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1.  Advanced grazing-incidence techniques for modern soft-matter materials analysis 
IUCrJ  2015;2(Pt 1):106-125.
Advanced grazing-incidence techniques have developed significantly during recent years. With the ongoing progress in instrumentation, novel methods have emerged which allow for an in-depth morphology characterization of modern soft-matter materials. Examples are in situ and in operando grazing-incidence small-angle X-ray scattering (GISAXS), micro- and nanofocused GISAXS, time-of-flight (TOF) grazing-incidence small-angle neutron scattering (GISANS) and surface-sensitive resonant soft X-ray scattering techniques, including the potential to investigate polarization. Progress in software for data analysis is another important aspect.
The complex nano-morphology of modern soft-matter materials is successfully probed with advanced grazing-incidence techniques. Based on grazing-incidence small- and wide-angle X-ray and neutron scattering (GISAXS, GIWAXS, GISANS and GIWANS), new possibilities arise which are discussed with selected examples. Due to instrumental progress, highly interesting possibilities for local structure analysis in this material class arise from the use of micro- and nanometer-sized X-ray beams in micro- or nanofocused GISAXS and GIWAXS experiments. The feasibility of very short data acquisition times down to milliseconds creates exciting possibilities for in situ and in operando GISAXS and GIWAXS studies. Tuning the energy of GISAXS and GIWAXS in the soft X-ray regime and in time-of flight GISANS allows the tailoring of contrast conditions and thereby the probing of more complex morphologies. In addition, recent progress in software packages, useful for data analysis for advanced grazing-incidence techniques, is discussed.
PMCID: PMC4285885  PMID: 25610632
grazing-incidence techniques; GISAXS; GIWAXS; resonant soft X-ray scattering; GISANS; morphology; soft matter
2.  Structural rearrangements in a lamellar diblock copolymer thin film during treatment with saturated solvent vapor 
Macromolecules  2010;43(1):418-427.
We have investigated the structural changes in thin films of lamellar poly(styrene-b-butadiene) diblock copolymers during treatment with saturated cyclohexane vapor, a solvent slightly selective for polybutadiene. Using real-time, in-situ grazing-incidence small-angle X-ray scattering (GISAXS), the swelling and the rearrangement of the lamellae were investigated with a time resolution of a few seconds, and the underlying processes on the molecular level were identified. After a few minutes in vapor, a transient state with a more well-defined and more long-range ordered lamellar orientation was encountered. Additional parallel lamellae formed which we attribute to the increased degree of coiling of the polymers in the swollen state. Eventually, the film became disordered. These changes are attributed to the increased mobility of the swollen polymers and the gradually decreasing segment-segment interaction parameter in the film as solvent is absorbed.
PMCID: PMC2841441  PMID: 20305742
polymer physics; diblock copolymers; thin films; grazing-incidence small-angle X-ray scattering
3.  A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS 
Journal of Applied Crystallography  2013;46(Pt 4):874-881.
Three-dimensional reciprocal space mapping by X-ray and electron diffraction [namely grazing-incidence X-ray diffraction (GIXD), reflection high-energy electron diffraction (RHEED) and grazing-incidence small-angle X-ray scattering (GISAXS)] was used to explore the internal structure and shape of differently oriented epitaxial Co/CaF2 facetted nanoparticles.
In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.
PMCID: PMC3769055  PMID: 24046491
cobalt-on-fluorite nanoparticles; grazing-incidence X-ray diffraction (GIXD); reflection high-energy electron diffraction (RHEED); grazing-incidence small-angle X-ray scattering (GISAXS); epitaxial growth; three-dimensional reciprocal space mapping
4.  Characterization of Lipid-Templated Silica and Hybrid Thin Film Mesophases by Grazing Incidence Small-Angle X-ray Scattering 
The nanostructure of silica and hybrid thin film mesophases templated by phospholipids via an evaporation-induced self-assembly (EISA) process was investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Diacyl phosphatidylcholines with two tails of 6 or 8 carbons were found to template 2D hexagonal mesophases, with the removal of lipid from these lipid/silica films by thermal or UV/O3 processing resulting in a complete collapse of the pore volume. Monoacyl phosphatidylcholines with single tails of 10–14 carbons formed 3D micellular mesophases; the lipid was found to be extractable from these 3D materials, yielding a porous material. In contrast to pure lipid/silica thin film mesophases, films formed from the hybrid bridged silsesquioxane precursor bis(triethoxysilyl)ethane exhibited greater stability toward (both diacyl and monoacyl) lipid removal. Ellipsometric, FTIR, and NMR studies show that the presence of phospholipid suppresses siloxane network formation, while actually promoting condensation reactions in the hybrid material. 1D X-ray scattering and FTIR data were found to be consistent with strong interactions between lipid headgroups and the silica framework.
