The authors have nothing to disclose.

Please be aware of all the related materials safety data sheets (MSDS) before beginning. In spite of the eco-friendly nature of this protocol, a few acids and oxidizers are used in the corresponding procedures. Also, use all the proper personal protective equipment (lab coat, gloves, safety glasses, etc.).
1. Preparation of Solution
Note: After complete sealing of the solution-containing vessel, vigorous magnetic stirring was applied to all the solutions at room temperature in sufficient time.
<ol>
	<li>Preparation of perchloric acid solution
	<ol>
		<li>Mix 100 mL of perchloric acid (HClO4, 60%) with 400 mL of absolute ethanol (C2H5OH, 100%) in 1 to 4 volume ratio.</li>
	</ol>
	</li>
	<li>Preparation of chromic acid solution
	<ol>
		<li>Dissolve 9.0 g chromic oxide (CrO3) and 20.3 mL phosphoric acid (H3PO4, 85%) in 479.7 mL deionized (D.I.) water (CrO3:H3PO4 = 0.18 M:0.56 M).</li>
	</ol>
	</li>
	<li>Preparation of sulfuric acid electrolyte
	<ol>
		<li>Mix 16.2 mL sulfuric acid (H2SO4, 98%) in 983.8 mL D.I. water resulting in molar concentration of 0.3 M.</li>
	</ol>
	</li>
	<li>Preparation of oxalic acid electrolyte
	<ol>
		<li>Dissolve 27.012 g anhydrous oxalic acid (C2H2O4) in 1 L D.I. water resulting in molar concentration of 0.3 M.</li>
	</ol>
	</li>
</ol>
2. Pretreatment of Al Substrate
<ol>
	<li>Machining Al specimen
	<ol>
		<li>Cut the purified Al specimen (&#62;99.99% pure) into rectangular parallelepiped shape (width x height x thickness = 20.0 mm x 50.0 mm x 1.0 mm) with right angles between all the adjacent surfaces, which is referred as &#34;substrate&#34; hereafter.</li>
		<li>Polish the multi-surfaces of the Al substrate mechanically using sandpaper with proper ISO/FEPA Grit Designation number more than P1000. 
		NOTE: See the Supplementary Information for more details.</li>
	</ol>
	</li>
	<li>Simultaneous electropolishing on multi-surfaces of the Al substrate
	<ol>
		<li>Pour approximate 350 mL of perchloric acid ethanol solution into double jacket beaker with maximum capability of 600 mL. Then, immerse four-fifths of the Al substrate into perchloric acid solution.</li>
		<li>Set the temperature of perchloric acid solution at 7 &#177;0.1 &#176;C using a bath circulator connected to a double jacket beaker.</li>
		<li>Clean the Al substrate through ultrasonication in acetone for 30-40 min, and rinse using acetone and D.I water a few times to remove organic residues on the surfaces of the Al substrate.</li>
		<li>Dry the Al substrate using air-gun or nitrogen (N2) gas blow for eliminating residual solvents. 
		NOTE: Natural drying under atmospheric environments is not be recommended because the solvent traces affect the electropolishing effects adversely.</li>
		<li>Connect the Al substrate working electrode (W.E.) to the positive (+) port and the platinum (Pt) wire counter electrode (C.E.) to the negative (-) port of programmable DC power supply, using alligator clips. The Al substrate and Pt wire should be parallel to each other (See the Figure S2).</li>
		<li>Apply forward bias of +20.0 V to the Al W.E. with respect to Pt C.E. for 2 - 4 min on average. Depending on the surface condition, such as contamination or roughness, the applying time could be maintained up to 5 min. Inspect all the surfaces immersed into the solution to check whether residues on the surface peel off and slide down into the solution. During this step, magnetic stirring is not recommended because inspection is difficult under stirring, and the solution flow might influence the electropolishing effect. 
		NOTE: Do not electropolish for more than 5 min, which might deteriorate the surfaces. 
		Option: Recording current-time (I-t) characteristics behavior via PC interface is helpful for monitoring the electropolishing procedure including abnormal points if they exist.</li>
		<li>Stop applying bias and disconnect the alligator clips. Pick up the Al substrate and Pt electrode carefully from the electropolishing solution. Then, remove residual solution on the surface of the Al substrate using ethanol (95%) and D.I water a few times. If the electropolishing is performed properly, mirror-like finished surfaces of the Al substrate can be identified (See the Figure S1 and Figure S3).</li>
