Colloquia - Spring Semester, 2006

January 24, 2006
Dr. Brandon J. Jordon-Thaden
Department of Physics and Astronomy
University of Nebraska-Lincoln
"Extensions of Polar Breakup of H3 and D3: Three Body Problem, Quantum/Classical Domain, and Chaotic Dynamics"
When three massive particles interact through a long-ranged potential, the long-term dynamics cannot be described by known functions. The Sun + Earth + Moon system has fascinated scientists since the time of Newton. In our lab we have access to a similar systems of three ions: H++H++H- (and D++D++D- ), where the Newtonian gravitational potential is replaced by the long-range Coulomb potential.  We have measured the final state center-of-mass (c.m.) energy partitioning in a triple coincidence experiment that Involves H3  (and D3) dissociating into the Coulomb interacting channel of H++H++H- (and D++D++D- ). When plotted as a function of total c.m. energy, the fraction of c.m. energy exhibits unique, repeatable structures.  To understand these patterns, classical simulations of the three Coulomb-interacting fragments were performed. The classical simulations offer insights into the quantum nature of the parent ion superimposed on the post-dissociation dynamics of three-body Coulomb interaction system. The measurement and simulations provide evidence of a bound H+-H- and (D+-D-) complex forming due to post-dissociation Coulomb interactions. For short times, these complexes exhibit highly eccentric, classical Keplerian-like orbits such that each fragment maintains its own uniqueness. The formation of these Keplerian pairs presents a new, unconsidered dissociation channel that may play a significant role in near-threshold polar breakups of molecules.
 

February 2, 2006
Various Distinguished Speakers
"Symposium: Nanoscale Materials for Optoelectronics and Biotechnology"
 

February 7, 2005
Dr. Floyd D. McDaniel
Department of Physics
University of North Texas
"Ion-Induced Emission Microscopy"
Radiation Effects Microscopy (REM) has been used at Sandia National Laboratories (SNL) for several years to study radiation-hard integrated circuits (ICs). As ICs become more radiation hardened, ions with larger linear energy transfer (LET in MeV/mg/cm2 ) are needed to study their response to radiation. This higher LET can be achieved by using high-energy heavy ions. To carry out REM on ICs, the ion beam has to be focused to a submicron spot, which is very difficult for these high-energy heavy-ions. A new high LET system was developed at SNAl, which combines two entirely new concepts in accelerator physics and nuclear microscopy. A Radio Frequency Quadrupole (RFQ) Linac is used to boost the energy of ions acceleratred by a conventional Tandem Van de Graaff Pelletron to energies of 1.9 MeV/amu. To circumvent the problem of focusing high-energy ions, the Ion-Electron Emission Microscope (IEEM), invented at SNL, is used. Instead of focusing the ion beam and scanning it over the device under test (DUT), the positions of the ion hits are determined by projecting ion-induced secondary electrons at high magnification onto a single electron position sensitive detector (PSD). Then the two position signals (x and y) are recorded in coincidence with each REM event. The Ion Photon Emission Microscope (IPEM), which was developed at SNL, is the first device that allows scientists to study microscopically the effec ts of single ions in air on semiconductors, microchips, and biological cells without having to focus the beam. I report on a prototype of the IPEM the size of a conventional optical microscope. The alpha-IPEM em0ploys alpha particles from a readioactive source and represents the first example of IBA imaging without an accelerator. I will give some details of the RFQ booster, the IEEM, and the IPEM systems, along with initial results on radiation hardened ICs. SNL received an R&D 100 Award for the IEEM in 2001 and another RED 100 Award in 2005 for the IPEM.

February 14, 2006
Dr. Gary Glass
Director, Louisiana Accelerator Center
University of Louisiana - Lafayette
"High-Energy Focused Ion Beams"
There is a critical need for novel instrumentation with which properties of nanomaterials can be observed, measured, altered and utilized. High energy ions can penetrate well below surfaces of materials and offer a means by which sub-surface regions can be studied and manipulated. Therefore, when high-energy ion beams are focused to sub-micron dimensions they can be used as probes to enable unique analyses and modifications of the nano-world.  Analytical capabilities of high-energy focused ion beam (HEFIB) systems include an increasing number of two- and three-dimensional techniques for materials with sub-micron spatial resolution. There are various techniques by which high-energy ions can affect nanoscale properties of materials.  In particular, the use of focused high energy (MeV) protons for direct-write lithography in a process called P-beam writing has several distinct advantages as a lithographic technique, which are: (a) a three dimensional (3-D) capability, (b) a maskless process, (c) creation of high aspect ratio structures, (e) significant reduction of proximity effects, and (f) a relatively fast process.  This presentation will provide an overview of HEFIB systems design, give some examples of the use of HEFIB for material analysis and modification, and look to the future of HEFIB systems advanced technology. Examples of P-beam writing in resist coatings and silicon will be shown. I will present initial work in the development of a new fabrication technique, high-energy heavy ion beam lithography (HI-beam writing).