PMCID: PMC2736351  PMID: 19496546
5.  Grazing-incidence small-angle X-ray scattering: application to the study of quantum dot lattices 
The modelling of grazing-incidence small-angle X-ray scattering (GISAXS) from three-dimensional quantum dot lattices is described.
The ordering of quantum dots in three-dimensional quantum dot lattices is investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Theoretical models describing GISAXS intensity distributions for three general classes of lattices of quantum dots are proposed. The classes differ in the type of disorder of the positions of the quantum dots. The models enable full structure determination, including lattice type, lattice parameters, the type and degree of disorder in the quantum dot positions and the distributions of the quantum dot sizes. Applications of the developed models are demonstrated using experimentally measured data from several types of quantum dot lattices formed by a self-assembly process.
PMCID: PMC3243409  PMID: 22186289
grazing-incidence small-angle X-ray scattering; GISAXS; quantum dot lattices; self-assembly
6.  Combined evaluation of grazing incidence X-ray fluorescence and X-ray reflectivity data for improved profiling of ultra-shallow depth distributions☆ 
Spectrochimica Acta. Part B  2014;99(100):121-128.
The continuous downscaling of the process size for semiconductor devices pushes the junction depths and consequentially the implantation depths to the top few nanometers of the Si substrate. This motivates the need for sensitive methods capable of analyzing dopant distribution, total dose and possible impurities. X-ray techniques utilizing the external reflection of X-rays are very surface sensitive, hence providing a non-destructive tool for process analysis and control.
X-ray reflectometry (XRR) is an established technique for the characterization of single- and multi-layered thin film structures with layer thicknesses in the nanometer range. XRR spectra are acquired by varying the incident angle in the grazing incidence regime while measuring the specular reflected X-ray beam. The shape of the resulting angle-dependent curve is correlated to changes of the electron density in the sample, but does not provide direct information on the presence or distribution of chemical elements in the sample.
Grazing Incidence XRF (GIXRF) measures the X-ray fluorescence induced by an X-ray beam incident under grazing angles. The resulting angle dependent intensity curves are correlated to the depth distribution and mass density of the elements in the sample. GIXRF provides information on contaminations, total implanted dose and to some extent on the depth of the dopant distribution, but is ambiguous with regard to the exact distribution function.
Both techniques use similar measurement procedures and data evaluation strategies, i.e. optimization of a sample model by fitting measured and calculated angle curves. Moreover, the applied sample models can be derived from the same physical properties, like atomic scattering/form factors and elemental concentrations; a simultaneous analysis is therefore a straightforward approach. This combined analysis in turn reduces the uncertainties of the individual techniques, allowing a determination of dose and depth profile of the implanted elements with drastically increased confidence level.
Silicon wafers implanted with Arsenic at different implantation energies were measured by XRR and GIXRF using a combined, simultaneous measurement and data evaluation procedure. The data were processed using a self-developed software package (JGIXA), designed for simultaneous fitting of GIXRF and XRR data. The results were compared with depth profiles obtained by Secondary Ion Mass Spectrometry (SIMS).
•The parameter optimization by curve fitting uses differential evolution (an evolutionary algorithm).•Implantation profiles are modeled by using the Pearson distribution system.•The implant distribution profile is discretized to allow calculation similar to a layered sample.•Total implanted dose, implantation depth and profile shape can be determined nondestructively.
PMCID: PMC4152003  PMID: 25202165
GIXRF; XRR; Ultra-shallow junctions; Ultra-shallow implants
7.  New approach for structural characterization of planar sets of nanoparticles embedded into a solid matrix 
Scientific Reports  2013;3:3414.
