The effect of sub-lethal chlorine stress on various strains/serotypes of Salmonella on biofilm formation and thermal resistance was studied. The effect of oxidative stress (induced by 150 ppm of chlorine in TSB) on Salmonella biofilm formation on polystyrene and stainless steel surfaces at three temperatures (4°C, 30°C, and room temperature) in nutrient rich (full strength TSB) and nutrient limited conditions (1/10th TSB) was evaluated. On polystyrene surface, chlorine stressed S. Heidelberg (strain ID 72), S. Newport (strain ID 107) and S. Typhimurium (ATCC 14028) formed stronger (P < 0.05) biofilms at 30°C. On stainless steel, the chlorine stressed S. Heidelberg (ATCC 8326) and S. Enteritidis (ATCC 4931) at room temperature formed stronger (P < 0.05) biofilms as compared to the non-stressed control cells. The thermal resistance of short-term (1h) and long-term (27d) chlorine stressed Salmonella Heidelberg and S. Typhimurium were compared with the non-stressed controls at three different temperatures (55°C, 58°C and 61°C) and two growth phases (logarithmic and stationary). The short-term stressed log phase cells (both serotypes) were found to be more sensitive (P< 0.05) to thermal inactivation in TSB. Upon long-term sub-lethal chlorine exposure, Salmonella developed a rugose morphotype on tryptic soy agar at 37°C. The rugose morphotype provided significant thermal protection (P< 0.05) against heat stress as compared to smooth morphotype. In chicken broth, at 55°C, short-term chlorine stressed stationary phase S. Typhimurium displayed a higher D55 value compared to non-stressed cells. The findings from this research reveal that some Salmonella strains have the potential to form stronger biofilms and exhibit higher thermal tolerance upon exposure to sub-lethal chlorine concentration.

In Canada 15% of greenhouse gas (GHG) emissions are produced by the residential sector’s energy demand. The majority of the energy demand is space heating which is primarily met with natural gas combustion. Motivation exists to reduce GHG emissions due to their contribution to climate change. Integrated Community Energy Harvesting (ICE-Harvest) systems seek to integrate thermal and electrical energy production, storage, redistribution, and consumption in a way that reduces GHG emissions. Borehole thermal energy storage (BTES) is implemented in ICE-Harvest systems as seasonal thermal energy storage. This thesis presents a novel model of BTES thermal response with reduced complexity to aid in early siting, design, optimization, and control systems development work for ICE-Harvest systems. The reduced model can be used to approximate periodic steady state BTES thermal response. The model provides information on average ground storage volume temperature, outlet fluid temperature, heat exchanger fluid to storage volume heat transfer rate, storage volume top loss heat transfer rate, storage volume side and bottom loss heat transfer rate, and annual thermal energy storage efficiency which aids system modelling efforts for BTES in solar thermal and ICE-Harvest systems. The reduced model is formed from a solution of the thermal energy balance equations for the BTES ground storage volume and heat exchanger fluid with simplified operating conditions for a yearly BTES charging and discharging cycle. Ground storage volume temperature is lumped as a single value. Heat transfer rates between the storage volume and the heat exchanger fluid and the storage volume and its surroundings are modelled with periodic steady state thermal resistance values for the charging and discharging timesteps. A TRNSYS DST simulation of BTES is validated against measurements from a BTES installation and TRNSYS DST is used to generate the periodic steady state thermal resistance values the reduced model requires. The periodic steady state thermal resistance values of BTES charging and discharging are dependent on BTES design parameters (spacing between boreholes, number of boreholes, borehole depth, and storage volume size) and ground thermal properties (thermal capacity and thermal conductivity) which is presented in a series of parameter sweeps with respect to a reference simulation. The reduced model predicts periodic steady state average storage volume temperature with a RMSD of 0.96°C for charging and 1.3°C for discharging when compared to the TRNSYS DST reference