Anodic Aluminum Oxide Substrate Research Articles

Gas Permeation through V2O5 Nanoribbons‐Based Membrane

AbstractMembrane separation processes play a crucial role in gas separation applications, with the need for ongoing development to fulfill new needs for today's challenges. For this purpose, novel 2D nanomaterials are progressively showing promise over conventional polymer‐based membrane material, exhibiting excellent molecular transport properties. Beyond the 2D materials already studied in this field, this article presents the first gas separation performances of vanadium pentoxide membrane. Brand new in gas separation topic, 2D van der Waals nanoribbons of V2O5 are successfully synthesized and layered on an anodic aluminum oxide substrate. Gas permeation analysis of He, N2, and CO2 are performed on various membranes made from different quantities of the nanomaterial. Gas permeance results suggest a deviation from an expected Knudsen diffusion mechanism of the V2O5‐based membrane for He separation. The ideal selectivities of He/N2 and He/CO2 are compared to Robeson's upper bound for polymeric membranes. V2O5 membranes, prepared with the highest V2O5 quantity, exceeded the upper bound from 2008 for He/N2 and 2019 (the most recent) for He/CO2, demonstrating the interesting potential of V2O5 2D materials for gas separation.

Bryophyte-Bioinspired Nanoporous AAO/C/MgO Composite for Enhanced CO2 Capture: The Role of MgO.

A composite material composed of anodized aluminum oxide (AAO), carbon (C), and magnesium oxide (MgO) was developed for CO2 capture applications. Inspired by the bryophyte organism, the AAO/C/MgO composite mirrors two primary features of these species-(1) morphological characteristics and (2) elemental composition-specifically carbon, oxygen, and magnesium. The synthesis process involved two sequential steps: electroanodization of aluminum foil followed by a hydrothermal method using a mixture of glucose and magnesium chloride (MgCl2). The concentration of MgCl2 was systematically varied as the sole experimental variable across five levels-1 mM, 2 mM, 3 mM, 4 mM, and 5 mM-to investigate the impact of MgO formation on the samples' chemical and physical properties, and consequently, their CO2 capture efficiency. Thus, scanning electron microscopy analysis revealed the AAO substrate's porous structure, with pore diameters measuring 250 ± 30 nm. The growth of MgO on the AAO substrate resulted in spherical structures, whose diameter expanded from 15 nm ± 3 nm to 1000 nm ± 250 nm with increasing MgCl2 concentration from the minor to major concentrations explored, respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that carbon serves as a linking agent between AAO and MgO within the composite. Notably, the composite synthesized with a 4 mM MgCl2 concentration exhibited the highest CO2 capture efficiency, as determined by UV-Vis absorbance studies using a sodium carbonate solution as the CO2 source. This efficiency was quantified with a 'k' constant of 0.10531, significantly higher than those of other studied samples. The superior performance of the 4 mM MgCl2 sample in CO2 capture is likely due to the optimal density of MgO structures formed on the sample's surface, enhancing its adsorptive capabilities as suggested by the XPS results.

Highly permeable and shelf-stable aquaporin biomimetic membrane based on an anodic aluminum oxide substrate

Aquaporin (AQP) biomimetic membranes are a coming-of-age technology for water purification. Although several studies have reported aquaporin biomimetic membrane fabrication to date, these membranes show low water flux mainly due to the low porosity and inherently dense structure of the polymeric substrate materials. Herein, we report a ceramic-based aquaporin biomimetic membrane based on anodic aluminum oxide (AAO) as a substrate, which has a uniform porous structure with a high aspect ratio and pore density compared to conventional polymer substrates and exhibits a high water flux of 27.6 ± 3.6 LMH (L m−2 h−1) and superior membrane selectivity of 0.11 g L−1. Briefly, the AAO substrate was functionalized with amino-silane followed by polydopamine coating, then the AQP vesicles were immobilized on the functionalized AAO substrate surface using an electrokinetic method, and the water rejection performance of the membrane was analyzed in a forward osmosis system. Furthermore, a simple cryodesiccation method is introduced to improve the storage stability and easy transportation of aquaporin membranes, which does not require special environmental conditions to transport or store them.

