Dendritic-pattern formation in anodic aluminum oxide templates

Friedman, Adam L.; Menon, Latika

doi:10.1063/1.2718882

Cited by 18 publications

(16 citation statements)

References 11 publications

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“…7 In these applications, one usual requirement is that the arrangement of the pore-channels inside the porous alumina should be hexagonally self-ordered, and this means that the growth of the porechannels during aluminum anodization should be a self-ordering process 1, 2 with as infrequent splitting, merging or termination as possible. 8,9 Plenty of previous efforts have been made to find the anodization conditions which can result in self-ordering porous alumina patterns. Masuda and Fukuda found that mild anodization conducted in 0.3 M oxalic acid at 40 V at 0 • C can result in selfordering patterns.…”

Section: Introductionmentioning

confidence: 99%

Quantitative characterization of acid concentration and temperature dependent self-ordering conditions of anodic porous alumina

Cheng¹,

Ng²,

Ngan³

2011

AIP Advances

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Acid concentration and temperature dependent self-ordering conditions of anodic porous alumina formed by anodization of aluminum in oxalic acid are quantitatively characterized by a new technique involving the distribution of the angular orientation of the triangles formed by neighboring pore centers, in order to detect the self-ordering domains in each porous pattern. This technique is found to be more sensitive in quantifying ordering of the patterns than the radial distribution function and angle distribution function. Using this technique, the optimal acid concentration which can result in the best self-ordering of the porous alumina under a given temperature is established. The optimal acid concentration is found to be approximately linearly increasing with temperature. The oxide growth rate increases approximately exponentially with acid concentration and also with temperature. The results suggest that anodization conducted at relatively higher temperatures at the corresponding optimal acid concentrations can enable fast production of self-ordered anodic porous alumina for industrial applications.

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Section: Introductionmentioning

confidence: 99%

Quantitative characterization of acid concentration and temperature dependent self-ordering conditions of anodic porous alumina

Cheng¹,

Ng²,

Ngan³

2011

AIP Advances

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“…One essential requirement for anodic porous alumina to be used as a template is the arrangement of the nanopore channels should be well ordered [69,93,94], with as infrequent splitting, merging or termination of pore channels as possible [101,175]. Because in disordered anodic porous alumina, plenty of the pore channels are not straight but branched from pore mouth to pore bottom, the deposited materials cannot be easily filled into the channels, during the commonly used methods such as electrochemical deposition, capillary force assisted nanoimprinting, or CVD [28,51,79,123,176], also the obtained nanowire, nanopillars, or nanotubes will not be straight.…”

Section: Mild Anodization and Hard Anodizationmentioning

confidence: 99%

“…However, in structures with disordered in-plane patterns, the straightness of the pore channels is usually not maintained during growth, and on progressing from the top to bottom, the growth of a given pore may fall behind its neighbors or even completely terminated, or the pore can branch to form two or more new ones [95]. As pore merging, termination, or splitting happens, the aspect ratio of the pore channels in disordered structures is usually not larger than 20 [93,101]. A thin scallop-shaped oxide barrier layer exists at the pore bottom which separates the metal substrate from the electrolyte in the pore channels during the anodization.…”

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confidence: 99%

Research Background and Motivation

Cheng

2015

Electro-Chemo-Mechanics of Anodic Porous Alumina Nano-Honeycombs: Self-Ordered Growth and Actuation

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Anodic porous alumina, which exhibits a characteristic nano-honeycomb structure, has received increasing attention both experimentally and theoretically . Due to the quasi-periodic arrangement of the nanopore channels, narrow distribution of pore sizes, and interpore distances, relative ease to control the porous scales and self-ordering qualities by anodization conditions, excellent thermal stability, and very low-cost anodic porous alumina has been extensively used as templates for fabrication of various nanostructured materials such as nanodots [22][23][24], nanowires [25][26][27][28][29], nanotubes [30][31][32], and many other types [33][34][35], especially to realize the collective functioning of arrays of nanoelements which may not be realized by individual nanoelements [5,36], for applications in high-density magnetic media [37][38][39][40][41][42] [95,96]. For neutral electrolytes with pH in the range of 5-7, such as boric acid solution, ammonium borate, or tartrate aqueous solution, only barrier-type anodic alumina films with a uniform thickness will be formed by anodization [1,97]. The configuration of anodic porous alumina is composed of closely packed arrays of nanopore channels perpendicular to the aluminum substrate with pore diameters on the order of several to hundreds of nanometers [58,[93][94][95]98]. When viewed from the top, the nanopores are usually arranged in a quasi-hexagonal porous pattern. The in-plane arrangement of pore channels generally exhibits local variations with ordered zones separated with disordered zone boundaries, which is much similar to the crystallographic grains and grain boundaries of the Al substrate. However, the perfect ordered zones are at most several micrometers big even for highly self-ordered patterns, while the grain

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“…As a result, the aspect ratio of the pore channel, i.e. the channel length to pore diameter, can be greater than 1000 for self-ordered AAO [92,101,102], while the ratio may be less than 20 for disordered AAO [92,103]. Because the in-plane porous patterns are just snap-shots during the growth of the AAO layer, it is the growth stability of pore channels during anodization which determines the self-ordering quality of AAO.…”

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confidence: 97%

Theoretical Pore Growth Models for Nanoporous Alumina

Cheng

Ngan

2015

Nanoporous Alumina

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Nanoporous alumina has been extensively used in a wide range of applications, including template materials for various types of nanomaterials, high surface-area structures for energy conversation and storage, bio/chemo sensors, electronic/photonic devices, and so on. However, the formation mechanism of the nanopores and the subsequent pore growth process towards self-ordered pore arrangements have been under investigation for several decades without clear conclusions. The present models may be divided into two main groups in terms of the driving force for pore initialization, as well as the subsequent pore growth process. One group considers that the driving force is the high electric field across the oxide barrier layer at the bottom of the pore channels, which assists metal oxidation at the metal/oxide interface, and oxide dissolution at the oxide/electrolyte interface. The other group of models assumes that the driving force is mechanical stress originating from the volume expansion of the metal oxidation process. This chapter reviews the development of these models for nanoporous alumina formation, and discusses their advantages and shortcomings. A recent model proposed by us is also described, and potential directions for further development are discussed.

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Dendritic-pattern formation in anodic aluminum oxide templates

Cited by 18 publications

References 11 publications

Quantitative characterization of acid concentration and temperature dependent self-ordering conditions of anodic porous alumina

Quantitative characterization of acid concentration and temperature dependent self-ordering conditions of anodic porous alumina

Research Background and Motivation

Theoretical Pore Growth Models for Nanoporous Alumina

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