simulation. The reduced model predicts the periodic steady state heat exchanger total energy transfer within 1.8% for the charging timestep and 2.8% for the discharging timestep when compared to the TRNSYS DST reference simulation. The reduced model’s periodic steady state thermal resistance values are demonstrated to be independent of heat exchanger fluid inlet temperature except for the side and bottom loss thermal resistance during discharging. The reduced model cannot replicate the change in heat transfer direction that occurs during BTES discharging when the temperature of the storage volume decreases below the temperature of the surrounding ground, however, the magnitude of the energy transfer that would occur is negligible compared to the magnitude of the BTES heat exchanger total energy transfer. / Thesis / Master of Applied Science (MASc)

Limited data are currently available characterizing the thermal resistance of foodborne pathogens in semolina flour and intermediate pasta matrices representative of commercial conditions during mixing, extrusion, and drying. These data are essential to pasta producers seeking to be compliant with federal regulations since Salmonella spp. and Escherichia coli demonstrate survival in wheat flour and dried pasta products. This study investigated the heat resistance of Salmonella, pathogenic E. coli, and E. faecium NRRL B-2354 in raw semolina flour and partially dried pasta intermediates via thermal death time (TDT) studies. This study also assessed the appropriateness of E. faecium NRRL B-2354 as a surrogate in semolina flour and pasta matrices. Inoculated pasta matrices equilibrated to target water activities of 0.85, 0.88, and 0.91 (measured at 25°C) underwent isothermal inactivation treatments at 65°C, 70°C, and 75°C. Serial dilution and direct plating methods allowed for estimation of bacterial survival at each treatment. In representative pasta matrices, the D-values for each microorganism increased as water activity decreased from 0.91 to 0.85. Surprisingly, Salmonella and E. coli did not exhibit significantly different thermal resistance in pasta. The greatest heat resistance was seen in semolina flour (aw 0.45). E. faecium was significantly more thermal resistant than both pathogens in all treatments when the temperature was ≤ 70°C. The results show that E. faecium strain NRRL B-2354 is not an ideal proxy for Salmonella and E. coli in semolina and pasta matrices. Analysis of the TDT data also found that a long-goods pasta drying process can achieve ≥7-log reductions of Salmonella and E. coli when following Good Manufacturing Practices.

Interconnects in power module result in thermal interfaces. The thermal interfaces degrade under thermal cycling, or chemical loading. Moreover, the reliability of thermal interfaces can be especially problematic when the interconnecting area is large, which increases its predisposition to generate defects (voids, delamination, or nonuniform quality) during processing. In order to improve the quality of the bonding process, as well as to be able to accurately assess interface reliability, it would be desirable to have a simple, reliable, and nondestructive measurement technique that would produce a 2-d map of the interface thermal resistance across a large bonded area. Based on the transient thermal method of JEDEC standard 51-14, we developed a measurement technique that involves moving a thermal sensor discretely across a large-area bonded substrate and acquiring the interface thermal resistance at each location. As detailed herein, the sensor was fabricated by packaging an IGBT bare die. An analytical thermal model was built to investigate the effects of thermal sensor packaging materials and structural parameters on the sensitivity of the measurement technique. Based on this model, we increased the detection sensitivity of the sensor by modifying the size of the sensor substrate, the material of the sensor substrate, the size of the IGBT bare die, the size of the heat sink, and the thermal resistance between sample and the heat sink. The prototype of the thermal sensor was fabricated by mounting Si IGBT on copper substrate, after which the Al wires were ultrasonic bonded to connect the terminals to the electrodes. The sensor was also well protected with a 3-d printed fixture. Then the edge effect was investigated, indicating