Events
CNS Seminar Series, Spring 2008
"Photosynthetic Architectures and Materials
for Organic Solar Cells"
Abstract: Organic solar cells use semiconducting thin films of molecules or polymers to replace the inorganic semiconductors found in more conventional solar cells. The motivation is the promise of lower costs. But to date, the efficiency and stability of organic solar cells remains uncompetitive with inorganic devices. This performance contrasts with that other molecular approach to solar energy conversion, photosynthesis – a self sustaining process that dominates the globe and fixes more than 100 Gtons of carbon annually at an equivalent power of 100 TW.
In this talk, we report the exploitation of photosynthetic materials and device architectures in organic solar cells.
The culmination of the work is an ‘organic solar concentrator’ (OSC), which adopts the photosynthetic architecture by separating the functions of light absorption and charge generation. We demonstrate OSCs based on both synthetic dyes and phycobilisomes - highly efficient light gathering structures evolved by algae. We report efficiencies of up to 6.8% at 1 sun. OSCs are a flexible new solar technology that can be used in concert with existing inorganic solar cells. Like other organic semiconductor devices, OSCs are compatible with low cost manufacturing and are expected to be inexpensive.
Prof. Marc Baldo
Dept. of Electrical Engineering and Computer Science
M.I.T.Thursday, Arpil 24, 2008
12:15 p.m., 700 Clark Hall
CNS Seminar Series, Fall 2007
"Spin Transport in Ferromagnet
Semiconductor Heterostructures "Abstract: A longstanding goal of research in semiconductor spintronics is the ability to inject, modulate, and detect electron spin in a single device. I will discuss recent progress in the study of spin transport in ferromagnet-semiconductor heterostructures, including the electrical detection of spin accumulation and the observation of spin precession in transport. The focus of our work is on epitaxial Fe/GaAs (100) heterostructures comprising a heavily doped Schottky barrier on an n-doped channel (n = 2x10^16 – 1x10^17 cm^-3). A non-equilibrium spin polarization is injected into the channel by tunneling through the Fe/GaAs Schottky barrier. Electrical spin detection is accomplished by measuring the electrochemical potential at a non-local detection contact. In this manner, a spin-valve signal which decays with increasing separation of the source and detector is observed. More importantly, the spin detection signal can be modulated by precession of the spin in the channel of the device. In a sufficiently large transverse field, the spin valve effect is completely suppressed by dephasing in the GaAs channel. This experimental approach allows for a direct comparison with optical measurements of spin polarization in the channel as well as a simple drift-diffusion model for the spin transport. The devices allow us to probe quantitatively the spin lifetime and diffusion constant as well as hyperfine fields that influence spin precession and dephasing. We show that the magnitude and sign of the accumulated polarization depend strongly on the bias voltage across the injector, although the details of this behavior are not understood. This work was supported by ONR, the NSF MRSEC, NNIN, and IGERT programs, and the Los Alamos LDRD program.
Spin Polarized ImageProf. Paul Crowell
School of Physics and Astronomy
University of MinnesotaThursday, November 29, 2007
12:15 p.m., 700 Clark Hall
"The Coupling of Mechanical and Magnetic Degrees of Freedom in Magneto Electromechanical Systems "
Abstract: The dynamics of small magnetic cantilevers is affected by the coupling between the mechanical and magnetic degrees of freedom Magnetization reversal is facilitated by torsional motion of the cantilever and magnetomechanical torques can be detected as line splittings in current-induced ferromagnetic resonance spectra.
We study theoretically the possible utilization of electric current-induced mechanical torques in ferromagnetic-normal-metal heterostructures generated by spin-flip scattering [4-6] or the absorption of transverse spin currents by a ferromagnet as discussed above. We propose a concept for a spin-transfer-driven electric nanomotor based on integrating metallic nanowires with carbon nanotubes, in which the current-induced mechanical torques drive a rotary motion.
Dr. Gerrit Bauer
Theoretical Physics Group
Kavli Institute of NanoScience
Delft UniversityTuesday, October 30, 2007
12:15 p.m., 700 Clark Hall
"Active Photonic nanomaterials: from disordered to periodic"
Abstract: Active photonic nanomaterials, which have high gain or large nonlinearity, are essential to the development of nanophotonic devices and circuits. In this talk, I will provide a review of our recent research activities related to the fabrication of active photonic nanomaterials and the development of photonic devices based on such materials. In particular, we focus on a wide bandgap semiconductor zinc oxide and fabricate a broad range of structures, from disordered to periodic, with various nanofabrication techniques. Lasing in the near-ultraviolet frequency has been realized in both periodic and random structures at room temperature under optical pumping.
Prof. Hui Cao
Department of Physics and Astronomy
Northwestern UniversityThursday, October 11, 2007
12:15 p.m., 700 Clark Hall
"Multiple Exciton Generation in Semiconductor Quantum Dots and Novel Molecules: Applications to Third Generation Solar Photon Conversion "
Abstract: In order to utilize solar power for the production of electricity and fuel on a massive scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency (delivered watts/m2) and low capital cost ($/m2). One potential, long-term approach to high efficiency is to utilize the unique properties of quantum dot nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer processes. To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers with femtosecond (fs) to ns time resolution. At NREL, we have been studying these fundamental dynamics in various bulk and nanoscale semiconductors (quantum dots (QDs), quantum rods/wires, and quantum wells) for many years using fs transient absorption, photoluminescence, and THz spectroscopy. Recently, we predicted that the generation of more than one electron-hole pair (which exist as excitons in QDs) per absorbed photon would be an efficient process in QDs . This prediction has been confirmed over the past 2 years in several classes of QDs. We have observed very efficient and ultrafast multiple exciton generation (MEG) from absorbed single high energy photons in Group IV-VI and recently in Si QDs. Efficient MEG has the potential to greatly enhance the conversion efficiency of solar cells that incorporate QDs for both solar electricity and solar fuel (i.e. H2) production. Selected aspects of this work will be summarized and recent advances will be discussed; a unique quantum mechanical model to explain efficient and ultrafast MEG based on the coherent superposition of multiple excitonic states (in collaboration with Al. L. Efros and A. Shabaev at NRL) will also be discussed. Various possible configurations for quantum dot solar cells that could produce ultrahigh conversion efficiencies for the production of electricity and solar fuels (e.g. H2 from H2O) will be presented, along with progress in developing such new types of solar cells. Finally, we have also predicted an analogous MEG effect in molecules (called singlet fission) that could be used in molecular chromophore-sensitized nanocrystalline TiO2 solar cells and new preliminary evidence for this effect will also be presented. .
