Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D13: SPS Undergraduate Research II |
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Chair: Gary White, American Institute of Physics Room: 309 |
Monday, March 16, 2009 2:30PM - 2:42PM |
D13.00001: SESSION BREAK |
Monday, March 16, 2009 2:42PM - 2:54PM |
D13.00002: Phase measurements on a subwavelength optical metamaterial based on metallic paired strips Kara Maller, Thomas Jarvis, Xiaoqin Li, Dmitriy Korobkin, Gennady Shvets, Marcelo Davanco, Xuhuai Zhang, Stephen R. Forrest There is no known naturally occurring material with negative index of refraction because the electrical and magnetic resonances in naturally occurring materials do not overlap in frequency. However, artificially engineered materials, known as metamaterials, can be designed to exhibit such peculiar properties. We study a subwavelength optical metamaterial composed of paired gold strips separated by a continuous gold film. According to theoretical calculations, this structure is expected to display a negative index of refraction in the near-infrared. We perform phase measurements of the material using a polarization interferometer and a tunable femtosecond laser. The phase information of the transmitted wave at various wavelengths is used to characterize the index of refraction. [Preview Abstract] |
Monday, March 16, 2009 2:54PM - 3:06PM |
D13.00003: Undergraduate Research with Josephson Qubits: From Fabrication to Spectroscopy Alyssa Wilson, Jerome Mlack, Anthony Tyler, Zechariah Thrailkill, Joseph Lambert, Roberto Ramos Josephson junctions are scalable solid state devices that can be used as qubits in quantum computing. In this talk we will describe the different stages involved in the fabrication, characterization and state measurement of a particular superconducting qubit known as the Josephson phase qubit. We have performed current-voltage measurements that determined the critical current of our device and produced histograms of switching currents that were needed to establish the quantum state of the junction. We will also report on the progress on microwave spectroscopy measurements involving multiple qubits coupled using on-chip capacitors. Spectroscopy reveals the various energy levels of entangled quantum states. We will discuss how physics undergraduates have contributed to this work. [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:18PM |
D13.00004: Degradation Studies of Polymer Blend Photovoltaics Brian Johnson, Enaanake Allagoa, Robert Thomas, Greg Stettler, Marianne Wallis, Justin Peel, Brian McNelis, Richard Barber We have measured the time dependence of device performance for photocells using blends containing the conjugated polymer, Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with different functionalized C$_{60}$ electron acceptor molecules: commercially available [6,6]-Phenyl C$_{61}$ butyric acid methyl ester (PCBM) or [6,6]-Phenyl C$_{61}$ butyric acid octadecyl ester (PCBO) produced in our laboratory. Performance was characterized by the maximum power output of the devices, with the time dependence typically following an exponential decay. Variations in the characteristic lifetime of the devices were observed to depend on the molar fraction of the electron acceptor molecules (calculated with respect to the MEH-PPV monomer fraction). Differences in the decay behavior between the PCBM and PCBO blends will be presented. [Preview Abstract] |
Monday, March 16, 2009 3:18PM - 3:30PM |
D13.00005: Coulomb Blockade I-V Characteristics in Nanowires Sarah Joy, Guneeta Singh-Bhalla, Arthur Hebard, Amlan Biswas, Selman Hershfield The current-voltage (I-V) characteristics of manganite nanowires seen in an experiment closely resemble the hallmark I-V curves of the Coulomb blockade. Unlike normal Coulomb blockade curves, these curves have multiple lines instead of one, branching out from the zero current point. In order to discover an explanation for these I-V curves a simulation based on the Coulomb blockade was done for multiple junctions, because the experiments were done in a regime where multiple islands of ferromagnetic material are separated by insulating regions, as a result of intrinsic phase separation. The simulation results show I-V curves that are in good qualitative agreement with the experiment. The branching of I-V curves is due to a large change in resistance between the islands -- not a change in the capacitance. Analytic work shows that the change in the junction resistance is too large to be explained by the tunneling magnetoresistance, but consistent with a change in the barrier thickness or composition. Simulations of the effect of gates show that the low voltage regime changes periodically with the gate voltage, while the high voltage regime is independent of gate voltage. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D13.00006: A quartz tuning fork as a force sensor for atomic force microscopy Arthur Ianuzzi, Julia Neff, John Timmerwilke, Amlan Biswas We are designing and building an atomic force microscope (AFM) to characterize the surface properties of perovskite oxides in low temperature ($\sim $10K) and high magnetic field (9T) environments. We are using a quartz tuning fork as the force sensor. The z-axis displacement of a conducting AFM tip due to surface features will be detected by observing the shift in resonance frequency of the tuning fork which is attached to the tip. The conducting tip will also allow us to perform conductive atomic force microscopy. The resonance characteristics of the tuning fork element were determined in various degrees of vacuum, with and without the tip installed, and as a function of the tip's proximity to the sample surface. We show that the high resonance frequency ($\sim $32kHz ) and quality factor ($\sim $30,000) of the tuning fork makes it an extremely sensitive force detector. The apparatus has also been designed with the capability of performing magnetic force microscopy on perovskite oxides. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D13.00007: Mossbauer Study of the xCr2O3-(1-x)$\alpha $-Fe2O3 nanoparticles system. Sean Krupa, Monica Sorescu The xCr2O3-(1-x)$\alpha $-Fe2O3 nanoparticles system was synthesized hydrothermally for x=0.0 to x=0.9. M\"{o}ssbauer spectroscopy was performed on the obtained samples as well as for samples subjected to thermal annealing at 550 C for one hour. At x=0.1, the as obtained samples began showing superparamagnetism and became completely superparamagnetic after x=0.4 concentration. The percent of the sample that was superparamagnetic increased with Cr2O3 substitution. This correlates with chromium decreasing the particle size of the powder. The thermally annealed samples appeared to have the hematite structure re-grown for concentrations x=0.1 to x=0.4 with the intensity of the hyperfine magnetic field decreasing with Cr2O3 concentration. For x=0.5 to x=0.9, the percent of superparamagnetic particles increased with Cr2O3 concentration, dominating the system by x=0.8. This system is believed to have applications in gas sensing and catalysis. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D13.00008: Construction of a semiconductor laser system for magneto-optical trapping of atomic rubidium Ian Dougherty, Michael Lim We report on the construction of a semiconductor laser system to generate light for magneto-optical trapping of rubidium. A DFB laser is used as a master oscillator with rapid frequency tuning accomplished by an acousto-optic modulator in double-pass configuration. The resulting beam seeds a 0.5-W tapered semiconductor amplifier chip. We spatially mode-match its output to a polarization-maintaining, single-mode fiber using lenses and two anamorphic prism pairs. At maximum efficiency the system generates more than 100 mW of TEM00 power at the fiber output. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D13.00009: Combinatorial Synthesis of (V$_{1-x}$,Cr$_{x})_{2}$GeC Epitaxial Films C. E. Steinmetz, J. R. Applegate, S. M. Benjamin, B. D. Adamson, J. D. Hettinger, S. E. Lofland, T. H. Scabarozi We report the synthesis of solid solutions of (V$_{1-x}$,Cr$_{x})_{2}$GeC epitaxial films on single crystal Al$_{2}$O$_{3}$ epi-polished substrates. The materials are sputtered from four cathodes; three are powered by rf-power supplies while one is driven by a dc-power supply. The materials are co-deposited at a temperature of 900\r{ }C and we get solubility across the whole range of compositions. The substrate-film interaction creates a strain which makes the new phase energetically favorable. The surface structure was measured using atomic force microscopy revealing that the composition has little impact on this property. We found a new MAX-phase material, (V$_{0.5}$Cr$_{0.5})_{4}$GeC$_{3}$ , which has never been synthesized in bulk form. We report the conditions required to make these materials. In addition, electrical transport characteristics as a function of composition will be reported. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D13.00010: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 4:30PM - 4:42PM |