the application of the thermal sensor is suitable for samples thinner than the value in TABLE 2 3. The working principle of the movable thermal sensor – Zth measurement and its structure function analysis – was then evaluated by sequence. The Zth measurement was evaluated by measuring the Zth change of devices induced by degradation in sintered silver die-attach layer during temperature cycling. At the end of the temperature cycling, failure modes of the sintered silver layer were investigated by scanning electron microscope (SEM) and X-ray scanning, to construct a thermal model for FEA simulation. The simulation results showed good agreement with the measured Zth result, which verified the accuracy of the test setup. The sensitivity of structure function analysis was then evaluated by measuring thermal resistance (Rth) of interface layers with different thermal properties. The structure function analysis approach successfully detected the Rth change in the thermal interface layer. The movable thermal sensor was then applied for 2d-mapping of the interface Rth of a large-area bonded substrate. Examining the test coupons bonded by sintered silver showed good and uniform bonding quality. The standard deviation of Rth is about 0.005 K/W, indicating the 95% confidence interval is about 0.01 K/W, which is commonly chosen as the error of measurement. The sensitivity of the movable thermal sensor was evaluated by detecting defects/heat channels of differing sizes. The 2-d mapping confirmed that the thermal sensor was able to detect defect/heat channel sizes larger than 1x1 mm2. The accuracy of the sensitivity was verified by FEA simulation. Moreover, the simulated results were consistent with the measured results, which indicates that the movable sensor is accurate for assessing interface thermal resistance. In summary, based on structure function analysis of the transient thermal impedance, the concept of a movable thermal sensor was proposed for two-dimensional mapping of interface thermal resistance. (1) Preliminary evaluation of this method indicated both transient thermal impedance and structure function analysis were sensitive enough to detect the thermal resistance change of thermal interface layers. With the help of transient thermal impedance measurement, we non-destructively tested the reliability of sintered silver die-attach layer bonded on either Si3N4 AMB or AlN DBA substrates. (2) An analytical thermal model was constructed to evaluate the design parameters on the sensitivity and resolution of the movable thermal sensor. A detailed design flow chart was provided in this thesis. To avoid edge effect, requirements on thickness and materials of test coupon also existed. Test coupon with smaller thermal conductivity and larger thickness had a more severe edge effect. (3) The application of the movable sensor was demonstrated by measuring the 2-d thermal resistance map of interface layers. The results indicated for bonded copper plates (k = 400 W/mK) with thickness of 2 mm, the sensor was able to detect defect/heat channel with size larger than 1x1 mm2. / Doctor of Philosophy / Interconnects in power module result in thermal interfaces. The thermal interfaces degrade during operation and their reliability can be especially problematic when the interconnecting area is large. In order to improve the quality of the bonding process, as well as to be able to accurately assess interface reliability, it would be desirable to have a simple, reliable, and nondestructive measurement technique that would produce a 2-d map of the interface thermal resistance across a large bonded area. Based on the transient thermal method of JEDEC standard 51-14, we developed a measurement technique that involves moving a thermal sensor discretely across a large-area bonded substrate and acquiring the interface thermal resistance at each location. As detailed herein, the sensor was fabricated by packaging an IGBT bare die, which allowed us to get a 2-d map of the interface thermal resistance. A thermal model was also constructed to guide the design of the sensor, to increase its performance. Moreover, the preliminary test of the test setup was conducted to prove its feasibility for the sensor. Eventually, the sensor’s performance and application was demonstrated by measuring the 2-d thermal resistance map of the bonded interfaces.

