Letteratura scientifica selezionata sul tema "Nanocristaux de diamant"

Les microscopies optiques super-résolues aident à mieux comprendre certains mécanismes biomoléculaires, notamment au sein des neurones. Nous avons construit un tel microscope de type STED (STimulated Emission Depletion) pour observer des défauts azote-lacune (NV) fluorescents dans le diamant, et avons atteint une résolution de 50 nm. À plus long terme, cet instrument permettra d'étudier l'organisation macromoléculaire de protéines impliquées dans la plasticité synaptique, et marquées avec des nanodiamants (ND) fluorescents. Dans cette perspective, nous avons étudié la limite de résolution du STED pour des ND de tailles sub-longueur d'onde. Nos expériences, menées avec l'équipe de Stefan Hell (Max Planck Institute for Biophysical Chemistry) ont montré que la taille du spot STED d'un NV dans un ND pouvait atteindre 10 nm, performance similaire à celle obtenue dans un diamant macroscopique. Nous pouvons aussi résoudre plusieurs centres NV dans un ND séparés de seulement ~15 nm. Ces résultats sont en accord avec les simulations numériques faites par l'équipe de Jean-Jacques Greffet (Laboratoire Charles Fabry). En parallèle, nous avons démontré l'internalisation spontanée de ND fluorescents dans des neurones corticaux d'embryons de souris en culture primaire, et étudié leur colocalisation avec des vésicules du réseau trans-Golgi. Enfin, nous avons débuté l'étude du trafic des vésicules contenant les ND et montré qu'il dépend du réseau de microtubules. Les paramètres du mouvement sont compatibles avec ceux des moteurs moléculaires, mais nous nous attendons à ce qu'ils soient différents dans le cas de la surexpression de protéines impliquées dans le trafic (travail en cours).

Les microscopies optiques super-résolues aident à mieux comprendre certains mécanismes biomoléculaires, notamment au sein des neurones. Nous avons construit un tel microscope de type STED (STimulated Emission Depletion) pour observer des défauts azote-lacune (NV) fluorescents dans le diamant, et avons atteint une résolution de 50 nm. À plus long terme, cet instrument permettra d’étudier l’organisation macromoléculaire de protéines impliquées dans la plasticité synaptique, et marquées avec des nanodiamants (ND) fluorescents. Dans cette perspective, nous avons étudié la limite de résolution du STED pour des ND de tailles sub-longueur d’onde. Nos expériences, menées avec l’équipe de Stefan Hell (Max Planck Institute for Biophysical Chemistry) ont montré que la taille du spot STED d’un NV dans un ND pouvait atteindre 10 nm, performance similaire à celle obtenue dans un diamant macroscopique. Nous pouvons aussi résoudre plusieurs centres NV dans un ND séparés de seulement ~15 nm. Ces résultats sont en accord avec les simulations numériques faites par l’équipe de Jean-Jacques Greffet (Laboratoire Charles Fabry). En parallèle, nous avons démontré l’internalisation spontanée de ND fluorescents dans des neurones corticaux d’embryons de souris en culture primaire, et étudié leur colocalisation avec des vésicules du réseau trans-Golgi. Enfin, nous avons débuté l’étude du trafic des vésicules contenant les ND et montré qu’il dépend du réseau de microtubules. Les paramètres du mouvement sont compatibles avec ceux des moteurs moléculaires, mais nous nous attendons à ce qu’ils soient différents dans le cas de la surexpression de protéines impliquées dans le trafic (travail en cours)
Super resolution microscopy techniques are a useful tool to understand some biomolecular mechanisms, particularly in neurons. We have built such a STED (STimulated Emission Depletion) microscope for observing Nitrogen-Vacancy (NV) fluorescent defect in diamond, and have reached a resolution of 50 nm. In the longer term, this instrument will study the macromolecular organization of proteins involved in synaptic plasticity and marked with fluorescent nanodiamonds (ND). In this context, we studied the resolution limit of STED for ND of subwavelength size. Our experiments, conducted with the team of Stefan Hell (Max Planck Institute for Biophysical Chemistry) showed that the STED spot size of an NV in ND could reach 10 nm, which is similar to performances obtained in a macroscopic diamond. We can also resolve several NV centers, which are separated from only ~15 nm in the same ND. These results are in agreement with numerical simulations carried out by the team of Jean-Jacques Greffet (Laboratoire Charles Fabry). In parallel, we have demonstrated the spontaneous internalization of fluorescent ND in primary culture of cortical neurons from mouse embryos, and studied their colocalization with vesicles of the trans-Golgi network. Finally, we started the study of trafficking vesicles containing ND and showed that it depends on the microtubule network. The motion parameters are compatible with those of molecular motors, but we expect them to be different in the case of overexpression of proteins involved in traffic (work in progress)

