[PDF] Thermal And Thermoelectric Transport Measurements Of One Dimensional Nanostructures eBook

Author : Liang Yin
Publisher :
Page : pages
File Size : 18,4 MB
Release : 2013
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This dissertation presents experimental and computational study of thermal and electrical transport in one-dimensional nanostructures. Synthesizing materials into one-dimensional nanowire has been proved very effective for suppressing the phonon contribution due to scattering at the wire boundaries. Three one-dimensional nanostructured thermoelectric candidates - SiGe nanowires, SrTiO3 nanowires, and ZnO nanowires - were presented and discussed in this dissertation. SiGe nanowires are successfully synthesized on a cleaned n-type (100) Si substrate coated with gold thin film as a catalytic metal, via the vapor-liquid-solid (VLS) growth method. The thermoelectric properties of SiGe nanowires with different diameter, Ge concentration, and phosphorus doping concentration were measured using a MEMS micro-device consisting of two suspended silicon nitride membranes in the temperature range of 60 K ~450 K. The experimental results were obtained by "simultaneously" measuring thermal conductivity, electrical conductivity, and thermopower. The ZT improvement is attributed to remarkable thermal conductivity reductions, which are thought to derive from the effective scattering of a broad range of phonons by alloying Si with Ge as well as by limiting phonon transport within the nanowire diameters. An improved model based on Boltzmann transport equation with relaxation time approximation was introduced for estimating thermoelectric properties of phosphorus heavily doped SiGe nanowires from 300 to 1200 K. All the electron and phonon scatterings were comprehensively discussed and utilized to develop the new model for estimating electrical conductivity, thermopower, and thermal conductivity of SiGe nanowires. As thermoelectric materials, oxide nanowires have great advantages comparing to other semiconductors. Two nanostructured materials, SrTiO3 nanotubes and ZnO nanowires, are introduced and successfully synthesized by simple methods. Thermal conductivity of ZnO nanowires with different diameter were characterized from 60 K to 450 K. In order to measure thermoelectric properties of one-dimensional nanostructures at temperature up to 800 K, a new temperature vacuum system was carefully designed and built from scratch. The thermal conductivity of ZnO nanowires with different diameters at high temperature were measured from 300 K to 800 K. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151175

Author : Hai-Peng Li
Publisher : Springer
Page : 94 pages
File Size : 49,22 MB
Release : 2018-09-08
Category : Science
ISBN : 9811326371

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In this Brief, authors introduce the advance in theoretical and experimental techniques for determining the thermal conductivity in nanomaterials, and focus on review of their recent theoretical studies on the thermal properties of silicon–based nanomaterials, such as zero–dimensional silicon nanoclusters, one–dimensional silicon nanowires, and graphenelike two–dimensional silicene. The specific subject matters covered include: size effect of thermal stability and phonon thermal transport in spherical silicon nanoclusters, surface effects of phonon thermal transport in silicon nanowires, and defects effects of phonon thermal transport in silicene. The results obtained are supplemented by numerical calculations, presented as tables and figures. The potential applications of these findings in nanoelectrics and thermoelectric energy conversion are also discussed. In this regard, this Brief represents an authoritative, systematic, and detailed description of the current status of phonon thermal transport in silicon–based nanomaterials. This Brief should be a highly valuable reference for young scientists and postgraduate students active in the fields of nanoscale thermal transport and silicon-based nanomaterials.

Author : Duksoo Kim
Publisher :
Page : pages
File Size : 25,6 MB
Release : 2014
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This dissertation presents development of a microfabricated device (testbench) for measuring thermal conductivity and Seebeck coefficient of low-dimensional materials in addition to electrical conductivity and discusses the thermal and thermoelectric transport in nanoscale systems based on measurements performed using testbench. Despite the potential and obvious advantages of thermoelectric transduction, widespread use of such systems for energy harvesting and refrigeration remains limited to niche and specialized applications due to low efficiency. The thermoelectric efficiency is represented by a dimensionless figure of merit ZT = [sigma]S2T/[kappa], where [sigma] is electrical conductivity, S is Seebeck coefficient, [kappa] is thermal conductivity, and T is absolute temperature. Low-dimensional structures are expected to have improved power factor ([sigma]S2) and suppressed lattice thermal conductivity, and can therefore exhibit higher ZT than their bulk counterparts. Thus, there is a critical need for understanding thermal and thermoelectric transport in low-dimensional materials. However, in the case of low-dimensional materials, the accurate measurement of the thermal and thermoelectric properties is extremely challenging because of their small size. In order to address this need, we have developed a microfabricated testbench that can be used to measure two-probe electrical conductivity, thermal conductivity, and Seebeck coefficient of a variety of low-dimensional materials. Using the testbench, the thermoelectric efficiency of bismuth telluride nanotubes has been investigated. The bismuth telluride is one of the most efficient thermoelectric materials. Although the efficiency of bismuth telluride nanowires and nanoplates was already reported by other groups, no enhancement in the ZT in these materials was observed. This has been primarily attributed to the unexpectedly small Seebeck coefficient caused by unintentional doping or surface band bending. Owing to small wall thickness (

