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.
Events: Departmental Colloquia
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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 -
Organic Spintronics
Guest: DR. THO NGUYEN, University of Utah
Tuesday, February 7, 2012 4:00 pm - 5:00 pm
Location: 202Organic 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.
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Hybrid nanomaterials and new designs for energy storage applications
Guest: Dr. Leela Mohana Reddy Arava, Rice University Department of Mechanical Engineering and Materials Science
Thursday, February 2, 2012 4:00 pm - 5:00 pm
Location: 202In response to the needs of modern society and emerging ecological concerns, it is now essential to provide efficient, low-cost, and environmentally friendly electrochemical energy conversion and storage devices. These electrochemical devices are expected to have pronounced technological impact on the society - especially for powering an increasingly diverse range of portable electronic and vehicular applications. Rechargeable Lithium-ion batteries and Supercapacitors are amongst the most promising candidates in terms of their wide spread applicability, owing to their high energy and power densities. The performance of these devices depends intimately on the properties of materials used to build them. This talk will focus on the new designs and performance of the next generation of energy and power delivery devices by the use of tailored nanostructured materials and by nanoscale engineering. Some of the current challenges pertaining to the energy storage technology and the effective utilization of new electrode materials such as Si nanostructures and graphene will be discussed. Furthermore, the talk will also evaluate approaches for optimization of the Li-ion battery performance with novel designs, leading to prototype nanoscale 3D battery architectures offering improvements in energy and power density with respect to the geometrical foot print of devices.
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Loschmidt, Boltzmann and the Second Law
Guest: Prof. Richard J. Creswick, Department of Physics and Astronomy, University of South Carolina
Thursday, January 26, 2012 4:00 pm - 5:00 pm
Location: Physics 202Since the last quarter of the 19th century, the status of the second law of thermodynamics has been fiercely debated. Boltzmann saw the 2nd law as a consequence of the complexity of molecular motions. Loschmidt argued that irreversibility cannot be derived from a fundamentally time-reversible dynamic principle. In this talk I will describe a special class of dynamical systems for which the "Loschmidt Echo" can be observed and what such observations tell us about irreversibility and the arrow of time
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The Interaction of the Solar (and Stellar) Winds with the Interstellar Medium
Guest: Prof. Gary Zank , Center for Space Plasma and Aeronomic Research, and Department of Physics, University of Alabama in Huntsville
Thursday, January 19, 2012 4:00 pm - 5:00 pm
Location: Physics 202The interaction of the solar wind with the interstellar medium is complicated by the presence of a substantial neutral component, interstellar hydrogen. The self-consistent inclusion of neutral hydrogen (and other heavier atoms) requires that models include the effects of charge exchange and scattering properly. With the crossing of the heliospheric termination shock by the Voyager 1 and 2 spacecraft, understanding the outer heliosphere and the heliospheric boundaries has become a topic of great interest. IBEX is now returning observations of Energetic Neutral Atoms (ENAs) created in the solar wind – interstellar medium boundary regions, and these are providing both new insights and new challenges to our understanding of the physics in this complex region. We will describe the status of modeling the solar wind-local interstellar medium interaction, its relationship to Voyager 1 and 2 and IBEX and other remote observations, and the implications for the interaction of stellar winds with their local interstellar environments. The discovery of the hydrogen wall around our heliosphere and other “astrospheres” will be discussed.
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Chaos and 3-cycle: Tales from UGA Physics
Guest: Prof. M. Howard Lee , UIGA Department of Physics
Thursday, January 12, 2012 4:00 pm - 5:00 pm
Location: Physics 202The progress on chaos made at UGA was not by design, but by some happenstance in circumstances, tales of which will be woven into this talk. The technical details are as follows:
The clearest definition of chaos is given by Sharkovskii's theorem, which says that the existence of a 3-cycle in a chaotic map implies chaos. Thus showing a 3-cycle exists is of deepest interest. For the logistic map I have solved the 3-cycle problem[1,2]. At the fully developed chaos I have also proved that the trajectories are ergodic as well by a concept from measure theory. The same conclusion is reached by my ergometric theory[3].
