Changes In Diffraction Intensity Research Articles

In-Operando Neutron Diffraction Investigation of Structural Transitions during Lithiation of Si Electrode in Li-Ion Battery

A major challenge for Si negative electrodes in Li-ion batteries is how to accommodate the large lithiation-induced volume expansion and prevent electrode fragmentation, such that impressive Li storage capacity of Si can be exploited in practice. Electrochemically etched Si mesoporous electrodes have significant potential in this context. This research is focused on an optimum mesoporous Si electrode structure that shows a very high energy storage density, electrochemically cycling well without cracking or fragmentation. To explore the factors causing the superior performance, this study performed in-operando neutron diffraction experiments on optimized electrode during lithiation-delithiation cycles in a simple in-situ electrochemical cell. It is shown that an unusual diffraction phenomenon arises from lithiation-induced expansion of Si leading to the development of mosaic structure in Si. This new phenomenon appears to arise from the increased contribution of kinematic diffraction from the lithiated Si, relative to the conventional dynamic diffraction. This is also supported by changes in diffraction intensities directly synchronizing with the volume changes in Si during lithiation-delithiation cycle. The in-operando experiments explain why the optimum mesoporous Si electrode possesses a high specific capacity without electrode fragmentation. The present findings can help to improve Si electrode designs for high energy density Li-ion batteries.

Electron Density Changes across the Pressure-Induced Iron Spin Transition.

High-pressure single-crystal x-ray diffraction is used to experimentally map the electron-density distribution changes in (Fe,Mg)O as ferrous iron undergoes a pressure-induced transition from high- to low-spin states. As the bulk density and elasticity of magnesiowüstite-one of the dominant mineral phases of Earth's mantle-are affected by this electronic transition, our results have applications to geophysics as well as to validating first-principles calculations. The observed changes in diffraction intensities indicate a spin-transition-induced change in orbital occupancies of the Fe ion in general accord with crystal-field theory, illustrating the use of electron density measurements for characterizing high-pressure d-block chemistry and motivating further studies characterizing chemical bonding under pressure.

Detection of heavy metal ion using photonic crystals of polymer brushes with reflective laser beam system

Polyacrylonitrile (PAN) brushes were grafted from the line array of halogen group-modified layer as photonic crystals (PCs). The tethered PAN PCs were further converted to tethered polyvinyltetrazole (PVT) PCs by a cyano-to-tetrazole reaction, employed to adsorb metal ions with the tetrazolyl groups. Geometrical structure of the PVT PCs was changed after metal ions adsorption due to the electrostatic force. A laser beam system was employed to analyze the optical feature with a characteristic diffraction effect of the PVT PCs at a 45° incident angle with respect to the surface of the line array, oriented such that its lines were parallel (LII) or perpendicular (LT) to the beam's projection onto the PC, was employed to analyze the two- and three-dimensional reflective diffraction signals of the PC. Change in diffraction intensity of the PVT PCs was correlated with the metal ion adsorption to obtain limit of detection (LOD) as low as 10 μg·L−1 of Cr(III) with linear range from 10 to 170 μg·L−1 and selectivity. Traces of the metal ions can be determined with less milliliter sample using the reflective diffraction intensity with PVT PC, which can provide a simple method to monitor the heavy ions in environment in-field.

Resonant Tender X-ray Diffraction for Disclosing the Molecular Packing of Paracrystalline Conjugated Polymer Films.

The performance of optoelectronic devices based on conjugated polymers is critically dependent upon molecular packing; however, the paracrystalline nature of these materials limits the amount of information that can be extracted from conventional X-ray diffraction. Resonant diffraction (also known as anomalous diffraction) occurs when the X-ray energy used coincides with an X-ray absorption edge in one of the constituent elements in the sample. The rapid changes in diffraction intensity that occur as the X-ray energy is varied across an absorption edge provide additional information that is lost in a conventional nonresonant experiment. Taking advantage of the fact that many conjugated polymers contain sulfur as heteroatoms, this work reveals pronounced resonant diffraction effects at the sulfur K-edge with a particular focus on the well-studied electron transporting polymer poly([N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)), P(NDI2OD-T2). The observed behavior is found to be consistent with the theory of resonant diffraction, and by simulating the energy-dependent peak intensity based on proposed crystal structures for P(NDI2OD-T2), we find that resonant diffraction can discriminate between different crystalline packing structures. The utilization of resonant diffraction opens up a new way to unlock important microstructural information about conjugated polymers for which only a handful of diffraction peaks are typically available.