In this work we demonstrate that Medium Energy Ion Scattering (MEIS) measurements in combination with Transmission Electron Microscopy (TEM) or Grazing Incidence Small Angle X-Ray Scattering (GISAXS) can provide a complete characterization of nanoparticle (NP) systems embedded into dielectric films. This includes the determination of the nanoparticle characteristics (location, size distribution and number concentration) as well as the depth distribution and concentration of the NP atomic components dispersed in the matrix. Our studies are performed considering a model case system consisting of planar arrangements of Au NPs (size range from 1 to 10 nm) containing three distinct Au concentrations embedded in a SiO2 film.
PMCID: PMC3849636  PMID: 24301257
8.  Reversible Morphology Control in Block Copolymer Films via Solvent Vapor Processing: An In Situ GISAXS study 
Macromolecules  2010;43(9):4253-4260.
The real time changes occurring within films of cylinder-forming poly(α-methylstyrene-block-4-hydroxystyrene) (PαMS-b-PHOST) were monitored as they were swollen in tetrahydrofuran (THF) and acetone solvent vapors. In situ information was obtained by combining grazing incidence small angle X-ray scattering (GISAXS) with film thickness monitoring of the solvent vapor swollen films. We show that for self assembly to occur, the polymer thin film must surpass a swollen thickness ratio of 212% of its original thickness when swollen in THF vapors and a ratio of 268% for acetone vapor annealing. As the polymer becomes plasticized by solvent vapor uptake, the polymer chains must become sufficiently mobile to self assemble, or reorganize, at room temperature. Using vapors of a solvent selective to one of the blocks, in our case PHOST-selective acetone, an order-order transition occured driven by the shift in volume fraction. The BCC spherical phase assumed in the highly swollen state can be quenched by rapid drying. Upon treatment with vapor of a non-selective solvent, THF, the film maintained the cylindrical morphology suggested by its dry-state volume fraction. In situ studies indicate that self-assembly occurs spontaneously upon attaining the threshold swelling ratios.
PMCID: PMC2992440  PMID: 21116459
9.  Scherrer grain-size analysis adapted to grazing-incidence scattering with area detectors 
Journal of Applied Crystallography  2009;42(Pt 6):1030-1034.
Various aspects of the application of the Scherrer formula to grain-size analysis in thin films of soft materials are discussed within the methodology of grazing-incidence small- and wide-angle scattering and in conjunction with the use of area detectors.
Ever since its formulation, the Scherrer formula has been the workhorse for quantifying finite size effects in X-ray scattering. Various aspects of Scherrer-type grain-size analysis are discussed with regard to the characterization of thin films with grazing-incidence scattering methods utilizing area detectors. After a brief review of the basic features of Scherrer analysis, a description of resolution-limiting factors in grazing-incidence scattering geometry is provided. As an application, the CHESS D1 beamline is characterized for typical scattering modes covering length scales from the molecular scale to the nanoscale.
PMCID: PMC2779741  PMID: 19953189
Scherrer formula; grazing-incidence small-angle scattering (GISAXS); grazing-incidence wide-angle scattering (GIWAXS); thin films; soft materials
10.  Solid-State Nanostructured Materials from Self-Assembly of a Globular Protein-Polymer Diblock Copolymer 
ACS nano  2011;5(7):5697-5707.
Self-assembly of three-dimensional solid-state nanostructures containing approximately 33% by weight globular protein is demonstrated using a globular protein-polymer diblock copolymer, providing a route to direct nanopatterning of proteins for use in bioelectronic and biocatalytic materials. A mutant red fluorescent protein, mCherryS131C, was prepared by incorporation of a unique cysteine residue and site-specifically conjugated to end-functionalized poly(N-isopropylacrylamide) through thiol-maleimide coupling to form a well-defined model protein-polymer block copolymer. The block copolymer was self-assembled into bulk nanostructures by solvent evaporation from concentrated solutions. Small-angle X-ray scattering and transmission electron microscopy illustrated the formation of highly disordered lamellae or hexagonally perforated lamellae depending upon the selectivity of the solvent during evaporation. Solvent annealing of bulk samples resulted in a transition towards lamellar nanostructures with mCherry packed in a bilayer configuration and a large improvement in long range ordering. Wide-angle X-ray scattering indicated that mCherry did not crystallize within the block copolymer nanodomains and that the β-sheet spacing was not affected by self-assembly. Circular dichroism showed no change in protein secondary structure after self-assembly, while UV-vis spectroscopy indicated approximately 35% of the chromophore remained optically active.
