Ultrafast Electron Crystallography Research Articles

Electronically Driven Fragmentation of Silver Nanocrystals Revealed by Ultrafast Electron Crystallography

We report an ultrafast electron diffraction study of silver nanocrystals under surface plasmon resonance excitation, leading to a concerted fragmentation. By examining simultaneously transient structural, thermal, and Coulombic signatures of the prefragmented state, an electronically driven nonthermal fragmentation scenario is proposed.

Real-Time Observation of Cuprates Structural Dynamics by Ultrafast Electron Crystallography

The phonon-mediated attractive interaction between carriers leads to the Cooper pair formation in conventional superconductors. Despite decades of research, the glue holding Cooper pairs in high-temperature superconducting cuprates is still controversial, and the same is true for the relative involvement of structural and electronic degrees of freedom. Ultrafast electron crystallography (UEC) offers, through observation of spatiotemporally resolved diffraction, the means for determining structural dynamics and the possible role of electron-lattice interaction. A polarized femtosecond (fs) laser pulse excites the charge carriers, which relax through electron-electron and electron-phonon couplings, and the consequential structural distortion is followed diffracting fs electron pulses. In this paper, the recent findings obtained on cuprates are summarized. In particular, we discuss the strength and symmetry of the directional electron-phonon coupling inBi2Sr2CaCu2O8+δ(BSCCO), as well as thec-axis structural instability induced by near-infrared pulses inLa2CuO4(LCO). The theoretical implications of these results are discussed with focus on the possibility of charge stripes being significant in accounting for the polarization anisotropy of BSCCO, and cohesion energy (Madelung) calculations being descriptive of thec-axis instability in LCO.

Ordered water structure at hydrophobic graphite interfaces observed by 4D, ultrafast electron crystallography

Interfacial water has unique properties in various functions. Here, using 4-dimensional (4D), ultrafast electron crystallography with atomic-scale spatial and temporal resolution, we report study of structure and dynamics of interfacial water assembly on a hydrophobic surface. Structurally, vertically stacked bilayers on highly oriented pyrolytic graphite surface were determined to be ordered, contrary to the expectation that the strong hydrogen bonding of water on hydrophobic surfaces would dominate with suppressed interfacial order. Because of its terrace morphology, graphite plays the role of a template. The dynamics is also surprising. After the excitation of graphite by an ultrafast infrared pulse, the interfacial ice structure undergoes nonequilibrium "phase transformation" identified in the hydrogen-bond network through the observation of structural isosbestic point. We provide the time scales involved, the nature of ice-graphite structural dynamics, and relevance to properties related to confined water.

4D Electron Diffraction Reveals Correlated Unidirectional Behavior in Zinc Oxide Nanowires

The confined electronic structure of nanoscale materials has increasingly been shown to induce behavior quite distinct from that of bulk analogs. Direct atomic-scale visualization of nanowires of zinc oxide was achieved through their unique pancake-type diffraction by using four-dimensional (4D) ultrafast electron crystallography. After electronic excitation of this wide-gap photonic material, the wires were found to exhibit colossal expansions, two orders of magnitude higher than that expected at thermal equilibrium; the expansion is highly anisotropic, a quasi-one-dimensional behavior, and is facilitated by the induced antibonding character. By reducing the density of nanowires, the expansions reach even larger values and occur at shorter times, suggesting a decrease of the structural constraint in transient atomic motions. This unanticipated ultrafast carrier-driven expansion highlights the optoelectronic consequences of nanoscale morphologies.

Direct Observation of Optically Induced Transient Structures in Graphite Using Ultrafast Electron Crystallography

We use ultrafast electron crystallography to study structural changes induced in graphite by a femtosecond laser pulse. At moderate fluences of < or =21 mJ/cm2, lattice vibrations are observed to thermalize on a time scale of approximately 8 ps. At higher fluences approaching the damage threshold, lattice vibration amplitudes saturate. Following a marked initial contraction, graphite is driven nonthermally into a transient state with sp3-like character, forming interlayer bonds. Using ab initio density functional calculations, we trace the governing mechanism back to electronic structure changes following the photoexcitation.

