Neste trabalho, diferentes tipos de microestruturas foram geradas por torneamento com ferramenta de diamante de ponta única e microendentação para serem replicadas através da prensagem a quente. Testes foram realizados para ser avaliada a geração destas microestruturas por dois métodos distintos: microdeformação e microusinagem, planejados para observar a replicação gerada por marca de endentação Vickers (piramidal) e, remoção de material (torneamento com ferramenta de diamante de ponta única). Uma revisão no processo de manufatura aplicada para a replicação de microestruturas é apresentada. Os materiais usados como molde e réplica foram o cobre eletrolítico e o polimetilmetacrilato (PMMA), respectivamente. Inicialmente, a usinabilidade do cobre eletrolítico foi avaliada sob diferentes condições de corte, a fim de determinar parâmetros apropriados de torneamento para obter um fino revestimento de superfície final (rugosidade). Observou-se que para avanços (f) de 10 mícrons por revolução e profundidade de corte (ap) de 5 mícrons, a superfície apresentou um baixo valor de rugosidade, isto é, 2,81 nm para rugosidade média (Ra) e 13,4 nm para rugosidade teórica (Rt). Além disso, observou-se que a microestrutura do material mostrou-se de fundamental papel na rugosidade, por conta da recuperação elástica dos grãos devido a anisotropia da estrutura policristalina do cobre. As microestruturas geradas para a replicagem foram: a) lente esférica, b) perfil senoidal e sulcos concêntricos. Os resultados mostraram que é viável a reprodução, com boa conformidade das microestruturas, por meio de prensagem a quente. Observou-se que as bordas e as superfícies finas com rugosidade em torno de 10 nm rms foram bem replicadas. / In this work, different types of microstructures were generated by single point diamond turning and microindentation for will replicated through the hot embossing. Tests were carried to evaluate the generation these microstructures by two distinct methods: micro-deformation and micro-machining, planned to observe the replication of the mark generated by the Vickers indenter (Pyramidal) and the latter by material removal (single point diamond turning). A review on several manufacturing processes applied to replication of microfeatures, is presented. The materials used as mould and replication workpiece were electroless copper and polymethylmethacrylate (PMMA), respectively. Initially, the machinability of electroless copper was evaluated under different cutting conditions to determinate appropriate turning parameters to obtain very fine surface finish (roughness). It was observed that for f = 10 microns of revolution (feed rate) and ap = 5 microns (depth of cut), the surface presented the roughness’ lowest value, i.e., 2,81 nm to medium roughness (Ra) and 13,4 nm to theoretical roughness (Rt). Moreover, it was observed that the microstructure of the material plays a fundamental role on roughness, because of the elastic recovery of grains due to the anisotropy of the polycrystalline structure of copper. The microfeatures generated were the following: a) spherical lens, b) sinusoidal profile and concentrical grooves. The results showed that it is feasible to reproduce, with good agreement, the microfeatures by means of hot embossing. It was observed that thin edges and fine surfaces with roughness around 10 nm rms were well replicated.

This thesis focuses on improving the adhesion of electroless metal layers plated to pit contacts in interdigitated, backside buried contact (IBBC) solar cells. In an electrolessly plated, pit contact IBBC cell, the contact grooves are replaced with lines of pits which are interconnected by the plated metal. It is shown, however, that electroless metal layers, plated by the standard IBBC plating sequence, are not adherent on pit contact IBBC solar cells. The cause of this adhesion problem is investigated by examining the adhesive properties of each of the metal layers in the electroless metallization sequence on planar test structures. This investigation reveals that Pd activation of heavily P diffused Si impedes Ni silicide growth and that, in the absence of a silicide at the Ni/Si interface, an electrolessly plated Cu layer will cause the underlying Ni layer to peel away from the substrate. It is also found that the Ni silicidation process itself intermittently causes the unreacted Ni to spontaneously peel away from the substrate. An electroless metallization sequence that results in thick, adhesive Cu deposits on planar &lt 100&gt surfaces is developed in this thesis. It is shown that this process leads to the formation of a Ni silicide on both n- and p- type, heavily diffused surfaces. Fully plated, pit contact IBBC solar cells were not able to be fabricated during the course of this work but it is reasonable to expect that the modified plating sequence developed in this work will result in the metal layers being adhesive on these cells.

