Affinity-based biosensors, or in short biosensors, are extremely powerful and versatile analytical tools which are used for the detection of a wide variety of bio-molecules. In recent times, there has been a need for developing low-cost and portable affinity-based biosensor platforms. Such systems need to have a high density of detection sites (i.e biosensing elements) in order to simultaneously detect multiple analytes in a single sample. This has led to the creation of integrated biosensors, which make use of integrated circuits (ICs) for bio-molecular detection. In such systems, it has been demonstrated that by taking advantage of the capabilities of semiconductor and very large scale integrated (VLSI) circuit fabrication processes, it is possible to build compact miniaturized biosensors, which can be used in wide variety of applications such as in molecular diagnostics and for environmental monitoring. Among the various detection modalities for biosensors, Electrochemical Impedance Spectroscopy (EIS) permits real-time detection and has label-free detection capabilities. EIS is fully electronic in nature. Hence, it can be implemented using standard IC technologies. The versatility and ease of integration of EIS makes it a promising candidate for developing integrated biosensor platforms. In this thesis, we first examine the underlying principles of EIS method of biosensing. By analyzing an immunosensor assay as an example, we show that EIS based biosensing is a highly sensitive detection method, which can be used for the detection of a wide variety of analytes. Since EIS relies on small impedance changes in order to perform detection, it requires highly accurate models for the electrode-electrolyte systems. Hence, we also introduce a compact modeling technique for the distributed electrode-electrolyte systems with non-uniform electric fields, which is capable of modelling noise and other non-idealities in EIS. In the second part of this thesis, we describe the design and implementation of an integrated EIS biosensor array, built using a standard complementary metal-oxide-semiconductor (CMOS) process. The chip is capable of measuring admittance values as small as 10nS and has a wide dynamic range (90dB) over a wide range of frequencies (10Hz-50MHz). We also report the results obtained from the DNA and protein detection experiments performed using this chip. / text

Electrolyte additives are generally used in commercial Li-ion cells to improve capacity retention and calendar life. Although it is apparent that electrolyte additives play an important role, the details of how they work are poorly understood. In order to be able to distinguish the effect of an additive on the positive or negative electrodes, an experimental method has been developed based on electrochemical impedance spectroscopy of symmetric cells constructed from electrodes of disassembled full cells similar to the method described by previous workers. This technique proved to be useful and showed that the effects of additives on both electrodes depend strongly on their concentration. It also showed that in some cases, when two additives are introduced in the same cell, both additives contribute to the formation of the surface layer of both electrodes. In other cases, each additive controls the formation of the surface layer of only one electrode.

Thesis (Ph. D.)--Ohio University, March, 2000. / Title from PDF t.p.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / Hamid Garmestani, Committee Member ; Arun M. Gokhale, Committee Member ; Rosario A. Gerhardt, Committee Chair.

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2006 Aug 12.

Oxide ion conductors have received much attention in recent years due to their application as solid oxide fuel cells (SOFC) electrolytes. A strong correlation exists between the oxide ion conductivity and the crystal structure of an oxide ion conductor. Consequently, to develop novel electrolytes it is important to discover new structural families of oxide ion conducting materials. In the present study, the electronic properties and crystal structure of the hexagonal perovskite derivative Ba3MoNbO8.5 are reported. Ionic transport number and variable oxygen partial pressure conductivity measurements evidenced that Ba3MoNbO8.5 presents solid oxide ion conduction. A bulk conductivity of 2.2 x 10-3 S cm-1 at 600 C was observed, which is comparable to other leading oxide ion conductors. Ba3MoNbO8.5 is the first hexagonal perovskite derivative to exhibit fast solid oxide ion conductivity. The Ba3MoNbO8.5 structure was described by a hybrid structural model composed by a superimposition of the 9R hexagonal perovskite and palmierite structures. (Mo/Nb)O4 units coexist with (Mo/Nb)O6 units within the structure, forming a disordered arrangement of Mo/Nb tetrahedra and octahedra. Variable temperature neutron diffraction experiments allowed determination of the structural factors at the basis of the oxide ion conduction. In particular, the flexible coordination of the Mo/Nb cations and the distortion of the Mo(1)/Nb(1) polyhedra are thought to enhance the electrical properties so that a conductivity comparable to other leading solid oxide ion conductors is observed. Study of the electrical and structural features of the Ba3Mo1 xNb1+xO8.5-x/2 (x = 0.10, 0.20, 0.30) series also evidenced that the relative ratio of (Mo/Nb)O4 tetrahedra to (Mo/Nb)O6 octahedra and the disorder of the oxygen sub lattice are important for the conduction of the Ba3MoNbO8.5 system. Impedance spectroscopy measurements on the hexagonal perovskite derivatives Ba7MoNb4O20 and Ba3WNbO8.5 showed evidence of ionic contributions in these systems. In addition, neutron diffraction experiments revealed that both Ba7MoNb4O20 and Ba3WNbO8.5 exhibit structural characteristics analogues to Ba3MoNbO8.5. The results of the present study indicate the prospect of designing new oxide ion conductors with mixed tetrahedral and octahedral d-metal units in the hexagonal perovskite family.

