Bulletin of the American Physical Society
2018 Annual Fall Meeting of the APS Ohio-Region Section
Volume 63, Number 15
Friday–Saturday, September 28–29, 2018; University of Toledo, Toledo, Ohio
Session C01: Poster Session |
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Chair: Nik Podraza, Randy Ellingson, University of Toledo Room: SU Ingman Room |
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C01.00001: Humeral bone strength and flight in eumaniraptoran dinosaurs Scott Lee The humeral section modulus is evaluated for 19 extinct dinosaurs from Dromaeosauridae, Troodontidae and Avialae as well as 17 species of extant birds in order to evaluate the flight potential of the extinct dinosaurs. All of the members of Avialae, four dromaeosaurids (Microraptor gui, Graciliraptor lujiahunensis, Buitreraptor gonzalezorum, and Changyuraptor yangi) and one troodontid (Jianianhualong tengi) had humeri that were strong enough for flight. This is a necessary, but not sufficient, condition for flight. This suggests that certain dromaeosaurids and troodontids might have been able to fly. |
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C01.00002: Using Kinematics to Identify Quarks and Gluons in Final Dijet States Allyson F Brodzeller, Ayana Arce, Isabel Ruffin Quarks and gluons produced in the LHC rapidly fragment into groupings of collinear particles referred to as jets. Quark-initiated and gluon-initiated jets leave similar signatures in the ATLAS detector. Improving the classification of jets has a variety of useful applications such as studies on jet substructure and in searches for physics beyond the standard model. A boosted decision tree classifier was trained using the Toolkit for Multivariate Analysis to identify quark leading jets in dijet events based on the event kinematics along with the subleading jet's mass. Evaluation of the kinematic jet classifier shows best performance at high η values and in the leading jet transverse momentum range of 1.5 TeV to 2.5 TeV. A kinematic-based jet classifier will provide useful samples from real collision data that can be used in the training and validation of jet substructure-based taggers. |
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C01.00003: A Taxonomy of Fluorinated Tail Free Triphenylenes Mitch Powers, Kunlun Wang, Zhe Li, Lewis Sharpnack, Dena Mae Agra-Kooijman, Scott Bunge, Satyendra Kumar, Brett Ellman, Robert Twieg Starting with 1,2,3,4-tetrafluorotriphenylene and adding a variety of substituents, we explore the complex phase behaviors that develop between closely packed, tail free, disc-like molecules. Notably, several molecules have been found to possess a discotic columnar liquid crystal mesophase. By examining the, at times subtle, differences between these discotic mesogens and their closely related but non-mesogenic counterparts, we hope to better understand the nature of the discotic columnar mesophase. |
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C01.00004: Self-Assembly of Organic Molecules on Gold Surfaces Abigail Hickin, Jessica Bickel Increasing conductivity of organic thin-films via crystallization of organic molecules prompts developments in organic electronics. Organic molecules deposited onto surface reconstructions demonstrate self-organization on the surface, growing organic thin-films with large crystalline areas. To grow these films, we need atomically flat Au (111) with a surface reconstruction. As-received Au films on Si wafers were imaged using scanning tunneling microscopy (STM), revealing the surface as several curved mounds with no flat, reconstructed area. Post annealing at 100°C in either N2 or high vacuum, the Au mounds showed evidence of flattening into terraces ~500nm2 in size; however, this area was not sufficient for our purposes. Depositing Au onto the Au/Si sample via thermal evaporation was tested at deposition rates of 0.07Å/s-1.4Å/s and substrate temperatures of 30°C-100°C. At all deposition parameters, small islands formed on the surface, demonstrating that the deposition had no flattening effects. Au deposition was continued on mica substrates at 115°C and revealed small step edges at the surface. Continued testing of Au on mica at higher temperatures will be beneficial towards growing larger gold plateaus on the surface necessary for organic film growth. |
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C01.00005: Diffusion of Small Charged Nanoparticles within a Semidilute Polyelectrolyte Solution Kavindya Kumari Senanayake, Ashis Mukhopadhyay We studied the diffusion of charged gold nanoparticles within a semidilute solution of weakly charged polyelectrolyte, polyacrylic acid (PAA) of high molecular weight (Mw=106 g/mol) by using fluctuation correlation spectroscopy (FCS). Nanoparticle size (2R) was varied between 5 nm to 40 nm and PAA volume fraction (Φ) in water ranged from about Φ* to 5Φ*, where Φ* is the overlap volume fraction. The measured diffusion coefficients (D) showed a scaling relation, D~(R/ξ)-1 in the range of 2R/ξ between 0.05 and 0.85. Additionally, rheology measurements showed a zero shear rate viscosity and shear thinning, which are typical of high molecular weight polyelectrolytes. The local viscosity experienced by the particles is slightly (a factor of 3-4) more compared to solvent viscosity and significantly smaller compared to zero shear rate viscosity. |
