Bulletin of the American Physical Society
2015 Annual Meeting of the Far West Section of the APS
Thursday–Saturday, October 29–31, 2015; Long Beach, California
Session S3: Condensed Matter II |
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Chair: Andreas Bill, California State University, Long Beach Room: CBA-139 |
Saturday, October 31, 2015 2:00PM - 2:12PM |
S3.00001: The Study of the Thermoelectric Properties of Phase Change Materials. Mohammed Abdi, Ming Yin, Godwin Mbamalu These research provides emphases on the study of the thermoelectric properties (characteristics of, resulting from, or using electrical phenomena occurring in conjunction with flow of heat) of novel phase-change materials (PCM). COMSOL Multiphysics software is used to design sample holder with the sample studying effectively the temperature and voltage differences in order to compute the Seebeck coefficient of sample. The results of elemental analysis and imaging studies such as XRD, UV-VIS, EDEX and SEM of the sample are obtained. A wave function using Arbitrary/ Function generator and a circuit setup is also designed to control the alternation of heaters embedded on the sample holder in order to confirm the flow of temperature from both sides of the sample is accurate. Factors affecting the thermoelectric properties of phase change memory are also discussed.. [Preview Abstract] |
Saturday, October 31, 2015 2:12PM - 2:24PM |
S3.00002: Quantum dot cluster self-assembly via topological defects in liquid crystal droplet and planar geometries Charles Melton Topological defects in nematic liquid crystals are known to drive the assembly of included particles. For example, large colloids have been seen to interact and assemble at defect locations and into colloidal crystals via elastic forces. Similar effects have been observed with nano-sized particles, in particular gold particles and quantum dots. Anchoring conditions affect how the liquid crystal orders around the particle, so using specially designed surface ligands is important. Recently, our research group showed that mesogenic surface ligands allow for self-assembly of well defined structures at the isotropic -- nematic phase boundary. For liquid crystals in spherical geometries that possess a well known bipolar configuration we demonstrate that quantum dots co-assemble with the formation of defects upon cooling from the isotropic phase. To further explore this system, a model based on the 2D XY-Model is presented to predict quantum dot placement on the surface of the droplet. We also investigate quantum dot clustering in planar liquid crystal as a function of concentration. Spatial and size controlled patterning of quantum dot clusters could be important in photonic applications such as developing a liquid crystal laser. [Preview Abstract] |
Saturday, October 31, 2015 2:24PM - 2:36PM |
S3.00003: Metal-Insulator Transition in Polyaniline Matthew Diefenbach Polyaniline emeraldine an organic semiconducting polymer is proven to be an effective material in electrical components and in various solar-cells. The Renewable Energy Laboratory at California State University East Bay is researching polyaniline emeraldine with the purpose of identifying the metal-insulator transition (MIT). Measuring the MIT will provide new information in understanding how these materials conduct electricity and may offer insight in improving its applications in renewable energy. In addition, our lab uses a doping technique with hydrochloric acid that effectively varies polyaniline's conductivity within the MIT regime. Experimentally, we have confirmed that the insulator-to-metal framework found in these conducting polymers exhibits similarities to traditional, inorganic doped semiconductors like crystalline doped silicon. [1] E. Tapavicza, A. M. Meyer, and F. Furche. Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations. Phys. Chem. Chem. Phys., 13:20986, 2011. [2] E. Tapavicza, G. D. Bellchambers, J. C. Vincent, and F. Furche. Ab initio non-adiabatic molecular dynamics. Phys. Chem. Chem. Phys., 15:18336–18348, 2013. [3] B. C. Arruda, J. Peng, B. Smith, K. G. Spears, and R. J. Sension. Photochemical ring-opening and ground state relaxation in alpha-terpinene with comparison to provitamin D3. J. Phys. Chem. B, 117(16):4696–4704, 2013. [4] Schalk, O.; Boguslavskiy, A. E.; Stolow, A. Two-Photon Excited State Dynamics of Dark Valence, Rydberg, and Superexcited States in 1,3-Butadiene. J. Phys. Chem. Lett., 5, 560-565, 2014. [Preview Abstract] |
