Grazing incidence small-angle X-ray scattering: an advanced scattering technique for the investigation of nanostructured polymer films

Hamburg workshop on the "application of synchrotron radiation in chemistry"With grazing incidence small-angle X-ray scattering (GISAXS) the limitations of conventional small-angle X-ray scattering with respect to extremely small sample volumes in the thin-film geometry are overcome. GISAXS turned out to be a powerful advanced scattering technique for the investigation of nanostructured polymer films. Similar to atomic force microscopy (AFM), a large interval of length between molecular and mesoscopic scales is detectable with a surface-sensitive scattering method. While with AFM only surface topographies are accessible, with GISAXS the buried structure is also probed. Because a larger surface area is probed, GISAXS also has a much larger statistical significance compared to AFM. Due to the high demand on collimation, GISAXS experiments are based on synchrotron radiation. Nanostructures parallel and perpendicular to the sample surface observable in thin poly(styrene- block-isoprene) diblock copolymer films are presented as an example of the possibilities of GISAXS.     

Total reflection X-ray fluorescence study of organic nanostructures

X-ray scattering techniques based on total external fluorescence study and development of X-ray standing wave method are presented and used for characterization of organic nanostructure Langmuir–Blodgett films of fatty acid salts and phospholipids. Spectral selectivity of data obtained allows us to detect structure position of different ions in organic systems, to obtain information about interdiffusion at the interfaces, about ion permeation through organic bilayers, thus allowing us to develop models of biomembranes.     

Atomic oxygen erosion resistance of sol–gel oxide films on Kapton

Silica, alumina and silica-alumina composite films were deposited on Kapton substrate via sol–gel method and their atomic oxygen (AO) erosion resistance was test in a ground-based AO simulator. The surface morphology and the structure of as-deposited films were investigated by scanning electronic microscope, X-ray photoelectron spectroscopy, and Fourier transformed infrared spectroscopy. After AO exposure, more cracks and micro-pores appear on the surface of silica and alumina films, respectively. For the silica-alumina composite films, their toughness and densification are good, and the stable interface is formed between the alumina and silica phases. Therefore, the silica-alumina composite-coated Kapton shows the best AO resistance and the erosion yield is two orders of magnitude less than that of pristine Katpon. Moreover, the composite-coated Kapton remains optically stable under AO exposure.     

Monte Carlo simulation of X-ray fluorescence spectra: Part 4. Photon scattering at high X-ray energies

The photon scattering model of a Monte Carlo simulation code for synchrotron radiation X-ray fluorescence (SRXRF) spectrometers is evaluated at high X-ray energies (60–100 keV) by means of a series of validation experiments performed at Beamline BW5 of HASYLAB. Using monochromatic X-rays, Compton/Rayleigh multiple scattering experiments were performed on polypropylene, Al and Cu samples. Especially in the case of the first two matrices multiple Compton scattering occurs with high probability. This work demonstrates that the simulation model provides a reliable estimate of the spectral distribution of the multiply scattered linearly polarized photon beam as observed by an HPGe detector. Next to variations in sample composition and thickness, the ability of the code to simulate various detection geometries has also been verified. As an application of the code, the achievable detection limits of SRXRF for rare earth elements as obtained with white beam and monochromatic (80 keV) excitation are compared.     

Solution-based assembly of conductive gold film on flexible polymer substrates

Conductive films of gold were assembled on flexible polymer substrates such as Kapton and polyethylene using a solution-based process. The polymer substrates were modified by using argon plasma and subsequent coupling of silanes with amino- or mercapto- terminal groups. These modified surfaces were examined by X-ray photoelectron spectroscopy and contact angle measurements. Colloidal gold was assembled onto the silane-modified surface from solution. The gold particles are attached to the surface by covalent interactions with the thiol or amine group. Formation of a conductive film is achieved by increasing the coverage of gold by using a "seeding" method to increase the size of the attached gold particles. Field emission scanning electron microscopy was used to follow the growth of the film. The surface resistance of the films, measured using a four-point probe, was about 1 Omega/sq.     