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C01.00006: Considering Spin in Analytic Solutions to Binary Inspirals Using the Dynamical Renormalization Group Formalism Shana Li, Adam Leibovich LIGO's detection of gravitational waves from coalescing binary black holes and neutron stars provided the unprecedented opportunity to study strong gravitational fields and compact binary dynamics. Furthermore, it has become vital for calculations of binaries' trajectories to have the highest possible efficiency and accuracy. When there exist many oscillations in the waveform due to binaries having lower masses, it is possible to calculate solutions to their motion via post-Newtonian expansions. The derivation of binaries' center-of-mass trajectories using the dynamical renormalization group (DRG) formalism was first introduced by Galley and Rothstein, who showed that the method had higher predictive power than and eliminates ambiguities in conventional orbit-averaged methods. While they included the radiation reaction force experienced by the binaries, we began to consider the binaries' spins as well. In this project, we derived the binaries' center-of-mass equations of motion in polar coordinates accounting for both radiation reaction and spin, generated graphical models of the trajectories, and began to derive the new DRG solution. |
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C01.00007: Surface Preparation of Weyl Semimetal Mn3Sn Zachary Huber, Wenhan Zhang, Weida Wu Weyl semimetals are a class of topological materials whose low-energy quasiparticle excitations behave like Weyl fermions, particles long predicted in high-energy physics. These unique excitations are related to several phenomena of interest including topologically-protected surface states called Fermi arcs. Recent ARPES and first-principle studies have suggested that Mn3Sn is a magnetic Weyl semimetal. However, experimental observation of the Weyl nodes and the Fermi arcs remain elusive. One major difficulty is that the naturally cleaved surface of Mn3Sn is not atomically flat, making it difficult to use surface-based techniques such as scanning tunneling microscopy and spectroscopy (STM/STS). To address this issue, we treated the surface with in-situ sputtering and annealing and found that the annealing temperature and duration were most important to cleaning the surface. The quality of the surface was assessed by STM and low-energy electron diffraction. We used our findings to begin to develop a reasonably reproducible recipe for improving the quality of the Mn3Sn surface, taking a step towards exploring the Weyl physics of this material with STM/STS. |
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C01.00008: Oscillator Strengths for Ultraviolet Transitions in P II - The Multiplet at 1308 Å Rabee B Alkhayat, Michael Brown, Rabee B Alkhayat, Richard Irving, Negar Heidarian, Jeremy Bancroftbrown, Steven Robert Federman, Song Cheng, Larry Curtis Singly-ionized phosphorus, the element's dominant ion in neutral diffuse interstellar gas, is used to probe depletion onto grains. Previous experimental results and recent theoretical calculations of the oscillator strengths and lifetimes for the P II multiplet at λ1308 reveal discrepancies. We seek a resolution to the question of the most appropriate ƒ-values to use for interstellar studies by extending our earlier work on the multiplet containing the line at 1153 Å through measurements of the pertinent data for the multiplet λ1308. Through beam-foil spectroscopic techniques, we present experimental lifetimes and branching fractions to derive oscillator strengths for transitions within the P II multiplet (3s23p2 3P - 3s3p3 3Po) at 1308 Å. These comprehensive beam-foil measurements, which are the most precise set currently available experimentally, resolve discrepancies involving the earlier experimental and theoretical results. Interstellar phosphorus abundances derived from λ1308 can now be interpreted with greater confidence. We also obtained an experimental lifetime for the 3p4s 3P0o level of P IV; it agrees well with the available theoretical calculation. |
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C01.00009: Steady-State Method to Measure the In-Plane Thermal Conductivity of Thin Sheet Materials Evgeny Pakhomenko, Andreas Jung, Souvik Das, Abraham Mathew Koshy, Andrew James Wildridge A new generation of silicon pixel detectors is required to cope with the unprecedented luminosities at the high-luminosity phase of the Large Hadron Collider (HL-LHC) in 2025. The HL-LHC will provide a high radiation and interaction rate environment for the innermost detector region of the Compact Muon Solenoid (CMS) detector. To address this challenge, the spatial coverage of the inner silicon detector will be increased while also decreasing the size of a pixel. This increases the number of readout channels significantly, which produces more heat compared to existing pixel devices. Therefore, the Phase II upgrade to the CMS experiment requires an improved light-weight heat removal scheme, which is addressed by using carbon fiber as one of the materials for the silicon detector support structure. To simulate and optimize the performance of this support structure, knowing the thermal conductivity is crucial. Because thermal conductivity of carbon fiber is anisotropic, measurements along and perpendicular to the fibers are performed separately. In-plane thermal conductivity measurements of several thin in-house cured carbon fiber sheets are performed. We measure the thermal conductivity of Carbon Fiber K13D2U/TC275-1 in the plane and along the fiber to be 515 ± 72 W/mK. |
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C01.00010: Establishing Baseline Models for High Efficiency CIGS Photovoltaic Devices Yasas Patikirige Solar cells based on the compound Copper Indium Gallium Diselenide, Cu(InxGa1-x)Se2, (or CIGS) are commercially important. As a quaternary compound, the electronic properties of CIGS can be controlled by varying the composition. Our work involves numerical analysis to establish four CIGS baseline device models for comparison to published data. These models include mid-gap defect concentration and band gap profiles that are Ga dependent. The models also consider the effects of metastable/multivalent defects. Numerical calculations of current-voltage (JV), quantum efficiency (QE), and capacitance-voltage (CV) were carried out using one dimensional simulation program SCAPS-1D. The results are compared to published data for a reference cell and calculations for similar models. Simulated efficiencies reached 20.1% -20.8% depending on the model. In subsequent work, the baseline models will be used to test various hypotheses regarding the electronic structure of the CIGS/buffer interface region. |
