Porous Anodic Alumina Oxide Templates Research Articles

Nanoporous fluorescent sensor based on upconversion nanoparticles for the detection of dichloromethane with high sensitivity.

A sensor with high sensitivity and response rate is still lacking in the detection of poisonous and volatile chemicals. Here, we report a highly sensitive nanoporous fluorescence sensor based on core@shell upconversion nanoparticles (UCNPs) for the detection of dichloromethane. UCNPs were deposited on porous anodic alumina oxide (AAO) templates supported by glass slides to form a thin film-like gas sensor in which UCNPs with active shells exhibit intense background-free fluorescence and simultaneously high optical sensitivity, while an AAO template acts as a porous substrate for UCNPs to increase the absorption capacity for molecules to be tested. A detection limit of 2.91 ppm was obtained for dichloromethane based on this sensor at room temperature. The involved response mechanism was attributed to lowered surface fluorescence quenching and scattering of UCNPs by dichloromethane.

Near-Infrared Reflection Spectra of Copper Nanowire Array Structures

We present a detailed study on near-infrared (NIR) reflection spectra of Cu nanowire arrays (NWAs) which are embedded in porous anodic alumina oxide templates and with pore diameters from 35 nm to 80 nm. We find that the NIR reflection of these samples is out of the frequency regime for surface-plasmon resonance induced by intra-and inter-band excitations. However, the intensity of the NIR reflection of Cu NWAs depends strongly on sample parameters and temperature. The measurements are carried out at temperatures setting to be 4 K, 77 K, 200 K, and at room temperature. The optical response of the Cu NWAs in NIR bandwidth is attributed to localized surface-plasmon oscillations and the NIR reflectance increases with temperature up to room-temperature. The physical mechanisms behind these interesting findings are discussed.

Magnetoresistance of Electrodeposited Co/Cu Multilayer Nanowires

Co/Cu multilayer nanowires were electrodeposited potentiostatically on highly ordered porous anodic alumina oxide templates. Scanning electron microscopy (SEM) showed that wires have diameters of about 250 300 nm and length of 40 50 μm. Co/Cu multilayer nanowire arrays embedded in anodic alumina oxide were mechanically polished with diamond in a suspension of oil until the wires appeared. Then the top and bottom surfaces of the material were coated with a layer of Au with a thickness of 100 nm for electrical contacts. Magnetic eld was applied by an electromagnet and resistance was measured by four point technique.

Magnetoresistance of Electrochemically Produced NiFe and CoNiFe Nanowires

CoNiFe and NiFe nanowires were electrochemically produced by dc electrodeposition on highly ordered porous anodic alumina oxide templates. Scanning electron microscope images of nanowires after removing the alumina membrane showed that these nanowires are uniform with the diameters of about 220 300 nm and about 25 30 μm length. The energy dispersive X-ray analysis showed that the composition of the nanowires is Ni88Fe12, Co7Ni82Fe11. Magnetic eld was applied by an electromagnet and resistance was measured by four point technique.

Magnetoimpedance Effects in Electrodeposited NiFe Nanowire Array

In this work, NiFe nanowires were grown in highly ordered porous anodic alumina oxide templates by dc electrodeposition at a pH value of 2.6. Scanning electron microscopy showed that wires have diameters of about 250 310 nm and length 25 30 μm. The energy dispersive X-ray analysis showed that the composition of the nanowires is Ni65Fe35. Electrical contacts were made on both sides of the nanowire array and their magnetoimpedance properties were investigated. All the magnetoimpedance curves showed single peak behavior due to the high shape anisotropy. The maximum magnetoimpedance change at the 79 MHz driving current frequency was ≈ 1.45%.

Optical properties of Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays

In this study, Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays are fabricated using standard techniques such as electrochemical deposition of metals into porous anodic alumina oxide templates having pore diameters of about 50 nm. We perform optical measurements on these nanowire array structures. Optical reflectance (OR) of the as-prepared samples is recorded using an imaging spectrometer in the wavelength range from 400 to 2,000 nm (i.e., from visible to near-infrared bandwidth). The measurements are carried out at temperatures set to be 4.2, 70, 150, and 200 K and at room temperature. We find that the intensity of the OR spectrum for nanowire arrays depends strongly on the temperature. The strongest OR can be observed at about T = 200 K for all samples in visible regime. The OR spectra for these samples show different features in the visible and near-infrared bandwidths. We discuss the physical mechanisms responsible for these interesting experimental findings. This study is relevant to the application of metal nanowire arrays as optical and optoelectronic devices.

