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

Archive: Seminars 2006

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December 21, 2006

"Metal Clusters: Physics on the 1-Nanometer Scale," Karl-Heinz Meiwes-Broer, University of Rostock

Abstract: Metal clusters at surfaces are model systems of nanostructure physics that allow for the study of quantum effects. Exciting material and size-dependent features open the possibility to create novel objects that might serve for future applications ( e.g., in the area of nanoelectronics or quantum information technology). This contribution aims at highlighting few specific features of metal clusters, starting from dynamics in ultracold helium droplets and their interaction with strong femtosecond laser fields. The latter being a playground to study the coupling of strong radiation into matter. In particular, nonstationary plasma effects lead to pronounced dynamics in the optical response. From beam work, it is known that the electron structure of small clusters often has not much to do with the respective bulk. The interaction with a surface, in addition, might change the particular electronic behavior. To investigate electronic properties, we employ the method of tunnelling transport in an STM at low temperatures. The resulting dI/dU curves are distinctly structured, which results from the size-dependent density of states. In addition, the underlying substrate influences the electronic properties, which will be demonstrated with the germanium (100) surface. The magnetic investigations are performed with Kerr effect and absorption with optical and synchrotron radiation. When concentrating onto the ratio of the magnetic orbital to spin moments, a strong cluster size dependence is observed. Even large particles with up to 15 nm show increased magnetic orbital moments.

December 20, 2006

“Vibrational Lifetimes of Hydrogen and Oxygen Defects in Semiconductors,” Baozhou Sun, Washington State University, hosted by Matthew Pelton

Abstract: Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow and of the coupling mechanisms between local modes and the phonon bath of the host material. From time-resolved studies of the lifetimes and dynamics of local vibrational modes, we can obtain the important information on the energy dissipation and decay channels of impurities in semiconductors. The lifetimes of the Si-H stretch modes in silicon are found to be extremely dependent on the local solid-state structures, ranging from a few picoseconds for interstitial-type defects to hundreds of picoseconds for hydrogen-vacancy complexes. The studies of bending modes in semiconductors reveal that the lifetime of bending modes can be explained by energy gap law (i.e, the decay time increases tremendously with increasing decay order). An isotope effect is found in the study of the vibrational lifetimes of interstitial oxygen in silicon. The decay mechanism of interstitial oxygen defects in silicon and germanium is discussed according to their phonon density calculations and the symmetry of their accepting modes. These studies provide a better understanding of the dissociation of Si-H or Si-O bonds and the strong hydrogen and deuterium isotope effect found in H-passivated semiconductor devices.

December 12, 2006

“Pinning and Dynamics of a Magnetic Vortex,” Robert L. Compton, University of Minnesota, hosted by Kristen Buchanan

Abstract: A magnetic vortex is often the ground state of micron-diameter soft ferromagnetic disks. Vortex magnetization curls in-plane except at the vortex center, where the magnetization turns sharply out-of-plane, defining a core region with length scale ~10 nm. Like domain walls, the vortex core can be pinned by material defects. But the zero-dimensional nature of a vortex core, compared with the one-dimensional nature of a thin-film domain wall, gives rise to unique pinning behavior. We have used time-resolved Kerr microscopy to investigate the dynamical behavior of micron-diameter disks patterned from sputtered Permalloy films. Broadband spin dynamics include a low-frequency vortex translational mode (vortex mode) that is expected to be nearly independent of field, based on analytical theory and previous experimental work. Instead, when excitation amplitude is small, we find that the translational mode frequency fluctuates with field by a factor of ~2. The quasi-periodic nature of the field dependence points to an origin in a random distribution of pinning defects. Upon increasing the excitation amplitude, the pinning hypothesis is born out by the observation of depinning threshold, accompanied by the complete disappearance of the frequency fluctuations. Finally, by mapping translational mode frequency as a function of orthogonal in-plane fields, we are able to image the distribution of pinning defects in real space with ~20-nm resolution.

December 11, 2006

“Plasmonics: Optics at the Nanoscale,” Naomi J. Halas, Rice University, hosted by Gary Wiederrecht

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 are understood to be a classical analog of 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 that is the simplest nanostructure with tunable plasmon resonances. Moreover, this picture provides a nanoscale design principle for predicting 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, a photonic analog of the spinless Anderson model. 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 and surface-enhanced infrared absorption can exploit these types of designed metallic nanostructures as tailored, high-performance 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 an all-optical nanoscale pH meter for optical biopsies, and a nanoshell-based approach to cancer therapy.

November 9, 2006

“Birck Nanotechnology Center at Purdue,” John R. Weaver II, Purdue University, hosted by Derrick Mancini and Judith Yaeger

Abstract: The Birck Nanotechnology Center at Purdue University has some unique capabilities due to a combination of facility design and equipment set. This presentation will to describe the facility and its capabilities and discuss ways that the Center can work with Argonne on nanoscale research projects. This will be an informal presentation with significant time allotted for interaction.

November 8, 2006

“Nanoscale Spectroscopy with Optical Antennas,” Neil Anderson, University of Rochester, hosted by Gary Wiederrecht

Abstract: Because of diffraction, propagating radiation cannot be localized to dimensions smaller than half the optical wavelength. To overcome this limit, (nanoscale) optical antennas are used to localize radiation to length scales much smaller than the wavelength of light. A laser-irradiated optical antenna, such as a bare metal tip, is placed a few nanometers above a sample surface to establish a localized optical interaction and a spectroscopic response (Raman scattering, fluorescence, absorption, etc.). A high-resolution, hyper-spectral image of the sample surface is recorded by raster-scanning the antenna pixel by pixel over the sample surface and acquiring a spectrum for each image pixel. This type of near-field optical spectroscopy has been used to map the vibrational modes of individual single-walled carbon nanotubes (SWNT) with a resolution of 10nm. The method is able to resolve defects in the nanotube structure as well as interactions with the local environment. Similar studies have recently revealed that electronic states (excitons) in carbon nanotubes are highly localized to defect-rich regions.

October 23, 2006

“Synthesis and Applications of Gold Nanoparticles,” Hongwei Liao, Rice University, hosted by Norbert Scherer and Eric Isaacs

October 17, 2006

 

“The Localization/Delocalization Dilemma and the Electronic Structure of f-Element Oxides,” Richard L. Martin, Los Alamos National Laboratory, hosted by Al Sattelberger

Abstract: The electronic structure of many of the oxides containing d- and f-elements has long been a challenge for theory. For example, the traditional workhorses of density functional theory, the local density approximation (LDA) and the generalized gradient approximations (GGA), predict many of these systems to be metallic, when in fact they are insulators with band gaps of several electron-volts. These problems reflect the localization/ delocalization dilemma faced in systems with weak overlap and seem to be largely overcome by the new generation of hybrid density functionals developed for molecular studies. Only recently has it been possible to apply these functionals to solids, but in the cases studied thus far we find a distinct improvement. The hybrid functionals predict the correct insulating ground state, band gap, lattice constant and magnetic behavior at 0K, where known. I will review the origin of the problem, how hybrid functionals differ from traditional ones, and recent applications to strongly correlated oxides.