Structural Preablation Dynamics of Graphite Observed by Ultrafast Electron Crystallography

By means of time-resolved electron crystallography, we report direct observation of the structural dynamics of graphite, providing new insights into the processes involving coherent lattice motions and ultrafast graphene ablation. When graphite is excited by an ultrashort laser pulse, the excited carriers reach their equilibrium in less then one picosecond by transferring heat to a subset of strongly coupled optical phonons. The time-resolved diffraction data show that on such a time scale the crystal undergoes a contraction whose velocity depends on the excitation fluence. The contraction is followed by a large expansion which, at sufficiently high fluence, leads to the ablation of entire graphene layers, as recently predicted theoretically.

4D electron imaging: principles and perspectives

In this perspective we highlight developments and concepts in the field of 4D electron imaging. With spatial and temporal resolutions reaching the picometer and femtosecond, respectively, the field is now embracing ultrafast electron diffraction, crystallography and microscopy. Here, we overview the principles involved in the direct visualization of structural dynamics with applications in chemistry, materials science and biology. The examples include the studies of complex isolated chemical reactions, phase transitions and cellular structures. We conclude with an outlook on the potential of the approach and with some questions that may define new frontiers of research.

Electron crystallography: imaging and single-crystal diffraction from powders

The study of crystals at atomic level by electrons - electron crystallography - is an important complement to X-ray crystallography. There are two main advantages of structure determinations by electron crystallography compared to X-ray diffraction: (i) crystals millions of times smaller than those needed for X-ray diffraction can be studied and (ii) the phases of the crystallographic structure factors, which are lost in X-ray diffraction, are present in transmission-electron-microscopy (TEM) images. In this paper, some recent developments of electron crystallography and its applications, mainly on inorganic crystals, are shown. Crystal structures can be solved to atomic resolution in two dimensions as well as in three dimensions from both TEM images and electron diffraction. Different techniques developed for electron crystallography, including three-dimensional reconstruction, the electron precession technique and ultrafast electron crystallography, are reviewed. Examples of electron-crystallography applications are given. There is in principle no limitation to the complexity of the structures that can be solved by electron crystallography.

Ultrafast Electron Crystallography. 3. Theoretical Modeling of Structural Dynamics

A systematic theoretical study of structural dynamics for a substrate and an adsorbate is presented and compared with experimental results of ultrafast electron crystallography. Using the harmonic lattice model of a chain of atoms, including anharmonic forces, we investigate influences of the impulsive force on the temporal behavior of Bragg diffraction; the roles of damping and anharmonicity are also discussed. Extensive simulations are made in order to gain an understanding of the controlling factors of the atomic motions in the substrate, with or without the adsorbate. The results elucidate the importance of coherent wave propagation in the nonequilibrium regime and provide the atomic-scale description of surface and bulk dynamics. The influence of the attenuation length of the impulsive force and the thickness of the substrate (adsorbate) are also considered. For adsorbates, the mismatch of force constants and the coupling with the substrate are examined, thus establishing the conditions for wave-type propagation.

Nonequilibrium Phase Transitions in Cuprates Observed by Ultrafast Electron Crystallography

Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Deltac) on fluence (F), with Deltac/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at approximately 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity.

Ultrafast Electron Crystallography. 2. Surface Adsorbates of Crystalline Fatty Acids and Phospholipids

In this account, the second in this series, we report our detailed studies of the structures and dynamics of adsorbates of crystalline fatty acids and phospholipids, using ultrafast electron crystallography (UEC). These macromolecules serve as model systems for biomembranes and allow for systematic studies under controlled conditions. The systems investigated are arachidic (eicosanoic) acid and dimyristoyl phosphatidic acid (DMPA), deposited on a substrate by the Langmuir−Blodgett technique. We studied these systems in monolayer, bilayer, and multilayer structures, and under different conditions (pH, pressure, and temperature) and on different substrates (hydrophobic and hydrophilic). The subunit cell −CH2−CH2−CH2− distances were determined for all structures. For fatty acid samples, the structure is orthorhombic, and a0 and b0 have the values, depending on conditions, of 4.7−4.9 Å and 8.0−8.9 Å, respectively. The c0 value is 2.54 Å and for a given sample the accuracy is milliangstrom. Structural dynamics, after an ultrafast temperature jump in the underlying substrate, were studied by observing changes of the diffraction patterns: Bragg spot position, intensity, width, and the rocking curves. All structures exhibit a coherent anisotropic nonequilibrium expansion along the aliphatic chains, accompanied by transient structural ordering on the ultrafast time-scale. This wave-type, not diffusive, motion is followed by contraction and restructuring at longer times due to energy redistribution and diffusion. The transient behavior is entirely different from that reported here at equilibrium temperatures, in the range of 100−380 K. From these results, we are able to draw a general picture for the structural dynamics of amphiphilic chain molecules and elucidate the important role of nonequilibrium behavior at short times.

