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

Archive: 2009 Colloquium Series

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Date Title

November 25, 2009

"Oxide Nanoelectronics," TJeremy Levy, University of Pittsburgh, hosted by Matthew Pelton

Abstract: Electronic confinement at nanoscale dimensions remains a central means of science and technology. In this talk, I will describe a new method for producing extreme nanoscale electronic confinement at the interface between two separately insulating oxides, LaAlO3 and SrTiO3. Using an approach reminiscent of the popular toy "Etch-a-Sketch," we scan an electrically biased probe on the surface of this heterostructure to create nanoscale conducting islands, nanowires, tunnel junctions, and field-effect transistors at the interface. The smallest feature size approaches one nanometer. These structures are created in ambient conditions at room temperature and can be erased and rewritten repeatedly. At low temperatures, a variety of quantum phases have been observed, including integer and fractional quantum Hall states and superconductivity. This new, on-demand nanoelectronics platform has the potential for widespread scientific and technological exploitation.

October 28, 2009

"Directed Self-Oriented Self-Assembly of Block Copolymers: Bottom-Up Meeting Top-Down," Thomas P. Russell, University of Massachusetts, hosted by Seth Darling

Abstract: As the size scale of device features becomes increasingly smaller, conventional lithographic processes are limited. Alternative routes need to be developed to circumvent this hard stop. Ideally, if existing technological processes can be used with novel materials, significant advances can be made. Block copolymers (BCPs), two polymer chains covalently linked together at one end, provide one solution. BCPs self-assemble into a range of highly ordered morphologies, and by controlling the orientation and lateral ordering of the nanoscopic microdomains, numerous applications will emerge. By combining the "bottom-up" self-assembly of BCPs with "top-down" microfabrication processes, faster, better, and cheaper devices can be generated in very simple, yet robust, ways.

September 30, 2009

"Self-Assembled Systems of Nanoparticles: Similarity with Biological Systems," Nicholas A. Kotov, University of Michigan, hosted by Paul Podsiadlo

Abstract: Self-organization phenomena at the nanoscale is a new field of nanotechnology research that brings out new experimental and theoretical results every day. Self-organization processes are also important from the practical perspective because they drastically simplify manufacturing process of nanodevices and nanomaterials with specialized optical/electronic properties. They can involve nearly spherical nanoparticles and monodispersed nanorods. However, more complex one-, two-, and even three-dimensional systems form from nanoparticles with strong anisotropy. Comparison of the processes in solution of CdTe and other nanocolloids reveals a number of surprising similarities with processes in proteins.One can conclude that this is the result of the fundamental analogy in the scales between proteins and nanoparticles. This conclusion will be substantiated by a variety of experimental and theoretical observations and demonstrated for CdTe, CdS, CdSe, Te, Se, and ZnO nanocrystals prepared in the laboratory of the presenter.

I will also address the challenges and opportunities opening for complex three-dimensional assemblies exhibiting dynamic behavior. One of the challenges is the development of tools necessary for the observation of structural transformations of nanoscale structures in liquid phase. One of the potential solutions here is to take the advantage of plasmon-exciton resonances produced when metal and semiconductor particles are combined in a single self-assembled structure. Both emission intensity and wavelength of the resulting new hybrid electronic state is dependent on the distance and special arrangement between the nanocolloids. Besides, providing insight to dynamics of the nanoscale self-assembled structures, modulation of exciton-plasmon interactions can serve as wavelength-based biodetection tool, which can resolve difficulties of quantification of luminescence intensity for complex media and optical pathways.

September 23, 2009

"Top emerging technologies: Nanogenerators and Nanopiezotronics," Zhong Lin Wang,Georgia Institute of Technology, hosted by Xiao-Min Lin

Abstract: Developing novel technologies for wireless nanodevices and nanosystems is of critical importance for sensing, medical science, defense technology, and even personal electronics. It is highly desirable for wireless devices and even required for implanted biomedical devices to be self-powered, without the use of batteries. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that can be used to power nanodevices.