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C01.00011: Swimming Bacteria Guided by Patterned Nematic Liquid Crystal Taras Turiv, Runa Koizumi, Chenhui Peng, Hao Yu, Qi-Huo Wei, Oleg D. Lavrentovich Micro-swimmers of biological nature such as motile bacteria exhibit highly correlated collective behavior. This collective behavior can be controlled by placing such microswimmers in a nematic liquid crystal (NLC) with long-range orientational order. The NLC environment can control the local concentration, trajectories, and net flow of active bacteria, thereby triggering a circular unidirectional motion of the bacteria around topological charges (Peng, Turiv et al., Science 2016). In this work, we explore the collective motion of motile B. subtilis dispersed in an aqueous solution of lyotropic chromonic NLC. The director field is set to be a smoothly varying in space, representing an alternating system of splay and bend regions imposed through photoalignment. The bacteria exhibit unidirectional collective motion along the splay regions of the director field. If the bacteria enter the patterned director field in the opposite direction of the collective motion, its motion is realigned. The experiments present a clear evidence of a highly compressible nature of bacterial dispersions in NLC. The demonstrated unidirectional linear motion can be applied to using such micro-swimmers as potential power materials. |
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C01.00012: A single-beam, potassium SERF magnetometer for the Global Network of Optical Magnetometers to search for Exotic physics (GNOME). Sunyool Park, Claire Perrin, Seraphina Nix, Jason Evan Stalnaker Ultralight axion-like particles are a candidate for dark matter. These particles can form topological defects that can be detected through their coupling with the spins of elementary particles. This coupling results in a pseudo-magnetic interaction. The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) searches for transient signals caused by the Earth going through these topological defects using several magnetometers located throughout the world to differentiate true signals from false positives. At Oberlin College, we have developed a single-beam spin exchange relaxation-free (SERF) magnetometer using potassium atoms with a helium buffer gas. We look at the absorption of circularly polarized light going through the vapor cell housed within four layered magnetic shields. The magnetic field dependence of the absorption is used to measure the magnetic field. We present the characterization of our magnetometer and discuss the development of a future co-magnetometer with improved sensitivity. |
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C01.00013: Performance of serpentine micromixers with non-rectangular cross-section Petru Stefan Fodor, Joshua A Clark Serpentine microchannels have been popular choices for microfluidic mixers due to their relative easy fabrication and possibility for re-use. The technique used in these types of microchannels aims to utilize the cross-sectional transversal (Dean) flows experienced by the fluids as they round a curved channel geometry. However, because of the reliance on centrifugal forces the mixing quality is strongly Reynolds number-dependent, with high quality mixing being achievable only at Re > 100. In the current work we show that employing channels with non-rectangular cross-sections can be an effective strategy to increase the mixing efficiency in these designs and lower the Reynolds number at which they can be employed. To this end, we seek to optimize the cross-sectional geometrical parameters to maximize their overall mixing performance. The results of the optimization process, namely the fluid flow characteristics, are obtained numerically through computational solutions of the Navier-Stokes equations and the convection-diffusion equation. We also include experimental results comparing the mixing performance of our optimized channels using non-rectangular cross-sections, to those with standard rectangular topology. |
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C01.00014: Effects of Deposition Parameters on the Optical and Piezoelectric Properties of Aluminum Scandium Nitride Rachel L Adams, Hadley A Smith, Zachary J Biegler, Madelyn J Hill, Said Elhamri, Albert M Hilton, Kurt G Eyink, Brandon M Howe, Amber N Reed Alloying aluminum nitride with scandium nitride could result in an increase of the piezoelectric coefficient, leading to impacts on next-generation RF-filters. Aluminum scandium nitride (Al1-xScxN) also has uses in opto-electronic applications. To incorporate Al1-xScxN in devices, a better understanding of growth, structural, optical, and piezoelectric properties is needed. In this work we report the impacts of various growth parameters on microstructure and surface morphology of Al1-xScxN films on (0001)-orientated sapphire substrates. Growth parameters were correlated with changes in optical and piezoelectric properties. Films were deposited from an Al0.9Sc0.1 target by reactive controllably unbalanced magnetron sputtering. X-ray diffraction was used to characterize crystallinity of the films. Comparing full-width half-maximum, peak intensity, and 2Θ position of diffraction peaks shows that crystallinity is affected by fN2, ji/jMe, Tsub, and WT. Atomic force microscopy (AFM) was used to determine surface morphology and piezoelectric coefficient of the films. AFM showed that at lower Tsub and WT the films had large clusters on the surface and high surface roughness. The optical properties were determined by spectroscopic ellipsometry. |
