Small-angle X-ray Scattering Signal Research Articles

Mirror to measure small angle x-ray scattering signal in high energy density experiments.

Small angle x-ray scattering (SAXS) is a well established technique to detect nanometer scale structures in matter. In a typical setup, this diagnostic uses a detector with a direct line of sight to the scattering target. However, in the harsh environment of high intensity laser interaction, intense secondary radiation and high-energy particles are generated. Such a setup would therefore suffer a significant increase of noise due to this background, which could eventually prevent such measurements. In this paper, we present a novel tool consisting of a mosaic graphite crystal that works as a mirror for the SAXS signal and allows us to position the detector behind appropriate shielding. This paper studies the performance of this mirror both by experiment at the European XFEL (X-Ray Free-Electron Laser Facility) laboratory and by simulations.

Nanostructures in n-Octanol Equilibrated with Additives and/or Water.

Fluid fatty alcohols are believed to be nanostructured but broadly amorphous (i.e., noncrystalline) fluids and solvents, including the most popular fatty tissue mimetic, hydrated n-octanol (i.e., hydro-octanol). To check this premise, we studied dry octanol and hydro-octanol as a model of relatively short fluid n-alkanols with small-angle X-ray scattering (SAXS). We also combined this alkanol with the matching alkane (i.e., octane) and with a common anti-inflammatory pain killer (ketoprofen). This revealed that (hydro-)octanol and arguably any other short fatty alcohol form a mesophase. Its basic structural motif are regularly packed polar nanoclusters, reflected in the inner peak in the SAXS diffractogram of (hydro-)octanol and other fluid n-alkanols. The nanoclusters arguably resemble tiny, (inverse) hydrated bilayer fragments, located on a thermally smeared para-crystalline lattice. Additives to hydro-octanol can change the nanoclusters only moderately, if at all. For example, octane and the drug ketoprofen added to hydro-octanol enlarge the nanoclusters only little because of the mixture's packing frustration. To associate with and to bring more water into hydro-octanol, an additive must hence transform the nanoclusters: it expands them into irregularly distributed aqueous lacunae that form a proto-microemulsion, reflected in the previously unknown Guinier's SAXS signal. A "weak" (i.e., a weakly polar or nonpolar) additive can moreover create only size-limited lacunae. Coexistence of nanoclusters and lacunae as well as size variability of the latter in hydro-octanol subvert the concept of octanol-water partition coefficient, which relies on the studied compartment homogeneity. In turn, it opens new possibilities for interfacial catalysis. Reinterpreting "octanol-water partition coefficient" data in terms of octanol-water association or binding constant(s) could furthermore diminish the variability of molecular lipophilicity description and pave the ground toward a more precise theoretical quantification and prediction of molecular properties.

Small-Angle X-Ray Scattering for Imaging of Surface Layers on Intact Bacteria in the Native Environment

Crystalline cell surface layers (S-layers) represent a natural two-dimensional (2D) protein self-assembly system with nanometer-scale periodicity that decorate many prokaryotic cells. Here, we analyze the S-layer on intact bacterial cells of the Gram-positive organism Geobacillus stearothermophilus ATCC 12980 and the Gram-negative organism Aquaspirillum serpens MW5 by small-angle X-ray scattering (SAXS) and relate it to the structure obtained by transmission electron microscopy (TEM) after platinum/carbon shadowing. By measuring the scattering pattern of X rays obtained from a suspension of bacterial cells, integral information on structural elements such as the thickness and lattice parameters of the S-layers on intact, hydrated cells can be obtained nondestructively. In contrast, TEM of whole mounts is used to analyze the S-layer lattice type and parameters as well as the physical structure in a nonaqueous environment and local information on the structure is delivered. Application of SAXS to S-layer research on intact bacteria is a challenging task, as the scattering volume of the generally thin (3- to 30-nm) bacterial S-layers is low in comparison to the scattering volume of the bacterium itself. For enhancement of the scattering contrast of the S-layer in SAXS measurement, either silicification (treatment with tetraethyl orthosilicate) is used, or the difference between SAXS signals from an S-layer-deficient mutant and the corresponding S-layer-carrying bacterium is used for determination of the scattering signal. The good agreement of the SAXS and TEM data shows that S-layers on the bacterial cell surface are remarkably stable.