We have demonstrated an innovative approach for converting nanoscale mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays. The operation mechanism of the electric generator relies on the unique coupling of the piezoelectric and semiconducting dual properties of ZnO as well as the elegant rectifying function of the Schottky barrier formed between the metal tip and the nanowire. Based on this mechanism, we have recently developed a DC nanogenerator driven by ultrasonic waves in bio-fluid. We have also used textile fibers for energy harvesting.

This presentation will introduce the fundamental principle of the nanogenerator and its potential applications. Finally, a new field in nano-piezotronics is introduced that usesthe piezoelectric-semiconducting coupled property for fabricating novel and unique electronic devices and components.

September 2, 2009 "Feynman's space-time quantum mechanics in photosynthesis," Gregory Scholes,University of Toronto, hosted by Gary Wiederrecht

Abstract: Photosynthesis is used by a diversity of plants, algae, and bacteria to convert solar energy into biological fuel. The first steps are somewhat like a highly sophisticated solar cell. Specialized proteins capture the sun's energy and transmit it to reactions centers that secure the energy as electrical potential. In recent work, it has been discovered that quantum-coherence can help to move energy among molecules and thereby assist processes such as light-harvesting in photosynthesis. Quantum-coherence means that light-absorbing molecules capture and funnel energy according to quantum-mechanical probability laws instead of classical laws. The subject has stimulated vigorous cross-disciplinary interest because it was previously thought that long-range quantum-coherence could not be sustained in such complex systems, even at low temperature. I will describe experimental observations of ambient temperature quantum-coherent "wiring" in antenna proteins isolated from photosynthetic marine cryprophyte algae. The results suggest that quantum probability laws may feasibly be employed in light-harvesting function within live cryptophyte marine algae to increase the cross-section for light capture and energy conversion.

August 19, 2009 "Advances in cluster expansions: New computational tools to study surfaces and nanoparticles, " Timothy Mueller, Massachusetts Institute of Technology y , hosted by Tiffany Santos

Abstract: The cluster expansion methodology has proven to be an invaluable tool for computational materials scientists, enabling the determination of ground state structures and calculation of phase diagrams for multicomponent bulk materials.However researchers are increasingly turning to complex and nano-scale materials to meet the demands of technological progress, and studying such materials using cluster expansions can be prohibitively expensive.I will provide an introduction to cluster expansions and present recent advances in the field, including:

  • A Bayesian approach that significantly reduces the computational cost of studying atomic order in nanoparticles and surfaces.
  • A method for determining the low-energy orientations of polyatomic ions in ionic materials.
  • An alternative to the Wulff construction for the prediction of the shape and energy of small nanoparticles.

I will demonstrate how these methods can be used to study the structure and thermodynamics of metallic nanoparticles as well as sodium alanate nanoparticles and lithium imide, promising hydrogen storage materials.

August 5, 2009 "Bio-Inspired Polymers as Nanoscale Building Materials, " Ronald Zuckermann, Lawrence Berkeley National Laboratory , hosted by Elena Shevchenko

Abstract: Peptoids are a novel class of non-natural biopolymer based on an N-substituted glycine backbone that are ideally suited for nanomaterials research. This bio-inspired material has many unique properties that bridge the gap between proteins and bulk polymers. Like proteins, they are a sequence-specific heteropolymer, capable of folding into specific shapes and exhibiting potent biological activities; and like bulk polymers, they are chemically and biologically stable and relatively cheap to make. Peptoids are efficiently assembled via automated solid-phase synthesis from hundreds of chemically diverse building blocks allowing the rapid generation of huge combinatorial libraries. This provides a platform to discover nanostructured materials capable of protein-like molecular recognition and function.

July 22, 2009

"Symmetry, Chaos, and Quantum Localization, " Stephen K. Gray, Group Leader, CNM Theory & Modeling Group, hosted by Matt Pelton

Abstract: While the correspondence principle establishes some links between classical mechanics and quantum mechanics, there can be situations when there are noticeable differences between classical and quantum mechanics. Of course there are some obvious situations (e.g., tunneling through barriers), but sometimes there can be more surprising classical/quantum discrepancies even when relatively high energies and many quantum states, usually associated with the classical limit, are involved. In studying the quantum dynamics of the three-dimensional motion of a lithium atom confined to move inside a C60 molecul ( i.e., the endofullerene Li@C60), a remarkable quantum localization effect was observed. The time average of the wave packet density was found to be very high in certain regions of coordinate space. The corresponding classical dynamics showed no such localization and led to a uniform distribution. This effect was found to be due to (i) the presence of a mirror plane symmetry element in the system coupled with (ii) the corresponding classical motion, for the principle energies contained in the wave packet, being highly chaotic. These two requirements are not particularly severe and many other physical systems should display this quantum localization effect. A second example, corresponding to a simple two-dimensional double well problem that is quite different from Li@C60 is used to illustrate this point.

