Colloquium Series

2017 - 2018 Academic Year Colloquium Series

Friday, December 1st, 2017 - 2:30pm
Dr. Zoe Boekelheide
Lafayette College

"Gd5Si4 micro- and nano-particles for self-regulating magnetic hyperthermia"

One developing application of nanomedicine is magnetic hyperthermia cancer treatment. Magnetic hyperthermia has been successful in clinical trials and is now commercially available to cancer patients in certain regions for treatment of glioblastoma, prostate cancer, and other cancers. In magnetic hyperthermia treatment, magnetic particles are directed toward a cancerous tumor and an alternating magnetic field (AMF) is applied, causing rapid switching of the particles’ magnetic moments causing heat dissipation. This heat can damage or kill cells of the tumor without damage to the normal cells, and can enhance other therapies such as radiation therapy by preventing DNA-damage repair. Currently, iron oxide nanoparticles are used primarily because of their high heating power and their biocompatibility. However, there are benefits to exploring other materials. One potentially beneficial magnetic property is a Curie temperature TC around the desired treatment temperature (43-45 °C) so that the heating is self-regulating, ensuring adequate heating at the tumor margin while preventing accidental overheating of healthy cells. One candidate material for self-regulated hyperthermia is Gd5Si4 and related alloys. This talk will discuss the synthesis, magnetic characterization, and heating power of Gd5Si4 micro- and nano-particles, assessing their promise for self-regulated hyperthermia.


Friday, November 10th, 2017 - 2:30pm
Dr. Aurelia Honerkamp-Smith
Lehigh University

"Using fluid flow to investigate lipid membranes"

While most life takes place in an aqueous environment, the physics of micro-scale movement in fluid environments can be counterintuitive. I will discuss recent experiments with the theme of building up a three-dimensional, microscopic picture of motion. Multi-component lipid membranes act like two-dimensional fluids, whose flow can be observed to couple closely to that of the surrounding water. This fluidity can be used to ask questions about the physical properties of lipids and membrane proteins.

Friday, November 3rd, 2017 - 2:30pm
Dr. John Q. Xiao
University of Delaware

"Current driven spin-orbital torque in magnetic bilayers"

Spin-orbital coupling driven toques have been observed in magnetic heterostructures consisting of ferromagnet (FM) and heavy metal (HM) or topological insulator (TI). It has been demonstrated that the spin-orbit torques driven by an in-plane electrical current can switch magnetization, manipulate magnetic domains, and excite magnetization auto-oscillation. These phenomena are currently applied to develop next-generation magnetic memory, logic device, and microwave source. In this presentation, we will introduce various exciting phenomena in magnetic heterostructures. We will also discuss how to develop instrumentation to measure these spin-orbit torques. Finally, we will discuss how to engineer interfaces to understand the physics behind these phenomena, mainly how to quantify the interface contribution due to Rashba effect and the bulk contribution due to spin Hall effect.

Friday, October 27th, 2017 - 2:30pm
Dr. Jacob Elmer
Villanova University

"Extracellular Hemoglobin: A Universal Donor Blood Substitute"

