VCU Department of Physics Colloquia

Unless indicated otherwise, Physics Colloquia are held on Fridays in Room 2310 at 701 W. Grace Street and begin at 4:00pm, with coffee at 3:50pm.

Note that faculty candidate seminars will often be held at other days and times and in other rooms.


The complete schedule of future and past colloquia can be found at:

https://rampages.us/physicscolloquium/




What Can Physics Tell Us About Sickle Cell Disease? (surprisingly, a lot)

March 31, 2017

Frank A. Ferrone, Department of Physics, Drexel University

Sickle cell disease is a genetic disorder that affects the blood of about 100,000 Americans, and millions world-wide.  It arises because a single point mutation allows the hemoglobin that fills the red cells to assemble into long, stiff, multistranded fibers.  These fibers deny the red cell its necessary pliability, and thus clog the circulation, depriving the tissues of the oxygen they require.  We now understand the mechanism by which this assembly proceeds in great detail.    Remarkably, basic physical principles — entropic forces, Hooke's law deformations, random barrier crossings, Brownian ratchets — play a significant role in understanding the nature of this disease, and in the strategies available to cure it.



Using Surface Charge of a Microchannel as a Tool for Studying Chemical and Biochemical Processes

April 7, 2017

Julio Alvarez, Department of Chemistry, Virginia Commonwealth University



Between topological strings and topological phases

April 14, 2017

Jeffrey Teo, Department of Physics, University of Virginia

Topological phases in two and three dimensions can be theoretically constructed by coupled-wire models whose fundamental constituents are electronic channels along strings.  On the other hand, the collective topological phases support further fractionalized emergent quasi-string excitations or defects such as flux vortices.  In this talk I will describe topological superconductors and Dirac (or Weyl) semimetals using coupled-wire models and discuss the fractional behavior of emergent topological strings.



Literature Seminar

April 21, 2017

Md Rezaul Karim Khan, Department of Chemistry, Virginia Commonwealth University



A Look at Selected Projects in NASA's Planetary Science Portfolio

April 28, 2017

Bill Knopf, Program Executive at NASA Headquarters, Washington, D.C.



Past Department of Physics Colloquia

Cluster-enhanced Nanopore Spectrometry

September 23, 2016

Joseph E. Reiner, VCU Physics


 Nanopore sensing is a powerful single molecule technique that utilizes Coulter-counting at the nanoscale.  The principle of operation is straightforward.  Individual molecules enter an isolated nanopore and block the flow of ions giving rise to current blockades that can be analyzed to learn about the size, charge and structure of a molecule.  The technique is relatively easy to implement and it enables label-free, rapid and non-destructive detection of a wide variety of molecules. Recent interest in nanopore technology has grown with the commercial availability of a miniaturized DNA sequencer (Minion, Oxford Nanopore Technologies).  This handheld sensor has demonstrated the potential to perform rapid genomic analysis in the field and motivates further study of the nanopore for detecting other molecules of interest.  To further advance nanopore sensing, researchers have continued to focus on understanding the physical and chemical phenomenon that give rise to current blockades.  This talk will describe my work in this area, which focuses on reducing blockade fluctuations and increasing analyte residence time with the use of metallic nanoclusters.  The goal is to utilize cluster-based nanopore spectrometry to improve the selectivity of the pore and this will be demonstrated for a number of biologically relevant peptides.



Investigation of Hydrogen Interactions with Metals and Carbon Nanostructures for Next Generation Energy Storage and Conversion Devices

November 4, 2016

Joseph Teprovich, Savannah River National Laboratory


Our experimental and theoretical investigation of the interaction of metal hydrides and complex metal hydrides with carbon nanostructure (C60, CNT’s, etc.) has demonstrated that these composites reversibly interact with hydrogen. Through a series of spectroscopic analysis of these materials, the active hydrogen storage material resembles a metal-doped hydrogenated fullerene. Owing to our ability to judiciously control the metal doping and hydrogen content of these materials, we can fine-tune the properties of the materials for new applications. This led to the remarkable enhancement in lithium ion conduction in LiBH4-C60 nanocomposites observed at room temperature. Experimental and theoretical work suggested a nanoionic mechanism is responsible for the enhanced ionic conduction due to the destabilization/breaking of the Li+/(BH4) ion pair by C60. Our recent work has been focused on evaluating the photophysical properties of these carbon nanocomposites. The hydrogen content of these materials can be used fine-tune the emissive properties of the material with potential applications in luminescence down-shifting devices. This presentation will cover these findings in detail as well as on-going and future research on similar materials.



