Carlos Silva, Universite de Montreal

Wednesday September 3, 2008, 12:00pm, NST 1.104

Charge Transfer Excitons in Strongly Coupled Organic Semiconductors

Understanding and controlling supramolecular electronic coupling in ð-conjugated materials is central to the development and exploitation of their semiconductor properties. We present temperature-dependent, time-resolved photoluminescence (TRPL) measurements on chiral, helical stacks of a sexithiophene derivative. Photoexcitation of the ð-ð* transition with femtosecond laser pulses yields primarily 1Bu excitons with bandwidth of order 280 meV, which places them in an intermediate regime between purely chromophoric excitons and those in traditional semiconductors. These undergo diffusive transport that is dictated by an energy landscape governed by correlated disorder. We observe a significant yield (~5%) of charge photogeneration; these undergo recombination with a distribution of rate constants producing delayed PL which decays with a stretched exponential time dependence over time windows spanning microseconds. The high yield of charged excitations is a result of the substantial electronic bandwidth due to strong intermolecular electronic coupling, giving access to charge-transfer states that are normally not accessible in conjugated polymer films.

Paulo Ferreira Seminar, The University of Texas at Austin

Wednesday September 10, 2008, 12:00pm, NST 1.104

Seeing Small: Transmission Electron Microscopy Applied to Nanomaterials

Joel Schindall Seminar, MIT

Wednesday October 15, 2008, 12:00pm, NST 1.104

Engineered Nanostructures for Efficient Electrical Energy Storage Devices

Our emerging ability to sculpt materials at a nano-dimensional level gives rise to the possibility of synthesizing nanostructured battery electrodes whose electrical behavior is similar to the chemical lattices used in traditional batteries, but which absorb electrolyte ions (and therefore store electrical energy) without the need for chemical bonding.  This talk will describe the development of an ultracapacitor with a nanotube-enhanced electrode which might achieve sufficient porosity to approach the energy storage density of an electrochemical battery, while also providing significantly increased lifetime and very high charge and discharge rates.

Thom LaBean Seminar, Duke University

Wednesday October 22, 2008, 12:00pm, NST 1.104

Programmable Molecular Self-Assembling for Nanoelectronics and Nanomedicine

Self-organization and self-assembly are used repeatedly on multiple length scales in the construction of natural biological materials systems. Taking inspiration from biology, we have created a variety of artificial molecular self-assemblies at the critical nanometer scale. Using nucleic acids, peptides, and proteins, we have created organized materials with increasingly complex patterns, shapes, and dynamics. In what could be characterized as programmable artificial biomineralization, these novel biomolecular matrices are being employed as scaffolds and templates for the directed-assembly of additional nano-scale objects such as metals, quantum dots, and other inorganics. The exciting, novel properties of these materials lend themselves to promising applications including fabrication of electronic and plasmonic devices and circuits in three-dimensions for integrated energy conversion, sensing, computation, and signal transduction. In addition, we are developing molecular assemblies containing bioactive proteins for a variety of medical applications.

UT Austin Graphene Symposium

Friday October 31, 2008, All day, NST 1.104

9:00 - Phaedon Avouris - IBM - “Carbon Based Electronics and Optoelectronics”

I will discuss the basic ground state electronic structure, transport properties and device physics of carbon nanotubes and graphene and demonstrate their potential in electronics. I will then focus on their excited states, their nature, generation, radiative and non-radiative decay and their potential use in a novel optoelectronic technology based on the same materials.

10:30 - Emanuel Tutuc - University of Texas at Austin - “High mobility, dual-gated graphene field effect transistors”

Graphene, an atomic layer of layer of carbon atoms in a hexagonal lattice structure, has received intense scrutiny lately thanks to its unique electronic properties. The linear energy-momentum dispersion, zero band-gap, and high (~10,000 cm2/Vs) carrier mobility distinguish graphene from most conventional semiconductors.
We discuss the fabrication and characterization of dual-gated graphene field effect transistors, with ALD Al2O3 high-k dielectrics. Our dual-gated devices show a carrier mobility as high as (~5,000 cm2/Vs) at room temperature. We address the device applications which may be enabled by such high mobility graphene layers bounded by ultra-thin dielectrics, as well as the graphene synthesis approaches currently pursued at the Microelectronics Research Center.
Work done in collaboration with S. Kim, L. Colombo, and S. Banerjee.

11:45-2:00 - Poster Session and Lunch

2:00 - Walt Deheer - Georgia Tech - “Epitaxial graphene: designing a new electronics material”

Since 2001 research at Georgia Tech with various collaborators has, demonstrated the extraordinary transport properties of epitaxial graphene, which is graphene that is grown on single crystal silicon carbide (SiC). Monolayer graphene can be grown on the silicon face of hexagonal SiC. Multilayered epitaxial graphene (MEG), consists of up to 100 graphene sheets, grows on the carbon face of SiC. MEG. Surprisingly its properties correspond to those of monolayer graphene rather than to those of graphite. The MEG structure as been extensively studied using a variety of probes, including STM, STS, AFM, LEED, XRD, IR spectroscopy. For example, its band structure is defined by a "Dirac cone"; it exhibits a non-trivial Berry's phase; weak anti-localization; and quantum confinement effects. Long (µm) phase coherence lengths have been measured. Transport properties confirm that the graphene chiral nature of the carriers in the material, which distinguishes it from Bernal graphite. Landau level spectroscopy further exhibits record-breaking room temperature mobilities and well resolved Landau levels well below 1 T, indicating extremely low carrier densities, good homogeneity of the material and very weak electron-phonon coupling Moreover MEG has recently successfully been converted in situ, to multilayered graphene oxide which is a semiconducting form of MEG. All these properties indicate that epitaxial graphene is an ideal platform for graphene-based electronics as well as for fundamental Dirac electron physics. Recent results on large scale patterning of FETs will also be presented.

3:30 - Rod Ruoff - University of Texas at Austin - “Graphene-based Materials”

Our top-down approaches [1,2] inspired physicists to study individual layers of graphite obtained by micromechanical exfoliation, but our current approach has been to convert graphite to graphite oxide (GO), generate aqueous colloidal suspensions containing individual layers of GO (we call them ‘graphene oxide’), and to use these ‘graphene oxide sheets’ in a variety of ways.  For example, we have embedded individual and reduced graphene oxide sheets in polymers such as polystyrene and evaluated their dispersion, morphology, and the electrical percolation and thus conductivity of the resulting composites.  In parallel paths, we have: (i) undertaken studies of individual graphene oxide and reduced graphene oxide sheets, to elucidate their chemical, optical, and electrical properties, (ii) embedded graphene oxide sheets in glass by a sol-gel route and made electrically conductive and transparent glass coatings, and (iii) produced 'graphene oxide paper', a material with intriguing  mechanical properties (iv) produced reduced graphene oxide powder with moderately high surface area and used this to study electrochemical double layer capacitance (v) made carbon-13 labeled graphite and thus carbon-13 labeled graphite oxide, and studied its detailed chemical structure with SS NMR.   This survey talk with present an overview of these.  Support of our work by the NSF, ONR/NRL, NASA, and DARPA is appreciated. 

Prior to joining The University of Texas at Austin as a Cockrell Family Regents Chair in Mechanical Engineering, Prof. Rod Ruoff served as Director of the Biologically Inspired Materials Institute at Northwestern University. He is a ‘Visiting Chair Professor’ at Sungkyunkwan University in South Korea. He received his B.S. in Chemistry from the U. of Texas (Austin) and Ph.D. from the University of Illinois-Urbana. He was a Fulbright Fellow at the Max Planck Institute-Goettingen, Germany.  From ‘89-’90, he was a Postdoctoral Fellow at the IBM T. J. Watson Research Center in New York. Prior to joining Northwestern in 2000, he was a Staff Scientist at the Molecular Physics Laboratory of SRI International and Associate Professor of Physics at Washington University. His research activities include global environment and energy; synthesis and physical/chemical properties of nanostructures and composites; nanorobotics, NEMS, and developing new tools for biomedical research. Prof. Ruoff has published 180 refereed journal articles in the fields of chemistry, physics, mechanics, & materials science.

Gary Wiederrecht - Argonne National Laboratory
IGERT Student-Hosted Seminar

Wednesday November 5, 2008, 12:00pm, NST 1.104

Hybrid plasmonics: new routes to nanoscale imaging and energy conversion

Surface plasmons are electromagnetic modes that are present at the interface of a metal and dielectric material. Depending upon the structure of the metal, surface plasmons demonstrate a wide range of characteristics, such as optical field enhancements, tunable resonances, and the ability to propagate in films or be confined at nanoparticle defects. As a result, surface plasmons continue to generate growing interest for new sensor technologies, energy transport, and photonics applications. In many cases, the most interesting advantages of surface plasmons lie in the optical near-field, significantly below the diffraction limit of conventional optics in at least one dimension. As a result, novel methods for imaging the spatial profile and propagation properties of surface plasmons are required. To add to the challenge, plasmons respond on an ultrafast time-scale to illumination, requiring time-resolved methods to characterize the available energy transfer and dissipation pathways, particularly when in contact with organic or semiconductor nanostructures (heterostructures). In this talk, recent efforts in our group for the imaging and spectroscopy of plasmonic heterostructures are discussed, specifically applied to plasmonic continuum spectroscopy, metal nanoparticle photoluminescence, and the unique optical states that arise from coupled excitons and plasmons. Lithographies and sub-wavelength imaging capabilities that exploit the optical near-field of the nanostructures are also described.

Hannu Hanninen, Helsinki University of Technology

Monday November 10, 2008, 12:00pm, NST 1.104

Development of High-Strength Stainless Steels and their Applications

The presentation covers the results obtained at HUT for the development of new high-strength stainless steels either by powder metallurgy (PM) for process and energy industry or by thermomechanical treatments of wrought steels for transportation industry. Also the corrosion properties of the steels are presented and the possibilities to improve the surface properties by photoactive TiO2 coating are described. New manufacturing techniques – forming and welding – are also considered. Finally proposals for development of new high-strength steels are made based on the understanding of the role of composition (especially Ni, Mn, N, C, Cu and H) on stacking fault energy (SFE), deformation mechanisms, and the mechanical properties of the austenitic (duplex) stainless steels. With this kind of scientific understanding the microstructure-mechanical properties connection can be understood and steel compositions can be optimized for TRIP, TWIP, delayed cracking etc. phenomena.

Bernd Kabius Seminar - Los Alamos National Laboratory

Wednesday November 12, 2008, 12:00pm, NST 1.104

Benefits of Aberration Corrected TEM for Material Science Problems

During the last 10 years several aberration-correction concepts for electron microscopes have succeeded in improving spatial resolution and analytical capabilities. Electron optical systems for correction of spherical aberration are now a valuable tool for material science research and several investigations have already exploited some of the benefits of Cs-correction for high-resolution TEM and STEM. The TEAM project is a collaborative DOE project which will extend the present capabilities of aberration correction technology. The goals for aberration correction within the TEAM project are:
- Correction of higher order aberrations such as fifth order spherical aberration is required for improving interpretability at sub-Angstrom resolution (TEM) and higher beam currents in smaller electron probes (STEM).
- Improving the information limit to 0.5Å by correction of chromatic aberration (Cc) and energy monochromation.
This progress in electron beam instrumentation is expected to have a strong impact on in-situ TEM, magnetic imaging and analytical electron microscopy. The benefits of Cs - and Cc - correction for material science problems requiring these methods will be discussed.

This work was supported by the US Department of Energy, BES-Materials Sciences, under Contract W-13-109-ENG-38.

Portfolio Student Presentations

Wednesday December 3, 2008 - Noon to 2pm - NST 1.104

Ignacio Gallardo - Characterization of Heterostructured Nanocrystals Generated by Laser Ablation of Microparticles

KAY HOFFMAN, JOHN W.KETO, Department of Physics, The University of Texas at Austin

Laser Ablation of Microparticles (LAM) is a process of nanoparticle formation in which microparticles in a flowing aerosol are continuously ablated by high power laser pulses1.  For the first time, we have produced CdSe/ZnS core/shell nanoparticles using a double ablation apparatus, designed to undergo a two step LAM process.  This process can be inverted to produce ZnS/CdSe core/shell nanoparticles.  The present work focuses on ~30nm diameter heterostructures and used high resolution transmission electron microscopy (HRTEM) to image core and shells2. For smaller particles, core shell structures have been detected with energy dispersive spectroscopy (EDS) 5nm spot size beam, and fast Fourier transform (FFT) spectra. Differences in the ablation behavior were measured between the two IIB-VIA type semiconductors.
To study the effects of the nanoparticles in the second cell under high UV laser pulses, thermodynamic numerical calculations3 were made and tested for well known Silver nanoparticles. We discuss temperature and size distributions for CdSe and ZnS nanoparticles. A two laser pulse experiment is designed to monitor nanoparticle size before and after laser interaction. We show HRTEM images of particles before and after surface evaporation. First results show that Ag nanoparticle radius decreases from 3.5nm  to 2.2nm, keeping a constant standard deviation of 20%. Our theoretical model is in good agreement with the experiments. 

(1) William T. Nichols;  Gokul Malyavanatham  , Dale E. Henneke , James R. Brock  , Michael F. Becker ,John W. Keto and Howard D. Glicksman , Gas and pressure dependence for the mean size of nanoparticles produced by laser ablation of flowing aerosols , Journal of Nanoparticle Research 2: 141–145, 2000.
(2)I Gallardo, K. Hoffmann and J. W. Keto, CdSe & ZnS core/shell nanoparticles generated by laser ablation of microparticle, Applied Physics A. (2008)
(3)K. L. Kompa et al. J. of Aerosol Sci., 19, 491, (1988)
We would like to thank The Center for Nano and Molecular Science and Technology, (CNM), the Robert A. Welch Foundation, the Strategic Partnership for Research In Nanotechnology, (SPRING), The Texas Materials Institute (TMI), and CONACYT for financial support.

