Argonne National Laboratory Center for Nanoscale Materials U.S. Department of Energy

Archive: 2010 Colloquium Series

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Date Title
November 10, 2010

"Anisotropic Semiconductor Nanocrystal Synthesis and Chemical and Biological Functionalization," Preston T. Snee, University of Illinois - Chicago, hosted by Richard Schaller

Abstract: Semiconductor nanocrystals (NCs, or quantum dots) are very bright chromophores that possess significant potential in alternative energy generation and for biological sensing and imaging applications. Our group has made significant advances in the synthesis of rods and multi-pods of near-infrared emitting PbSe NCs through a previously unobserved mechanism. Characterization of anisotropic PbSe NCs show that they have much more robust chemical properties compared to cubic or "dot"-shaped NCs.

Also presented are recent advances on the chemical and biological functionalization of bright NCs. While there are ostensibly many methods for chemical functionalization of water soluble NCs, most of the reagents used in these methods either quench the NCs or have very low reaction yields. We have circumvented these problems by synthesizing polymers which serve as NC functionalization reagents; the polymer-NC-activated intermediate has increased stability and allows us to conjugate chemical and biological vectors to the NCs with 100% reaction yield. We use this method to functionalize NCs with organic fluorophores that can report on the local chemical and biological environment. We have synthesized several ratiometric, or "self-calibrating" sensors, for pH, toxic metals, DNA, and proteins. In our recent work on protein sensing, we have developed an all optical method for sensing un-labeled proteins with a better detection limit than any currently existing technology.

October 27, 2010

"Synthesis and Applications of FePt and Their Composite Nanoparticles, " Shouheng Sun, Brown University, hosted by Elena Shevchenko

Abstract: I will summarize our recent efforts in synthesizing FePt alloy and its composite nanoparticles with controlled composition and structure for active/durable fuel cell catalysis and effective therapeutic applications.

October 13, 2010

"Plasmonic Nanostructrures: Artificial Molecules," Peter Norlander, Rice University, hosted by Matt Pelton

Abstract: The recent observation that metallic nanoparticles possess plasmon resonances that depend sensitively on the shape of the nanostructure has led us to a fundamentally new understanding of the plasmon resonances supported by metals of various geometries. This picture, "plasmon hybridization," reveals that the collective electronic resonances in metallic nanostructures are mesoscopic analogs of the wave functions of simple atoms and molecules, interacting in a manner that is analogous to hybridization in molecular orbital theory.  The new theoretical insight gained through this approach provides an important conceptual foundation for the development of new plasmonic structures that can serve as substrates for surface enhanced spectroscopies and subwavelength plasmonic waveguiding and other applications. The talk is comprised of general overview material of relevance for chemical applications interspersed with a few more specialized "hot topics" such as plasmonic interference  effects, quantum effects, and single-molecule SERS and LSPR sensing.

September 29, 2010 "From Assembly Science to Assembly Engineering," Sharon Glatzer, University of Michigan, hosted by Paul Podsiadlo
September 15, 2010

Hierarchical Structure Control in Conjugated Polymers,” Rachel Segalman, University of California, Berkeley, hosted by Seth Darling

Abstract: Control over structures on a molecular through nanoscopic lengthscales is vital to optimize polymeric devices for energy generation. For example, while molecular structure affects the electronic properties of semiconducting polymers, the crystal and grain structure greatly affect bulk conductivity, and nanometer lengthscale is vital to charge separation and recombination in photovoltaic and light emitting devices. Careful control over the organic/inorganic interface appears to play a vital role in thermoelectric effects. Block copolymers have been the subject of intense interest for their ability to form intricate, predictable 10nm lengthscale patterns. Unfortunately, this immense background of research has generally focused on classical, flexible polymer molecules. Semiconducting polymers for photovoltaics and other applications are characterized by a rigid, liquid crystalline chain shape and transport properties which rely crucially on crystallinity, which adds complexity to the thermodynamics of self-assembly. In this seminar, I will discuss our work to understand the effect of chain shape on polymer self-assembly and routes to control both self-assembly and crystallization on multiple dimensions, as is required for these applications. The effect of carefully controlled morphology on photovoltaic device performance as well as possible applications in thermoelectrics will be discussed.