Prof. Arthur Nozik
Center for Basic Sciences
National Renewable Energy Laboratory
Golden, CO 80401
and
Department of Chemistry
University of Colorado, Boulder
Thursday, September 27, 2007
12:15 p.m., 700 Clark Hall
CNS Seminar Series,Spring 2007
"Nanowire Building Blocks for Photonics & Electronics "
Abstract: Nanowires are of both fundamental and technological interest. They represent the critical components in the potential nanoscale electronic and photonic device applications. Achieving high level of synthetic control over nanowire growth allows us to explore some of their very unique and exciting physical properties. For example, semiconductor nanowires can function as self-contained nanoscale lasers, sub-wavelength optical waveguides, frequency converters and photodetectors. It was also discovered that the thermoconductivity of the silicon nanowires can be significantly reduced when the nanowire size in the 20 nm region, pointing to a very promising approach to design better thermoelectrical materials for energy conversion. In this talk, I will outline our recent efforts in the direction of using nanowires for photonics, electronics and energy conversion applications.
Prof. Peidong Yang
Department of Chemistry
University of Califonia at Berkeley
Thursday, April 5, 2007
12:15 p.m., 700 Clark Hall
"Chirality-resolved single-walled carbon nanotubes"
Abstract: The utilization of single-walled carbon nanotubes (SWNTs) in large quantities for molecular electronics, optoelectronics, biosensors, and medical applications will require SWNTs of the same physical structure, electronic type, and band gap. Since current methods of synthesis produce mixtures of nanotubes with different physical structures and electrical properties, the development of strategies for the post-production separation of these one-dimensional materials is highly desirable. In this work, we demonstrate a scalable method for separating SWNTs by their diameter and electronic type (i.e., semiconducting versus metallic) using density gradient ultracentrifugation (DGU). Since DGU is a technique commonly utilized to separate and isolate different sub-cellular components, DNA from RNA, and even different sequences of DNA by their compositions, we initially focused on the bulk sorting of DNA wrapped SWNTs in aqueous density gradients [1]. This process led to enrichment of SWNTs by diameter – especially in the small diameter regime (i.e., SWNT diameter = 0.7 – 1.0 nm). However, DNA wrapping possessed several undesirable characteristics including prohibitive expense in large scale production, irreversible wrapping, and inefficient wrapping for SWNTs with diameters exceeding 1 nm. Consequently, subsequent work has focused on DGU of surfactant encapsulated SWNTs [2]. In particular, bile salt surfactants, such as sodium cholate (SC), have overcome the drawbacks of DNA. Furthermore, additional control over the density-structure relationship has been achieved by using co-surfactant mixtures of SC and sodium dodecyl sulfate (SDS). For example, highly efficient metal versus semiconductor separation has been achieved with SDS:SC co-surfactant ratios ranging from 1:4 to 3:2. Characterization of the resulting sorted SWNT samples includes optical absorption spectroscopy, photoluminescence spectroscopy, atomic force microscopy, and direct charge transport measurements. Since DGU produces relatively large quantities of monodisperse SWNTs, this talk will conclude with our most recent efforts to realize enhanced performance in SWNT devices, such as thin-film field effect transistors, using SWNTs sorted by DGU.
Prof. Mark Hersam
Materials Science and Engineering Dept ,
Northwestern UniversityThursday, March 29, 2007
12:15 p.m., 700 Clark Hall
"Cold molecules - the new frontier in the ultacold world "
Dr. Jun Ye
JILA and the National Institute of Standards and Technology
Thursday, February 22, 2007
12:15 p.m., 700 Clark Hall
CNS Seminar Series, Fall 2006
"Electrical Soliton Modelocking - Taming Electrical Solitons"
Abstract: Solitons are a unique class of nonlinear pulse waves that have captivated scientists for over a century. Electrical solitons, which are created on nonlinear transmission lines (electromagnetic waveguides whose dielectric constant changes with the electric field applied), are especially interesting as they allow the use of the fascinating physics of solitons in a medium that touches our everyday lives, modern electronics.
In this talk, I will describe the first electrical soliton oscillator (electrical soliton modelocked system) that my research group has recently developed. Made by looping a nonlinear transmission line around an amplifier, the soliton oscillator self-generates a stable train of electrical solitons, initially growing them from background noise. By nature, solitons are unruly, and solitons circulating in an oscillatory loop tend towards chaos. The key to our success in building the stable oscillator was finding a way to tame the unruly behaviors and realizing it in the amplifier. The successful soliton control shown in this work with the latest prototype in a tiny silicon microchip may herald widespread use of solitons in electronics, especially in all-electronic ps-resolved time-domain metrology & in wireless system applications.
(Co-workers) David Ricketts and Xiaofeng Li
Prof. Donhee Ham
Electrical Engineering,
Harvard University
Thursday, November 30, 2006
12:15 p.m., 700 Clark Hall
Harvard Electronics & IC Research Laboratory
"Recent Developments in Mid-infrared Quantum Cascade Lasers"
Abstract: Quantum Cascade (QC) lasers are a rapidly evolving mid-infrared semiconductor laser technology based on intersubband transitions in multiple coupled quantum wells. The lasers’ key strengths are their considerable wavelength tailorability, high power and high-speed operation, and fascinating design potential.
We will first give an overview of QC lasers followed by a discussion of several recent highlights. In particular, we will discuss QC lasers with active region cascades that are “multi-functional”; i.e. they are capable of multiple-wavelength or broadband emission, or also incorporate quantum wells with resonant intersubband optical nonlinearities. As an example for the latter, a QC laser with active regions specially designed to incorporate a giant optical nonlinearity emitted light at pump and second harmonic wavelengths of 9.1 and 4.55µm, respectively, with up to few milliwatts of second harmonic power and a nonlinear power conversion efficiency of up to 36 mW/W2.
We will conclude with a short review on the state of the art of QC laser performance and applications, especially in trace gas sensing. An outlook at the challenges and promises ahead in the QC laser area will close the talk.
Prof. Claire Gmachl
Electrical Engineering,
Princeton University
Thursday, November 16, 2006
12:15 p.m., 700 Clark Hall
"Quantum Interference Control of Charge and Spin in Semiconductors"
Abstract: Optical phase is not often considered as a control parameter in semiconductor photonics. However, when two light beams with different wavelengths or polarizations couple valence and conduction band states, quantum interference of the absorption pathways permits generation and phase control of charge and spin currents. I will review some of our recent work on quantum interference control of currents in GaAs and Si, including optical control of the spin Hall effect.
