Orientador: Paulo Roberto Bueno / Coorientador: Flávio Cesar Bedatty Fernandes / Banca: Hideko Yamanaka / Banca: Marina Ribeiro Batistuti / Resumo: Desde a primeira descrição de biossensor reportada por Clark e Lyons em 1962, houve um extenso trabalho no desenvolvimento e aprimoramento de novas técnicas de biossensoriamento para detecção de biomarcadores com relevância médica. Destaca-se nesse processo o estudo de superfície de eletrodos, pois esse influencia diretamente em aspectos como; sensibilidade, estabilidade e qualidade do sinal. Portanto, este projeto consiste em avaliar comparativamente três superfícies de eletrodos baseadas em nanoestruturas contendo nanopartículas de azul da Prússia, funcionando com sonda redox do sistema, e materiais carbonáceos (como óxido de grafeno e nanotubos de carbono) para aplicação em biossensores. Foram avaliados aspectos como composição, características capacitivas redox e estabilidade de sinal. A técnica de análise utilizada é a espectroscopia de capacitância eletroquímica (ECE) que apresenta vantagens como não usar amplificadores de sinal (sondas redox) em solução, configuração esta, importante para métodos de diagnóstico point-of-care. Das superfícies analisadas, a composta por nanopartículas de azul da Prússia e óxido de grafeno (PBNP+GO) apresentou os melhores parâmetros de estabilidade e compatibilidade com os aspectos teóricos da técnica de ECE, sendo então selecionada para realização de testes de biossensoriamento que, através da funcionalização da superfície com anticorpos Anti-IL-6, detectaram seletivamente a presença do biomarcador IL-6. / Abstract: Since the first description of biosensor reported by Clark and Lyons in 1962, numerous works related to the development and enhancement of novel medical biosensing techniques have been published. In that context, it must be highlighted the study of electrode surfaces as it has direct influence in aspects like; sensitivity, stability and signal quality. Therefore, this project aims to evaluate three electrode surfaces based on nanostructures with Prussian blue nanoparticles, as redox probe, and carbonaceous materials (like graphene oxide and carbon nanotubes) and their application in biosensors. It was evaluated aspects like composition, redox capacitive characteristics and signal stability. The electrochemical capacitance spectroscopy technique (ECE) was used as it offers several advantages like no need of signal amplifiers (redox probes) in solution and, then, making this technique more adequate for point-of-care diagnosis. Among the analysed surfaces, the one composed by Prussian blue nanoparticles and graphene oxide (PBNP+GO) was identified as the best surface in terms of stability and compatibility to the theoretical aspects of ECE. Therefore, that structure was selected to further biosensing essays, by functionalizing the surface with Anti-IL-6 antibodies, that indicated the selective detection of the IL-6 biomarker. / Mestre

O crescimento de pontos quânticos a partir do descasamento dos parâmetros de rede tem sido alvo de intensos estudos nos últimos dez anos. Conhecer as propriedades eletrônicas destes materiais é chave para a engenharia de sistemas quânticos. O objetivo deste trabalho é estudar as propriedades eletrônicas de pontos quânticos (QD) de InAS1-x Px enterrados em GaAs, através de Espectroscopia de Capacitância (CV). A Espectroscopia CV é uma técnica que permite determinar os estados eletrônicos e a distribuição de cargas do sistema. As amostras de InAS1-x Px foram crescidas por MOCVD (Low-Pressure Metalorganic Chemical Vapor Deposition) sobre um substrato de GaAs:Cr (001). A estrutura das amostras é do tipo MIS (Metal-Isolante-Semicondutor) com um contato traseiro do tipo n. As medidas de capacitância foram feitas a 4,2 K para diferentes valores de freqüência e campo magnético. A partir da dispersão dos estados confinados com o campo magnético aplicado perpendicular ao plano dos pontos quânticos, pode-se determinar, &#9690, a freqüência natural do sistema. A partir de &#9690, determinou-se &#87470, o comprimento característico da função de onda. A concordância entre os valores de &#87470 com as dimensões laterais dos pontos quânticos obtidos por microscopia eletrônica de transmissão (TEM) é boa. Finalmente, através das medidas de espectroscopia CV pode-se separar os efeitos de confinamento lateral e vertical, permitindo um melhor entendimento dos espectros de fotoluminescência (PL), assim como os detalhes da forma dos QD obtidos por TEM. / The growth of quantum dots in the Stranski-Krastranov mode has been subject of intense investigation in the last decade. Knowing the electronics properties of these materials is key for performing quantum systems engineering. The objective of this work is to study the quantum dots (QD) electronic properties of the InAS1-x Px embedded in GaAs. The study was done by capacitance spectroscopy (CV), which is an experimental tool that allows the evaluation of the electronic states and the charge distribution of a given quantum device. The samples of InAS1-x Px were grown by Low-Pressure Metalorganic Chemical Vapor Deposition on GaAs:Cr (001) substrates. They consist of metalinsulator-semiconductor structures with an n-type back contact. The measurements were performed at 4.2 K for different values of frequencies and magnetic field. From the confined states dispersion as a function of the applied magnetic field, perpendicular to the QD plane, the system natural frequency, &#9690, was determined. From the &#9690, we could determine the wave function characteristic length, &#87470. The concordance between the &#87470, values and the lateral sizes obtained by Transmission Electronic Microscopy (TEM) is good. Finally, by CV spectroscopy we could separate the lateral and vertical confinement effects, leading to a more complete understanding of the Photoluminescence (PL) spectra, as well as the details of the QD shape obtained by TEM.