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C01.00015: Atmospheric Plasma Processing of Undoped and p-Silicon (100) for Thin Oxide Films Uma Ramabadran, Susan Farhat, Graham Garner, Jesse Burghdoff, Kyle Keen The growth of very thin oxide layers on p-doped and undoped Si was explored using atmospheric plasma processing (APP) with ionized air at room temperature and at 150oC. The number of passes were varied with plasma jet power, scan speed and gas flow rate held constant. Sample surfaces were characterized by measuring the water drop contact angle (CA) with a tensiometer and oxide thickness with an ellipsometer. X-ray photoelectron spectroscopy determined elemental makeup of the oxide layer. After APP with ionized air at room temperature the oxide thickness for undoped samples increased up to 325+/-17Å from the as received value of 18.4+/-0.8Å for 5 passes. Oxide thickness after APP for heated undoped samples increased with number of passes attaining a maximum of 80+/-4.4Å at 9 passes. Similar trends were noted for doped substrates although oxide layers were thinner. CAs for APP treated samples decreased immediately after treatment, but increased over time. The distribution in CA values for was higher at 150oC for both substrates indicating greater non-uniformity of sample surfaces when temperature is increased. APP with nitrogen plasma had considerably less impact on oxide thickness and CA measurements compared to ionized air plasma. |
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C01.00016: Raspberry Pi Polarimeter and Beam Profiler Benjamin Lewis Groves, Edward Carlo Samson Knowing the polarization of light is essential for many optical systems and experiments. The issue is not the availability to a quality polarimeter, but rather the cost and mobility of it. By implementing a Raspberry Pi both of these problems are resolved effectively. The size of the Pi allows for the entire polarimeter to be no larger than 7in in length and 4in in width. With an easily attachable high resolution camera, multiple USB ports, and price it makes the Raspberry Pi an ideal candidate for this project. Furthermore by using a Pi streamlines the construction process as it has no moving parts, and allows for an overall simpler design without compromising functionality. By utilizing Savart plates, and the Raspberry Pi camera, four images can be created denoting the intensity of the beam, its horizontal, vertical, and/or circular polarity. With the code that is being implemented also being fairly flexible the same device can be used for an uncoupled beam profiler. Having a polarimeter and beam profiler in one compact and cost effective unit makes this tool ideal for smaller optical laboratories. |
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C01.00017: Measurement of defect densities in Ge films grown on Si Christina E Scott, Yining Liu, Jay A Mathews Si is used in electronics because of its high conductive properties and cost efficiency. To make Si more optically favorable Ge and GeSn can be grown on top of Si, lowering its band gap. Researchers at AFRL have found a new method of growing Ge on Si using a plasma gas chamber. The newly grown material had to be tested for growth defects to determine if it was consistent with the other materials grown by methods previously used. To test the material, the samples were separated into three Ge layer thicknesses. Using the etchant “Schimmel,” the results showed a decrease in defects as the Ge layer thickened. Two other etchants, “Dash” and “Secco,” both agreed with the negative correlation of defect density as the Ge layer thickened. The density of defects with this new method of growth agreed with literature results for other methods of growing Ge on Si. Two other samples with similar thicknesses of the Ge layer were tested, one annealed for 10 seconds at 750 C and one not annealed. After etching these samples the results showed a large decrease in defects in the sample that was annealed compared to the one that was not. These results show the quality of growth of the material using the new method is consistent with other methods and this technique produces high quality material. |
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C01.00018: Black Hole Entropy: A Violation of the Second Law of Thermodynamics Pierre-Marie Robitaille According to modern theory, black holes are said to possess entropy, SBH = kBc3A/4ħG, where kB, c, ħ, and G correspond to Boltzmann’s constant, the speed of light, Planck’s constant divided by 2π, and the universal constant of gravitation, while A corresponds to the area of the event horizon. In this expression, SBH is not extensive, as the area of the event horizon, A, the only property governing the situation, is not extensive. It is volume which is an extensive property, not area. Relative to black holes it is easy to establish that entropy is not extensive by also considering that the area of the event horizon which is given by A = 2π(RS)2, where RS corresponds to the Schwarzschild radius. It is well accepted that RS = 2GM/c2, where M now corresponds to the mass of the black hole. As a result, black hole entropy becomes proportional and solely dependent upon M2, all other terms being constants. Mass is an extensive property. However, M2 is not. Extensive properties must be additive. In thermodynamics, it is essential that the entropy of large systems be extensive. To claim otherwise is a violation of the second law. As a result, black holes and their entropy cannot be reconciled with the known laws of thermodynamics. |
