Anodizing Behavior of Aluminum Foil Patterned with SiO[sub 2] Mask

Abstract

SiO 2 -patterned anodic aluminum oxide ͑AAO͒ is fabricated on the surface of aluminum ͑Al͒ foil by combining both photolithography and anodizing technique. Tilted pores and ridge-like features on the Al surface are observed under the SiO 2 mask by scanning electron microscopy characterization. A mechanism based on the deflection of electric field due to the existence of SiO 2 barrier on Al surface has been proposed to explain the observed anodizing behavior. Moreover, large-scale ordered metallic Al patterns are also revealed by removing the AAO film and SiO 2 mask.Anodic aluminum oxide ͑AAO͒, a kind of typical self-ordered nanochannel material, has been attracting continuous attention from interdisciplinary researchers due to its many potential technical applications. 1-4 The material, formed by anodizing aluminum ͑Al͒ in appropriate acid solution, is usually composed of many hexagonally arranged cells with cylindrical pores in the center. 5 The porous structure exhibits local ordered close-packed hexagonal arrays with alumina walls. These characters make AAO an ideal template to construct various one-dimensional ͑1D͒ nanoscaled materials including nanotubes and nanowires. [6][7][8][9] Design and realization of patterned porous material provide us many opportunities in practical applications such as in electronic devices, 10,11 photonic crystals, 12 microfluidic devices, 13 et al. Recently, Masuda and co-workers 14,15 reported a series of fabrications of highly ordered AAO structures with different pore shapes by patterning Al foils using nanoindentation technique. In their work, long-range-ordered AAO patterns with nanoscale pore diameter and special pore distance were fabricated by suitable pretexture of Al surfaces before anodizing. Although the research work from Masuda provides a promising approach to prepare large-area ordered AAO template, the fragility of AAO template still remains a big problem toward various applications. In order to address the challenge, Atanassov and co-workers 16,17 developed another method to indirectly pattern Al foil surfaces by using SiO 2 as a protecting mask. SiO 2 can exhibit good adhesion to the Al foil and prevent Al from being anodized by acidic electrolyte. The SiO 2 pattern used in their work was hundreds of micrometers wide and a few micrometers thick. Finally, patterned AAO nanopore arrays with intermittent Al supports were obtained and were supposed to enhance the mechanical strength of AAO template. In addition, they have also observed another phenomenon, the growth of tilted pores underneath the SiO 2 mask, but they did not give a reasonable explanation. In principle, the anodizing mechanism of AAO based on the electrical field distribution at pore tips has been generally accepted to explain the porous oxide growth. 18 Pore growth relies on the equilibrium of two processes. One is oxide dissolution at the oxide/electrolyte interface that was enhanced by electric field, and another is oxide growth at the metal/oxide interface. Further refined models and theories 19-...

Patterned anodic aluminium oxide fabricated with a Ta mask

“…In our previous report [22], the growth mechanism of the tilted pores was attributed to the deflection of the electric field due to the existence of an insulator barrier layer in the case of SiO 2 masking. When the anodic voltage was applied, the potential would increase in the SiO 2 covered regions, further inducing deflection of the electric field at the borders of SiO 2 mask and leading to the lateral growth of AAO pores.…”

“…Such tilted pore structures were first reported to be observed by abruptly decreasing the anodic voltage during the anodizing process [19][20][21]. In our previous work [22], a thick layer of SiO 2 pattern was deliberately coated on the metallic Al surface as a mask before anodizing. A radially tilted pore structure was evidently observed underneath the SiO 2 mask after anodization.…”

“…The standard photolithography procedure was employed as reported in our previous work [22]. A layer of 20 nm Ta film was then deposited on the Al substrates by DC magnetron sputtering.…”

Patterned Nanorod Arrays Produced from Hydrophobically Masked Templates

“…Presently, patterning can be achieved through seeded nucleation or the use of physically patterned or masked templates. [12][13][14][15][16][17] Seeded nucleation, which does not require a template for nanorod growth, involves the deposition of nanorod seeds in the desired pattern and subsequent nanorod growth from these seeds. [12][13][14] A second approach is to use a physically patterned template by either applying a mask to a * Author to whom correspondence should be addressed.…”

“…uniform template or masking the template during pore formation. [15][16][17] While both methods are able to produce patterned arrays, physical patterning is labor intensive and seeded nucleation has only been demonstrated for a limited number of compositions, most notably ZnO nanorods and carbon nanotubes.…”