October 12, 2006

“Synthesis and Assembly of Nanoparticle Into Superlattices and Gels,” Christopher M. Sorensen, Kansas State University, hosted by Xiao-Min Lin

Abstract: This talk will give an overview of research the author has been performing over the past several years. Topics will include:

  1. Nanoparticles with narrow size distributioncan be synthesized via a process we call “digestive ripening,” which involves heating a suspension of particles in the presence of a surface active ligand, typically alkyl thiols, amines, or phosphines. With time, a polydisperse system will become nearly monodisperse. Another feature of digestive ripening is that mixtures of colloids of different metals will alloy during digestion. Reversible size and shape control can be achieved by changing the ligand.
  2. Nanoparticle suspensions act as solutions and thereby the distinction between suspension and solution blurs. I will show temperature dependent solubility data for nanoparticle solutions that can be made to precipitate to form 2d and 3d superlattices.
  3. Finally I will go to the gas phase and show that nanoparticle aerosols can gel. Timescales for gelation are in a reasonable range only when the system is nano. This aerosol gelation yields very low-density, high-surface-area solids similar to aerogels that may have important technical application.

October 5, 2006

“Biofunctionalization and Detection of Magnetic Nanoparticles,” Glenn Held, IBM, hosted by G. Brian Stephenson

Abstract: Methods of synthesizing monodisperse, strongly magnetic ferrite nanoparticles have been well documented. However, encapsulation of these particles within an overlayer of biologically active molecules has remained problematic. Such bio-functionalized magnetic nanoparticles would provide the crucial component in ultrasensitive magnetic detection of both proteins and nucleic acids. In addition, such particles could be used to bind and transport proteins and, following introduction into a living organism, they could provide a means of monitoring and influencing cellular processes. In this talk, I will present a method for bio-functionalizatizing manganese ferrite nanoparticles. Following biofunctionalization with DNA or biotin, these particles can be site selectively bound to appropriately patterned silicon oxide substrates. Imaging these substrates with scanning SQUID microscopy provides evidence that these particles retain their magnetic properties. Finally, a novel method of detecting the hybridization of these magnetic nanoparticles to a substrate at room temperature using a biosensor comprised of a protein patterned magnetic tunnel junction situated in orthogonal magnetic fields will be discussed.

September 27, 2006

“Optical Properties of Silicon Clusters and Quantum Dots: Is 'Nano' Really that Different from the Bulk?” Serdar Ogut, University of Illinois Chicago, hosted by Peter Zapol

Abstract: For almost two decades now, there has been an increasing tendency to get excited about any research activity in condensed matter and materials physics with the word “nano” in it. Active research on the optical properties of silicon nanostructures is one good example. In this talk, I will present some of my previous and ongoing research in ab initio modeling of the optical properties of silicon nanostructures, such as hydrogenated silicon quantum dots up to a few nm in size and medium-size atomic Sin (n = 20 – 28) clusters. I will argue, using various examples from these systems, that while “nano” typically presents rather interesting physics, most of this interesting physics can be understood in terms of bulk Si properties with the right boundary conditions.

September 25, 2006

“Reduction of Spin Transfer Currents and Low Temperature Anomalies in the Free-layer Nanomagnet Behavior of Nanopillar Spin Valves," Ozhan Ozatay, Cornell University, hosted by Axel Hoffman

Abstract The idea of employing electron spin for information technologies has unique advantages over the conventional charge-based electronics because it potentially enables nonvolatile data storage, improved data processing speed, and more efficient power consumption as well as high integration density. In metallic spintronics, the interaction of the spin of a current-carrying electron and a localized moment of a ferromagnet has two important outcomes: the spin-dependent scattering of the current carrying electrons leading to magnetoresistance effects and to the ability to manipulate the local moment through a mutual spin transfer torque. In this talk, I will present a series of experiments that address issues regarding the latter, spin-transfer phenomenon and that addresses some of the challenges for advancing this phenomenon toward technological applications. In the first part of the talk, I will discuss the nucleation and subsequent depinning of a domain wall driven by a nonuniform spin polarized current injection into a nanomagnet. This is accomplished by defining a 20-to 30-nm-diameter aperture inside a 3.5-nm-thick AlOx in between the Cu spacer and permalloy (Py) free layer of a Py/Cu/Py nanopillar spin valve. The resulting concentrated spin polarized current injection into the free layer nucleates and applies pressure to a domain wall at the contact region. The magnetic reversal is via the propagation of the domain wall driven by spin torque. This mechanism reduces the absolute level of spin transfer switching currents required to achieve magnetization reversal by two orders of magnitude. In the second part of my talk, I will focus on the adverse effects of sidewall oxides in a Py nanomagnet on both field and current driven switching characteristics as a function of temperature. Analytical electron microscopy and surface sensitive x-ray photoemission spectroscopy measurements reveal that the Py surface has NiO, FeO, and Fe2O3 native antiferromagnetic oxides. These adventitious oxides can have a major impact on the efficiency of spin torque switching as well as field driven switching by enhancing magnetic damping as well as causing unstable switching fields due to a rotatable anisotropy. I will show that the passivation of such an oxide layer results in minimal temperature dependence of spin transfer switching currents as well as in stabilizing the switching fields.

September 22, 2006

“Design of Biologically Inspired Nanostructured Materials,” Szu-Wen Wang, University of California, Irvine, hosted by Eric Isaacs and Lee Makowski

Abstract: The precision of natural protein nanostructures is remarkable, and they can be used as scaffolds upon which to build new functionalities. We are investigating the use of protein assemblies as biomaterials for applications such as dispensing pharmaceutically-active molecules and directing the optical properties of inorganic arrays. Our current work focuses on the in vivo synthesis, self-assembly, and materials characterization of several engineered macromolecular complexes, including nanocapsules, protein polymers, and crystalline arrays. By finely defining architecture at both the molecular and nanoscale levels through genetic engineering, such an approach enables us to tailor unique material properties.

