Anodic Aluminum Oxide Substrate Research Articles

Tuning the Hydration and Lubrication of the Embedded Load-Bearing Hydrogel Fibers.

One of the most prominent properties of hydrogels is their excellent hydrolubrication that derives from the strong hydration of the gel network. However, excessive hydration makes hydrogels exhibit a very poor mechanical property, which limits their practical applications. Here, we prepared a novel composite surface of hydrogel nanofibers embedded in an anodic aluminum oxide substrate which exhibited both excellent lubrication and a high load-bearing capacity. Through the copolymerization of acrylic acid and 3-sulfopropyl methacrylate potassium salt, the gel network swelled sufficiently in aqueous solution and caused high osmotic pressure repulsion to bear heavy loads and hence exhibited excellent aqueous lubrication (μ ≈ 0.01). Notably, the friction coefficient of gels showed no dependence on the load in the experiment, whereas it was strongly influenced by the sliding velocity. Additionally, both electrolyte solution and ionic surfactants affect the conformation of the polymer chains, which results in a significant impact on the friction properties of hydrogel fibers.

The Tethered Fibrillar Hydrogels Brushes for Underwater Antifouling

The development of antifouling surfaces to prevent bioattachment is an urgent demand for marine coating and biomedical applications. In this paper, two types of anionic and zwitterionic gel fibers are synthesized based on anodic aluminum oxide (AAO) substrate and their antifouling properties against oil and algal attachment are systematically investigated. To begin with, gel surfaces exhibit underwater superoleophoic property and extremely low oil adhesion. The effect of electrolyte on underwater wetting behavior is studied. It is shown that the adhesion of oil droplets on gel fibers significantly increase upon immersing in electrolyte solutions and ionic surfactants, which could be attributed to electrostatic screening effect of salt solution and ion‐pairing interaction. Notably, in regard to Dunaliella tertiolecta and Navicula sp., almost 90% and 95% decrease of fouling algae density are achieved for P(AA/SPMA) and P(AA/SBMA) gel fibers, respectively, comparing with AAO substrate for control. The excellent antifouling property and high structural stability of gel fibers make them effective antifouling surfaces.

HfO2/porous anodic alumina composite films for multifunctional data storage media materials under electric field control

New materials for achieving direct electric field control of ferromagnetism and resistance behavior are highly desirable in the development of multifunctional data storage devices. In this paper, HfO2 nanoporous films have been fabricated on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. Electrically induced resistive switching (RS) and modulated room temperature ferromagnetism are simultaneously found in a Ag/HfO2/PAA/Al (Ag/HP/Al) heterostructure. The switching mechanism between low resistance state and high resistance state is generally attributed to the formation/rupture of conductive filaments which may consist of oxygen vacancies. The combination of the electric field control of magnetization change and RS makes HP films possible for the multifunctional data storage media materials.

Evaporating metal nanocrystal arrays

Anodic aluminum oxide (AAO) substrates with a self-ordered triangular array of nanopores provide the means to fabricate multiple forms of nano materials, such as nanowires and nanoparticles. This study focuses on nanostructures that emerge in thin films of metals thermally evaporated onto the surface of AAO. Previous work showed that films of different evaporated metals assume dramatically different structures, e.g. an ordered triangular array of nearly monodisperse nanoparticles forms for lead (Pb) while a polycrystalline nanohoneycomb structure forms for silver (Ag). Here, we present investigations of the effects of substrate temperature and deposition angle that reveal the processes controlling the nano particle array formation. Our findings indicate that arrays form provided the grain nucleation density exceeds the pore density and the atomic mobility is high enough to promote grain coalescence. They introduce a method for producing films with anisotropic grain array structure. The results provide insight into the influence of substrate nano-morphology on thin film growth energetics and kinetics that can be harnessed for creating films with other novel nano-structures.

