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Open AccessArticle

Determination of Crystal Growth Geometry Factors and Nucleation Site Densities of Electrodeposited Ferromagnetic Cobalt Nanowire Arrays

1
Graduate School of Engineering, Nagasaki University, Bunkyo-machi 1-14, Nagasaki 852-8521, Japan
2
Faculty of Engineering, Nagasaki University, Bunkyo-machi 1-14, Nagasaki 852-8521, Japan
*
Author to whom correspondence should be addressed.
Crystals 2019, 9(3), 142; https://doi.org/10.3390/cryst9030142
Received: 20 February 2019 / Revised: 6 March 2019 / Accepted: 6 March 2019 / Published: 10 March 2019
(This article belongs to the Special Issue Nanowires and Quantum Dots for IoT Applications)
The time-dependence of electrochemical reduction current, which was observed during the one-dimensional (1-D) crystal growth of ferromagnetic cobalt nanowire arrays, was analyzed by Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. Textured hcp-Co nanowire arrays were synthesized by potentio-static electrochemical reduction of Co2+ ions in anodized aluminum oxide (AAO) nanochannel films. Crystal growth geometry factor n in the JMAK equation was determined to be ca. 1. Hence, the electrochemical crystal growth process of a numerical nanowires array can be explained by 1-D geometry. The crystal nucleation frequency factor, k in JMAK equation was estimated to be the range between 10−4 and 10−3. Our experimental results revealed that the crystal nucleation site density Nd increased up to 2.7 × 10−8 nm−3 when increasing the overpotential for cobalt electrodeposition by shifting the cathode potential down to −0.85 V vs. Ag/AgCl. The (002) crystal orientation of hcp-Co nanowire arrays was, remarkably, observed by decreasing Nd. Spontaneous magnetization behavior was observed in the axial direction of nanowires. By decreasing the overpotential for cobalt electrodeposition, the coercivity of the nanocomposite film increased and reached up to 1.88 kOe, with a squareness of ca. 0.9 at room temperature. View Full-Text
Keywords: Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory; electrodeposition; cobalt; nanowire array; crystal growth geometry; nucleation site density; crystal orientation; uniaxial magnetization Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory; electrodeposition; cobalt; nanowire array; crystal growth geometry; nucleation site density; crystal orientation; uniaxial magnetization
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Saeki, R.; Ohgai, T. Determination of Crystal Growth Geometry Factors and Nucleation Site Densities of Electrodeposited Ferromagnetic Cobalt Nanowire Arrays. Crystals 2019, 9, 142.

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