Fabrication of Self-Ordered Alumina Films with Large Interpore Distance by Janus Anodization in Citric Acid

Abstract

Self-organized porous anodic alumina (PAA) formed by electrochemical anodization have become a fundamental tool to develop various functional nanomaterials. However, it is still a great challenge to break the interpore distance (Dint) limit (500 nm) by using current anodization technologies of mild anodization (MA) and hard anodization (HA). Here, we reported a new anodization mode named “Janus anodization” (JA) to controllably fabricate self-ordered PAA with large Dint at high voltage of 350–400 V. JA naturally occurs as anodizing Al foils in citric acid solution, which possessing both the characteristics of MA and HA. The process can be divided into two stages: I, slow pore nucleation stage similar to MA; II, unequilibrium self-organization process similar to HA. The as-prepared films had the highest modulus (7.0 GPa) and hardness (127.2 GPa) values compared with the alumina obtained by MA and HA. The optical studies showed that the black films have low reflectance (<10 %) in the wavelength range of 250–1500 nm and photoluminescence property. Dint can be tuned between 645–884 nm by controlling citric acid concentration or anodization voltage. JA is a potential technology to efficiently and controllably fabricate microstructured or hybrid micro- and nanostructured materials with novel properties.

Towards Self-Organized Anodization of Aluminum in Malic Acid Solutions—New Aspects of Anodization in the Organic Acid

“…Analyzing the ia(t) curves in Figure 3, it can be stated that the process conducted in 0.15 M is very similar to the ones observed during anodization in other organic electrolytes [19][20][21][33][34][35][36]. At the beginning of the process, the ia decreases rapidly to the lowest value (within few seconds) after Analyzing the i a (t) curves in Figure 3, it can be stated that the process conducted in 0.15 M is very similar to the ones observed during anodization in other organic electrolytes [19][20][21][33][34][35][36]. At the beginning of the process, the i a decreases rapidly to the lowest value (within few seconds) after passing through a current overshoot, and then it starts to grow to a maximum value (ca.…”

“…Analyzing the i a ( t ) curves in Figure 3 , it can be stated that the process conducted in 0.15 M is very similar to the ones observed during anodization in other organic electrolytes [ 19 , 20 , 21 , 33 , 34 , 35 , 36 ]. At the beginning of the process, the i a decreases rapidly to the lowest value (within few seconds) after passing through a current overshoot, and then it starts to grow to a maximum value (ca.…”

“…Recently, the self-ordered alumina with large period (up to ca. 900 nm) was produced during anodization in citric acid solutions [ 20 , 21 ]. The anodization was conducted in high citric acid solution (1.5 M), low temperature (0 °C) and high voltage (400 V).…”

Electrochemical Nanolithography on Silicon: An Easy and Scalable Method to Control Pore Formation at the Nanoscale

“…The reason for this choice is that larger pores enable the control of the overall ordering of the pores by a self-ordering process, favored by a less dendritic shape of the larger pores, as shown in Figure 2 below. The self-ordering of electrochemical pore formation has already been demonstrated for larger pores in the case of alumina [27] and other materials [28] on larger scales.…”

Advances in Optical Biosensors and Sensors Using Nanoporous Anodic Alumina

“…Several parameters should be optimized for the fabrication of NAA such as applied potential, temperature, and electrolyte. Both the inorganic acid (selenic acid [ 43 , 44 ], sulfuric acid [ 45 , 46 ], phosphoric acid [ 40 , 47 ]) and organic acid (oxalic acid [ 48 , 49 , 50 , 51 ], malonic acid [ 51 , 52 ], citric acid [ 53 ], etidronic acid [ 54 , 55 ], tartaric acid [ 56 ]) can be used as an electrolyte for the NAA fabrication.…”