Because of the harsh climate of Saudi Arabia, residential buildings on average, consume more than half of the total consumed energy. A substantial share of energy goes to the air-conditioning of buildings. Cooling buildings during summer is a major environmental problem in many Middle Eastern countries, especially since the electricity is highly dependent on fossil fuels. The aim of this study is to obtain a clearer picture of how various measures on the building envelope affects the buildings energy consumption, which can be used as a tool to save energy for buildings in the Middle East. In this study, different energy efficiency measures are evaluated using energy simulations in IDA ICE 4.7 to investigate how much energy can be saved by modifying the building envelope. A two-storey residential building with 247 m2 floor area is used for the simulations. The measures considered are; modifications of the external walls, modification of the roof, window type, window area/distribution, modification of the foundation, shading, exterior surface colour, infiltration rate and thermal bridges. All measures are compared against a base case where the building envelope is set to resemble a typical Saudi Arabian residential. First, all measures are investigated one by one. Thereafter, combinations of the measures are investigated, based on the results from single measure simulations. All simulations are carried out for two cities in Saudi Arabia, both with arid desert climate. Riyadh (midlands) with moderately cold winters and Jeddah (west coast) with mild winter. The results from simulations of single measures show the highest energy savings when changing the window type from single clear glass to double glass with reflective surface saving 27 % energy (heating &amp; cooling) in Riyadh and 21 % in Jeddah. Adding insulation to an uninsulated roof saved up to 23 % and 21 % energy for Riyadh respectively Jeddah. Improvements of the thermal resistance of the exterior walls show 21 % energy savings in Riyadh and only 11 % in Jeddah. Lowering the window to wall ratio from 28 % to 10 % and changing the window distribution results in 19 % (Riyadh) and 17 % (Jeddah) energy savings. Adding fixed shades saves up to 8 % (Riyadh) and 13 % energy (Jeddah) when dimensioned for the peak cooling load. Using bright/reflective surface colour on the roof saves up to 9% (Riyadh) and 17 % (Jeddah) when the roof is uninsulated. For the exterior walls, bright/reflective surface saves up to 5 % (Riyadh) and 10 % (Jeddah) when the walls are uninsulated. The other single measures investigated show less than 7 % energy savings. The results for combined measures show the highest energy savings for two combined measures when improving the thermal resistance of the exterior walls and changing window area/distribution saving up to 52 % (Riyadh) and 39 % (Jeddah). When performing three measures the addition of improved thermal resistance and reflectance of the windows resulted in the highest energy savings, saving up to 62 % (Riyadh) and 48 % (Jeddah). When adding a fourth measure, improving the thermal resistance of the slab shows the highest energy savings, 71 % (Riyadh) and 54 % (Jeddah). Applying all measures on the building envelope results in 78 % (Riyadh) and 62 % (Jeddah) energy savings. Significant energy savings can be achieved with measures on the building envelope. Major savings can be made by adding only 50-100 mm of insulation to the exterior walls and roof. Decreased window area and improvements on the thermal resistance and reflectance on the windows result in significant energy savings. Energy savings achieved with shadings and reflective surface colours decrease significantly when the thermal resistance of the roof and external walls are improved. All measures concerning thermal resistance have a higher impact in Riyadh than in Jeddah due to that a large part of the total heating and cooling is air handling unit (AHU) cooling in Jeddah. AHU cooling is not affected significantly by measures on the building envelope. To optimise energy savings, measures on the building envelope should be considered in combination with measures concerning the AHU. / På grund av det hårda klimatet i Saudiarabien, konsumerar bostadshus mer än