Bulletin of the American Physical Society
2017 Annual Meeting of the Far West Section
Friday–Saturday, November 3–4, 2017; Merced, California
Session F3: Materials Science |
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Chair: Michael Scheibner, University of California Merced Room: COB1 263 |
Saturday, November 4, 2017 2:00PM - 2:12PM |
F3.00001: Magnetic Characterization of Bithermally Deposited Iron Phthalocyanine Thin Films Santos Fuentes, Thomas Gredig Metallo-phthalocyanine thin films are best known for applications based on their optical and electronic properties. Amongst the family of metallo-phthalocyanines, the iron compound stands out with unique magnetic properties.~The~grain size of~iron phthalocyanine can be tuned with the deposition~temperature. Higher substrate growth temperatures lead to larger coercivity values in the magnetic hysteresis loop below 5 K, when measured at 100 Oe/s. We expand this idea and grow iron~phthalocyanine thin films in two thermal stages. Each~layer of iron~phthalocyanine is grown at a different temperature. We compare the magnetic and physical properties of~these bithermally grown heterostructures to the control samples deposited with a single growth temperature. [Preview Abstract] |
Saturday, November 4, 2017 2:12PM - 2:24PM |
F3.00002: Optical Properties of Copper- and Manganese-Phthalocyanine Thin Films Anh Nguyen, Thomas Gredig Metallo-phthalocyanine-based thin films have been widely used in applications, such as electronic and photonic devices, organic photovoltaic devices, and gas sensors. In these devices, thin films lower the cost and provide mechanical flexibility. The electronic properties are dominated by the energy gaps of the materials. Copper phthalocyanine (CuPc) and manganese phthalocyanine (MnPc) thin films are deposited on cleaned glass substrates by using thermal evaporation at several deposition temperatures. The deposition temperature changes the morphology, grain size, surface roughness, and structural properties of the thin film. Here, the optical properties are characterized. The energy band gap is measured from the optical spectrum of the transmission data. The fundamental energy band gap of MnPc has one gap near 3.6 eV, which is inthe Soret band. In contrast, CuPc thin films show two energy band gaps, both in the Soret band region at 3.05(5) eV and in the Q-band region at 1.71(2) eV. For the highest deposition temperatures, the energy band gap of both CuPc and MnPc thin films decreases by about 0.1 eV, which is attributed to structural changes. [Preview Abstract] |
Saturday, November 4, 2017 2:24PM - 2:36PM |
F3.00003: The effect of electron extraction layers on the excitonic properties of hybrid perovskite thin films Katerina Nikolaidou, Som Sarang, Denzal Martin, Vincent Tung, Jennifer Lu, Sayantani Ghosh Optimum interaction between light harvesting media and electron extraction layers is critical for the efficient operation of photovoltaic devices. In this work, we study the effect that various morphologies of ZnO substrates have on the excitonic properties of hybrid perovskite (PVSK) thin films. The ZnO susbtrates employed include single crystalline (SC), micro-structured (MS), and nano-structured (NS) ZnO. Characterization of the PVSK/ZnO interface is achieved via electron microscopy, as well as temperature, power, and time-resolved photoluminescence (PL) spectroscopy to probe interfacial charge transfer. We observe that SC-ZnO acts as an effective electron extraction layer as indicated by PL quenching, reduced recombination lifetime and reduced exciton density in the PVSK thin film. However, MS- and NS-ZnO demonstrate PL enhancement, while reducing recombination lifetime. These results vary with temperature and can be correlated with variations in exciton binding energy of PVSK, underlining the effect of the electron extraction layer on the excitonic properties of the PVSK film. We conclude that while SC-ZnO can be used for electron extraction in photovoltaic devices, MS- and NS-ZnO can be implemented as scaffold in optical devices that require high quantum yield. [Preview Abstract] |
Saturday, November 4, 2017 2:36PM - 2:48PM |
