11 A.M. MONDAY, NOV. 17 - SCIENCE LIBRARY, ROOM 212
Cathy Wong, University of California, Berkeley
"Inter-molecular order at a hidden interface in a small-molecule organic semiconductor
Solution processing is required for the large-scale manufacture of small-molecule organic semiconductors and can result in crystalline domains with high charge mobility. However, the interfaces between these domains impede charge transport, degrading device performance. Although understanding these interfaces is essential to improve device performance, their intermolecular and electronic structure is unknown: they are smaller than the diffraction limit, are hidden from surface probe techniques and cannot be directly resolved using X-ray methods. We have used transient absorption microscopy to inspect a drop-cast thin film of 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene, a material cited for high hole mobility and singlet fission. The crystal and electronic structure of the domains has been characterized, but analogous information for the domain interfaces is unknown. Using a judicious selection of light polarization, we isolate a signal at the interface that is not observed in either of the adjacent bulk domains, exposing the exciton dynamics and inter-molecular structure of this hidden interface. Surprisingly, instead of finding an abrupt grain boundary, we reveal that the interface can be composed of nanoscale crystalline aggregates interleaved by a web of interfaces that compound decreases in charge mobility.
11 A.M. JULY 23, 2014 - CENTER OF EXCELLENCE SYMPOSIUM HALL
Marius Grundman, Leipzig University
"Bipolar oxide electronics - Materials and Devices"
Recent advances in the fabrication of oxide and transparent p-conducting thin films are reported. In conjunction with n-type epitaxial ZnO on Al2O3 and amorphous ZTO (zinc tin oxide) thin films, bipolar diodes with (by far) the highest rectification reported for oxide diodes are presented.
(i) p-type amorphous material derived from ZnCo2O4 spinel (ZCO)
ZCO has been deposited at room temperature using pulsed laser deposition. Hetero pn-diodes have been fabricated with rectification beyond 1010 and are stable for at least a year . JFETs with ZnO channel and p-type a-ZnCo2O4 gate exhibit on/off current ratio larger than 107 and low subthreshold slope of S = 91 mV/dec . Fully amorphous diodes from a-ZCO/a-ZTO exhibit rectification larger than 106 .
(ii) p-type zincblende cuprous iodide (CuI)
CuI is the first reported transparent conductive material . We have fabricated CuI thin films using iodization of copper thin films and direct thermal evaporation . We report epitaxial growth on ZnO(00.1) and NaCl(001). p-CuI/n-ZnO diodes exhibit rectification larger than 106 . We report on transparent photovoltaic cells from p- CuI/n-ZnO hetero-structure diodes . The device physics of type-II band alignment heterojunction diodes is discussed.
(iii) p-type amorphous nickel oxide (NiO)NiO is a well-known p-type oxide. a-NiO/ZnO
pn-diodes have been fabricated with rectification beyond 1010, also a diode with type-II
band alignment, exhibiting an ideality factor of 2. We report on (semi-)transparent
photovoltaic cells from such diodes .
11:30 A.M. DEC. 11, 2013 - SL-212
Richard Wilson, Argonne National Laboratory"Protactinium to Plutonium: Chemical
Periodicity in the Actinide Elements"The observed chemical behavior of the early actinide
elements, Th to Am, is exceptionally diverse in comparison to the lighter lanthanide
4f series of elements. This is typified by the multitude of accessible oxidation states
in the early actinide elements, trivalent to heptavalent, contrasting with the predominantly
trivalent behavior of the lanthanide elements. This rich chemistry can be traced to
the relative energetics of the valence orbitals, principally the 5f and 6d orbitals.
The 5f orbitals become stabilized relative to the 6d orbitals upon moving from thorium
across the series to americium. Importantly, the periodic stabilization of the 5f
orbitals relative to the 6d's results in a crossing of the orbitals' relative energies
at protactinium, the element between Th and U, making the chemical and spectroscopic
properties of Pa, and heavier actinides, of potentially critical importance for understanding
5f electronic structure and bonding. Understanding and quantifying the chemistry of
the actinide elements is paramount for developing nuclear energy technologies particularly
as is relates to the exceptionally complex systems encountered in the nuclear fuel
cycle. Recent results highlighting the effects of chemical periodicity on the early
actinide elements encompassing trends in coordination chemistry, structure and spectroscopic
properties will be presented.This work is funded by the U.S. DOE Early Career Research
Award program and was performed at Argonne National Laboratory for the U.S. DOE, OBES,
Division of Chemical Sciences, Geosciences, and Biosciences, under contract DE-AC02-06CH11357.
