Because of their direct bandgaps and atomic-scale thickness, monolayer transition metal dichalcogenides have emerged as appealing materials for both classical and quantum optoelectronics. These 2D semiconducting materials, such as MoS2 and its related compounds, can support diverse non-trivial optical phenomena such as valley-selective exciton-polaritons and quantum emission from localized excitonic defects. Harnessing these interesting features for applications requires controlled tuning and manipulation to tailor the optical phenomena. Here, I will discuss examples of manipulating the optical and electronic environment of transition metal dichalcogenides that take advantage of the unique properties of these layered materials. Direct control over light-matter coupling is demonstrated through microcavity engineering in photonic devices. Quantum light sources are integrated into 2D optoelectronics for electrically pumped emission. I also show how coating with highly-customizable organic molecules leverages the exposed 2D surface of these materials for control of optical phenomena. The ability to influence optical response and defect emission using configurable organic molecules highlights the potential for optoelectronic engineering in low-dimensional heterostructures.
Events: Applied Physics Seminars
-
Engineering Excitons, Polaritons, and Defects for 2D Semiconductor Optoelectronics
Guest: Prof. Nathaniel P. Stern, Department of Physics and Astronomy, Northwestern University
Friday, November 22, 2019 12:20 pm - 1:20 pm
Location: CSP Conference Room (322) -
The molecular mechanism of influenza virus inactivation by hypothiocyanite
Guest: Professor Balazs Rada, Department of Infectious Diseases, UGA
Friday, April 26, 2019 12:30 pm - 1:30 pm
Location: CSP Conference Room (322)Respiratory viral infections are the most common illnesses worldwide affecting people today. One of them is influenza virus (IV) that causes ongoing epidemics with high morbidity and variable mortality. The ability of IV to rapidly change allowed it to stay ahead of vaccination efforts. Novel therapeutic approaches are needed to fight influenza. We have previously described an extracellular oxidative antimicrobial mechanism utilized by the respiratory innate immune system to inactivate IV. The lactoperoxidase/thiocyanate system produces reactive oxygen species, mainly hypothiocyanite anions, that have strong antiviral properties against IV in vitro. Our main focus is to reveal the molecular mechanism by which hypothiocyanite inactivates influenza viruses and whether it also prevents in vivo infections. Our data shows that hypothiocyanite is able to inactivate several IV strains including A and B strains and those resistant to current antiviral ostetamivir therapies. This data was also backed up by neuraminidase activity assays showing no reduction in viral NA activity when exposed to hypothiocyanite. Additionally, pre/co-incubation of IV with hypothiocyanite prevents infection of a variety of host epithelial cells by the virus. The ability of IV to bind to target cells is also strongly reduced when exposed to hypothiocyanite. These results suggest that hypothiocyanite primarily targets the surface hemagglutinin molecules of IV to prevent viral binding to and infection of target cells. This hypothesis represents a novel mechanism of viral inactivation utilized by the immune system.
-
Magnetic Resonance Imaging, Iron, and Machine Learning:from brain connectivity to stem cell tracking
Guest: Prof. Qun Zhao, Department of Physics & Astronomy, University of Georgia
Friday, April 12, 2019 12:00 pm - 1:00 pm
Location: CSP Conference Room (322)Iron is an essential trace element involved in a variety of biological mechanisms, such as oxygen transport, protein synthesis, and mitochondria respiration, in a living human or animal body. As a contrast agent, iron greatly improves MRI sensitivity in detecting iron-related biological process, including imaging of brain connectivity and tracking of stem cells. To improve mapping of brain connectivity, novel machine learning techniques are used to further enhance neuroimaging sensitivity.
