Ordered Iron Oxide Nanotube Arrays of Controlled Geometry and Tunable Magnetism by Atomic Layer Deposition

• Published in: Journal of the American Chemical Society Vol. 129; no. 31; pp. 9554 - 9555
• Main Authors: Bachmann, Julien, Jing, Knez, Mato, Barth, Sven, Shen, Hao, Mathur, Sanjay, Gösele, Ulrich, Nielsch, Kornelius
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08-08-2007
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja072465w

Iron oxide nanotubes of 50−150 nm outer diameter and 2−20 nm wall thickness are prepared in ordered arrays. Atomic layer deposition (ALD) of Fe2O3 from the precursor iron(III) tert-butoxide at 130−180 °C yields very smooth coverage of the pore walls of anodic alumina templates, with thickness growth of 0.26(±0.04) Å per cycle. The reduced Fe3O4 tubes are hard ferromagnets, and variations of the wall thickness d w have marked consequences on the magnetic response of the tube arrays. For 50 nm outer diameter, tubes of d w = 13 nm yield the largest coercive field (H c > 750 Oe), whereas lower coercivities are observed on both the thinner and thicker sides of this optimum.