Carlos Andres Aguilar - Photoelectron Spectroscopy of ZnO Nanowires

Photoelectron spectroscopy is a particularly powerful experimental method for studying the electronic structure and properties of materials; when carried out with low energy photons focused onto individual nanowires, as will be described, important new information about surface and “bulk” nanowire electronic properties can be gleaned. In this talk, low energy photoelectron spectroscopy was utilized to study zinc oxide (ZnO) nanowires, both clean and “engineered” through the adsorption of self-assembled monolayers (SAMs) of polar molecular groups. The molecule-induced modification of the electronic properties measured here demonstrates an effective platform to study other reversible molecular adsorption events for next-generation sensors, photovoltaics and optoelectronic devices.

Ion Garate - Upper Critical Field of Thin Film Superconductors

We present a microscopic mean field theory calculation of the upper critical magnetic field H_{c2} as a function of temperature T for an ultra-thin film superconductor. We show that confinement-induced quantum well states (QWS) are conducive to multiple superconducting gaps, provided that the highest occupied QWS has a small enough Fermi surface. Under such condition H_{c2} vs. T displays an anomalous (upwards) curvature even in absence of disorder and sample inhomogeneities, which is reminiscent of the "hockey stick" found in recent experiments
conducted at the University of Tenneessee. We discuss on how film thickness, doping and disorder affect the curvature anomaly, and asses the experimental relevance of our Fermi surface argument.

Danielle Smith - Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

Gold nanorods and magnetic nanocrystals are two materials that are being studied for their suitability as imaging contrast agents in biological systems. Magnetic nanocrystals can be used to enhance magnetic resonance imaging (MRI) contrast, for labeling of cancer cells, and also for intracellular labeling. The magnetic response of a nanocrystal can be tuned by varying the size of the nanocrystal as well as the composition. Gold nanorods are being explored for biological and medical use as optical contrast agents for dark field and two-photon luminescence diagnostic imaging and photothermal therapy of cancer cells. They are attractive candidates for medical imaging because their optical response can be tuned to near-infrared wavelengths, which penetrate deep into cells and tissue; furthermore, they do not photobleach or blink, and are chemically inert and biologically compatible.

Though as-synthesized gold nanorods are soluble in water, the bilayer of CTAB on their surface may render these particles harmful to living systems. As-synthesized magnetic nanocrystals are not soluble in water because they are capped with organic ligands. By coating both of these materials with silica, they are made water soluble and can thus be introduced into biological systems. Furthermore, when a fluorescent dye is embedded into the silica coating of the nanocrystals, an additional imaging modality is added. Thus, the final fluorescent dye doped silica coated nanocrystal is a heterostructure with dual imaging modality.

Special Seminar

Junghoon Lee, Seoul National University

Friday June 6, 2008, 2:00pm, NST 1.104

"Mechanical Response of Biomolecules and Cells"

Mechanochemistry has been known as a key principle behind various biochemical processes such as ligand-receptor recognitions and cellular responses to stimuli. Recent progress in microscale and nanoscale fabrication technologies enabled the measurement and use of the mechano-chemical forces on molecular and cellular levels. In this talk I will introduce micro/nano platforms developed in our lab for understanding the molecular interaction and cellular responses via mechanochemistry. Thin membrane technology can be used to detect biochemical interactions such as DNA hybridization and protein recognition with the chemical-mechanical coupling through surface forces. Cells grown on flexible substrates with varying stiffness respond differently, showing, for example, migrations (fibroblasts) and self-beating at different periods (cardiac cells). I will also discuss the molecular detection with DNA-carbon nanotube hybrids, and cell proliferation and differentiation on surface-grown carbon nanotubes. 

Optical profilometer view of thin membrane transducer fabricated, and schematic diagram illustrating chemo-mechanical sensing of DNA hybridization.

Schematic diagram illustrating the precipitation of DNA solubilized SWNTs with complementary single-strand DNA.

Milan Mrksich, University of Chicago

Wednesday January 16, 2008, 12:00pm, NST 1.104

“Engineering Active Interfaces Between Cells and Materials”

This lecture will describe a chemical approach to integrating mammalian cells and electrical components. The strategy is based on self-assembled monolayers of alkanethiolates on gold that are modified with peptide ligands which promote cell adhesion. The monolayers are then engineered with electroactive moieties such that application of an electrical potential to the gold film results in modulation of the activities of immobilized ligands. In one example, an electroactive monolayer could turn on the migration of fibroblast cells that were originally confined to circular patterns on the substrate. This example, which was based on a monolayer that could be switched from an inert state to a state that promotes cell adhesion, establishes the feasibility of engineering active interfaces that can translate electrical signals into biological signals. A second example demonstrated an active monolayer that could selectively release immobilized ligands, and even individual cells. The lecture will describe these and several other strategies for creating functional interfaces between cells and electronics, and will address the opportunities for applying these strategies to creating hybrid devices comprising electrical and cellular components.

Harry Tuller, MIT

Wednesday January 23, 2008, 12:00pm, NST 1.104

“Micro-Ionics: A Revolution in Portable Power Generation and Environmental Sensing”

Ionic conductors have long been known to be the basis of electrochemical devices ranging from batteries and fuel cells to chemical sensors.   In this presentation, I examine options for embedding miniaturized solid state ionic thin film structures as sensors or power sources together with MEMS components in the same wafer platform. 

By applying microelectronics process technology, one accesses means for tailoring electrolyte and electrode geometry with exceptionally high dimensional reproducibility.  Lower process temperatures commonly lead to films with nanoscale dimensions with implications for performance including higher sensitivity in sensors and improved energy densities and shorter charge/discharge in batteries and fuel cells.  But one must temper these advantages with potentially more rapid degradation. Attention is focused on the special challenges that integration of nanostructured solid state ionic materials entails as well recent materials breakthroughs achieved enabling operation of micro-devices to elevated temperatures in harsh environments. Attention will be focused particularly on micro-sensor arrays and micro-solid oxide fuel cells (mSOFC).

Xiaoyang Zhu, University of Minnesota

Wednesday February 6, 2008, 12:00pm, NST 1.104

"Charge Carriers in Organic Semiconductors"

Charge carrier generation and transport are central to the operation of all organic electronic and optoelectronic devices, such as organic light-emitting diodes (OLEDs), field effect transistors (OFETs), and photovoltaic cells (OPVs). A fundamental distinction from their inorganic counter parts is the localized nature of charge carriers and electronic excitations in organic semiconductors. Localization is a fundamental character resulting from the narrowness of the electronic band, the flexibility of the organic molecule, the deformability of the van der Waals bonded lattice, and the low dielectric constants of organic materials. This is in addition to the prevalence of structural and chemical defects that form the bulk of charge carrier traps in organic semiconductors. We study the localization problem in organic semiconductors using two spectroscopic approaches. The first approach relies on in situ IR and NIR spectroscopy to directly monitor molecular vibrations and electronic transitions associated with charge carriers in gate-doped organic semiconductors. The second approach relies on femtosecond time-resolved two-photon photoemission (TR-2PPE) spectroscopy to follow the formation and decay of excitons and small polarons in organic semiconductors. These experiments are beginning to answer the following critical questions: How do charge carriers separate at organic heterojunctions in an OPV? How does a charge carrier move in an OFET? What is the mechanism for the metal-to-insulator transition in a gate doped conducting polymer?

Moungi Bawendi, MIT

Wednesday February 20, 2008, 12:00pm, NST 1.104

“Science and Technology of Semiconductor Nanocrystal Quantum Dots”

Semiconductor nanocrystals, aka quantum dots, have become the prototypical material for the emergence of new properties when dimensions are reduced to the nanometer range. In the case of quantum dots it is the exciton radius in the bulk that determines the size transition from bulk-like electronic behavior to the size dependent properties that have made quantum dots a popular nanomaterial. In the size range of ~2 to 10 nm, the electronic structure of quantum dots becomes discrete at room temperature, leading to the size dependence of their band gap and of their fluorescence. The size dependent properties of excitons and multiexcitons in quantum dots, coupled with a material that can be processed from solution, has led to potential applications in fields that include emissive displays, solar energy conversion, and biological and biomedical fluorescence imaging. A fundamental understanding of exciton processes is critical for any of these applications to become realized. Synthesis of well characterized materials is obviously key, not only of the functional inorganic particle itself, but also the ligand shell that protects it and couples it chemically to molecules and matrices of interest. This talk will introduce the chemistry and photophysics of quantum dots and then explore the fundamential properties and challenges behind broadly applying quantum dots as light emitters and light absorbers in devices and for biological imaging.

Erich Stach, Purdue University

Wednesday February 27, 2008, 12:00pm, NST 1.104

“Understanding the onset of plasticity in materials using quantitative in-situ nanoindentation”

Nanoindentation is widely accepted as the preferred technique to study localized mechanical deformation phenomena in materials. However, the mechanisms of deformation can only be inferred from the load -displacement data obtained during a typical instrumented nanoindentation test. In order to elucidate the underlying physics of these process, we have developed and exploited a new technique, that of in-situ nanoindentation in a transmission electron microscope (TEM). In this technique, a voltage-actuated piezoceramic tube is used to position a sharp diamond in plane with the edge of an electron transparent sample. The tip is driven into the material in order to induce deformation and the corresponding deformation is observed in real time and at high spatial resolution. In this talk, I will review the details of our experimental technique, as well as summarize our results from selected materials systems. In particular, we have studied thin films of aluminum deposited on top of microfabricated wedges of silicon, allowing us to observe such effects as initial deformation modes, size effects on hardening, grain boundary motion and dislocation nucleation, as well as the effects of solute additions on both dislocation propagation and grain boundary movement. Additionally, experiments on harder materials have permitted the observation of unexpected deformation modes. In the case of single crystal silicon, we have found a size-dependent transition from pressure-induced phase transformation to room temperature deformation by dislocation nucleation and propagation.

Portfolio Student Presentations - Spring 2008 Graduates

Wednesday April 16, 2008, 12:00-2:30pm, NST 1.104

1st Place - Alexander Khajetoorians - "Tuning Surface Energy Landscapes of Quantum Metal Thin Films with Alkali Adsorbates"

2nd Place - John H. Slater - "Engineering Endothelial Cell Adhesion and Behavior via Cell-Surface Interactions with Chemically-Defined Fibronection Nanopatterns"Dayne Fanfair - "Twin-Related Branching of Solution-Grown ZnSe nanowires"

Ryan Fitzpatrick - "CVD Boron Carbo-Nitride as a Potential Passivation Layer for Germanium"

J. Ruben Morones - "Novel Synthesis of Polymer-Metal nanocompostites: Tailoring Properties for Applications from Biocides to Optical Switches in Drug Delivery Systems"

Se-Hyuk Im - "Dynamics of Wrinkling in Elastic Thin Films on Soft Substrates"

Anastassios Mavrokefalos - "Thermoelectric and structural characterization of individual nanowires and patterned thin films”

G.P. Li, University of California, Irvine

Wednesday October 10 , 2007, 12:00pm, NST 1.104

"Life Chips Research and Development at UC Irvine"

Concurrent revolutions in biology, medicine, physical sciences and engineering at the micro and nano scale, accompanied by advances in instrumentation, are bringing these historically separate disciplines into convergence. This exciting trend has the potential to bring about dramatic and important changes to life science and micro/nanoelectronics technology: in the results of research, in the way that research is performed, and in the development of a new hybrid industry based on this convergence.

LifeChips is the study of nature’s 3 billion years of evolution ( technology of life), and development of micro- and nano-scale technologies, systems and devices that combines methods developed by life scientists and technologists to help solve fundamental problems in the life sciences and in engineering (technology for life). LifeChips represents a new research paradigm that has driven the need for collaborations among researchers from traditionally different backgrounds and cultures, namely life scientists (biologists, medical researchers) and technologists (physical scientists, engineers). It also represents the fusion of two major industries, the microelectronic chip industry with the life science industry.

UC Irvine is spearheading development in LifeChips on many fronts: initiating graduate training programs, developing design methodologies, defining new applications, promoting commercialization, creating research programs, and pursuing novel LifeChips manufacturing techniques. LifeChips research projects at UC Irvine provide excellent examples of potential new science discovery and engineering products, including implantable microdevices, minimally invasive devices, cell analysis chips, and biosensors. In addition to utilizing micro/nano chip technologies, each project and device has unique requirements for its design, manufacture and deployment. These requirements (and limitations) drive the need for advances in nano/micro fabricaiton and system-integration at manufacturing level, building the foundations for a new LifeChips industry. We will discuss several projects at UC Irvine to illustrate the flavor of LifeChips research.

Chris Dames, University of California Riverside

Wednesday October 17 , 2007, 12:00pm, NST 1.104

"Thermal Properties of Nanostructures: Thermoelectric Applications"

Thermoelectric energy conversion using the Seebeck and Peltier effects is an established technology for refrigeration and power generation. Thermoelectrics are appealing because of their reliability, compact size, and lack of moving parts. However, because of their low efficiency, traditional thermoelectric materials have largely been limited to niche applications. Recent research has shown that nanostructured thermoelectrics can be dramatically more efficient than their bulk counterparts, greatly broadening the pool of possible applications.

In this talk we explore the fundamental size effects on electrons and phonons that can be used to enhance the thermoelectric performance of nanostructures. Emphasis is placed on the thermal properties of nanowires, nanotubes, and self-assembled superlattices, studied using both modeling and experimental approaches.

