X-ray diffraction study of the structure of detonation nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.     

Size distribution of nanoparticle aggregates in an aqueous magnetic fluid based on atomic-force microscopy data

Atomic-force microscopy (AFM) has been applied in a fluid environment to determine the size distribution function of nanoparticle aggregates in an aqueous magnetic fluid with magnetite particles coated by polyacrylic acid for stabilization. It is proposed to use an external magnetic field to anchor aggregates on the substrate. The data are compared with the AFM data for dried precipitates of the system under consideration, formed during evaporation of the liquid carrier under different conditions, as well as with the particle size distribution in the initial system obtained from small-angle X-ray scattering data.     

Study of the structural features of ε-Co nanoparticles synthesized by cobalt carbonyl decomposition in the presence of surfactant

Cobalt nanoparticles (3–7 nm in size) obtained by cobalt carbonyl decomposition in 1,2-dichlorobenzene in the presence of surfactants (trioctylphosphine oxide and oleic acid) have been studied by a complex of structural methods: small-angle X-ray scattering, electron diffraction, and transmission electron microscopy. The nanoparticles synthesized are found to consist of the cubic ε-Со phase; their crystal structure is described within the sp. gr. P4₁32, a = 6.097 Å. Using small-angle X-ray scattering, the size and shape of nanoparticles have been determined directly in the liquid dispersion. Most of the particles have a spherical shape; their average size is ≈3.5 ± 0.5 nm, which agrees with the electron microscopy data. Possible factors causing the ε-phase formation during synthesis of metallic Co nanoparticles are discussed.

     

Study of the Solution Stability in the Analysis of Polydisperse Systems by Small-Angle Scattering

The stability of the solution to the problem of restoring the volume size distribution of nanoparticles for theoretical small-angle scattering data sets calculated within six different models has been investigated. The influence of the data noise level on the deviation of the found solution from the specified theoretical model is analyzed. Recommendations on the optimal search scheme of size distributions for complex polydisperse systems are given.     

Small-angle X-ray scattering study of the structure of powder fullerene C<Subscript>60</Subscript> and fullerene soot

Powder samples of fullerene C₆₀ and fullerene soot have been studied by the small-angle X-ray scattering method. The radii of gyration of scattering elements have been determined by constructing small-angle diffraction patterns in Guinier coordinates. The data obtained agree well with the results of wide-angle X-ray scattering study, the available data on the structure of the powder fullerene C₆₀ prepared by the Huffman-Krätschmer technique, and the structure of the C₆₀ molecules. Conglomerates of two C₆₀ molecules, along with crystallites ～20 nm in size that are distributed in an amorphous matrix, are present in fullerene powders. Fullerene soot contains C₆₀ crystallites 20–25 nm in size and graphite crystallites ～2–3 nm in size that are distributed in an amorphous matrix.     

Small-angle X-ray scattering,synchrotron radiation,and the structure of bio- and nanosystems

Small-angle X-ray scattering is a universal diffraction method for studying the supra-atomic structure of matter. The potential of this technique has greatly increased in recent years due to the development of bright synchrotron radiation sources. The extensive use of these sources, in combination with new techniques for analyzing scattering data and structure modeling, made small-angle scattering one of the most effective analytical methods for studying nanoscale structures. In this review, after a brief outline of the basic principles of small-angle scattering by isotropic dispersed nanosystems, we consider two areas of nanodiagnostics, in which the progress in the small-angle experiment and the latest techniques for interpreting scattering data has become pronounced in recent years. These areas—the analysis of the structure of biological macromolecules in a solution and structural studies of metal nanoparticles synthesized in polymer and aqueous media—are illustrated by examples of practical biological and nanotechnologycal applications.     

Determination of the size and phase composition of silver nanoparticles in a gel film of bacterial cellulose by small-angle X-ray scattering,electron diffraction,and electron microscopy

The nanoscale structural features in a composite (gel film of Acetobacter Xylinum cellulose with adsorbed silver nanoparticles, stabilized by N-polyvinylpyrrolidone) have been investigated by small-angle X-ray scattering. The size distributions of inhomogeneities in the porous structure of the cellulose matrix and the size distributions of silver nanoparticles in the composite have been determined. It is shown that the sizes of synthesized nanoparticles correlate with the sizes of inhomogeneities in the gel film. Particles of larger size (with radii up to 100 nm) have also been found. Electron microscopy of thin cross sections of a dried composite layer showed that large particles are located on the cellulose layer surface. Electron diffraction revealed a crystal structure of silver nanoparticles in the composite.     

