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GALLIANI, DANIELA. "Poly(3,4-ethylendioxythiophene) based materials for thermoelectric applications". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199131.
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I polimeri intrinsecamente conduttori sono una classe di materiali con caratteristiche uniche. In quanto materiali polimerici sono leggeri e flessibili, possono essere facilmente processati e stampati. Al contempo, però, possono condurre corrente elettrica, raggiungendo anche conducibilità metalliche. Questa combinazione eccezionale ha consentito lo sviluppo di dispositivi elettronici stampati e flessibili, i quali risultano interessanti nell’ambito dei dispositivi portabili, sia integrati nel corpo umano sia indossabili.
L’applicazione termoelettrica di questi polimeri conduttori ha recentemente guadagnato rilievo in campo scientifico. Un dispositivo termoelettrico (organico) può convertire il calore in energia elettrica grazie all’effetto Seebeck. Il dispositivo può così recuperare il calore di scarto dissipato in tutti i processi che coinvolgono il consumo di energia e trasformarlo in energia utilizzabile.
Anche se i polimeri conduttori hanno già mostrato interessanti proprietà termoelettriche, il loro utilizzo in questo campo è ancora molto limitato per via delle basse efficienze di conversione termoelettrica raggiunte finora, che impediscono a questi materiali di essere competitivi con i più diffusi materiali inorganici per questa applicazione, ovvero i tellururi.
Il design di un polimero conduttore che abbia elevate prestazioni termoelettriche parte necessariamente da una conoscenza approfondita di quali tecniche e trattamenti influenzino le proprietà finali di trasporto di carica. La complessità intrinseca di questi sistemi, tuttavia, rende spesso difficoltoso ottenere queste informazioni, impedendo la comprensione di fenomeni coinvolti.
Questo progetto di dottorato ha riguardato lo studio dell’impatto di diversi parametri sulle proprietà termoelettriche dei polimeri conduttori, con lo scopo di raggiungere una comprensione approfondita di come il trasporto di carica ne venga influenzato.
Nello specifico, lo studio ha riguardato il poli(3,4-etilendiossitiofene) -PEDOT-, il quale è stato studiato modificando diversi parametri a tre livelli di perturbazione del sistema.
In primo luogo, un’indagine è stata svolta sul ruolo delle condizioni di polimerizzazione e su quello dei trattamenti effettuati dopo la polimerizzazione. In particolare, è stata studiata l’influenza di diverse tecniche di polimerizzazione, diversi ossidanti e diversi solventi sulla vi
qualità finale del film polimerico. Inoltre, il livello di ossidazione del PEDOT è stato modificato dopo la polimerizzazione, ottenendo un’ottimizzazione dell’efficienza termoelettrica.
Ad un secondo livello di perturbazione, la struttura molecolare del monomero è stata modificata per preparare un copolimero. Il copolimero includeva una porzione centrale coniugata (e quindi, conduttiva) e due porzioni laterali non coniugate (isolanti), che hanno comportato una modifica sostanziale delle proprietà di trasporto del materiale finale. I risultati ottenuti sulla nuova struttura mostrano la versatilità di questa strategia e come le proprietà di trasporto possano essere finemente modificate grazie all’introduzione di modifiche della struttura molecolare.
Infine, al terzo livello, le proprietà macroscopiche del PEDOT sono state modificate grazie all’introduzione di nanostrutture di natura inorganica. Questa strategia è solitamente utilizzata per migliorare l’efficienza termoelettrica dei materiali inorganici, grazie agli effetti benefici dovuti alla nanostrutturazione. Due tipologie diverse di nanoparticelle di ossidi metallici (CuO e Mn3O4) sono state sintetizzate in diverse forme e dimensioni e introdotte nella matrice di PEDOT in diverse concentrazioni. Grazie allo studio dell’effetto dell’umidità sulle proprietà di trasporto ed allo studio sulla variazione dello stato di ossidazione è stato possibile ottenere nuove informazioni sul comportamento elettrico dei nanocompositi.Intrinsically conductive polymers (ICPs) are a class of organic materials characterized by unique features. They are lightweight, flexible and easy to process and print, as expected from polymers, but, also, they can conduct electricity up to metallic conductivities. Such an exceptional pairing of characteristics enables the development of flexible and printed electronic devices, which are of a particularly appealing for portable electronic devices, even integrated in the human body (e.g. implantable biosensors) or worn (e.g. smartwatches). Even thermoelectric (TE) application of ICPs recently gained a lot of attention. An organic TE generator (OTEG) can convert heat into electrical energy by means of the Seebeck effect. This technology aims to recover heat produced as low-grade side-product of energy consumption and to transform it into exploitable energy. Even though ICPs showed promising TE properties, their use is still hindered by low TE efficiencies, which cannot compete with the inorganic benchmark (i.e. tellurides). The design of better ICPs for TE application must start from a deep knowledge of which techniques and treatments impact the charge transport features. The intrinsic complexity of ICP systems, however, often makes this task difficult, preventing a full comprehension of the phenomena involved. This PhD project focused on the impact of different parameters on TE properties of ICPs, aiming at the needed deeper understanding on how charge transport is affected. The specific ICP poly(3,4-ethylendioxythiophene) -PEDOT- was investigated modifying different parameters at three different levels of system perturbation. First, the role of polymerization conditions and post-polymerization treatments was studied. Different polymerization techniques, oxidants and solvents have been used for the same ICP, and the occurring changes have been investigated. Moreover, PEDOT oxidation level was tuned to optimize TE efficiency. At a second level, the monomer molecular structure was modified to prepare a PEDOT-based copolymer. The copolymer included conjugated (i.e. conductive) and not conjugated (i.e. not conductive) portions, which deeply impacted the charge transport behaviour. The results show the versatility of this strategy, still barely explored in TE field, and how final transport properties can be finely tuned by means of molecular modifications. Finally, at a third level, PEDOT macroscopic features were tuned by embedding inorganic nanostructure. Such a strategy is usually exploited to improve TE efficiency by means of nanostructuration beneficial effects already known in inorganic materials. Nanoparticles of two different metal oxides (CuO and Mn3O4) of different size and shape were dispersed in PEDOT matrix. Evaluation of humidity and oxidation level effects on charge transport features allowed to obtain novel insights into transport properties in nanocomposites.
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Hsieh, Yu-Yun. "Nanostructured Carbon-Based Composites for Energy Storage and Thermoelectric Applications". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin157322525150617.
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Hao, Qing. "Nanocomposites as thermoelectric materials". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61606.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
Thermoelectric materials have attractive applications in electric power generation and solid-state cooling. The performance of a thermoelectric device depends on the dimensionless figure of merit (ZT) of the material, defined as ZT = S2o-T / k, where S is the Seebeck coefficient, o is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. In recent years, the idea of using nanotechnology to further improve the figure of merit of conventional thermoelectric materials has triggered active research and led to many exciting results. Most of the reported ZT enhancements are based on thin films and nanowires in which the thermal conductivity reduction plays a central role. We pursue the nanocomposite approach as an alternative to superlattices in the quest for high ZT materials. These nanocomposites are essentially nano-grained bulk materials that are synthesized by hot pressing nanoparticles into a bulk form. The interfaces inside a nanocomposite strongly scatter phonons but only slightly affect the charge carrier transport. Therefore, we can significantly reduce the lattice thermal conductivity and even somewhat increase the power factor S2 U, resulting in higher ZT than for bulk materials. Compared with expensive thin-film superlattices, nanocomposites will have significant advantages in mass production, device construction and operation. This thesis covers my studies on bismuth antimony telluride nanocomposites and some recent work on Co 4Sb12-based nanocomposites. In bismuth antimony telluride nanocomposites, we have achieved a peak ZT of 1.4 at 100 'C, a 40% increase in ZT over the bulk material. This is the first significant ZT increase in this material system in fifty years. The same approach has also yielded a peak ZT around 1.2 in Yb filled Co4Sbi 2 nanocomposites. During the process, great efforts were dedicated to assuring accurate and dependable property measurements of thermoelectric nanocomposites. In addition to comparing measurement results between the commercial setups and a homebuilt measurement system, the high ZT obtained in bismuth antimony telluride nanocomposites was further confirmed by a device cooling test. To better understand the measured thermoelectric properties of nanocomposites, theoretical analysis based on the Boltzmann transport equation was performed. Furthermore, frequency-dependent Monte Carlo simulations of the phonon transport were conducted on 2D periodic porous silicon and 3D silicon nanocomposites. In the thermoelectrics field, the latter one provided the first accurate prediction for phonon size effects in a given nanocomposite. For charge carriers in thermoelectric nanocomposites, their transport can be significantly affected by the interfacial electronic states. To address this, impedance measurements were conducted on nanocomposites to determine the electronic barrier height at the grain interfaces, which is critical for the detailed theoretical analysis of the interfacial charge transport and energy conversion processes. Although large amount of work has been done using this technique to understand the defect states and the barrier height on the grain boundaries of polycrystalline silicon or oxides, this method has not been applied to thermoelectric materials. Along another line, a simple bandgap measurement technique with nanopowders was developed based on the Fourier Transform Infrared Spectroscopy. This provided a convenient way to quickly check the bandgaps of various thermoelectric nanocomposites, which is also crucial for theoretical studies.
by Qing Hao.
Ph.D.
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Muto, Andrew (Andrew Jerome). "Device testing and characterization of thermoelectric nanocomposites". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44915.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 67-68).
It has become evident in recent years that developing clean, sustainable energy technologies will be one of the world's greatest challenges in the 21st century. Thermoelectric materials can potentially make a contribution by increasing energy efficiency of some systems. Thermoelectric materials may play a role in the large scale energy industry, specifically in the applications of refrigeration and waste heat recovery. In this work a novel thermoelectric material will be tested for conversion efficiency. A Bi₂Te₃ nanocomposite has been developed by the joint effort of Prof. Gang Chen's group at MIT and Prof. Zhifeng Ren's group at Boston College. The material exhibits enhanced thermoelectric properties from optimized nanoscale structures and can be easily manufactured in large quantities. In order to better characterize its performance a novel power conversion measurement system has been developed that can measure the conversion efficiency directly. The measurement system design will be described in detail; important design considerations will be addressed such as measuring heat flux, optimizing the load matching condition and reducing electrical contact resistance. Finally the measured efficiency will be compared to the calculated efficiency from a temperature-dependent properties model. It will be shown that a Ni layer must be attached to the nanocomposite to allow soldering and power conversion testing. Results of this work will show that the nanocomposite efficiency is higher than the commercial standard. Electrical contact remains a challenge in realizing the potential efficiency.
by Andrew Muto.