D13.00011: Thermodynamic Properties of Ising Spins on the Triangular Kagom\'{e} Lattice Bilin Zhuang, Courtney Lannert The triangular Kagom\'{e} lattice can be constructed by inserting a lattice site on each bond of the Kagom\'{e} lattice. Each unit cell contains 6 $a$-sites, 3 $b-$sites, 6 \textit{aa-}bonds and 12 \textit{ab-}bonds. The lattice with antiferromagnetic \textit{aa}-bonds is known to exhibit geometrical frustration at low temperatures. We applied analytical methods and Monte Carlo simulations to study a system of Ising Spins on the lattice and investigated its thermodynamics properties. In particular, the heat capacity of the model exhibits interesting features based on the strength and the sign of coupling constants J$_{aa}$ and J$_{ab}$. In the case when the \textit{aa-}interaction is antiferromagnetic, the heat capacity shows two broad peaks at kT/$\vert $J$_{ab}\vert \cong $1.8 and at kT/$\vert $J$_{aa}\vert \cong $1.8. In the case when the \textit{aa-}interaction is ferromagnetic, the heat capacity shows a sharp peak at kT/$\vert $J$_{ab}\vert \cong $1.9 and another low broad peak at around kT/$\vert $J$_{aa}\vert \cong $1.4. We also studied a much simpler system of two $a-$trimers connected with $b-$sites to reproduce the thermodynamics behaviors of the more complicated triangular Kagom\'{e} lattice and to further understand the origin of its interesting properties. [Preview Abstract] |
Monday, March 16, 2009 4:42PM - 4:54PM |
D13.00012: Monte Carlo Simulations of a $111$-Ising Dipolar Model on the Hyper-kagom\'{e} Lattice Patrick Carter, John Hopkinson, Matthew Enjalran Motivated by the physics of dipolar spin ice, we investigate the hyper-kagom\'{e} lattice with $111$-Ising spins. The hyper-kagom\'{e} lattice can be generated by a selective removal of one site per tetrahedron of the pyrochlore lattice to yield a lattice of corner-sharing triangles. The spin-$1/2$ Ir$^{4+}$ ions of Na$_4$I$_3$O$_8$ represent an experimental realization of the hyper-kagom\'{e} structure. We report preliminary results from Monte Carlo simulations of the $111$-Ising dipolar hyper-kagom\'{e} model, which represents a yet to be studied disorder-free limiting case of diluted spin ice. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:06PM |
D13.00013: Thermal measurements of the MAX-phase material Cr$_{2}$GeC D. T. Piwowar, P. Abbazia, D. Filomena, D. Dorofy, M. Garzon, S. E. Lofland, J. D. Hettinger, T. H. Scabarozi We have measured the specific heat and thermal transport in bulk Cr$_{2}$GeC samples that have been hot-isostatically-pressed or hot pressed. We observe no difference in the results based upon the synthesis procedure. We find the low temperature specific heat is fit well by the standard expression. These measurements suggest a large density of states at the Fermi level or a large electron-phonon coupling in this material. The Debye temperature, extracted from the phonon contribution to the specific heat, is found to be 460 K which roughly correlates with the Debye temperature extracted from the ultrasonic elastic measurements. The phonon contribution to the thermal conductivity will also be reported. [Preview Abstract] |
Monday, March 16, 2009 5:06PM - 5:18PM |
D13.00014: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 5:18PM - 5:30PM |
D13.00015: Borosilicate films as permeability barriers J. R. Applegate, C. E. Steinmetz, J. D. Hettinger, J. F. Carroll, R. Krchnavek Borosilicate films have been deposited using rf-sputtering techniques from a composite target at room temperature onto polypropylene (PP), high density polyethylene(HDPE), low density polyethylene(LDPE), and polyethylene terephthalate (PETG) substrates. Films were found to be smooth, flexible, with excellent adhesion to the substrates. Repeated rolling the coated substrates on a radius of 0.5mm resulted in no discernable damage for films less than 200nm in thickness. Creasing the substrates did result in local damage. However excellent adhesion did not allow the fractured glass to come off the substrate. Heat generated during deposition only influenced the films grown on LDPE where the thermal expansion mismatch between the film and substrate induced strains caused fractures in thick films. Modifications to processing parameters allowed thick films to be grown without fractures. Permeability measurements of nitrogen resulted in significant improvements in comparison to uncoated substrates. [Preview Abstract] |
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