Prof. Henry van Driel
Dept. of Physics and Institute for Optical Sciences
University of Toronto
Thursday, November 2, 2006
12:15 p.m., 700 Clark Hall
Institute for Optical Sciences
"Electron transport across single σ-bonded Molecular Monolayers:
Are we asking the relevant questions?"
Abstract: We study the title question with semiconductor/alkyl monolayers/metal structures, by combining transport and photoemission (Kahn, Ueno, Umbach, Naaman) measurements with theoretical (DFT) calculations (Kronik). Our results lead to questions, such as what is the relevance of the HOMO/LUMO concept for these systems, is there a well-defined transport barrier and width, and, more trivial(?), what are the contact areas in molecular electronics? I will try to present a semi-coherent picture of this on-going study.
Prof. David Cahen
The Rowland and Sylvia Schaefer Chair in Energy Research
Weizmann Institute
Thursday, October 26, 2006
12:15 p.m., 700 Clark Hall
Optoelectronic Materials Group
"Well-Defined Single Molecule Circuits::
Structure-Conductance Relationships Using Amine-Gold Linkages"
Abstract: We recently demonstrated that the conductance of single molecule junctions formed by breaking Au point contacts in an environment of molecules with amine linkages can be measured reliably and reproducibly1. We have now studied junctions formed by approximately 30 different amine terminated molecules, allowing systematic study of the correlation between molecular properties and single molecule junction conductance. This talk will focus on the relation between molecular conductance and molecule conformation for the simple case of a biphenyl, two benzene rings linked together by a single C-C bond. Our results from a series of seven biphenyl derivatives show that the molecular junction conductance depends on the twist angle. Specifically, we find that the planar molecule has the highest conductance, and the conductance for the series decreases with increasing twist angle, consistent with a cosine squared relation predicted theoretically2.
- L. Venkataraman, J.E. Klare, I.W. Tam, C. Nuckolls, M.S Hybertsen and M. Steigerwald, Nano Letters, vol. 5, pp. 458-462, 2006.
- L. Venkataraman, J.E. Klare, C. Nuckolls, M.S Hybertsen and M. Steigerwald, Nature, vol. 442, pp. 904-907, 2006.
Dr. Latha Venkataram
Department of Physics
Center for Electron Transport in Molecular Nanostructures
Columbia UniversityThursday, October 19, 2006
12:15 p.m., 700 Clark Hall
"Towards nanocrystal electronics: high-resolution device
fabrication and controlled particle assembly"
Abstract: Nanocrystals are tunable crystals a few nanometers in size, exhibiting a range of quantum phenomena at room temperature. Efforts to explore nanocrystals unite the frontiers of chemistry, physics and engineering, and open up new applications ranging from electronics to biology. In this talk, I will discuss the assembly of spherical and rod-like CdSe and PbSe semiconductor nanocrystals into electronic devices, their electronic properties and the basic mechanisms of charge transport, both in the limit of large arrays and the limit of only a few quantum dots. I will show how local charge transport behavior can be directly imaged by electrostatic-force microscopy and correlated to nanopatterns observed with transmission electron microscopy.
I will also describe transmission electron beam ablation lithography (TEBAL); a new and highly flexible top-down technique for fabricating device components roughly one order of magnitude smaller than what is possible with other top-down techniques. TEBAL is based on ablation of atoms from a continuous metal film with the ~ 5 Å diameter imaging beam of a high-resolution transmission electron microscope (HRTEM). Arbitrary patterns (nanogaps, nanorings, curved nanowires, etc.) may be “carved out” with sub-nanometer accuracy at precise locations. Because TEBAL is performed inside a HRTEM, atomic resolution in situ imaging of the ablation action is easily obtained and allows for real-time feedback control.
Prof. Marija Drndic
Department of Physics and Astronomy
University of Pennsylvania
Thursday, October 5, 2006
12:15 p.m., 700 Clark Hall
"Photonic Crystal deviced and circuits for classical and
quantum
information processing"
CANCELLED
Abstract: We have recently demonstrated a number of classical and quantum information processing devices enabled by strong light-matter interaction in photonic crystals, including a quantum dot-photonic crystal cavity single photon source and an ultrafast nanocavity laser with low threshold. I will describe these devices, their efficient design and fabrication methods we have developed, as well as our recent success in combining them into small quantum networks on a chip.
Prof. Jelena Vuckovic
Electrical Engineering
Stanford University
Thursday, September 7, 2006
12:15 p.m., 700 Clark Hall
Vuckovic Research Group
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CNS Seminar Series, Spring 2006
"Silicon Lasers"
Abstract: Silicon, the wonder material of the 20th century, appears to have one more trick up its sleeve. After dominating the digital electronic industry, the bedrock of the digital world, it is now being considered as a platform of choice for building optoelectronic devices. Today, most of the building blocks that make up an optical communication system are already available in silicon. A silicon laser would complete the highly anticipated silicon photonics tool box. But, conventional wisdom holds that silicon cannot lase because of its indirect bandgap. Taking this axiom as a motivation rather than a deterrent, researchers have been rushing to prove their predecessors wrong and to unleash the mighty silicon laser.
This talk will begin with a tutorial on why lasing is not possible in bulk silicon showing that while the indirect bandgap plays a role, it’s the absorption by free carriers that prevents optical amplification, the prerequisite to lasing. It will then review the recent breakthroughs based on nanophotonics as well as Raman Effect. The talk will conclude by arguing that silicon is the ideal Raman medium for mid wave IR (MWIR) wavelengths where high power sources of coherent radiation are needed for biochemical detection, infrared counter measure and other pressing applications.
Prof. Bahram Jalali
Electrical Engineering,
UCLA
Thursday, April 27, 2006
12:15 p.m., 700 Clark Hall
Optoelectronics Circuits and Systems Laboratory
"Synthesis of Micro- and Nanoscale Hydrogel Structures"
Abstract: Poly (N-isopropylacrylamide) (PNIPAm) belongs to the class of crosslinked polymer networks called hydrogels, which can respond to an external stimulus with a change in their size and shape. External stimulus can be a change in any ambient parameter such as temperature, pH, electrical or magnetic field. Due to their stimuli-responsive nature, micropatterned hydrogels are increasingly finding applications as flow valves in microfluidics, cell and tissue scaffolds, targeted drug delivery, controlled release etc. By using higher resolution lithographic techniques, one may also pattern hydrogels at nanoscale. Compared to their micropatterned counterparts, nanopatterned hydrogels would possess faster response to external stimulus due to their small size and high surface-to-volume ratio.