Fabrication of nanopore and nanoparticle arrays with high aspect ratio AAO masks

How to use high aspect ratio anodic aluminum oxide (AAO) membranes as an etching and evaporation mask is one of the unsolved problems in the application of nanostructured arrays. Here we describe the versatile utilizations of the highly ordered AAO membranes with a high aspect ratio of more than 20 used as universal masks for the formation of various nanostructure arrays on various substrates. The result shows that the fabricated nanopore and nanoparticle arrays of substrates inherit the regularity of the AAO membranes completely. The flat AAO substrates and uneven AAO frontages were attached to the Si substrates respectively as an etching mask, which demonstrates that the two kinds of replication, positive and negative, represent the replication of the mirroring of Si substrates relative to the flat AAO substrates and uneven AAO frontages. Our work is a breakthrough for the broad research field of surface nano-masking.

A Two-Dimensional Lamellar Membrane: MXene Nanosheet Stacks.

Two-dimensional (2D) materials are promising candidates for advanced water purification membranes. A new kind of lamellar membrane is based on a stack of 2D MXene nanosheets. Starting from compact Ti3 AlC2 , delaminated nanosheets of the composition Ti3 C2 Tx with the functional groups T (O, OH, and/or F) can be produced by etching and ultrasonication and stapled on a porous support by vacuum filtration. The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m-2 h-1 bar-1 ) and favorable rejection rate (over 90 %) for molecules with sizes larger than 2.5 nm. The water permeance through the MXene membrane is much higher than that of the most membranes with similar rejections. Long-time operation also reveals the outstanding stability of the MXene membrane for water purification.

A Two‐Dimensional Lamellar Membrane: MXene Nanosheet Stacks

AbstractTwo‐dimensional (2D) materials are promising candidates for advanced water purification membranes. A new kind of lamellar membrane is based on a stack of 2D MXene nanosheets. Starting from compact Ti3AlC2, delaminated nanosheets of the composition Ti3C2Tx with the functional groups T (O, OH, and/or F) can be produced by etching and ultrasonication and stapled on a porous support by vacuum filtration. The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m−2 h−1 bar−1) and favorable rejection rate (over 90 %) for molecules with sizes larger than 2.5 nm. The water permeance through the MXene membrane is much higher than that of the most membranes with similar rejections. Long‐time operation also reveals the outstanding stability of the MXene membrane for water purification.

Enhanced Thermal Stability of a Gadolinia-Doped Ceria Capped Metal Electrode for Durable Low-Temperature Solid Oxide Fuel Cells

A gadolinia-doped ceria (GDC) capping layer was fabricated on a metal Pt cathode via a sputtering technique to enhance the thermal stability and oxygen-reduction reaction (ORR) kinetics. By varying the thickness of the GDC thin film on the Pt cathode, we fabricated thermally durable low-temperature solid oxide fuel cells (LT-SOFCs) on porous anodized aluminum oxide (AAO) substrates while securing very high performance. The GDC protective layers subsequently mitigated the agglomeration of the Pt morphology by hindering the coarsening of metal grains, and enhanced the cathodic kinetics as a result of the increased TPB density at the Pt-electrolyte interface. Enhanced performance of fuel cells and thermo-stable behavior with the GDC capping layer were demonstrated by employing transmission electron microscopy (TEM) and electrochemical analysis. An enhanced peak power density of 258 mW/cm2 was obtained with a degradation of 56.4% of the Pt cathode over 25 hours of operation at 450°C.

Microstructures and room temperature ferromagnetism of ordered porous ZrO2 thin films sputter deposited onto porous anodic alumina substrates

Ordered porous ZrO2 films with pore diameters in the 5–45nm range have been prepared on porous anodic alumina substrates using DC-reactive magnetron sputtering of pure Zr targets. A saturation magnetization (MS) value as high as 119emu/cm3 was obtained for the ZrO2 film with pores of 45nm in diameter when the external field was perpendicular to the film surface. The significant out-of-plane saturation magnetization is associated with the porous structure of the film. Experimental and theoretical results showed that the origin of the room temperature ferromagnetism (RTFM) is closely related to the ordered porous structure and the single charged oxygen vacancies of the films. These findings suggest that porous ZrO2 films are promising to be applied to the spin electronic devices.