High performance microheater-based catalytic hydrogen sensors fabricated on porous anodic alumina substrates

Catalytic combustion-type gas sensors are widely used in industry and everyday life for detecting flammable gases. However, high power consumption is one of the main drawbacks of the catalytic sensors. Replacing the platinum wire heating element with a thin-film microheater can significantly reduce power consumption, but maintaining high sensitivity and long-term stability of such devices is a challenge. Here we developed microheater-type catalytic hydrogen sensors based on porous anodic aluminium oxide served simultaneously as a substrate for platinum microheater and as a carrier for a catalyst. The fabricated sensors have a high sensitivity of 76 mV/vol% hydrogen. The deviation of the sensor response during continuous operation for 14 days is less than 4%. The relative humidity of the ambient atmosphere does not affect the sensor response. The fast sensor response time (0.4 s) makes it possible to use the pulsed power supply mode to reduce the power consumption to 3.2 mW without sacrificing the measurement accuracy. The performance of the developed catalytic hydrogen sensors promotes the high competitiveness in the market and the prospects for industrial applications.

Ultrathin Water-Responsive Zwitterionic Hydrogel Brush Coatings for Long-Term Corrosion Protection.

Preventing metal corrosion has usually been associated with water-repellent coatings that inhibit the penetration of aggressive chloride ions. Contrary to this conventional wisdom, we engineered ultrathin superhydrophilic zwitterionic hydrogel brushes rooted in a nanoporous anodic aluminum oxide (AAO) substrate that effectively hampered the adsorption of hydrated chloride ions (Cl-·H2O) on the Al alloy surface. The hydrogel brush coating enhanced corrosion resistance by 3 orders of magnitude, with corrosion current density declining from 1.518 to 1.567 × 10-3 μA cm-2. Despite suffering from long-term salt-spaying tests, zwitterionic hydrogel brush coating retained 2 orders of magnitude of corrosion resistance. Direct Raman spectroscopic evidence manifested that interfacial water comprised both highly ordered hydrogen-bonded water and disordered water containing hydrated Cl- ions. Under the hydration effect of zwitterionic hydrogel brushes, an interfacial disordered water structure dynamically transformed into a hydrogen-bonded water film. We correlated the structure and quantities of interfacial water with the corrosion current density and chloride adsorption. Hydrogen-bonded water improved by zwitterionic hydrogel brushes weakened the affinity and adsorption of hydrated Cl- ion water on the oxide film, resulting in excellent corrosion protection. Therefore, employing localized hydration tuning strategies, these findings are anticipated to generally empower ordered interfacial water to enhance metal corrosion resistance through precise interfacial engineering.

(Invited, Digital Presentation) Copper Nanowire 3-D Interconnects for Mm-Wave Applications

Small, lightweight mobile devices are the beneficiaries of fabrication miniaturization that follow Moore’s law predictions, advances in complex integration concepts, and wireless technology. Successful implementations have therefore stimulated unprecedented growth in mobile applications. Within these miniaturized devices, contact electrodes with small form factors in some applications are needed but unfortunately present many challenges and can lead to unwanted parasitic effects. Identifying ways to meet this need without introducing parasitic effects is essential to minimize signal distortion and loss in integrated circuits. The plethora of applications, however, produce large number of users and also generate extremely large amounts of data that require higher data rates. Higher frequency designs satisfy bandwidth requirements and maintain miniature size; unfortunately, this comes at a cost. When operating frequencies increase, available power decreases due to transistor technology limitations and the corresponding shrinkage in circuit size results in higher resistance leading to more power consumption. To address this conundrum, approaches are needed that allow losses to much be managed, and ideally reduced to achieve the desired performance requirements.This talk will present the investigation of copper nanowire (CuNW) technology for use in millimeter wave regime (30 GHz to 300 GHz) interconnect design in silicon integrated circuits. The parallel nature of nanowires to behave like bundles offers the potential to minimize loss and parasitic effects at millimeter wave frequencies. Co-integration of CuNW into coplanar waveguide (CPW) interconnect configurations that are single and multi-layer architectures will be discussed. Two types of interconnects are studied: vertical via and CuNW integrated into CPW lines. The findings from the study of these structures will include a discussion on the fabrication and characterization methods used for each technology followed by the loss performance results observed for the different types of designs.At 40 and 60 GHz, vertical CuNW via loss values of 0.095 dB and 0.149 dB was observed, respectively. These responses were lower than those of other via technologies and comparable to those in anodized aluminum substrates. Thus, they were favorable and indicate that CuNW can be used in a co-integrate manner to incorporate small contact features into designs that can maintain or reduce loss in the millimeter wave regime. CuNWs integrated CPW interconnects can also be used as a transmission line. In this case, loss responses, observed in the millimeter wave regime, can be reduced. In one design, loss values of 0.48 dB/mm and 0.59 dB/mm at 90 and 180 GHz, respectively, were determined, suggesting that conductor loss can be reduced in upper millimeter regime. At these frequencies, higher order mode suppression is essential to minimize unwanted substrate losses. Another design, however, improved losses in the low RF and microwave frequency regime, suggesting that low frequency designs can also experience conductor loss reduction. The conclusion thus far is that CuNW co-integration into CPW lines show promise for improving the performance of interconnect design across the RF to millimeter-wave spectrum when designed carefully.

