Instrumentation on Multi-Scaled Scattering of Bio-Macromolecular Solutions

The design, construction and initial tests on a combined laser light scattering and synchrotron X-ray scattering instrument can cover studies of length scales from atomic sizes in Angstroms to microns and dynamics from microseconds to seconds are presented. In addition to static light scattering (SLS), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD), the light scattering instrument is being developed to carry out studies in mildly turbid solutions, in the presence of multiple scattering. Three-dimensional photon cross correlation function (3D-PCCF) measurements have been introduced to couple with synchrotron X-ray scattering to study the structure, size and dynamics of macromolecules in solution.     

Morphological and structural characterization of polypropylene based nanocomposites

Nanocomposites based on isotactic polypropylene and montmorillonite were studied, investigating the polymorphism of the polymer, and examining the interaction between polypropylene and silicate. Wide angle X-ray diffraction (WAXD) was used to study the crystallization of the matrix, particularly the influence of additives and processing. Small angle X-ray scattering (SAXS) was employed to assess the lamellar morphology, estimating how silicate dispersion could affect this factor. Interaction between polymer and clay was quantified from WAXD and SAXS profiles; by the position and shape of the clay basal peaks, two different degrees of interaction were identified, characterized by a different affinity between the constituents. Observation of the samples' morphology by transmission electron microscopy (TEM) confirmed the results of X-ray diffraction methods. A fitting procedure was applied to SAXS profiles and the dimensions of the clay stratifications were estimated. These results were successfully compared with those drawn by application of Scherrer equation on (001) WAXD peaks.     

On the determination of platinum particle size in carbon-supported platinum electrocatalysts for fuel cell applications

Using a conventional laboratory diffractometer, small angle X-ray scattering (SAXS) was used to determine the average platinum particle size in samples of carbon with a range of platinum loadings. The results obtained were compared with those obtained from wide-angle X-ray diffraction (WAXS) studies. SAXS was more effective than WAXS for determining the average platinum particle size in samples where the grains were so small that the resultant diffraction peaks in the WAXS profiles were too broad to accurately determine the peak width for use in the Scherrer equation.     

Ultrashort pulse laser processing of silica at high repetition rates—from network change to residual strain

We report on the analysis of silica-based glasses after processing with ultrashort laser pulses at high repetition rates. Heat accumulation leads to strong local heating of the glass. The subsequent quenching results in a fictive temperature rise that scales with the repetition rate. Consequently, the relative volume change leads to residual tensile strain within the modified volume of larger than 10⁻³, which is confirmed by wide-angle X-ray scattering (WAXS) measurements. Studying the surface topography after cleaving of laser-modified regions allows for quantification of the corresponding elastic strain as well as the glass density behavior on the fictive temperature.     

Structure of nanodiamonds

The structure of nanodiamonds is considered within the model of icosahedral nanoparticles with a local diamond-like order and a shell structure. The diffraction from nanoparticles with noncrystallographic (in particular, icosahedral) packings of atoms is analyzed. It is demonstrated that the method proposed for calculating the intensity of coherent scattering by clusters of identical polyatomic aggregates is applicable to the entire diversity of carbon structures existing in the nanoworld.     

Theoretical X-ray scattering intensity of carbons with turbostratic stacking and AB stacking structures

The theoretical X-ray scattering intensities of carbons with AB-stacking and turbostratic stacking structures were simulated as a function of lattice constants and crystallite sizes using the Debye and Warren-Bodenstein equations, and the scale factor, K of the Scherrerr equation was also estimated. The 002 diffraction line in the simulated pattern shifted toward the lower angle side in the case of crystallite size smaller than 3 nm due to the insufficient cancellation effect of interference function in the Debye and Warren-Bodenstein equations. Moreover, for the turbostratic carbon, the 10 and 11 lines also shifted to the higher angle side due to the Warren effect. These simulation results indicate that the lattice constants obtained from the experimentally observed X-ray diffraction pattern are not accurate values. The K value was not constant, but depended on the crystallite size and the kinds of the diffraction lines used and the form of layer stacking.     

Determining the disordered nanostructure of calcium silicate hydrate (C-S-H) from broad X-ray diffractograms

Calcium silicate hydrate (C-S-H), the main binder of Portland cement, is one of the most complex nanostructured materials, making the retrieval of its highly defective atomic arrangement a long-standing challenge. This drawback prevents the development of realistic molecular models to guide the optimization of the physicochemical properties of Portland cement materials. Here, we applied Debye function analysis (DFA), an ab initio X-ray diffraction (XRD) analysis method suitable to disordered nanostructured materials, to identify the atomic and nanoscale structural-disorder features that dictate C-S-H's scattering properties. By examining the DFA theoretical calculations of C-S-H with different sizes, crystal defects, and stacking faults, we discovered that random layer rotations are a critical feature in the C-S-H phases, which has been largely overlooked by other XRD analysis methods. Moreover, the DFA calculations disclosed that C-S-H consists of layered, plate-like nanoparticles with ∼10 nm in lateral size and defined crystal defects, in agreement with previous neutron scattering and spectroscopic studies. These findings may not only enable the construction of more accurate nanoscale models of hydrated cement but have potential wider application to similar complex layered structures, such as phyllosilicates, in ceramic and geological materials.     