"Nanomaterials and Nanostructures" - UT - France Workshop

Monday October 22 and Tuesday October 23, NST 1.104

Anatoly Frenkel, Yeshiva University

Wednesday October 17 , 2007, 12:00pm, NST 1.104

"Negative Thermal Expansion and Other Anomalies in Supported Metal Nanoparticles"

Negative thermal expansion (NTE), a peculiar effect reported in 1996 in zirconium tungstate and other framework solids and not expected in fcc metals, was recently observed in alumina-supported Pt nanoparticles. In the smallest particles studied (0.9nm in diameter) the Pt-Pt distance decreased gradually by 0.04 Å over the 500 K range. Such effect was attributed to the charge transfer between the cluster and support. Recently, more experimental information on structure and dynamics of Pt clusters was obtained for different sizes, support materials and atmospheres. Experimental results combined with the first principles, real-time calculations uncovered dynamic structure of supported metal clusters that exhibit large dynamic fluctuations. This dynamic behavior, previously unaccounted for by ground state DFT calculations, is characterized by very peculiar electronic and structural properties in these supported clusters that can explain their various unusual phenomena, including the NTE, large disorder and red-shift of the x-ray absorption edge.

Jan Liphardt, University of California, Berkeley

Wednesday November 7 , 2007, 12:00pm, NST 1.104

"Plasmonics, Radiating Nanowires, and Light-Powered E.Coli"

In the last decade, new materials such as quantum dots and semiconductor nanowires have been developed. Now, methods are needed to efficiently and accurately integrate these pieces into larger heterostructures that collect, emit, and control light. I will discuss several complementary ways of putting small things together, including self-assembly, optical trapping, DNA hybridization, and the use of re-programmed bacteria. Then, I'll discuss the physics of what happens when certain combinations of materials interact with light. Examples will include tuning of the electrical field using plasmon coupling and nonlinear optical processes occurring inside optically trapped potassium niobate nanowires.

Michael Sheetz, Columbia University

Wednesday November 14, 2007, 12:00pm, NST 1.104

"Shaping Cells by Force and Rigidity Through Protein Stretching"

Mechanical factors are critical in determining the observed cell shape and fate. At the microscope level, the integral of many stereotypical cell movements determines the shape. Thus, mechanical factors (external force and substrate rigidity) control cell movements (Vogel and Sheetz, 2006. Nature Rev. Mol. Cell Biol., 7:265). A prominent example is the substrate rigidity response wherein transformed cells can grow on soft agar whereas normal cells die, showing that transforming proteins are involved in cell mechanics (reviewed in Giannone and Sheetz, 2006. Trends Cell Biol. 16:213). Our working model for rigidity sensing postulates that rearward pulling of the cytoskeleton and linked matrices produces force to prime substrate for phosphorylation and possibly displace it from kinase if the surface is soft. In spreading on a rigid fibronectin substrate, cells pull periodically, establish early adhesion complexes, condense the lamellipodial actin and commence the next cycle (Giannone et al., 2007. Cell 128:561). In correlation, mechanical stretching of p130Cas primes it for tyrosine phosphorylation by active Src family and Abl kinases and the unfolded, phosphorylated form of p130Cas is found in the periphery of spreading cells (Sawada et al., 2006. Cell 127:1015). Further, in neurons as well as fibroblasts, movement on rigid fibronectin causes increased tyrosine phosphorylation of p130Cas by Fyn (Kostic and Sheetz, 2006. Mol Biol Cell 17:2864 and Kostic et al 2007. schJ Cell Sci In Press). This reinforces the hypothesis that the unfolding of cytoskeleton-associated proteins is a major force-sensing mechanism in many cell movements. At a general level, mechanical (rigidity and force) and biochemical steps are linked in cell movements, which is hard to duplicate in vitro. Consequently, stereotypical cell movements should be described by the forces, displacements, velocities, times as well as biochemical processes involved in each distinct step of the function, such as periodic contraction or earlier spreading movements. Stereotypical cell movements constitute the tools that cells can use to test and modify the mechanical and chemical aspects of their environment.

Jürgen P. Rabe, Humboldt University Berlin

Joint Atomic & Molecular IGERT/Portfolio Seminar

Wednesday November 28 , 2007, 12:00pm, NST 1.104

"A Workbench for Single Molecular Nanostructures"

Macromolecular and supramolecular nanostructures constitute modules in living systems which most efficiently perform key elementary functions in sensors, actuators, and for energy conversion. The understanding of structure-property relationships on the level of single molecular nanostructures is promising insight that may lead to new concepts for artificial biomimetic systems. We developed a workbench for single molecular nanostructures to determine and correlate structure and dynamics with mechanical, electronic, optical properties. The workbench consists of an inert, conductive, single crystalline substrate, covered with a weakly bound fluid or nanostructured molecular layer, and a scanning tip of a scanning probe microscope. It is used for both the assembly of molecular nanocomposites and the determination of their properties (e.g. Barner et al. Angew. Chem. 2003; Ecker et al. Macromolecules 2004; Jahnke et al. Angew. Chem. 2006). A key role can be played by the physisorbed molecular layer, which together with the forces exerted by a scanning force microscope probe may be employed to bend, stretch, overstretch and finally break dsDNA, as well as to control structure and orientation of single polyelectrolytes (Severin et al. Nano Lett. 2004 & 2006). At solid-liquid interfaces, scanning tunneling microscopy and spectroscopy have been used to develop concepts for single molecule rectifyers and a single molecule transistor with nanometer-sized gates (Jäckel et al. Phys. Rev. Lett. 2004 & Müllen & Rabe, Acc. Chem. Res. in press). Finally, insights into processes on the single molecule level may be related to thin films relevant, e.g., for organic electronic devices (Koch et al., Org. Electron. 2006 & 2007).

Portfolio Student Presentations

Wednesday December 5, 2007, 12:00pm, NST 1.104

1st Place - Yaoyu Pang - "Surface Evolution and Self Assembly of Epitaxial Thin Films: Nonlinear and Anisotropic Effects"

Hongki Min - "Pseudospin Magnetism in Graphene"

Ted Gaubert - "NOBIL and its Applications for Studying Nanoscale Cell Surface Interactions"

Samaresh Guchhait - "Group IV Magnetic Semiconductor Alloys"

Arvind Battula - "Optical Near-Field Enhancement for Submicron Patterning and Plasmonic Optical Devices"

Zhong Lin Wang, Georgia Institute of Technology

Thursday August 9, 2007, 3:00pm, NST 1.104

"From Nanogenerators to Nano-Piezotronics"

Developing novel technologies for wireless nanodevices and nanosystems are of critical importance for in-situ, real-time and implantable biosensing, biomedical monitoring and biodetection. It is highly desired for wireless devices and even required for implanted biomedical devices to be self-powered without using battery. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that will be used to power nanodevices without using battery. We have demonstrated an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire (NW) arrays. We have recently developed DC nanogenerator driven by ultrasonic wave, which is a gigantic step towards application in practice.

Jacob Israelachvili, University of California, Santa Barbara

Thursday August 9, 2007, 3:30pm, WRW 102

"Adhesion, Friction, and Failure of Surfaces: Nano- and Micro-Scale Studies on the Transition from Liquid-Like to Solid-Like Behavior"

Recent experiments using the Surface Forces Apparatus and various surface imaging techniques have been conducted to study the adhesion, friction and fracture processes of various polymer and material surfaces and films. The aim was to investigate the transition between pure liquid/ductile and solid/brittle behavior. Both cross-linked and uncross-linked polymers were studied over a large range of molecular weights and viscoelastic properties, and sugars over a range of temperatures, thereby spanning the purely liquid- or ductile-like (T > glass transition temperature, Tg) to the glassy, elastomeric and brittle regimes (T < Tg). We investigated how the deformations and pathways of failing junctions change on passing through Tg, starting with liquid-like rupture at high T (determined by surface tension and viscous forces) and ending up with fracture via micro-cracks, determined by completely different material properties.

Dr. Colin Nuckolls, Columbia University

Wednesday January 17, Noon to 1PM, NST 1.104

"Reaction chemistry meets lithography"

This talk will focus on using reaction chemistry and self-assembly as a means to construct nanoscale electrical devices. Through these studies we are developing molecular-based materials that forge a connection (both literally and figuratively) between the ultra-fine lithographic tools of the semiconductor industry and reaction chemistry that has largely driven the chemical and pharmaceutical industries. The meeting of these seemingly disparate fields is the nanometer length-scale, which holds the future for molecular electronics. At these lengthscales the interfacial propertiesdominate. The chemistry at the interfaces pertinent to electrical devices is poorly understood. The concepts outlined in this presentation reveal how informationally rich molecules may be programmed for placement, assembly, and functionality in electrical circuits. The studies draw from a combination of device fabrication, self-assembly, and programmed reactivity to allow the study of individual molecules, isolated nanostructures, and chemical reactions. Three main topics will be: 1) Interfacial self-assembly of F0-systems; 2) designing functional metal-molecule interfaces; 3) synthesizing single-molecule devices.

Dr. Michael Wong, Rice University

Wednesday February 7 - Noon to 1PM, NST 1.104

"Nanoparticle Engineering of Palladium on Gold for Water-phase Environmental Catalysis"

Groundwater remediation through the catalytic breakdown of the undesired contaminants is a more effective and desirable approach than the conventional physical displacement methods of air-stripping and carbon adsorption. Palladium (Pd) catalysts are known to catalyze the hydrodechlorination of trichloroethene in water, at room temperature, and in the presence of hydrogen. We recently discovered that palladium-on-gold nanoparticles (Pd/Au NPs) can be two orders of magnitude more active than Pd supported on alumina on a per-Pd gram basis.

In this talk, I will describe our progress in improving the feasibility of these NP catalysts for groundwater remediation and in understanding how the gold enhances the Pd catalytic activity so dramatically. I will discuss the synthesis and characterization of Pd/Au NPs using 4-nm Au NPs and variable Pd content. These NPs showed a distinct volcano-shaped activity dependence on Pd, with the most active composition considerably more active (12.7 wt% Pd, 2100 L/gPd/min) than pure Pd NPs (54 L/gPd/min) and conventionally prepared Pd/Al2O3 (47 L/gPd/min). To gain some insight into the structure-property relationship for this catalyst and catalytic reaction, we calculated initial turnover frequency values using the pseudo-first-order reaction rates corrected for mass-transfer effects, and correlated them to Pd surface coverage. The TOF-surface coverage curve suggested 3 different catalytic activity ranges were present. I will discuss the applicability of this catalyst for the water-phase hydrodechlorination of other chlorinated compounds, as well as efforts to immobilize these NPs onto solid supports.

Dr. John Rogers, University of Illinois at Urbana-Champaign

Wednesday February 21 - Noon to 1PM, NST 1.104

"Tubes, Wires, and Ribbons for Flexible Electronics"

Solution processable conductors, dielectrics and semiconductors represent enabling materials for electronic circuits that can be fabricated on plastic sheets by continuous, high speed printing techniques. These types of systems, which can cover large areas, might be important for new
applications in consumer electronics. This talk describes the operational aspects of flexible transistors and circuits that use printable semiconductors based on organized collections of single walled carbon nanotubes, and of ribbons and wires of single crystal silicon, gallium arsenide, indium phosphide and gallium nitride. High mobilities, optical transparency, GHz switching speeds, mechanical bendability and even full stretchability represent a few of the unusual characteristics that can be achieved. These and other aspects, including progress on applications in imaging, photovoltaic and display systems, will be discussed.

Dr. Ananth Dodabalapur, Department of Electrical and Computer Engineering, University of Texas at Austin

IGERT SEMINAR SERIES

Wednesday February 28, 2007 - Noon to 1PM, NST 1.104

“Organic Thin Film Transistors: History and Current Developments”

This presentation will describe the history and important developments in organic/polymer transistors, including materials, performance levels, fabrication methods and device structures. First, the most important classes of materials will be reviewed along with performance figures. The important phenomena involved in charge transport (both steady-state) and dynamic will be described so as to represent current understanding. The scaling behaviour and properties of small geometry organic transistors will be surveyed. The second part of the talk will begin with a discussion on organic transistor speeds and what sort of circuits can be built with them. This will lead to a discussion of applications for organic transistors including electronic paper, displays, RFID tags, and in sensors/actuators.

HRTEM Workshop

Wednesday March 7 - Noon to 1PM, NST 1.104

Dr. Yang Shao-Horn, MIT

Wednesday March 21 - Noon to 1PM, NST 1.104

“Electrochemical Conversion and Storage for a Sustainable Energy Future: Material Design at the Nanometer Scale” 

The depletion of fossil fuels and the increasing environmental concerns demand efficient, clean energy technologies.  Electrochemical conversion and storage directly converts chemical energy to direct-current electrical energy via electrochemical reactions, which has high efficiency, and has shown great promise as key energy storage technologies in hybrid energy systems for transportation and stationary applications. However, practical energy and power densities and the cost of electrochemical systems such as lithium rechargeable batteries and fuel cells limit their competitiveness relative to conventional technologies. These performance characteristics are strongly dependent on the thermodynamics and kinetics of electrochemical reactions, and transport within bulk materials. The ability to modify the reactivity of materials through size provides a new opportunity in material design in addition to controlling bulk composition and microstructure.

Reduction of particle size has been shown not only to provide more surface energy but also to fundamentally change the catalytic activity of materials such as gold and silver. We will discuss how the electronic, surface and crystal structures can be tailored to design better nanoparticle electrocatalysts for oxygen reduction, and better materials for lithium storage.

The Academy of Medicine, Engineering and Science of Texas

Wednesday April 4 - Thursday April 5 - Hyatt Town Lake

"The Best Little Nano Conference in Texas"

Dr. Albena Ivanisevic, Purdue University

Wednesday April 11 - Noon to 1PM, NST 1.104

"Fabrication and Characterization of Biological and Chemical Architectures"

The talk will describe the fabrication of micro and nano patterned surfaces. The development of surface chemistry strategies to immobilize unique peptides to inorganic and organic surfaces will be presented. The approaches used include unconventional lithographic methodologies to precisely place the peptides on various substrates and a host of surface spectroscopic techniques to understand the chemical composition, molecular conformation and mechanical properties of the molecules on the patterned surface. The fundamental knowledge gained is being utilized to fabricate much improved microfabricated sensors for diagnostic purposes and advanced platforms for tissue engineering applications.

