Anodic Aluminum Oxide Surface Research Articles

Analysis of anti-condensation mechanism on superhydrophobic anodic aluminum oxide surface

Wetting theory about superhydrophobic surfaces reveals that hydrophobicity of surfaces has great relationship with surface roughness and surface free energy. Adopt electrochemical plus fluorine silane modified method to prepare superhydrophobic surface on anodic aluminum oxide surface, which not only enhances surface roughness, but also reduces surface free energy, even the static contact angle can reach 159.2° and anti-condensation is authenticated. Based on the experimental findings, analyze the reason of anti-condensation on superhydrophobic surfaces: one is that the density of droplets formed on superhydrophobic surfaces is low and the number of droplets is little; the other is bigger static contact angle and smaller rolling angle on superhydrophobic surfaces make droplets easy to detach on smaller tilt angle. This research can solve some condensation problems of equipment using in HVAC systems, such as heat exchangers in air conditioning system, cold radiation boards, air supply outlets, and so on.

Pulsatile Releasing Platform of Nanocontainers Equipped with Thermally Responsive Polymeric Nanovalves

Polymer-gated reservoirs built of an ordered porous anodic aluminum oxide (AAO) platform equipped with poly(N-isopropylacrylamide) (PNIPAM) brushes grafted from the surface using atom transfer radical polymerization were fabricated and studied. The brushes of different lengths were grafted from the AAO surface with pores having diameters of 30, 50, and 80 nm, respectively. Polymer brushes served as thermally responsive valves that can immediately open and close the pores just by crossing the PNIPAM lower critical solution temperature. Calcein was used as a model fluorescent molecule to follow a release process from the platform of the gated nanocontainers. The studied systems enable the burst release of the loaded substance, followed by diffusion-controlled release that depends on the pores’ diameter. These platforms are characterized by a high loading capacity in comparison to polymer films and can be loaded repeatedly. Importantly, the opening/closing of the nanocontainers is reversible, and a pulsatile...

Nanoporous Aluminium Oxide Membranes as Cell Interfaces

Nanoporous anodic aluminium oxide (AAO) has become increasingly important in biomedical applications over the past years due to its biocompatibility, increased surface area, and the possibility to tailor this nanomaterial with a wide range of surface modifications. AAO nanopores are formed in an inexpensive anodisation process of pure aluminium, which results in the self‐assembly of highly ordered, vertical nanochannels with well‐controllable pore diameters, depths, and interpore distances. Because of these outstanding properties AAO nanopores have become excellent candidates as nanostructured substrates for cell‐interface studies. In this comprehensive review previous surveys on cell adhesion and proliferation on different AAO nanopore geometries and surface modifications are highlighted and summarised tabularly. Future applications of nanoporous alumina membranes in biotechnology and medicine are also outlined, for instance, the use of nanoporous AAO as implant modifications, coculture substrates, or immunoisolation devices.

Thermally annealed Ag nanoparticles on anodized aluminium oxide for SERS sensing

In this paper we report a study of novel thermally stable surface enhanced Raman scattering (SERS) substrates consisting of Ag nanoparticles immobilized on an anodized aluminum oxide (AAO) support. The morphological and chemical characteristics and the SERS activity of the Ag nanoparticles before and after the thermal treatment were evaluated using SEM, XPS, UV-vis and Raman spectroscopy. Our results show that the nanoporous surface of AAO significantly hinders the fusion of Ag nanoparticles to single large particles at up to 400 °C, preserving high SERS enhancement. XPS and SERS results indicate that exposure to high temperatures efficiently ‘cleanses’ the surface from citrate remnants, opening more binding sites for analytes on Ag nanoparticles. In addition, thermal decomposition of silver oxide occurs at 400 °C, ensuring a pure metallic surface and further enhancing SERS activity.

Fabrication of superhydrophobic AAO-Ag multilayer mimicking dragonfly wings

Inspired by the co-coupling of the non-smooth structure and the waxy layer inducing the hydrophobicity of dragonfly wing surface, we developed a simple and versatile method to fabricate a superhydrophobic surface with the dragonfly wing structures. In this work, Ag nanorods grew on highly ordered anodic aluminum oxide (AAO) surface via a galvanic reduction approach. Then the AAO-Ag multilayer was fabricated. Furthermore, the surface free energy of AAO-Ag multilayer was reduced by modifying with perfluorodecanethiol. The modified AAO-Ag multilayer was superhydrophobic and the static contact angle reached as high as 168°. X-ray photoelectron spectra (XPS) were used to characterize the chemical structure of the obtained products. The morphologies of AAO-Ag multilayer was similar to microstructure of dragonfly wing surface and presented hierarchical rough structure. The results showed that the co-coupling of the rough structure and low surface free energy induced the superhydrophobic performance of the AAO-Ag multilayer surface.

