As silicon-based transistor technology continues to scale ever downward, anticipation of the fundamental limitations of ultimately-scaled devices has driven research into alternative device technologies as well as new materials for interconnects and packaging. Additionally, as power dissipation becomes an increasingly important challenge in highly miniaturized devices, both the implementation and verification of high mobility, high thermal conductivity materials, such as low dimensional carbon nanomaterials, and the experimental investigation of heat transfer in the nanoscale regime are requisite to continued progress. This work furthers the current understanding of structure-property relationships in low dimensional carbon nanomaterials, specifically carbon nanotubes (CNTs) and graphene, through use of combined thermal conductance and transmission electron microscopy (TEM) measurements on the same individual nanomaterials suspended between two micro-resistance thermometers. Through the development of a method to measure thermal contact resistance, the intrinsic thermal conductivity, [kappa], of multi-walled (MW) CNTs is found to correlate with TEM observed defect density, linking phonon-defect scattering to the low [kappa] in these chemical vapor deposition (CVD) synthesized nanomaterials. For single- (S) and double- (D) walled (W) CNTs, the [kappa] is found to be limited by thermal contact resistance for the as-grown samples but still four times higher than that for bulk Si. Additionally, through the use of a combined thermal transport-TEM study, the [kappa] of bi-layer graphene is correlated with both crystal structure and surface conditions. Theoretical modeling of the [kappa] temperature dependence allows for the determination that phonon scattering mechanisms in suspended bi-layer graphene with a thin polymeric coating are similar to those for the case of graphene supported on SiO₂. Furthermore, a method is developed to investigate heat transfer through a nanoscale point contact formed between a sharp silicon tip and a silicon substrate in an ultra high vacuum (UHV) atomic force microscope (AFM). A contact mechanics model of the interface, combined with a heat transport model considering solid-solid conduction and near-field thermal radiation leads to the conclusion that the thermal resistance of the nanoscale point contact is dominated by solid-solid conduction. / text

This thesis is devoted to the calculation of thermal contact resistance in various molecular systems based on carbon nanotubes (CNTs) and few layer graphene (FLG). This work has been performed through equilibrium molecular dynamics (EMD) simulations. We adopted the temperature difference fluctuations method in our EMD calculations. This method only needs the input of the temperatures of the subsystems whereas the heat flux, which is involved in all the other approaches, remains more difficult to compute in terms of simulation time and algorithm. Firstly, three cases were studied to validate this method, namely: (i) Si/Ge superlattices; (ii) diameter modulated SiC nanowires; and (iii) few-layer graphenes. The validity of the temperature difference fluctuations method is proved by equilibrium and non-equilibrium MD simulations. Then, by using this method, we show that an azide-functionalized polymer (HLK5) has a lower contact resistance with CNT than the one between CNT and PEMA, because HLK5 could form covalent bonds (C-N bonds) with CNT through its tail group azide, while only weak Van der Waals interactions exist in the case of CNT-PEMA contact. The data from our EMD simulations match with the results from experiments in a reasonable range. We then report the thermal contact resistance between FLG and a SiO2 substrate, which could be tuned with the layer number. Taking advantage of the resistive interface, we show that a SiO2 /FLG superlattices have a thermal conductivity as low as 0.30 W/mK, exhibiting a promising prospect in nano-scale thermal insulation. In the last part, we investigated the layer number dependence of the cross-plane thermal resistances of suspended and supported FLGs. We show that the existence of a silicon dioxide substrate can significantly decrease the cross-plane resistances of FLGs with low layer numbers, and the effective thermal conductivities were increased accordingly. The Frenkel-Kontorova model was introduced to explain the substrate-induced band gaps in FLG dispersion relations and the corresponding thermal energy transfer. The enhanced thermal conduction in the cross-plane direction is ascribed to the phonon radiation that occurs at the FLG-substrate interface, which re-distributes the FLG in-plane propagating energy to the cross-plane direction and to the substrate.

