Fabrication of Anodized Alumina Membrane

The growth of porous oxide on aluminum in various electrolytes under anodic bias has been studied for some time [10]. When aluminum is anodized in certain electrolytes, like phosphoric, sulfuric or oxalic acids, using a two-step process followed by etching, an array of close packed cells (pores) arranged in a near hexagonal pattern develops. Each cell contains a cylindrical pore and the axis of the cell is perpendicular to the surface. 

Recently there has been a report of the use of Ar+ ion milling (500 eV) to open the bottom cap in the anodized alumina using a normal ion milling machine. The rate of milling can be controlled by the ion beam current density (generally 1 mA cm ) and also the incident angle. The nominal milling rate is 100 A min at normal incidence for a current density of 1 mA cm [12]. 

There are also reports of opening the barrier layer by anodic dissolution [13]. An applied voltage less than the anodic oxidation voltage ( 10-20 V) can lead to dissolution of the barrier oxide. For this to happen the dissolution rate has to be more than the anodic oxidation rate. This method is particularly suitable for cases where the alumina is being grown as a template on a substrate and the membrane is thin and supported by a substrate. 

Generally the AM films are composed of polycrystalline y-alumina which is expected to have defects. The body of the membrane is more compact and crystalline 

Anodized Alumina Membrane as a Mask for Physical Vapor Deposition 

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