Palladium decorated silicon carbide nanocauliflowers for hydrogen gas sensing application

Silicon carbide (SiC) nanostructures have attracted significant attention for device applications due to their unique structural, electronic and catalytic properties. Here, the efficiency of three dimensional SiC nano-cauliflowers (NCs) for hydrogen gas sensing application has been investigated. We have deposited a vertically aligned, ordered Pd decorated SiC NCs directly on a silver (Ag) coated porous anodic alumina (AAO) substrate by DC magnetron cosputtering and then it used as a gas sensor without additional processing. The sensor shows remarkably high and selective responses to hydrogen gas with low detection range 2–500ppm at relatively high temperature range (30–500°C). Our results demonstrate the potential application of Pd decorated SiC NCs for fabricating highly sensitive and selective hydrogen gas sensors.

Sputtered Synthesis of MnO2 Nanorods as Binder Free Electrode for High Performance Symmetric Supercapacitors

Among numerous active electrode materials, manganese oxides are promising electrodes in supercapacitors. Manganese oxides research has thus far focused on the synthesis of one-dimensional (1-D) metal oxide nanostructured materials, which can have superior electrochemical performance. Several chemical methods are used to synthesize metal oxide nanostructured which involve toxic reagents, solvents and introduction of byproducts. However, physical method offers an eco-friendly path to develop contamination free 1-D metal oxide nanostructured materials. Here, we report the fabrication of binder free supercapacitor electrode of MnO2 nanorods on Nickel (Ni) coated porous anodic aluminum oxide (AAO) by DC magnetron sputtering for first time. Ni coated porous AAO substrate act as excellent current collector, enhancing the specific capacitance of MnO2 to 649F/g. The binder free symmetric supercapacitor device delivered a high areal capacitance (112.6 mF/cm2), specific capacitance (194.23 Fg−1), good cyclic ability (89.83%) retention in capacitance after 5000 cycles), energy density (4.2 Whkg−1), and power density (1.4 kWkg−1 at 0.718 Whkg−1). These outstanding electrochemical performances, suggest their tremendous potential as supercapacitor electrode in energy storage application.

Nanoporous Anodic Aluminum Oxide (AAO) Thin Film Fabrication with Low-Grade Aluminium

Anodic aluminum oxide (AAO) is well known for its nanoscopic structures and its applications in microfluidics, sensors and nanoelectronics. The pore density, the pore diameter, and the interpore distance of an AAO substrate can be controlled by varying anodization process conditions. In this research, the self-organized two-step anodization is carried out with a low-grade (Al6061) aluminium substrate using a 40V voltage at the temperature of 2 to 5 °C. Three experiments are done with the anodization time of 24 hours, 48 hours and 72 hours. The structural features of AAO are characterized by a field emission electron microscope (FE-SEM). The data from FE-SEM show that the average pore diameter increases with the anodization time, and that the Al6061 aluminium substrate can be used to fabricate a nanoporous AAO film with an average pore diameter smaller than 17 nanometers.

PEALD YSZ-based bilayer electrolyte for thin film-solid oxide fuel cells

Yttria-stabilized zirconia (YSZ) thin film electrolyte deposited by plasma enhanced atomic layer deposition (PEALD) was investigated. PEALD YSZ-based bi-layered thin film electrolyte was employed for thin film solid oxide fuel cells on nanoporous anodic aluminum oxide substrates, whose electrochemical performance was compared to the cell with sputtered YSZ-based electrolyte. The cell with PEALD YSZ electrolyte showed higher open circuit voltage (OCV) of 1.0 V and peak power density of 182 mW cm−2 at 450 °C compared to the one with sputtered YSZ electrolyte(0.88 V(OCV), 70 mW cm−2(peak power density)). High OCV and high power density of the cell with PEALD YSZ-based electrolyte is due to the reduction in ohmic and activation losses as well as the gas and electrical current tightness.

Preparation and magnetic properties of DC-sputtered porous HfO2 films

Ordered hafnium oxide films were successfully prepared on porous anodic alumina substrates using DC-reactive magnetron sputtering, and remarkable room-temperature ferromagnetism has been observed in them. A saturation magnetization (MS) value as high as 128emu/cm3 was obtained for 80nm thick HfO2 film with the external field perpendicular to the film surface. Experimental and theoretical results indicate that the single charged oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism. The coupling between single charged oxygen vacancies may be explained either by direct exchange interactions between oxygen vacancies (Vo+-Vo+) or by mediation of conduction electrons (Vo+-e−-Vo+). These observations may be useful in the development of HfO2-based spintronics devices.

