Inelastic X-ray scattering with very high resolution at the ESRF

The investigation of phonon dispersion in crystalline materials and collective atom motions in disordered matter such as liquids and glasses by inelastic X-ray scattering has attracted a diversified user community with the advent of 3^rd generation synchrotron sources. The present article provides a short historical account of the research field and discusses selected highlights of research performed on the ESRF inelastic scattering beamlines ID16 and ID28 in the past ten years.     

In situ monitoring and control of lysozyme concentration during crystallization in a hanging drop

Fiber optic Raman spectroscopy combined with a partial least-squares regression model was demonstrated as a monitor of lysozyme concentration during crystallization in a hanging drop experiment in real time. Raman spectral features of the buffer and protein were employed to build the regression model. The use of fiber optic technology coupled with Raman spectroscopy, which is ideal for use with aqueous solutions, results in a powerful noninvasive probe of the changing environment within the solution. Lysozyme concentrations were monitored in experiments at a constant reservoir ionic strength. Data from these uncontrolled experiments were used to determine rates of supersaturation, induction times, and the number and size of the resultant lysozyme crystals. Control experiments were performed by introducing step changes in the reservoir ionic strength. The step changes were initiated by comparing in situ rates of supersaturation with the rates of supersaturation calculated from the uncontrolled data. Monitoring the concentration changes of the lysozyme within the hanging drop permits a measurement of the level of supersaturation of the system and enhances the possibility of dynamic control of the crystallization process.     

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.     

Small-angle X-ray scattering study of conditions for the formation of growth units of protein crystals in lysozyme solutions

The structural composition of lysozyme solutions favorable for the formation of the tetragonal form of protein crystals was studied by synchrotron-based small-angle X-ray scattering depending on the protein concentration and the temperature. Along with lysozyme monomers, dimers and octamers are found in crystallization solutions; the octamer content increases with an increase in the protein concentration.     

Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO₂ · nH₂O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ～100 Å. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ～(2000–2500) Å. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ～ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (～10¹⁶ and ～10¹³ cm^?3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.     

In situ and real-time analysis of TGZM phenomena by synchrotron X-ray radiography

The development of brilliant third-generation synchrotron X-ray sources, together with advances in X-ray optics and detectors, has provided timely efficient tools for in-depth understanding of physical phenomena in a broad spectrum of situations. Synchrotron X-ray radiography enables in situ and real-time observation of microstructure evolution, i.e. a direct access to dynamical phenomena which could not be anticipated from post-mortem analysis. Dedicated experiments are carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France) in Al-based alloys to study the dynamics of temperature gradient zone melting (TGZM) phenomenon. TGZM occurs when a liquid–solid zone is submitted to a temperature gradient and leads to the migration of liquid droplets or channels through the solid, up the temperature gradient. The thorough characterisation of both the initial solid during the thermal stabilisation phase prior to solidification (static TGZM) in Al–3.5 wt% Ni alloy and the dendritic microstructure in the later stage of solidification in Al–7.0 wt% Si alloy is performed. Based on experimental observations, quantitative data (in particular liquid-migration velocity) are measured and a very good agreement is found with theoretical analysis.     

Small-angle X-ray scattering study of the influence of solvent replacement (from H<Subscript>2</Subscript>O to D<Subscript>2</Subscript>O) on the initial crystallization stage of tetragonal lysozyme

The composition of lysozyme solutions in D₂O under conditions favorable for the formation of tetragonal crystals has been investigated at different protein concentrations by small-angle X-ray scattering using the synchrotron radiation. In addition to lysozyme monomers, dimeric and octameric species are found in the crystallization solutions; the octamer content increases with an increase in the protein concentration. A comparison of the data with those obtained under similar conditions but with H₂O used as a solvent has shown that the replacement of light water with heavy one leads to increase of octamer volume fraction in solution.     

Study of the gel films of Acetobacter Xylinum cellulose and its modified samples by 1H NMR cryoporometry and small-angle X-ray scattering

Gel films of Acetobacter Xylinum cellulose and its modified samples have been investigated by 1H nuclear magnetic resonance (NMR) cryoporometry and small-angle X-ray scattering. The joint use of these two methods made it possible to characterize the sizes of aqueous pores in gel films and estimate the sizes of structural inhomogeneities before and after the sorption of polyvinylpyrrolidone and Se₀ nanoparticles (stabilized by polyvinylpyrrolidone) into the films. According to small-angle X-ray scattering data, the sizes of inhomogeneities in a gel film change only slightly upon the sorption of polyvinylpyrrolidone and nanoparticles. The impregnated material is sorbed into water-filled cavities that are present in the gel film. ¹H NMR cryoporometry allowed us to reveal the details of changes in the sizes of small aqueous pores during modifications.     

Light scattering dynamic study of the gelation process

Light scattering is a choice method for studying the dynamic properties of fractal structures and growth processes. We present preliminary light scattering measurements to characterize the formation of small silica particles prepared in highly basic TMOS/methanol/water sols and the transformation of sol into gel employing digital clipped autocorrelation spectroscopy. The light scattering is due to gel clusters.     