N-isopropylacrylamide is known to undergo crosslinking in bulk, when irradiated with gamma rays, x-rays and e-beam. PNIPAm hydrogels can be patterned using x-ray and electron beam lithography to address the question “how small can a hydrogel structure be and still retain its stimuli-response behavior?” Fabricating nanopatterned hydrogels by direct e-beam writing also provides the unique possibility to tailor their stimuli-response properties by creating artificial network morphologies. These fabrication techniques are also amenable for direct integration of such functional patterned hydrogels into NEMS and BioMEMS devices.
The presentation will be prefaced with a brief introduction to the Center for Nanoscale Materials at Argonne National Laboratory.
Acknowledgment: This work has been supported in part by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under contract No. W-31-109-Eng-38
Derrick Mancini
Project Manager, Argonne National Laboratory
Thursday, April 13, 2006
12:15 p.m., 700 Clark Hall
"What's new in Nanoscale Structures? -- Fluctuations and Transformations"
Abstract: The nanoscale world is not a scaled-down version of the macroscopic world. Nanoscale structures have special properties by virtue of their smallness alone, which yields quantum confinement, high surface-to-volume ratio and susceptibility to fluctuations. Direct imaging at the atomic scale using scanned probe techniques allows the latter effect, fluctuations, to be observed and quantified. Quantitative characterization of these fluctuations using the tools of statistical mechanics yields correlation functions as well as more direct measures of stochastic behavior such as first-passage properties
The stochastic vs. deterministic factors in the behavior of individual nanoscale structures will be illustrated for the case of supported lead crystallites. silver structures decorated with fullerenes, and metallic and semiconducting electrical conductors.
Acknowledgment: Different aspects of this work have been supported by the NSF-MRSEC, LPS and the DCI post-doc program.
Prof. Ellen Williams
Materials Research Science and Engineering Center
University of Maryland College Park
Thursday, March 30, 2006
12:15 p.m., 700 Clark Hall
"Electromagnetic Field Enhancement near Ag Nanocrystals: Single Molecule Raman Spectroscopy, Optical Forces, and Surface Photochemistry"
Abstract: Two 30nm Ag nanocrystals exhibit junction a junction "hot spot" in their local electromagnetic field enhancement when separated by a few nm. If the a molecule is chemisorbed in the junction and also electronically resonant with the laser, this enhancement is sufficient to enable single molecule Raman spectroscopy. The laser-induced ac polarization in the Ag which creates the "hot spot" also creates a very strong attractive potential between the nanocrystals that squeezes the junction. We calculate these optical forces by integration of the Maxwell stress tensor. The Ag local field enhancement can also be used for photochemistry, to control the shape of Ag nanocrystals growing via surface photoreduction of Ag ion.
Prof. Louis Brus
Chemistry Department
Columbia University
Thursday, March 2, 2006
12:15 p.m., 700 Clark Hall
"Silicon-chip-based optical resonators with Q factor > 100 million "
Abstract: A novel processing method has been applied to create optical micro-resonators having Q factors as high as 500 million on silicon wafers. These devices open up many new applications for lab-on-a-chip experimental work. After describing the processing and passive optical properties of these devices, the consequences of resonant energy buildup in a microscale, ultra-high-Q system will be described. Demonstrations of micro Raman and micro OPO lasers based on these cavity structures will be reviewed. Finally, radiation confined within a vessel exerts pressure upon its walls. If the vessel is a high-Q micro-cavity, then a weak power level, coupled to the cavity, can exert a substantial, resonantly-enhanced pressure on the internal micro-cavity walls. Such a pressure will deform the cavity structure and change the resonant condition. This effect has been theorized to produce a parametric oscillation in the mechanical modes of the optical resonator. The first observation of this effect will be described.
Radiation pressure induced mechanical oscillation in a whispering gallery micro-toroid (below threshold left; above threshold right)
Prof. Kerry Vahala
Applied Physics
California Institute of Technology
Thursday, February 23, 2006
12:15 p.m., 700 Clark Hall
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CNS Seminar Series, Fall 2005
Abstract: Since the development of the light microscope in the 16th century, optical device size and performance has been limited by diffraction. Photonic devices of today are composed of dielectric materials with modest dielectric constants, and are much bigger than the smallest electronic devices for this reason. However subwavelength spatial confinement of light at dimensions down to less than 10% of the free-space wavelength is possible using plasmonic components. Ultimately it may be possible to employ plasmonic components to form the building blocks of a chip-based optical device technology that is scaleable to molecular dimensions, with potential imaging, spectroscopy and interconnection applications in computing, communication and chemical/biological detection.
In this talk I will describe recent opportunities presented by plasmonics for chip-scale integration of photonic and electronic devices, including i)design of metal-insulator-metal plasmon waveguides that optimize the trade-off between mode localization and propagation loss in the visible and near-infrared ii) on-chip Si CMOS compatible light near-infrared light sources for coupling into plasmonic networks iii) plasmon-enhanced emission from quantum dots, and iv) opportunities for active plasmonic devices based on electro-optic and all-optical modulation of plasmon propagation.
Prof. Harry A. Atwater
Thomas J Watson Laboratory of Applied Physics
California Institute of Technology
Thursday, November 10, 2005
12:15 p.m., 700 Clark Hall
Abstract: In normal metals electrons travel only very short distances, on the order of Angstroms, before they are scattered. In contrast, in specially engineered semiconductor materials disorder can be reduced to an exceptionally low level, allowing electrons to travel distances a million times longer, up to nearly a millimeter, before scattering. Despite this remarkable achievement, the influence of disorder in these materials is very important and not well understood. The technique described in this talk takes advantage of a special property of two-dimensional electronic systems. In large magnetic fields, a 2D layer of electrons has a very peculiar behavior: small changes in the local electron density can cause a patch of electrons to change from being a metal to an insulator. Applying voltages to a metal scanning probe tip modifies the local electron density to create a ring-shaped region of insulating electrons centered at the position of the tip. Not all patches of insulating electrons are created equal: in some cases, the inherent disorder in the sample can creates small islands inside the insulating ring. Single electron resonant tunneling through these islands can allow electrons to traverse the insulating ring. The results show that transport through insulating regions of this 2D quantum Hall system is strongly affected by these islands, and they act as stepping stones for transporting electrons through the frozen background. The images thereby provide a direct view of disorder in very clean samples.
Prof. Raymond Ashoori
Physics
M.I.T.Thursday, October 13, 2005
12:15 p.m., 700 Clark Hall
Abstract: Single-wall carbon nanotubes provide a model system to investigate the nature of electrons confined in a 1-dimensional system. The ground-state properties and unique electronic transport properties have extensively studied. The nature of the excited states, as revealed in the optical measurements, is, however, less understood. Recently there have been several important advances in this regard, including the observation of nanotube luminescence and electro-luminescence.
