Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B28: SPS Undergraduate Research I |
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Sponsoring Units: SPS Chair: Gary White, AIP/SPS Room: C124 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B28.00001: The Fabrication and Characterization of Flexible TiO$_{2}$ Memory Devices Laurie Stephey, Nadine Gergel-Hackett, Barbara Dunlap, Curt Richter Recently, work was published demonstrating the physical realization of a device with electrical properties consistent with a memristor, the theoretical missing fourth circuit element. Memristors can be switched from a low resistance state to a high state and will remain in this state until the opposite polarity bias is applied. Memristors also demonstrate unique electrical behaviors, including multi-state/analogue switching. In this study, devices with memristor characteristics were fabricated inexpensively on a flexible substrate and electrically characterized. Potential applications of these devices include serving as inexpensive memory for disposable electronics. Two different sizes of flexible memristors (2 mm x 2 mm and 100 $\mu $m x 100 $\mu $m) with various film thicknesses were fabricated and characterized. A correlation between film thickness and the threshold switching bias was observed. Parameters including charge magnitude, current magnitude, bias magnitude, and resistance were also investigated to search for potential trends in switching behavior. Preliminary analysis indicates that charge magnitude may be a contributing factor to switching and also that switching mechanisms may display some area-dependence. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B28.00002: Photocapacitance measurements on GaP alloys for high efficiency solar cells Dan Hampton, Tim Gfroerer Large bandgap materials are an essential component of ultra-high efficiency solar cells. While multi-junction devices harness more of the solar spectrum for electricity production, challenges in the construction of a lattice-mismatched system lead to defects that trap charge carriers and inhibit overall efficiency. This work uses photocapacitance measurements to obtain optical escape energies from defect levels in high-bandgap GaInP and GaAsP alloys. We combine these optical results with previous thermal measurements to construct a working model that incorporates a lattice configuration-dependent energy structure. The model explains why the optical escape energy is significantly larger than the thermal capture and escape energies, and in the GaAsP device, it helps explain why the number of escaping carriers depends on the energy of the incident light. We also observe persistent photocapacitance in the GaAsP device after a large capacitance change with illumination. The magnitude of the trap signal is comparable to that of the dopants, which suggests the presence of AX complexes in the p-doped region of the device. [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B28.00003: Scanning tunneling microscopy of self-assembled viral nanostructures Benjamin Anacleto, Nat Steinsultz, Prashant Sharma We use scanning tunneling microscopy to investigate self-assembled monolayers of M13 bacteriophages on graphite surface. The bacteriophages we use have gold binding peptide motifs on their outer protein coat ($\sim$1$\mu$m long, $\sim$10 nm diameter) allowing us to self-assemble gold nanoparticles on graphite. Using scanning tunneling microscopy we are able to resolve sub-molecular structure of the protein coat of M13 bacteriophage. Scanning tunneling spectroscopy allows us to study the binding of gold nanoparticles to the peptide motif on the bacteriophage. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B28.00004: Mechanical response of carbon nanotube turfs under lateral strains Melinda Lopez, David Bahr Carbon nanotubes (CNTs) have a broad array of applications due to their remarkable mechanical, electrical, and thermal properties. In particular, they have been observed to possess the greatest tensile and elastic moduli of any tested material. A great deal of research has been conducted on the mechanical properties of single carbon nanotubes under stress. However, very little mechanical studies have been performed on large collections of carbon nanotubes deposited on substrates, or ``turfs,'' under different strains. In this work, we examine these mechanical responses by nanoindentation. The data show that a CNT turf at 0{\%} strain has a higher elastic modulus than when at 3.5{\%} strain. This may be attributed to the change in CNT density of the turfs as lateral strain is applied to the substrate. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B28.00005: Density Functional Studies of Metal-Graphene Interfaces Pinar Bozkurt, Stephen Cannon, Romain Perriot, You Lin, Matthias Batzill, Ivan Oleynik Graphene, one-atom-thick layer of carbon has attracted great interest due to unusual physical properties and promising applications. One of the major ways to synthesize graphene is its growth on metal substrates. In addition, the metal/graphene interfaces play important role in establishing electrical contacts to graphene-based electronic devices. Therefore, the understanding of the atomic and electronic structure of metal/graphene interfaces is of key interest for graphene scientific community. In this talk we present results of density functional theory studies of Ni/graphene and copper/graphene interfaces. The strength of metal/graphene interactions was quantified by calculating the work of separation for different adsorption geometries. The electronic structure of the metal/graphene interfaces were compared to those of pure graphene by performing band structure calculations. Connection between the theory and experiment will be discussed as well. [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B28.00006: Terahertz Spectroscopy of Mn12-Acetate Claire Watts, Beth Parks, Chris Beedle, David Hendrickson Mn12-acetate is a single-molecule magnet with spin S = 10. It has been observed to exhibit quantum tunneling of the magnetization. The energy levels associated with this quantum tunneling have been probed using time-domain terahertz spectroscopy. We observe absorptions corresponding to excitations between spin states, but we also observe what seems to be emission at nearby frequencies. The emission frequency changes with applied field in the same way that absorptions do, but its explanation is unclear. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B28.00007: Evidence for a U(1)$_{B-L}$ Gauge Interaction in $\nu$ Oscillation Anomalies Netta Engelhardt The recent short baseline neutrino experiments LSND and MiniBooNE exhibit an anomalous behavior unexplained by the standard theory of neutrino oscillations. The experiments indicate that neutrino oscillation probability depends on the both the energy scale and the chirality of the neutrinos concerned, and are consistent with the $U(1)_{B-L}$ gauge interaction model with 6 neutrinos and 3+2 mixing proposed by Nelson. This paper will present a minimalistic 3+1 mixing described by the same model. A numerical analysis shows that the 3+1 mixing model provides an improved explanation for the LSND and MiniBooNE anomalies over the standard theory of neutrino oscillation. This model is moreover in good agreement with the long baseline data from MINOS. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B28.00008: Experimental Characterization of Azimuthal Velocity with Varying Reynolds Numbers in short Taylor-Couette Flow Cyprian Czarnocki, Mark Nornberg, Erik Spence, Hantao Ji, Michael Burin Simulations of Taylor-Couette flow are difficult to reconcile with experimental measurements since the available Reynolds number of the simulations is normally much smaller than in most experiments. The ability to increase fluid viscosity by adding glycerol to water will allow for experiments to be run with a lower Reynolds number, allowing for the experimental results to be compared with simulations. In this experiment a Laser Doppler Velocimeter (LDV) is used to measure internal flow velocity within a short Taylor-Couette apparatus. The azimuthal velocity profiles are measured over a range of radial and axial positions with varying fluid viscosities. A comparison of both simulation and experimental results of azimuthal velocity profiles is presented. The goal for this experiment is to achieve good agreement between the experimental and simulation results and to help better understand the Ekman circulation and its suppression in the Princeton Magnetorotational Instability (MRI) Experiment. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B28.00009: Friction, force chains, and falling fruit Jacqueline Krim, Robert Behringer Friction is of great concern from both a national security and quality-of-life point of view, and the economic impact of energy efficiency, wear, and manufacturing cannot be underestimated. Theorists have always believed that friction plays a great role in avalanche-like collapse of a granular piles, but the predictions have proven difficult to test. We devised an experimentally controlled way to prove it, accessible to all who dare try, and report on it here [1,2]. With the aid of a middle school assistant, we studied and filmed piles of apples, oranges, and onions as one or more pieces of fruit were removed. Among other things, we discovered that increasing the friction of the onions (by peeling them) vastly decreased the likelihood of collapse. Our work includes videos written by, produced, and starring our seventh grade assistant, some of which are posted on the Physics Today YouTube channel [1] and featured in the Sept. 2009 issue of Physics Today [2]. \\[4pt] [1] Youtube.com, keywords ``unpeeled onions'', with full set at www.dukefruit.info. \\[0pt] [2] J. Krim and R.P. Berhinger, Physics Today (Sept., 2009) volume 62, pp.66-67 [Preview Abstract] |
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