JOINT SEMINAR - Center for Mechanics of Solids, Structures and Materials &
Center for Nano and Molecular Science and Technology

Dr. Paul Weiss, Pennsylvania State University

Thursday May 10 - 3:30PM to 4:30PM, NST 1.104

“Designing, Measuring and Controlling Molecular- and Supramolecular-Scale Properties for Molecular Devices”

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be designed, directed, measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns, and to control and to stabilize function. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We employ some of these approaches in directed assembly to enable bioselective and biospecific binding. We also selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements. We quantitatively compare the conductances of molecule-substrate junctions. We demonstrate the importance of these junctions in conductance switching of single molecules.

Dr. Rodney Ruoff, Northwestern University

Wednesday May 30 - Noon to 1PM, NST 1.104

"Fracture Mechanics of Carbon Nanotubes and The Advent of Graphene-based Materials"

A brief update is given on experimental fracture mechanics of carbon nanotubes,  specifically single-walled (SWCNTs) of known diameter and chirality.  I then turn to discussing a new class of materials, the graphene-based materials.  Our top-down approaches [1,2] inspired physicists to study individual layers of graphite prepared by micromechanical exfoliation, but our current approach has been to convert graphite to graphite oxide (GO), generate colloidal suspensions of individual layers of GO (we call them ‘graphene oxide’) in water, and to use these individual layers in a variety of ways.  For example, we have embedded individual and reduced 'graphene oxide' sheets in polymers such as polystyrene and evaluated their dispersion, sheet morphology, and the electrical percolation and conductivity of the resulting composites.  In parallel paths, we have: (i) undertaken studies of individual graphene oxide and reduced graphene oxide sheets, to elucidate their optical and electrical properties, (ii) embedded graphene oxide sheets in glass by a sol-gel route and made electrically conductive and transparent glass coatings, and (iii) produced 'graphene oxide paper', a material with intriguing  mechanical properties.   Support of our work by the NSF, ONR/NRL, NASA, and DARPA is appreciated. 

Harrington Symposium on Solid State Quantum Electrodynamics

October 6-7

New developments in semiconductor and superconductor-based nanotechnology have made possible the investigation of light-matter coupling in solid state systems with cavity-confined electromagnetic modes.

The solid state nature of these systems gives a new perspective to quantum effects that have been traditionally investigated in atomic and molecular systems.

This Harrington symposium will provide a timely platform for an active discussion on this very exciting frontier area.

Topics

* Rabi oscillations and Purcell effect in Quantum Dots
* Superconductor Cavity QED
* BEC and Dynamics of Microcavity Polaritons
* Applications of cavity QED to Quantum Information
* Cavity QED with Organic Optical Media
* Optical Nanoresonators

Ken Shih, Physics Department, UT Austin

Wednesday October 25 - Noon to 1PM

"Quantum Engineering of Nanostructures: Electronics and Photonics"

ABSTRACT
Over the past few years, the rapid advancement of nanoscience has provided exciting possibilities to quantum -- mechanically engineer the physical properties of nanostructures. In this talk, I will cover a few novel aspects related to engineering of the electronic and photonic properties of nanostructures. First, I will discuss how confinement of single-particle electronic states can profoundly impact the thermodynamic stability of metallic nanostructures. I will then discuss that such Quantum Size Effect (QSE) can also impact the kinetic processes of the nanostructure formation as well as the collective electronic properties such as superconductivity. I will then discuss two types of quantum engineering of photonic propertiesof semiconductor quantum dots (SQDs), also referred to as artificial atoms. The first involves with "active" manipulations of quantum states in SQDs using laser beams to drive and shape the wave function of the quantum states. Concrete examples of such active manipulations are driven Rabi-oscillations and related qubit operations. The second type involves with "passive" control of quantum optical properties of SQDs through the modification of environmental electromagnetic field, namely the cavity. Specific examples are novel single QD layer laser and Purcell effects.

Nanomaterials Conference - NST Opening Meeting

Thursday November 2 - Friday November 3

Speakers: Paul Barbara, Brian Korgel, Maxim Tsoi, Lynn Loo, Dick Crooks, Masuhara, Ananth Dodabalapur, MacDonald, Gilbert, Lozano

Marek Potemski, Grenoble High Field Laboratory, Universite Joseph Fourier, Grenoble France

Wednesday November 15 - Noon to 1PM

Dr. Sanjay Banerjee, MRC, UT Austin

Wednesday November 29 - Noon to 1PM

"Microelectronics: The Beginning of the End or the End of the Beginning"

ABSTRACT
Naysayers have been claiming for some time now that the dramatic progress of microelectronics in accordance with Moore's law over the last several decades is about to come to crashing halt in a decade or so due to fundamental device scaling limits. We will give examples from novel semiconductor memory and logic devices that indicate that the future is likely to be even more exciting, with the morphing of microelectronics into nanoelectronics. We will give some examples of work being pursued under the auspices of the South West Academy for Nanoelectronics.

PORTFOLIO STUDENT SEMINARS - Graduate Portfolio Program Research Colloquium

Wednesday December 6 - Noon to 5PM, NST 1.104

Daniel Fine, PhD Candidate and Portfolio Program Student, Electrical & Computer Engineering, UT Austin

12:00PM to 12:30PM

"Organic Field Effect Transistors and their use as Chemical Sensors"

Thin film transistor (TFT) sensors, using such semiconductors as pentacene, copper phthalocyanine and polythiophene, were fabricated to investigate their chemical sensing responses to a number of analytes for a series of channel lengths, ranging from 22 nm to 300 micron. Other micro-scale devices were modified with small molecule receptors in an effort to make the devices more sensitive to particular chemical functional groups such as alcohols or ketones. Guarding electrodes as close as 20 nm to the two sides of the channel were employed to suppress spreading currents and a thin dielectric layer was grown locally in the active area to suppress short channel effects in the nano-scale devices. The drain current exhibited opposite responses to the same analyte when the channel length shrunk fromhundreds of microns down to 22 nanometers, with the crossover observed at a certain channel length relative to the average grain size of the polycrystalline semiconductor film. The drain current also changed with the addition of the receptors, showing magnified responses and thus indicating a possibility to improve sensitivity and functional group selectivity.

Donald Owens, PhD Candidate and Portfolio Program Student, Chemical Engineering, UT Austin

12:30PM to 1:00PM

"Externally-triggered Metal Polymer Nanocomposites as Intelligent Therapeutic Systems"

Research in the field of biomaterials and advanced drug delivery is moving toward individually-tailored intelligent therapeutic systems which are capable of responding to and correcting undesirable conditions, on a molecular level, within the body. These systems mimic natural biosystems in their size, structure, and function and thus need to be miniaturized using advanced nanofabrication techniques. Furthermore, thermally-responsive polymer-based systems appear to be the most likely candidates for use in injectable intelligent therapeutic systems because of the relative ease with which temperature can be controlled locally. In recent years a variety of synthetic polymer systems have been developed in the hopes of achieving intelligent therapeutic function. Currently, these systems are typically prepared as bulk polymer films which can then either be implanted subcutaneously or crushed into microparticles, neither of which would be acceptable forms for injectable intelligent therapeutics. In addition to the bulk polymer films, thermally-responsive polymer nanoparticles have also been prepared; however, these systems utilize lower critical solution temperature polymers, such as poly(N-isoproylacrlyamide), which are not the ideal thermally-responsive mechanism for injectable controlled drug delivery systems. Hence, there is a need to design intelligent therapeutic systems that can synergistically incorporate the aspects of intelligent response, imaging, and non-invasive externally triggered therapeutic control into one complete nanocomposite system. Such systems will achieve a higher standard of disease management, patient compliance, and quality of life. This work describes the synthesis and characterization of novel core-shell nanocomposite systems. These systems were created by the encapsulation of a gold nanoparticle (diameter ~ 50 nm) within a poly(acrylamide)/poly(acrylic acid) interpenetrating polymer network (PAAm/PAA IPN) shell (thickness ~ 150 nm) via an in situ free-radical inverse emulsion polymerization method. PAAm/PAA IPN shells were selected due to their unique upper critical solution temperature (UCST) sigmoidal swelling behavior, which makes them an ideal on/off mechanism for controlled drug delivery. Non-invasive triggering of therapeutic release and imaging were then achieved using an external laser source which was readily absorbed by the gold nanoparticle core of the system and converted to heat. This localized heating triggered the swelling of the surrounding polymer shell as well as the production of broadband ultrasound waves, which were then used to photoacoustically image the nanocomposite particles. Therefore, the successful encapsulation of gold nanoparticles within thermally-responsive polymeric shells, forming novel metal-polymer nanocomposite based intelligent therapeutic systems, was demonstrated. Furthermore, these nanocomposite systems exhibited for the first time ever the combination of thermally-responsive UCST swelling, photoacoustic imaging, and non-invasive externally triggered control in a single intelligent therapeutic device.

Forrest Davidson, PhD Candidate and Portfolio Program Student, Chemical Engineering, UT Austin
1:00PM to 1:30PM

"Lamellar Twinning in Semiconductor Nanowires"

Gallium arsenide and gallium phosphide nanowires as small as 8 nm in diameter were synthesized in supercritical hexane and seeded by alkanethiol-stabilized 7 nm gold nanocrystals. The wires are single crystal with a zinc-blende structure and grow exclusively in the <111> direction. The importance of precursor degradation kinetics was explored. Multiple lamellar {111} twins are observed in GaAs, GaP and InAs nanowires synthesized by supercritical fluid-liquid-solid (SFLS) and solution-liquid-solid (SLS) approaches. All of these nanowires have zinc blende (cubic) crystal structure and were grown in the <111> direction. The twins cross-section the nanowires to give them a "bamboo"-like appearance in TEM images. In contrast, Si and Ge nanowires with <111> growth direction do not exhibit {111} twins, even though this is a common twin plane with relatively low twin energy in diamond cubic Ge and Si. However, Si and Ge nanowires with <112> growth directions typically have several {111} twins extending down the length of the nanowires. A semi-quantitative model that explains the observed twinning in III-V and IV nanowires is presented.


Roman Caudillo, PhD Candidate and Portfolio Program Student, Materials Science & Engineering, UT Austin

1:30PM to 2:00PM

"Ferromagnetic Behavior of Carbon-encapsulated Ag Nanoparticles"

The structure and magnetic properties of a silver and carbon nanocomposite will be presented. The as-synthesized nanocomposite consists of a matte-black powder composed of Ag nanoparticles encapsulated in carbon nanospheres (~10 nm diameter) that are interconnected in necklace-like structures. Magnetic measurements of the Ag and C nanocomposite, in its powder form, showed weak ferromagnetic behavior up to at least room temperature with a coercive field of 389 Oe at 2 K and 103 Oe at 300 K, from which we estimate magnetic ordering up to 425 K. However, pressing the Ag-C powder samples into tablets suppressed the ferromagnetism; the pressed samples instead exhibited diamagnetic behavior. Chemical analysis with EDS and trace metal analysis with ICP-MS indicated that there are no magnetic contaminants in the sample. Therefore, we attribute the ferromagnetism to the carbon nanospheres and propose a model for the observed magnetism. We also measured a pronounced peak in the magnetization between 50 and 90 K that was completely suppressed when measurements were made upon cooling; we attribute this peak to a first-order spin reorientation.


The structure and magnetic properties of a silver and carbon nanocomposite will be presented. The as-synthesized nanocomposite consists of a matte-black powder composed of Ag nanoparticles encapsulated in carbon nanospheres (~10 nm diameter) that are interconnected in necklace-like structures. Magnetic measurements of the Ag and C nanocomposite, in its powder form, showed weak ferromagnetic behavior up to at least room temperature with a coercive field of 389 Oe at 2 K and 103 Oe at 300 K, from which we estimate magnetic ordering up to 425 K. However, pressing the Ag-C powder samples into tablets suppressed the ferromagnetism; the pressed samples instead exhibited diamagnetic behavior. Chemical analysis with EDS and trace metal analysis with ICP-MS indicated that there are no magnetic contaminants in the sample. Therefore, we attribute the ferromagnetism to the carbon nanospheres and propose a model for the observed magnetism. We also measured a pronounced peak in the magnetization between 50 and 90 K that was completely suppressed when measurements were made upon cooling; we attribute this peak to a first-order spin reorientation.

Andrew Barron, Department of Chemistry, Department of Mechanical Engineering and Materials Science, Rice University

January 25, 2006 - Noon – 1:00 PM, ACES 2.302

“Fullerene Amino Acids as a Passport for Peptides through Cell Membranes”

ABSTRACT
Intracellular drug delivery and targeted diagnostic probe delivery are of the utmost importance in drug development, disease diagnosis and disease treatment. The development of a new approach to intracellular delivery will be discussed, with the use of a hydrolytic stabile fullerene substituted phenylalanine derivative, "Bucky amino acid" (Baa), as part of a peptide based drug system synthesized by SPPS. A series of fullerene substituted phenylalanine derivatives have been prepared. The N-Boc- and Fmoc-protected derivative readily undergoes coupling with the appropriate amino acid derivatives. The presence of a fullerene-based amino acid acts as a passport for intracellular delivery, allowing the transport of cationic peptides into HEK-293, HepG2, and neuroblastoma cells where the peptides in the absence of the fullerene amino acid cannot enter the cell. Specific delivery of the fullerene species to either the cytoplasm or nucleus of the cell is also demonstrate

d. The NLS fullerene peptide can actively cross over the cell membrane and accumulate significantly around the nucleus of

HEK-293 and neuroblastoma cells, while others accumulates in the cytoplasm.