Performance of High Energy Density Symmetric Supercapacitor Based on Sputtered MnO2 Nanorods

AbstractHere, we demonstrate the fabrication of binder free and very efficient supercapacitor electrodes based on MnO2 nanorods on silver (Ag) coated porous anodic aluminum oxide (AAO) substrate in a very simple way by DC magnetron sputtering. The Ag coated porous AAO substrate acts as excellent current collector and also enhances high specific capacitance of MnO2 up to ∼796 F/g. A symmetric supercapacitor device in form of α‐MnO2 nanorods/Ag/AAO electrode has been fabricated, characterized and its performance has been investigated in detail. The binder free supercapacitor device delivered a high capacitance (132 F/g), good cycling ability (95.52 % capacitance retention after 3000 cycles), high energy density (26.4 Wh/kg), and also a high power density (∼36 kW/kg at 6 Wh/kg) in a voltage range of 1.3 V. These observed excellent electrochemical performances of the present MnO2 nanorods based device, suggest it tremendous potential as supercapacitor electrodes in energy storage applications.

Morphological and optical properties of ultra‐thin nanostructured Cu films deposited by RF sputtering on nanoporous anodic alumina substrate

Nanoporous materials have attracted considerable technological interest due to their wide range of applications. In this study, highly ordered nanoporous anodic alumina substrates (NAAS) were fabricated by two-steps anodisation. Radio-frequency (RF) magnetron sputtering was used to deposit ultrathin Cu layers of different morphologies on the top surface of NAAS. From the field emission-scanning electron microscope images, the Cu/NAAS morphologies were tuned from nanoporous ultra-thin Cu layer, to nanoporous-grains of Cu aggregates, then to a continues layer of Cu nanostones as the deposition time increased from 1 to 4 min. The reflection spectra of the Cu/NAAS samples were dominated with localised surface plasmon modes; longitudinal, transverse and higher-order modes. The surface plasmon resonances of the fundamental and higher-order longitudinal modes were shifted to longer wavelengths as the deposition time increased. In addition, the transverse surface plasmon resonances were shifted to longer wavelengths for deposition time ≤3 min (nanoporous Cu film) and suddenly shifted to shorter wavelengths for deposition time ≥4 min (continuous film). The correlations between the structural parameters and the shift of surface plasmon resonance modes were discussed. The strong red-shifted of the surface plasmon modes to the NIR region suggests a unique opportunity for the design of biomedical sensor based on the proposed structures.

Fabrication of Gold-Coated Ultra-Thin Anodic Porous Alumina Substrates for Augmented SERS.

Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures for possible maximization of SERS was addressed. Anodization was carried out on ultra-thin films of aluminum on glass and/or silicon, followed by pore-opening. Gold (Au) was overcoated and micro-Raman/SERS measurements were carried out on test target analytes. Finite integration technique simulations of the APA-Au substrate were used both for the experimental design and simulations. It was observed that, under optimized conditions of APA and Au thickness, the SERS enhancement is higher than on standard APA-Au substrates based on thin (~100 nm) APA by up to a factor of ~20 for test molecules of mercaptobenzoic acid. The agreement between model and experimental results confirms the current understanding of SERS as being mainly due to the physical origin of plasmon resonances. The reported results represent one step towards micro-technological, integrated, disposable, high-sensitivity SERS chemical sensors and biosensors based on similar substrates.