Ultrafast Electron Crystallography. 1. Nonequilibrium Dynamics of Nanometer-Scale Structures

In this paper, the first in a series, we give a full account of the development of ultrafast electron crystallography (UEC) and its applications in the study of nanometer-scale semiconductors and t...

Ultrafast Electron Crystallography of Phospholipids

The structure and dynamics of monolayer and bilayer (see picture) phospholipids have been studied with spatiotemporal resolutions by ultrafast electron crystallography. The expansion and restructuring of the chains were observed after a femtosecond temperature jump in the substrate, and a transient structural ordering was revealed. The atomic forces were identified to be coherent in the non-equilibrium state of the assembly.

Interfacial Water on Cl- and H-Terminated Si(111) Surfaces from First-Principles Calculations

The properties of interfacial water on Cl- and H-terminated Si(111) surfaces are investigated using a first-principles approach and characterized by means of energetic analysis combined with hydrogen-bond counting. The interaction of water with both substrates is found to be significantly weak, although bonding with the Cl-terminated Si(111) surface is relatively stronger because of the electrostatic contribution. According to a molecular picture for attributing the hydrophilic/hydrophobic character, both surfaces should be considered hydrophobic, at variance with the interpretation of recent ultrafast electron crystallography experiments, which seems instead to support a hydrophilic nature of the Cl-terminated Si(111) substrate.

4D ULTRAFAST ELECTRON DIFFRACTION, CRYSTALLOGRAPHY, AND MICROSCOPY

In this review, we highlight the progress made in the development of 4D ultrafast electron diffraction (UED), crystallography (UEC), and microscopy (UEM) with a focus on concepts, methodologies, and prototypical applications. The joint atomic-scale resolutions in space and time, and sensitivity reached, make it possible to determine complex transient structures and assemblies in different phases. These applications include studies of isolated chemical reactions (molecular beams), interfaces, surfaces and nanocrystals, self-assembly, and 2D crystalline fatty-acid bilayers. In 4D UEM, we are now able, using timed, single-electron packets, to image nano-to-micro scale structures of materials and biological cells. Future applications of these methods are foreseen across areas of physics, chemistry, and biology.

Atomic-scale dynamical structures of fatty acid bilayers observed by ultrafast electron crystallography

The structure and dynamics of a biological model bilayer are reported with atomic-scale resolution by using ultrafast electron crystallography. The bilayer was deposited as a Langmuir-Blodgett structure of arachidic (eicosanoic) fatty acids with the two chains containing 40 carbon atoms (approximately = 50 angstroms), on a hydrophobic substrate, the hydrogen terminated silicon(111) surface. We determined the structure of the 2D assembly, establishing the orientation of the chains and the subunit cell of the CH2 distances: a0 = 4.7 angstroms, b0 = 8.0 angstroms, and c0 = 2.54 angstroms. For structural dynamics, the diffraction frames were taken every 1 picosecond after a femtosecond temperature jump. The observed motions, with sub-angstroms resolution and monolayer sensitivity, clearly indicate the coherent anisotropic expansion of the bilayer solely along the aliphatic chains, followed by nonequilibrium contraction and restructuring at longer times. This motion is indicative of a nonlinear behavior among the anharmonically coupled bonds on the ultrashort time scale and energy redistribution and diffusion on the longer time scale. The ability to observe such atomic motions of complex structures and at interfaces is a significant leap forward for the determination of macromolecular dynamical structures by using ultrafast electron crystallography.