Exploring the Piezophilic Behavior of Natural Cosolvent Mixtures

Proteins are only marginally stable and are hence very sensitive to environmental conditions, such as high and low temperatures or high hydrostatic pressures. In nature, living organisms are able to compensate for extreme environmental conditions and hence rescue proteins from denaturation by using osmolytes. Organic osmolytes are accumulated under anhydrobiotic, thermal, and pressure stresses. Among those osmolytes are amino acids, polyols and sugars (e.g., glycerol and trehalose), methylamines such as trimethylamine-Noxide (TMAO), and urea. TMAO has been found to enhance protein folding and ligand binding most efficiently. On the other hand, urea, a highly concentrated waste product in mammalian kidneys, is a perturbant. It is also a major organic osmolyte in marine elasmobranch fishes. Interestingly, TMAO has been found to counteract perturbations imposed by urea and hydrostatic pressure in deep-sea animals, most effectively at a 2:1 urea:TMAO ratio. In the deep sea, hydrostatic pressures up to the 1 kbar (100 MPa) range prevail, and living organisms have to cope with such extreme environmental conditions. High hydrostatic pressure generally destabilizes the protein structure, inhibits polymerization of proteins and ligand binding. Interestingly, TMAO has been shown to largely offset these pressure effects. In fact, it was found that the amount of TMAO in the cells of a series of marine organisms increases linearly with the depth of the ocean. For that reason, TMAO is thought to serve as pressure counteractant. The term “piezolyte” has been coined for such kind of cosolute. About the underlying mechanism of stabilization by TMAO at ambient pressure conditions several experimental and theoretical (molecular dynamics simulations) articles have been published in recent years. TMAO is largely excluded from the protein surface and enhances the water structure causing greater organization through more and stronger hydrogen bonding among water molecules. However, the mechanism of this “chemical chaperon” at high hydrostatic pressure (HHP) conditions is still unclear. To yield a deeper understanding of this phenomenon, we determined the intermolecular interaction of dense protein solutions in the absence and presence of cosolvent mixtures of TMAO and urea also under HHP conditions. Small-angle Xray scattering (SAXS) experiments on dense lysozyme solutions have been carried out in the pressure range from 1 bar up to 4 kbar. The SAXS technique accurately monitors structural alterations of the protein solution and yields quantitative information on the state-dependent protein– protein interaction potential. As lysozyme is a highly stable protein, pressure-induced effects will only be attributed to changes in the protein–protein interaction of the native protein and how this is influenced by osmolytes. No pressureinduced unfolding of the protein occurs in the pressure range covered. Complementary thermodynamic data, that is, the temperature of unfolding and the volume change upon unfolding of the protein, were obtained by differential scanning (DSC) and pressure perturbation calorimetry (PPC), respectively. To verify that the protein is folded at all solution conditions studied, SAXS measurements on diluted lysozyme solutions (cP= 10 mgmL ) were carried out in the whole pressure range covered. For diluted protein solutions, the scattering intensity I(q) is proportional to the form factor P(q) (q= (4p/l)sin(V/2) is the wave vector transfer, l the wavelength of the X-rays, and V the scattering angle), which depends on the structure and size of the protein. For dilute lysozyme solutions, the radius of gyration of the particle, Rg, could be determined. We found a constant Rg value of (15.1 0.4) up to 4 kbar, indicating the absence of unfolding even at the highest pressure applied. In the case of concentrated protein solutions, the interaction between the particles gives rise to an additional scattering contribution. This SAXS signal can be described as the product of the form factor and an effective structure factor, which is related to the intermolecular structure factor S(q). To relate the structure factor to the protein–protein interaction potential, statistical mechanical model approaches have to be employed. Here, the mean-spherical approximation (MSA) in combination with the DLVO (Derjaguin– Landau–Verwey–Overbeek) potential V(r) has been used. The pair potential V(r) is given as the sum of a hard sphere potential VHS(r), a repulsive screened Coulomb-like potential VSC(r) and an attractive Yukawian potential VY(r), which is frequently used to describe protein–protein interactions (for details, see the Supporting Information). [*] Y. Zhai, Prof. Dr. R. Winter Fakult t Chemie, TU Dortmund Physikalische Chemie—Biophysikalische Chemie Otto-Hahn Str. 6, 44227 Dortmund (Germany) E-mail: roland.winter@tu-dortmund.de

Influence of Monomer Feeding on a Fast Gold Nanoparticles Synthesis: Time-Resolved XANES and SAXS Experiments