REIS JÚNIOR, Daniel Valim dos. Espectroscopia Vibracional e de Impedância de A1-xA’xTaWO6.nH2O (A=H, Li, A’ = Ag,H). 2009. 121 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2009. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-04T18:11:28Z No. of bitstreams: 1 2009_tese_dvreisjunior.pdf: 3014923 bytes, checksum: d5b180893837986bd0a9df72ba4a2d01 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T15:00:37Z (GMT) No. of bitstreams: 1 2009_tese_dvreisjunior.pdf: 3014923 bytes, checksum: d5b180893837986bd0a9df72ba4a2d01 (MD5) / Made available in DSpace on 2015-05-07T15:00:37Z (GMT). No. of bitstreams: 1 2009_tese_dvreisjunior.pdf: 3014923 bytes, checksum: d5b180893837986bd0a9df72ba4a2d01 (MD5) Previous issue date: 2009 / We have performed the characterization of doped pyrochlore (H1−xAgxTaWO6.H2O) and trirutile (Hx Li1−x TaWO6 ) samples. Raman spectroscopy and infrared transmitance thechniques were used to investigate the structural properties of doped trirutile. The studies revealed that HxLi1−xTaWO6 samples belong to the tetragonal polar symmetry P421m(D32d). Raman spectroscopy studies were also used to identify the nature of the Raman active modes of the pyrochlore materials. Among the Raman modes we can highlight the ones observed at 340 and 720 cm−1 which originate from ν4 and ν3 infrared active modes. Their presence in the Raman spectra indicates a positional disorder of the Ta and W cations. Furthermore, we studied the dependence of the frequency of these modes on the Ag+ concentration, wich revealed a monotonic decrease of the wave number with the dopant concentration x (wich was only broken for a concentration x = 0.5). Impedance spectroscopy study was performed to the electric characterization of the pyrochlore materials. The experiment consisted of measuring the dependence of the im- pedance of these system on the temperature, throughout the heating (25 to 110 o C) and the cooling (110 to 25 o C) processes. The goal was to try to avoid the humidity effect in the impedance spectra. However, for the sample with x = 0.20, we observed an anomalous response for the conductivity during the cooling process. To explain these results, we performed a microstructural characterization of the samples with x = 0.80, 0.67 and 0.20. The result is that the sample with x = 0.20 are well characterized by the model of “easy-path”, having high porosity, while the other two should have a Suzuki-type precipitate phase structure. These results explain the anomaly in the Arrehnius plot observed for the x = 0.20 concentration sample as an effect of the different microstructures. In this study we could also verify that the doped samples had a clear dependence of the activaction energies on the dopant concentration. With the exeption of the sample with concentration x = 0.20, the activation energies during the cooling process were observed to be between 0.60 and 0.23 eV, wich are the values of their pure counterparts, as reported in the literature. / Realizamos a caracterização das amostras H1−x AgxTaWO6.H2O pirocloro e Hx Li1−xTaWO6 trirrutilo. Técnicas de espectroscopia Raman e transmitância de infravermelho foram usadas com o objetivo de investigar propriedades estruturais do trirrutilo dopado. Os estudos revelaram que as amostras HxLi1−xTaWO6 pertencem ao sistema tetragonal polar P421m (D32d). Os estudos Raman serviram também para identificar a natureza dos modos Raman ativos dos materiais pirocloro. Dentre os modos Raman que podemos destacar aqueles observados a 340 e 720cm−1 que são originários dos modos infravermelho ativos ν4 e ν3. A presença destes modos indica desordem posicional dos cations Ta e W. Além disso, estudamos a dependência do número de onda destes modos com relação a concentração de Ag+, que revelou um decréscimo monotônico do número de onda com a concentração (que só foi quebrada para a concentração x = 0,5). Estudo de espectroscopia de impedância foi feito para a