		<li>Store the electropolished Al substrate in ethanol (95%) until the next procedure to minimize surface oxidation.</li>
	</ol>
	</li>
</ol>
3. Massive Fabrication of AAOs under Oxalic Acid Electrolyte
Note: For AAOs with a long-range arrangement of nanopores&#39; periodicity, two-step SMSAs procedure were used, in which periodically textured Al multi-surfaces were obtaining through pre-SMSA, and then, main-SMSA was conducted for fabricating the highly qualified AAOs. Repetitive application of a unit sequence can keep producing plural and almost identical AAOs until the Al substrate remains. &#34;n&#34; denotes number of the applied sequence.
<ol>
	<li>n th Pre-SMSA
	<ol>
		<li>Pour approximate 650 mL of oxalic acid aqueous solution with molar concentration of 0.3 M into a double jacket beaker with maximum capability of 1.0 L. Then, immerse about three quarters of the Al substrate into the oxalic acid solution.</li>
		<li>Set the temperature of oxalic acid electrolyte at 15 &#177;0.1 &#176;C using a bath circulator connected to a double jacket beaker.</li>
		<li>Pick up the electropolished Al substrate from ethanol, and remove the residual solvent using an air-gun or N2 gas blow.</li>
		<li>Connect the electropolished Al substrate to W.E. (+) and Pt wire to C.E. (-) of programmable DC power supply using an alligator clip. The Al substrate and Pt wire should be parallel to each other. Then, immerse the electropolished portion of the Al substrate into oxalic acid electrolyte. 
		NOTE: Make sure that enough space (e.g., approximate 1 cm) exists between the top of the acidic electrolyte and the bottom of the alligator clip connected to the Al substrate, otherwise severe corrosion occurs at the alligator clip connected position.</li>
		<li>Apply anodic bias of +40.0 V to W.E. with respect to C.E. for more than 1-2 h under moderate magnetic stirring of 100-150 rpm for maintaining electrolyte temperature. 
		NOTE: If the Pre-SMSA time is too short, multi-surfaces of the Al substrate will not be textured properly. 
		Option: Recording I-t characteristics behavior via PC interface is helpful for understanding typical behaviors in SMSA.</li>
		<li>Stop applying anodic bias after finishing pre-SMSA, and disconnect the alligator clips. Pick up the sample carefully from acidic electrolyte, and rinse the pre-SMSAed Al substrate using acetone and D.I water a few times.</li>
	</ol>
	</li>
	<li>n th Pre-AAOs etching
	<ol>
		<li>Set the temperature of chromic acid aqueous solution at 60 -&#160;65 &#176;C.</li>
		<li>Immerse the pre-SMSAed Al substrate into chromic acid solution for 1 -&#160;2 h to remove pre-AAOs on the Al substrate.</li>
		<li>Rinse the pre-AAOs removed Al substrate with acetone and D.I. water a few times. Measure the resistance of the Al substrate to confirm whether the pre-AAOs have been completely removed on the surface. If not, repeat the etching procedure again (step 3.2.2).</li>
	</ol>
	</li>
	<li>n th Main-SMSA
	<ol>
		<li>Re-set up all the experimental conditions and connections as those used in step 3.1. 
		NOTE: It should be noted that oxalic acid electrolyte can be used in a couple of sequences, and this does not influence the qualities of the main-AAOs. However, for quantitative comparisons, it is recommended that the electrolyte is used in one whole sequence, and then exchanged with a fresh one.</li>
		<li>Apply anodic bias of +40.0 V to W.E. with respect to C.E.; applying time can be varied depending on a desirable thickness of AAO. AAO growth rate was estimated to be about 8.0 and 7.5 &#956;m/h on the front and back surface of the Al substrate at the electrolyte temperature of 15 &#176;C, respectively (Refer to reference57 for more details).</li>
	</ol>
	</li>
	<li>n th SRBs-detachment
	<ol>
		<li>Stop applying the anodic bias and stirring after finishing the main-SMSA, and connect the main-SMSAed Al substrate to C.E. (-) and Pt wire to W.E. (+) of the programmable DC power supply by switching each alligator clip.</li>
		<li>Apply the SRBs, and inspect typical bubbling effects along to the multi-edges of the Al substrate covered with main-AAOs. Details of SRBs condition, such as intensity of the beginning RB, number of stairs, and duration in each stair, are closely correlated with the thickness of main-AAOs. For main-AAOs thicker than 60 &#956;m, stair in SRBs was controlled from -21 V to -24 V with the increment of -1 V and without time interval between adjacent stairs. The duration for -21 V, -22 V, and -23 V was fixed at 10 min, and the final stair of -24 V was maintained until the detaching procedure completed (See reference57 for more details including the case of thinner AAOs). 
