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

Archive: Seminars 2009

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December 17, 2009

"Nanoplates by design and novel acoustic plasmons," Bogdan Diaconescu, University of New Hampshire, hosted by Jeffrey Guest

Abstract: Bottom-up synthesis methods open a path toward the growth of advanced and designable functional nanomaterials. I will show how rational self-assembly can be achieved on the basis of specific hierarchies of interactions between the molecular components. One compelling method for initiating the growth of nanostructured materials is to employ the natural tendency of layered thin films of dissimilar materials to form ordered arrays of misfit dislocation networks. On such systems, the self-assembly is driven by strain relaxation in the metal film. Another avenue is to use the intermolecular interactions to form ordered molecular arrays, where designed molecules yield predictable structures. This talk will focus on a few test systems highlighting such self-assembly processes and unraveling the underlying driving interactions. I will compare the different self-assembly mechanisms of molecules on strained metallic films of Ag on Ru(0001) and Au(111). Both growth processes are generally applicable to many functionalized C60 molecules, thus opening avenues towards functional and designable self-assembled structures based on a lock-and-key type approach.

The recent discovery of a fundamentally new sound-like plasmon on a bare metal surface of beryllium may introduce a new research direction in the area of plasmonics. While conventional surface plasmons are optical modes and have finite excitation energy of a few electron-volts, the novel acoustic surface plasmon (ASP) mode can be excited with very low energies of a few milli-elelctron-volts. This allows, in principle, for coupling with infrared and visible light for optical signal processing and advanced microscopies as well as low-energy chemistry on metallic surfaces. I will present results showing the acoustic character of the new plasmon as measured on the compact surfaces of beryllium, copper, and gold. Furthermore, I will show that the novel ASP is a general phenomenon on metal surfaces that support a partially occupied surface state within a wide bulk energy gap. The ASP is caused by the nonlocal screening of the surface electrons due to bulk electrons.

December 15, 2009

"Exploring Photomechanical Molecular Switching at Surfaces," Jongweon Cho, University of California - Berkeley, hosted by Nathan Guisinger

Abstract: The possible reduction of mechanical devices to molecular length scales provides many exciting possibilities for enhanced speed, device density, and new functionality. Optical actuation of nanomechanical systems through the conversion of light to mechanical motion is particularly desirable because it promises reversible, ultrafast remote operation. Past studies in this area have mainly focused on solution-based molecular machine ensembles, but surface-bound photomechanical molecules are expected to be important for future applications in this area. We have used cryogenic ultrahigh-vacuum scanning tunneling microscopy to study the surface-based photomechanical switching properties of a photomechanical molecular candidate called azobenzene. I will discuss our observations of the switching properties of individual azobenzene derivatives on gold, including wavelength-dependent photoswitching cross sections, new surface-based photoswitching dynamical pathways, and the effects of molecular environment on molecular photoswitching behavior.

December 10, 2009

"Molecular Technologies for Sustainable Energy, Nanoelectronics and Gene Delivery Applications: Contributions from Modeling Towards Rational Design,"Sean C. Smith, University of Queensland

Abstract: We summarize several recent modeling studies within the Centre for Computational Molecular Science at The University of Queensland, which shed light "from the bottom up" on key structural, dynamical, and mechanistic questions that are central to attempts at rational design strategies in the application areas of the title. Specifically, the following topics are considered: (i) control of TiO2 nanoparticle morphology and visible light response for enhanced photocatalytic properties, (ii) exploration of electronic properties of novel nanotube and nanoribbon systems for nanoelectronic and spintronic devices and (iii) modeling of gene-nanoparticle complexation to facilitate a rational design approach to optimizing gene delivery efficiencies in mammalian cells.

December 3, 2009

"Radiative Coupling and Decay Properties of Quantum Confined Semiconductors,"Julian Sweet, University of Arizona, hosted by Matthew Pelton

Abstract: The first portion of my talk will explore excitonic polaritons in quasi-crystals. In contrast to traditional periodically spaced multiple quantum wells. Fibonacci-spaced multiple quantum wells represent an exciting example of a quasi-crystal; a structure that while lacking complete periodicity, still exhibits self-similarity and long range order. These active one-dimensional quasi-crystals can be grown by using a quantum well stack where the spacing between each quantum well is defined by the Fibonacci recursion relation.

As with its traditional periodic counterpart, a high reflectivity stop band arises when the Bragg condition is fulfilled. However, unique to the Fibonacci structure are both broad and fine structure dips within its stopband. The spectrally broad heavy-hole susceptibility curve and its proximity to the light hole make the nonlinear properties of this active Fibonacci quasi-crystal an excellent candidate for optical switching and slow light applications.

In the second part of my talk, I will discuss the radiative decay properties of self-assembled indium arsenide (InAs) quantum dots grown by molecular beam epitaxy. The measurement of radiative lifetime is used to determine dipole moment. In addition, evidence is presented of radiative lifetime reduction for quasi-resonant and strictly resonant time-resolved measurements. This lessening is attributed to carrier correlations that exist during resonant excitation but are not present during above-band pumping. Time-resolved PL spectra will be presented with respect to excitation power, energy,and polarization as well as sample temperature in order to determine dephasing times.

The final aspect will cover recent progress in the fabrication of GaAs photonic crystal slab nanocavities for use in cavity QED experiments. Factors such as cavity axis orientation and employing a potassium hydroxide etch to remove debris resulted in a substantial improvement in cavity quality factor.

November 20, 2009

"A Salt and Batteries: Applications of Nonresonant Inelastic X-Ray Scattering to Model and Applied Systems," Ken Nagle, University of Washington, hosted by Jorg Maser

Abstract: The rational design of improved electrodes for lithium ion batteries faces many barriers, not the least of which is a correct, fundamental understanding of the changes in electronic structure that accompany insertion and removal of lithium. For this reason, the DOE report "Basic Research Needs for Electrical Energy Storage" singled out nonresonant inelastic X-ray scattering (NIXS) as a promising technique for in situ studies of these basic electrochemical processes. NIXS at ~1-eV energy resolution provides a bulk-sensitive alternative to X-ray absorption spectroscopy for studies of low-energy (<1.5-keV) electronic transitions. Furthermore, at sufficiently high momentum transfer, NIXS is sensitive to dipole-forbidden transitions, providing additional information about electronic structure. After illustrating these issues with a study of Na 1s core excitons in NaCl and NaF, I will discuss the application of NIXS to ex situ and in situ studies of lithiation of transition met!

November 19, 2009

"Study of Novel Materials for Nanoelectronics: A Scanning Probe Microscope Study of Graphene and Graphite Oxide," Deepak K. Pandey, Purdue University, hosted by Nathan Guisinger

Abstract: Approaching the miniaturization limit of silicon based microelectronics has presented ample research and development opportunities to grow and characterize materials for next-generation electronic devices. Scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and atomic force microscopy (AFM) offer unique capabilities for investigating the structural and electronic properties of these materials. Novel materials such as hybrid organomolecular silicon, graphene, and graphite oxide were examined during this study.

STM and STS studies were performed on two organic molecules, 4-trifuoromethylbenzenediazonium tetrafluoroborate and 4-methylbenzenediazonium tetrafluoroborate, covalently bonded to hydrogen passivated Si(111) substrate. It was established that STS can provide reproducible current-voltage response, I(V), on organic films of these molecules covalently bonded to Si(111) substrate. With the help of STS we were able to demonstrate that conductance is strongly dependent on the terminal molecular end-group of the molecule attached to the substrate.

STM studies were performed on epitaxial graphene films grown on the carbon face of 4H-SiC (0001) substrate by thermal annealing. The hexagonal arrangement of carbon atoms on few-layer graphene (FLG) were identified, conforming the good quality of graphene prepared.

STM and AFM studies were also performed on graphene films grown by chemical vapor deposition (CVD) on a thin metal film of nickel/copper and transferred on to silicon dioxide (SiO2) substrate. Large area STM/AFM scans (5 × 5 μm) demonstrated the presence of ridges and wrinkles arising from thermal mismatch of the carbon and the metal underneath. High-resolution STM images demonstrated the hexagonal lattice of carbon atoms, confirming the growth of FLG.

