Rainer Gehrke

Small-angle options of the upgraded ultrasmall-angle x-ray scattering beamline BW4 at HASYLAB

We present the upgrade and present status of the ultrasmall-angle x-ray scattering (USAXS) beamline BW4 at the Hamburg Synchrotronstrahlungslabor. In order to extend the accessible scattering vector range, new small-angle setups have been established, making use of the high flux and small divergence of BW4. In standard transmission geometry using a beam size of B=400×400μm2 (horizontal×vertical), typical small-angle resolution ranges from dmax=90to650nm, depending on sample-to-detector distance. Additionally a new microfocus option has been established. This microfocus option allows reducing the sample size by one order of magnitude. Using parabolic beryllium compound refractive lenses, a new standard beam size of B=65×35μm2 (horizontal×vertical) can be provided. The μ-SAXS resolution is as high as dmax=150nm. Using μ-SAXS in combination with grazing incidence (μ-GISAXS) on a standard noble metal gradient multilayer, we prove the feasibility of μ-GISAXS experiments at a second generation source.

P03, the microfocus and nanofocus X-ray scattering (MiNaXS) beamline of the PETRA III storage ring: the microfocus endstation

The MiNaXS (P03) beamline of the new third-generation synchrotron radiation source PETRA III (DESY, Germany) has been designed to perform small-, ultra-small- and wide-angle X-ray scattering in both transmission and grazing-incidence geometries. The high photon flux available at the beamline enables time-resolved investigations of kinetic phenomena with a time resolution below 100 ms. The microfocus endstation started user operation in May 2011.

Mapping the local nanostructure inside a specimen by tomographic small-angle x-ray scattering

Small-angle x-ray scattering is combined with scanning microtomography to reconstruct the small-angle diffraction pattern in the direction of the tomographic rotation axis at each location on a virtual section through a specimen. These data yield information about the local nanoscale structure of the sample. With rotational symmetry present in the diffraction patterns, e.g., for isotropic or fiber-textured scatterers, the full reciprocal space information in the small-angle scattering regime can be reconstructed at each location inside the specimen. The method is illustrated investigating a polymer rod made by injection molding.

Nanostructure of Nafion membrane material as a function of mechanical load studied by SAXS

The nanostructure of a perfluorinated membrane material (Nafion 117 by DuPont) is investigated as a function of strain and load by smallangle X-ray scattering (SAXS) at a synchrotron source. Two-dimensional SAXS patterns are evaluated utilizing the multi-dimensional chord distribution function (CDF). Anisotropy of the extruded material is considered. Both the ionomer domain and matrix polymer nanostructure are studied. For the neat material the classical ionomer domain model (domains as inverted micellae interconnected by channels) is confirmed and refined. Matching the plastic deformation behavior of the material, the domain structure in the relaxed and in the elongated state are found to be very similar. During elongation, ionomer channels open to form hollow ionomer layers(‘slits’) that are oriented parallel to the strain with a thickness of 1.9 nm and a long period of 3.8 nm. The slit height increases from 3 nm at elongation 1 ¼ 0:5 to 6 nm at 1 ¼ 1:25; whereas the slit width decreases to 1.5 nm. The ultimate structure is characterized by ensembles of not more than three slits that are in good lateral register. In the polymer matrix during elongation, cylindrical crystallites with a thickness of 2.5 nm and a most probable height of 7 nm are disrupted and parallelized with respect to the straining direction. The ultimate structure before sample failure is characterized by a broad domain height distribution ranging from a most probable domain height of 4 nm with a corresponding ultimate inclination of 408 to some perfectly parallelized domains of 20 nm height. q 2003 Elsevier Science Ltd. All rights reserved.

Dewetting of Thin Polymer-Blend Films Examined with GISAS

Abstract The morphology of dewetted thin polymer-blend films of deuterated polystyrene (dPS) and polyparamethylstyrene (PpMS) on top of silicon surfaces is investigated. The film thickness of the originally homogeneous films is varied between 19 and 104 A. Compared to the radius of gyration of the unperturbed molecule, R g =106 A , the as-prepared films are confined in the direction perpendicular to the sample surface. The dewetting results from the storage of the samples under toluene vapor atmosphere. Atomic force microscopy (AFM) and grazing incidence small-angle scattering (GISAS) are used. From the differences in the GISAS data measured with X-rays compared to data measured with neutrons a random distribution of the molecules inside the individual droplets is determined. Thus from dewetting under toluene atmosphere no periodicity in the internal structure exists. The, within all methods derived, most prominent in-plane length corresponds to the mean droplet distance. Its function of film thickness is explainable by the spinodal dewetting model.