Author : Arden Lot Moore
Publisher :
Page : 420 pages
File Size : 35,1 MB
Release : 2010
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This work presents the development and application of analytical, numerical, and experimental methods for the study of thermal and electrical transport in nanoscale systems, with special emphasis on those materials and phenomena which can be important in thermoelectric and semiconductor device applications. Analytical solutions to the Boltzmann transport equation (BTE) using the relaxation time approximation (RTA) are presented and used to study the thermal and electrical transport properties of indium antimonide (InSb), indium arsenide (InAs), bismuth telluride (Bi2Te3), and chromium disilicide (CrSi2) nanowires. Experimental results for the thermal conductivity of single layer graphene supported by SiO2 were analyzed using an RTA-based model and compared to a full quantum mechanical numerical BTE solution which does not rely on the RTA. The ability of these models to explain the measurement results as well as differences between the two approaches are discussed. Alternatively, numerical solutions to the BTE may be obtained statistically through Monte Carlo simulation for complex geometries which may prove intractable for analytical methods. Following this approach, phonon transport in silicon (Si) sawtooth nanowires was studied, revealing that thermal conductivity suppression below the diffuse surface limit is possible. The experimental investigation of energy transport in nanostructures typically involved the use of microfabricated devices or non-contact optical methods. In this work, two such approaches were analyzed to ascertain their thermal behavior and overall accuracy as well as areas for possible improvement. A Raman spectroscopy-based measurement design for investigating the thermal properties of suspended and supported graphene was examined analytically. The resulting analysis provided a means of determining from measurement results the thermal interface conductance, thermal contact resistance, and thermal conductivity of the suspended and supported graphene regions. Previously, microfabricated devices of several different designs have been used to experimentally measure the thermal transport characteristics of nanostructures such as carbon nanotubes, nanowires, and thin films. To ascertain the accuracy and limitations of various microdevice designs and their associated conduction analyses, finite element models were constructed using ANSYS and measurements of samples of known thermal conductance were simulated. It was found that designs with the sample suspended were generally more accurate than those for which the sample is supported on a bridge whose conductance is measured separately. The effects of radiation loss to the environment of certain device designs were also studied, demonstrating the need for radiation shielding to be at temperatures close to that of the device substrate in order to accurately calibrate the resistance thermometers. Using a suspended microdevice like those analyzed using finite element analysis, the thermal conductivities of individual bismuth (Bi) nanowires were measured. The results were correlated with the crystal structure and growth direction obtained by transmission electron microscopy on the same nanowires. Compared to bulk Bi in the same crystal direction, the thermal conductivity of a single-crystal Bi nanowires of 232 nm diameter was found to be 3 - 6 times smaller than bulk between 100 K and 300 K. For polycrystalline Bi nanowires of 74 nm to 255 nm diameter the thermal conductivity was reduced by a factor of 18 - 78 over the same temperature range. Comparable thermal conductivity values were measured for polycrystalline nanowires of varying diameters, suggesting a grain boundary scattering mean free path for all heat carriers in the range of 15 - 40 nm which is smaller than the nanowire diameters. An RTA-based transport model for both charge carriers and phonons was developed which explains the thermal conductivity suppression in the single-crystal nanowire by considering diffuse phonon-surface scattering, partially diffuse surface scattering of electrons and holes, and scattering of phonons and charge carriers by ionized impurities such as oxygen and carbon of a concentration on the order of 1019 cm−3. Using a similar experimental setup, the thermoelectric properties (Seebeck coefficient, electrical conductivity, and thermal conductivity) of higher manganese silicide (HMS) nanostructures were investigated. Bulk HMS is a passable high temperature thermoelectric material which possesses a complex crystal structure that could lead to very interesting and useful nanoscale transport properties. The thermal conductivities of HMS nanowires and nanoribbons were found to be reduced by 50 - 60 % compared to bulk values in the same crystal direction for both nanoribbons and nanowires. The measured Seebeck coefficient data was comparable or below that of bulk, suggesting unintentional doping of the samples either during growth or sample preparation. Difficulty in determining the amorphous oxide layer thickness for nanoribbons samples necessitated using the total, oxide-included cross section in the thermal and electrical conductivity calculation. This in turn led to the determined electrical conductivity values representing the lower bound on the actual electrical conductivity of the HMS core. From this approach, the measured electrical conductivity values were comparable or slightly below the lower end of bulk electrical conductivity values. This oxide thickness issue affects the determination of the HMS nanostructure thermoelectric figure of merit ZT as well, though the lower bound values obtained here were found to still be comparable to or slightly smaller than the expected bulk values in the same crystal direction. Analytical modeling also indicates higher doping than in bulk. Overall, HMS nanostructures appear to have the potential to demonstrate measurable size-induced ZT enhancement, especially if optimal doping and control over the crystallographic growth direction can be achieved. However, experimental methods to achieve reliable electrical contact to quality four-probe samples needs to be improved in order to fully investigate the thermoelectric potential of HMS nanostructures.