L'échange sécurisé d'une clé secrète entre deux interlocuteurs est une tâche compliquée. Dans un monde " classique ", il n'est pas possible de garantir qu'un espion n'a pas effectué une copie de cette clé lors de son échange. En 1984, un protocole basé sur les propriétés de la mécanique quantique a démontré la possibilité d'un échange inconditionnellement sûr d'une clé secrète entre deux interlocuteurs. Idéalement, le protocole utilise une source de photons uniques. L'information est alors codée, par exemple, sur la polarisation des photons. La sécurité est garantie par un choix aléatoire de la base de polarisation (Linéaire, Circulaire). Dans ce contexte, cette étude porte sur la réalisation d'une source de photons uniques et son application à la cryptographie quantique. Une source de photons uniques est obtenue par l'excitation impulsionnelle d'un dipôle unique. Le dipôle étudié dans ce travail est le centre NV dans le cristal de diamant. Il est constitué d'un atome d'azote et d'une lacune en substitution dans la maille cristalline du diamant. L'étude sous excitation continue de ce dipôle, à l'aide d'un microscope confocal, et d'un montage d'autocorrélation d'intensité montre que de par sa simplicité d'utilisation et de sa photo stabilité intrinsèque, il est un candidat de choix pour une source de photons uniques. En excitation impulsionnelle, on démontre que la source de photons uniques ainsi produite présente une grande efficacité de production de photons, et un très faible taux d'impulsions contenant deux photons. Finalement, cette source a été utilisée dans un montage de cryptographie quantique. Après une description des dispositifs expérimentaux de l'émetteur et du récepteur, nous décrivons une expérience de cryptographie quantique. Les résultats obtenus montrent un avantage quantitatif dans le taux de pertes admissibles en ligne en comparaison avec des prototypes basés sur une source cohérente atténuée
Secure key distribution between two persons is a complicated task. In a classical world, it is impossible to guarantee that an eavesdropper doesn't create a copy of the key during the exchange. In 1984 has been proposed a protocol based on the properties of quantum mechanics that assures an unconditionally secure exchange of secret keys. Ideally, the protocol uses single photon sources, the information being coded on the polarisation of the photons. The security is guaranteed by choosing randomly the polarisation base (Linear, Circular). In this context, this work describes the realisation of a single photon source, and it's application to quantum cryptography. A single photon source is obtained by pulsed excitation of a single dipole. The dipole studied in this work, is the NV center in diamond. It is composed of a Nitrogen atom and a Vacancy substituting two carbon atoms. Under continuous excitation the center has been studied with a confocal microscope and an intensity autocorrelation set-up. It has turned out to be a very good candidate for a single photon source since it is easy to manipulate and photostable. Under pulsed excitation, we show that this single photon source has great production efficiency, and a very low number of two-photon pulses. Finally, this source has been used in a quantum cryptography prototype. After a description of the experimental set-ups of the emitter and the receiver, we describe the realisation of a quantum cryptography experiment. The achieved performances show a quantitative advantage in the maximum tolerated tosses, compared to prototypes using faint laser pulses