In this talk we will describe measurements of the properties and dynamics of nanotube luminescence and its relation to the fundamental photophysics of carbon nanotubes. Using the distinctive selection rules of nonlinear spectroscopy, we also demonstrate the excitonic nature of the optical transitions in carbon nanotubes. Finally we present recent results in which electronic transitions of individual single-wall nanotubes have been investigated by resonant Rayleigh scattering. This method provides new possibilities for the investigation of environmental effects and tube-tube interactions at the single nanotube level.
Prof. Tony Heinz
Physics
Columbia University
Thursday, September 29, 2005
12:15 p.m., 700 Clark Hall
Abstract: The developments of photonic crystals and nanophotonic devices allow unprecedented control over the behavior of light. In particular, the resonant states in these structures that are on the wavelength or even sub-wavelength scales can be used as a basic building block to create new optical physics and devices. In this talk, we give examples on non-reciprocal resonators; on coherent stopping, storage and time-reversal of light; and on new meta-materials with geometrically controlled dielectric constants.
Prof. Shanhui Fan
Electrical Engineering
Stanford UniversityThursday, September 15, 2005
12:15 p.m., 700 Clark Hall
"
Charged colloidal quantum dots:color, conductivity,
luminescence
and carrier dynamics"
Abstract: Colloidal nanoparticles can potentially be used to create materials with optimized or novel functions. Semiconductor quantum dots are one such promising building block where a few electrons dramatically modify their properties. Injecting charges in films of colloidal quantum dots can be achieved by using optical excitation, reducing species, electrochemical or solid state gating. In particular, electrochemical gating coupled with optical spectroscopy has allowed a detailed and quantitative study of the influence of charges on transport. Low-temperature measurements show the films to conduct via variable range hopping and this model also explain the 150% positive magnetoresistance that appears at very low temperature. n-type dots should also display different luminescent properties and this is indeed observed, with significantly reduced lasing threshold for charged films. Finally, n-type dots allowed to study the electron intraband relaxation in the absence of the electron-hole Auger processes, and it has been found that intraband relaxation is then likely induced by coupling to molecular vibrations of the surface ligands.
Prof. Philippe Guyot-Sionnest
Physical Chemistry
University of Chicago
Thursday,
September 1, 2005
12:15 p.m., 700 Clark Hall
http://chemistry.uchicago.edu/fac/guyot-sionnest.shtml
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" Optical Control in Semiconductor Dots for Quantum Operations "
Abstract: Semiconductor quantum dots have optical properties similar to simple atomic systems, unlike higher dimensional semiconductor structures that are dominated by manybody physics associated with the continuum states. They also provide a potentially ideal electronic structure appropriate for quantum computing. We will present data showing that these structures can be coherently controlled on a time scale short compared to the quantum decoherence time and that entangled states of qubits (represented by exciton optical Bloch vectors) can be created. The system is remarkably robust against pure dephasing and we have been able to demonstrate a simple conditional quantum logic device involving multiple Rabi flops of the exciton and biexciton.
The future of this work lies in coherence engineering of the materials to provide longer coherence times for the qubits. To this end, our group is now working on single electron doped quantum dots where the spin, with long coherence time, is the qubit. Measurements show that we can coherently control the spin state of a single electron.
This work done in collaboration with Dan Gammon (NRL) and L.J. Sham (UC-SD) with support from AFOSR, ARO/ARDA/NSA, ONR and NSF.
Prof. Duncan Steel
The Harrison M. Randall Laboratory, FOCUS Center
University of MichiganThursday, May 5, 2005
12:15 p.m., 700 Clark Hall
"Molecular Nanostructures: Modeling Assembly, Transport, Hysteresis And Switching"
Abstract: Molecular nanoscience poses challenges first in understanding structure, and next in mastering properties. In the first part of the talk, we will utilize a combination of non-equilibrium Greens functions and polaron theory to discuss transport, hysteresis and switching in molecular current transport junctions. The effectiveness of relatively simple models in understanding (at least on a semi-quantitative basis) complex transport structures will be emphasized, and some conclusions will be drawn concerning the appropriate limits in which simple pictures can be recovered.
The second part of this discussion will focus on use of agent-based ideas to analyze assemblies comprising molecular subunits. This algorithmic approach has real promise for understanding the complex behavior of molecular nanostructure assembly.
Prof. Mark Ratner
Chemistry Department
Northwestern University
Thursday,
April 21, 2005
12:15 p.m., 700 Clark Hall
"Watering Silicon Nanograss: How to Get Droplets to Roll or Stick on Demand"
Abstract: An ability to manipulate microscopic volumes of liquids with the high precision becomes increasingly important with the recent progress in micro- and nanofluidics and its rapid penetration in various industrial applications. Dynamic control over the interaction of liquids with the solid substrate constitutes a very important aspect of this problem. Nanostructured solid surfaces offer a promising way to achieve this goal. In this talk we discuss recently demonstrated dynamically tunable nanostructured surfaces. The behavior of these surfaces can be reversibly switched between superhydrophobic and hydrophilic states by the application of electrical voltage and current. The proposed approach potentially allows novel methods of manipulating microscopically small volumes of liquids. This includes almost frictionless liquid transport, the ability to selectively immobilize the droplets at any given time or position, as well as dynamic control over the penetration on liquids through the nanostructured layer. The obtained results potentially open new and exciting opportunities in microfluidics, optics, thermal management of microelectronics, chemical microreactors, bio/chemical detection, and many other areas.
Dr. Tom Krupenkin
Lucent Technologies
Thursday,
April 7, 2005
12:15 p.m., 700 Clark Hall
"Quantum Control and Nano-Photonics in Quantum Information Science"
Abstract: New challenges from quantum information processing and quantum metrology provide compelling motivation for interdisciplinary research that draws together wide-ranging areas of science and engineering. In this talk I will describe two ongoing projects that pursue novel integrations of control theory and nanotechnology with atomic physics. In the first, we are utilizing tools from control theory to develop novel approaches to feedback-stabilized quantum state preparation and robust sub-shotnoise magnetometry with atoms. In the second, we are attempting to develop "integrated quantum nodes" for a quantum communication network that will combine chip-scale atom traps with photonic bandgap structures.
