Time-resolved X-ray Diffraction Techniques Research Articles

Tracking the structural changes in pure and heteroatom substituted aluminophosphate, AIPO-18, using synchrotron based X-ray diffraction techniques

We report the structural changes that occur during the thermal removal of organic template molecules that occlude the pores of small pore nanoporous zeolitic solids, AlPO-18, SAPO-18, CoAlPO-18, ZnAlPO-18 and CoSAPO-18. The calcination process is a necessary step in the formation of active catalysts. The studies performed using time-resolved High Resolution Powder Diffraction (HRPD) and High Energy X-ray Diffraction (HEXRD) techniques at various temperatures reveal that changes that take place are dependent on the type of heteroatom present in the nanoporous solids. While time-resolved HRPD shows clear changes in lattice parameters during the removal of physisorbed water molecules and subsequent removal of the organic template, HEXRD data show changes in various near neighbour distances in AlPO-18, SAPO-18, CoAlPO-18, CoSAPO-18 and ZnAlPO-18 during the calcination process. In particular HEXRD reveals the presence of water molecules coordinated to Al(III) ions in the as-synthesised materials. Upon removal of the template and water, these solids show contraction in the cell volume at elevated temperatures while first and second neighbour distances remained almost unchanged.

Structural Dynamics of Polycrystals under Shock Compression Observed via Nanosecond Time-resolved X-ray Diffraction

ABSTRACTDynamics of structural phase transition in polycrystalline samples (tetragonal stabilized zirconia and bismuth) under laser-shock compression has been studied using nanosecond time-resolved X-ray diffraction technique based on synchrotron radiation. Tetragonal zirconia shows the structural phase transition to the monoclinic phase within 20 ns during shock compression without any intermediate and reverts back to the tetragonal phase during pressure release. Bismuth shows more complex phase transition dynamics. The Bi-I phase, which is the stable phase at ambient pressure and temperature, transfers to Bi-V phase within 4 ns under shock compression and gradually reverts back following the path of Bi-V →Bi-III → Bi-II → Bi-I within 30 ns during pressure release.

Laser induced shock studies at RRCAT, Indore

The knowledge of material response under shock compression is important in terms of proper understanding of the process and in view of the wide range of technological applications associated with it. At the Laser Plasma Division, RRCAT, Indore, among other things, we are also involved in studying the material response from two different perspectives. On one front, we have developed capability for acquiring Equation of State (EOS) of materials using laser generated shock waves with long pulse lasers (>200 ps). On the other front, we have started shock experiments on single crystals using time resolved x-ray diffraction technique, using ultra-short pulse lasers (< 1 ps). In these initial experiments, characteristic sub-picosecond, high brightness Kα x-ray pulses generated by Ti: sapphire femtosecond laser produced plasmas of different target materials (Ti, Fe, and Cu) were used to probe the effect of compression generated by moderately intense (GW/cm2) sub-nanosecond laser (200 ps) pulse irradiation on the crystal surface. The dynamics of the shock propagation is manifested in terms of the temporal evolution of the rocking curve of shocked sample. The shock velocity deduced from these measurements is 12 km/s, consistent with the predicted velocities and probe depth. The observed maximum compression is 0.4 % which corresponds to a pressure of 0.8 GPa.

Time-resolved X-ray diffraction studies of phase evolution including liquid phase and grain structure during solidification process in stainless steel welds

The solidification process in stainless steel welds was analyzed using a time-resolved X-ray diffraction technique. By using an undulator beam and a novel X-ray detector, not only the phase evolution during the solidification process but also the grain structure and liquid reduction during the solidification process were analyzed in the reciprocal lattice space. Furthermore, to estimate the temperature that stimulates stray grain formation, the temperature profile at the centerline of a weld bead was measured by using a radiation thermometer with immersion-type optical fiber.

