Bulletin of the American Physical Society
2018 Annual Meeting of the Far West Section
Volume 63, Number 17
Thursday–Saturday, October 18–20, 2018; Cal State Fullerton, Fullerton, California
Session B01: Experimental Condensed Matter Physics and Material Science |
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Chair: Roopali Kukreja, University of California, Davis Room: Titan Student Union Ontiveros A-B |
Friday, October 19, 2018 2:00PM - 2:12PM |
B01.00001: Measurement of hard-sphere like dynamics in concentrated alpha-crystallin suspensions using X-ray Photon Correlation Spectroscopy Vidanage Nuwan C Karunaratne The dynamics of concentrated suspensions of the ocular protein, alpha crystallin have been measured using X-ray Photon Correlation Spectroscopy (XPCS). Measurements were made at wavevectors corresponding to the first peak in the hard-sphere structure factor. The dynamics were measured at volume fractions close to the critical volume fraction for the glass transition, where the intermediate scattering function, f (q, τ ) could be well fit using a double exponential decay. The measured relaxation times were in reasonable agreement with published molecular dynamics simulations for the relaxation times of hard-sphere colloids. |
Friday, October 19, 2018 2:12PM - 2:24PM |
B01.00002: Unconventional Charge Separation in Mixed Dimensional InSe-C70 van der Waals Heterojunctions Shaowei Li, Chengmei Zhong, Alex Henning, Mark Hersam Two-dimensional InSe is a direct bandgap semiconductor promising for high performance photodetectors and solar cells. Mixed dimensional p-n heterojunction between InSe and organic molecules integrates desirable properties of both. Electronic structure of surface states is critical for optimal band offsets at the heterojunction. Although there is no consensus on the type of intrinsic doping, few-layered InSe field-effect transistors showed exclusively n-type behavior. Here, we report that the atomically clean surface of mechanically exfoliated InSe is unintentionally p-doped. STS taken over the native surface selenium vacancies resolves occupied defect states near the valance band edge. These defect states lead to an upward band bending near the InSe surface, rendering InSe surface p-type. In prototype InSe/C70 heterojunction, PL spectroscopy and STS both indicate formation of a type-II heterojunction. Electrons can transfer between InSe and C70 evidence from mutual PL quenching of both InSe and C70. STS in vacuum and KPFM in the ambient consistently reveal the electron transfer from InSe to C70 resulting in a photovoltage of ~0.25 eV. This study reveals the unusual electron donor behavior of InSe in an organic-inorganic heterostructure. |
Friday, October 19, 2018 2:24PM - 2:36PM |
B01.00003: Signature of the orbital character in the electronic band structure of C60 through photoemission experiments Ryan Reno, Drew W Latzke, Jonathan Denlinger, Alessandra Lanzara, Claudia Ojeda-Aristizabal Using Angle-Resolved Photoemission Spectroscopy (ARPES), we have observed strong photon-dependent oscillations of C60 valence band clusters’ intensity. These oscillations have been reported in the literature and are related to the spherical geometry of the C60 molecule, where photoelectron waves emanating from each carbon atom in the molecule experience interference inside the molecule. Here, we report the analysis of such oscillations coming from a highly ordered C60 thin film crystal. Using Fourier transform analysis, we show that the frequency and phase of these oscillations are intimately related to the orbital character of the different C60 valence band clusters. These results open avenues to probe the orbital character of the band structure of other fullerene or large molecule thin films. |
Friday, October 19, 2018 2:36PM - 2:48PM |
B01.00004: NMR Studies of TmVO_4 Zhipan Wang, Ziwen Mei, Paulo Menegasso, Tanat Kissikov, Pierre Massat, Ian Fisher, Nicholas James Curro TmVO4 undergoes a tetragonal to orthorhombic structural phase transition below 2.2K due to a cooperative Jahn-Teller distortion. The Tm ions experience a crystal-field effect with a non-Kramer’s ground state doublet. We have performed 51V NMR in a single crystal to investigate the role of magnetic and quadrupolar fluctuations. We find that the spin lattice relaxation rate varies strongly with field orientation, which reflects the role of quadrupolar(nematic) fluctuations near the critical temperature. We have also observed strong angular dependence of the 51V NMR Knight shift. |
Friday, October 19, 2018 2:48PM - 3:00PM |
B01.00005: Specific heat of Pr1-xNdxOs4Sb12 Yeh-Chia Chang Rare earth compound shows a variety of strongly correlated behaviors, which attract our interests. PrOs4Sb12 exhibit unconventional superconductivity when the temperature is lower than 1.85K and NdOs4Sb12 display ferromagnetism below 0.9K. We want to understand how the Nd doping affects the PrOs4Sb12. In order to figure out the properties of the material, we decide to evaluate Pr1-xNdxOs4Sb12 heat capacity varying with the temperature. The specific heat of filled skutterudites Pr1-xNdxOs4Sb12 has been measured with different Nd concentrations: x= 0.10, 0.25, 0.30, 0.45, 0.50, 0.55, 0.60, 0.75, 0.80, and 1.00 from 10K to 300K. The specific heat data was analyzed by a combination of the Debye, Einstein, and Sommerfeld models, which tell us the information of Debye temperature, Einstein temperature, and electronic specific heat coefficient respectively. In turn, these parameters refer to the stiffness of the crystalline lattice, rattling effect, and electron correlation of each sample. The value acts as a guide to determine the behaviors of this substitution system. |
Friday, October 19, 2018 3:00PM - 3:12PM |