<p>The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.</p>

<p>Materials prepared on the nanoscale often exhibit many different properties compared to the same materials in their bulk-state. Interest in nanostructured materials has increased because of these properties in fields such as microelectronics, catalysis, optics and sensors. This increased interest in nanostructured materials calls for new and more precise fabrication techniques.</p><p>This thesis describes how to use the porous anodic aluminium oxide as a template for the fabrication of a variety of nanostructured materials. Palladium and copper nanoparticles were deposited along the pore walls in anodic aluminum oxide using electroless deposition and atomic layer deposition. In both cases, it was possible to control the size of the nanoparticles by carefully monitoring the deposition parameters. The thesis also describes how Prussian blue nanoparticles and nanotubes can be fabricated using the anodic aluminium oxide as a template. The deposition of Prussian blue was performed by a sequential wet-chemical method. By using atomic layer deposition, it was also possible to deposit thin films of amorphous Nb2O5 on the pore walls. When the template was removed by etching, freestanding nanotubes were obtained. The anodic aluminium oxide membrane was also used as a mask for high energy (MeV) ion irradiation of an underlying substrate. The tracks produced were etched away with hydrogen fluoride. In this way, it was possible to transfer the highly ordered porous pattern from the mask onto other oxides such as SiO2 and TiO2.</p><p>All fabricated structures were characterized using a variety of analysis techniques: scanning electron microscopy for evaluating sample morphology; transmission electron microscopy for better resolved investigations of the morphology; X-ray diffraction to assess crystallinity; energy dispersive spectroscopy and X-ray fluorescence spectroscopy to determine the elemental composition and identify possible contaminants.</p><p>The general aim of the work described in this thesis has been to create a set of tools for use in the fabrication of a variety of nanostructured materials, whose dimensions composition can be tailored by selecting appropriate fabrication methods and parameters.</p>

Materials prepared on the nanoscale often exhibit many different properties compared to the same materials in their bulk-state. Interest in nanostructured materials has increased because of these properties in fields such as microelectronics, catalysis, optics and sensors. This increased interest in nanostructured materials calls for new and more precise fabrication techniques. This thesis describes how to use the porous anodic aluminium oxide as a template for the fabrication of a variety of nanostructured materials. Palladium and copper nanoparticles were deposited along the pore walls in anodic aluminum oxide using electroless deposition and atomic layer deposition. In both cases, it was possible to control the size of the nanoparticles by carefully monitoring the deposition parameters. The thesis also describes how Prussian blue nanoparticles and nanotubes can be fabricated using the anodic aluminium oxide as a template. The deposition of Prussian blue was performed by a sequential wet-chemical method. By using atomic layer deposition, it was also possible to deposit thin films of amorphous Nb2O5 on the pore walls. When the template was removed by etching, freestanding nanotubes were obtained. The anodic aluminium oxide membrane was also used as a mask for high energy (MeV) ion irradiation of an underlying substrate. The tracks produced were etched away with hydrogen fluoride. In this way, it was possible to transfer the highly ordered porous pattern from the mask onto other oxides such as SiO2 and TiO2. All fabricated structures were characterized using a variety of analysis techniques: scanning electron microscopy for evaluating sample morphology; transmission electron microscopy for better resolved investigations of the morphology; X-ray diffraction to assess crystallinity; energy dispersive spectroscopy and X-ray fluorescence spectroscopy to determine the elemental composition and identify possible contaminants. The general aim of the work described in this thesis has been to create a set of tools for use in the fabrication of a variety of nanostructured materials, whose dimensions composition can be tailored by selecting appropriate fabrication methods and parameters.

The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.

Le développement récent des nanotechnologies a apporté un renouveau dans le domaine de recherche de la thermoélectricité. Ces dernières années, de nombreux travaux théoriques et expérimentaux ont montré qu’il était possible d’améliorer grandement le facteur de mérite ZT en utilisant des structures semi-conductrices de basse dimensionnalité. Plus particulièrement, les nanofils de Silicium ont été présentés comme de bons candidats pour des applications thermoélectriques. De nombreuses études ont effectivement souligné le fait qu’il est possible de réduire la conductivité thermique au sein des nanofils sans altérer le transport électrique, ce qui va bien évidemment dans le sens d’une amélioration du facteur de mérite. Cependant, il existe peu d’études expérimentales permettant de confirmer ces affirmations. Ici, nous proposons des expériences de microscopie thermique à balayage permettant d’effectuer de l’imagerie thermique de nanofils individuels avec une résolution spatiale de l’ordre de 100nm. A partir des images réalisées et d’un modèle décrivant le comportement thermique de la sonde utilisée, nous déterminons la conductivité thermique des nanofils caractérisés. La technique de mesure proposée est actuellement la seule permettant d’effectuer une mesure thermique statistique sur un grand nombre de nanostructures de type nanofil. Nous validons également la faisabilité d’une mesure de conductivité électrique de nanofils individuels par une technique de microscopie de résistance d’étalement. La conductivité électrique est également un paramètre déterminant, à prendre en compte dans l’évaluation du facteur de mérite thermoélectrique. / The recent development of nanotechnologies is like a revival for the field of research on thermoelectricity. Over the past decade, several studies have underlined the fact that the thermoelectric figure of merit can be drastically enhanced in low dimensional semiconductor systems. In particular, silicon nanowires have been recently presented as good candidates for thermoelectric applications. Although bulk silicon is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the electrical resistivity, Si nanowires show promise as high-performance thermoelectric materials. However, the experimental investigations on this topic do not abound in literature. Here, we propose experiments based on Scanning Thermal Microscopy which allows us to carry out thermal images of individual Si nanowires with a spatial resolution around 100 nm. Then, a model describing the SThM probe thermal behavior enables us to extract thermo-physical properties from the thermal images and finally to evaluate the thermal conductivity of the individually imaged Si nanowires. The technique proposed here is a promising one to perform statistical thermal conductivity measurements on a wide range of one-dimensional nano-objects with different compositions and geometries. Besides, we validate the feasibility of electrical conductivity measurements on individual Si nanowires, using Scanning Spreading Resistance Microscopy. Electrical conductivity is also a key parameter to determine the thermoelectric figure of merit.