Pore diameter-dependence wettability of porous anodized aluminum oxide membranes

Porous anodized aluminum oxide membranes with different diameters are fabricated and characterized, and the relation between the pore diameters and the wettability is investigated. The results indicate that changing the diameter of the porous anodized aluminum oxide from 15 to 220 nm causes the wettability on the surface of porous anodized aluminum oxide within the range from hydrophilicity to hydrophobicity. The presence of nanopores is recognized as one of the main causes of the transform of the wettability on the surfaces of the porous anodized aluminum oxide. The wettability-controllable anodized aluminum oxide surface can be an excellent platform on which to elucidate the physical nature of the wetting phenomenon related to the nanostructure and has promising potential in technological applications.

Fabrication of a Super-Hydrophobic Micro-Nanoporous Aluminum Surface by Anodic Oxidation

A novel and stable super-hydrophobic film was prepared by stearic acid (C18H36O2), which was chemically adsorbed onto the anodized aluminum surface. The maximum static water contact angle (WCA) of the super-hydrophobic surface was 157.5º ± 2.0º and the contact angle hysteresis was less than 3º. The superhydrophobic property is attributed to the micro-nanoporous surface morphology and stearic acid. The pore size on the surface of anodic aluminum oxide is an important factor for controlling the superhydrophobic adhesiveness. The superhydrophobic surface is a factor to reduce device-associated infection and can be used in metal packaging practice.

Analysis on the Scattering Characteristics of Two Stray Light Removing Metal Surfaces

For the purpose of stray light suppression, black anodized and sandblasted aluminum alloy is widespread used in spaceborne cameras. Base on the relative measuring method, in the white light irradiation, measure relative backscatter intensity and BRDF of two black anodized and sandblasted sample surfaces. Contrast these surfaces scattering characteristics. Finally BRDF curves have been drawn with measurement data. In the curves, the BRDF of sandblasted aluminum surface is nearly linear relation. Anodized surface curve, it’s pulse pattern that BRDF sharply increases among the region of critical angles. It is indicate that in critical angle range, anodized aluminum surface specularity is visible and can be treated as specular reflection which harm for stray light suppression. This experiment research can provide objective reference of these two material’s scattering characteristics in specific optical system design.

Synthesis of Carbon Nanotube and Carbon Nanofiber in Nanopore of Anodic Aluminum Oxide Template by Chemical Vapor Deposition at Atmospheric Pressure

Carbon nanotube (CNT) is one of the most attractive materials for the potential applications of nanotechnology due to its excellent mechanical, thermal, electrical and optical properties. We demonstrated the fabrication of carbon nanotube and carbon nanofiber (CNF) inside the pore and at the surface of anodic aluminum oxide (AAO) membrane by chemical vapor deposition method at atmospheric pressure. Ethanol was used as a hydrocarbon source and Co–Mo as catalyst. CNT was synthesized at different temperature. High graphitic multiwall carbon nanotube (MWCNT) was found at 750°C, while CNF was found at 800°C and above temperature analyzing by Raman spectroscopy.

Research on Inhibition Marine Microbial Adherence of a Novel Nano-TiO<sub>2</sub> Coating on Aluminum

A novel nano-TiO2 coating is prepared by vacuum dip-coating TiO2 sol–gel onto the anodized aluminum surface. The particles of TiO2 anatase is filled into the Al2O3 nano-pores formed by anodization. The structure and composition of the coatings are characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The preponderant bacterium is identified as Pseudomonas lindanilytica strain IPL-1 through analysis of the sequences of S16 nRNA gene segment. In addition, the electrochemical results show that the TiO2 coatings significantly reduce the corrosion rate of Al substrates. The UV reflection spectroscopy is used to determine and analyze that the nano-TiO2 coatings could improve the light photo catalytic activity which decreases microbial influencing corrosion acceleration inhibition (MICI).