February 21, 2006
Dr. Arkadii Krokhin
Department of Physics
University of North Texas
"Natural & Artificial Nanostructures: Between Order and Disorder"
In this talk I will give an overall view of electronic and optical properties of low-dimensional periodic and disordered nanostructures, including DNA molecules, microwave waveguides, semiconductorsuperlattices, photonic crystals, and plasmonic devices. The role of order, disorder and statistical correlations will be discussed. I will briefly explain some principal physical effects and phenomena that govern electron and photon transport in these structures. They are: Anderson localization, Bragg reflection, dynamical chaos, birefringence, and optical anisotropy.
 

February 28, 2006
Dr. G.A. Luna-Acosta
Instituto de Fisica, BUAP
Puebla, Mexico
"Effects of Impurities and Random Disorder in Microwave Photonic Kronig-Penney Model"
We have investigated a microwave realization of a one-dimensional (1-D) photonic array consisting of sets of Teflon pieces alternating with air spaces in a microwave guide. We consider only single-mode propagation, so the model is essentially 1-D and obeys the Helmholtz equation. For the case of finite periodic arrays, transmission measurements reveal a well-defined band structure that is reproduced well by transfer matrix calculations for the corresponding photonic Kronig-Penney model. Further, we construct arrays with various types of single impurities and find that our transfer matrix calculations agree extremely well with experimental data. We obtain exact closed-form expressions from which we can determine the impurity levels, their intensities, and the band profiles. Finally, we present our experimental and numerical results for the case of random positional disorder, obtained by varying randomly the air spaces. We find the Teflon resonances strongly inhibit Anderson localization of states predicted for 1-D random potentials. Our results are relevant for the Kronig-Penney model in quantum mechanics and solid state physics.
 

March 7, 2006
Ron DiIluio
Department of Physics
University of North Texas
"Kuiper Belt Objects: Comets, Meteorites, Asteroids or Planets?"
I will discuss the NASA Missions called Stardust, Deep Impact and New Horizons. I will give their scientific consequences and how they can be justified to the general public. I will also briefly present the status and future of the astronomy program at UNT.
 

March 21, 2006
Dr. Jim Roberts
Department of Physics
University of North Texas
"A History of Radio Astronomy: Music from the Cosmos"
During the past 40 years radio astronomy has been one of the most effective tools to study our universe. Numerous discoveries have been made from radio wave signals all the way to microwave signals. This information enables us to identify molecules in interstellar space through their microwave emissions. The “spin-flip” transition in hydrogen enables us to locate the distribution of hydrogen in our galaxy and to characterize its structure. The emissions from hydrogen interfere with some telephone signals that have carrier frequencies near 1400 MHz. This talk will address some of the discoveries and their implications for cosmological models. The talk will be accessible to the general public as well as to those who have a scientific understanding of the cosmos.

March 28, 2006
Dr. Michael B. Santos
Department of Physics
University of Oklahoma
"Electronic Properties of InSb: Quantum Wells and Mesoscopic Structures"
In narrow-gap semiconductors, electrons have properties that are much different than in free space. For example, the effective mass in InSb is nearly two orders of magnitude smaller than the mass in free space. This property can be exploited in applications, such as magnetic read heads or ballistic transport devices, where a high mobility or a long mean free path is required. The strength of the interaction between an electron's spin and a magnetic field is also enhanced in InSb. The consequences of a small effective mass and large spin-orbit coupling are seen in far-infrared spectroscopy and charge transport measurements performed on structures with n nanometer-scale dimensions in one or more directions.
 

April 4, 2006
Dr. James Espinosa
Department of Physics
University of West Georgia
PowerPoint of Dr. Espinosa's talk
"Einstein's Tests of General Relativity Through the Eyes of Newton"
Einstein suggested three possible tests of his Theory of General Relativity: bending of starlight by the Sun Precession of Mercury's orbit Gravitational redshift of spectra  Experimental and observational results of these tests are in excellent agreement with General Relativity. We reinterpret the three classical tests of Einstein completely within the framework of Newtonian physics. We formulate a law of gravity that assumes this force travels at the speed of light and, when combined with Newton's second law, arrive at results identical to those of Einstein's theory: a deflection angle of 1.75" arc seconds for light passing near the Sun  An angle of precession of 43.1" for the orbit of Mercury A gravitational redshift of 2.5 X 10-15 for the Pound-Rebka experiment.  The steps leading to an analytical expression will be discussed.
 

