“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.
“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.
“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.
“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.
“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.
"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.
"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.
“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.
“Application of Unsupervised Learning to Classification of Movements in a Fruit Fly”
“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.
“On the Uncertainty of Disbelief”
"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.
“Big Bang or Big Bounce”
"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.