Determination of the temperature and time dependence of the absolute small-angle X-ray scattering intensity of partially crystalline polymers employing synchrotron radiation

A method was developed to correct the influence of variations of the cross section of the synchrotron radiation beam on the intensity of small-angle X-ray scattering (SAXS). By means of this method the change of the SAXS intensity of poly(ethylene terephthalate) during heating and cooling was quantitatively evaluated. Three different effects could be distinguished: (1) changes in Δϱ, the difference between the densities of the crystalline and the amorphous regions, (2) partial melting and (3) recrystallization. By separation of the three effects, it becomes possible to measure the kinetics of partial melting and recrystallization. By comparing the change of the SAXS power Q with the change of the degree of crystallinity as determined by wide-angle X-ray scattering, it was proved that partial melting and recrystallization takes place within the spherulites without changing the spherulitically crystallized volume of the sample. The measurements of Δϱ indicate that an orientation of the chains by drawing leads to an increase of the glass transition temperature and to a decrease of the thermal expansion coefficient of the amorphous regions.

Route to create large-area ordered polymeric nanochannel arrays

Depositing polymdimethylsiloxane (PDMS) from an isopropanol solution onto a glass slide surface by wiping with a fuzz-free wipe results in highly ordered structures. Dewetting of the highly diluted PDMS solution and evaporation of the solvent yields nanostructures. The structure is well characterized as polymer nanochannels, separated by a mean distance of 166nm. The mean height of the shallow channels is 3nm only. The proof of having aligned structures on very large surface areas with a well defined orientation is performed with a very high resolution grazing incidence small angle x-ray scattering setup.

Large-scale and local-scale structures in polymer-blend films: a grazing-incidence ultra-small-angle X-ray scattering and sub-microbeam grazing-incidence small-angle X-ray scattering investigation

Phase-separation structures are installed by solution casting and flow of a binary polymer-blend solution of polystyrene and poly-n-butylacrylate in toluene on silicon. Optical microscopy and scanning-probe microscopy measurements provide the surface topography. Large-scale structures are probed with high-resolution or grazing-incidence ultra-small-angle X-ray scattering enabled by high reciprocal-space resolution. Correspondingly, structures of up to 13 µm are resolved. Local-scale structures are detected with sub-microbeam grazing-incidence small-angle X-ray scattering, providing a high real-space resolution of 1 µm. Nanometre-size cavities are found in the polystyrene-rich parts of the blend film.

Combining imaging ellipsometry and grazing incidence small angle X-ray scattering for in situ characterization of polymer nanostructures

A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging ellipsometry is introduced as a new versatile tool for the characterization of nanostructures. μGISAXS provides a local lateral and depth-sensitive structural characterization, and imaging ellipsometry adds the position-sensitive determination of the three-dimensional morphology in terms of thickness, roughness, refractive index, and extinction coefficient. Together μGISAXS and imaging ellipsometry enable a complete characterization of structure and morphology. On the basis of an example of buildup of nanostructures from monodisperse colloidal polystyrene nanospheres on a rough solid support, the scope of this new combination is demonstrated. Roughness is introduced by a dewetting structure of a diblock copolymer film with one block being compatible with the colloidal nanoparticles and one block being incompatible. To demonstrate the potential for kinetic investigations, μGISAXS and imaging ellipsometry are applied to probe the drying process of an aqueous dispersion of nanospheres on such a type of rough substrate.

Spatially Resolved Investigation of Solution Cast Nanoparticle Films by X-ray Scattering and Multidimensional Data Set Classification

A combinatorial high-throughput approach is used to investigate a solution cast gradient consisting of colloidal gold nanoparticles on top of a silicon substrate by means of a X-ray nanobeam. Classification algorithms are used to reveal and visualize structural transitions from a frozen colloidal solution to a well-defined nanostructure. Prominent length scales on the order of 100 nm are observed. A periodic change in the nanostructure along the gradient is explained by a simplified stick-slip model.