Francisco Trivinho-Strixino

Active waveguide effects from porous anodic alumina: An optical sensor proposition

We present in this paper an active waveguide effect observed in porous anodic alumina (PA), which can be applied in optical sensors. The spectral position, shape, and polarization effect of the narrow waveguide modes is described. An analytical test with a commercial pesticide was performed.

Tetragonal to monoclinic phase transition observed during Zr anodisation

Plasma electrolytic oxidation (PEO) is a coating procedure that utilises anodic oxidation in aqueous electrolytes above the dielectric breakdown voltage to produce oxide coatings that have specific properties. These conditions facilitate oxide formation under localised high temperatures and pressures that originate from short-lived microdischarges at sites over the metal surface and have fast oxide volume expansion. Anodic ZrO2 films were prepared by subjecting metallic zirconium to PEO in acid solutions (H2C2O4 and H3PO4) using a galvanostatic DC regime. The ZrO2 microstructure was investigated in films that were prepared at different charge densities. During the anodic breakdown, an important change in the amplitude of the voltage oscillations at a specific charge density was observed (i.e., the transition charge density (QT)). We verified that this transition charge is a monotonic function of both the current density and temperature applied during the anodisation, which indicated that QT is an intrinsic response of this system. The oxide morphology and microstructure were characterised using SEM and X-ray diffraction experiments (XRD) techniques. X-ray diffraction analysis revealed that the change in voltage oscillation was correlated with oxide microstructure changes during the breakdown process.

Desenvolvimento de um sistema automatizado para a fabricação de filmes automontados

In this technical note, we describe the construction of a low-cost computer controlled device for layer-by-layer film fabrication. The software allows to control multiple material deposition, washing and drying steps and the time for each operation. To test the device, we produced and characterized self-assembled films of conductive polymers by alternating poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA) via the layer-by-layer technique.

Luminescence in Anodic ZrO2 Doped with Eu(III)ions

Photoluminescence and structure properties of anodically prepared ZrO2 oxide films doped with Europium (III) ions were investigated. Microstructural analysis reveals that the predominant crystallographic structure is the monoclinic phase with small quantities of tetragonal and cubic phases. Important crystallite size and isotropic strain are observed for the monoclinic phase and they are related to the incorporation of Europium (III) ions inside the oxide matrix. The photoluminescence spectrum reveals a broad emission band in the range between 350–650 nm related to the ZrO2. Emission lines corresponding to transitions from the lowest emitting 5D0 level of Eu(III) to several sublevels of the ground state level 7F0, 1, 2, 3, 4 were also observed.

COMPARAÇÃO E CONSTRUÇÃO DE REATORES DE "MILD" E "HARD ANODISATION" PARA FABRICAÇÃO DE ALUMINA ANÓDICA POROSA

The mild anodization (MA) reactor is exemplified for its operational simplicity and its excellent control over the experimental parameters that are involved in the anodization process. This method provides porous anodic alumina films with a regular cell-arrangement structure. This offers a better cost-benefit ratio than the other equipment configurations that are used to fabricate nanoporous structures (i.e., ion beam lithography). Conversely, the hard anodization (HA) reactor produces oxides at a rate that is 25 to 35 times faster than the MA reactor. The produced oxides also have greater layer thicknesses and interpore distance, and with a uniform nanopore spatial order (> 1000). In contrast to MA reactors, the construction of an HA reactor requires special components to maintain anodisation at a high potential regime. Herein, we describe and compare both reactors from a technical viewpoint.

Electrochemical Synthesis of Nanostructured Materials

Abstract This chapter addresses the application of electrochemical synthesis techniques, such as electrodeposition and anodic oxidation of metals, from a practical standpoint. Some fundamental aspects of electrochemistry are addressed, and examples of the use of the electrodeposition technique for obtaining metallic structures, such as nanoscale bi- or multilayers, are presented. Techniques for characterization of metallic nanostructure, such as atomic force microscopy and the use of electrochemical quartz crystal microbalance, are also described. The synthesis of nanostructures from anodic oxides is discussed, with application to porous anodic alumina and titanium dioxide nanotubes as examples. The anodic doping technique can be used to modify the properties of these oxides. Thus, through simple explanations, using didactic language, and with the aid of figures taken from the literature, we provide the reader with a basic guide to the synthesis of new nanomaterials using electrochemical methods.

SÍNTESE ELETROQUÍMICA DE MATERIAIS NANOESTRUTURADOS

Este capitulo aborda, de forma pratica, a aplicacao de tecnicas eletroquimicas de sintese como a eletrodeposicao e a oxidacao anodica de metais. Alguns aspectos fundamentais da eletroquimica sao abordados, e sao apresentados exemplos da utilizacao da tecnica de eletrodeposicao para obtencao de estruturas metalicas com bi- ou multicamadas em escala nanometrica. Tambem sao descritas tecnicas de caracterizacao do deposito metalico, como a microscopia de forca atomica e a microbalanca eletroquimica de cristal de quartzo. A sintese de nanoestruturas a partir de oxidos anodicos e abordada, com exemplos de aplicacao da alumina anodica porosa e dos nanotubos de dioxido de titânio. A tecnica de dopagem anodica pode ser utilizada para modificar as propriedades destes oxidos. Dessa forma, atraves de explicacoes simples, em linguagem didatica e com o auxilio de figuras com exemplos da literatura, o leitor encontrara um guia basico para sintese de novos materiais na escala nanometrica utilizando metodos eletroquimicos.