PMCID: PMC4059825  PMID: 21696135
self-assembly; block copolymer; mCherry; PNIPAM; bioconjugation
11.  Limited-Angle X-ray Luminescence Tomography: Methodology and Feasibility Study 
Physics in medicine and biology  2011;56(12):3487-3502.
X-ray Luminescence Tomography (XLT) has recently been proposed as a new imaging modality for biological imaging applications. This modality utilizes phosphor nanoparticles which luminesce near-infrared light when excited by X-ray photons. The advantages of this modality are that it uniquely combines high sensitivity of radioluminescent nanoparticles and high spatial localization of collimated X-ray beams. Currently, XLT has been demonstrated using X-ray spatial encoding to resolve the imaging volume. However, there are applications where the X-ray excitation may be limited by geometry, where increased temporal resolution is desired, or where a lower dose is mandatory. This paper extends the utility of XLT to meet these requirements by incorporating a photon propagation model into the reconstruction algorithm to recover dimensions remaining in an X-ray limited angle (LA) geometry. This enables such applications as image-guided surgery, where the ability to resolve lesions at depths of several centimeters can be the key to successful resection. The hybrid X-ray/diffuse optical model is first formulated and then demonstrated in a breast-sized phantom, simulating a breast lumpectomy geometry. Both numerical and experimental phantoms are tested, with lesion-simulating objects of various sizes and depths. Results show localization accuracy with median error of 2.2mm, or 4% of object depth, for small 2–14mm-diameter lesions positioned from 1cm to 4.5cm in depth. This compares favorably with fluorescence optical imaging, which is not able to resolve such small objects at this depth. The recovered lesion size has lower size-bias in the X-ray excitation direction than the optical direction, which is expected due to the increased optical scatter. However, the technique is shown to be quite invariant in recovered size with respect to depth, as the standard deviation is less than 2.5mm. Sensitivity is a function of dose; radiological doses are found to provide sufficient recovery for μg/ml concentrations, while therapy dosages provide recovery for ng/ml concentrations. Experimental phantom results agree closely with the numerical results, with positional errors recovered within 8.6% of the effective depth for a 5mm object, and within 5.2% of the depth for a 10mm object. Object size median error is within 2.3% and 2% for the 5mm and 10mm objects, respectively. For shallow-to-medium depth applications where optical and radio-emission imaging modalities are not ideal, such as in intra-operative procedures, LAXLT may be a useful tool to detect molecular signatures of disease.
PMCID: PMC4132056  PMID: 21606553
12.  Application of small-angle X-ray scattering for differentiation among breast tumors 
Small-angle X-ray scattering (SAXS) is an X-ray diffraction-based technique where a narrow collimated beam of X-rays is focused onto a sample and the scattered X-rays recorded by a detector. The pattern of the scattered X-rays carries information on the molecular structure of the material. As breast cancer is the most widespread cancer in women and differentiation among its tumors is important, this project compared the results of coherent X-ray scattering measurements obtained from benign and malignant breast tissues. The energy-dispersive method with a setup including X-ray tube, primary collimator, sample holder, secondary collimator and high-purity germanium (HpGe) detector was used. One hundred thirty-one breast-tissue samples, including normal, fibrocystic changes and carcinoma, were studied at the 6° scattering angle. Diffraction profiles (corrected scattered intensity versus momentum transfer) of normal, fibrocystic changes and carcinoma were obtained. These profiles showed a few peak positions for adipose (1.15 ± 0.06 nm−1), mixed normal (1.15 ± 0.06 nm−1 and 1.4 ± 0.04 nm−1), fibrocystic changes (1.46 ± 0.05 nm−1 and 1.74 ± 0.04 nm−1) and carcinoma (1.55 ± 0.04 nm−1, 1.73 ± 0.06 nm−1, 1.85 ± 0.05 nm−1). We were able to differentiate between normal, fibrocystic changes (benign) and carcinoma (malignant) breast tissues by SAXS. However, we were unable to differentiate between different types of carcinoma.