September 20, 2006

“Heterogeneous Nanomaterials: Spanning Supramolecular Templating, TiO2 Surface Defects, and Metal Oxide Morphologies,” Bryan M. Rabatic, Chemistry Division, hosted by Tijana Rajh

Abstract: Nanoscale materials comprised of organic and inorganic components are becoming a cornerstone of nanotechnology. Self-assembled organic systems can act as part of such a hybrid material by serving as a template for the synthesis of inorganic structures having features inaccessible with known lithographic techniques. In this regard, peptide-based amphilphilic molecules having an unsymmetrical molecular design are capable of self-ordering in aqueous environments to form one-dimensional scaffolds with 5-nm widths and lengths up to several micrometers. These bioinspired nanoobjects can preferentially complex cadmium ions for the directed precipitation of cadmium sulfide nanocrystals to form a hybrid material having features commensurate with the self-assembled organic template. Furthering this template-based method, we show that the cores of one-dimensional titanium dioxide nanotubes, with lengths up to 300 nm, can serve as templates for the precipitation of silver metal nanowires having diameters of 6-8 nm. We also demonstrate the compliment to the organic template approach; inorganic nanoobjects can serve as templates for organic, biological molecules. In this regard, site-specific defects at the distal tips of ellipsoid-shaped TiO2 nanoparticles, direct the surface functionalization of the nanoobject with the biomolecule dopamine. The defect sites of the inorganic template were identified with high-resolution transmission electron microscopy, and found directly related to the size and shape of the nanoparticle. By templating biotin at the defect sites, tip-to-tip serial self-assembly of these bio-hybrid nanocomposites, via conjugation with the glycoprotein avidin, is shown. Finally, we have been able to produced unusual structures of zirconia using a completely surfactant-free synthetic approach. These materials are synthesized via an aqueous, hydrothermal treatment to form extremely high aspect-ratio nanotube and nanowhip

September 19, 2006

“Evaporation-Induced Self-Assembly of Porous and Composite Thin film Nanostructures, " C. Jeffrey Brinker, University of New Mexico/Sandia National Laboratories, hosted by Eric Isaacs

Abstract: Nature combines hard and soft materials often in hierarchical architectures to get synergistic, optimized properties and combinations of properties with proven, complex functionalities. Emulating such natural material designs in robust engineering materials using efficient processing approaches amenable to manufacturing represents a fundamental challenge to materials scientists and engineers. Currently there is considerable interest in evaporation-driven self-assembly as a means to create porous and composite thin film nanostructures using simple commercial procedures like dip or spin-coating and ink-jet printing. This presentation will first review recent progress on evaporation-induced silica/surfactant self-assembly (EISA) to prepare porous thin film nanostructures of interest for membranes, sensors, and low k dielectrics. Starting with a homogenous solution of surfactant plus hydrophilic oligosilicic acid precursors, solvent evaporation concentrates the depositing film in precursors and surfactant inducing micelle self-assembly and further self-organization into thin film silica/surfactant mesophases. Exploiting the steady, continuous nature of dip-coating, it is possible to spatially resolve the complete evaporation-induced self-assembly pathway (in the coating direction) and interrogate it using spectroscopy and/or grazing incidence SAXS. I will then discuss surfactant self-assembly as a means to organize simultaneously hydrophilic and hydrophobic precursors into hybrid (organic/silica or metal/silica) nanocomposites that are optically or chemically polymerizable, patternable, or adjustable. For example, the co-self-assembly of amphiphilic photoacid generators with silica precursors results in photosensitive thin film mesophases in which the pore size, pore volume, surface area, and refractive index may be continuously varied over a range depending on the UV exposure time. Incorporation of switchable, hydrogel or azobenze moieties provides a means to create nanostructures exhibiting chemo-, thermo- or opto-mechanical actuation. Biocompatible self-assembly, using phospholipids as the structure-directing agents, allows cell immobilization in a robust self-contained, self-sustaining environment of interest for stand-alone cell-based sensors. However, we observe that cells co-opt the EISA process, altering significantly the self-assembly pathway and creating a unique bio/nano interface. As a new direction in self-assembly, we have exploited mechanically-based re-assembly to create superhydrophobic, fractal silica surfaces mimicking those of the Lotus leaf and desert beetle. These surfaces are self-cleaning and fundamentally affect flow, making them of general interest for fluidic-based microsystems.

September 8, 2006

“Nanopatterning of Biomolecules,” Joseph Kakkassery, Northwestern University, sponsored by Tijana Rajh

Abstract: The emerging field of nanobiotechnology relies on precise patterning of biological molecules on surfaces with nanometer resolution. A few examples include the generation of DNA, protein, virus and cell arrays that have potential applications in the areas of biosensing, proteomics and theranostics. Currently a number of techniques exist for generating nanoscale features of biological molecules. These include electron-beam lithography, dip-pen nanolithography (DPN), nanografting, nanoimprint lithography, nanopipet deposition and contact printing. Each of these techniques has a set of capabilities that differentiate it from the rest, and all possess both strengths and weaknesses with regard to resolution, speed, materials compatibility, complexity, and cost. This talk will focus on the generation of single influenza virus nanoarrays by dip-pen nanolithography and its applications in studying cell infection.

August 28, 2006

“Synthesis and Development of Functional, Biocompatible Nanocomposites,” Dolly Batra, Materials Science Division, hosted by Tijana Rajh

Abstract: An important step in the development of functional nanoscale devices is the synthesis of meso- and nanostructured “soft” materials that can be used to incorporate and organize nanoscale features such as biomolecules or nanoparticles. Organic polymers are an attractive class of such soft materials, as their properties can be tuned according to their chemical or biochemical functionalities. Protein-based soft materials, for example, require the synthesis of biocompatible, mesostructured materials that organize biomolecules into highly ordered, functional arrays. To that end, a matrix comprising a two-dimensional hexagonal, mesoporous network of crosslinked polyvinyl alcohol (PVA) has been fabricated that exhibits potential for the integration and organization of soluble and membrane proteins. Several novel polymers based on self-assembled ionic liquids have also been developed, where the liquid crystalline architecture can be controlled via changes in the water content. These soft, nanostructured materials are useful as templates for the in situ synthesis, trapping and ordering of metal (Au) and semiconducting (CdS, PbS) nanoparticle arrays. These composite materials have applications for the fabrication of novel photonic materials and all ‘solid-state’ solar cell devices where the spacing between nanoparticles can be tuned for optimum photovoltaic efficiency.

August 11, 2006

“Advanced DSC Techniques in Mettler-Toledo Thermal Analysis Instrument,” Matthias Wagner , Mettler -Toledo, Inc., hosted by Xiao-Min Lin

August 11, 2006

"Charge Transfer and Recombination in Semiconductor Nanostructures Designed for Photovoltaic Applications," Istvan Robel, University of Notre Dame, hosted by Xiao-Min Lin

Abtract: Several approaches for improving the efficiency of nanomaterial-based photovoltaic devices will be discussed in the talk. The use of hybrid assemblies such as type-II semiconductor-semiconductor heterostructures and semiconductor-carbon nanotube composites lead to modified electronic properties beneficial for light harvesting. Photoinduced charge transfer- and recombination dynamics and photoelectrochemical properties will be discussed in two heterostructures (CdSe-TiO2 and CdS-CNT) as well as in semiconductor nanowires (CdSe).