		NOTE: It is highly recommended for a beginner to utilize PC interfaced control of SRBs and record the I-t characteristic curves during this procedure.</li>
		<li>Quit applying SRBs after finishing the detachment, and disconnect the alligator clips. Pick up the sample carefully from acidic electrolyte, and rinse them carefully with acetone and D.I water a sufficient number of times.</li>
		<li>Separate each AAO from corresponding Al surface completely. Right after step 3.4.3, upper parts of the detached AAOs are still connected to the Al substrate, which should be manually broken.</li>
	</ol>
	</li>
	<li>n th Residual alumina etching
	<ol>
		<li>Set the temperature of chromic acid solution at 60-65 &#176;C, and immerse the AAOs-detached Al substrate for about 30 min to eliminate residual alumina.</li>
		<li>Pick up the etched Al substrate, and rinse with acetone and D.I. water a few times. Measure the resistance to confirm complete removal of residual alumina. If not, repeat step 3.5.2.</li>
	</ol>
	</li>
	<li>n+1th sequence
	<ol>
		<li>Go to step 3.1, and repeat the whole sequence using the residual alumina-etched Al substrate.</li>
	</ol>
	</li>
</ol>
4. Massive Fabrication of AAOs under Sulfuric Acid Electrolyte
NOTE: In this section, clearly different conditions from those in step 3 are pointed out.
<ol>
	<li>nth Pre-SMSA
	<ol>
		<li>Pour approximate 650 mL of sulfuric acid aqueous solution (0.3 M) into a double jacket beaker with maximum capability of 1.0 L. Then, about three quarters of the Al substrate is immersed into the sulfuric acid solution.</li>
		<li>Set the temperature of the electrolyte at 0 &#177;0.1 &#176;C.</li>
		<li>Remove the residual solvent on the electropolished Al substrate using an air-gun or N2 gas blow, and connect the Al substrate to a programmable DC power supply using alligator clips (Refer to step 3.1.4)</li>
		<li>Apply anodic bias of +25.0 V to W.E. with respect to C.E. for more than 1 - 2 h under moderate magnetic stirring (100 - 150 rpm).</li>
		<li>Quit applying the anodic bias after finishing pre-SMSA, and disconnect the alligator clips. Pick up and rinse the pre-SMSAed Al substrate using acetone and D.I water a few times. 
		NOTE: For nth Pre-AAOs etching, refer to step 3.2.</li>
	</ol>
	</li>
	<li>nth Main-SMSA
	<ol>
		<li>Re-set up all the experimental conditions and connections as those used in step 4.1.</li>
		<li>Apply the same anodic bias. Applying time can be varied depending on a desirable AAO thickness. AAO growth rate was estimated to be about 5.3 &#956;m/h (Refer to reference56 for more details).</li>
	</ol>
	</li>
	<li>nth SRBs-detachment
	<ol>
		<li>Quit applying the anodic bias and stirring after finishing the main-SMSA, and connect the main-SMSAed Al substrate to C.E. (-) and Pt wire to W.E. (+) of programmable DC power supply by switching each alligator clip.</li>
		<li>Apply SRBs, and inspect typical bubbling effects along to the multi-edges of the sample. Stair in SRBs was controlled from -15 V to -17 V with the increment of -1 V and without time interval between adjacent stairs. The duration for -15 V and -16 V was fixed at 10 min, and final stair of -17 V was maintained until the detaching procedure completed. 
		NOTE: Based on the more fragile nature of AAOs fabricated under sulfuric acid electrolyte, the current level was abruptly increased at the detaching moments accompanied with noticeable clicking sounds.</li>
		<li>Quit applying the SRBs after finishing the detachment, and disconnect the alligator clips. Pick up the sample carefully from the acidic electrolyte, and rinse carefully with acetone and D.I water a sufficient number of times.</li>
		<li>Separate each AAO from the corresponding Al surface mechanically by breaking the upper parts of as-detached AAOs. 
		NOTE: For nth Residual alumina etching refer to step 3.5.</li>
	</ol>
	</li>
	<li>n+1 th sequence
	<ol>
		<li>Go to step 4.1, and repeat the whole sequence using the residual alumina-etched Al substrate.</li>
	</ol>
	</li>
</ol>