Dr. Harry Atwater, Applied Physics and Materials Science, California Institute of Technology

Wednesday, February 01, 2006Noon – 1:00 PM, ACES 2.302

“Plasmonics: A Route to Nanoscale Optical Devices”

ABSTRACT
Since the development of the light microscope in the 16th century, optical device size and performance has been limited by diffraction. Photonic devices of today are composed of dielectric materials with modest dielectric constants, and are much bigger than the smallest electronic devices for this reason. However subwavelength spatial confinement of light at dimensions down to less than 10% of the free-space wavelength is possible using plasmonic components. Ultimately it may be possible to employ plasmonic components to form the building blocks of a chip-based optical device technology that is scaleable to molecular dimensions, with potential imaging, spectroscopy and interconnection applications in computing, communication and chemical/biological detection.
In this talk I will describe recent opportunities presented by plasmonics for chip-scale integration of photonic and electronic devices, including i)design of metal-insulator-metal plasmon waveguides that optimize the trade-off between mode localization and propagation loss in the visible and near-infrared ii) on-chip Si CMOS compatible light near-infrared light sources for coupling into plasmonic networks iii) plasmon-enhanced emission from quantum dots, and iv) opportunities for active plasmonic devices based on electro-optic and all-optical modulation of plasmon propagation.

Dr. Naomi Halas, Chemistry and Electrical & Computer Engineering, Rice University

February 08, 2006 - Noon – 1:00 PM, ACES 2.302

“Nanoshells: From Plasmon Physics to Cancer Therapy”

ABSTRACT
In recent years we have shown that certain metallic nanoparticles possess plasmon resonances that depend very sensitively on the shape of the nanostructure. This interesting observation has led to a fundamentally new understanding of plasmon resonances of metallic nanostructures- “Plasmon Hybridization”- where the collective electronic resonances in a metallic nanostructure is rigorously analogous to the single electron quantum states of simple atoms and molecules. The Plasmon hybridization picture explains the tunability of nanoshells, a dielectric core, metallic shell nanoparticle which is the simplest nanostructure with tunable plasmon resonances. Moreover, this picture provides a nanoscale “design rule” for understanding the plasmon resonances of an entire new family of plasmonic nanostructures: reduced symmetry nanostructures (nanoeggs and nanorice), multilayer nanoshells (nanomatryushkas), nanoscale dimers, trimers, and N-mers, and a metallic nanosphere adjacent to a thin metallic film (nanoantenna). Since the plasmon resonances give rise to large local field enhancements on the nanostructure surfaces, a variety of surface enhanced spectroscopies such as Surface Enhanced Raman Scattering (SERS) can exploit these types of designed metallic nanostructures as tailored, high-performance SERS substrates. In addition, by tuning plasmon resonances into the near infrared region of the spectrum, the physiological “water window” can be accessed, where blood is essentially transparent and light penetrates maximally through human tissue. With bioengineers, we have developed a suite of applications for nanoshells in the human body, such as a nanoshell-based approach to cancer therapy which will be described.

Jose L Elechiguerra, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Chemical Engineering, University of Texas at Austin

Wednesday, February 15, 2006 - Noon – 1:00 PM, WEL 2.304

“Inhibition of HIV-1 by Silver Nanoparticles”

ABSTRACT
Nanotechnology provides the ability to engineer the properties of materials by controlling their size, composition and shape. Some of the most attractive cases are noble-metal nanoparticles, which exhibit interesting properties due to phenomena such as quantum size effects and high surface-to-volume ratio. Several promising uses for these nanostructures involve biological applications, including biosensors, labels for cells and biomolecules, and cancer therapeutics. As a result, the interaction of nanoparticles with biomolecules and microorganisms is an expanding field of research. Nevertheless, an area that has been largely unexplored is the interaction of metal nanoparticles with viruses.

On the other hand, there is an urgent necessity for the development of safe and effective inhibitors for HIV. Microbicides may offer one of the most promising preventive alternatives that could be safe, effective, inexpensive, and widely available. Among noble-metals, silver has long been known to have strong bactericidal properties. The higher reactivity of silver nanoparticles compared to other silver compounds make silver nanoparticles an interesting candidate for bactericidal activity and significant research in the area has been conducted. For these reasons we decided to extend this field of study to determine, for the first time ever, the antiviral properties of silver nanoparticles.

In my research project, we have demonstrated that silver nanoparticles undergo specific interaction with HIV-1 via preferential binding with the gp120 subunit of the viral envelope glycoprotein, inhibiting the virus from binding to host cells. Although the mechanism of HIV infection is not yet fully understood, there are two steps that are broadly agreed to be critical. The first step involves binding of gp120 to the CD4 receptor site on the host cell. Then, a conformational change is induced in gp120, resulting in exposure of new binding sites for a chemokine receptor. Therefore, by directly interacting with the gp120 glycoprotein, silver nanoparticles block the virus from binding with host cells, thereby preventing infection. The flexibility of nanoparticle preparation methods and the facile incorporation of nanoparticles into a variety of media provide the incentive for further research on this topic and might generate new paths to fight the AIDS epidemic.

Liangfeng Sun, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Department of Physics, University of Texas at Austin

Wednesday, March 01, 2006 - Noon - 1:00 PM, WEL 2.304

"Second-harmonic light from silicon nano-interfaces"


ABSTRACT
Embedded silicon nanocrystals (NCs) underlie flash memory and light-emitting devices. Their unique charge-trapping and light-emitting properties originate from the sharply curved interfaces between the silicon NCs and their host (e.g. glass). However, the electronic structure of these nano-interfaces remains poorly understood, partly because of a lack of suitable experimental probes. Optical second-harmonic generation (SHG), which is widely used in probing planar interfaces, can also effectively probe these nano-interfaces, despite their overall centrosymmetry. In this talk I will present results using a traditional single-beam, and a novel two-beam configuration. Similar techniques may be applicable to biological nano-interfaces. Related applications of SHG (e.g., in situ monitoring of nanocrystal growth, and quasi-phase-matched frequency doubling "crystal") will also be discussed.

Professor Vinayak Dravid, Materials Science and Engineering, Northwestern University

Wednesday, March 08, 2006 - Noon - 1:00 PM, ACES 2.302

"Nanopatterning of Functional Inorganics"

ABSTRACT
Our recent research efforts at Northwestern University are geared towards designing intricate architecture of functional nanostructures, as well as using them as building blocks for device systems for sensing, diagnostics and therapeutics. Embedded in this scheme are several nanopatterning approaches, some are based on the original invention of Dip-Pen Nanolithography (DPN) developed at Northwestern. The original DPN approach is modified to pattern, at the nanoscale, templates for inorganic and organic-inorganic complexes of arbitrary shape/size on arbitrary substrates, thus extending the efficacy and elegance of DPN. Subsequently, several direct methods (e.g. nano-fountain-pen) in conjunction with sol-based precursors have been developed for site- and shape-specific patterning of functional inorganics at nanoscale, thus circumventing the two-step template-based approach. The talk will outline modified DPN and sol-based precursor "inks" as an enabling approach to pattern and characterize magnetic, electronic, chemical- and optical active nanostructures at the nanoscale. Success is already evident for magnetic oxides, inorganic mesoporous structures, ferroelectrics and optically-active nanostructures. The real need for characterizing structure/crystallography, 3-D morphology, local chemistry and conformation of such nanopatterns, as well as unambiguous measurement of their local properties, will be emphasized. The prospects for patterning at single-molecule resolution, especially for bioactive molecules, both by themselves and as templates for inorganics, will also be discussed. It will be argued that functional nanostructures go beyond the "hype", and present challenging yet exciting opportunities for synthesis-structure-architecture-form-function-performance relationships, especially in hybrid organic-inorganic systems.

Yi Lu, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Department of Mechanical Engineering, University of Texas at Austin

Wednesday, March 29, 2006 -Noon – 1:00 PM, WEL 2.304

“Laser-assisted Micro/Nano Fabrication of Polymeric Materials”

ABSTRACT
In the presentation, two micro/nano fabrication techniques will be introduced. Firstly, inspired by the laser dry cleaning, we developed a method that allows nanopatterning structures on solid surfaces with lasers. Silica and polystyrene nanospheres with diameters in the order of the laser wavelength were deposited on a silicon surface and arrange themselves into hexagonally close-packed form due to capillary force. Irradiation with lasers produced dent structures underneath these spheres. Laser light was intensified by nanospheres due to near-field effects. Hexagonally arranged nano dent structures were formed due to the redistribution of material underneath the spheres. Competition between the thermocapillary force and chemicapillary force was revealed in the course of the dent formation process; Secondly, we have developed a simple and fast, layer-by-layer microstereolithography system, based on a digital micro-mirror masking device, that allows fabrication of complex internal features along with precise spatial distribution of biological factors inside a single scaffold. Photo-crosslinkable poly(ethylene glycol) diacrylates were used as the scaffold material, and murine bone marrow-derived cells were successfully encapsulated or seeded on fibronectin-functionalized scaffolds. We demonstrated that precisely controlled pore size and shapes could be easily fabricated using a simple, computer-aided process. This technique was also capable of ultra-fast forming of polymer microlens array in a single-step, massive-parallel fashion. It provided significant flexibility in controlling and designing the lens geometry. Moreover, the design was performed in a computer and is executed through a computer-controlled dynamic photomask. It took minutes from initiating a new design to fabrication.

Dr. Paulo Ferreira, Assistant Professor, Materials Science and Engineering Program, UT Austin

April 5, 2006 - Noon - 1:00 PM, ACES 2.302

"In-Situ Transmission Electron Microscopy: MapQuest for Materials"

ABSTRACT
In-situ TEM has emerged as a powerful tool for the dynamic characterization of materials. The advent of electronic cameras, and the continued developments in electron optics and stage designs enable scientists and engineers to enhance the capabilities of previous TEM analyses. Currently, novel in-situ experiments observe and record the behavior of materials in various heating, cooling, straining, or gas environments. They can validate static TEM experiments and inspire new theories and new experimental approaches by understanding and characterizing dynamic microstructural changes. In this talk, an overview of in-situ TEM techniques will be presented and related to the quest for mapping materials. Next, the following examples of TEM work and its applications will be shown: First, in-situ heating TEM, used to observe, in real time, the stress relaxation behavior in 1.8 microns and 180 nm wide Cu interconnects, and second, in-situ straining in an environmental cell TEM, used to study hydrogen/metal interactions. Finally, work on the inverse Hall-Petch effect observed for nanocrystalline materials will be discussed.

Domingo G Gutierrez, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Materials Science and Engineering Program, University of Texas at Austin

Wednesday, April 12, 2006 - Noon - 1:00 PM, WEL 2.304

"Elemental Localization in Novel Nanostructures based on TEM Related Techniques"


ABSTRACT
High Angle Annular Dark Field (HAADF) and Electron Energy Loss Spectroscopy were investigated as characterization tools for chemical element localization in novel nanostructures. The nanostructures analyzed in the present study were Pt-Au core-shell bimetallic nanoparticles and semiconductor doped layers Pt-Au bimetallic nanoparticles were synthesized by the polyol method and characterized with the techniques previously mentioned; temperature effect on this synthesis was also investigated. EDS results confirmed the bimetallic nature of the synthesized nanoparticles. HAADF was determinant in the identification of core-shell nanoparticles. This was possible due to the presence of strain fields in the interface between the core and the shell elements produced by the difference in their lattice parameter. The presence of these strain fields produced an anomalous contrast on the HAADF images, which enabled the identification of this interface, and hence of the core-shell nanostructures. UV-Visible absorption spectra (experimental and simulated) in combination with EXAFS results allowed the identification of Au on the shell of the nanoparticles and Pt in the core. HAADF was proved to be a useful technique for core-shell nanoparticles identification. Several doped semiconductor nanostructures were also studied; B doped Si FinFET nanostructures, As doped Si samples and Ge1-xCx thin layers. For the case of the B doped Si FinFET nanostructures strain fields produced by the implantation of B atoms into the Si lattice allowed a qualitative determination of the 2-dimensional B dopant profile with the use of HAADF, just as in the case of the core-shell nanoparticles. In the As doped Si samples, EELS is proposed as a quantitative characterization tool for the determination of dopant concentrations based on the relationship described in the free-electron gas model between the characteristic plasmon peak energy (located in the low loss region of the EELS spectrum) and the electron density. Promising results obtained in the present study indicate the feasibility of using EELS as a quantitative tool for dopant concentration studies. Finally, a proper analysis of the EELS results allowed the observation of preferential segregation of C atoms to the interface between the Ge1-xCx thin layers and the Si substrate where these layers were grown. We interpret this result as a mechanism of strain relaxation in Ge1-xCx layers grown directly on Si substrates. Both techniques, HAADF and EELS, were confirmed to give reliable information related to the localization of different elements conforming novel nanostructures when a careful and controlled analysis is performed.

Dr. Maxim Tsoi, Assistant Professor, Physics Department, UT Austin

Wednesday, April 19, 2006 Noon - 1:00 PM, ACES 2.302

"Spin-Transfer in Magnetic Nanostructures"


ABSTRACT
It is well known that the magnetic state of a ferromagnet can affect the electrical transport properties of the material; for example, the relative orientation of the magnetic moments in magnetic multilayers underlies the phenomenon of giant magnetoresistance. The inverse effect, in which a large electrical current density perturbs the magnetic state of a ferromagnet, has been observed in experiments on current-driven spin-wave generat on, magnetization reversal, and magnetic domain wall motion. The novel mechanism responsible for these observations is termed spin transfer because the spin angular momentum is delivered from conduction electrons to the magnetic material. In my presentation I will describe a series of spin-tra sfer studies involving point contacts and lithographically patterned samples. First I will focus on point-contact experiments. Point contacts were instrumental both for our original observation of current-induced excitations and in providing the first data on frequencies of the current-induced spin waves. Recently, we have demonstrated that point-contact technique can also provide valuable information about wavenumbers of the current-induced excitations. I will discuss various aspects of the current-induced excitations, including its temperature dependence, coupling to lattice vibrations, symmetry, etc., which shade light on the underlying physical mechanisms. I will also discuss another manifestation of spin-transfer phenomena in magnetic nanostructures - motion of magnetic domain walls traversed by an electrical current. We have observed the current-induced propagation of magnetic domain walls in magnetic nonostripes. We monitor the domain-wall propagation by electrical transport measurements, magnetic force microscopy and/or MOKE imaging. The device geometry allows us to distinguish between various mechanisms of interaction between an electrical current and domain walls; we find that spin transfer dominates.

