SPRING 2007

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 ato