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Friday, April 8th, 2011 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A
light lunch will be served at 11:45 a.m. Eric I. Altman Professor of Chemical and Environmental Engineering,
Yale University Formation
of Alkaline Earth Template Layers for Oxide Epitaxy on Semiconductors: Surface
Alloying and Self- Organization Oxide epitaxy with abrupt interfaces on
Si and Ge(100) surfaces is a promising route towards integrating new
functionality such as non-volatile transistors, chemical sensors, and magnetic
devices into traditional semiconductor devices. All successful oxide eptiaxy on these surfaces has required
the initial formation of an alkaline earth template layer. To understand how this layer promotes
oxide epitaxy while inhibiting oxidation of the underlying semiconductor, we
have been using scanning tunneling microscopy (STM) complemented by electron
diffraction and density functional theory (DFT) to characterize the formation
of the template layer on the atomic scale. The results reveal a complex series of phase transitions as
Sr or Ba are deposited onto Ge(100).
Interestingly, each phase transition is accompanied by drastic changes
in the surface morphology that can only be explained by mass transfer induced
by formation of an alloy surface.
Through comparison of the bias dependence of atomic-resolution images
with DFT predictions of the image contrast, structural models of two of the
surface alloy phases have been deduced.
Incorporation of the larger alkaline earth atoms into the surface
creates stress that is ultimately relieved by the formation of remarkably
well-ordered arrays of trenches on the surface. The alloy formation mechanism leads to double-height steps
on the surface, resulting in unidirectional trenches extending thousands of Angstroms. Simon Mochrie Professor of Physics and Applied
Physics, Yale University String
Theory with Charges--- Forced Unravelling of DNA Toroids When a charged semiflexible polymer
interacts with multivalent counterions, the polymer-counterion complex
undergoes collapse to form a toroidal condensate. This phenomenon has been
observed for DNA complexed with a wide variety of counterions, with the
possibility of engineering cation-condensed toroidal DNA for
non-viral gene therapy being a driver in several cases. Nature exploits
DNA condensation via positively-charged proteins extensively: Eukaryotic cells
package DNA via histone proteins, leading to the superhelical chromatin 30
nm-fiber; In spermatozoa, protamines give rise to a DNA-protein complex that
shows toroidal structure, in which the DNA is ten-fold more condensed than in
somatic nucleii; DNA condensation via positively-charged proteins may
facilitate DNA assembly into viral capsids; etc. Here, we
present single-molecule measurements of the forced unravelling of DNA
superhelices induced by exposure to histone protein H1. By averaging multiple
pull-relax cycles, we have determined the force-versus-extension relation
of the complex, revealing the existence of discrete states, distinguished by
the number of turns in the toroid. We have applied Crooks' fluctuation theorem
to establish the free energies of the states observed using the measured
force-versus-extension curves, which permits us to experimentally determine the
complete six-state free energy landscape of the superhelical DNA-H1 toroid. We
also compare our experimental measurements of the force and the free energy
landscape to the predictions of a simple theoretical model.
Friday, March 25th, 2011 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A
light lunch will be served at 11:45 a.m. Tarek Fahmy Associate Professor of Biomedical
Engineering and Chemical & Engineering, Yale
University Close Encounters of the T Cell Kind Abstract The immune
system is made up of a complex network of molecules and cells that can screen
its own components, protect itself, and attack invaders such as bacteria and
viruses. Immune system malfunction can lead to pathogenesis of many
common chronic and autoimmune disease, and even progression of cancer.