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C01.00019: Systematic Study of the Effects of Incorporation of Carbon Nanotubes into Ge_xSe_1-x Glass System Wayne Bresser, Chari Ramkumar, John Adamick, John Rademacher We have successfully synthesized Ge_xSe_1-x(x = 0.225) glass samples and have doped commercially produced (US ReasearchNanomaterials, Inc.) carbon nanotubes (CNTs) and commercial carbon (Sigma Aldrich) into them. We have investigated the glass transition temperature (T_g) using Modulated Differential Scanning Calorimetry (MDSC). This glass without the CNTs has a T_g of 213(°C). We found that the T_g lowers when 5% CNTs by mass is added as compared to the base Ge_xSe_1-x glass. Additionally, we find the presence of a crystalline phase developing (T_x approx. 300°) in the first heating scan of the glass sample. In the second heating scan both T_g and T_x disappear and finally, a melting of the material (T_m) occurs at T_m approx. 210°C in the third heating. The pure carbon in the Ge_xSe_1-x produced different results (no crystalline phase) than the CNT, but more work needs to be done for conclusive results. The decrease in T_g with 5% CNT indicates the occurrence of an intermediate phase (stress-free glass systems) at lower temperature, which could be potentially useful in material science applications. |
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C01.00020: The Effects of Crosslinker on Polymeric Microgels Samantha C Tietjen, Jacob Adamczyk, Kiril A Streletzky Microgels are nanoparticles suspended in solution and comprised of crosslinked polymer chains. Due to the amphiphilic property of the parent polymer, microgels exhibit a reversible volume phase transition, de-swelling with an increase in temperature. Microgels in this study were synthesized by crosslinking hydroxypropylcellulose (HPC) in a surfactant solution. The amount of crosslinker used for synthesis was varied by a factor of a hundred. Using dynamic light scattering, microgels were characterized at various temperatures and scattering angles to determine the particles’ hydrodynamic radius (Rh) and dynamics both in the swollen and de-swollen states. It was shown that for low crosslinker concentrations, microgels exhibit standard behavior, with a decrease in radii as crosslinker concentration increases. Above a certain concentration, the behavior switches from standard behavior to microgel growth with temperature increase. Also observed was that some particles exhibiting standard microgel behavior increase in size at very high temperatures, possibly due to non-uniform crosslinker distribution. |
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C01.00021: Advanced Optical Simulation of Photovoltaic Devices Dustin Etts, Marco Nardone Optical absorption enhancement is an effective route to improve photovoltaic (PV) power conversion efficiency. Numerical simulation can assist with the implementation of certain design features such as layer thicknesses/properties, anti-reflective coatings, textured surfaces, plasmonic effects, and other means to optimize absorption while reducing materials usage. In this work, COMOSL Multiphysics wave optics and semiconductor interfaces are used to solve Maxwell's equation for the optical electromagnetic field in a PV device and the transport equations to predict the resulting PCE. Quantum efficiency data for a copper indium gallium diselenide (CIGS) cell is used for model validation. We compare our results to the freeware program e-ARC. Both programs have pros and cons that will be discussed. |
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C01.00022: Band Gap Tuning of Organic-Inorganic Metal Halide Perovskites for Photovoltaics Travis Maenle, Isaac Long, Khagendra P Bhandari As a result of the tremendous research efforts across the world, hybrid organic-inorganic metal halide perovskite based solar cells are now comparable to other previously existing high efficient technologies with power conversion efficiency exceeding 20%. The existence of intrinsic and extrinsic instability in these materials remains a major challenge to commercialization of the solar cells. However, mixed halides are expected to solve instability problems. Here we investigate experimentally the effect of halogen on the structural, electronic and optical properties of mixed halide MAPb(I1-xBrx)3, MAPb(I1-xClx)3 and MAPb(Br1-xClx)3 perovskites. Single-step deposition method with the application of doctor blade coating is used to fabricate perovskite thin films on glass substrates. As the Br and Cl contents ‘x’ increase from 0.0 to 1.0, the band gap energy increases as a linear function. The photo-absorption coefficients are calculated showing blue-shift of the absorption onsets for higher Br or Cl concentrations. We also investigate a systematic long term stability of these materials in ambient atmosphere. |
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C01.00023: Earth-Abundant Chalcopyrite (CuFeS2) Nanocrystals: Structural, Optical and Hole Transport Properties Ebin Bastola, Randy J. Ellingson Chalcopyrite nanocrystals (NCs), especially CuFeS2, have attracted considerable attention of the researchers due to their earth-abundance, low toxicity, and solution-processing for the fabrication of the thin film devices. However, control over the phase purity and stability during the synthesis of ternary and quaternary NCs remains challenging. Here, we report the thermal-injection colloidal synthesis of CuFeS2 NCs using iron (II) bromide (FeBr2), copper (II) acetaylacetonate (Cu(acac)2), and elemental sulfur (S) as Fe, Cu and S sources respectively. Controlled reaction temperature and growth time yields stable and phase-pure ternary CuFeS2 NCs, exhibiting tetragonal crystal structure in the chalcopyrite phase. With increasing growth time, the optical absorption peak slightly red shifts, and eventually disappears at longer growth times. The relationship between the optical properties and the two intermediate bands located within the fundamental band gap is also discussed. The electronic properties CuFeS2 NCs based films show that this material is a promising hole transport material for energy harvesting applications. |