hälften av den totala energi som förbrukas. En stor del av den förbrukade energin går till luftkonditionering. Kylningen av byggnader är ett stort miljöproblem i många länder i Mellanöstern, särskilt eftersom elektriciteten till stor del är helt beroende av förbränning av fossila bränslen. Syftet med denna studie är att få en tydligare bild av hur olika åtgärder på klimatskalet påverkar byggnaders energiförbrukning. Tanken är att resultaten ska kunna användas som ett hjälpmedel vid design av mer energieffektiva byggnader i Mellanöstern. I denna studie är olika energieffektivitetsåtgärder utvärderade med hjälp av energisimuleringar i IDA ICE 4.7 för att undersöka hur mycket energi som kan sparas genom att modifiera klimatskalet. Ett bostadshus med 247 m2 golvyta i två våningar används för simuleringarna. De åtgärder som övervägs är; modifieringar av ytterväggar, modifiering av tak, fönstertyp, fönster area/ distribution, modifiering av fundamentet, skuggning, ytskikt, infiltration och köldbryggor. Alla åtgärder jämförs mot ett Base Case där klimatskalet är inställt för att likna en typisk bostad i Saudiarabiens. Först undersöks alla åtgärder en åt gången. Därefter undersöks kombinationer av de studerade åtgärderna, baserat på resultat från simuleringar av enskilda åtgärder. Alla simuleringar utförs för två städer i Saudiarabien, både med torrt ökenklimat. Riyadh (inlandet) med måttligt kalla vintrar och Jeddah (västkusten) med mild vinter. Resultatet från simuleringar av enskilda åtgärder visar högst energibesparing när fönstertypen byts ut från enkelt klarglas till dubbelt reflekterande glas. Med byte av fönstertyp sparas upp till 27 % energi (uppvärmning och kylning) i Riyadh och 21 % i Jeddah. Att isolera taket sparar upp till 23 % och 21 % för Riyadh respektive Jeddah. Förbättrat värmemotstånd i ytterväggarna resulterar i upp till 21 % energibesparing i Riyadh och endast 11 % i Jeddah. Minskning av fönsterarean från 28 % av väggytan till 10 % och omplacering av fönsterna ger19 % (Riyadh) och 17 % (Jeddah) energibesparingar. Solavskärmning med hjälp av fasta skärmtak och fenor sparar 8 % (Riyadh) och 13 % energi (Jeddah) när de är dimensionerad för maximalt kylbehovet. Använda ljus/reflekterande yta på taket sparar upp till 9 % (Riyadh) och 17 % (Jeddah) när taket är oisolerad. För ytterväggar, sparar ljust/reflekterande ytskikt upp till 5 % (Riyadh) och 10 % (Jeddah) när väggarna är oisolerad. De övriga enskilda åtgärderna som undersökts visar mindre än 7 % energibesparing. Resultaten för kombinerade åtgärder visar högst energibesparingar för två kombinerade åtgärder när ytterväggens värmemotstånd förbättras tillsammans med mindre fönsterarea och ändrad fönsterplacering. De två åtgärderna sparar upp till 52 % energi i Riyadh och 39 % i Jeddah. När tre åtgärder utförs, fås den högsta energibesparingen med de två åtgärderna ovan med tillägg av förbättrade fönster med lägre u-värde och högre reflektants. Tillsammans resulterar de tre åtgärderna i en energibesparing upp till 62 % för Riyadh och 48 % för Jeddah. När man lägger till en fjärde åtgärd, fås den högsta besparingen med tillägg av förbättrat u-värde på grunden till de tre tidigare åtgärderna. De fyra åtgärderna sparar upp till 71 % energi i Riyadh och 54 % i Jeddah. Tillämpning av alla åtgärder på klimatskalet resulterar i 78 % (Riyadh) och 62 % (Jeddah) energibesparing. Betydlig reducering av energianvändningen kan uppnås med åtgärder på byggnadens klimatskal. Stora besparingar fås med endast 50 – 100 mm isolering i ytterväggar och tak. Att minska fönsterarean och förbättra fönsternas u-värde och reflektivitet bidrar till stora energibesparingar.  Besparingarna som fås vid solavskärmning och reflektiva ytor på tak och väggar minskar signifikant när taket och ytterväggarna isoleras. Alla åtgärder som förbättrar u-värdet på klimatskalet har en större inverkan i Riyadh än i Jeddah på grund av att en större andel av total uppvärmning och kylning upptas av kylning av inkommande luft i ventilationen. Energin som behövs för att kyla inkommande luft påverkas inte nämnvärt av åtgärderna på klimatskalet. För att optimera energibesparingarna ytterligare, bör åtgärder på klimatskalets övervägas tillsammans med energieffektivitetsåtgärder av ventilationen.