Orientador: Paulo Roberto Bueno / Coorientador: Flávio Cesar Bedatty Fernandes / Banca: Maria Del Pilar Taboada Sotomayor / Banca: Paulo Inácio da Costa / Resumo: O sucesso no tratamento de muitos tipos doenças passa pela detecção seletiva e sensível de biomarcadores proteicos que permitam um diagnóstico precoce. A dengue é uma doença infecciosa de diagnóstico clínico impreciso e diagnóstico laboratorial demorado e custoso, a qual não possui tratamento ou vacina efetivos. Portanto se requer de ferramentas diagnósticas precisas, baratas e portáveis que permitam o diagnóstico rápido para realizar um tratamento adequado de sintomas e identificar os focos infecciosos para prevenir o espalhamento da doença. Um biomarcador útil na detecção da dengue, é a proteína NS1 que vem sendo utilizada com sucesso em diferentes plataformas de diagnóstico. Porém, nenhuma das plataformas oferecidas a nível comercial, consegue combinar a precisão, portabilidade, baixo custo e facilidade de manuseio. Portanto, o melhoramento de ditas ferramentas é o foco de bastantes pesquisas. Neste trabalho se apresenta uma plataforma que se amostra útil para a detecção de diferentes biomarcadores, incluindo a proteína NS1. Esta plataforma combina o uso de uma técnica eletroquímica como é a Espectroscopia de Capacitância Eletroquímica (ECE), com o uso de peptídeos redox e está baseada na funcionalização de eletrodos de ouro mediante formação de monocamadas auto-organizadas (SAM) confeccionadas com um peptídeo redox (Fc-Glu-Gli-Ser-Gli-Ser-Cys) desenhado para ser ancorado em superfícies metálicas, ao mesmo tempo que tem capacidade de ancorar uma sonda redox e um biorecepto... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Success in the treatment of many kinds of illnesses depends on the selective and sensitive detection of protein biomarkers that allow an early diagnosis. Dengue is and infectious disease of imprecise clinical diagnostic and delayed and expensive laboratorial diagnostic. This disease does not have an effective vaccine or treatment. Therefore, precise, cheap and portable diagnostic tools are necessary to allow a fast diagnostic in order to treat the symptoms, identify focuses of infection, and thus prevent the spreading of the disease. A useful biomarker in the detection of dengue is the protein NS1, which has been successfully used in different diagnostic platforms. However, none of the commercially available platforms combines precision, portability, low cost and user friendliness. Consequently, the improvement of such tools is object of ample research. This work, introduces a platform, which is useful for the detection of various biomarkers, including the protein NS1. This platform combines the usage of an electrochemical technique such as Electrochemical Capacitance Spectroscopy (ECS) and the use of redox peptides. It is based in the functionalization of gold electrodes through formation of Self Assembled Monolayers (SAM) formed by a redox peptide (Fc-Glu-Gli-Ser-Gli-Ser-Cys) designed to bind to metallic surfaces as well as to anchor a redox probe and a bioreceptor in the same structure/molecule. It presents the additional advantage of forming anti-fowling SAMs, which is a ... (Complete abstract click electronic access below) / Mestre

O crescimento de pontos quânticos a partir do descasamento dos parâmetros de rede tem sido alvo de intensos estudos nos últimos dez anos. Conhecer as propriedades eletrônicas destes materiais é chave para a engenharia de sistemas quânticos. O objetivo deste trabalho é estudar as propriedades eletrônicas de pontos quânticos (QD) de InAS1-x Px enterrados em GaAs, através de Espectroscopia de Capacitância (CV). A Espectroscopia CV é uma técnica que permite determinar os estados eletrônicos e a distribuição de cargas do sistema. As amostras de InAS1-x Px foram crescidas por MOCVD (Low-Pressure Metalorganic Chemical Vapor Deposition) sobre um substrato de GaAs:Cr (001). A estrutura das amostras é do tipo MIS (Metal-Isolante-Semicondutor) com um contato traseiro do tipo n. As medidas de capacitância foram feitas a 4,2 K para diferentes valores de freqüência e campo magnético. A partir da dispersão dos estados confinados com o campo magnético aplicado perpendicular ao plano dos pontos quânticos, pode-se determinar, &#9690, a