Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y25: Focus Session: Thermoelectrics - Organic and Nanomaterials |
Hide Abstracts |
Sponsoring Units: DMP GERA FIAP Chair: Lakshmi Krishna, Colorado School of Mines Room: 503 |
Friday, March 7, 2014 8:00AM - 8:12AM |
Y25.00001: Designing $\pi$-stacked molecular structures to be thermal insulators but electric conductors Gediminas Kirsanskas, Qian Li, Martin Leijnse, Gemma Solomon, Karsten Flensberg We show that $\pi$-stacked molecular structures in transport junctions can be designed to have a reduced thermal phonon conductance, while maintaining a high electric conductivity. The relevant contribution to the phonon thermal conductance, up to room temperature, comes from the center of mass motion of the molecules. Therefore, we propose a molecular design consisting of two large masses coupled to each other and to the leads. By having a small coupling (spring constant) between the masses, it is possible to reduce the phonon thermal conductance. This can be achieved by a $\pi$-stacking of the molecules. For the proposed model, the effects of mass' asymmetry, coupling asymmetry, and coupling strength are also examined. The resulting heat conductance is compared with the situation when the molecule is modeled as a single mass. The effective coupling strengths (spring constants) for the simplified model are extracted from density functional theory calculations. [Preview Abstract] |
Friday, March 7, 2014 8:12AM - 8:24AM |
Y25.00002: Lorenz number of conducting PEDOT:PSS Xiaojia Wang, Nelson Coates, Rachel Segalman, David Cahill The electronic thermal conductivity is related to the electrical conductivity through the Wiedemann-Franz law (WFL), which predicts that the ratio of the electronic thermal conductivity to the electrical conductivity is proportional to the absolute temperature. The WFL has been validated for various materials; however, deviations may arise under certain circumstances, in which the relaxation times for the electrical and thermal processes are not identical. In this work, we investigate the Lorenz number, the proportionality factor in the WFL, of conjugated polymers. We prepare samples made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with tunable electrical conductivity. The in-plane electrical resistivity is characterized with setups of both 4-point probe and Van der Pauw configurations. To determine the thermal conductivity along the same direction as that for the electrical resistivity, we measure the through-plane thermal conductivity of the cross section of PEDOT:PSS using time-domain thermoreflectance. The effects of anisotropy and inhomogeneity on the thermal conductivity of PEDOT:PSS are also examined. [Preview Abstract] |
Friday, March 7, 2014 8:24AM - 8:36AM |
Y25.00003: Effect of Alkyl Ligand Size on Thermoelectric Properties of Gold Nanocrystal Arrays William Chang, Boris Russ, Jeffrey Urban, Rachel Segalman Traditional thermoelectric materials suffer from low efficiencies due to inverse coupling of the Seebeck coefficient and electrical conductivity, which limits the power factor. Decoupling of these two physical properties represents an exciting opportunity, and has previously been demonstrated in molecular junctions. Using molecular junction design principles for guidance, we designed gold nanocrystal arrays with varying alkyl linkers. We demonstrate that the conductivity of these nanocrystal arrays follows a conventional tunneling model, where the length between nanoparticles dictates conductance. Interestingly, the Seebeck coefficients are not explained by single molecule tunneling junction theory. Metal ligand charge transfer theory, in conjunction with optical spectroscopy, is used to explain thin film charge transport. We compare these macroscale thin film transport properties to single molecule electronic transmission measurements reported in previous studies. This result will lend further insight into how molecular junctions and nanocrystal arrays can be integrated for materials with higher power factors. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 8:48AM |