Saturday, October 31, 2015 2:36PM - 2:48PM |
S3.00004: Real-time non-adiabatic modeling of time-resolved pump-probe spectra using time-dependent density functional theory Enrico Tapavicza, Travis Thompson, Noel Baluyot, Wilberth Narvaez, Cecilia Cisneros, Nhi Nguyen, Oiver Schalk, Roseanne Sension We model non-adiabatic excited state decay of organic molecules using time-dependent density functional theory surface hopping [1,2]. Based on the surface hopping trajectories we compute time-resolved transient absorption spectra [3], time-dependent photoelectron ionization spectra [4], and time-depnednt circular dichroism spectra. Calculated spectra and molecular structures are used to unravel features in experimental spectra that are not directly accessible from experiments. Our trajectories allow to analyze parallel decay channels separately and asses the effect of substituents on the excited state decay and stereoselectivity of electrocyclic reactions. Applications include provitamin D and its model systems cyclohexadiene, alpha-terpinene, and phellandrene. [1] E. Tapavicza, A. M. Meyer, and F. Furche. Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations. Phys. Chem. Chem. Phys., 13:20986, 2011. [2] E. Tapavicza, G. D. Bellchambers, J. C. Vincent, and F. Furche. Ab initio non-adiabatic molecular dynamics. Phys. Chem. Chem. Phys., 15:18336–18348, 2013. [3] B. C. Arruda, J. Peng, B. Smith, K. G. Spears, and R. J. Sension. Photochemical ring-opening and ground state relaxation in alpha-terpinene with comparison to provitamin D3. J. Phys. Chem. B, 117(16):4696–4704, 2013. [4] Schalk, O.; Boguslavskiy, A. E.; Stolow, A. Two-Photon Excited State Dynamics of Dark Valence, Rydberg, and Superexcited States in 1,3-Butadiene. J. Phys. Chem. Lett., 5, 560-565, 2014. [Preview Abstract] |
Saturday, October 31, 2015 2:48PM - 3:00PM |
S3.00005: Conformational control in the photochemistry of hexatriene derivatives Dan Kim, Enrico Tapavicza, Travis Thompson The photochemistry of hexatriene (HT) is determined by the ground state equilibrium of different rotamers. Different side chains and their relative positions on the HT backbone structure have different effects on the equilibrium between the different rotamers. To investigate the influence of the side chains on the relative statistical weight of the rotamers at equilibrium, we studied HT and two of its derivatives: (3Z)-2-isopropyl-5-methylhexa-1,3,5-triene (IPMHT) and (3Z,5E)-3,7-dimethylocta-1,3,5-triene (DOT). To effectively sample the ground state equilibrium of these molecules we use ab initio replica exchange molecular dynamics (REMD) based on density functional theory (DFT). We perform the simulation with and without empirical correction for dispersion forces. Based on the equilibrium of structures in the ground state we calculate electronic absorption spectra using time-dependent DFT (TDDFT). Results from the study show that there is an influence of the conformation of the molecules on the excitation energy. This principle can be used to selectively excite a group of rotamers. Our calculated data will be compared to experimental data in order to determine the accuracy of the empirical correction for dispersion forces and if rotamers can be selectively excited experimentally. [Preview Abstract] |
Saturday, October 31, 2015 3:00PM - 3:12PM |