The kinetic effect on structural behavior of mixed LiMn 2O 4–LiNi 1/3Co 1/3Mn 1/3O 2 cathode materials studied by in situ time-resolved X-ray diffraction technique

How the structural changes of each active material in mixed cathode systems take place at different charge–discharge rates is quite important in the application of the system in which the mixed cathode materials with different rate capabilities are formed into one composite electrode. Here we report the results of the real time structural change studies of mixed LiMn 2O 4–LiNi 1/3Co 1/3Mn 1/3O 2 composite cathode in a Li-ion cell by using in situ synchrotron-based time resolved x-ray diffraction (TR-XRD) technique. The layer structured component in the mixed composite cathode system shows less utilization at fast discharge rate (high power mode) whereas the spinel structured component is fully utilized. This clearly demonstrates that the reduced capacity at fast discharge rate for this system is caused by the less utilization of the layer structured component. The real time monitoring of the structural behavior at various discharge rates is a great tool to design the best ratios of active materials with different rate capabilities in the mixed cathode systems for different applications.

Time-Resolved X-ray Diffraction Measurements of High-Density InAs Quantum Dots on Sb/GaAs Layers and the Suppression of Coalescence by Sb-Irradiated Growth Interruption

Self-assembly of high-density InAs quantum dots (QDs) on Sb-irradiated GaAs buffer layers was observed in-situ by a time-resolved X-ray diffraction (XRD) technique using a combination of XRD and molecular beam epitaxy. Evolution of dot height and lattice constant was analyzed during InAs QD growth and subsequent growth interruption (GI), and as a result, dislocated giant dots due to coalescence and coherent dots were separately evaluated. An Sb-irradiated GI (Sb-GI) method to be applied after InAs growth was attempted for the suppression of coalescence. Using this method, the XRD intensity of giant dots decreased, and the photoluminescence intensity of InAs QDs was enhanced. High-density InAs QDs without giant dots were produced by using the combination of the QD growth on the Sb-irradiated GaAs buffer layers and the Sb-GI.

Ultrafast X-ray diffraction in liquid, solution and gas: present status and future prospects

In recent years, the time-resolved X-ray diffraction technique has been established as an excellent tool for studying reaction dynamics and protein structural transitions with the aid of 100 ps X-ray pulses generated from third-generation synchrotrons. The forthcoming advent of the X-ray free-electron laser (XFEL) will bring a substantial improvement in pulse duration, photon flux and coherence of X-ray pulses, making time-resolved X-ray diffraction even more powerful. This technical breakthrough is envisioned to revolutionize the field of reaction dynamics associated with time-resolved diffraction methods. Examples of candidates for the first femtosecond X-ray diffraction experiments using highly coherent sub-100 fs pulses generated from XFELs are presented in this paper. They include the chemical reactions of small molecules in the gas and solution phases, solvation dynamics and protein structural transitions. In these potential experiments, ultrafast reaction dynamics and motions of coherent rovibrational wave packets will be monitored in real time. In addition, high photon flux and coherence of XFEL-generated X-ray pulses give the prospect of single-molecule diffraction experiments.

Time-resolved X-ray Diffraction Studies of Coherent Lattice Dynamics Using Synchrotron Radiation

Significant progress in recent development of synchrotron radiation (SR) sources has offered the opportunity for time-resolved X-ray diffraction studies of fast lattice dynamics in the atomic scale. The coherent atomic motion, as seen in coherent optical and acoustic phonons which are induced by femtosecond pulsed laser irradiation of semiconductor surface has directly been observed with the time-resolved X-ray diffraction technique. In this article, the time-resolved diffraction methods using an SR beam are summarized, and the demonstrations for acoustic pulse echo, coherent acoustic phonon, and optical phonon are reviewed as examples of the investigation on coherent lattice dynamics. The future prospective on the investigation of lattice dynamics using time-resolved X-ray diffraction experiments is also discussed.

Dynamics of phase transformation during thermal explosion in the Al–Ni system: Influence of mechanical activation

Time-resolved X-ray diffraction (TRXRD) techniques, which allowed for in-situ investigation of the dynamics of phase transformation during rapid, gasless heterogeneous reactions, were used to study the thermal explosion (TE) process in the stoichiometric Ni–Al system. Comparison of the phase transformation sequences for initial mixtures of the precursors and those after short-term high-energy ball milling shows that while for the former case the necessary condition for TE is melting of the reactive media, in the latter case TE occurs solely through solid- state reactions. It is also concluded that the rates of solid-state reaction are significantly enhanced due to an increase of oxygen-free contact surface area and a decrease of the scale of heterogeneity in the composite particles formed during mechanical treatment.