S.M.
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Доброжан, Олександр Анатолійович, Александр Анатольевич Доброжан, Oleksandr Anatoliiovych Dobrozhan, Анатолій Сергійович Опанасюк, Анатолий Сергеевич Опанасюк, Anatolii Serhiiovych Opanasiuk, Денис Ігорович Курбатов i in. "Thermoelectric properties of the colloidal Bi2S3-based nanocomposites". Thesis, Jadavpur University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/65347.
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In this work we present the proof of the concept of the novel strategy to improve the thermoelectric
properties of Bi2S3based nanostructured bulk materials by blending the metallic nanoinclustions with
the semiconductor nanoparticles forming the nanocomposites (NCts). The obtained NCts were
composed of Bi2S3nanorods (length - 100 nm and width – 10 nm) and Ag nanoparticles (diameter - 2-
3 nm) synthesized by colloidal method. The morpohology, phase and chemical composition,
electrical conductivity and Seebeck coefficient of NCts were investigated by using transmission
electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray analysis (EDAX), 4-point probes
method and static dc-method. This strategy is the perspective way to improve the conversion
efficiency of others thermoelectric materials.
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Lee, Hohyun 1978. "Modeling and characterization of thermoelectric properties of SiGe nanocomposites". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/50589.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Page 164 blank.
Includes bibliographical references.
Direct energy conversion between thermal and electrical energy based on thermoelectric effects is attractive for potential applications in waste heat recovery and environmentally-friendly refrigeration. The energy conversion efficiency is related to the thermoelectric figure of merit ZT, which is proportional to the electrical conductivity, the square of the Seebeck coefficient, and the inverse of the thermal conductivity. Currently, the low ZT values of available materials restrict the large scale applications of this technology. Recently, however, significant enhancements in ZT were reported in nanostructured materials such as superlattices mainly due to their low thermal conductivities. According to the studies on heat transfer mechanisms in nanostructures, the reduced thermal conductivity of nanostructures is mainly attributed to the increased scattering of phonons at interfaces. Based on this idea, nanocomposites are also expected to have a lower thermal conductivity than their bulk counterparts of the same chemical configuration. Nanocomposites are materials with constituents of less than 100 nm in size. They can be fabricated with a low cost just by mixing nano sized particles followed by consolidation of nano sized powders. In this thesis, SiGe nanocomposites are investigated for power generation at high temperature. The material properties are characterized at different temperatures, and the optimized process conditions are explored experimentally. In addition, theoretical studies are carried out for better understanding of transport phenomena and our experimental results.
(cont.) Grain boundaries in nanocomposites can scatter phonons, when their mean free paths are longer than the grain size. Mean free paths of electrons are usually shorter than the grain size of nanocomposites, so that the electrical conductivities of nanocomposites are not expected to change significantly. However, the experimental results show that nanostructures indeed affect electron transport. The grain boundary effects on electron transport are investigated to explain the experiments. Furthermore, the effects of nanosized pores are explored. Our experimental results show that pores in nanocomposites degrade the electrical conductivity more than predicted by effective medium theories. A scattering model is developed to understand the transport phenomena in porous materials. These modeling studies can also be used to guide sample preparation conditions.
by Hohyun Lee.
Ph.D.
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Yelgel, Ovgu Ceyda. "Thermoelectric properties of V-VI semiconductor alloys and nanocomposites". Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14110.
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Thermoelectric materials are materials which are capable of converting heat directly into electricity and vice versa. They have long been used in electric power generation and solid-state cooling. The performance of a thermoelectric device determined by the dimensionless figure of merit (ZT) of the material, defined as ZT = (S2 σ/κ)T, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity, and T is the absolute temperature. The total thermal conductivity consists of contribution from electrons, electron-hole pairs and phonons. Since the 1960s, the best thermoelectric material has been Bi2Te3 alloys, with a ZT of 1.0 at room temperature. In recent years, the idea of using nanotechnology has opened up the possibility of engineering materials at nanoscale dimensions to achieve higher values of ZT in other words to have more efficient thermoelectric devices. This thesis starts with a broad introduction to thermoelectricity including various thermoelectric effects and their applications. The state-of-the-art thermoelectric materials and the optimisation methods to enhance the value of ZT have also been reviewed. A systematic theoretical modelling of the thermoelectric properties of three dimensional bulk semiconductors has been presented in Chapter 2. Electronic properties (Fermi level, Seebeck coefficient, and electrical resistivity) and thermal conductivity contribution from carriers (donor electrons or acceptor holes) have been derived by using the nearly-free electron approximation and the Fermi-Dirac statistics. Other thermal conductivity contributions originated from electron-hole pairs and phonons have also been described in detail. In Chapter 3, this theoretical study is extended to two dimensional semiconducting quantum well structures bearing in mind that the Fermi level should change with the temperature as well as the quantum well width and additional interface scattering mechanisms (interface mass-mixing and interface dislocation scatterings) should be included for the definition of anharmonic scattering rate. Thermoelectric properties of n-type (Bi2Te3)0.85(Bi2Se3)0.15 single crystals doped with 0.1 wt.% CuBr and 0.2 wt.% SbI3 and p-type (Bi2Te3)x(Sb2Te3)1−x single crystals doped with 3 wt.% Te (0.18 ≤ x ≤ 0.26) have been explored in Chapter 4 and 5, respectively. It has been found that p-type Bi2Te3 based alloys showed higher values of ZT due to their larger power factor (S2σ) and smaller thermal conductivity values. These calculations have concluded that the influence of the composition range of semiconductor alloys together with its type and amount of dopant plays an important role in enhancing the ZT. In Chapter 6, a detailed theoretical investigation and comparision of the thermal conductivities of these single crystals have been reported including frequency dependence of the phonon thermal conductivity for different temperatures. In Chapter 7, based on temperature and well width dependent Fermi level, a full theory of thermoelectric properties has been investigated for n-type 0.1 wt.% CuBr doped Bi2Se3/Bi2Te3/Bi2Se3 and p-type 3 wt.% Te doped Sb2Te3/Bi2Te3/Sb2Te3 quantum well systems. Different values of well thicknesses have been considered for both types of quantum well systems to study the effect of confinement on all thermoelectric transport coefficients. It has been found that reducing the well thickness has a pronounced effect on enhancing the ZT. Compared to bulk single crystals studied in Chapter 4 and 5, significantly higher thermoelectric figure of merits have been estimated theoretically for both n- and p-type semiconducting quantum well systems. For the n-type Bi2Se3/Bi2Te3/Bi2Se3 quantum well system with taking 7 nm well width the maximum value of ZT has been estimated to be 0.97 at 350 K and for the p-type Sb2Te3/Bi2Te3/Sb2Te3 quantum well with well width 10 nm the highest value of the ZT has been found to be 1.945 at 440 K. Chapter 8 briefly recapitulates the results presented in this thesis and outlines possibilities for future work.
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Dai, Prè Marta/M. "Nanocomposites for optical applications". Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422168.
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Nanotechnology is one of the most important fields in the last decades because novel material development involve chemistry, physics, the medicine and also engineering science.
Nanomaterials exhibit size-dependent properties and large surface to volume ratio which can be exploited in a number of applications especially in the optical field.
The main work presented here regards the synthesis of the nanocomposites using different methods, according to the desidered quality of the final material, the easiness and the industrial processability, the size control distribution and the homogeneous dispersibility.
The whole activity of my thesis project can be divided in two parts:
a) nanoparticles and nanocomposites for photovoltaic applications;
b)NIR emitting nanoparticles and nanocomposites.
The first part was partially founded by an European project, ORION, entitled "Optimization of Si solar cells, plastic materials and technologies for the development of more efficient concentRatION photovoltaic systems". The main objective of this project is base on the optimization of materials and technologies involved in Concentration PhotoVoltaic System production in order to reduce the system cost/watt and increase the system efficiency. The goal of my work is to study and develop plastic nanocomposites doped with down-converting nanoparticles for modification of the solar spectrum in order to enhance the absorption efficiency of solar cells. The functional properties of the obtained materials have to be fine-tuned to fulfil the customers' needs in terms of process ability and performance. The material must have good optical properties such as, transmittance of 85-90% for 1-2 mm and light-conversion from 300-500 nm to 600-900 nm. The most important polymers for optical applications is Polymethyl Methacrylate (PMMA).
Different kinds of NPs, ZnS:Mn, CdS:Mn and ZnO, that absorb in the UV range and emit in the visible range, have been synthesized with different colloidal techniques. Precipita\-tion-redispersion protocols have been set up in order to purify and concentrate the particles and transfer them into a suitable organic solvent to direct mixing with the polymer.
Furthermore the major part of the energy losses (~52%) is related to the spectral mismatch, known as thermal or quantum losses. A large part of high-energy photons is lost as heat through phonon scattering, resulting in the limitation of power conversion efficiency of Si solar cells. The ultraviolet (UV) part of the solar spectrum (about 7% of the entire solar
spectrum) cannot efficiently be used by Si solar cells.
So coating of the same nanoparticles were deposited on the front surface of solar cells and comparative electro-optical characterizations have been performed before and after the deposition of the nanostructures to determine the effect of antireflection and down-shifting on the efficiency.