A comprehensive study of the mechanism of gold nanoparticle formation has been conducted using third-generation synchrotrons. The particles were obained by reduction of AuCl(3) by BH(4)(-) in toluene. Gold oxidation state was monitored by X-ray absorption near edge spectroscopy (XANES), while the size and concentration of the nanoparticles were assessed by small-angle X-ray scattering (SAXS). A time-resolution of 100 ms has been achieved for a total formation time of a few seconds. The change with time of the total amount of Au(0) present in the solution is obtained by XANES. The change of the amount of Au(0) inside the nanoparticles is obtained from the SAXS signal. The comparison between these two quantities shows that a measurable amount of Au(0) exists transiently as monomers (or very small entities) in solution and this quantity is linked to an observed burst of nucleation of nanoparticles. The reduction kinetics is strongly influenced by the presence of ligands and a change in temperature. A model coupling the observed reduction kinetics and nucleation and growth laws is able to recover the final size and number densities of the explored experimental conditions.

Dynamic Dislocation-Defect Analysis and SAXS Study of Nanovoid Formation in Aluminum Alloys

Crystalline defects other than the essential dislocations are produced by dislocation intersections resulting in debris, which can transform into loops, point defects, and∕or nanovoids. The stress concentrations ahead of slip clusters promote void formation leading to incipient cracks. To evaluate the progression of these processes during deformation, dynamic dislocation-defect analysis was applied to nominally pure aluminum, Al–Mg, and Al–Cu alloys. In the case of nanovoid formation, small angle X-ray scattering (SAXS) was used to quantitatively assess if the void size and its volume fraction can be determined to directly correlate with the measured thermodynamic response values. The SAXS signal from the nanovoids in nominally pure aluminum is distinctly measurable. On the other hand, thermomechanical processing of even nominally pure aluminum results in the formation of nanoprecipitates, which requires future calibration.

Sample Holder for Small-Angle X-ray Scattering Measurements and Density Fluctuation of Supercritical Xenon

We constructed a sample holder of Xe for small-angle X-ray scattering (SAXS) experiments. The holder was designed to attain a very small path length of a sample that corresponds to the large X-ray absorption of Xe. For the easy and convenient operation of the experiments in synchrotron radiation facilities, a cell was contrived so as to vary the path length despite the presence of a high-pressure sample inside. The path length varies from 0.05 to 3.5 mm. The holder is applicable not only to supercritical Xe but also to liquids, solutions and other supercritical fluids under highly pressured conditions using relatively low-energy X-rays. SAXS measurements were carried out for supercritical Xe in a wide density range. Density fluctuations for the fluid at various thermodynamic states were obtained from SAXS signals.

Material Structure of Microcrystalline Silicon Deposited with an Expanding Thermal Plasma

AbstractExpanding thermal plasma CVD (ETP CVD) has been used to deposit thin microcrystalline silicon films. In this study we varied the position at which the silane is injected in the expanding hydrogen plasma: relatively far from the substrate and close to the plasma source, giving a long interaction time of the plasma with the silane, and close to the substrate, resulting in a short interaction time. The material structure is studied extensively. The crystalline fractions as obtained from Raman spectroscopy as well as from X-ray diffraction (XRD) vary from 0 to 67%. The average particle sizes vary from 6 to 17 nm as estimated from the (111) XRD peak using the Scherrer formula. Small angle X-ray scattering (SAXS) and flotation density measurements indicate void volume fractions of about 4 to 6%. When the samples are tilted the SAXS signal is lower than for the untilted case, indicating elongated objects parallel to the growth direction in the films. We show that the material properties are influenced by the position of silane injection in the reactor, indicating a change in the plasma chemistry.

3D Small Angle X-Ray Scattering (SAXS) on deformed PVDF Foils

ABSTRACT3D Small Angle X-ray scattering (3D – SAXS) was applied to study the microstructure and the deformation mechanism in PVDF – foils (polyvinyhdene fluoride). SAXS is a powerful tool to investigate structural changes in deformed polymers to reveal morphology at the nanometer scale. When PVDF is strained the structure changes from spherohtic isotropie to a highly anisotropie fiber bundle structure, which requires a full three-dimensional analysis of the SAXS signal.

