Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session D1: Condensed Matter II |
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Chair: Cyrill Slezak, Utah Valley University Room: Science Building 031 |
Friday, October 17, 2014 1:50PM - 2:14PM |
D1.00001: Magnetic nanoparticles in fluids: aggregation and its affect on biomedical applications Invited Speaker: Karen Livesey Magnetic nanoparticles are attracted or repelled from one another due to dipolar interactions. In zero applied field and when they are placed in a fluid, they aggregate and form small rings or long chains. In applied fields, chains predominate as these minimize the magnetic energy. Biomedical applications of such systems include: magnetic hyperthermia (killing disease with heat when an alternating kHz field is applied), MRI contrast agents, and guided drug delivery. Most theoretical models of these applications consider isolated magnetic particles, although there is evidence that they aggregate. The question then is: how does this aggregation affect the effectiveness of biomedical treatments involving magnetic nanoparticles? We have built a molecular dynamics simulation to calculate how the shape and net magnetization of aggregates changes as fields are applied. Random forces due to finite temperature buffeting of the particles must be included. In particular, we aim to calculate the amount of heat that can be produced in hyperthermia treatments. The shape of aggregates substantially alters the amount of heat that is produced by a constant number of magnetic nanoparticles. The thermal energy may be either increased or decreased compared to the output from isolated magnetic particles. [Preview Abstract] |
Friday, October 17, 2014 2:14PM - 2:26PM |
D1.00002: The construction and implementation of a small angle light scattering instrument as a micron-scale structural probe of porous systems Greggory McPherson The ability to measure changes in the porosity of materials across multiple length scales as a function of chemical and physical processes is of interest to research from energy storage to long-term remediation of environmental pollutants. Ultra-small and small-angle neutron scattering have proven effective in studying structural features from nanoscopic to mesoscopic scales, but are limited in their ability study larger features. Employing longer wavelengths, small-angle light scattering (SALS) is able to probe structural features from one to hundreds of microns, bridging the gap in accessible Q-range between neutrons at smaller length scales and quantitative large-scale structural data extractable from electron microscopy. Though SALS has been well developed for studying polymers and biomolecules, its applications in solid multiphase systems is less established. To test the application of this technique to measuring changes in multi-scale porosity of geological rock samples subject to geochemical processes, a SALS instrument was designed and built by the Geochemistry and Interfacial Sciences group at Oak Ridge National Laboratory. Here will be discussed the instrument's design, challenges, some initial data, and future applications. [Preview Abstract] |
Friday, October 17, 2014 2:26PM - 2:38PM |
D1.00003: Tunable band gaps of protein enclosed nanocrystals for high efficiency solar energy conversion Stephen Erickson, Trevor Smith, Richard Watt, John Colton Multi-junction solar cells increase efficiency limits on solar energy conversion by breaking up the incident spectrum to be absorbed by layers of different semiconductors. However, such devices have a limited library of compatible materials due to the need for lattice matching between the different layers. The spherical protein shell ferritin is used as a template for synthesizing a wide variety of nanocrystals, mitigates the effects of photocorrosion, and may act as a structural interface between different layers of a multi-junction solar cell. By controlling the size and chemical composition of the enclosed nanocrystals, band gaps ranging from 1.60 to 2.29 eV can be synthesized. A detailed balance model for a current matched multi-junction solar cell using these materials with a silicon substrate gives maximum efficiencies of 41.6{\%} for unconcentrated sunlight and 50.0{\%} for maximally concentrated sunlight. [Preview Abstract] |
Friday, October 17, 2014 2:38PM - 2:50PM |
D1.00004: SU-8 Micro-filters Abstract Aubrey Hatch I have designed and flow-tested filters made of the polymer SU-8. SU-8 is a negative epoxy-based photoresist, and the filters are patterned using standard photolithography processes. Pore sizes on the filters have ranged from 5 microns to 20 microns with varying pore geometry. I have successfully removed the SU-8 from the substrate and taken SEM images of the resulting filters. The filters have been flow-tested up to flow rates of 210 mL/min with resulting pressures of up to 0.85 psi. [Preview Abstract] |
Friday, October 17, 2014 2:50PM - 3:02PM |
D1.00005: Porous Resonators for Chemical Detection Steven Noyce, Robert Davis, Richard Vanfleet Porous resonators offer many advantages in the field of chemical detection, but have traditionally proved difficult to fabricate. Such resonators have an exceptionally higher surface area than corresponding solid resonators, allowing a much higher adsorbate mass which does not proportionally decrease with larger cantilever dimensions. This allows for larger devices, leading to higher quality factors in more diverse environments. Here we present initial work on the fabrication and characterization of porous resonators. [Preview Abstract] |
Friday, October 17, 2014 3:02PM - 3:14PM |
D1.00006: Electron Transfer Using Non-Orthogonal Basis Functions Tzu-Cheng Wu, David Dunlap, Steve Valone, Susan Atlas We reconsider standard models of electron transfer in molecular solids formulated with non-orthogonal wavefunctions characterized by weak coupling matrix element $V$ and small wavefunction overlap $S$. Using the method of Weisskopf and Wigner, we derive a new expression for the phonon-assisted electron hopping rate (Marcus rate) between non-degenerate sites separated by energy difference $\Delta$. We show that electron localization occurs for a particular value of the ratio $S\Delta/V$, and we discuss the implication this has for the Marcus inverted regime. [Preview Abstract] |
Friday, October 17, 2014 3:14PM - 3:26PM |
D1.00007: Using Non-Equilibrium Green's Functions to Study Nanoscale Thermoelectricity Arunima Coomar, Charles Stafford The Green's function is a concept that gives us the response at any point inside or outside a conductor due to an applied excitation at any other. The nonequilibrium Green's Function (NEGF) formalism (aka the Keldysh formalism) is a powerful tool that provides a microscopic theory for interacting quantum systems out of equilibrium. In this poster, we demonstrate the use of the Keldysh approach to predict and calculate thermoelectric quantities such as the Thermopower (S) and the dimensionless figure of merit (ZT) across a single-molecule junction (SMJ). We show that it is possible to get very large thermoelectric effects in SMJs with cross-conjugated molecules, which exhibit destructive quantum interference of the electron waves. These studies are potentially useful in the development of efficient thermoelectric devices to constitute a commercially viable solution for many heating and cooling problems at both the macro and nanoscale, with no operational carbon footprint. [Preview Abstract] |
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