Bulletin of the American Physical Society
Joint Spring 2014 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 59, Number 2
Thursday–Saturday, March 20–22, 2014; Abilene, Texas
Session A1: Poster Session I |
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Chair: Rusty Towell, Abilene Christian University Room: Hunter Welcome Center C |
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A1.00001: Dielectric properties of endohedral fullerenes Shusil Bhusal, Rajendra Zope, Tunna Baruah, Koblar Jackson We investigate the response of the applied static electric field to a series of endoherdal fullerenes using density functional theory. Using an approach to obtain the site-specific polarizabilities implemented in our massively parallel NRLMOL code, we examine the screening of the applied electric field by the pi-electrons on the fullerene cage. In the site specific polarizability scheme, the total cluster polarizability is decomposed into local dipole (LD) and charge-transfer (CT) parts. The local dipole part measures the redistribution of charge within an atomic volume, while the CT part describes the movement of charge between volumes. Our results show distinct differences in the relative contributions of the LD and CT components to the total polarizability in endohedral fullerenes and that fullerene cages behave, to a significant extent, as Faraday cages. [Preview Abstract] |
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A1.00002: Molecular dynamics study of phthalocyanine and sulfonated-phthalocyanine and C60 interface Carlos Diaz, Marco Olguin, Tunna Baruah, Rajendra Zope Organic photovolatics (OPV) hold promise as cheap large-area technology for power generation. The fundamental mechanism of power conversion in OPV is dominated by interfacial processes such as charge transfer and charge separation. The energetics and dynamics of these processes depend on the morphology of the donor and acceptor (DA) interfaces. In experiments, these DA complexes are usually deposited on metal surfaces using spin coating or similar technique. To understand the morphology of interface and growth of the OPV on surface, we use molecular dynamics simulations with various layers of phthalocyanine and sulfonated phthalocyanine molecules on a Ag(111) surface. We examine the effect of sulfonation on the morphology of thin films. By introducing the acceptor molecules such as C60 in various concentrations we examine the variation in the morphology of OPV films with the different forms of phthalocyanine surfaces. We then select a few configurations of the DA complexes from the molecular dynamics trajectories and determine the charge transfer energies and the transport gap at the quantum mechanical level. Finally, by averaging over the configuration we obtain insights into the charge transfer energetics and the energy level alignments at the organic DA interface. [Preview Abstract] |
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A1.00003: Charge transfer excited states of complexes of ZnTPP with dye-attached fullerenes Marina Paggen, Amanda Garnica, Rajendra Zope, Tunna Baruah Organic photovoltaics (OPV) are prevalent in research as they exhibit high potential for flexible and cheaper solar cells. The fullerene or fullerene derivatives such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are used as electron acceptors in the bulk heterojunction type solar cells. Often, functionalization of fullerenes is used to achieve optimal separation between the frontier molecular orbitals of the donor and acceptor molecules. Another purpose of such functionalization is to increase the absorption range of the active materials which can lead to higher photocurrent. Recently, one group of dye-attached fullerenes has been synthesized. We carried out a computational study on the electronic structure and charge transfer excited states of such dye-attached fullerenes in conjunction with Zn-tetraphenyl porpohyrin. Our calculations are done using density functional theory at the all-electron generalized gradient level. We study two different dye-attached fullerenes and compare their charge transfer excited states in a complex with ZnTPP. [Preview Abstract] |