In Situ Growth of MOF-303 Membranes onto Porous Anodic Aluminum Oxide Substrates for Harvesting Salinity-Gradient Energy.

As an emerging metal-organic framework (MOF) material in recent years, the MOF-303 membrane has shown great potential applications in seawater desalination, dehydration, and atmospheric water harvesting. Herein, we report on a dense and uniform MOF-303 membrane fabricated by a facile in situ hydrothermal synthesis approach in the presence of an anodized aluminum oxide (AAO) channel membrane acting as the only Al source and substrate. Interestingly, the MOF-303 isomer can be obtained due to an insufficient amount of organic ligand caused by the less hydrophilic and larger pore size of the AAO substrate. The MOF-based composite membranes possessed surface-charge-governed ionic transport behavior. Moreover, the MOF-303/AAO membrane yielded an output power density of 1.87 W/m2 under a 50-fold KCl concentration gradient. Under a 50-fold gradient of artificial seawater and river water, a maximum power density of 1.46 W/m2 can be obtained. After 30 days of stability testing, the composite membrane still maintained the power output, and the power density was higher than 1.20 W/m2. This work provides a facile and effective strategy for constructing Al-based MOF composite membranes and boosts their applications in harvesting salinity-gradient energy.

Aptamer-Modified Porous Anodized Aluminum Substrate for Rapid and Ultrasensitive Detection of Tetracycline via Surface Enhanced Raman Spectroscopy Couple with Electric Field Enrichment

Aptamer-Modified Porous Anodized Aluminum Substrate for Rapid and Ultrasensitive Detection of Tetracycline via Surface Enhanced Raman Spectroscopy Couple with Electric Field Enrichment

Magnetron sputtering process for deposition of multilayered thin diamond-like carbon films with silver nanoparticles for anti-reflective coatings and refractometric sensing

Multilayered film stacks serving optical applications usually require multiple target sources for deposition. In this work, we present a convenient method for the deposition of single- and multilayered thin films with varying diamond-like carbon (DLC) and silver content employing a single magnetron in the deposition system. For this, a reactive magnetron sputtering system was utilized and the silver target was poisoned based on desired structure: clean target and argon gas resulted in a pure silver film, completely poisoned target and acetylene and argon gas resulted in a DLC film, and anything in between resulted in a nanocomposite DLC:Ag film. The films were deposited on fused quartz, crystalline silicon, and porous anodized aluminum oxide substrates. We investigated the optical properties of these films and showed their applications for anti-reflective, black-appearing coatings and refractometric sensors, both experimentally and by simulation methods.

Fabrication of Low-Temperature Solid Oxide Fuel Cells via Development of Magnetron Sputtering Process