Donated blood is the safest and most effective treatment for patients with severe blood loss. Red blood cells must be constantly refrigerated (never frozen) making donated blood unavailable in remote areas with no proper storage facilities, while rare blood cells are frequently in short supply. This has motivated the search for a “blood substitute” that can safely be stored for long periods of time at high temperatures and act as a universal donor material. To date, blood substitutes have used human or cow hemoglobin as a starting material. Side effects observed in clinical trials have been attributed to the fact that human and cow hemoglobin are intracellular proteins that are designed to function within the protective environment of a red blood cell. A better approach may be to use one of the naturally occurring extracellular hemoglobins (erythrocruorins) found in most worms and some snails or clams. The erythrocruorin of the common earthworm Lumbricus terrestris (LtEc, shown below) constitutes an attractive blood substitute, due to its higher structural & thermal stability, slower oxidation rate, and high molecular weight (3,600,000 g/mol). Our preliminary studies in mice and hamsters indicate that LtEc safely delivers oxygen without causing adverse side effects. The exact reaction mechanisms which allow LtEc to avoid the side effects observed with other blood substitutes need to be elucidated. Specifically, we are investigating the biophysical interactions between the heme iron and various ligands (oxygen, nitric oxide, etc.) and the formation of different oxidation states (Fe2+, Fe3+, Fe4+, & hemi/hemochrome) using techniques such as electron paramagnetic resonance (EPR) and Mossbauer spectroscopy. The high molecular weight of the LtEc polymer also endows it with a uniquely high viscosity, which may induce a mechano-transduction response in vivo that has not yet been fully investigated. The physics involved in each of these phenomena will be specifically discussed, with an overall goal of explaining what experiments still need to be done with LtEc to prepare it for clinical trials in humans.

Friday, October 20th, 2017 - 2:30pm
Dr. Goran Karapetrov
Drexel University

"Evolution of Superconductivity in Mesoscopic Systems"

Superconductors are one of the few materials that exhibit coherent electron behavior on macroscopic distances. As the size of the superconductor shrinks, the behavior of the superconducting Cooper pairs begins to reveal the intrinsic nature of the Bose condensate. Today’s scanning probe microscopy and spectroscopy tools allow us to image the spatial modulation of the superconducting condensate with atomic precision. In this talk I will show how one can explore the rich physics of superconductors on the example of magnetically coupled superconductor-ferromagnet hybrids. Ferromagnet materials are used as a template that modulates the superconducting order parameter on nanometer scale. As we change the external parameters such as temperature and magnetic field, we can track the evolution of superconductivity in these templated systems. In the process we have an opportunity to find clues about the superconductor itself and the new ways to control the behavior of the superconductors on the nanoscale.

April 2, 2014

Dr. David Chuss, National Aeronautics and Space Administration, Goddard Space Flight Center

“The Cosmic Microwave Background and Inflation”

The March 2014 announcement by the BICEP2 collaboration claimed a detection of the long-sought-after primordial “B-mode” polarization of the cosmic microwave background (CMB). Such a signal is expected to be produced by gravitational waves generated by cosmic inflation, the exponential expansion of the universe in the first ~10-32 seconds that had been postulated in the 1980’s as a mechanism to explain the initial conditions of the Big Bang. If this signal is verified, it will have profound implications on our understanding of physical cosmology by providing tangible evidence for inflation and a window into physics at energy scales a trillion times larger than those of the Large Hadron Collider. In this talk, I will review the state of physical cosmology, discuss the BICEP2 results, and describe near-future experiments poised to independently test inflation by measuring the polarization of the cosmic microwave background on large angular scales where the inflationary polarization signal should be significantly larger than at the degree angular scale to which BICEP2 is sensitive. The Cosmology Large Angular Scale Surveyor (CLASS) is a Johns Hopkins University-led ground based telescope array that will survey the CMB from the Atacama Desert in Chile at frequencies below 200 GHz. The Primordial Inflation Polarization Explorer (PIPER) is a NASA Goddard Space Flight Center-led balloon-borne polarimeter that will survey the CMB at frequencies above 200 GHz. The combined spectral information will be advantageous in separating the CMB polarization from that of the Galactic foregrounds, and the unique instrument design will enable excellent separation of the CMB signal from instrumental artifacts. 

 

March 28, 2014

Dr. Stan Mertzman, Earl D. Stage and Mary E. Stage Professor of Geosciences, Department of Earth & Environment, Franklin & Marshall College

“Planetary Geology: More Than Just Looking at Surface Features: Reflectance Spectroscopy and X-ray Fluorescence (XRF) - A Match Made in Heaven (So to Speak)”

Seeing vivid images that detail all the small-scale as well as large-scale surface features from another planetary body provides a rich starting point for interpreting how that body has evolved over geologic time. These qualitative assessments are fine as far as they go, but when combined with data concerning the mineralogy and chemistry of surface sediments and rock outcrops, the interpretations that can be fashioned are much more robust. Today’s presentation focuses on the integration of mineral reflectance spectroscopy with x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectroscopy. When mounted on a rover vehicle like Curiosity (MSL: Mars Science Laboratory) or an orbiter like Cassini at Saturn or Dawn in the Asteroid Belt, our ability to unravel the evolution of planets like Mars, moons like Europa and Titan, and asteroids like Vesta and Ceres is greatly enhanced.

