Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B06: Undergraduate Research IIUndergraduate
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Sponsoring Units: APS SPS Chair: Kiril Streletzky, Cleveland State Univ Room: LACC 153A |
Monday, March 5, 2018 11:15AM - 11:27AM |
B06.00001: Investigating Traps in Organic Field-Effect Transistor through Field Dependent Mobility Sajant Anand, Katelyn Goetz, John Anthony, Oana Jurchescu Organic semiconductors can be processed in ambient conditions, a low-cost manufacturing process compatible with substrates such as paper, plastic, or fabric. Unfortunately, the electrical properties displayed by thin-film devices based on these materials do not match the performance requirements of consumer applications. While several compounds exhibit excellent performance in single crystal form, efficient charge carrier transport is mitigated in thin film devices by the presence of electronic traps. Here we report on the study of traps in organic semiconductors by performing electric field-dependent mobility measurements in organic field-effect transistors (OFETs). We were able to tune the mobility five orders of magnitude, from 0.001 to 10 cm2 V-1 s-1 through varying device geometry and the choice of dielectric layers. We correlated the mobility value with its field dependence, quantified using the Poole-Frenkel model, and found that the field dependence is reduced with increasing mobility and that mobility is independent of the applied field when the trap-free regime is reached. We show that the devices with highest mobility and field-independent operation display band-like transport, while devices with low mobility display activated transport and strong field dependence. |
Monday, March 5, 2018 11:27AM - 11:39AM |
B06.00002: Automating Electronic Transport Measurements at Low Temperatures and Performing Angle Resolved Photoemission Spectroscopy (ARPES) Data Analysis Using Python Ryan Reno, Drew Latzke, Alessandra Lanzara, Claudia Ojeda-Aristizabal Low temperature electron transport experiments on low dimensional nanomaterials are ruled by exciting quantum effects. In order to extract meaningful information from these experiments, data must be collected and analyzed in an organized and efficient manner. We present a method using the Python programming language and open source libraries to control the acquisition, interactive visualization, and analysis of data from a closed cycle cryostat and different measurment instruments. Additionally, we show the data analysis of a large amount of ARPES data corresponding to the modulation of the intensity of C60 band clusters with the incident photon energy. |
Monday, March 5, 2018 11:39AM - 11:51AM |
B06.00003: High-Velocity Saturation in Graphene Encapsulated by Hexagonal Boron Nitride Megan Yamoah, Wenmin Yang, Eric Pop, David Goldhaber-Gordon While mainly probed for its unique low-field electrical characteristics, graphene holds potential in practical device applications such as amplifiers or high-current interconnects. These applications rely on our understanding of the high electric field behavior and especially on our ability to minimize loss and maximize carrier velocities in graphene devices. Under high electric field, the drift velocity approaches a constant saturation velocity which can be limited by intrinsic or substrate phonons, heating, and substrate impurities. We present devices with graphene encapsulated by hexagonal boron nitride (hBN) which, due in part to the superior thermal conductivity and low impurity density of the hBN/graphene interface, produces saturation velocities higher than on all other common graphene substrates to date and suggest that hBN substrate phonons are the primary limiting factor for saturation velocity in our devices. |
Monday, March 5, 2018 11:51AM - 12:03PM |