The second part of the work was focused on the synthesis of PbSe nanoparticles (Quantum Dots) and core-shell nanoparticles with a PbSe core and a CdSe shell in order to increase the stability of emission properties of such materials. Then these nanoparticles were introduced in several matrix like Ormocer and PMMA keeping the photoluminescence properties. The future applications are optical microcavity incorporating quantum dots and lithography.Negli ultimi anni le nanotecnologie sono diventate uno dei maggiori campi di interesse e di rilevanza scientifica e la ricerca di nuovi materiali riguarda la chimica, la fisica, la medicina e anche l'ingegneria. I nanomateriali vengono classificati in base alla loro dimensione ed al rapporto superficie/volume, caratteristiche che permettono il loro impiego in numerose applicazioni, soprattutto nel campo ottico. In questi lavoro di tesi sono stati valutati differenti nanocompositi sintetizzati con tecniche messe a punto in modo tale da ottenere peculiari caratteristiche di dimensione, distribuzione, omogeneità e di facile produzione, anche a livello industriale. Il progetto di dottorato può essere suddiviso in due parti: a) nanoparticelle e nanocompositi per applicazioni nel fotovoltaico; b) nanoparticelle e nanocompositi che emettono nel NIR. La prima parte del lavoro si inserisce nel progetto Europeo ORION, ovvero "ottimizzazione di celle solari al silicio, materiali plastici e tecnologie per lo sviluppo di più efficienti sistemi fotovoltaici a concentrazione". Ha riguardato principalmente la messa a punto di materiali e di tecnologie dei sistemi a concentrazione tali da riuscire a ridurre il rapporto costo/watt ed aumentare l'efficienza. Sono stati quindi studiati e sviluppati nanocompositi plastici contenenti nanoparticelle che sono in grado di modificare lo spettro solare e di aumentare di conseguenza l'efficienza di assorbimento delle celle solari. Inoltre le proprietà funzionali dei materiali sviluppati sono state messe a punto in termini di processabilità e di prestazioni. Infatti il materiale deve avere buone proprietà ottiche tra cui una trasmittanza dell'85-92% per 1-2 mm di spessore ed una conversione della luce nel range tra 300-500 nm e 600-900 nm. Il polimetilmetacrilato (PMMA) è risultato essere il polimero di selezione per applicazioni ottiche. Diversi tipi di nanoparticelle che assorbono nell'UV, tra cui ZnS:Mn, CdS:Mn e ZnO, sono state sintetizzate utilizzando tecniche colloidali. Sono stati messi a punto protocolli di precipitazione-ridispersione in modo da purificare, concentrare le nanoparticelle e ridisperdere in seguito in appositi solventi organici, dove è solubile anche il PMMA. Dal momento che la maggior parte dell'energia dissipata (~ 52%) dipende dal mismatch spettrale, definito come perdita termica o quantica, mentre la grande parte ad alta energia viene persa sotto forma di calore legato allo scattering di fotoni e quindi riduce maggiormente l'efficienza di conversione dell'energia delle celle solari a base di silicio. La parte dell'ultravioletto (UV) dello spettro solare (circa 7% dell'intero spettro) non può essere sfruttato completamente dalle celle solari al Si. Sono state così valutate le caratteristiche elettro-ottiche prima e dopo deposizione sulla superficie delle celle solari delle stesse nanoparticelle inserite nel polimero determinando l'effetto antiriflesso e della down-shifting sull'efficienza. La seconda parte del lavoro si è focalizzata sulla sintesi di nanoparticelle di Seleniuro di Piombo (PbSe) and di core-shell, dove l'interno di PbSe è rivestito da uno strato di CdSe, così da stabilizzare le proprietà di emissione di questi materiali. Infine queste nanoparticelle sono state incorporate in diverse matrici, tra cui Ormocer e PMMA mantenendo le loro proprietà di luminescenza. Questi nuovi materiali trovano future applicazioni in microcavità ottiche che incorporano quantum dots e litografia.
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Akdogan, Volkan. "Thermoelectric power generator for automotive applications". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/37702/.
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A thermoelectric generator (TEG) converts thermal energy into electrical energy corresponding to temperature gradient across both hot and cold surfaces with a conversion efficiency of approximately 5%. In spite of the conversion efficiency, TEGs can be implemented effectively for waste heat recovery systems within the power rating of kilowatts. The insufficiency of natural resources, frequently increasing oil costs and emission regulations have become an incentive factor of the recent increased interest in TEG applications. This thesis introduces a practical implementation of the thermoelectric generator for an automotive exhaust system which has a rapid transient response to produce electrical energy from the waste heat which flows through the exhaust pipe. In addition to automotive TE power generator implementation, an H-Bridge DC-DC converter within the operation of maximum power point tracking method is introduced in this thesis to obtain the maximum power transfer between the thermoelectric power generator and the load. This thesis presents a transient solution to the two-dimensional heat transfer equation with variant ambient temperature that determines heat transfer and electrical potential across the thermoelectric pellet. This equation is applied into a designed two-dimensional heat transfer MATLAB model and a comparison of simulation and experimental results approves the accuracy of the designed model. In addition to heat transfer simulation, a dynamic large scale thermoelectric power generator simulation program is introduced in this thesis to provide data analysis of actual implementation.
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Alothman, Abdulmohsen Abdulrahman. "Modeling and Applications of Thermoelectric Generators". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79846.
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We develop a simplified one-dimensional numerical model that simulates the performance of thermoelectric generators (TEG). The model is based on the energy and electrical potential field equations. The Seebeck coefficient, thermal conductivity, electrical resistivity and Thomson coefficient of the TEG material are used to predict the harvested power. Bismuth-telluride is used as semiconductors materials of the TEG, which is the most commonly used material by industry. Experiments on three TEG modules were performed to validate the numerical model. A comparison with predicted levels of harvested energy based on the TEG specifications is also performed. The results show differences between the experimental and numerical values on one hand and the predicted ones on the other hand. The reason for these differences are discussed. A procedure to estimate the sensitivity of the harvested power to different inputs and TEG parameters is detailed.
In the second part of the dissertation, we integrate a thermoelectric generator with an organic storage device. The performance of the integrated system for different values of load resistances and temperature gradients is determined. Finally, we demonstrate that power generated from a TEG is related to the flow rate in a pipe and can, thus, be used as a flow meter. Particularly, a dimensionless relation between the TEG's peak power and Reynolds number is determined.Ph. D.
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Perrot, Solène. "Semi-metallic polymers for thermoelectric applications". Thesis, Bordeaux, 2021. http://www.theses.fr/2021BORD0043.
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Les matériaux thermoélectriques (TE) ont le potentiel de convertir de grandes quantités de chaleur directement en électricité, et par conséquent de réduire la dépendance aux combustibles fossiles. En thermoélectricité, le concept d'un verre de phonons/cristal électronique est souvent utilisé pour décrire un matériau thermoélectrique idéal. Selon ce concept, un bon matériau TE devrait inhiber la conduction de phonons (ayant ainsi une faible conductivité thermique) tout en assurant efficacement une bonne conduction des porteurs de charges (conductivité électrique importante). Afin de quantifier l'efficacité des systèmes TE, la figure de mérite, ZT, est utilisée comme mesure de performance. Récemment, les polymères conducteurs ont gagné de l'élan dans la communauté TE pour des applications à température ambiante. Leur grand avantage est une conductivité thermique intrinsèquement faible à température ambiante (0.2-0.6 W.m-1K-1) qui est complétée par leur facilité de traitement et leur faible coût. Les films minces de dérivés de poly (3,4-éthylènedioxythiophène) (PEDOT) dopés avec des molécules de p-toluènesulfonate (Tos) peuvent présenter un ZT aussi élevé que 0,25 à température ambiante, soulignant ainsi le potentiel élevé de tels systèmes pour les applications futures. Dans cette thèse, nous nous sommes focalisés sur la compréhension des propriétés des films minces de PEDOT:Tos en jouant sur la méthode de polymérisation. Nous avons démontré que la conductivité électrique peut être améliorée en ajoutant des additifs dans la formulation du matériau. De plus, la concentration en p-toluènesulfonate est un paramètre permettant d’influencer la conductivité électrique sans modifier la valeur du coefficient Seebeck. Finalement, l’hybridation des précurseurs de PEDOT:Tos avec des copolymères à blocs a permis de concevoir des structures de PEDOT:Tos à l’échelle nanométriqueThermoelectric (TE) materials have the potential to convert vast amounts of waste heat directly into electricity, therefore reducing the dependence on fossil fuel. In thermoelectrics, the concept of a phonon glass/electron crystal is often used to describe an ideal thermoelectric material. According to this concept, a good TE material should inhibit the conduction of phonons (thus having a low thermal conductivity) while efficiently conducting electronic charge carriers (high electrical conductivity). In order to quantify the efficiency of TE systems, the figure of merit, ZT, is used as a measure of performance. Recently, conducting polymers have gained momentum in the TE community for applications at room temperature. Their great advantage is an intrinsically low thermal conductivity at room temperature (0.2-0.6 W.m-1K-1) that is complemented by their easy processability and their low cost. Thin films of poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives doped with p-toluenesulfonate (Tos) molecules can exhibit a ZT as high as 0.25 at room temperature underlining the high potential of such systems for future applications. In this thesis, we focused on the understanding of PEDOT:Tos thin films properties by playing on the polymerization method. We demonstrated that the electrical conductivity can be improved by adding additives to the formulation of PEDOT:Tos materials. Moreover, the concentration of p-toluenesulfonate is an important parameter to tune the electrical conductivity without changing the Seebeck coefficient. Finally, the hybridization of PEDOT:Tos precursors with block copolymers allows us to design PEDOT:Tos nanostructures
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Thiagarajan, Suraj Joottu. "Thermoelectric properties of rare-earth lead selenide alloys and lead chalcogenide nanocomposites". Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196263620.
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Thiagarajan, Suraj Joottu. "Thermoelectric properties of rare-earth lead selenide alloys and lead chalcogenide nanocomposites". The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1196263620.
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Maheshwari, Gunjan. "Carbon Nanocomposites for Industrial Applications". University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1226522545.
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Schwall, Michael [Verfasser]. "Heusler compounds for thermoelectric applications / Michael Schwall". Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1062496027/34.
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Hamawandi, Bejan. "Formation of NiGeSn Material for Thermoelectric Applications". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-143781.
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Group IV-based nanowires are excellent designed thermoelectric materials for high temperature applications. Ni silicide (germanide) has been widely used to reduce the contact resistance for group IV nanowires. In this work, the interaction of Ni with relaxed, compressive and tensile strained GeSn was investigated. The layers were epitaxially grown by chemical vapor deposition in temperature range 290-350 °C and the phase transformation of germanides was studied for three different rapid thermal annealing (RTA) temperatures of 350, 450, and 550 °C. The germanide layers were characterized using scanning electron microscopy, high resolution X-ray diffraction, and four point resistivity measurements. The results showed that NiGeSn phase with lowest resistivity is formed at 450 °C annealing and was stable up to 550 °C. The thermal stability of NiGeSn is dependent on the type, amount of the strain and the Sn content. The thickness of germanide layer for a certain RTA treatment was dependent on strain.
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Katayoun, Zahmatkesh Encheh Keikanlou. "Characterization of SiGe Nanowire for Thermoelectric Applications". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-180955.
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Thermoelectric devices directly convert heat into electricity or vice versa through simple structures without moving parts. SiGe materials are promising candidates for thermoelectric energy conversion. This study presents the electrical characterization of p- and n-type Si0.53Ge0.47 alloy nanowires (NWs) with an average diameter of 60 nm in the temperature range of 248 K to 473 K. The SiGe NWs were fabricated by two methods: Sidewall Transfer Lithography (STL) and conventional Iline lithography followed by Focus Ion Beam (FIB) thinning. A new approach was developed to characterize the electrical and thermal properties of the NWs. The SiGe material was grown by Reduced Pressure Chemical Vapor Deposition (RPCVD) using SiH4 and GeH4 precursors on Silicon on Insulator substrates (SOI). These samples were then condensed to Si0.53Ge0.47 layers. Doping of layers was performed through diffusion with two different sources gas of B2H6 or PH3 at 800°C. The electrical conductivity and thermopower of the SiGe NWs, fabricated by both methods, were studied and compared. The results showed an enhancement of thermopower, electrical conductivity and power factor of SiGe NWs compared to Si NWs, revealing their potential for thermoelectric material (TE) device applications.
