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| Date | Host | Speaker | Title of the talk | Abstract |
| Sept. 1 | Hor | William Ratcliff NIST |
The Multiferroic Renaissance |
As early as 1894, Pierre Curie
found
that there were materials in which the magnetic and dielectric
properties were coupled. These magnetoelectric materials were
studied for some time, but the coupling was relatively weak.
Later, people studied multiferroic materials in which both spontaneous
ferroelectric and magnetic ordering occurs. In these
materials, the coupling could be much stronger, but the materials were
exceeding rare. Recently, several new compounds such as TbMnO3 have been discovered and the field has enjoyed a renaissance, culminating in the award of the 2010 James C. McGroddy Prize for New Materials for research on these compounds. During this talk, I will talk about the history of this field and the current state of the research. I will focus on one of the most technologically promising materials, BiFeO3 and the critical role neutron scattering has played in understanding the physics of these materials. |
| Sept. 8 | Hor |
Jay A. Switzer S&T |
Epitaxial electrodeposition of metal oxides for solid-state memory | As the size
of
nonvolatile memory continues to shrink, there is increasing demand for
highly scalable memory devices. An emerging technology is resistive
random access memory (RRAM) that is based on resistance switching in
materials such as transition metal oxides. Although electronic
materials are traditionally processed by physical vapor deposition
methods, we use electrodeposition to deposit candidate materials for
RRAM. Previously in our group we have shown that electrodeposition can
be used to produce epitaxial films of Cu2O, ZnO, Bi2O3, Fe3O4, Tl2O3,
PbO2, and CuO. In addition to epitaxial films, we have produced
nano-layered materials known as superlattices by pulsing the applied
potential during deposition. Besides the low cost of electrodeposition,
it also offers advantages such as the ability to deposit conformal
layers on nano-crossbar arrays. The materials only deposit onto
conducting elements that are electrically poised. The two materials we
have electrodeposited for RRAM applications are magnetite, Fe3O4, and
vanadium dioxide, VO2. Both of these materials undergo a
metal-to-insulator (MIT) phase transition that we utilize for
resistance switching. The MIT for Fe3O4 occurs at 120 K, and the MIT
for VO2 occurs at 341 K. Of the two materials, VO2 is the most
promising because it shows resistance switching at room temperature. |
| Sept. 15 | Hor |
Michael A.
McGuire Oak Ridge National Lab |
Iron
compounds in energy applications: superconductors, thermoelectrics, and
ferromagnets |
I will
present
recent results, primarily experimental, from several iron containing
materials. Our interest in these materials is motivated by their
relevance to energy applications. Over the past several years, work in
our group has focused heavily on iron-based superconductors, and
closely related compounds. I will give an overview of this relatively
new and active field, and discuss in some detail several of the
contributions in this area from Oak Ridge National Laboratory. In the
remainder of the presentation, I will address some recent work on the
thermoelectric material iron-silicide (FeSi), and the quest for better
permanent magnet materials that do not contain rare-earth
elements. |
| Sept. 22 | Hor | Alexey
Snezhko ANL |
Active
Materials: Self Assembly and Control Far-From-Equilibrium |
New
self-assembled materials composed of simple building blocks that
spontaneously organize into desired structures whose constituents can
assemble, disassemble, and reassemble autonomously or on command will
enable functional materials capable of self-repair, multi-tasking, and
even structure adjustment – set of properties currently exhibited only
by biological systems. To support this kind of structural complexity
and functional diversity these new self-assembled materials should rely
on an external energy intake and “live” outside of equilibrium.
Ensembles of interacting colloidal particles subject to an external
periodic forcing often develop nontrivial collective behavior. We study
emergent phenomena in magnetic colloidal ensembles suspended at
liquid-liquid or liquid-air interfaces and driven out of equilibrium by
alternating magnetic fields. Experiments reveal new types of
nontrivially ordered dynamic self-assembled structures (in particular,
“asters”, “snakes”, “clams”) emerging in such systems in a certain
range of excitation parameters. Transition between different
self-assembled phases with parameters of external driving magnetic
field is observed. Above certain frequency threshold dynamic self-assembled structures spontaneously break the symmetry of self-induced surface flows (symmetry breaking instability) and turn into swimmers. Induced self-propulsion of robust aster-like structures in a presence of small in-plane DC field perturbations has been discovered. A possibility of the directed cargo transport at the interface by self-assembled structures is demonstrated. Some features of the self-localized structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density. Molecular dynamic simulations capturing microscopic mechanisms of the non-equilibrium self-assembly in our system are presented. |
| Sept. 29 | Hor |
Eric Majzoub UMSL |
Thermodynamics
and Kinetics of Nano-cluster and Nano-confined Complex Hydrides |
The
equilibrium plateau pressure of a metal hydride at a given temperature
is a characteristic thermodynamic quantity, and determines the
application and engineering required for a hydrogen storage system.
While recent interest has focused on complex metal hydrides such as
NaAlH4 and Ca(BH4)2, these compounds are not as easily tunable as the
interstitial metallic hydrides through alloying with other metal atoms,
due to the strongly ionic character of the cohesive energy. However,
the complex hydrides are superior on a wt.% hydrogen basis, and are the
preferred materials for vehicular transport. In order to address
thermodynamic tunability, we investigate these materials at the
nanoscale, where the ratio of surface to bulk atoms impacts the
energetics. Recent theoretical work indicates that small clusters of
MgH2, for example, can significantly lower the desorption enthalpy with
respect to bulk. Small metal or hydride clusters may be incorporated
into nanoporous frameworks such as metal organic frameworks (MOFS),
block co-polymer (BCP) templates, or nanoporous hard carbons, for
example, to prevent agglomeration and perhaps even improve tunability
through particle/surface interactions. We present theoretical results
for desorption energetics of free nanoclusters of NaAlH4 as a function
of temperature and pressure. Prototype geometries for the clusters were
generated using a well-validated electrostatic ground state approach to
a global optimization of the cluster total energy using a recently
developed non-conventional Monte Carlo random walk in energy space.