Investigation of the interaction of dimethyl sulfoxide with lipid membranes by small-angle neutron scattering

The influence of dimethyl sulfoxide (CH₃)₂SO (DMSO) on the structure of membranes of 1,2-dimiristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in an excess of a water-DMSO solvent is investigated over a wide range of DMSO molar concentrations 0.0 ≤ X _DMSO ≤ 1.0 at temperatures T = 12.5 and 55°C. The dependences of the repeat distance d of multilamellar membranes and the thickness d _b of single vesicles on the molar concentration X _DMSO in the L _β’ gel and L _α liquid-crystalline phases are determined by small-angle neutron scattering. The intermembrane distance d _s is determined from the repeat distance d and the membrane thickness d _b. It is shown that an increase in the molar concentration X _DMSO leads to a considerable decrease in the intermembrane distance and that, at X _DMSO = 0.4, the neighboring membranes are virtually in steric contact with each other. The use of the deuterated phospholipid (DMSO-D6) and the contrast variation method makes it possible, for the first time, to determine the number of DMSO molecules strongly bound to the membrane.     

In situ fabrication of waveguide-compatible glass-embedded silver nanoparticle patterns by masked ion-exchange process

We report a study on the properties of silver nanoparticles formed in glass using a masked silver–sodium ion-exchange technique, a process that has been used to fabricate patterned optical waveguides. Characterizations reveal that spherical nanoparticles with a diameter of 5–10 nm are concentrated below the mask edge at a depth of 50–100 nm from the surface. The amount of nanoparticles and the wavelength of the associated localized surface plasmon resonance can be controlled by the spacing between adjacent mask openings. After gentle etching, the surface morphology of the sample shows well-defined nanoparticle patterns. These closely packed nanoparticles embedded in the glass surface have a potential to be used for high-sensitivity surface enhanced spectroscopy, in a glass waveguide device.     

Characterization of oligomerization of a peptide from the ebola virus glycoprotein by small-angle neutron scattering

Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) studies showed that model peptides QNALVCGLRQ (G33) and QNALVCGLRG (G31) corresponding to region 551–560 of the GP protein of the Sudan Ebola virus are prone to oligomerization in solution. Both peptides can form amyloid-like fibrills. The G33 peptide forms fibrils within one day of incubation, whereas the fibrillogenesis of the G31 peptide is observed only after incubation for several months. The possible role of the observed processes in the pathogenesis and the possibility of applying a combination of the TEM and SANS techniques to search for new compounds that are able to influence the protein oligomerization are discussed.     

Effect of surfactant excess on the stability of low-polarity ferrofluids probed by small-angle neutron scattering

The structures of ferrofluids (FFs) based on nonpolar solvent decahydronaphthalene, stabilized by saturated monocarboxylic acids with hydrocarbon chains of different lengths, C16 (palmitic acid) and ?12 (lauric acid), with an excess of acid molecules, have been studied by small-angle neutron scattering. It is found that the addition of acid to an initially stable system with optimal composition leads to more significant structural changes (related to aggregation) than those observed previously for this class of FFs. A comparison of the influence of monocarboxylic acids on the stability of nonpolar FFs suggests that the enhancement of aggregation is much more pronounced in the case of palmitic acid excess. This fact confirms the conclusion of previous studies, according to which an increase in the hydrocarbon chain length in a saturated acid reduces the efficiency of the corresponding FF stabilization.     

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.     

Diffuse X-ray scattering study of the temperature variation of elastic constants in indium arsenide

The elastic constants of indium arsenide have been determined in the temperature range from 80 to 750 K on n-type samples with a carrier concentration of about 8 · 10¹⁷ cm⁻³ by Wooster's method from the measurements of the thermal X-ray diffuse scattering intensities. An average decrease in the elastic constants with increasing temperature over the above mentioned temperature range is found to be about 8%.     

Effect of P2O5 on the early stage crystallization of K-fluorrichterite glass-ceramics

The addition of 2 mol% P₂O₅ to stoichiometric K-fluorrichterite (KNaCaMg₅Si₈O₂₂F₂, KFR) has been reported to enhance the mechanical properties and improve the in vitro biocompatibility of this glass-ceramic by promoting the formation of enstatite and fluorapatite (FA). Here, the effect of further increasing the P₂O₅ concentration on phase evolution of KFR has been investigated. XRD data showed that mica crystallized in samples with 4 and 5 mol% P₂O₅ (GP4 and GP5, respectively) at 650 °C, but no diopside was detected at higher temperatures, in contrast with the general phase evolution in KFR based glass-ceramics. More importantly, however, the addition of ?4 mol% P₂O₅ induced phase separation of the glass into a silica glass matrix and phosphate rich droplets prior to crystallization. EDS traces taken from samples heat-treated at 600 °C, revealed that the silica glass matrix was deficient in Mg and unlikely to be the host for crystallization of mica. Conversely, the P₂O₅ rich regions contained excess Mg and were considered to be the host for the formation of mica and FA.