近幾年來，熱電材料蓬勃發展是許多物理、化學以及材料科學家的熱門研究的方向，然而此一跨領域的基礎研究工作處於萌芽的階段。熱電材料的益處在於可將熱機或是冷凍機之上所產生的廢熱轉化成電能。本研究利用鉍化碲(Bismuth Tellurium)在室溫附近具有一熱電優質係數(ZT)為1.0的熱電表現，其具有非常低的熱傳導率以及適當的載子傳輸性質，因此Bi-Te的合金系列成為大家研究的趨勢，成為另一項重大的焦點引發相當的關注。鉍化碲元素皆是地球殼中豐富的元素，且鉍化碲是對人無毒且對環境無害的化合物，相較於其他高性能熱電材料(一般由稀少元素/貴金屬組成)，具有非常大商業化的潛力。鉍化碲本身為非常穩定的多層層狀結構(Quintuple Layer)，表現出極低的熱傳導率以及良好的導電性。為了未來能製作出微小的熱電模組，本研究利用射頻磁控濺鍍系統(Radio-Frequency Magnetron Sputtering System)調控濺鍍參數的方式，得到最佳熱電性質之薄膜後，再使用半導體製程技術製作微結構的陣列熱電薄膜，利用光微影製程及金屬遮罩兩種分別不同的方式決定所需之電極和薄膜陣列之圖形。本論文使用磁控濺鍍設備，靶材n-type和p-type分別選用Cu0.02Bi2Te2.7Se0.3 和Bi0.5Sb1.5Te3+0.33 wt% Aerogel之熱電材料，經由實驗改變磁控濺鍍的工作壓力、RF power，再透過ZEM-3、EDS對薄膜的研究分析得到(最佳鍍膜參數) 最佳鍍膜品質參數(seebeck、電阻)。決定鍍膜參數後使用本研究開發的兩種方式製作微結構熱電元件，一使用光微影半導體製程，二使用金屬遮罩，針對兩種製程方式所得的n-type和p-type陣列熱電薄膜成長過程做比較與研究探討。 / In recent years, physicists, chemists and material scientists at many major universities and research institutions throughout the world are attempting to create novel materials with high thermoelectric (TE) efficiency. It will be beneficial to harvest waste heat into electrical energy. Especially heating and cooling are other major applications for this class of new TE materials. At present the thermoelectric (TE) material bismuth telluride (Bi2Te3) baesd systems exhibit best figure of merit (ZT). Bismuth and tellurium are earth-abundant elements and Bi2Te3 is non-toxic to human beings and the environment. Therefore, it has great potential in commercial implements. Bismuth telluride is a quintuple layer-structured compound possessing ultralow thermal conductivity and moderate electrical conductivity. In this work, the TE thin film and device are fabricated and optimized by Radio-Frequency Magnetron Sputtering System (RFMSS) and the influence of the preparative parameters such as working pressure and working power of RF sputtering are investigated. In this study, we used the magnetron sputtering equipment and the thermoelectric materials n-type target and p-type target were Cu0.02Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3+0.33 wt% aerogel, respectively. In this study, the experimental changes the magnetron sputtering working pressure, RF power before the ZEM-3, EDS analysis the thin film thermoelectric properties to get the best thin film quality parameters (Seebeck coefficient, resistivity, power factor). After the thin film parameters were determined, the microstructural thermoelectric 442 pairs device were fabricated by the photolithography semiconductor process, and n-type and p-type arrays used by photolithography to define a pattern and deposit Au electrodes onto the substrate by thermal evaporation.

In order to reliably test thermoelectric modules, it is necessary to have a adequate measuring apparatus. The presented diploma thesis deals with the design of measuring apparatus capable of performing both long-term testing of thermoelectric modules at a constant high temperature and thermal cycling extension has been designed. Both types can be changed in a short time.

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Die thermoelektrische Energiekonversion auf der Basis des Seebeck-Effekts ist eine Methode zur direkten Erzeugung elektrischer Energie aus thermischer Energie. Für die wesentlichen anwendungsrelevanten Parameter Temperaturbereich, elektrische Leistung und Herstellungskosten sind Materialauswahl und Aufbau der TEG entscheidend. In der vorliegenden Arbeit wurden erstmalig thermoelektrische Oxidkeramiken in monolithischen TEG verwendet, die auf der Grundlage des transversalen thermoelektrischen Effekts arbeiten. Die TEG wurden mit industriell skalierbaren Keramiktechnologien hergestellt, untersucht und hinsichtlich ihrer Parameter detailliert theoretisch und experimentell bewertet. Als Modellsystem für die Materialien wurde La1-xSrxCuO4 in Kombination mit Ag bzw. Ag6Pd1 verwendet. Es konnte belegt werden, dass diese monolithischen TEG im Bereich kleiner elektrischer Leistungen eine vorteilhafte Alternative zu herkömmlichen longitudinalen thermoelektrischen Generatoren sein können.