Effect of orientation on the relative dispersion of PMDA-ODA polyimide and polypropylene

The relative dispersion of birefringence, D_b, is determined for isotactic polypropylene and Kapton HA PMDA-ODA polyimide films. D_b is then used to identify the dependence of dispersion on the orientation of polymers and is interpreted in terms of fringe jumping. Optical relationships between the in-plane birefringence and wavelength are formulated to predict the in-plane birefringence of oriented Kapton HA PMDA-ODA polyimide films at any wavelength. These relations can be used for the direct comparison of the in-plane birefringence of Kapton PMDA-ODA polyimide films obtained from different optical techniques (i.e., polarized microscopy, polarized refractometry, wave guide coupling, etc.). © 1995 John Wiley & Sons, Inc.     

Anisotropic Picosecond X-ray Solution Scattering from Photo-selectively Aligned Protein Molecules

Anisotropic X-ray scattering patterns of transiently aligned protein molecules in solution are measured by using pump-probe X-ray solution scattering. When a linearly polarized laser pulse interacts with an ensemble of molecules, the population of excited molecules is created with their transition dipoles preferentially aligned along the laser polarization direction. We measured the X-ray scattering from the myoglobin protein molecules excited by a linearly polarized, short laser pulse and obtained anisotropic scattering patterns on 100 ps time scale. An anisotropic scattering pattern contains higher structural information content than a typical isotropic pattern available from randomly oriented molecules. In addition, multiple independent diffraction patterns measured by using various laser polarization orientations will give substantially increased amount of structural information compared with a single isotropic pattern. By monitoring the temporal change of the anisotropic scattering pattern from 100 ps to 1 μs, we observed the orientational dynamics of photo-generated myoglobin with the rotational diffusion time of ～15 ns.     

Self-assembled photoactive polyelectrolyte/perylene-diimide composites

A new class of polyelectrolyte-surfactant (PE-surf) composites having potential applications as thin film organic semiconductors is introduced. These materials are comprised of cationic asymmetrically substituted perylene diimides and oppositely charged poly(acrylate) polyanions. Thin films of the composite materials are prepared by mixing and drop casting aqueous solutions of the two precursors onto appropriate substrates. The resulting materials yield photovoltages of >140 mV for approximately equal to 0.6 W/cm(2) illumination intensities, when incorporated in p-n heterojunction devices. Solution-phase spectra obtained from the PE-surf complexes exhibit excimer-like emission and evidence for formation of weakly coupled aggregates in the ground state. Wide-angle X-ray scattering data show the composite films are locally amorphous, while small-angle X-ray data are consistent with a mixture of polymorphic structures that incorporate planar PE-surf bilayers of 3.9-nm repeat distances. Images obtained by conventional far-field light microscopy and multiphoton-excited fluorescence microscopy (MPEFM) indicate that the films are heterogeneous, incorporating submicrometer sized clusters dispersed among much thinner film regions that also incorporate dye. Polarization-dependent MPEFM studies prove the clusters are semiorganized, yielding order parameters (s and P(4)) of 0.09 and 0.01 for in-plane alignment of the chromophores, consistent with a relatively high degree of disorder.     

Low energy X-ray radiation impact on coated Si constructions

Low energy X-ray radiation impact on the coated Si structures is discussed in this paper. Experimental sandwich structures consisting of amorphous hydrogenated a:C–H or SiO_x-containing DLC films were synthesized on Si 〈1 1 1〉 wafers using direct ion deposition method and exposed to low energy (medical diagnostic range) X-ray photons. Irradiation of samples was performed continuously or in sequences and protective characteristics of the irradiated DLC films were investigated. Experimental data were used as the input data for Monte Carlo modelling of X-ray scattering effects in the coated silicon constructions, which affect significantly the “signal to noise ratio” in DLC-coated Si structures proposed for their application in medical radiation detectors. Modelling results obtained in the case of DLC coatings were compared to the results of calculations performed for other commonly used combinations coating–detector material.The evaluation method of coated structures for their possible application in medical radiation detector constructions has been proposed in this paper. It is based on the best achieved compatibility between the appropriate mechanical characteristics, coating’s resistance against the radiation damage and the lowest estimated scattering to total dose ratio in the coated radiation sensitive volume.     