B01.00006: Thermopower Measurement Probe Design by Using Type-T Thermocouple Andrea Nataly Capa Salinas, Yeh-Chia Chang, Jesus Velasquez, Pei-Chun Ho The Seebeck effect is a phenomenon by which an electromotive force is generated when a temperature difference is imposed at the ends of a material. This effect can be characterized by the Seebeck coefficient. Understanding the Seebeck coefficient will result in comprehending the physical properties of the material, its normal state behavior, and progress on further applications, such as thermoelectric generators, refrigeration systems, and temperature measurement devices. In our laboratory, a thermopower probe has been developed to ultimately measure the Seebeck coefficient of filled-skutterudite compounds. Before thermopower measurements of these compounds could be started, we had proceeded to test the functionality and resolution of the probe design. Nickel 201 alloy and platinum samples were used to check the accuracy of the measurement probe, and thus it was concluded that our device provides measurements above 100K within a 3% error. Nonetheless, measurements below this point are still yet to be improved. The data is thought to be limited by the operating range of the type-T thermocouple used. For future improvement of the probe, we plan to implement a Cernox thermometer in the hot side, so that the thermocouple can be prescinded from the design. |
Friday, October 19, 2018 3:12PM - 3:24PM |
B01.00007: Surface modification of stainless steel using a radio-frequency generated atmospheric pressure plasma Sara Margala, Wing Jong Chan, Nina Abramzon Atmospheric pressure plasma alters the surface properties of a material while leaving the bulk characteristics unchanged. The free radicals in the plasma cause an increase in the hydrophilicity of a material’s surface. This treatment has been shown to enhance adhesion of coatings. However, there is still a need to understand the mechanism. By utilizing an atmospheric pressure plasma on stainless steel surfaces, a change in surface energy was observed. The plasma was produced with a Surfx technologies reactor-A using a mixture of He and O2 gases. The longevity of the treatment, as well as the surface energy changes as oxygen flow rate changes between 0.1 L/min and 0.35 L/min, were measured using the contact angle technique. The data shows that a 5-second plasma treatment at an oxygen flow rate of 0.20L/min results in the lowest contact angle. The longevity measurements show that 6 hours after a 1-minute treatment, the sample retains a 35% higher surface energy compared to the control. Emission spectra from the plasma were collected and show that more reactive species are present at lower oxygen flow rates. The results indicate the potential of plasma for stainless steel surface modification as well as demonstrate correlation between ROS concentration and the surface energy. |
Friday, October 19, 2018 3:24PM - 3:36PM |
B01.00008: Structure Investigation of Cadmium Sulfide and Cadmium Selenide Nanocrystals Deposited by Chemical Bath Deposition Technique Liangmin Zhang, Ivan Mondragon Cadmium compounds, including cadmium sulfide (CdS) and cadmium selenide (CdSe) are semiconductor materials and have been widely used in many fields due to their unusual optical and electronic properties. The quantum dots of these materials have received considerable attention because of their tunable band gaps, which can vary their optical response from the infrared to the ultraviolet ranges. The bandgaps of CdS and CdSe quantum dots can be tailored from 2.6 – 1.85 eV and 2.42 eV - 1.71 eV, respectively. We use the chemical bath deposition technique to deposit CdS and CdSe thin film on glass substrates. In order to deposit CdS thin films, we use cadmium sulfate (CdSO4), ammonia water (NH4OH) and thiourea (CS(NH2)2) as reaction agents. For CdSe thin films, we use cadmium acetate as cadmium ion source and sodium selenosulfate / thiourea as a selenium / sulfur ion sources. Aqueous ammonia is used as a complex reagent and also to adjust the pH of the final solution. The as-deposited thin films using this technique are optically transparent, adherent, homogeneous and yellowish for CdS and redish for CdSe without powdered precipitation. |
Friday, October 19, 2018 3:36PM - 3:48PM |
B01.00009: Electrochemical Characterization of Titanium Alloys Subjected to an Atmospheric Pressure Plasma Treatment Kevin Robles, Sara Margala, Nina Abramzon, Vilupanur A Ravi Test coupons of three different titanium alloys, i.e., Ti-6 Al-4 V, Ti-6 Al-4 V-0.01 B and Ti-6 Al-4 V - 1.09 B (all in mass%), were polished to a mirror-like finish using standard metallographic procedures. These alloy coupons were exposed to an atmospheric pressure plasma containing a mixture of helium and oxygen for 5 seconds. Contact angles of water with respect to the pre- and post-treated samples were measured. The contact angles decreased significantly for all of the alloy coupons when the measurements were conducted immediately after the cold plasma treatment and slowly increased when measured after 2 h from the time of treatment. Electrochemical characterization of the pre- and post-plasma treated alloys were carried out in deaerated 3.5 mass% sodium chloride solution. The electrochemical tests included three distinct stages: (i) a 1 h open circuit exposure during which voltage Vs time data (OCV) were obtained (ii) a linear polarization scan from -30 mV to +30 mV relative to the OCV to obtain the linear polarization resistance (LPR) and (iii) a Tafel plot from -400 mV to + 400 mV relative to the OCV. Results thus far indicate that the corrosion potentials increased after plasma treatment, i.e., the alloys indicated more nobility after the exposure. |
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