Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D19: Focus Session: Grazing Incidence Scattering and New Imaging Techniques |
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Sponsoring Units: DPOLY Chair: Marcus Cicerone, National Institute of Standards and Technology Room: 320 |
Monday, March 16, 2009 2:30PM - 3:06PM |
D19.00001: Probing kinetics and dynamics of nanocomposites with grazing-incidence small-angle x-ray scattering. Invited Speaker: Synthesizing complex nanocomposites and superstructures is of great interest in all areas of materials science and involving biology, chemistry, physics and engineering applications such as the fabrication of novel electronic, magnetic, and photonic devices. Since the entire synthesis and assembly process can take place far from equilibrium conditions, a controlled process has to be guided by a thorough understanding of the kinetics and dynamics in the composites. This requires measurement of the structure in situ and in real time with subnanometer spatial resolution and millisecond to subsecond temporal resolution. As an increasingly important structural-characterization technique, grazing-incidence small-angle x-ray scattering (GISAXS) finds vast applications in the research of nanostructures and nanocomposites at surfaces and interfaces. Most significantly, as a complementary method to conventional surface-sensitive tools such as scanning probe microscopy and electron microscopy, GISAXS can be used in situ and in real time to monitor the formation of the nanostructure or nanocomposite, which makes it most suitable for studying the kinetics of nanoassembly processes. The GISAXS technique can also be an integral part of numerous research, for example, those involving kinetics of mesoscaled ordered block copolymer thin films, kinetics of sol-gel processes, quantum dots, nanoparticles in ultrathin films, and dynamics and phase transitions 2D nanocrystal superlattices. Here, I will focus on the applications of GISAXS in real-time structure characterization, the dynamics in polymer/nanoparticle nanocomposies, and the challenges to elucidate nanostructure formation in nanoscience and nanotechnology. [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:18PM |
D19.00002: Single beam approach for GISAXS Byeongdu Lee, Chieh-Tsung Lo, Pappannan Thiyagarajan, Zhongwei Niu, Qian Wang The multiple scattering effects present in the grazing incidence small-angle x-ray scattering (GISAXS) data are addressed theoretically as well as experimentally with measurement of a series of patterns at different incident angles, referred to as ``incident-angle-resolved GISAXS'' (IAR-GISAXS). We found that under certain conditions, it is possible to extract the correct structural features of the materials from the GISAXS data using the kinematic SAXS formalisms assuming a single beam, without the need to use the distorted wave Born approximation (DWBA) to account for the scattering by the reflected beam. Furthermore, the Kiessig fringes in GISAXS enable the measurement of average distance between the particle and the substrate, similar to the measurement of film thickness using the fringes in the x-ray reflectivity data. We believe that the methods developed here will expand the application of GISAXS as they enable the use of model-independent and kinematic SAXS theories to nanostructured 2D-ordered films. [Preview Abstract] |
Monday, March 16, 2009 3:18PM - 3:30PM |
D19.00003: Surface Dynamics of Free PS Chains on Chemically Identical Polymer Brushes: An XPCS Study Gokce Ugur, Bulent Akgun, Zhang Jiang, Suresh Narayanan, William J. Brittain, Mark D. Foster We found no relaxation of fluctuations of the brush surfaces within the range of time (0.2 -1100 s) and length scale (0.6-3 um) studied by X-ray photon correlation spectroscopy(XPCS). This is true for PS brushes of thicknesses of 9 - 101 nm and grafting density of 0.12-0.6 chains/nm$^{2}$ at temperatures up to 130C above bulk T$_{g}$. Results on the dynamics of a layer of untethered 2.2k PS chains on top of a PS brush surface show that placing the PS chains atop the brush dramatically slows down the surface relaxations of the film surface. As the ratio of the thickness of the layer of untethered chains to the thickness of the highly dense brush drops below $\sim $0.5, the surface relaxations become too slow to be observed readily with XPCS. Reducing grafting density of the underlying brush markedly slows the surface dynamics. The surface dynamics of the layer of ``free'' PS chains are coupled with those of the underlying brush. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D19.00004: X-ray Standing Wave Studies of Stability and Dynamics in Poly(4-bromostyrene)/Poly(4-vinylpyridine) Thin Films Yan Sun, Kenneth Shull, Jin Wang The thermodynamic stability and wetting behavior in systems consisting of two or three distinct layers of polymeric thin films have been investigated with atomic force microscopy (AFM) and x-ray standing waves (XSW) generated via total external reflection from an x-ray mirror. We have probed the structural evolution of thin poly(4-bromostyrene) (PBrS) films with various degrees of bromination, prepared on top of a poly(4-vinylpyridine) (P4VP) layer whose dynamics is influenced by its interaction with the underlying substrate and couples to that of PBrS. The addition of a top poly(styrene) (PS) layer was also used in some cases. The samples were subjected to annealing treatments above the polymer glass transition temperatures. Reflectivity and x-ray fluorescence from bromine markers in the PBrS layer were tracked. Dewetting of the PS occurred with sufficient annealing time, though the results suggest that this proceeded faster with low PBrS bromination. AFM studies on the PBrS/P4VP system revealed a clear PBrS thickness dependence on the dewetting morphology and dynamics of this layer. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 4:18PM |
D19.00005: Quantitative electron tomography and its application to polymer nanostructures Invited Speaker: The transmission electron microtomography (TEMT) is a powerful tool to visualize three-dimensional (3D) structures in many fields of materials science. Recently, researchers are trying not only to visualize 3D nano-structures but also to quantify them in order to seek a possible correlation between the 3D structures and materials' properties. However, one of the serious problems that prohibit TEMT from truly quantitative 3D images is the ``missing wedge'' in the Fourier space that is caused by the limitation of angular range available in transmission electron microscopes (TEM). Please note that the computerized tomography (CT), on which TEMT is based, requires projections from entire tilt angles, i.e. $\pm$90$^{\circ}$. Thus, the most faithful tactics for the CT is to tilt specimen over $\pm$90$^{\circ}$. In order to realize such requirement, a rod-shaped ZrO$_2$/polymer nano-composite whose diameter is ca. 150 nm was attached at the tip of a specially modified specimen holder without any supporting film. A complete set of tomograms has been generated for the first time from the 181 projections that were taken over the angular range of $\pm$90$^{\circ}$. One of the structural parameters characterizing the nano-composite, a volume fraction of ZrO$_2$, $\varphi$, was measured as a function of the maximum tilt angle, $\alpha$. It was found that $\varphi$ was in excellent agreement with the known volume fraction of ZrO2 when $\alpha$=90$^{\circ}$, i.e., $\pm$90$^{\circ}$ tilt, while $\varphi$ increased with decreasing $\alpha$. When $\alpha$=60$^{\circ}$ that is a typical maximum tilt angle, the measured $\varphi$ was larger by 20$\sim$30\% than the true value. In addition to the above TEMT experimental technique, some applications of TEMT to polymer nano-structures will be presented at the conference time. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D19.00006: Three-dimensional subwavelength imaging with phase-less power extinction tomography. Alexander A. Govyadinov, George Y. Panasyuk, John C. Schotland Modern near-field methods extend the spatial resolution of optical microscopes beyond the classical diffraction limit. However the majority of these methods only recover two-dimensional maps of optical intensity near the sample surface. The interpretation of these maps for manifestly inhomogeneous samples has been proven to be problematic. Here we derive an analytical technique which allows unique subwavelength 3D reconstruction of both real and imaginary parts of susceptibility of an inhomogeneous sample. Our technique is based upon the solution to the linearized near-field inverse scattering problem arising in the sample -- near-field tip system. The proposed approach requires neither phase measurements nor control over the phase of illuminating fields. The reconstruction is based on simple measurements of the power extinguished from illuminating waves in the total internal reflection mode and is intrinsically nondestructive. [Preview Abstract] |
Monday, March 16, 2009 4:30PM - 4:42PM |
D19.00007: Helium ion microscopy and its application to organic materials Steven Hudson, Andras Vladar, Bin Ming Helium ion microscopy (HeIM) is a new scanning probe microscopy that uses a He$^{+}$ ion beam. This microscope has improved resolution and depth of field in comparison to SEM, as demonstrated through imaging of metal particles. Organic materials, including patterned polyelectrolyte multilayers and organic semiconductor crystals, have also been imaged. The surface sensitivity, image contrast and qualitative secondary electron yield have been evaluated, in an effort to understand beam/specimen interactions and compare them with electron beam/sample interactions. [Preview Abstract] |
Monday, March 16, 2009 4:42PM - 4:54PM |