Ordered structures based on self-organized Au and CdSe nanoparticles

Methods for obtaining cadmium selenide and gold nanoparticles have been developed. The sizes of the nanoparticles are determined and the morphology, structure, and chemical composition of these nanoparticles and their ensembles are studied by a complex of structural methods: electron diffraction, X-ray diffraction, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, and small-angle X-ray scattering. Gold nanoparticles are mainly spherical and have an average size of 10 nm. They are single-phase and have an fcc crystal structure. Samples of synthesized CdSe nanoparticles contain monodisperse spherical particles 12 nm in size with a wurtzite structure. The deposition of nanoparticles on a carbon substrate is accompanied by their self-organization into a closely packed two-dimensional structure with a pronounced texture in which all nanoparticles are oriented in the [001] direction perpendicularly to the carbon substrate plane.     

Effects of poly(vinyl alcohol) additions on the structure of silica xerogels

Poly(vinyl alcohol)/silica hybrid xerogels were prepared from sonohydrolysis of tetraethoxysilane (TEOS) and additions of water-solution of poly(vinyl alcohol) (PVA). The samples were studied by small-angle X-ray scattering (SAXS), nitrogen adsorption, and differential scanning calorimetry (DSC). On drying at room temperature the resulting xerogels exhibit a fairly bimodal porous structure composed by small mesopores and micropores. The pore size distribution of the mesopores was found to follow approximately a power-law with the pore size. The micropore structure was associated to an evolution at a high resolution level of the mass fractal structure of the original wet gels. The role of the PVA addition on the pore structure of the xerogels is to diminish the specific surface area and the pore volume without to change substantially the pore mean size.     

Evaluation of the Solution Stability When Reconstructing the Volume Particle Size Distribution from Small-Angle X-Ray Scattering Data for a Silicasol Solution

The results of studying the stability of the solution to the problem for determining the volume nanoparticle size distribution using experimental small-angle X-ray scattering (SAXS) data for a silicasol solution are presented. The possibility of reconstructing solutions using indirect Fourier transform and nonlinear minimization methods for a two-component model of spherical polydisperse particles has been investigated. The results obtained are compared with the simulation data obtained previously for theoretical data sets.     

Small-angle neutron scattering from samples of expanded carbon

The subatomic structure of expanded graphite has been investigated by small-angle neutron scattering. Samples were synthesized during quick thermal decomposition of intercalated compounds based on oxidized graphite. They had a low bulk density (up to 0.1 g/cm³) and were characterized by considerable small-angle scattering. It has been established that majority of the volume of expanded graphite samples is occupied by participles with characteristic sizes in two ranges: from 6 to 8 nm and from 20 to 30 nm. Small particles have properties of a surface fractal with the dimension D _s = 2.4–2.6, whereas the larger particles are mainly smooth and have the dimension D _s = 2.0–2.1. The specific surface of the samples studied was determined from the small-angle scattering data.     

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C₆₀ in carbon disulfide CS₂ have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 Å in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.     

Growth and melting of metallic nanoclusters in glass: A review of recent investigations

The mechanisms of nucleation and growth and the solid-to-liquid transition of metallic nanoclusters embedded in sodium borate glass were recently studied in situ via small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). SAXS results indicate that, under isothermal annealing conditions, the formation and growth of Bi or Ag nanoclusters embedded in sodium borate glass occurs through two successive stages after a short incubation period. The first stage is characterized by the nucleation and growth of spherical metal clusters promoted by the diffusion of Bi or Ag atoms through the initially supersaturated glass phase. The second stage is named the coarsening stage and occurs when the (Bi-or Ag-) doping level of the vitreous matrix is close to the equilibrium value. The experimental results demonstrated that, at advanced stages of the growth process, the time dependence of the average radius and density number of the clusters is in agreement with the classical Lifshitz-Slyozov-Wagner (LSW) theory. However, the radius distribution function is better described by a lognormal function than by the function derived from the theoretical LSW model. From the results of SAXS measurements at different temperatures, the activation energies for the diffusion of Ag and Bi through sodium borate glass were determined. In addition, via combination of the results of simultaneous WAXS and SAXS measurements at different temperatures, the crystallographic structure and the dependence of melting temperature T _m on crystal radius R of Bi nanocrystals were established. The experimental results indicate that T _m is a linear and decreasing function of nanocrystal reciprocal radius 1/R, in agreement with the Couchman and Jesser theoretical model. Finally, a weak contraction in the lattice parameters of Bi nanocrystals with respect to bulk crystals was established. The text was submitted by the authors in English.     