September 1, 2010

Biomolecules as building blocks for directing the structure and function of new materials, "Nathaniel Rosi, University of Pittsburgh, hosted by Sarah Hurst

Abstract: This talk will detail our work investigating the use of biomolecules as building blocks for constructing new materials. In particular, half of the talk will focus on the use of nucleobases as building blocks for constructing porous materials. Some potential biomedical and environmental applications of these materials will also be presented. The second half of the talk will focus on the development of a new methodology for constructing nanoparticle superstructures that relies on a new class of peptide conjugate molecules which are designed to direct the simultaneous synthesis and assembly of inorganic nanoparticles. Particular focus will be dedicated to a discussion of various nanoparticle superstructures that can be constructed using this methodology and the mechanism of their formation.

August 25, 2010

"Platforms for the Mechanical, Thermal, and Electrochemical Characterization of Nanoscale Materials," John P. Sullivan, Sandia National Laboratories, hosted by Anirudha Sumant

Abstract: The challenge in characterizing nanoscale materials (e.g., nanowires, nanoparticles) is related to the difficulties in resolving small responses to large external stimuli and to isolating the response of individual particles. In this talk, we describe the integration of individual nanoscale structures with chip-based testing platforms and the use of these platforms to characterize the nanostructure's properties. A suite of these testing platforms has been developed for the mechanical, thermal, and electrochemical characterization of nanoscale materials. We describe the development of microscale tensile test structures for measuring the stress-strain behavior of metallic nanowires, thermal platforms for measuring thermal conductivity and phonon surface scattering in semiconducting nanowires and nanoligaments, and in situ transmission electron microscopy (TEM) platforms for measuring the electrochemical behavior of nanowire anode and cathode materials for use in lithium-ion batteries. The goal of this work is to determine structure-property or size-property relationships that are derived from studies of well-characterized isolated structures.

August 18, 2010

"Quantum effects in photosynthetic energy transfer," Cesar Rodriguez-Rosario, Harvard University

Abstract: The efficiency of exciton transfer in the photosynthetic Fenna-Matthews-Olson complex is astonishing, 99% of the absorbed photons driving a chemical reaction. Recent experiments have detected long-lived quantum coherences in this complex, but the question remains: are these coherences responsible for the high efficiency?

We develop tools inspired in quantum information and quantum thermodynamic to analyze the efficiency of such systems, towards learning from photosynthesis to designing nanostructures for novel photovoltaic technologies. We study a simple model for exciton transport and show how it behaves like a quantum engine driven by both dephasing and relaxation. We also present how dephasing can assists quantum transport in a network, such as the quantum walk of an exciton through the FMO complex.

This is work done as part of the Center for Excitonics at Harvard/MIT.

August 4, 2010 Sang-Hyun Oh, University of Minnesota
July 21, 2010 John Sullivan, Sandia National Laboratories
July 7, 2010

In Kyeong Yoo, Samsung

June 23, 2010

"Macromolecular Surfactants," Frank Bates, University of Minnesota, hosted by Seth Darling

Abstract: Block copolymers belong to a broad class of amphiphilic compounds that includes lipids, soaps, and nonionic surfactants. A macromolecular architecture affords certain unique advantages over conventional low molecular weight amphiphiles in constructing nanoscale objects with prescribed morphologies and desirable physical properties. In this presentation I will describe the structure and dynamics of block copolymers dispersed in aqueous and hydrocarbon media based on small-angle X-ray and neutron scattering and various cryogenic electron microscopy. These fundamental results will be augmented by a discussion of an application to thermoset epoxies, where the dispersion of block copolymer micelles has resulted in extraordinarily tough plastics.