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1. M H Lee, J Math Phys 50, 1227 (2009).
2. M H Lee, Acta Phys Pol B 42, 1071 (2011).
3. M H Lee, Phys Rev Lett 87, 250601 (2001).
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Black Holes and Gravitational Waves: The Quest to Verify Einstein's Predictions
Guest: Dr. Deirdre Shoemaker, Georgia Tech, School of Physics
Thursday, December 1, 2011 4:00 pm - 5:00 pm
Location:Einstein's theory of General Relativity predicts a Cosmos with black holes and gravitational waves. Although neither black holes nor gravitational waves have been directly detected, their presence is already felt throughout the Universe. This decade will witness observations for which gravitational waves are the messengers that deliver information in exquisite detail about astrophysical phenomena, among them the collision of two black holes, a system completely invisible to the eyes of traditional telescopes. In support of this new gravitational wave astronomy, modeling what to expect is crucial for the success of this endeavor. Modeling sources of gravitational radiation requires solving the Eintein equations of General Relativity using the most powerful computer hardware and most sophisticated numerical algorithms. In this talk I will review these challenges, how we have overcome them, and what we have learned along the way. Our predictions of the gravitational waves from the black holes collisions is one crucial step in ushering in the new era of gravitational-wave astronomy.
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Antihydrogen Trapped
Guest: Dr. Francis Robicheaux, Auburn University, Department of Physics
Thursday, November 17, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202Atoms made of a particle and an antiparticle are unstable, usually surviving less than a microsecond. Antihydrogen, the bound state of an antiproton and a positron, is made entirely of antiparticles and is believed to be stable. It is this longevity that holds the promise of precision studies of matter-antimatter symmetry. Low energy (Kelvin scale) antihydrogen has been produced at CERN since 2002. I will describe the experiment which has recently succeeded in trapping antihydrogen in a cryogenic Penning trap for times up to approximately 15 minutes.
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TBA
Guest: Dr. Matteo Mariantoni, University of California, Santa Barbara, Department of Physics
Thursday, November 10, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202 -
TBA - (Kirkpatrick Award Colloquium)
Guest: Dr. John Gibbs, Max Planck Institute
Thursday, November 3, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202 -
Strands of Superconductivity at the Nanoscale
Guest: Dr. Paul Goldbart, Georgia Tech, School of Physics
Thursday, October 20, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202Superconducting circuitry can now be fabricated at the nanoscale, e.g., by depositing suitable materials on to single molecules, such as DNA or carbon nanotubes. I shall discuss various themes that arise when superconductivity is explored in this new regime, including the thermal passage over and quantum tunneling through barriers by the superconducting condensate as a whole, as well as a strange, hormetic effect that magnetism can have on nanoscale superconductors. I shall describe nanoscale superconducting quantum interference devices, which are subtly sensitivity to magnetic fields and patterns of supercurrent -- features that hint at uses of superconducting nanocircuitry, e.g., in mapping quantum phase fields and testing for superconducting correlations in novel materials. I shall also mention settings in which superconducting nanosamples show a particular sensitivity to their geometry or topology, and shall conclude by touching on two emerging themes: the interplay between graphene and superconductivity, and what nanoprobes might be revealing about exotic forms of superconductivity.
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Driving to Contact: Single Molecular Electronics and Biophysics
Guest: Dr. Bingqian Xu, UGA Engineering
Thursday, October 13, 2011 4:00 pm - 5:00 pm
Location: Auditorium 202Single molecule study, where science and engineering met, applies the tools and measurement techniques of nanoscale physics and chemistry to generate remarkable new insights into how physical, chemical, and biological systems function. It permits direct observation of molecular behavior that can be obscured by ensemble averaging and enables the study of important problems ranging from the fundamental physics of electronic transport in single molecule junctions and biophysics of single molecule interactions, such as the energetics and non-equilibrium transport mechanisms in single molecule junctions and the energy landscape of biomolecular reactions, associated lifetimes, and free energy, to the study and design of single molecules as devices-molecular wires, rectifiers and transistors and high‐affinity, anti‐cancer drugs.