B06.00004: The Role of Defects and Grain Boundaries in the Electronic Structures of Hybrid and Inorganic Tin Iodide Perovskites: a DFT Study Joseph Wong, Yuheng Li, Jianli Cheng, Kesong Yang Perovskite have recently become a topic of intense interest in the field of material science due to their promising applications as light harvesting materials in solar cell devices. The champion perovskite at this time is CH3NH3PbI3 (MAPbI3), however there is a major concern with the toxicity of the lead atom. Using first principles density functional theory (DFT) calculations, we examine the electronic properties of point defects and grain boundaries (GBs) in two tin-based perovskite alternatives, MASnI3 and CsSnI3. We find evidence that defects and GBs in both hybrid and inorganic perovskites are beneficial to electronic performance due to intrinsic p-doping without the generation of deep states. We also show that MASnI3 is intrinsically less stable than CsSnI3 according to chemical potential diagram and formation energy comparisons. We also provide evidence to support experimental observations of charge collection and separation at the GB due to band bending at the interface. Furthermore, we find wider bandgaps at the GB, pointing to a synergistic effect between charge collection and increased charge carrier lifetime at the interface. |
Monday, March 5, 2018 12:03PM - 12:15PM |
B06.00005: CVD Growth and Dry Transfer of Large High Quality Graphene Crystals Brian Ellsworth, Eva Andrei Graphene and other 2D materials revealed electronic properties that are fundamentally different from those in their bulk counterparts, and they carry the promise of novel device applications. Thus far, the best quality 2D layers are prepared by mechanical exfoliation, but this labor-intensive method does not lend itself to large-scale production. Alternatively, chemical vapor deposition (CVD) can be used to consistently produce large samples, but in this case, the substrate surface roughness limits the maximum size of single crystals and introduces grain boundaries, which degrade the carrier mobility. For CVD production of graphene, the substrate of choice is copper. We describe a method of electrochemical polishing (ECP) of copper which results in larger crystals. By optimizing the voltage range and chemical composition of the etchant, we achieved single-crystal domains that are significantly larger than those attained by mechanical exfoliation. The crystals are then transferred from the copper substrate to boron nitride using the dry-transfer method [1]. We show that by using ECP, CVD, and dry transfer, it is possible to consistently and reliably obtain large, high-quality graphene samples. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B06.00006: Chemical Vapor Deposition of Two-Dimensional Heterostructures Tania Diaz Marquez, Prasana Sahoo, Humberto Gutierrez Two dimensional (2D) materials such as transition metal dichalcogenides (TMDs) are being |
Monday, March 5, 2018 12:27PM - 12:39PM |
B06.00007: Measuring the double-layer capacitance of graphene devices in solution Geoffrey Rath, Michael Crosser Graphene, a two dimensional metal made from carbon, has been studied extensively as a sensor in biological systems. Biological systems produce voltages that can be detected by the graphene device. Effectively, the voltage creates a capacitance layer at the graphene/liquid interface, which then inhibits conduction through the graphene. When modeling this interaction, it is typical to assume the capacitive layer is identical to that in a liquid/metal interface. To test whether this is a valid assumption, the capacitance for a macroscopic system is compared to a graphene device for several concentrations of salt water. This work may prove important for studies of supercapacitors. |
Monday, March 5, 2018 12:39PM - 12:51PM |
B06.00008: Critical Films on Graphene Substrates Renee Beneski, Adrian Del Maestro, Juan Vanegas, Valeri Kotov When depositing a substance onto a surface, it follows that as one adds more of the substance, the thickness of the film formed on the surface will grow. However, a particle's ability to adsorb onto the surface is dependent on the interaction potential and geometry. For atomically flat two-dimensional materials such as graphene, it is predicted that the interactions between the graphene sheet and light atoms in a nearby gas are so weak that film growth may become arrested at a critical thickness. We report on molecular dynamics simulations of nitrogen near graphene to explore the existence and properties of the predicted critical film and investigate the role of temperature and pressure during the adsorption process. |
Monday, March 5, 2018 12:51PM - 1:03PM |