Structure refinement from ‘digital’ large angle convergent beam electron diffraction patterns

We use semi-automated data acquisition and processing to produce digital large angle CBED (D-LACBED) patterns. We demonstrate refinements of atomic coordinates and isotropic Debye–Waller factors for well-known materials using simulations produced with a neutral, spherical independent atom model. We find that atomic coordinate refinements in Al2O3 have sub-pm precision and accuracy. Isotropic DWFs are accurate for Cu, a simple fcc metal, but do not agree with X-ray measurements of GaAs or Al2O3. This lack of agreement is probably caused by bonding and change transfer between atoms. While it has long been appreciated that CBED is sensitive to bonding, examination of D-LACBED data shows that some regions exhibit large changes in diffracted intensity from small changes in the periodic crystal potential. Models of bonding will be essential to fully interpret D-LACBED data.

Reply to “Comment on ‘Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3 ' ”

In this reply to S. Durbin's comment on our original paper Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3, we concur that his final equations 8 and 9 more accurately describe the change in diffracted intensity as a function of Ti displacement. We also provide an alternative derivation based on an ensemble average over unit cells. The conclusions of the paper are unaffected by this correction.

Local terahertz field enhancement for time-resolved x-ray diffraction

We report local field strength enhancement of single-cycle terahertz (THz) pulses in an ultrafast time-resolved x-ray diffraction experiment. We show that patterning the sample with gold microstructures increases the THz field without changing the THz pulse shape or drastically affecting the quality of the x-ray diffraction pattern. We find a five-fold increase in THz-induced x-ray diffraction intensity change in the presence of microstructures on a SrTiO3 thin-film sample.

Fixed target matrix for femtosecond time-resolved and in situ serial micro-crystallography.

We present a crystallography chip enabling in situ room temperature crystallography at microfocus synchrotron beamlines and X-ray free-electron laser (X-FEL) sources. Compared to other in situ approaches, we observe extremely low background and high diffraction data quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number of protein crystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA). The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes in diffraction intensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs.

Alternative phasing method in macromolecular crystallography

Selenium is the most widely used heavy atom for experimental phasing, either by single anomalous scattering (SAD) or multiple-wavelength anomalous diffraction (MAD) procedures. The use of the single isomorphous replacement (SIR) or single isomorphous replacement with anomalous scattering (SIRAS) phasing procedure with selenomethionine (Mse) containing proteins is not so commonly used, as it requires isomorphous native data. Several non-redundant X-ray diffraction data sets from various Mse derivatised protein crystals were collected at energies far below the absorption edge before and after exposing the crystal to ultraviolet (UV) radiation with 266 nm lasers. A detailed analysis revealed that significant changes in diffracted intensities were induced by ultraviolet irradiation whilst retaining crystal isomorphism. These intensity changes allowed the crystal structures to be solved by the radiation damage-induced phasing (RIP) technique [1]. These can be coupled with the anomalous signal from the dataset collected at the selenium absorption edge to obtain SIRAS phases in a UV-RIPAS phasing experiment [2]. Inspection of the crystal structures and electron-density maps demonstrated that covalent bonds between selenium and carbon at all sites located in the core of the proteins or in a hydrophobic environment were much more susceptible to UV radiation-induced cleavage than other bonds typically present in Mse proteins. The rapid UV radiation-induced bond cleavage opens a reliable new paradigm for phasing at synchrotron [1,2] and at in-house X-ray source [3].

