Norman M.R.,Argonne National Laboratory
Reviews of Modern Physics | Year: 2016
Quantum spin liquids form a novel class of matter where, despite the existence of strong exchange interactions, spins do not order down to the lowest measured temperature. Typically, these occur in lattices that act to frustrate the appearance of magnetism. In two dimensions, the classic example is the kagome lattice composed of corner sharing triangles. There are a variety of minerals whose transition metal ions form such a lattice. Hence, a number of them have been studied and were then subsequently synthesized in order to obtain more pristine samples. Of particular note was the report in 2005 by Dan Nocera's group of the synthesis of herbertsmithite, composed of a lattice of copper ions sitting on a kagome lattice, which indeed does not order down to the lowest measured temperature despite the existence of a large exchange interaction of 17 meV. Over the past decade, this material has been extensively studied, yielding a number of intriguing surprises that have in turn motivated a resurgence of interest in the theoretical study of the spin 1/2 Heisenberg model on a kagome lattice. This Colloquium reviews these developments and then discusses potential future directions, both experimental and theoretical, as well as the challenge of doping these materials with the hope that this could lead to the discovery of novel topological and superconducting phases. © 2016 American Physical Society.
Rozhkova E.A.,Argonne National Laboratory
Advanced Materials | Year: 2011
This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends. This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Ilavsky J.,Argonne National Laboratory
Journal of Applied Crystallography | Year: 2012
Nika is an Igor Pro-based package for correction, calibration and reduction of two-dimensional area-detector data into one-dimensional data (lineouts). It is free (although the user needs a paid license for Igor Pro), open source and highly flexible. While typically used for small-angle X-ray scattering (SAXS) data, it can also be used for grazing-incidence SAXS data, wide-angle diffraction data and even small-angle neutron scattering data. It has been widely available to the user community since about 2005, and it is currently used at the SAXS instruments of selected large-scale facilities as their main data reduction package. It is, however, also suitable for desktop instruments when the manufacturers software is not available or appropriate. Since it is distributed as source code, it can be scrutinized, verified and modified by users to suit their needs. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.
Kuzmenko I.,Argonne National Laboratory
Physical Review Letters | Year: 2010
We report a structural study of cholesterol-DPPC (1,2-dipalmitoyl-sn- glycero-3-phophocholine) monolayers using x-ray reflectivity and grazing incidence x-ray diffraction. Reflectivity reveals that the vertical position of cholesterol relative to phospholipids strongly depends on its mole fraction (χCHOL). Moreover, we find that at a broad range of χCHOL cholesterol and DPPC form alloylike mixed domains of short-range order and the same stoichiometry as that of the film. Based on the data presented, we propose a new model of cholesterol-phospholipid organization in mixed monolayers. © 2010 The American Physical Society.
Dauter Z.,Argonne National Laboratory
Acta Crystallographica Section D: Biological Crystallography | Year: 2013
There are currently no rules for a unified, standard way of placing macromolecular structures in the crystal lattice. An analysis of all possible symmetry-equivalent representations of molecular structures in various space groups leads to the concept of the anti-Cheshire symmetry and suggests that the center of a unique structural motif can always be placed within the selected asymmetric unit of the anti-Cheshire cell. The placement of structures according to this suggestion will ensure uniformity of presentation of all structurally equivalent Protein Data Bank models and will therefore diminish the possibility of confusing less crystallographically knowledgeable users of the PDB. The anti-Cheshire cells and their asymmetric units are defined and tabulated for all 65 space groups relevant to macromolecular crystallography that exhibit only rotational symmetry operations. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.
Snezhko A.,Argonne National Laboratory |
Aranson I.S.,Argonne National Laboratory
Nature Materials | Year: 2011
Self-assembled materials must actively consume energy and remain out of equilibrium to support structural complexity and functional diversity. Here we show that a magnetic colloidal suspension confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters, which exhibit locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, we show that asters can capture, transport, and position target microparticles. The ability to manipulate colloidal structures is crucial for the further development of self-assembled microrobots. © 2011 Macmillan Publishers Limited. All rights reserved.