Nanomaterials can be engineered in ways that can rectify functional responses
of these cells and detect their presence in health and disease. An
attractive feature of these synthetic systems is that they can be ÔtunedÕ in
predictable, designable ways to optimize detection of cellular function for
fast immunodiagnostics or used to manipulate the magnitude and direction of an
immune response for immunotherapy
Udo Schwartz Professor of Mechanical
and Chemical Engineering, Yale University Friction Revisited: From Atomically Resolved Lateral Forces to
Scaling Laws for Superlubric Sliding Abstract Even after centuries of research, the atomic origins of friction are
still poorly understood. Therefore, new tools have been introduced in the last
three decades that allow novel aspects and systems to be investigated. In an
introductory part, we show how scanning force microscopy-based methods offer
insight into the origins of friction by visualizing lateral forces with atomic
resolution. Once the basic
mechanism is understood, we can transition from individual atoms to assembling
larger and larger contact areas. When
atomically flat model interfaces are prepared in ultrahigh vacuum, we surprisingly find two
coexisting frictional states: While some contacts show ÒnormalÓ levels of
friction that increase linearly with size, others exhibit extraordinarily low
friction values. Analysis suggests that this
state is due to superlubricity, a theoretically predicted state where lattice
mismatch at the interface causes a decrease of shear stress with increasing
contact area.
Friday, February 25th, 2011 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A
light lunch will be served at 11:45 a.m. Minjoo Larry Lee Assistant Professor of
Electrical Engineering, Yale University
New Directions in Self-Assembled Quantum Dots Self-assembled
quantum dots (SAQDs) are being actively explored for applications ranging from
telecommunication to quantum optics on a chip. In this talk, I will present
some recent results from two projects in my group that may take SAQDs into new
territory. First, I will discuss my group's demonstration of the growth and
electroluminescence of InGaAs SAQDs on GaP substrates. Photoluminescence from
these SAQDs has been observed from 14-300K, and we have recently demonstrated
transparent-substrate red LEDs based on them. Since GaP has a similar lattice
structure and atomic spacing to Si, we believe that our InGaAs/GaP SAQDs may
represent a new path to integrated laser sources for Si photonics. Next, I will
discuss our efforts to understand and exploit the coupled effects of strain and
surface orientation on self-assembly. While the vast majority of SAQD research
has been done on (001) substrates, the strain-driven self-assembly process on
(110) and (111) surfaces appeared until recently to be fundamentally hindered.
By understanding strain relaxation behavior as a function of the sign and
direction of applied strain, our group has demonstrated control over
self-assembly on both the (110) and (111)A surfaces of GaAs. Some future areas
of study will be suggested.
Assistant Professor of Chemical and Environmental Engineering, Yale University High Performance Bulk Metallic Glass Nanowires for Direct Alcohol Fuel Cell Applications Fuel cells were once championed as viable alternatives
over existing battery technology for portable electronic devices; however, a
key remaining issue is the meager performance of these devices due to poor
efficiency and durability of the catalysts. Developing a new class of materials
that can circumvent Pt-based anode poisoning and the agglomeration/dissolution
of supported catalysts during long-term operation is of critical importance.
Here we report a CMOS compatible approach using Pt58Cu15Ni5P22
bulk metallic glass (BMG) to create a new class of high performance nanowire
catalysts for fuel cells. Friday, January 28th, 2011 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A
light lunch will be served at 11:45 a.m. Eugenio Culurciello Associate Professor
Electrical Engineering, Yale University
Synthetic Eyes, Vision, and Tools to Reverse Engineer the Brain
from the E-Lab Team @ Yale A Douglas Stone Carl A. Morse Professor of Applied Physics and Physics, Yale University Coherent Perfect Absorbers and Interferometric Control of Absorption in Lossy Media Friday, November 19th, 2010 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A
light lunch will be served at 11:45 a.m. Xiaoming Wang Department of Electrical Engineering Advisor: Professor Haller Aqueous
Phase Reforming over Carbon Nanotube Supported Catalysts Rebecca Milot Department of Chemistry Advisor: Professor Schmuttenmaer ÒUsing Terahertz Spectroscopy to Study
Systems with Solar Energy Applications Megan Mauter Department
of Chemical Engineering Advisor: Professor Elimelech ÒAligned Nanocomposite Thin-Films for Water
and Energy Applications Yuncheng Song Department of Electrical Engineering Advisor: Professor Lee ÒSelf-assembled In0.5Ga0.5As quantum dots
on GaP Weihua Guan Department of Electrical Engineering Advisor: Professor Reed ÒNon-vanishing ponderomotive AC electrophoretic (ACEP) force
for particle trapping Friday, September 24th, 2010 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A light lunch will be served at 11:45
a.m. Fred J.