An imprinted crystalline colloidal array chemical-sensing material for detection of trace diethylstilbestrol

Based on a combination of the molecular imprinting technique and polymerized crystalline colloidal array, we have developed an imprinted crystalline colloidal array (ICCA) chemical-sensing material for the real-time and label-free detection of diethylstilbestrol (DES) in aqueous solution. This novel sensing material was prepared by a noncovalent and self-assembly approach using liquid monodispersed DES-imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous nanocavities were derived from DES imprinting. Thus, the inherent high affinity of the nanocavities allowed ICCA to recognize DES with high specificity, and changes of the ordered periodic structure enabled ICCA to transfer the recognition events into readable optical signals (label-free). Owing to the special opal structure and without interference from the bulk hydrogel film, the ICCA enabled the rapid and sensitive detection of the target analyte. The understanding of the recognizing response has also been advanced by using molecular modeling software to compute rational interaction between the template molecules and the function monomers. After careful optimization of the assay conditions, the ICCA could decrease its diffraction intensity within just 7 min according to the DES concentration from 2 ng mL(-1) to 8.192 μg mL(-1), whereas there were no obvious diffraction intensity changes for the DES analogues. The adsorption results showed that the homogenous structure and large surface area of ICCA could improve its adsorption capacity. Therefore, such a sensing material with high selectivity, high sensitivity, high stability, and easy operation might offer an attractive alternative for establishing optical sensors for the rapid real-time monitoring of different residues in food and the environment.

Effect of surface plasmon polariton of Ag nanoparticles on the photoluminescence property of up-conversion materials

Silver nanoparticles are added into Yb3+ and Er3+ co-doped NaYF4 up-conversion materials using co-sintering process. Changes in diffraction intensity and surface morphology are inspected by X-ray diffraction and scanning electron microscope measurement, respectively. The optical absorption and Photoluminescence spectra are measured using UV/visible spectrophotometer and photoluminescence measurements. By optimizing the quantity of Ag nanoparticles, we obtain obvious enhancements of the photoluminescence intensities of Yb3+ and Er3+ co-doped NaYF4 materials, which shows a 28% enhancement in 300—800 nm wavelength range and a 55% enhancement at 544 nm. Different mechanisms are proposed for light quenching and surface plasmon enhanced absorption with Ag nanoparticles adjustment.

Detection of bisphenol A using an opal photonic crystal sensor

A new opal photonic crystal sensor (OPCS) that allows the detection of label-free bisphenol A (BPA) is proposed in the current study. The concept of developing photonic-based sensors using combined photonic crystal technology and molecular imprinting techniques is introduced. First batches of the BPA-imprinted monodisperse PMMA spheres with a diameter of 220 (±5)nm were prepared based on the suspension polymerization, so numerous nanocavities derived from BPA imprinting were distributed in the PMMA spheres. The liquid monodisperse microspheres were made into a polymerized crystalline colloidal array (PCCA) opal photonic crystal sensor. The inherent high affinity of the nanocavities distributed in the sphere allows OPCS to recognize BPA specifically. The sensor is characterized by a 3D-ordered interconnected lattice structure. Between the monospheres, there are well-arranged pores allowing the target molecules to embed and transport. As a result, changes in diffraction intensity which are related to BPA concentrations can be observed with the sensor. The detection ranges of OPCS are at 1ng/ml–1μg/ml level. The new sensory system has high selectivity of the target molecules in their natural forms, is easy to use, and costs low. Overall, the proposed approach provides a versatile analytical system for the establishment of a new sensor for the detection of endocrine-disrupting chemicals.

Modeling of the hysteretic phenomena in RHEED intensity variation versus temperature for GaAs and InAs surfaces

This paper describes a study of the reflection high energy electron diffraction intensity change against temperature for GaAs and InAs surfaces. The reflection high energy electron diffraction intensity variation against temperature shows different hysteretic characters for the two materials. To date, the explanations for these phenomena were also different for the two substances. Here, we put forward an explanation for these hysteretic phenomena in general terms, applicable to both materials by using the hyperbolic model of hysteresis for coupled systems. Experimental results presented in the paper are in good agreement with the model predictions, supporting the proposed common explanation.

