Time-resolved Diffraction Data Research Articles

Quantum tomography of molecules using ultrafast electron diffraction.

We propose a quantum tomography (QT) approach to retrieve the temporally evolving reduced density matrix in electronic state basis, where the populations and coherence between the ground state and excited state are reconstructed from the ultrafast electron diffraction signal. In order to showcase the capability of the proposed QT approach, we simulate the nuclear wavepacket dynamics and ultrafast electron diffraction of photoexcited pyrrole molecules using the abinitio quantum chemical CASSCF method. From the simulated time-resolved diffraction data, we retrieve the evolving density matrix in a crude diabatic representation basis and reveal the symmetry of the excited pyrrole wavepacket. Our QT approach opens the route to make a quantum version of "molecular movie" that covers the electronic degree of freedom and equips ultrafast electron diffraction with the power to reveal the coherence between electronic states, relaxation, and dynamics of population transfer.

Synchronous RNA conformational changes trigger ordered phase transitions in crystals

Time-resolved studies of biomacromolecular crystals have been limited to systems involving only minute conformational changes within the same lattice. Ligand-induced changes greater than several angstroms, however, are likely to result in solid-solid phase transitions, which require a detailed understanding of the mechanistic interplay between conformational and lattice transitions. Here we report the synchronous behavior of the adenine riboswitch aptamer RNA in crystal during ligand-triggered isothermal phase transitions. Direct visualization using polarized video microscopy and atomic force microscopy shows that the RNA molecules undergo cooperative rearrangements that maintain lattice order, whose cell parameters change distinctly as a function of time. The bulk lattice order throughout the transition is further supported by time-resolved diffraction data from crystals using an X-ray free electron laser. The synchronous molecular rearrangements in crystal provide the physical basis for studying large conformational changes using time-resolved crystallography and micro/nanocrystals.

Structural-electrochemical relations in the aqueous copper hexacyanoferrate-zinc system examined by synchrotron X-ray diffraction

The storage process of Zn2+ in the Prussian blue analogue (PBA) copper hexacyanoferrate (Cu[Fe(CN)6]2/3·nH2O - CuHCF) framework structure in a context of rechargeable aqueous batteries is examined by means of in operando synchrotron X-ray diffraction. Via sequential unit-cell parameter refinements of time-resolved diffraction data, it is revealed that the step-profile of the cell output voltage curves during repeated electrochemical insertion and removal of Zn2+ in the CuHCF host structure is associated with a non-linear contraction and expansion of the unit-cell in the range 0.36 < x < 1.32 for Znx/3Cu[Fe(CN)6]2/3·nH2O. For a high insertion cation content there is no apparent change in the unit-cell contraction. Furthermore, a structural analysis with respect to the occupancies of possible Zn2+ sites suggests that the Fe(CN)6 vacancies within the CuHCF framework play an important role in the structural-electrochemical behavior of this particular system. More specifically, it is observed that Zn2+ swaps position during electrochemical cycling, hopping between cavity sites to vacant ferricyanide sites.

Spatially resolved temporal stress evolution during laser surface spot hardening of steel

The time-dependent stress evolution, the resulting residual stresses as well as the microstructure of the heat treatable low alloyed steel AISI 4140 induced by laser surface spot hardening was investigated systematically by means of synchrotron X-ray diffraction. In‐situ stress analyses with a time resolution up to 100ms were carried out at the synchrotron beamlines P05@PETRAIII(*), DESY, Hamburg and PDIFF@ANKA, Karlsruhe, by the application of the measurement and evaluation approach for very fast X-ray diffraction stress analyses. During the laser surface spot hardening using a homogenization working optic with a spot size of approx. 8×8mm2 at a maximum temperature TA,max of 1150°C and heating/cooling rates vheat/cool of 1000 K/s time-resolved diffraction data were collected for various measurement positions inside and outside of the processed zone aiming to analyze the different origins for residual stress build-up. The in-situ tests were supplemented by X-ray residual stress analyses and microscopical investigations of the microstructure subsequent to the laser hardening process (ex-situ analyses).The results show that inside of the martensitic transformed region (process zone) in radial and in tangential direction homogeneous compressive residual stresses are generated. The data of the in-situ diffraction experiments reveal that these compressive residual stresses develop due to (i) local compressive elasto-plastic deformations and (ii) local phase specific transformation strains. Outside the process zone, the compressive residual stresses are balanced by rather high inhomogeneous tensile residual stresses. By means of the in-situ determined diffraction data it is proven that these tensile residual stresses have their origin in the superposition of (i) quenching effects outside the process zone, (ii) local elasto-plastic deformations and (iii) the effect of phase transformations in the nearby process zone.

Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation

The electron-phonon coupling and the corresponding energy exchange was investigated experimentally and by ab initio theory in non-equilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean squared displacement in laser-excited thin free-standing films was monitored by femtosecond electron diffraction. The electron-phonon coupling strength was obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics (DFT-MD) simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a non-thermal lattice model (NLM) for describing non-thermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principle calculations besides the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.

Time-resolved in situ neutron diffraction studies of Li-ion battery materials

Lithium-ion batteries are ubiquitous in society, used in everything from children's toys to mobile electronic devices, providing portable power solutions. There is a continuous drive for the improvement of these batteries to meet the demands of higher power devices and uses. A large proportion of the function of lithium-ion batteries arises from the electrodes, and these are in turn mediated by the atomic-scale perturbations or changes in the crystal structure during an electrochemical process (e.g. battery use). Therefore, a method to both understand battery function and propose ideas to improve their performance is to probe the electrode crystal structure evolution in situ while an electrochemical process is occurring inside a battery. Our work has utilized the benefits of in situ neutron diffraction (e.g. sensitivity towards lithium) to literally track the time-resolved evolution of lithium in electrode materials used in lithium-ion batteries (see Figure 1). With this knowledge we have been able to directly relate electrochemical properties such as capacity and differences in charge/discharge behaviour of a battery to the content and distribution of lithium in the electrode crystal structure. This talk will showcase some of our in situ investigations of materials in lithium-ion batteries, such as LiCoO2, LiFePO4, Li1+yMn2O4, LiNi0.5Mn1.5O4 and Li4Ti5O12/TiO2 electrodes. In addition, selected examples of our work using time-resolved in situ X-ray diffraction to probe other batteries types, such as primary lithium and secondary (rechargeable) sodium-ion batteries will be presented. Using time-resolved diffraction data, a comprehensive atomic-scale picture of battery functionality can be modelled and permutations can be made to the electrodes and electrochemical conditions to optimize battery performance. Therefore, crystallography and electrochemistry can mesh together to solve our energy needs.

Real time monitoring of phase transformation and strain evolution in LTT weld filler material using EDXRD

For a newly developed 10% Cr and 10% Ni low transformation temperature (LTT) weld filler material, the local phase transformation kinetics and the strain evolution during gas tungsten arc welding (GTAW) under real welding conditions was studied. An experimental set-up and a measuring and evaluation strategy are presented to gain a real time insight into the welding process. The experiments were carried out at the beam line ID15@ESRF using a two detector EDXRD (energy dispersive X-ray diffraction) set-up and high energy synchrotron X-rays. The time-resolved diffraction analysis during welding was carried out locally throughout the weld in longitudinal as well as in transverse direction to the weld line to examine the interdependence of the strain state and the transformation kinetics. This comprehension is crucial for the optimization of the weld process, and thus for the tailoring of the resulting residual stress states, which is one of the main issues for the application of LTT alloys. Using the herein proposed approach EDXRD diffraction pattern can be monitored during real welding with a counting rate of 5Hz. By means of the time resolved diffraction data the local transformation temperatures and times were determined and the local phasespecific strain evolutions are discussed with respect to the transformation rates and the time-delayed phase transformations.

Determination of transient atomic structure of laser-excited materials from time-resolved diffraction data

The time evolution of the Bragg peaks of photo-excited gold nanofilms is measured using transmission ultrafast electron diffraction (UED) with 3.0 MeV electron pulses and the corresponding structure evolution is calculated using two-temperature molecular dynamics (2T-MD). The good agreement obtained between the measured and calculated Bragg peaks, over the full experimental timescale, enables the lattice temperature effects and the structural changes to be disentangled for the first time. The agreement demonstrates that 2T-MD is a reliable method for solving the inverse problem of structure determination of laser irradiated metals in UED measurements.

Time-Resolved in Situ Neutron Diffraction under Supercritical Hydrothermal Conditions: A Study of the Synthesis of KTiOPO4

In the first in situ neutron powder diffraction study of a supercritical hydrothermal synthesis, the crystallization of KTiOPO(4) (KTP) at 450 °C and 380 bar has been investigated. The time-resolved diffraction data suggest that the crystallization of KTP occurs by the reaction between dissolved K(+)(aq), PO(4)(3-)(aq), and [Ti(OH)(x)]((4-x)+)(aq) species.