Electric field control of magnetization in Cu2O/porous anodic alumina hybrid structures at room temperature

Cu2O nanoporous films are deposited on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. This paper focuses on voltage driven magnetization switching in Cu2O/PAA (CP) composite films prepared by DC-reactive magnetron sputtering. By applying a dc electric field, the magnetization of the CP composite films can be controlled in a reversible and reproducible way and shows an analogous on-off behavior. The magnitude of the change in the magnetization was about 75 emu/cm3 as the electric field was switched on and off. Resistive switching behavior was also observed in as-prepared CP composite films. Further analysis indicated that the formation/rupture of conducting filaments composed of oxygen vacancies is likely responsible for the changes in the magnetization as well as in the resistivity. Such reversible change of magnetization controlled by an electric field at room temperature may have applications in spintronics and power efficient data storage technologies.

Photoelectronic Effects with Graphene Channels Interfaced with Quantum Dots Arrays

The electrical and photo-electronic properties of graphene-based field effect transistors (GFETs) were studied when the single layer graphene served as the transistor channel, while interfaced with well organized, isolated semiconductor quantum dots (QD) array. The photoluminescence (PL) of the QDs as a function of the drain-source (Vds) and the gate-source (Vgs) bias was studied. Graphene, a two-dimensional, single layer thick crystalline form of carbon atoms, has outstanding physical properties, such as high conductivity, chemical inertness, mechanical robustness and unusual dispersion relations [1]. In the past, we studied graphene layer(s) when suspended over nano-pore structures [2-6]. Here we used anodized aluminum oxide (AAO) as the perforated substrate, and core/shell CdSe/ZnS semiconductor quantum dots (QD) as the photo-sensitive material. The QD were imbedded in the AAO pores. The GFETs were fabricated by transferring a single layer of graphene on top of the QD imbedded AAO. The array of holes on the AAO substrate were 25-30 nm in diameter and with a pitch of 100 nm. For the photoluminescence (PL) measurements, a 10 mW Ar ion laser at 488 nm was used in confocal arrangement. Coupling of the incident and/or emitted light with the surface Plasmon/Polariton (SPP) mode was observed as a peak in PL curve as a function of the sample's tilt angle with respect to the incident optical beam. The fluorescence peak of the QDs decreased monotonously as a function of Vgs and Vds alluding to the control of PL by the biasing potentials. The effect of white-light intensity on the sample conductivity was studied, as well: the difference in Ids between illuminated and non-illuminated cases was substantially affected by the biasing potentials. [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva and A.A. Firsov, “ Electric Field Effect in Atomically Thin Carbon Films”, Science, 306, 666 (2004). [2] A. Banerjee, R. Li and H. Grebel, “Surface Enhanced Raman with Graphenated Anodized Aluminum Oxide Substrates: the Effect of Sub-Wavelength Patterns”, Nanotechnology, 20 (29), art. no. 295502 (2009). [3] A. Banerjee and H. Grebel, “Depositing Graphene Films on Solid and Perforated Substrates”, Nanotechnology, 19 1-5 art. no. 365303 (2008). [4] Ruiqiong Li, and Grebel Haim, “Surface Enhanced Fluorescence”, IEEE Sensors, 10(3), 465-468 (2010) doi: 10.1109/JSEN.2009.2038513. [5] R. Li, A. Banerjee and H. Grebel, “The possibility for surface plasmon lasers”, Optics Express, 17, 1622-1627 (2009). [6] A. Banerjee, R. Li and H. Grebel, "Surface plasmon lasers with quantum dots as gain media", Appl. Phys. Letts., 95, 251106 (2009); doi:10.1063/1.3276273.

Enhancing gas sensing properties of graphene by using a nanoporous substrate

Substrate engineering is shown to be a viable approach for improving the use of graphene thin films for gas sensor applications. The performance of two-terminal devices fabricated on smooth SiO2 and nanoporous anodized aluminum oxide (AAO) substrates are compared. Raman studies indicated that both types of samples exhibit similarly low point-defect densities, but the mobility values of the SiO2-supported films were found to be three times larger than those on porous AAO substrates. However, the AAO-supported graphene devices exhibit a 3-fold enhanced sensitivity to both NO2 and NH3 gases when compared to the devices supported on SiO2. We attribute this sensitivity enhancement to the inhomogeneous electrostatic potential landscape that results from the porous nature of the AAO substrate, as well as extended defects made of wrinkles or folds originated from AAO. This substrate design strategy could be extended to other semiconductor-based sensor devices.