-
Over 100-THz bandwidth selective difference frequency generation at LaAlO<sub>3</sub>/SrTiO<sub>3</sub> nanojunctions
Guest: Prof. Jeremy Levy, Department of Physics and Astronomy, University of Pittsburgh. Pittsburgh Quantum Institute
Friday, April 5, 2019 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)The ability to combine continuously tunable narrow-band terahertz (THz) generation that can access both the far-infrared and mid-infrared regimes with nanometer-scale spatial resolution is highly promising for identifying underlying light-matter interactions and realizing selective control of rotational or vibrational resonances in nanoparticles or molecules. Here, we report selective difference frequency generation with over 100 THz bandwidth via femtosecond optical pulse shaping. The THz emission is generated at nanoscale junctions at the interface of LaAlO3/SrTiO3 (LAO/STO) that is defined by conductive atomic force microscope lithography, with the potential to perform THz spectroscopy on individual nanoparticles or molecules. Numerical simulation of the time-domain signal facilitates the identification of components that contribute to the THz generation. This ultra-wide-bandwidth tunable nanoscale coherent THz source transforms the LAO/STO interface into a promising platform for integrated lab-on-chip optoelectronic devices with various functionalities.
-
Models for Evaluating Next Generation Vaccines and Diagnostics for Tuberculosis
Guest: Professor Frederick Quinn, Department of Infectious Diseases, UGA
Friday, March 22, 2019 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)Due to the lack of an effective vaccine, sensitive and specific point-of-care diagnostics and the continuing development of drug resistance, tuberculosis is evolving to become an untreatable disease for a growing number of people. Models that can effectively mimic the various disease states will help generate accurate markers/diagnostics, and subsequently improve the vaccine and treatment options. My research program focuses on identifying and studying genetic mechanisms of Mycobacterium tuberculosis and M. bovispathogenesis, and using these factors as therapeutic, diagnostic and vaccine targets. Most recently, we have begun to employ the use of novel animal models, including the ferret transmission model.
-
Current Trends in Micro and Nano Robotics
Guest: Professor Ramviyas N. Parasuraman, Department of Computer Science, UGA
Friday, February 1, 2019 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)An autonomous microrobot or a nanorobot with a controllable manipulation system opens up huge potential in nanomedicine, surgery, manufacturing and chemical technology. For example, robots navigating through blood vessels has applications drug delivery and non-invasive surgery. In this talk, we will review the literature in micro-scale and nano-scale robotics research work. While doing so, we will also analyze the literature from a swarm intelligence perspective.
-
The Quantum Limit of Interacting Magnetic Waves
Guest: Prof. Michael E. Flatte’, Department of Physics and Astronomy, University of Iowa
Thursday, January 24, 2019 11:00 am - 12:00 pm
Location: CSP Conference Room (322)The dynamic response of magnetic materials lacks time-reversal symmetry and can often be described through the propagation and evolution of waves of magnetic orientation, or spin waves. These spin waves, or magnons when quantized, can move without electric charge motion, yet spin-orbit interactions allow the spin waves to couple, sometimes very strongly, both to voltages and to illumination. I will describe progress over the last several years in calculating and understanding, in collaboration with experimentalists, the coupling of magnons to microwave and optical photons as well as the manipulation of spin-wave propagation with a voltage. In analogy with optomechanics, two photons will interact, within a cavity containing a ferrite, with a magnon mode to coherently modify the spontaneous emission rate, to exhibit electromagnetically-induced transparency and even to reach the strongly-coupled quantum regime. Patterned magnetic media can also amplify voltage-dependent effects to produce voltage-tunable oscillators or filters.
-
Ultrafast X-Ray Molecular Dynamics
Guest: Prof. Stephen R. Leone, Departments of Chemistry and Physics and Lawrence Berkeley National Laboratory, University of California, Berkeley
Friday, January 18, 2019 11:15 am - 12:15 pm
Location: Chemistry Building, Room 400Transient absorption in the extreme ultraviolet and x-ray spectral regimes is used to probe chemical dynamics on both the femtosecond and attosecond timescales. Laser-produced high-order harmonics in the soft x-ray can investigate dissociating molecules, ring opening, passage through conical intersections, singlet to triplet transitions, and electronic and vibrational coherences. By extending the probe photon energies to 300 eV in the soft x-ray, carbon species are now readily investigated to reveal atom-specific electronic orbitals during electronic transformations of molecules. Product branches are observed directly and time measurements are obtained for the production of various excited state species. Transient features, indicative of x-ray spectroscopic transitions to dissociative or intermediate states are characterized. On ultrashort timescales, electronic and vibrational wave packet dynamics are observed. A remarkable time-resolved x-ray spectroscopic revolution provides novel opportunities for molecular dynamics investigations on femtosecond and attosecond timescales.
