CNST Nanotechnology Seminar Series

UNDERSTANDING NANOSTRUCTURE NUCLEATION, GROWTH AND GROWTH TERMINATION THROUGH REAL TIME TEM OBSERVATIONS

Eric A. Stach
Purdue Electron Microscopy Consortium

In order for nanostructure materials to find application in real technologies, we must have a thorough understanding of how to create reproducible materials. I will detail our work using environmental and ultra-high vacuum transmission electron microscopy methods to image nanostructure nucleation and growth as it happens, thereby allowing unique insights into both growth mechanisms and kinetics. In particular, I will describe in detail the kinetics of the vapor-liquid-solid growth of silicon nanowires, with a focus on the kinetics of both Au dissolution in the AuSi eutectic liquid, and on the nucleation of Si from this same liquid at higher saturations. Careful quantification of the images and correlation with a simple model of the process indicates that the nucleation process is highly repeatable down to very small scales (of order 10 nm), and that we can extract information regarding the critical supersaturations required for nucleation. I will also discuss our latest results concerning growth termination during the creation of carbon nanotube ‘carpets’, wherein we correlate the end of growth with an Ostwald ripening of the catalysts require to mediate the conversion of hydrocarbon source gases to carbon nanotubes. Throughout, I will try to demonstrate the power of the in-situ TEM technique to visualize how things happen during nanostructure creation.

STUDIES OF TOP-DOWN FABRICATED SILICON NANOWIRES: STRESS, MOBILITY, AND THEN SOME

Lidija Sekaric
IBM, T. J. Watson Research Center

Silicon nanowires are being investigated as a potential next generation CMOS device and as such they motivate studies of some of their basic properties which are largely unknown at the very small scale. Using top-down methods we fabricate and study silicon nanowire FETs with diameters in the range of 5-20nm. We investigate carrier mobility as a function of size scaling and we study the possible role that process-induced stress may have in modifying electrical properties of these nanowires. We employ silicon surface functionalizaton as a way of modifying the electrical properties of ultra-small nanowires a nd find them to be superb charge sensors for a variety of chemical species and useful for light sensing.

"POWERING" THE FUTURE WITH NANOTECHNOLOGY

Pradeep Haldar
University at Albany, SUNY

The field of alternative energy provides a platform for some of nanotechnology’s most exciting contributions. Silicon and thin film based Solar Cells already utilize nanoscale processes, materials and devices developed in semiconductor manufacturing. Moreover, discoveries in nanotechnology have led to what many consider the next generation of solar technology: ultra-thin amorphous silicon, organic and inorganic solar cells derived from nanocrystals. Nanotechnology applied to Fuel Cells enables more efficient and reduced use of precious metals along with improved membrane function and durability. Nanoengineered electrodes in the form of cathodes and anodes are currently being manufactured and incorporated in solid oxide and polymer electrode-based fuel cells that provide higher efficiency and performance. The Energy and Environmental Technology Applications Center (E2TAC) at the College of Nanoscale Science & Engineering (CNSE) works with companies in the rapidly emerging energy and environmental industries and is focused on commercialization of these technologies in partnership with industry.

THERMOMECHANICAL PROBES AT THE NANOMETER SCALE

William P. King
University of Illinois at Urbana-Champaign

This talk describes fundamentals and applications of nanometer-scale thermal probes. Atomic force microscope (AFM) cantilevers with integrated heaters can reach temperature above 1000 °C and can be heated as fast as 1 usec. The ultra small hot spot at a tip-substrate can be used for nanometer-scale manufacturing, metrology, and surface science measurements. In one application, the heated probe tip can be used like a miniature soldering iron. In another application, the cantilever heaters can also be used as sensors, where the heating can be used to modulate cantilever resonant frequency or to clean and refresh the cantilever surface. Nanometer-scale heated probes can be used to measure spatially resolved glass transition temperature, decomposition temperature, and mechanical properties in films as thin as 5 nm.

FERROMAGNETIC RESONANCE IMAGING WITH MAGNETIC RESONANCE FORCE MICROSCOPY

P. Chris Hammel
Ohio State University

Magnetic resonance force microscopy achieves very high resolution three-dimensional imaging capabilities of magnetic resonance imaging by taking advantage of very high sensitivity force detection. This enables non-contacting, microscopic studies and imaging of a broad range of materials. We have demonstrated scanned probe Ferromagnetic Resonance (FMR) imaging in ferromagnets where the the strong interactions between spins invalidates the assumptions underlying conventional magnetic resonance imaging. We present a new approach to localizing the resonant volume in an FMR measurement in ferromagnetic films. Our model accurately describes our FMR images and provides the basis for submicron scanned probe FMR imaging of films and buried ferromagnetic elements.

Ref: "Local Ferromagnetic Resonance Imaging with Magnetic Resonance Force Microscopy," Yu. Obukhov, D.V. Pelekhov, J. Kim, P. Banerjee, I. Martin, E. Nazaretski, R. Movshovich, S. An, T.J. Gramila, S. Batra, and P. C. Hammel, PRL 100, 197601 (2008).

GATED CARBON ELECTRONICS

Charles Marcus
Harvard University

We discuss techniques for making gated nanoelectronics based on carbon nanotubes and graphene, and some of the new physics and possible applications that is available in these systems. Here we will focus on few-electron quantum dots in nanotubes –ndash; possibly for application to quantum information –ndash; and p-n junctions in graphene.