Cette these s'inscrit dans le cadre d'un projet visant a utiliser un nanocristal de cdse individuel en tant que nano-source de photons excitee a l'aide des electrons issus de la pointe d'un stm. Nous avons devloppe une methode de synthese permettant d'obtenir des solutions bien purifiees de nanocristaux et de nanobatonnets de cdse. Parallelement, nous avons mis au point une methode de depot par injection pulsee sous ultra-vide permettant de deposer ces nano-objets sur les surfaces de silicium hydrogenee, diamant hydrogenee et graphite, propres et reconstruites. Grace au stm, nous avons pu verifier que ces surfaces demeurent propres et reconstruites apres le depot des nanocristaux. Nous avons egalement procede a l'observation de ces nanocristaux sur la surface de silicium hydrogenee ainsi qu'a des mesures de spectroscopie tunnel afin de caracteriser la double jonction tunnel surface-nanocristal-pointe. Grace a cette methode de depot permettant de preserver la structure et la proprete de la surface, nous avons mis en evidence un phenomene d'orientation spontanee des nanobatonnets sur les surfaces de silicium hydrogenee et de graphite. Le calcul des differentes energies d'interaction entre le nanobatonnet et la surface nous a permis de conclure que cette orientation spontanee decoule de l'interaction anisotrope des ligands des nanobatonnets avec ces surfaces. Ce phenomene montre l'interet de pouvoir deposer ces objets sur des surfaces structurees a l'echelle atomique afin de controler leur orientation via l'interaction ligand-surface
This thesis is the first step of a project aiming to use a single isolated nanocristal as a photon nano-source, excited by the electrons of a stm. We have developped a way to synthesize very pure solutions of cdse nanocrystals and nanorods. At the same time, we have developped a deposition method by pulsed injection under uhv, allowing to deposit these nano-objects on clean and reconstructed hydrogenated silicon, hydrogenated diamond and graphite surfaces. With the stm, we verified that these surfaces remain clean and were reconstructed after the deposition and we performed tunneling spectroscopy measurements in order to characterise the double barrier tunnel junction formed by the surface-nanocrystal-tip. Thanks to this deposition method which preserves the surface structure, we have shown that the nanorods are spontaneously orientated (with respect to the surface structure) when they are deposited on the hydrogenated silicon and graphite surfaces. We concluded from the estimation of the different interaction energies between the nanorod and the surface that this spontaneous orientation is due to the anisotropic interaction of the nanorod's ligands with these surfaces. This phenomenon shows that the deposition of such objects on atomically structured surfaces can be used to control their organisation through the ligand-surface interaction

L'objectif de ces travaux de thèse était de synthétiser des nanomatériaux hautement diffusant à faible absorption neutronique, constitués uniquement de carbone et de fluor, ceci afin de combler le gap de réflectivité des neutrons lents dans la plage de vitesse des neutrons 90-600 m/s (se situant entre le meilleur supermiroir et le graphite). Les matériaux retenus étaient des nanodiamants de diamètre calibré (5 nm) et des graphites fluorés. Parmi les graphites fluorés, la phase (C2F)n, possède la distance interfeuillet la plus élevée (9 Å) permettant une réflectivité jusqu'à 220 m/s. Malgré la difficulté d'obtention de cette phase (C2F)n, de par son domaine de température de fluoration restreint (350-400 °C), la tendance à la surfluoration et le risque d'exfoliation, nous sommes parvenus à synthétiser des poudres de graphites fluorés à haute teneur en (C2F)n dont la teneur maximale obtenue est de 96 % de (C2F)n, avec une distance interplannaire d'environ 9 Å. Les mesures de réflectivité des neutrons sur ces échantillons ont révélé qu'un graphite fluoré riche en (C2F)n peut être utilisé comme un réflecteur efficace pour les neutrons lents. Des feuilles de graphites ont également été fluorées afin de palier l'impossibilité de densifier les poudres de graphite fluoré, critère essentiel pour la création de réflecteurs de neutrons. Des taux élevés en (C2F)n ont été obtenus, soit ~75 % et aucune exfoliation n'a été constatée. Toutes ces caractéristiques font que les feuilles de graphite fluoré se révèlent très prometteuses en tant que réflecteurs de neutrons lents. Les nanodiamants de détonation choisis pour ce travail, car disponibles en quantité industrielle, contiennent en surface une couche de carbone sp2 et des groupements hydrogénés et oxygénés absorbeurs de neutrons, ainsi que des impuretés métalliques activables sous flux neutronique. Il est montré dans ces travaux de thèse que l'utilisation de dichlore permet d'éliminer efficacement les impuretés métalliques des nanodiamants de détonation, et que la combinaison avec du fluor moléculaire convertie les groupements hydrogénés et oxygénés à la surface de ces nanoparticules en liaisons C-F apportant un caractère hydrophobe empêchant tout adsorption de molécules d'eau. Une méthode de concentration des impuretés métalliques a été développée au cours de ces travaux de thèse, ce qui a permis de lever le verrou que représente la limite des détections des appareils de caractérisation utilisés. Il s'est également avéré que le suivi de la température de combustion des nanodiamants de détonation constituait un bon indicateur de la pureté de ces derniers. Par ailleurs, la combinaison des traitements de chloration et de fluoration a permis d'augmenter de 200 °C la stabilité thermique de ces composés