caracterização elétrica dos materiais pirocloros. O experimento consistiu em medidas da dependência da impedância destes sistemas com a temperatura, durante o aquecimento (25 a 110 oC), e resfriamento (110 a 25 oC). O objetivo foi tentar evitar o efeito da umidade no espectro de impedância. No entanto, para amostra com x = 0,20, obtemos uma resposta anômala da condutividade durante o resfriamento. Para explicar esse resultado, realizamos caracterização de microestrutura nessa amostra e nas amostras com x = 0,80 e 0,67. O resultado é que a amostra com x = 0,20 é bem caracterizada pelo modelo de “easy-path” por possuir elevada porosidade enquanto nas outras duas devem possuir estrutura de precipitado de fase tipo Suzuki. Estes resultados serviram para explicar porque a anomalia no gráfico de Arrehnius ocorreu somente na amostra com concentração 0,20: diferença de microestrutura. Neste estudo podemos constatar também que as amostras dopadas tiveram uma dependência das energias de ativação com relação às taxas de concentração. Com exceção da amostra com taxa de concentração 0,20, as energias de ativação no resfriamento, encontram-se entre os valores de 0,60 e 0,23 eV de suas contrapartes puras registradas na literatura.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-14Bitstream added on 2014-06-13T19:12:22Z : No. of bitstreams: 1 braunger_ml_me_rcla.pdf: 1994940 bytes, checksum: 93302556a6228fb6bcbdf01e53c83e00 (MD5) / Neste trabalho foi avaliada a condutividade elétrica de vidros com composição (mol%) 22Na2O·8CaO·65SiO2·5MO2, com M = Si, Ti, Ge, Zr, Sn e Ce, sem e com troca iônica Ag+↔Na+ em 350 ºC por 1 hora. Após a troca iônica, amostras também foram submetidas a tratamento térmico em 500 ºC durante 24 horas. As medidas elétricas foram realizadas com um analisador de impedâncias Solartron. Foram analisados gráficos de Z” vs. Z’ e de σ’ vs. f em função da temperatura com o objetivo de se determinar, de duas maneiras diferentes, as energias de ativação para a condutividade elétrica, Eσ. Os valores das resistências elétricas das amostras são obtidos a partir de gráficos Z” vs. Z’ quando Z” se anula para baixas frequências. Conhecendo-se o parâmetro geométrico da amostra, calcula-se a condutividade para corrente contínua, σdc. Através das curvas σ’ vs. f determina-se σdc quando f → 0. Gráficos de Ln σdc vs. T-1 possibilitaram determinar 0,724 < Eσ < 0,826 eV, valores que concordam com os encontrados na literatura. Após submetidas à troca iônica, as amostras apresentaram aumento da condutividade. Por outro lado, o tratamento térmico posterior diminui a condutividade da maioria das amostras, provavelmente, devido à formação de nanopartículas de prata metálica na matriz vítrea. Para verificar alterações da composição devido à troca iônica e ao tratamento térmico utilizamos a técnica de espectroscopia de energia dispersiva de raios-X, EDS, no volume e na superfície das amostras. Verificou-se que a Ag migra para o volume durante o tratamento térmico, tendendo a tornar constante a sua distribuição, dependendo do cátion tetravalente, M4+, presente na matriz vítrea. A espectroscopia de reflexão difusa no infravermelho, DRIFT, indicou alterações na estrutura da superfície das... / In this work, it has been evaluated the electrical conductivity of glasses with composition (mol%) 22Na2O·8CaO·65SiO2·5MO2, with M = Si, Ti, Ge, Zr, Sn and Ce, without and with ion exchange Ag+↔Na+ at 350 ºC for 1 hour. After the ion exchange, samples were also submitted to thermal treatment at 500 ºC for about 24 hours. Electrical measurements were carried out with a Solartron impedance analyzer. Z” vs. Z’ and σ’ vs. f plots were analyzed as a function of temperature in order to determine, by two distinct approaches, the activation energies for the electrical conductivity, Eσ. The values of the electrical resistances of the samples are obtained from Z” vs. Z’ plots when Z” nulls itself at low frequencies, and knowing