Amorphous silicon films and solar cells deposited by HWCVD at ultra-high deposition rates

The deposition conditions for hydrogenated amorphous silicon, deposited by hot wire chemical vapor deposition, are linked to the film structure as we increase deposition rates ( R d) to >100 Å/s. At low R d (<20 Å/s), films with optimal properties are deposited under low silane depletion conditions, and all measures of structure (X-ray diffraction, Raman spectroscopy, H evolution, small-angle X-ray scattering (SAXS)) indicate a compact material. At high R d (>100 Å/s), optimum films are deposited under silane depletion conditions as high as 75–80%, and all structural properties except for the SAXS results once again indicate a compact material. We relate changes in the film electronic structure (Urbach edge) with increasing R d to the increase in the SAXS signals, and note the invariance of the saturated defect density versus R d, discussing reasons why these microvoids do not play a role in the Staebler–Wronski effect for these films. Finally, we present device results over the whole range of R d that we have studied and suggest why, at high R d, device quality films can be deposited at such high silane depletions.

Structural properties of hot wire a-Si:H films deposited at rates in excess of 100 Å/s

The structure of a-Si:H, deposited at rates in excess of 100 Å/s by the hot wire chemical vapor deposition technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). The films examined in this study were chosen to have roughly the same bonded H content CH as probed by infrared spectroscopy. As the film deposition rate Rd is increased from 5 to &amp;gt;140 Å/s, we find that the short range order (from Raman), the medium range order (from XRD), and the peak position of the H evolution peak are invariant with respect to deposition rate, and exhibit structure consistent with a state-of-the-art, compact a-Si:H material deposited at low deposition rates. The only exception to this behavior is the SAXS signal, which increases by a factor of ∼100 over that for our best, low H content films deposited at ∼5 Å/s. We discuss the invariance of the short and medium range order in terms of growth models available in the literature, and relate changes in the film electronic structure (Urbach edge, as-grown defect density) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus Rd, measured after light soaking, and discuss possible reasons why the increase in the microvoid density apparently does not play a role in the Staebler–Wronski effect for this type of material.

Films and Devices Deposited by Hwcvd at Ultra High Deposition Rates

ABSTRACTThe structure of a-Si:H, deposited at rates in excess of 100Å/s by the hot wire chemical vapor deposition (HWCVD) technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). As the film deposition rate (Rd) is increased, we find that the XRD, Raman and the H evolution peak curves are invariant with Rd, and exhibit structure consistent with state-of-the-art, compact a-Si:H films deposited at low Rd. The only exception is the SAXS signal, which increases by a factor of ∼100 over that for our best low Rdfilms. We relate changes in the film electronic structure (Urbach edge) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus Rd, and discuss possible reasons why the increase in the SAXS does not play a role in the Staebler-Wronski Effect for this type of material. Finally, device results are presented.

Small-Angle X-Ray Scattering Studies of Glow-Discharge-Produced a-SiGe:H Alloys

ABSTRACTElectron density fluctuations associated with microstructural features on a scale from about 1 to 25 nm in glow-discharge-deposited a-Si1-xGex:H films were studied by the technique of small-angle x-ray scattering (SAXS). Films prepared in four different deposition systems (in different laboratories) have been characterized and a general increase in the SAXS signal with increasing x is observed. Density deficiencies determined from film flotation measurements lead to the correlation of the increased scattering intensities with increases in the volume fractions of micro voids. Modeling of the data yields void size distributions that demonstrate significantly more of the larger voids (2 to 6 nm) than found at x=0 (around 1 nm). For the alloys with x&gt;0.4, the scattering at the smallest angles was observed to decrease substantially upon tilting of the sample relative to the x-ray beam. This result contrasts with the small or no changes in SAXS upon tilting device-quality x=0 films. This anisotropie scattering associated with the tilting experiments has been modeled with distributions of ellipsoidal microvoids that are preferentially oriented with their major axes normal to the film plane. This latter result is consistent with a columnar-like microstructure. However, one film with x=0.37 shows no evidence for such microstructure.

Small angle X-ray scattering from microvoids in the a-SiC:H alloy

Small-angle X-ray scattering (SAXS) measurements on a series of a-SiC:H alloy films deposited in a glow discharge reactor using SiH/sub 4//CH/sub 4/ gas mixtures are discussed. It was found that the introduction of C into the a-Si matrix produces a large SAXS signal, which suggests a sizable microvoid density, and which further increases with increasing C content. A Guinier analysis shows that these microvoids are spherical and have an average radius of approximately 6 AA, which increases only slightly with C content. Other measurements (infrared, photoconductivity, film density, optical) made on identically prepared material are included to identify the possible origins of these microvoids and to determine how they affect material quality. >