PMCID: PMC2786093  PMID: 20041048
Breast tumor; coherent scattering; small-angle X-ray scattering
13.  Morphology and photoluminescence study of titania nanoparticles 
Colloid and Polymer Science  2011;289(8):943-953.
Titania nanoparticles are prepared by sol–gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol–gel components—hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer—are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol–gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13–20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies.
PMCID: PMC3102206  PMID: 21765580
Titania; μGISAXS; Sol–gel; PL; DSSC
14.  X-ray based tools for the investigation of buried interfaces in organic electronic devices 
Organic Electronics  2013;14(2):479-487.
Graphical abstract
► We fabricated orthogonal soluble polymer stacks and probed the buried interface by X-ray reflectivity. ► Depending on the used solvent of the organic semiconducting material the interface morphology changed significantly. ► Grazing incidence X-ray diffraction exhibits the molecule alignment in the investigated polymer stack. ► The buried interface roughness within the polymer stack was correlated to the OTFT performance containing the stack.
X-ray reflectivity combined with grazing incidence diffraction is a valuable tool for investigating organic multilayer structures that can be used in devices. We focus on a bilayer stack consisting of two materials (poly-(3-hexylthiophene)) (P3HT) and poly-(4-styrenesulfonic acid) (PSSA) spin cast from orthogonal solvents (water in the case of PSSA and chloroform or toluene for P3HT). X-ray reflectivity is used to determine the thickness of all layers as well as the roughness of the organic–organic hetero-interface and the P3HT surface. The surface roughness is found to be consistent with the results of atomic force microscopy measurements. For the roughness of P3HT/PSSA interface, we observe a strong dependence on the solvent used for P3HT deposition. The solvent also strongly impacts the texturing of the P3HT crystallites as revealed by grazing incidence diffraction. When applying the various PSSA/P3HT multilayers in organic thin-film transistors, we find an excellent correlation between the determined interface morphology, structure and the device performance.
PMCID: PMC3608035  PMID: 23565069
X-ray reflectivity; Buried interface morphology; Organic thin film transistor; Grazing incidence X-ray diffraction; Atomic force microscopy; Mobility enhancement
15.  Controlling Morphology and Molecular Packing of Alkane Substituted Phthalocyanine Blend Bulk Heterojunction Solar Cells† 
Systematic changes in the exocyclic substiution of core phthalocyanine platform tune the absorption properties to yield commercially viable dyes that function as the primary light absorbers in organic bulk heterojunction solar cells. Blends of these complementary phthalocyanines absorb a broader portion of the solar spectrum compared to a single dye, thereby increasing solar cell performance. We correlate grazing incidence small angle x-ray scattering structural data with solar cell performance to elucidate the role of nanomorphology of active layers composed of blends of phthalocyanines and a fullerene derivative. A highly reproducible device architecture is used to assure accuracy and is relevant to films for solar windows in urban settings. We demonstrate that the number and structure of the exocyclic motifs dictate phase formation, hierarchical organization, and nanostructure, thus can be employed to tailor active layer morphology to enhance exciton dissociation and charge collection efficiencies in the photovoltaic devices. These studies reveal that disordered films make better solar cells, short alkanes increase the optical density of the active layer, and branched alkanes inhibit unproductive homogeneous molecular alignment.
PMCID: PMC3624905  PMID: 23589766
16.  A customizable software for fast reduction and analysis of large X-ray scattering data sets: applications of the new DPDAK package to small-angle X-ray scattering and grazing-incidence small-angle X-ray scattering 
Journal of Applied Crystallography  2014;47(Pt 5):1797-1803.
DPDAK is a software for simple and fast on- and offline reduction and analysis of X-ray scattering data. It is an open-source software with a plug-in structure allowing tailored extensions.