We herein report the development of the sputtering process for the fabrication of thin film low-temperature solid oxide fuell cells (LT-SOFCs) supported by anodized aluminum oxide (AAO). The process development has been conducted for each component, anode, electrolyte, electrolyte/cathode interlayer, and cathode to achieve not only high performance but also durability. In order to fabricate catalyst-ion conducting anode cermet, Ni and GdCe co-sputtering is utilized. Since the AAO is an electrical insulator, the electrons produced from the anode requires to pass through the thin anode layer to be collected which can lead to high current collecting resistance. Therefore, sputtering conditions such as power, pressure, and time are adjusted to produce the anode with minimal ohmic loss stemming from current collection. For the electrolyte (YSZ) and interlayer (GDC), a ceramic sputtering recipe has been developed to achieve high density and uniformity, which are the most critical requirement for these components. Through optimization of the gun angle, power, pressure, and the target to substrate distance (TSD), a highly dense and uniform ceramic electrolyte can be deposited on various AAO substrate sizes. For the cathode, a mixed ionic electronic conducting cathode sputtering recipe has been developed to enhance oxygen reduction reaction (ORR) at low operating temperatures. We have been developing the sputtering process to fabricate a nanocrystalline and highly porous LSC-GDC cathode with desired microstructure to enhance the ORR activity. Through the integration of the aforementioned sputtering process development, durable and high performance LT-SOFCs have been successfully fabricated on AAO substrates up to 15cm x 15cm size. Suppered thin film cells have shown superior performance at low operating temperatures, e.g., peak power density of 1.5W/cm2 at 550oC with hydrogen fuel.

Preparation of ordered nanoporous WO3 thin films and the mechanism of large room-temperature ferromagnetism

Undoped porous WO3 nanofilms with large surface area were fabricated on porous anodic alumina substrates by magnetron sputtering. The nanofilms exhibited significant room-temperature ferromagnetism, at least one order of magnitude stronger than other reported undoped WO3 films. By controlling the oxygen partial pressure and the sputtering time during the deposition process, the saturation magnetization of the samples could be tuned over a large range, from 0.1 to 21.7 emu/cm3. Obvious magnetic anisotropy was found in the porous samples, indicating that the magnetic behavior is related to the regular pore structure perpendicular to the surface. Moreover, the first theoretical evidence that the Curie temperature of the sample is higher than room temperature was provided. When annealed in argon, the WO3 nanofilms turned black and showed a combination of a narrowed bandgap and enhanced ferromagnetism. These interesting phenomena are explained based upon the concept of hydrogen-like impurity states associated with oxygen vacancies.

Thermally/mechanically robust anodic aluminum oxide (AAO) microheater platform for low power chemoresistive gas sensor

The semiconductor metal oxide gas sensors are getting high attention owing to their high sensitivities and fast responses. They require high temperature for the reaction with target gases, and suspended silicon membrane microheaters are typically used to reduce the heating power consumption. However, they have low durability for long-term uses, and high probability of fracture by thermal stress or mechanical impact. In this study, as an alternative to the silicon membrane microheater, anodic aluminum oxide (AAO)-based microheater platform gas sensor was fabricated for low power consumption and high thermal/mechanical stabilities. Nanoscale air gaps of the AAO substrate reduce the heat loss transferred to the substrate. Therefore, AAO-based microheater platforms do not require suspended structures sustained by very thin bridges, which dramatically enhances thermal/mechanical stabilities. The temperature of fabricated microheater platform reached to 250 °C by a heating power of 27.4 mW. The excellent thermal/mechanical stabilities of the AAO-based microheater platforms were verified by cyclic on-off and mechanical shock test. The pulsed heating operation was adopted, and it reduced the heating power consumption to 9 mW. The fabricated AAO-based gas sensors showed much higher responses to NO2 gas compared to the SiO2 membrane-based gas sensors.

Membrane Reactor Supported by MXene (Ti3C2TX) for Hydrogen Production by Ammonia Decomposition

Hydrogen (H2) production by ammonia (NH3) decomposition offers a solution to the energy problem. In this work, an MXene (titanium carbide, Ti3C2TX) membrane was successfully synthesized by depositing it onto the anodic aluminum oxide (AAO) substrate using vacuum-assisted filtration. Then, a membrane reactor supported by MXene was developed for H2 production by NH3 decomposition. The MXene membrane reactor could achieve an H2 permeance of 2.85 × 10–7 mol m–2 s–1 Pa–1 and an H2/N2 selectivity of 20 at 773.15 K. Next, a Ni-La/γ-Al2O3 catalyst prepared by impregnation and sintering was added to catalyze the NH3 decomposition process. The experimental results showed that the reactor could achieve a 99% NH3 conversion at 773.15 K, i.e., 9% higher than that of the packed catalytic reactor (without membrane). A mathematical model of the membrane reactor was developed to explain the experimental results. The calculated activation energies (Ead) of the MXene membrane for H2 and N2 permeances were 64.95 and 69.53 kJ mol–1, respectively. The activation energy (Ear) of NH3 decomposition was 147.8 kJ mol–1. Both the experimental and modeling results showed that the membrane reactor could enhance NH3 conversion and promote the production of high-purity H2.