Sigwortth Prof. Dept. of Cellular and Molecular Physiology, Dept.
of Biomedical Engineering Yale School of Medicine Protein
Structures from Electron Microscopy Charles T. Black Scientist and
Group Leader for Electronic Nanomaterials Center for
Functional Nanomaterials, Brookhaven National Laboratory Enabling
Nanotechnology Research at the Center for Functional Nanomaterials Friday, April 30, 2010 Noon to 1:00 p.m. 9 Hillhouse Avenue – Mason Lab 107 A light lunch will be served at 11:45
a.m. Jennifer A. Hollingsworth Los Alamos National Laboratory Chemistry Division and
Center for Integrated Nanotechnologies Novel Functional Semiconductor Nanocrystal
Quantum Dots and Nanowires for Applications Involving Energy Conversion To advance the state-of-the-art in the use of nanoparticles
as functional building blocks for next-generation optoelectronic and
photovoltaic devices, both new types of active nanomaterials and new
synthesis/assembly approaches are needed. Here, I describe an overview of our
efforts to address the former by (1) developing novel functional nanoscale
Òarchitectures that greatly expand the utility of colloidal semiconductor
nanocrystal quantum dots (NQDs) for light emission applications and (2)
developing new approaches for the fabrication and ordering of anisotropic semiconductor nanomaterials,
known as quantum- or nanowires (NWs), for light harvesting applications. Specifically, I describe a functionally new class of NQD,
the so-called giant NQD (g-NQD), that, due to its unique physical and
electronic nanoscale architecture, exhibits unusual and useful photophysics for
light-emission applications. Similar to epitaxial QDs, these solution-grown
g-NQDs possess a very thick, defect-free inorganic shell, and are characterized
by an altered NQD electronic structure. Together, these factors result in NQDs
that do not photobleach, are insensitive to changes in surface chemistry and
show markedly suppressed blinking (Chen, et al. J. Am. Chem. Soc. 2008), as well as suppressed nonradiative Auger
recombination (Garcia-Santamaria et al. Nano
Lett. 2009). Significantly, g-NQDs afford new exciton→photon
conversion pathways, including efficient multiexciton emission. Secondly, we address the opposite technological need
– nanoparticles that convert light into electric energy. Here, I describe
the first solution-phase synthesis of high-quality CuInSe2 nanowires
(NWs) (Wooten et al. J. Am. Chem. Soc. 2009).