Measurement of Structural Changes in Tetragonal PZT Ceramics under Static and Cyclic Electric Fields Using a Laboratory X-ray Diffractometer

In situ structural characterization techniques that are capable of characterizing piezoelectric ceramics under different electrical loading conditions are important to understand the behavior of materials during their use. In this work, we report the use of a laboratory X-ray diffractometer for the measurement of various structural changes in tetragonal La-doped lead zirconate titanate (PZT) ceramics under the application of static and cyclic electric fields. The changes in the volume fractions of the 90 degrees domains parallel to the electric field direction are calculated from the intensities of the {002} diffraction peaks. In addition, the components of lattice strains are monitored from the changes in the (111) crystallographic planes. It is observed that, under the application of static electric fields, both 90 degrees domain switching and the 111 lattice strains showed similarity with the macroscopic strain-electric field hystersis loop. To measure the structural changes under cyclic electric fields, a time-resolved X-ray diffraction technique was used. Under application of a square-wave electric field of amplitude +/-650 V/mm and frequency 0.3 Hz, a change of approximately 5% in the volume fraction of the 90 degrees domains and approximately 0.07% strain of the 111 lattice planes are observed. Both the amount of 90 degrees domain switching and the 111 lattice strains are observed to increase with an increase in the amplitude of the cyclic electric field. The implications of the measured structural changes for the macroscopic piezoelectric properties of ceramics are discussed.

Effect of tip velocity on weld solidification process of hot-work tool steel

In order to clarify the effect of tip velocity on the weld solidification process of hot-work tool steel (SKD61) during welding, information about microstructure evolution was obtained by the combination of a liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. From the experimental results, it was found that the solidification mode was changed from FA mode (L → L+δ → L+δ+γ → L+γ → γ) to A mode (L → L+γ → γ) at high tip velocity. Moreover, the effect of tip velocity on the microstructure selection during solidification between the primary δ, ferrite and the primary γ, austenite was theoretically proven by the Kurz, Giovanola and Trivedi model. Therefore, it was understood that the solidification cracking susceptibility of hot-work tool steel (SKD61) weld metal was increased due to the δ to γ transition of the primary phase.

Comment on “Theoretical Investigation of Perylene Dimers and Excimers and Their Signatures in X-Ray Diffraction”

The structures of the ground and excimer states of perylene pairs are calculated [using density functional theory (DFT) and time-dependent DFT techniques] in a free as well as a crystal environment, and their spectroscopic properties are studied for the most stable configurations. The vertical transition energies for the absorption and emission bands are obtained, and they are in good agreement with experimental data. In these calculations, up to six excited states are considered. With the calculated structures of the ground and excimer states, the scattering factors are analyzed as a function of the concentration of excimers in a crystal. The intensity of the 110, 005, and 0 10 0 reflections are found to be fairly sensitive to the presence of excimers in the crystal. The finite (nanosecond) lifetime of the excimer may make it possible to observe this state using time-resolved X-ray diffraction techniques.

Effects of Sulfation Level on the Desulfation Behavior of Presulfated Pt-BaO/Al2O3 Lean NOx Trap Catalysts: A Combined H2 Temperature-Programmed Reaction, in Situ Sulfur K-Edge X-ray Absorption Near-Edge Spectroscopy, X-ray Photoelectron Spectroscopy, and Time-Resolved X-ray Diffraction Study

