Surface versus confinement induced morphology transition in triblock copolymer films: a grazing incidence small angle neutron scattering investigation

The internal nanostructure resulting from microphase separation in triblock copolymer films of polyparamethylstyrene-block-polystyrene-block-polyparamethylstyrene, P(pMS-b-Sd8-b-pMS), has been investigated with grazing incidence small angle neutron scattering (GISANS). X-ray reflectivity, grazing incidence small-angle X-ray scattering (GISAXS), optical microscopy and atomic force microscopy (AFM) complement the investigation. The influence of two limiting interfaces present in confinement is compared to the presence of only one surface. GISANS allows for the detection of structures in the very limited sample volume of confined films as well as for a depth sensitivity to probe the near free surface part of bulk films. With respect to the surface a perpendicular oriented lamella is observed. In contrast to the shrinkage of the characteristic lamellar spacing in confinement at the free surface, a slight increase is determined.     

Synchrotron light scattering on nanostructured V/Ce oxide films intercalated with Li+ ions

Vanadium oxide and new V/Ce oxide films on a glass substrate were obtained by the sol-gel process. The morphology of these nanostructured and porous films was studied by grazing-incidence small-angle X-ray scattering (GISAXS) at the ELETTRA synchrotron (Italy, Trieste). The aim of performing GISAXS was to study changes, which might occur in the grain sizes and the porosity of vanadium oxide and V/Ce oxide at 38 and 55 atom % of V, upon the intercalation of Li+ ions. The average grain radius obtained by GISAXS varied with the layer thickness and upon the intercalation of Li+ ions. The layer structure in V/Ce oxides was revealed by the grazing-incidence X-ray reflectivity (GIXR) method. The average grain radius , obtained by GISAXS, was correlated with the intercalation of Li+ ions. The specific surface area of these films was also determined and generally varied from 0.5 nm(-1) to 0.03 nm(-1).     

Comparative analysis of nanostructured diblock copolymer films

Nanostructured polymer films of poly(styrene-block-paramethylstyrene) diblock copolymers P(Sd-b-pMS) on silicon substrates with a native oxide layer are investigated. Resulting from a storage under toluene vapor, a surface structure is installed. The early stages, characterized by the creation of a host structure out of an initially continuous film, are addressed. Grazing incidence small-angle X-ray scattering (GISAXS) experiments were performed as a function of exposure time. Results are compared to modelling of the scattering pattern and other experimental techniques, such as grazing incidence small-angle neutron scattering (GISANS) and atomic force microscopy (AFM) data. Possibilities and limits of the techniques are discussed.     

Time-resolved ultrathin cobalt film growth on a colloidal polymer template

Cobalt (Co) sputter deposition onto a colloidal polymer template is investigated using grazing incidence small-angle X-ray scattering (GISAXS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). SEM and AFM data picture the sample topography, GISAXS the surface and near-surface film structure. A two-phase model is proposed to describe the time evolution of the Co growth. The presence of the colloidal template results in the correlated deposition of an ultrathin Co film on the sample surface and thus in the creation of Co capped polystyrene (PS) colloids. Well below the percolation threshold, the radial growth is restricted and only height growth is observed.     

Small-angle scattering in materials science

The use of small-angle scattering techniques in the study of inhomogeneities and microstructural changes in inorganic materials is reviewed with emphasis on X-ray scattering. Recent applications of anomalous scattering with synchrotron radiation and kinetic studies in amorphous and crystalline systems are stressed.     

Calcium carbonate mineralization: X-ray microdiffraction probing of the interface of an evaporating drop on a superhydrophobic surface

The liquid/air interface of calcium bicarbonate solution drops was probed by synchrotron radiation microbeam scattering. The drops were deposited on a nanopatterned superhydrophobic poly(methyl methacrylate) surface and raster-scanned during evaporation by small-angle and wide-angle X-ray scattering. The appearance of about 200-nm-size calcite crystallites at the interface could be spatially resolved at the onset of crystallization. Diffuse scattering from the interface is attributed to a dense nanoscale amorphous calcium carbonate phase. Calcite was found to be the major phase in the solid residue with vaterite as minor phase.     