Les générateurs thermoélectriques (TEG), associant des modules thermoélectriques à des échangeurs de chaleur adaptés, permettent de produire de l’électricité à partir d’une source chaude et d’une source froide. Leur utilisation, réservée actuellement à des applications de niche, va s’avérer judicieuse pour différentes applications industrielles ou domestiques en raison de la disponibilité imminente de nouveaux matériaux thermoélectriques permettant des rendements améliorés et des coûts moindres. Pour rendre plus attractive l’utilisation des TEG et améliorer le rendement global des futures installations, une conception et une utilisation optimisées sont indispensables.La conception de TEG performants nécessite le développement de modèles numériques intégrant tous les éléments de la chaîne énergétique (source chaude, source froide, échangeurs, convertisseurs électriques). L’objectif de la thèse est de créer un outil de simulation du fonctionnement des générateurs sur l’ensemble du cycle de production de chaleur et donc sur des fonctionnements réels dépendant du temps. Le modèle développé en 3D pour les transferts de chaleur prend en compte la dépendance à la température des propriétés des matériaux et l’effet Thomson pour le modèle thermoélectrique.La validation de cet outil de simulation a nécessité la comparaison des prédictions du modèle à des résultats expérimentaux. Un dispositif expérimental a été complété et amélioré afin de mieux répondre aux attentes des études en régime instationnaire. Ce banc d'essai permet d'effectuer des tests avec différentes configurations de générateur thermoélectrique et différentes conditions de fonctionnement. Le modèle a montré une estimation correcte des températures du système et de la production électrique du TEG. Le modèle numérique est validé et peut être utilisé pour la prédiction du fonctionnement d’un TEG dans diverses conditions. / Thermoelectric generators (TEG), combine thermoelectric modules with heat exchangers, making it possible to produce electricity from a hot source and a cold source. Their use, which is currently reserved for niche applications, will prove useful for various industrial or domestic applications due to the imminent availability of new thermoelectric materials allowing improved yields and lower costs. To make the use of TEGs more attractive and to improve the overall efficiency of future installations, optimized design and use are essential.The high-performance TEG design requires the development of numerical models integrating all the elements of the energy chain (hot source, cold source, exchangers, electric converters).The aim of the thesis is to create a tool for simulating the operation of generators over the entire heat production cycle and thus on real time-dependent operations. The model developed in 3D for heat transfer takes into account the temperature dependence of the properties of the materials and the Thomson effect for the thermoelectric model.The validation of this simulation tool required the comparison of model predictions with experimental results. An experimental device has been completed and improved to match better the expectations of unsteady studies. This test bench allows testing with different thermoelectric generator configurations and different operating conditions.The model showed a correct estimation of system temperatures and electrical output of TEG. The numerical model is validated and can be used to predict the operation of a TEG under various conditions.