Oxygen-diffusion limited metal combustions in Zr, Ti, and Fe foils: Time- and angle-resolved x-ray diffraction studies

The transient phase and chemical transformations of diffusion controlled metal combustions in bulk Zr, Ti, and Fe foils have been investigated, in situ, using novel time- and angle-resolved x-ray diffraction (TARXD). The TARXD employs monochromatic synchrotron x-rays and a fast-rotating diffracted beam chopper resolving the diffraction image temporally in time-resolution of ∼45 μs along the azimuth on a 2D pixel array detector. The metal foil strips (10–25 μm in thickness) are ignited using a pulsed electrical heating with a typical heating rate of ∼106 K/s. The x-ray results indicate that the combustion occurs in molten metals, producing a wide range of stoichiometric solid oxides. It reflects an enhanced oxygen solubility and mobility of molten metals with respect to those of solid metals. However, the initial oxides formed are mainly oxygen-deficient metal oxides of ZrO, TiO, and FeO/Fe3O4 —the lowest suboxides stable at these high temperatures. These transition metal monoxides further react with unreacted molten metals, yielding the secondary products of Zr3O, Ti3O, and Ti2O — but not in FeO/Fe3O4. On the other hand, the higher stoichiometric oxides of ZrO2 and TiO2 are formed in the later time only on the metal surface. These results clearly indicate that the combustion process of metal strips is diffusion limited and strongly depends on the solubility and diffusivity of oxygen into molten metals. The time-resolved diffraction data reveals no evidence for metal oxidation in solids, but a series of temperature-induced polymorphic phase transitions. The dynamic thermal expansibility of Fe measured in the present fast heating experiments is similar to those in static conditions (3.3*10−5/K vs 3.5*10−5/K for α-Fe and 6.5*10−5/K versus 7.0*10−5/K for γ-Fe).

LASER– a program for response-ratio refinement of time-resolved diffraction data

The programLASER2010is described. It is specifically designed for the refinement of externally induced structural changes in crystalline solids, including time-resolved laser-pump X-ray probe experiments. The refinement is based on the measured relative intensity changes rather than on the integrated reflection intensities.

Recent progress in the use of in situ X-ray methods for the study of heterogeneous catalysts in packed-bed capillary reactors

Synchrotron-based X-ray techniques, such as Diffraction and Absorption Spectroscopy (XAS), can be readily employed to study catalysts in action, thereby offering great potential for revealing the mechanism and behaviour of catalytic solids both during preparation and reaction. The continued advancement of X-ray generation and collection mean that it is now possible to obtain high quality data from catalysts under reaction conditions with second/sub-second time resolution. In this paper, we describe in detail a specific setup which can be used to obtain transmission in situ data. It is able to mimic industrial preparation/reaction environments and has been developed to such an extent that such measurements are now routine. To illustrate its applicability, we present time-resolved diffraction data obtained from an iron molybdate-based catalyst under pseudo industrial operating conditions revealing its bulk solid-state chemistry and stability, and further show how the catalyst behaviour changes as a function of the Fe/Mo ratio. We also illustrate the versatility of this setup in obtaining data using simultaneous multiple techniques (including non-X-ray-based methods, e.g. UV–vis) from an iron molybdate catalyst under methanol/air-flow. We conclude with a brief outlook towards the future, in which we identify new possibilities for studying catalysts in action which could yield insight into their preparation and behaviour.

Transformation of ferrihydrite to hematite: anin situinvestigation on the kinetics and mechanisms

AbstractThe kinetics and mechanisms of the transformation of 2-line ferrihydrite (FH) to hematite (HM), in the presence of Pb at elevated temperatures and high pH condition, were elucidated using synchrotron-based,in situenergy dispersive X-ray diffraction (EDXRD). The time-resolved diffraction data indicated that HM crystallization occurred via a two-stage process. Based on the EDXRD data, combined with high-resolution electron microscopic images, an aqueous-aided 2D growth mechanism is proposed for both HM crystallization stages.

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.

On the refinement of time-resolved diffraction data: comparison of the random-distribution and cluster-formation models and analysis of the light-induced increase in the atomic displacement parameters

Expressions for the random-distribution and cluster-formation models for light-induced changes in crystals studied by time-resolved diffraction are presented. The two models can be distinguished on the basis of differences in the predicted intensities. The light-induced increase in the atomic displacement parameters is analyzed with both simulated and experimental data sets.