We will describe our pioneered highly integrated SPM-based approaches to (1) simultaneously fabricate, control, modulate, and monitor the electronic and mechanical properties of molecular junction devices at the single-molecule level. (2) Probe the biophysical mechanism of single‐molecule interactions, including the binding affinity and specificity. Our recent research examples will be used in the discussions.
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M Dwarf Variability: A Barrier to Detecting Rocky Planets?
Guest: Dr. Angelle Tanner, Mississippi State University, Department of Physics and Astronomy
Thursday, October 6, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202We are on the verge of potentially the most significant scientific discovery of the past century. The detection of a habitable planet around a star in our solar neighborhood. Currently, infrared radial velocity surveys with precisions of 5-10 m/s are marginally sensitive to Earth-mass planets in the habitable zone of late-M dwarfs (RV signatures of > 5 m/s for an Earth around an M9 star).Indeed, M dwarfs are the primary focus of multiple up-coming infrared RV observing programs with new instruments (ESPRESSO on the VLT) and instrument upgrades (NIRSPEC on Keck and CSHELL on the IRTF). However, if our goal is to detect Earth-mass planets in the habitable zone of a solar-type star (an RV signature of 0.1 m/s for a solar-type star), then it will be advantageous for us to determine the intrinsic jitter inherent to each star in order to better design these observationally intensive observing programs. Optical RV planet search programs have shown that, while in many cases stars with indicators of high photospheric activity also have large RV jitter and there are hints that such activity is correlated with stellar spectral type, the known activity indicators do not always predict the degree of jitter for every star. Here we summarize the need for observing programs to focus on the jitter properties of the nearest stars M dwarfs which are prone to large starspot populations and flares. Future ground-based, milli-mag photometry and star spot modeling as well as the statistical results from the Kepler, MOST and Corot missions will provide starspot rotation periods (a few days to weeks) which are directly related to the RV jitter. The results of this study will be used to infer limits to Earth-mass planet detections around solar-type stars an issue which has not been thoroughly addressed observationally despite the critical limit of a precision of 0.1 m/s needed to detect them in the habitable zone.
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Photoprotection in biomolecules following UV absorption
Guest: Dr. Vasilios Stavros, University of Warwick, Department of Chemistry
Thursday, September 29, 2011 4:00 pm - 5:00 pm
Location:Through evolution, molecular function has been finely tuned, such that even the most complex of chemical processes occurring in humans takes place with exceptional efficiency. To understand why nature has chosen a particular set of molecular building blocks, a surge in gas-phase experiments has recently targeted the resistance to photochemical damage (photoprotection) of key DNA bases, amino acids and their corresponding subunits. This has, in turn, provided insight into their properties. The talk gives an overview of our group's efforts to unravel some of the photoprotection mechanisms of heteroaromatic biomolecules following UV absorption using time-resolved spectroscopy. It also discusses our group's latest endeavors at extending these measurements to the condensed phase.
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New Insights into the Influence of Nano-Structure on Exciton Dynamics
Guest: Dr. Ken Knappenberger, Florida State University
Thursday, September 22, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202Shape- and crystal structure-dependent exciton dynamics of semiconducting nanoparticles were investigated using time- and polarization-resolved magneto-photoluminescence spectroscopy. Experiments were performed at low temperature (<2 K) in magnetic fields up to 17.5 T to investigate spin-dependent radiative relaxation in CdSe quantum dots and nanorods. In contrast to 0-D quantum dots, one-dimensional CdSe nanorods displayed a high degree of spin polarization even at relatively low magnetic field strengths (2 T). The observed spin polarization, evident in intensity-integrated and wavelength-resolved photoluminescence and time-correlated single-photon counting measurements, resulted from spin-polarized excitons that were formed upon highly efficient mixing of “dark” and “bright” fine-structure states. The relative population of these fine-structures was dependent upon the strength of the applied magnetic field. These results demonstrate the potential use of particle shape and crystal structure, two key nanostructure design parameters, to control photoinduced nanoscale dynamics. The findings may impact significantly technologies such as solar-to-electric energy conversion, spintronics, and chemical lasers, which all employ the nanocrystal platform.