July 25, 2006

“Spin Dynamics in Lateral Thin-Film Nanostructures," Sergio O. Valenzuela, Massachusetts Institute of Technology, hosted by Axel Hoffmann

Abstract: Spintronics aims to replace charge with spin as the main computational element in devices. Much effort is being devoted to understand how the electron spin is transferred through interfaces and to identify fundamental processes that modify the spin polarization or that can be used for spin manipulation. Lateral structures are a unique tool to study these phenomena because of the ease to fabricate them in multi-terminal configurations. This will be illustrated by some of our recent experimental results in thin-film devices, where the output voltage is exclusively determined by the spin degree of freedom, and provides valuable information on spin-flip scattering mechanisms, spin-polarized tunneling, spin-orbit interaction and the spin Hall effect.

July 24, 2006

“Molecular Assembly from Functional Building Blocks,” Huisheng Peng, Tulane University, hosted by Seth Darling

Abstract: There is a growing interest in the synthesis of functional materials by supramolecular assembly. Recent attention has been directed toward understanding the assembly mechanism, the incorporation of desired functionalities, and the applications. My research focuses on studying self-assembly of organic/inorganic hybrid molecules (e.g., bridged silsesquioxanes, with a structure of (RO)3Si-R’-Si(OR)3) and polymers. For the self-assembly of bridged silsesquioxane, four functional organic groups, (i.e. polydiacetylene, oligothiophene, perylenediimide, and porphyrin) are readily incorporated into an ordered silica network, and the resultant assemblies show interesting structures and great applications as optoelectronic devices and sensor materials. Polymer assembly is performed in common solvents to produce smart thin films or nanoparticles, and their applications as sensors and controlled drug-delivery vehicles, respectively, have been investigated.

July 14, 2006

“Magnetic and Mechanical Responses of Soft Multiphase Materials,” Brian D. Pate, Massachusetts Institute of Technology, hosted by Tijana Rajh

Abstract: The ability of organic matter to undergo reversible structural and electronic reorganization in response to environmental stimuli is directly responsible for the broad utility of soft materials in natural and synthetic systems. In particular, assemblies of molecules or macromolecules engineered to exhibit hard/soft or liquid crystalline phases exhibit a wide range of tunable responses to external electromagnetic and mechanical fields. Recently, the metal-dependent structural reorganization of a series of mesogenic metalloporphyrazines in the presence of applied magnetic fields has been predicted and characterized. A method to magnetically process these liquid crystals to obtain long-range uniaxial orientation of the columnar superstructures has been demonstrated. The alignment of these materials using mechanical fields will also be described, and contrasted with that of two related macromolecular systems, including a novel functionalized polyiptycene and a new series of thermoplastic polyurethanes

July 12, 2006

“Achieving Enzymatic Catalysis in Abiotic Supramolecular Systems,” Andrew J. Goshe, CNM Distinguished Postdoctoral Appointee, Chemistry Division, hosted by Tijana Rajh

Enzymes, one of the classes of nanoscaled machines in biology, accomplish a stunning variety of chemical transformations with high specificity and activity. The synthetic replication of the activesites of these enzymes, however, seldom results in catalytically active species. Recent efforts have been directed toward the construction of nanoscaled systems capable of reactivating synthetically derived hydrogenase activesite mimics for the production of hydrogen. The design, synthesis, and properties of such systems will be discussed.

July 12, 2006

“Magnetic Nanoparticle Antibody Conjugates for Potential Cancer Therapies,” Dorothy Farrell, London Centre for Nanotechnology, hosted by Seth Darling

Abstract: Numerous biomedical applications for magnetic nanoparticles have been proposed and developed in the past decade. High magnetic susceptibility superparamagnetic nanoparticles are currently being investigated as magnetic hyperthermia and drug delivery agents. In hyperthermia, cancerous cells are destroyed by heat generated in magnetic nanoparticles by an appropriately tuned, externally applied ac magnetic field. If the particles can be confined to the cancerous regions through antigen binding, nearby healthy tissue would be unharmed. Targeting can be further improved using in vivo magnetic actuation of the particles with external magnetic fields. However, up to now the ac power loss profile of particles used in hyperthermia studies has not been sufficient for use in clinical applications. The standard co-precipitation reactions of Fe2+ and Fe3+ salts in alkaline solutions produce non-stoichiometric magnetite 5-15 nm in diameter, with only moderate heating properties.

Along with researchers at the Royal Free and University College Medical School, I am currently developing antibody-nanoparticle conjugates with improved properties for hyperthermia applications. We have conjugated carboxymethyl dextran coated iron oxide nanoparticles to an antibody fragment specific to carcinoembryonic antigen, a protein expressed on many epithelial cancers. Immunoassays studies show that these conjugates maintain reactivity against the target antigen, suggesting that the conjugates can be directed to target tumors within the body. Current work focuses on the preparation of nanoparticles capable of significant heating at the low concentrations (~1mg/cc) attainable in vivo using antigen targeted delivery. To create an optimized hyperthermia agent, iron oxide particles of varying size, shape, phase and crystallinity have been synthesized and their heat generation profiles studied. Using a modified reaction procedure in a biocompatible organic solvent (1,2-propanediol), particles 30-40 nm in diameter have been synthesized. Dispersions of these samples show rises in temperature two times greater than commercially available particles using clinically relevant field conditions.

July 5, 2006

"Understanding the Materials Behavior of Tetrahedral Amorphous Carbon Using MEMS Resonators," David A. Czaplewski, Cornell University, hosted by Leo Ocola

Abstract: Tetrahedral amorphous carbon (ta-C) films have been used to fabricate micro-electromechanical systems (MEMS) with broad applications, such as electronics ( clocks, filters, switches, etc.), sensors (for chemicals, biological agents, pressure, acceleration, etc.), and metrology (scanning probe microscopy). These films have advantageous properties compared to other common MEMS films, such as silicon, polysilicon, silicon nitride, and silicon dioxide. The Youngs’ modulus of ta-C (approximately 80% sp3 bonding) is roughly four times that of the other common films, which can aid in the realization of high-frequency oscillators for filter and other applications. Additionally, the ta-C films are resistant to stiction and auto-adhesion and have an abrupt surface termination, which helps prevent surface-related mechanical dissipation. Understanding dissipation mechanisms that limit the quality factor, Q, in ta-C is essential for realization of components for electronic or sensor applications since the bandwidth for electronic components scales as Q-1 and the sensitivity of sensors scales as Q-½. Additionally, for some devices,, such as a proposed tunable frequency source for space-based electronics, knowledge of the temperature dependence of the elastic constants and Q of ta-C is of primary importance.

In this talk, I will discuss our recent work to understand the fundamental mechanisms that control mechanical dissipation in ta-C and of the experimental measurement of the thermal stability and temperature dependence of the mechanical properties of this material.