X-ray scattering experiments at synchrotron sources are characterized by large and constantly increasing amounts of data. The great number of files generated during a synchrotron experiment is often a limiting factor in the analysis of the data, since appropriate software is rarely available to perform fast and tailored data processing. Furthermore, it is often necessary to perform online data reduction and analysis during the experiment in order to interactively optimize experimental design. This article presents an open-source software package developed to process large amounts of data from synchrotron scattering experiments. These data reduction processes involve calibration and correction of raw data, one- or two-dimensional integration, as well as fitting and further analysis of the data, including the extraction of certain parameters. The software, DPDAK (directly programmable data analysis kit), is based on a plug-in structure and allows individual extension in accordance with the requirements of the user. The article demonstrates the use of DPDAK for on- and offline analysis of scanning small-angle X-ray scattering (SAXS) data on biological samples and microfluidic systems, as well as for a comprehensive analysis of grazing-incidence SAXS data. In addition to a comparison with existing software packages, the structure of DPDAK and the possibilities and limitations are discussed.
PMCID: PMC4180741  PMID: 25294982
small-angle X-ray scattering; grazing-incidence small-angle X-ray scattering; data reduction; data analysis; computer programs
17.  Raman spectroscopy explores molecular structural signatures of hidden materials in depth: Universal Multiple Angle Raman Spectroscopy 
Scientific Reports  2014;4:5308.
Non-invasive 3D imaging in materials and medical research involves methodologies such as X-ray imaging, MRI, fluorescence and optical coherence tomography, NIR absorption imaging, etc., providing global morphological/density/absorption changes of the hidden components. However, molecular information of such buried materials has been elusive. In this article we demonstrate observation of molecular structural information of materials hidden/buried in depth using Raman scattering. Typically, Raman spectroscopic observations are made at fixed collection angles, such as, 90°, 135°, and 180°, except in spatially offset Raman scattering (SORS) (only back scattering based collection of photons) and transmission techniques. Such specific collection angles restrict the observations of Raman signals either from or near the surface of the materials. Universal Multiple Angle Raman Spectroscopy (UMARS) presented here employs the principle of (a) penetration depth of photons and then diffuse propagation through non-absorbing media by multiple scattering and (b) detection of signals from all the observable angles.
PMCID: PMC4058876  PMID: 24930768
18.  Self-Assembly and Thermal Stability of Binary Superlattices of Gold and Silicon Nanocrystals 
The journal of physical chemistry letters  2013;4(21):10.1021/jz401964s.
Simple hexagonal (sh) AB2 binary superlattices (BSLs) of organic ligand-capped silicon (A; 5.40(±9.8%) nm diameter) and gold (B; 1.88(±10.1%) nm diameter) nanocrystals were assembled by evaporation of colloidal dispersions and characterized using transmission electron microscopy (TEM) and grazing incidence small-angle X-ray scattering (GISAXS). When deposited on tilted substrates by slow evaporation, the sh-AB2 superlattice contracts slightly towards the substrate with centered orthorhombic structure. Heating the BSL to 200°C in air led to gold coalescence and segregation to the surface of the assembly without disrupting the Si nanocrystal sublattice, thus creating a simple hexagonal superlattice of Si nanocrystals.
PMCID: PMC3855828  PMID: 24327828
Si nanocrystal; Monodisperse; Binary superlattice; colloids; self-assembly
19.  Non-resonant Mie scattering: Emergent optical properties of core-shell polymer nanowires 
Scientific Reports  2014;4:4607.
We provide the in-depth characterization of light-polymer nanowire interactions in the context of an effective Mie scattering regime associated with low refractive index materials. Properties of this regime sharply contrast with these of resonant Mie scattering, and involve the formation of strictly forward-scattered and coupling-free optical fields in the vicinity of core-shell polymer nanowires. Scattering from these optical fields is shown to be non-resonant in nature and independent from incident polarization. In order to demonstrate the potential utility of this scattering regime in one-dimensional (1D) polymeric nanostructures, we fabricate polycarbonate (PC) - polyvinylidene difluoride (PVDF) core-shell nanowires using a novel iterative thermal drawing process that yields uniform and indefinitely long core-shell nanostructures. These nanowires are successfully engineered for novel nanophotonics applications, including size-dependent structural coloration, efficient light capture on thin-film solar cells, optical nano-sensors with ultrahigh sensitivity and a mask-free photolithography method suitable for the straightforward production of 1D nanopatterns.