F3.00004: Exploring the roles of morphology and lead halide precursors in hybrid perovskite luminescent solar concentrators Benaz Mendewala, Katerina Nikolaidou, Som Sarang, Christine Hoffman, Vincent Tung, Boaz Ilan, Sayantani Ghosh Hybrid metal-halide perovskite thin films have recently emerged as highly suitable candidates for broadband luminescent solar concentrators (LSCs) due to their broad absorption, large Stokes shift, and high quantum yield, but device design remains yet to be optimized. We examine the correlation between film thickness, lead halide source utilized in the precursors, morphology, and optical efficiency of planar perovskite LSCs. After synthesizing and testing sixteen different types of PVSK samples, we report a maximum optical efficiency of 34.7{\%}, which is close to the highest value reported in any type of LSC to date. Correlating scanning electron microscopy with spatially-resolved photoluminescence measurements and 3D Monte Carlo simulations, we accurately estimate self-absorption, surface losses, and scalability, providing a route toward optimizing thin film PVSK materials for these and other optoelectronic and photovoltaic applications. [Preview Abstract] |
Saturday, November 4, 2017 2:48PM - 3:00PM |
F3.00005: Exciton-phonon coupling in ZnSe/CdSe alloyed quantum dots Anne Kelley, Ke Gong, David Kelley Zinc to cadmium cation exchange of ZnSe quantum dots has been used to produce a series of alloyed Zn$_{\mathrm{1-x}}$Cd$_{\mathrm{x}}$Se quantum dots. As x increases, the lowest-energy exciton shifts to the red, initially broadening and then sharpening as x approaches 1. Resonance Raman spectra obtained with excitation near the lowest excitonic absorption peak show a gradual shift of the longitudinal optical phonon from 251 cm$^{\mathrm{-1}}$ in pure ZnSe to 210 cm$^{\mathrm{-1}}$ in nearly pure CdSe with strong broadening at intermediate compositions. The overtone to fundamental intensity ratio, a rough gauge of exciton-phonon coupling strength, is much larger for intermediate compositions than for either pure ZnSe or pure CdSe. Partial localization of the hole in locally Cd-rich regions of the alloyed particles increases the strengths of local internal electric fields, increasing the coupling between the exciton and polar optical phonons. [Preview Abstract] |
Saturday, November 4, 2017 3:00PM - 3:12PM |
F3.00006: Strong electron-hole symmetric Rashba spin-orbit coupling in graphene/monolayer transition metal dichalcogenide heterostructures Mark Lohmann, Bowen Yang, David Barroso, Ingrid Liao, Zhisheng Lin, Yawen Liu, Ludwig Bartels, Kenji Watanabe, Takashi Taniguchi, Jing Shi Despite its extremely weak intrinsic spin-orbit coupling (SOC), graphene has been shown to acquire considerable SOC by proximity coupling with exfoliated transition metal dichalcogenides (TMDs). I will present our results of strong induced Rashba SOC in graphene that is proximity coupled to a monolayer of MoS$_{\mathrm{2}}$ and WSe$_{\mathrm{2}}$ grown by chemical-vapor deposition with drastically different Fermi level positions. We observed strong induced graphene SOC that manifests itself in a pronounced weak-antilocalization (WAL) effect in the graphene magnetoconductance. The spin-relaxation rate extracted from the WAL analysis varies linearly with the momentum scattering time and is independent of the carrier type. This indicates a dominantly Dyakonov-Perel spin-relaxation mechanism caused by the induced Rashba SOC. Our analysis yields a Rashba SOC energy of $\sim $1.5 meV in graphene/WSe$_{\mathrm{2}}$ and $\sim $0.9 meV in graphene/MoS$_{\mathrm{2}}$. The nearly electron-hole symmetric nature of the induced Rashba SOC provides a clue to possible underlying SOC mechanisms. [Preview Abstract] |
Saturday, November 4, 2017 3:12PM - 3:24PM |
F3.00007: Largely tunable anisotropic thermal conductivity of pristine and lithiated MoS2 Shunda Chen, Aditya Sood, Eric Pop, Kenneth Goodson, Davide Donadio Understanding heat transport in two-dimensional (2D) layered materials is of importance for potential applications in energy storage, nanoelectronics and optoelectronics. The vibrational properties of 2D layered materials could be tailored in several different ways either by chemical modifications or mechanically. Here we investigate heat transport in MoS2, upon lithium intercalation and cross-plane strain, by first principles calculations. We find that both the in-plane and cross-plane components of the thermal conductivity of MoS2 are extremely sensitive to both strain and electrochemical intercalation. Furthermore, since in-plane thermal conductivity and cross-plane thermal conductivity respond in different ways to intercalation and strain, the thermal conductivity anisotropy can be modulated over two orders of magnitude. The underlying mechanisms for such large tunability of the anisotropic thermal conductivity of MoS2 are explored by computing phonon dispersion relations, relaxation time and mean free paths. Since both intercalation and strain can be applied reversibly their stark effect on the thermal conductivity can be exploited to design novel phononic devices, as well as for thermal management in MoS2-based electronics and optoelectronic systems. [Preview Abstract] |