Prof. Hideo Mabuchi
Caltech
Thursday,
March 17, 2005
12:15 p.m., 700 Clark Hall
http://minty.caltech.edu/hmabuchi/
"Oxide-Semiconductor Materials for Quantum Computation "
Abstract: Quantum computers, as yet undeveloped, are believed to be able to solve certain problems exponentially faster than ordinary computers. One of these problems, number factorization, can be used to defeat public key encryption schemes like RSA, which is widely used in the internet. The potential of these and other applications has led to a worldwide race to build the first working quantum computer. The state of experimental quantum computation is primitive--neither quantum bits (qubits) nor quantum gates (qugates) have been demonstrated in a scalable form. In this talk, I will describe a proposal to create a quantum processor using ferroelectrically coupled electron spins in Silicon. Quantum information is stored in the spin of electrons, which form a conveninent two-level system. The electrons are confined in the semiconductor (Si) using the static polarization from an epitaxial ferroelectric. Fast optical gating occurs using the nonlinear process of optical rectification. Ge quantum dots are used as "windows" that allow light to initialize or "boot" the quantum computer. Initial steps toward the development of quantum information technology using ferroelectric/semiconductor heterostructures will be presented.
Prof. Jeremy Levy
University of Pittsburgh
Thursday,
March 10, 2005
12:15 p.m., 700 Clark Hall
"Silicon Photonic Crystals and Photonic Wires Circuits"
Integration of optics at the chip scale is seen as key to significantly reducing the cost of optical components. Silicon or more specifically silicon on insulator is an attractive platform for integration owing to its high refractive index that offers strong light confinement and therefore ultra-compact devices. By adopting a substrate material that is CMOS compatible, decades of materials and process knowledge can be leveraged. Feasibly both passive and active optical elements could be combined with electronics on a single chip to achieve monolithic optoelectronic integration.
Single-mode strip waveguide and W1 photonic crystal waveguide fabricated on SOI wafer.
We performed detailed experimental study of transmission properties of PhC-based and photonic wire-based components as sharp bends, wide-angle Y-splitters, and more complicated devices as Mach-Zehnder modulators and compare their performance in terms of losses, bandwidth and dispersion. We will discuss how the unique properties of photonic crystals may be incorporated into photonic integrated circuits and what improvement in functionality they might provide.
Dr. Yurii Vlasov
IBM T.J. Watson
Research Center
Yortown Heights,
NY
Thursday,
February 10, 2005
12:15 p.m., 700 Clark Hall
"
Precision Radiofrequency Measurements of Nanomechanical Systems
"
Abstract: There is much interest in the fabrication and properties, both static and dynamic, of nanoscale systems. At UC Santa Barbara we have been developing top-down lithographic approaches to fabricating highly integrated electromechanical systems, that include electronic means for monitoring the motion, and other degrees of freedom, of these systems. In this talk I will briefly described some approaches that we have explored, and discuss in somewhat more detail recent measurements on nonlinear mechanical resonators, in which an interesting measurement scheme that relies on the nonlinear behavior allows precision determination of the resonator parameters.
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Prof. Andrew ClelandUniversity of California
Santa BarbaraThursday, January 27, 2005
12:15 p.m., 700 Clark Hall
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CNS Seminar Series, Fall 2004
"
Plastic Solar Cells: Promise and Progress "
Abstract: In a world where energy demands are soaring and oil supplies are peaking, research on renewable energy sources is gaining increasing attention. Among renewable energy sources, solar energy production is growing fast with an annual growth rate of 35%. Fifty years after the invention of the first crystalline silicon solar cell, worldwide photovoltaic sales are still based on bulk high-purity crystalline silicon. However, some new technologies based on thin films are on the threshold of commercialization and others are near the horizon. Organic semiconductors that can be printed over large-area, light-weight substrates show great potential for photovoltaic technologies.
In this talk, we will discuss the challenges that need to be overcome before plastic solar cells can fulfill their true promise. We will show that their performance is very sensitive to the ability to control the electronic and optical properties of the organic materials at the nanoscale. Charge transport properties will be discussed in particular for a variety of different materials with morphologies ranging from amorphous to polycrystalline, to liquid crystalline. Recent progress in the fabrication, modeling and optimization of organic multilayer thin-film devices will be presented.
Prof. Bernard Kippelen
School of Electrical and Computer Engineering
Georgia TechThursday, December 2, 2004
12:15 p.m., 700 Clark Hall
" Feeling the magnetism of individual spins:
recent results from magnetic resonance force microscopy "
Abstract: Is it possible to build a microscope that can look below surfaces and image molecules and materials with atomic resolution in three dimensions? Such a microscope would revolutionize structural molecular biology and be an important tool for nanoscale science and technology. Magnetic resonance force microscopy (MRFM) is an attempt to address this "holy grail" of microscopy.
In this talk, we describe the basic principles of MRFM and discuss recent results that demonstrate the detection of an individual electron spin buried within a silica sample. We review various innovations that set the stage for single spin detection, including attonewton force detection using ultrathin silicon cantilevers. We also discuss spin manipulation techniques, including using MRFM for real-time control of spin fluctuations. Finally, we consider some of the challenges remaining before 3D atomic imaging and real-time quantum state readout can be realized.
Dr. Daniel Rugar
IBM Research Division
Almaden research CenterThursday, November 4, 2004
12:15 p.m., 700 Clark Hall
" Geometry and Scale in Photonics"
Abstract: The scaling of optoelectronics devices to smaller and smaller spatial dimensions results, at least theoretically, in an increased device density and reduced optical systems size. Additionally, and perhaps more importantly, there is also a corresponding increase in the strength of light-matter interactions with reduced size scale, an effect which can dramatically alter the power, speed, and efficiency of an optical device. Geometry below or at the wavelength scale also plays an intricate role in optics, as demonstrated recently in the work on engineered photonic crystals and so-called "left-handed" materials. In this talk I will discuss the application of geometry and scale in optical structures to several different areas of our own current research: chip-scale atom-cavity QED, microcavity surface -emitting Quantum Cascade Lasers, and silicon microphotonics.
