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

Abstract

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 Co 2+ 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 N d 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 N d . 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. could synthesize the Co nanowires with a diameter of ca. 15 nm by using a solvothermal chemical process. In their report, the coercivity of 10.6 kOe was achieved at room temperature [5]. However, the average length of Co nanowires was only ca. 200 nm. Hence, there are still several issues to overcome in addressing the gap, which is required for the permanent magnetic applications with anisotropic performance. In the template-assisted method, ferromagnetic metal is electrodeposited into the template with numerous nanochannels with large aspect ratio (cylinder-like nanopores). This method is a very attractive approach to synthesizing ferromagnetic metal nanowires because it can be carried out using simple experimental devices and its cost is low [6]. Typical template materials include ion track-etched polycarbonate films [7-10] and anodic aluminum oxide (AAO) films [11]. In particular, pore diameter and thickness of AAO templates can be adjusted by changing experimental conditions such as anodic oxidation voltage. As a result, the diameter (d), length (L) and aspect ratio (L/d) of nanowires, which are electrodeposited into nanochannels, can be adjusted. Therefore, many researchers have synthesized ferromagnetic metal nanowire arrays by using the AAO templates [6,[12][13][14][15][16]. In addition, hexagonal close-packed cobalt (hcp-Co) has large magneto-crystalline anisotropy along the c-axis [17,18]. Hence, the magnetic anisotropy of the cobalt nanowire arrays could be enhanced, when the long axis of nanowires corresponds to the c-axis by adjusting the cobalt crystal orientation.Research to date has focused on the crystal structure and the magnetic properties of ferromagnetic cobalt nanowire arrays, which were synthesized ...

Robust Trioptical-State Electrochromic Energy Storage Device Enabled by Reversible Metal Electrodeposition

“…The parameter n reveals the growth dimension of crystal grains. 47 The n values (different cycles) are slightly higher than 2, indicating that the initial film formation is due to 2D nuclei growth.…”

“…To analyze the Avrami coefficient value and the crystal nucleation frequency during cycling, we conducted Johnson−Mehl− Avrami−Kolmogorov (JMAK) analysis. 47,48 The current− time (i−t) curves (absolute current values) were extracted every 500 cycles for a total of 5000 cycles (Figure 3A,B).…”

“…This work evaluates the Cu electrodeposition kinetics in a hybrid electrolyte over long cycling, where nucleation and film growth analysis would elucidate a fundamental understanding of the electrodeposition. To analyze the Avrami coefficient value and the crystal nucleation frequency during cycling, we conducted Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis. , The current–time ( i – t ) curves (absolute current values) were extracted every 500 cycles for a total of 5000 cycles (Figure A,B). Current values were normalized over the saturation current, and double logarithmic plots of −ln­(1 – X ) versus time for every 500 cycles are presented (Figure C,D).…”

“…Current values were normalized over the saturation current, and double logarithmic plots of −ln­(1 – X ) versus time for every 500 cycles are presented (Figure C,D). The parameter n reveals the growth dimension of crystal grains . The n values (different cycles) are slightly higher than 2, indicating that the initial film formation is due to 2D nuclei growth.…”

Mechanical Properties of Solder-Jointed Copper Rods with Electrodeposited Sn-Zn Alloy Films

“…As shown in Figure 2b, the cathode potential shifts to a less noble direction with an increase in the current density over the range from 0.5 to 5 mA/cm 2 . It is well-known that the electrodeposited metals nucleation site density increases with an increase in the electrodeposition overpotential, which corresponds to the difference between the cathode potential and the equilibrium potential of metal, during the charge transfer process which is controlling the reduction rate of metallic ions [25]. Hence, the decrease in the average crystal grain size seems to be caused by the increase in the nucleation site density.…”