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A1.00004: Electronic structure and charge transfer excitation energies of a Sc$_{3}$N@C$_{80}$ -Zinc phthalocyanine (Znpc) complex Fatemeh Amerikheirabadi, Luis Basurto, Tunna Baruah, Rajendra Zope Organic photovoltaics (OPVs) have attracted considerable research interest due to their mechanical flexibility and low cost manufacturing. Organic donor-acceptor moieties form the main component of the organic photovoltaics. The donor molecule, which is a chromophore, absorbs a photon from sunlight and subsequently the excited electron is transferred to the acceptor molecule creating a charge transfer state in which a hole resides on the donor and a particle resides on the acceptor. The energy of the charge transfer state is important from the perspective of the organic photovoltaic device efficiency since it determines the achievable open-circuit voltage of such devices. We present the charge transfer energetics of the Sc$_{3}$N@C$_{80}$ -Zinc phthalocyanine (Znpc) complex which helps to have an insight into the CT process. We present a density functional theory study of the electronic structure of the Sc$_{3}$NC$_{80}$-Znpc. In this complex, the Sc$_{3}$N@C$_{80}$ plays the role of the acceptor molecule and Znpc would be the donor part. This molecular conjugate is very large to be analyzed using quantum chemical methods so in this work we use density functional theory as implemented in the NRLMOL code. We study a few charge transfer excited state energies of the mentioned molecular complex using our perturbative delta-SCF method. Our calculations are done at the all-electron generalized gradient level. We will also present the results of the analysis of the isolated donor and acceptor molecules. [Preview Abstract] |
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A1.00005: Radon Plateout on Copper to ilLUMINAte Background Levels in the Super Cryogenic Dark Matter Experiment Mayisha Nakib, Matthew Bruemmer, Jodi Cooley, Silvia Scorza The Laboratory for Ultra-pure Material, Isotope and Neutron Assessment (LUMINA) at Southern Methodist University houses one of only five existing UltraLo 1800 production model alpha counters made commercially available by XIA LLC. The instrument has an electron drift chamber with a 707 cm$^{2}$ or 1800 cm$^{2}$ counting region which is determined by selecting the inner electrode size. The SMU team operating this device is part of SuperCDMS materials and screening working group, and uses the alpha counter to study the background rates from the decay of radon in materials used to construct the SuperCDMS experiment. We will present updated thorium-230 calibration of the instrument along with results from initial studies on copper samples exposed to thorium sources in our lab in order to understand radon plateout, on copper and optimal storage conditions for copper. [Preview Abstract] |
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A1.00006: Cost-Effective Construction of a Cloud Chamber Palmer Wilson A cloud chamber is a device that contains supersaturated vapor that is used to detect charged particles by the condensation trails that they produce. The build described is this presentation utilizes Peltier elements to cool the system, while conventional cloud chambers use liquid nitrogen or dry ice. The use of Peltier elements allows for the device to run without the continued purchase, use, or storage associated with liquid nitrogen or dry ice. The materials used to construct the cloud chamber itself includes low-cost ABS plastic, aluminum support tubes, a clear glass vase, Peltier elements, a CPU heat sink, and an ATX computer power supply. The low-cost construction of this cloud chamber allows for resources to be spent elsewhere while providing a productive, responsive, and effective experimental apparatus. While the minimum operating surface temperature achieved using liquid nitrogen or dry ice is lower than that achieved using Peltier elements, an operational surface temperature of -20 $^{\circ}$C was reached using the apparatus described in this presentation, allowing for adequate resolution of the paths of charged particles inside the chamber. Future plans include increasing the viewing area, optimization of the power grid, and a dynamic Peltier microcontroller sub-system. [Preview Abstract] |
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A1.00007: Comparing pairs of successive corotating interaction regions Derric Edwards, Charles Knight, Kevin Pham, Ramon Lopez Coronal holes on the Sun emit solar wind at a higher speed than the areas around them. The faster streams of solar wind catch up to the slower solar wind, which was emitted before them, and compress the slower solar wind. This causes an increase in density and magnetic fields which is known as a corotating interaction region (CIR). In this study, we are primarily concerned with pairs of successive CIRs. Successive CIRs are two CIR's that are produced by the same coronal hole on the Sun and are observed on successive rotations of the Sun, where one rotation is about 27 Earth days. Once all of the CIR sets are obtained, we will compare and contrast various parameters, such as magnetic field and velocity, between the two CIRs within each set. We expect the two successive CIRs to behave in a similar manner and have similar parameters. [Preview Abstract] |