Picosecond–milliångström lattice dynamics measured by ultrafast X-ray diffraction

Fundamental processes on the molecular level, such as vibrations and rotations in single molecules, liquids or crystal lattices and the breaking and formation of chemical bonds, occur on timescales of femtoseconds to picoseconds. The electronic changes associated with such processes can be monitored in a time-resolved manner by ultrafast optical spectroscopic techniques1, but the accompanying structural rearrangements have proved more difficult to observe. Time-resolved X-ray diffraction has the potential to probe fast, atomic-scale motions2,3,4,5. This is made possible by the generation of ultrashort X-ray pulses6,7,8,9,10, and several X-ray studies of fast dynamics have been reported6,7,8,11,12,13,14,15. Here we report the direct observation of coherent acoustic phonon propagation in crystalline gallium arsenide using a non-thermal, ultrafast-laser-driven plasma — a high-brightness, laboratory-scale source of subpicosecond X-ray pulses16,17,18,19. We are able to follow a 100-ps coherent acoustic pulse, generated through optical excitation of the crystal surface, as it propagates through the X-ray penetration depth. The time-resolved diffraction data are in excellent agreement with theoretical predictions for coherent phonon excitation20 in solids, demonstrating that it is possible to obtain quantitative information on atomic motions in bulk media during picosecond-scale lattice dynamics.

IN SITU STUDIES OF THE PROPERTIES OF MATERIALS UNDER HIGH-PRESSURE AND TEMPERATURE CONDITIONS USING MULTI-ANVIL APPARATUS AND SYNCHROTRON X-RAYS

▪ Abstract Increased access to multi-anvil high-pressure devices interfaced to synchrotron X-ray radiation sources has led to a new class of experiments. These new capabilities include (a) high-precision crystal structure determination and refinement from powder X-ray diffraction data; (b) the determination of kinetic parameters and structure from time-resolved diffraction data; (c) the determination of absolute pressures by the combined use of ultrasonic techniques at high pressures and temperatures with simultaneous monitoring of X-ray diffraction; and (d) the determination of the strength and rheological properties of materials through the monitoring of the relaxation of broadened diffraction peak widths in the presence of a well-characterized deviatoric stress field generated in the multi-anvil high-pressure apparatus.

Real-Time Probe of Reaction Centers in Solid Combustions by QEXAFS on the Sub-Second Time Scale

A QEXAFS (quick-scanning EXAFS) technique has been devised to follow the local atomic coordination changes about selected reactants in a class of highly exothermic solid combustion reactions. Real-time EXAFS measurements during the combustion were made in the time frame of a few seconds. By tuning the monochromator to a specific energy, at which maximum changes occur in an EXAFS feature of an element transforming from the reactant to the product phase, a time resolution of 20 ms was achieved. The Ni + Al → NiAl reaction has been investigated in some detail in light of a possible intermediate phase in the so-called after-burn region. The present QEXAFS findings together with the recent time-resolved diffraction data on the same system lends, for the first time, experimental insights into the structural macrokinetics of this class of combustion systems.

Real-time probe of reaction centers in solid combustions on the subsecond time scale.

A quick-scanning extended x-ray-absorption fine-structure (QEXAFS) technique has been devised to follow the local atomic coordination changes about selected reactants in a class of highly exothermic solid-combustion reactions. Real-time EXAFS measurements during the combustion were made in the time frame of a few seconds. By tuning the monochromator to a specific energy, at which maximum changes occur in an EXAFS feature of an element transforming from the reactant to the product phase, a time resolution of 20 ms was achieved. The Ni+Al\ensuremath{\rightarrow}NiAl reaction has been investigated in some detail in light of a possible intermediate phase in the so-called ``after-burn'' region. The present QEXAFS findings together with the recent time-resolved diffraction data on the same system lends experimental insights into the structural macrokinetics of this class of combustion systems.

Techniques for Time-Resolved X-Ray Diffraction Using a Position Sensitive Counter

To make feasible X-ray analysis of rapidly changing structures, a method for collecting time-resolved diffraction data has been developed. The method is based on detection of the times and positions of X-ray photons scattered from the specimen under a structural change by means of a multiwire position sensitive counter and on recording this information in computer memory. Data measured over many cycles of the transition are processed by a computer program to obtain diffraction diagrams at arbitrary phases of the periodic change with the highest time resolution of 50 µs. The system is useful for dynamic study of muscle contraction and other transient phenomena involving rapid change of atomic or molecular structure on a millisecond time scale.