April 11, 2006
Dr. Felix Izrailev
Instituto de Fisica, BUAP
Puebla, Mexico
"Anomalous Transport in Disordered Models with Long-Range Correlations"
Abstract: Transport properties of one-dimensional (1D) and quasi-1D solid-state models with random potentials are fully described by single-parameter scaling. In other words, all transport properties of finite samples depend only on the ratio of their localization length (LL) to their size. Due to an exponential localization of all eigenstates in 1D and quasi-1D geometry, the LL determined by the inverse Lyapunov exponent is finite in the whole range of energy. Recently, it was found that long-range correlations in disordered potentials may lead to a very strong enhancement or suppression of the LL [1]. As a result, specific long-range correlations can result in windows of complete transparency or reflection in the energy spectra. Moreover, the method of constructing random potentials with prescribed correlations has been used experimentally to create wave guides with selective transport properties [2]. In this talk we discuss the general ideas related to the role of long-range correlations in disordered models, with possible applications to solid-state models, electromagnetic wave guides, conducting polymers, DNA, etc.
 

April 25, 2006
Dr. Wolfgang Schleich
Abteilung fur Quantenphysik
University of Ulm, Germany
"Quantum Entanglement and the Riemann Zeta Function"
We show that the auto-correlation function of an appropriately prepared wave packet in a specific anharmonic oscillator leads directly to the Riemann Zeta function. For this procedure only interference is needed. Therefore, an interferometer of classical light could achieve this realization of the Riemann Zeta function. However, in order to obtain the analytic continuation entanglement of two quantum systems is needed. The procedure is reminiscent of the method to create Schroedinger cats in micro-wave cavities or in the center-of-mass motion of ions as demonstrated experimentally by Haroche (Paris) and Wineland (Boulder). We discuss these techniques and make contact with the corresponding experiments.
Background: One of the main unsolved problems of number theory is the location of the zeros of the Riemann Zeta function. There exists a conjecture by Riemann that these zeros all lie on a line parallel to the imaginary axis with real part 1/2. Moreover, it was Riemann who showed that there is an immediate connection between these zeros and the distribution of prime numbers.The ladder had been found much earlier by Carl Friedrich Gauss empirically by just fitting a curve to this distribution. The standard definition of the Riemann Zeta function is given by an infinite series. However, this definition is only valid in a domain of complex space where the Riemann Zeta function does not display any zeros. In order to get into the domain where the zeros have been found numerically one has to perform an analytic continuation.
Click here to see Dr. Schleich's PowerPoint presentation
 

April 26, 2006
Dr. Daryush Ila
Director, Alabama A&M University
Research Institute, Carnegie Bldg.
Normal, Alabama
"Thermoelectric Materials and Carbon Composite Based Materials"
See http://cim.aamu.edu/
 

April 25, 2006
Dr. Ken Forster
U.T. Southwestern Medical School
Dallas, TX
"Applied Physics in Medicine"
Physics is a very mature field of study with many of fundamentals of our field dating back centuries.  The application of physics to medicine is still a relatively new field that is expanding very quickly. Medical physics fifty years ago was fairly routine work. Today physics is the backbone for radiology, nuclear medicine, and radiation therapy. An overview of the new opportunities for physicists will be presented with many examples.


May 2, 2006
Dr. Hui Chen
Texas Center for Superconductivity
University of Houston
"Cluster Ion Beam Modification of Material Surfaces"
The use of slow cluster beams, where the energy per atom is a few keV/atom or less, is becoming an important tool in shallow junction formation, surface smoothing, and thin film deposition. The interaction between clusters and solids produces different phenomena compared to monomer ion solid interaction. The experimental and theoretical characteristics of the interactions between cluster ion and solid will be described. The impact of an accelerated cluster ion upon a solid surface deposits a huge energy density into a small impact region and produces more localized lattice damage than a monomer ion with comparable energy. One consequence is a strong non-linear lattice damage buildup in Si induced by cluster ion irradiation. We have developed an analytical overlap model to explain this effect. Another difference between cluster ions and monomer ions is the smoothening effect of cluster ions. We have applied this effect of smoothening to the crosshatched surface of SiGe. We developed a mesoscopic model to explain qualitatively the smoothening effect under normal cluster beam bombardment and ripple formation under off-normal bombardment. We can also use cluster ion beams to deposit diamond-like carbon thin films that can be used as a flexible field emitter with high emission current. This is promising as a basis in the fabrication of flexible flat-panel displays. (Chen, J. R. Liu, K. B. Ma, W.K. Chu)
Click here to see Dr. Chen's PowerPoint presentation