|Date||Host||Speaker||Title of the talk||Abstract|
||Filling the world with new light: Physics Nobel Prize 2014
U. of Florida
|Thermal Transport at Extreme Environments from Atomistic Simulation
thermal transport studies have explored rather conventional conditions
of temperature, pressure and irradiation. Extreme environments place
materials under conditions not usually encountered; the thermal
response under these conditions allows the better elucidation of the
physics of the various phenomena. While the conditions of high
temperature, high pressure and irradiation are interesting from a
fundamental perspective, they are also relevant technologically. For
example, irradiation effects are crucial for the understanding thermal
transport and therefore performance characteristics of nuclear fuels.
As another example, the high pressure and temperature conditions
present in the Earth’s interior greatly affect thermal conductivity of
the mantle and influence its heat balance and consequently evolution.
In this presentation, we will discuss how these conditions influence
thermal conductivity and demonstrate insights obtained with the
combination of the atomistic simulations techniques such as molecular
dynamics and lattice dynamics on the basis of classical potentials and
first principles methods.
||Handan Yildirim, Purdue U.
||Atomistic Scale Modeling of Materials for Applications in Electrochemical Energy Storage
electrochemical energy storage that would allow wider use of renewable
electricity requires new and advanced functional electrode materials to
be developed for Li ion batteries, as well as those beyond Li ion
technologies. This grand challenge places an ever-growing demand for
the design of efficient electrode materials, providing suitable
energetics and fast diffusion kinetics to enable far more efficient and
longer lifetimes for electrical energy storage devices. Therefore,
there have been substantial research efforts for developing advanced
materials with capabilities exceeding those of the current electrode
Accelerating the speed of discovery and the deployment of advanced functional materials will benefit from fundamental understanding of materials properties and behavior at long time and length scales, utilizing hierarchical modeling across the scales. Complementing the advanced characterization techniques, such predictive modeling and simulation offers an exciting possibility to provide fundamental atomistic level understanding, and accelerate the discovery of advanced materials for energy storage applications.
In this talk, I will present some examples of the computational studies of materials for electrochemical energy storage applications, in particular for Li ion batteries. Broad focus of these studies is to obtain atomistic level understanding of the processes and materials performances in Li ion battery environment. In particular, I will discuss the lithiation characteristics of negative electrode materials, promising role of nanostructured materials, the mechanism leading to the stability of negative electrode material under extreme condition, the feasibility of an engineered electrode material to store more Li, and ion diffusion characteristics in electrode materials. Finally, enabling computational modeling approaches and basic research needs for future Li ion battery design will be presented.
U. of Colorado Boulder
|Computational Design of New Materials for Energy Applications from First Principles
new functional material is a crucial scientific grand challenge. Most
currently used technology-critical materials were discovered by luck or
trial-and-error experiment, and then subsequently improved
incrementally over tens of years, at significant R&D cost. In this
talk, I will present how to design new materials for energy
applications by a more effective approach of “inverse design”: given a
set of target properties, predict the material that has them. This
approach, powered by theory that guides experiment, places
functionality first, and uses search and optimization strategies based
on first principles calculations. As an example, this talk will focus
on the inverse design of new earth-abundant thin-film photovoltaic
absorber materials, which are critical in realizing the promise of
thin-film solar cells for reducing the cost of sunlight-to-electricity
compared to conventional crystalline silicon. I will present our
recently developed novel selection metric of “Spectroscopic Limited
Maximum Efficiency”. This metric takes into account the leading physics
related to solar cell efficiency and goes beyond the commonly adopted
“Shockley-Queisser Limit Efficiency” that depends solely on material
band gap. Applying this metric to ternary chalcogenide (e.g., I-III-VI,
I-VI-VI) materials has identified a set of promising thin-film PV
absorber materials (e.g., CuSbS2 and Cu3SbS4). At last, I will
also discuss the research challenges and opportunities in materials
design for various applications.