freqüência natural do sistema. A partir de &#9690, determinou-se &#87470, o comprimento característico da função de onda. A concordância entre os valores de &#87470 com as dimensões laterais dos pontos quânticos obtidos por microscopia eletrônica de transmissão (TEM) é boa. Finalmente, através das medidas de espectroscopia CV pode-se separar os efeitos de confinamento lateral e vertical, permitindo um melhor entendimento dos espectros de fotoluminescência (PL), assim como os detalhes da forma dos QD obtidos por TEM. / The growth of quantum dots in the Stranski-Krastranov mode has been subject of intense investigation in the last decade. Knowing the electronics properties of these materials is key for performing quantum systems engineering. The objective of this work is to study the quantum dots (QD) electronic properties of the InAS1-x Px embedded in GaAs. The study was done by capacitance spectroscopy (CV), which is an experimental tool that allows the evaluation of the electronic states and the charge distribution of a given quantum device. The samples of InAS1-x Px were grown by Low-Pressure Metalorganic Chemical Vapor Deposition on GaAs:Cr (001) substrates. They consist of metalinsulator-semiconductor structures with an n-type back contact. The measurements were performed at 4.2 K for different values of frequencies and magnetic field. From the confined states dispersion as a function of the applied magnetic field, perpendicular to the QD plane, the system natural frequency, &#9690, was determined. From the &#9690, we could determine the wave function characteristic length, &#87470. The concordance between the &#87470, values and the lateral sizes obtained by Transmission Electronic Microscopy (TEM) is good. Finally, by CV spectroscopy we could separate the lateral and vertical confinement effects, leading to a more complete understanding of the Photoluminescence (PL) spectra, as well as the details of the QD shape obtained by TEM.

Orientador: Varlei Rodrigues / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T03:02:40Z (GMT). No. of bitstreams: 1 Rodrigues_KevinLiu_M.pdf: 15717954 bytes, checksum: 0231043634d153e2ddc45e00a8630aaa (MD5) Previous issue date: 2015 / Resumo: O estudo de nanopartículas é desafiador devido à complexidade destes sistemas, que estão na interface entre o pequeno e o grande. A física dos sólidos deixa de valer em muitas das partículas menores devido ao alto grau de confinamento, e a fração de átomos de superfície para átomos no núcleo. Devido à natureza pequena dos \textit{clusters}, as medidas realizadas nestes sistemas são medidas de alto grau de precisão. Com o objetivo de caracterizar feixes de fontes de agregados de maneira rápida e acessível, um circuito capacímetro é utilizado para medir a influência da deposição de nanopartículas na região dielétrica de um capacitor, uma proposta em aberto na área de nanopartículas. Como essa medida captura a contribuição de inúmeros agregados diferentes, todos depositados na região dielétrica do capacitor, um filtro seletor de massas pode ser utilizado para estreitar a largura da distribuição de tamanhos e obter a influência causada por esse tamanho específico apenas. Neste trabalho será apresentado o projeto para a implementação de um filtro com esse propósito, original de Issendorf e Palmer, cujo princípio de operação é o tempo de voo das partículas, e tem resolução esperada de uma parte em quarenta. Medidas de capacitância também foram realizadas na tentativa de caracterizar a variação da capacitância em função da quantidade de material depositado, com resultados promissores, mas que requerem um maior refinamento das medidas. Os nanoagregados foram produzidos depositados e analisados no Grupo de Física de Nanossistemas e Materiais Nanoestruturados (GFNMN) da física da Unicamp / Abstract: The study of nanoparticles is a challenging one because of the complexity of these systems, which lie on the interface between the small and the big. By that it is meant that many crystals and solids approximations cease to work, and confinement effects begin to appear, as well as surface phenomena which gain strength as surface to volume atoms increase. Due to the small particle sizes, measurements become increasingly difficult, requiring higher and higher precision techniques. With