Controlling Factor of Self-Ordering of Anodic Porous Alumina

Ono, Satoshi; Saito, M.; Ishiguro, Miyuki; Asoh, Hidetaka

doi:10.1149/1.1767838

Cited by 343 publications

(293 citation statements)

References 23 publications

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“…26 However, the ratio of barrier layer thickness to anodization voltage (∼1.0 nm/V) in PAA is 20% lower, showing a "hard anodization" characteristic. 26 Considering the applied voltage (400 V) is much higher than the reported breakdown voltage in citric acid (245 V), 27 this could be ascribed to the relatively high current density involved in the anodization process in accordance with the high field conductivity theory. 2,13,26 A more straightforward evidence of the defects guided process can be found based on the substrates with artificially pre-defined nanoconcaves ( Figure 1c).…”

Section: Resultsmentioning

confidence: 90%

“…However, smaller defects still remain on polished Al foils, which are sufficient to create electric field inhomogeneity and initial the pore formation under lower voltages. The conventional anodization voltages in sulfuric, 31 oxalic, 31 phosphoric, 31 citric acid, 27 and malonic acid 32 solutions are usually lower than the critical voltages required to form BAA. That could be the reason why we rarely observe BAA under general anodization conditions.…”

Section: Resultsmentioning

confidence: 99%

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Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Yang

Huang

Lin

et al. 2014

ACS Appl. Mater. Interfaces

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Aluminum (Al) anodization leads to formation of porous structures with a broad spectrum of applications. Naturally or intentionally created defects on Al surfaces can greatly affect pore initiation. However, there is still a lack of systematic understanding on the defect dependent morphology evolution. In this paper, anodization processes on unpolished, polished, and nanoimprinted Al substrates are investigated under high voltages up to 600 V in various acid solutions. A porous structure is obtained on the unpolished and nanoimprinted Al foils with rough surface texture, whereas a compact film can be rationally obtained on the polished Al foil with a highly smooth surface. The observation of surface roughness dependent oxide film morphology evolution could be originated from the high voltages, which increases the threshold requirement of defect size or density for the pore initiation. Electrostatics simulation results indicate that inhomogeneous electric field and its corresponding localized high current induced by the surface roughness facilitate the initiation of nanopores. In addition, the porous films are utilized as templates to produce polydimethylsiloxane nanocone and submicrowire arrays. The nanoarrays with different aspect ratios present tunable wettability with the contact angles ranging from 144.6°to 56.7°, which hold promising potentials in microfluidic devices and self-cleaning coatings.

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Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Yang

Huang

Lin

et al. 2014

ACS Appl. Mater. Interfaces

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“…At 200 Am -2 , the applied potential increased rapidly to over 200 V within 12 min, and intense gas evolution was observed from the aluminum anode due to "burning" by the electric current [28]. From these electrochemical measurements, constant-voltage anodizing over the range of 100-150 V (yellowish region in Fig.…”

Section: Characterization Of the Anodized Specimensmentioning

confidence: 82%

“…1 summarizes the anodizing electrolytes that have been reported to date for porous alumina fabrication. Sulfuric (H 2 SO 4 ), oxalic ((COOH) 2 ), and phosphoric (H 3 PO 4 ) acids are well-known, self-ordering anodizing solutions for porous alumina fabrication, and highly ordered porous alumina can be obtained by anodizing in these solutions at constant voltages of 18-25 V, 40 V, and 160-195 V, respectively [24][25][26][27][28][29]. Malonic acid (HOOC-CH 2 -COOH) and tartaric acid (HOOC-(CHOH) 2 -COOH), typical dicarboxylic acids, have also been reported to support the fabrication of highly ordered porous alumina fabrication at 120 V and 195 V, respectively [30,31].…”

