Physics Colloquium

Fall 2012

Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
  Colloquium organizer: Yew San Hor
(Link to main colloquium page)

Green - open date
Yellow - tentative (reserved)
Red - firm commitment


Date Host Speaker Title of the talk Abstract
Aug. 30 Hor Dr. Xinhua Liang
Chemical & Biological Engineering,
Missouri S&T

Ultrathin Films Coated on Ultrafine Particles via Atomic/Molecular Layer Deposition (ALD/MLD)

Fine particles have gained increased interest in a variety of fields for different applications. The performance of the particle applications could be improved when such particles are coated with ultra-thin inorganic or organic films. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are thin film growth techniques based on sequential, self-limiting surface chemical reactions, and have been employed to grow films with precise atomic or molecular layer control. ALD has focused principally on the formation of thin film oxides, metals, or semiconductor alloys on solid substrates. MLD, which is similar to ALD, can be utilized to deposit polymer films. The MLD technique offers the same advantages for polymer film deposition as ALD does for ceramic films. MLD can also deposit hybrid polymer films using suitable precursors. Fluidized bed reactors are well suited for large scale coating operations. In this process, the particles are normally fluidized under reduced pressure conditions using an inert gas. Precursor doses can be delivered to the bed of particles sequentially and, in most cases, can be utilized at nearly 100% efficiency without precursor breakthrough and loss with the assistance of an in-line downstream mass spectrometer. Several examples of the applications of conformal ALD and MLD coatings will be discussed, including ultra-thin microporous/mesoporous metal oxide films prepared from dense hybrid MLD polymer films, well-dispersed thermally stable noble metal nanoparticles prepared by ALD, and biocompatible interface films deposited within porous polymers by ALD for tissue engineering application.

Sept. 6 Medvedeva
Dr. Mohsen Asle Zaeem
Materials Science and Engineering,
Missouri S&T

Phase FieldFinite Element Models for Microstructural Evolution

Predicting and controlling nano- and microstructural evolution of materials play important roles in design and manufacturing of engineering structures. With recent progress in computer resources, computational models have become commanding modules in materials science and engineering. Recently, phase field modeling has emerged as a powerful computational tool to study nano- and microstructural evolution, and consequently to predict material properties and mechanical behavior of alloys during different engineering processes. A broad spectrum of moving boundary problems in engineering and physics, such as those in solidification, grain growth, multi-phase fluid flow, and solid state phase transformation, can be successfully simulated with phase field models.  
In this seminar, a Cahn–Hilliard* phase field model will be presented for diffusion-controlled solid state
phase transformation in binary alloys, coupled with elasticity of the solid phases. A new Galerkin finite element formulation will be introduced with mixed-order interpolation functions to simultaneously solve the fourth- and second-order partial differential equations governing the phase-field and elasticity, respectively. To demonstrate convergence of the mixed interpolation scheme, a study of the nucleation and growth of an intermediate phase in a thin-film diffusion couple with elasticity effects will be reviewed.
Other phase fieldfinite element models will be presented, including examples for solid state phase transformation, solidification of pure and multi-component lightweight metals, grain growth in polycrystalline materials, and oxidation of zirconium alloys in nuclear power plants.
*J.W. Cahn and J.E. Hilliard, Free energy of a nonuniform system. I. Interfacial free energy, J. Chem. Phys. 28 (1958) 258–267.

Sept. 13 Hagen Dr. Andrew Detwiler
South Dakota School of Mines & Technology

Current Problems in Thunderstorm Electrification and New Observing Systems for Thunderstorm Studies

Progress is being made in in studies of thunderstorm electrification. Lightning mapping array (LMA) systems provide observations of all lightning in storms, both cloud-to-ground and intercloud. Locations in storms where initial lightning breakdown occurs can be identified. The distribution of polarity of charge in thunderstorms also can be discerned from analysis of LMA data. In situ measurements using airborne platforms are providing more detailed mapping of charge regions and in addition provide microphysical observations to test theories of charge separation. The detailed physics of the charge separation discharge process and the lightning discharge process remains an active area of research, particularly the physics behind separation of charge during non-inductive ice particle collisions, the physics of triggering the initial breakdown in a lightning flash, the emission of X-ray and gamma radiation during some lightning events,  and the variable charge distribution in different thunderstorms. New instrumentation and research platforms will facilitate advances in these areas.