STM/STS and AFM studies were performed on atomically thin graphite oxide flakes deposited on highly oriented pyrolytic graphite (HOPG) substrate. AFM topography and phase images indicated the presence of graphite oxide flakes of mean area 5 μm 2 on HOPG. AFM images also showed varied topography including wrinkles, folds, and cracks in graphite oxide flakes, possibly arising during deposition process. Low-resolution STM images supported the topography obtained by the AFM study. High-resolution STM images revealed a surface decorated with a rectangular lattice of oxygen atoms with lattice constants 0.273±0.008 nm and 0.406±0.013 nm. STS measurement indicated the presence of a finite band gap of 0.25 eV when graphite oxide is deposited on HOPG.

November 5, 2009

"Understanding Porphyrin Supermolecules for Energy Conversion In Dye-sensitized Solar Cells," Chunxing She, Northwestern University, hosted by Matthew Pelton

Abstract: The Ru-dye based champion dye-sensitized solar cell (~11% efficiency) faces the challenge of gaining more photovoltage without enhancing recombination and sacrificing photocurrent. One strategy to this challenge is using supramolecular chemistry — dyes with high extinction coefficient to shorten transport distance and thus reduce recombination, and replacing redox shuttle. We are developing porphyrin supermolecules and understanding charge separation and energy transfer in those supermolecules for eventually replacing conventional Ru-based dyes. I will show what we have learned about photophysical and photochemical properties of such supramolecular systems. Relevance of those understanding to applications in DSSCs will be discussed. Examples of applications will also be given.

November 5, 2009

"Plasmonic Nanostructures for Unifying Surface Enhanced Raman Scattering and Infrared Absorption Spectroscopy," Janardan Kundu, Rice University, hosted by Elena Shevchenko

Abstract: Plasmon resonances control the electromagnetic near-field and far-field properties of various metallic nanostructures (e.g., nanoparticles, nanoshells, metallic thin films). The enhanced electromagnetic near-field, strongly localized on the metal surface, has been successfully exploited for a variety of surface enhanced spectroscopies. Visible and near-infrared surface enhanced Raman spectroscopy (SERS) is an example of such a technique that has attracted substantial attention due to its huge enhancement factors (~108-109) and wide range of applications. However, surface-enhanced infrared absorption (SEIRA) spectroscopy, complementary to SERS, has not received nearly the same attention because engineering the necessary strong near-fields in the mid-IR is challenging.

This talk outlines the successful efforts for developing rationally designed gold nanoshell-based substrates for SEIRA and for combining SERS and SEIRA to unify the field of surface enhanced vibrational spectroscopy for comprehensive biochemical sensing applications. Specifically, I will talk about the utilization of interparticle junction hot spots for SEIRA. Applications of SEIRA in conjunction with SERS are demonstrated for a variety of biologically relevant processes such as drug intercalation in lipid membranes, lipid transfer/exchange, and adsorption of nucleic acid bases. Finally, the random aggregate geometry for SEIRA is elegantly extended into two-dimensional periodic array of nanoshells that truly unifies SERS and SEIRA on a common single substrate by simultaneously enhancing both Raman and infrared signals in two diverse frequency regimes with high spectral sensitivity. I will conclude the talk with a brief mention of e-beam lithography-fabricated nanostructure assembly for LSP R sensing application.

November 3, 2009

Recent Advances in Electron-Beam Patterning with and without Resists,” J. Todd Hastings, University of Kentucky, hosted by Alexandra Imre

Abstract: Focused electron-beam induced deposition (EBID) and etching (EBIE) allow the direct (resistless) deposition or removal of materials at the nanoscale. These techniques are important for nanoscale rapid prototyping and mask/template repair. Traditionally, EBID and EBIE have been implemented by using gaseous reactants; for example, metalorganic precursors are often used for deposition processes. Such gaseous precursors introduce high impurity levels (up to 80%), limit materials that can be processed, are expensive and/or toxic, and yield low processing rates and efficiency.

Recently, the Hastings group has developed a new approach to EBID and EBIE that relies on bulk liquid reactants. Dr. Hastings will present results showing that deposition from true liquids can dramatically improve material purity (>85at.% Pt using chloroplatinic acid solutions) and deposition rate, while retaining high resolution (sub-30-nm features on a 60-nm pitch).

Electron-beam lithography (EBL) using resists remains the primary process for direct-write nanofabrication and mask/template patterning. EBL can attain sub-10-nm resolution; however, the nanometer-level pattern placement accuracy and critical dimension control required for next-generation electronic and photon devices remain elusive. In addition, the high cost and inadequate throughput of EBL limits its application in many other areas of interest.

Dr. Hastings will discuss the recent efforts of his group and its collaborators to improve accuracy in EBL through feedback control for electron beam position, beam shape, and pattern dose. In addition, he will present the first steps toward integration of these techniques with a highly parallelizable electron-beam micro-column developed by Novelx Inc. This combination holds the potential to reduce cost and increase throughput in order to greatly expand the range of EBL applications.

October 29, 2009

"Inventions and Patents at Argonne – Who, What, How and Why?," Mark D. Hillard, Chief Patent Counsel, Argonne National Laboratory, hosted by Derrick Mancini

Abstract: An invention is a novel and nonobvious idea or discovery that can only be protected by the timely filing of a patent application. Argonne's inventions are a valuable asset that are essential to the Laboratory's technology transfer mission and, if patentable, can return significant research funds to the Laboratory. To protect the Laboratory's intellectual property, DOE requires the Laboratory to report Argonne's inventions in a timely manner. The presentation will review the Laboratory's process for reporting and patenting Argonne's inventions and the benefits to inventors, the Laboratory and DOE of the patenting process.

October 28, 2009

"Synthesis and Characterization of Colloidal Semiconductor Nanocrystals: CuInSe2, CuInS2, and CdTe/CdSe/CdTe," Bonil Koo, University of Texas at Austin, hosted by Elena Shevchenko

Abstract: Colloidal semiconductor nanocrystals are interesting candidates as new light-absorbing materials since they can be synthesized in large quantities and easily dispersed in common organic solvents, two key characteristics that facilitate the production of nanocrystal inks. This presentation will focus on the synthesis and characterization of I-III-VI2 semiconductor nanocrystals (e.g., CuInSe2 and CuInS2) and also CdTe/CdSe/CdTe heterojunction nanorods. I will also expand on experimental subtleties that I have found to affect nanocrystal morphology, monodispersity, and crystalline phase.

October 23, 2009

"Excited State Distortions Caused by Photo-Induced Electron Transfer," Rachel Stephenson, University of California-Los Angeles, hosted by Matt Pelton

Abstract: Charge-transfer compounds exhibit a change in normal coordinates (bond lengths and angles) due to electron rearrangement after absorption of a photon. The magnitude of these excited-state distortions are obtained from electronic and resonance Raman spectra modeled within the time-dependent theory of spectroscopy. These methods are applied to two distinct types of systems.

  1. The first system is a supramolecular [2]rotaxane that displays an intermolecular charge transfer from the thread component to the ring component. The active modes are identified and the absolute change in the normal coordinates in Ångstrom units are calculated.
  2. In the second system, diammino(o-benzoquinonediimine)dichlororuthenium(II), a metal- to-diimine intramolecular charge transfer causes a change in the Ru-N bond distance. Detailed information about the wavepacket dynamics can be obtained from the presence of overtone bands of the Ru-N stretching fundamental observed in the resonance Raman spectrum. These overtones provide an internal clock that will be used to determine the absolute change in normal coordinates.
October 22, 2009

"Soft Lithography: Materials and Applications to Surface Plasmonic Resonance Sensing and Surface-Enhanced Raman Scattering," Tu Truong, University of Illinois at Urbana-Champaign, hosted by Yugang SUn

Interest in unconventional techniques for nanofabrication has grown exponentially in recent years because of demanding requirements in mico/nanoscale structures for photonics, microfluidics, biotechnology, and flexible electronics. Soft lithographic methods use elastomeric stamps, molds, and conformable photomasks as patterning elements to provide capabilities that are unavailable with conventional techniques: patterning at molecular-scale resolution (~1 nm); ability to form three-dimensional structures directly, in a single step; experimental simplicity and applicability to large areas. In this presentation, we explore the use of a commercially available perfluoropolyethylene (a-PFPE) in a variety of soft lithographic techniques for high-fidelity, high-resolution patterning. As an application example, we describe classes of quasi-three-dimensional plasmonic crystals for biosensing and well as surface-enhanced Raman scattering, with connection to theoretical results obtained in collaboration with S. Gray and others at Argonne.