Dr. Gregory Scholes, Dept. of Chemistry and Institute for Optical Sciences,
University of Toronto

Wednesday, April 26, 2006 - Noon - 1:00 PM, ACES 2.302

"Excitons in Nanoscience"

ABSTRACT
Nanoscale materials provide a fascinating intermediate ground between molecular materials and the bulk. An exciting aspect of nanoscience is that relationships between structure and electronic properties are being revealed through a combination of synthesis, structural characterization, chemical physics, and theory. A challenge in this field is that the materials under investigation are often quite complex; they contain many atoms, they can be structurally disordered or influenced by surface effects, and samples often have an inhomogeneous composition in terms of structural disorder and size polydispersity. Nonetheless, rapid progress has been made in our understanding of a diverse range of materials. Our current understanding of excitons will be discussed for a selection of nanostructured materials, with a particular emphasis on new aspects of exciton photophysics that have been elucidated. In particular, the seminar will describe recent studies of the ultrafast dynamics of exciton spin relaxation in quantum dots and rods.

April Schricker, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Chemical Engineering, University of Texas at Austin

2-in-1 NANOTECHNOLOGY SEMINAR

September 28, 2005 - Noon – 1:00 PM, ACES 3.202

“Electrical Properties of Single GaAs, Bi2S3, and Ge Nanowires”

ABSTRACT
The electrical properties of single nanowires will be discussed. Focused Ion Beam Lithography techniques were used to make electrical connection to and address individual nanowires. The current-voltage (IV) curves for GaAs nanowires were found to be non-linear and exhibited space charge limited currents. Temperature dependent measurements revealed an exponential distribution of traps. Current-voltage (IV) curves for single Bi2S3 were measured under nitrogen as a function of temperature. The data revealed activated transport that followed a Meyer-Neldel relationship. Annealing under vacuum decreased the nanowire resistance by nearly four orders of magnitude. The annealed nanowires followed an inverse Meyer-Neldel relationship. Single germanium nanowire FETs were made using FIB techniques and exhibited p-type behavior when gated. Mobility and resistivity were evaluated as a function of temperature. Input voltage was inverted across the active device. In an effort to improve transconductance a dual gate structure was fabricated and tested. Finally, germanium nanowire FET transconductance improvements were made with the addition of a charge storage molecule.

Felice Shieh, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Chemical Engineering, University of Texas at Austin

“Semiconductor Nanocrystal, Nanorods, and Nanowires, and Applications in Biomolecular Integration”

ABSTRACT
Semiconductor II-VI cadmium telluride nanocrystals were synthesized via thermal decomposition of organometallic precursors and integrated with biomolecules for use as optical probes in prostate cancer detection. Cadmium telluride (CdTe) nanocrystals were first rendered water soluble and biocompatible by ligand exchange from tri-octylphosphine oxide (TOPO) to mercapto-propionic acid (MPA) followed by partial ligand exchange with thiolated polyethylene glycol (PEG). MPA-PEG-capped CdTe nanocrystals were attached to biomolecules, such as aptamers, single-stranded DNA or RNA molecules with a three-dimensional structure that enhances target binding, via well known biotin-avidin interaction. Aptamers targeting prostate specific membrane antigen (PSMA), a type II integral membrane glycoprotein overly expressed in prostate carcinoma, were attached to CdTe nanocrystals. CdTe- PSMA aptamer bioconjugates were tested for binding specificity in vitro against positive control LNCaP cell line, a prostate cell carcinoma overexpressing PSMA, and negative control PC3 cell line, known to lack PSMA expression. In vitro studies showed binding specificity of the CdTe-aptamer bioconjugate to its target. To emulate in vivo environment, tissue phantoms were constructed with each cell line. Not only did tissue phantoms studies show the applicability of bioconjugates within a cell matrix, but these studies also allowed an understanding of bioconjugate penetration through tissue structure. The success of tissue phantom studies paved the path for current in vivo experiments. Preliminary studies are in progress, where “naked”, not bioconjugated, CdTe nanocrystals are delivered through both tail vein and intratumor injections to understand the impact of delivery method and the accumulation of dots within the organs and tumors. Initial studies have been successful, but in vivo cell labeling continues to require further experimentation.

Ali Shakouri, Associate Professor, Department of Electrical Engineering, University of California- Santa Cruz

Wednesday, October 05, 2005 - Noon – 1:00 PM, ACES 2.302

“Nanoscale Energy Conversion Devices”

ABSTRACT
Semiconductor superlattices and embedded metallic nanoparticles can be used to engineer the interaction between heat, light and electricity inside devices. Thin film SiGe superlattices have been used to demonstrate micro refrigerators on a chip. Localized cooling power density exceeding 500W/cm2 has been achieved. In order to measure temperature distribution in IC chips, visible and near IR thermo-reflectance are developed. These allow topside and through the substrate thermal mapping with up to 6mK temperature resolution and submicron spatial resolution. Activities at the multi university Thermionic Energy Conversion Center will be described. Here the goal is to use solid state and vacuum emitters to improve direct thermal to electric energy conversion systems. Theoretical calculations show that thermionic energy converters can achieve 20% efficiency and an energy density >1W/cm2 with hot side temperature of 300-600C. Experimental results with the new nanostructured metallic material (ErAs/InGaAs and TiN/GaN) and preliminary system testing results will be presented. Finally the possibility to achieve electrically pumped optical refrigeration will be briefly discussed.

Kyung-Suk Kim, Professor, Division of Engineering, Brown University

Wednesday, October 12, 2005 -Noon – 1:00 PM, UTC 4.110
(Note: The Seminar Location is University Teaching Center-UTC)

“Friction and Fracture of Carbon Nanotube Structures”

ABSTRACT
Under certain conditions, a solid surface is suspended on a dense array of nanostructures while at other conditions, the surface is imprinted by the nanostructure array. The first part of the talk will be focused on the contact suspension friction of carbon nanotube structures associated with solid surface suspension and imprinting caused by high grafting density contacts and molecular interactions at the interface. Carbon nanotube arrays of high grafting density, greater than one hundred million arrays per square millimeter, are used to study the nanoscale contact suspension friction of plastically deforming solids and the imprintability of high density nanoscale contacts. The study is motivated by the need to develop effective technology for fabricating surface nanostructures and is intended to further the understanding of nanoscale friction and wear.
The second part of the talk will discuss fracture processes of single wall nanotubes in water under certain sonication conditions. In industry and research laboratories it is required to control the length of single wall carbon nanotubes to be used for bio-molecular tracing and for fabricating nano-electronic devices. The experimental results on sonication cutting and sorting of single wall nanotubes are compared with molecular dynamics model simulations. In addition, some other methods of cutting carbon nanotubes such as chemical and ball milling methods will be compared with the sonication methods.

Daniel Feldheim, Department of Chemistry, North Carolina State University

Today, October 26, 2005 - Noon – 1:00 PM, ACES 2.302

“Materials Discovery through RNA In Vitro Selection”

Solid-state materials have played such a significant role in the development of humankind that we now mark the passage of time with such terms as Iron Age and Bronze Age. Today there is no shortage of materials needs, yet the landscape of possible solid-state inorganic compounds is almost incomprehensively vast. Considering all the possible combinations of the 30 transition metal elements alone yields over 1030 different materials. How can we possibly hope to find the perfect combination of atoms for the materials so desperately needed for advanced fuel cell technology, high temperature superconductivity, hydrogen production, etc., if each composition is to be explored one-by-one or even using the best high-throughput screening methods available?

In nature materials discovery has taken the form of evolution and natural selection. Nearly every living organism on Earth has evolved mechanisms for forming solid-state materials, some for structural integrity or protection against predation, others for biosphere function such as light focusing or magnetotaxis. The hypothesis of the work to be presented is that the propensity of biomolecules to evolve in response to selection pressures can be harnessed to synthesize novel “abiological” materials such as superconductors and fuel cell catalysts. Indeed, it will be shown that RNA, and RNA containing key chemical modifications, can evolve in vitro until sequences are found that catalyze the formation of materials with novel morphologies and physical properties. The use of RNA sequences to assemble spatially well defined materials assemblies in solution and on surfaces will also be discussed

Dimitrie Culcer, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant
Physics Department, University of Texas at Austin

November 9, 2005 - Noon – 1:00 PM, ACES 2.302

“Spin Transport in Semiconductors”

Motivated by recent interest in novel spintronics effects, I will discuss two ways we propose to generate a spin polarization in systems with spin-orbit interactions. The first involves a spin current. I will discuss the various contributions to the spin current and how it may generate a spin polarization at the edge of the sample. The second method involves a torque on the spins which acts when an electric field is present and can be used to generate a spin polarization in the bulk. I will review experiments for both cases.

Tae-ho Jung, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant
Electrical and Computer Engineering, University of Texas at Austin

“Nanoscale N-Channel and Ambipolar Organic Field Effect Transistors”

ABSTRACT
Small molecule and polymer-based organic thin-film transistors (OTFTs) have been intensely explored due to their low-cost, processibility and compatibility with large-area flexible substrates. Complementary circuits have emerged as a promising circuit technology for organic semiconductors due to low power consumption and high noise margins. While many efforts to improve OFET performance involve new materials and device structures, decreasing channel length will greatly enhance device performance by increasing switching frequency, which is inversely proportional to the square of the channel length. In this study nanoscale n-channel organic transistors and ambipolar transistors with the heterostructure bi-layer scheme are fabricated and characterized.

Dr. Costas Grigoropoulos, Department of Mechanical Engineering, University of California- Berkeley

Wednesday, November 16, 2005 - Noon – 1:00 PM, ACES 2.302

“Laser-Assisted Directed Nanostructure Synthesis and Nanoparticle-based Processing”

ABSTRACT
Recent research results on laser-assisted nanomachining, nanolithography and nanodeposition will be presented. Ultra-fast and nanosecond pulsed lasers have been coupled to near-field-scanning optical microscopes (NSOMs) through apertured bent cantilever fiber probes as well as with atomic force microscope (AFM) tips in apertureless configurations. Experiments have been conducted on the surface modification of metals, polymers and semiconductor materials in both ambient air and controlled environments. By combining nanoscale ablative material removal with subsequent chemical etching steps, ablation nanolithography and patterning of fused silica and crystalline silicon wafers has been demonstrated. Confinement of laser-induced crystallization to nanometric scales has been shown. Nucleation and growth of semiconductor materials has been achieved by nanoscale laser chemical vapor deposition (LCVD). Work on nanoscale chemical analysis will be discussed.

The concept of effective laser curing of nanoparticle suspensions (NPS) with a laser beam is presented. The work is based on the significant depression of the melting point of nanoparticles compared to bulk gold. Gold nanoparticle suspension is printed on glass and polymer substrates and cured with laser irradiation. Microlines of low resistivity are produced. Pulsed laser radiation is utilized to process the deposited microlines for the fabrication of active and passive functional device cmponents on flexible substrates.

2-in-1 NANOTECHNOLOGY SEMINAR

Wednesday, November 30, 2005 - Noon – 1:00 PM, ACES 2.302

Yongqiang Jiang, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant
Electrical and Computer Engineering, University of Texas at Austin

“Photonic Crystal Waveguides Based Slow Photon for Silicon Optical Modulator Devices and True-Time Delay Structured Phased-Array Antenna Systems”

ABSTRACT
Nanophotonics including photonic crystals promises to have a revolutionary impact on photonics technology. Photonic crystals are a new class of artificial optical materials with periodic dielectric structures, which result in unusual optical properties and promise to provide revolutionary solutions to the miniaturization of photonic devices. We experimentally demonstrated an ultra-compact silicon electro-optic modulator based on silicon photonic crystal waveguides for the first time to our knowledge. Modulation operation was demonstrated by carrier injection into an 80 µm-long silicon photonic crystal waveguide of a Mach-Zehnder interferometer structure. The π phase shift driving current across the active region is as low as 0.15 mA. We also experimentally demonstrated tunable optical true time-delay modules based on highly dispersive photonic crystal fibers to provide continuous radio-frequency squint-free beam scanning for an X-band (8-12GHz) phased array antenna system. The novel cladding structure of photonic crystal fibers consisting of an array of micrometer-sized air holes allows for flexible tailoring of the dispersion curve. The far field radiation patterns of a 1´4 subarray were measured from –45o to 45o scanning angles. Squint-free operation is experimentally confirmed.

