Suspended nanostructured alumina membranes (original) (raw)
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Nanostructures fabrication by template deposition into anodic alumina membranes
Chemical Engineering Transactions, 2009
In recent years, nanostructured materials have attracted growing interest due to their specific properties, which allow application in several fields such as photonics, nanoelectronics, thermoelectronics (Kelsall et al., 2005). For the fabrication of nanostructures, different methods have been proposed. Template synthesis is extremely interesting due to its simplicity and versatility (Martin, 1996). A variety of materials including metals, oxides, conductive polymers, and semiconductors can be deposited within the pores of either polycarbonate or anodic alumina membranes (AAM). The deposition process produces nanotubes (NTs), nanowires (NWs), or nanorods, whose dimensions can be easily controlled by adjusting template pore geometry and deposition conditions (Inguanta et al., 2007a). In this work, different nanostructures of metals (Ni, Cu and Pd), alloys (Co-Sn), and metal oxides (Cu 2 O, CeO 2 , PbO 2 ) have been fabricated, by electrochemical methods (electroless deposition, electrodeposition and displacement deposition), using AAM as template. Ni electroless deposition resulted in the formation of short metal nanotubes (about 5 μm long). Different results were obtained by Ni electrodeposition, performed applying unipolar pulsed voltage perturbations. With a triangular wave, we have fabricated ordered arrays of metal nanowires, whilst with a square perturbation Ni nanotubes were produced. By electrochemical deposition, amorphous Sn-Co nanowires were also obtained. Co content in the alloy, length and crystallographic structure of nanowires varied with the deposition time. Large arrays of aligned copper(I) oxide nanowires were, also, produced by electrodeposition. Two fundamental parameters were studied: potential perturbation and bath composition. We have found that these parameters influence both composition and crystallographic nature of Cu 2 O nanowires. The electrochemical route was also used to fabricate CeO 2 nanotubes from a non-aqueous electrolyte. The results, obtained by Raman spectroscopy, demonstrate that CeO 2 nanotubes are suitable for catalytic applications. PbO 2 nanowires having high aspect ratios were grown by potentiostatic electrodeposition under anodic polarization. Different electrolytic solutions were used in order to obtain nanowires of pure α-PbO 2 , pure β-PbO 2 , or an α + β mixture. In all deposition conditions, perfectly cylindrical wires, having uniform diameters throughout length were obtained. In this paper we describe also a novel method for the fabrication of a regular and uniform array of metal nanowires into anodic alumina membranes. The method is based on the metal displacement deposition realized into template pores by using a special arrangement, properly designed in order to optimize the processes.
In-Situ Preparation of Polymer-Coated Alumina Nanopowders by Chemical Vapor Synthesis
Chemical Vapor Deposition, 2003
Nanocrystalline alumina particles coated with polyethylene have been prepared by a two-step chemical vapor synthesis (CVS) process using a hot-wall reactor to synthesize the nanocrystalline alumina core, and a RF plasma reactor for the subsequent polymer coating. The particle radius is about 4 nm, with the radius of the ceramic core being about 2.5 nm and the coating thickness about 1.5 nm. The powders have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer±Emmett±Teller (BET), small-angle neutron scattering (SANS), and high-resolution transmission electron microscopy (HRTEM).
Alumina nanotemplate fabrication on silicon substrate
Nanotechnology, 2004
ABSTRACT Alumina nanotemplates integrated on silicon substrate with pore diameters of 12–100 nm were prepared by galvanostatic (constant current) anodization. High current density (e.g. 100 mA cm−2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solution. Alumina formation rates of 2000 and 1000 nm min−1 were achieved at current densities of 100 and 50 mA cm−2, respectively. These rates were approximately two orders of magnitude greater than other reports in the literature. Different electrolytes of sulfuric acid (1.8–7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acids were evaluated as anodizing solutions. At fixed current density, sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I–V characteristics of aluminium anodization show the measured voltages at given current densities strongly depend on solution composition, operating temperature, and bath agitation. The pore diameter of the silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm V−1, which is slightly smaller than reported data.