The aim of this PhD work was to synthesize highly scattering nanomaterials with low neutron absorption, consisting solely of carbon and fluorine, in order to close the slow neutron reflectivity gap in the 90-600 m/s neutron velocity range (between the best supermirror and graphite). The materials selected were nanodiamonds with a calibrated diameter (5 nm) and fluorinated graphites. Among fluorinated graphites, the (C2F)n phase has the highest interplanar distance (9 Å), enabling reflectivity of up to 220 m/s. Despite the difficulty of obtaining this (C2F)n phase, due to its restricted fluorination temperature range (350-400°C), the tendency to over-fluorinate and the risk of exfoliation, we successfully synthesized fluorinated graphite powders with a high (C2F)n content, with a maximum content of 96 % (C2F)n and an interplanar distance of around 9 Å. Neutron reflectivity measurements of these samples revealed that (C2F)n-rich fluorinated graphite can be used as an effective reflector for slow neutrons. Graphite foils have also been fluorinated to overcome the impossibility of densifying fluorinated graphite powders, an essential criterion for the creation of neutron reflectors. High levels of (C2F)n were also obtained, i.e. ~75%, and no exfoliation was observed. All these characteristics make fluorinated graphite foils very promising as slow neutron reflectors. The detonation nanodiamonds are chosen for the purpose of developing new slow neutron reflectors because they are available in industrial quantities. They unfortunately contain a sp2 carbon shell on their surface and hydrogenated and oxygenated neutron-absorbing impurities, as well as metallic impurities that can be activated under neutron flux. It was shown in this study that the use of chlorine effectively eliminates metallic impurities from detonation nanodiamonds, and that the combination with molecular fluorine converts the hydrogenated and oxygenated groups present on the surface of these nanoparticles into C-F bonds, providing a hydrophobic character that prevents any subsequent adsorption of water molecules. A method for concentrating metallic impurities was developed during the course of this PhD work, which made it possible to overcome the detection limit of the characterization equipment used. It also proved that the combustion temperature of detonation nanodiamonds was a good indicator of their purity. In addition, the combination of chlorination and fluorination treatments increased the thermal stability of these compounds by 200 °C

Devido à tendência de aglomeração o desenvolvimento na funcionalização e posterior dispersão do pó de nanodiamante (ND) produzido por detonação pode se tornar um desafio. O pó do ND foi purificado por meio de tratamento térmico e dois tipos de funcionalizações foram alcançadas ND-COOH e ND-H. A purificação e as funcionalizações foram alcançadas com sucesso e foram verificadas por TGA e FT-IR. A análise de AFM mostrou que o tratamento térmico de oxidação que fornece a funcionalização do ND-COOH reduz os aglomerados em cerca de 74\% do tamanho original. O tamanho médio dos aglomerados do ND-COOH conforme medido por dispersão dinâmica de luz foi substancialmente reduzido em 95\% do tamanho original após a funcionalização e desagregação mecânica do pó em meio líquido. A estabilidade da dispersão do ND em solvente polar tetrahidrofurano aumentou consideravelmente apresentando um potencial zeta de -31 mV. Esta tese contemplou o desenvolvimento de uma nova metodologia para a dispersão dos aglomerados de nanodiamante (ND) em meio líquido. Filmes de carbono tipo diamante (DLC - Diamond-Like Carbon) contendo nano partículas de diamante foram depositados sobre amostras planas de liga de titânio Ti6Al4V pela técnica de DC pulsada PECVD (Plasma Enhanced Chemical Vapor Deposition). Soluções precursoras para deposição de filme de DLC foram preparadas. Filmes de DLC e DLC-ND foram produzidos a partir de diferentes solventes de natureza polar e apolar e as suas propriedades foram avaliadas. Análises comparativas de perfilometria, coeficiente de atrito, espectroscopia de espalhamento Raman foram abordadas. As análises de MEV e AFM revelaram a presença do ND no filme.