-
Smartphone based optical spectroscopy
Guest: Prof. Zhiwen Liu, Department of Electrical Engineering, The Pennsylvania State University
Friday, November 9, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)Smartphone based optical sensing has recently attracted a lot of interests. The wide availability of smartphones and their advanced computational and wireless communicational capabilities coupled with chemical sensing abilities of optical techniques provide intriguing possibilities of “lab on a palm.” In this talk I will present our work on smartphone based optical spectroscopy. Compact spectrometers are developed by using a G-Fresnel device with the dual functionalities of focusing and wavelength dispersion, which can enable miniaturization of optical spectrometers and thus the integration of optical spectroscopy with smartphone technology. The fabrication and characterizations of the smartphone based spectrometer are presented. I will discuss potential applications of smartphone based optical spectroscopy. Specifically, the use of smartphone based diffuse reflectance spectroscopy for hemoglobin sensing and for detecting plant diseases will be discussed.
-
Deep-subwavelength Confinement in Dielectric Optical Resonators
Guest: Professor Sharon M. Weiss, Department of Electrical Engineering, Vanderbilt University
Friday, October 19, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)The ability to highly localize light with strong electric field enhancement is critical for enabling higher-efficiency light sources, modulators, and solar cells, and can dramatically enhance nonlinear properties. While deep-subwavelength modes can be realized with plasmonic resonators, large losses in these metal structures preclude most practical applications. In this presentation, we discuss an approach enabling two levels of spatial localization of photons in a dielectric material, leading to the demonstration of a silicon bowtie photonic crystal structure that supports mode volumes commensurate with plasmonic elements and quality factors that reveal ultralow losses. Both the electromagnetics principles underlying the design of the bowtie photonic crystal and potential applications of the structure will be addressed.
-
Combined molecular dynamics-spin dynamics simulations of BCC iron
Guest: Professor David P. Landau, Department of Physics and Astronomy, Center for Simulational Physics, UGA
Friday, October 12, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)The understanding of the magnetic properties of real materials demands consideration of both magnetic and structural degrees of freedom as well as the inclusion of possible defects. Using an atomistic model that treats both translational and spin degrees of freedom, we have performed combined molecular dynamics - spin dynamics simulations to study dynamic properties of BCC iron. Atomic interactions are described by an empirical many-body potential while spin interactions are handled by a Heisenberg-like Hamiltonian with a coordinate dependent exchange interaction. By calculating the Fourier transform of spatial and temporal correlation functions, vibrational and magnetic excitations have been studied. Comparison of the results with that of the stand-alone molecular dynamics and spin dynamics simulations reveal that the dynamic interplay between the phonons and magnons leads to a shift in the respective frequency spectra and a decrease in the lifetimes. Moreover, in the presence of lattice vibrations, additional longitudinal magnetic excitations were observed with the same frequencies as the longitudinal phonons. The inclusion of vacancies in the material induces splitting of the characteristic transverse spin-wave excitations, indicating the production of additional excitation modes. By merging two vacancies to form a nearest neighbor pair, we found that these modes become more distinct. Investigation of longitudinal spin-wave excitations revealed interactions between constituent components of the split transverse excitations.