This research was supported in part by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2016R1C1B1016344 and 2016R1E1A2915664).

In this paper, we successfully demonstrated a facile, high yield, and environmentally clean method to fabricate nanoporous AAOs through SMSA and SRBs-detachment, which could be repeated to the same Al substrate for significantly enhancing mass-producibility as well as usability of limited natural resource. As shown in the flow chart of Figure 1a, our AAO fabricating strategy is based on the conventional two-step anodization, which was modified on multi-surfaces situation. Individual procedures functioned well independent of the other surfaces, because electric fields in the electropolishing and two-step SMSAs procedures were formed in the normal directions on the multi-surfaces, where the electrochemical reaction occurs simultaneously. In this point of view, position of each surface and corresponding AAO will be defined with respect to the counter electrode, as shown in Figure 1b; e.g., &#34;Front&#34; designate a surface confronting the Pt counter electrode, and so on.
Pristine Al substrate showed rougher surfaces due to mechanical polishing, which became much smoother after electropolishing procedure. Each surface of the electropolished Al substrate looked like a mirror in macroscale, however, it was covered with irregularly distributed nanoscale concaves as shown in the inset (ii) of Figure 1a. Therefore, not only every cleaning but also drying treatment were also very important, owing to the fact that solvent traces could significantly affect surface morphologies in procedures after electropolishing. Once deteriorated, surfaces never recovered, and kept the poor morphologies. In this regard, excessive electropolishing treatment would not be good either. If electropolishing time is too long, periodically arranged wavy valleys were formed on the entire Al surfaces, which could increase an adhesive strength between AAOs and Al. A unit sequence depicted by a blue-dashed box shown in Figure 1a consists of nth pre-SMSA, nth pre-AAOs etching, nth main-SMSA, nth SRBs-detachment, and nth residual alumina etching, where n is number of the applied sequence (n = 1, 2, 3, &#8230;).
Figure 2 compares the I-t characteristic curves of pre-/main-SMSA and SRBs-detachment from 1st to 5th sequences. In both SMSAs, the current level gradually decreased with increasing applying time. These typical features were only observed in a multi-surfaces situation attributing to the gradual reduction of total anodizing area as well as accumulation of mechanical stresses due to the viscous flow23,58 and volume expansion23,59,60,61,62 during simultaneous formations of plural AAOs56,57. Previous reports on these SMSA and SRBs-detachment proposed the stress-released direct detaching mechanism, which could be further optimized through appropriate SRBs conditions for relatively thinner thickness of AAO (Refer to reference57 for more details).
An intuitive schematic illustration implying massive producibility is successfully realized in Figure 3 and Figure 4 exhibiting results of about total 5th times iterations of the unit sequence under oxalic and sulfuric acid electrolyte, respectively. Each photograph clearly shows that all the AAOs having the exact equal dimensions to those of corresponding front and back surfaces (See the Supplementary Information for the AAOs detached from sides and bottom surfaces). Barrier side SEM images of all sequences indicate that cleavage planes are beneath the barrier oxides in both acidic electrolytes, which are similar results about cathodic delamination of a relatively thicker AAO on mono-surface50,51. As an alternative approach for obtaining AAO with through-hole structures (i.e., without barrier oxide), anodic voltage pulse detachment using another detaching electrolyte7,41,42,52,53,54,55 or two-layer anodization incorporating normal AAO into a sacrificial one fabricated from acidic electrolyte of extremely high concentration (12.0 M)63 might be taken into consideration.
The SMSA and SRBs-based strategy appears to possess an acid-type independent nature, therefore, its various advantages and strengths are worth expanding into phosphoric acid electrolyte and/or HA condition, which will enrich the potentials of nanoporous AAOs toward more versatile applications.