June 30, 2006

“The Development of Bio-Inorganic Nanostructures for Device Applications,” Brian D. Reiss, Materials Science Division, hosted by Tijana Rajh

Abstract: The integration of biomolecules with inorganic substrates is rapidly generating innovative materials with potential applications ranging from solar power to medical diagnostics. In this presentation two approaches towards the development of biomolecule-based functional materials that may ultimately form the basis of nanoscale devices will be presented. In the first photosynthetic reaction centers from R. Sphaeroides are being investigated for their potential applications in opto-electronic devices. Efforts are currently underway to isolate this protein on inorganic electrodes with controlled orientation, a challenging approach because novel chemistry must be developed to simultaneously link the protein to multiple electrodes. The second system under study uses the technique of phage display offers a way to rapidly identify peptide ligands for any desired material, and such ligands could be used to link biological species to inorganic substrates as desired. Recently, a peptide has been isolated using this approach that selectively binds the ferroelectric material lead zirconium titanate, and this unique system is currently being developed as the basis of a valve for nanofluidic systems.

June 26, 2006

“Tailoring Mesomorphic Structure and Crystalline Morphology in Polymer Films,” Raluca Gearba, Institut de Chimie des Surfaces et Interfaces, hosted by Seth Darling

Abstract: Since their discovery, columnar mesophases have become increasingly important in fundamental research and in practical applications because of their peculiar supramolecular architectures, which allow one-dimensional charge transport. Although the most studied columnar phases are formed by disc-shaped molecules, it is now recognized that such phases can also be formed by dendrimers, main- or side-chain polymers with or without mesogenic moieties, phasmids, and board-like molecules. The electronic and optical properties of the liquid crystalline (LC) phases strongly depend on the chemical structure of the molecules and the way there is self-assembly at different scales in bulk and at interfaces. In particular, the organization at the mesoscopic scale, spanning from several nanometers to some hundreds of nanometers, must be tailored to control features such as the size and orientation of the LC mono-domains.

The lecture will show and discuss how the influence of the molecular architecture (degree of flexibility of molecules) and specific interactions such as hydrogen bonding can play on the supramolecular organization. We will demonstrate that using hydrogen bonds to “clamp” the molecules along the columns results in the smallest intermolecular distance (3.18 Å) ever found for columnar mesophases. At the same time, it will be shown how flexible star-shaped molecules self-assemble to give rise to a unique double helical crystal. Interestingly, the growth of the helical crystals can be tailored at the scale of one columnar diameter (2-4 nm) via a monotropic columnar mesophase. This scale is one order of magnitude smaller than the characteristic size of the block-copolymer morphology. By actively playing with the chemical structure, we can identify some of the factors responsible for the structure formation.

June 19, 2006

“Structural Landscapes of Biomimetic Supramolecular Nanomaterials by Solution X-Ray Scattering,” Xiaobing Zuo, Chemistry Division, hosted by Tijana Rajh

Abstract: Biomimetic supramolecular nanomaterials are increasingly being designed for applications in solar energy conversion and storage, catalysis, environmental clean-up, and so on. The dynamic features of these molecular materials make in situ structural characterization a critical challenge. Our early studies have demonstrated that wide-angle solution X-ray scattering (WAXS) is a powerful, discriminating, high-throughput technique for in situ supramolecular structural characterization that can be applied with 100 to 1 Å spatial resolution and 100 ps time resolution for mapping structural dynamics along excited state reaction coordinates. This talk will focus on using coordinate-based analyses for wide-angle solution X-ray scattering to in situ characterize the structures and conformational dispersion of supramolecules, from nanocrystals which have rigid and ordered internal structures, to DNA, synthetic molecular squares, and self-folding polymer which is disordered and flexible in conformation. Designs and characterizations of light-induced molecular electronics and machines with time-resolved X-ray scattering will also be discussed.

June 14, 2006

“MicroPIV Measurement of Turbulent and Transitional Flow Characteristics in Microchannels,” by Hao (Stephen) Li, Iowa State University

June 9, 2006

“Multiscale Coarse-Grained Modeling of Nanoparticle and Supramolecular Systems,” Sergey Izvekov, University of Utah, hosted by Peter Zapol

Abstract: A novel and systematic methodology for the development of accurate coarse-grained (CG) models for simulations of nanoscale and biological systems is described. The method is called the multiscale coarse-graining (MS-CG) method and is based on matching of the effective interactions in the coarse-grained system to an underlying all-atom simulation. The MS-CG models open up the possibility of a dramatic speed up of molecular dynamics simulations of complex condensed-phase, biological, and nanoscale systems while retaining high accuracy in the prediction of structural and often thermodynamic properties. Several past and future applications of the MS-CG methodology will be presented, which include molecular liquids, biological membranes, proteins, and the self-assembly of carbonaceous nanoparticles.

May 30, 2006

“Andreev Reflection at the normal-metal/heavy-fermion superconductor interface: Point contact spectroscopy of CeCoIn5,” Laura H. Greene, Swanlund Professor of Physics, University of Illinois at Urbana-Champaign, hosted by Eric Isaacs

Abstract: Point-contact spectroscopy results are obtained with normal-metal gold tips on single crystals of the heavy-fermion superconductor CeCoIn5. Contacts are shown to be in the Sharvin (ballistic) limit. Asymmetry observed in the background conductance starting at T* (~45 K), increasing with decreasing temperature to Tc (2.3 K), signifies the emerging heavy-fermion liquid. Below Tc, the enhancement of the sub-gap conductance arises from Andreev reflection. According to standard theory, the Fermi velocity mismatch between these materials should yield no Andreev reflection. The signal we do observe is several times lower than that observed in conventional superconductors, but consistent with other heavy-fermion superconductor data reported. Data taken in the (001), (110), and (100) orientations provide consistent and reliable spectroscopic evidence of a dx2-y2 superconducting order parameter.

May 29, 2006

“(1) Periodic Calculations with Gaussian Basis Sets” and "(2) First Principles Simuation of Liquid Water near Hydrophobic Surfaces,” Konstantin Kudin, Princeton University, hosted by Eric Isaacs

Abstract: In the first part of my talk, I will discuss the implementation of periodic boundary conditions in the Gaussian suite of programs (Gaussian03). The code can carry out efficient density functional (DFT) and Hartree-Fock (HF) calculations for systems periodic in one, two, and three dimensions. I will mention several applications of this computational tool, specifically, studies of pristine and fluorinated carbon nanotubes, BN nanotubes, oxidized graphite, and uranium oxide (UO2) solid.

In the second part I will talk about Car-Parrinello molecular dynamics simulations of liquid water near hydrophobic surfaces. Peculiar properties of water layer near the surface that emerge from these calculations will be discussed.

