Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S36: Energy Conversion |
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Sponsoring Units: GERA Chair: Sanghamitra Neogi, University of Colorado - Boulder Room: 299 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S36.00001: Dynamical generation and detection of a single-electron Gaussian wave packet Sungguen Ryu, Masaya Kataoka, Heung-Sun Sim A quantum-dot pump, formed by dynamic potential barriers of gigahertz operation, is an on-demand single-electron source with the unique property of emitting a hot electron above Fermi-level. In order to utilize the pump in fermion version of optics and related quantum processing, it is crucial to generate an electron in a prescribed form of wave function. We propose how to pump an electron Gaussian wave packet using a quantum-dot pump of realistic parameters.\footnote{Sungguen Ryu, M. Kataoka, and H.-S. Sim, Phys. Rev. Lett. \textbf{117}, 146802 (2016)} In the pumping process, an electron occupies a coherent state in the pump, with the help of strong magnetic confinement. It is emitted out of the pump into a Gaussian wave packet when the Landauer-Buttiker traversal time of the electron for tunneling through the potential barrier is much smaller than the passage time of the coherent state. We also demonstrate that the measurement of the energy and time distribution of the Gaussian packet is possible, with a resolution reaching the Heisenberg minimal uncertainty $\hbar/2$. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S36.00002: Defect induced carrier transport in semiconductor junctions Sanghamitra Neogi, Vitaly Proshchenko Thermal management technologies are of critical importance to maintain the temperatures of myriad devices within the required temperature limits, regardless of the external environment or thermal loads imposed from operations. As opposed to conventional bulky passive heat exchanger mechanisms, thermoelectric (TE) devices have the potential to provide targeted localized cooling, and thereby, drastically reduce the thermal budget of a system. Significant progress has been made to enhance ZT with the development of nanostructured TE materials, and thin-film superlattice structures are often reported to have improved performance over bulk materials. However, understanding the mechanism of thermal transport across various dissimilar materials is critical to the development of TE devices with predictable, robust and optimal performance. We combine atomistic and first-principle methods to analyze both phononic and electronic transport across Si/Ge interfaces by solving Boltzmann transport equations. We investigate the change in spectral properties of heat carriers near the interface under imperfect conditions. Our results will establish a relationship between interfacial thermal transport and nanoscale interfacial structures, dictated by methods of fabrication and processing. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S36.00003: Noise of a Tunnel Junction Biased in Temperature Samuel Larocque, Edouard Pinsolle, Christian Lupien, Bertrand Reulet Caloritronic in small systems has been of high interest in the recent years as new ways to manipulate electronic heat currents at the nanoscale have been developped, such as heat pumps and refrigerators based on quantum dots or diodes. In such systems, the link between average heat and electrical currents has been studied (Seebeck and Peltier effects). The next logical step in the characterization of caloritronics is to measure the link between heat or electrical current fluctuations in the presence of a temperature gradient. We present the measurements of electrical current fluctuations across a tunnel junction driven out of equilibrium by a temperature difference between the contacts, i.e. in the presence of a heat current but no electrical current. In order to create a controlled temperature difference, we use a micro-wire heated by Joule effect as one electrode of the tunnel junction while the second is in contact with a thermal reservoir at millikelvin temperatures. We observe how the current noise is affected by the presence of the heat current and compare our results with theory. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S36.00004: Characterization of UV fluorophores for application to luminescent solar concentrators Kaitlin Hellier, Sue Carter The implementation of solar as an alternative energy source faces many challenges, including the competition for space with agriculture and the environmental impacts of solar farms in deserts. As a solution to these problems, the Carter Lab has developed Luminescent Solar Concentrator (LSC) panels for applications to greenhouses. These panels utilize a luminescent dye compatible with the spectrum used in photosynthesis for the plants below and front-facing PV cells, achieving power enhancement of greater than 20{\%} compared with the cells alone. To increase this enhancement, additional portions of the unused spectrum must be harvested. In this talk, we will discuss the characterization of UV absorbing fluorophores, including spectra, quantum yield, and the enhancement of light output and power generation. We will also address the combination of these UV dyes with the original LSC dye in low and high concentration, and the FRET efficiency and potential applications associated with high concentration films. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S36.00005: Abstract Withdrawn
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Thursday, March 16, 2017 12:15PM - 12:27PM |
S36.00006: Radiative and Auger recombination of degenerate carriers in InN Andrew McAllister, Dylan Bayerl, Emmanouil Kioupakis Group-III nitrides find applications in many fields -- energy conversion, sensors, and solid-state lighting. The band gaps of InN, GaN and AlN alloys span the infrared to ultraviolet spectral range. However, nitride optoelectronic devices suffer from a drop in efficiency as carrier density increases. A major component of this decrease is Auger recombination, but its influence is not fully understood, particularly for degenerate carriers. For nondegenerate carriers the radiative rate scales as the carrier density squared, while the Auger rate scales as the density cubed. However, it is unclear how these power laws decrease as carriers become degenerate. Using first-principles calculations we studied the dependence of the radiative and Auger recombination rates on carrier density in InN. We found a more complex dependence on the Auger rate than expected. The power law of the Auger rate changes at different densities depending on the type of Auger process involved and the type of carriers that have become degenerate. In contrast, the power law of the radiative rate changes when either carrier type becomes degenerate. This creates problems in designing devices, as Auger remains a major contributor to carrier recombination at densities for which radiative recombination is suppressed by phase-space filling. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S36.00007: Electronic and optical properties of atomically thin GaN and InN quantum wells from first principles Dylan Bayerl, Emmanouil Kioupakis Nanostructured group-III-nitrides are of interest for efficient solid-state light emitters in the deep-UV and visible ranges. GaN/AlN and InN/GaN heterostructures with ultrathin GaN or InN layers only a few monolayers thick are especially promising for efficient radiative recombination. We use first-principles calculations to predict the electronic and optical properties of such ultrathin heterostructures and compare to experimental results. Our first-principles approach uses density functional theory plus the GW method to calculate accurate electronic band structures, and the Bethe-Salpeter equation method to predict excitonic properties. We ultimately predict the electronic and optical gaps, exciton binding energies, and radiative lifetimes of GaN/AlN and InN/GaN heterostructures in the ultrathin regime. Our results demonstrate enhancement of excitonic light emission and tunability of the electronic and optical properties in ultrathin III-nitride heterostructures. This work was supported by the NSF DMREF program under Award No. 1534221. Computational resources were provided by the DOE NERSC facility (DE-AC02-05CH11231). [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S36.00008: Carrier Lifetimes in a GaPAsN Intermediate Band Semiconductor James Heyman, Adam Schwartzberg, Elliot Weiss, Joshua Rollag, Kin Man Yu, Alex Luce, Oscar Dubon, Janjin Kuang, Charles Tu, Wladek Walukiewic Multiband semiconductors may form the basis of efficient intermediate band solar cells, if sufficiently long carrier lifetimes can be engineered. We used transient absorption spectroscopy to measure carrier lifetimes in GaP$_{\mathrm{y}}$As$_{\mathrm{1-x-y}}$N$_{\mathrm{x}}$. These measurements probe carrier populations in the conduction band, intermediate band and valance band as a function of time after an excitation pulse. ~ Following photoexcitation of GaP$_{\mathrm{0.32}}$As$_{\mathrm{0.67}}$N$_{\mathrm{0.01\thinspace }}$we find that the electron population in the conduction band decays exponentially with a time constant $t_{\mathrm{CB}} \quad =$23ps. Electrons in the intermediate band exhibit bimolecular recombination with holes with recombination constant $r \quad =$ 2\textbullet 10$^{\mathrm{-8}}$ cm$^{\mathrm{-3}}$/s. An optical pump pulse excited electrons from the valance band to the intermediate and conduction bands, and the change in interband absorption was probed with a delayed white light pulse. We modeled the optical properties of our samples using the band anti-crossing model to extract carrier densities as a function of time. We will also report THz Transient photoconductivity measurements in these materials. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S36.00009: Determination of band gap in epitaxial delafossite Cu oxide using optical techniques Alejandro Cabrera, R. Wheatley, B. Seifert, S. Wallentowitz, T. joshi, D. Lederman Highly epitaxial delafossite CuFeO2 and CuFe1-xGaxO2 films were grown using Pulsed Laser Deposition techniques. The sample thicknesses were estimated to be 21 nm, 75 nm.The estimated gallium fraction of substituted ferric atoms was x$=$0.25 for the composite sample. We present the study of the fundamental band gap(s) for each sample via observation of their respective optical absorption properties in the NIR-VIS region using transmittance and diffuse reflection spectroscopy. Predominant absorption edges measured were between 1.1eV and 3.1eV from transmittance spectra. The sample of CuFe1-xGaxO2 showed measurable absorption features located at 2.4eV and 2.8eV. This study also found evidence of changes between apparent absorption edges between transmittance and diffuse reflectance spectroscopies of each sample and it may be resultant from absorption channels via surface states. Future photoluminescence experiments are planned to determine the photo-induced semiconductor behavior of these materials. ACNOWLEDGEMENTS: This work was supported by FONDECyT 1130372 and Proyecto Anillo ACT1409 at PUC and supported in part by the WV Higher Education Policy Commission (grant HEPC.dsr.12.29) and by FAME sponsored by MARCO and DARPA (contract {\#} 2013-MA-2382). [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S36.00010: The role of metallic ions in nano-bio hybrid catalysts from \emph{ab initio} first principles Sushant Behera, Pritam Deb We employ high-accuracy linear-scaling density functional theory calculations [\emph{PRB} $\bf{84}$, 165131, 2011] with a near-complete basis set and a minimal parameter implicit solvent model, within the self-consistent calculation, on silver ion assimilated on bacteriorhodopsin (bR) at specific binding sites. The geometry optimization indicates the formation of stable active sites at the interface of nano-bio hybrid and density of states reflects the metallic behavior of the active sites. Detailed kinetics of the catalytic reaction is revealed using \emph{ab initio} electronic structure calculations. We observed that the metal ion incorporated active sites are more efficient in electrolytic splitting of water than pristine sites due to their less value of Gibbs free energy for hydrogen evolution reaction and strong synergistic effect [\emph{PCCP} $\bf{18}$(33), 23220, 2016]. The volcano plot analysis and free energy diagram are considered to understan hydrogen evolution efficiency. Moreover, the essential role of metallic ion on catalytic efficiency is elucidated. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S36.00011: Effect of Onboard Compressors on Natural Gas Cycling in Microporous Carbon Adsorbed Natural Gas Tanks Matthew Prosniewski, Peter Pfeifer The search for cheaper and cleaner fuel sources has driven the study of carbon based adsorbed natural gas tanks. One drawback to these tanks is some non-methane components of natural gas are selectively adsorbed by the carbon and not released under standard discharge conditions. Permanently adsorbed gas decreases the amount of useable fuel stored and is normally extracted by a regeneration process of heating the tank while under vacuum. One proposed way to eliminate the need for regeneration is the use of an onboard compressor connected to the tank. At the University of Missouri, we used a 40L flat panel tank assembly to test the effect of a compressor over twenty fill and discharge cycles. By measuring the delivered mass during discharges and the mass added during fills we have tracked how the tank's efficiency changes with increasing use. Finding that even with the use of a compressor, in as little as five cycles, there was over a 2.5{\%} drop in delivered gas during a discharge and an increase of 898g in the tank's mass at minimum operating pressure. This decrease in efficiency and mass gain shows that the use of a compressor does not eliminate the need for regeneration. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S36.00012: Adsorption of Natural Gas Mixtures in Nanoporos Carbon Carlos Wexler, Ian Crawford-Goss, Drew Lemke, Michael Roth Natural gas (NG) is promising fuel due to its smaller CO$_2$ emissions per unit energy compared to other hydrocarbons [1]. Storage via adsorption into carbon nanostructures permits the operation of storage tanks at significantly reduced pressures, resulting in cost savings, added safety and smaller loss of cargo volume. Since NG is mostly comprised of methane (87-99\%), other components are often ignored, even though heavier species are likely to adsorb preferentially and possibly result in long-term performance issues [2]. We performed Molecular Dynamics (MD) simulations to understand the behavior of heavier components of NG adsorbed into carbon nanostructures. We focused on mixtures involving methane, ethane and propane. We show that the heavier components have significant preferential adsorption, partially inhibiting the adsorption of methane, and resulting in its saturation at lower pressures. Under room temperature conditions, propane adsorbs quasi irrevesibly, though remaining mobile within the pores. We discuss the diffusion regime of all gases and address methods to remove the adsorbed heavier gases by thermal cycling the tank. References: [1] L. Ortiz, {\em et al.}, Mat. Res. Exp. {\bf 3}, 055011 (2016). [2] M. Golebiowska, {\em et al.}, Carbon {\bf 50}, 225-234. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S36.00013: Relative wettability alteration of calcite surfaces Sanjay Prabhakar, Jian Liu, Sokrates Pantelides Enhancement of crude oil recovery from calcite reservoirs remains a major challenge in the oil industry. Crude oil recovery can be enhanced by modifying the relative wettability of calcite reservoirs by injecting sea water. In this work, we consider acetic acid as a model component of crude oil and use the changes of adsorption energies of oil and water molecules induced by additives as a measure of relative wettability alteration of the calcite surface. More specifically, we investigate the influence of Na$^{\mathrm{+}}$, Mg$^{\mathrm{2+}}$, Ca$^{\mathrm{2+}}$, SO4$^{\mathrm{2-}}$ and Cl$^{\mathrm{-\thinspace }}$ions on the adsorption energies of water and acetic acid. It is expected that crude oil recovery is enhanced if the modified acetic acid molecule binds weaker than acetic acid. We use density functional theory calculations and show that the presence of Na$^{\mathrm{+}}$ ions reduces oil recovery whereas the presence of Mg and SO$_{\mathrm{4}}$ ions enhance oil recovery. Additionally, we propose a novel possibility of lifting two oil molecules by one Mg$^{\mathrm{2+}}$ ion, which yields enhanced oil recovery, as observed. We also found that Cl merely binds to the surface and has no effect on the adsorption energy of acetic acid, which means that Cl has no effect on oil recovery. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S36.00014: QCM and AFM Study of atomic scale polishing and roughening of surfaces exposed to nanoparticle suspensions of diamond, Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and SiO$_{\mathrm{2}}$. Jacqueline Krim, Biplav Acharya, Melanie Chestnut, Antonin Marek, Olga Shendarova, Alex Smirnov The addition of nanoparticles to conventional automotive lubricants is known in many cases to result in increased energy efficiency, but the atomic scale mechanisms leading to the increased efficiency are yet to be established. To explore this issue, we studied surface uptake and nanotribological properties of nanoparticle suspensions of diamond, Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and SiO$_{\mathrm{2}}$ dispersed in water and/or oil (PAO6) in real time by means of an \textit{in situ} Quartz Crystal Microbalance (QCM) technique, with a focus on the impact of the suspension on the surface roughness and texture of the QCM electrode and how the results compared to macroscopic reductions in friction and increased energy efficiency for the same materials' combinations. The frequency and dissipative properties (mechanical resistance) of QCM's with both gold and nickel surface electrodes were first studied for immersed samples upon addition of the nanoparticles. Nanodiamonds resulted in an increased mechanical resistance while the addition of Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ and SiO$_{\mathrm{2}}$ nanoparticles resulted in a decreased resistance, indicating a reduced resistance of the fluid to the motion of the QCM. Atomic Force Microscope (AFM) measurements were then performed on the QCM electrodes after exposure to the suspensions, to explore potential polishing and/or roughening effects. The results are closely linked to the macroscopic friction and wear attributes. [Preview Abstract] |
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