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Brun, Mathieu. "Électrodes nanocomposites pour applications en microfluidique". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00744588.
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Le travail de thèse présenté dans ce manuscrit s'inscrit dans une dynamique d'intégration de matériaux non conventionnels en systèmes microfluidiques. Il vise à démontrer le potentiel du cPDMS, un matériau nanocomposite formé d'une matrice de polydiméthylsiloxane rendu conducteur par l'ajout de nanoparticules de carbone. Compatible avec les procédés technologiques habituels, le cPDMS peut être structuré dans une large gamme d'épaisseurs et de géométries mais présente surtout l'avantage de pouvoir être collé irréversiblement sur verre, PDMS et silicium. Son intégration est parfaitement étanche, rapide à mettre en oeuvre, et très économique. La première partie du manuscrit est consacrée à la caractérisation de ce matériau. Ses propriétés électriques et de surface, pouvant être critiques pour une utilisation en microfluidique, ont été particulièrement étudiées. Les champs électriques offrant de nombreuses possibilités pour réaliser des fonctions clés en microfluidique (détection, séparation, manipulation de fluides ou de particules), nous avons choisi d'évaluer l'intérêt d'électrodes de cPDMS dans deux types d'applications. Les aspects de détection ont d'abord été mis en évidence à l'aide de mesures électrochimiques. Cette méthode a permis à la fois de caractériser la surface du cPDMS tout en validant son utilisation potentielle pour des applications d'analyses électrochimiques. Dans la dernière partie du manuscrit, le matériau a été testé pour la manipulation de particules à travers l'observation de différents phénomènes électrocinétiques. Ceux-ci ont conduit à la mise au point de dispositifs microfluidiques (intégrant des lectrodes de cPDMS) dédiés à la lyse et à l'électrofusion de cellules.
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Fogelström, Linda. "Polymer Nanocomposites in Thin Film Applications". Doctoral thesis, KTH, Ytbehandlingsteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12400.
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The introduction of a nanoscopic reinforcing phase to a polymer matrix offers great possibilities of obtaining improved properties, enabling applications outside the boundaries of traditional composites. The majority of the work in this thesis has been devoted to polymer/clay nanocomposites in coating applications, using the hydroxyl-functional hyperbranched polyester Boltorn® as matrix and montmorillonite clay as nanofiller. Nanocomposites with a high degree of exfoliation were readily prepared using the straightforward solution-intercalation method with water as solvent. Hard and scratch-resistant coatings with preserved flexibility and transparency were obtained, and acrylate functionalization of Boltorn® rendered a UV-curable system with similar property improvements. In order to elucidate the effect of the dendritic architecture on the exfoliation process, a comparative study on the hyperbranched polyester Boltorn® and a linear analogue of this polymer was performed. X-ray diffraction and transmission electron microscopy confirmed the superior efficiency of the hyperbranched polymer in the preparation of this type of nanocomposites. Additionally, an objective of this thesis was to investigate how cellulose nanofibers can be utilized in high performance polymer nanocomposites. A reactive cellulose “nanopaper” template was combined with a hydrophilic hyperbranched thermoset matrix, resulting in a unique nanocomposite with significantly enhanced properties. Moreover, in order to fully utilize the great potential of cellulose nanofibers as reinforcement in hydrophobic polymer matrices, the hydrophilic surface of cellulose needs to be modified in order to improve the compatibility. For this, a grafting-from approach was explored, using ring-opening polymerization of ε-caprolactone (CL) from microfibrillated cellulose (MFC), resulting in PCL-modified MFC. It was found that the hydrophobicity of the cellulose surfaces increased with longer graft lengths, and that polymer grafting rendered a smoother surface morphology. Subsequently, PCL-grafted MFC film/PCL film bilayer laminates were prepared in order to investigate the interfacial adhesion. Peel tests demonstrated a gradual increase in the interfacial adhesion with increasing graft lengths.QC20100621
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Parsons, James. "Nanoparticles and nanocomposites for display applications". Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/84573.
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The optical response of metallic structures has attracted significant interest for various applications in recent years. Of particular relevance to display applications is the ability to optimize the intensity and wavelength of the radiation which is scattered by the structure. In this thesis, original studies are presented across three main sections which investigate the optical response of a variety of composite structures formed from metal and dielectric elements.
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Ciocan, Cristina Elena. "Matériaux lamellaires nanocomposites : synthèse et applications". Thesis, Montpellier, Ecole nationale supérieure de chimie, 2010. http://www.theses.fr/2010ENCM0008.
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L'objectif de cette thèse a été l'optimisation de la synthèse et des performances catalytiques des matériaux lamellaires au W et Mo dans les réactions d'oxydation de plusieurs composés organiques en présence d'H2O2. Le travail réalisé au cours de cette thèse est le développement de nouveaux catalyseurs hétérogènes pour la réaction d'oxydation qui est réalisée sélectivement en systèmes catalytiques homogènes, mais pour un développement durable, la catalyse hétérogène demeure beaucoup plus porteuse d'avenir au niveau industriel. La réaction d'oxydation de composés soufrés a un grand intérêt, en particulier dans l'élimination des composés organiques soufrés (thiophènes, sulfures) contenus dans les carburants et les coupes pétrolières, réalisée dans des conditions douces de température et pression, en présence de l'eau oxygénée. Les objectifs principaux de cette étude ont été les suivants: 1. élaboration des matériaux catalytiques : a) préparation des précurseurs de type hydrotalcites (HDL) à base de Mg-Al-NO3, Mg-Al-terephthalate et Ni-Mg-Al-NO3. b) préparation des matériaux hybrides par intercalation des espèces de Mo et W par deux voies de synthèse : réaction d'échange anionique et synthèse hydrothermale. 2. caractérisation de la structure, la texture et la nature des sites catalytique par différentes techniques : DRX, adsorption d'azote, ATG, spectroscopie Raman et UV-Vis, MEB etc. 3. applications de ces catalyseurs à la réaction d'oxydation des composes soufrés (sulfures, thiophènes, sulfoxydes), epoxydation de cyclooctene et oxydation d'anthracène. Les catalyseurs ont été stables au recyclage et aucun phénomène de leaching n'a été observéThe objective of this thesis was the optimization of the synthesis and catalytic performances of nanocomposites materials containing W and Mo in the oxidation with H2O2 of a wide range of model organic compounds. The work achieved during this thesis is the development of new heterogeneous catalysts for the oxidation reaction who is carried out selectively in homogeneous catalytic systems, heterogeneous catalysis is still much more promising in future. The oxidation reaction of sulfur compounds has great interest, especially in the removal of organic sulfur compounds (thiophene, sulfide) contained in fuels and petroleum fractions, performed in mild conditions of temperature and pressure in the presence of H2O2. In this study were as follows : 1. elaboration of materials : a) preparation of precursors of type hydrotalcites (HDL) based on Mg-Al-NO3, Mg-Al-Ni-terephthalate and Mg-Al-NO3. b) preparation of hybrid materials by intercalation species of Mo and W by two synthetic routes : reaction of anion-exchange and hydrothermal synthesis. 2. characterization of the structure, texture and nature of catalytic sites by different techniques : XRD, nitrogen adsorption, TGA, Raman spectroscopy and UV-Vis, SEM, etc. 3. application of these catalysts in the reaction of oxidation of sulfur compounds (sulfides, thiophenes, sulfoxides), epoxidation of cyclooctene and oxidation of anthracene. The catalysts were stable under operating conditions
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Baker, M. Christina Opimo. "Applications of polyaniline nanofibers and nanocomposites". Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1666392621&sid=19&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Saotome, Tsuyoshi. "Transparent polymer nanocomposites for aerospace applications". Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1970611211&sid=54&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Luo, Jinji. "Investigation of Polymer Based Materials in Thermoelectric Applications". Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-170961.