O Mycobacterium bovis causa a tuberculose zoonótica, doença que afeta os animais e o homem podendo causar a morte, sendo o leite uma importante via de transmissão da doença para o homem. A pasteurização do leite é a principal medida para quebrar essa cadeia de transmissão, cujos parâmetros de tempo e temperatura foram definidos através de experimentos que datam desde o fim do século XIX, com base na resistência térmica do M. bovis e da Coxiella burnetti, então considerados os mais resistentes patógenos não formadores de esporos que contaminam o leite. No Brasil são aprovados os binômios 62&ordm;C a 65&ordm;C por 30 minutos e 72&ordm;C a 75&ordm;C por 15 a 20 segundos. Entretanto, com o passar dos anos e surgimento de novas tecnologias (PCR, Spoligotyping e outras técnicas biomoleculares) foi possível observar diferenças genéticas intra-espécie. Assim, este projeto tem por objetivo avaliar e comparar o comportamento de dois espoligotipos de M. bovis (SB0120 e SB1033) frente aos dois protocolos de pasteurização utilizados no país. Para tanto, leite integral UHT foi contaminado com esses espoligotipos e submetido aos dois processos térmicos, em Banho-Maria. O leite foi semeado em meio sólido Stonebrink-Leslie e a contagem de colônias foi feita após 45 dias de incubação a 37&ordm;C. Não houve neste experimento diferença entre as resistências térmicas dos dois espoligotipos, no entanto detectou-se uma maior importância da fase de aquecimento na redução do agente do que da fase de manutenção da temperatura, para os dois espoligotipos, nos dois processos. / Mycobacterium bovis causes zoonotic tuberculosis disease that affects animals and humans and can cause death, the milk is an important route of disease transmission to humans. The pasteurization of milk is the main measure to break the transmission chain, whose time and temperature parameters were defined by experiments dating from the late nineteenth century, based on thermal resistance of M. bovis and Coxiella burnetti, considered then the most resistant non-spore-forming pathogens that contaminate the milk. In Brazil, there are two approved binomials 62&ordm;C to 65&ordm;C for 30 minutes and 72&ordm;C to 75&ordm;C for 15 to 20 seconds. However, over the years and the emergence of new technologies (PCR, spoligotyping and other biomolecular techniques) was observed genetic differences intra-species. Thus, this project aims to evaluate and compare the behavior of two spoligotypes of M. bovis (SB0120 and SB1033) compared to the two pasteurization protocols used in the country. To this end, UHT milk was contaminated with these spoligotypes and subjected to two thermal processes in a water bath. The milk was streaked on solid medium Stonebrink-Leslie and colony counting was done after 45 days of incubation at 37&ordm;C. This experiment showed that there was no difference between the thermal resistances of the two spoligotypes, however it was detected a greater importance of the heating phase in reducing the agent that the maintenance phase of temperature for the two spoligotypes, in both cases.

<p>The thesis covers the following topics:</p> <p>1. aggregation and size effect on metal-polymer nanocomposite thermal interface materials</p> <p>2. diffusion limited cluster aggregation lattice simulation on thermal conductivty</p> <p>3. thermal interfacial resistance reduction between metal and dielectric materials by inserting an intermediate metal layer</p> <p>4. absence of coupled thermal interfaces in al2o3/ni/al2o3 sandwich structure</p> <p>5. ultra-efficient low-cost radiative cooling paints</p>

This dissertation presents thermal and thermoelectric measurements of nanostructures. Because the characteristic size of these nanostructures is comparable to and even smaller than the mean free paths or wavelengths of electrons and phonons, the classical constitutive laws such as the Fourier’s law cannot be applied. Three types of nanostructures have been investigated, including nanoscale constrictions patterned in a sub-100 nm thick silicon film, monatomic thick graphene ribbons supported on a silicon dioxide (SiO₂) beam, and indium antimonide (InSb) nanowires. A suspended measurement device has been developed to measure the thermal resistance of 48-174 nm wide constrictions etched in 35-65 nm thick suspended silicon membranes. The measured thermal