May 17, 2006

“Electronic and Excitonic Interactions in Molecular and Nanoscale Materials and Devices,” Cherie R. Kagan, IBM T. J. Watson Research Center, hosted by Eric Isaacs

Abstract: Molecular and nanoscale materials are being aggressively pursued for a wide range of applications in low-cost, large-area, flexible macroelectronics and optoelectronics and potentially as a post-CMOS alternative to high-density, high-performance nanoelectronics. For these systems to realize their potential, a fundamental understanding of the chemical and physical properties of molecular, supramolecular, and nanostructured assemblies is required. I will describe the synthesis, assembly, and characterization of molecular monolayers, multilayers, and thin films and the intermolecular, intramolecular, and interfacial interactions important to charge transport and exciton transfer and separation. Spectroscopic, microscopic, and electrochemical techniques are used to characterize molecular, supramolecular, and nanostructured assemblies. I will show solution processable, thin films form the active channels of transistors with field-effect mobilities (in micron scale devices) of ~1 cm2/V-sec and ION/IOFF>106, comparable to amorphous silicon TFTs. To probe inter- and intramolecular charge transport in molecular monolayers and multilayers, I will draw on silicon processing to fabricate nanometer scale device test structures and use novel chemical routes to assemble molecular materials at the device interfaces and to bridge the junctions. Integrating molecular assemblies in device test structures provides a platform to probe the underlying physics of charge transport necessary to develop structure-function relationships in molecular materials. Spectroscopic and optoelectronic techniques are used to explore the fate of excitations in molecular and nanoscale assemblies giving rise to energy transfer and charge separation.

May 15, 2006

“Atomic-Scale Catalyst Design from First Principles,” Jeffrey P. Greeley, Technical University of Denmark, hosted by Peter Zapol

Abstract: Recent advances in Density Functional Theory (DFT) algorithms, combined with the ever-increasing availability of raw computer power, have put forth the tantalizing possibility that first-principles methods may soon contribute to the efficient, atom-by-atom design of heterogeneous catalysts and other materials. For such computational design efforts to be successful, however, key catalytic parameters for the reactions of interest (binding energies, activation barriers, etc.) must be identified, techniques for assessing the stability of nanoscopic surface structural features in reactive environments must be developed, and an efficient scheme for finding alloys that optimize design criteria for activity and stability must be found.

In this talk, I describe a general methodology for materials design using atomic-scale simulation methods. The method employs DFT calculations to determine important features of catalytic performance, including catalyst activity, structure, and stability, and it is applied to the analysis of hundreds of transition metal alloys for use in two reactions of interest in electrochemistry, the hydrogen evolution and oxygen reduction reactions.

April 28, 2006

“Correlating Atomic Scale Structural and Magnetic Properties by Spin-Polarized STM,” Dr. Matthias Bode, Institute of Applied Physics and Microstructure Research Center, Hamburg, Germany, hosted by Eric Isaacs

 

April 27, 2006

"How far can we go? – An Update of Zone Plate Fabrication at Stony Brook,” Ming Lu, SUNY at Stony Brook, hosted by Leo Ocola

Abstract: Fresnel phase zone plates are the most important focusing optics for soft X-ray scanning transmission microscopes. In collaboration with NJNC at Bell Labs/Lucent Technologies, the Stony Brook X-ray optics group has been working on zone plate fabrication for more than a decade. In this talk, I will give a survey of our latest progress. Factors that limit zone plate performance under current fabrication flow, as well as our strategies for improvement, will be discussed. For example, a newly discovered effect in e-beam lithography (orientation dependence of linewidth variation, or ODLW) and its correction method will be presented for the first time.

April 25, 2006

“Electron Transport in Artificial Nanosolids,” Igor Beloborodov, Fermi Scholar, Materials Science Division, hosted by Peter Zapol

Abstract: Artificial materials composed of metallic nanoparticles have emerged as the next frontier of new materials, where quantum phenomena can be tailored to generate novel bulk materials behavior. These nanosolids can have programmable electronic properties arising from the fact that the interaction strength and degree of disorder in these materials can be controlled by varying the size and composition of the granules. Each building block of these new materials can be viewed as a tiny cluster of atoms of metallic or semiconducting elements. These clusters are not as small as molecules but not as large as macroscopic samples. I will review progress made in the last several years in understanding the properties of artificial nanosolids. In particular, I will discuss the following topics:

  1. Introduction to physics of artificial nanosolids,
  2. Novel transport regimes,
  3. Phase diagram of artificial nanosolids, and
  4. Future opportunities.

April 17, 2006

“Nanoscale Theory and Simulation: Light Interactions with Metallic Nanosystems,” Tae-Woo Lee, Chemistry Division, hosted by Peter Zapol

Abstract: Materials processing techniques can now engineer materials with nanoscale features. When light interacts with such nanosystems, complex electromagnetic wave phenomena can emerge through strong near-field interactions. For example, surface plasmons (SPs), collective resonances of free electrons in a metal, can be excited in metallic nanosystems. SPs yield intriguing near-field phenomen,a such as highly localized fields and strong intensities. With strong, yet complex, near-field interactions, such systems provide ways of controlling light at the subwavelength scale. First-principles computational modeling tools provide invaluable insights about the complex wave phenomena inherent in light interactions in metallic nanosystems. They also can be used to conduct inexpensive feasibility studies of novel device ideas and allow one to optimize device designs prior to fabrication. First, we address usefulness of numerical approaches in nanophotonic research. Next, three new types of nanosystem are proposed and explored numerically:

  1. A cone-shaped silver nanoparticle interacting with chirped optical pulses. Rigorous numerical simulations reveal how spatio-temporal control of an SP local hot spot can be achieved. The simulations also demonstrate counterintuitive negative group velocity in some situations.
  2. A way to increase surface plasmon polariton (SPP) propagation length and intensity is proposed. (An SPP is a propagating SP excitation.) The underlying mechanism involves reflecting back radiation losses to propagating metal surface region, regenerating SPPs. Extensive finite-difference time-domain simulations, including coupling of external light into the system, demonstrate significant improvements.
  3. Redirecting light propagation with a sharp angle turn is a decades-long problem in photonic integrated-circuit research.

In this study, we discuss light propagating and bending in a slit waveguide. The discussion is based on accurate numerical solutions of Maxwell’s equations. The results, using a realistic model for silver at optical wavelengths, show that good right-angle bending transmission can be achieved for wavelengths greater than 600 nm. The bending efficiency is shown to correlate with a focusing effect at the inner bend corner. Possible experimental realization of these systems is also indicated.