Introduction

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article McMillan Paul F. and Clary David C. 2005IntroductionPhil. Trans. R. Soc. A.363311–313http://doi.org/10.1098/rsta.2004.1512SectionYou have accessIntroduction Paul F. McMillan Paul F. McMillan Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London WC1H 0AJ, UK and The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UK () Google Scholar Find this author on PubMed Search for more papers by this author and David C. Clary David C. Clary Department of Physical and Theoretical Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK Google Scholar Find this author on PubMed Search for more papers by this author Paul F. McMillan Paul F. McMillan Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London WC1H 0AJ, UK and The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UK () Google Scholar Find this author on PubMed Search for more papers by this author and David C. Clary David C. Clary Department of Physical and Theoretical Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK Google Scholar Find this author on PubMed Search for more papers by this author Published:15 February 2005https://doi.org/10.1098/rsta.2004.1512 Next Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Usabiaga I, Camiruaga A, Calabrese C, Veloso A, D’mello V, Wategaonkar S and Fernández J (2020) Exploration of the theobromine–water dimer: comparison with DNA microhydration, Physical Chemistry Chemical Physics, 10.1039/D0CP02397C, 22:27, (15759-15768) Kwon O, Ortalan V and Zewail A (2011) Macromolecular structural dynamics visualized by pulsed dose control in 4D electron microscopy, Proceedings of the National Academy of Sciences, 10.1073/pnas.1103109108, 108:15, (6026-6031), Online publication date: 12-Apr-2011. Schuster P (2008) Modeling in biological chemistry. From biochemical kinetics to systems biology, Monatshefte für Chemie - Chemical Monthly, 10.1007/s00706-008-0892-6, 139:4, (427-446), Online publication date: 1-Apr-2008. Zewail A (2006) 4D ULTRAFAST ELECTRON DIFFRACTION, CRYSTALLOGRAPHY, AND MICROSCOPY, Annual Review of Physical Chemistry, 10.1146/annurev.physchem.57.032905.104748, 57:1, (65-103), Online publication date: 1-May-2006. Wilding M, Wilson M and McMillan P (2006) Structural studies and polymorphism in amorphous solids and liquids at high pressure, Chemical Society Reviews, 10.1039/b517775h, 35:10, (964), . McMillan P (2005) Pressing on: The legacy of Percy W. Bridgman, Nature Materials, 10.1038/nmat1488, 4:10, (715-718), Online publication date: 1-Oct-2005. This Issue15 February 2005Volume 363Issue 1827Discussion Meeting Issue ‘Configurational energy landscapes and structural transitions in clusters, fluids and biomolecules’ organized by Paul F. McMillan and David C. Clary Article InformationDOI:https://doi.org/10.1098/rsta.2004.1512Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online15/02/2005Published in print15/02/2005 License: Citations and impact

Diffraction, crystallography and microscopy beyond three dimensions: structural dynamics in space and time

In this article we highlight recent developments of ultrafast electron diffraction and crystallography at Caltech. These developments have made it possible to resolve transient structures, both spatially (0.01 A) and temporally (picosecond and now femtosecond), in the gas phase and condensed media--surfaces, interfaces, and crystals--with wide-ranging applications. With the extension to ultrafast electron microscopy, discussed here and elsewhere, we present an overview of one major research area at our centre, the Laboratory for Molecular Sciences.

Structures and dynamics of self-assembled surface monolayers observed by ultrafast electron crystallography.

In this communication, we report our first study of self-assembled adsorbates on metal surfaces. Specifically, we studied single-crystal clean surfaces of Au(111) with and without a monolayer of reaction involving the assembly of 2-mercaptoacetic acid from 2,2'-dithiodiacetic acid. We also studied monolayers of iron hemes. With ultrafast electron crystallography, we are able to observe and isolate structural dynamics of the substrate (gold) and adsorbate(s) following an ultrafast temperature jump.

Cover Picture: Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution (Angew. Chem. Int. Ed. 20/2004)

Surface structural dynamics are determined with unprecedented spatial and temporal resolution by ultrafast electron crystallography. The dynamics are initiated by a femtosecond laser pulse, and transient surface structures are imaged by an ultrashort electron pulse: A diffraction snapshot is obtained at a given time, δt, and allows the real‐time observation of surface structural dynamics with atomic‐scale resolution. For more details see the Communication by A. H. Zewail and co‐workers on page 2705 ff.