Nanomodification of Glass Using fs Laser

We review the interaction of glass with intense ultrashort laser pulses revealing new phenomena and recent demonstrations of rewritable 5D optical memory and polarization imaging filter mediated by the self-organization of nanostructure. Particularly, we experimentally verify linearly polarized intense ultrashort pulses can control the direction of local optical anisotropy in homogeneous medium based on the interference between photon and electron plasma. These so-called “nanogratings” composed of the photoinduced oxygen defects emerge in the course of multiple laser pulses and are oriented perpendicularly to the laser polarization direction. The nanograting structures, which exhibit form birefringence, have evolved from residual birefringence along with lowering threshold for defect formation into self-assembly of oxygen defects.     

Structure Determination in Colloidal Crystal Photonic Bandgap Structures

Structure/optical property relationships in photonic bandgap structures are evaluated by a novel combination of sample sectioning, microscopy, and image analysis. Disordered colloidal crystals of solution-derived, monosized SiO₂ particles were sectioned by focused ion beam (FIB) milling and then imaged using field emission scanning electron microscopy (FE-SEM). Pair correlation and radial distribution functions of the particulate arrangement were generated directly from a binary color scale rendering of the FE-SEM images, therein defining the level of order or disorder in the structure. These experimentally obtained spatial correlation functions were used to compute the scattering spectral properties in an analogous, although inverse (i.e., solving the inverse scattering problem), method to that used in X-ray diffraction for structure determination. Using a first-order approximation to the scattering from a disordered structure, the bandwidth and midgap values for the colloidal crystal photonic bandgap materials were within 15% of those measured. This new methodology promises to provide a simple and direct approach for quantifying the structure/optical property relationships in ordered and disordered photonic crystals directly from standard microstructural imaging techniques.     

Ultra-small angle X-ray scattering from bulk nanoporous carbon produced from silicon carbide

The technique of ultra-small angle X-ray scattering has been applied in parallel with the X-ray diffraction method for structural studies of bulk nanoporous carbon materials chemically produced from polycrystalline SiC powders with certain variations in the technology. The experiments were performed with MoKα and CuKα radiation. The integral absorption and scattering coefficients have been estimated for different types of samples. The experimental data reveal a strong correlation between the diffraction patterns and angular distributions of the scattering intensity. The correlation is associated with graphite-like nanoclusters that can be formed on carbonization of the SiC precursor under certain technological conditions. By analyzing the combined scattering and diffraction data, it is shown that the nanoclusters are quasi-two-dimensional. Their size parameters, concentration, volume fraction, and contribution to the scattering coefficient have been found.     

An investigation into the structure of poly(ethylene terephthalate) fibres by the use of optical transforms

An investigation has been made into the structural changes in poly(ethylene terephthalate) fibres brought about by drawing in a texturing machine. Evidence from both wide-angle and small-angle X-ray scattering is presented. The main feature of the small-angle X-ray scattering is a transition from two, meridional diffraction peaks to a symmetrical, four-point pattern as the draw ratio is increased. Optical transform methods have been used to investigate possible structural changes which could produce the observed transition. A tentative structure for poly(ethylene terephthalate) fibres is proposed.     

Ultrafast 2D IR vibrational echo spectroscopy

The experimental technique and applications of ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy are presented. Using ultrashort infrared pulses and optical heterodyne detection to provide phase information, unique information can be obtained about the dynamics, interactions, and structures of molecular systems. The form and time evolution of the 2D IR spectrum permits examination of processes that cannot be studied with linear infrared absorption experiments. Three examples are given: organic solute-solvent complex chemical exchange, dynamics of the hydrogen-bond network of water, and assigning peaks in an IR spectrum of a mixture of species.     

Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X-ray Diffraction

Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X-ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics.     

聚乙烯薄膜拉伸过程中结构变化的原位研究

使用差示扫描量热分析(DSC)研究了其拉伸前后结晶动力学与热力学行为的区别,使用同步加速器小角X射线散射(SAXS)和广角X射线衍射(WAXD)研究了薄膜拉伸过程中晶体结构、尺寸和长周期的变化.结果表明,拉伸使薄膜结晶度提高;拉伸过程中,二维散射图案发生明显变化,片晶结构被破坏后高应力诱导下重新结晶,拉伸使薄膜晶体取向...     