 

March 14, 2014

Dr. Kate Stebe, Department of Chemical and Biomolecular Engineering, University of Pennsylvania

“Energy Stored in Deformation Fields: Opportunities for Directed Assembly in Soft Matter”

Colloidal particles are often directed to assemble by use of applied external fields-e.g. by exploiting particle charge or ferromagnetism, and by applying electro-magnetic fields to induce interactions and to steer the particles into well-defined structures at given locations.  Here, we exploit fields that arise spontaneously when microparticles are placed in contact with deformable matter. In particular, we have been exploring energy stored in deformation fields around microparticles as a means of directing colloidal assembly. 

In one context, we use capillary interactions that occur between anisotropic microparticles at fluid interfaces. The microparticles have undulated contact lines owing to wetting boundary conditions; the fluid interface deforms, creating an area field around the particle that bears the signature of the particle shape and wetting.  The product of this area and surface tension is an energy field, which we exploit to direct particles to migrate, orient and assemble.  We focus on the role of particle shape in determining pair interactions.  At planar interfaces, interactions in the far field obey a universal form.  In closer proximity, particle aspect ratio impacts preferred alignment.  Near contact, faceting, corners, and particle roughness can dominate the capillary energy landscape, dictating equilibrium configurations.  On curved interfaces, particle deformation fields couple to interface curvature in analogy to charges migrating in applied electric fields.  Particles orient and migrate in curvature gradient.  Even planar particles, which would not interact on planar interfaces, migrate in curvature fields. 

In another context, we exploit elastic energies and defect fields that arise in confined liquid crystals. For example, when a nematic liquid crystal is confined using surfaces with well-defined anchoring energies, the director field and associated defect fields can be molded to store elastic energy.  This energy can be used to steer particles within the bulk or particles that are trapped at the nematic-air interface.  We explore this theme using topographically patterned solid surfaces to define defect fields that steer particles trapped at fluid interfaces into assemblies mimicking the defect texture.  Related examples for particle migration in smectic films, with either free surfaces or on topographically complex surfaces are discussed. 

 

February 25, 2014

Dr. Christopher Moore, Department of Chemistry & Physics, Coastal Carolina University

“Charge Transport at the Surface of Electronic Materials and Applications in Light and Gas Sensing Devices”

The chemical reactions that occur at the surface of semiconducting materials can contribute greatly to their electrical properties, with implications for light and gas sensing. In particular, my research group has shown that a process called surface electron energy band bending can result in the slow response observed for some photodetectors, and that interface effects contribute greatly to enhanced sensitivity for some gas sensor geometries. In this talk, I will discuss the recent work published by my undergraduate research group.  We use a combination of physics, chemistry, and electrical engineering principles to learn about how the interfaces and surfaces of materials can be exploited in the creation of novel electronic devices. I will also discuss how two students this past summer transformed a $250 digital light projector into a micrometer-scale photolithography system that we have used to fabricate tiny and sophisticated devices. Another student during the same summer worked with an international team in my lab on new device structures incorporating nano-scale materials. I will finally discuss the extension of some of these projects along with some new ideas on which Villanova students could begin working in the fall.