Knope K.E.,Argonne National Laboratory |
Soderholm L.,Argonne National Laboratory
Chemical Reviews | Year: 2013
A study was conducted to demonstrate solution and solid-state structural chemistry of actinide hydrates and their hydrolysis and condensation products. The investigations focused on providing a detailed metrical description of a hydrated ion's coordination environment and how it changed as it further reacted with water through hydrolysis. The study emphasized on facilitating information transfer and comparisons between these two approaches to the same problem. It also focused on relating the metal-ligand correlated moieties and aggregates identified from thermodynamics with molecular level structures for which the theorist assessed the results. A number of An hydrates, mononuclear hydrolysis products, and polynuclear complexes were highlighted where polynuclear complexes resulted from metal-ion hydrolysis and condensation in aqueous and nonaqueous solution.
Liu G.,Argonne National Laboratory
Chemical Society Reviews | Year: 2015
Photon upconversion in rare earth activated phosphors involves multiple mechanisms of electronic transitions. Stepwise optical excitation, energy transfer, and various nonlinear and collective light-matter interaction processes act together to convert low-energy photons into short-wavelength light emission. Upconversion luminescence from nanomaterials exhibits additional size and surface dependencies. A fundamental understanding of the overall performance of an upconversion system requires basic theories on the spectroscopic properties of solids containing rare earth ions. This review article surveys the recent progress in the theoretical interpretations of the spectroscopic characteristics and luminescence dynamics of photon upconversion in rare earth activated phosphors. The primary aspects of upconversion processes, including energy level splitting, transition probability, line broadening, non-radiative relaxation and energy transfer, are covered with an emphasis on interpreting experimental observations. Theoretical models and methods for analyzing nano-phenomena in upconversion are introduced with detailed discussions on recently reported experimental results. This journal is © The Royal Society of Chemistry.
Back B.B.,Argonne National Laboratory |
Esbensen H.,Argonne National Laboratory |
Jiang C.L.,Argonne National Laboratory |
Rehm K.E.,Argonne National Laboratory
Reviews of Modern Physics | Year: 2014
In this review the main advances in heavy-ion fusion research that have taken place over the last decade are addressed. During this period, experimental studies have been extended to deep sub-barrier energies to reveal the unexpected phenomenon of fusion hindrance. The coupled-channels descriptions have been refined to include the effects of nucleon transfer and to account for the fusion hindrance in terms of the ion-ion potential in the strongly overlapping region. Substantial progress has been made in time-dependent Hartree-Fock theory to the point that this approach now can make parameter-free predictions of heavy-ion fusion excitation functions. As several heavy-ion fusion reactions are of crucial importance in late-stage giant-star evolution, these reactions continue to be studied with better experimental and theoretical tools in order to provide improved input to astrophysical models. The effects of loosely bound valence nucleons on the fusion cross sections are the focus of a number of experimental studies involving radioactive beams, which have only recently become available. And finally, as the active field of synthesizing superheavy elements relies on heavy-ion fusion to reach the nuclei of interest, it is important to understand the fusion dynamics that plays a crucial role in both the "cold-fusion" and "hot-fusion" approaches to the superheavy island of stability. Also this area has seen significant progress in several different approaches to the problem of predicting the cross sections for formation and survival of these rare nuclei. © 2014 American Physical Society.
Jiang Z.,Argonne National Laboratory
Journal of Applied Crystallography | Year: 2015
GIXSGUI is a MATLAB toolbox that offers both a graphical user interface and script-based access to visualize and process grazing-incidence X-ray scattering data from nanostructures on surfaces and in thin films. It provides routine surface scattering data reduction methods such as geometric correction, one-dimensional intensity linecut, two-dimensional intensity reshaping etc. Three-dimensional indexing is also implemented to determine the space group and lattice parameters of buried organized nanoscopic structures in supported thin films. © 2015 International Union of Crystallography.