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Making the Milky Way -- A Continuing Saga
Guest: Dr. Jay Lockman, National Radio Astronomy Observatory, Green Bank
Thursday, September 15, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202This talk will be in two parts. First I will describe the Green Bank Telescope, a 100-meter diameter radio telescope that is one of the largest moving objects on land, and, owing to recent upgrades, is now our largest mm-wave radio telescope. I'll discuss its unusual origin, its capabilities, and topics from some of its recent scientific programs including the search for gravitational radiation, Mercury's molten core, interstellar anions, and the growth and evolution of galaxies.
The second part of the talk will continue the topic of growth and evolution of galaxies, with a focus on the Milky Way. Several lines of evidence indicate that our Galaxy must have been accreting low metallicity gas at the rate of about 1 solar mass per year for a substantial portion of its life, but the details of this process are unclear as is the origin of the fresh material. Observations in the 21cm Hydrogen line have recently found a dramatic example of this process in action in the form of a cloud with more than a million solar masses of gas on a trajectory to intersect the Milky Way disk in a few tens of million years. I will discuss this object and the information it gives us on evolution of the Galaxy, the structure of the gaseous halo,and its possible relationship to dark matter halos.
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Higgs and top quark physics in high-energy colliders
Guest: Dr. Nikoloas Kidonakis, Kennesaw State University, Department of Biology and Physics
Thursday, September 8, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202I present a brief overview of the Standard Model of particle physics, its theoretical underpinnings in Quantum Field Theory, and its experimental verification in high-energy colliders. I discuss two major aspects of current particle physics research: the search for the Higgs boson and the study of the top quark.
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Graphene: Synthesis, Raman and UV-Vis Spectroscopy
Guest: Dr. Apparao M. Rao, Clemson University, Department of Physics
Thursday, August 25, 2011 4:00 pm - 5:00 pm
Location: Auditorium, Physics 202A single sheet of sp2-hybridized carbon atoms, called graphene, is presently the most widely studied material in the scientific community. Following a brief introduction of graphene and its unique properties, I will present two popular methods for preparing graphene for spectroscopic studies. In carbon science, spectroscopy has played a dominant role in unraveling several fundamental properties of nanostructured carbons like fullerenes and carbon nanotubes. Drawing from these spectroscopic studies, the effective roles of Raman and UV-vis spectroscopy in elucidating the vibration and electronic properties of graphene will be discussed.
This work was done jointly by R. Podila (Clemson University), R. Rao (Wright-Patterson Air Force Base), and Masa Ishigami (University of Central Florida).
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Cummings Day
Thursday, April 21, 2011 3:00 pm
Location: -
Quantum Computation: A Computational Perspective
Guest: Dr. Rod Canfield, University of Georgia, Department of Computer Science
Thursday, April 14, 2011 4:00 pm - 5:00 pm
Location: Physics 202In recent years, computer scientists and physicists have begun to investigate the possibility of a computer whose hardware utilizes quantum phenomena, such as superposition and entanglement. There has developed a notion of a quantum algorithm, and examples are known of computational problems whose solution can be carried out in significantly less time by a quantum algorithm than by the currently best known traditional algorithm. The lecture has the goal of giving the audience a succinct and meaningful definition of a quantum computer, some appreciation of what all the fuss is about, and the capability of interpreting future developments.