Collapse transition in thin films of poly(methoxydiethylenglycol acrylate)

The thermal behavior of poly(methoxydiethylenglycol acrylate) (PMDEGA) is studied in thin hydrogel films on solid supports and is compared with the behavior in aqueous solution. The PMDEGA hydrogel film thickness is varied from 2 to 422?nm. Initially, these films are homogenous, as measured with optical microscopy, atomic force microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering (GISAXS). However, they tend to de-wet when stored under ambient conditions. Along the surface normal, no long-ranged correlations between substrate and film surface are detected with GISAXS, due to the high mobility of the polymer at room temperature. The swelling of the hydrogel films as a function of the water vapor pressure and the temperature are probed for saturated water vapor pressures between 2,380 and 3,170?Pa. While the swelling capability is found to increase with water vapor pressure, swelling in dependence on the temperature revealed a collapse phase transition of a lower critical solution temperature type. The transition temperature decreases from 40.6?°C to 36.6?°C with increasing film thickness, but is independent of the thickness for very thin films below a thickness of 40?nm. The observed transition temperature range compares well with the cloud points observed in dilute (0.1?wt.%) and semi-dilute (5?wt.%) solution which decrease from 45?°C to 39?°C with increasing concentration.     

In situ GISAXS investigation of gold sputtering onto a polymer template

Microphase-separation structures in mixed diblock-triblock copolymer thin films are used for the incorporation of gold atoms inside the polymer matrix via sputtering of gold. Polystyrene (PS) spheres are arranged in a liquidlike type with a well defined nearest neighbor distance inside a polyisoprene matrix acting as a template for directing the gold atoms. Sputtering conditions are selected with a very low sputtering rate to avoid clustering in the atmosphere so that gold reaches the polymer surface in its atomic state. Due to the mobility of the gold atoms and the selective interaction with the PS parts of the microphase separation structure, gold is accumulated inside the polymer film in the PS spheres, as probed in situ with grazing incidence small-angle X-ray scattering (GISAXS). Nominally 4.3 A of gold is deposited, which by diffusion is spread out vertically over a thickness of 280 nm. UV-vis spectroscopy reveals a small blue shift for the gold sputtered polymer film. Atomic force microscopy proves the absence of gold clusters on the film surface. For low sputtering rate, GISAXS proves good sensitivity for gold migration inside the polymer film and opens new possibilities for studying polymer-metal interaction.     

Grazing incident small angle x-ray scattering study of polymer thin films with embedded ordered nanometer cells

Analysis of nanostructures is of increasing importance with advances of nanotechnology. Embedded nanostructures in thin films in particular are of recent interest. Grazing incident small angle x-ray scattering (GISAXS) has been recognized to be a powerful method to probe such embedded nanostructures; however, quantitative analysis of scattering pattern is not always trivial due to complex refraction and reflection at surface and interfaces. We prepared nanocellular thin films using block copolymer template with carbon dioxide (CO(2)); CO(2) "bubbles" were formed in the CO(2)-philic block domains. Such nanocellular structures were analyzed by GISAXS and simulated using distorted wave Born approximation (DWBA). Unlike traditional transmission x-ray scattering, GISAXS requires a careful choice of incident angle to analyze the form factor of scatters embedded in a thin film. Nevertheless, the GISAXS measurements under optimized geometry with quantitative calculations using DWBA revealed that the nanocells are spherical and aligned in a single layer of hexagonal lattice and are surrounded by CO(2)-philic block domains.     

