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Evanston, IL, United States

Hong Y.P.,Northwestern University | Gleber S.-C.,Argonne National Laboratory | O'Halloran T.V.,Northwestern University | Que E.L.,Northwestern University | And 5 more authors.
Journal of Synchrotron Radiation | Year: 2014

X-ray fluorescence nanotomography provides unprecedented sensitivity for studies of trace metal distributions in whole biological cells. Dose fractionation, in which one acquires very low dose individual projections and then obtains high statistics reconstructions as signal from a voxel is brought together (Hegerl & Hoppe, 1976), requires accurate alignment of these individual projections so as to correct for rotation stage runout. It is shown here that differential phase contrast at 10.2 keV beam energy offers the potential for accurate cross-correlation alignment of successive projections, by demonstrating that successive low dose, 3 ms per pixel, images acquired at the same specimen position and rotation angle have a narrower and smoother cross-correlation function (1.5 pixels FWHM at 300 nm pixel size) than that obtained from zinc fluorescence images (25 pixels FWHM). The differential phase contrast alignment resolution is thus well below the 700 nm × 500 nm beam spot size used in this demonstration, so that dose fractionation should be possible for reduced-dose, more rapidly acquired, fluorescence nanotomography experiments.© 2014 International Union of Crystallography. Source


Young K.L.,Northwestern University | Ross M.B.,Northwestern University | Blaber M.G.,Northwestern University | Rycenga M.,Northwestern University | And 7 more authors.
Advanced Materials | Year: 2014

Epsilon-near-zero behavior and an optically metallic response are predicted using electrodynamics simulations in superlattices comprising silver nanoparticles. Programmable DNA-mediated assembly is used to synthesize both silver and binary silver-gold nanoparticle superlattices, which are characterized using small-angle X-ray scattering, transmission electron microscopy, and elemental mapping. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Hoel C.A.,Northwestern University | Buchholz D.B.,220 Campus Drive | Chang R.P.H.,220 Campus Drive | Poeppelmeier K.R.,Northwestern University
Thin Solid Films | Year: 2012

Thin films of corundum-type In 2 - 2xZn xSn xO 3 (cor-ZITO) were grown on lattice-matched substrates using pulsed laser deposition. The (001) of the corundum-type film grew heteroepitaxial to the (001) of a LiNbO 3 substrate with large grains along the in-plane and out-of-plane orientation characterized by glancing incidence X-ray diffraction and four-circle Φ-scans. A film with 34% In (metals basis) exhibited a wide optical gap of 3.9 eV and a modest conductivity of 134 S/cm, which suggests cor-ZITO is a potential low-cost transparent conducting oxide. © 2011 Elsevier B.V. All rights reserved. Source


Tsai W.-W.,Northwestern University | Tevis I.D.,Northwestern University | Tayi A.S.,220 Campus Drive | Cui H.,220 Campus Drive | And 2 more authors.
Journal of Physical Chemistry B | Year: 2010

Conjugated organic molecules can be designed to self-assemble from solution into nanostructures for functions such as charge transport, light emission, or light harvesting. We report here the design and synthesis of a novel hairpin-shaped self-assembling molecule containing electronically active sexithiophene moieties. In several nonpolar organic solvents, such as toluene or chlorocyclohexane, this compound was found to form organogels composed of nanofibers with uniform diameters of 3.0 (±0.3) nm. NMR analysis and spectroscopic measurements revealed that the self-assembly is driven by π-π interactions of the sexithiophene moieties and hydrogen bonding among the amide groups at the head of the hairpin. Field effect transistors built with this molecule revealed p-type semiconducting behavior and higher hole mobilities when films were cast from solvents that promote self-assembly. We propose that hydrogen bonding and π-π stacking act synergistically to create ordered stacking of sexithiophene moieties, thus providing an efficient pathway for charge carriers within the nanowires. The nanostructures formed exhibit unusually broad absorbance in their UV-vis spectrum, which we attribute to the coexistence of both H and J aggregates from face-to-face π-π stacking of sexithiophene moieties and hierarchical bundling of the nanowires. The large absorption range associated with self-assembly of the hairpin molecules makes them potentially useful in light harvesting for energy applications. © 2010 American Chemical Society. Source

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