the geometric parameter of the sample, the continuous current conductivity, σdc, can then be calculated. Through σ’ vs. f plots, one can determine σdc when f → 0. We were able to determine 0,724 < Eσ < 0,826 eV by Ln σdc vs. T-1 plots, and those values agree with the ones found in the literature. When submitted to ion exchange, the samples showed an increased conductivity. On the other hand, a subsequent thermal treatment diminishes the conductivity for most of the samples, probably due to the formation of metallic silver nanoparticles in the vitreous matrix. In order to check for compositional modifications due to the ion exchange and thermal treatment, we have employed the energy dispersive X-ray spectroscopy technique, EDS, in the bulk and surface of the samples. It has been observed that Ag migrates towards the bulk during the thermal treatment, tending to reach a constant distribution, depending on the tetravalent cation, M4+, in the vitreous matrix. The diffuse reflectance infrared Fourier transform, DRIFT, have pointed changes in the surface structure of the samples... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:23:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-08-16Bitstream added on 2014-06-13T18:50:17Z : No. of bitstreams: 1 benites_ta_me_araiq_parcial.pdf: 365660 bytes, checksum: 563ff4de53643caf527ab2319e2ffd76 (MD5) Bitstreams deleted on 2014-11-14T12:17:01Z: benites_ta_me_araiq_parcial.pdf,Bitstream added on 2014-11-14T12:17:46Z : No. of bitstreams: 1 000721769.pdf: 1532537 bytes, checksum: 1f1f903eabe42a2227cf65971f622a31 (MD5) / O estudo das propriedades dielétricas das monocamadas automontadas de alcanotióis sobre o ouro (SAMs) é importante no campo da biotecnologia, já que essas camadas proporcionam uma estrutura fundamental na construção dos eletrodos quimicamente modificados, com sua principal aplicação na confecção dos biossensores. A análise das propriedades de bloqueio pelas SAMs é frequentemente feita por meio de técnicas eletroquímicas e de resposta em frequência, pois são extremamente eficazes no entendimento das características físico-químicas interfaciais de modificação desses filmes, além de apresentarem praticidade e velocidade de realização. Uma forma bastante apropriada de analisar a capacidade dielétrica das SAMs é quantificando a velocidade de transferência eletrônica frente a uma espécie eletroativa. Nesse trabalho foram caracterizadas monocamadas de diferentes espessuras em um meio com espécie eletroativa em concentrações variadas, a partir do cálculo da constante de transferência heterogênea de elétrons, feitas pelas metodologias propostas por diferentes autores e por uma metodologia inédita que será detalhada no corpo do trabalho / The study of the dielectric properties of self-assembled monolayers of alkanethiols on gold (SAMs) is of paramount importance to biotechnology, as these layers provide a fundamental structure in the construction of chemically modified electrodes, with its main application in fabrication of biosensors. The analysis of the blocking properties of SAMs is often done by electroanalytical techniques and frequency response, as they are extremely effective in understanding the physico-chemical interfacial modification of these films, and offer convenience and speed of execution. A very appropriate manner of evaluating the blocking ability of SAMs is quantifying dielectric constant and the heterogeneous electron transfer rate across from one electroactive species in solution. In this study monolayers of different thicknesses were characterized in a medium with electroactive species in different concentrations to calculate of the heterogeneous electron transfer constant by classical methods which were compared with a new methodology detailed in the present work

Made available in DSpace on 2014-10-09T12:34:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:48Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP