Electrochemical fabrication of sandwich nanostructures based on anodic alumina

Abstract

Este trabalho apresenta o projeto e a preparação bem sucedidos de um filme de alumina porosa anódica do tipo sanduíche (PAA/Al 2 O 3 /PAA). Utilizou-se o processo usual, em duas etapas, de anodização de ambos os lados de uma folha de alumínio. A estrutura do filme foi determinada por microscopia eletrônica de mapeamento e emissão de campo (SEM). Os resultados obtidos na microscopia SEM mostraram que as membranas PAA têm uma nano estrutura bem definida. Todos os nano buracos apresentaram-se de forma simétrica em ambos os lados da camada de barreira. O diâmetro médio do poro encontrado foi da ordem de 40 nm.A sandwich porous anodic alumina (PAA/Al 2 O 3 /PAA) film was successfully designed and fabricated using the customary two-step anodization approach on both sides of an aluminum foil. The structure of the film was determined with field emission scanning electron microscopy (SEM). The SEM shows the PAA membranes has a well-defined nanostructure. All nanoholes stand symmetrically on both sides of the barrier layer. The average pore diameter reaches 40 nm. Keywords: porous alumina membrane, anodization, template IntroductionThe structure of porous anodic alumina (PAA) has been known as early as 1932 1 and it consists of an array of uniformly sized straight and parallel pores. Under appropriate anodic oxidation conditions, very regular self-ordered, honeycomb-like hexagonal arrays with a circular pore at the center of each hexagon can be obtained.2 The pore diameters are tunable in the range of 4 to several hundred nanometers, making PAA an ideal template for creating arrays of nanostructrured materials.3 It has been explored as template growth of metallic nanowires, 4-11 semiconductor nanowires, 12-15 magnetic nanowires 16 or carbon nanotube. 17,18However, all the above mentioned PAA membranes have only been formed on one side of the aluminum foil; the other side of the aluminum foil had to be removed. In contrast, if both sides of the aluminum foil are anodically oxidized to form two PAA membranes, a sandwich structure will be obtained. Peng and Chen 19 prepared a PAA/Al/PAA using two different anodic processes on each side of the aluminum foil. In this paper, the sandwich PAA/Al 2 O 3 /PAA membrane can be simply and rapidly fabricated by using the customary two-step oxidation process.Here two graphite sheets are used as counter electrodes during the fabrication of PAA films. A schematic representation of the whole procedure is shown in Figure 1. In the first step, a clean aluminum sheet is anodically oxidized to form an alumina membrane (A) at 40 V and 15°C in a solution of 0.3 mol L -1 oxalic acid. This preformed membrane is subsequently removed by a phosphocromic acid solution to form a textured pattern of concave substrate (B) for the second anodic oxidation process. After another anodic oxidation of B under the same condition as the first step, a well-ordered PAA/Al 2 O 3 /PAA membrane (C) with ordered pores is formed. The two-step process results in a more ordered pore structure in the final template. Beca...

On the structural and electrical properties of metal–ferroelectric–high k dielectric–silicon structure for non-volatile memory applications

“…Low intensity peaks at 2θ = 55 • were observed in all the samples corresponding to 312 orientation of the Al 2 O 3 film compared to the data JCPDS-86-1410. When compared with the XRD pattern of Al 2 O 3 films annealed at different temperatures, it is observed that the film annealed at 425 • C has minimum intensity peaks indicating the fully amorphous nature [35].…”