Neste trabalho, diferentes tipos de microestruturas foram geradas por torneamento com ferramenta de diamante de ponta única e microendentação para serem replicadas através da prensagem a quente. Testes foram realizados para ser avaliada a geração destas microestruturas por dois métodos distintos: microdeformação e microusinagem, planejados para observar a replicação gerada por marca de endentação Vickers (piramidal) e, remoção de material (torneamento com ferramenta de diamante de ponta única). Uma revisão no processo de manufatura aplicada para a replicação de microestruturas é apresentada. Os materiais usados como molde e réplica foram o cobre eletrolítico e o polimetilmetacrilato (PMMA), respectivamente. Inicialmente, a usinabilidade do cobre eletrolítico foi avaliada sob diferentes condições de corte, a fim de determinar parâmetros apropriados de torneamento para obter um fino revestimento de superfície final (rugosidade). Observou-se que para avanços (f) de 10 mícrons por revolução e profundidade de corte (ap) de 5 mícrons, a superfície apresentou um baixo valor de rugosidade, isto é, 2,81 nm para rugosidade média (Ra) e 13,4 nm para rugosidade teórica (Rt). Além disso, observou-se que a microestrutura do material mostrou-se de fundamental papel na rugosidade, por conta da recuperação elástica dos grãos devido a anisotropia da estrutura policristalina do cobre. As microestruturas geradas para a replicagem foram: a) lente esférica, b) perfil senoidal e sulcos concêntricos. Os resultados mostraram que é viável a reprodução, com boa conformidade das microestruturas, por meio de prensagem a quente. Observou-se que as bordas e as superfícies finas com rugosidade em torno de 10 nm rms foram bem replicadas. / In this work, different types of microstructures were generated by single point diamond turning and microindentation for will replicated through the hot embossing. Tests were carried to evaluate the generation these microstructures by two distinct methods: micro-deformation and micro-machining, planned to observe the replication of the mark generated by the Vickers indenter (Pyramidal) and the latter by material removal (single point diamond turning). A review on several manufacturing processes applied to replication of microfeatures, is presented. The materials used as mould and replication workpiece were electroless copper and polymethylmethacrylate (PMMA), respectively. Initially, the machinability of electroless copper was evaluated under different cutting conditions to determinate appropriate turning parameters to obtain very fine surface finish (roughness). It was observed that for f = 10 microns of revolution (feed rate) and ap = 5 microns (depth of cut), the surface presented the roughness’ lowest value, i.e., 2,81 nm to medium roughness (Ra) and 13,4 nm to theoretical roughness (Rt). Moreover, it was observed that the microstructure of the material plays a fundamental role on roughness, because of the elastic recovery of grains due to the anisotropy of the polycrystalline structure of copper. The microfeatures generated were the following: a) spherical lens, b) sinusoidal profile and concentrical grooves. The results showed that it is feasible to reproduce, with good agreement, the microfeatures by means of hot embossing. It was observed that thin edges and fine surfaces with roughness around 10 nm rms were well replicated.

No description available.

Cílem této diplomové práce jse najít nejnižší možnou tloušťku nikl-fosforového povlaku, který může být galvanicky pokoven mědí bez defektů na horčíkové slitině, nikl-fosforového nebo měděného povlaku. V teoretické části jsou shrnuty poznatky o hořčíkových slitinách a jejich korozi. Navíc se teoreticá část zaměřuje na popis procesu bezproudého niklování a elektrochemického pokovování mědí a jejich porovnání. Na konci teoretické části je shrnut současný výzkum o elektrochemickém pokovování hořčíkových slitin. V experimentální části byl popsán proces přípravy povlaků Ni-P a Cu na horčíkové slitině AZ91. Na jedné vrstvě a dvojité vrstvě Ni-P povlaku byla provedena elektrodepozice mědi. Navíc byl diskutován vliv předůpravy před samotnou elektrodepozicí mědi. Za účelem zjištění korozních vlastností vzorků byl vykonán potenciodynamický test. Následně byly připraveny metalografické výbrusy jednotlivých vzorků a pomocí světelného a rastrovacího elektronového mikroskopu byla provedena charakterizace. Na konec bylo zjištěno prvkové složení jednotlivých povlaků pomocí EDX analýzy.