June 24, 2009

"Bridging the Environment Gap Using First-Principles-Based Catalyst Modeling," William Schneider, University of Notre Dame, hosted by Jeff Greeley

Abstract: Molecular-scale modeling based on density functional theory (DFT) is a common feature of the catalysis research landscape today. These simulations have contributed significantly to the understanding of catalytic reaction mechanisms, to trends in reactivity amongst metals, and even to the prediction of new catalyst compositions. One of the principal challenges in applying molecular simulation to heterogeneous catalysis is incorporating the often significant effect of the reaction environment (temperature, reactant and product concentrations, catalyst support, poison) on chemical composition and structure and thus on reaction mechanism and activity.

Despite the importance of these environment-induced reaction patterns, molecularly detailed models remain sparse. Here we describe our work over the last several years to combine DFT simulations with first principles thermodynamic and chemical kinetic models to describe the reactivity of metal surfaces and particles as a function of environment.

June 10, 2009

"Teaching Old Materials New Tricks: Nanopatterning and Localized Properties of Multifunctional Oxides," Vinayak Dravid, Northwestern University, hosted by Xiao-Min Lin

Abstract: The natural evolution of functional materials architecture calls for their confinement in spatial and dimensional modes. Here, spatial confinement refers to inevitable attachment of materials to a substrate or an overlayer, for example. Dimensional constraint arises from the emerging need for materials to be confined to 0 (i.e., nanocrystals), 1 (nanolines) and 2 (i.e., films or membranes) dimensions. Further, by juxtaposing two or more functional materials in close proximity, there are exciting new opportunities for synergistic coupling of disparate phenomena in such hybrid confined materials systems.

In this context, surface patterned nanoscale architecture and colloidal form of nanostructures offer unprecedented opportunities to revisit fundamental materials science phenomena, which flirt with thermodynamics of constrained systems on one hand and dynamics of nanoscale processes on the other.

The presentation will cover synthesis and patterning of oxides down to nanoscale, with an emphasis on multifunctional phenomena. Advanced scanning probe;in situ and ex situ electron, ion, and photon microscopy; spectroscopy; and synchrotron X-ray scattering approaches are being employed to fathom the most intricate details of the internal "microstructure" of nanostructures, coupled with innovative tools to validate their functional identity and localized properties.

The presentation topics will range from soft-eBL nanopatterned ferromagnetics/ferroelectrics for investigating solid-state phenomena to colloidal synthesis of nanostructures for biomedical applications. It will be argued that multifunctional nanostructures go beyond the "hype" and present challenging yet exciting opportunities for synthesis-structure-architecture-form-function-performance relationships in complex oxide systems.

May 27, 2009

"Carbon-Based Nanoelectronic Devices," Debdeep Jena, University of Notre Dame, hosted by Anirudha Sumant

Abstract: Since the discovery of buckyballs (one-dimensional carbon nanostructures), there has been substantial interest in using carbon nanostructures for electronic and optoelectronic devices. The subsequent discoveries of one-dimensional carbon nanotubes (CNTs) and two-dimensional graphene — all sp2-bonded lattices of carbon — has facilitated electronic devices with remarkable charge transport properties. CNTs and graphene are now being actively considered for electronic devices. In our group, we have studied two-dimensional graphene and graphene nanoribbons and compared their transport and device properties with traditional sp3 bonded semiconductor nanostructures. The picture that emerges is that for novel devices such as tunneling field-effect transistors (FETs), graphene nanoribbons have an advantage due to tunable bandgaps and ease of electrostatic gating. However, for high-performance FETs, an even more attractive option would be sp3-bonded carbon nanowires that potentially offer excellent charge and heat transport properties, and a large bandgap. In the seminar, I will connect our current studies with what can be done with sp3-bonded carbon nanowires and outline various characterization techniques we can apply to these novel nanostructures being studied at CNM.