S3.00006: \textbf{Magnetic and Structural Properties of Doped Barium Hexaferrite Films Formed by Aerosol Deposition for Microwave Absorption} Christopher Gonzalez, Scooter Johnson The focus of this research is to verify that magnetic and structural properties of a proprietary doped barium hexaferrite material, H18 produced by \textit{Temex Ceramics}, are preserved after films are created using aerosol deposition. There has not been any published research or reports characterizing the properties of Temex H18; this work fills that void. Magnetic and structural properties have been characterized and compared between the starting powder, pressed and sintered pucks, and the resulting films. Film deposition is achieved by aerosolizing the powder in a chamber and accelerating into the deposition chamber containing the substrate held at a much lower pressure. The as-received particles have an approximate particle size of 700 nm, The pressure difference created between the two chambers accelerates the particles through the deposition chamber where they collide with the substrate and fracture into particles approximately 200 nm in diameter and adhere to the substrate. Barium hexaferrite is a material with electromagnetic properties that allow it to resonate and absorb electromagnetic radiation. A scanning electron microscope has been used to measure approximate particle sizes of the raw starting powder, deposited films, compressed powder, and annealed compressed powder. X-Ray Diffraction has been used to compare features of the starting powder and deposited films. Hysteresis curves were generated of the samples using a Vibrating Sample Magnetometer to analyze the coercivity, magnetization saturation, and remanence. This paper will present results from this effort and discuss similarities and differences in magnetic properties between the starting powder and resulting films. Additional work is underway to demonstrate the applicability of the deposited powder as an absorber using a custom waveguide setup. [Preview Abstract] |
Saturday, October 31, 2015 3:12PM - 3:24PM |
S3.00007: Crystal Structure and Magnetic Properties of Novel Double Perovskite Ca$_{\mathrm{2}}$ScOsO$_{\mathrm{6}}$ David Russell, Shahab Derakhshan, Brent Melot Transition metal oxides (TMOs) with face centered cubic arrangement of magnetic ions are composed of triangular sub-lattices. When antiferromagnetic (AFM) interactions of the same strengths between all three pathways in triangular settings are in place, spin constraints cannot be fulfilled simultaneously and the system undergoes geometric magnetic frustration (GMF). The new B-site ordered double perovskite, Ca$_{\mathrm{2}}$ScOsO$_{\mathrm{6}}$, was synthesized in polycrystalline form by a solid-state method, and predicted to exhibit the GMF phenomenon. The crystal structure of Ca$_{\mathrm{2}}$ScOsO$_{\mathrm{6\thinspace }}$was refined from powder x-ray diffraction data. This system crystallizes in the monoclinic P2$_{\mathrm{1}}$/n space group with a$=$ 5.4719(1)A, b $=$ 5.6197(1)A, c $=$ 7.8184 (1)A and $=$ 89.893(2) degrees. The temperature-dependent magnetic susceptibility data reveal that the system undergoes a long-range AFM ordering below 67K. The magnetic frustration index, $f \quad \approx $3.17 suggest that the system exhibits moderate geometric magnetic frustration. The relative strength of various magnetic exchange interactions was calculated employing spin dimer analysis method. [Preview Abstract] |
Saturday, October 31, 2015 3:24PM - 3:36PM |
S3.00008: Control of rewriteable doping patterns in graphene/boron nitride heterostructures Salman Kahn, Jairo Velasco Jr., Long Ju, Dillon Wong, Juwon Lee, Hsin-Zon Tsai, Chad Germany, Sebastian Wickenburg, Jiong Lu, Takashi Taniguchi, Kenji Watanabe, Alex Zettl, Feng Wang, Michael Crommie Spatial control of charge doping in 2D materials is a promising technique for designing future electronic devices. Electrostatic gating and chemical doping are common methods to achieve control of charge doping in 2D materials. However, these approaches suffer from complicated fabrication processes that introduce impurities, change material properties irreversibly, and lack flexibility. Here, we introduce a new method for patterning rewriteable doping profiles with local interface charge transfer from defects in a tunable BN substrate into an adjacent layer of graphene. This will enable many novel device designs for 2D materials, including atomically thin p-n junctions and rewriteable memory devices. [Preview Abstract] |
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