the objective of quickly characterizing beams produced by nanoaggregates sources, a capacitance measuring circuit was created with the intent of measuring the influence of the aggregates on the dielectric constant of the medium between the electrodes, a technique which has not been applied to cluster beams yet. In combination with the capacitance measurements, a mass selecting device was built in order to make the capacitance measurements reflect only a narrow mass distribution, allowing the study of properties of a single cluster size provided they are small enough. In this study will be discussed the project for such a mass filter, original by Issendorf and Palmer, and its implementation on a cluster source. Its principle of operation is the time of flight mass spectrometry, and its projected resolution of about one part in forty. Capacitance measurements were also performed to try and characterize the capacitance change as a function of the density of deposited material. The results were promissing but require further refinement for a strong correlation. All the particle beams were produced at the cluster source operating at the GFNMN group at the department of applied physics at IFGW Unicamp / Mestrado / Física / Mestre em Física / 2011/15018-7 / FAPESP

In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

Les travaux développés dans cette thèse sont dédiés à l’étude des propriétés électroniques de diodes Schottky de silicium amorphe hydrogéné (a-Si:H) et d'hétérojonctions entre silicium amorphe hydrogéné et silicium cristallin, a-Si:H/c-Si au moyen de spectroscopies de capacité de jonctions.Lors de la fabrication des cellules solaires à haut rendement plusieurs paramètres d’une hétérojonction a-Si:H/c-Si doivent être considérés. Premièrement, la densité d’états dans le gap du a-Si:H est d’une grande importance car il s’agit de défauts qui favorisent le piégeage et la recombinaison de porteurs. Deuxièmement, la détermination des désaccords des bandes entre la couche amorphe et la couche cristalline est indispensable puisque ceux-ci contrôlent le transport à travers la jonction et déterminent la courbure des bandes dans c-Si, ce qui va notamment influencer la recombinaison des porteurs sous lumière, donc la tension de circuit ouvert des cellules. Cette thèse a pour but d’étudier la spectroscopie de capacité comme technique d'analyse de paramètres clés pour les dispositifs à hétérojonctions de silicium : la densité d’états dans le a-Si:H et les désaccords des bandes entre a-Si:H et c-Si.La première partie est dédiée à l’étude de la capacité de diodes Schottky. Nous nous concentrons sur un traitement simplifié de la capacité en fonction de la température et de la fréquence reposant sur une expression analytique obtenue par une résolution approchée de l'équation de Poisson. Ce traitement permet en principe d’extraire la densité d’états au niveau de Fermi dans le a-Si:H et la fréquence de saut des électrons depuis un état localisé au niveau de Fermi vers la bande de conduction. En appliquant ce traitement simplifié à la capacité calculée sans approximation à l'aide de deux logiciels de simulation numérique, nous montrons que sa fiabilité et sa validité dépendent fortement de la distribution des états localisés dans la bande interdite du a-Si:H et de la position du niveau de Fermi. Puis nous abordons l’étude de la capacité des hétérojonctions entre a-Si:H de type p et c-Si de type n, et nous mettons particulièrement en avant l’existence d'une couche d’inversion forte à l’interface dans le c-Si, formant un gaz bidimensionnel de trous. Dans une première partie, nous présentons une étude par simulation numérique de la dépendance de la capacité en fonction de la température, pour laquelle un ou deux échelons peuvent être mis en évidence à basse température. Leur analyse montre qu’un des ces échelons est attribué à l’activation de la réponse de la charge dans le a-Si:H, alors que l’autre, présentant une énergie d'activation plus grande, est lié à la modulation de la concentration des trous dans la couche d’inversion forte, lorsque celle-ci existe. On présente ensuite une discussion de résultats expérimentaux. Le régime quasi-statique de la capacité fait ainsi l’objet d’une discussion. Nous mettons en relief le fait que l’approximation de la zone