June 16, 2010

"From molecular adsorbates to atomic membranes: How interfacial atomic structure influences nanotribology in carbon-based systems," Robert Carpick, University of Pennsylvania, hosted by Anirudha Sumant

Abstract: Many carbon-based materials, including diamond, carbon nanotubes, diamond-like carbon (DLC), graphite, and graphene, exhibit unusual and extreme material properties. The tribological behavior of these materials is no less interesting: Diamond can function as an abrasive or a solid lubricant; DLC can exhibit extremely low macroscopic friction, yet shows rather high nanoscale friction; DLC has lower friction when dry, while diamond has lower friction when wet. I will briefly review some of the important and at times contradictory behavior that is seen in these materials. I will also mention the application areas where these materials can be applied. I will then focus on the atomistic origins of two particularly interesting effects: (1) the critical environmental sensitivity of friction and wear for diamond interface and (2) the unusual stick-slip friction behavior seen in thin graphene and other atomically thin sheets.

June 9, 2010

"Dynamics of Nanomechanical Cantilever Devices in Fluid Environments," John E. Sader, University of Melbourne, Australia, hosted by Matt Pelton

Abstract: Nanomechanical sensors are often used to measure environmental changes with extreme sensitivity. Controlling the effects of surfaces and fluid dissipation presents significant challenges to achieving the ultimate sensitivity in these devices. Particularly, the fluid-structure interaction of resonating microcantilevers in fluid has been widely studied and is a cornerstone in nanomechanical sensor development. In this talk, I will give an overview of work being undertaken in our group dedicated to exploring the underlying physical processes in these systems. This will include exploration of recent developments that focus on cantilever sensors with embedded microfluidic fluid channels and examination of the effects of surface stress on the resonant properties of cantilever sensors.

May 26, 20106/

"Metal-insulator transition in vanadium oxide nanobeams," David H. Cobden, University of Washington, hosted by Anand Bhattacharya and Matthias Bode

Abstract: Because of the change in structure, the latent heat, and the need for nucleation, first-order phase transitions involving a solid phase tend to be very sensitive to inhomogeneities and difficult to study in bulk material. For solid-solid transitions the situation is particularly bad, with random domain formation, high strain, and fracture being almost unavoidable. I will discuss how working with nanoscale systems, which are small compared with the scale of inhomogeneities and domains, allows much improved control of such transitions. It also opens up possibilities to investigate phase transitions in reduced dimensionality, where the physics may be qualitatively different from that in three dimensions and may be more theoretically tractable as well. These advantages will be illustrated in two systems: a solid-solid transition driven by electron-electron c correlations in a vanadium dioxide nanobeam; and vapor-liquid-solid transitions occurring in a monolayer of gas atoms adsorbed on a carbon nanotube.

May 26, 2010

A protein scaffold for nanotechnology and structured enzyme complexes for biofuels,” Chad Paavola, NASA-Ames, hosted by Nathan Ramanathan

Abstract: The thermoacidiphilic archaeon Sulfolobus shibatae produces heat-inducible chaperonins comprised of ~60 kDa protein subunits assembled into 18-mer double rings. These double rings can, in turn, assemble into higher order structures such as two-dimensional crystals or bundled filaments. We have exploited this hierarchical self-assembly to create templates for nanoscale ordered materials incorporating metallic, semiconductor, or magnetic particles. We have also turned this structural scaffold to the purpose of understanding the interactions among enzymes in the bacterial cellulosome, with the goal of producing new systems for deconstruction of plant cell wall biomass. This work has resulted in an enzyme complex that exhibits enhancement of enzymatic activity characteristic of previous work on cellulosomal enzymes. Chaperonin-based complexes are proving useful in examining combinations of cellulosomal enzymes in ratios similar to those observed in nature.

May 16, 2010

"Metal-insulator transition in vanadium oxide nanobeams, " David Cobden, University of Washington

May 12, 2010

"Coherent Excitonic Transport through Disordered Molecular Systems: Extracting Design Principles from Photosynthesis," Greg Engel, University of Chicago

Abstract: Life on earth is effectively solar powered, yet the way in which energy moves through photosynthetic complexes before the biochemical steps of photosynthesis is still not completely understood. Evidence for a purely quantum-mechanical mechanism of energy transfer in photosynthetic complexes was discovered in the Fenna-Matthews-Olson (FMO) complex of Chlorobium tepidum in 2007. The quantum beating phenomenon observed in this complex is now much better understood. Further, data indicate that this mechanism is not specific to FMO, but manifests in reaction centers of purple bacteria and antenna complexes of higher plants. Having observed such a mechanism in disparate photosynthetic complexes, we are exploring what the minimal requirements are to support quantum coherence transfer in a biological environment and how such an environment might be reproduced synthetically using nanomaterials. Emerging details in this story will be presented along with preliminary data from experimental efforts to dissect the details of energy transfer, the basis for the efficiency of the energy transfer process and efforts to isolate signals at room temperature.

