Advances in the Fabrication of Nanoporous Anodic Aluminum Oxide and Its Applications to Sensors: A Review

Abstract

Nanoporous anodic aluminum oxide (AAO) is an important template for 1D nanomaterial synthesis. It is used as an etching template for nanopattern transfer in a variety of contexts, including nanostructured material synthesis, electrical sensors, optical sensors, photonic and electronic devices, photocatalysis, and hardness and anticorrosion improvement. In this review, we focus on various fabrication methods, pore geometry modification, and recent advances of AAO, as well as sensor applications linked to our environment, daily life, and safety. Pore geometry is concerned with the material composition, applied voltage mold, electrolyte type, temperature, and anodizing time during the fabrication of AAOs and for adjusting their pore size and profile. The applied voltage can be divided into four types: direct current anodization (DCA), reverse pulse anodization, pulse anodization (PA), and hybrid pulse anodization (HPA). Conventional AAOs are fabricated using DCA and mild anodization (MA) at a relatively low temperature (−5~15 °C) to reduce the Joule heating effect. Moreover, the issues of costly high-purity aluminum and a long processing time can be improved using HPA to diminish the Joule heating effect at relatively high temperatures of 20–30 °C with cheap low-purity (≤99%) aluminum. The AAO-based sensors discussed here are primarily divided into electrical sensors and optical sensors; the performance of both sensors is affected by the sensing material and pore geometry. The electrical sensor is usually used for humidity or gas measurement applications and has a thin metal film on the surface as an electrode. On the contrary, the AAO optical sensor is a well-known sensor for detecting various substances with four kinds of mechanisms: interference, photoluminescence, surface plasma resonance, and surface-enhanced Raman scattering (SERS). Especially for SERS mechanisms, AAO can be used either as a solid support for coating metal nanoparticles or a template for depositing the metal content through the nanopores to form the nanodots or nanowires for detecting substances. High-performance sensors will play a crucial role in our living environments and promote our quality of life in the future.

Design and Study of Composite Film Preparation Platform

“…A. Chepluki, Tiago E. A. Frizon, and others developed a low-cost spin-coater for thin film deposition, serving as a cost-effective alternative to highpriced commercial equipment [11][12][13][14][15]. This research delves into the intricacies of integrating and optimizing composite thin film preparation platforms [16]. By consolidating the preparation processes of magnetron sputtering and vacuum evaporation within the same vacuum cavity, the creation of composite films tailored to the requirements of diverse high-tech fields on a single substrate is achieved [17].…”

“…This research delves into the intricacies of integrating and optimizing composite thin film preparation platforms [16]. By consolidating the preparation processes of magnetron sputtering and vacuum evaporation within the same vacuum cavity, the creation of composite films tailored to the requirements of diverse high-tech fields on a single substrate is achieved [17].…”

Correlation of Fabrication Methods and Enhanced Wear Performance in Nanoporous Anodic Aluminum Oxide with Incorporated Molybdenum Disulfide (MoS2) Nanomaterials

“…Though AAO has significant history, its fabrication process and applications remain of current interest [ 3 ]. Researchers have refined AAO nanopore engineering and modification for various applications like sensors [ 4 ], catalysis [ 5 , 6 ], and wear [ 7 , 8 ]. MoS 2 , existing naturally in the form of molybdenite, has been used as a lubricant for various materials for decades [ 9 , 10 ].…”

Influence of Anodic Aluminum Oxide Nanostructures on Resistive Humidity Sensing

“…Ceramic materials possess good thermal stability among various types of humidity sensors, and their manufacturing processes are relatively environmentally friendly. Anodic aluminum oxide (AAO) is a well-known nanomaterial template for various electrical and optical sensing mechanisms and methods [27][28][29]. Also, AAO humidity sensors have gained significant research attention over the past several decades.…”