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C01.00024: Spectral Stability of Gravitationally Interacting Rods Carlos Owusu-Ansah, John F. Lindner We investigate the spectral stability of equilibrium configurations of two line-masses (slashes or rods) interacting via gravity. The Euler-Lagrange formalism provides the equations of motion. We determine the positions, orientations and angular velocities of the slashes at their equilibrium configurations. All equilibrium solutions are checked using the equations of motion. The spectral stability of each equilibrium configuration is determined by linearizing the equations of motion about the equilibrium configurations and analyzing the path of the slashes when they are perturbed. The parameter values that cause equilibrium configurations to be spectrally stable are illustrated. |
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C01.00025: Optical Modeling of Perovskite/Chalcopyrite Thin Film Tandem Solar Cells Hashem Barudi For high efficiency thin film solar cells, two-terminal tandem designs are under development using narrow and wide bandgap components. The active component materials of recent interest for an all-thin-film tandem include the hybrid organic-inorganic perovskite (MA)PbI3 (MA: CH3NH3+) as the wide bandgap component (Eg=1.61 eV) and the chalcopyrite CuInSe2 (Eg=1.02 eV) as the narrow bandgap component. For both material systems, bandgap variations are possible through alloying. By using the mixed-halide perovskite MAPb(I1-xBrx)3, band gaps over the range from 1.62 eV to 1.73 eV are possible for x increasing from 0 to 0.2. This variation enables optimization of the performance of the tandem for a CuInSe2 bottom cell. In this study, we develop a realistic optical structure for the tandem solar cell and predict the external quantum efficiency spectra, total matched current collection, and inactive layer optical losses. Such predictions require accurate optical spectra of all individual component layers in the form of their complex dielectric functions (ε1, ε2) which have been determined using spectroscopic ellipsometry measurements. |
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C01.00026: Shortcut to Adiabaticity for Harmonic and Anharmonic Traps using BFGS Algorithm Hok Wai Chang, John Femiani, Edward Carlo Samson Transportation for a delicate quantum system at a fast rate is crucial for the development of quantum-enabled devices. However, fast transport is typically incompatible in preserving quantum fidelity. Therefore researchers have come up with shortcuts-to-adiabaticity (STA), which are a specific quantum protocol that can generate a trajectory for the system such that the fidelity can stay high even with high-speed transport. STA in the current stage is only developed for harmonic traps, while STA for anharmonic traps still has their limitations. In this study, we use computation methods to design trajectories for both harmonic and anharmonic traps. Specifically, the BFGS algorithm is implemented in optimizing the trajectory. BFGS is a quasi-Newton method that has been previously used in optimal control problem, such as designing optimal laser fields for controlling molecular-dynamics. We show preliminary results for transport of a quantum system held in a Gaussian trap. |
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C01.00027: Reaction-diffusion wavefronts colliding with obstacles Nathaniel Smith, Rebecca Glaser, Vincent W.H. Hui, John F. Lindner, Niklas Manz We developed an Obj-C computer simulation to study the propagation behavior of initially planar reaction-diffusion wavefronts colliding with convex obstacles in narrow two-dimensional channels. We used finite-difference numerical integration of the two-variable Tyson-Fife reduction for a set of three coupled differential equations, called the Oregonator model of the chemical Belousov-Zhabotinsky reaction. |
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C01.00028: Enhanced Grain Size and Crystallinity in CH3NH3PbI3 Perovskite Films by Metal Additives to the Single-Step Solution Fabrication Process Zahrah S. Almutawah, Suneth C. Watthage, Zhaoning Song, Ramez H. Ahangharnejhad, Kamala K. Subedi, Niraj Shrestha, Adam B. Phillips, Yanfa Yan, Randy J. Ellingson Methods of obtaining large grain size and high crystallinity in absorber materials play an important role in fabrication of high-performance methylammonium lead iodide (MAPbI3) perovskite solar cells. Here we study the effect of adding small concentrations of Cd2+, Zn2+, and Fe2+salts to the perovskite precursor solution used in the single-step solution fabrication process. Enhanced grain size and crystallinity in MAPbI3 films were obtained by using 0.1% of Cd2+ or Zn2+in the precursor solution. Consequently, solar cells constructed with Cd- and Zn-doped perovskite films show a significant improvement in device performance. These results suggest that the process may be an effective and facile method to fabricate high-efficiency perovskite photovoltaic devices. |
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C01.00029: Numerical Modeling of Front Contact Alignment for High Efficiency Cd1-xZnxTe and Cd1-xMgxTe Solar Cells for tandem devices Geethika K. Liyanage, Adam B. Phillips, Fadhil K. Alfadhili, Michael J. Heben Wide bandgap Cd1-xZnxTe and Cd1-xMgxTe have drawn attention as top cells in tandem devices. These materials offer flexibility of tuning the band gap over a wide range by controlling the Zn (or Mg) concentration in CdTe with little alteration to its properties. Historically, CdS has been extensively used as a heterojunction partner for these devices. However, these devices show significantly low open circuit voltage than expected for wide bandgap absorbers due to poor band alignment at the CdS-absorber interface. Recent work shows that, by using wide band gap oxides to create this energetic “spike” at the window layer-absorber interface, device performance can be significantly improved. In this study, we will use SCAPS 1D software to model the wider band gap Cd1-xZnxTe and Cd1-xMgxTe devices to determine the appropriate alignment between the absorber and the window layer. We will also investigate how the material properties of TCO and window layer will affect the front contact alignment to determine the optimized device structure for high efficiency Cd1-xZnxTe and Cd1-xMgxTe. |