Microstructural analysis of nanoporous paracrystalline atomistic models of amorphous silicon

A detailed microstructural analysis of amorphous silicon is performed via numerical modeling technique. Nanoporous paracrystalline models have been proposed. Intermixed nanocrystallites and nanovoids of various sizes and concentrations have been introduced into a continuous random network that was generated with a vacancy model. Using the conjugate gradient method, the structures have been relaxed by minimizing their total strain energy described by the anharmonic Keating model. The obtained nanoporous structures are energetically competitive with the voidless paracrystalline networks. Nanoporous models with large voids are energetically more favorable than those with small voids. The nanoporous paracrystalline model is less dense than the crystalline phase, contrary to the paracrystalline model. This density decreases with increasing the void size for a fixed void volume fraction. Nanoporous paracrystalline structures reproduce the experimental structure factor better than the paracrystalline network. They account for, in particular, the intense small-angle scattering observed for some a-Si samples. The paracrystallites form amorphous zones but with local and topological ordering neatly better than the surrounding matrix. Such structural heterogeneity gives so a satisfactory explanation of the nanoscale fluctuation electron microscopy data reported recently by Treacy and Gibson.     

A SAXS observation of the crystallization of an Al85Y10Ni5 amorphous alloy in the supercooled liquid state

The medium-range structure of a heat-treated Al₈₅Y₁₀Ni₅ amorphous alloy was investigated by small-angle X-ray scattering, calorimetric analysis, wide-angle X-ray diffraction and transmission electron microscope measurements. It is observed that crystalline particles having a definite boundary are precipitated by annealing at supercooled liquid temperatures and that most of the precipitates consist of the Al fcc crystalline phase. The integrated intensities of the small-angle scattering and the Guinier radii of the precipitates increase on annealing for time duration <5.4 ks. However, as the annealing time becomes > 5.4 ks, the integrated intensities and the Guinier radii are invariant, i.e., growth of the precipitates ceases. After annealing for 518.4 ks, the diameters of the precipitates exhibit a narrow distribution centered around 200 Å.     

Small-angle neutron scattering study of high-pressure sintered detonation nanodiamonds

The structure of detonation diamonds sintered at a high pressure (7 GPa) and temperatures of 1200–1700°C has been investigated by small-angle neutron scattering. It is shown that sintering leads to an increase in the particle size from 6 to 30 nm and established that this increase is due to the chainlike oriented attachment of particles. This study supplements the oriented-attachment model, which was suggested based on the X-ray diffraction spectra of detonation nanodiamonds (DNDs) sintered under the same conditions.     

Database for rapid protein classification based on small-angle X-ray scattering data

A method was developed for rapid protein classification based on comparison of the experimental small-angle X-ray scattering data with scattering curves calculated for proteins with known structures. For this purpose, a database was compiled from about 1500 theoretical scattering curves for proteins with known structures. The potential of this method was illustrated by its application to analysis of the experimental scattering data from sperm whale myoglobin.     

Solution structures of human immunoglobulins IgG and IgM and rheumatoid factor IgM-RF

The low-resolution structures of human immunoglobulins M (IgM) and G (IgG) and the rheumatoid factor (IgM-RF) in solution were determined from synchrotron-radiation small-angle X-ray scattering by the method of dummy atom modeling (bead models). The structural models of IgM determined on the assumption that the molecule has a fivefold symmetry axis are in good agreement with the atomic structure of this protein proposed earlier. The molecular structure of the rheumatoid factor IgM-RF reconstructed by dummy atom modeling differs from the model of the IgM molecule: the F(ab)2 regions in the IgM-RF pentamer are asymmetric. This result confirms the earlier assumption that these regions in IgM-RF are different both structurally and biochemically. The typical shape of the IgG molecule in solution was demonstrated to be closer to the Y type, with the maximum size being larger than the size of the known crystallographic models.     

Small-angle neutron scattering from non-crystalline materials on a pulsed neutron source

The small-angle neutron scattering technique is illustrated for a variety of amorphous materials by results obtained on the LOQ instrument at the ISIS pulsed neutron source. The simultaneous use of neutron wavelengths of 2–10 Å is a particular advantage of the pulsed source which gives good results over a wide Q range. Coupled with neutron contrast variation this gives a valuable insight into the structure of materials in the size range 10–1000 Å.