Magnetic,Multilayered Nanotubes of Low Aspect Ratios for Liquid Suspensions |
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Authors: | Robert Zierold Zhenyu Wu Johannes Biskupek Ute Kaiser Julien Bachmann Carl E. Krill III Kornelius Nielsch |
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Affiliation: | 1. Institute of Applied Physics, University of Hamburg, Jungiusstra?e 11, 20355 Hamburg, Germany;2. Institute of Micro and Nanomaterials, Ulm University, Albert‐Einstein‐Allee 47, 89081 Ulm, Germany;3. Central Facility of Electron Microscopy, Ulm University, Albert‐Einstein‐Allee 11, 89081 Ulm, Germany |
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Abstract: | This work presents a synthesis route for low‐aspect‐ratio nanotubes consisting of a layer of magnetite (Fe3O4) sandwiched between SiO2 layers. In this template‐based strategy, self‐ordered porous alumina membranes are combined with the atomic layer deposition of SiO2 and Fe2O3. An optimized electrochemical setup yields nanoporous Al2O3 membranes on 4‐inch Al substrates, which serve as templates for the large‐scale fabrication of nanotubes. A selective chemical etching step releases the magnetic tubes for suspension in a carrier fluid and permits recycling of the underlying aluminum foils for the fabrication of subsequent nanotube batches. The nanotubes consisting of an iron oxide layer protected by a silica shell are magnetically characterized in suspensions as well as in dried form on a substrate. High‐resolution transmission electron imaging reveals a polycrystalline, magnetite spinel structure of iron oxide, with the proper stoichiometry proven by the presence of the Verwey transition. Furthermore, field‐dependent viscosity measurements show an enhancement of the magnetoviscosity, thus demonstrating the technological potential of nanotube suspensions as a new class of ferrofluidic solutions. Owing to the tubular shape being closed at one end, these nanoparticles might additionally function as magnetic containers for targeted drug‐delivery or as chemical nanoreactors. |
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Keywords: | magnetic nanoparticles nanotubes porous materials thin films colloids |
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