Nanopores Of Anodic Alumina Research Articles

Poly(diethylene glycol methylether methacrylate) Brush-Functionalized Anodic Alumina Nanopores: Curvature-Dependent Polymerization Kinetics and Nanopore Filling.

We report on the synthesis and characterization of poly(diethylene glycol methylether methacrylate) (PDEGMA) brushes by surface-initiated atom transfer radical polymerization inside ordered cylindrical nanopores of anodic aluminum oxide with different pore radii between 20 and 185 nm. In particular, the dependence of polymerization kinetics and the degree of pore filling on the interfacial curvature were analyzed. On the basis of field emission scanning electron microscopy data and thermal gravimetric analysis (TGA), it was concluded that the polymerization rate was faster at the pore orifice compared to the pore interior and also as compared to the analogous reaction carried out on flat aluminum oxide substrates. The apparent steady-state polymerization rate near the orifice increased with decreasing pore size. Likewise, the overall apparent polymerization rate estimated from TGA data indicated stronger confinement for pores with increased curvature as well as increased mass transport limitations due to the blockage of the pore orifice. Only for pores with a diameter to length ratio of ∼1, PDEGMA brushes were concluded to grow uniformly with constant thickness. However, because of mass transport limitations in longer pores, incomplete pore filling was observed, which leads presumably to a PDEGMA gradient brush. This study contributes to a better understanding of polymer brush-functionalized nanopores and the impact of confinement, in which the control of polymer brush thickness together with grafting density along the nanopores is key for applications of PDEGMA brushes confined inside nanopores.

Polymer dynamics under cylindrical confinement featuring a locally repulsive surface: A quasielastic neutron scattering study.

We investigated the effect of intermediate cylindrical confinement with locally repulsive walls on the segmental and entanglement dynamics of a polymer melt by quasielastic neutron scattering. As a reference, the corresponding polymer melt was measured under identical conditions. The locally repulsive confinement was realized by hydrophilic anodic alumina nanopores with a diameter of 20 nm. The end-to-end distance of the hydrophobic infiltrated polyethylene-alt-propylene was close to this diameter. In the case of hard wall repulsion with negligible local attraction, several simulations predicted an acceleration of segmental dynamics close to the wall. Other than in attractive or neutral systems, where the segmental dynamics is slowed down, we found that the segmental dynamics in the nanopores is identical to the local mobility in the bulk. Even under very careful scrutiny, we could not find any acceleration of the surface-near segmental motion. On the larger time scale, the neutron spin-echo experiment showed that the Rouse relaxation was not altered by confinement effects. Also the entanglement dynamics was not affected. Thus at moderate confinement conditions, facilitated by locally repulsive walls, the dynamics remains as in the bulk melt, a result that is not so clear from simulations.

Influence of Sulfur Incorporation into Nanoporous Anodic Alumina on the Volume Expansion and Self-Ordering Degree

Self-ordering degree of anodic alumina nanopores is related to the volume expansion of the aluminum oxide. However, little is known about how the ionic species derived from electrolyte affect parameters inducing self-ordering of the nanopores. The influence of sulfur incorporation into nanoporous anodic aluminum oxide (AAO) films on volume expansion and self-ordering degree has been investigated under potentiostatic conditions (14–25 V) in different sulfuric acid electrolytes (3–20 wt %), the average current densities of each anodization being in the range of 0.1–10 mA cm–2. Rutherford backscattering spectroscopy (RBS) reveals that the incorporation of sulfur species into AAO, as well as the volume expansion factor (VEF), follows a logarithmic dependence on the average current density regardless of the applied voltage and sulfuric acid concentration. The relationship between volume expansion and the S/Al ratio is linear for each concentration of acid in the electrolyte. Furthermore, self-ordering regimes ...