April 28, 2010

"Ambipolar Transport in Organic Thin Film Transistors," Cherie Kagan, University of Pennsylvania, hosted by Elena Shevchenko

Abstract: Organic semiconductors have received enormous attention as alternative channel materials for low-cost and flexible thin-film transistors (TFTs). But organic semiconductors are commonly classified as either n-type or p-type as different materials typically show unipolar behavior in TFTs with exclusively electron or hole transpor,t respectively. In many organic thin-film semiconductors that were known to be the best hole conductors, the absence or poor transport of electrons has been attributed to extrinsic factors: (i) high barriers for electron injection at the metal-semiconductor interface; (ii) trap sites for electrons at the dielectric-semiconductor interface; and (iii) the generation of electron traps upon exposure to different environments. Recently, reports have shown that ambipolar transport (showing both n-type and p-type character) is an intrinsic property of organic semiconductors and ambipolar organic TFTs were achieved employing low-workfunction (such as calcium) source and/or drain electrodes, to inject electrons but low workfunction electrodes typically have poor stability . We report ambipolar pentacene TFTs using self-assembled thiolate and carbodithiolate monolayers to enhance charge injection at the metal-organic interface of stable high- workfunction gold source and drain electrodes and polymer gate dielectrics that prevent electron trapping at the organic-dielectric interface in the TFTs. Pentacene is deposited by spin-coating a soluble precursor and thermally retro-converting the precursor thin films at mild temperatures (120-200 ºC) to pentacene. Hole and electron mobilities of 0.1-0.5 cm2/V s and 0.05-0.1 cm2/V s are achieved. We have implemented a wide range of aromatic and aliphatic thiolate and carboditholate chemistries to achieve ambipolar pentacene TFTs. Using these ambipolar FETs, we demonstrate CMOS-like inverters with gains of up to 110. We have further developed processes to integrate the solution-processable precursor route to ambipolar pentacene transistors onto flexible plastic substrates.

April 14, 2010

"Nanoparticles in Biology: Engineering the Interface for Delivery and Sensing," Vince Rotello, University of Massachusetts, hosted by Elena Shevchenko

Abstract: A key issue in the use of nanomaterials is controlling the interfacial interactions of these complex systems. Our research program focuses on the tailoring of interfaces by coupling the atomic-level control provided by organic synthesis with the fundamental principles of supramolecular chemistry. Using these tailored monolayers, we are developing particles for biological applications in particular delivery and sensing. This talk will focus on the interfacing of nanoparticles with biosystems, and will discuss our use of nanoparticles for delivery applications as well as our use of polymer-nanoparticle systems for sensing and identification of proteins, bacteria, and cancer detection/identification of mammalian cells.

March 17, 2010

"Magnetically Responsive Photonic Nanostructures," Yadong Yin, University of California - Riverside, hosted by Gary Wiederrecht and Yugang Sun

Abstract:: This presentation focuses on recent work on magnetically tunable photonic nanostructures. Superparamagnetic iron oxide colloidal particles are synthesized by using a high-temperature hydrolysis reaction and then self-assembled into ordered photonic crystal structures in solution phase using external magnetic fields. The colloids form chain-like structures with regular interparticle spacing of a few hundred nanometers along the direction of the external field so that the system strongly diffracts visible light. The balance between attraction (in this case, magnetic dipole interaction) and repulsion (such as electrostatic and solvation force) dictates interparticle spacing and therefore optical properties. By changing the relative strength of these two forces, we can tune the peak diffraction wavelength over the entire visible spectrum. By controlling the surface properties of the magnetic particles (so that the repulsive forces involved), we have been able to assemble the photonic structures in water, alcohols, and nonpolar solvents. The fast, reversible response and the feasibility for miniaturization impart these photonic materials great potential in applications such as optoelectronic devices, sensors, and color displays. In this presentation, I will also demonstrate high resolution patterning of multiple structural colors by a single "ink" material, the color of which is magnetically tunable and lithographically fixable. The fabrication of color and shape coded micro-objects by using this unique photonic material will also be discussed.

