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Magnetic, Multilayered Nanotubes of Low Aspect Ratios for Liquid Suspensions
Author(s) -
Zierold Robert,
Wu Zhenyu,
Biskupek Johannes,
Kaiser Ute,
Bachmann Julien,
Krill Carl E.,
Nielsch Kornelius
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201001395
Subject(s) - materials science , nanoporous , nanotechnology , nanotube , chemical engineering , fabrication , magnetite , layer (electronics) , nanoparticle , oxide , magnetic nanoparticles , chemical vapor deposition , iron oxide nanoparticles , carbon nanotube , medicine , alternative medicine , pathology , engineering , metallurgy
This work presents a synthesis route for low‐aspect‐ratio nanotubes consisting of a layer of magnetite (Fe 3 O 4 ) sandwiched between SiO 2 layers. In this template‐based strategy, self‐ordered porous alumina membranes are combined with the atomic layer deposition of SiO 2 and Fe 2 O 3 . An optimized electrochemical setup yields nanoporous Al 2 O 3 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.