Fabrication of Low-Temperature Solid Oxide Fuel Cells via Development of Magnetron Sputtering Process

We herein report the development of the sputtering process for the fabrication of low-temperature thin film solid oxide fuel cells (TF-SOFCs) supported by anodized aluminum oxide (AAO). The process development has been conducted for each component, anode, electrolyte, electrolyte/cathode interlayer, and cathode to scale up the cell from 1cm x 1cm to 15 cm x 15 cm. In order to fabricate a uniform thin film regardless of the size of AAO, sputtering conditions such as power, pressure, angle, target-to-substrate distance (TSD), and time have been developed. The recipe for the anode and cathode has aimed at a porous structure with nano-grains for high reactivity. In contrast, the recipe for the electrolyte has been optimized for thickness uniformity and high density. With these sputtering recipes TF-SOFCs with the required microstructure and thickness uniformity have been successfully fabricated on 15 cm x 15 cm AAO substrates.

Controlled deposition of graphene oxide on an anodic aluminum oxide substrate via coffee-ring effect

The suppression of the coffee-ring effect is important for obtaining uniform colloid deposition. In this study, the controlled deposition of graphene oxide on anodic aluminum oxide (AAO) through the suppression of the coffee-ring effect was investigated. The effect of factors such as the AAO’s thickness and pore diameter, the external temperature, and the applied electric potential on downward capillary flow through pores in the presence of outward capillary flow associated with the coffee-ring effect was studied. When graphene oxide (GO) suspension was drop-casted on an AAO substrate, an increasing AAO thickness led to enhanced downward capillary flow, which suppressed the coffee-ring effect. An increase in the pore diameter resulted in greater suppression the coffee-ring effect since GO flakes could not completely block the pore entrance. Furthermore, an elevated temperature suppressed the coffee-ring effect on the AAO substrate through the rapid evaporation of the droplet, which reduced the outward capillary flow. When an electric potential was applied to the droplet, the downward capillary flow improved because of electrowetting and the outward capillary flow was reduced by the Coulomb force. In particular, the effect of the varied electric potential was adjusted by the AAO thickness. These observations indicated that the coffee-ring effect could be suppressed by appropriately setting the outward and downward capillary flows on the AAO substrate. Furthermore, the pore diameter had a stronger influence than the AAO thickness on the drop-casted GO film’s thickness. Notably, optimized GO film manipulation and GO film thickness control could be achieved by manipulating the hydrodynamic flow. The findings of this study have the potential to be used in applications such as filtration, gas separation, and wearable sensors, where a uniform thin film is required.

회전경사증착 기법을 이용한 Ni-GDC 연료극이 적용된 AAO 기반의 저온작동 박막 고체산화물 연료전지의 저항 특성 연구

In this study, we fabricated thin film solid oxide fuel cells on nanoporous anodic aluminum oxide (AAO) substrate for low-temperature operation using the all-through sputtering method. To deposit up to a three-micrometer thick anode with both porosity and electrical conductivity, we used the glancing angle deposition and co-sputtering methods. For the anode materials, we used nickel gadolinium-doped-ceria (Ni-GDC) mixed ionic and electronic conductor (MIEC), which improved hydrogen oxidation reaction reactivity at the anode side. TF-SOFCs were successfully operated at 500℃, and 223.6 mW/cm² was their highest measured maximum power density. We conducted structural and electrochemical analyses to figure out cells’ unique resistant characteristics; ohmic resistance through the anode thin film and polarization resistance of reaction area near the narrowed anode pores. We found how the anode thin film thickness affects the current collecting performance and the anode reactivity, and their effects were qualitatively and quantitatively compared.

