Estimation of cobalt coating layer thickness on acicular Fe₃O₄ powder using HR-TEM

The thicknesses of cobalt coating layers grown on four different types of acicular Fe₃O₄ particles were estimated from the analysis of lattice images and from the determination of the Co depth profile using high-resolution transmission electron microscopy (HR-TEM) coupled with an energy dispersive X-ray (EDX) analysis system. It was observed that the coating thickness might vary with the crystallite size resulting from the growth mechanism of the coating layer. In this study, two different layer thicknesses, 40 Å and less than 10 Å, were evidenced for crystallite sizes of 390 Å and 350 Å, respectively.