Section: Introductionmentioning

confidence: 99%

Fabrication of Anodic Porous Alumina by Squaric Acid Anodizing

Kikuchi¹,

Yamamoto²,

Natsui³

et al. 2014

Electrochimica Acta

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The growth behavior of anodic porous alumina formed via anodizing in a new electrolyte, squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione), is reported for the first time. A high-purity aluminum foil was anodized in a 0.1 M squaric acid solution at 293 K and a constant applied potential of 100-150 V. Anodic oxides grew on the aluminum foil at applied potentials of 100-120 V, but a burned oxide film was formed at higher voltage. Anodic porous alumina with a cell size of approximately 200-400 nm and sub-100-nm-scale pore diameter was successfully fabricated by anodizing in squaric acid. The cell size of the anodic oxide increased with anodizing time because of the uneven growth of the porous layer. The anodic porous alumina obtained by squaric acid anodizing consists of amorphous Al 2 O 3 containing 5-6 at% carbon from the electrolyte. Fig. 1). The morphology of anodic porous alumina, especially its cell size (identical meaning to interpore distance) and pore diameter in the porous layer, is limited by the electrolyte and voltage (electrochemical potential) applied during anodizing [23,24]. Fig. 1 summarizes the anodizing electrolytes that have been reported to date for porous alumina fabrication. Sulfuric (H 2 SO 4 ), oxalic ((COOH) 2 ), and phosphoric (H 3 PO 4 ) acids are well-known, self-ordering anodizing solutions for porous alumina fabrication, and highly ordered porous alumina can be obtained by anodizing in these solutions at constant voltages of 18-25 V, 40 V, and 160-195 V, respectively [24-29]. Malonic acid (HOOC-CH 2 -COOH) and tartaric acid (HOOC-(CHOH) 2 -COOH), typical dicarboxylic acids, have also been reported to support the fabrication of highly ordered porous alumina fabrication at 120 V and 195 V, respectively [30,31]. In addition, several other electrolytes, such as chromic (H 2 CrO 4 ) [32,33], malic (HOOC-CH(OH)-CH 2 -COOH) [23,34], citric (HOCO-CH 2 -C(OH)(COOH)-COOH)) [23], and glycolic (CH 2 OH-COOH) [23] acids, have been reported as anodizing electrolytes to date. However, the formation of thick porous alumina with straight nanopores by anodizing in chromic acid is difficult because of branching and colony-forming nanopores [35]. Although citric acid anodizing has already been used for nanostructure fabrication [36], other organic electrolytes, including malic and glycolic acid solutions, cause the formation of non-uniform anodic porous alumina [23,34]. Therefore, five self-ordering electrolytes, namely, sulfuric, oxalic, and phosphoric acids, are generally selected for anodic porous alumina fabrication by many researchers.In recent years, new anodizing procedures using an effective experimental approach and optimal anodizing conditions have been reported by several researchers to control the nano-scale features of anodic porous alumina. Lee et al. studied the rapid formation of ordered porous alumina by a hard anodizing procedure involving a powerful cooling stage and obtained an ultra-high aspect ratio (>1,000) of anodic porous alumina by anodizing in oxalic acid at 120-150...

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“…Porous alumina consists of nano-scale hexagonal cells perpendicular to the substrate, and each cell possesses a nanopore at its center [1,2]. These cells are self-ordered by anodizing under appropriate electrochemical conditions, especially under a high electric field [3,4]. When anodic porous alumina is immersed in boiling distilled water after anodizing, the nanopores are filled by hydroxide (pore-sealing) [5,6].…”

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confidence: 99%

Fabrication of anodic porous alumina via anodizing in cyclic oxocarbon acids

Kikuchi

Nakajima

Kawashima

et al. 2014

Applied Surface Science

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The growth behavior of anodic porous alumina formed by anodizing in novel electrolyte solutions, the cyclic oxocarbon acids croconic and rhodizonic acid, was investigated for the first time. High-purity aluminum specimens were anodized in 0.1 M croconic and rhodizonic acid solutions at various constant current densities. An anodic porous alumina film with a cell size of 200-450 nm grew uniformly on an aluminum substrate by rhodizonic acid anodizing at 5-40 Am -2 , and a black, burned oxide was formed at higher current density. The cell size of the porous alumina increased with current density and corresponding anodizing voltage. Anodizing in croconic acid at 293 K caused the formation of thin anodic porous alumina films as well as black, thick burned oxides. The uniformity of the porous alumina improved by increasing the temperature of the croconic acid solution, and anodic porous alumina films with a uniform film thickness were successfully obtained. Our experimental results showed that the cyclic oxocarbon acids croconic and rhodizonic acid could be employed as a suitable electrolyte for the formation of anodic porous alumina films.Key words: Aluminum; Anodizing; Anodic Porous Alumina; Croconic Acid; Rhodizonic Acid IntroductionThe anodizing of aluminum in several different acidic solutions causes the formation of anodic porous alumina (i.e., porous anodic oxide film) with characteristic nanofeatures on aluminum substrates. Porous alumina consists of nano-scale hexagonal cells perpendicular to the substrate, and each cell possesses a nanopore at its center [1,2]. These cells are self-ordered by anodizing under appropriate electrochemical conditions, especially under a high electric field [3,4]. When anodic porous alumina is immersed in boiling distilled water after anodizing, the nanopores are filled by hydroxide (pore-sealing) [5,6]. The sealing process causes the formation of a highly crystalline hydroxide layer on the surface of the anodic oxide, and the hydroxide layer is highly dissolution-resistant in acidic and alkaline solutions. Using these characteristic structural and chemical properties, anodic porous alumina has been widely investigated for many applications: antireflection structures [7,8] [50] acid have been reported to date for the fabrication of anodic porous alumina. Oxalic and malonic acid anodizing have been reported to give rise to self-ordering behavior under suitable anodizing conditions. The organic and inorganic electrolytes used to fabricate anodic porous alumina possess low dissociation constant (pKa) in aqueous solution, except for glycolic and formic acid, are diacids or triacids. However, glycolic and formic acid form dimers via hydrogen bonding in aqueous solution and may behave like diacids [52,53]. The nanofeatures of anodic porous alumina, including cell size (i.e., interpore distance) and pore diameter, are limited by these electrolytes during anodizing. Therefore, the discovery of additional electrolytes is very important in expanding the applicability of porous alum...

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Controlling Factor of Self-Ordering of Anodic Porous Alumina

Cited by 343 publications

References 23 publications

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

Fabrication of Anodic Porous Alumina by Squaric Acid Anodizing

Fabrication of anodic porous alumina via anodizing in cyclic oxocarbon acids

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