Bulletin of the American Physical Society
2015 Annual Fall Meeting of the APS Ohio-Region Section
Volume 60, Number 12
Friday–Saturday, October 16–17, 2015; Cleveland, Ohio
Session E2: Condensed Matter and Material Science - Experimental |
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Chair: Petru S. Fodor, Cleveland STate University Room: SC311C&D |
Saturday, October 17, 2015 9:15AM - 9:27AM |
E2.00001: Latent Heat Recovery Modification from Sodium Acetate Trihydrate due to Structural Changes Caused by Silver Nanoparticles Gillian Ryan, Uma Ramabadran, Frederick Garcia Phase change materials (PCMs) have great potential as energy storage devices through the storage of thermal energy at low temperatures. Sodium acetate trihydrate (SAT) is a PCM commonly used for storing thermal energy for non-electric personal warmers, and releases that energy as latent heat during the phase transition from a supersaturated liquid state to a solid, crystal state at room temperature. SAT is an inexpensive, non-toxic PCM. These characteristics make SAT ideal for the development of reusable, non-electric neonatal blankets. This application requires careful optimization of the maximum temperature attained by the SAT solution, balanced by a prolonged heat release that will last hours. It is hypothesized that latent heat release will be prolonged if crystal growth rate is slowed via the interference of additives with the crystallization process. In this work we investigate the effects of adding nanoparticles to a solution of SAT and water. We find that the nanoparticles expedite the crystal growth, but that the growth rate of SAT crystals is non-monotonic with increasing nanoparticle concentration. Powder X-ray diffraction data indicate that the crystal structure is not affected with larger size particles are added, but strongly modified with the addition of 10nm size silver nanoparticles. [Preview Abstract] |
Saturday, October 17, 2015 9:27AM - 9:39AM |
E2.00002: Ultrafast spectroscopy of exciton and exciton dynamics in mono to few layers of WS$_{2}$ Sudiksha Khadka, Shrouq Aleithan, Max Livshits, Jeffery Rack, Martin Kordesch, Eric Stinaff 2D materials, beyond Graphene, having a direct band gap in visible spectrum are monolayer of group 6 transitional metal dichalcogenides (MX$_{2})$ that have possibile application in optoelectronic devices, photovoltaics and photodetection, molecular sensing, 'valleytronics', and flexible transparent electronics. Tungsten Disulphide (WS$_{2})$, one of the MX$_{2\, }$, has direct band gap of 2.2 eV and a large valley splitting of about 0.4 eV. This leads to the existence of two distinct and direct excitons A and B. Here, we present a detailed study of exciton states and their decay mechanisms in mono and few layer WS$_{2}$ using femto-second transient absorption spectroscopy. Originally, this set up was designed for the study of macroscopic samples, so we modified it to perform microscopic FTAS on CVD grown flakes of WS$_{2}$. Here, we report a new peak at 3.01 $+$/- 0.1 eV whose origin in k space is under further investigation. The tri-exponential fitting of decay curve of the exciton A reveals three time components as 1.7$+$/-0.3 ps, 33.5$+$/-10 ps and 670$+$/-15 ps, most likely corresponding to carrier-carrier scattering, carrier-phonon scattering, and radiative relaxation respectively. [Preview Abstract] |
Saturday, October 17, 2015 9:39AM - 9:51AM |