 

February 21, 2014

Dr. Kathryn Mayer, Department of Chemistry, Tufts University

“Optical Single-Molecule Studies at the Nano-Bio Interface"

Single molecule techniques are rapidly changing the way we think about quantitative measurements. As these techniques gain prevalence, the question of what actually happens at surfaces at the single molecule level will become an essential one. Three optical techniques that can be used to study the behavior of molecules at surfaces are LSPR sensing, super-resolution imaging, and microwell array analysis. Localized surface plasmon resonance (LSPR) sensing is a label-free technique that uses the plasmon resonance of metal nanoparticles to transduce molecular binding signals. This technique is sensitive enough to measure single-molecule antibody-antigen interactions. Super-resolution imaging allows us to directly visualize the locations of molecules on surfaces, and to probe nanoparticle-molecule interactions. For example, we can image a gold nanowire with sub-diffraction-limited resolution and measure the position and intensity of fluorophores tethered to the nanowire surface. Microwell array analysis is another complementary technique which can provide detailed kinetics data on single molecules, including enzymes and nanocatalysts. By applying and combining these three optical techniques, we can reveal the details of the nano-bio interface.

 

February 18, 2014 

Dr. Taryl Kirk, Department of Physics & Astronomy, Rowan University

"How to Build a High Resolution Scanning Microscope on a Tight Budget"

 For many years there has been an increasing trend towards using scanning electron microscopy (SEM) with lower beam energies, due to image enhancement capabilities. In low voltage SEM (LVSEM), the penetration depth of the impinging electrons is small, which gives rise to greater surface sensitivity. Consequently, the penetration depth of the impinging electron beam reduces towards the escape depth – nullifying the so-called “edge effect.” In addition, the secondary electron (SE) yield is higher and the total emitted signal approaches unity, which also reduces charging in semiconducting and insulating samples. Novel LVSEM techniques, e.g. Very Low-Energy SEM (VLSEM), allow for crystalline, diffraction, and dopant contrast mechanisms. Although VLSEM delivers surface sensitivity with numerous contrast capabilities, it does not exhibit the high resolution observed with the scanning probe microscopies, such as scanning tunneling microscopy (STM). In STM, the shape of the tunneling barrier (and hence the tunneling current) is determined by the atomic-level shapes of both the probe surface and the sample surface. When combined with the ultrahigh-precision position resolution of the piezoelectric device – of the order of picometers – used to maneuver the tip, atomic structures can be observed.

I will describe the combination of the aforementioned types of microscopy into a single technique “Near Field Emission Scanning Electron Microscopy” (NFESEM) that combines some of the best features of VLSEM and STM. In essence, NFESEM is an intermediate technique in which electrons are emitted from a needle tip via field electron emission (FE), and then impinge on and interact with the sample. As a result, electrons are ejected from the sample surface and detected. NFESEM differs from VLSEM, in that there is no remote electron gun column. Instead, the electron source is positioned locally using a piezoelectric device, as in STM. However the field emitter is positioned at a distance much further from the sample than in STM. I will present a summary of the progress made, as well as discuss future upgrades, student projects, and some possible collaborations.

February 1, 2013

Dr. Jeremy Carlo, Department of Physics, Villanova University

"Adventures in Frustrated Magnetism"

In recent years the topic of frustrated magnetism has attracted significant interest.   Magnetic frustration occurs when the geometric arrangement of ions prevents magnetic order, such as ferromagnetism or antiferromagnetism, from arising.   Frustrated materials are known for a wide variety of ground states and the accessibility of subtle physics normally masked in ordinary magnetic materials. I will give an introduction to the topic of magnetic frustration, and an overview of some of the work my group has done and will be doing in the field. I will focus on materials exhibiting face-centered structural symmetry, including the double perovskites, which allow for systematic studies of the effects of lattice distortion, moment size, doping and spin-orbit coupling.