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With the advancements in the field of wireless sensor networks (WSNs), more and more applications require the sensor nodes to have long lifetime. Energy harvesting sources, e.g. thermoelectric generators (TEGs), can be used to increase the lifetime and capability of the WSNs. Integration of energy harvesters into sensor nodes of WSNs can realize self powered systems, providing the possibility for maintenance free WSNs. TEGs can convert the existing temperature differences into electricity. The efficiency of TEGs is directly related to the dimensionless figure of merit (ZT) of materials, which is given as ZT=σS^2 T/k, where σ is the electrical conductivity, S is the Seebeck coefficient, k is the thermal conductivity, T is the temperature and σS^2 is the power factor. Traditional thermoelectric (TE) materials are based on inorganic materials, of which the thermal conductivity is high. Over the past decade, the use of nanostructuring technology, e.g. superlattice, could decrease the thermal conductivity in order to enhance the efficiency of TE materials. However, the high cost and the rigidity of inorganic TE materials are limiting factors. As alternatives, polymer based materials have become the research focus due to their intrinsic low thermal conductivity, high flexibility and high electrical conductivity. Moreover, polymer based materials could be fabricated in solution form, giving the possibility for employing printing techniques hence a decrease in the production cost. Unlike the typical approach, in which secondary dopants are added into PEDOT:PSS solutions to modify the power factor of polymer films, this thesis is focused on a more efficient method to improve TE properties. This thesis demonstrates for the first time that post treatment of PEDOT:PSS films with the secondary dopant DMSO as the medium results in a much larger power factor than the traditional addition method. The post treatment method also avoids the usually required mixing step involved in the addition method. Different solvents were selected to discuss the impact factors in the modification of the power factor by this post treatment approach. The post treatment of PEDOT:PSS films was then extended to utilize a green solvent EMIMBF_4 (an ionic liquid) as the medium. EMIMBF_4 is found to exchange ions with PEDOT:PSS films. As a result, the EMIM^+ cations remain in the films and reduce the oxidation level of PEDOT chains, which affects the Seebeck coefficient and the electrical conductivity. Furthermore, TE materials based on hybrid composites with polymer as the matrix and Te nanostructures as the nanoinclusions were investigated. This thesis successfully developed a green synthesis method to obtain Te nanostructures, in which a non toxic reductant and a non toxic Te sources were used. Well controlled Te nanostructures including nanorods, nanowires and nanotubes were synthesized by wet chemical and hydrothermal synthesis. Those as synthesized Te nanowires were then integrated into PEDOT:PSS solution for composite films fabrication. A high Seebeck coefficient up to 200 μV/K was observed in the composite filmMit den Weiterentwicklungen der Drahtlosen Sensornetzwerke (engl. WSN, wireless sensor networks) stellen immer mehr Anwendungen die Forderung einer langen Lebensdauer der Sensorknoten. Energiegewinnungssysteme (engl. Energy Harvesters) wie z.B. thermoelektrische Generatoren (TEGs) können genutzt werden, um die Lebensdauer und Leistungsfähigkeit der WSN zu steigern. Mit der Integration von Energy Harvesters können WSN ohne äußere Stromversorgung realisiert und somit die Möglichkeit zur Wartungsfreiheit geschaffen werden. TEGs liefern Energie durch die Umwandlung einer Temperaturdifferenz in Elektrizität. Die Effektivität der TEG ist direkt verbunden mit der Material-Kennzahl ZT und ist gegeben durch ZT=σS^2 T/k, wobei σ die elektrische Leitfähigkeit ist, S der Seebeck Koeffizient, k die thermische Leifähigkeit, T die Temperatur und σS^2 der Leistungsfaktor. Herkömmliche thermoelektrische (TE) Materialien basieren auf anorganischen Materialien, von denen die thermische Leitfähigkeit hoch ist. Im Laufe des letzten Jahrzehnts konnte durch den Einsatz der Nanostrukturierung die thermische Leitfähigkeit verringern werden um damit die Effizienz von TE-Materialien zu steigern. Die Steifigkeit dieser Materialien ist ein anderer Aspekt. Als Alternative für anorganische TE Materialien sind Polymer basierte TE Materialien zum Fokus der Forschung geworden aufgrund einer intrinsisch niedrigen thermischen Leitfähigkeit, hohen Flexibilität und hohen elektrischen Leitfähigkeit. Des Weiteren können diese Polymere in gelöster Form verarbeitet werden, was die Möglichkeit für den Einsatz von Drucktechnologien und damit geringeren Produktionskosten gibt. Anders als der herkömmliche Ansatz den Leistungsfaktor der Polymerfilme durch die Ergänzung von sekundären Dotanten in PEDOT:PSS Lösungen zu verändern, wurde in dieser Arbeit eine effizientere Methode zur Verbesserung der TE Eigenschaften gesucht. In dieser Arbeit wird zum ersten Mal gezeigt, dass die Nachbehandlung von PEDOT:PSS Schichten mit sekundären Dotanten Dimethylsulfoxid (DMSO) als Medium der Nachbehandlung zu einem viel höheren Leistungsfaktor führt als bei der Zugabemethode und außerdem die sonst erforderliche Mischprocedur vermeidet. Es wurden verschiedene Lösungsmittel ausgewählt um die Einflussfaktoren bei der Modifikation des Leistungsfaktors durch die Nachbehandlung von Polymerschichten zu diskutieren. Die Nachbehandlung von PEDOT:PSS Schichten wurde nachfolgend erweitert um das umweltfreundliche Lösungsmittel EMIMBF4 (eine ionische Flüssigkeit) als das Medium einzusetzen. EMIMBF4 ist bekannt für den Austausch von Ionen mit PEDOT:PSS Schichten, so dass EMIM Kationen in der Schicht verbleiben, die Oxidationsstufe der PEDOT-Ketten senken und damit den Seebeck-Koeffizient und die elektrische Leitfähigkeit beeinflussen. Des Weiteren konzentriert sich diese Arbeit auf TE Materialien basierend auf Kompositen aus Polymeren mit Nanoeinlagerungen. Erfolgreiche Syntheseansätze wurden für Tellur-Nanostrukturen entwickelt, bei denen keine giftigen Reduktionsmittel und keine giftigen Tellur-Quellen zur Verwendung kamen. Es erfolgte die Erzeugung von kontrollierten Tellur-Nanostrukturen, einschließlich Nanostäben, Nanodrähten und Nanoröhren, mit nass-chemischer und hydrothermaler Synthese. Die so hergestellten Nanodrähte wurden dann in PEDOT:PSS Lösungen integriert für die Herstellung von Komposite-Schichten. Dabei konnte ein hoher Seebeck-Koeffizienten, bis zu 200 μV/K, festgestellt werden
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Tang, Shuang Ph D. Massachusetts Institute of Technology. "Materials Physics for Thermoelectric and Related Energetic Applications". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98735.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 118-122).
Thermoelectrics study the direct inter-conversion between heat flow and electrical power, which has a wide range of applications including power generation and refrigeration. The performance of thermoelectricity generation and the refrigeration is characterized by a dimensionless number called the Figure-of-Merit (ZT), defined as ZT = [sigma]-S 2T / [kappa], where a is the electrical conductivity, K is the thermal conductivity, S is the Seebeck coefficient, and T is the absolute temperature. Before 1993, the upper-limit of ZT was barely 1. After the efforts of more than twenty years, the upper-limit of ZT has been pushed up to ~2. However, for the thermoelectric technology to be commercially attractive, the value of ZT and the cost of production have to be further improved. Most of the ZT enhancing strategies that have been proposed since 1993 involve the changing and the controlling of the dimension of materials systems, the scattering mechanism(s) of carriers, the shape of the electronic band structure and the density of states, and the magnitude of the band gap. As further research is carried out, it is found that these strategies do not always work to enhance ZT. Even for a working materials system, the improvement margin of increasing ZT can be small. The balancing between [sigma] and S 2 / [kappa] has significantly limited the improvement margin for our ZT enhancing goal. Therefore, we have two problems to explore: (1) how can we deal with the strong correlation between [sigma] and S2 / [kappa] , when trying to enhance ZT, and (2) how can we make the above mentioned strategies more convergent as we change the dimension of materials systems, the scattering mechanism(s) of carriers, the shape of electronic band structure, and the magnitude of the band gap? This thesis aims to explore the solutions to these two major problems at the research frontier of thermoelectric ZT enhancement. The first problem is discussed by providing a new framework of pseudo-ZTs, where the electronic contribution (zte) and the lattice contribution (ztL) to the overall ZT can be treated in a relatively separate manner. The second problem is discussed under this new framework of pseudo-ZTs, through four subsections: (i) scattering and system dimension; (ii) band structure; (iii) density of states; (iv) band gap. The one-to-one correspondence relation between the carrier scattering mechanism(s) and the maximum Seebeck coefficient is further studied. A new tool for scattering mechanism(s) inference and for the Seebeck coefficient enhancement is provided. For the band structure and the band gap part, advanced band engineering methods are provided to study nanostructured narrow-gap materials, the Dirac cone materials, and the anisotropic materials, which are historically found to be good thermoelectric materials. To further demonstrate the newly developed theories, this thesis has also illustrated the application of these models in some specific materials systems, including the graphene system, the transition metal dichalcogenides monolayer materials systems, the Bi1 -xSbx alloys system, the In1.xGaxN alloys system, and the (BiiySby) 2(S1_xTex)3 alloys system.
by Shuang Tang.
Ph. D.
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Jovovic, Vladimir. "Engineering of Thermoelectric Materials for Power Generation Applications". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1248125874.
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Vijayakumar, Vishnu. "Highly oriented conducting polythiophene films for thermoelectric applications". Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE004.
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Cette thèse concerne la fabrication de matériaux thermoélectriques (TE) à base de films minces orientés de polythiophènes (PBTTT). Le brossage à haute température produit des films minces de cristallinité et d’orientation contrôlées. Différentes méthodes de dopage avec des dopants tels F4TCNQ, F6TCNNQ et FeCl3 ont permis de fabriquer des films polymère conducteurs orientés aux propriétés TE anisotropes. Une combinaison de spectroscopie UV-vis-NIR polarisée et de MET donne accès à l’orientation et à la quantité de dopants intercalés dans les cristaux polymère. Le coefficient de diffusion du dopant est corrélé à la longueur des chaînes alkyls des polymères : les PBTTTs ayant des chaînes alkyls en C12 présentent les meilleurs propriétés TE en raison d’une diffusion rapide et efficace des dopants dans le polymère. Finalement, nous avons étudié l’effet du type de dopant (son électronégativité, sa taille) sur les propriétés TE des films. Le dopage de films orientés de C12-PBTTT avec FeCl3 permet d’atteindre des valeurs records de conductivité de 2.105 S/cm et des facteurs de puissance de l’ordre de 1 mW/mK2The aim of this thesis is to develop new polymeric thermoelectric (TE) materials based on oriented polythiophene (PBTTT) films. High-temperature rubbing produces oriented films of controlled orientation and crystallinity. Various doping methods with suitable dopants (F4TCNQ, F6TCNNQ and FeCl3) produced enhanced TE properties along the rubbing direction. A combination of polarized UV-Vis-NIR spectroscopy and TEM uncovered the amount and orientation of dopants intercalated in the crystals of PBTTT. The diffusion coefficient of dopants is correlated to the length of alkyl side chains : PBTTT with C12 side chains shows the best TE properties because of a fast and effective diffusion of dopants in the polymer films. Finally, we evaluated the impact of dopant (geometry, electronegativity) on the TE properties. Doping oriented PBTTT with FeCl3 helped reach record electrical conductivity of 2×105 S/cm and TE power factors of 1 mW/mK2
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Goyal, Amita. "Titanium dioxide-germanium nanocomposites for photovoltaic applications". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file Mb., 104 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435250.
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Chu, Chun. "Development of polymer nanocomposites for automotive applications". Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37128.
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Polymer nanocomposites (PNCs) have gained significant interest because they have outstanding performance that allows cost reduction, weight reduction, and product improvement. This research study focuses on the manufacture and characterization of PNCs in order to explore their potential in automotive applications. More specifically, polypropylene (PP) nanocomposites reinforced with xGnP and nanokaolin were fabricated by manufacturing methods that optimize their performances. Exfoliated graphite nanoplatelets (xGnP) are promising nanofillers that are cost effective and multifunctional with superior mechanical, thermo-mechanical and electrical properties. Nanokaolin is a newly introduced natural mineral mind in Georgia that has not been studied as of now. PNCs reinforced with these two nanofillers were characterized in terms of mechanical, thermo-mechanical, and various other properties, and then compared to talc- reinforced PP composites, which are the current state of the art for rear bumpers used by Honda Motor. Characterization results indicated that xGnP had better performance than talc and nanokaolin. Furthermore, the addition of xGnP introduces electrical conductivity in the PNCs, leading to more potential uses for PNCs in automotive applications such as the ability to be electrostatic painted. In order to fabricate PNCs with a desired conductivity value, there is need for a design tool that can predict electrical conductivity. Existing electrical conductivity models were examined in terms of model characteristics and parameters, and model predictions were compared to the experimental data. The percolation threshold is the most important parameter in these models, but it is difficult to determine experimentally, that is why a correlation between thermo-mechanical properties and electrical conductivity is also investigated in this study.