de déplétion ne permet pas de reproduire cette augmentation de la capacité en fonction de la température. Du fait de l’existence de la couche d’inversion forte, la chute de potentiel dans la zone de déplétion du c-Si est plus faible que la valeur déterminée par le calcul attribuant toute la chute de potentiel à la zone de déplétion. Par conséquent, cette approximation conduit à sous-estimer la capacité ainsi que son augmentation avec la température. Nous présentons alors un calcul analytique complet qui tient compte à la fois de la distribution particulière du potentiel dans le a-Si:H, et des trous dans le c-Si dont la contribution à la concentration totale de charges n'est pas négligeable dans la couche d’inversion forte. Le calcul analytique complet permet de bien reproduire les résultats expérimentaux de capacité en fonction de la température; ceci confirme la présence de la couche d’inversion forte dans les échantillons étudiés. / In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

Submitted by RAPHAEL MAZZINE BARBOSA DE OLIVEIRA (mazzine.r@gmail.com) on 2018-08-31T12:54:04Z No. of bitstreams: 1 DISSERTACAO_RMAZZINE.pdf: 2481284 bytes, checksum: e17b453dc770c4f6b899c9c0a5de342a (MD5) / Approved for entry into archive by Ana Carolina Gonçalves Bet null (abet@iq.unesp.br) on 2018-09-05T12:38:02Z (GMT) No. of bitstreams: 1 oliveira_rmb_me_araiq_int.pdf: 2195098 bytes, checksum: 013fbe713d5edbed6ff4d629e660b906 (MD5) / Made available in DSpace on 2018-09-05T12:38:02Z (GMT). No. of bitstreams: 1 oliveira_rmb_me_araiq_int.pdf: 2195098 bytes, checksum: 013fbe713d5edbed6ff4d629e660b906 (MD5) Previous issue date: 2018-08-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Desde a primeira descrição de biossensor reportada por Clark e Lyons em 1962, houve um extenso trabalho no desenvolvimento e aprimoramento de novas técnicas de biossensoriamento para detecção de biomarcadores com relevância médica. Destaca-se nesse processo o estudo de superfície de eletrodos, pois esse influencia diretamente em aspectos como; sensibilidade, estabilidade e qualidade do sinal. Portanto, este projeto consiste em avaliar comparativamente três superfícies de eletrodos baseadas em nanoestruturas contendo nanopartículas de azul da Prússia, funcionando com sonda redox do sistema, e materiais carbonáceos (como óxido de grafeno e nanotubos de carbono) para aplicação em biossensores. Foram avaliados aspectos como composição, características capacitivas redox e estabilidade de sinal. A técnica de análise utilizada é a espectroscopia de capacitância eletroquímica (ECE) que apresenta vantagens como não usar amplificadores de sinal (sondas redox) em solução, configuração esta, importante para métodos de diagnóstico point-of-care. Das superfícies analisadas, a composta por nanopartículas de azul da Prússia e óxido de grafeno (PBNP+GO) apresentou os melhores parâmetros de estabilidade e compatibilidade com os aspectos teóricos da técnica de ECE, sendo então selecionada para realização de testes de biossensoriamento que, através da funcionalização da superfície com anticorpos Anti-IL-6, detectaram seletivamente a presença do biomarcador IL-6. / Since the first description of biosensor reported by Clark and Lyons in 1962, numerous works related to the development and enhancement of novel medical biosensing techniques have been published. In that context, it must be highlighted the study of electrode surfaces as it has direct influence in aspects like; sensitivity, stability and signal quality. Therefore, this project aims to evaluate three electrode surfaces based on nanostructures with Prussian blue nanoparticles, as redox probe, and carbonaceous materials (like graphene oxide and carbon nanotubes) and their application in biosensors. It was evaluated aspects like composition, redox capacitive characteristics and signal stability. The electrochemical capacitance spectroscopy technique (ECE) was used as it offers several advantages like no need of signal amplifiers (redox probes) in solution and, then, making this technique more adequate for point-of-care diagnosis. Among the analysed surfaces, the one composed by Prussian blue nanoparticles and graphene oxide (PBNP+GO) was identified as the best surface in terms of stability and compatibility to the theoretical aspects of ECE. Therefore, that structure was selected to further biosensing essays, by functionalizing the surface with Anti-IL-6 antibodies, that indicated the selective detection of the IL-6 biomarker. / 1583843