Muhammad Mustafa Hussain, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Electrical and Computer Engineering, University of Texas at Austin

“Advanced Fabrication Processes for Sub-50nm CMOS”

ABSTRACT
Scaling CMOS technology into sub-50nm has presented a significant new challenge for the semiconductor industry. In these devices, silicon oxide gate dielectric and poly-silicon gate electrode need to be replaced with high-k and metal, respectively, due to the limitation of scaling gate dielectrics and high gate leakage current. Therefore, alternative high-k materials have been studied to allow further scaling and reduce gate leakage at the same time. Poly- silicon gate electrode shows “gate depletion effect” that add 3~5Å to the total dielectrics thickness. Also it shows incompatibility with high-k dielectrics in the PMOS due to boron penetration and Fermi level pinning. Therefore, replacing poly-gate with metal gate is an effective way to solve those problems. This is now a major field that researchers are working on to identify two metals with the right work function that will replace N-poly and P-poly. One of the major challenges in this new high-k/metal CMOS implementation is the advanced process integration of dual metal gates to realize nano-scale CMOS operation. In deposition-etch-deposition approach to implement dual metal gate CMOS , deposition of high-k, 1st metal and hard-mask respectively, selective wet etch of the 1st metal (Fig. b) and then the hard mask and finally the 2nd metal deposition steps are performed sequentially (Fig. c). Wet-etch is preferred to dry etch as it reduces possible damage on high-k film. Critical aspect of this step includes wet-etch selectivity between mask and underlying high-k. This process flow is quite different from the conventional approach. The problem begins as no specific suitable metals have been identified yet that can satisfy the requirement for replacing N+ and P+ poly gate electrodes. Therefore the study of metals is a continuing process along with the issues whether the suitable metals would be compatible with the underneath high-k insulator and hard mask, etch selectivity, thermal stability for the subsequent processing steps, film morphology, etc. To address all these issues properly, extensive in-depth research with specific focus is a fundamental requirement. Therefore, study of the advance processes for nanoscale dual metal gate CMOS integration is the objective of this proposal.

Aaron Saunders, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Chemical Engineering, University of Texas at Austin

December 7, 2005 - Noon – 1:00 PM, ACES 2.302

“Interparticle Interactions, Self-Assembly and Shape-Control of Colloidal Nanocrystals”

ABSTRACT
Only relatively recently have synthetic advances enabled the general use of sterically stabilized nanocrystals to form ordered colloidal solids, both for studying self-assembly behavior on the nanometer lengthscale as well as for determining the collective properties of colloidal nanocrystals. Of particular interest is the use of nanocrystals to form "meta-materials" - nanocrystal solids exhibiting "bulk" properties arising from the unique combination of the individual properties of different kinds of nanocrystals, or from hierarchal ordering which gives rise to unique properties at several different lengthscales. My research has focused both on methods which give rise to the spontaneous self-assembly of such materials, and also on experiments which provide a fundamental understanding of the solvent-mediated nanocrystal interparticle interactions which are essential to the assembly process. Small-angle X-ray scattering (SAXS), for example, is used to quantitatively measure nanocrystal interactions in supercritical or conventional solvents as a function of nanocrystal size or the chemistry of the capping ligand. We also experimentally explore the self-assembly of complex nanocrystal solids under both near-equilibrium and non-equilibrium deposition conditions. The former is used to assemble ordered binary nanocrystal superlattices (ordered 2D and 3D arrays of two sizes of nanocrystals), while the latter can be used to form inverse opal nanocrystal superlattice films. Finally, recent work on the synthetic shape control of II-VI semiconductor nanocrystals will be discussed, and the opportunities for tuning the optical properties and composition of the resulting materials.

Professor Norbert F. Scherer, Department of Chemistry,The University of Chicago

Wednesday, December 8, 2004 - Noon – 1:00 PM, ACES 2.302

“Ultrafast Dynamics and Nonlinearity in Nano-Plasmonic Materials: Single Rods and 2-D Arrays”

ABSTRACT
Transducing optical fields into propagating material excitations is a promising route to nanoscale optical manipulation. Surface plasmon resonance excitation in metal nano-structures allows creating plasmonics structures and devices. This talk will address plasmon excitations in Au nanoparticle arrays and Au nanorods. Ultrafast optical studies of ensembles and single rods establish the relaxation dynamics and address new opportunities in field-induced material nonlinearities in single objects. Synthesized Au nanosquare arrays and atomic Au clusters are presented as new materials with promise as plasmonic arrays and in photonics. Time permitting; study of 2-D linear and nonlinear plasmonic arrays will be presented.

Professor Carlos Bustamante, Dept. of Molecular & Cell Biology, Dept. of Physics, Dept. of Chemistry, University of California at Berkeley, Investigator, Howard Hughes Medical Institute

January 19, 2005 - Noon – 1:00 PM, ACES 2.302

“Unfolding of a Single RNA Molecule by Force”

ABSTRACT
We apply mechanical force to induce and follow the unfolding and refolding of single RNA molecules at nanometer length scales, using optical tweezers. To characterize the mechanical unfolding of major RNA structural motifs, we first unfold a simple RNA hairpin, then a related molecule containing a three-helix junction, and finally, P5abc, a domain of the T. thermophila ribozyme that contains the previous elements but adopts a specific tertiary structure in the presence of Mg2+. The hairpin, the three-helix junction, and P5abc (the latter only in the absence of Mg2+) can be mechanically unfolded at equilibrium. When kept at constant force, these molecules display bi-stability and hop between folded and unfolded states. By using different preset forces, we directly control and follow the thermodynamics and kinetics of their folding reactions. These experiments yield the force dependence of the rate constants for folding/unfolding a single RNA molecule under these conditions, the force-dependent equilibrium constants, and the position of the transition state along the reaction coordinate.

Professor Karen L. Wooley, Center for Materials Innovation and Department of Chemistry and Department of Chemistry, Washington University

Wednesday, January 26, 2005 - Noon - 1PM, ACES 2.302

“Polymer Structures as Delivery Systems: Nanoparticles and nanochannels designed as intricate vessels for guest sequestration, packaging and release”

ABSTRACT

The domains or channels that are present throughout well-defined nanostructured materials, derived from the phase segregation of block copolymers or incompatible polymer mixtures, offer interesting opportunities for the packaging and release of guest molecules. The nanoscale dimensions and large interfacial surface areas are expected to provide for high loading capacities within uniform host environments. This presentation will detail two different systems, each constructed from a general methodology that involves the kinetic, in situ cross linking of thermodynamically-driven phase segregated states of polymer assemblies, based upon shell cross linked (SCK) polymer micelles as discrete Nan objects having an amphiphilic core-shell morphology and macroscopic cross linked networks composed of amphiphilic nanodomains dispersed throughout the material. The uptake and release of guests from hydrophobic vs. hydrophilic domains within each of these types of discrete Nan objects and macroscopic materials, of varying compositions, structures, and sizes, will be discussed. Extensions toward increasingly complex architectures, including approaches toward the accurate engineering of the external surface and internal cavity of the SCK colloidal nanoparticles, and their nanocage derivatives, for optimized biochemical interactions and packaging of guests, respectively, will also be discussed.

Professor Mostafa A. El-Sayed Director, Laser Dynamics Laboratory, Julius Brown Chair and Regent Professor, School of Chemistry and Biochemistry, Georgia Institute of Technology

February 02, 2005 - Noon – 1:00 PM, ACES 2.302

“Shape Dependent Properties of Some Semiconductor and Metallic Nano-crystals”

ABSTRACT
The property of a material is characterized by a specific length scale for the motion of its electrons. If the material is reduced in size below this length scale, new properties are found. A great deal of studies has been carried out on the size dependence of the properties of nanoparticles. Less study has been published on the changes in the properties of nanocrystal as their shape changes.

In this talk, we will discuss results on the changes in the ultrafast electron-hole dynamics as the shape of semiconductor nanoparticles is changed. Using femtosound transient bleach spectroscopy, two systems were examined. In one, the effect of changing the spherical CdSe nanocrystal into nanorods was studied. In the second system, the time it takes an electron and a hole (positive charge) to cross the interface between two different materials in a nanoparticle is determined.

The observed results on the effect of shape on the radiative, surface enhanced Raman, and photo-thermal properties of gold nanocrystals will also be presented and discussed.

Swaroop Ganguly, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Electrical and Computer Engineering (Solid-State Electronics), University of Texas at Austin

February 09, 2005 - Noon - 1PM, CPE 2.212

“Bias-controlled Magnetization Switching in a Dilute Ferromagnetic Semiconductor Resonant Tunneling Diode”

ABSTRACT
We predict that the Curie temperature Tc in a dilute magnetic semiconductor (DMS) resonant-tunneling diode (RTD), i.e. an RTD with a DMS well, will decrease abruptly, to approximately half its equilibrium value, when the downstream chemical potential falls below the quantum well resonance energy. This conclusion will be shown to follow from elementary quantum transport theory considerations combined with a mean field theory of DMS ferromagnetism. We have developed a simulation program which numerically and self-consistently solves the non-equilibrium Green function (NEGF), magnetic mean field, and Poisson equations - the results obtained from such simulations will be shown to corroborate the aforementioned theoretical prediction.

Prof. Vladimir Shalaev, The Robert and Anne Burnett Professor of Electrical and Computer Engineering, School of Electrical and Computer Engineering (Solid-State Electronics), Purdue University

Wednesday, February 16, 2005 - Noon – 1:00 PM, ACES 2.302

“Plasmonic Nanophotonics”

ABSTRACT
There is ample evidence that photonic devices can be reduced to the nanoscale using optical phenomena in the near field, but there is also an incompatibility between light wavelength at the microscale and devices and processes at the nanoscale which must first be addressed. Plasmonic nanostructures can act as nanoantennae and thus serve as optical couplers across the nanomicro interface. Recent advances in this rapidly developing area now enable us to mount a systematic approach toward the goal of full systems-level integration of photonics with nanotechnology using nanoscale plasmonics. Plasmonic nanophotonics also promises to create entirely new prospects for guiding light on the nanoscale, some of which may have revolutionary impact on present-day optical technologies. In this talk I outline some of our recent studies on manipulating light and sensing molecules with plasmonic nanostructures.

Prof. Ray Baughman, Robert A. Welsh Professor of Chemistry, Dept. of Chemistry and Nanotech Institute, UT Dallas

February 23, 2005 - Noon – 1:00 PM, ACES 2.302

“Draw-Twist-Spun Multi-walled Nanotube Yarns for Artificial Muscle, Structural, Energy Storage, Energy Harvesting, and Field Emission Applications”

ABSTRACT
We describe a new method for spinning polymer-free carbon nanotube yarns that have promising properties for multifunctional material applications, including as artificial muscles that are either electrically or chemically powered. This spinning method is conducted at room temperature in the dry state for multi-walled carbon nanotubes, which are much cheaper to produce that our previously used single-walled carbon nanotube fibers. Remarkable properties are achieved that relate to high temperature and low temperature actuators and to other multifunctional material applications. The yarns have maximum failure strength of above 460 MPa (850 MPa after polymer infiltration), they are highly resistant to creep and to knot or abrasion-induced failure, and they provide a giant Poisson’s ratio for stretch in the fiber direction. High creep resistance and high electrical conductivity are observed, and retained when yarn strength is substantially increased to 850 MPa by infiltrating polymer into the yarn. Also, these fibers have comparable toughness to the polymers used for antiballistic vests. Experimental results will be provided for diverse applications, especially artificial muscles, energy storage, thermal energy harvesting, and electron field emission. Our advances towards making single walled carbon nanotubes of one type and twist-draw spinning single walled nanotubes will also be described

Michael Sigman, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Chemical Engineering, University of Texas at Austin

Wednesday, March 9, 2005 - Noon – 1:00 PM, CPE 2.212

“Solventless Synthesis, Characterization, and Self-Assembly of Colloidal Nanocrystals”

ABSTRACT
New and general synthetic methods for materials confined to nanometer length scales are needed to provide both an experimental route for exploring material properties as a function of size and a viable means of production for commercial applications. A solventless synthesis technique was developed to produce metal sulfide and oxy-chloride nanocrystals including Cu2S, Bi2S3, and Pb3O2Cl2. A metal thiolate or metal chloride-octanoate serves as the molecular precursor for particle formation via thermolytic decomposition. Monodisperse Cu2S nanoplatelets were synthesized with the c-axis of the hexagonal high chalcocite crystal structure oriented across the width of the disks and the {100} facets oriented along the edges. Preferred adsorption and increased surface reactivity of dodecanethiol on the more energetic {100} crystal facets results in the hexagonal prism morphology.

In comparison, Bi2S3 nanorods and nanowires with the orthorhombic bismuthinite crystal structure grow preferentially in the [001] direction. The aspect ratio depends on the choice of sulfur source. Nanowires were formed using dodecanethiol, while elemental sulfur results in shorter nanorods. Increased reaction temperature produced crossed networks of nanofabric with highly oriented growth resulting from the heterogeneous nucleation of wires 90o from the surface of existing wires. Pb3O2Cl2 nanobelts with the orthorhombic mendipite crystal structure were also produced. These belts are highly birefringent with a difference in the refractive index of ~1.1 with respect to the [010] and [100] crystallographic directions compared to the value of 0.07 for bulk mendipite.

Wei Wei, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Chemistry and Biochemistry, University of Texas at Austin

March 23, 2005 - Noon – 1:00 PM, CPE 2.212

“Directly probing the hybrid bonding of styrene on Cu (111)”

ABSTRACT
The interfacial electronic structure of chemisorbed styrene on Cu(111) was successfully investigated with two-photon photoemission (2PPE) spectroscopy. We observed unoccupied states 3.5 eV above the Fermi level and occupied states 2.0 eV below the Fermi level. Polarization results reveal that the occupied and unoccupied states arise from bonding and antibonding orbitals formed by hybridization of copper (surface state and d-band orbitals) and styrene (π1* and π2* orbitals).

Cindy Stowell, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Chemical Engineering, University of Texas at Austin

Wednesday, March 30, 2005 - Noon – 1:00 PM, CPE 2.212

“Aspects of Colloidal Nanocrystals: Patterning, Catalysis, and Doping”

ABSTRACT
Colloidal nanocrystals have many advantages over those synthesized by other means due to the flexibility not only in the colloidal synthesis conditions but in post-synthesis assembly. I will present my work on three aspects of colloidal nanocrystals that demonstrate this versatility: the self-assembled patterning of nanocrystals into arrays through the use of fluid dynamics, the catalytic properties of iridium nanocrystals as a function of ligand type and recycling, and the doping of III-V semiconductor nanocrystals with magnetic atoms during colloidal synthesis.