May 20, 2007 "Supramolecular Approaches for Mixed Ligand Coated Nanoparticles and for Stamping Techniques," Francesco Stellacci, Massachusetts Institute of Technology, hosted by Elena Shevchenko

Abstract: It is known that specific molecules can spontaneously arrange on various surfaces forming two-dimensional polycrystalline monomolecular layers called self-assembled monolayers (SAMs). We will show that when mixed SAMs are formed on surfaces with a radius of curvature smaller than 20 nm, they spontaneously phase-separate in highly ordered phases of unprecedented size. In the specific case of mixed SAMs formed on the surface of gold nanoparticles, the molecular ligands separate into 5-Å-wide phases of alternating composition that encircle or spiral around the particle metallic core. This new family of nanostructured nan-materials shows properties due solely to this unique morphology, both in terms of fundamental properties such as interface energy and in terms of complex interaction with biological materials such as proteins and cells.

Additionally, it will be shown how patterned DNA SAMs can be used as masters for a novel printing technique for organic materials called supramolecular nanostamping (SuNs). This method, like DNA/RNA information transfer, uses the reversible assembly of DNA double strands as a way of transferring patterns from a surface onto another. One of the main advantages of SuNs is that multiple DNA strands (each encoding different information) can be printed at the same time, thus allowing for a complex chemical pattern to be formed, much like Gutenberg movable type.

May 13, 2009

"Ultrafast photoemission electron microscopy: Imaging light with electrons on the femto/nano scale," Hrvoje Petek, University of Pittsburgh, hosted by Matthew Pelton

Abstract: Light interacting with a metal surface can excite both single-particle (e-h pair) and collective (plasmon) excitations. While most of the incident field will be coherently reflected, a small fraction can be absorbed to excite electron-hole pairs within the skin depth of the metal, or localized and propagating plasmon modes. We investigate electron excitation at clean, single-crystal metal surfaces by ultrafast nonlinear momentum and energy, resolved photoemission spectroscopy and photoemission electron microscopy. We describe the optimal geometry for coupling structures for introducing surface plasmon polaritons into continuous metal films. We discuss the imaging of surface plasmon polariton dynamics on silver surfaces and the function of simple plasmonic optical elements.

April 29, 2009

"Nanostructured Polymer Semiconductors: Charge Transport and Photovoltaic Properties," Samson A. Jenekhe, University of Washington, Seth Darling

Abstract: Advances in the controlled synthesis, processing, and tuning of the properties of conjugated polymer semiconductors promise improvement in the performance of organic semiconductor devices and are accelerating the emerging era of plastic electronics. Our laboratory is exploring a molecular engineering approach to readily processable and robust, high-charge carrier mobility materials needed for developing next-generation high-performance organic light-emitting diodes for displays and solid-state lighting, field-effect transistors, logic circuits, and low-cost solar cells. At the nanoscale, polymer semiconductors are expected to have unique properties resulting from size confinement and restricted dimensionality. We are beginning to test this expectation by investigating the self-assembly, nanoscale morphology, charge transport, and electronic and optical properties of various classes of polymer semiconductor nanostructures. In this talk, I will use examples of nanostructured conjugated polymers, including polymer semiconductor nanowires and assemblies of block copolymers to illustrate some of our recent approaches and efforts in these areas. For example, polymer semiconductor nanowires with widths of 5-30 nm and aspect ratios of up to 1000, that are readily assembled from solution, were found to be promising building blocks for nanoelectronics and solar energy applications. Our results show that polymer semiconductor nanostructures can have better properties and enable high performance devices than simple two-dimensional films.