Y25.00004: Developing P-type Nanocomposites for Optimized Thermoelectrics A.D. Avery, K.S. Mistry, B.L. Zink, M.L. Olsen, P.A. Parilla, J.L. Blackburn, A.J. Ferguson Nanocomposites constructed of conducting polymers with organic inclusions such as single-walled carbon nanotubes are promising candidates for materials where the thermal and electrical transport properties can be decoupled, with the aim of realizing more efficient organic thermoelectric composites. Successful realization of high-performance organic thermoelectric devices requires a detailed fundamental understanding of the factors governing thermal and electrical transport through these materials. Additionally, in reduced geometries, many of these materials are expected to be anisotropic, necessitating the ability to measure these properties in the sample plane. In this talk, we describe our suspended membrane technique for directly measuring the in-plane thermal and electrical transport in the same sample, and present results for several different thin films. We present our approach to developing p-type materials with tunable transport behavior, through fabrication of composites consisting of single-walled carbon nanotubes (SWCNTs) dispersed in a polymer matrix. Finally, we discuss post-fabrication treatments of the SWCNT thin films and the benefits offered by nanostructuring these architectures to optimize the thermoelectric dimensionless figure-of-merit, ZT. [Preview Abstract] |
Friday, March 7, 2014 8:48AM - 9:00AM |
Y25.00005: Tailoring thermopower of single-molecular junctions by temperature-induced surface reconstruction Chiung-Yuan Lin, Bailey Hsu, Yau-Shian Hsieh, Yu-Chang Chen Recent experiments revealed that surface reconstruction occurs at around 300-400K in the interface of C$_{60}$ adsorbed on Cu(111) substrate by scanning tunneling microscope techniques. To understand effects of such reconstruction on thermopower, we investigate the Seebeck coefficients of C$_{60}$ single-molecular junctions without and with surface reconstruction as a function of temperature at different tip-to-molecule heights from first-principles. Our calculations show that surface reconstruction can enhance or suppress Seebeck coefficients according to junctions at different tip heights. We further observe that the Seebeck coefficient of the junction at $d =$3.4{\AA} may change from p- to n-type under surface reconstruction. [Preview Abstract] |
Friday, March 7, 2014 9:00AM - 9:12AM |
Y25.00006: Predicting the Influence of Secondary Phases on the Thermoelectric Performance in Cobalt Containing Spinels (ACo$_2$O$_4$; A=\{Co,Ni,Zn\}) Terence Musho, Anveeksh Koneru, David Mebane A promising new compositional space comprised of cobalt containing spinels bound by three end-members, Co$_2$(Co)O$_4$, Co$_2$(Ni)O$_4$ and Co$_2$(Zn)O$_4$, has brought to issue the presence of secondary phases (CoO, NiO, ZnO). These secondary phases are a result of not achieving a complete solid solution across the compositional space. It is hypothesized that under controlled fabrication the geometry and dispersion of these secondary phase can be leveraged to not only limit phonon transport but possibly increase electrical transport resulting in enhanced thermoelectric performance. To understand the influence of these secondary phases, a computational model has been developed that relies on a two dimensional non-equilibrium Green's function (NEGF) formalism to predict both the electrical and thermal contributions to the overall thermoelectric performance. This presentation will discuss the electrical and thermal transport models and approaches taken to incorporate dissipative carrier mechanisms into the quantum models. In addition, computational results predicting the optimal geometry and spacing of the secondary phases will be discussed. In closing, remarks will be made on how these models are currently being integrated into a high-throughput framework for materials discovery. [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:24AM |