AAOs which were formed by anodizing Al substrate in an acidic electrolyte, have attracted great interest in diverse fundamental science and industry, for example, hard templates for nanotubes/nanowires1,2,3,4,5, energy storage devices6,7,8,9, bio-sensing10,11, filtering applications12,13,14, masks for evaporating and/or etching15,16,17, and capacitive humidity sensors18,19,20,21,22, owing to their self-ordered honeycomb structure, high aspect ratio of nanopores, and superior mechanical properties23. For applying the nanoporous AAOs to these various applications, they should be freestanding forms with a highly and long-range ordered array of nanopores. In this regard, strategies for obtaining AAOs must consider both formation (anodizing) and separation (detaching) procedures.
In the viewpoint of the AAO formation, mild anodization (hereafter referred as MA) was well established under sulfuric, oxalic, and phosphoric acidic electrolytes23,24,25,26,27. However, MA processes exhibited low-yields of AAO fabrication due to their slow growth rate depending on relatively low intensities of anodic voltages, which would further deteriorate through a two-step MA process for improving nanopores&#39; periodicity28,29. Thus, hard anodization (HA) techniques were proposed as alternatives of MA by applying higher anodic voltages (oxalic/sulfuric acid electrolyte) or using more concentrated electrolyte (phosphoric acid)30,31,32,33,34,35,36,37,38,39,40. HA processes show distinct enhancements of growth rates as well as periodic arrangements, whereas resulting AAOs became more fragile, and the density of nanopores were reduced30. In addition, an expensive cooling system is required for dissipating Joule&#39;s heating caused by high current density31. These results restrict the potential applicability of the AAOs via HA processes.
For separating an AAO from the corresponding surface of Al plate, selective chemical etching of the remaining Al substrate was most widely utilized in both the MA and HA processes using toxic chemicals, such as copper chloride35,39,41,42 or mercury chloride16,17,43,44,45,46,47,48,49. However, this method induces disadvantageous side effects, e.g., a longer reaction time proportional to the remaining thickness of the Al, contamination of AAO by heavy metal ions, harmful residues to human body/natural environments, and inefficient usage of valuable resources. Therefore, many attempts have been made for realizing direct detachment of an AAO. Although both cathodic voltage delamination50,51 and anodic voltage pulse detachment7,41,42,52,53,54,55 present a merit that the remaining Al substrate can be reused, the former technique takes almost comparable time with those in chemical etching methods50. Notwithstanding clear reduction of the processing time, harmful and highly reactive chemicals, for examples butanedione and/or perchloric acid, were used as detaching electrolytes in the latter techniques55, where an additional cleaning procedure is needed because of the changing electrolyte between the anodizing and detaching procedure. Especially, the detaching behaviors and quality of the detached AAOs severely influence the thickness. In the case of the AAO with relatively thinner thickness, the detached one might contain cracks and/or apertures.
All the experimental approaches listed above have been applied to a &#34;single-surface&#34; of the Al specimen, excluding surface protecting/engineering purposes, and this feature of the conventional technologies exhibits critical limitations of the AAO fabrication in terms of yield as well as processibility, which also influences the potential applicability of the AAOs56,57.
To satisfy the increasing demands in the AAO-related fields in terms of facile, high yield, and green technological approaches, we previously reported on SMSA and direct detachment through SRBs under sulfuric56 and oxalic57 acid electrolyte, respectively. It is a well-known fact that plural AAOs can be formed on the multiple surfaces of the Al substrate immersed into acidic electrolytes. However, SRBs, a key distinction of our methods, enable the detachment of those AAOs from the corresponding multi-surfaces of the Al substrate in the same acidic electrolyte used for the SMSAs indicating mass-production, simplicity, and green technological characteristics. We would like to point out that SRBs-based detachment is an optimal strategy for plural AAOs fabricated by SMSAs56,57 and even valid for relatively thinner thicknesses of AAOs57 when compared with cathodic delamination (i.e., constant reverse bias) on single-surface51. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, avoiding complicated procedures and toxic/reactive chemicals, which reinforces the advantages of our strategies and also guarantees the efficient usage of natural resources.