30
Xu, Bin. "Shape memory polymeric nanocomposites for biological applications". Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2489.
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The aim of this work is to develop novel shape memory polymers (SMPs) and nanocomposites for potential biological applications. A kind of commercial SMP, shape memory polyurethane (SMPU), was used to prepare nanocomposites by incorporating nano-clay into the SMPU substrate. The mechanical behaviour, thermal property and shape memory efficiency were studied with various nanofiller loadings. Chemical synthesis methods were also employed to prepare the other designable SMP and its nanocomposites, i.e. the shape memory polystyrene co-polymer (SMPS). Multiple technologies were adopted to enhance the SMPS matrix such as modifying the chemical components, introducing various functional nanoparticles into the polymeric network and improving the dispersion of the nanoparticles. Different methods were used to characterize the overall performance of the obtained materials. Mechanical tests were performed at different dimensional scales with a varied degree of localisation. Nanoindentation was firstly applied to assess the micro-mechanical properties of shape memory polymer nanocomposites at scales down to particle size. The micro-mechanical analysis provided the fundamental information on the SMPs and their nanocomposites for bio-MEMS applications. Potential applications were also explored through manufacturing different type of device models and testing their shape recovery efficiencies. Finally, theoretical contributions were made in two areas. The first one was the theoretical analysis on the nanoparticles enhancement to the soft polymeric matrix. The other was in developing a constitutive model to describe the thermo-viscoelastic property and shape memory behaviour for SMP nanocomposites.
31
sang, zhen. "CONDUCTIVE ELASTOMER NANOCOMPOSITES FOR STRAIN SENSORS APPLICATIONS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554126739899435.
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Liu, Tingting. "Novel Hierarchically Structured Nanocomposites for Biomedical Applications". Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/55103.
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It is a great challenge to design hierarchically structured nanocomposites with multicomponents for biomedical applications. Here, we demonstrate the synthesis of a library of biocompatible nanocomposites, possessing diverse structures with various functionalities. As a proof of concept, the nanocomposites have been used for diagnosis and therapy applications. This study developed the synthesis protocols for multicomponent nanocomposites, and gave suggestions on how to design effective nanocomposites for biomedical applications.
33
Athikam, Pradeep kumar. "Thermoelectric Properties of Polydimethylsiloxane (PDMS) - Carbon Nanotube (CNT) Composites". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595848598234548.
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Kulwongwit, Nuth. "P-type, misfit layered structure cobaltite for thermoelectric applications". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/ptype-misfit-layered-structure-cobaltite-for-thermoelectric-applications(c967ef03-5dd2-444d-b99b-1a1f784d10f0).html.
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The thermoelectric properties and microstructure of two families of misfit type layered structure cobaltites were investigated for thermoelectric applications. Firstly, Bismuth strontium cobaltite ceramics with the formulations Bi2+xSr2Co2Oy (x=0, 0.1 and 0.2), Bi1.74Sr2Co1.8Oy and Bi2Sr2Co1.8Oy were produced using solid-state reaction (MO) method. The same powders were also used to produce ceramics by Spark Plasma Sintering (SPS) fabrication technique. SEM, high resolution XRD and HRTEM techniques has been employed to characterise the microstructure and crystal structures of the ceramics. Figure of merit (ZT) was also determined from measurement of electrical resistivity, Seebeck coefficient and thermal conductivity. Together with the above, calcium cobaltite of formulation Ca3-xBixCo3O9 (x=0 and 0.3) was also produced via MO and SPS routes. The same characterisation techniques were used for characterisation of calcium cobaltite. For Bi2+xSr2Co2Oy ceramics, it was found that SPS fabrication is essential to obtain high density samples. Excess bismuth has a major role in the adjustment of the microstructure and thermoelectric properties. The room temperature microstructure contains two minor phases with compositions of CoO and Bi0.75Sr0.25O1.26. The crystal structure of the main phase was successfully indexed and refined as misfit type structure having monoclinic symmetry with I2/a space group. A high ZT of 0.12 was achieved in both x=0.1 and 0.2 MO samples. For Bi2Sr2Co1.8Oy ceramics, the microstructure contains only one minor phase, Bi0.75Sr0.25O1.26. A high ZT of 0.16 was obtained at 900 K for this composition. For Bi1.74Sr2Co1.8Oy, it was not possible to obtain high density ceramics by MO route and SPS fabrication was necessary. However, SPS sample showed a low ZT of 0.04 at 900 K.For ceramics of formulation Ca3-xBixCo3O9 (x=0 and 0.3), it was difficult to obtain high density calcium cobaltite ceramics by MO route and SPS fabrication was found to be essential. In addition to improved density, SPS produced textured microstructure. Similar to bismuth strontium cobaltite, excess bismuth played a major role in microstructure development and thermoelectric properties. Single phase and high density Ca3Co4O9 ceramics were obtained by SPS. A minor phase of Bi2Ca2Co2Oy was found in the microstructure of Ca3-xBixCo3O4 (x=0.3) samples. A high ZT of 0.25 was obtained for Ca3Co4O9 SPS samples at 900 K through improvement of power factor. In-situ synchrotron XRD in the temperature range of 300-1223 K was performed on both Bi2Sr2Co2Oy and Ca3Co4O9 to obtain their high temperature structural characteristics. The crystal structure of both compounds remains unchanged till 1223 K. For, Bi2Sr2Co2Oy the CoO and Bi0.75Sr0.25O1.26 minor phases disappear above 1073 K and a new minor phase containing (Bi-Sr-O) or (Bi-Co-O) starts forming. On heating, the lattice volume and coefficient of thermal expansion change linearly for both compounds. Thermal expansion coefficient was found to be 0.0000353-0.0000343 and 0.0000296-0.0000288 K-1 over the temperature range of 300-1223 K for Bi2Sr2Co2Oy and Ca3Co4O9 respectively.
35
Shelley, Matthew. "Theory and simulation of semiconducting nanowires for thermoelectric applications". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6860.
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In this Thesis we present novel, robust and general algorithms for combining planewave density-functional theory with the Landauer-Buttiker transport formalism. The method automates this process with minimal user input to allow a high throughput of calculations. We make use of a maximally-localised Wannier function basis to describe systems using short-ranged Hamiltonians. Further, these Hamiltonians may be used as "building-blocks" to create model Hamiltonians of much larger (10,000+ atom) systems, thus allowing electronic transport properties of structurally complex systems to be determined with first-principles accuracy. A similar building-block method is applied to construct model dynamical matrices from those of smaller systems, from which the lattice thermal conductivity Kl may be inferred. The methods were applied to investigate the thermoelectric properties of (110), (111) and (211) Si nanowires (SiNWs) that contain axial heterostructures of Ge. Their performance is measured by the figure of merit, [equation included here], where S, G , Ke and T are the Seebeck co-efficient, electronic conductance, electronic contribution to the thermal conductance and average temperature between the sample's contacts, respectively. We find the thermoelectric power factor S2G is reduced by the presence of heterostructures, however, as a result of the differences between phonon density of states in the Si and Ge regions, low Kl values (< 0.1 nWK-1) are reported. Thus greater values of zT are found compared to the pristine SiNW case. Of the growth directions studied, the (111) direction is found to display the greatest values of zT, with values as large as three in systems with periodic arrangements of heterostructures. More modest values of 1.6 are found in structures that model disorder in the heterostructure length, which may occur experimentally; this is still a factor of four greater than the pristine case. In addition, we observe that trends in S2G, KI and zT that are predicted for systems containing a single heterostructure can often be used to predict trends in systems with many heterostructures.
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Mitra, Sunanda. "Chalcogenide of type I-V-VI₂ for thermoelectric applications". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS562/document.
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Ce travail de thèse porte sur une série d’échantillons de composition nominale AgBiSe2-xSx (avec x= 0 à 2), appartenant à la famille des chalcogénures ternaires de type I-V-VI₂. Les analyses structurales et thermiques ont mis en évidence une solution solide complète sans gap de miscibilité, et des transitions de phase pour toutes les compositions. Nous avons pu obtenir des composés monophasés à la fois des phases hexagonale et cubique, et notre étude de DRX en température à mis en évidence une phase rhomboédrique pour certaines compositions (x=1 à 2 dans AgBiSexS2-x). Les résultats de DSC ont confirmé la présence de transitions de phase pour toutes les compositions, avec un déplacement des températures de transition en fonction de la fraction de soufre/sélénium. Notre étude de DRX sous pression de l’échantillon AgBiSe₂ a montré une transition de phase induite par la pression d’une phase hexagonale à rhomboédrique puis cubique. Suite à cette observation, l’application d’une pression chimique, par la substitution de 30% du Bi par du Sb a été utilisée avec succès pour stabiliser la phase cubique pour toutes les compositions. Le dopage par Nb des échantillons substitués par l’antimoine l’a pas eu d’influence sur la nature des phases stables à l’ambiante en comparaison aux échantillons non dopés. Nous avons ensuite étudié l’influence du dopage sur les propriétés de transport. Les valeurs négatives de S pour toutes les compositions indiquent un comportement de semi-conducteur de type n dans la gamme (50-300K). Par ailleurs, nos mesures ont montré à a fois de très faibles valeurs de κ mais aussi une décroissance de ∣S∣ et ρ avec l’augmentation de la fraction de Nb. Ces résultats devraient permettre d’optimiser le facteur de puissance pour améliorer les valeurs de ZT. Enfin, une étude en collaboration avec une équipe chinoise a permis d’obtenir une valeur de ZT de 1.3 à 890K dans un composé AgPbmSnSe₂Here, we report on a series of samples with nominal compositions AgBiSe2-xSx (with x= 0 to 2) belonging to the class of ternary chalcogenides of type I-V-VI₂. The structural and thermal analysis result shows a complete solid solution without miscibility gap and phase transitions for all compositions. We have succeeded in obtaining single phase compounds, of both hexagonal and cubic phase, and the high temperature XRD study showed the rhombohedral phase too for selected compositions (x=1 to 2 in AgBiSexS2-x). The DSC results confirmed the presence of the phase transitions for all compositions, with a shift of the temperature of transition as a function of the sulfur/selenium fraction. The high pressure XRD investigation of the compound AgBiSe₂ showed a pressure induced phase transition from hexagonal-to-rhombohedral-to-cubic phase. In this respect, chemical pressure with 30% Sb on the Bi site has been successfully applied to stabilize the cubic phase for all compositions. Nb doping in the Sb-substituted samples does not show any change in the phase behavior at RT in comparison with the undoped samples. The influence of doping on transport properties was analyzed. The negative value of S for all compositions indicates n-type semiconducting behavior over the range (50-300K). Further, the results not only shows very low value of κ but the ∣S∣ and ρ value also decreases for each composition from Nb fraction 0.02 to 0.04. This gives us the opportunity to optimize the power factor in order to improve the ZT value. At last, collaborative study with Chinese team showed that ZT of 1.3 at 890 K can be achieved for AgPbmSnSe2+m (m = 50)
37
SOFFIENTINI, ALESSANDRO. "Synthesis and characterization of nanostructured oxides for thermoelectric applications". Doctoral thesis, Università degli studi di Pavia, 2018. http://hdl.handle.net/11571/1214883.
