Orientador: Lauro Tatsuo Kubota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-08T22:44:52Z (GMT). No. of bitstreams: 1 Kisner_Alexandre_M.pdf: 3973690 bytes, checksum: 2810b47ecfaaac028a1bf271a3fc25a0 (MD5) Previous issue date: 2007 / Conjuntos de transistores de efeito de campo sensíveis a íons (ISFETs) foram desenvolvidos no presente trabalho. Implementou-se durante a fabricação destes uma etapa adicional de anodização que possibilitou a formação de uma fina camada de alumina porosa sobre suas portas. Esta serviu como dielétrico e também molde para o crescimento de nanocristais de Ag e Au sobre os dispositivos. Os transistores desenvolvidos foram divididos em dois conjuntos, onde as dimensões de porta de cada conjunto foram de 10 x 50 mm e 50 x 50 mm. Utilizando-se um processo simples de anodização, obteve-se sobre a porta dos transistores uma fina camada de alumina de aproximadamente 60 nm de espessura, contendo uma alta densidade de poros (~ 10 poros/cm) com diâmetro médio de 30 + 6 nm e distribuídos de forma regular. A implementação desta possibilitou não só um aumento significativo na área de porta, bem como molde para o crescimento de nanoestruturas de Ag e Au sobre os transistores, atuando assim como nanoeletrodos de porta. Os testes destes como sensores para soluções com diferentes valores de pH, mostraram que os dispositivos apresentam um curto tempo de resposta (t < 30 s) e que as nanoestruturas metálicas são capazes de aumentar a sensibilidade dos dispositivos em relação àqueles formados apenas por alumina. Os primeiros testes para a detecção de moléculas como glutationa, demonstraram que os ISFETs fabricados são capazes de detectar esta, mesmo sendo uma espécie com baixa densidade de carga, em concentrações submicromolares / Arrays of ion-sensitive field effect transistors (ISFETs) were developed in this work. An additional step in the fabrication process was employed to implement a thin film of porous anodic alumina on the gate. This porous layer works as dielectric and template to the vertical growth of Ag and Au nanocrystals on the gate. The produced ISFETs were divided in two groups, which the gate dimensions were 10 x 50 mm and 50 x 50 mm. Using a simple anodizing process, a 60 nm thickness porous anodic alumina was developed on the gate. This porous film presented a high density porosity (~ 10 pores/cm) with an average pore diameter of 30 + 6 nm and a regular distribution on the gate of those ISFETs. This porous film lead to a significant increase in the gate area and also worked as a template to the growth of Ag and Au nanocrystals, which were used as gate nanoelectrodes. The results of such sensors to detect different pH of the solutions showed that the produced ISFETs present a short response time (t < 30 s). Moreover, the presence of such Ag and Au nanostructures increased the sensors sensitivity in comparison to those observed without nanoelectrodes. The first results to detect species such as glutathione, indicated that the ISFETs are even sensitive to detect small charged species in a submicromolar concentration range / Mestrado / Quimica Analitica / Mestre em Química

Since the first isolation of graphene in 2004 interest in superconductivity and the superconducting proximity effect in monolayer or few-layer crystals has grown rapidly. This thesis describes studies of both the proximity effect in single and fewlayer graphene flakes, as well as the superconducting transition in few unit cell chalcogenide flakes. Optical and atomic force microscopy and Raman spectroscopy have been used to characterise the quality and number of molecular layers present in these flakes. Graphene structures with superconducting Al electrodes have been realised by micromechanical cleavage techniques on Si/SiO2 substrates. Devices show good normal state transport characteristics, efficient back-gating of the longitudinal resistivity, and low contact resistances. Several trials have been made to investigate proximity-induced critical currents in devices with junction lengths in the range 250-750 nm. Unfortunately, no sign of proximity supercurrents was observed in any of these devices. Nevertheless the same devices have been used to carefully characterise proximity doping, (due to the deposited electrode), and weak localisation/anti-localisation contributions to the conductivity in them. In addition this work has been extended to investigations of the superconducting transition in few unit-cell dichalcogenide flakes. Four-terminal devices have been realised by micromechanical cleavage from a 2H-NbSe2 single crystal onto Si/SiO2 substrates followed by the deposition of Cr/Au contacts. While very thin NbSe2 flakes do not appear to conduct, slightly thicker flakes are superconducting with an onset ܶ௖ that is only slightly depressed from the bulk value (7.2K). The resistance typically shows a small, sharp, high temperature transition followed by one or more broader transitions, which end in a wide tail to zero resistance at low temperatures. These multiple transitions appear to be related to disorder in the layer stacking rather than lateral inhomogeneity. The behaviour of several flakes has been characterised as a function of temperature, applied field and back-gate voltage. The resistance and transition temperatures are found to depend weakly on the gate voltage. Results have been analysed in terms of available theories for these phenomena.