Hsiao-Wei Liu, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Chemistry and Biochemistry, University of Texas at Austin

April 6, 2005 - Noon – 1:00 PM, CPE 2.212

“Single-Molecule FRET studies of Important Intermediates in the Nucleocapsid Protein Chaperone Minus-strand Transfer Step in HIV-1 Reverse Transcription”

ABSTRACT
The HIV-1 nucleocapsid protein (NC) is a nucleic acid chaperone, which facilitates rearrangements of nucleic acids into their thermodynamically most stable structure with the maximum number of base-pairs. In the viral replication of HIV-1, the genetic information carried on a single-stranded RNA genome is reverse transcribed into a double-stranded proviral DNA. To complete the synthesis of this double-stranded DNA, NC promotes several annealing reactions in the reverse transcription process. Among these annealing reactions, NC has been shown to play a crucial role in mechanism of the TAR DNA:RNA annealing during the minus-strand transfer.

In this work, we present single-molecule fluorescence resonance energy transfer (FRET) measurements directed toward elucidating the mechanism of TAR DNA:RNA annealing assisted by NC. To capture the potential intermediates, we employed single-molecule FRET measurements using various oligonucletides and TAR DNA. We found that there are two potential mechanisms of TAR DNA:RNA annealing. Both mechanisms are assumed to proceed through a “Y” structure of TAR DNA. Annealing of TAR DNA to RNA can go either through a “zipper” complex or a “kissing” complex. We conclude that the annealing of TAR DNA:RNA assisted by NC may occur through multiple pathways.

Dr. Huajian Gao, Max Planck Institute for Metals Research, Stuttgart, Germany

Wednesday, April 13, 2005 - Noon – 1:00 PM, ACES 2.302

“Flaw Tolerant Nanostructures of Biological Materials”

ABSTRACT
Bone-like biological materials have achieved superior mechanical properties through hierarchical composite structures of mineral and protein. Gecko and many insects have evolved hierarchical surface structures to achieve extraordinary adhesion capabilities. We show that the nanometer scale plays a key role in allowing these biological systems to achieve their superior properties. We suggest that the principle of flaw tolerance may have had an overarching influence on the evolution of the nanostructures of bone and gecko. We demonstrate that the nanoscale sizes allow the mineral nanoparticles in bone to achieve optimum fracture strength and the spatula nanoprotrusions in Gecko to achieve optimum adhesion strength. In both systems, strength optimization is achieved by restricting the characteristic dimension of the basic structure components to nanometer scale so that crack-like flaws do not propagate to break the desired structural link. Properties to be discussed include stiffness, toughness, structure stability and adhesion strength. We also discuss how application of the flaw tolerance principle at all hierarchical levels allows the stiffness and toughness of biological materials to be optimized up to macroscopic legth scales.

Frank Liang Wang, Graduate Student, Nanotechnology Doctoral Portfolio Program Participant, Department of Electrical and Computer Engineering, University of Texas at Austin

April 27, 2005 - Noon – 1:00 PM, CPE 2.212

“Nanoscale Organic/Polymeric Field-effect Transistors as Chemical Sensors”

ABSTRACT
Nanotechnology promises high sensitivity for chemical sensors based on field effect transistors. However, it is technically difficult to pattern the active semiconductor layer at nanoscale dimensions. As a result, the undesirable spreading currents which travel outside the defined channel significantly contribute to the measured signal. A novel four-terminal geometry was designed to successfully exclude the background from large-scale parallel conduction pathways. This design ensures that the detected signal is truly the sensing response from the nanoscale active area. With this methodology, I discovered that by scaling down the device geometry to nanoscale, the sensing behavior of organic and conjugated polymeric transistors is remarkably different from that of larger devices composed of the same materials for the same analyte. The direction and amplitude of sensing responses were found to be correlated to the channel length and the grain sizes of the organic semiconductor as sensing layer. To explain this phenomenon, I proposed a sensing mechanism for polycrystalline organic/polymeric thin films. The overall sensing response is the result of a combination of two competing factors, i.e., trapping at grain boundaries and doping at grains, with different factors dominating at different length scales.

Niraj N. Kulkarni, Doctoral Candidate, Nanotechnology Doctoral Portfolio Program Participant, Material Science and Engineering, University of Texas at Austin

Wednesday, May 4, 2005 -Noon – 1:00 PM, CPE 2.212

“Synthesis and Field Emission Studies of 1-D Nanostructures”

ABSTRACT
1-D nanostructures, namely nanowires and nanotubes have been touted as potential electron sources in field emission based vacuum microelectronic devices including displays. 1-D Nanostructures are particularly attractive since they have extremely sharp tip radii and a high aspect ratio and can serve as efficient electron sources. Synthesis and field emission characteristics of three materials systems will be presented, namely carbon nanotubes, silicon nanowires and graphitic nanocones. The carbon nanotubes are grown in anodic alumina templates via thermal CVD, whereas silicon nanowires were grown by Vapor-Liquid-Solid (VLS) technique. In the case of silicon nanowires, the effect of post-growth processing on the field emission characteristics will be discussed.

Victor I. Klimov, Softmatter Nanotechnology and Advanced Spectroscopy Team, Chemistry Division, Los Alamos National Laboratory

October 6 - Noon -1:00 pm, ACES 2.304

"Functional Nanocrystal-Quantum-Dot Assemblies: From light-emitting diodes and multicolor lasers to carrier-multiplication-based solar cells"

ABSTRACT
Using modern colloidal chemistry, semiconductor nanocrystals (NCs), known also as NC quantum dots, can be fabricated with nearly atomic precision in a wide range of sizes and shapes. They exhibit high photoluminescence quantum yields and narrow, size-controlled emission lines. They can easily be manipulated into complex two-dimensional (2D) and 3D assemblies or incorporated into glasses or photonic and electronic devices. Size-controlled tunability of electronic and optical properties along with chemical flexibility make NCs ideally suited for studies of size/structure-dependent quantum mechanical interactions as well as ideal building blocks for nanoscale engineering. This presentation focuses on the physics of multiexciton interactions (e.g., Auger recombination and impact ionization) and interfacial effects (e.g., energy transfer) relevant to NC applications in light emitting, lasing, and photovoltaic devices. By using shape-controlled NCs or multi-shell NC heterostructures, we can almost independently manipulate carrier confinement energies (i.e., emission wavelengths) and their relaxation dynamics [1, 2]. This approach allows us to significantly suppress nonradiative Auger recombination, which simplifies the achievement of optical amplification and lasing regimes across a wide range of visible and infra-red wavelengths [3, 4]. We also develop and study novel types of hybrid epitaxial/colloidal nanostructures, which allow efficient electrical pumping of NC emitters via either “noncontact” exciton transfer [5] or direct charge injection from epitaxial layers of wide gap semiconductors. Finally, we show that confinement-enhanced exciton-exciton interactions result in unusually large rates of impact ionization and highly efficient carrier multiplication in NCs (up to 100% efficiency of conversion of single excitons into multiexcitons is observed in PbSe nanoparticles) [6]. The effect of direct carrier multiplication can be used to significantly enhance the power conversion efficiencies of NC-based solar cells.

Rodney S. Ruoff, John Evans Professor of Nanoengineering, Director, NU BIMat Center, Department of Mechanical Engineering, Northwestern University

Wednesday, October 20, 2004 - Noon – 1:00 p.m, CPE 2.206

Mechanics of Nanostructures and Nanocomposites

The topics to be discussed: (I) Experimental studies by my group of carbon nanotubes and nanocoils, boron and metal boride nanowires, and carbon nanotubes projecting from the fracture surface of CNT composites (a) subjected to tensile loading (b) driven into mechanical resonance by mechanical or electrical excitation. (II) The ideal strength of materials & fracture in nanostructures (a) ab initio calculations of ideal strength (b) experimental work on nanostructure fracture (c) modeling of the fracture strength of nanostructures with 0, 1, 2 adjacent, 3 adjacent, …, n adjacent defects (d) following this summary of prior work, a new theory (developed with Nicola Pugno, Politecnico di Torino) for fracture of nanoscale structures will be presented: Quantized Fracture Mechanics.

Dr. Xiang Zhang, Associate Professor, Director of NSF Nano-Scale Science and engineering Center, University of California, Berkeley

Wednesday, October 27, 2004 - Noon – 1:00 p.m, CPE 2.206

"Engineering Sub-wavelength Metamaterials: An route towards Nano-plasmonics"

Dr. Xiang Zhang is an Associate Professor and the Director of NSF Nano-scale Science and Engineering Center at University of California, Berkeley. He also serves as the director of Department of Defense MURI Center on metamaterials and devices. He is a recipient of NSF CAREER Award (1997); Engineering Foundation Award (1997); SME Dell K. Allen Outstanding Young Manufacturing Engineer (1998) and ONR Young Investigator Award (1999). He was nominated in 2004 for the Millennium Technology Prize, the world’s largest technology award. His current research focused on nano-scale engineering, meta-materials, and nano-photonics and molecule engineering. He has published over 70 technical papers including one in “Science”, and given more than 50 invited talks at international conferences and institutions. His research was featured by media such as BBC, Science Daily, Photonics Spectra, Laser Focus World, PhysicsWeb, He received Ph.D from UC Berkeley (1996) and MS/BS from Nanjing University, China.

So-Jung Park, Department of Chemistry and Biochemistry & the Center for Nano and Molecular Science and Technology, University of Texas at Austin

November 10, 2004 - Noon - 1PM, CPE 2.206

“Nano-scale Building Blocks: From DNA/Nano-particle Hybrids to Conjugated Polymers”

ABSTRACT
“Bottom-up” materials synthesis has emerged as a new way to create functional materials from Nano-scale or molecular building blocks, where materials properties are determined by their assembly structures. To this end, it has been an important issue to develop ways to control the assembly parameters and to understand the structure-function relationship in materials and devices that are composed of inorganic Nano-particles or organic conjugated molecules. This talk concerns these issues and presents 1) a highly programmable assembly method for inorganic Nano-particles based on DNA’s molecular recognition and 2) the effect of chain arrangements in conjugated polymers on their optoelectronic properties. The first topic will describe a systematic study aimed at understanding the structure and fundamental properties of DNA-linked gold Nano-particle assemblies, which led us to develop a highly selective and sensitive DNA detection method. The second topic will describe single molecule spectroscopy studies of conjugated polymers incorporated in a charge injection device. The charge injection to single conjugated polymers was observed to be controlled by the molecules’ chemical states and the environments, and the oxidation/reduction dynamics were affected by various factors including deep traps in the charge transport layer and heterogeneity of the device.

Steven J. Sibener, The James Franck Institute and Department of Chemistry, The University of Chicago

November 17, 2004 - Noon – 1:00 PM, ACES 2.302

“Nano-scale Surface Dynamics of Polymers, Metals, and Self-Organizing Molecular Over layers”

ABSTRACT
The formation, physical characterization, dynamical properties, and reactivity of thin films are central to our understanding of interfacial science including Nano-scale systems. This presentation will focus on the characteristics of “soft” thin films, including polymers and self-assembling organic over layers. The first part of this talk will discuss issues pertaining to defect mobility and thermal annealing, spatial organization, and the prospect for func­tional decoration of diblock copolymer surface structures. This effort has demonstrated that atomic force microscopy imaging can be used in a time-lapse manner to track the in­teractions of topological defects. Combining rules for various dislocation and disclination pairs have been established. Strong polymer alignment has been realized in dewetted an­nular structures and on lithographically generated grating substrates in which intention­ally selected depths and widths have been used to guide the assembly of highly-aligned polymeric interfaces. Recent activities have focused on guiding the formation of phase separated polymeric structures in complex geometries, as well as the hierarchical decora­tion of these thin film materials with Nano-particles. The second part of the talk will ex­amine structural and dynamical phenomena associated with self-assembling monolayers, including the delicate interplay of adsorbates with reconstructed surfaces. Inelastic atom scattering in conjunction with complementary numerical simulations will examine the transition from single-phonon to many-phonon processes in gas-surface collisional energy exchange, including the discovery of a new channel for non-thermal and directionally specific ejection of atoms embedded within these films. This is, in a sense, a new type of structure scattering, in which the molecular organization within the film leads to the ob­served and unexpected angular dependent scattering. If time permits, this talk will close with comments on reactivity in adsorbed molecular films and nanoscale time-lapse imaging studies of metallic faceting transitions.

Tobias Hanrath, Graduate Research Assistant, Department of Chemical Engineering, The University of Texas at Austin

Wednesday, December 1, 2004 - Noon – 1:00PM, CPE 2.206

“Germanium Nanowires: Synthesis, Characterization, and Utilization”

One-dimensional semi-conducting nanomaterials have attracted intensive research efforts due to their broad potential technological applications. The continued drive toward size and cost reduction in microelectronic devices has led to the proposed use of these nanowires as building blocks in future nanoscale electronic devices. The successful implementation of such technology requires precise control over the size, composition and morphology, but also involves a paradigm shift toward the bottom-up fabrication of functional devices. Ge nanowires with diameters as small as 4 nm and several micrometers in length were prepared in supercritical fluid flow reactor. High-resolution transmission electron microscopy was used for the structural characterization of the nanowires, focusing on crystallographic aspects such as the growth direction, surface faceting, and defects. Nanowire surface chemistry, which is essential for the processing and technological application of the nanowires, was investigated by high-resolution x-ray photoelectron, and infrared spectroscopy. Chemical passivation of the nanowire surface was explored via various routes, including sulfide, oxide, hydride and chloride termination, and covalently bonded organic monolayers. The impact of surface chemistry on surface state dominated electron transport in single nanowire devices was investigated by room temperature field effect measurements. Complimentary to the device measurements, fundamental electrical and optical properties were probed via electron energy loss spectroscopy on individual nanowires inside the transmission electron microscope.

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