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Gnanaseelan, Minoj [Verfasser], Brigitte [Gutachter] Voit i Nikhil Kumar [Gutachter] Singha. "Development of thermoelectric materials based on polymer nanocomposites / Minoj Gnanaseelan ; Gutachter: Brigitte Voit, Nikhil Kumar Singha". Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226902200/34.
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Aydin, Erkin. "Biodegradable Polymer - Hydroxyapatite Nanocomposites For Bone Plate Applications". Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612252/index.pdf.
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Long bone fractures are fixed with bone plates to restrain movement of bone fragments. Fracture site must experience some pressure for proper healing. Bone plates are mostly made up of metals having 5 - 10 times higher elastic modulus than bones and most of the load is carried by them, leading to stress shielding and a bony tissue with low mineral density and strength. To avoid these problems, biodegradable polymer-based composite plates were designed and tested in this study.
Poly(L-lactide) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biodegradable polymer composite fibers containing hydroxyapatite (HAP) nanoparticles were produced by extrusion and spinning techniques to reinforce the polymeric bone plates. The composite fibers were expected to mimic the natural organization of bone so that HAP nanorods aligned parallel to the loading axis of bone plate. Also, lactic acid was grafted on HAP surfaces and had a positive effect on the mechanical properties of the PLLA composites.
A 50% (w/w) HAP nanoparticle content was found to increase tensile modulus value (4.12 GPa) ca. 2.35 times compared to the pure polymeric fiber with a reduction to one third of the original UTS (to 50.4 MPa). The fibers prepared were introduced to polymeric plates with their long axes parallel. Fiber reinforced bone plates were compression tested longitudinally and up to a 4% increase in the Young&rsquos Modulus was observed. Although this increase was not high was not high probably due to the low fiber content in the final plates, this approach was found to be promising for the production of biodegradable polymeric bone plates with mechanical values closer to that of cortical bones. Biological compatibility of fibers was validated with in vitro testing. The osteoblasts attached and spread on the fibers indicating that bone fractures fixed with these could attract of bone forming osteoblasts into defect area and help speed up healing.
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Satarkar, Nitin S. "REMOTE CONTROLLED HYDROGEL NANOCOMPOSITES: SYNTHESIS, CHARACTERIZATION, AND APPLICATIONS". UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/85.
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There is significant interest in the development of hydrogels and hydrogel nanocomposites for a variety of biomedical applications including drug delivery, sensors and actuators, and hyperthermia cancer treatment. The incorporation of nanoparticulates into a hydrogel matrix can result in unique material characteristics such as enhanced mechanical properties, swelling response, and capability of remote controlled (RC) actuation. In this dissertation, the development of hydrogel nanocomposites containing magnetic nanoparticles/carbon nanotubes, actuation with remote stimulus, and some of their applications are highlighted.
The primary hydrogel nanocomposite systems were synthesized by incorporation of magnetic nanoparticles into temperature responsive N-isopropylacrylamide (NIPAAm) matrices. Various nanocomposite properties were characterized such as temperature responsive swelling, RC heating with a 300 kHz alternating magnetic field (AMF), and resultant collapse. The nanoparticle loadings and hydrogel composition were tailored to obtain a nanocomposite system that exhibited significant change in its volume when exposed to AMF. The nanocomposites were loaded with model drugs of varying molecular weights, and RC pulsatile release was demonstrated.
A microfluidic device was fabricated using the low temperature co-fired ceramic (LTCC) processing technique. A magnetic nanocomposite of PNIPAAm was placed as a valve in one of the channels. The remote controlled liquid flow with AMF was observed for multiple on-off cycles, and the kinetics of the RC valve were quantified by pressure measurements.
The addition of multi-walled carbon nanotubes (MWCNTs) in NIPAAm matrices was also explored for the possibility of enhancement in mechanical properties and achieving remote heating capabilities. The application of a radiofrequency (RF) field of 13.56 MHz resulted in the remote heating of the nanocomposites. The intensity of the resultant heating was dependent on the MWCNT loadings.
In order to further understand the RC actuation phenomenon, a semi-empirical heat transfer model was developed for heating of a nanocomposite disc in air. The model successfully predicted the temperature rise as well as equilibrium temperatures for different hydrogel dimensions, swelling properties, nanoparticles loadings, and AMF amplitude. COMSOL was used to simulate temperature rise of the hydrogel nanocomposite and the surrounding tissue for hyperthermia cancer treatment application.
41
Polisski, Sergej. "Porous silicon/noble metal nanocomposites for catalytic applications". Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545317.
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Today, bulk silicon is one of the best studied semiconductors. However, in its different nano-modifications, e.g. as porous silicon, totally new properties are exhibited. Despite the fact, that porous silicon is widely known and has been extensively studied since the 1990s, many unique features of this material are still unexplored. In this work, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated. Since this study was in-part industry oriented, the emphasis has been placed upon the investigation of porous silicon nanostructures, made from low cost metallurgical grade polycrystalline silicon powder. It has been previously demonstrated that porous silicon exhibits a very large, hydrogenated internal surface area (up to 500 m2 g−1). It is verified in this work, that morphological properties of this material result in a high reductive potential of its internal surface due to hydrogen passivation. Therefore, in this thesis, we would like to show that porous silicon-based reactive templates are promising for their applications in nanometal-supported catalysis. We used salts of platinum, gold, palladium, silver and their mixtures, which were reduced on the silicon nanocrystalline internal surface, resulting in formation of metal nanoparticles embedded into porous silicon matrix. Various experimental techniques were used to evaluate the morphology, size and composition of metal nanoparticles, as well as their growth rates. Hydrogen effusion experiments proved the crucial difference between porous silicon and other chemically inert supporting templates for the process of metal nanoparticles formation. The catalytic activity of the synthesised materials was evaluated in gas phase conversion of CO to CO2. Furthermore, the new porous silicon-based catalysts were tested in gas/liquid phase reactions as well, using hydrogenation, oxidation, dehalogenation and C-C coupling class reactions. Following the trends of “state of the art” current Si technology, we present the design of the developed flow microreactor, based on patterned Si wafer, which can be implemented in future work to catalyse selected reactions. Results obtained in this work suggest that porous silicon matrices are promising supports for metal nanoparticle based catalysis.
42
Heine, Jason Randall 1972. "Characterization and device applications of II-VI nanocomposites". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8447.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references.
This thesis describes the synthesis and characterization of CdSe core - ZnS shell (CdSe)ZnS nanocrystals, which behave as quantum dots (QDs), their incorporation into transparent polymers and ZnS, and possible device applications of the resulting luminescent materials. The crystalline structure of these quantum dots is examined using XRD. The nature of the core-shell interface is inferred by comparison of the XRD spectra with calculated spectra and in consideration of TEM images of the QDs. The influence the addition of a shell material over the CdSe core has on the QD exciton energy is examined by comparing the measured and calculated change in band edge emission energy when ZnS or CdS are used as overcoat materials. Methods of incorporating the QDs into various polymers are considered and the emission of a GaN LED/ QD-containing polymer composite structure is simulated and compared with the output of actual devices. The simulation is also used as a design tool in the production of a white-light LED. Embedding the QDs into ZnS films via an electrospray technique is carried out and the resulting films characterized with x-ray diffraction and photoluminesence measurements. QD film / ZnS film structures are also considered, with atomic layer deposition used as the method for depositing the ZnS to improve the film uniformity as well as to maintain high quality deposition at temperatures low enough to be compatible with the presence of QDs. Finally, thin film devices are synthesized and the behavior of the QD photoluminescence when an electric field is applied is studied.
(cont.) Significant levels of photoluminescence quenching is observed when a voltage is applied across an ITO/ZnS/QD/ZnS/Al, and similar, devices. Various reasons for this quenching are considered.
by Jason Randall Heine.
Ph.D.
43
Pooyan, Parisa. "Bio-inspired polymer nanocomposites for tissue engineering applications". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53439.
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Increasing emphasis has been placed on the use of renewable resources, on decreased reliance on petroleum in order to better utilize global energy needs. Biological structures available in nature have been a constant inspiration to the design and fabrication of the new line of functional biomaterials whose unique phenomena can be exploited in novel applications. In tissue engineering for example, a natural biomimetic material with close resemblance to the profile features existed in a native extracellular matrix could provide a temporary functional platform to regulate and control cellular interactions at a molecular level and to subsequently direct a tissue regeneration. However, the lack of rigidity of natural materials typically limits their mass production. One promising approach to address this shortcoming is to introduce a biomimetic composite material reinforced by high purity nanofibers found in nature. As an attractive reinforcing filler phase, cellulose nanowhiskers (CNWs) offer exceptional properties such as high aspect ratio, large interface area, and significant mechanical performance. As such, CNWs could integrate a viable nanofibrous porous candidate, resulting in superior structural diversity and functional versatility. Inspired by the fascinating properties of cellulose and its derivatives, we have designed two bio-inspired nanocomposite materials reinforced with CNWs in this work. The successful grafting of CNWs within the host matrix and their tendency to interconnect with one another through strong hydrogen bonding gave rise to the formation of a three-dimensional rigid percolating network, fact which imparted considerable mechanical strength and thermal stability to the entire structure with only a small amount of filler content, i.e. 3 wt.%. Also, the biocompatibility of the nanocomposite was probed by in-vitro incubation of human-bone-marrow-derived mesenchymal stem cells (MSCs), which resulted in the invasion and proliferation of MSCs around the nanocomposite at day 8 of culture. The green functional biomaterial with its unique features in this work could open new perspectives in the self-assembly of nanobiomaterial for tissue-engineered scaffolding, while it could make the design of the next generation of fully green functional biomaterial a reality.