March 11, 2010

"Supramolecular Materials for Separation/Sensing/Release/   Energy Conversion & Hand-Operated Nanotechnology," Katksuhiko Ariga, National Institute for Materials Science (Japan), hosted by Elena Rozhkova

Abstract:: Supramolecular materials have been wisely constructed via bottom-up approaches as seen in preparation of molecular complexes and organized nanostructures. These materials are used for various functions such as one-pot materials separation, selective sensing, auto-modulated drug release, and photo-energy conversions as reported in our recent researches. In addition, we have proposed a novel methodology "hand-operating nanotechnology" where molecular orientation, organization and even functions in nanometer-scale can be operated by our bulk (hand) operation. For example, we successfully manipulated molecules at the air-water interface upon bulk (10-100 cm size) motion of the entire monolayer and realized "capture and release" of aqueous guest molecules using molecular machine as well as mechanically controlled chiral recognition.

March 3, 2010

"Tuning optical properties of polymer films using nanorods and Janus particles," Russell J. Composto, The University of Pennsylvania, hosted by Seth Darling and Nathan Ramanathan

Abstract: The optical properties of polymer films are tuned using novel nanoparticles.  First, nanorods (NRs) of gold are organized and aligned within polymer films. The plasmon adsorption is investigated as a function of nanoparticle concentration as well as matrix type.  NR organization and dispersion are compared with a model consisting of noninteracting rods as well as simulations of rod-rod interactions.  At NR concentrations ranging from 1 to 15vol%, the NRs disperse very uniformly with a spacing that decreases linearly with the volume fraction.  Surprisingly, even at 1 vol%, NRs are locally ordered. and this ordering increases linearly with the volume fraction of rods.  Second, multiregion and patchy, opticall -active Janus particles were synthesized via a hierarchical self-assembly process. Gold nanoparticles were assembled on the top surfaces of nano- and sub-micron silica particles, which were selectively protected on their bottom surfaces by covalent attachment to a copolymer film. The m orphologies of the gold particle layer, and the resulting optical properties of the Janus particles, were tuned by changing the surface energy between the silica and gold particles, followed by annealing.

February 24, 2010

"Interfacial Electron Transfer Dynamics from Single Quantum Dots," Shengye Jin,Emory University, hosted by Gary Wiederrecht

Abstract: Understanding the dynamics of charge transfer to and from quantum dots (QDs) is essential to their many applications, ranging from solar cells to light-emitting diodes to biological imaging. Unlike molecular chromophores, previous studies showed that single QDs exhibit dynamic fluctuation of fluorescence intensity (i.e., "blinking"). To understand how interfacial electron transfer can affect and be affected by the blinking dynamics, we investigated electron transfer dynamics from single CdSe core shell QDs to various semiconductor nanomaterials.

Single QDs on TiO2 showed pronounced and correlated fluctuations of fluorescence intensity and lifetime. Compared with QDs on glass, the presence the interparticle ET pathway on TiO2 led to smaller on-state and larger off-state probability densities, as well as a shortened lifetime of the on-state.

Furthermore, the electron transfer dynamics from the same QDs to the (110) surface of a rutile TiO2 single crystal have also been studied as a model system for QD/TiO2 nanoparticles. Atomic force microscopy study of QDs on the TiO2 (110) surface revealed that QDs are preferentially adsorbed on the step edges. The distribution of lifetimes of QDs on the single crystal is much narrower than that on TiO2 nanoparticles, suggesting a considerably less heterogeneous distribution of electron transfer rates on the single crystal surface. However, interfacial electron transfer can be inactivated for QDs on highly n-doped semiconductors. Compared with the QDs on In2O3 and glass, the QDs on ITO show significantly reduced lifetimes and suppressed blinking activity due to the charging of QDs. 