Thermoelectric materials are solid state devices having the capability to convert heat to electrical energy and vice versa. These materials are simple, have no moving parts and use no greenhouse gases. But the major drawback of these materials is their low conversion efficiency. Hence enhancement of thermoelectric efficiency is required to make the use of these devices widespread. Thermoelectric efficiency is related to a parameter termed figure of merit, ZT which is associated with the inter-related transport properties such as Seebeck coefficient, electrical and thermal conductivity. Efficient thermoelectric material should possess high Seebeck coefficient (S), high electrical conductivity () and low thermal conductivity (). The present investigation revolves around improvement of ZT of CoSb3 either by chemical doping or through microstructural modifications. These materials possess structural voids, which can be filled with foreign atoms. The rattling motion of these filler atoms reduces the thermal conductivity of these materials, thereby increasing the thermoelectric efficiency. The rattler atoms chosen for the present study are Mn and Yb. Both coarse and fine-grained MnxCo4Sb12 (x = 0. 0.2, 0.4, 0.8, 1.2 and 1.6) and Yb0.19Co4Sb12 have been synthesized and subjected to various structural and functional property characterizations. The structural study based on Rietveld Analysis and the corresponding difference Fourier maps confirms the void occupancy by Mn and Yb in MnxCo4Sb12 (x 0.2, 0.4 and 0.8) and Yb0.19Co4Sb12. In higher Mn content, x=1.2 and 1.6, Mn was found to partially substitute Co site and partially fill the voids and the remaining precipitated out as free particles. A comparative study of coarse and fine-grained CoSb3 has thrown light in to the grain size effect on the thermoelectric properties. Lowering of grain size helped in enhancement of ZT in CoSb3. Seebeck coefficient (thermoelectric power), electrical and thermal conductivity have been measured for different concentrations of the filler Mn atoms between 300K and 673K. A change in sign of the Seebeck coefficient from negative to positive occurs, when Mn concentration exceeds x=0.8. Electrical resistivity values was found to decrease initially with Mn filling with the minimum value at Mn content, x=0.4 and then gradually increase as Mn content increases. The thermal conductivity value decreases with Mn content in the CoSb3 indicating their rattling property which helps in the enhancement of the overall thermoelectric efficiency. There is a reduction in the value of ktotal in Mn filled CoSb3 than that of the unfilled counterpart. This decrease in the ktotal is a clear indication of the rattling motion of the filler Mn atom in the structural void of CoSb3. Highest ZT of 0.36 is achieved by Mn0.4Co4Sb12 at 373K. Higher concentration of Mn (with x= 1.2 and 1.6) proved to be detrimental in terms of improvement of the value of ZT. Grain size reduction helped in improvement of ZT in Mn0.2Co4Sb12. Maximal ZT of 0.06 at 523K is achieved in hot pressed Mn0.2Co4Sb12. The corresponding coarse-grained material is found to possess ZT of 0.01 at the said temperature. The enhancement can be attributed to high / ratio and high density. Similarly, fine grained Yb0.19Co4Sb12 shows higher ZT compared to the coarse-grained sample because high / and high S.

Les matériaux thermoélectriques (TE) permettent de convertir directement de la chaleur en électricité et vice-versa. Les objectifs de cette thèse étaient de tenter d'améliorer les performances TE de trois familles de matériaux et de mieux comprendre le lien entre les propriétés physiques (électriques, thermiques, magnétiques) généralement mesurées dans une large gamme de température (5–700 K) et les microstructures/compositions chimiques observées. Généralement, les matériaux ont été synthétisés par des techniques de métallurgie des poudres et densifiés par spark plasma sintering. La majeure partie de nos travaux a concerné la famille des matériaux tétraédrites, dérivés du minéral naturel (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13, présentant des propriétés TE prometteuses, récemment mises en évidence. D’abord, les propriétés TE de huit tétraédrites naturelles de provenance différente ont été étudiées. Nous avons montré que leurs propriétés physiques sont plutôt prévisibles selon leur composition chimique et finalement peu différentes selon leur origine. Les propriétés TE de mélanges de tétraédrites naturelles et synthétiques obtenus par broyage mécanique ont ensuite été déterminées. Ce procédé fortement énergétique produit des particules de taille nanométrique des deux phases qui forment une solution solide pendant le frittage. Par contre, un broyage manuel conserve la présence des deux phases, ce qui conduit à de plus faibles performances TE. Ensuite, nous avons montré que la substitution Sb <-> As, usuelle dans les spécimens naturels, n’influence que faiblement les propriétés TE. Enfin, les propriétés TE de manganites de calcium et de polymères conducteurs ont également été étudiées / Thermoelectric (TE) materials allow direct conversion between heat and electricity. The aim of this thesis was to try to improve the thermoelectric performance of three different families of materials and to better understand the link between the various physical properties (electrical, thermal, magnetic) generally measured in a broad temperature range (5–700 K) and the observed microstructure/chemical composition. In general, the materials were synthesized by powder metallurgy techniques and densified by spark plasma sintering (SPS). The major part of our studies concerns the tetrahedrite family of materials, derived from the mineral tetrahedrite, (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13, whose promising thermoelectric properties were only recently discovered. In a first approach, the TE properties of eight natural tetrahedrites of different geographic origin are studied. It is shown that they all behave rather predictably and uniformly. Next, the properties of ball milled mixtures of natural and synthetic tetrahedrites are investigated. This high-energy process yields nanoscale particles of the two phases, which form a solid solution during the sintering. Low-energy hand grinding preserves the two-phase nature and results in inferior TE performance. Because arsenic is a common substituent in natural specimens, several As-substituted tetrahedrites are synthesized and characterized. It is shown that the TE properties are only weakly influenced by the substitution of As for Sb. Besides tetrahedrites, calcium manganese oxides and conductive polymers are also studied