Adhesion-enhanced thick copper film deposition on aluminum oxide by an Ion-beam-mixed Al seed layer

We report a highly-adherent 30-µm Cu conductive-path coating on an aluminum-oxide layer anodized on an aluminum-alloy substrate for a metal-printed circuit-board application. A 50-nm Al layer was first coated with an e-beam evaporative deposition method on the anodized oxide, followed by ion bombardment to mix the interfacial region. Subsequently, a Cu coating was deposited onto the mixed seed layer to the designed thickness. Adhesions of the interface were tested by using tape adhesion test, and pull-off tests and showed commercially acceptable adhesions for such thick coating layers. The ion beam mixing (IBM) plays the role of fastening the thin seed coating layer to the substrate and enhancing the adhesion of the Cu conductive path on the anodized aluminum surface.

Comparison of anodised aluminium surfaces from four fabrication methods

This study presents a comparative analysis of surface characteristics and properties of anodised aluminium cylinders produced by sand casting, permanent mould casting, extrusion, and high pressure die casting. Differences in micro structure and distribution of silicon particles in the aluminium, due to the fabrication method and the silicon content in the alloy, resulted in varying thickness of the oxide layers (mean thicknesses between 7 and 19μm) and surface topography. The oxide layer was unevenly thick for the permanent mould cast and the sand cast cylinders, resulting in a surface with higher plateaus and lower areas. This was more prominent for the sand cast surface. The oxide of the extruded cylinder was thick and even and its surface was smooth. The high pressure die cast surface had an oxide that was very thin and uneven. The surfaces displayed different results in the scratch test due to the variations in the surface structure. For the permanent mould cast and the sand cast surfaces the silicon particles present in the oxide deflected the cracks that were formed during the scratching. This resulted in smaller wear debris. The nanohardness values of the oxides had a large scattering due to the inhomogeneous nature of the oxide layers, with pores and particles. However, the highest nanohardness values were between 5000 and 6000MPa for the four surfaces, which is significantly lower than that of sintered alumina. In the micro abrasion test the wear mechanism for all four surfaces was microcutting resulting in chippings.

Modification of Anodised Aluminium Surfaces Using a Picosecond Fibre Laser for Printing Applications

The use of an ultrafast fibre laser at a wavelength of 1064 nm has allowed the surface modification of anodised aluminium plates coated with a 2 micron thick anodised layer for potential industrial applications. The micro- and nano-scale structuring of the anodised aluminium using picosecond pulses of approximately 25 ps duration at 200 kHz repetition rate was investigated. The interaction of the laser with the substrate created a hydrophilic surface, giving a contact angle of less than 10 degrees. On examination under a Scanning Electron Microscope (SEM), a morphology created due to laser induced spallation was observed. It has been found that these laser processed hydrophilic surfaces revert to a hydrophobic state with time. This has potential for application in the printing industry and offers reusability and sustainability of the process materials. This has been confirmed in initial trials.

Growth of vertically aligned carbon nanotubes over self-ordered nano-porous alumina films and their surface properties

Nanoporous anodic aluminum oxide (AAO) with self-organized arrays of uniform nanopores have been used for various applications in the fields of sensing, storage, separation and template-based fabrication of metal nanowires, carbon nanotubes, oxides and polymers. The work presented here involves the production and use of AAO templates for growth of aligned multi walled carbon nanotube arrays. AAO templates were formed by electrochemical oxidation of aluminum in different electrolyte solutions containing sulfuric, oxalic and phosphoric acid. SEM was used for the analysis of the surface morphology of the AAO films. The porous structures with pore size in the range of 25–120nm were observed. Pore sizes were correlated with the type of acidic solutions used as the electrolyte. Finally, AAO surfaces have been used as substrates for the growth of vertically aligned carbon nanotubes through chemical vapor deposition technique, which showed super-hydrophobic behavior as confirmed by contact angle measurements.

Reflectivity Spectra and Colors of Porous Anodic Aluminum Oxide Containing Silver Nanoparticles by Plasmonic Absorption

The reflectivity spectra and color of porous anodic aluminum oxide (AAO) nanostructures containing the assembly of silver (Ag) nanoparticles (NPs) with a diameter of -10 nm were investigated. The Ag NPs were assembled inside the pores of AAO with a diameter of -60 nm by dip-coating process during which Ag NPs adsorbed on the surface of AAO and driven inside the pores by capillary force upon the evaporation of solvent. The reflectivity spectra and associated colors of AAO with Ag NPs were determined by the plasmonic absorption of light by Ag NPs. Even with the monolayer coverage of Ag NPs in the pores of AAO, the reflectivity is significantly reduced specifically at -465 nm wavelength by a strong plasmonic absorption, resulting in its golden color. Aggregating Ag NPs by post-annealing at 300 and 400 degrees C changed the color to pink due to the red-shift of absorption. These results are indicative of potential color-engineering of NPs/AAO platform by wavelength-selective reduction of reflected light intensity and using it in direct optical read-out of change of surface and morphology conditions.

