Vertically aligned multi walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst, were integrated into a resistive sensor design. The steady state sensitivities as high as 5% and 10% for 100 ppm of NH3 and NO2 respectively at a flow rate of 750 sccm were observed. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH3 and NO2 flow rates. An equivalent circuit model was developed to understand the operation and propose design changes for increased sensitivity. Multi Walled Carbon NanoTubes (MWCNTs) – Polymer composite based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO2 substrates via xylene pyrolysis using chemical vapor deposition technique. Polymers like PEDOT:PSS and Polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-Propanol and Ethylene Glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100ppm) of gases like NH3 and NO2. Effect of various solvents on the sensor response imparting selectivity to CNT – Polymer nanocomposites was investigated extensively. Sensitivities as high as 28% was observed for a MWCNT – PEDOT:PSS composite sensor when exposed to 100ppm of NH3 and -29.8% sensitivity for a MWCNT-PANI composite sensor to 100ppm of NO2. A novel nanostructured electrode design for Li based batteries and electrochemical capacitor applications was developed and tested. High density and highly aligned metal oxide nanowire arrays were fabricated via template assisted electrochemical deposition. Nickel and Molybdenum nanowires fabricated via cathodic deposition process were converted into respective oxides via thermal treatments and were evaluated as electrodes for batteries and capacitor applications via Cyclic Voltammetery (CV). Several chemical baths were formulated for the deposition of pristine molybdenum nanowires. Superior electrochemical performance of metal (Ni and Mo) oxide nanowires was observed in comparison to the previously reported nano-particle based electrodes.

Vertically aligned Multiwalled Carbon Nanotubes (MWCNTs) were grown in the pores of Anodized Aluminum Oxide (AAO) templates and investigated for resistive sensor applications. High Sensitivity of 23% to low concentration (100 ppm) of ammonia was observed. An equivalent circuit model was developed to understand the current flow path in the resistive sensor. This helped us in achieving high sensitivities through amorphous carbon (a-C) layer thickness tailoring by employing post-growth processing techniques like plasma etching. A simulation model in MATLAB was developed to calculate the device resistance and the change in the sensitivity as a function of device parameters. The steady state response and transient response of the model to the number of ammonia molecules and its adsorption rate were studied. Effects of oxygen plasma, argon plasma and water plasma etch on thinning of the a-C layer were studied. In order to enhance the sensitivity, the top and bottom a-C layers were replaced by a more conductive metal layer. This also helped in understanding the current flow in the device and in the estimation of the resistivity of the a-C layer.

Magnetic materials when reduced to the nanoscale promote the emergence of new properties and the specific functionalization of these magnetic nanostructures are key tools in the development of improved devices for information technology (memory and data processing) and detection. In this thesis were electro-deposited magnetic nanotubes in anodic aluminum membranes. The properties of magnetic nanotube networks of Ni, Co, FeCo and FeNi with different geometric parameters were investigated. The porous aluminum oxide membranes were prepared using the hard anodizing process, in a self-ordering regime with pore distances Dint=300nm. This process offers substantial advantages over conventional anodizing processes in terms of processing time, allowing for faster oxide growth, with better arrangement and high aspect ratio of nanopores. The nanotubes were electrodeposited through the potentiostat mode, using porous membranes as the basis for their structure. Samples with external diameter of 140nm, 180nm and 220nm were obtained. In addition, the nanotubes have an additional degree of freedom given by the thickness of the tube walls. In this way, nanotubes with constant external diameter and different wall thicknesses of the tube were also synthesized. The structure and morphologies of the synthesized samples were characterized by scanning electron microscopy, x-ray dispersion spectroscopy and x-ray diffraction. The magnetic characterization was performed through the vibrating sample magnetometer. Through the nanotubes with different diameters it was possible to observe that the global anisotropy of the matrix is the result of the competition between the magnetostatic interactions, magnetocrystalline anisotropy and form anisotropy. With the increase of the diameter of NTs and the decrease of the distance between them it was observed that the magnetostatic interactions prevail. Nanotubes with different wall thicknesses were produced, maintaining constant the external diameter and the distance