Sept. 20
Sept. 27 Hor Dr. Edward Kinzel
Mechanicall & Aerospace Engineering,
Missouri S&T
Optical Antennas for Nanolithography, Near-field Imaging, and Energy Applications

Antennas are structures that couple far-field propagating waves to a localized near-field source.  Most people have some familiarity with antennas at radio/microwave frequencies, but the same concepts can be scaled down to the infrared/optical wavelengths.  This permits light to be concentrated below the diffraction limit which is useful for multiple applications such as nanofabrication, imaging/spectroscopy, and data storage.  Antenna elements also form the building blocks of metamaterials. These are materials that can be engineered to have properties not found in nature. By careful design of the antenna structure, a surface can be engineered with specific absorbance/reflectance/transmittance at a given wavelength/angle of incidence. This involves scaling down Frequency Selective Surfaces (FSS) concepts.  In the last decade, this approach has been used to create devices such as Fresnel zone plates, band pass/stop filters, and quarter waveplates at infrared frequencies.  From Kirchhoff’s law and reciprocity the emissivity of a surface is equal to its absorptivity.  The ability to design, fabricate, and characterize these structures opens up new possibilities for radiative heat-transfer and energy harvesting.

In this talk I will present the design of ridge aperture-based antennas and their implementation for direct-write nanolithography.  This system has been successfully demonstrated writing multiple sub-100 nm lines in parallel. This work also led to studying arrays of apertures at infrared frequencies for polarization, spectral control, as well as light-trapping in weakly absorbing media such as solar cells.  I will then describe the development of a scanning near-field optical microscope for resolving the amplitude and phase responses of antennas and FSSs in the infrared.  Finally I will present my recent studies of structures showing control of both the reflected phase as well unity absorptivity/emissivity over a spectral region. 

Dr. Kinzel received his B.S., M.S. and Ph.D. in Mechanical Engineering from Purdue University 2003, 2005, and 2010.  He was a postdoctoral researcher in the department of Physics and Optical Sciences at the University of North Carolina at Charlotte.  His research interests include optical/infrared antennas for nanofabrication, sensing and energy harvesting.  More specifically nanolithography, phase-resolved near-field scanning optical microscopy (NSOM), frequency-selective surfaces/metamaterials, infrared sensing, infrared signature control, and engineering radiative properties of surfaces for heat-transfer, photon management, and energy transport.
Oct. 5
(Friday 4.00 pm)
Bieniek Dr. John Farley
University of Nevada,
Las Vegas
Going beyond the lecture:
What have we learned  from physics education research?

In recent decades, physics research has been dramatically transformed by the use of computers, lasers, and automated instruments. In contrast, physics education has changed very little. Traditional lectures reign supreme. The new discipline of physics education research has applied the scientific method to the process of teaching and learning. A critical advance is the use of pre- and post-testing of classes to measure student learning. One surprising conclusion is that traditional lecturing is remarkably ineffective.  I discuss a number of ways in which teaching can be improved, using pedagogy that is more effective than traditional lecturing. Finally, I discuss the NSF-funded physics Research Experience for Undergraduates (REU) program at UNLV, one of the longest-running REU programs in the country, which teaches undergraduates how to conduct physics research.

Oct. 12
(Friday 4.00 pm)
Schulz Dr. Jason Alexander
Cold Atom Optics Group
Sensors and Electron Devices Directorate
U.S.Army Research Laboratory