April 14, 2006

“Nanotechnology at Intel Corporation,” Dr. Bryan Rice, Intel Corporation, hosted by Ahmed Hassanein

April 14, 2006

“Reactive Molecular Dynamics Simulations of Network-forming Systems with Multiple Coordination States,” Liping Huang, University of Michigan, hosted by Peter Zapol

Mar. 31, 2006

"Nanotechnology from the Bottom Up: Light-directed Synthesis of DNA Molecules," Prof. Franco Cerrina, University of Wisconsin – Madison, hosted by Leo Ocola

Abstract: One of the dreams of nanotechnology is to enlist the help of existing organisms as “nanofabricators.” This is routinely done today when bacteria are used to produce designer molecules by inserting a specific strand of DNA in a vector. The next step would be to use more advanced organisms, such as diatoms, to generate controlled and user-specified structures. This requires both the knowledge of the genome and the ability to synthesize DNA “on demand,” at a reasonable cost and turnaround time.

Indeed, the direct synthesis of DNA constructs in the length of 2,000 to 20,000 base pairs (bp) is at the root of a revolution in genetic engineering. As more and more genomes are decoded, and the function of the genes understood, there is the possibility of actually reprogramming some of the genetic material to achieve specific functions, from medicine to synthetic biology. The well-known base-by-base synthesis of DNA can be greatly enhanced by combinatorial techniques, whereby a large number of single-stranded DNA sub-units (oligonucleotides) are synthesized in parallel and later assembled in longer constructs. Using light-directed synthesis of the oligonucleotides, hundred of thousands of different short sequences (40-70b) can be created in a few hours.

After amplification, these sequences can be assembled in longer units in a hierarchical, multiple stages process. The final product – a synthetic gene – can then be used in a multiplicity of biological applications.

We will review the state of the art of the base-by-base DNA synthesis, with particular emphasis on chip-based methods, and discuss the problem of the errors found in the sequence of synthetic DNA. Many applications require error-free DNA, and this can be guaranteed only by sequencing the final product. Typically, samples extracted from the final product are cloned and sequenced, to find the correct one – an expensive and time consuming process. The number of clones to be sequenced is a strong function of the error rate in the DNA synthesis, so that a rate of less than 1 error per 10,000 bp is necessary to produce a viable process for the synthesis of 2,000 bp genes. We have recently proposed several error-removal methods that can improve the purity of synthesized materials, and produce error-free output material. To achieve this goal it is necessary to combine optimized micro-fabrication techniques in the synthesis and purification of the oligomers, with biological and statistical methods for error removal.

Mar. 22, 2006

"Single Spin Detection Using Magnetic Resonance Force Microscopy," Dr. Raffi Budakian, University of Illinois Urbana-Champaign, hosted by Eric Isaacs

Abstract: Magnetic resonance force microscopy (MRFM) is an emerging technique for direct nondestructive three-dimensional imaging with potential applications to imaging of individual molecules, buried interfaces, nanostructures and inhomogeneous solids. MRFM combines ultrasensitive force detection and magnetic resonance to manipulate and detect subsurface electron or nuclear spins with high sensitivity and spatial resolution.

Recently, we have used MRFM to image a single electron spin with 25-nm lateral resolution located as deep as 100 nm below the surface of a silica sample containing a low concentration of silicon dangling bonds. Achieving this high detection sensitivity has been due in part to a novel spin manipulation protocol that allows us to detect the statistical imbalance in small spin ensembles.

In addition to the detection of single electron spin, we have used this technique to follow the statistical fluctuations in a small ensemble of spins and apply real-time feedback to control the time evolution of the spin orientation. Through the use of feedback, we have demonstrated that spins can be hyperpolarized or "cooled" in the rotating frame of the measurement, transferred and stored in the lab frame and later read out. With modest improvement to the current detection signal-to-noise ratio, MRFM could be used to initialize and readout the quantum state of a single electron spin in real time.

Feb. 28, 2006

“Near-field Optical Scanning Microscopy and Magneto-Optics of Photonic Nanostructures,” Alexander Mintairov, University of Notre Dame, hosted by Gary Wiederrecht

Abstract: Experiments that use a near-field scanning optical microscope operating at temperatures 5-300 K and magnetic field strength 0-10 T to study semiconductor quantum dots and photonic crystal structures are presented. The set of experiments includes utilization of nanoindentation to tune the emission properties of a single quantum dot, studying the emission mechanism of blue-green InGaN quantum dot structures, and probing confined optical modes in photonic crystal nanocavities.

Feb. 20, 2006

“Nanostructures with Controlled Shapes, Properties and Applications,” Yugang Sun, University of Illinois at Urbana-Champaign, hosted by Derrick Mancini and Gary Wiederrecht

Abstract: This presentation summarizes a number of approaches for generating nanostructures with controlled shapes. “Bottom-up” approaches (e.g., polymer-mediated polyol process) provide route to the large-scale synthesis of silver nanostructures with various well-defined shapes. These silver nanostructures can serve as physical and/or chemical templates to generate core-shell (e.g., nanocables) and hollow structures (e.g., nanoboxes, nanocages, nanotubes, and nanorattles) through surface modifications and galvanic replacement reactions. On the other hand, semiconductor nanowires and ribbons have been fabricated from high-quality, single-crystal, bulk wafers through a “top-down” approach by combining photolithography and anisotropic chemical etching. These nanostructures have well-controlled shapes and exhibit unique properties compared to their bulk materials. In addition, preliminary results indicate they are promising candidates for applications in electronics, optoelectronics, clinical diagnosis, medical therapy, and energy storage/conversion.

Feb. 13, 2006

“Plasmons in Single Gold Nanorods: Ultrafast Nonlinearities and Optical Trapping,” Matthew Pelton, University of Chicago, hosted by Gary Wiederrecht

Abstract: The development of functional plasmonic devices will require the ability to construct precisely arranged metallic nanostructures, as well as an understanding of the inherent linear and nonlinear optical properties of the individual elements in the structures. We have therefore measured for the first time nonlinear optical scattering from plasmons in single gold nanorods. Surprisingly, the measured ultrafast nonlinearity does not exhibit any coherent effect associated with plasmon oscillation, indicating a previously unobserved damping of strongly driven plasmons. As well, we have made progress towards constructing ordered arrays of gold nanorods, by optically trapping and orienting individual rods. The optical forces are enhanced by the nanoparticle plasmons, representing the first use of material resonances to trap particles in solution. This result also opens up the possibility of sensitive separation of metal nanoparticles according to their shape, and of three-dimensional plasmon-assisted microscopy in solution.