Prof. Oskar Painter
Applied Physics
California Institute of TechnologyThursday, September 30, 2004
12:15 p.m., 700 Clark Hall
"
Functional Nanocrystal-Quantum-Dot Assemblies:
Putting Dots to Work"
Abstract: Using modern colloidal chemistry, semiconductor nanocrystals (NCs), known also as NC quantum dots, can be fabricated with nearly atomic precision in a wide range of sizes and shapes. They exhibit high photoluminescence quantum yields and narrow, size-controlled emission lines, and they can easily be manipulated into complex two-dimensional (2D) and 3D assemblies. All of these properties make NCs ideally suited for studies of size/ structure-dependent quantum mechanical interactions as well as ideal building blocks for nanoscale engineering. This presentation focuses on light emitting properties of semiconductor NCs in the regimes of both optical and electrical pumping. By using shape-controlled NCs or multi-shell NC heterostructures, we can almost independently manipulate carrier confinement energies (i.e., emission wavelengths) and their relaxation dynamics [1, 2]. This capability is particularly useful for achieving the optical amplification/lasing regime. We use different types of "engineered" II-VI and IV-VI nanocrystals to demonstrate amplified spontaneous emission with colors tunable from the near infrared to the blue [3, 4]. We also develop and study novel types of hybrid epitaxial/colloidal nanostructures, which allow efficient electrical pumping of NC emitters via either "noncontact" exciton transfer [5] or direct charge injection from epitaxial layers of wide gap semiconductors.
1. H. Htoon, J.A. Hollingsworth, R. Dickerson, and V.I. Klimov, Phys. Rev. Lett 91, 227401 (2003).
2. V. Klimov, A. Mihkailovsky, D. McBranch, C. Leatherdale, and M. Bawendi, Science 287, 1011 (2000).
3. V. Klimov, A. Mikhailovsky, S. Xu, A. Malko, J. Hollingsworth, C. Leatherdale, and M. Bawendi, Science 290, 314 (2000).
4. R.D. Schaller, M.A. Petruska, and V.I. Klimov, J. Phys. Chem. B 107, 13765 (2003).
5. M. Achermann, M.A. Petruska, S. Kos, D. Smith, D.D. Koleske, and V.I. Klimov, Nature 429, 642 (2004).
Dr. Victor I. Klimov
Los Alamos National Laboratory
Chemistry Division, C-PCSThursday, September 16, 2004
12:15 p.m., 700 Clark Hall
" Engineering Ferroelectrics Using Strain"
Abstract: Molecular beam epitaxy (MBE) has achieved unparalleled control in the customization of semiconductors at the nanometer level; its use for the customization of ferroelectric oxides with similar nanoscale customization appears promising. This talk will describe the use of reactive MBE to synthesize dielectric and ferroelectric perovskite oxides, including new compounds and metastable superlattices, whose structures are engineered using epitaxy.
Prof. Darrell G. Schlom
Dept. of Materials Science & Engineering
Penn State UniversityThursday, September 2, 2004
12:15 p.m., 700 Clark Hall
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CNS Seminar Series, Spring 2004
"
Molecular Materials and Devices "
Abstract: Efforts to fabricate devices based on active molecular components have been driven by both the fundamental interest in using chemistry to build function at the molecular level and the looming technological expectation of the end of Moore 's law. In this talk, we describe the directed assembly of organic and metal-metal bonded supramolecular systems that are interesting materials for potential electronic and memory device applications. Molecules are chosen with head groups that bind to metal or oxide surfaces and tail groups that bind to metal electrodes or that template the growth of the particular molecular system. Optical spectroscopy, scanning probe microscopy, and electrochemistry are used to characterize the chemistry and physics of molecular assemblies. We incorporate these molecular systems in nanometer scale device "test" structures aimed at understanding the electronic characteristics of two- and three-terminal molecular devices.
Dr. Cherie Kagan
IBM
T.J. Watson Research CenterThursday, April 29, 2004
12:15 p.m., 700 Clark Hall
"
Circuit Quantum Electrodynamics:
Observing Strong Coupling Between a Superconducting Qubit and a Photon"
Abstract: I will describe recent experiments in which the strong coupling limit of cavity quantum electrodynamics has been realized for the first time using superconducting circuits. In our approach, we use a Cooper pair box acting as an artificial atom coupled to a transmission line resonator forming a one-dimensional cavity. The strong coupling limit is reached as the vacuum Rabi frequency for the coupling of cavity photons to quantized excitations of the qubit exceeds the damping rates of both the cavity and the qubit. When the qubit is detuned from the cavity resonance frequency a high-fidelity dispersive quantum non-demolition read-out of the qubit state is achieved. Using this read-out technique we have characterized the qubit properties spectroscopically and attained coherence times greater than 100 ns, indicating that this architecture is extremely attractive for quantum computing and control.
Prof. Rob Schoelkopf
Departments of Applied Physics and Physics
Yale UniversityThursday, April 15, 2004
12:15 p.m., 700 Clark Hall
" Lead-Salt Nanocrystals: Strong Quantum Confinement of Electrons "
Abstract: I will introduce the basic properties of semiconductor quantum dots, and then focus on the properties of lead-salt (PbS, PbSe, PbTe) nanocrystals. These structures are ideal for studies of strong confinement of charge carriers and investigations of the vibrational modes of nanocrystals. They are also technologically relevant, because they are among the few material systems that can produce strongly size-quantized optical transitions at infrared wavelengths between one and three microns. Examples of established properties will be presented along with open questions that are the subject of current research.
Prof. Frank Wise
Applied and Engineering Physics
Cornell UniversityThursday, April 01, 2004
12:15 p.m., 700 Clark Hall
"Magnetic Quantum Tunneling in Single Molecule Magnets"
Abstract: Single molecule magnets (SMMs) are magnetic nanostructures that consist of a core of strongly exchange-coupled transition metal ions with a large collective magnetic moment per molecule, thus far up to 26 Bohr magnetons, and a predominantly uniaxial magnetic anisotropy. Their molecular nature enables experimental studies of nearly monodisperse ensembles of nanomagnets with well-defined size, shape, chemical composition, and magnetic anisotropy. This talk will present experiments that address the origin of magnetic quantum tunneling (MQT) in the prototype SMM Mn 12 -acetate and, in particular, the nature of the transverse interactions that produce quantum tunneling. Recent experiments that employ microwave fields to modulate MQT and characterize quantum superpositions states of "up" and "down" spin-projections will also be described.
Prof. Andrew Kent
Department of Physics
New York UniversityThursday, March 04, 2004
12:15 p.m., 700 Clark Hall
"Current-induced transverse spin wave instability in a thin nanomagnet "
Abstract:It has been experimentally verified that a spin polarized electric current incident on a thin ferromagnet can change the orientation of the magnetization via a mechanism known as "spin transfer". We show that an unpolarized electric current incident on a thin ferromagnet can excite a spin-wave instability transverse to the current direction if source and drain contacts are not symmetric, although it can not change the over-all magnetization direction.