October 21, 2009

"Diamond-based Nanomaterial Platforms for High Efficiency Cancer Treatment," Dean Ho, Northwestern University, hosted by Anirudha V. Sumant

Abstract: Nanodiamond surface properties mediate clinically relevant improvements to drug delivery that can be realized through enhanced cancer treatment efficiency. Additional characteristics that enable their application as versatile drug delivery vehicles include their functionalization with a broad array of therapeutics that includes small molecules, proteins, antibodies, and RNA/DNA for applications in cancer treatment, cardiovascular medicine, wound healing, and beyond. In addition, nanodiamonds possess uniform dimensions (~4nm in diameter per particle) and material stability that are coupled with observed biocompatibility in vitro and in vivo. Furthermore, nanodiamonds can be batch-purified and functionalized for scalable and high-yield processing. Among other functional groups, nanodiamonds also possess an abundance of surface-bound carboxyl groups, which are conducive towards facile, application-dependent molecular linking/conjugation onto the diamond surface. Furthermore, nanodiamonds can be functionalized with additional chemical species to enable direct drug conjugation. Our previous studies have confirmed robust drug binding to nanodiamonds through transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) coupled with in vitro tracking of cellular internalization and quantitative demonstration of bio-amenable cell response through quantitative real time polymerase chain reaction (RT-PCR) assays of inflammatory and apoptosis-regulating gene expression programs. Furthermore nanodiamond-mediated drug release against HT-29 and Raw 264.7 cell lines has also been observed. Toward the broadening of nanodiamonds applicability in clinically significant treatment scenarios, recent work pertaining to simultaneous high-efficacy/high-biocompatibility gene delivery, nanodiamond-based microfilm device formation for localized chemotherapy, pH-dependent therapeutic protein release, and preclinical trials will be discussed.

October 20, 2009

"Atomistic Simulations for Understanding the Effect of the Local Environment on the Properties at the Nanoscale," Handan Yildirim, University of Central Florida, hosted by Jeffrey Greeley

Abstract: In the first part of the talk, using the examples of homo- and hetero-epitaxial systems, I will show how an understanding of the microscopic processes that control the diffusion of metal adatoms and then clusters on metal surface can lead to prediction of growth modes and morphological evolution of surfaces, interfaces, and thin films. For example, the excess energy for a single atom to overcome a step (Ehrlich-Schowebel barrier) presents significant differences from one system to another, which may be related to the observed dissimilarities in growth modes. Single-atom diffusion barriers, both on strained terraces and near (strained) step edges, show that their strain dependence is universal and may be used to manipulate growth modes. In addition, I will talk about the pre-exponential factors for single-atom and cluster diffusion for both homo and hetero systems and discuss the origin of the quasi-constant prefactors. The contribution of the substrate dynamics to the calculatio n of the prefactors will also be discussed.

In the second part of the talk, I will use the example of a set of 34-atom bimetallic nanoparticles AgnCu34-n to show how the degree of alloying affects the vibrational dynamics, the thermodynamic,s and the electronic structure of each nanoparticle in this family.

September 30, 2009


"An ab initio Perspective of the Nickel Catalyzed Hydrocarbon Dissociation," Bin Liu, Colorado School of Mines, hosted by Jeffrey Greeley

Abstract: Theoretical methods represented by density functional theory (DFT) among others have made a tremendous leap in dealing with clusters, oxides, surfaces defects, and interfaces that are involved in heterogeneous catalysis. Thanks to the advancement of computation power, the modeling can be performed in a practical manner such that knowledge obtained this way can be used directly to explain experimental observations. Nickel has been a very important catalyst for reactions such as steam reforming and Fischer-Tropsch. This talk will present DFT calculations performed on various forms of nickel to study their catalytic properties, using the dissociation reactions of hydrogen and methane as examples. The goal is to understand how the reactivity of nickel clusters and nickel single-crystal surfaces can be related to respective sizes and geometries. For example, the icosahedral Ni13 clusters are found to show higher reactivity for methane dissociation by lowering the C-H bond breaking energy barrier compared to the Ni(111) surface. DFT calculations were also used to obtain thermochemical properties, and kinetic parameters of surface reactions. The knowledge gained from DFT calculations will not only help us explain the experimental phenomena, but also guide us design more effective catalyst surfaces to meet specific requirements in industrial applications.

September 24, 2009

"Metallic film growth on quasi-crystals," Joseph A. Smerdon, University of Liverpool, hosted by Matthias Bode

Abstract: Quasi-crystals, alloys of two or more metals, exhibit structures that, before their discovery, were considered impossible in condensed matter, relying as they do on a kind of order not based on periodicity. They also exhibit some unusual physical and electronic properties, such as high hardness, low frictional coefficients (comparable to Teflon), and a negative thermal coefficient of resistance. They are also bulk-terminated, meaning that their surfaces do not reconstruct and as such are as well-ordered and aperiodic as the bulk of the material. This opens up the study of quasi-crystals to standard surface microscopy, diffraction, and photoemission techniques. Also, it allows for the growth of epitaxial films that adopt the ordering of the quasi-crystal substrate, as the study and elucidation of structural, physical, and electronic properties should be easier for an elemental film as opposed to the chemically complex quasi-crystalline substrate.

This talk will explore some of the recent work done in the Surface Science Research Centre in the University of Liverpool. Many systems in which an elemental overlayer will adopt the structure of the underlying quasi-crystals have been identified, and I will explore two particular systems in depth: Cu/AlPdMn and Bi/AlPdMn. Copper deposited on the fivefold surface of icosahedral Al-Pd-Mn forms a multilayered film, of which the structure is an intriguing mix of aspects of crystalline copper and the AlPdMn substrate. The film has been extensively studied with STM, LEED, and MEIS in Liverpool and through a collaboration between Liverpool, PSU, and Lappeenranta University, Finland, also with LEED-IV. These studies have demonstrated the possibility of applying Monte Carlo techniques to the study of aperiodic systems.

Bismuth deposited on the fivefold surface of icosahedral Al-Pd-Mn forms an initial quasi-crystalline wetting layer followed by islands of various types. Unprecedented STM resolution of bismuth nanoclusters and comparison with DFT results has allowed the unambiguous determination of the nucleation network for this film and has followed the nucleation and growth of the film to the monolayer. Similarly well-resolved data of the surfaces of bismuth islands atop the wetting layer shows evidence of a phase change of the crystalline islands that can be controlled by manipulating the growth rate of the film.

The benefit of this work for the quasi-crystal community has been in the initial observation that it is surprisingly common for elemental overlayers to adopt the quasi-crystalline symmetry, the identification of the nucleation process for quasi-crystalline monolayers, and the demonstration that conventional computational techniques can contribute to the elucidation of aperiodic structures.

September 18, 2009

"MEMS Thrusters and Inertial Sensors for Space Applications," Herbert R. Shea, Ecole Polytechnique Federale de Lausanne, hosted by Daniel Lopez

Abstract: Microelectromechanical systems (MEMS) offer great promise for increasing the functionality of spacecrafts while decreasing their mass, thus enabling new satellite architectures and allowing nanosatellites to match the performance of conventional spacecraft. Our lab at the EPFL in Switzerland develops micromachined thrusters and inertial sensors for spacecraft propulsion and navigation, as well as polymer-based microactuators and components for chip-scale atomic clocks for use on Earth and in space.

An overview of our lab's activities will be given, with an emphasis on three topics: 1) arrays of microfabricated colloid thrusters emitting ions at 35 km/s; 2). MEMS inertial sensor directly measuring the gravity gradient in orbit, used as an Earth sensor requiring no optical access; 3) micro-actuators based on silicone membranes with compliant electrodes that generate vertical displacements greater than 50% of the device radius, with applications in tunable optics and cell manipulation.