Due to agglomeration tendency the development of functionalization and subsequent dispersion of detonation nanodiamond (ND) powder can become a challenge. ND powder was purified by heat treatment and two types of functionalizations were achieved ND-H and ND-COOH. Purification and functionalizations were successfully achieved and were verified by TGA and FT-IR. AFM analysis showed that the thermal oxidation treatment which provides ND-COOH functionalization reduces the agglomerates in about 74\% of the original size. The average size of ND-COOH agglomerates as measured by dynamic light scattering has been significantly reduced by 95\% of its original size after functionalization and mechanical shearing of the powder in a liquid medium. The stability of ND dispersion in polar solvent tetrahydrofuran increased considerably having a zeta potential of -31 mV. Development of a new method for the dispersion of agglomerated nano diamond (ND) in a liquid medium was included in this thesis. Diamond-Like Carbon (DLC) films with nano diamand particles were deposited on flat samples of titanium alloy Ti6Al4V by pulsed DC Plasma Enhanced Chemical Vapor Deposition (PECVD). Precursor solutions for DLC films deposition were presented. DLC and DLC-ND films were produced from different polar and nonpolar solvents and their properties were evaluated. Comparative analyzes profilometry, friction coefficient, Raman spectroscopy have been addressed. SEM and AFM analysis revealed the presence of ND in the film.

Mestrado em Materiais e Dispositivos Biomédicos
O presente trabalho consistiu no desenvolvimento de um termistor de diamante CVD (chemical vapour deposition) dopado com boro, através da deposição de um filme por deposição química em fase de vapor assistida por filamento quente (HFCVD) num substrato cerâmico de nitreto de silício (Si3N4). O objectivo deste termistor é a sua aplicação na biomedicina, nomeadamente na medicina dentária, funcionando como um sensor de temperatura na ajuda ao diagnóstico à vitalidade dos dentes. A adição de boro foi realizada através da dissolução de B2O3 em etanol, sendo o transporte da mistura realizado com árgon através de um borbulhador. Os substratos de nitreto de silício foram produzidos através de uma mistura de pós comerciais de 89,3% α – Si3N4 (Starck Grade C) + 7,0% Y2O3 (Starck Grade M11) + 3,7% Al2O3 (ALCOA CT-3000SG) em um meio de isopropanol. A suspensão resultante foi seca e peneirada, de seguida foi sujeita a uma maquinação através de pressão uniaxial isostática, sendo sinterizada sem pressão aplicada numa atmosfera de nitrogénio. Este tipo de substrato apresenta-se como um candidato ideal para deposição de diamante, devido á sua elevada dureza, mas sobretudo devido ao seu coeficiente de expansão térmica ser bastante próximo do diamante. Os substratos sofreram um tratamento superficial prévio através de dois métodos: riscagem mecânica (ou manual) com um pó de diamante monocristalino com granolumetria entre 0,5-1 μm, e de seguida uma riscagem em ultrasons numa suspensão de diamante em etanol com a granolumetria de 15μm, com o objectivo de ajudar à nucleação do filme no substrato. Através do método de análise de Taguchi criou-se uma matriz de ensaios através de uma tabela L9, com o objectivo de saber as condições ideias de deposição HFCVD para obter o comportamento eléctrico desejado. Foram variadas condições como a razão CH4/H2 e Ar/H2, a pressão, a distância do substrato ao filamento. A caracterização dos filmes foi feita por microscopia electrónica de varrimento (SEM), difracção de raios-X, e espectroscopia Raman. Através de SEM foi observado que existe uma grande variedade a nível morfológico e de tamanho de grão. Também foi possível medir a espessura de filme a sua taxa de crescimento. Através de DRX (LIBAD) foi analisada a cristalinidade dos filmes e o tamanho de cristalite, e de espectroscopia Raman a sua qualidade e fases de carbono (sp2/sp3). Foram também realizados testes eléctricos com o objectivo de saber o