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C01.00030: Characterization of mode-locked fiber lasers Kyle Hagan, Andy Chong Ultrafast lasers have applications that span many disciplines from materials science to medicine. Traditionally, ultrafast lasers are assembled from a Ti:Sapphire (T:S) gain medium due to a fast pulse duration (5fs) and high output power. However, a large drawback to T:S is the cost and size. An ultrafast fiber laser (FL) can be developed for a lower cost and take up less space. Drawbacks to a FL is low power output and long pulse duration (20fs). A goal in FL development is to match the performance of a T:S laser. Characterizing performance of these lasers involves measurement of output power, repetition rate, and pulse duration. The assembly of the laser requires splicing optical fiber from a pump diode to fiber of several optical components. The laser is then mode-locked. Mode-locking is the process of generating an ultrashort pulse in the laser cavity by introducing a component called a saturable absorber. Mode-locking is crucial to producing an ultrafast laser. The mode-locked power is 58.5mW and the repetition rate is 45.5MHz, offering a pulse energy of 1.26nJ. The pulse duration is measured with a technique called second-harmonic intensity autocorrelation. Autocorrelation is necessary as the pulse is too fast for electronics to respond. The pulse duration is 97.4fs. |
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C01.00031: Optical design of perovskite solar cells for applications in tandem configuration with CuInSe2 bottom cells Ramez Hosseinian Ahangharnejhad, Zhaoning Song, Adam B Phillips, Suneth Watthage, Zahrah Almutawah, Dhurba Raj Raj Sapkota, Prakash Koirala, Robert w. Collins, Yanfa Yan, Michael J. Heben Thin film tandem solar cells consisting of a high bandgap perovskite top cell and a low bandgap thin film bottom cell are expected to reach higher power conversion efficiencies (PCEs) with lower manufacturing cost and environmental impacts than the market-dominant crystalline silicon photovoltaics. There have been several demonstrations of 4-terminal and 2-terminal perovskite tandem devices with CuInGaSe2 (CIGS) or CuInSe2 (CIS) and, similar to the other tandem structures, the optimization of this device relies on optimal choice for the perovskite bandgap and thickness. Therefore, further advancement will be enabled by tuning the perovskite absorber to maximize the photocurrent limited by the current match condition. Here, we model the photocurrent generations in both perovskite and CIS subcells while varying the perovskite layer and estimate the performances of projected tandem devices by considering results of fabricated devices. Our results show that PCEs above 20% can be achieved by perovskite/CIS tandem solar cells for 2- and 4-terminal devices. |
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C01.00032: Luminescence Spectroscopy of Holmium-Doped Crystals Madelyn Hoying Luminescence spectroscopy involves using a monochromator to find the emission spectrum of a material. In this case, that material is a crystal lattice with some of the ions in the lattice structure replaced with Holmium ions. When an Argon laser with a wavelength of 457.9 nm hits a Holmium-doped crystal, the Holmium ions oscillate between an excited state and a lower energy level by absorbing and releasing energy with a characteristic wavelength depending on the energy level transition. The optical setup of this experiment was optimized for use with a monochromator, and several crystals with varying concentrations of Holmium ions were tested in order to produce a clear luminescence spectrum of Holmium in both the s and p polarizations. |
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C01.00033: Multidisciplinary REU site at Cleveland State University: Synthesis, Assembly, and Characterization of Soft Matter. Kiril A Streletzky, Jessica Bickel Researchers at Cleveland State University’s Department of Physics and Department of Chemical & Biomedical Engineering collaboratively study the unique properties and applications of soft matter materials. In 2017, these departments joined forces to start a new NSF-sponsored Research Experiences for Undergraduates (REU) site. The objective of our site is to involve undergraduate physics and engineering majors in meaningful interdisciplinary research projects within soft matter science and engineering. One of our overarching goals is to encourage students to continue in STEM fields as either graduate students or workforce members. CSU’s focus on Engaged Learning has cultivated a strong culture of support for undergraduate research, and REU participants benefit from this culture. Students receive one-on-one mentoring from experienced faculty and participate in a variety of professional development opportunities. This poster will give an overview of the student research accomplishments and program challenges encountered in the first year of our multidisciplinary REU. It will also discuss the benefits of the experience to both students and faculty mentors. |
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C01.00034: The Physics of Getting Better at Corn Hole Joseph S Sawyer The movement of a corn hole bag was analyzed. Equations of motion were calculated for the movement of the corn hole bag. The angle of release and how hard it needs to be thrown to get in the corn hole hole were examined . A optimal combination was calculated and the range of possible initial conditions were calculated.