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Testing the Limits of Complex Organic Chemistry in the Interstellar Medium
Guest: Dr. Susanna Widicus-Weaver, Emory University, Department of Chemistry
Thursday, April 7, 2011 4:00 pm - 5:00 pm
Location: Physics 202Fundamental biological molecules such as amino acids and sugars have been discovered in meteorites, but none of these species have yet been definitively detected in the interstellar medium (ISM). While both the number of detected interstellar molecules and their chemical complexity continue to increase, understanding of the processes leading to their formation is lacking. Recent chemical models suggest that organic radicals formed during the photolysis of interstellar ices provide the building blocks for the larger organic molecules found in star-forming regions. In order to investigate these interstellar prebiotic chemical pathways, we are developing a terahertz (THz) cavity ringdown spectrometer to study the unstable, reactive molecules that are key reaction intermediates. In this talk, I will present the initial results of the instrument development and spectroscopic studies. I will also outline our future plans for this instrument and the link to our ongoing projects in observational astronomy and astrochemical modeling.
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Novel Photorefractive Materials for Beam Coupling Applications
Guest: Dr. Dean R. Evans, Air Force Research Laboratory
Thursday, March 31, 2011 4:00 pm - 5:00 pm
Location: Physics 202This presentation will be centered around the photorefractive effect, particularly, photorefractive beam coupling. Over the years, we have improved beam coupling in various geometries using novel photorefractive materials. Both inorganic and hybrid (organic-inorganic) photorefractive materials will be discussed, as well as the methods of improving these novel materials to give more efficient beam coupling. Techniques to increase the space charge field and the optical gain will be explored for inorganic systems; the enhancement of the beam coupling gain in liquid crystal photorefractive hybrids through the use of ferroelectric nanoparticles will also be explored, with an emphasis on the production and characterization of 9 nm ferroelectric nanoparticle – a size that has never been achieved in the past.
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Connecting Star Formation, Galaxy Evolution and the X-ray Background
Guest: Dr. David Ballantyne, Georgia Institute of Technology, School of Physics
Thursday, March 24, 2011 4:00 pm - 5:00 pm
Location: Physics 202As we now know, the growth of galaxies and their central black holes is connected through some unknown mechanism. The cosmic X-ray background encodes within it the entire history of accretion onto supermassive massive black holes and so provides an unique view of the role of AGN in the assembly of galaxies. This talk presents results of recent work that is attempting to exploit the information contained in the X-ray background (and ancillary multiwavelength studies) to construct a testable scenario for the evolution of AGN and their host galaxies.
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Spring Break
Thursday, March 17, 2011 4:00 pm
Location: -
New Insights on Jet Physics
Guest: Dr. Eric Perlman, Physics and Space Sciences Department, Florida Institute of Technology
Thursday, March 10, 2011 4:00 pm - Thursday, March 17 5:00 pm
Location: Physics 202Jets are one of the classic manifestations of the active galactic nucleus (AGN) phenomenon, with the first example having been discovered in 1918: what Heber Curtis described as a "curious straight ray" in the galaxy M87. Today we know that jets are high-energy streams of matter and energy that emerge from the nuclear regions at relativistic speeds and have emissions that are seen from the radio through the gamma-rays. The flows carry with them immense kinetic energy, comparable to the luminosity of the AGN itself, and are now understood to be a transformative force that feeds back into the evolution of the surrounding galaxy and cluster. In this talk, I will concentrate on the physics of jets. I will begin with a review of the field, focusing on structural elements, variability, and the production of high energy radiation. I will then turn to the open questions, emphasizing the unique information that can be revealed by polarimetry. I will then talk about HST polarimetry and Chandra X-ray observations of nearby jets, where we are learning new information about the jet structure and the role of magnetic fields in particle acceleration. Of particular interest will be the M87 jet, where thanks to its proximity, we have been successful in for the first time isolating a violently variable region within the jet. This gives us powerful insight into the physical processes that surround its variability and response to stimuli.
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