 

January 24, 2014  

Dr. Alain Phares, Department of Physics, Villanova University

“Adsorption of Dimers on Nanotube Surfaces Having a Square Geometry”

Dimer adsorption on infinitely long square nanotube surfaces with increasing diameter and keeping the lattice constant fixed corresponds to an increasing number M of atomic sites in the normal section of the nanotube. Based on a transfer matrix method developed by the author, the low temperature energy phase diagram of the system is obtained for all possible first and second neighbor dimer-dimer interactions. The occupational characteristics of the system are the coverage, q0, and the numbers of first- and second-neighbors per sites, q and b. Crystallization patterns (phases) occur at values of the set (q0, q, b) given explicitly as functions of M. The regions of the phase diagram in which they are found have been determined for any M, allowing an exact extrapolation to the infinite M limit.

 

January 17, 2014

Dr. Primoz Ravbar,  Janelia Farm Research Campus, Howard Hughes Medical Institute

“Application of Unsupervised Learning to Classification of Movements in a Fruit Fly”

 

December 6, 2013

Dr. Dale Gary, Department of Physics, New Jersey Institute of Technology

“New Observations of Coherent Radio Emission from the Sun”

 It has long been known that the Sun produces several types of coherent radio emission (due to collective motions of electrons produced by wave-particle interactions in the solar atmosphere).  Coherent radio bursts are most easily seen and identified in dynamic spectrograph (frequency vs. time) data.  Such emission is of great scientific interest in its own right, and in addition is responsible for intense radio interference affecting wireless communication and navigation systems at Earth.  We have recently used the newly expanded Jansky Very Large Array radiotelescope and other radio instruments operated by NJIT at Owens Valley Radio Observatory in California to image and therefore spatially locate these bursts for the first time.  Comparing the radio locations with imaging data from other wavelengths, including extreme ultraviolet (EUV) data from the Solar Dynamics Observatory (SDO) and hard X-ray data from the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft provide new understanding of these long-known but poorly understood events.  A particular type of burst, called millisecond spikes, is due to Electron-Cyclotron Maser emission, and seems to be associated with the turbulent magnetic reconnection outflow high in the solar corona.  I will present new findings on these spatial relationships, which are clearly seen in a recent, well-observed event from 2012.

 

November 15, 2013          Mendel Medal Lecture

Dr. S. James Gates, University System of Maryland Regents Professor, John S. Toll Professor of Physics, and Center for String & Particle Theory Director, University of Maryland

“On the Uncertainty of Disbelief”

 

November 1, 2013

Dr. Ahmad Hoorfar, Electrical Engineering, Villanova University

"Seeing Through Walls: An Electromagnetic Perspective"

The ability of electromagnetic waves to penetrate through various building materials has made see-thru-wall radar technology of increasing importance in a wide range of both civilian and defense applications. In many situations, the building’s exterior walls induce shadowing effects on targets within the building, resulting in image degradation, errors in geo-locating, or complete target masking. In addition, in most practical situations the imaging of targets should be done in real-time, requiring the development of highly efficient microwave imaging techniques that can fully account for wave propagation through various walls. In this talk I will give an overview of the latest electromagnetic-based techniques, mostly developed at Villanova, which can aid in mitigating the negative wall effects and enhance the efficient imaging and classification of targets behind walls. Imaging of various real-life scenarios using both numerical simulations and laboratory measurements will be given in the presentation.

 

October 4, 2013     Physics Dept 75th Anniversary

Dr. Paul Steinhardt, Albert Einstein Professor of Science, Professor of Theoretical Physics, Princeton University

“Big Bang or Big Bounce”          

 

September 20, 2013

Dr. Yu Gu, Department of Physics, St. Joseph's University

"Low-cost Reconfigurable Optofluidic Switch"

The miniaturization of traditional chemical and biochemical functionalities called Lab- On-Chip (LOC) has many advantageous over existing laboratory methods, such as portability, small sample size, multiplexing and simpler automation and standardization . In recent years, the integration of microfluidic and microoptical elements together onto monolithic platforms has led to the new term “optofluidics”. We present a low-cost, reconfigurable, optofluidic switch which take advantage of a material called ferrofluid. The combination of precise actuation, novel materials and microoptal design will enable the next generation of integrated devices for biochemical analysis, sensing and telecommunications.