<table border="0" cellpadding="0" cellspacing="0" width="850">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Sulfuric Acid &#62;98%</td>
			<td style="width:212px;">DUKSAN reagent</td>
			<td style="width:119px;">5950</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Oxalic Acid Anhydrous, 99.5-100.2%</td>
			<td style="width:212px;">KANTO chemical</td>
			<td style="width:119px;">31045-73</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Phosphoric Acid, 85%</td>
			<td style="width:212px;">SAMCHUN chemical</td>
			<td style="width:119px;">P0463</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Perchloric Acid, 60%</td>
			<td style="width:212px;">SAMCHUN chemical</td>
			<td style="width:119px;">P0181</td>
			<td>Highly Reactive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Chromium(VI) Oxide</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:119px;">232653</td>
			<td>Strong Oxidizer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Ethanol, 95%</td>
			<td style="width:212px;">SAMCHUN chemical</td>
			<td style="width:119px;">E0219</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Absolute Ethanol, 99.9%</td>
			<td style="width:212px;">SAMCHUN chemical</td>
			<td style="width:119px;">E1320</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Double Jacket Beaker</td>
			<td style="width:212px;">iNexus</td>
			<td style="width:119px;">27-00292-05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Low Temperature Bath Circulator</td>
			<td style="width:212px;">JEIO TECH</td>
			<td style="width:119px;">AAH57052K</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Programmable DC Power Supply</td>
			<td style="width:212px;">PNCYS</td>
			<td style="width:119px;">EDP-3001&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Aluminum Plate, &#62;99.99%</td>
			<td style="width:212px;">Goodfellow</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Platinum Cylinder</td>
			<td style="width:212px;">Whatman</td>
			<td style="width:119px;">444685</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:352px;">Pure &#38; Ultra Pure Water System (Deionized Water)</td>
			<td style="width:212px;">Human Science</td>
			<td style="width:119px;">Pwer II &#38; HIQ II</td>
			<td></td>
		</tr>
	</tbody>
</table>

simultaneous multi-surface anodizations and stair-like reverse biases detachment of anodic aluminum oxides in sulfuric and oxalic acid electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