Saturday, November 4, 2017 3:24PM - 3:36PM |
F3.00008: Study of electrode ink rheology and coating quality for pem fuel cell application Donglei Yang, Abel Chuang Proton Exchange Membrane (PEM) fuel cell is one of the most promising energy conversion devices that are environmental friendly. It converts chemical energy stored in hydrogen direct to electricity with only water and heat as by-products. These reactions take place in the electrode layer, which is most commonly made from ink coating and drying process. The electrode ink, consists of polymer/binder, inorganic catalytic particles and dispersant media, is therefore an important component that has a significant impact on fuel cell performance and durability. Most existing literature investigated the electrode film after coating and drying regarding its structural, material and electrochemical perspectives by altering the ink composition. Little attention has been paid to understanding the ink due to its highly opaque and heterogeneous nature. In our work, we focus on three aspects: 1) characterizing the rheological properties of the electrode ink; 2) assessing the dispersibility of the electrode ink by the means of zeta-potential; and 3) evaluating the relation between ink rheology and the coating quality. [Preview Abstract] |
Saturday, November 4, 2017 3:36PM - 3:48PM |
F3.00009: Advanced Networking Technology Utilization in Research Applications Juan Ramirez Chavez, Arijit Das In this period of the technological era, ongoing research has been devoted to adapting and utilizing advanced networking tools and software for the purpose of allowing greater connectivity between various, independently-run hardware components to achieve the tasks of a unified system. Such systems are capable of collecting and processing information regardless of scripting involved if practical network frameworks are established to communicate effectively. Throughout this investigation, two projects were conducted to validate questions regarding distributive data analysis. First, research was done on Simrad 4G radar and RTI IntegRadar XIR3000 radar system integration using Robotic Operating System (ROS) as a method of processing navigational information to a database with TCP and JavaScript web sockets. Second, research was also done on a 3-server setup running Red Hat Enterprise Linux with Cloudera's Manager Hadoop configuration software which allows for high-performance computing based on powerful data distribution. Regarding the ROS research, our results indicate that enabling communication between the two components is possible using TCP/IP and web socket protocols in order to transfer data to be analyzed. [Preview Abstract] |
Saturday, November 4, 2017 3:48PM - 4:00PM |
F3.00010: Thermal Properties of Bimetallic Disks: Theoretical and Experimental Comparison Joe Zuchegno, Maureen Smith, Matthew Moelter, Nathan Heston Thermal expansion and the corresponding internal material stresses and strains in a bimetallic shell can cause a ``snap'' action in which the concavity of the shell is symmetrically inverted. The 1953 paper, ``Stability of a Bimetallic'' Disk by W.H. Wittrick provides a mathematical model for examining the behavior of disks initially set to the shape of a spherical cap. In particular, the shape of the shell and both the trip and reset temperatures are presented. The direct use of this model has been fairly limited, but using modern computing capabilities we replicate the model and apply it to disks significantly larger than those typically used in practical application. Comparison with experimentally measured thermal properties are presented and we find good agreement for the temperature behavior of the disk shape, and the trends for the snap and reset temperatures. [Preview Abstract] |
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