Desulfation by hydrogen of presulfated Pt (2 wt %)-BaO(20 wt %)/Al2O3 with various sulfur loading (S/Ba = 0.12, 0.31, and 0.62) were investigated by combining H2 temperature programmed reaction (TPRX), X-ray photoelectron spectroscopy (XPS), in situ sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and synchrotron time-resolved X-ray diffraction (TR-XRD) techniques. We find that the amount of H2S desorbed during the desulfation in the H2 TPRX experiments is not proportional to the amount of initial sulfur loading. The results of both in situ sulfur K-edge XANES and TR-XRD show that at low sulfur loadings, sulfates were transformed to a BaS phase and remained in the catalyst rather than being removed as H2S. On the other hand, when the deposited sulfur level exceeded a certain threshold (at least S/Ba = 0.31) sulfates were reduced to form H2S, and the relative amount of the residual sulfide species in the catalyst was much less than at low sulfur loading. Unlike samples with high sulfur loadin...

Development of Picosecond Time-Resolved Microbeam X-ray Diffraction Technique for Investigation of Optical Recording Process

A time-resolved structural investigation of the data storage process in a digital versatile disk (DVD) or Blu-ray disk media is desired for better understanding of the fast phase-change mechanism for designing a higher performance optical recording material. Thus, the development of an in situ structural observation technique at the picosecond level has been carried out for the investigation of the fast phase-change phenomena using synchrotron radiation pulsed X-rays and synchronized femtosecond laser irradiation. Then, for Ge2Sb2Te5 (GST) and Ag3.5In3.8Sb75.0Te17.7 (AIST), the technique has been applied to a snapshot of X-ray diffraction pattern in the nanosecond crystallization process from the amorphous to the crystal phase, which corresponds to the erasing process of the DVD recording system. The key to success of the time-resolved experiment was to optimize the measurement timing system efficiency for both sufficient counting statistics, i.e., counting quantity and precision of time resolution, i.e., counting quality. Our time-resolved experimental system has sufficient accuracy, so that our previous study showed a significant difference in the crystal growth process between GST and AIST, indicating that the crystal growth process is key to fast phase change. To increase the precision of data in terms of signal-to-noise ratio and counting statistics, we developed a highly repetitive pump-probe measurement system combined with an X-ray microbeam technique providing high counting quantity, and used it to demonstrate a snapshot of an X-ray diffraction profile of GST. The measurement system has a time resolution of 50 ps and a 1 kHz repetition rate. Our development of the technique to take a snapshot for the structural visualization of phase-change phenomena with the time-resolved microbeam X-ray diffraction is described.

Controlling nickel silicide phase formation by Si implantation damage

In the context of fabrication process of contacts in CMOS integrated circuits, we studied the effect of implantation-induced damage on the Ni silicide phase formation sequence. The device layers of Silicon-on-insulator samples were implanted with 30 or 60keV Si ions at several fluences up to amorphization. Next, 10 or 30nm Ni layers were deposited. The monitoring of annealing treatments was achieved with time-resolved X-ray diffraction (XRD) technique. Rutherford Backscattering Spectrometry and pole figure XRD were also used to characterize some intermediate phase formations. We show the existence of an implantation threshold (1ions/nm2) from where the silicidation behaviour changes significantly, the formation temperature of the disilicide namely shifting abruptly from 800 to 450°C. It is also found that the monosilicide formation onset temperature for the thinner Ni deposits increases linearly by about 30°C with the amount of damage.

Theoretical Investigation of Perylene Dimers and Excimers and Their Signatures in X-Ray Diffraction

The structures of the ground and excimer states of perylene pairs are calculated [using density functional theory (DFT) and time-dependent DFT techniques] in a free as well as a crystal environment, and their spectroscopic properties are studied for the most stable configurations. The vertical transition energies for the absorption and emission bands are obtained, and they are in good agreement with experimental data. In these calculations, up to six excited states are considered. With the calculated structures of the ground and excimer states, the scattering factors are analyzed as a function of the concentration of excimers in a crystal. The intensity of the 110, 005, and 0 10 0 reflections are found to be fairly sensitive to the presence of excimers in the crystal. The finite (nanosecond) lifetime of the excimer may make it possible to observe this state using time-resolved X-ray diffraction techniques.

