Events Calendar View

• Departmental Colloquium Feb 7, 2012

  Organic Spintronics

  

  Guest: DR. THO NGUYEN, University of Utah
  Tuesday, February 7, 2012 4:00 pm - 5:00 pm
  Location: 202

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  Organic semiconductors (OS) have been used as active layers in devices such as organic light-emitting diodes (OLEDs), photovoltaic cells, field-effect transistors, and lasers.  Recently there has been a growing interest in spin and magnetic field effects in these materials. These include optically detected magnetic resonance where long spin coherence time was demonstrated; OLEDs where both conductivity and electroluminescence have been strongly modulated by an external magnetic field; and organic spin valves (OSV) where spin injection from ferromagnetic (FM) electrodes and spin transport in OS were obtained. The interest in spin transport in OS has been motivated by the weak spin-orbit interaction that is caused by the light building block elements such as carbon and hydrogen, and the small hyperfine interaction (HFI) with the nuclei.

  In this talk the status of the young field of ‘Organic Spintronics’ will be reviewed. The necessary ingredients needed for the success of this field will be summarized, and evaluated by recent experiments. In particular the role of the HFI in magneto-transport will be elucidated via the isotope effect. Two applications of Organic Spintronics will be discussed: organic diodes with two FM electrodes for use as OSV; and organic diodes with no FM electrodes for use as magnetic sensors.

   

• CSP Lunch Seminar Feb 14, 2012

  Universality of the order parameter probability distribution function: symmetric and asymmetric cases: Ising and Blume-Capel model as examples

  

  Guest: Joao Plascak, Universidade Federal de Minas Gerais
  Tuesday, February 14, 2012 12:30 pm - 1:30 pm
  Location: CSP Conference Room (322)

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• Departmental Colloquium Feb 14, 2012

  Noble Metal Materials at the Nanoscale: A Golden Key to Addressing Challenges in Solar Energy Conversion and Nanomedicine Development

  

  Guest: Wei Qian, IMRA America, Inc.
  Tuesday, February 14, 2012 4:00 pm - 5:00 pm
  Location: 202

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  In this talk, I will present two of research projects I have conducted, which shed some light on important roles of noble metal nanoparticles, such as gold and silver, in providing revolutionary solutions to intractable issues in a variety of areas from clean energy supply to disease control and prevention. In the first part of my talk, I will start with a brief discussion of ultrafast nonadiabatic electronic movements at conical intersection in silicon naphthalocyanine (SiNc) chromophores freely diffusing in solution studied at both low chromophore concentration (10 uM) and low pulse fluence (100 pJ) by using femtosecond polarized laser spectroscopy.  As one of naphthalocyanine derivatives, SiNc chromophore has gained interest from the scientific community because it has a similar chemical structure to biologically important porphyrins, such as chlorophyll, that play a vital role in photosynthesis. Then, I will move further to a study of chromophore confined in protein, which provides a unique and highly optimized environment for the photoinduced processes in chromophore. In our case, it is retinal enclosed inside pocket of Bacteriorhodopsin (bR). bR, biological solar cell for Halobacteria, is a paradigmatic system of transmembrane protein that functions as a light-driven vectorial proton pump. Following sub-picosecond photoisomerization of its retinal chromophore, bR visits a series of intermediates with different lifetimes ranging from femtosecond to millisecond and finally pumps a proton across a membrane. The photocycle of bR after absorbing a single photon in visible is among the most striking and beautiful phenomena in nature. I will discuss some experiments I did that showed how to manipulate the bR photocycle process by plasmonic field of a nearby metal nanoparticle. In the second part of my talk, I will first report a new instrument we have designed for live cell imaging via the detection of scattered light from metal nanoparticles. This new instrument is free of photobleaching and blinking problems suffered by fluorescence microscopy and  enables us to carry out continuous and intermittence-free light scattering imaging of live cell over 30 hours. Then,  I will demonstrate how advance in technique and instrumentation allow us to directly track the full cycle of cancer cells from birth to division and to investigate possible mechanism for cytokinesis arrested in cancer cells caused by nucleus-targeting gold nanoparticles.