Hydrophobic-oleophilic surfaces based on chemical modification of nanoporous alumina

Hydrophobic/oleophilic nanoporous anodic alumina substrates were fabricated by two-step anodization method following of chemical modification with 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS). Surface morphology was characterized using a scanning electron microscopy. The influence of the topography and the pore size of the surface in the contact angle measurements with different solvents have been studied. The water repellence capacity of the nanoporous anodic alumina structure as fabricated depends on pore diameter but, there is a critical value of pore size beyond which the water contact angle decrease. After chemical modification of the surface, this effect is not observed. The porous topography of the material is not an advantage for the oleophibicity. The CA values for the non-porous surface using different solvents are lower than the structured surface.The results obtained in this study can be used to desire wettability properties. Modified NAA exhibit hydrophobicity and at the same time permeability for solvents with low surface tension.

Fabrication of Superhydrophobic Surface on Anodized Aluminum Through a Wet-Chemical Route

Fabrication of superhydrophobic surfaces on anodized aluminum substrates by wet-chemical grafting using cost-effective chemicals through a simple immersion process is described in this work. Formation of formate-alumoxane is possible by treating the anodized and sealed aluminum substrate with formic acid at around 50 °C. On treatment with sodium salts of higher-order carboxylic acids (stearic acid, lauric acid, and palmitic acid), the formate ions are replaced by higher-order carboxylates. A possible bonding mechanism of the longer chain carboxylic acids with aluminium surfaces has been suggested based on IRRAS and XPS studies. The as-prepared superhydrophobic aluminum substrates exhibited a static water contact angle of up to 167° with a sliding angle not higher than 6°, with decent resistance against abrasion in addition to good UV, environmental and thermal stabilities. Aluminium substrates of any size, shape and surface finish can be easily rendered robust and superhydrophobic without the use of expensive chemicals and sophisticated machinery.

Characterization of Electrodeposited Cobalt/Copper (Co/Cu) Granular Multilayered Thin Films onto the Anodic Aluminum Oxide (AAO) Substrates

Herein, we report on the characterization of a series of cobalt/copper granular thin films alloys electrodeposited onto the previously pre-treated aluminum substrates, at different deposition time. And a systematic study of their structural and magneto-optical properties were investigated. The proper deposition potentials of Co, and Cu were obtained from the cyclic voltammetry method. It was observed that the easy axis direction of magnetization was parallel to the film plane for all films. The X-ray diffraction (XRD) results revealed that all films had a mixture of hexagonal close-packed (hcp) and face centered cubic (fcc) phases. The Scanning electron microscope images (SEM) and atomic force microscopy (AFM) showed some parallelepiped and ellipsoid shaped rods with an averaged dimension about of 600 nm length, 600 nm width and 200 nm thickness for a sample electrodeposited at room temperature. These rods are irregularly arranged. Their irregular arrangement could explain the large d-spacing in the sample at this temperature. The magnetic analysis of the granular thin films alloys showed the saturation magnetization increased and the coercivity decreased as the deposition time increased. These results showed that the changes in magnetic and structural properties of granular cobalt/copper alloys deposits were substantially depending on the variation of deposition time. Therefore, the change of the deposition time was seen to control the properties of the alloys deposits and hence their properties could be modified for desired purpose.

CF4 plasma-based atomic layer etching of Al2O3 and surface smoothing effect

Plasma-based Al2O3 atomic layer etching (pALE) has a reaction mechanism similar to thermal Al2O3 ALE (tALE). The main difference between the two methods is that pALE uses plasma instead of HF in tALE to fluorinate Al2O3 to AlF3. In this study, the CF4 plasma source commonly used for dry etching is combined with a self-developed low-ion-bombardment remote Al2O3 plasma-based ALE system to obtain Al2O3 plasma fluorination conditions, and then the AlCl(CH3)2 (dimethylaluminum chloride) precursor is used to develop the pALE Al2O3 process. In addition to using x-ray photoelectron spectroscopy to investigate ideal fluorination conditions of CF4 plasma for Al2O3 films and establishing the linear etching rate curves of pALE at different process temperatures (250–400 °C), we used atomic force microscopy to analyze the surface morphology of the Al2O3 films after dry etching and pALE. We showed that pALE can smooth Al2O3 films with a root mean square surface roughness of 1.396–0.655 nm and used anodic aluminum oxide substrates with nanotrench structures to demonstrate that pALE can improve the surface roughness of nonplanar structures.