Dean of Engineering & Computing, Missouri S&T
|Beyond Nano: Spinning; Dazed and Confused!
||Recent predictions of room
temperature ferromagnetism in transition metal doped wide bandgap
semiconductors such as GaN have spawned a great interest for their use
in the field of semiconductor-based spintronics. Spintronic devices
differ from traditional electronics in that they are based on the
electron spin instead of its charge. Both improved processing and
efficiency within existing devices, as well as novel functionalities
such as reconfigurable logic, nonvolatile chip-based memory, and a
solid state quantum computing may be possible within magnetic
semiconductor systems. If these devices can be implemented at room
temperature, they will advance the state of the art in spintronics and
create a new technological revolution similar to the invention of the
Dilute magnetic semiconductors (DMS), which consist of semiconductors doped with rare earth or transition metals to provide magnetic functionality, have been suggested to be a suitable platform for spintronics due to their inherent similarity and compatibility with the existing III-V material technological base. A number of novel features have been demonstrated in Ga1-xMnxAs, such as spin-polarized luminescence from light emitting diodes. Unfortunately the Curie temperature of Ga1-xMnxAs is much less that room temperature, making it unsuitable for practical room temperature spintronics.
Attention for room temperature spintronics has thus turned to the wide bandgap nitrides and oxides based on theoretical predictions of room temperature ferromagnetism in this system using a mean field approximation to the Zener model for carrier-mediated ferromagnetism. Reports of room temperature ferromagnetism in these materials are complicated by disparate crystalline quality and phase purity in these materials, as well as conflicting theoretical predictions as to the nature of ferromagnetic behavior in this system. It is not well understood whether the ferromagnetism derives from an intrinsic material property or from nano-scaled cluster distributions in the system. A complete understanding of these materials, and ultimately intelligent design of spintronic devices, will require an exploration of the relationship between the processing techniques, resulting transition metal atom configuration, defects, and electronic compensation as related to the structure, magnetic, and magneto-optical properties of this material.
In this presentation, we will review the current theoretical and experimental status of the transition metal doped nitrides and discuss their suitability for future spintronic applications. A series of GaN samples grown by metalorganic chemical vapor deposition doped with Mn, Fe, and Cr have been investigated. A comparison of the predominant theoretical models and predictions for ferromagnetism in the nitrides will be compared with the available literature for Ga1-xMnxN and GaN doped with other transition metals produced by a variety of techniques, including molecular beam epitaxy and ion implantation. In particular, the correlation of the structural, optical, and magnetic behavior will be analyzed in relation to theories of ferromagnetism in these materials. Recent results obtained on ferromagnetic nanostructures and Gd-doped GaN will also be reviewed. A spin-polarized LED with evidence for spin injection has been produced using GaGdN and the emission could be manipulated an external magnetic field.
||David J. Singh, Oak Ridge National Laboratory
are solid state energy conversion materials. They can be used to
produce electrical power from temperature differences and can also be
used for solid state refrigerators. They have been widely used in for
spacecraft power as well as a number of niche applications. There is
increasing interest in thermoelectric materials motivated in part by
recent progress and in part by the potential of these materials in
various energy technologies. Thermoelectric performance is a multiply
contra-indicated property of matter. For example, it requires (1) high
thermopower and high electrical conductivity, (2) high electrical
conductivity and low thermal conductivity and (3) low thermal
conductivity and high melting point. The keys to progress are finding
an optimal balance and finding ways of using complex electronic and
phononic structures to avoid the counter-indications mentioned above.
In this talk, I discuss some of the issues involved in the context of
recent results. One key aspect is optimization of the doping level in a
given thermoelectric material. While this has long been understood in
terms of standard semiconductor parabolic band models, we find
surprisingly different results for many thermoelectric materials when
the actual first principles band structures are used. This has led to
prediction of a number of useful thermoelectrics, some that are new,
and surprisingly some that are old. A key theme is the connection of
high thermoelectric performance with complex band structures. This
leads to the connection between thermoelectrics and topological
||Mark Lusk, Colorado School of Mines
||Energy Pooling Upconversion in Organic Molecular Systems
frequency of available light is often lower than desired for a given
task. For instance, low-energy light can take advantage of an optical
transparency window of biological tissue and penetrate to ingested
theranostic nanoparticles, but the photoactivated release of cancer
drugs requires energy in the UV range. Motivated by such disconnects
between the desired light and that available, a number of strategies
have been developed to upconvert light to higher frequencies. From the
perspectives of biocompatibility, environmental safety, expense, and
resource abundance, it would be advantageous to use organic materials
to carry out such processes.