D19.00008: Robust Tips for High Resolution Chemical Imaging Carlos Barrios, Andrey Malkovskiy, Alexander Kisliuk, Alexei Sokolov, Mark Foster Tip enhanced Raman spectroscopy (TERS) combines scanning probe microscopy with Raman spectroscopy, taking advantage of apertureless near-field optics. A plasmonic structure at the apex of a sharp tip provides signal amplification required for chemical imaging. Plasmonic structure characteristics such as roughness, shape, and radius determine the spatial resolution and signal enhancement. Unfortunately, noble metal nanostructures have limited lifetimes due to mechanical, chemical, and thermal degradation. Lifetime extension requires slowing degradation processes while minimizing unfavorable influences on the optical response. An ultrathin SiO$_{x}$ protective coating provides lifetime improvement of silver plasmonic nanostructures on SPM tips. Controlled physical vapor deposition (PVD) of Al can be used to create ultrathin ($\sim $2-3 nm) Al$_{2}$O$_{3}$ coatings that improve significantly the stability and wear resistance of plasmonics structures without substantial degradation of optical properties. Such a coating completely prevented decay in plasmonic activity after 40 days of use. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:06PM |
D19.00009: Broadband CARS microscopy Marcus Cicerone, Joung Lee, Yeon Ho Kim, Sapun Parekh Coherent anti-Stokes Raman scattering (CARS) microscopy has exciting potential for rapid chemical imaging of materials and noninvasive imaging of biological systems, both in-vivo, and as these systems interact with materials. Although CARS is as much as 10$^{6}$ times more sensitive that spontaneous Raman scattering, it is accompanied by a nonresonant background (NRB) signal which can mask the resonant signal of interest. This background is generally of sufficient amplitude to make chemical imaging of biological systems difficult or impossible. We will present recent advances made in our lab, both experimental and in numerical data recovery, towards ameliorating the negative aspects of the NRB and facilitating non-invasive chemical microscopy for cell-material interactions. [Preview Abstract] |
Monday, March 16, 2009 5:06PM - 5:18PM |
D19.00010: Intensity Fluctuations of Optical Microscopy as a Means to Measure Axial Diffusion Malvika Bihari, Thomas Russell, David Hoagland Via optical microscopy, geometrically hindered motions of a single large solute (particle or polymer) can be imaged in real time. Here, intensity fluctuations of confocal fluorescence microscopy admit another way to probe such motions, one convenient when motions are perpendicular to a planar substrate. The focal plane is positioned within the substrate (lying on the microscope stage) and intensity fluctuations arise from motions in-and out- of the focal volume. Two experiments illustrate the new approach, diffusion within pores of a planar membrane or in solution near a solid wall. In the first, diffusion coefficients of spherical particles were measured inside pores of a track-etched polycarbonate membrane as functions of particle and pore size. In the second, anisotropic diffusion (perpendicular/parallel) of the same particles was measured within a few particle diameters of a solid boundary. Theory for hydrodynamically hindered diffusion in both cases is well developed, and data are compared to predictions. Two ways to assess particle/polymer motion, tracking single particles and correlating intensity fluctuations, will be discussed. [Preview Abstract] |
Monday, March 16, 2009 5:18PM - 5:30PM |
D19.00011: Three-Dimensional Imaging of Polymeric Nanostructures by Molecular Switching in Far Field Fluorescence Microscopy Chaitanya Ullal, Roman Schmidt, Alexander Egner, Benjamin Harke, Jan Keller, Douglas Adamson, Lars Kastrup, Stefan Hell Morphological studies of self assembled polymeric structures with length scales of interest below 100 nm have typically been conducted either by scattering-based techniques or electron and scanning probe microscopes. These techniques, however, do not provide easy access to truly 3D-structural information. In contrast, Far-field optical methods retain the advantage of simultaneously providing local, dynamic, and \textit{in situ} three-dimensional (3D) structural information. The diffraction limited resolution of its standard variants, however, restricts the minimum feature size that can be examined. We exploit molecular transitions of the fluorophores to circumvent the diffraction barrier and demonstrate the power of emerging far-field fluorescence microscopy with nanoscale resolution for the study of self-assembly. We simultaneously improve both the lateral ($x$,$y)$ and the axial ($z)$ resolution of stimulated emission depletion (STED) microscopy. The increased 3D resolution is used to unambiguously map the morphology of self assembled polymeric nanostructures in a facile manner. [Preview Abstract] |
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