Anodic porous alumina

A very early use of anodic alumina as a template involved colonization of the alumina by depositing nanometals in the pores [39]. Somewhat later, Kawai and Ueda templated cobalt and nickel in alumina by electrodeposition [40]. Other metals were deposited by Andersson et al. [41] and Patel et al. [42]. The use of anodic alumina as a template increased after Furneaux et al. developed a convenient voltage-reduction method for detaching the porous anodized alumina from the underlying aluminum [38]. 

Porous anodized alumina (plateshaped membranes), mean pore diameter 80-250 nm. Reactants enter the reactor from opposite membrane sides. 

Thompson GE (1997) Porous anodic alumina fabrication, characterization and applications. Thin Solid Films 297 192-201... 

Eiu Y, Alwitt RS, Shimizu K (2000) Cellular porous anodic alumina grown in neutral organic electrolyte-I. Structure, composition, and properties of the films. J Electrochem Soc 147 1382-1387... 

Fig. 2. SEM images of the top surfaces of porous anodic alumina templates anodized in (a) 4 wt% H2C2O4 and (b) 20 wt% H2SO4. The average pore diameters in (a) and (b) are 44 nm and 18 nm, respectively.

Govyadinov, A. N., and Zakhvitcevich, S. A., Field emitter arrays based on natural self-organized porous anodic alumina. J. Vac. Sci. Technol. B 16,1222 (1998). 

DICHROMATIC LUMINESCENT IMAGES ON THE BASIS OF POROUS ANODIC ALUMINA... 

We report on a method for development of dichromatic luminescent images on the basis of porous anodic alumina grown in several electrolytes with the use of europium deposition fiom alcoholic solution of lanthanide nitrates. 

The same effect can be observed if the stage of spin-on deposition of sol is replaced by immersion of the sample in solution of europium salt. These examinations show that porous anodic alumina grown in oxalic acid which displays inherent blue PL can be used for fabrication of dichromatic luminescent images only, while red luminescence related to Eu is not observed from the same area of the sample. 

Figure 3. PL spectra measured from dichromatic luminescent image (a) blue area of porous anodic alumina film of 30 pm thickness after anodizing in oxalic acid electrolyte (b) red area of a porous anodic alumina film of 20 pm thickness after anodizing in orthophosphoric acid electrolyte, followed by immersion in europium nitrate and subsequent heat treatment at 200 °C for 30 min.

Some useful advantages of PAA for fabrication of stable magnetic nanoparticles are presented by porous anodic alumina (PAA) as a matrix to deposit magnetic material. Magnetic material is deposited into the pores... 

DEFECTS IN POROUS ANODIC ALUMINA FILMS FORMED ON HIGH-PURITY ALUMINIUM... 

The formation of defects in porous anodic alumina films fabricated in phosphoric acid solutions has been studied. TEM and SEM examinations revealed that defects appear at the triple point junctions of the cell boundaries, where neighbouring celis meet. The defects represent voids in the anodic alumina and develop into spatial structures that comprise a central void at the triple-point junction extending into tubular branches that pass toward the pore wall. The defects are generated continuously during the anodic film growth under appropriate anodising conditions. Additional post-anodising treatment also results in periodic arrays of circular nanoholes in the pore walls. 

Figure 1. SEM images of the fracture sections of porous anodic alumina films formed in 1 vol.% phosphoric acid...

Figure 3. TEM images of ion beam-thinned porous anodic alumina films formed in phosphoric acid electrolyte (a) 0.3M acid at MOV (b) 1.2 M acid at a constant current of 5 mA/cm. ...

Imperfections that are inherent to all of the discussed test structures are minimized partially in case of application of porous anodic alumina. It is known that anodic alumina has sharp pore edges [4]. Therefore it may be used as tiplike grating. In order to combine the benefits of porous anodic alumina and a nanoscale tip array a one-step electrochemical approach is used to fabricate nanoscale alumina tips (tip-like anodic alumina) [5]. However, a curvature radius of pore edges or alumina nanotips of these structures is too high for ultrasharp SPM tip characterization. 

Porous anodic alumina films were formed by a two-step anodic oxidation of aluminum foil (99.99% purity) (thickness 100 jum) or of thin aluminum film sputtered onto silicon substrate. First step was performed under lOmA/cm constant current density in 40 g/1 aqueous solution of (COOH)2 during 60 min. After first anodization the formed anodic oxide was removed in the aqueous solution of 0.35 M H3PO4 and 0.2 M CrOs at 90°C. The second anodization was performed in the same regimes as the first one. The formed oxide was removed from the specimen after the first anodization. Nanostructured aluminum samples were rinsed in deionized water and dried in an argon flow. 

The t wo-stage porous an odization w as ma de f rom th e f ront s ide of the samples. At the first stage, the 5 pm thick porous anodic alumina layer with ordered matrix of hexagonal pores was formed due to the self-organization process. The anodization time was about 5 min. 

To get more detail on the light transfer by the anodic alumina oxide film, the light intensity enhancement from a flat white light emitting diode panel was examined. The porous anodic alumina film was placed between LEDs and a detector at a variable LED film distance and the light intensity Laa was... 

Figure 3. The ratio of light intensities with the porous anodic alumina film between the LED panel and the detector and without the film depending on the distance between the film and the LED...

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