THE BRIGHT FUTURE OF NANOPHOTONICS: RECENT ADVANCES AND CHALLENGES

Federico Capasso
Harvard University

Nanophotonics in which light is manipulated at subwavelength scales is emerging as one the most exciting and potentially useful areas of physical optics. I will highlight recent research in my group aimed at a new class of light-sources in which the near field and the far-field properties are fundamentally altered by means of plasmonic nanostructures and metamaterials monolithically integrated on the laser facets. As a platform to demonstrate these new beam shaping concepts, such as reduction of beam divergence, nanospot light concentration, super-focusing and polarization control, we have used mid-infrared and near-IR lasers but these techniques are broadly applicable to all solid-state lasers.
I will also discuss a novel technique called nanoskiving that combines photolithography, thin-film metal deposition, and thin-film sectioning, and demonstrate its capabilities in the realization of metallic nanowires with engineered plasmon resonances and frequency selective surfaces.

IMAGING ULTRAFAST DYNAMICS WITH ELECTRON MICROSCOPY: RECENT ADVANCES, CHALLENGES AND OPPORTUNITIES

Vladimir A. Lobastov
California Institute of Technology

Miniaturization of electronic devices with atomic-scale active components is a great technological undertaking and presents a major challenge in metrology. To understand the underlying physics and behavior at the molecular level, which by the very definition is not a static but essentially dynamic process, our group is developing an ultrafast electron microscope (UEM). This methodology combines extreme spatial and temporal resolutions, which allows for the simultaneous characterization of spatiotemporal properties at relevant scales. The versatility of the UEM technology and its applications in electronics, photonics and biotechnology will be illustrated with two distinct examples. The first is the "conventional" pump-probe imaging of ultrafast dynamics during a phase transition in vanadium dioxide, and the second is the direct visualization of a laser controlled reversible transformation in molecular crystals.

BIOMIMETIC NANOSCIENCE: CHALLENGES AND OPPORTUNITIES

Joanna Aizenberg
Harvard University

The adaptive pressures displayed across the flora and fauna result in a variety of sophisticated nanostructured materials that are perfected to perform multiple biological functions. Our understanding of the underlying principles of their formation provides ample opportunities in the synthesis of next generation, bio-inspired, nanostructured materials. To date, there has been demonstrable progress in materials fabrication harnessing the functional power of biological systems. There is, however, a number of challenges related to the characterization of both biological and synthetic bio-related structures. I will exemplify this point by describing new synthetic strategies and devices that have been inspired by the study of two organisms – echinoderms and sponges. The topics will include self-assembly, control of crystallization, adaptive optical structures, fiber-optics, biomechanics, hybrid materials and novel actuation systems.

UNDERSTANDING THE SURFACES OF QUASI-1D METAL OXIDES: FROM SPECTROMICROSCOPY OF SINGLE WIRES TO PROTOTYPE CHEMICAL SENSORS

Andrei Kolmakov
Physics Department, Southern Illinois University Carbondale

 
The growing amount of exiting demonstration of photovoltaic, (photo-) catalytic and sensor devices based on quasi 1D and 2D metal oxide nanostructures requires the fundamental understanding of their surfaces affecting the transport and the optical properties. In conjunction with transport measurements, we have applied a range of spectroscopic and imaging techniques to individual metal oxide nanostructure to address the chemical and photochemical processes taking place on its surface. In particular, we use an array of scanning probe, electron, and synchrotron radiation based photoelectron emission spectro-microscopies to investigate in situ the evolution of structural, electronic and chemical particularities in an operating nanodevice under wide range of the experimental conditions such as temperature, chemical environments (including liquids) electrostatic field, sensitization with catalyst particles, radiation etc,. Benefiting from the gained knowledge, we develop the real world prototypes for nanowire based (photo-) catalytic and chemical sensor platforms.

SEMICONDUCTOR NANOWIRES: FROM MATERIALS SCIENCE TO DEVICE PHYSICS

Lars Samuelson
Nanometer Structure Consortium, Lund University, Sweden

In this talk I will give examples of the rapid development in the areas of growth, processing and applications of semiconductor nanowires. The approach is based on the combination of top-down patterning and self-organized growth, as guided self-assembly. Axial and radial heterostructures, also of non lattice-matched combinations, can be formed with abruptness on the atomic level, thus allowing great freedom in design of electronic and opto-electronic devices. I will describe the state-of-the-art in materials properties, in control of dimensions and positions as well as give examples of the use of semiconductor nanowires in different quantum device applications. 

SURFACE RESTRUCTURING OF NANOPARTICLES: AN EFFICIENT ROUTE FOR EXTENDED CHARGE SEPARATION

T. Rajh
Center for Nanoscale Materials, Argonne National Laboratory

Semiconductor photocatalysis using nanoparticlate TiO₂ has proven to be a promising technology for use in photocatalytic reactions, in the cleanup of water, or as a photoactive material in nanocrystalline solar cells. We have found that reconstructed surface of metal oxide nanoparticles differs form the bulk by the presence of highly reactive under-coordinated surface. This can be viewed as a curse or as an opportunity. The under-coordinated surface metal atoms trap light-induced charges, but also exhibit high affinity for oxygen-containing ligands. As a result of this strong interaction, delocalized bands of metal oxide nanoparticles are electronically coupled to organic linkers, improving their optical properties in the visible region and photovoltaic response due to enhanced charge separation across nanoparticle interface. In the same manner we use photoinduced charge separation in order to control and manipulate processes within living cells.