September 11, 2009

"Synthesis, characterization and functionalization of advanced hybrid carbon nanomaterials," G.R. S. Iyer, Nanotechnology and Integrated Bio-Engineering Research Center (UK), hosted by Anirudha Sumant

Abstract:  Over the last two decades, nanocarbon materials have attracted great interest due to their ability to bond in different configurations (sp3, sp2), leading to various new carbon nanostructures (CNSs) with unique properties. Material preparation, characterization, and device fabrication are intertwined in the development of nanoscience and nanotechnology. The development of new CNSs is the trend in miniaturization of devices for various path-breaking applications such as sensing, energy storage, and permeable membranes.

In the first instance, I’ll describe how diamond nanoflake/nanorod spherules (DNFSs), a novel hybrid carbon nanostructure, composed of nanoflakes or nanorods with a diamond core and graphitic envelope, was synthesized using the MPCVD system. The microstructure composition was investigated by HRTEM and the electronic structure by spatially resolved microscopic XPEEM coupled with NEXAFS. These nanorods/flakes are electron-emitting spherules, exhibiting a low-threshold, high-current-density (10 mA/cm2 at 2.9 V/m) field emission. Low-energy nitrogen ion bombardment was another exciting area of research to tailor the surface selectivity, and understand the surface chemistry of the carbon-host system to tune the materials for new applications.

 In another instance, I shall describe the use of novel, nontoxic single-step method by nitrogen-ECR plasma, an unconventional technique from the acclaimed chemical methods for the purification (i.e., the removal of metal catalyst) of nanotubes and how that can be used for the purification, functionalization and tip opening of the nanotubes. Further studies carried out on understanding the nitrogen bonding configuration with carbon nanotubes using NEXAFS techniques will also be discussed .

August 31, 2009

"Compositional tuning of ultra-thin oxides grown on metal and alloy substrates via externally applied electric fields: A molecular dynamics simulation study," Subramanian Sankaranarayanan, Harvard University, hosted by Stephen Gray

Abstract: Synthesis of ultrathin metal oxides with controlled functional properties is desirable for a plethora of technological applications but is elusive because of growth kinetics. These applications include but are not limited to tunneling barriers in electronic devices, templates for model catalysts, and passivation layers to protect against corrosion. Three important factors can affect the functional properties: oxide density, oxide stoichiometry, and oxide composition in case of alloys.

Using representative examples of aluminum, zirconium, and Ni-Al oxidation, we demonstrate the ability to modify the density, stoichiometry (metal/oxygen), and alloy composition of ultrathin oxides grown on metal surfaces at room temperature by using externally applied electric fields such as those typically generated in photon-assisted synthesis. Molecular dynamic simulations employing dynamic charge transfer between metal atoms are used to model the oxidation process in the presence of external electric fields. Precise understanding of the microscopic processes involved in electric-field-assisted oxidation of metal substrates is provided by atomistic models employing dynamic charge transfer between atoms. We show that electric-field-assisted synthesis can be used to overcome the activation energy barrier for ionic migration. leading to significantly enhanced oxidation kinetics, which enables us to control the oxide composition at atomic length scales.

Our simulations indicate that the rate of oxygen incorporation into the near-surface regions of the passive oxides can be dramatically enhanced with atomic oxygen and/or electric field compared wtih natural oxidation. Increasing the electric field (~ 107 V/cm) drives the surface chemisorbed oxygen to the vacancy sites in the oxide interior, leading to dramatic density and stoichiometry improvements in ultrathin oxide film grown on pure metals.

For Ni-Al alloy oxidation, our atomistic simulations suggest that photo  n-assisted synthesis overcomes the activation energy barrier for chemisorption through the creation of activated atomic oxygen and ionic migration due to an electric field produced across an oxide film, leading to significantly enhanced oxidation kinetics, which enables us to control the complex oxide composition at atomic length scales. Our simulations thus demonstrate a pathway to athermally controlled oxygen concentration in near-surface regions that is of great importance to contemporary problems in the use of ultrathin oxides, ranging from catalysis to energy technologies.

August 27, 2009

"Determining Interactions and Interfaces Between Self-Assembled Peptide  Amphiphile Nanofibers and Biological Molecules, " Chung-Yan Koh, Northwestern Univeirsity, hosted by Elena Rozhkova

Abstract:: Self-assembled peptide amphiphile (PA) nanofibers are versatile building blocks for the creation of biomimetic cell scaffolds and delivery systems. One obstacle with using this platform is accurately determining optimal interfacial interactions with biological molecules and also determining the interaction between the PA and biologically significant molecules. Using model systems with immobilized enzymes mimicking membrane-bound cellular receptors to probe the biological accessibility of these nanofibers, we found that the recognition and rate of degradation trends with the placement of the recognition site in the primary structure of the PA. Interestingly, incorporation of aromatic moieties decreased accessibility to undetectable levels, allowing for a wide range of tailored biological accessibility from a single molecular platform. In order to study the interface between PA nanofibers and biomacromolecules, I examined complexes formed from PA with protein and PA with double-stranded plasmid DNA. Through hydrogen-deuterium exchange analysis, I mapped the interaction surface between a PA nanofiber and a developmentally important protein, Activin A. We found that changes in the binding interface, even with equivalent binding strengths, significantly impacted in vitro cellular response. Through biophysical and biochemical assays, we found that PA-DNA complexes are significantly more efficient transfection agents for cellular aggregates compared to commercially available agents such as Lipofectamine.

August 10, 2009

"Steps on Vicinal Surfaces: Density-Functional Theory Calculations and Transcending Minimal Statistical-mechanical Models, " Rajesh Sathiyanarayanan, University of Maryland, hosted by Jeff Greeley

Abstract: Steps on vicinal surfaces can be used as templates for fabrication of metallic nanowires and for microstructure growth. They can also enhance the catalytic activity of a surface, especially when they have many kinks. This makes the modeling of stepped surfaces technologically important. Using a combination of density-functional theory calculations and Monte Carlo simulations, we have computed various parameters, such as stiffness, step formation energy, and step-step interaction strength, that are normally used to model morphological evolution on stepped surfaces. We show that in certain cases, a minimal model is not sufficient to get accurate results. This talk discusses such scenarios and ways to handle them.

August 3, 2009

"Atomistic Studies of Oxidation Catalysis and Surface  Poisoning on RuO2(110) Surface," Dr. Hangyao Wang, University of Notre Dame, hosted by Jeffrey Greeley

Abstract: Base-metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO and NO. As an example, ruthenium metal becomes active for catalytic oxidation only after partial surface oxidation. The (110) surface of RuO2 is a convenient model for the oxidized metal surface because it is active for CO oxidation and well characterized. In this study, we employ plane-wave, supercell DFT calculations to examine the mechanisms of oxygen activation, CO/NO oxidation as well as surface poisoning on RuO2(110) surface.

We first consider O2 adsorption and dissociation and show that the molecular O2 species observed in TPD experiments and identified as a precursor to O2 dissociation is in fact a spectator present only at high coverages of surface O. We then study the CO and NO oxidation mechanisms on the RuO2(110) surface and compare the fundamental differences that lead to complete different catalytic reactivity of this surface on CO and NO oxidations.

Practical applications of oxidation catalysts are limited by surface poisoning, so it is important to understand and ultimately to learn to bypass surface poisoning. We investigate catalytic CO oxidation and its competition with surface poisoning by employing first-principles thermodynamics as well as micro-kinetic modeling method.  We identify both carbonate and bicarbonate surface poisons and show that the coverage of the latter is highly sensitive to water concentration and likely accounts for the surface poisoning observed experimentally.

