold-electron-bunches-extracted-from-a-laser-cooled-gas
#15
J G H Franssen, T L I Frankort, E J D Vredenbregt, O J Luiten
We present measurements of the pulse length of ultracold electron bunches generated by near-threshold two-photon photoionization of a laser-cooled gas. The pulse length has been measured using a resonant 3 GHz deflecting cavity in TM110 mode. We have measured the pulse length in three ionization regimes. The first is direct two-photon photoionization using only a 480 nm femtosecond laser pulse, which results in short (∼15 ps) but hot (∼10(4 )K) electron bunches. The second regime is just-above-threshold femtosecond photoionization employing the combination of a continuous-wave 780 nm excitation laser and a tunable 480 nm femtosecond ionization laser which results in both ultracold (∼10 K) and ultrafast (∼25 ps) electron bunches...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28396878/molecule-specific-interactions-of-diatomic-adsorbates-at-metal-liquid-interfaces
#16
Jan Philip Kraack, Andres Kaech, Peter Hamm
Ultrafast vibrational dynamics of small molecules on platinum (Pt) layers in water are investigated using 2D attenuated total reflectance IR spectroscopy. Isotope combinations of carbon monoxide and cyanide are used to elucidate inter-adsorbate and substrate-adsorbate interactions. Despite observed cross-peaks in the CO spectra, we conclude that the molecules are not vibrationally coupled. Rather, strong substrate-adsorbate interactions evoke rapid (∼2 ps) vibrational relaxation from the adsorbate into the Pt layer, leading to thermal cross-peaks...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28345010/distortion-dependent-intersystem-crossing-a-femtosecond-time-resolved-photoelectron-spectroscopy-study-of-benzene-toluene-and-p-xylene
#17
Anne B Stephansen, Theis I Sølling
The competition between ultrafast intersystem crossing and internal conversion in benzene, toluene, and p-xylene is investigated with time-resolved photoelectron spectroscopy and quantum chemical calculations. By exciting to S2 out-of-plane symmetry breaking, distortions are activated at early times whereupon spin-forbidden intersystem crossing becomes (partly) allowed. Natural bond orbital analysis suggests that the pinnacle carbon atoms distorting from the aromatic plane change hybridization between the planar Franck-Condon geometry and the deformed (boat-shaped) S2 equilibrium geometry...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28345009/optically-induced-lattice-deformations-electronic-structure-changes-and-enhanced-superconductivity-in-yba2cu3o6-48
#18
R Mankowsky, M Fechner, M Först, A von Hoegen, J Porras, T Loew, G L Dakovski, M Seaberg, S Möller, G Coslovich, B Keimer, S S Dhesi, A Cavalleri
Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28191484/photoinduced-molecular-chirality-probed-by-ultrafast-resonant-x-ray-spectroscopy
#19
Jérémy R Rouxel, Markus Kowalewski, Shaul Mukamel
Recently developed circularly polarized X-ray light sources can probe the ultrafast chiral electronic and nuclear dynamics through spatially localized resonant core transitions. We present simulations of time-resolved circular dichroism signals given by the difference of left and right circularly polarized X-ray probe transmission following an excitation by a circularly polarized optical pump with the variable time delay. Application is made to formamide which is achiral in the ground state and assumes two chiral geometries upon optical excitation to the first valence excited state...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28191483/shaped-cathodes-for-the-production-of-ultra-short-multi-electron-pulses
#20
Ariel Alcides Petruk, Kostyantyn Pichugin, Germán Sciaini
An electrostatic electron source design capable of producing sub-20 femtoseconds (rms) multi-electron pulses is presented. The photoelectron gun concept builds upon geometrical electric field enhancement at the cathode surface. Particle tracer simulations indicate the generation of extremely short bunches even beyond 40 cm of propagation. Comparisons with compact electron sources commonly used for femtosecond electron diffraction are made.
July 2017: Structural Dynamics (Melville, N.Y.)
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