Y25.00007: Large Enhancements in Thermopower and Electrical Conductivity in Nano-structured Half-Heusler Alloys Alexander Page, Anton van der Ven, Pierre Poudeu, Ctirad Uher Recent improvements have often been made to thermoelectric materials by adding nano-structures in order to scatter heat carrying phonons, however, the reduction in thermal conductivity is accompanied by large drops in the electrical conductivity caused by mobility reductions. In this work we show that Half-Heusler (HH) alloys can be combined with nano-scale Full-Heusler (FH) inclusions to simultaneously improve the power factor and reduce thermal conductivity. HH structures are of the form MNiSn and MCoSb (M$=$ Ti, Zr, or Hf) and the FH counterparts are created by filling the vacancies on the Ni or Co planes respectively, giving MNi$_{\mathrm{2}}$Sn and MCo$_{\mathrm{2}}$Sb. Experimental results show FH nano-inclusions were coherently integrated into the matrix HH material resulting in enhanced ZT which is attributed to energy filtering effects that occur at the HH-FH grain boundaries as well as moderate reductions in thermal conductivity by nano-inclusion phonon scattering. \textit{Ab Initio} calculations, in combination with a cluster expansion, are used to test the stability of FH structures in HH matrix and create thermodynamic pseudo-binary phase diagram for MNiSn-MNi2Sn compositions, elucidating the possibilities for future approaches to enhance ZT. [Preview Abstract] |
Friday, March 7, 2014 9:24AM - 9:36AM |
Y25.00008: Fabrication and Thermoelectric Properties of Bulk Si$_{0.8}$Ge$_{0.2}$-FeSi$_{2}$ Nanocomposite Amin Nozariasbmarz, Mohamed AbuDakka, Lobat Tayebi, Daryoosh Vashaee We report enhancement of thermoelectric figure of merit (ZT) in bulk nanocomposites of n-type Si$_{0.8}$Ge$_{0.2}$-FeSi$_{2}$. The nanocomposite material was prepared via rapid sintering of the mixed powder of Si$_{0.8}$Ge$_{0.2}$ and FeSi$_{2}$ in a die under axial pressure. The thermoelectric properties of the samples were measured versus temperature. A remarkable reduction in thermal conductivity was observed while the thermoelectric power factor (Seebeck coefficient squared times the electrical conductivity) was maintained compared to the corresponding properties of the crystalline Si$_{0.8}$Ge$_{0.2}$. As a result the ZT increased to about 1.2 at 950 C, which is 20{\%} more than that of the n-type crystalline silicon germanium. [Preview Abstract] |
Friday, March 7, 2014 9:36AM - 9:48AM |
Y25.00009: Nanoscale thermoelectric properties of fs-laser induced nanotracks on Sb$_{2}$Te$_{3}$ Jenna Walrath, Yen-Hsiang Lin, Yuwei Li, Vladimir Stoica, Lynn Endicott, Kevin Pipe, Ctirad Uher, Roy Clarke, Rachel Goldman Antimony telluride (Sb$_{2}$Te$_{3}$) is a canonical material for thermoelectric applications. It was recently shown that $\sim$20 nm diameter Sb$_{2}$Te$_{3}$ nanowires, fabricated by the vapor-liquid-solid method, exhibit $\sim$20{\%} enhancement in the Seebeck coefficient, S, in comparison to that of the bulk [1]. In addition, nanotrack formation was recently induced by fs-laser irradiation of Sb$_{2}$Te$_{3}$ [2]. Here, we report on the nanoscale thermoelectric properties of such fs-laser induced nanotracks on Sb$_{2}$Te$_{3}$ using scanning tunneling spectroscopy (STS) to probe the local density of states near the surface, and scanning thermoelectric microscopy (SThEM) to probe the local Seebeck coefficient just below the surface [3]. In the pristine (nanotrack) regions of Sb$_{2}$Te$_{3}$, STS reveals a bandgap of $\sim$0.3 eV (\textgreater 1 eV), suggesting the presence of an insulating surface layer in the irradiated regions. However, SThEM shows similar thermovoltages across both the pristine and nanotrack regions, presumably due to the buried regions of Sb$_{2}$Te$_{3}$. These data suggest that the nanotracks are buried beneath an insulating surface layer, consistent with our recent transmission electron microscopy observations. \\[4pt] [1] Y.M. Zuev, J.S. Lee, C. Galloy, H. Park, P. Kim, Nano Lett., \textbf{10}, 3037 (2010).\\[0pt] [2] Y. Li, V. A. Stoica, L. Endicott, G. Wang, H. Sun, K.P. Pipe, C. Uher, R. Clarke, Appl. Phys. Lett. \textbf{99}, 121903 (2011).\\[0pt] [3] J.C. Walrath, Y.H. Lin, K.P. Pipe, R.S. Goldman, Appl. Phys. Lett., in press (2013). [Preview Abstract] |
Friday, March 7, 2014 9:48AM - 10:00AM |