between the structures. Through the characterization of these structures it was observed that for nearby nanotubes, with distances smaller than their diameter, it is the wall thickness that determines the magnetic interaction between the nanotubes of the network. The magnetization inversion processes for NTs with different wall thicknesses were investigated through the analysis of the coercive field as a function of the applied field. It can be seen that the same structure can present two types of magnetization inversion, the transverse mode or vortex, and that this inversion can be determined by adjusting the NT wall thickness. The comparative study between the nanotubes with different compositions and geometric parameters showed that the magnetic properties are strongly correlated with the geometric parameters. / Materiais magnéticos quando reduzidos à escala nanométrica promovem o surgimento de novas propriedades e a funcionalização específica dessas nanoestruturas magnéticas são ferramentas chave no desenvolvimento de dispositivos aprimorados para tecnologia da informação (memória e processamento de dados) e detecção. Nesta tese foram sintetizados nanotubos magnéticos eletrodespositados em membranas de alumínio anódico. Foram investigadas as propriedades de redes de nanotubos magnéticos de Ni, Co, FeCo e FeNi, com diferentes parâmetros geométricos. As membranas de óxido de alumínio poroso foram preparadas utilizando o processo de anodização dura, em um regime de auto-ordenação com distâncias entre poros Dint=300nm. Este processo oferece vantagens substanciais em relação aos processos convencionais de anodização em termos do tempo de processamento, permitindo um crescimento mais rápido de óxido, com um melhor ordenamento e alta razão de aspecto dos nanoporos. Os nanotubos foram eletrodepositados através do modo potenciostato, utilizando as membranas porosas como base para sua estrutura. Foram obtidas amostras com diâmetro externo de 140nm, 180nm e 220nm. Além disso, os nanotubos apresentam um grau de liberdade adicional dado pela espessura das paredes do tubo. Dessa forma, também foram sintetizados nanotubos com diâmetro externo constante e com diferentes espessuras de parede do tubo. As estrutura e morfologias das amostras sintetizadas foram caracterizadas por microscopia eletrônica de varredura, espectroscopia de dispersão de raio-x e difratometria de raio-x. A caracterização magnética foi realizada através do magnetômetro de amostra vibrante. Através dos nanotubos com diferentes diâmetros foi possível observar que a anisotropia global da matriz é o resultado da competição entre as interações magnetostáticas, anisotropia magnetocristalina e anisotropia de forma. Com o aumento do diâmetro dos NTs e a diminuição da distância entre eles foi observado que as interações magnetostáticas prevalecem. Nanotubos com diferentes espessuras de parede foram produzidos, mantendo constante o diâmetro externo e a distância estre as estruturas. Através da caracterização dessas estruturas foi observado que para nanotubos próximos, com distâncias menores que seu diâmetro, é a espessura da parede que determina a interação magnética entre os nanotubos da rede. Os processos de inversão de magnetização para NTs com diferentes espessuras de parede foi investigado através da análise do campo coercivo em função do campo aplicado. Mostrando que a mesma estrutura pode apresentar dois tipos de inversão de magnetização, o modo transversal ou vórtice, e que esta inversão pode ser determinada através do ajusta da espessura de parede do NT. O estudo comparativo entre os nanotubos com diferentes composições e parâmetros geométricos mostrou que as propriedades magnéticas são fortemente correlacionadas com os parâmetros geométricos.

L'objectif premier de ce projet est la mise au point de procédés de fabrication microélectroniques/microtechnologiques compatibles avec l'utilisation d'un support papier. Pour cela, des techniques comme l'évaporation thermique sous vide, la photolithographie, l'électrodéposition et l'anodisation d'aluminium ont été développées et adaptées à ce support. Des bancs de caractérisations structurels, électriques et flexibles ont été aussi mis en œuvre pour étudier la fiabilité des couches déposées sur un tel substrat. En application, un capteur d'humidité à base d'oxyde d'aluminium flexible a été fabriqué et les tests en humidité ont montré d'excellents résultats permettant de valider le travail effectué. / The primary objective of this project is the implementation of microelectronics/microtechnology processes compatible with the use of paper-based substrate. For this purpose, techniques such as thermal vacuum evaporation, photolithography, electroplating and anodizing aluminum have been developed and adapted to this substrate. Structural, electrical and flexible characterizations benches have also been implemented to study the reliability of the layers deposited on such substrate. A moisture sensor based on flexible aluminum oxide was made and humidity tests have shown excellent results which validate the work.