Numerical study on energy harvesting from concentration gradient by reverse electrodialysis in anodic alumina nanopores

Energy harvesting from a concentration gradient by reverse electrodialysis in anodic alumina nanopores was numerically investigated. Power generation from the nanopores when they are placed between two reservoirs containing potassium chloride solutions with different concentrations was examined. The current–potential characteristics of the nanopores were calculated by solving the strongly coupled Poisson equation, the Nernst–Planck equation, and the Navier–Stokes equations. Alumina nanopore arrays were also investigated experimentally to obtain the proper values of the surface charge density for the numerical model. The effects of various engineering parameters, such as the pore length, pore radius, and concentration, on the power generation were investigated on the basis of the developed numerical model. Finally, it was shown that a power output density of 9.9 W/m2 can be achieved using the alumina nanopores. This indicates that the alumina nanopores have the potential to be used as ion-selective membranes for microbatteries and micro power generators.

Multifunctional three-dimensional nanodiamond-nanoporous alumina nanoarchitectures

Hybrid composite nanomaterials provide an attractive and versatile material platform for numerous emerging nano- and biomedical applications by offering the possibility to combine diverse properties which are impossible to obtain within a single material. In this work, we present the fabrication of novel hybrid diamond and amorphous diamond-like carbon (DLC) coated nanoporous alumina materials that exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. These multifunctional nanohybrid materials are fabricated using the plasma-induced carbonization method that effectively modifies the surface and the inside of the nanopores of anodic alumina, producing a homogenous ultrathin DLC protecting layer over the whole external and internal surfaces of the membranes. We demonstrate that the interplay between internal and external carbon supply is a critical factor for the formation of the ultrathin sp3-bonded carbon layer in the nanopores. This study brings new insights in the DLC growth mechanisms in confined nanospaces and opens new avenues to fabricate hybrid, chemically resistant and biocompatible carbon-coated nanoarchitectures on other inorganic supports.

Low-Temperature Atomic Layer Deposition of Platinum Using (Methylcyclopentadienyl)trimethylplatinum and Ozone

Thermal atomic layer deposition (ALD) of platinum is usually achieved using molecular oxygen as the reactant gas and deposition temperatures in the 250–300 °C range. In this work, crystalline thin films of metallic Pt have been grown by ALD at temperatures as low as 100 °C using (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) as the Pt precursor and ozone as the reactant gas. The novel process is characterized by a constant growth rate of 0.45 A per cycle within the 100–300 °C temperature window. The Pt films are uniform with low impurity levels and close-to-bulk resistivities even at the lowest deposition temperature. We show that the initial growth on SiO2 surfaces is nucleation-controlled and islandlike and demonstrate the good conformality of the low-temperature ALD process by Pt deposition on anodic alumina nanopores and mesoporous silica thin films.

Energy harvesting from salinity gradient by reverse electrodialysis with anodic alumina nanopores

Power generation by reverse electrodialysis from anodic alumina nanopores is experimentally investigated by placing an alumina nanopore array with a nominal pore radius of 10 nm between two sodium chloride solutions with various combinations of concentrations. Both bare and silica-coated alumina nanopore arrays are used in the present study. The current–potential characteristics are measured for various electrolyte concentration levels, and the transference number and the electrical conductance of the nanopore arrays are obtained from these characteristics. The transference numbers of the bare and silica-coated alumina nanopore arrays are 0.30 and 0.72, respectively; these values are nearly independent of the concentration of the sodium chloride solutions when it is less than 200 mM. Therefore, the bare and silica-coated alumina arrays can be used as anion selective and cation selective membranes, respectively, for micro batteries and micro power generators. Finally, power generation by reverse electrodialysis using an alumina nanopore array is presented. The highest power generation measured is 542 nW, which is several orders of magnitude higher than those measured in previous studies based on nanofluidic channels or nanopores.

Gradient and alternating diameter nanopore templates by focused ion beam guided anodization

Ordered arrays of anodic alumina nanopores with uniform pore diameters have been fabricated by self-organized anodization of aluminum. However, gradient or alternating diameter nanopore arrays with designed interpore distances have not been possible. In this study, focused ion beam lithography is used to fabricate hexagonally arranged concaves with different diameters in designed arrangements on aluminum surfaces. The patterns are then used to guide the further growth of alumina nanopores in the subsequent oxalic acid anodization. Gradient and alternating nanopore arrangements have been attained by FIB patterning guided oxalic acid anodization. The fundamental understanding of the process is discussed.