2016
Ordered nanostructure arrays are attracting intensive scientific attention because of their many and varied applications. However, it is still a challenge to achieve ordered nanostructure patterning over a relatively large area (for instance on the wafer scale) by a technique that will allow high throughput, large pattern area and low equipment costs. Part of the work reported here is the achievement of facile transferring of ultrathin alumina membranes (UTAMs) which have been attached on wafer-scale substrates without any twisting, folding, cracking or contamination because of the unique design of the fabrication and transferring processes. The crucial element of this method is fixing the prepared 4-inch UTAM onto a wafer-scale substrate before removing the remaining Al and the alumina barrier layer. The thickness and surface smoothing of the UTAMs play a vital role in this process. By using these perfectly transferred UTAMs as masks, various nanostructuring patterns including nano...
Structural and thermal characterisation of nanostructured alumina templates
Current Applied Physics, 2006
Nanostructured anodic aluminium oxide materials containing a two dimensional array of high aspect ratio aligned pores of 200 nm diameter have been heat treated in air at temperatures up to 1340°C. Thermal analysis shows two discrete irreversible exothermic events at 850°C and 1020°C. XRD and 27 Al MAS NMR show the progressive development of local and long range order in the heated structures and indicate a reaction sequence of amorphous Al 2 O 3 ! h-Al 2 O 3 ! a-Al 2 O 3 (corundum). NMR shows the coexistence of aluminium in 4, 5 and 6-coordinated sites through most of the heating sequence until the stable (6-coordinated) corundum phase is established. Phosphorus impurities incorporated during the membrane fabrication process crystallise as an AlPO 4 phase above 850°C and play an important role in directing the chemical, physical and structural outcomes of the heat treatment.
Preparation and Characterization of High‐Temperature Thermally Stable Alumina Composite Membrane
Journal of the American Ceramic …, 1991
A crack-and pinhole-free composite membrane consisting of an a-alumina support and a modified y-alumina top layer which is thermally stable up to 1100°C was prepared by the sol-gel method. The supported thermally stable top layer was made by dipcoating the support with a boehmite sol doped with lanthanum nitrate. The temperature effects on the microstructure of the (supported and unsupported) La-doped top layers were compared with those of a common y-alumina membrane (without doping with lanthanum), using the gas permeability and nitrogen adsorption porosimetry data. After sintering at 1100°C for 30 h, the average pore diameter of the La-doped alumina top layer was 17 nm, compared to 109 nm for the common alumina top layer. Addition of poly(viny1 alcohol) to the colloid boehmite precursor solution prevented formation of defects in the 'yalumina top layer. After sintering at temperatures higher than 900"C, the common alumina top layer with addition of poly(viny1 alcohol) exhibits a bimodal pore distribution. The La-doped alumina top layer (also with addition of poly(viny1 alcohol)) retains a monopore distribution after sintering at 1200°C. [
Organized porous alumina membranes for high density silicon nanowires growth
Microelectronic Engineering, 2011
In this paper, we present results on the fabrication of porous alumina membranes on silicon substrates with a long-range order induced by nanoimprint lithography. Fabricated porous alumina matrices present a perfect triangular array of vertical cylindrical pores on areas of 500 Â 500 lm 2 corresponding to the imprinted surfaces. Also, we demonstrate that it is possible to have a directed density multiplication during the pore formation, compared to the nanoimprint mold, by the initial indentation of only one third of the expected alumina pores. The gold catalyst, needed for nanowires growth, is deposited at the bottom of each pore by electrochemistry. The proposed process is scalable to wafer-scale areas, compatible with microelectronics fabrication standards and is not limited to non-fragile substrates like direct bulk aluminum nanoindentation.
ACS Nano, 2015
Ordered nanostructure arrays have attracted intensive attention because of their various applications. However, it is still a great challenge to achieve ordered nanostructure patterning over a large area (such as wafer-scale) by a technique that allows high throughput, large pattern area and low equipment costs. Here, through a unique design of the fabrication and transferring processes, we achieve a facile transferring of wafer-scale ultrathin alumina membranes (UTAMs) onto substrates without any twisting, folding, cracking and contamination. The most important in our method is fixing the UTAM onto the wafer-scale substrate before
Fabrication of alumina nanotubes and nanowires by etching porous alumina membranes
2002
Porous alumina membranes are commercially available and have been widely used in recent nanoscale research, for example, as templates in nanowire fabrication through electrodeposition. In this report, we present a new use for porous alumina membranes in the fabrication of alumina nanotubes/nanowires desired in electrochemical devices and catalytic applications. A high yield of alumina nanotubes/nanowires is obtained by etching porous alumina membranes in an aqueous sodium hydroxide solution.