resistance is more than ten times larger than the diffusive thermal resistance calculated from the Fourier’s law. The discrepancy is attributed to the ballistic thermal resistance component as a result of the smaller constriction width than the phonon-phonon scattering mean free path. Because of diffuse phonon scattering by the side walls of the constriction with a finite length, the phonon transmission coefficient is 0.015 and 0.2 for two constrictions of 35 nm x 174 nm x220 nm and 65 nm x 48 nm x 50 nm size. Another suspended device has been developed for measuring the thermal conductivity of single-layer graphene ribbons supported on a suspended SiO₂ beam. The obtained room-temperature thermal conductivity of the supported graphene is about 600 W/m-K, which is about three times smaller than the basal plane values of high-quality pyrolytic graphite because of phonon-substrate scattering, but still considerably higher than for common thin film electronic materials. The measured thermal conductivity is in agreement with a theoretical result based on quantum mechanical calculation of the threephonon scattering processes in graphene, which finds a large contribution to the thermal conductivity from the flexural vibration modes. A device has been developed to measure the Seebeck coefficients (S) and electrical conductivities ([sigma]) of InSb nanowires grown by a vapor-liquid-solid process. The obtained Seebeck coefficient is considerably lower than the literature values for bulk InSb crystals. It was further found that decreasing the base pressure during the VLS growth results in an increase in the Seebeck coefficient and a decrease in the electrical conductivity, except for a nanowire with the smallest diameter of 15 nm. This trend is attributed to preferential oxidation of indium by residual oxygen in the growth environment, which could cause increased n-type Sb doping of the nanowires with increasing base pressure. The deviation in the smallest diameter nanowire from this trend indicates a large contribution from the surface charge states in the nanowire. The results suggest that better control of the chemical composition and surface states is required for improving the power factor of InSb nanowires. On approach is to use Indium-rich source materials for the growth to compensate for the loss of indium due to oxidation by residual oxygen. / text

Carbon nanotube (CNT) forests have outstanding thermal, electrical, and mechanical properties, which have generated significant interest as thermal interface materials (TIMs). Some drawbacks to using CNTs as TIMs include poor substrate adhesion, high interface resistances inhibiting thermal transport, and lack of electrical insulation in electronic component applications. It is thus useful to be able to modify CNTs to reduce their electrical conductivity while maintaining high thermal conductivity and interface conductance, and high mechanical compliance. A recent report suggests that nanoscale oxide coatings could be applied to CNTs in forests without changing the mechanical deformation behavior of the forests. Oxide coatings could also provide environmental stability as well as better adhesion to the substrate compared to pristine CNT forests. In this study, we investigated thermal and electrical resistance of CNT forests with an oxide coating. Low-pressure chemical vapor deposition (LPCVD) was used to produce CNTs on high-conductivity Si substrates. Plasma-enhanced atomic layer deposition (PALD) was used to deposit Al2O3 on individual CNTs in forests. This process was facilitated by O2 plasma pretreatment to functionalize the surface of the CNTs and nucleate oxide growth. Several analytical techniques were used to characterize the CNT-oxide composites, including scanning electron microscopy, Raman and X-ray photoelectron spectroscopy. Thermal conductivity and thermal interface resistance were measured using a modified photoacoustic technique. The oxide coating had no significant effect on the effective thermal conductivity of the forests, in contrast to expectations of increased phonon scattering. Electrical resistivity measurements were made and a threefold increase was observed for the oxide-coated forests. This approach could emerge as a promising route to create a viable TIM for thermally conductive and electrically insulating applications.

