Component Of Scattering Vector Research Articles

Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers.

We demonstrate that spatial confinement can be used to control the orientational and translational order of cubic nanoparticles. For this purpose we have combined X-ray scattering and scanning electron microscopy to study the ordering of iron oxide nanocubes that have self-assembled from toluene-based dispersions in nanofluidic channels. An analysis of scattering vector components with directions parallel and perpendicular to the slit walls shows that the confining walls induce a preferential parallel alignment of the nanocube (100) faces. Moreover, slit wall separations that are commensurate with an integer multiple of the edge length of the oleic acid-capped nanocubes result in a more pronounced translational order of the self-assembled arrays compared to incommensurate confinement. These results show that the confined assembly of anisotropic nanocrystals is a promising route to nanoscale devices with tunable anisotropic properties.

Influence of length and conformation of saccharide head groups on the mechanics of glycolipid membranes: Unraveled by off-specular neutron scattering.

The mechanical properties of multilayer stacks of Gb3 glycolipid that play key roles in metabolic disorders (Fabry disease) were determined quantitatively by using specular and off-specular neutron scattering. Because of the geometry of membrane stacks deposited on planar substrates, the scattered intensity profile was analyzed in a 2D reciprocal space map as a function of in-plane and out-of-plane scattering vector components. The two principal mechanical parameters of the membranes, namely, bending rigidity and compression modulus, can be quantified by full calculation of scattering functions with the aid of an effective cut-off radius that takes the finite sample size into consideration. The bulkier "bent" Gb3 trisaccharide group makes the membrane mechanics distinctly different from cylindrical disaccharide (lactose) head groups and shorter "bent" disaccharide (gentiobiose) head groups. The mechanical characterization of membranes enriched with complex glycolipids has high importance in understanding the mechanisms of diseases such as sphingolipidoses caused by the accumulation of non-degenerated glycosphingolipids in lysosomes or inhibition of protein synthesis triggered by the specific binding of Shiga toxin to Gb3.

Evanescent-wave dynamic light scattering at an oil-water interface: Diffusion of interface-adsorbed colloids

A light-scattering goniometer for evanescent-wave dynamic light scattering (EWDLS) measurements at a liquid-fluid interface is introduced, and used for measurements on two charge-stabilized polystyrene colloid systems adsorbed to alkane-water interfaces. The goniometer allows an independent variation of the penetration depth and the scattering vector components parallel and perpendicular to a liquid-fluid interface. The possible illumination geometries are compared. Ellipsometry at the liquid-fluid interface is implemented as a complementary tool. In EWDLS measurements, the absence of diffusive motion perpendicular to the interface is demonstrated, which confirms the adsorption of the particles. The two-step decay of the autocorrelation function is interpreted in terms of diffusion within a two-dimensional interface lattice of colloidal particles, stabilized by repulsive electrostatic interactions, and a desorption process. A significant slowing down of the in-plane diffusion of the colloids as compared to the bulk diffusion is observed.

Mechanical properties of interacting lipopolysaccharide membranes from bacteria mutants studied by specular and off-specular neutron scattering

Specular and off-specular neutron scattering are used to study the influence of molecular chemistry (mutation) on the intermembrane interactions and mechanical properties of the outer membrane of Gram-negative bacteria consisting of lipopolysaccharides (LPSs). For this purpose, solid-supported multilayers of mutant LPS membranes are deposited on silicon wafers and hydrated either at defined humidity or in bulk buffers. The planar sample geometry allows to identify out-of-plane and in-plane scattering vector components. The measured two-dimensional reciprocal space maps are simulated with membrane displacement correlation functions determined by two mechanical parameters (vertical compression modulus and bending rigidity) and an effective cutoff radius for the membrane fluctuation wavelength. Experiments at controlled humidity enable one to examine the influence of the disjoining pressure on the saccharide-mediated intermembrane interactions, while experiments in bulk buffers (i.e., in the absence of an external osmotic stress) reveal the effect of divalent cations on LPS membranes, highlighting the role of divalent cations in the survival mechanism of bacteria in the presence of antimicrobial molecules.

Modulation of intermembrane interaction and bending rigidity of biomembrane models via carbohydrates investigated by specular and off-specular neutron scattering

We designed artificial models of biological membranes by deposition of synthetic glycolipid membrane multilayers on planar silicon substrates. In contrast to commonly used phospholipid membranes, this offers the unique possibility to study the influence of membrane-bound saccharide chains (cell glycocalix) on the membrane mechanics. Taking advantage of the planar sample geometry, we carried out specular and off-specular neutron scattering experiments to identify out-of-plane and in-plane scattering vector components. By considering the effects of finite sample sizes, we were able to simulate the measured two-dimensional reciprocal space maps within the framework of smectic liquid-crystal theory. The results obtained both at controlled humidity and in bulk water clearly indicate that a subtle change in the molecular chemistry of the saccharides strongly influences intermembrane interactions and membrane bending rigidities.

Anisotropy of Brownian motion caused only by hydrodynamic interaction with a wall

The diffusivity of spherical colloidal particles close to a planar hard wall is studied by dynamic light scattering with evanescent illumination. A novel setup allows us to independently vary the scattering vector components parallel Q parallel and normal Q perpendicular to the wall. An expression for the initial decay rate Gamma of the time autocorrelation functions is derived as a function of both Q parallel and Q perpendicular, as well as the penetration depth of the evanescent wave, where hydrodynamic interactions of particles with the wall are included. This makes it possible to study the viscous wall drag effect quantitatively for particles as small as 85 nm in radius.

Soft X-ray resonant magnetic scattering from a Ni layer with modulated magnetic anisotropy.

Soft X-ray resonant magnetic scattering studies on a magnetically modulated, but nominally chemically homogenous, 5 nm Ni layer in a Cu/Ni/Cu/Co/NiO/GaAs(110) system are reported. It was possible to estimate the main chemical structure of the sample on the basis of the results from specular reflectivity and rocking scans, probing the scattering vector components in the perpendicular and in-plane direction to the Ni wires, respectively. The magnetic scattering using polarized X-rays demonstrates the magnetic modulation of the Ni layer.

Determination of the interlayer superexchange in the two-dimensional ferromagnet Rb2CrCl4−xBrx by means of quasielastic neutron scattering (abstract)

The 2D ferromagnets Rb2CrCl4−xBrx; x=0, 1, 2 were studied by means of quasielastic neutron scattering. The compounds order between Tc=52.2 and 57.0 K. Rods of quasielastic diffuse scattering can be observed along the [001] direction. The wave vector dependent modulation of the width and the intensity of the diffuse scattering can be explained as resulting from the effect of the weak interplanar exchange coupling J′. By means of a mean field model, we describe the wave vector dependent susceptibility as function of the scattering vector components with respect to the reciprocal lattice vector. From the data around Tc, we derive that the ratio of the inter/intralayer superexchange changes from J′/J=2.3×10−4 to 10.2×10−4 upon increasing value of x.