Can we play bowling with electrons?

November 11, 2016

Jongsoo Yoon, Department of Physics, University of Virginia


 Much of the electronic properties of metals can be understood in the framework of the independent or free electron model, where the electron-electron interaction is ignored. In such a model electrons move freely within the metal, much like bowling balls rolling in a lane. Conventional theories expect that the ground state of the electron systems in two dimensions should be localized, or an electrically insulating state; in bowling analogy, the bowling balls rolled in a lane should never reach the pins.

Experiments, however, have shown a strong indication that the ground state is actually conducting. Although the mechanism behind the unexpected conducting ground state is still mysterious, the electron-electron interaction is believed to hold the key to the mechanism. Interestingly, unexpected conducting ground states with very similar characteristics are observed in systems where the electron-electron interaction is repulsive (electrons confined in the semiconductor interface) as well as the interaction is attractive (superconducting ultra-thin films where the superconductivity is suppressed).

In this talk, we concentrate on the experimental results of the mysterious conducting state observed on ultra-thin superconducting tantalum films. We will identify non-trivial electronic transport properties that are intrinsic to the mysterious conducting state, and map the three-dimensional phase diagram in magnetic field-temperature-disorder space.



A glass transition in population genetics: Emergence of clones in populations

November 18, 2016

Marija Vucelja, Department of Physics, University of Virginia

The fields of evolution and population genetics are undergoing a renaissance, due to the abundance of sequencing data. On the other hand, the existing theories are often unable to explain the experimental findings. It is not clear what sets the time scales of evolution, whether for antibiotic resistance, an emergence of new animal species, or the diversification of life. The emerging picture of genetic evolution is that of a strongly interacting stochastic system with large numbers of components far from equilibrium. In this talk, I plan to focus on the clone competition and discuss the diversity of a random population that undergoes selection and recombination (sexual reproduction). Recombination reshuffles genetic material while selection amplifies the fittest genotypes. If recombination is more rapid than selection, a population consists of a diverse mixture of many genotypes, as is observed in many populations. In the opposite regime, selection can amplify individual genotypes into large clones, and the population reaches the so-called “clonal condensation”. I hope to convince you that our work provides a qualitative explanation of clonal condensation. I will point out the similarity between clonal condensation and the freezing transition in the Random Energy Model of spin glasses. I will conclude with a summary of our present understanding of the clonal condensation phenomena and describe future directions and connections to statistical physics.


Measuring and manipulating 2D and other nanomaterials with high-speed atomic force microscopy

December 14, 2016

11:00 am, Wednesday, December 14, 2016

Loren Picco,
Royal Academy of Engineering Enterprise Fellow
H H Wills Physics Laboratory
University of Bristol, UK

Room 2403, 701 West Grace St (Laurel Street Entrance)

I will describe recent research highlights from my work at the University of Bristol. I will explain how our high-speed atomic force microscope can measure the sizes, shapes and material properties of tens of thousands of nanostructures with a speed and accuracy superior to typical electron microscopy techniques, providing unprecedented statistical confidence and insight into nanostructure distributions.
 
The tool has demonstrated the ability to distinguish between 2d materials such as TiS2, MoS, graphene, carbon nitride and black phosphorous as well as proving itself as a valuable tool for assessing critical industry challenges such as nanoscale corrosion and carburisation in metals.  


Physics of the B Meson

January 20, 2017

Muruges Duraisamy, Department of Physics, Virginia Commonwealth University

The Standard Model (SM) of particle physics, even though very successful, is expected to break down at some energy scale and make way for a more complete theory. Exploration of what lies beyond the SM can be carried out at the energy frontier in colliders such as the LHC or at the intensity frontier at high luminosity experiments. In the intensity frontier, the B factories, BaBar and Belle, have produced an enormous quantity of data in the last decade. There is still a lot of data to be analyzed from both experiments. The B factories have firmly established the CKM mechanism as the leading order contributor to CP violating phenomena in the flavor sector involving quarks. New physics (NP) effects can add to the leading order term producing deviations from the SM predictions. In this talk, I will give a brief overview of the physics of B meson and CP violation, and discuss some of the current experimental results in various B meson decays.