April 15, 2009

"The Surface Chemistry of CdSe Quantum Dots, and Its Role in Their Optical Properties," Emily Weiss, Northwestern University, hosted by Gary Wiederrecht

Abstract: Organically passivated colloidal semiconductor quantum dots (QDs) are versatile chemical and biological sensors. The yield and wavelength of photoluminescence (PL) from excited states (called "excitons") of a QD changes in the presence of a variety of analytes, which electrostatically or optically couple with, or exchange electrons with, the QD. The intensity of the PL and photostability of the QDs (‹and, consequently, the sensitivity, specificity, and lifetime of QD-based sensors) is limited, however, by the presence of nonradiative pathways for decay of these excited states. The magnitude of the contribution of nonradiative decay depends on the immediate chemical environment of the fluorescent core of the QD (that is, the structure of its surface atoms, and of the monolayer of coordinated organic molecules that passivate them). This talk will describe methods to link the chemical structure of the surfaces of organically passivated colloidal QDs to their PL quantum yield using a combination of ultrafast transient absorption spectroscopy, structural characterization methods, and ligand exchange studies.

April 1, 2009

"Efficient Thermionic Energy Conversion Based on Doped Diamond Films," Robert Nemanich, Arizona State University,hosted by Anirudha Sumant

Abstract: The process of thermionic emission of electrons from a surface can be utilized to convert heat directly into electrical energy. High efficiencies are predicted because the process involves transport of electrons. While the advantages (and limitations) of thermionic energy conversion (TEC) systems have been known for many years, the potential development of a system based on doped diamond films could enable TEC devices that operate efficiently at temperatures less than 600C. In this study, the advantages of a TEC based on negative electron affinity surfaces of doped diamond are modeled, and the output power and efficiency are calculated. The potential of nanostructured carbon materials that involve field-dependent effects are also considered. Spectroscopic analysis of the thermionic emission from N-doped diamond is presented and related to the specific materials properties of a multilayered thin-film structure. These results establish that the Fermi level of the material is within a few tenths of eV of the vacuum level, and the barrier to emission is less than 1.4 eV. Results are presented that demonstrate direct energy conversion based on engineered N-doped diamond thin film structures.

March 16, 2009

"Molecular dynamics simulations of complex biomolecular systems," Benoit Roux, University of Chicago, hosted by Jeffrey Greeley

March 4, 2009

"Nanostructures to examine transport, dissipation, and correlations," Doug Natelson, Rice University, hosted by Jeff Guest

Abstract: Over the last decade, significant advances have been made in the fabrication of nanostructures and their use as tools to examine fundamental issues in condensed matter physics. I will describe two sets of experiments that take advantage of the particular capabilities enabled by the ability to make electrical probes separated on the nanometer scale. In the first, we use such probes to examine electronic transport and Raman response in single molecules. Transport measurements on molecules with unpaired electrons allow the study of the strongly correlated Kondo state driven out of equilibrium, while single-molecule Raman measurements open up the possibility of examining electron-vibrational dissipation with unprecedented precision. In the second set of experiments, we fabricate nanoscale electronic devices that directly incorporate a strongly correlated transition metal oxide, magnetite. In this system at low temperatures we find a nonequilibrium phase transition driven by the application of large electric fields. The small size of the devices allows us to delineate between possible transition mechanisms, since extremely large electric fields may be applied even with very modest voltages. I'll conclude by highlighting exciting possible future experiments made possible by nanostructure techniques.

January 21, 2009

"Electrochemical Interfaces: Structural and Catalytic Properties," Nenad M. Markovic, Material Sciences Division, Argonne National Laboratory, hosted by Jeff Greeley

Abstract: The last decade has witnessed some remarkable advances in the elucidation of microscopic processes at the electrified metal-solution interfaces. One class of electrochemical systems of particular significance, which has turned out to be suitable for characterization by in situ surface sensitive probes, vibrational spectroscopes, and electrochemical methods, is electrocatalysis of fuel cell reactions on single-crystal surfaces. Interest in these systems stems from the opportunity to establish both key structure-composition relationships and a deeper understanding of the activity pattern of metal nanoparticles in the size range of a few nanometers. Although the field is still in its infancy, a great deal has already been learned, and trends are beginning to emerge that give new insight into the relationship between the structure of electrochemical interfaces and catalytic activity/stability of nanoparticles.

To give an overview of the field, this presentation will provide a carefully balanced selection of results for the oxygen reduction reaction and the electrooxidation of CO first on platinum monometallic and bimetallic single-crystal surfaces and then on corresponding real nanoparticles supported on carbon.

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