Experiments in Cold Atom Optics at the U.S. Army Research Laboratory

I will describe the work we have been doing in the Cold Atom Optics Group at U.S. Army Research Laboratory. After a brief review of the basics of laser cooling and trapping I will discuss our progress towards a couple of experiments on manipulating cold atoms on a chip for quantum sensing. The first experiments are directed towards developing a compact atom interferometer on an atom chip using a double-well potential. The interferometer uses 87Rb atoms magnetically confined in an atomic waveguide produced by wires on the surface of a lithographically patterned chip.  Finite element modeling of combinations of different current configurations with various external bias fields indicated a means of coherently splitting the atomic cloud through dynamically adjusting the currents and bias fields.  In these experiments we investigate real-time transformations between different double-well configurations adiabatically and non-adiabatically, and study their effects on the initially trapped atoms. Coherence properties of the two atomic wavepackets are examined. In another set of experiments we investigate the properties of bosons confined to (quasi) one dimension in our magnetic waveguide. When the atom-atom repulsive interaction becomes much larger than the kinetic energy, bosons confined in one dimension can enter a new state of matter, the Tonks-Girardeau gas, in which they behave like non-interacting fermions. However, the bosons can still occupy the same momentum state and therefore the gas cannot be fully described by either Bose-Einstein or Fermi-Dirac statistics.  This transition has been observed in optical lattices but not in magnetic atom chip waveguides. We discuss the conditions for obtaining a Tonks-Girardeau gas with 87Rb atoms in our atom chip waveguide as well as a novel signature for observing the transition in our system.  Finally, I would like to spend a few minutes proposing some new experiments. These experiments would combine the techniques of laser cooling and atom chip traps with the cold target recoil ion momentum spectroscopy (COLTRIMS) techniques I learned at MS&T from Professor Schulz to investigate few-body dynamics in cold and ultracold collisions, In these collisions, mostly total cross-sections are measured assuming a certain model (the 1st Born approximation) and determined by atom trap loss rates.
Oct. 18 Schulz Dr. Nhan V. Tran

 Discovery of the Higgs boson or something like it

On July 4th, 2012, the CMS and ATLAS collaborations at the Large Hadron Collider announced the discovery of a new bosonic particle at a mass near 125 GeV.  It is one of the most significant results in high energy particle physics over the past 30 years.  I will give an overview of the search at CMS for the Higgs boson hypothesized by the Standard Model of particle physics, including a broad introduction to general experimental techniques, and a review of the anatomy of the discovery.  There will also be a brief discussion on the implications of the discovery on physics beyond the Standard Model and what next steps are planned to better characterize this new particle.

Oct. 25

Nov. 1 Jentschura Dr. Robert Ehrlich
George Mason University
The Superluminal Neutrino Hypothesis: Searching for Tachyons or Unicorns?

With a recent claim of superluminal neutrinos shown to be in error, 2012 may not be a propitious time to review the evidence that one or more neutrinos may indeed be tachyons with v > c and m^2 < 0.   Nevertheless, there are a growing number of observations that continue to suggest this possibility -- albeit with a mass-squared having a much smaller magnitude than was implied by the original OPERA claim.  In addition to summarizing this evidence, this talk also discusses a possible 3 + 3 mirror neutrino model incorporating one superluminal neutrino pair, as well as a large number and variety of tests of the superluminal neutrino hypothesis.  One of these tests involves a surprising prediction concerning an unreported aspect of the SN 1987A neutrino data.

Nov. 8 Hor Dr. Michael Schulz
Missouri S&T
The Overlooked Role of Projectile Coherence in Atomic Fragmentation Processes

It is well established that the Schrödinger equation is not analytically solvable for more than two mutually interacting particles even if the underlying force is precisely known.  This fundamental problem, known as the few-body problem, has motivated atomic scattering research for decades and resisted a general solution until today.  However, for certain kinematic regimes the few-body dynamics in some atomic fragmentation processes were thought to be basically understood until about a decade ago.  This assumption was seriously shaken when qualitative and puzzling discrepancies between experiment and theory were found for a situation that was regarded as relatively “easy” for theory.  These studies were vividly debated for many years, but a major breakthrough towards a solution was only achieved recently by experimental developments.  It was demonstrated that atomic scattering cross sections can depend on the projectile coherence properties and, since this was not accounted for in theory, that this could explain some of the discrepancies between theory and experiment in past studies.  In this talk a series of experimental studies on the role of projectile coherence will be presented and analyzed.

Nov. 15 Hor
Dr. Thomas Vojta
Missouri S&T
The 2012 Nobel Prize in Physics
Nov. 29 Hor 19th Annual Laird D. Schearer Prize Competition
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