We coupled the solution-liquid-solid (SLS) growth method with a single-source
chemical precursor to yield this complex ternary compound, an important
photovoltaic material. Finally, we advance the state-of-the-art in SLS growth
by establishing flow-SLS as an alternative solution-phase processing approach
that provides unprecedented control over NW internal structure and vertical
ordering. Thursday, April 22, 2010 10:00 a.m. to 11:00 a.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 Light refreshments will be served at 9:45
a.m. Robert A. Wolkow Department of Physics University of
Alberta National
Institute for Nanotechnology, Edmonton, Alberta Canada Controlled
Coupling and Occupation of Silicon Atomic Quantum Dots at Room Temperature It is demonstrated
that the zero-dimensional character of the silicon atom dangling bond (DB)
state allows controlled formation and occupation of a new form of quantum dot
assemblies - at room temperature. Coulomb repulsion causes DBs separated
by less than ~2 nm to experience reduced localized charge. The unoccupied
states so created allow a previously unobserved electron tunnel-coupling of
DBs, evidenced by a pronounced change in the time-averaged view recorded by
scanning tunneling microscopy. It is shown that fabrication geometry
determines net electron occupation and tunnel-coupling strength within multi-DB
ensembles and moreover that electrostatic separation of degenerate states
allows controlled electron occupation within an ensemble. Friday, January 29, 2010 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A light lunch will be served at 11:30
a.m. Y.W. Park Department of Physics and Astronomy & Nano Systems
Institute-National Core Research Center, Seoul National University, Seoul
151-747, Korea Fundamental
Properties and Applicability of Carbon based
Nanostructures Implication for Biomolecular Sensors Fundamental properties and applicability of carbon based
nanostructures such as polymer nanofibers, carbon nanotubes and the polymer
encapsulated carbon nanotubes (polymers@CNTs) are investigated. The results of magnetoresistance (MR)
for polyacetylene nanofibers show zero MR up to 30 tesla at high electric fields, which proves the predicted spinless charged soliton tunneling
conduction in polyacetylene. On the other hand, our measurements on polyaniline
nanofibers reveal a large MR that shows no decrease in similar electric fields proving the polaronic conduction with
spin and charge in polyaniline nanofibers. An electric field modulated high
magnetic field switching device can be developed as a potential application of
polyacetylene nanofibers. The applicability of carbon based nanostructures
(conducting polymer nanofibers, carbon nanotubes and their composites) such as
the polymer nanofiber Field Effect Transistors (FET), ansiotropic FET mobility
of pentacene single crystal, PEAPOD single electron transistor (SET) and random telegraph signal (RTS), CNT
gated CNT cross junction, three terminal CNT nanorelay, single molecule
conduction, and polymers@CNTs,
are envisaged. The polymers@CNTs can be utilized as
highly efficient light weight rechargeable battery electrodes in Li-polymer
batteries. The CNT and functionalized CNTs
are deposited on top of a CMOS chip to apply for biomolecular sensors. Friday, January 22, 2010 Noon to 1:00 p.m. J. Robert Mann, Jr. Engineering Student Center 10 Hillhouse Avenue - Dunham Lab 107 A light lunch will be served at 11:30
a.m. Robert Crabtree Professor
of Chemistry Hydrogen Storage to Virtual Hydrogen Storage Intermittent and dilute
alternative energy sources such as solar & wind power need energy storage
so that they can contribute to supplying continuous power needs. One popular
suggested approach – classical hydrogen storage – is conversion of
electrons into hydrogen by water electrolysis, then storage of the hydrogen in
a solid matrix. Disadvantages of this approach are discussed. In virtual hydrogen
storage, proposed by the present author, [1] electrons and protons are stored
together in a liquid organic medium via electroreduction of azaarenes. Energy
is released by reversing the procedure. I thank YINQE for funding. 1. Hydrogen
storage in liquid organic heterocycles, Crabtree RH, Energy & Environmental Science, 1, 134-138, 2008. Fred Walker Senior Research Scientist, Department of
Applied Physics and Center for Research on Interface Structure and Phenomena Atomically Engineered oxides: developing a new device
logic paradigm The field effect transistor
(FET) is a common device found in our computers, cell phones and cameras with
over 1018 transistors/year being produced. The FET is the
fundamental device for performing logic functions in computers where the
on-state of the transistor is a 1 and the off-state is a 0. Computers have been made faster by
decreasing the size of the transistor, but the function of the transistor has
not changed in the last 50 years.
A major drawback of the transistor is that when power is removed, memory
of the on or off state of the transistor is lost. This drawback was recognized more than 50 years ago when a
device was proposed that remembered its state even when the power is
removed. The Center for Research
on Interface Structure and Phenomena is developing special materials that are
engineered at the atomic level in order to realize this elusive device. While the immediate impact of such a
device will be instant-on computing (imagine your lap-top or cell phone turning
on instantly), a more profound impact will be felt as this device enables
changes in how computation is done from hardware that can be reconfigured by
software to artificial neurons. |