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C01.00035: Differential Dynamic Microscopy in soft matter research Namita Shokeen, Ashis Mukhopadhyay Studying the dynamics of nanoparticles inside polymers provide important information about the mechanical and viscoelastic properties which are useful in various medical and technological fields. We focus on studying the diffusion of different sized particles in various polymer solutions using a new optical technique known as Dynamic differential microscopy (DDM). DDM is based upon analyzing the motion of particles in Fourier space that can extract useful information about their wave-vector dependent dynamics. This technique had been developed recently and was used to study a wide range of problems, including active motion of particles inside cells, bacterial motility, fluctuations in non-equilibrium systems, etc. We have implemented DDM in our own research to characterize the dynamics of nanometer sized particles within concentrated polymer solutions, and thus extended its capability at nanoscale.
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C01.00036: LabVIEW-Based Software for a Photovoltaic External Quantum Efficiency Measurement System Adam Halaoui, Adam B Phillips, Zhaoning Song, Michael J. Heben, Randy J. Ellingson An important characteristic of any solar cell is how efficiently it can convert the Sun’s photons into charge carriers. The method used to quantify this efficiency is known as the “external quantum efficiency (EQE)” spectral measurement, defined as the wavelength-dependent measurement of the ratio of the rate of photocurrent electron collection (electrons/second) to the rate of incident photons (photons/second). Commercial systems to measure the EQE of a solar cell often use instruments sourced from other manufacturers in tandem with software written and sold by these retailers. The hardware is fairly easy and inexpensive to purchase and setup for a lab, but the software is unique, not sold separately from the system and is inaccessible to the end-user after purchasing a system. Here, we have developed a LabVIEW-based program to control commercial instrumentation, leading to higher performance and significant cost savings. In addition, we demonstrate the significant value inherent in controlling the software development process, which allows for complete customization. |
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C01.00037: Improving the Forecasting of the Drivers of Sever Space Weather David A. Falconer, Sanjiv Tiwari, Ronald L. Moore, Megan Fisher The Sun produces large flares which often produce solar proton events that endanger astronauts. MAG4 is a forecasting technique for an active region’s (AR’s) next day production rate of flares from an AR’s free energy proxy. The free-energy proxy is measured from an HMI vector magnetogram of the AR. We quantify the improvements in MAG4’s major-flare forecasting performance that result from using HMI forecasting curves instead of using MDI forecasting curves. We use a Monte Carlo division to divide the magnetograms into two halves: control and experimental samples. Forecasting curves are made from the control sample and then that curve is used to make a forecast for each magnetogram in the experimental sample. These forecasts are then compared to the major-flare productivity of the experimental-sample and the Heidke skill score is calculated. From histograms of the differences in the Heidke scores from the two MAG4 magnetogram databases, we find an increase in Heidke score of over 0.1 from using HMI forecasting curves instead of MDI forecasting curves. MAG4 will soon be upgraded to use HMI forecasting curves for more accurate forecasts. |
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C01.00038: A High-Resolution H- and K-Band Spectroscopic Sequence of Ultracool Dwarf Stars Jennifer J. Greco, Michael C. Cushing, Mark S. Marley Brown dwarfs are substellar objects too low mass to initiate the hydrogen fusion necessary to be considered stars. We have obtained high-resolution near-infrared spectra in the H and K bands of a sequence of brown dwarfs and low mass stars (known as ultracool dwarfs). All data were obtained using the Immersion Grating INfrared Spectrometer (IGRINS) on the 4.3 m Discovery Channel Telescope at a resolving power of R~45,000. Our sequence spans the spectral types from M6V to T2, covering the temperature range from 1300-3000K. We are performing model comparisons between our data and a new generation of model atmospheres created by Marley and collaborators. This will allow us to measure specific properties including temperature, surface gravity and cloud properties of our objects. Surface gravity is a measurement of the gravitational acceleration at the surface of a star, and allows the estimation of a star’s mass. By observing objects with different surface gravities, we are also able to empirically search our spectra for features that are especially sensitive to changes in brown dwarf surface gravity.
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