Using Physical Principles to Predict Product Shelf Life

January 27, 2017

David B. Kane, Altria Client Services

 

Defects in Semiconductors

February 3, 2017

Michael Reshchikov, Department of Physics, Virginia Commonwealth University

In spite of many years of research, point defects with deep levels in semiconductors are still not well understood. The defects create unwanted paths of charge carriers recombination, which leads to premature breakdown in high-power electronic devices, reduces efficiency of the light-emitting devices and shortens their lifetime.  Gallium Nitride (GaN) is a relatively new semiconductor, which is currently used in blue light emitting devices (LEDs, laser diodes), and is expected to transform all lighting technology in near future. Point defects in GaN can be studied by several techniques, among which photoluminescence (PL) appears to be the strongest tool.

In this presentation, the history of investigations into point defects in semiconductors will be reviewed, including showing interesting examples where incorrect theoretical predictions caused biased and incorrect explanations of experimental results and vice versa. A simple configuration coordinate model will be used to explain PL spectra from defects. The PL results will be compared with theoretical predictions and experimental results obtained by using other techniques, such as deep-level transient spectroscopy (DLTS) or positron annihilation spectroscopy (PAS).

Fibrin Fiber Formation and Mechanics

February 10, 2017

Christine Helms, Department of Physics, University of Richmond

Fibrin fibers are a major constituent of blood clots.  They perform the mechanical task of stemming the flow of blood. The structure and strength of fibrin fibers relates to the medical outcome of an individual.  Therefore, we measure the structure of fibrin clots and strength of individual fibrin fibers to understand better the mechanism(s) leading to poor clinical outcomes.   Previous research showed that environmental factors, such as pH and ion concentration, affect clot structure and fiber diameter.  Recently we added to that body of work by showing that high concentrations of nitric oxide also affect clot structure through the oxidation of important proteins. Conditions with altered clot structure often have an altered rate of fiber formation, altered fiber diameter and altered clinical responses, as well. This leads to the question, what is the mechanism responsible for the change?  If we could understand the individual fibers, we may understand why changes to the clot are associated with heart attack and stroke.  Therefore, we measured the modulus of an individual fibrin fiber using the atomic force microscope. Fibrin fibers have interesting mechanical properties from a materials standpoint because they form a regular structure but are extremely extensible.  In addition, we found that the modulus of fibrin fibers is dependent on the diameter of the fiber, suggesting irregular density inside the individual fibers.   In this talk, I will discuss the role of fibrin in health and try to convince you that the mechanism responsible for altered clot structure and stiffness is packing of the monomers inside the individual fibers.  I will do this through the presentation of our recent data on the modulus of fibrin fibers.



What We Know So Far: An Introduction to the Standard Model

February 17, 2017

Kevin Grizzard, Department of Medical Physics, Virginia Commonwealth University

The modern understanding of nature at its most fundamental level is built on two foundations. One is general relativity, which describes gravity and the large scale structure of the universe. The other is commonly known as the Standard Model of particle physics ("the SM"), which incorporates quantum mechanics and special relativity in a description of the known elementary particles and their interactions via the electromagnetic force, the strong nuclear force, and the weak nuclear force.  It also describes how elementary particles acquire mass via the Higgs mechanism, and the detection of a Higgs boson at the Large Hadron Collider in 2012, some fifty years after its proposal, was one of the greatest confirmations of a theoretical prediction in history.  I will give an overview of the SM, noting some of its motivations and successes while emphasizing its essential conceptual features (e.g., the least-action principle; symmetries including Poincare invariance and gauge symmetry; the Higgs mechanism).