Stacking structure of concentrated shear ordered dispersions by two scattering methods

In this paper, the ordering in concentrated charge stabilized colloidal dispersions is considered. Despite the impressive Bragg reflections obtained for shear ordered dispersions by light (LS), small-angle neutron (SANS), and small-angle X-ray scattering (SAXS), a number of open questions remain. Sheared dispersions are usually ordered in layers. For such systems, two questions arise: (1) What is the structure in a layer? (2) What is the stacking structure perpendicular to the layers? The second question requires a method to determine the structure perpendicular to the layers. Although originally interested only in structural aspects, we were forced to consider different methods. Two methods are treated both applicable to neutron and X-ray scattering from concentrated dispersions. One has been used by physicists and chemists for many years to determine the structure of crystals by sample rotation. In colloid science, we have used it previously in neutron and X-ray scattering. A second method is treated here which can be applied in small-angle scattering from a Couette cell. It gives the scattering intensity in a certain direction without sample rotation. Although very useful with the Couette cell, it cannot be found in any of the well-known references on colloid science. A theoretical explanation and experimental examples obtained by synchrotron X-ray scattering from a Couette cell are given in the paper.     

Stacking of main chain-crown ether polymers in thin films

Thin films (9-70 nm) of a series of polymers containing in the main chain dibenzo-18-crown-6 ether unit (DB18C6) linked to an aliphatic spacer of different length (10C and 14C) and nature have been prepared, from chloroform solutions, by spin coating on a silicon substrate. The quality and homogeneity of the polymer coatings was revealed by their reflectivity spectra and atomic force microscopy (AFM). The grazing incidence small-angle X-ray scattering (GISAXS) patterns show an out-of-plane structure correlation (interference maximum near the horizon) of scale size related to the polymer repeating unit length. Above this Bragg reflection, the shape of the scattering observed, in the GISAXS pattern, reveals an orientation of the stacked molecular columns in the coated polymer. A thermal treatment of the samples improves the nanostructure by increasing the lamellar coherence size (in y-direction) as well as the vertical orientation of the molecular columns.     

Instruments and methods for small-angle scattering with synchrotron radiation

Some aspects of small-angle X-ray scattering (SAXS) instrumentation for synchrotron radiation (SR) are considered below. The basic layout of instruments as well as some of the problems arising from the nature of the source and of the type of experiments are discussed. Further, a survey of the instruments available at major SR facilities is given.     

Scattering curves of ordered mesoscopic materials

Analytical expressions for the scattering functions of ordered mesoscopic materials are derived and compared to experimentally determined scattering curves. Ordered structures comprising spheres (fcc, bcc, hcp, sc), cylinders (hex, sq), and lamellar structures are considered. The expressions take into account particle size distributions and lattice point deviations, domain size, core/shell structures, as well as peak shapes varying analytically between Lorentzian and Gaussian functions. The expressions allow one to quantitatively describe high-resolution synchrotron small-angle X-ray (SAXS) and neutron scattering (SANS) curves from lipid and block copolymer lyotropic phases, core/shell nanoparticle superstructures, ordered nanocomposites, and ordered mesoporous materials. In addition, the diffuse out-of-plane scattering of grazing incidence GISAXS and GISANS experiments of laterally ordered thin films can be quantitatively analyzed.     

GISAXS: A versatile tool to assess structure and self-assembly kinetics in block copolymer thin films

Over the past two decades grazing incidence small-angle scattering (GISAXS) has morphed into a powerful tool for the determination of the structure and self-assembly kinetics of block copolymer thin films. An overview of the scattering process and the interpretation of GISAXS data is given and experimental requirements are discussed. The application of the technique for the characterization of block copolymer thin films is illustrated with selected examples.     

Characterisation of structure and aggregation processes of aquatic humic substances using small-angle scattering and X-ray microscopy