This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.

В работе проведено исследование оптических характеристик коллоидных квантовых точек (КТ) InP/ZnS различных размеров (QD-1, QD-2, QD-3) и композитных наноструктур анодированного оксида алюминия (AAО) с КТ методами спектрофотометрии и люминесцентной спектроскопии. Выполнен литературный обзор, касающийся электронных состояний в идеальном нанокристалле (НК), синтеза КТ на основе InP, использования НК для создания нанокомпозитов и расчёта цветовых характеристик излучателей. Описаны методики подготовки образцов и проведения измерений спектров оптического поглощения (ОП) и фотолюминесценции (ФЛ). По анализу спектров ОП КТ определены значения энергий оптических переходов. Полосы с наименьшей энергией соответствуют первому экситонному пику поглощения ядра InP. Другие могут быть приписаны оболочке из ZnS. По синему сдвигу осуществлена оценка размера ядер образцов КТ. Для QD-1 исследована температурная зависимость первого экситонного пика поглощения. Спектры ФЛ позволяют предположить, что полосы свечения формируются как экситонными переходами, так и дефектами кристаллической решётки ядра InP. Синтезирован ряд структур нанопористого оксида алюминия, отожженного при различных температурах, с осаждёнными КТ и исследована их ФЛ. Показано, что после осаждения в AAО НК InP/ZnS, сохраняют свои флуоресцентные свойства, следовательно, можно говорить об успешном создании композитных люминофоров InP/ZnS@AAO. Обсуждаются цветовые характеристики изучаемых образцов. / This study deals with the investigation of optical characteristics of differently sized InP/ZnS colloidal quantum dots (QD-1, QD-2, QD-3) and composite nanostrucrures of anodic aluminum oxide with QDs by means of spectrophotometry and luminescence spectroscopy techniques. The literature review concerning electronic states in an ideal nanocrystal (NC), synthesis of InP-based QDs, use of NCs for creating nanocomposites and calculating color characteristics of emitters was carried out. The methods of sample preparation and measurements of optical absorption (OA) and photoluminescence (PL) spectra are described. Values of optical transition energies are determined according to the analysis of QD OA spectra. The bands with the lowest energy correspond to the first exciton absorption peak of the InP core. The other transitions can be attributed to the ZnS shell. The core size of the QD samples was evaluated using the blue shift. The temperature dependence of the first exciton absorption peak was investigated for the QD-1. PL spectra of QDs indicate that the emission bands are formed by exciton transitions and defects of the InP crystal lattice. A series of structures of nanoporous aluminum oxide, annealed at different temperatures, with deposited QDs were synthesized and their PL were studied. Fluorescent properties of the QDs are found to be retained after the deposition, therefore, InP/ZnS@AAO composite phosphors were successfully created. Сolor characteristics of the samples under study are discussed.