-
Applications of Atomic Physics and Condensed Matter Physics in Studies of the Interstellar and Circumgalactic Medium
Guest: Professor Varsha P. Kulkarni, Department of Physics & Astronomy, University of South Carolina
Friday, September 28, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)The interstellar space in the Milky Way contains diffuse gas and solid dust grains. There is constant recycling of matter and energy between this interstellar medium (ISM) and the stars. Likewise, there is constant recycling between galaxies and the circumgalactic medium (CGM). I will describe two applications of atomic physics and condensed matter physics relevant to our studies of the ISM and the CGM. First, I will describe our ongoing efforts to improve the atomic physics needed for interpretation of absorption-line spectroscopy of the ISM and the CGM. This work is motivated by the fact that the inferred properties of the gas depend sensitively on the atomic parameters used for the spectral features, e.g. the oscillator strengths used for the relevant transitions, which remain uncertain for a significant fraction of the transitions. Our work includes calculations and compilations of oscillator strengths for the lines of greatest interest, and examination of their implications for studies of distant galaxies. Second, I will describe our ongoing efforts to determine the nature of the solid particles (dust grains) in the ISM and the CGM. We have made the first detection of silicate dust grains in distant galaxies out to redshifts z~1.5. The dust grains in these distant galaxies appear to be more silicate-rich than the grains in the Milky Way ISM. Furthermore, in some cases, these grains appear to be crystalline, unlike the amorphous grains observed in the ISM of the Milky Way. These differences may be caused by differences in grain properties (e.g. the grain composition or size distribution), or differences in their environment (e.g. cosmic ray fluxes). Improvements to both the atomic physics of the relevant transitions in the ISM/CGM, and the condensed matter physics of dust grains mixed in with the diffuse gas will be crucial for improving our understanding of the evolution of stars and galaxies.
-
Mechanisms Underlying Highly Efficient Solar Energy Conversion in Photosynthetic Organisms
Guest: Prof. Gary Hastings, Department of Physics and Astronomy, Georgia State University
Friday, September 14, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)In photosynthetic organisms light energy drives electrons from a donor chlorophyll species via a series of acceptors across a biological membrane. This light-induced electron transfer process is remarkably efficient, indicating a near complete inhibition of unproductive charge recombination reactions. Unproductive charge recombination reactions can be inhibited if they occur in the, so-called, inverted region. However, inverted region electron transfer has never been demonstrated in any native photosynthetic system.
Here I will describe our recent studies using time-resolved visible and infrared (FTIR) spectroscopy to study solar energy conversion processes in native and (cofactor) modified photosystem I photosynthetic reaction centers. From these studies I will show that unproductive charge recombination in native photosystem I does occur in the inverted region.
Computational modeling of light-induced electron transfer processes in photosystem I indicate a decrease in photosynthetic quantum efficiency, from 98% to below 72%, if the unproductive charge recombination does not occur in the inverted region. Inverted region electron transfer is therefore shown to be an important mechanism driving the efficient solar energy conversion process in photosystem I.
The unproductive charge recombination reactions do not occur in the inverted-region in other photosystems, such as purple bacterial reaction centers. Photosystem I is highly reducing (compared to any other photosystem), and it is likely because of the highly reducing nature of photosystem I, and the energetic requirements placed on the pigments to operate in such a regime, that the inverted-region electron transfer mechanism becomes important.
-
Intravital Imaging of MSCs and Bone Regeneration
Guest: Luke Mortensen, Assistant Professor of Regenerative Medicine and Engineering, University of Georgia
Friday, September 7, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)Mesenchymal Stem Cells (MSCs) are promising therapeutics for inflammatory diseases and musculoskeletal regeneration; but challenges in identifying highly potent cells and evaluating their in vivo behavior have slowed clinical translation. Dr. Mortensen’s research program develops advanced intravital 2 photon imaging strategies including laser ablation, adaptive optics correction, and super-resolution imaging to probe mesenchymal stem cell (MSC) therapies for inflammation and bone disease and the study of regenerative processes.
-
Physical Principles of Brain Folding: Computational Modeling and Data Interrogation
Guest: Xianqiao Wang, Associate Professor of College of Engineering, University of Georgia
Friday, August 31, 2018 12:00 pm - 1:00 pm
Location: CSP Conference Room (322)Recent years have witnessed the explosive growth of interests in the health-related research from the computational modeling and data interrogation perspectives. In this talk, I would like to take the brain folding as an example to discuss the role of computational modeling in explaining the physical formation of complex brain structure. Via computational modeling and data analysis, we demonstrate that, in additional to biological cues, physical factors such as cortex stiffness, thickness, and growth speed may play crucial roles in brain gyral formation and functionality. Our findings may provide a plausible avenue to describe the relationships amongst cortical morphology, connection, and function, thereby offering clues towards novel diagnostics and treatments of neurological disorders.