PMCID: PMC3980223  PMID: 24714206
20.  Experimental verification of T-matrix-based inverse light scattering analysis for assessing structure of spheroids as models of cell nuclei 
Applied optics  2009;48(10):D20-D25.
Inverse light scattering analysis (ILSA) seeks to associate measured scattering properties with the most probable theoretical scattering distribution, making it a useful tool for assessing structure in biological materials. The accuracy of ILSA depends on the compatibility of the light scattering geometry with the light scattering model. In this study, we compare the accuracy obtained when analyzing light scattering data from spheroids using a numerical implementation of Mie theory, and the T matrix, a numerical method of solving light scattering from spheroids. Our experimental data are acquired using novel optical phantoms containing spheroidal scatterers and angle-resolved low-coherence interferometry, a depth- and angle-resolved light scattering measurement modality. The results show that Mie theory can accurately assess spheroidal structure despite the geometric incompatibility provided measurements are taken in multiple orientations of the sample relative to the incident polarization and the measured scattering angle. In comparison, analysis using the T-matrix method is highly accurate and more reliable yet requires measurements from only a single orientation.
PMCID: PMC2840713  PMID: 19340110
21.  Orienting Periodic Organic-Inorganic Nanoscale Domains Through One-Step Electrodeposition 
ACS nano  2010;5(1):565-573.
One of the challenges in the synthesis of hybrid materials with nanoscale structure is to precisely control morphology across length scales. Using a one-step electrodeposition process on indium tin oxide (ITO) substrates followed by annealing, we report here the preparation of materials with preferentially oriented lamellar domains of electron donor surfactants and the semiconductor ZnO. We found that either increasing the concentration of surfactant or the water to dimethyl sulfoxide ratio of solutions used resulted in the suppression of bloom-like morphologies and enhanced the density of periodic domains on ITO substrates. Furthermore, by modifying the surface of the ITO substrate with the conductive polymer blend poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), we were able to alter the orientation of these electrodeposited lamellar domains to be perpendicular to the substrate. The long-range orientation achieved was characterized by 2D grazing incidence small angle X-ray scattering. This high degree of orientation in electronically active hybrids with alternating nanoscale p-type and n-type domains is of potential interest in photovoltaics or thermoelectric materials.
PMCID: PMC3127581  PMID: 21142087
electrodeposition; lamellar; Zinc Oxide; Zinc Hydroxide; hybrid; nanoscale; orientation; alignment
22.  Myelin Organization in the Nodal, Paranodal, and Juxtaparanodal Regions Revealed by Scanning X-Ray Microdiffraction 
PLoS ONE  2014;9(7):e100592.
X-ray diffraction has provided extensive information about the arrangement of lipids and proteins in multilamellar myelin. This information has been limited to the abundant inter-nodal regions of the sheath because these regions dominate the scattering when x-ray beams of 100 µm diameter or more are used. Here, we used a 1 µm beam, raster-scanned across a single nerve fiber, to obtain detailed information about the molecular architecture in the nodal, paranodal, and juxtaparanodal regions. Orientation of the lamellar membrane stacks and membrane periodicity varied spatially. In the juxtaparanode-internode, 198–202 Å-period membrane arrays oriented normal to the nerve fiber axis predominated, whereas in the paranode-node, 205–208 Å-period arrays oriented along the fiber direction predominated. In parts of the sheath distal to the node, multiple sets of lamellar reflections were observed at angles to one another, suggesting that the myelin multilayers are deformed at the Schmidt-Lanterman incisures. The calculated electron density of myelin in the different regions exhibited membrane bilayer profiles with varied electron densities at the polar head groups, likely due to different amounts of major myelin proteins (P0 glycoprotein and myelin basic protein). Scattering from the center of the nerve fibers, where the x-rays are incident en face (perpendicular) to the membrane planes, provided information about the lateral distribution of protein. By underscoring the heterogeneity of membrane packing, microdiffraction analysis suggests a powerful new strategy for understanding the underlying molecular foundation of a broad spectrum of myelinopathies dependent on local specializations of myelin structure in both the PNS and CNS.