Light Output Enhancement of AlGaInP Light Emitting Diodes with Nanopores of Anodic Alumina

In this paper, we describe the improvement in the light extraction efficiency of AlGaInP light-emitting diodes (LEDs) upon use of a porous anodic alumina (PAA) film and pore widening. Acting as an intervening layer between air and the GaP window layer, PAA increased the critical angle to reduce the internal light reflection of LEDs. The nanopores of the PAA film provided a rough surface that enhanced the light output extraction. These factors resulted in the LEDs with PAA films exhibiting a light output power 29% higher than that of a conventional LED (without PAA film). Furthermore, following a pore-widening treatment for 40 min, the light output improvement increased to 39%. Therefore, the use of PAA film and a suitable pore-widening treatment increases the light extraction efficiency of LEDs.

Long‐Range Resonant Energy Transfer for Enhanced Exciton Harvesting for Organic Solar Cells

Exciton harvesting is of fundamental importance for the efficient operation of organic photovoltaic devices. The quantum efficiencies of many organic and hybrid organic-inorganic devices are still limited by low exciton harvesting efficiencies. This problem is most apparent in planar heterostructures that suffer from a direct tradeoff between light absorption and exciton harvesting. The bulk heterojunction concept [1,2] was designed to alleviate the problem of limited exciton migration by intimately blending the donor and acceptor phases on the nanometer length scale. In some polymer/fullerene systems, such as poly(2-methoxy,5-(3,7-dimethyloctyloxy)-1,4phenylenevinylene) (MDMO-PPV)/(6,6)-phenyl C61-butyric acid methyl ester (PCBM), time resolved spectroscopy shows the photoinduced formation of the radical anions and cations on femtosecond timescales. [3] This ultrafast formation of the polaron signature is only possible if every exciton is formed on a polymer chain segment that is immediately adjacent to one or more fullerene molecules. However, in other systems, very large domains prevail and, consequently, exciton harvesting is inefficient. [4] This has made the fabrication of efficient devices incorporating new materials difficult because each new material leads to a new morphology with its own characteristic length scale. The ordered bulk heterojunction architecture is intended to alleviate these issues by using a pre-patterned nanostructured scaffold [5–7] that has been engineered to have both straight pathways to the electrodes to ensure efficient carrier collection, and controlled domain size to ensure efficient exciton harvesting. Recently, chain alignment has been shown to be promoted for regioregular poly(3-hexyl thiophene) (RR-P3HT) in straight nanopores of anodic alumina leading to a 20-fold increase in hole-mobility in these structures. [8] For solar cell applications, higher mobilities reduce the effects of space charge [9] and increase the probability of separating the geminate pair formed immediately after exciton dissociation. [10–13] While the ordered bulk heterojunction architecture shows promise, existing structures have domains too large [14,15] for efficient exciton harvesting with singlet diffusion lengths only ca. 3–8 nm. [16–18] At this time, few alternatives other than nanostructuring have been proposed to increase exciton harvesting. Triplet excitons have been shown to have large diffusion lengths due to their long lifetimes, [18–20] but except in a few examples [21,22] this usually comes at the expense of a loss in energy of 0.4–0.8 eV associated with intersystem crossing between the photoexcited singlet to the first excited triplet. [23–25]

Enhanced Hole Mobility in Regioregular Polythiophene Infiltrated in Straight Nanopores

AbstractWe demonstrate that the hole mobility in regioregular poly(3‐hexylthiophene) can be enhanced by a factor of 20 by infiltrating it into straight nanopores of anodic alumina. Optical characterization shows that the polymer chains are partially aligned in the charge‐transport direction.

