Analysis of Effect of Ultrasound on the Magnetic Topography of Electroplated Ni Films by Magnetic Force Microscopy (MFM)
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INTRODUCTION
ELECTRODEPOSITION of nickel has been investigated intensely during the past decades for its notable magnetic properties, mechanical properties, and numerous applications in industry.[1–3] Nickel is a 3d transition metal and exhibits ferromagnetism with large spontaneous magnetization at room temperature. The magnetic properties of thin film depend on their crystalline structure and their interface with the substrate and film morphology. The use of sonication during electrosynthesis, which is called sonoelectroplating, may have many benefits over the conventional (silent) electrodeposition.[4–8] These benefits are claimed to include increased deposit hardness, enlarged film thickness, improved deposition rates and efficiencies, better adhesion of the deposits and acceleration, and modification of crystallization phenomena.[9–13] When the film is electrodeposited, the nucleation and growth mechanism plays a crucial role on film structure and properties. There may be two general nucleation and growth mechanisms: mononuclear growth (twodimensional [2-D] nucleation) and polynuclear growth (three-dimensional [3-D] nucleation). In mononuclear film formation, deposition takes place through layer-bylayer growth of adatoms onto the depositing front whereas polynuclear growth leads to random incorporation of isolated supercritical nuclei on substrates. And the mode of appearance of nuclei may manipulate the orientation and magnitude of magnetic moments of atoms. The study of nucleation and growth mechanism via electrodeposition can be determined by an analysis of current transients (a current vs time plot) as a function of potential from chronoamperometric (CA) measurements. A typical CA current transient reaches to ARPITA DAS, Research Scholar, ARCHANA MALLIK, Assistant Professor, and BANKIM CHANDRA RAY, Professor, are with the Department of Metallurgical and Materials Engineering, National Institute of Technology, Rourkela, 769008 Odisha, India. Contact e-mail: [email protected] Manuscript submitted April 11, 2011. Article published online November 3, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
a maximum point (Im, tm) and then falls exponentially when multiple nuclei form and grow on the electrode surface and their local zones of reduced nucleation rate spread out and gradually overlap. The shape of the transients may vary depending on the mode and kinetics of nucleation process. Furthermore, the phase formation onto a substrate usually considers two extreme cases of nucleation: instantaneous and progressive. In instantaneous nucleation, all nuclei form at the same time and grow comparatively slowly. In progressive nucleation, new nuclei form during the course of deposition process and grow relatively faster. Hence, many researchers have attempted to describe the nucleation mechanism through theoretical models. Usually, the equations are used in the form of dimensionless curves, in which either (I/Im) or (I/Im)2 is plotted against (t/tm), with Im and tm being the current maximum of the measured potentiostatic t
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