טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentTzipi Cohen-Hyams
SubjectElectrodeposition of Thin Metallic Magnetic Films
DepartmentDepartment of Materials Science and Engineering
Supervisors Full Professor Kaplan Wayne D.
Professor Emeritus Yahalom Joseph


Abstract

The present research deals with the correlation of the electrodeposition process, the microstructure, and magnetic properties of electrodeposited Cu-Co. Heterogeneous Cu-Co alloy thin films prepared by electrodeposition are promising materials for giant-magnetoresistance (GMR) applications, especially for magnetic sensor applications. GMR refers to a significant change in the electrical resistance of a film or a device when an external magnetic field is applied. The magnetic and structural properties of Cu-Co alloys were studied extensively. However, very little work has been done on the correlation of the microstructure with the electrodeposition process, and the magnetic properties.


The microstructural findings from polarization, magnetic, Auger electron spectroscopy (AES), in-situ scanning tunneling microscopy (STM), X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), and elemental mapping via electron spectroscopic imaging (ESI) showed that electrodeposition of [Cu92.5-Co7.5] (at.%) results in inhomogeneous films composed of more than one phase; fcc copper, a solid solution of fcc Cu-Co with preferred orientation of {ııı} planes, and a columnar microstructure of  Co.


The as-deposited Cu-Co alloy is inhomogeneous; the bulk of the film is richer in Co while the surface and the bottom of the film are Co-poor. The cobalt deposition rate is limited at the beginning and at the end of the electrocrystallisation process, due to a much faster kinetic process of copper compared to cobalt, and due to the formation of copper grains after the electrodeposition process by chemical exchange between the copper ions in the solution with the cobalt in the Cu-Co film.


The nucleation and growth of Cu and/or Co follows 3-D instantaneous nucleation limited by mass transfer. A proposed mechanism of the kinetic process exhibits excellent fitting to the experimental results. According to the kinetic analysis, there is a phase shift between the electrocrystallisation rates of copper and cobalt. The nucleation rate and the number density of actives sites for nucleation of copper are at least one order of magnitude higher than for cobalt, over a large over-potential range, indicating that an inhomogeneous microstructure will form independent of the over-potential, as was shown by the AES measurements.