Effect of solidification velocity on weld solidification process of alloy tool steel

In order to clarify the effect of solidification velocity on the weld solidification process of alloy tool steel during the welding, the information about microstructure evolution was obtained by the concurrent experiments of liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. It was found from the experiments that the solidification mode was transferred from an FA to an A mode at the high solidification velocity. The effect of solidification velocity on the phase selection during solidification between the primary δ-ferrite and γ-austenite was theoretically proved by the Kurz, Giovanola and Trivedi (KGT) model. It is thus explained that the solidification cracking susceptibility of the weld metal of alloy tool steel was enhanced due to the δ to γ transition of the primary phase.

Time resolved X-ray diffraction observations of phase transformations in transient arc welds

In situ X-ray diffraction methods have been developed at Lawrence Livermore National Laboratory for direct observation of microstructural evolution under quasi-steady state and transient welding conditions. Using intense highly collimated synchrotron radiation, the crystal structures in the weld heat affected and fusion zones are probed in real time to monitor solidification and solid state phase transformations during welding. Here the authors review recent work on the development and use of the time resolved X-ray diffraction (TRXRD) technique during transient welding and illustrate its unique capabilities to: directly observe the solidification mode; discover, in real time, the definitive sequence of phase transformations that lead to the final microstructure; and provide quantitative kinetic data of phase transformations through synthesis of TRXRD data with the temperature history obtained through heat transfer modelling. The TRXRD technique has been used to investigate welding induced phase transformations in titanium alloys, low alloy steels, and stainless steel alloys. The results show some of the first real time observations of the weld solidification mode and the evolution of equilibrium and non-equilibrium phases during rapid heating and cooling. When combined with numerical modelling, quantitative phase transformation kinetic data are obtained, allowing for its use in a wide variety of isothermal and non-isothermal processing. The potential for future applications of this and similar techniques is also addressed.

Water-Induced Morphology Changes in BaO/γ-Al2O3 NOx Storage Materials: an FTIR, TPD, and Time-Resolved Synchrotron XRD Study

The effect of water on the morphology of BaO/Al2O3-based NOx storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multispectroscopy study reveal that in the presence of water surface Ba-nitrates convert to bulk nitrates and water facilitates the formation of large Ba(NO3)2 particles. The conversion of surface to bulk Ba-nitrates is completely reversible (i.e., after the removal of water from the storage material a significant fraction of the bulk nitrates reconverts to surface nitrates). NO2 exposure of a H2O-containing (wet) BaO/Al2O3 sample results in the formation of nitrites and bulk nitrates exclusively (i.e., no surface nitrates form). After further exposure to NO2, the nitrites completely convert to bulk nitrates. The amount of NOx taken up by the storage material, however, is essentially unaffected by the presence of water regardless of whether the water was dosed prior to or after NO2 exposure. On the basis of the results of this study, we are now able to explain most of the observations reported in the literature on the effect of water on NOx uptake on similar storage materials.

Towards an Understanding of the Temperature/ Pressure Configurational and Free-Energy Landscape of Biomolecules

Besides temperature, we used hydrostatic pressure as a physical parameter for studying the stability and energetics of biomolecular systems. High pressure is also an important feature of certain natural environments, and the high-pressure phase behaviour of biomolecules is of increasing biotechnological interest. By using thermodynamic, spectroscopic, and scattering techniques, the temperature and pressure-dependent structure and phase behaviour of model biomembrane systems and proteins have been studied. The results demonstrate that combined temperature–pressure-dependent studies can help delineate the conformational and free-energy landscape of biomolecules and hence help to elucidate which features and thermodynamic parameters are essential in determining their stability. Moreover, we present data on the effect of various types of cosolvents on the temperature- and pressure-dependent structure and stability of proteins. We also introduce pressure as a kinetic variable. Applying the pressure-jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction and spectroscopic techniques, the kinetics of lipid phase transitions and un/refolding reactions of proteins have been studied. Finally, recent advances in using the pressure axis for studying misfolding, aggregation, and amyloid fibril formation of proteins and its potential biotechnological and biomedical relevance will be discussed. We conclude with an outlook of the perspectives of high pressure research.