July 16, 2009

"Charge Transfer in DNA and Its Application for Mismatch Detection," Tetsuro Majima, Osaka University, hsoted by Tijana Rajh

Abstract:: Charge transfer (CT) in DNA offers a unique approach for detectng a single-base mismatch in a DNA molecule. While a single-base mismatch would significantly affect the CT in DNA, the kinetic basis for the drastic decrease in CT efficiency through DNA containing mismatches remains unclear. Recently, we determined the rate constants of CT through fully matched DNA, and we can now estimate the CT rate constant for a certain fully matched sequence. We assumed that further understanding of the kinetics in mismatched sequences can lead to detection of the DNA single-base mismatch based on kinetics. In this study, we investigated the detailed kinetics of CT through DNA containing mismatches and tried to detect a mismatch sequence based on the kinetics of the CT in DNA containing a mismatch.

July 7, 2009

Polymer-Assisted Deposition, ”Anthony K. Burrell, Los Alamos National Laboratory, hosted by Al Sattelberger

Abstract: Polymer-assisted deposition (PAD) is a chemical solution route to high-quality thin films of metal oxides, nitrides, and carbides. This technique employs metal ions coordinated to polymers as the film precursor. The use of polymer bound metals has several advantages. The polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal oxide, nitride, and carbide films. The nature of the metal oxide, nitride, and carbide deposition is dominated by bottom-up growth, leading to ready formation of crack-free epitaxial metal oxides, nitrides, and carbides and the ability to coat nanofeatured substrates in a conformal fashion. Incorporation of nanomaterials in the thin films yields composite materials with interesting properties.

June 22, 2009

"Materials and Processes Development for Advanced Micro/Nanotechnologies," Jyoti K. Malhotra, Brewer Science, Inc., hosted by Derrick C. Mancini

Abstract: The fabrication of surfaces and films with controlled features has been a very active area of research for Brewer Science. Brewer Science's R&D division has many years of experience in developing polymeric thin-film technologies and advanced materials and processes for micro- and nanofabrication.

The following technologies are an extension of Brewer Science's knowledge and expertise in polymeric coatings and will be highlighted in the presentation:

  • Smart surface imaging for nanodevices: Beyond its immediate applications to advanced lithography, SSI also holds promise as a means to selectively deposit nanomaterials into defined arrays for device and non-device fabrication purposes, including the creation of three-dimensional nanostructures.
  • Functionalizing carbon nanotubes for biosensing applications: Microelectronics-grade carbon nanotube (CNT) aqueous solution has been prepared by using Brewer Science's purification protocols. CNT and polymer composite materials are being developed by blending and dissolving polymers into CNT solutions. The proposed work can be used to bind biomolecules on the surfaces of CNTs. This process promises exciting applications, such as constructing intelligent drug vector systems, designing biosensors for the assay of biomolecules, and elucidating protein structures.
  • Alkaline and acid deep silicon wet etching for micro-electro-mechanical systems (MEMS) fabrication: Traditionally, silicon nitride and metal hardmasks have been used in the development of wet- and dry-etched silicon via formation. Brewer Science has developed new polymeric etch protective coatings that provide attractive alternatives for deep silicon wet etching in alkaline etchants. Development of coatings that protect from acidic etchants is under way. These advancements will enable low-cost through-silicon via etching and wafer protection during sensitive wafer handling steps. Applications can be found in the production of future devices, such as sophisticated pressure sensors in MEMS.

June 19, 2009

"Nano and biotechnologies for development of an array of electrochemical biosensors," Mihaela Ilie, Institute of Photonics and Nanotechnology, National Research Council, Rome, and University 'Politehnica' Bucharest, Romania , hosted by Ralu Divan

Abstract: Biosensors, as functional analogs of chemoreceptors, are based on the direct spatial coupling of immobilized biologically active compounds, acting as a chemical recognition system, with a signal transducer and an electronic amplifier. If the physicochemical changes caused by either the complex formation or the chemical conversion of the analyte (e.g., owing to enzymes) are of an electrical nature (charge or enzyme activity), they can be detected by means of potentiometric or amperometric electrodes. A continuous flow micro-cell array that works on this principle has been developed by the IFN/CNR-ENEA/Biosensing Lab team, with potential applications in environmental and clinical analysis.

The cell contains miniaturized electrochemical electrodes in a fluidic chamber and their connections to the control and processing unit. The sensitivity of the chrono-amperometric measurement performed with the cell is increased by (a) integrating the reference electrode on the same chip with the counter and working electrodes, (b) designing a specific pattern of gold electrodes, and (c) serially distributing them along the pipeline reservoir. Borosilicate glass is used as substrate for the electrodes, allowing, via its transparency, an accurate and easy pad-to-pad alignment of the up-side-down chip versus a PCB soldered on a standard DIL 40 socket. This alignment is necessary to accomplish the elastomer-based solderless electric contact between chip and PCB. The solderless contact significantly improves both reliability and signal processing accuracy. The reservoir and its cover are micromachined of silicone rubber or photosensitive glass to easily assemble the fluidic chamber without damage. Both the thickness and the elasticity of the photosensitive glass render the device less brittle. A plug-in-plug-flow device with improved characteristics has been obtained with a modular structure that allows further extension of the number of electrodes and array integration. Details of the fabrication, data acquisition, and functional testing are given. The results are compared with those obtained from a nanoelectrode assembled on screen-printed substrates.

June 15, 2009

"Efficient Prediction and Optimization of thermoelectric and Photovoltaic Properties," Maria Kai Yee Chan, Massachusetts Institute of Technology, hosted by Jeff Greeley

Abstract: The accurate prediction and optimization of physical properties in the vast spaces of nanoscale structures and chemical compounds is made increasingly possible through the use of atomistic and ab initio computation. In this talk I will describe two specific examples, the prediction and optimization of lattice thermal conductivity in SiGe nanostructures and the prediction of bulk semiconductor band gaps, which are of importance for thermoelectric and photovoltaic applications respectively. In the former, the use of classical molecular dynamics to predict lattice thermal conductivity in the Kubo-Green formalism allows for the selection of optimal nanostructures.

Additional optimization with respect to alloy configuration is carried out by cluster expansion. In the latter, I propose a method for efficient ab initio estimation of bulk semiconductor band gaps.

June 9, 2009

"Junctions and Interfaces in Bottom-Up Nanoscale Semiconductor Devices," Yu-Chih Tseng, University of California at Berkeley, hosted by Seth Darling

Interface and junction between materials critically determine the behavior of bulk semiconductor devices. Similar studies have not been carried out in a direct and systematic way for nanoscale devices based on bottom-up materials, such as carbon nanotubes and semiconductor nanowires, because of the smallness of the junctions in question. Capacitance-voltage measurement is commonly used to characterize bulk semiconductor devices and interfaces. An instrument capable of measuring capacitances as small as a few attofarads (10-18 F) at low temperatures was developed and used extensively in this work. This method is applied to characterize the metal-carbon nanotube Schottky contact, and various kinds of junctions in nanowires. This study should shed light on the electrical properties of nanoscale semiconductor interfaces, and be valuable in providing direct feedback to novel fabrication techniques.

June 3, 2009

"Spatial Light Modulators and Photonic Integrated Microsystems," Il Woong Jung, Stanford University, hosted by Daniel Lopez

Abstract: The ability of spatial light modulators (SLMs) to modulate the amplitude and/or phase of light make it a compelling technology for a variety of applications in displays, adaptive optics, and communications. An important functional advantage of MEMS implementation is that the small size and mass of the elements allow high switching speeds. This also leads to a compact design resulting in systems that are much more economical to fabricate with the millions of elements required of some applications. The size, complexity, and required precision of the devices introduced in this talk show the unique capability of MEMS technology but also its many technical challenges.

In this talk, I will first present my PhD dissertation research on the design and fabrication of SLMs for applications in adaptive optics and optical maskless lithography and more recent work with Agilent Labs on the development of tunable filters with vertical mirrors micro-assembled on movable MEMS platforms for applications in communications and spectroscopy.

It has been shown theoretically and experimentally that broadband mirrors with high reflectivity can be made from freestanding two-dimensional photonic crystal (PC) slabs and from PCs placed on a thin dielectric film on a silicon substrate. By controlling the structure and geometrical dimensions, PC slabs can support guided resonances that couple to external radiation in ways that profoundly change its optical properties. This can be utilized to design compact optical devices such as mirrors, filters, lasers, and sensors. The main advantage of 2-dimensional PC slabs is that they can be designed to achieve comparable performance of one-dimensional PCs, or Bragg-stacks, but in a more compact form.

