Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session F2: Transport in Condensed Matter |
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Chair: Patrick Hopkins, University of Virginia Room: Salon C |
Friday, November 11, 2016 8:30AM - 9:06AM |
F2.00001: Novel Approach to Achieve High ZT Thermoelectric Materials Invited Speaker: Helmut Baumgart High efficiency thermoelectric materials have attracted considerable attention because of their application potential in power generation and refrigeration systems. The efficiency of thermoelectric materials is expressed by the figure of merit (ZT), ZT = S2𝝈T/ (𝜿L + 𝜿e), where S is Seebeck coefficient, 𝝈 is electrical conductivity, T is the absolute temperature, and 𝜿L + 𝜿e are the thermal conductivity due to the lattice and electron contribution. It is observed that higher thermoelectric efficiency can be obtained by increasing the electron conductivity and reducing the thermal conductivity. A decrease of thermal conductivity could be achieved by a low dimensional superlattice structure, due to the quantum confinement or phonon scattering. Metal telluride based compounds such as bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) alloys have a high figure of merit and work best for thermoelectric devices used for the temperature range of 200 to 400 K, while lead chalcogenides such as PbTe, PbS, and PbSe are ideal for the temperature range of 350 to 600 K. Here we review advances in the ALD synthesis of composite thermoelectric nanolaminates of alternating Bi2Te3 and Sb2Te3 thin films, and PbSe and PbTe films. Extensive physical and electrical characterizations were performed in order to elucidate the ALD nanolaminate growth mechanism. Nanolaminate structure of alternating ALD Bi2Te3 and Sb2Te3 layers exhibiting localized epitaxial growth within individual islands as revealed by high resolution TEM cross-section analysis, because of the similar lattice constants between the Bi2Te3 and Sb2Te3 ALD layers. The alternating telluride films grow localized in graphene like fashion in hexagonal layers. We discuss various approaches to enhance the figure of merit ZT and the Seebeck coefficient for ALD PbTe & PbSe films employing quantum wells, quantum dots, and nanolaminates, which introduce a large density of interfaces to enhance phonon scattering resulting in an effective reduction of the thermal conductivity, and a concurrent significant improvement of ZT. [Preview Abstract] |
Friday, November 11, 2016 9:06AM - 9:36AM |
F2.00002: Potential of layered materials for thermionic devices: a first-principles study Invited Speaker: Keivan Esfarjani Solid-state heat to electrical energy conversion is usually done by using thermoelectric materials, which are thought to perform better than thermionic devices. Here, we would like to show that layered materials which are usually bonded by van der Waals interactions, have considerable potential to be used for cooling or heat to electrical energy conversion, of performance comparable to thermoelectrics. This claim is backed by first-principles calculations. The reason for this good performance is the low cross-plane thermal conductivity of these materials due to their weak bonding. Furthermore, the energy barrier for electrons to cross the device can be relatively easily tuned because of the large choice of layered materials of various band gaps and the variation of the bandgap with the number of layers. This implies that the device performance can easily be optimized. [Preview Abstract] |
Friday, November 11, 2016 9:36AM - 10:06AM |
F2.00003: Nanoscale Thermal Transport in Polymers Invited Speaker: Zhiting Tian Polymers are an interesting class of soft matter which have a wide range of applications. Nanoscale thermal transport processes in polymers are of increasing importance due to the tremendous advancement in nanostructured polymeric materials and devices with great flexibility and scalability. Thermal conductivity of polymers is highly morphology-dependent. Our group has been working on thermal transport properties of different polymers at the nanoscale. In this talk, I will first present the chain confinement effects observed in amorphous polymer thin films, which highlights the fundamental difference in heat conduction between crystalline polymers and amorphous polymers. I will then discuss the topology and morphology effects on thermal transport using a novel class of polymers -- bottlebrush polymers. Finally, thermal rectification in tapered bottlebrush polymers will be covered. [Preview Abstract] |
Friday, November 11, 2016 10:06AM - 10:36AM |
F2.00004: Donor doped cadmium oxide: An extreme-mobility oxide conductor Invited Speaker: Jon Paul Maria The widespread interest in plasmonic technologies surrounds a wealth of emergent optoelectronic applications, such as plasmon lasers, transistors, sensors, and information storage. While materials for UV-VIS and near infrared wavelengths applications have been found, the mid-infrared range remains a formidable challenge to address: only a few known systems can achieve sub-wavelength optical confinement with low loss. Here, we undertake this challenge. A combination of experiments and \textit{ab-initio} modeling demonstrate and understand an extreme peak of electron mobility in Dy-doped CdO that is achieved through ``\textit{defect equilibrium engineering}''. In so doing, we create a tunable plasmon host that satisfies the demanding criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials like Ag and Au. Extrinsic doping pins the CdO Fermi level above the conduction band minimum. It increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy-doping is sufficiently small, allowing mobility values around 500 cm$^{2}$/V\textbullet s for carrier densities above 10$^{20}$/ cm$^{3}$. CdO:Dy resembles the ideal "lossless metal", a potentially new material for exploring integrated mid-IR plasmonic applications. Our claim is based on temperature dependent transport, mid-IR spectroscopy, thermal transport, and \textit{ab-initio} characterizations showing that 1) CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical, and thermal properties; 2) oxide conductors so prepared are ideal candidates for plasmonic devices; and 3) the defect engineering approach for property optimization is generally applicable to other conducting metal oxides. [Preview Abstract] |
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