Single isomorphous replacement phasing of selenomethionine-containing proteins using UV-induced radiation damage

The most commonly used heavy-atom derivative, selenium, requires the use of a tunable beamline to access the Se K edge for experimental phasing using anomalous diffraction methods, whereas X-ray diffraction experiments for selenium-specific ultraviolet radiation-damage-induced phasing can be performed on fixed-wavelength beamlines or even using in-house X-ray sources. Several nonredundant X-ray diffraction data sets were collected from three different selenomethionine (Mse) derivatized protein crystals at energies far below the absorption edge before and after exposing the crystal to ultraviolet (UV) radiation using 266 nm lasers of flux density 1.7 × 10¹⁵ photons s⁻¹ mm⁻² for 10-50 min. A detailed analysis revealed that significant changes in diffracted intensities were induced by ultraviolet irradiation whilst retaining crystal isomorphism. These intensity changes allowed the crystal structures to be solved by the radiation-damage-induced phasing (RIP) technique. Inspection of the crystal structures and electron-density maps demonstrated that covalent bonds between selenium and carbon at all sites located in the core of the proteins or in a hydrophobic environment were much more susceptible to UV radiation-induced cleavage than other bonds typically present in Mse proteins. The rapid UV radiation-induced bond cleavage opens a reliable new paradigm for phasing when no tunable X-ray source is available. The behaviour of Mse derivatives of various proteins provides novel insights and an initial basis for understanding the mechanism of selenium-specific UV radiation damage.

Irradiation effects on copper

Copper, one of the most significant metals, is exposed to IR radiation. A Nd:YAG laser (1064 nm, 1.1 MW, 12 ns) has been used to irradiate fine polished and annealed samples (4 N, 1×1×0.3 cm3) with 100 laser shots under a vacuum of ∼10−6 torr. The laser focal spot size and power density on the target were 12 μm and 3×1012 Wm−2 respectively. The surface and structural studies were performed by analyzing scanning electron micrographs and X-ray diffractograms (XRDs), respectively. Laser ablation results in boiling, splashing, hydrodynamical sputtering and exfoliation along with other relevant phenomena. The XRD patterns of the exposed sample indicate a change in diffraction intensity and grain sizes. The atomic planes remain undisturbed for the irradiated target. The information collected is useful for investigating the complexities found in radiation–metal interactions.

Heterogeneous Deformation Behavior Studied by in Situ Neutron Diffraction during Tensile Deformation for Ferrite, Martensite and Pearlite Steels

Tensile behavior was investigated by using in situ TOF neutron diffraction comparatively for ferritic steels; ferrite (F), as-quenched martensite (QM), tempered martensite (TM) and pearlite (P) steels. Changes in lattice spacing, diffraction intensity and FWHM with increasing of the applied stress were measured. Preferential plastic flow takes place depending on crystal orientation, so that intergranular stresses are yielded due to the misfit plastic strains in differently oriented [hkl] family grains for steel F, in blocks for the other steels. Because of the existence of cementite in steels TM and P, phase stresses are superposed upon the intergranular stresses. When the averaged phase strain is subtracted from the measured lattice strain, the trend in generation of intergranular strain in steel TM is similar to that observed in steels F and QM, while that in steel P differs from the other steels. The changes in [hkl] diffraction intensity and FWHM with tensile deformation are similar in steels F, TM and P, while those in steel QM are different from the others. FWHM decreases with tensile deformation suggesting the decrease in dislocation density in steel QM. That is, dislocations induced during martensitic transformation move preferentially and are annihilated by coalescence of dislocations with different signs in the beginning of deformation and hence transformation induced dislocation structure changes to deformation induced one that shows lower dislocation density but higher resistance to tensile flow. The preferential movement of transformation induced dislocations in steel QM leads to a different texture evolution which is recognized from the change in diffraction intensity with tensile deformation.