comportamento eléctrico dos filmes, nomeadamente a sua variação da resistência com a temperatura, e calculando o valor de B, um factor que avalia a variação da resistência em função da temperatura, para um dado um material. Através do método Taguchi foram conseguidas as condições óptimas e foram construídos dois termistores com contactos ohmicos de WC. O seu comportamento foi comparado com o de um termistor comercial de 10k . O seu comportamento quando sujeito a ciclos contínuos de aquecimento e arrefecimento, revelou tempos de resposta bastante mais rápidos do que o termistor comercial. Decréscimos na ordem dos 31% e 67% foram conseguidos para os termistores T1 e T2 respectivamente em ciclos de aquecimento, ao passo que no arrefecimento foram conseguidos decréscimos na ordem dos 77% e 46% para T1 e T2. Os ciclos foram feitos num intervalo de temperatura entre os 24ºC e os 32ºC. Estes resultados suportam a aplicabilidade de termistores de diamante na medicina dentária com melhorias significativas no diagnóstico.
The present work aimed at the development of a diamond based termistor, using the Hot Filament Chemical Vapour Deposition (HFCVD) technique. The boron doped diamond coatings were deposited on silicon nitride based ceramics. This devices were developed bearing in mind biomedical applications, namely in dentistry, working as a temperature sensor to help in the teeth vitality diagnose. Boron addition in the gas mixture was accomplished by the dissolution of B2O3 in ethanol, carried along with argon trough a bubbler. Silicon nitride (Si3N4) based ceramic substrates were obtained by mixing commercial powders α -Si3N4 (Starck grade C), Y2O3 (Starck grade M11) and Al2O3 (ALCOA CT-3000SG) in a 89,3%/7,0%/ 3,7% weight proportion, in a isopropyl alcohol media. The resulting suspension was dried and sieved, consolidated by uniaxial and isostatic pressing and finally pressureless sintered in a nitrogen atmosphere. The Si3N4 substrates are an ideal candidate for diamond deposition, due to their high hardness and toughness, but specially for possessing a thermal expansion coefficient close to that of diamond. Prior to diamond deposition the ceramic surface was pretreated with a manual scratching with a 0,5-1 μm diamond powder and then sonicated in a 15μm diamond suspension in ethanol, to increase the diamond nucleation density. A Taguchi matrix was designed to study the HFCVD diamond deposition parameters, using a L9 orthogonal array, where CH4/H2 and Ar/H2 gas ratios, the pressure and the substrate-filament distance were used as controllable factors. The characterization of the coatings was performed by SEM, XRD and μ- Raman spectroscopy. SEM allowed the evaluation of the coatings morphology and thickness (cross-sectional micrographs), thus the determination of the growth rate. XRD (LIBAD) allowed the determination of the grain size for nanocrystalline diamond, as well as the crystallographic orientation. μ-Raman spectroscopy allowed the evaluation of the carbon phase content (sp2/sp3) in the coatings. The electrical behavior of the films was accessed, namely the dependence of the resistance with the temperature, allowing the calculation of the B parameter, which is a set parameter of each material, for a given range of temperature. Using the Taguchi Method the optimal Diamond deposition conditions were achieved and two diamond termistors were built with WC ohmic contacts. Their electrical behavior was compared to that of a commercial termistor with resistances of the order of 10k . However, their electrical response to cyclic heating and cooling steps evidence much fasters response times. Decreases in response time on the order of 31% and 67% were achieved respectively for T1 and T2 upon heating, and 77% and 46% for respectively T1 and T2 termistors during cooling in the temperature range of 24-32ºC. These results support the applicability of diamond based termistors in the field of dentistry with significant improvements in the diagnose accuracy.