Y25.00010: Enhancement of thermoelectric figure of merit of nanostructured FeSb$_{2}$ by adding Cu nanoparticles Machhindra Koirala, Huaizhou Zhao, Mani Pokharel, Shuo Chen, Cyril Opeil, Gang Chen, Zhifeng Ren We present the enhancement of thermoelectric properties of FeSb$_{2}$ through modulation doping by Cu nanoparticles. Since, FeSb$_{2}$ and Cu have matched work function, the electrical conductivity of this Kondo-like system can be increased dramatically without affecting Seebeck coefficient. The optimized nanocomposite FeSb$_{2}$Cu$_{0.045}$ has enhancement of power factor by 90{\%} compared to pure nanostructured FeSb$_{2}$. The further reduction of thermal conductivity from FeSb$_{2}$/Cu interface gives the total enhancement of figure of merit (ZT) by 110{\%}. This strategy has been widely used on other semiconductors to improve ZT. Our result demonstrates that the potential of the modulation doping technique can also be extended to Kondo insulator systems. [Preview Abstract] |
Friday, March 7, 2014 10:00AM - 10:12AM |
Y25.00011: Predicting Phononic and Thermal Properties of Nanocrsytal Superlattice Structures Using Atomistic Models Mehdi Zanjani, Jennifer Lukes We use fully atomistic models with MD simulations to predict phononic and thermal properties of nanocrystal superlattices (NCSLs). NCSLs are formed by assembly of nanocrystals into organized structures with interesting and tunable properties. They present new phononic behaviors by combining dissimilar materials structured on the nanometer scale. The small thermal conductivity of these materials makes them promising candidates for thermoelectric applications as well. We have calculated phonon dispersion curves of NCSLs by generalizing the lattice dynamics methods. We also calculated thermal conductivity of these materials using 3-D equilibrium MD simulations and the Green-Kubo method. Atomistic models along with MD simulations provide a complement to experiments for understanding the behavior of NCSLs, and help us modify the design of these structures to achieve better phononic and thermal properties. [Preview Abstract] |
Friday, March 7, 2014 10:12AM - 10:24AM |
Y25.00012: Thermoelectric Study of Copper Selenide Mengliang Yao, Weishu Liu, Zhifeng Ren, Cyril Opeil Nanostructuring has been shown to be an effective approach in reducing lattice thermal conductivity and improving the figure of merit of thermoelectric materials. Copper selenide is a layered structure material, which has a low thermal conductivity and p-type Seebeck coefficient at low temperatures. We have evaluated several hot-pressed, nanostructured copper selenide samples with different dopants for their thermoelectric properties. The phenomenon of the charge-density wave observed in the nanocomposite, resistivity, Seebeck, thermal conductivity and carrier mobility will be discussed. [Preview Abstract] |
Friday, March 7, 2014 10:24AM - 10:36AM |
Y25.00013: Thermoelectric Properties of Nanostructured CeAl$_{3}$ Mani Pokharel, Tulashi Dahal, Zhifeng Ren, Cyril Opeil Past investigations into the heavy fermion compound CeAl$_{3}$ reveal a complex low-temperature physics resulting from the strong hybridization of localized 4f states with delocalized conduction electrons. This phenomenon gives rise to unusual electronic, thermal, and magnetic properties. We investigate the low-temperature thermoelectric properties of this strongly correlated system for its potential application as a $p$-type Peltier cooling element. In our work, nanostructured samples of CeAl$_{3}$ have been prepared using dc hot-press method and evaluated for their thermoelectric properties. Effects of different hot-pressing temperatures on the nanostructure and the thermoelectric properties will be discussed. Our results on CeAl$_{3}$ will be compared with our previous work on CeCu$_{6}$. [Preview Abstract] |
Friday, March 7, 2014 10:36AM - 10:48AM |
Y25.00014: Electronic structure of Zr-Ni-Sn systems: the role of nanostructures and clustering in Half-Heusler and Heusler limits Dat Do, S.D. Mahanti Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr-Ni-Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler limit (FH), ZrNi2Sn. Recently Makogo et al. [J. Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the formation of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in HH$_{1-x}$FH$_x$ systems near the HH and FH ends. These results and the effects of nanostructures on electronic structure and thermoelectric properties will be discussed in this talk. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700