1s2p resonant inelastic X-ray scattering of iron oxides

1s2p resonant inelastic X-ray scattering (RIXS) spectroscopy has been measured for a series of iron oxides, including octahedral and tetrahedral Fe(II) and Fe(III) systems. Their spectral shapes have been analyzed and explained using crystal-field multiplet simulations. The RIXS planes and the K-edge and L-edge X-ray absorption spectra related to these RIXS planes will be discussed with respect to their analytical opportunities. It is concluded that the full power and possibilities of 1s2p RIXS needs an overall resolution of 0.3 eV. This will yield a technique with more detailed information than K-edge and L-edge X-ray absorption combined, obtained in a single experiment. Another major advantage is that 1s2p RIXS involves only hard X-rays, and experiments under essentially any condition and on any system are feasible.     

垂直取向介孔薄膜的制备

垂直取向介孔薄膜是指薄膜内部孔道垂直于基底定向排列的一类介孔薄膜,其在催化、吸附与分离、化学传感器、太阳能电池等领域具有广阔的应用前景。本文就近几年内垂直取向介孔薄膜的制备方法以及在若干领域的应用进行了回顾和综述。在此基础上,对这种特殊的薄膜材料未来的发展进行了展望。     

Determination of order parameter of YMn0.5Fe0.5O3 epitaxial thin films by anomalous X-ray scattering technique

The crystal structure of an orthorhombic YMn_0.5Fe_0.5O₃ (010) (YMFO) epitaxial films on YAlO₃(010) substrate was studied using X-ray diffraction, X-ray absorption spectroscopy, and anomalous X-ray diffraction techniques. Due to the utmost similar scattering factors of Mn and Fe atoms, it is hard to distinguish them at specific sites of the unit cell from the variations in the diffraction peak intensity. Therefore, anomalous X-ray scattering was used to determine the order or disorder structure of YMFO films. To estimate the order parameter of the YMFO film, the incident X-ray energies have been scanned around the Mn K-edge and Fe K-edge, resulting in enhanced diffraction intensities of the forbidden YMFO (010) peak by 15–20 times, respectively. This in turn revealed that YMFO films have a partially ordered structure of about 40 ± 10% in the epitaxially grown thin film.     

X-ray diffraction and DOSY NMR characterization of self-assembled supramolecular metallocyclic species in solution

Wide-angle X-ray scattering and diffusion NMR techniques have been used to obtain structural information on three self-assembled metallacyclic supramolecular complexes in solution: a rectangle, a triangle, and a three-diminsional cage. The low-angle region of the measured diffraction patterns and hydrodynamic radii calculations, determined from DOSY NMR experiments, suggest that the supramolecular assemblies retain their shape when dissolved in nitromethane. The experimental structure functions for the large-angle region have been analyzed, and the intramolecular contributions of the platinum-platinum interactions are discussed. These scattering measurements provide evidence that the supramolecular assemblies are not as rigid in solution as they are in the single crystal. Finally, by analysis of the radial distribution functions of the solutions, direct structural information (e.g., platinum-platinum intramolecular distances and coordination number) about the supramolecular assemblies has been obtained.     

X-ray scattering and multivariate analysis for classification of organic samples: a comparative study using Rh tube and synchrotron radiation

This work compares the performance of X-ray tube induced and synchrotron induced energy dispersive X-ray fluorescence in generating scattering profiles when organic samples are irradiated. In the first case, this effect produces sharper peaks, well defined in the spectra, whereas synchrotron-induced scatter are seen as broad bands. These effects may be used for classifying simple materials like graphite, coke, activated carbon and carbon nanotubes, all having the same composition but different structures, using multivariate data analysis. In a second sample set, the method was applied to liquid samples of different alcohols (methanol, ethanol, 1-propanol and 2-propanol). Classifications were obtained in both cases independent of the X-ray source (synchrotron radiation or X-ray tube radiation), showing that the use of chemometric tools combined with X-ray spectrometry can efficiently distinguish organic samples by using scattering effects.     