Highly Efficient Nanostructured "Smart Coatings" by Self-Assembly Fabrication

February 24, 2017

Antonio Checco, Soft and Biomolecular Materials, Brookhaven National Laboratory

A current challenge in materials science is the fabrication of highly efficient "smart interfaces" with extreme and reconfigurable wetting, adhesion, and friction properties, or exquisite selectivity to target biomolecules. Here we demonstrate novel, large area superhydrophobic/anti-fogging silicon surfaces with ~20 nm feature size defined by block-copolymer self-assembly and plasma etching. We investigate by means of optical and scanning probe microscopies, and x-ray scattering how the nanoscale texture morphology influences macroscopic water wettability, resistance to water infiltration under (static and dynamic) pressure, dew formation, and hydrodynamic slippage. Our findings show that fine-tuning the texture size and morphology is crucial to optimal superhydrophobic, anti-fogging, and water slippage properties. Further, we illustrate strategies for further functionalization of the nanostructured silicon templates using graphene or membrane proteins for enabling the selective, tunable, and efficient translocation of water, or target ions and biomolecules.



Ultrafast Fluid Dynamics and Cavitation Studies with X-ray Lasers

March 1, 2017

Claudiu Stan, Stanford PULSE Institute, SLAC National Accelerator Facility

Wednesday, March 1, 2017 at 1:00 PM
in Room 2403 at 701 West Grace Street (Laurel St. Entrance)

The extreme intensity of X-ray lasers, combined with their angstrom wavelengths and femtosecond pulse durations, enable scientists to observe the instantaneous structure of matter with atomic scale resolution. Another promising but less explored application of X-ray lasers is to drive rapid processes and transformations in materials. I will present our investigations on the dynamics of X-ray laser ablation in liquid microjets and microdrops. We found that the phenomena induced by X-ray lasers have unique features compared to the case of optical ablation. In particular, the X-ray laser produced highly symmetric liquid explosions, and we were able to model their basic fluid dynamics. In a following study, we used shock waves produced by X-ray lasers to induce and study cavitation in water on a few-nanosecond time scale. At these time scales, cavitation occurred in extremely metastable conditions, characterized by negative pressures that exceed significantly those achieved previously in bulk water. Our cavitation experiment enables the study of water under highly metastable conditions, and provides an avenue to understand the nucleation of cavitation in water. More generally, X-ray laser ablation has the potential to control with (sub)nanosecond precision the nanoscale dynamics of pressure-driven processes such as nucleation, phase transitions, and mechanical failure.



Designing Advanced Materials for Energy and Nanoelectronic Applications

March 3, 2017

Liping Yu, Department of Physics, Temple University

Today, the needs for new or improved functional materials are greater than ever. In this talk, I will present our recent research advances in designing new materials for energy and nanoelectronic applications. I will focus on three examples: (i) designing super solar-light absorbing materials for nanoscale thin-film solar cell applications, (ii) designing highly conductive oxide interface materials for next-generation nanoelectronics, and (iii) designing functional layered two-dimensional materials for flexible electronics and energy applications. Some newly discovered functional materials, their experimental validation, as well as the underlying structure-property relationships (or design principles) will be presented.  Along with these examples, I will show an inverse materials design approach powered by quantum-mechanical density functional theory and high-throughput first principles calculations. This approach places functionality first, searches for the material that has a set of physical properties optimized for such functionality, and aims to dramatically shorten the process of finding new materials. The research challenges and opportunities in the fields as exemplified above will also be briefly discussed.



Use the Force: High-Bandwidth Nanosensing for Materials Science and Healthcare

March 17, 2017

Loren Picco, H H Wills Physics Laboratory, University of Bristol, UK

Friday, March 17, 2017 at 3:55 pm
Room 2310, 701 West Grace St (Laurel Street Entrance)

There is an unmet need for faster and more accurate measurements of nanoscale materials and devices. With compelling new applications in fields such as energy, electronics and healthcare there is an increasing drive to develop novel materials and scale-up from proof-of-concept demonstrations to practical implementations. Similarly, in industry, it is becoming apparent that understanding the nanoscale origins of metal fatigue and corrosion holds the key to more accurate lifetime estimations and the development of next generation coatings and components.

The high-speed atomic force microscope I have developed at the University of Bristol is an ideal diagnostic tool for the rapid characterisation of nanoscale surfaces. It is 1,000 times faster than a conventional atomic force microscope and enables the direct observation of molecular interactions and nanoscale processes with millisecond temporal resolution. In this talk I will discuss the development of the tool, including the underlying physics that empower it, key application areas enabled by these MHz measurements and future opportunities afforded by the technology.