A flow cell for transient voltammetry and in situ grazing incidence X-ray diffraction characterization of electrocrystallized cadmium(II) tetracyanoquinodimethane

An easy to fabricate and versatile cell that can be used with a variety of electrochemical techniques, also meeting the stringent requirement for undertaking cyclic voltammetry under transient conditions in in situ electrocrystallization studies and total external reflection X-ray analysis, has been developed. Application is demonstrated through an in situ synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) characterization of electrocrystallized cadmium (II)-tetracyanoquinodimethane material, Cd(TCNQ)₂, from acetonitrile (0.1 mol dm⁻³ [NBu₄][PF₆]). Importantly, this versatile cell design makes SR-GIXRD suitable for almost any combination of total external reflection X-ray analysis (e.g., GIXRF and GIXRD) and electrochemical perturbation, also allowing its application in acidic, basic, aqueous, non-aqueous, low and high flow pressure conditions. Nevertheless, the cell design separates the functions of transient voltammetry and SR-GIXRD measurements, viz., voltammetry is performed at high flow rates with a substantially distended window to minimize the IR (Ohmic) drop of the electrolyte, while SR-GIXRD is undertaken using stop-flow conditions with a very thin layer of electrolyte to minimize X-ray absorption and scattering by the solution.     

C60-polymer nanocomposites: evidence for interface interaction

Polyaniline-fullerene (PA-C₆₀) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline-emeraldine base (PA-EB) and C₆₀, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C₆₀. The Raman bands peaking at 1330-1370 cm⁻¹, associated with a protonated structure were used as indicative for changes of the PA-EB phonon spectrum resulting from C₆₀ doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (Au or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C₆₀⁻) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA-C₆₀ reveals the existence of two polymeric structures: a doped PA (doped with C₆₀⁻ ions) and an undoped one, the latter with a structure of ‘pendant chain’ type. Structural (XRD) data reveal the presence of C₆₀ nano-zones, with a lattice parameter increase of 0.3-0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an ‘expanded’ lattice, induced by ionic interface effects.     

A pulse plating method for the electrosynthesis of ZnSe

Polycrystalline, thin films of ZnSe semiconductor compound were formed by cathodic electrodeposition from acidic aqueous selenite solutions of zinc sulphate, by using a potentiodynamic technique involving the application of repeated double pulses of controlled potential. Conditions for obtaining coherently uniform deposits with enhanced ZnSe to Se ratios were specified, on the basis of X-ray diffraction (XRD) and scanning electron microscopy results, by investigating the combined effect of the potential and length of each pulse as determined by duty cycle and frequency. It was shown that pulse plating process is a viable alternative to potentiostatic electrodeposition allowing improved control of the solid phase composition.     

Scanning X-ray nanodiffraction: from the experimental approach towards spatially resolved scattering simulations

An enhancement on the method of X-ray diffraction simulations for applications using nanofocused hard X-ray beams is presented. We combine finite element method, kinematical scattering calculations, and a spot profile of the X-ray beam to simulate the diffraction of definite parts of semiconductor nanostructures. The spot profile could be acquired experimentally by X-ray ptychography. Simulation results are discussed and compared with corresponding X-ray nanodiffraction experiments on single SiGe dots and dot molecules.     

Crystal structures of poly(n-methylen-di-O-methyl-l-tartaramide)s with n=3, 5, 7 and 9

The structural characterization of poly(n-methylen-di-O-methyl-l-tartaramide)s with n=3, 5, 7 and 9 has been carried out using optical microscopy, thermal analysis, X-ray diffraction and electron microscopy. X-ray diffraction of powder and fiber samples were analyzed together with electron diffraction patterns of single crystals obtained from isothermal crystallization in solution. Experimental results based on crystallographic data were used to build a crystal model using the Cerius program. This model is based in chain packing with an arrangement of hydrogen-bonded sheets, being the resultant crystal structure similar to the exhibited in conventional polyamides.     

In situ X-ray analysis under controlled potential conditions: An innovative setup and its application to the investigation of ultrathin films electrodeposited on Ag(1 1 1)

An innovative setup to combine electrochemical and in situ surface X-ray diffraction (SXRD) measurements is described. This electrochemical cell has a different design from the other ones commonly used for X-ray diffraction studies. It allows the sample surface to stay always completely immersed into the solution under controlled potential conditions even during the SXRD measurements. The X-ray beam crosses the liquid (about 1 cm) and the cell walls. Because of the high X-ray energy, the beam attenuation is negligible and by an appropriate positioning of the detector arm slits it is possible to minimize the diffuse scattering induced by the liquid and cell walls in order to still detect the minima of the crystal truncation rods (CTRs). The liquid solution in the cell is managed by a special device, which allows the controlled exchange of the electrolyte solutions necessary in the electrochemical atomic layer epitaxy (ECALE) growth. The whole setup can be remotely controlled from outside the experimental hutch by a dedicated computer. As an example we report measurements on S layers deposited at underpotential on the Ag(1 1 1) surface, and on CdS films of increasing thickness.