Combining X-ray scattering with dielectric and calorimetric experiments for monitoring polymer crystallization

In order to understand nucleation; crystallization and other phase transitions in polymers, polymer based composites, or in liquid crystals simultaneous experiments with a combination of different methods are useful. Due to different sample geometry, contact faces with the sample holder, and thermal conditions it is usually difficult to compare the results of several individual experiments. As an important supplement to the classical techniques for studying crystallization like X-ray scattering, or differential scanning calorimetry, measurements which test molecular mobility like dielectric or mechanical spectroscopy are of interest during isothermal and non-isothermal crystallization. From such simultaneous experiments one can learn about the existence of pre-ordered structures before formation of crystals, as detected by DSC or X-ray scattering.In this contribution we present the development of a device for simultaneous measurements of electrical properties and X-ray scattering intensities, which was extended to a microcalorimeter and allows measuring thermal properties like heat capacity and thermal conductivity additionally at the same time and at the same sample volume.     

Resonant X-ray scattering studies of the B2 phase formed by bent-core molecules

We have performed resonant X-ray scattering on two bent-core liquid crystal compounds exhibiting the B2 phase using three sample geometries: free-standing film and two others with free surface arrangements. The results conclusively demonstrate the two-layer orientational periodicity in this phase suggested by optical studies. We have performed the first resonant scattering experiments on liquid crystals at the chlorine K-edge, opening up a new class of compounds for resonant X-ray scattering studies. Furthermore, we have achieved an excellent alignment of the B2 phase with a free surface.     

Resonant X-ray scattering studies of the B2 phase formed by bent-core molecules

We have performed resonant X-ray scattering on two bent-core liquid crystal compounds exhibiting the B2 phase using three sample geometries: free-standing film and two others with free surface arrangements. The results conclusively demonstrate the two-layer orientational periodicity in this phase suggested by optical studies. We have performed the first resonant scattering experiments on liquid crystals at the chlorine K-edge, opening up a new class of compounds for resonant X-ray scattering studies. Furthermore, we have achieved an excellent alignment of the B2 phase with a free surface.     

An X-ray refractive lens comprising two sections cut from a gramophone record for a portable total reflection X-ray fluorescence spectrometer

An X-ray refractive lens is assembled from two sections cut from a gramophone record. The refractive lens is placed in a portable total reflection X-ray fluorescence (TXRF) spectrometer, and it is used for collimation of the incident X-ray beams. A TXRF spectrum measured with the refractive lens is compared with that measured with a waveguide. Compared with the refractive lens, the waveguide enhances the intensities of the X-rays illuminating an analyte. Therefore, fluorescent X-ray intensities increase when using the waveguide. On the other hand, the vertical angular divergence of the incident X-ray beams is smaller when using the refractive lens, and the smaller angular divergence results in a reduction of the scattering of the incident X-rays from a sample holder. Therefore, the spectral background is reduced when using the refractive lens, resulting in an increase of the signal to background ratios of the fluorescent X-rays. Detection limits for 3d transition metals obtained with the refractive lens are sub-nanograms to a few nanograms, and the detection limits are similar to those obtained with the waveguide.     

Win X-ray: a new Monte Carlo program that computes X-ray spectra obtained with a scanning electron microscope.

A new Monte Carlo program, Win X-ray, is presented that predicts X-ray spectra measured with an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) operating between 10 and 40 keV. All the underlying equations of the Monte Carlo simulation model are included. By simulating X-ray spectra, it is possible to establish the optimum conditions to perform a specific analysis as well as establish detection limits or explore possible peak overlaps. Examples of simulations are also presented to demonstrate the utility of this new program. Although this article concentrates on the simulation of spectra obtained from what are considered conventional thick samples routinely explored by conventional microanalysis techniques, its real power will be in future refinements to address the analysis of sample classifications that include rough surfaces, fine structures, thin films, and inclined surfaces because many of these can be best characterized by Monte Carlo methods. The first step, however, is to develop, refine, and validate a viable Monte Carlo program for simulating spectra from conventional samples.