Nanowire Arrays with Specialized Geometries for Magnetoelectronics (Invited)

This work focuses on the fabrication of magnetic nanowires with specialized geometries, such as Y-junctions, tapers and multilayers, for magnetoresistive sensor arrays. First, anodic alumina nanopores were grown with diameters of 20–250nm and lengths up to tens of microns. These pores were removed from their Al substrates and the barrier oxide was removed. Co nanowires were initially grown inside the pores by electrochemical deposition. It was shown that the coercivity and remnant magnetization could be tripled in (100)-oriented Co by shrinking the pore diameter/interpore spacing from 150/300nm to 40/80nm. These properties were further enhanced by fabricating (002)-oriented Co using the proper pH and applying a magnetic field during growth. The ability to connect two or more nanostructures is critical to the long term success of nanoelectronics and circuits. Here, Y-junctions were grown by subsequent growth of 40nm then 20nm pores such that two smaller pores extended from the bottom of each larger pore. These pores were then filled with Co in order to produce Y-junctions in the magnetic nanowires. Next, multilayered nanowires were fabricated with alternating layers of Cu and Co. The Co layer thickness was varied in order to study the affect of shape anisotropy on the magnetic properties of Co layers inside arrays. Finally, several configurations for magnetoresistive magnetic field sensors were described.

Conformal Coating on Ultrahigh-Aspect-Ratio Nanopores of Anodic Alumina by Atomic Layer Deposition

Anodic alumina (AA) membranes are composed of highly uniform, nanometer-scale pores arranged in a hexagonal close-packed array. Depositing conformal films inside the nanopores is extremely difficult because the nanopores have an ultrahigh aspect ratio of L/d ≈ 103. Atomic layer deposition (ALD) is a thin film growth technique that can deposit highly uniform films on high-aspect-ratio substrates with monolayer thickness control. In this study, AA membranes were coated with Al2O3 and ZnO ALD films and subsequently analyzed using cross-sectional scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). SEM analysis of individual nanopores revealed that the AA membranes with nanopore diameters of d = 65 nm and lengths of L = 50 μm could be coated conformally by Al2O3 ALD using sufficient reactant exposure times. Zn concentration profiles measured by EPMA following ZnO ALD showed the progressive infiltration of the ZnO ALD into the nanopores with increasing exposure times for aspect ratios as...

Preparation of Fe-Pt Nanowires through Anodic Oxidation of Sputtered Aluminum on Glass Surface

ABSTRACTNew process for the preparation of Fe-Pt nanowires has been developed through anodic oxidation and electro deposition technique. Aluminum thin film sputtered on ITO thin film on a glass surface was decomposed into alumina by anodic oxidation technique. The anodic alumina layer possessed nanometer size pore array standing on the glass surface. The barrier layer at the bottom of nanopores was removed by acid etching to attain DC field smooth electro deposition. Fe-Pt components were introduced into nanopores of anodic alumina by electro deposition. The magnetization of Fe-Pt nanowires was investigated. The magnetization perpendicular to the glass surface was very strong and the in-plane magnetization was very small, indicating that the magnetic Fe-Pt nanowires could be potentially applied to ultra high density magnetic recording. The density of the nanowires was estimated to be about 1T bits /inch2.

Investigation of the Metal Deposited into Nanopores of Anodic Alumina upon Fabricating Substrates for Microelectronic Devices

Anodic alumina containing nickel deposited into its nanopores was investigated using a scanning electron probe microanalyzer and an X-ray microdiffractometer. It was demonstrated that electrochemically deposited nickel contains no foreign impurities, has the crystal structure, and is uniformly distributed over the nanopore height.

Structural, Magnetic Properties of the Electrochemically Deposited Arrays of Nickel Nanowires

ABSTRACTThe room temperature structural, magnetization and magnetoresistive properties of Ni-nanowires of diameters 18, 30 and 78 nm and various lengths, fabricated by electrochemical deposition of Ni in the nanopores of anodic alumina, are investigated. The crystallographic orientation depends on the diameter of nanowires. Nanowires show perpendicular magnetic anisotropy and enhanced coercivity (Hc) and remanent magnetization (Mr) values of up to 500 Oe and 50% respectively. An electrodeposited Ni-layer (5 μm) on copper substrate shows in plane magnetic anisotropy and the Hc and Mr values are 97 Oe and 37%. Ni-nanowires and Ni-layer show an anisotropic magnetoresistive behaviour.