-
Recent developments and new opportunities in quantum computation
Guest: Prof. Michael Geller, UGA Department of Physics and Astronomy
Friday, August 17, 2018 12:20 pm - 1:20 pm
Location: CSP Conference Room (322)Quantum computers, which promise enormous computational power for certain specialized tasks, are being developed by universities, government labs, and technology companies worldwide. I will briefly review the current status of quantum computers, their demanding requirements for error correction, and the current attempts at prethreshold (non-error- corrected) quantum computation. I will also highlight areas where I think there will be significant future opportunities for physicists and materials scientists.
-
Synchronization of nonlinear oscillators under time-delayed coupling
Guest: Mukesh Dhamala, Associate Professor of Physics, Georgia State University
Friday, July 27, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322)In many physical, biological and technological oscillatory systems, useful functions emerge from collective synchronization of an ensemble of constituent oscillators. Examples include working of neurons in the brain during perceptual and cognitive processes, phase-locking of Josephson junction arrays, the dynamics of power grids. Transitions to synchronization depend on several factors, including interaction time-delays, which are often unavoidable in spatially distributed systems of oscillators like the interactions among brain neurons due to active axonal signal transmission processes. In this talk, I will discuss our recent findings on (i) the effects of time-delayed coupling in synchronization of nonlinear oscillators (theory), and (ii) on oscillatory network activity in the brain during perceptual decision-making processes (experiment).
-
Phase Transitions in Ferroelectric, Relaxor-Ferroelectric and Antiferroelectric Materials
Guest: Prof. Nazanin Bassiri-Gharb, G.W. Woodruff School of Mechanical Engineering, School of Materials Science and Engineering Georgia Institute of Technology
Friday, July 13, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322)Ferroelectric solid-solutions have very large dielectric, piezoelectric and pyroelectric properties (up to two orders of magnitude higher than their non-ferroelectric polar counterparts), and therefore offer an opportunity for integrating multiple functionalities at the micrometer and nanometer scales, including sensing and actuation capabilities, integrated switches and filters for radio systems, energy harvesting for self-powered devices, miniaturized multilayer capacitors, and mechanical relays for low power embedded microcontrollers. This multi-functional nature presents a pathway towards a "More than Moore" (MtM) era.
Compositional disorder and structural transitions, induced via thermal, electric or elastic fields lie at the heart of the enhanced functional response of many ferroic systems. This presentation will discuss the effects of the presence of phase transitions and domain wall motion in ferroelectric, relaxor-ferroelectric and antiferroelectric materials. Effective strategies for enhancing the phase transition and increase the functional electromechanical response of thin films will be discussed.
-
Vapor-Liquid-Solid Mechanism: Programming Heterogeneity at the Nanoscale
Guest: M. Filler, School of Chemical & Biomolecular Engineering, Georgia Institute of Technology
Thursday, June 28, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322) -
Developing ultrafast spectroscopies with frequency combs: new frontiers in ultra-sensitive and multidimensional measurements
Guest: M. Reber, Department of Chemistry, University of Georgia
Friday, June 15, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322) -
Super-Resolution Microscopy
Guest: P. Kner, College of Engineering, University of Georgia
Friday, June 1, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322) -
Gas Phase Reaction Dynamics: An Experimental Perspective
Guest: Professor Henning Meyer, Department of Physics & Astronomy, University of Georgia
Friday, May 4, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322) -
Nanoparticles to Enhance Photodynamic Therapy and Radiation Therapy
Guest: J. Xie, Nanoparticles to Enhance Photodynamic Therapy and Radiation Therapy
Friday, April 20, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322) -
Glancing Angle Deposition for Plasmonics
Guest: Prof. Yiping Zhao, UGA Department of Physics and Astronomy
Friday, April 6, 2018 11:30 am - 12:30 pm
Location: CSP Conference Room (322)
Page 1 of 1, showing 24 records out of 24 total, starting on record 1, ending on 24