La spectroscopie EPES (Elastic Peak Electron Spectroscopy) permet de mesurer le pourcentage he d'électrons rétrodiffusés élastiquement par la surface d'un échantillon soumis à un bombardement électronique. C'est une méthode non destructive et extrêmement sensible à la surface. L'objectif de ce travail est de modéliser le cheminement des électrons élastiques dans la matière grâce à une simulation informatique basée sur la méthode Monte Carlo. Cette simulation contribue de manière essentielle à la connaissance et à l'interprétation des résultats expérimentaux obtenus par spectroscopie EPES. Nous avons, de plus, adapté cette simulation à différentes surfaces transformées à l'échelle micrométrique et nanométrique. A l'aide d'une méthode originale, basée sur une description couche par couche du matériau, j'ai réalisé un programme informatique (MC1) rendant compte du cheminement des électrons élastiques dans les différentes couches du matériau. Le nombre d'électrons ressortant de la surface dépend de nombreux paramètres comme : la nature du matériau à étudier, l'énergie des électrons incidents, l'angle d'incidence, les angles de collection des analyseurs. De plus, je me suis intéressé à l'effet de la rugosité de la surface et j'ai démontré qu'elle joue un rôle déterminant sur l'intensité du pic élastique. Ensuite, grâce à l'association de la spectroscopie EPES et de la simulation Monte Carlo, j'ai déduit les modes de croissance de l'or sur substrat d'argent et de cuivre. Les effets de l'arrangement atomique et des pertes énergétiques de surfaces ont ensuite été étudiés. Pour cela, une deuxième simulation MC2 tenant compte de ces deux paramètres a été réalisée permettant d'étudier les surfaces à l'échelle nanométriques. Ces paramètres jusqu'alors non pris en compte dans notre simulation MC1, joue un rôle essentiel sur l'intensité élastique. Ensuite, j'ai obtenu une formulation simple et exploitable pour l'interprétation des résultats obtenus par la simulation MC2 pour un analyseur RFA. Afin de valider, les différents résultats de la simulationMC2, j'ai réalisé des surfaces de silicium nanostructurées, à l'aide de masques d'oxyde d'alumine réalisés par voie électrochimique. J'ai pu créer des nano-pores par bombardement ionique sous ultravide sur des surfaces de silicium. Afin de contrôler la morphologie de la surface, j'ai effectué de l'imagerie MEB ex-situ. La simulation Monte Carlo développée associée aux résultats EPES expérimentaux permet d'estimer la profondeur, le diamètre et la morphologie des pores sans avoir recours à d'autres techniques ex-situ.Cette simulation MC2 permet de connaître la surface étudiée à l'échelle nanométrique.

La spectroscopie EPES (Elastic Peak Electron Spectroscopy) permet de mesurer le pourcentage he d’électrons rétrodiffusés élastiquement par la surface d’un échantillon soumis à un bombardement électronique. C’est une méthode non destructive et extrêmement sensible à la surface. L'objectif de ce travail est de modéliser le cheminement des électrons élastiques dans la matière grâce à une simulation informatique basée sur la méthode Monte Carlo. Cette simulation contribue de manière essentielle à la connaissance et à l'interprétation des résultats expérimentaux obtenus par spectroscopie EPES. Nous avons, de plus, adapté cette simulation à différentes surfaces transformées à l’échelle micrométrique et nanométrique. A l’aide d’une méthode originale, basée sur une description couche par couche du matériau, j’ai réalisé un programme informatique (MC1) rendant compte du cheminement des électrons élastiques dans les différentes couches du matériau. Le nombre d’électrons ressortant de la surface dépend de nombreux paramètres comme : la nature du matériau à étudier, l’énergie des électrons incidents, l’angle d’incidence, les angles de collection des analyseurs. De plus, je me suis intéressé à l’effet de la rugosité de la surface et j’ai démontré qu’elle joue un rôle déterminant sur l’intensité du pic élastique. Ensuite, grâce à l’association de la spectroscopie EPES et de la simulation Monte Carlo, j’ai déduit les modes de croissance de l’or sur substrat d’argent et de cuivre. Les effets de l’arrangement atomique et des pertes énergétiques de surfaces ont ensuite été étudiés. Pour cela, une deuxième simulation MC2 tenant compte de ces deux paramètres a été réalisée permettant d’étudier les surfaces à l’échelle nanométriques. Ces paramètres jusqu’alors non pris en compte dans notre simulation MC1, joue un rôle essentiel sur l’intensité élastique. Ensuite, j’ai obtenu une formulation simple et exploitable pour l’interprétation des résultats obtenus par la simulation MC2 pour un analyseur RFA. Afin de valider, les différents résultats de la simulationMC2, j’ai réalisé des surfaces de silicium nanostructurées, à l’aide de masques d’oxyde d’alumine réalisés par voie électrochimique. J’ai pu créer des nano-pores par bombardement ionique sous ultravide sur des surfaces de silicium. Afin