Electrical conductive adhesives (ECAs) containing silver filler and polyaniline co-filler were characterized for their electro-mechanical properties. Polyaniline is a conductive polymer and has a moderate conductivity in between those of the silver and epoxy. Incorporation of polyaniline (μm sized) in silver-epoxy facilitated the electrical conduction in ECAs and reduced the percolation threshold- a minimum volume of filler necessary to initiate the conduction. It also prevented the localization of charge carriers due to aggregation of silver filler particles. ‘Bridging effect’ was observed due to addition polyaniline in which the polyaniline enhanced the tunneling of electrons over the silver filler particles. We have investigated the polyaniline co-fillers as a promising alternative way to tune the mechanical and electrical properties of the ECAs and have provided a detailed analysis of the electro-mechanical properties of silver-epoxy (Ag-epoxy) and silver-polyaniline-epoxy (Ag-PANI-epoxy) system in both partially-cured/ viscoelastic and fully-cured states. Analysis of electro-mechanical properties of silver-epoxy and silver-polyaniline-epoxy also provided the insights into electrical contact resistance of ECAs under compressive force. Electro-mechanical properties of ECAs were measured ‘in-situ’ using micro-indentation technique. We also synthesized the electrically conductive and highly crystalline nanotubes of polyaniline by mini-emulsion polymerization of aniline. The motivation behind the synthesis of polyaniline was to propose a potential filler/co-filler for replacement of metallic filler in ECAs. Electrical conductivity of polyaniline nanotubes was tuned by in-situ doping using hydrochloric acid as a dopant. Increase in dopant caused the polyaniline crystallite to grow along (400) plane. Optical, structural, electrical and thermal properties of polyaniline nanotubes are reported with varying amount of dopant. We fabricated the flexible electrically conductive coating of polyaniline tubes with uniform dispersion of polyaniline. Electrical performance of as-synthesized flexible coating is also revealed.

Thin-film solar cells are widely recognised to have the potential to compete with fossil fuels in the electricity market due to their low cost per peak Watt. The Thin-Film Group at the University of New South Wales (UNSW) is engaged in developing polycrystalline silicon (poly-Si) thin-film solar cells on glass using e-beam evaporation technology. We believe our solar cells have the potential of significantly lowering the manufacturing cost compared to conventional, PECVD-fabricated thin-film solar cells. After years of materials research, the focus of the Group??s work is now moving to the metallisation of evaporated solar cells. Minimising various kinds of losses is the main challenge of the cell metallisation procedure, within which the contact resistance is always a big issue. In this thesis, the contact resistance of aluminium contacts on poly-Si thin-film solar cells on glass is investigated. To the best of the author??s knowledge, this is the first ever contact resistance investigation of Al contacts on evaporated poly-Si material for photovoltaic applications. Various transmission line models (TLM) are employed to measure the contact resistance. An improved TLM model is developed to increase the measurement precision and, simultaneously, to simplify the TLM pattern fabrication process. In order to accommodate the particular requirements of poly-Si coated glass substrates, a TLM pattern fabrication process using photolithography is established. Furthermore, a Kelvin sense tester is set up to ensure an accurate measurement of the contact resistance. After establishment of the TLM technique at UNSW, it is successfully tested on singlecrystalline silicon wafer samples. The thermal annealing process of the contacts is also optimised. Then, the general behaviour of Al contacts on uniformly doped poly-Si films (i.e., no p-n junction) is investigated using the verified TLM technique. The long-term stability of the contacts is also studied. This is followed by an investigation of the contact resistance of the back surface field and emitter layers of different types of poly-Si thin-film solar cells. Finally, a novel contact resistance measurement model is proposed that is believed to be able to overcome the measurement bottleneck of the transmission line models.