B06.00009: Interface Magnetism of Magnetic Multilayers with Interfacial Dzyaloshinskii-Moriya Interaction Baiyi Kong, Zhongying Yan, Xiao Wang, Andy Clark, Kui-Hon Ou Yang, Minn-Tsong Lin, Yongseong Choi, Axel Hoffmann, Suzanne te Velthuis, Xuemei Cheng Interfacial Dzyaloshinskii-Moriya Interaction (DMI) plays a significant role in stabilizing magnetic skyrmions at room temperature in multilayered films. Our previous results have shown magnetic skyrmions tuned with different top heavy metal (HM) layers in [Pt/Co/HM]n varied in size, but the mechanism for this size tuning effect needs further study. Here we report the investigation of the interface magnetism in [Pt/Co/HM]n multilayers using x-ray magnetic circular dichroism (XMCD) methods. [Pt(1.5nm)/Co(1nm)/HM(1nm)]n multilayers (HM=Ir and Au) were deposited by DC magnetron sputtering with a Ta buffer on SiO2/Si substrates. XMCD spectra were measured at the Advanced Photon Source of Argonne National Laboratory and the National Synchrotron Radiation Research Center (NSRRC) in Taiwan. The XMCD results show well-defined XMCD peaks at Ir L2,3 and Au L3 edges. The inversion of XMCD peaks with opposite magnetic fields demonstrates clear induced moments in Ir and Au multilayered thin films. |
Monday, March 5, 2018 1:03PM - 1:15PM |
B06.00010: Piezoresponse Force Microscopy Studies of Ferroelectric Domain Structures in Co-Polymer PVDF-TrFE Thin Films Spencer Prockish, Ashley Holland, Zhiyong Xiao, Jennifer Hamblin, Jingfeng Song, Stephen Ducharme, Xia Hong We report an in situ piezo-response force microscopy (PFM) study of the thermal effect on ferroelectric domain structures in ultrathin ferroelectric co-polymer polycrystalline poly(vinylidene-fluoride-trifluroethylene) (PVDF-TrFE) films. We prepared 9 monolayers (18 nm) PVDF-TrFE using the Langmuir-Blodgett approach, with a surface roughness of 1.2 nm. Stripe-shape domains have been created by applying 9 V to a conductive AFM tip while it is scanning the film surface at room temperature. The sample has then been subjected to progressively higher temperatures up to the ferroelectric Curie temperature TC of about 90 C. We then image the domain structures using PFM, from which we can examine quantitatively the evolution of domain wall roughness and thermal induced spontaneous polarization reversal. Our study has shed light on the energy competition among thermal roughening, elastic energy and the disorder on the domain stability in layered ferroelectric polymer thin films. We compare the results obtained on these layered polymers with those on perovskite ferroelectric oxides, which exhibits 3D ferroelectricity. |
Monday, March 5, 2018 1:15PM - 1:27PM |
B06.00011: Synthesis and Characterization of Lithium Carboxylates for Use in Lithium-Loaded Liquid Scintillator Melissa Schmitz, Christopher Bass Lithium-6 can be used for neutron tagging in scintillator-based detectors due to its large neutron capture cross-section and Q-value of the neutron capture reaction. One method for incorporating lithium-6 into organic liquid scintillator utilizes aqueous solutions of enriched lithium emulsified within the scintillator by surfactants. However, at lithium-loading fractions above a few percent by mass, emulsions can undergo phase instabilities resulting in poor optical performance. An alternative loading method involving the direct dissolution of organic lithium salts into liquid organic scintillator may circumvent the deleterious effects of emulsification. We discuss the synthesis of several lithium carboxylates and their properties when loaded into the commercial liquid scintillator cocktail Ultima Gold AB and a comparable formulation without surfactants. Performance of carboxylates was analyzed in terms of solubility and light transmittance properties via UV-Vis spectroscopy. |
Monday, March 5, 2018 1:27PM - 1:39PM |