E2.00003: Exciton Plasmon Interaction in Au coated Hybrid Organic GaAs Core Multi-shell Nanowire Heterostructures. Masoud Kaveh, Qiang Gao, Chennupati Jagadish, Gerd Duscher, Hans-Peter Wagner We investigate exciton energy transfer from semiconductor nanowires (NWs) to the Au nanoparticles in Au/Alq3 coated GaAs-AlGaAs-GaAs core-shell NWs using temperature- and intensity-dependent time-integrated as well as time resolved (TR) photoluminescence (PL). Organic-plasmonic NW heterostructures were fabricated by organic molecular beam deposition. PL measurements at 14K show emission peaks at 1.515 eV, 1.495 eV and 1.469 eV attributed to the free exciton, the carbon free to bound transition and tentatively to an emission from deeply trapped electron or hole states, respectively. Plasmonic NWs with a \textasciitilde 10 nm thick Au coating but without Alq3 spacer layer reveal a significant reduction of the PL intensity for all emission bands compared with the uncoated NW sample. Organic-plasmonic NWs with the same Au coverage and an additional Alq3 interlayer of 5 or 10 nm thickness show a noticeably stronger PL intensity which increases with rising Alq3 spacer thickness. The PL quenching is mainly attributed to Forster energy-transfer from free GaAs excitons to plasmon oscillations in the deposited Au film. TR PL measurements support our interpretation by showing an increase in the exciton decay times as we increase the spacer thickness. Au coated NWs also reveal a strong polarization dependent absorption which is mainly due to the significant dielectric mismatch between the NWs and the adjacent vacuum environment. [Preview Abstract] |
Saturday, October 17, 2015 9:51AM - 10:03AM |
E2.00004: Magnetic and exchange bias properties of Ni1.4Mn2Ga0.6 intermetallic alloy abdullah albagami, Mahmud Khan The understanding of magnetic exchange interactions in magnetic materials is important for new innovations in science and technology. This is because magnetic materials have many multifunctional properties that are utilized in numerous technologies. Exchange bias is one such property that results from competing magnetic interactions in certain materials. Here we present an experimental study on the magnetic and exchange bias properties of Polycrystalline Ni1.4Mn2Ga0.6 alloy. The material exhibit a ferromagnetic Curie temperature of 299.58 K. The magnetization versus field data obtained at 5 K under zero field condition exhibits a double shifted hysteresis loop that disappears at higher temperatures. When the sample is cooled from room temperature to 5 K in applied magnetic fields, exchange bias is observed, whose magnitude is strongly dependent on the cooling field. A maximum exchange bias field of 730 Oe is observed under field cooling condition at 5 K. Interestingly, a negative magnetization is observed in the magnetization versus field data obtained at magnetic fields smaller than 75 Oe. The experimental results are explained in terms of the competing ferromagnetic and antiferrromangnetic exchange interaction that exist in the materials due to the Mn atoms occupying multiple crystalline sites resulting in a spin glass type frustrated ground state. [Preview Abstract] |
Saturday, October 17, 2015 10:03AM - 10:15AM |
E2.00005: Magnetocaloric properties of Ni$_{2}$Mn$_{0.55}$Cr$_{1-x}$Co$_{x}$Ga Heusler alloys Jeffrey Brock, Ramakanta Chapai, Mahmud Khan Since the discovery of the giant magnetocaloric effect in Gd5(Si1-xGex)4 near room temperature [V. K. Pecharsky, et al., Phys. Rev. Lett. 78, 4494 (1997)], the research activities in search for materials exhibiting similar effects have been continuously accelerating. Although many materials exhibiting large magnetocaloric effects have been discovered [K. A. Gschneidner, Jr., et al., Rep. Prog. Phys. 68, 1479 (2005)], only a few have been reported to exhibit such effects in the vicinity of room temperature [O. Tegus, et al., Nature (London) 415, 150 (2002)][M. Khan, et al., J. Appl. Phys. 101, 053919 (2007)]. Here, we present an experimental study on the magnetic properties of Ni2Mn0.55Cr1-xCoxGa Heusler alloys. The alloys have been investigated by magnetization. It is shown that by partial substitution of Cr by Co the ferromagnetic ordering temperature of Ni$_{2}$Mn$_{0.55}$Cr$_{1-x}$Co$_{x}$Ga can be tuned over a wide range of temperatures, that is from 265 K (x$=$ 0) to 306 K (x $=$ 0.2). Over the entire temperature range the alloy system exhibits large magnetocaloric effect. [Preview Abstract] |
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