Shape Transition and Growth of CoxFe(1-x) Alloy Nanocrystals By Electrochemical Deposition

Abstract

Nanocrystals were interesting materials for applications such as photocatalyst, biocatalyst, solar cells, sensors, lithium batteries, magnetic resonance imaging, water splitting, and etc. These properties were dependent on their shape and composition. Therefore, researches of the nanocrystal synthesis, shape and composition control have been significantly important. Nanocrystals were prepared by chemical vapor deposition, hydrothermal methods, sol-gel techniques, spraying methods, and electrochemical synthesis methods. Among the these methods, electrochemical synthesis was great method since this method has advantages that simple process, low cost, low synthesis temperature, selective decoration on conductive substrates, various materials synthesis such as metal, semiconductor, and oxides. In addition to this, the nanocrystals were easily tuned by changing synthesis conditions, electrolyte concentration, pH, applied potential, and addictives. The CoFe alloys were well known at magnetic materials due to their high magnetic saturation and show potential for the magnetic application. Despite the advantages of electrochemical synthesis methods, studies of the nanocrystal growth were restricted for mainly noble metals1 and oxides2. There were few studies of synthesis of the alloy nanocrystals, PtNi, PtFe, PtCo, and etc.3Therefore, studies of the alloy nanocrystal synthesis were still required. In this research, The CoxFe1-x nanocrystals were synthesized by electrochemical synthesis method at various synthesis conditions such as applied potential, charge density, and electrolyte concentration. These nanocrystals were characterized by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. From the SEM images, there was shape transition from non-cube to cube shape when applied potential was increased. This shape transition was caused by composition change. The Co-rich CoxFe1-x nanocrystals show non-cube, which was nearly spherical, shape, while the 1:1 CoFe and the Fe-rich CoxFe1-xnanocrystals show cube shape. In addition to this, particle reduction phenomenon was observed as potential increased. This phenomenon was different with electrochemical deposition behavior that nucleation density was exponentially dependent on the potentials.