B06.00012: Application of Direct Stress Using a Multilayered Actuator to tune Transport Properties of Manganites Julian Brodie, Ambika Shakya, Ashkan Paykar, Amlan Biswas Substances that undergo a first order phase transition can show coexistence of two phases. The manganite compound La0.33Pr0.34Ca0.33MnO3 has a first order transition between a ferromagnetic metallic phase and a nonmagnetic insulating phase and at certain temperatures the two phases coexist. In this phase separated state, the compound is extremely sensitive to external perturbations such as strain. Here, we use a multilayered actuator (MLA) composed of Lead Zirconate Titanate (PZT) to apply direct stress to an La0.33Pr0.34Ca0.33MnO3 thin film and measure the effect of strain on electrical resistance. We obtained a strain of only ∼10-6 . However, our experiments showed that even such a small strain is sufficient to induce a shift in the phase transition temperature of La0.33Pr0.34Ca0.33MnO3 making it a promising material for strain sensors. |
Monday, March 5, 2018 1:39PM - 1:51PM |
B06.00013: Local Chemical Environments in Magnetic High Entropy Alloys Daniel Mukasa, Brent Fultz, Hillary Smith, Matt Lucas Chemical and magnetic ordering in the body-centered cubic high entropy alloy FeCoCrNiAl2 was investigated. Characterization and parametrization of chemical ordering in this and other high entropy alloys is non-trivial due to the large number of elemental components. To investigate the preference for ordering in this alloy, materials were prepared by arc melting or melt-spinning followed by thermal annealing to vary the chemical homogeneity. Magnetization measurements show a dependence on cooling rate (i.e. preparation method) and thermal treatment, suggesting differences in the local chemical environments in this multicomponent alloy. The local chemical arrangements around Fe atoms were studied by 57Fe Mossbauer spectroscopy between 77K and 300K. Preliminary results suggest that the different thermal treatments altered the local chemical environments in the alloy and that there are two chemical zones for bcc-phase Fe with different Curie temperatures. Correlations between the bulk magnetic properties and local chemical ordering will be discussed. |
Monday, March 5, 2018 1:51PM - 2:03PM |
B06.00014: Detection of magnetic biomarkers using a single giant magneto-impedance microwire Claire Albrecht, Tatiana Eggers, Ongard Thiabgoh, Manh-Huong Phan A combination of magnetic sensors and superparamagnetic nanoparticles provides a novel biosensing platform for detection of cancer cells and biomolecules. In this study, we demonstrate the excellent capacity of detecting 10 nm iron oxide nanoparticles at various concentrations up to 40 mg using a single microwire (Co69.25Fe4.25Si13B12.5Nb1; d=60 µm) based sensor. The change in impedance of the microwire was measured using an impedance analyzer (1 MHz – 1 GHz) when exposed to the stray magnetic field from the nanoparticles. The detection sensitivity of the sensor is greatly enhanced by supplying a small DC field just below the anisotropy field of the microwire (HK = 3.5 Oe). The external field dependence of the detection demonstrates the microwire as a tunable RF magnetic sensor for small magnetic fields. In addition, we utilize the linear low-field impedance response as a new method for determination of the stray field strength of the detected nanoparticles. |
Monday, March 5, 2018 2:03PM - 2:15PM |
B06.00015: Analysis of the Molar Specific Heat of Pr1-xNdxOs4Sb12 Shoji Hishida, Jesus Velasquez, Taylor McCullough-Hunter, Pei-Chun Ho, M Brian Maple, Tatsuya Yanagisawa The compounds PrOs4Sb12and NdOs4Sb12 have attracted interest due to their low temperature properties. They exhibit unconventional heavy-fermion superconductivity and ferromagnetism respectively. The series of compounds Pr1-xNdxOs4Sb12 is being studied to understand the interaction between these effects. Previous studies have shown competition between the superconducting and ferromagnetic states and that for particular concentrations of Nd and Pr, the two coexist within the sample. The specific heat was measured in the normal state above 10 K, and thermodynamic parameters were extracted from the specific heat data for each sample, including the Debye and Einstein Temperatures and the electronic specific heat coefficient. Specific heat and parameter values will be reported for measured samples with low Nd concentrations. A minimum in the Debye and Einstein Temperatures was found around x = 0.55, which suggests a form of lattice-softening taking place at the Nd concentration where the superconductivity disappears. |
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