A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

Cette thèse se concentre sur le calcul des résistances thermique de contact dans plusieurs systèmes moléculaires à base de nanotubes de carbone (NTCs) et de quelques couches de graphène (QCG). Ce travail a été réalisé en utilisant la méthode de simulation par dynamique moléculaire à l’équilibre (DME). Nous avons utilisé la méthode basée sur les fluctuations de la différence de température dans nos simulations de DME. Cette méthode ne nécessite que l’entrée des températures des sous-systèmes quand le flux thermique, qui intervient dans toutes les autres approches, reste plus difficile à calculer en terme de durée de simulation et d’algorithme. Premièrement, trois cas ont été étudiés pour valider cette méthode : (i) des super-réseaux Si/Ge ; (ii) des nanofils de SiC de plusieurs diamètres ; et (iii) QCGs. La validité de la méthode par fluctuation de la différence de température est démontrée par des simulations de dynamique moléculaire à l’équilibre et hors-équilibre. Ensuite, avec cette méthode, nous montrons qu’un polymère fonctionnalisé azoture (HLK5) a une plus faible résistance de contact avec un NTC que la résistance entre un NTC et un PEMA, car HLK5 forme des liaisons covalentes (C-N bonds) avec un NTC par le groupement azoture de sa queue, quand seul de faibles interactions de van der Waals existent dans le cas d’un contact NTC-PEMA. Les données de nos simulations de DME concordent raisonnablement avec les résultats expérimentaux. Nous rapportons ensuite la résistance thermique de contact entre QCG et un substrat de SiO2, qui peut être contrôlée par le nombre de couches de graphène. Avec l’avantage d’une interface résistante, nous montrons que des super-réseaux SiO2/QCG ont une conductivité thermique descendant sous 0.30 W/mK, ce qui est une perspective prometteuse pour l’isolation thermique à l’échelle du nanomètre. Dans la dernière partie, nous recherchons la dépendance de la résistance thermique inter-plan avec le nombre de couches de graphène pour des QCG suspendus ou supportés. Nous montrons que la présence d’un substrat de dioxyde de silicium peut significativement réduire les résistances inter-plan de QCG possédant peu de couches de graphène, et la conductivité thermique effective est augmentée en accord. Le modèle de Frenkel-Kontorova a été introduit pour expliquer les bandes interdites induites par le substrat dans la relation de dispersion de QCG et le transfert d’énergie thermique correspondant. L’augmentation de la conduction thermique inter-plan est attribuée au rayonnement de phonons à l’interface QCG-substrat, qui redistribue l’énergie se propageant dans le plan du QCG en énergie dans la direction inter-plan et dans le substrat. / This thesis is devoted to the calculation of thermal contact resistance in various molecular systems based on carbon nanotubes (CNTs) and few layer graphene (FLG). This work has been performed through equilibrium molecular dynamics (EMD) simulations. We adopted the temperature difference fluctuations method in our EMD calculations. This method only needs the input of the temperatures of the subsystems whereas the heat flux, which is involved in all the other approaches, remains more difficult to compute in terms of simulation time and algorithm. Firstly, three cases were studied to validate this method, namely: (i) Si/Ge superlattices; (ii) diameter modulated SiC nanowires; and (iii) few-layer graphenes. The validity of the temperature difference fluctuations method is proved by equilibrium and non-equilibrium MD simulations. Then, by using this method, we show that an azide-functionalized polymer (HLK5) has a lower contact resistance with CNT than the one between CNT and PEMA, because HLK5 could form covalent bonds (C-N bonds) with CNT through its tail group azide, while only weak Van der Waals interactions exist in the case of CNT-PEMA contact. The data from our EMD simulations match with the results from experiments in a reasonable range. We then report the thermal contact resistance between FLG and a SiO2 substrate, which could be tuned with the layer number. Taking advantage of the resistive interface, we show that a SiO2 /FLG superlattices have a thermal conductivity as low as 0.30 W/mK, exhibiting a promising prospect in nano-scale thermal insulation. In the last part, we investigated the layer number dependence of the cross-plane thermal resistances of suspended and supported FLGs. We show that the existence of a silicon dioxide substrate can significantly decrease the cross-plane resistances of FLGs with low layer numbers, and the effective thermal conductivities were increased accordingly. The Frenkel-Kontorova model was introduced to explain the substrate-induced band gaps in FLG dispersion relations and the corresponding thermal energy transfer. The enhanced thermal conduction in the cross-plane direction is ascribed to the phonon radiation that occurs at the FLG-substrate interface, which re-distributes the FLG in-plane propagating energy to the cross-plane direction and to the substrate.