11:30 A.M. NOV. 6, 2014 - SL-212
Christopher Prince, marketing application engineer, GE Digital Energy
"Seeing the Forest for the Trees"
The title is an idiom to say "You're so busy focusing on the one tree that you don't realize there's a whole forest."' "You are looking with blinders on."; or "There is so much more than what you see." The power grid has so many complexities and inter-relations that it's easier to break the problem down to the "trees" – but addressing the "forest" can be missed. The policymakers, the regulatory agents and the technology vendors have discreet influencing factors on the "forest" – yet the utility serves as the caretaker for the "trees," the ward of the "forest" and the mediator to the consumers – who derive the value in the direct products of the trees and the indirect benefits of the forest.The title is a common and simple statement, yet not often used in the system engineering circles...let alone in the vernacular of the power grid. This presentation will present the fundamentals of the systems within an "organism" of supplying electrical power and then take a microscopic view to see the deeper and more extensive systemic relationships that must be considered to manage the most complex systems on the globe.The objective of this discussion is to discover the opportunities for solutions that provide benefits across the entire system in an industry that is 130 years old -- but never more crucial to mature and growing societies.
11:30 A.M. OCT. 23, 2013 - SL-212
Arumugam Manthiram, Joe C. Walter Chair in Engineering and Director of the Texas Materials
Institute and the Materials Science and Engineering Graduate Program, University of
Texas at Austin
"Materials Challenges and Prospects of Electrical Energy Storage"
11:30 A.M. OCT. 9, 2013 - SL-212 - CANCELED DUE TO THE GOVERNMENT SHUTDOWN
John Lemmon, Pacific Northwest National Laboratory
11 A.M. SEPT. 16, 2013 - SL-212
Stephen Whitelam, Molecular Foundy, Lawrence Berkeley National Laboratory
"Nanoscale self-assembly and phase change at surfaces and in confinement"
Many important physical processes happen at surfaces or in confinement. I will discuss two examples, the first being the self-assembly of molecules on surfaces, the second being nucleation in pores. In the first example, I will show how a combination of quantum mechanics and statistical mechanics allows us to identify the physics that governs the self-assembly of small organic molecules into nonperiodic networks on a gold surface. I will also show that the same physics governs assembly of networks formed by a set of apparently unlike building blocks, which range in size from atoms to micron-scale polymers. In the second example, I will discuss how to predict where in a heterogeneous porous medium nucleation will happen. In both examples, simple features of geometry are key to determining the behavior of the system in question.
NOON SEPT. 11, 2013 - SL-212
Ilias Belhaouek, Argonne National Laboratory
"Lithium-Sulfur: Current Status and Prospective"
The talk will review works on the room temperature lithium sulfur batteries since the year 2000. Namely, progresses in capacity, cycle life and efficiency of the cells will be discussed from science and engineering standpoints. The sulfur cathode in the Li-S battery offers superior theoretical capacity (1672 mAh.g-1) compared to all Li-ion battery cathodes. Li-S batteries have the advantages of using an abundant, nontoxic and low-cost cathode material. However, several performance-related issues prevent the development of practical Li-S batteries. These issues are rapid capacity fading and low coulombic efficiency, which are believed to be linked to the dissolution of lithium polysulfides from the sulfur electrode into the electrolyte. In this context, we will discuss our most recent results based on the development of a novel electrolyte that was designed to solve the cycling instability and inefficiency that are inherent to the Li-S battery. The new electrolyte consisted of lithium polysulfide species (Li2Sx) dissolved in dimethoxyethane solvent. This conceptually new approach is based on mitigating the sulfur loss by leveling the concentration gradient of the polysulfide species at the cathode/electrolyte interface. Therefore, when these species are produced at the cathode, they do not readily migrate into the electrolyte; instead, they are retained at the cathode interface.