PMCID: PMC4077703  PMID: 24984037
23.  Double-Gyroid Network Morphology in Tapered Diblock Copolymers 
Macromolecules  2011;44(10):3910-3915.
We report the formation of a double-gyroid network morphology in normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b- styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 volume percent of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semi-batch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (TODT’s) of the network-forming tapered block copolymers were depressed when compared to the TODT of their non-tapered counterpart, with the P(I-SI-S) showing the greater drop in TODT. These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the TODT, while maintaining the ability to form complex network structures.
PMCID: PMC3119550  PMID: 21709811
self-assembly; network; gyroid; block copolymer; tapered copolymer; tapered block copolymer; anionic polymerization; order-disorder transition; nanostructure
24.  Tricontinuous Cubic Nanostructure and Pore Size Patterning in Mesostructured Silica Films Templated with Glycerol Monooleate 
The fabrication of nanostructured films possessing tricontinuous minimal surface mesophases with well-defined framework and pore connectivity remains a difficult task. As a new route to these structures, we introduce glycerol monooleate (GMO) as a template for evaporation-induced self-assembly. As deposited, a nanostructured double gyroid phase is formed, as indicated by analysis of grazing-incidence small-angle x-ray scattering data. Removal of GMO by UV/O3 treatment or acid extraction induces a phase change to a nanoporous body-centered structure which we tentatively identify as based on the IW-P surface. To improve film quality, we add a co-surfactant to the GMO in a mass ratio of 1:10; when this co-surfactant is cetyltrimethylammonium bromide, we find an unusually large pore size (8-12 nm) in acid extracted films, while UV/O3 treated films yield pores of only ca. 4 nm. Using this pore size dependence on film processing procedure, we create a simple method for patterning pore size in nanoporous films, demonstrating spatially-defined size-selective molecular adsorption.
PMCID: PMC3091003  PMID: 21572556
Evaporation-induced self assembly; porous films; tricontinuous phases; gyroid; glycerol monooleate; grazing-incidence small-angle X-ray scattering; film patterning
25.  Small-Angle X-ray Scattering of Reduced Ribonuclease A: Effects of Solution Conditions and Comparisons with a Computational Model of Unfolded Proteins 
Journal of molecular biology  2008;377(5):1576-1592.
The disulfide-reduced form of bovine ribonuclease A (RNAse A), with the Cys thiols irreversibly blocked, was characterized by small-angle x-ray scattering (SAXS). To help resolve the conflicting results and interpretations from previous studies of this model unfolded protein, scattering profiles were measured using a range of solution conditions and were compared with the profiles predicted by a computational model for a random-coil polypeptide. Analysis of the simulated and experimental profiles reveals that scattering intensities at intermediate angles, corresponding to interatomic distances in the range of 5–20 Å, are particularly sensitive to changes in solvation and can be used to assess the internal scaling behavior of the polypeptide chain, expressed as a mass fractal dimension, Dm. This region of the scattering curve is also much less sensitive to experimental artifacts than is the very small angle regime (the Guinier region) that has been more typically used to characterize unfolded proteins. The experimental SAXS profiles closely matched those predicted by the computational model assuming relatively small solvation energies. The scaling behavior of the polypeptide approaches that of a well solvated polymer under conditions where it has a large net charge and at high urea concentrations. At lower urea concentrations and neutral pH, the behavior of the chain approaches that expected for θ-conditions, where the effects of slightly unfavorable interactions with solvent balance those of excluded volume, leading to scaling behavior comparable to that of an idealized random walk chain. Though detectable, the shift towards more compact conformations at lower urea concentrations does not correspond to a transition to a globule state and is associated with little or no reduction in conformational entropy. This type of collapse, therefore, is unlikely to reduce greatly the conformational search for the native state.
PMCID: PMC2651769  PMID: 18329044
Ribonuclease A; unfolded proteins; small-angle x-ray scattering; scaling laws; fractal dimension; solvation energy

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