Experimental and theoretical analyses have been conducted upon electrical connector contacts under low frequency fretting conditions. The phenomena of "fretting" -relative micromovements in the components parts of an electrical contact - is known to take a major role in the degeneration of electrical contacts. Low frequency fretting is of particular interest and is typically caused by thermal differential expansion of the component parts due to temperature changes in the environment or the device itself. This thesis begins with a survey of possible failure mechanisms of the contact system. These are analysed and classified into three groups of chemical, physical, and mechanical degradation mechanisms. Fretting has been classified under the mechanical mechanism of degradation but is reported to exacerbate other degradation mechanisms resulting in the phenomena of "fretting corrosion". Developments in contact technology are then surveyed with the emphasis of this study on lubrication of the contact system. A novel fretting simulation apparatus has been developed to study the degradation mechanisms upon the contact system resulting from low frequency micromovements. The study includes investigations on the simulation apparatus of the contact system under different conditions. Particular! y emphasis is given to contacts under the conditions of electrical load and lubrication. Novel trends in the contact performance are reported with respect to electrical contact resistance, corrosion and wear of the contact interface. It is shown that electrically loading or lubricating the contact system has dramatic effects upon the contact performance. Chemical, physical and mechanical mechanisms at the contact interface are presented to explain the contact behaviour under several conditions of low frequency fretting. A "Two Process Model" is proposed which summarises the interaction of these different mechanisms. This model consists of two processes in balance - contact cleaning and contact degradation processes - which either increases or reduces the electrical area of contact. A theoretical computer simulation model is proposed for evaluating contact resistance behaviour of a fretting contact system under several conditions, particularly conditions of electrically loaded and lubricated conditions. Chemical, physical and mechanical mechanisms and their interact are simulated in the model using the Monte Carlo technique.

La production d'acier fait partie des productions mondiales les plus consommatrices d'énergie. L'état de l'art montre que les brames, après la coulée continue, sont refroidies à l'air libre de 900 °C à la température ambiante. Durant ce processus 540 MJ/tonne d'acier sont perdues. Cette thèse a permis de définir une méthode et un équipement aptes à extraire de l'énergie à haute valeur exergétique lors du refroidissement.Deux voies de récupérations sont présentées. La première voie est via un cycle thermodynamique direct. Le cycle choisi pour cette voie est le cycle de Hirn avec resurchauffe ayant un rendement global de 30 % produisant 10 MW de puissance électrique. La deuxième voie est via un système indirect utilisant le SYLTHERM 800 comme fluide caloporteur entre la brame et un cycle ORC, fonctionnant avec du R-245fa et avec un rendement globale de 17,6 %. Dans les deux configurations, les transferts thermiques choisis sont la conduction et le rayonnementUn banc d'essais, dimensionné utilisant la technique de similitude, a permis d'étudier les transferts thermiques intervenant dans l'équipement de récupération. La variation de la résistance de contact à l'interface brame-sole est étudiée en fonction de la température ainsi que le comportement thermique de l'échangeur de conduction. L'étude thermodynamique ainsi que l'étude thermique ont permis d'effectuer un pré-dimensionnement de l'équipement de récupération pour les deux configurations étudiées.Un modèle numérique utilisant la méthode des réseaux de composants est élaboré. Ce modèle est capable de reproduire les mêmes phénomènes physiques que ceux intervenant dans l'équipement de récupération / Steel production industry is one of the most energy consuming sectors. The state-of-the-art indicates that steel slabs leaving the continuous casting process are cooled without energy recovery by radiating to the atmosphere and convection. Not only a large amount of energy is wasted but this type of cooling is time consuming. During the cooling process of steel slabs from an initial temperature of approximately 900°C to outdoor air temperature, 580 MJ per ton of steel are wasted. This study has defined a method and an equipment capable of extracting the energy at high exergy value during cooling.The energy could be recovered using two different systems. The first is a direct thermodynamic generation cycle. The selected direct cycle is the Hirn cycle with intermediate reheating having an overall efficiency of 30 % and producing about 10 MW electric power. The second is an indirect system using SYLTHERM 800 as an intermediate heat transfer fluid between the metal slabs and an organic Rankine cycle using R-245fa as a working fluid with 17.6 % efficiency and producing about 6 MW. In both systems the dominant heat transfers to recover heat are conduction for the floor heat exchanger and radiation for the ceiling heat exchanger.A test bench was mounted, using a similitude technique, to study heat transfers. The variation of the thermal contact resistance as a function of the contact temperature is studied as well as the thermal behaviour of the conduction heat exchanger. The thermodynamic and the thermal studies led to a preliminary design of the recovery equipment.A numerical model is developed using the component interaction network. This model can reproduce the same physical phenomena taking place in the recovery equipment.

Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity. Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.