Small domestic hot water boilers burning solid fuels represent a significant source of air pollu-tion. It is therefore an effort to increase their combustion efficiency and to reduce the produc-tion of harmful emissions. For this reason, the operation of older and currently unsatisfactory types of household boilers has been legally restricted. Preferred types of boilers are low-emission boilers, especially automatic or gasification boilers. Most of them, however, in compar-ison with previous types of boilers, also require connection to the electricity grid. If there is a long-term failure in electricity grid, the operation of newer boiler types is limited. Wood and coal gasification boilers are currently available on the market and can be operated even in the event of a power failure, but only in heating systems with natural water circulation. In heating systems with forced water circulation, these boilers, fireplaces or fireplace inserts with hot-water heat exchangers cannot be operated without external battery supply in the event of a power failure. The dissertation thesis therefore deals with the question of whether it would be possible by thermoelectric conversion of waste heat of flue gases of small-scale low-emission combustion hot water domestic boilers to obtain sufficient electricity, to power supply their circulation pumps and to ensure operation in systems with forced water circulation independently of elec-tricity supply from the grid. In order to answer this question, a simulation tool predicting the power parameters of ther-moelectric generators was created. Compared to previously published works, the calculations and simulations include the influence of the generator on the boiler flue gas functionality. To verify the simulation tool, an experimental thermoelectric generator was built using the waste heat of the flue gas of an automatic hot water boiler for wood pellets. In addition to this genera-tor, there was also created an experimental thermoelectric fireplace insert and other equipment related to these experiments.

Doctor of Philosophy / Department of Physics / Jingyu Lin / III-nitride nanostructures and devices were synthesized by metal organic chemical vapor deposition (MOCVD) for their applications in various photonic, optoelectronic, and energy devices such as deep ultraviolet (DUV) photodetectors, solar cells, visible emitters, thermometric (TE) power generators, etc. Structural and optical properties in thicker AlN epilayers were found to be better than those in thinner AlN epilayers. Full-width at half maxima (FWHM) of x-ray diffraction (XRD) rocking curves as small as 63 and 437 arcsec were measured at (002) and (102) reflections, respectively in a thick AlN epilayer (4 m). The dark current of the fabricated AlN detectors decreases drastically as AlN epilayer thickness increases. DUV photoluminescence (PL) spectroscopy and x-ray diffraction (XRD) measurements were employed to study the effect of biaxial stress in AlN epilayers grown on different substrates. Stress-induced band gap shift of 45 meV/GPa was obtained in AlN epilayers. The potential of InGaN alloys as TE materials for thermopower generation has been investigated. It was found that as In content increases, thermal conductivity decreases and power factor increases, which leads to an increase in the TE figure of merit (ZT). The value of ZT was found to be 0.08 at 300 K and reached 0.23 at 450 K for In0.36Ga0.64N alloy, which is comparable to that of SiGe based alloys. Single phase InxGa1−xN alloys inside the theoretically predicted miscibility gap region (x = 0.4 to 0.7) were successfully synthesized. A single peak of XRD -2 scans of the (002) plane in InGaN alloys confirms that there is no phase separation. Electrical properties and surface morphologies were found to be reasonably good. It was found that growth rate should be high enough (>400 nm/hr) to achieve high quality and single phase InxGa1−xN alloys in this miscibility gap region. Mg-doped InxGa1-xN alloys were synthesized and characterized by Hall-effect and PL measurements for their application as visible emitters. P-type conductivity was measured up to x = 0.35 with accepter activation energy as low as 43 meV, which is about 4 times lower than that of Mg-doped p-type GaN. Resistivity as low as 0.4 -cm with a free hole concentration as high as 5x1018 cm-3 was measured in Mg-doped In0.22Ga0.78N. PL intensity decreased ~3 orders in magnitude when x increased from 0 to 0.22 in Mg-doped InxGa1-xN alloys.

With technology scaling, the amount of transistors on a single chip doubles itself every 18 months giving rise to increased power density levels. This has directly lead to a rapid increase of thermal induced issues on a chip and effective methodologies of removing the heat from the system has become the order of the day. Thermoelectric (TE) devices have shown promise for on-demand cooling of ICs. However, the additional energy required for cooling remains a challenge for the successful deployment of these devices. This thesis presents a closed loop control system that dynamically switches a TE module between Peltier and Seebeck modes depending on chip temperature. The autonomous system harvests energy during regular operation and uses the harvested energy to cool during high power operation. The system is demonstrated using a commercial thin-film TE device, an integrated boost regulator and few off chip components. The feasibility of the integration of the TEM and the automated mode switching within the microprocessor package is also evaluated. With continuous usage of thermoelectric modules, it starts to degrade over time due to thermal and mechanical induced stress which in turn reduces the cooling performance over time. Impact of thermal cycling on thermoelectric cooling performance over time is evaluated using the developed full chip package model.