Flow chart of nth AAO fabricating sequence mainly consisting of two-step SMSAs, SRBs-detachment, and related chemical etching was presented schematically in Figure 1a. Each inset show a scanning electron microscope (SEM) image of the corresponding surface morphology at each individual procedure and a photograph taken immediately after SRBs-detachment. A schematic illustration after the total 5th repetition of the unit sequence exhibited advantages of SMSA and SRBs-based strategies (Figure 1b). I-t characteristic curves of the pre- and main-SMSAs up to the 5th sequences were compared in Figure 2a and Figure 2b, respectively. A comparison of I-t characteristic curves from each SRBs-detaching procedure are shown in Figure 2c. Photograph and corresponding SEM images of the main-AAOs obtained from front and back surfaces under oxalic and sulfuric acid electrolytes are presented in Figure 3 and Figure 4, respectively.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56432/56432fig1.jpg" /> 
Figure 1:&#160;nth AAOs fabrication procedures (n = 1, 2, 3 &#8230;). (a) Schematic flow chart including corresponding SEM images in nth AAOs fabricating sequence: (i) Pristine Al substrate, (ii) Electro polishing, (iii) nth pre-SMSA, (iv) nth pre-AAOs etching, (v) nth main-SMSA, (vi) nth SRBs-detaching, (vii) nth residual alumina etching. A unit sequence was depicted using blue-dashed box. (b) Schematic illustration showing that plural AAOs with equal dimensions of corresponding surfaces were successfully obtained from multi-surfaces of a single Al plate through 5th repetitive applications of the unit sequence. <a href="https://cloudflare.jove.com/files/ftp_upload/56432/56432fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56432/56432fig2.jpg" /> 
Figure 2: Peculiar behaviors during two-step SMSAs and SRBs-detachments of AAOs under oxalic acid electrolyte at 15 &#176;C. I-t characteristic curves of (a) pre- and (b) main-SMSAs from 1st to 5th sequences, respectively. (c) I-t characteristic curves of SRBs-detaching procedures from 1st to 5th sequences. <a href="https://cloudflare.jove.com/files/ftp_upload/56432/56432fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56432/56432fig3.jpg" /> 
Figure 3: Photograph of the remaining Al substrate and main-AAOs after 5th repetitive applications of the unit sequence under oxalic acid electrolyte. AAOs obtained from front and back surfaces were distinguished by red- and blue-dashed boxes, respectively. Insets: Open-pore and barrier side SEM images of the corresponding 1st to 5th main-AAOs. <a href="https://cloudflare.jove.com/files/ftp_upload/56432/56432fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56432/56432fig4.jpg" /> 
Figure 4:Photograph of the remaining Al substrate and main-AAOs after 5th repetitive applications of the unit sequence under sulfuric acid electrolyte. AAOs obtained from front and back surfaces were distinguished by red- and blue-dashed boxes, respectively. Insets: Open-pore and barrier side SEM images of the corresponding 1st to 5th main-AAOs. <a href="https://cloudflare.jove.com/files/ftp_upload/56432/56432fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Information: <a href="https://cloudflare.jove.com/files/ftp_upload/56432/Supplementary_Information.docx" target="_blank">Please click here to download this file.</a>

Watch this Scientific Journal Video about Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte at JoVE.com

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

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Nanyang Technological University

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Engineering

7.2K Views.  Sungkyunkwan University. A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

Video: Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...

Experimental Procedure for Warm Spinning of Cast Aluminum Components

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to improve material properties. With a wide array of processing parameters which can affect both the shape attained and resulting material properties, this type of processing is notoriously difficult to commission. A simplified, light-duty version of the process has been designed and implemented for full-size automotive wheels. The apparatus is intended to assist in understanding the deformation mechanisms and the material response to this type of processing. An experimental protocol has been developed to prepare for, and subsequently perform forming trials and is described for as-cast A356 wheel blanks. The thermal profile attained, along with instrumentation details are provided. Similitude with full-scale forming operations which impart significantly more deformation at faster rates is discussed.

An experimental protocol for instrumented warm rotary forming of cast aluminum alloys employing a bespoke industrially scaled apparatus is presented. Experimental considerations including thermal and mechanical effects are discussed, as well as similitude with full-scale processing of automotive wheels.

High performance, cast aluminum automotive wheels are increasingly being incrementally formed via flow forming/metal spinning at elevated temperatures to ...