Aquatic humic substances (HS), an important part of the dissolved organic carbon in freshwater systems, are polyfunctional natural compounds with polydisperse structure showing strong aggregation/coagulation behaviour at high HS concentrations and in the presence of metal ions. In this study, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS) and X-ray microscopy (XRM) were applied to characterise the structure and aggregation processes of HS in solution. In SAXS and XRM the high brilliant synchrotron radiation was used as X-ray source. Applying small-angle scattering, information about the size distribution and shape of aquatic HS was obtained. Spherical HS units were found which were stable in a wide concentration range in a kind of "monomeric" state almost independent of pH and ionic strength. At higher concentrations they formed chain-like agglomerates or disordered HS structures. In studies on the coagulation behaviour of HS after addition of copper ions, a linear relationship between Cu(2+) concentration and the formation of large disordered HS-Cu(2+) agglomerates was obtained. By using X-ray microscopy, single "huge" particles were found in older solutions and in solutions with high HS concentrations. Over a threshold Cu(2+) concentration of approx. 300 mg/L, the formation of an extensive HS-Cu(2+) network structure was observed within a few minutes. The presented structures show the ability of the methods used to characterise processes between diluted phase and suspended matter, which play an important role particularly in the region of phase interfaces.     

Small-angle x-ray scattering from poly(tetramethyl-p-silphenylene) siloxane (TMPS) fractions

Small-angle x-ray scattering studies were made on bulk-crystallized samples and annealed oriented films of TMPS. The temperature dependence of the small-angle scattering was determined over a range of annealing conditions. The effect of sample molecular weight on the small-angle peaks was also studied. The peak intensity, measured at room temperature after annealing, was strongly dependent on the annealing conditions. The position of the peak gradually moved to smaller angles (larger d spacings) as the annealing temperature was raised. Surface free energies were deduced from the melting point dependence of the crystallite size. This surface energy was found to increase with molecular weight in accord with values deduced for spherulite growth rate-temperature dependence.     

Assessment and formation mechanism of laser-induced periodic surface structures on polymer spin-coated films in real and reciprocal space

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.     

Further application of size-exclusion chromatography combined with small-angle X-ray scattering optics for characterization of biological macromolecules

Size-exclusion chromatography (gel filtration chromatography or gel permeation chromatography) in conjunction with online synchrotron radiation solution small-angle X-ray scattering optics, absorbance, and/or refractive index detectors was further assessed by application of biological macromolecules, such as the hollow sphere protein complex, apoferritin, and a linear polysaccharide, pullulan. The net X-ray scattering patterns of the eluted 24-mer molecule of apoferritin showed the specific character for the hollow spherical shape. The chromatographic (time-resolved) X-ray scattering data of the linear polysaccharide pullulan revealed the flexible chain structure during the chromatographic separation in an aqueous solution. These further applications demonstrated that the present measurement technique will be useful for not only the determination of the radius of gyration value of less than about 10?nm and molecular weight below several hundred thousand but also for the structural characterization of the various macromolecules during the chromatography.

Phase separation in PS/PVME thin and thick films

Phase separation in both thin and thick films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) was studied by small-angle laser light scattering (SALLS), atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Blend films with controlled thickness were obtained by spin-coating polymer-toluene solutions with various concentrations. Films with thicknesses smaller and larger than the maximum wavelength of concentration fluctuations were considered. Morphology of the blend films was characterized during and after phase separation. The obtained peculiar morphology was related to surface enrichment with the lower-surface-energy component, as was verified by XPS analyses.     

Solvent vapor annealing of block copolymer thin films: removal of processing history

The ordering processes of PS-b-P2VP block copolymer thin films with different processing histories were studied during solvent vapor annealing by in situ grazing incidence small-angle X-ray scattering (GISAXS). We compared cylinder-forming PS-b-P2VP thin films with 34 kg/mol molecular weight that were prepared in three different ways: spin coating, spin coating and subsequent solvent vapor annealing where the solvent vapor was removed instantaneously, and spin coating and subsequent solvent vapor annealing where the solvent vapor was removed slowly. Block copolymer thin films retained the morphology resulting from the different “processing histories” at smaller swelling ratios. This processing history was erased when the samples reached a higher swelling ratio (~1.4). After the solvent was slowly removed from the swollen film, the surface morphology was characterized by ex situ AFM. All samples showed the same morphology after solvent annealing regardless of the initial morphology, indicating the morphology of solvent annealed samples is determined by the polymer concentration in the swollen film and the solvent vapor removal rate, but not the processing history.