• Departmental Colloquium Feb 16, 2012

  Coherent Optical Control of Rydberg States in Silicon

  

  Guest: Vinh Q. Nguyen, Department of Physics/Institute for Terahertz Science and Technology, University of California at Santa Barbara
  Thursday, February 16, 2012 4:00 pm - 5:00 pm
  Location: 202

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  One of the great successes of quantum physics is the description of the long-lived Rydberg
  states of atoms and ions. Of particular interest, because they can be employed in quantum control of one atom by another, are excited Rydberg states, where wavefunctions are expanded from their ground-state extents of less than 0.1 nm to several nanometers and even beyond; this allows atoms far enough apart to be non-interacting in their ground states to strongly interact in their excited states. For eventual application of such states, a solid-state implementation is very desirable. I demonstrate here the coherent optical control of impurity wavefunctions in the most ubiquitous donors and acceptors in silicon. In our experiments, I take advantage of a terahertz radiation from a free-electron laser to stimulate and observe population lifetimes, photon echoes for coherent lifetimes - the orbital analogue of the Hahn spin echo, and Rabi oscillations familiar from magnetic
  resonance spectroscopy. As well as extending atomic physicists’ explorations of quantum
  phenomena to the solid state, the work adds coherent terahertz radiation, as a particularly precise regulator of orbitals in solids, to the list of controls, such as pressure and chemical composition, already familiar to materials scientists.
  [1]. N. Q. Vinh, et al., P. Natl. Acad. Sci. USA 105, 10649 (2008)
  [2]. P. T. Greenland, et al., Nature 465, 1057 (2010).

• Departmental Colloquium Feb 23, 2012

  Coated Nanoparticles in Solution and at Interfaces

  

  Guest: Dr. Gary S. Grest, Sandia National Laboratories
  Thursday, February 23, 2012 4:00 pm - 5:00 pm
  Location: Physics 202

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  Among the most prevalent ways to control the assembly and integration of nanoparticles is to coat them with organic molecules whose specific functionalized groups modifies their inter particle interactions as well as the interaction of nanoparticles with their surrounding, while retaining their inherent properties. While it is often assumed that uniformly coating spherical nanoparticles with short organic will lead to symmetric nanoparticles, I will show using explicit-atom molecular dynamics simulations of model nanoparticles that the high curvature of small nanoparticle and the relatively short dimensions of the coating can produce highly asymmetric coating arrangements. In solution geometric properties dictate when a coating’s spherical symmetry will be unstable and that the chain end group and the solvent play a secondary role in determining the properties of surface patterns. At the water-vapor interface the anisotropic nanoparticle coatings seen in bulk solvents are reinforced by interactions at the interface. The coatings are significantly distorted and oriented by the surface and depend strongly on the amount of free volume provided by the geometry, end group, and solvent properties. At an interface any inhomogeneity or asymmetry tends to orient with the surface so as to minimize free energy. These asymmetric and oriented coatings are expected to have a dramatic effect on the interactions between nanoparticles and can influence the structures of aggregated nanoparticles which self-assemble in the bulk and at surfaces

• NanoSEC Seminar Feb 24, 2012

  Rational Engineering of Nanowire Crystal Structure and Superstructure

  

  Guest: Professor Michael A. Filler, School of Chemical & Biomolecular Engineering, Georgia Institute of Technology
  Friday, February 24, 2012 4:00 pm - 5:00 pm
  Location: Riverbend Research South Laboratory Auditorium

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  Semiconductor nanowires promise exciting advances in fields as diverse as optoelectronics, photonics, quantum computing, and energy harvesting. The physical properties of these materials, and nanostructures in general, are intimately connected to their structure, which must be controlled with atomic-level precision. This remains a challenging task in many systems and stems from an inadequate chemical understanding of common synthetic routes. This presentation will provide an overview of our recent efforts to bridge this knowledge gap. In particular, realtime in-situ infrared spectroscopy measurements coupled with post-growth electron microscopy demonstrate the important, and as of yet unrecognized, role of transient surface chemistry during vapor-liquid-solid nanowire growth. Our findings indicate that covalently bonded hydrogen atoms are directly responsible for the planar defects (e.g. twinning boundaries) and growth direction transitions (e.g. <111> vs. <112>) that are frequently observed for Si nanowires. We subsequently leverage this fundamental knowledge to create complex semiconductor superstructures via temporal modulation of growth chemistry. For example, the use of “molecular masks,” which either allow or prevent conformal epitaxy, enables the fabrication of diameter-modulated nanowires with user-defined periodicity. These and other newly developed synthetic strategies open a number of new avenues to rationally engineer the crystal structure and properties of nanoscale semiconductors.

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