Prof. Piet Brouwer
Physics
Cornell UniversityThursday, February 19, 2004
12:15 p.m., 700 Clark Hall
" Optics on the Nanometer Scale "
Abstract: Nano-optics is motivated by the rapid advance of nanoscience and nanotechnology. It aims at exploring optical phenomena and techniques beyond the diffraction limit of light. Among the applications are high-resolution microscopy and spectroscopy, nanolithography, and nanomanipulation. In this seminar I will discuss the main ideas behind nano-optics and I will give an overview of topics pursued in the nano-optics group at the University of Rochester.
(a) Confocal and (b) near-field Raman scattering images of the same area of a carbon nanotubesample acquired at 2615 cm^-1 (G'-band). Near-field Raman imaging increases spatialresolution by a factor 10-20.
(c) Raman scattering spectrum recorded on an individual single-walled carbon nanotube. The spectrum uniquely identifies the chemical nature of the sample.
Prof. Lukas Novotny
The Insitute of Optics
University of RochesterThursday, February 5, 2004
12:15 p.m., 700 Clark Hall
The Nano-Optics Home Page
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CNS Seminar Series, Fall 2003
" The Structure
and Growth of Single-
and Double-Walled Carbon Nanotubes "
Abstract: Single- and double-walled carbon nanotubes have potential applications for future electronics and nanomachines. However, as-grown carbon nanotubes have a dispersion of structures, which differ in both diameter and chirality, and electric and mechanical properties. Characterization of these nanotubes has been a challenge. Recently, we developed a coherent electron diffraction/imaging technique by forming a nanometer-sized parallel beam of electrons that can be used to record diffraction patterns from individual nanotubes. Furthermore, the combination of coherence and high angular resolution allows the over-sampling of diffraction pattern and solution of phase problem by ab-initio phase retrieval, thus, imaging of carbon nanotubes (Ref 1) . Using this technique, we have investigated a large number of single- and double-walled carbon nanotubes. We found that neither zig-zag nor arm-chair tubes is preferred for growth. Double-walled carbon nanotubes are generally incommensurate and there is a peaked distribution of spacings between two tubes. The implication of these findings will be discussed based on the growth mechanism of carbon nanotubes. The technique of coherent electron nanodiffraction and diffractive imaging by the solution of the phase problem is general and applicable to other nanostructures.
Prof. Jian-Min (Jim) Zuo*
F. Seitz Materials Research Laboratory
University of Illinois , Urbana-Champaign
Thursday,
December 4, 2003
12:15 p.m., 700 Clark Hall
*In
collaboration with J. Tao, J. Bording, Boquan Li, M. Gao,
R.Twesten
and I. Petrov
Ref 1. See, e.g., J.M. Zuo, I. Vartanyants, M. Gao, R. Zhang and L.A. Nagahara, "Atomic Resolution Imaging of A Single Double-Wall Carbon Nanotube From Diffraction Intensities," Science, 300, 1419-1421 (2003).
"Soft Materials and Nanopatterning Techniques for Electronics"
Abstract: Organic materials have a strong potential to play important roles in future electronic and photonic systems. Additive printing and lamination techniques can be used directly with these classes of soft materials to build unusual devices with dimensions deep into the sub-micron regime. This talk describes the operational aspects of transistors and light emitting diodes that are fabricated with these techniques using small molecule organics, polymers and carbon nanotubes as the active components. it provides examples of working prototypes, such as flexible paperlike displays, that demonstrate some promising applications.
Dr. John Rogers
Department of Materials Science and Engineering
University of Illinois at UrbanaThursday, November 20, 2003
12:15 p.m., 700 Clark Hall
" Exploring surfaces and cavities in nanotubulites with a sub-nm electron beam "
Abstract: Since their discovery by Iijima, the specific morphology of nanotubes with an empty cylindrical core space and the presence of large surface areas on both outer and inner sides of the walls, has captured the interest of many researchers who have demonstrated quite diversified types of fillings with gases, molecules or solid compounds. In particular, new families of nano-objects have been identified, such as nanowires, nanocontainers, peapods. They offer strong potentialities for exhibiting novel properties and for developing new applications as transport components, storage devices or reaction chambers. On the other hand, the combination of intense electron probes of near-atomic dimension (in a STEM microscope) with highly efficient 2D detectors for recording electron energy-loss spectra (EELS) within a few milliseconds, has provided quite powerful tools to explore individual nanostructures with unprecedented spatial (sub-nm) and energy (sub-eV) resolutions. In particular, following the demonstration of the identification of single atoms encaged in fullerene molecules along peapods structures , we have further used this technique for analyzing the presence of trapped molecules within SWNTs or for detecting the presence of thin layers, acting as potential wetting agents, at the interfaces between the encapsulating nanotube and its filling. Beyond performing sub-nm elemental analysis on such hybrid nano-objects, the EELS technique has also been used to locally investigate their electronic states and dynamics. We can either measure the unoccupied density of states accessible through the EELS fine structures observed on core edges or the collective behavior of the electron population deduced from the bulk and surface plasmon modes of excitation, investigated with the primary electron probe in an intersecting or a grazing incidence. New examples related to the exploration of clean or activated surfaces will be presented.
Prof. Christian Colliex
Universite Paris Sud
Monday,
November 17, 2003
3 :30 p.m., 700 Clark Hall
"Gaining Control in the Synthesis of Single Walled Carbon Nanotubes"
Dr. L . Liu
Department of Chemistry
Duke
University
Thursday,
October 23
12:15 p.m., 700 Clark Hall
"Imaging the atomic-scale chemistry and electronic structure inside nanodevices"
Prof. David Muller
Applied and Engineering Physics
Cornell University
Thursday,
October 9
12:15 p.m., 700 Clark Hall
"Taking nuclear magnetic resonance to the nanoscale using cantilevers"
Prof. John Marohn
Department of Chemistry and Chemical Biology
Cornell University
Thursday,
September 25
12:15 p.m. , 700 Clark Hall
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CNS Seminar Series, Spring 2003
"Localized Charge Properties of Individual Semiconductor Quantum Rods"
Dr. Todd Krauss
University of RochesterThursday, May 1
12:15 PM, Clark Hall 700
"Magnetic Memory, Spintronics, and Magnetic Nanostructures"
Dr. Jonathan Sun
IBM
T. J. Watson Research Center, Yorktown Heights, NYThursday, April 17
12:15 PM, Clark Hall 700
"Metal Nanocrystal Nonvolatile Memories"
Prof. Edwin Kan
Electrical and Computing Engineeering
Cornell UniversityThursday, March 27
12:15 PM, Clark Hall 700
Back to the Top"30 nm Channel Length Pentacene Transistors"
Prof. George Malliaras
Materials Science & Engineeering
Cornell UniversityThursday, March 13, 2003
12:15 PM, Clark Hall 700
