Anodic Aluminum Oxide Channels Research Articles

Syntheses of rare-earth metal oxide nanotubes by the sol–gel method assisted with porous anodic aluminum oxide templates

In this paper, we report a versatile synthetic method of ordered rare-earth metal (RE) oxide nanotubes. RE (RE=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) oxide nanotubes were successfully prepared from corresponding RE nitrate solution via the sol–gel method assisted with porous anodic aluminum oxide (AAO) templates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction (XRD) have been employed to characterize the morphology and composition of the as-prepared nanotubes. It is found that as-prepared RE oxides evolve into bamboo-like nanotubes and entirely hollow nanotubes. A new possible formation mechanism of RE oxide nanotubes in the AAO channels is proposed. These high-quantity RE oxide nanotubes are expected to have promising applications in many areas such as luminescent materials, catalysts, magnets, etc.

Nanoporous Carbon Nanotubes Synthesized through Confined Hydrogen-Bonding Self-Assembly

We report a simple and direct synthetic method for the preparation of nanoporous carbon nanotubes with larger pores (>10 nm) on the tube wall. The method combines the use of anodic aluminum oxide (AAO) as a template for the tube diameter and block copolymer/carbohydrates self-assembly within thin films confined inside AAO pore channels to form nanopores. It involves coating the AAO inner pore channel surface with block copolymer (polystyrene-co-poly(vinylpyridine)) and carbohydrates in dimethylformamide (DMF) solution. Drying of DMF induced microphase separation of PS-PVP and formation of ordered PS and PVP/carbohydrate domains. Within the coating, the carbohydrates stay specifically only in the pyridine domains surrounding PS domains due to the hydrogen bonding between carbohydrates and pyridine blocks. After carbonization at high temperature (>460 degrees C) in argon, PS was removed, forming the nanopores and carbohydrates, and PVP was carbonized, forming the framework of nanoporous carbon tubes within AAO channels. Removal of AAO led to the formation of individual monodisperse nanoporous carbon nanotubes with a tube wall of approximately 16 nm. The ease with which these nanoporous carbon nanotubes can be fabricated, and the ability to tune tube nanostructures and surface chemistry through the choice of block copolymers used and carbonization temperature, should facilitate investigations of their scope for practical applications.

Elongation of arrays of amorphous carbon tubes

Due to its special properties, amorphous carbon (a-C) materials have been reported to display novel functions for many potential optical [1,2], frictional [3] and electronic [2,4] applications. These include protective coating, ultra durable anti-reflection coatings [1,2], mechanical devices [2,3], and electron emitters [4]. The ability to fabricate a-C into desired physical shapes has attracted much attention. For example, anodic aluminum oxide (AAO) has been used as templates to shape a-C into tubular shapes by pyrolyzing propylene inside the AAO channels [5]. In our study herein we report on a process to grow a-C tubes (a-CT) by coupling two fabrication methods we recently developed [6,7]. First, a layer of short aligned a-CT was deposited by LPCVD from SiCl3CCl3 on an AAO substrate [6]. Then, by employing the Na-filled AAO (Na@AAO) reactive template method, we were able to significantly elongate the a-CT [7]. Using a hot-wall LPCVD reactor with a base pressure of 10 1 Pa, SiCl3CCl3 (Aldrich, 97%) was evaporated at 273 K without carrier gas. The precursor was decomposed at 1273 K and 10 Pa to deposit a layer of carbon on AAO substrates (Whatman Anodisc 13, observed pore diameter: 280 nm, thickness: 60 lm). After 3 h, the AAO substrates turned black and the product a-C film on AAO (a-C/AAO) was obtained. As shown by the scanning electron microscope (SEM, JEOL JSM-6330F at 15 kV) images in Fig. 1, the average diameter of the open-ended a-CT, 330–340 nm, is close to the channel diameter in the AAO. The average thickness of the a-CT wall was 30 nm. In Fig. 1(b), the average thickness of the array layer was estimated to be 800 nm, much thinner than the AAO thickness of 60 lm. We speculate that the activated species generated from SiCl3CCl3, :CCl2, cannot diffuse effectively into the AAO channels to form a thick carbon layer. Fig. 1(b) also shows that the a-CT array is connected as a layer of film on top of the AAO. Using energy dispersive spectroscopy (EDS), the composition of the isolated tube array layer was confirmed to be carbon. Thus, the data support the conclusion that we have successfully deposited a-C on AAO (a-C/AAO) in the form of short a-CT array. We also attempted to perform this process on a home-made AAO with a channel diameter of 30 nm. However, :CCl2 apparently could not diffuse into the narrow AAO channels to grow into an a-CT layer. After the short a-C/AAO layer was fabricated by LPCVD, we explored the possibility of extending the tube length by the sodium reactive template method that had been previously developed [6]. By decomposing NaH (Aldrich, 0.2 g, 8 mmol) on a-C/AAO inside a tube furnace at 623 K under 1 atm of Ar (flow rate: 30 sccm) for 0.5 h, Na filled the channels of AAO to generate Na@a-C/AAO. Further reaction of Na@a-C/AAO with Carbon 43 (2005) 2618–2641

Template Assisted Fabrication of Tin Nanospheres by Thermal Expansion and Rapid Solidification Process

Tin (Sn) nanospheres with diameters ranging from 100 to 300 nm were fabricated by thermal expansion and rapid solidification process. The Sn melt was injected into an anodic aluminum oxide (AAO) template to form Sn nanowires. The Sn nanowire and AAO composite was then heated to the Sn melting temperature (∼232°C) and quenched to low temperature (8°C). The Sn melt exhibits high surface tension and AAO has nanoscale roughness on its surface. These two properties caused Sn nanospheres to form easily on the AAO surface when the partial Sn melt expanded out from AAO channels and rapidly solidified on the AAO surface.

Field‐Dependent Growth Patterns of Metals Electroplated in Nanoporous Alumina Membranes

Novel core–shell cable structures (see Figure) of metal alloys are described as one application of field-controlled electroplating of metals in anodic aluminum oxide (AAO) templates. At high current density (∼ 20–300 mA/cm2), the electroplating process occurs relatively fast through the surface of the AAO channels to form nanotubes. A second metal is then electroplated at low current density, forming cores inside.