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 natural… Show more
“…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.…”
Section: Resultssupporting
confidence: 58%
“…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.…”
Section: Resultssupporting
confidence: 55%
“…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).…”
In this work, aluminum (Al) anodization in malic acid electrolytes of different concentrations (0.15 M, 0.25 M, and 0.5 M) was studied. The close-packed hexagonal pore structure was obtained for the first time in this organic acid in a 0.5 M solution, at 250 V and temperature of 5 °C. Moreover, the process was investigated as a function of the number of cycles carried out in the same electrolyte. A repetition of anodization under seemingly the same external electrochemical parameters (applied voltage, temperature, etc.) induced serious changes in the electrolyte. The changes were reflected in the current density vs. time curves and were most evident in the higher concentrated electrolytes. This phenomenon was tentatively explained by a massive incorporation of malate anions into anodic alumina (AAO) framework. The impoverishment of the electrolyte of the malate anions changed internal electrochemical conditions making easier the attraction of the anions to the Al anode and thus the AAO formation. The electrolyte modification was advantageous in terms of pore organization: In a 0.25 M solution, already after the second anodization, the pore arrangement transformed from irregular towards regular, hexagonal close-packed structure. To the best of our knowledge, this is the first observation of this kind.
“…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.…”
Section: Resultssupporting
confidence: 58%
“…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.…”
Section: Resultssupporting
confidence: 55%
“…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).…”
In this work, aluminum (Al) anodization in malic acid electrolytes of different concentrations (0.15 M, 0.25 M, and 0.5 M) was studied. The close-packed hexagonal pore structure was obtained for the first time in this organic acid in a 0.5 M solution, at 250 V and temperature of 5 °C. Moreover, the process was investigated as a function of the number of cycles carried out in the same electrolyte. A repetition of anodization under seemingly the same external electrochemical parameters (applied voltage, temperature, etc.) induced serious changes in the electrolyte. The changes were reflected in the current density vs. time curves and were most evident in the higher concentrated electrolytes. This phenomenon was tentatively explained by a massive incorporation of malate anions into anodic alumina (AAO) framework. The impoverishment of the electrolyte of the malate anions changed internal electrochemical conditions making easier the attraction of the anions to the Al anode and thus the AAO formation. The electrolyte modification was advantageous in terms of pore organization: In a 0.25 M solution, already after the second anodization, the pore arrangement transformed from irregular towards regular, hexagonal close-packed structure. To the best of our knowledge, this is the first observation of this kind.
“…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.…”
Lithography on a sub-100 nm scale is beyond the diffraction limits of standard optical lithography but is nonetheless a key step in many modern technological applications. At this length scale, there are several possible approaches that require either the preliminary surface deposition of materials or the use of expensive and time-consuming techniques. In our approach, we demonstrate a simple process, easily scalable to large surfaces, where the surface patterning that controls pore formation on highly doped silicon wafers is obtained by an electrochemical process. This method joins the advantages of the low cost of an electrochemical approach with its immediate scalability to large wafers.
“…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.…”
This review paper focuses on recent progress in optical biosensors using self-ordered nanoporous anodic alumina. We present the fabrication of self-ordered nanoporous anodic alumina, surface functionalization, and optical sensor applications. We show that self-ordered nanoporous anodic alumina has good potential for use in the fabrication of antibody-based (immunosensor), aptamer-based (aptasensor), gene-based (genosensor), peptide-based, and enzyme-based optical biosensors. The fabricated optical biosensors presented high sensitivity and selectivity. In addition, we also showed that the performance of the biosensors and the self-ordered nanoporous anodic alumina can be used for assessing biomolecules, heavy ions, and gas molecules.
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