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A1.00008: Studying Alfven waves in high speed streams that follow a corotating interaction region Soha Aslam, Christopher Sherrill, Kevin Pham, Ramon Lopez There is always a constant outflow of plasma away from the Sun, which we call the solar wind. The regions of solar wind originating from coronal holes are called high speed streams when their velocity is greater than 500 km/s. When a high speed stream overtakes the slower solar wind, it creates a compressed boundary between the fast and slow solar wind. This compressed layer is known as a corotating interaction region (CIR). In the CIR, and corresponding high speed stream, there are large amplitude Alfven waves that travel along the magnetic field and transverse to the propagation. The Alfven waves cause oscillations in the velocity and strength of the interplanetary magnetic field. By looking for specific deviations in plasma velocity and magnetic field magnitude, we will attempt to identify the presence of Alfven waves. [Preview Abstract] |
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A1.00009: Thin Film CdS/CdTe Diodes for Nuclear Radiation Detection Julianna Calkins In this study we have investigated thin film, polycrystalline CdS/CdTe PN diodes as solid state charged particle detectors. Solid state neutron detectors rely on the indirect detection of neutrons via a nuclear reaction, which produces charged particles detected by a semiconductor diode. The CdS/CdTe diodes were evaluated in terms of their sensitivity to alpha and gamma radiation when connected to a charge sensitive preamplifier. The devices were found to have an alpha particle counting efficiency of greater than 90{\%}. The pulse height response of these diodes due to alpha radiation is found to be a function of applied bias, angle of incidence, and energy of the incident alpha particles. Preliminary gamma sensitivity measurements indicate an intrinsic gamma detection efficiency of less than 1x10$^{-6}$. The CdS/CdTe results were calibrated using a 1 cm$^{2}$ Ortec ULTRA silicon PIN detector and were also compared to data collected from silicon detectors fabricated at UT Dallas. The CdS/CdTe devices offer the possibility of large area neutron detectors with high gamma rejection rates and affordable production costs. [Preview Abstract] |
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A1.00010: XY Lithography Table Kent Grimes, Taylor Freehauf The objective of this project was to create an XY Lithography table that will scan the surface of an object with a laser and photometer. This project utilized a relatively inexpensive set of materials including stepper motors, a stepper motor drive card to drive the motors, motion relay switches and slide rods. This table is comprised of some scrap wood to assemble the structure. With the table built, it can be used to produce a light intensity mapping of the surface of an object placed under the table. Using the programing software LabVIEW and Microsoft Excel, we were able to program the table to map a photometrical sketch of any surface or object within its one foot square area. [Preview Abstract] |
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A1.00011: Measuring Light's Motion on a Rotating Platform Charles Rogers, Richard Selvaggi This experiment uses a concentric optical cavity to measure the direction of the motion of light in a rotating frame of reference. Our hypothesis asks what affect does motion have on the measured trajectory of photons? Does the trajectory of light measured in a rotating platform differ from that measured in a non-rotating platform? The apparatus set-up, operation, and measured results are presented. [Preview Abstract] |
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A1.00012: The interaction between lasers and dielectric surfaces assisted by an isotropic source of energy Md. Raju, Md. Khairuzzaman, N. Lanning, W-T. Hsu, C. Bahrim Our method of polarization of light incident at the Brewster angle on a dielectric surface allows finding indices of refraction with a precision of 0.0001 [1]. This precision allows us to generate accurate dispersive curves in visible and near visible range using relative inexpensive equipment. We propose a simple method for finding the dispersive curve for non-magnetic dielectrics using relative inexpensive diode lasers and an isotropic energy source. The idea is based on the scalar addition of energy from various sources on a dielectric surface. Our interpretation is inspired from the classical dipole oscillator model [2]. We use this technique to eventually create a strong coupling between two laser fields assisted by an isotropic source of energy, which simultaneously interact with the same dipoles of the dielectric. This experiment could be used as a simple experimental prove of the destructive interaction between a strong coupling laser and a weak probe laser with the creation of electromagnetic induced transparency in optical materials.\\[4pt] [1] Bahrim C and Hsu W-T, 2009 Am. J. Phys 77(4) 337-343.\\[0pt] [2] Eugene Hecht `Optics' 4th ed., Addison-Wesley Longman 2002. [Preview Abstract] |
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