Dielectric RheoSANS &#8212; Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and microstructural properties of complex fluids is presented. The instrument consists of a Couette geometry contained within a modified forced convection oven mounted on a commercial rheometer. This instrument is available for use on the small angle neutron scattering (SANS) beamlines at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). The Couette geometry is machined to be transparent to neutrons and provides for measurement of the electrical properties and microstructural properties of a sample confined between titanium cylinders while the sample undergoes arbitrary deformation. Synchronization of these measurements is enabled through the use of a customizable program that monitors and controls the execution of predetermined experimental protocols. Described here is a protocol to perform a flow sweep experiment where the shear rate is logarithmically stepped from a maximum value to a minimum value holding at each step for a specified period of time while frequency dependent dielectric measurements are made. Representative results are shown from a sample consisting of a gel composed of carbon black aggregates dispersed in propylene carbonate. As the gel undergoes steady shear, the carbon black network is mechanically deformed, which causes an initial decrease in conductivity associated with the breaking of bonds comprising the carbon black network. However, at higher shear rates, the conductivity recovers associated with the onset of shear thickening. Overall, these results demonstrate the utility of the simultaneous measurement of the rheo-electro-microstructural properties of these suspensions using the dielectric RheoSANS geometry.

Here, we present a procedure for the measurement of simultaneous impedance, rheology and neutron scattering from soft matter materials under shear flow.

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and ...

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape method or individual WS2 nanotubes by dispersing the suspension of WS2 nanotubes. The selected samples have been fabricated into devices by the use of the electron beam lithography and electrolyte is put on the devices. We have characterized the electronic properties of the devices under applying the gate voltage. In the small gate voltage region, ions in the electrolyte are accumulated on the surface of the samples which leads to the large electric potential drop and resultant electrostatic carrier doping at the interface. Ambipolar transfer curve has been observed in this electrostatic doping region. When the gate voltage is further increased, we met another drastic increase of source-drain current which implies that ions are intercalated into layers of WS2 and electrochemical carrier doping is realized. In such electrochemical doping region, superconductivity has been observed. The focused technique provides a powerful strategy for achieving the electric-filed-induced quantum phase transition.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape ...

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m-2, and a maximum current efficiency of 1.15 cd A-1. The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A protocol is presented for fabricating high-performance, pure blue ZnCdS/ZnS-based quantum dots light-emitting diodes by employing an autoxidized aluminum cathode.

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed electric body force has to be induced by ionic motions in liquid. On the other hand, positive and negative charges attract each other, and electroneutrality is maintained everywhere in equilibrium conditions. Furthermore, an increase in an applied voltage has to be suppressed to avoid water electrolysis, which causes the solutions to become unstable. Usually, EHD flows can be induced in non-aqueous solutions by applying extremely high voltages, such as tens of kV, to inject electrical charges. In this study, two methods are introduced to generate EHD flows induced by electrical charge separations in aqueous solutions, where two liquid phases are separated by an ion-exchange membrane. Due to a difference in the ionic mobility in the membrane, ion concentration polarization is induced between both sides of the membrane. In this study, we demonstrate two methods. (i) The relaxation of ion concentration gradients occurs via a flow channel that penetrates an ion-exchange membrane, where the transport of the slower species in the membrane selectively becomes dominant in the flow channel. This is a driving force to generate an EHD flow in the liquid. (ii) A long waiting time for the diffusion of ions passing through the ion-exchange membrane enables the generation of an ion-dragged flow by externally applying an electric field. Ions concentrated in a flow channel of a 1 x 1 mm2 cross-section determine the direction of the liquid flow, corresponding to the electrophoretic transport pathways. In both methods, the electric voltage difference required for an EHD flow generation is drastically reduced to near 2 V by rectifying the ion transport pathways.

The rectification of ion transport pathways is an effective method to generate one-directional ion-dragged electrohydrodynamic flows. By setting an ion-exchange membrane in a flow channel, an electrically polarized condition is generated and causes a liquid flow to be driven when an electric field is externally applied.

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

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