Author : Stefano Lepri
Publisher : Springer
Page : 418 pages
File Size : 37,2 MB
Release : 2016-04-07
Category : Science
ISBN : 3319292617

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Understanding non-equilibrium properties of classical and quantum many-particle systems is one of the goals of contemporary statistical mechanics. Besides its own interest for the theoretical foundations of irreversible thermodynamics(e.g. of the Fourier's law of heat conduction), this topic is also relevant to develop innovative ideas for nanoscale thermal management with possible future applications to nanotechnologies and effective energetic resources. The first part of the volume (Chapters 1-6) describes the basic models, the phenomenology and the various theoretical approaches to understand heat transport in low-dimensional lattices (1D e 2D). The methods described will include equilibrium and nonequilibrium molecular dynamics simulations, hydrodynamic and kinetic approaches and the solution of stochastic models. The second part (Chapters 7-10) deals with applications to nano and microscale heat transfer, as for instance phononic transport in carbon-based nanomaterials, including the prominent case of nanotubes and graphene. Possible future developments on heat flow control and thermoelectric energy conversion will be outlined. This volume aims at being the first step for graduate students and researchers entering the field as well as a reference for the community of scientists that, from different backgrounds (theoretical physics, mathematics, material sciences and engineering), has grown in the recent years around those themes.

Author : Zhifeng Ren
Publisher : CRC Press
Page : 1102 pages
File Size : 25,76 MB
Release : 2017-11-06
Category : Science
ISBN : 1351649809

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This book provides an overview on nanostructured thermoelectric materials and devices, covering fundamental concepts, synthesis techniques, device contacts and stability, and potential applications, especially in waste heat recovery and solar energy conversion. The contents focus on thermoelectric devices made from nanomaterials with high thermoelectric efficiency for use in large scale to generate megawatts electricity. Covers the latest discoveries, methods, technologies in materials, contacts, modules, and systems for thermoelectricity. Addresses practical details of how to improve the efficiency and power output of a generator by optimizing contacts and electrical conductivity. Gives tips on how to realize a realistic and usable device or module with attention to large scale industry synthesis and product development. Prof. Zhifeng Ren is M. D. Anderson Professor in the Department of Physics and the Texas Center for Superconductivity at the University of Houston. Prof. Yucheng Lan is an associate professor in Morgan State University. Prof. Qinyong Zhang is a professor in the Center for Advanced Materials and Energy at Xihua University of China.

Author : Annie C. Weathers
Publisher :
Page : 148 pages
File Size : 22,41 MB
Release : 2012
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ISBN :

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Thermal transport in nanowires and nanotubes has attached much attention due to their use in various functional devices and their use as a model system for low dimensional transport phenomena. The precise control of the crystal structure, defects, characteristic size, and electronic properties of nanowires has allowed for fundamental studies of phonon and electron transport in a variety of nanoscale systems. The thermal conductivity in nanostructured materials can vary greatly compared to bulk values owing to classical and quantum size effects. In this work, two model systems for investigating fundamental phonon transport were investigated for potential use in thermoelectric and thermal management applications. The thermoelectric properties of twin defect indium arsenide nanowires and the thermal conductivity of polythiophene nanofibers with improved polymer chain crystallinity were measured with a microfabricated measurement device. The effects of twin planes on reducing the mean free path of phonons in indium arsenide and the effects of improved chain alignment in increasing the thermal conductivity in polymer fibers is discussed.

Author : David Michael Rowe
Publisher : CRC Press
Page : 1120 pages
File Size : 50,80 MB
Release : 2018-10-03
Category : Technology & Engineering
ISBN : 1439840423

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Comprising two volumes, Thermoelectrics and Its Energy Harvesting reviews the vast improvements in technology and application of thermoelectric energy with a specific intention to reduce and reuse waste heat and improve novel techniques for the efficient acquisition and use of energy.Materials, Preparation, and Characterization in Thermoelectrics i