As another part of this talk, I will present the many applications of two-dimensional PC slab integrated optical microsystems and applications such as my work on PC mirror MEMS scanners for high-power beam steering and PC fiber tip sensors for remote sensing in harsh environments.

May 28, 2009

"First-principles nanoelectronics: Oxide thin-film devices by design," Massimiliano Stengel, Ecole Polytechnique Federale de Lausanne, hosted by Stephen K. Gray

Abstract: With the continued demand for portability and speed in consumer electronics, there is an increasing motivation to consider alternative paradigms to conventional silicon-based semiconductor designs. Heterostructures based on ferroelectric and/or magnetic complex oxide thin films are a very promising route to the realization of ultracompact and ultrafast electronic devices, due to the high tunability and multiple functionality of these materials. Such properties, however, are often dramatically modified at the nanoscale, and the physics of this size reduction is often poorly understood. First-principles electronic structure methods are a very powerful tool in addressing these key questions with high predictive power. However, proper treatment of an applied external bias potential in density-functional theory, which is mandatory for the simulation of realistic devices, has been a very challenging task until very recently. In the first part of this talk, I will show how our recent methodological advances in finite-field techniques have overcome this obstacle, thus providing full control over the electrical boundary conditions in periodic insulators and capacitors. In the second part of this talk, I will present some recent applications of these methods to a number of important technological problems, including the dielectric "dead layer" in paraelectric and ferroelectric thin-film capacitors, carrier-mediated magnetoelectricity at the interface between an insulator and a ferromagnetic metal, and the nonlinear piezoelectric response of PbTiO3 in high electric fields.

May 14, 2009

"Epitaxial Growth of Oxides on Semiconductors using MBE," Venu Vaithyanathan, Seagate Technologies, hosted by Stephen K. Streiffer

Abstract: Integration of functional oxides on semiconductors (such as Si, GaN) in an epitaxial form is useful for a variety of device applications. Integrating epitaxial oxides on semiconductors is lot more challenging compared to homoepitaxial or heteroepitaxial growth of oxides on single crystal oxide substrates, even using MBE. An overview of the challenges involved and the processes developed using MBE (Penn State University) to overcome these issues will be presented with some examples.

April 23, 2009

"Fabrication and Experiments on Electron Fabry-Perot Interferometer," Fernando Camino, Center for Functional Nanoscale Materials, Brookhaven National Laboratory, hosted by Leonidas Ocola

Abstract: We report fabrication and experiments on GaAs/AlGaAs heterostructure-based quantum interferometers in the integer quantum Hall regime. These devices consist of a lithographically defined two-dimensional electron island connected to the bulk electron region via two wide constrictions. When tunneling between counterpropagating edge channels occurs at the constrictions, electrons perform closed orbits around the electron island, causing an interferometric Aharonov-Bohm signal in the conductance. We observe conductance oscillations on quantum Hall plateaus at fillings f =1, 2, and 4. For a given filling, we observe f oscillations per flux period h/e. However, for all fillings, we observe one oscillation per charge period of e, corresponding to the addition of one electron to the area of the interference path.

April 17, 2009

"Organic Semiconductor Based Resistive Switching Memory," Yue Shao, hosted by Derrick C. Mancini

Abstract: Organic memory devices are receiving considerable attention as possible alternatives for conventional semiconductor memories because of their simple device structures, ease of processing, low cost, and compatibility with flexible substrates. In this talk, organic semiconductor-based memory devices with a metal/insulator/metal sandwich structure are demonstrated. It was found that resistive switching in these organic memory devices occurred in localized areas of the device. To investigate the localized conductive pathways,a focused ion beam was used to prepare a cross section of the device. It was found that the distance between the two electrodes was not uniform in the device. The closest distance was about 5 nm, while the average distance in the uniform area was about 50 nm. Transmission electron microscope-energy dispersive X-ray analysis of the cross section of the device confirmed that metal ions were injected into the polymer film by a locally enhanced electric field near the irregularities of the electrodes.

April 14, 2009

"Extending Electron Beam Lithography: Variable Pressure, Soft Lithography, Direct Writing," Benjamin D. Myers, Northwestern University, hosted by Derrick C. Mancini

Abstract: The development of tools and processes for fabrication of nanometer-scale structures is critical for the implementation of practical nanoscale devices and the study of the unique phenomena at this length scale. Electron- beam lithography (eBL) using focused electron-beam irradiation of organic thin-film resists is among the most promising and widely applied techniques, owing largely to its capability for high-resolution patterning. We extend the use of this technique for nonstandard substrates and material systems and address some of the inherent limitations of conventional eBL.

Electron-beam exposure carried out under high-vacuum conditions for nonconductive substrates often leads to charging effects that can result in significant pattern distortion and displacement. We have developed a variable pressure eBL (VP-eBL) process that allows in situ charge dissipation for direct patterning on insulating substrates with no conductive coating or additional process steps. This is accomplished through the introduction of a low gas pressure (~1 Torr H2O, Ar, N2) to the chamber, which generates positive gas ions to balance the surface charge. In addition to the utility of this method for fabrication of structures on technologically significant substrates, such as GaN, Si3N4, glass and polymers, the VP-eBL method serves as a useful platform to study the scattering of the primary electron beam by the chamber gas. We have also developed a technique that utilizes eBL for soft lithographic patterning of a range of materials from functional ceramics (ferroelectric, ferromagnetic, optoelectronic) to conducting polymers. In this process, we create trenches in a PMMA resist layer, which are subsequently filled by spin coating liquid or sol-gel precursors and then lift-off processed in acetone to remove the PMMA and material outside the trenches. In addition to resist-based processes, we have used eBL for the direct modification of supraspherical nanoparticle films to form nanoporous metal structures with controlled size and shap. The dual-beam focused ion beam/scanning electron microscope offers unique capabilities for nanofabrication and materials characterization and recent work on this instrument will be presented.

April 3, 2009

"Design and Fabrication of Surface Plasmon Polariton Supporting Structures on Silver Thin Films," Alexandra Imre, Argonne National Laboratory, hosted by Derrick C. Mancini

Abstract: In this talk, a set of recent experiments on the launching, focusing, and propagation of surface plasmon polaritons (SPPs) on nanostructured silver surfaces will be introduced. The constructive interference of SPPs launched by slits through silver films allows us to focus the SPP near-field intensity into a spot of subwavelength size. We show that the high SPP intensity in the focal spot can be launched and propagated on silver strip guides with a 250 by 75 nm cross section, the SPP wavelength is 509 nm in the experiment. Furthermore, a plasmonic device that generates and steers tightly focused plasmon beams between neighboring subwavelength Ag strip waveguides is demonstrated. The local electromagnetic-field enhancement in the focal spot is studied experimentally by near-field scanning optical microscopy, and it is applied for surface enhanced Raman spectroscopy (SERS). By exploiting the polarization dependence of the focusing effect, a Raman signal enhancement of a factor of ~6 is observed from Rhodamine 6G molecules.

The basic properties of SPP-based planar devices, and further developments towards viable SERS sensors will be discussed.

March 30, 2009

"Assembly, Spectroscopy and Applications of Semiconductor Nanocrystals," Andrey L. Rogach, Ludwig-Maximilians-Universität München, hosted by Elena Shevchenko and Tijana Rajh

Abstract: High-quality semiconductor nanocrystals with controllable surface properties and strong, size-dependent emission can be synthesized nowadays by methods of colloidal chemistry. They are attractive objects for use as building blocks in different functional nanostructures, in particular in combination with polymers. Advanced optical spectroscopy provides important insights into fundamental photophysical properties of semiconductor nanostructures. Different application aspects of functional composites based on semiconductor nanocrystals ranging from energy and charge transfer structures to biological markers will be discussed.

March 27, 2009

"Polymer-Based Nanomedicine: Multivalent Targeting and Rolling-Based Cell Capturing," Seungpyo Hong, University of Illinois, Chicago, hosted by Derrick C. Mancini

Abstract: Cancer remains one of the world's most devastating diseases, with more than 10 million new cases every year. With the ongoing efforts in cancer research, mortality from cancer has decreased in the past two years owing to better understanding of tumor biology and improved diagnostic devices and treatments. This presentation will discuss the current technology to improve cancer treatment approaches. The enhancement could be achieved via targeted drug delivery and targeted capturing of specific cells.