First-principles density functional theory applied to the prototype
clusters was used for full free energy calculations of the clusters and
decomposition products. Results will be discussed with relation to
recent experimental work on incorporation of complex hydrides in
nanoporous framework materials, and the importance of the surface
chemistry of the frameworks. |
| Oct. 6 | Jentschura | Christian Schubert Universidad Michoacana de San Nicolás de Hidalgo |
Application of String Theory Concepts to Phenomenology | During the
last
fifteeen years, first-quantized path integral methods have emerged as a
viable, and sometimes superior, alternative to the standard approach in
quantum field theory based on second quantization and Feynman diagrams.
In this talk, I will first explain the history of this worldline path
integral approach, which goes back to Feynman but gained popularity
only through certain developments in string theory, and then present a
number of sample calculations, with an emphasis onquantum
electrodynamics. |
| Oct. 7 |
Hale |
Shawn
M. Kathmann PNNL |
Understanding the Chemical
Physics of Nucleation |
The
chemical physics of nucleation is currently of great interest to the
DOE because the new phase’s characteristics, such as catalytic,
electronic and optical properties, depend strongly on size, shape,
phase, mixing state, and composition. Subtle variations in interaction
potentials, excited states, free energetics, quantum nuclear degrees of
freedom, etc., can alter nucleation rates by many orders of magnitude
and thus motivate the need to understand their relative influences when
absolute accuracy remains intractable. Nucleation is complicated
because the condensing molecules configurations, bulk and interfacial
reactions, energy flow, electrochemistry, neutral and ionic
thermodynamics, and electronic structure must be considered and
adequately sampled. I will summarize our computational efforts toward
understanding the chemical physics of nucleation in aqueous systems
including: molecular interactions, reaction coordinates, phase space
sampling, computing rate constants, sensitivity analysis, anharmonic
effects, potentials of mean force, activation energies, and molecular
vs continuum treatments. Finally, a discussion of outstanding
challenges for future work will be presented. |
| Oct. 13 | Yamilov | Lihong Wang WashU |
Photoacoustic Tomography: Ultrasonically Breaking through the Optical Diffusion Limit | Photoacoustic tomography (PAT), combining optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale non-ionizing functional and molecular imaging. Light offers rich tissue contrast but does not penetrate biological tissue in straight paths as x-rays do. Consequently, high-resolution pure optical imaging (e.g., confocal microscopy, two-photon microscopy, and optical coherence tomography) is limited to depths within the optical diffusion limit (~1 mm in the skin). Ultrasonic imaging, on the contrary, provides good image resolution but suffers from poor contrast in early-stage tumors as well as strong speckle artifacts. In PAT, pulsed laser light penetrates the tissue and generates a small but rapid temperature rise, which induces emission of ultrasonic waves due to thermoelastic expansion. The ultrasonic waves, ~1000 times less scattering than optical waves in tissue, are then detected to form high-resolution images at depths up to 7 cm, breaking through the optical diffusion limit. Further depths can be reached by using microwaves or RF waves as the excitation source. PAT, embodied in the forms of scanning photoacoustic microscopy or photoacoustic computed tomography, is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs with consistent contrast. Such a technology has the potential to enable multiscale systems biology and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to the earliest detection of cancer by in vivo label-free quantification of hypermetabolism, the quintessential hallmark of cancer. The technology is commercialized by several companies. |
| Oct. 20 | Yamilov | Clifford
Will WashU |
The Confrontation between General Relativity and Experiment | We review the experimental evidence for Einstein's general relativity. Tests of the Einstein Equivalence Principle support the postulates of curved spacetime, while solar-system experiments strongly confirm weak-field general relativity. We discuss the results of the recently concluded Gravity Probe B experiment, and of observations of binary pulsar systems. Future tests of the theory in the radiative and strong-field regimes may be possible using gravitational-wave observatories on Earth and in space, and using observations of stars orbiting the central black hole in our galaxy. |
| Oct. 27 | ||||
| Nov. 3 | Yamilov |
Eighteenth Annual Laird D. Schearer Prize Competition | ||
| Nov. 10 | Yamilov |
|||
| Nov. 17 | Hor | Kim Fook Lee Michigan Technology University |
Optical
Quantum Technology for Communication, Imaging and Biophotonics |
Superposition
and entanglement are the foundations for quantum information
processing. One of the great challenges of quantum information science
is to develop tools to prepare and manipulate the quantum state of a
physical system. I will discuss the generation of high purity fiber
based entanglement source in telecom-band for practical quantum
communication such as entanglement distribution over a distance of 100
km in a WDM network environment. Generation of photon-pair in
silicon-on-insulator waveguide is also presented. I will talk about my
recent works of developing a new protocol based on weak coherent states
for quantum key generation [Phys. Rev. A 83, 030302(R) (2011)], optical
phase-space imaging through Kirkwood-Rihaczek distribution [Phys. Rev.
A 81, 063826 (2010)], and optical phase-space-time-frequency tomography
for biophotonics [Optics Express 19, 9352-9363 (2011).] |
| Dec. 1 | Dubois |
Jeff
Shinpaugh East Carolina University |