O estudo de filmes de carbono-tipo diamante (DLC) é atualmente de grande interesse da comunidade científica e tecnológica devido às suas propriedades, como baixo coeficiente de atrito, elevada dureza, inércia química, alta aderência a superfícies metálicas com diferentes formas e obtenção em grandes escalas. As suas propriedades podem ser significativamente aumentadas pela presença de nanopartículas em sua estrutura, com substanciais mudanças em suas propriedades tribológicas e mecânicas. O foco da investigação deste trabalho está centrado na obtenção de filmes de DLC com cristais de diamante incorporados em sua estrutura, a partir de altas taxas de deposição, utilizando um sistema 3D barato e escalonável, o que ainda não tinha sido possível de se obter. As vantagens desse novo filme estão em combinar as propriedades de dureza, baixa rugosidade, coeficiente de atrito e biocompatibilidade, tanto do diamante-CVD cristalino como do DLC, adicionando as possibilidades de obtenção desse novo material híbrido em grandes áreas e altamente aderente aos substratos metálicos. Os resultados mostram: (1) a deposição de filmes de DLC a partir de diferentes líquidos hidrocarbonetos, obtendo assim altas taxas de crescimento; (2) esses líquidos hidrocarbonetos permitem a incorporação de nanopartículas diversas nos filmes pela dispersão de partículas no líquido; (3) filmes de DLC contendo nanopartículas de dióxido de titânio foram produzidos e sua ação bactericida comprovada; (4) filmes de DLC contendo nanopartículas de diamante cristalino foram produzidos pela primeira vez, por um processo totalmente inédito; (5) a homogeneidade dos filmes de DLC contendo nanopartículas de diamante foi avaliada sob diferentes formas de operação (carga e velocidade); (6) uma nova aplicação para os filmes de DLC contendo partículas de diamante foi descoberta: a proteção contra corrosão; (7) esses filmes também mostram-se eficientes contra a tribocorrosão. Dessa forma, espera-se ampliar o potencial de aplicação para a utilização em áreas sujeitas ao atrito em ambiente corrosivo.

Mestrado em Engenharia Física
Neste trabalho é descrito o estudo de estruturas híbridas de grafeno e diamante nano-cristalino (GDH) sintetizadas por deposição química em fase vapor por plasma de micro-ondas (MPCVD) em cobre. Foram investigadas técnicas de controlo da nucleação do diamante nano-cristalino, tendo sido encontrados dois processos com sucesso. Procedeu-se ainda à caracterização estrutural, morfológica e ótica das amostras por análise de SEM, TEM, AFM, EFM, medidas de transmitância UV-Vis e espetroscopia de Raman. A avaliação das propriedades de transporte destes materiais foi efetuada pela medição da curva de transferência de transístores de efeito de campo produzidos para o efeito, sendo os GDHs produzidos o material ativo do canal. Foram observadas baixas mobilidades devido à hidrogenação do grafeno. Em linha com resultados teóricos da literatura, foram encontradas evidências de abertura do hiato energético do grafeno, um potencial desenvolvimento para a aplicação em dispositivos de comutação lógica.
In this work, hybrid structures of graphene and nano-crystalline diamond (GDH) produced by microwave plasma chemical vapor deposition (MPCVD) in copper substrates are studied. The control of the diamond clusters nucleation was investigated, having two different approaches been identified as promising. Structural, morphological and optical characterization was carried out by SEM, TEM, AFM, EFM, UV-Vis transmittance, and Raman spectroscopy. The transport properties of this material were analyzed through the transfer curve of field-effect transistors with GDH channels. Low mobilities were found due to graphene hydrogenation. In line with theoretical studies, evidences were found of graphene band gap opening, a potential breakthrough for the development of logical switching devices.