For the development of nanocarriers for targeted drug delivery, we performed a fundamental study on the biological interactions of synthetic polymers, which revealed that polycationic polymers of linear and dendritic architecture induce membrane permeabilization (nanoscale hole formation) in living cells. Polyamidonamine dendrimers were further studied to be used as a targeted delivery vector. The targeted dendritic nanodevices provide the multivalent interaction with a receptor protein target as observed in unprecedented quantitative and systematic evidence. These data support the hypothesis that multivalency, rather than an enhanced rate of endocytosis, is the key factor resulting in the improved biological targeting by these drug delivery platforms, thus providing a design guide for future receptor targeting agents. A strategy to capture/separate specific target cells based on cell rolling will be also discussed, focusing on the development of controlled covalent immobilization methods of proteins and its translation into device technology. This approach is essential for mimicking relevant complexities of the in vivo rolling response and for future development of devices for isolating specific cell types such as circulating tumor cells with metastasis potential.

March 20, 2009

"Materials-by-Design: The Membrane Analysis and Simulation System (MASS) and Possible Application to Nanomaterials Design," Ron S. Faibish, Nuclear Engineering Division, Argonne National Laboratory, hosted by Derrick C. Mancini and Michael Sternberg

Abstract: A multidisciplinary team at Argonne is conducting advanced research in membrane science and applications for the advancement of energy-efficient separation processes and better materials design paths for new and improved membranes. The Membrane Analysis and Simulation System (MASS) would offer a revolutionary modeling tool to a priori determine the combination of materials that would yield a suitable membrane for any given separation applications (both for gas and liquid phase separations). The simulation and modeling tool employs advanced modeling tool, such as molecular dynamics, computational fluid dynamics, and Lattice Boltzmann methods. The multiscale, multi-physics tool will also introduce an economic module that would evaluate and optimize the economics of the large-scale engineering system as part of the overall membrane system design. It is envisioned that the tool could support the design of, among other membranes types, membranes for advanced high-temperature separations (e.g., for reducing greenhouse gas emissions), membranes to replace energy-intensive distillation processes, and high temperature membranes for desalination of seawater in energy-water cogeneration applications. The tool is expected to save millions of U.S. dollars in development costs of membrane systems and optimize the design process. Other uses of a modified version of the tool for general materials-by-design applications are also foreseen.

March 19, 2009

"Scattering of Surface Plasmon Polaritions by Metallic Nanostructures," Lina Cao, Columbia University, hosted by Stephen Gray and Norbert Scherer

Abstract: We present a comprehensive study of linear and nonlinear effects observed in the scattering process of surface plasmon polaritions (SPPs) from localized surface deformations at a metal/dielectric interface. The electromagnetic field at the fundamental frequency is first determined by solving the corresponding set of reduced Rayleigh equations. The complete solution of these equations then allows us to investigate both the complex structure of the scattered electromagnetic field as well as the subtle mechanisms by which incident SPPs are scattered into radiative modes (light) and outgoing SPP waves. Furthermore, the electromagnetic field at the fundamental frequency is used to determine the nonlinear surface polarization at the second harmonic and subsequently both the electromagnetic field distribution as well as the amount of light generated at the second harmonic. We will discuss our results, including the size dependence of the scattering into both surface and radiated waves for several defect shapes. Our talk will also discuss the computational issues and the physical phenomena of the scattering process. Finally, we will comment on potential applications for our findings in surface spectroscopy, surface chemistry, or new surface-defect imaging techniques.

March 9, 2009

Bioinspired Molecular Machines for Manipulation of Molecules," Kazushi Kinbara, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, hosted by Elena Rozhkova

Abstract: Molecular machinery is a hot issue in nanotechnology. We have been taking two approaches for construction of elaborate molecular machines: (1) a bottom-up approach based on synthetic organic chemistry and (2) a semi-biological approach based on chemical modification of biological molecular machines. The topics include light-driven molecular scissors that undergo scissoring motion upon irradiation of ultraviolet or visible light, supramolecular machines that can transfer motions through intermolecular interactions, molecular glues that can control protein assemblies, and nanocontainers consisting of biological molecular machines called chaperonin proteins, where catch and release of the guest molecules can be controlled by stimuli such as ATP and light.

March 9, 2009

"Multifunctional Self-Assembled Transition-Metal Oxide Nanotubes: A View from the Bottom," Lia Krusin-Elbaum, IBM T.J. Watson Research Center, hosted Stephen K. Streiffer and George Crabtree

Abstract: Self-organization offers to nanotechnology a powerful alternative to standard nanofabrication approaches. Using self-assembly we have synthesized nanotubes of transition-metal oxides, such as VOx or RuOx, using monoamines as structure-directing templates. In this talk I will focus on the mixed-valent oxides of vanadium that belong to the class of strongly correlated systems which can host unusual spin states and exhibit a wide variety of charge transport and optical behaviors. I will discuss the quantum spin-liquid formed in the `as-assembled' nanotubes with a spin-gap Ds ~ 665 K, that succumbs to ferromagnetism upon electron or hole doping, and how this magnetic particle-hole complementarity can arise from the low-dimensionality of the nanotube structure with crystal field splittings that enforce a Mott gap. Strong electron interactions in VOxl2 can lead to a 1st order metal-insulator transition with an abrupt change in conductivity that can be as much as 11 orders of magnitude; at this transition there is also a sharp change in optical transmission in the infrared spectrum. Thus, numerous applications such as electrical, optical, and spin ─ temperature- or voltage-controlled ─ switches can be envisioned.

March 4, 2009

Understanding Oligo (Ethylene Glycol) Monolayers," Julia Ruemmele, Boston University, hosted by Seth Darling

Abstract: A concern for the design of biosensors for protein interactions is fouling of, or nonspecific binding to, the sensor surface that corrupts the signal due the binding event of interest. Two-component mixed oligo(ethylene glycol) (OEG) self -ssembled monolayers (SAMs) have become a standard surface coating used to minimize fouling of gold sensor surfaces. The source of fouling resistance is still uncertain and it has been shown that the resistance integrity can be affected by the method of SAM fabrication. Toward understanding what gives rise to this behavior, the mole fraction, phase segregation, stability, and pKa of OEG SAMs were investigated under a variety of fabrication conditions and correlated with the fouling resistance of the SAMs with respect to standard proteins. The results imply that a difference in the structure of OEG molecules in the SAMs may regulate fouling resistance.

March 3, 2009

"CuAlNi Shape Memory Alloy and Some Thin Film Studies," Hanshen Zhang, University of California, Berkeley, hosted by Jorg Maser

Abstract: Mr. Hanshen Zhang is a final-year PhD candidate. His research mainly includes shape-memory alloy (SMA) and thin-film synthesis. Shape-memory alloy exhibits special atomic microstructures that can experience reversible phase transformations. Mr. Zhang’s work is focused on CuAlNi SMA, which despite its significant application potential, has been less investigated than other SMAs. He will show the complex mechanical behaviors of this material, which open the potential for in situ experimental studies, such as synchrotron and TEM. His discovery about the underlying complex phase transformation mechanisms and further hypothesis of SMA martensite variant formation show promising scientific endeavors. Mr. Zhang will also briefly talk about his experience with thin-film synthesis, such as filtered cathodic vacuum arc, radio-frequency sputtering, and ion-beam implantation. These topics will show his broad understanding of materials sciences and invite discussions of possible collaborative research.

March 2, 2009

"STM studies of high-temperature superconductors: clues to the pairing mechanism," Vidya Madhavan, Boston College, hosted by Matthias Bode

Abstract: The question of the pairing mechanism in the high-temperature cuprates is an important issue. Scanning tunneling spectroscopy (STS) is the one of the best techniques to obtain information on bosonic modes (phonons, spin excitations, etc.) that couple to electrons. We present STS data on the electron-doped superconductor Pr0.88LaCe0.12CuO4-δ (PLCCO). Below the superconducting transition temperature Tc in addition to the superconducting gap, STM spectra show features at approximately 3 and 10 meV (gap-referenced) that can be associated with bosonic modes. A comparison of these energy scales with neutron scattering data on the same material indicates that both features may be associated with spin resonance modes.