Temperature Measurement of Polyethylene Exposed to Partial Discharge

We measured the temperature of a polyethylene film exposed to partial discharge using an X-ray diffractometer based on the fact that thermal vibration of the polyethylene molecules attenuates the diffracted intensity exponentially. Polyethylene (PE) resin is known to be a crystalline polymer that can adopt a folded chain conformation. In bulk, PE is composed of amorphous and crystalline regions. With increased temperature, the molecular chains move and the PE transforms from the crystalline state that exists before heating. When a film temperature was at less than 60 degrees above room temperature, the diffracted intensity was at the same value as at room temperature.Parallel plate electrodes (two glass plates with an aperture in between) were attached to the goniometer of the X-ray diffractometer to generate partial discharge. Discharge by the electrodes only did not change the diffracted intensity. As such, the effect of X-ray dispersion by the electric field or discharge-generated gas was considered. A discharge was generated by applying a PE film to each glass plate electrode and the change in diffracted intensity was recorded. After the discharge had stopped, the PE film was heated to determine the temperature which gave the same diffracted intensity as that obtained by discharge. The discharge was found to increase the temperature of the PE film by 16 degrees above room temperature. This temperature rise is considered an average value resulting from penetration of the PE film by X-rays.

Deformation and fracture behavior of poly(vinylidene fluoride‐trifluorethylene) ferroelectric copolymer films under uniaxial tension

AbstractThe deformation and fracture behavior under uniaxial tension was characterized for P(VDF‐TrFE) 68/32 mol % copolymer films prepared under two different processing conditions. It was found that the copolymer films prepared by solution casting and then annealing show a typical polymeric brittle fracture feature. For the copolymer films prepared by stretching the solution‐cast films and then annealing process, a typical linearly strengthening stage occurs in the stress–strain curve after yielding, and the polymer film samples fracture at a much larger maximum strain and a higher tensile strength than those prepared by the former process. SEM observation and XRD analysis were carried out to examine the morphology and microstructure change during uniaxial tension. The results show that for the stretched film samples, the polymer chains undergo slipping or further reorientation during uniaxial tension, causing the increase of the peak intensity in the X‐ray diffraction pattern. For the directly annealed ones, no yielding phenomenon is observed and there is no apparent X‐ray diffraction intensity change. It was suggested that the highly‐oriented fibril structure of the stretched film samples contributes to the linearly strengthening stage after yielding in the stress–strain curve. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3255–3260, 2005

Magnetostriction observed by X-ray diffraction in iron

A new technique to observe magnetostriction by X-ray diffraction was reported. We found that a symmetry part of the relative diffraction intensity change induced by applying magnetic field was proportional to a Bragg angle shift. It was a differential measurement on the rocking curve. The Bragg angle and its shift gave quantitative magnetostrictive coefficients. Sensitivity of the present method on the magnetostrictive coefficient for an iron specimen approached to 10/sup -7/.

Effect of Tl content on the growth of TlGaAs films by low-temperature molecular-beam epitaxy

TlGaAs layers with various Tl contents have been grown on GaAs(001) substrates by solid-source molecular-beam epitaxy at a substrate temperature of 210 °C and an As/Ga beam equivalent pressure ratio of 100. The Tl content was characterized by Rutherford backscattering spectrometry, secondary-ion mass spectrometry, and electron microprobe analysis. Nomarski microscope observation revealed that the surfaces of the TlxGa1−xAs layers were mirror like until a Tl content of x=7.0% while Tl droplets appeared on the surfaces of samples with a Tl content of x=7.7%. X-ray diffraction (XRD) curves showed clearly resolved epi-layer peaks until a Tl content of x=6.4%. We estimated the epitaxial thickness hepi, at which single-crystalline growth is replaced by polycrystalline growth, by two different methods using the XRD data. In one method we measured the change in diffracted intensity of the epi-layer peak after progressive gradual etching of the TlGaAs layers grown. The other was on the basis of a simulation of the diffraction curves of the as-grown samples within dynamical diffraction theory. The values of hepi estimated by the two methods agreed well and showed a remarkable decrease with an increase in Tl content. Cross-sectional transmission electron microscopy confirmed the reliability of the estimated value of hepi. In addition, the lattice mismatch was analyzed utilizing both symmetric and asymmertic XRD data. The analysis indicated that the lattice constant of an imaginary zinc-blende type crystal of stoichiometric TlAs (aTlAs) is slightly smaller than that of InAs (aInAs).