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Abeywickrama, Thulitha Madawa. "Metal-Organic Hybrid Nanocomposites For Energy Harvesting Applications". TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1748.
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Various synthetic methods have been developed to produce metal nanostructures including copper and iron nanostructures. Modification of nanoparticle surface to enhance their characteristic properties through surface functionalization with organic ligands ranging from small molecules to polymeric materials including organic semiconducting polymers is a key interest in nanoscience. However, most of the synthetic methods developed in the past depend widely on non-aqueous solvents, toxic reducing agents, and high temperature and high-pressure conditions. Therefore, to produce metal nanostructures and their nanocomposites with a simpler and greener method is indeed necessary and desirable for their nano-scale applications. Hence the objective of this thesis work is to develop an environmentally friendly synthesis method to make welldefined copper and iron nanostructures on a large-scale. The size and shape-dependent optical properties, solid-state crystal packing, and morphologies of nanostructures have been evaluated with respect to various experimental parameters.
Nanostructures of copper and iron were prepared by developing an aqueous phase chemical reduction method from copper(II) chloride and Fe(III) chloride hexahydrate upon reduction using a mild reducing agent, sodium borohydride, under an inert atmosphere at room temperature. Well-defined copper nanocubes with an average edge length of 100±35 nm and iron nanochains with an average chain length up to 1.70 μm were prepared. The effect of the molar ratios of each precursor to the reducing agent, reaction time, and addition rate of the reducing agent were also evaluated in order to develop an optimized synthesis method for synthesis of these nanostructures. UV-visible spectral traces and X-ray powder diffraction traces were obtained to confirm the successful preparation of both nanostructrues. The synthesis method developed here was further modified to make poly(3-hexylthiophene) coated iron nanocomposites by surface functionalization with poly(3-hexylthiophene) carboxylate anion. Since these nanostructrues and nanocomposites have the ability to disperse in both aqueous-based solvents and organic solvents, the synthesis method provides opportunities to apply these metal nanostructures on a variety of surfaces using solution based fabrication techniques such as spin coating and spray coating methods.
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Khlebtsov, B. N., i N. G. Khlebtsov. "Theranostic Applications of Au-Ag Nanocages and Nanocomposites". Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34937.
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We report two novel biomedical applications of Au/Ag alloy nanoparticles called nanocages. In the first
case, composite nanoparticles consisting of a nanocage core and a mesoporous silica shell doped with a photodynamic
sensitizer Yb-2,4-hematoporphyrin were fabricated, characterized, and tested in vitro and ex vivo.
In the second part of the study, Ag nanocubes and Au/Ag nanocages were applied to a multiplexed dot
immunoassay. The assay principle is based on the staining of analyte drops on a nitrocellulose membrane
strip by using multicolor nanoparticles conjugated with biospecific probing molecules.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34937
46
Li, Molan. "Thermoelectric-Generator-Based DC-DC Conversion Network for Automotive Applications". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42358.
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As waste heat recovering techniques, especially thermoelectric generator (TEG technologies, develop during recent years，its utilization in automotive industry is attempted from many aspects. Previous research shows that TEG as a waste heat harvesting method is feasible. Even though efficiencies for TEGs are as low as 3-5% with existing technology, useful electricity generation is possible due to the great amount of waste heat emitted from the internal combustion engine operation. This thesis proposes the innovative concept of thermoelectric-generator-based DC-DC conversion network. The proposed structure is a distributed multi-section multi-stage network. The target is to tackle problems facing the traditional single-stage system and to advance TEG application in automotive settings. The objectives of the project consists of providing optimal solution for the DC-DC converter utilized in the network, as well as developing a systematic and bottom-up design approach for the proposed network. The main problems of the DC-DC converters utilized in the TEG system are presented and analyzed, with solution to dynamic impedance matching suggested. First, theoretically-possible approaches to balance the large TEG internal resistance and small converter input resistance are discussed, and their limitations are presented. Then, a maximum power point tracking (MPPT) regulation model is developed to address the temperature-sensitive issue of converters. The model is integrated into a TEG-converter system and simulated under Simulink/Simscape environment, verifying the merits of MPPT regulation mechanism. With the developed model, MPPT matching efficiency over 99% is achieved within the hot side temperature range of 200°C ~300°C. A design flow is suggested for the proposed network. Analysis is conducted regarding aspects of the design flow. Several state-of-the-art thermoelectric materials are analyzed for the purpose of power generation at each waste heat harvesting location on a vehicle. Optimal materials and TE couple configurations are suggested. Besides, a comparison of prevailing DC-DC conversion techniques was made with respect to applications at each conversion level within the network. Furthermore, higher level design considerations are discussed according to system specifications. Finally, a case study is performed comparing the performances of the proposed network and traditional single-stage system. The results show that the proposed network enhances the system conversion efficiency by up to 400% in the context of the studied case.
47
Mangelis, Panagiotis. "Structural and physical properties of chalcogenide materials for thermoelectric applications". Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/76846/.
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Investigations of structural and thermoelectric properties of shandite-type sulphides and diamond-like quaternary chalcogenides have been carried out. Electron and hole doping is investigated in Co3Sn2S2 through the chemical substitution of cobalt by its neighbouring elements. The synthesis of two series, Co3-xNixSn2S2 (0 ≤ x ≤ 3) and Co3-xFexSn2S2 (0 ≤ x ≤ 0.6) is described. Powder neutron diffraction experiments have been carried out for both series, while 119Sn and 57Fe Mössbauer spectroscopy measurements have been conducted for Co3-xFexSn2S2 (0 ≤ x ≤ 0.6). The materials become more metallic with increasing nickel content, while the substitution of Co by Fe induces a metal-to-n-type-semiconductor transition, and an increase in the thermoelectric figure-of-merit (ZT) is achieved to a maximum of 0.2 at 525 K. Further improvement in ZT is achieved by the simultaneous substitution at the transition metal and main-group metal sites. In the series Co2.667Fe0.333Sn2-yInyS2 (0 ≤ y ≤ 0.7), the materials become more semiconducting with increasing In content and a marked increase in the Seebeck coefficient is observed. Co2.667Fe0.333Sn1.4In0.6S2 exhibits ZT = 0.28 at 473 K. The quaternary chalcogenides A2ZnCQ4 (A = Cu, Ag; C = Sn, Ge; Q = S, Se) were synthesized and investigated using powder neutron diffraction. Rietveld analysis reveals that all phases crystallize in the kesterite structure at room temperature and the Cucontaining compounds exhibit partial Cu/Zn disorder in the z = 0.25 and 0.75 planes. For Cu2ZnGeS4, an irreversible phase transition is observed at 1123 K from the kesterite to the wurtzite-stannite structure. For Cu2ZnGeSe4, the cations in z = 0.25 and 0.75 planes become fully disordered at 473 K, while simultaneously, Cu vacancies are created. Hole doping in Cu2+xZnGe1-xSe4 (0 ≤ x ≤ 0.15) results in a marked decrease in electrical resistivity, increasing the ZT to 0.18 at 573 K.
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Hojabri, Arash. "Synthesis and characterization of Germanium quantum dots for thermoelectric applications". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-180953.
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Energy resources are a main factor for the development of industry and human life, however, the use of fusil fuels as energy is harmful to the environment. Taking these two matters into consideration, the use of waste energy is a good response. The thermoelectric phenomena, which was, discovered in the 18th century plays a main role in converting waste heat energy to electricity and vice-versa. Germanium quantum dots (Ge QDs) have received special attention due to their unusual electrical and optical properties, which are correlated to the quantum confinement effect. In thermoelectric devices amazing electrical property of Ge QDs are utilized. Ge QDs can be applied in thermoelectric devices to increase the electrical conductivity while decreasing the thermal conductivity, resulting in an increasing of the figure of merit (ZT); a characteristic for thermoelectric devices that should be as high as possible. In this study, Reduced Pressure Chemical Vapor Deposition (RPCVD) was used to synthesize Ge QDs utilizing GeH4 gas on silicon at a temperature of 450℃ with deposition times of 23s, 25s, 30s, 60s, 120s and 240s, and at a total and partial pressure of 20 Torr and 20 mTorr respectively. RPCVD was used to fabricate multi-layer Ge dots on silicon wafers, which were sandwiched between thin silicon films. Process parameters used in this study to deposit thin interlayers silicon film were as follows: Total pressure: 20 Torr, temperature: 500℃ and partial pressure of 10 mTorr. Deposition times of 150s, 300s and 600s were used to deposit interlayers of silicon utilizing Si2H6 gas to connect and disconnect carrier transfer between Ge QDs perpendicularly and to investigate the surface roughness. Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive Spectroscopy (EDS), and High Resolution X-Ray Diffraction (HRXRD) were employed to investigate the Ge dots and interlayers silicon films. These characterizations showed that the smallest dots are obtained from 23s deposition time which means higher tunneling of electrons and an increase of electrical conductivity. The data also showed that a shorter deposition time results in a higher relative strain which means higher carrier mobility and higher electrical conductivity. Finally, multilayers of Si/strained Ge-dots analyzed to find the smoothest surface, and the smoothest surface was obtained with 23s deposition time of Ge dots, which means less electrical noise in thermoelectric devices. Such structures are ready to be grown on silicon on insulator (SOI) wafer to make advanced coupled or uncoupled dots for future thermoelectric applications.
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Iyengar, Ananth Shalvapulle. "Synthesis and characterization of micro/nano material for thermoelectric applications". Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1276182370.
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Wei, Kaya. "Skutterudite Derivatives: A Fundamental Investigation with Potential for Thermoelectric Applications". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5152.
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Thermoelectric devices allow for direct conversion of heat into electricity as well as solid-state refrigeration. The skutterudite family of compounds continues to be of considerable interest both scientifically and technologically due to their unique physical properties, in particular as promising thermoelectric materials. In this thesis, the basic thermoelectric phenomena and some background history on skutterudites will be reviewed. Rhombohedral derivatives of the cubic skutterudite CoSb3, namely Co4-xFexGe6Se6 with x=0, 1, 1.5 (p-type) and rare-earth filled Ce0.13Co4Ge6Se6 and Yb0.14Co4Ge6Se6 (n-type), were synthesized and their synthesis and low temperature transport properties will be discussed.
Reitveld refinement and elemental analysis were used to identify the structure and stoichiometry of these compositions. Both Fe substitution and rare-earth filling reduced the thermal conductivity compared with Co4Ge6Se6 skutterudite derivative. In addition the electrical and thermal properties of these compounds are greatly affected by doping. This fundamental investigation reveals new insight and is intended as part of the continuing effort to explore different skutterudite compositions and structure types for potential thermoelectric applications.