While prior STM data on hole-doped BSCCO revealed coupling to a phonon mode, our data is the first indication that spin excitations have a substantial effect on the electronic density of states. The implications of this will be discussed. We will also briefly discuss recent atomic resolution images and spectroscopy on the parent compound of a pnictide superconductor, SrFe2As2. We will compare our data with LEED on identical samples and discuss the implications.

February 18, 2009

"Tailoring the Glow of Nanostructured Metals: From Thermophotovoltaics to Thermal Beaming," David J. Norris, University of Minnesota, hosted by Gary Wiederrecht

Abstract: When materials are heated that are structured on an optical length scale, their thermal emission can be modified. This has been explored as a possible route to eliminate unwanted heat from thermal emission sources, such as the filament in a conventional light bulb. In addition, this effect may lead to efficient thermophotovoltaic devices, which convert heat (from the sun or another source) into electricity. Here, we will discuss two recent results on the thermal emission of periodically structured metals. First, we will examine tailoring the thermal emission spectrum. In particular, we will show that in thermophotovoltaic applications, properly designed molybdenum structures at 650°C should generate over ten times more electrical power than solid emit­ters while having an optical-to-electrical conversion efficiency above 32%. At such relatively low tempera­tures, these emitters have potential not only in solar energy but also in harnessing geothermal and industrial waste heat. Second, we will discuss tailoring the thermal emission direction. In particular, we examine simple metallic films with surfaces that are patterned with a series of circular concentric grooves (a bull's eye pattern). Due to thermal excitation of surface plasmons, a single beam of light can be emitted from these films in the normal direction that is amazingly narrow, both in terms of its spectrum and its angular divergence. Thus, metallic films can generate laser-like beams of light by a simple thermal process.

February 16, 2009

"Fabrication of Si Single-Electron Transistor with Oxide Tunnel Barriers for a High-Operating- Temperature Device," Vishwanath Joshi, University of Notre Dame, hosted by Derrick Mancini

February 12, 2009

"Synthesis, Characterization, and Applications of Novel Monodisperse Nanoparticles"
Sheng Peng, Brown University
hosted by Gary Wiederrecht and Yugang Sun

Abstract: Monodisperse nanoparticles in the size range below 20 nm are of intense current interest for a variety of applications, not only for the general miniaturization of devices, but also for their novel physical and chemical properties. Recent advances in organic-phase chemical synthesis have led to various monodisperse nanoparticles with controlled size, shape, composition, and crystallinity. In this talk, I will present my recent work on the development of monodisperse nanoparticles of magnetic iron, cobalt, FeCo, and SmCo5, as well as metallic gold and AuAg nanoparticles for various applications in high-density magnetic energy storage, catalysis, and biomedicine.

January 23, 2009

“Towards Non-Centrosymmetric Arrangement of an Electro-Optically Active De Novo Designed Protein”
H. Christopher Fry, University of Pennsylvania
hosted by Tijana Rajh

Abstract: The de novo design of helical bundles capable of binding natural heme complexes is well established. Extending this knowledge to include abiological metalloporphyrin-based chromophores will enhance the utility as well as test the reliability of computationally derived proteins. Success has been found in the design and characterization of a series of a-helical bundles that incorporate the synthetic metalloporphyrins, FeDPP and ZnDPP (DPP = diphenylporphyrin). The incorporation of an abiological, nonlinear optic chromophore ((porphinato)zinc-ethyne-(terpyridyl)ruthenium complex, RuPZn) into a computationally designed, asymmetric single chain helix bundle (SC_RPZ) exploits the natural helical chirality potentially enhancing and macroscopically organizing the complex of interest. Furthermore, generation of self-assembled monolayers on silicon surfaces present a significant advancement towards controlling the spatial orientation of the active chromophore necessary for devising a functional nonlinear optic material.

January 20, 2009

“Part 1: Bioengineering of Protein Nanotubes and Protein-Nanomaterial Composites"
Part 2: DNA Scaffolding Precision Assembly of Nano-Objects and DNA Devices”
Tilak Kumara Mudalig, Center for Functional Nanomaterials, Brookhaven National Laboratory
hosted by Tijana Rajh

Abstract Part 1: An E. coli flagellin protein, termed FliTrx, was investigated for use as a novel form of self-assembling protein nanotube. This protein was genetically engineered to surface display constrained peptide loops with a series of different thiol, cationic, anionic, and imidazole functional groups. Various metal ions were bound to peptide loops and reduced in a controlled manner to generate nanoparticle arrays and nanotubes. Quantum dots (CdTe, ZnS) of 3 ±0.3-nm diameters were bound to histidine peptide loops to generate ordered arrays of quantum dots on the flagella.The optical properties of these assembled quantum dots were studied. The flagella with cysteine loops aggregated through disulfide bond formation to form bundles that could be dissociated into single flagella nanotubes by a reducing agent such as TCEP. The nanotube bundles exhibited an interesting behavior in optical traps generated with 1064 nm laser light. They were repelled by the laser beam instead of being trapped, resulting in their escape. Significant results of these studies will be presented.

Abstract Part 2: We studied a system for analyzing the assembly pathway of DNA nanostructures, which enables the identification, explanation, and avoidance of obstacles to proper structure formation. Potential problems include strand end-pinning and misfolding caused by the structural bias of nominally flexible junctions. We have used this system to guide the construction of parallel motifs that had previously, for unknown reasons, resisted assembly. Further, I will discuss the use of DNA scaffolding for the precision assembly of nano-objcets via multiple anchors and the use of DNA-based mechanical devices to reconfigure nanoparticle assemblies.

January 16, 2009

Nanoparticle Functionalization and its Application for Cancer Imaging and Treatment,”
Yan Zhao, University of Chicago, Ben May Institute for Cancer Research
hosted by Tijana Rajh

Abstract:Surface chemistry and ligand structure are both important for successfully functionalizing nanoparticles. By using the ligand which comprised hydrophobic and hydrophilic part, we prepared highly stabilized gold nanorods, which are ready to conjugate with various organic and bioorganic molecules. One significant property of this ligand is that it made the nanoparticle hydrophilic and lipiphilic at the same time, and dissolve in water as well as in many organic solvent. Dithiocarbamate formation was applied as a simple method for conjugating amines onto metal surfaces, and form strongly adsorbed species which are stable under various types of environmental stress. This method should expand the range of synthetic or biomolecular structures for applications involving surface or nanoparticle functionalization.

As a promising alternative to current organic dyes, quantum dots (QDs) are widely studied as targeted imaging agent, while the desorption of conjugated ligands and nonspecific binding are frequently encountered issues which will lead to reduced contrast or unsuccessful labeling. In this work, estradiol (E2) ligand conjugated QDs were prepared and successfully applied to staining MCF-7 K1 cell with over expressed estrogen (ER) receptor by blocking nonspecific binding sites using E2 ligand-free QDs. By substituting E2 with fluorescein, we studied the numbers of conjugated ligand per QDs and free ligand in the QDs solution, both of which are important in controlling the staining intensity and best results were achieved by balancing the two factors.

January 15, 2009

"Surface Templates for Assembly of Polystyrene Nanoparticles and Oligonucleotides," Dorjderem Nyamjav, Loyola University, hosted by Tijana Rajh

Abstract Template-based approaches to fabricate surface structures have been investigated extensively in the last decade. Among them, scanning probe microscope (SPM)-based nanolithography offers an ability to generate templates with unprecedented precision in a preprogrammed manner. Novel approaches to pattern oligonucleotides and nanoparticles onto silicon substrates via SPM-based nanolithography and microcontact printing technique will be discussed. The patterned oligonucleotides maintained their biological activity. The strategy does not require premodified substrates and offers a cheap and robust way to immobilize oligonucleotides or nanoparticles on electronically important semiconductor surfaces. The method can be utilized in the construction of novel structures and biosensors.

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