De nos jours, l'industrie microélectronique utilise des fréquences de fonctionnement plus élevées dans les composants commercialisés. Ces fréquences entraînent des températures de fonctionnement plus élevées et limitent donc l'intégrité et la durée de vie des composants électroniques. Cependant, les besoins actuels nécessitent des dispositifs miniaturisés et de haute densité de puissance. De ce fait, la dissipation thermique dans les composants microélectroniques s’avère capitale. Ainsi, des drains thermiques sont utilisés pour évacuer la chaleur produite par le fonctionnement du composant. Les drains thermiques actuels sont composés de métaux, tels que le cuivre et l’aluminium, présentant des conductivités et des coefficients de dilatation thermiques élevés. Néanmoins, les coefficients de dilatation thermique des différents matériaux présents dans un circuit peuvent induire des contraintes thermo-mécaniques aux interfaces et engendrer une défaillance des composants après plusieurs cycles de fonctionnement. Dans ce contexte, nous proposons de remplacer ces drains métalliques par un système composite à matrice cuivre renforcée par du carbone, sur lequel est déposé un diffuseur thermique sous forme de diamant. Ces composites Cu/C présentent des propriétés thermo-mécaniques adaptatives pouvant palier aux contraintes induites durant l’utilisation des composants. Le transfert optimal des propriétés dans les MMC est souvent compromis par l'absence de liaison chimique interfaciale, en particulier dans les systèmes non réactifs telsque Cu/C. Cependant, pour un assemblage thermiquement efficace, l'interface devrait permettre un bon transfert de charges thermo-mécaniques entre les matériaux. L'objectif de cette étude est de combiner les propriétés exceptionnelles du diamant et les propriétés thermo-mécaniques adaptatives des MMC. Les composites à matrice de cuivre renforcés au carbone sont synthétisés à l'aide d'un processus dit semi-liquide pour obtenir des gradients de composition et des propriétés optimisées d'interface matrice - renfort. Par conséquent, des éléments d'alliage sont insérés dans le matériau pour former des interphases de carbure à l'interface Cu/C. Le film mince de diamant est obtenu par dépôt chimique en phase vapeur assisté par laser. Cette méthode de dépôt permet d’agir sur la qualité du film ainsi que sur l’adhésion avec le substrat composite. Finalement, une importance particulière est portée à l’influence des interfaces sur les propriétés thermiques tant au sein du matériau composite (interface matrice – renfort), qu’au sein de l’assemblage film diamant – MMC.Ces travaux ont été menés dans le cadre d’un accord franco-américain de cotutelle de thèse entre l’Institut de Chimie de la Matière Condensée de l’Université de Bordeaux, en France, et le département d’Ingénierie Electrique de l’Université du Nebraska-Lincoln, aux Etats-Unis. Ils ont été financés, en France, par la Direction Générale de l’Armement (DGA), et par l’équivalent Américain aux Etats-Unis. / Today, the microelectronics industry uses higher functioning frequencies in commercialized components. These frequencies result in higher functioning temperatures and, therefore, limit a component’s integrity and lifetime. Until now, heat-sink materials were composed of metals which exhibit high thermal conductivities (TC). However, these metals often induce large coefficient of thermal expansion (CTE) mismatches between the heat sink and the nonmetallic components of the device. Such differences in CTEs cause thermomechanical stresses at the interfaces and result in component failure after several on/off cycles.To overcome this issue, we suggest replacing the metallic heat sink materials with a heat-spreader (diamond film) deposited on metal matrix composites (MMCs), specifically, carbon-reinforced copper matrices (Cu/C) which exhibit optimized thermomechanical properties. However, proper transfer of properties in MMCs is often compromised by the absence of effective interfaces, especially in nonreactive systems such as Cu/C. Therefore, the creation of a chemical bond is ever more relevant. The goal of this research was to combine the exceptional properties of diamond by means of a thin film and the adaptive thermomechanical properties of MMCs. Carbon-reinforced copper matrix composites were synthesized using an innovative solid-liquid coexistent phase process to achieve designed composition gradients and optimized matrix/reinforcement interface properties. In addition, the lack of chemical affinitybetween Cu and C results in poor thermal efficiency of the composites. Therefore, alloying elements were inserted into the material to form carbide interphases at the Cu/C interface. Their addition enabled the composite’s integrity to be optimized in order to obtain thermally efficient assemblies. The diamond, in the form of a thin layer, was obtained by laser-assisted chemical vapor deposition. This process allowed action on the film’s phase purity and adhesion to the substrate material. Of particular importance was the influence of the interfaces on thermal properties both within the composite material (matrix-reinforcement interface) and within the diamond film-MMC assembly. This work was carried out within the framework of a Franco-American agreement between the Institute of Condensed Matter Chemistry of the University of Bordeaux in France and the Department of Electrical Engineering at the University of Nebraska-Lincoln, in the United States. Funding, in France, was provided by the Direction Générale de l’Armement (DGA), and by the American equivalent in the United States.