Besides semiconductor nanomaterials, interfacial electron transfer dynamics from single QDs to organic dye molecule (Fluorescein 27) were also investigated. A combination of ensemble transient absorption and single QDs measurements revealed a correlated single QD blinking and interfacial electron transfer dynamics. The origins of the intermittent electron transfer dynamics were discussed and an electron transfer and blinking model was suggested.

February 17, 2010

"Spintronics," Sam Bader, Argonne National Laboratory, hosted by Seth Darling

Abstract: Spintronics encompasses the ever-evolving field of magnetic electronics. It is an applied disciple that is so progressive that much of the research that supports it is at the center of basic condensed matter and materials physics. The talk provides a brief perspective on recent developments in switching magnetic moments by spin-polarized currents, electric fields and photonic fields. Developments in the field of spintronics continue to be strongly dependent on the exploration and discovery of novel material systems. An array of novel transport and thermoelectric effects dependent on the interplay between spin and charge currents have been explored theoretically and experimentally in recent years. The talk highlights select areas that hold promise for future investigation, and features some recent work at Argonne.

February 3, 2010

"Materials Synthesis Using Atomic Layer Depositions," Jeffrey Elam, Argonne National Laboratory, hosted by Matthew Pelton

Abstract: Atomic layer deposition (ALD) is a thin-film growth technique that uses alternating, self-limiting chemical reactions to deposit materials in an atomic layer-by-layer fashion. Although this process is already used commercially for microelectronics manufacturing, ALD promises to have a much broader impact extending far beyond microelectronics. In particular, the capability to infiltrate and coat porous substrates coupled with a broad palate of available materials make ALD a versatile technique for synthesizing nanostructured materials. Consequently, we are pursuing a variety of new applications for ALD, including photovoltaics, catalysis, and large-area detectors. A central theme in these efforts is that we use ALD to apply precise, conformal coatings onto nano- or micro-structured scaffolds to impart the desired optical, electrical, or chemical properties to suit the application. In this presentation, I will describe some of our recent research and development work at Argonne to advance these technologies.

January 20, 2010

"A Discussion of the Utility of Dealloyed Nanoporous Metals for Electrocatalysis," Jonah Erlebacher, Johns Hopkins University , hosted by Jeffrey Greeley

Abstract: Dealloying refers to the electrochemical dissolution of a majority component from a uniform multicomponent alloy.  In certain controlled cases, the remaining components diffuse along the metal/electrolyte interface to restructure each grain of the polycrystalline alloy to possess high surface area and open porosity.  Depending on the system of interest, one may find extremely small pores and extremely high surface areas, rivaling nanoparticles but with the added advantage of good electrical contact to all surfaces (e.g., ~2-nm ligaments and pores with ~50 m^2/g in dealloyed Ni/Pt).  Dealloyed metals are also quite beautiful porous materials where the underlying crystallography is strikingly apparent, such as in dealloyed Ag/Au alloys. In this talk, I will discuss our current understanding of the physics and chemistry controlling the competition between dissolution and surface diffusion that leads to porosity evolution, as well as electrochemical methods to control pore and ligament size and the relative core/shell compositions of the dealloyed materials.

Dealloyed nanoporous materials naturally find utility in electrochemical catalysis, and we will also discuss their activity toward electrochemical oxygen reduction in aqueous solution.  Oxygen reduction is famous for its inefficiency in hydrogen/oxygen fuel cells and the dealloyed Ni/Pt system is quite interesting for this application.  Large roughness factors, well over 100, are easily fabricated, and we have measured half-waves for oxygen reduction in rotating disk electrode experiments over 0.98 V vs. RHE, a less than 250 mV over potential.  The origin of this effect is related to the high surface area, but not in a simple way, and we will argue that the effective "active area" of the porous metal is itself dependent on the overpotential.  Finally, we will discuss composite nanoporous metals that further improve oxygen reduction activity. 

 

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