de contrôler la morphologie de la surface, j’ai effectué de l’imagerie MEB ex-situ. La simulation Monte Carlo développée associée aux résultats EPES expérimentaux permet d’estimer la profondeur, le diamètre et la morphologie des pores sans avoir recours à d’autres techniques ex-situ.Cette simulation MC2 permet de connaître la surface étudiée à l’échelle nanométrique. / EPES (Elastic Peak Electron Spectroscopy) allows measuring the percentage he of elastically backscattered electrons from the surface excited by an electron beam. This is a non destructive method which is very sensitive to the surface region. The aim of this work is to model the trajectory of elastic electrons in the matter with a computer simulation based on Monte Carlo method. This simulation allows interpreting experimental results of the EPES spectroscopy. We have moreover adapted this simulation for different surfaces transformed to micrometer and nanometer scales. Using an original method, based on a description of material layer by layer, I realized a computer program (MC1) that takes into account the path of elastic electrons in different layers of material. The number of electrons emerging from the surface depends on many parameters such as: the electron primary energy, the nature of the material, the incidence angle and the collection angles of the analyzer. In addition, I was interested in the effect of surface roughness and I showed that it plays an important role in the intensity of the elastic peak. Then, through an association of the EPES and the Monte Carlo simulation results, I deduced the growth patterns of gold on silver and copper substrates. The effects of the atomic arrangement and the surface excitations were then studied. For this, a new simulation MC2 that takes into account these two parameters has been developed to study nanoscale surfaces. These parameters not previously included in our MC1simulation play a important role in the elastic intensity. Then I have got a simple formula for interpreting the results obtained by the simulation for a RFA analyzer. To validate the different results of the simulation MC2, I realized nano-structured silicon surfaces, using aluminium oxide masks. Nano-pores have been created by Ar+ ions bombardment in UHV chamber on silicon surfaces.To control the morphology of the surfaces, I realized SEM images (Techinauv Casimir) ex-situ. The Monte Carlo simulations, developed here, associated with the EPES experimental results can estimate the depth, the diameter, the morphology of pores without the help of other ex-situ techniques.

The goal of the current paper is to synthesize and characterize composites based on carbon nanotubes and metal oxides. Multiwalled CNT were synthesized within the pores of anodic aluminum oxide and nanotubular structures of titanium dioxide on the course of this study. There were the methods to obtain a catalyst for synthesis process such as electrochemical deposition, sol-gel technique and sputtering. The synthesis variations based on sol-gel technique and magnetron sputtering resulted in obtaining of CNT@AAO and CNT@TiO2-NT composites respectively. The research of carbon samples by Raman spectrometry was conducted. Characterization of obtained composites by electron microscopy method was done. The analysis of gathered SEM images by specialized software package SIAMS was made. Studies of CNT@TiO2-NT composites by means of impedance spectroscopy method were held. Thus the methodology for CNT@AAO and CNT@TiO2-NT composites synthesis had been developed. Advantages of reviewed techniques regarding ones known at scientific society were indicated. Developed synthesis methods are applied in lab works of Masters with specialization «Electronics and nanoelectronics». / Целью работы являлся синтез и аттестация композитов на основе углеродных нанотрубок и оксидов металлов. В ходе работы выполнен синтезмногостенных УНТ внутри пор анодированного оксида алюминия, а также в нанотубулярных структурах диоксида титана. Катализатор для проведения синтеза подготавливался тремя разными способами: методом электрохимического осаждения, золь-гель способом, напылением. Золь-гель метод приготовления катализатора позволил получить композит УНТ@АОА. Используя метод магнетронного напыления удалось синтезировать композиты УНТ@TiO2-НТ. Выполнены исследования синтезированного углеродного материала методом Рамановской спектрометрии. Аттестация полученных композитов проведена методом электронной микроскопии. С помощью программно-аппаратного комплекса анализа изображений SIAMS был проведен анализ полученных СЭМ-изображений. Проведены исследования композита УНТ@TiO2-НТ методом импедансной спектроскопии. В итоге разработана методология получения композитов УНТ@АОА и УНТ@TiO2-НТ. Отмечены достоинства данных методов относительно известных в научном сообществе. Разработанная методика синтеза используется в лабораторных работах магистров направления «Электроника и наноэлектроника».