Label-free reflectometric interference microchip biosensor based on nanoporous alumina for detection of circulating tumour cells

In this report, a label-free reflectometric interference spectroscopy (RIfS) based microchip biosensor for the detection of circulating tumour cells (CTCs) is demonstrated. Highly ordered nanoporous anodic aluminium oxide (AAO) fabricated by electrochemical anodization of aluminium foil was used as the RIfS sensing platform. Biotinylated anti-EpCAM antibody that specifically binds to human cancer cells of epithelial origin such as pancreatic cancer cells (PANC-1) was covalently attached to the AAO surface through multiple surface functionalization steps. Whole blood or phosphate buffer saline spiked with low numbers of pancreatic cancer cells were successfully detected by specially designed microfluidic device incorporating an AAO RIfS sensor, without labour intensive fluorescence labelling and/or pre-enhancement process. Our results show that the developed device is capable of selectively detecting of cancer cells, within a concentrations range of 1000–100,000cells/mL, with a detection limit of <1000cells/mL, a response time of <5min and sample volume of 50μL of. The presented RIfS method shows considerable promise for translation to a rapid and cost-effective point-of-care diagnostic device for the detection of CTCs in patients with metastatic cancer.

Superhydrophobic RTV Silicone Rubber Coatings on Anodized Aluminium Surfaces

A superhydrophobic surface was elaborated using two inexpensive industrial processes: surface anodization in phosphoric acid and spin coating of the anodized surface by RTV silicone rubber. Scanning electron microscopy (SEM), atomic force microscopic (AFM) and water contact angle measurements have been performed to characterize the morphological features, and wettability of the surfaces. The water static contact angle of the elaborated surface reached 157 ° at room temperature. At supercool temperature (-10°C) the superhydrophobic coating showed an important delayed freezing time.

Migration Enhanced Molecular-Beam Epitaxy of III-V Quantum Dot Arrays Using Non-Lithographic AAO Template

We report a highly effective method on selective growth of ordered arrays of III-V quantum dots (QDs) on GaAs(100) substrate by migration enhanced molecular-beam epitaxy (ME-MBE) using anodic aluminum oxide (AAO) template. ME-MBE method can enhance the migration and evaporation of group III adatoms on AAO template resulting in highly selective growth with no visible nucleation on the surface of AAO. The shadowing and blocking effects commonly experienced with conventional molecular-beam epitaxy (MBE) are significantly reduced. Uniform arrays of III-V QDs with mean diameter of 60 nm and periodicity of 100 nm are obtained. Our results show that ME-MBE method has potential applications for selective growth of semiconductor hetero- nanostructures.

Effects of thickness and field strength of anodic oxide film on aluminum on its compressive rupture

The rupture behavior of an anodized aluminum surface was investigated in a borate buffer solution using an in situ micro-indentation test, in which transients of the indentation load and flowing current were monitored during loading and unloading of a sapphire indenter. A pair of anodic current peaks emerged during both downward and upward drives of the indenter due to rupture and repair of an anodic oxide film. The total area of film ruptured during both drives, as well as the area of radial cracks, increased with an increase in film thickness and with a decrease in electric field applied while an area of circular cracks was almost constant. It was suggested that the film–rupture owing to radial cracks formation was enhanced by tensile stress accumulated in the anodic oxide film by thickening of the oxide film and lowering of the electrostriction.

Template Assisted Fabrication of Pt–Sn Core–Shell Nanospheres

Sub-micron or nano-scale spheres are typically fabricated using conventional powder metallurgy processes; however, it is difficult to control the diameter and shape of each nanoparticle such that they are uniform. In this work, tin (Sn) was first sputtered on an anodic aluminum oxide (AAO) template. Then tin spheres were formed on the AAO by sinking tin-deposited AAO into silicone oil through the thermal-reflowing process. The size and quantity of the spheres were controlled with the sputtering time and power. The thermal-reflowed tin nanospheres were subsequently coated with thin platinum (Pt) film by DC sputtering, forming Pt–Sn core–shell nanospheres. The total surface area of the tin sphere on AAO and specific surface area of the Pt spherical shell were determined. The specific surface areas of Pt shell on the Sn nanospheres were 8.1–16.2, 10.3–20.6, and 12.8–25.6 (m 2 g −1) with wetting angles at 100°, 120°, and 150°, respectively between the Sn sphere an AAO.