This talk will consider one such upconversion process known as energy pooling in which the energy of two electrons in excited states is transferred to the third electron. The associated dynamics access virtual states to mediate upconversion; therefore, there is no residence time during which an excited state has the chance to lose energy to phonons.
A combination of molecular quantum electrodynamics, perturbation theory, and ab initio calculations was used to create a computational methodology capable of estimating the rate of energy pooling in organic molecular assemblies. The approach was applied to quantify the conditions under which such relaxation rates become meaningful for two test systems, stilbene−fluorescein and hexabenzocoronene−oligothiophene. Both exhibit low intramolecular conversion, but intermolecular configurations exist in which pooling efficiency is at least 90% when placed in competition with more conventional relaxation pathways. A set of design rules for the optimization of energy pooling will be discussed.
||Claudia Ojeda-Aristizabal, UC Berkeley
||Graphene : Quantum phenomena and layered heterostructures
the one atom thick layer of carbon, has opened a fruitful field of
research in condensed matter physics. Even today, ten years after its
discovery, graphene produces approximately ten thousand papers per
year. Having reached a suitable understanding of graphene’s fundamental
properties and applications, scientists are now turning their attention
to structures composed of different 2D crystals. Significant effort has
been put into the production of 2D crystals other than graphene,
ranging from thin insulators (like hexagonal boron nitride) to thin
semiconductors (like molybdenum disulfide). Combination of these
materials into structures named van der Waals heterostructures could
allow for the engineering of tunable phenomena at the interface.
In this talk, I will give an introduction to the Physics of graphene and I will describe two different quantum phenomena that can be observed in this two dimensional crystal: universal conductance fluctuations and superconducting proximity effect. I will present tunable phenomena that can be found at the interface between graphene and other materials like pentacene, a well-known organic semiconductor, and C₆₀, the 0 dimensional version of graphene. To conclude, I will expose layered materials that rest unexplored and layered heterostructures that can lead us to exciting Physics.
||Heng Pan, Mechanical Engineering
||Electronics Manufacturing with Laser Processing of Nanoscale Materials and Fundamentals
processing (heating, sintering, melting, crystallization and ablation)
of nanoscale materials has been extensively employed for electronics
manufacturing including both integrated circuit and emerging printable
electronics. This presentation will firstly review some recent
developments in this topic. It will then focus on fundamental transport
phenomena in laser annealing/crystallization. Many applications in
semiconductor devices require annealing step to fabricate high quality
crystalline domains on substrates that may not intrinsically promote
the growth of high crystalline films. Applications include thin film
transistors for advanced displays, high performance thin film solar
cells, 3D electronic devices, and memory devices, etc. Various energy
sources including scanning continuous wave (CW) lasers, electron beam
sources, graphite strip heaters, and pulsed lasers, have been utilized
to crystallize amorphous materials in thin film configurations.
Recently, the emergence of FinFETs (Fin-shaped Field Effect Transistor)
and 3D Integrated Circuits (3D-IC) has inspired the study of
crystallization of amorphous materials in nano/micro confined domains.
Using Molecular Dynamics (MD) simulation, we study the characteristics
of unseeded crystallization within nano/microscale confining domains.
It is demonstrated that unseeded crystallization can yield single
crystal domains facilitated by the confinement effects. The stochastic
nature of this process and the mechanisms leading to single crystal
formation are revealed. A phenomenological model has been developed and
tailored by MD simulations, which was applied to quantitatively
evaluate the effects of domain size and processing laser pulse width on
single crystal formation.
||44nd Annual Harold Q. Fuller Prize Colloquium