Submitted by Veronica Neshmi Salaues Mendoza (neshmi_salaues@hotmail.com) on 2018-04-18T15:18:38Z No. of bitstreams: 1 Salaues_M_Dissert_Araraiq.pdf: 2461056 bytes, checksum: b0790442c72a5c574565c09b578075df (MD5) / Approved for entry into archive by Ana Carolina Gonçalves Bet null (abet@iq.unesp.br) on 2018-04-18T19:43:41Z (GMT) No. of bitstreams: 1 mendonza_vns_me_araiq_int.pdf: 2392917 bytes, checksum: 3697fdc59d96b5ae59f7207b7abe76e6 (MD5) / Made available in DSpace on 2018-04-18T19:43:41Z (GMT). No. of bitstreams: 1 mendonza_vns_me_araiq_int.pdf: 2392917 bytes, checksum: 3697fdc59d96b5ae59f7207b7abe76e6 (MD5) Previous issue date: 2018-03-13 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O sucesso no tratamento de muitos tipos doenças passa pela detecção seletiva e sensível de biomarcadores proteicos que permitam um diagnóstico precoce. A dengue é uma doença infecciosa de diagnóstico clínico impreciso e diagnóstico laboratorial demorado e custoso, a qual não possui tratamento ou vacina efetivos. Portanto se requer de ferramentas diagnósticas precisas, baratas e portáveis que permitam o diagnóstico rápido para realizar um tratamento adequado de sintomas e identificar os focos infecciosos para prevenir o espalhamento da doença. Um biomarcador útil na detecção da dengue, é a proteína NS1 que vem sendo utilizada com sucesso em diferentes plataformas de diagnóstico. Porém, nenhuma das plataformas oferecidas a nível comercial, consegue combinar a precisão, portabilidade, baixo custo e facilidade de manuseio. Portanto, o melhoramento de ditas ferramentas é o foco de bastantes pesquisas. Neste trabalho se apresenta uma plataforma que se amostra útil para a detecção de diferentes biomarcadores, incluindo a proteína NS1. Esta plataforma combina o uso de uma técnica eletroquímica como é a Espectroscopia de Capacitância Eletroquímica (ECE), com o uso de peptídeos redox e está baseada na funcionalização de eletrodos de ouro mediante formação de monocamadas auto-organizadas (SAM) confeccionadas com um peptídeo redox (Fc-Glu-Gli-Ser-Gli-Ser-Cys) desenhado para ser ancorado em superfícies metálicas, ao mesmo tempo que tem capacidade de ancorar uma sonda redox e um bioreceptor na mesma estrutura/molécula, com a vantagem adicional que a SAM obtida tem propriedades anti-incrustantes desejáveis em biossensoriamento. Ensaios realizados com a proteína NS1 permitiram a detecção de esta proteína em concentrações de 2 µg/ml. / Success in the treatment of many kinds of illnesses depends on the selective and sensitive detection of protein biomarkers that allow an early diagnosis. Dengue is and infectious disease of imprecise clinical diagnostic and delayed and expensive laboratorial diagnostic. This disease does not have an effective vaccine or treatment. Therefore, precise, cheap and portable diagnostic tools are necessary to allow a fast diagnostic in order to treat the symptoms, identify focuses of infection, and thus prevent the spreading of the disease. A useful biomarker in the detection of dengue is the protein NS1, which has been successfully used in different diagnostic platforms. However, none of the commercially available platforms combines precision, portability, low cost and user friendliness. Consequently, the improvement of such tools is object of ample research. This work, introduces a platform, which is useful for the detection of various biomarkers, including the protein NS1. This platform combines the usage of an electrochemical technique such as Electrochemical Capacitance Spectroscopy (ECS) and the use of redox peptides. It is based in the functionalization of gold electrodes through formation of Self Assembled Monolayers (SAM) formed by a redox peptide (Fc-Glu-Gli-Ser-Gli-Ser-Cys) designed to bind to metallic surfaces as well as to anchor a redox probe and a bioreceptor in the same structure/molecule. It presents the additional advantage of forming anti-fowling SAMs, which is a highly desirable property for biosensing. Tests made with NS1 protein allowed the detection of this protein in concentrations as low as 2 µg/ml. / 190233/2015-0