Magnetic field control of fluorescent polymer nanorods

Nanoscale objects that combine high luminescence output with a magnetic response may beuseful for probing local environments or manipulating objects on small scales. Ideally, thesetwo properties would not interfere with each other. In this paper, we show that a fluorescentpolymer host material can be doped with high concentrations of 20–30 nm diameter magneticγ-Fe2O3 particles and then formed into 200 nm diameter nanorods using porous anodic aluminaoxide templates. Two different polymer hosts are used: the conjugated polymerpolydioctylfluorene and also polystyrene doped with the fluorescent dye LumogenRed. Fluorescence decay measurements show that 14% by weight loading of theγ-Fe2O3 nanoparticles quenches the fluorescence of the polydioctylfluorene by approximately 33%, but thepolystyrene/Lumogen Red fluorescence is almost unaffected. The three-dimensional orientationof both types of nanorods can be precisely controlled by the application of a moderate strength (∼0.1 T) external field with sub-second response times. Transmission electron microscope imagesreveal that the nanoparticles cluster in the polymer matrix, and these clusters may serveboth to prevent fluorescence quenching and to generate the magnetic moment that rotatesin response to the applied magnetic field.

Preparation and wettability of Zn–Al layered double hydroxide film directly grown on highly porous anodic alumina oxide template

Zinc–aluminum layered double hydroxide (Zn–Al LDH) thin films were prepared by direct precipitation on the surface of porous anodic alumina oxide (AAO) template. The Zn–Al LDH was assigned to Zn6All2(OH)16CO3·nH2O according to the XRD and EDX data. The nano-pores provided channels and the nano-sized wall-edges for supplying Al3+and highly active reaction sites, thereby the Zn–Al LDH films can be grown more efficiently on porous AAO membrane than those on flat bulk alumina oxide surface. The water contact angle (CA) of the as-prepared Zn–Al LDH films was measured to be 122°, indicating a hydrophobic surface, but after calcination at 600 °C for 2 h, the water CA became 65°, suggesting a hydrophilic surface. Comparative analyses of the surface morphological characteristics and elements with respect to the as-prepared and calcined films implied a thermal induced reconstruction of the Zn–Al LDH structure, which was ascribed to the changes of surface wettability.

Crystallization and Orientation of Syndiotactic Polystyrene in Nanorods

Syndiotactic polystyrene (sPS) nanorods of 200 and 80 nm diameters were prepared by infiltrating porous anodic alumina oxide templates with polymer melt, and the crystallinity and orientation of various forms of sPS crystals in the nanorods were studied by FTIR spectroscopy and electron diffraction. For sPS crystallized from amorphous state at lower temperatures, α-form crystals were found in the nanorods with random orientation and the same degree of crystallinity as that in the bulk. However, for sPS crystallized from molten state at 260 °C, while no preferred orientation was found for the chains in the melt, the β-crystals formed in the nanorods oriented preferentially with the c-axis aligning perpendicular to the axial direction of the nanorod, and the degree of crystallinity was significantly lower than that in the bulk. The crystallinity decrease was more profound for nanorods of smaller diameter. These results were also supported by electron diffraction data and can be attributed to competition bet...

Ordered Co48Pb52 Nanowire Arrays Electrodeposited in the Porous Anodic Alumina Oxide Template with Enhanced Coercivity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ordered Co48Pb52 Nanowire Arrays Electrodeposited in the Porous Anodic Alumina Oxide Template with Enhanced Coercivity

Co-Pb nanowire arrays with an average diameter of 20 nm and lengths up to several micrometers were grown in ordered anodic alumina templates using AC electrodeposition. The as-deposited samples were annealed at different temperatures. The structure and magnetic properties of Co-Pb nanowires were analyzed by X-ray diffraction and a vibrating sample magnetometer. We found that the sample annealed at 700 °C had large perpendicular coercivity He (as high as 2660 Oe) and high squareness (M R /M s ) (about 0.97), which was much larger than that of pure Co nanowires annealed at 700 °C (2170 Oe, 0.9). The change in coercivity and squareness associated with the microstructure was discussed.