Feb. 13, 2006

"Directed Self-Assembly of Block Copolymer Blends into Nonregular Device-Orientated Structures," Mark P. Stoykovich, University of Wisconsin-Madison, hosted by Leonidas Ocola

Abstract: The future of many applications at the nanoscale rests upon the ability to produce well-defined patterns with nanometer precision. An emerging approach to nanofabrication is the integration of self-assembling materials into existing manufacturing strategies so as to simultaneously achieve molecular-level process control and the ability to produce useful architectures. Diblock copolymers are promising self-assembling materials that form ordered nanostructures, including spheres, cylinders, and lamellae, whose shape and dimensions depend on the molecular weight and composition of the polymer. Block copolymer lithography refers to the use of these ordered structures in thin films as templates for patterning through selective etching or deposition. Prior applications of block copolymer lithography have been limited to the fabrication of devices that do not require perfect structure ordering and that are formed of periodic arrays of structures, such as flash memory devices, magnetic storage media, silicon capacitors, and quantum dots. Our approach, in comparison, utilizes block copolymer lithography to achieve pattern perfection over macroscopic areas, dimensional control of features within exacting tolerances and margins, and registration and overlay with tailored interfacial interactions. In addition, we have demonstrated that by directing the assembly of blends of block copolymers and homopolymers on chemically nanopatterned substrates, it is possible to pattern nonregular device-oriented structures such as sharp bends. Mean field simulations indicate that the local redistribution of homopolymer within the blend domains greatly facilitates the formation of these nonregular geometries. In the short term, the technological implication of this hybrid top-down bottom-up technique is that the molecular control of structure dimensions afforded by self-assembling block copolymer materials may be harnessed for applications that require patterns significantly more complex than simple periodic arrays.

Feb. 6, 2006

“Ultrafast Meets Ultrasmall: Optically Driven Quantum Gates Based on Single Quantum Dots,” Xiaoqin (Elaine) Li, University of Colorado at Boulder, hosted by Gary Wiederrecht

Abstract: Laser pulses as short as 10 femtosecond (10-15 s) have become a routinely available tool in many laboratories. Such laser pulses have a wide range of applications in machining, optical metrology, and probing fast dynamics in chemical, biological, and physical systems. Following a brief introduction of ultrafast science and technology, I will discuss the concept of quantum dots and their general applications. The dynamics of electrons confined in individual quantum dots can be probed directly by using short laser pulses. In addition, I will explain how to manipulate these localized electrons optically to build universal quantum logic gates, the building blocks of quantum computers.

Jan. 31, 2006

 

“Assembling n- and p-type PbSe Quantum Dot Superlattice FETs,” Christopher B. Murray, Manager, Nanoscale Materials and Devices, IBM Watson Research Center, hosted by Xiao-Min Lin

 

Jan. 25, 2006

 

"Geometrically Confined Magnets," Kristen Buchanan, Materials Science Division, hosted by Stephen Streiffer

Abstract: Magnetic materials play an important role in a variety of modern devices, for example, computer hard drives, iPods, and electric motors. In general, the magnetic properties of ferromagnets can be understood in terms of competition among the magneto-crystalline, exchange, and magnetostatic energies due to long range dipole-dipole interactions. When the size of a magnet is reduced to the nanoscale, confinement alters the energetics and leads to new magnetic states, for example, vortices. Nanomagnets have great potential for enhancing existing technologies, such as magnetic storage media and magnetic sensors, and they may also find new applications in biomedicine and spintronics, an emerging field that exploits not only the charge of the electron but also its spin. Through advanced patterning and thin-film growth processes, model micromagnetic systems that demonstrate unique behavior in restricted geometries can be fabricated and investigated. My talk will discuss two related avenues of investigation: (1) static properties, in particular the magnetization reversal process in systems relevant to spintronic device design [e.g., layered F/N/F (giant magnetoresistive) and F/AF (exchange-biased) nanomagnets] and (2) spin dynamics, including our recent experimental detection of dynamic vortex interactions in patterned ferromagnetic ellipses. Understanding the static and the dynamic properties of nano-sized magnets is key for future device development.

Jan. 24, 2006

“Coaxing Nanoscale Material Systems to Build Themselves,” Seth Darling, Glenn T. Seaborg Distinguished Postdoctoral Fellow, Materials Science Division, hosted by Stephen Streiffer

Abstract: Both top-down and bottom-up approaches to creating nanostructured materials suffer from inherent limitations. Only by combining both methodologies in the form of directed self-assembly can one achieve the full potential of nanotechnology. Lithographic guidance of the orientation of block copolymer domains illustrates the promise of this technique. The value of phase segregated block copolymers to nanoscience derives from the expedient tunability of the size, shape, and periodicity of their self-assembled domains by means of manipulating molecular characteristics. Thin polymer films, by themselves, have limited device applications, but myriad functions can be addressed with hybrid hard/soft matter systems in which the organic layer is used as a scaffold for the nanoscale organization of inorganic materials. This hierarchical approach to create ordered nanostructures removes the linear correlation of size and patterning time associated with traditional lithographic techniques by self-assembling the entire surface in parallel. Applications to magnetic storage media will be discussed in addition to a spectrum of future directions.

Jan. 20, 2006

"Spin-Dependent Transport in Nanoscale Systems," Yi Ji, CNM Distinguished Postdoc, Materials Science Division, hosted by Stephen Streiffer

Abstract: Spintronics is an emerging area of science and technology, where electron spins are utilized to realize new effects and process information. Very rich spintronic phenomena can be generated in nanoscale metallic heterostructures involving ferromagnetic (FM) and nonmagnetic (NM) metals. In this talk, I will describe two examples: nonlocal lateral spin valve and spin-transfer torque effects. A lateral spin valve consists of a NM nanowire connected with two FM electrodes, one as the spin injector and the other as the spin detector. The electrical spin injection is carried out in such a way that the spin current and the charge current are partially separated. A pure spin current without charge flow can be obtained and utilized for new spintronic effects. Spin-transfer torque is the inverse effect of giant magnetoresistance. A spin-polarized current, flowing through a FM/NM/FM trilayer, can transfer spin angular momentum from conduction electrons to the magnetization of the FM layers. The transferred spin angular momentum acts as a torque, and is able to switch the magnetization. We also demonstrated that spin-transfer torque can be generated in a single FM layer, an effect unexpected by the original theoretical prediction.

Jan. 10, 2006

“Plasmonic Materials for Surface-Enhanced Spectroscopy," Xiaoyu Zhang, Northwestern University, hosted by Gary Wiederrecht

Abstract: An update on the fabrication of size-tunable silver nanoparticles using nanosphere lithography (NSL) will be provided. Three examples of new NSL-derived materials will be described: (1) the application of electrochemistry to “fine tune” the structure of silver nanotriangles and the wavelength of its localized surface plasmon resonance (LSPR), (2) the growth of ultrathin protective layers on silver nanoparticles using atomic layer deposition (ALD), and (3) the fabrication of ordered arrays of in-plane, triangular cross-section nanowells with the aid of reactive ion etching (RIE). Furthermore, the highly tunable LSPR of these nanostructures have been explored to establish the first set of optimization conditions for surface-enhanced Raman spectroscopy (SERS). Finally, these optimization conditions have been applied to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture.

 

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