Magnetic Field Induced Self-assembly Of Cobalt Nanoparticles And The Preparation And Characterization Of Y-Co Nanofilms

With the invention and application of Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) in last80s, we entered in an new age in which the nanotech developed rapidly. New progress appears constantly in this area. The matters we care mostly now are still how to simply, efficiently organize materials (molecules, molecular clusters, polymers etc.) into precise, predetermined nanostructures that can be preserved in a robust engineering form, and how to prepare new nano-meterials which have more excellent performance in application.Self-assembly is an easy and promising way to synthetise new-type nanostructures. It has a big application potential in semiconductor, environment, medicine and source of energy. Nanoscaled magnetic materials have big values too in application because of its excellent magnetic properties. In this article we take the element of Co and Y-Co alloy nanofilms as the object of study. We studied the magnetic field induced self-assembly of cobalt nanoparticles and the preparation Y-Co nanofilms, characterized the morphology, crystal structure and magnetic properties of the Co particles, studied the self-assembly of Co particles under magnetic field, and analysised the influence of experiment parameters and preparation technique to the nanostructures of the product. The main contents and results of the article is as follows:In Chapter2, we synthetised cobalt nanoparticles with the size of8nm,12nm and 16nm respectively, through the pyrolysis of Co2(CO)8. The TEM images show that the Co particles have a narrow size-distribution and good disperation, which are packed by a2nm-thick oleic acid molecular layer, forming a core-shell structure. We confirm the particle is ε-Co through SAED. We draw the hysteresis loops of the particles through SQUID, and verify that the particles of8nm are superparamagnetic, and the particles of12nm and16nm are weak ferromagnetic at room temperature. At the same time we determined that the more Co2(CO)8taking part in the chemical reaction, the bigger Co particles we get.In Chapter3, we studied the self-assembly of Co particles under the vertical DC static magnetic field. First we conduct the experiment using the Co particles of12nm and16nm. We study the influence of the intensity of the magnetic field to the results of the self-assembly, and find that when the intensity of the magnetic field is weak, we get the nanostructures interlinked together and when the intensity is strong, we get isolated islands. We think the reason of this result is the changing external magnetic field who changes the magnetic dipole moment interaction between Co particles. Then we study the influence of the concentration of the colloidal solution to the results of self-assembly, we find that when the concentration is big, the Co particles cover the whole substrate almostly with many random-shaped gaps in it, and when the concentration is small, we get nanostructures in the regular shape of columns or blocks. After analysis the series of experimental results, we draw the map of the assembly results of the colloidal solutions with diffierernt concentrations. Lastly we get macro-scale columnar bumps under the magnetic field using superparamagnetic Co particles of8nm. We think these bumps, which are in the shape of cylinder, originate from the instability of the interface of magnetic fluid under external magnetic field.Lastly in Chapter4, we prepared Y-Co nanofilms through cluster beam deposition and magnetron sputtering respectively. The particles of the sample get from cluster beam deposition have a good disperation, the average size of the particles is5nm, but the coercivity is only51Oe, after annealing under800℃of the sample, the coercivity is enhanced to131Oe. We think the reason why the coercivity is so small is that the sample doesn’t crystallize entirely and that the oxygenolysis of the sample isn’t prevented effectly. The coercivity of the Y-Co nanofilms prepared through magnetron sputtering is bigger, we study the influence of the temperature of deposition and the time of annealing to the magnetic properties of the product and confirm that the higher temperature of deposition we use, the higher coercivity we get, and that the in situ annealing after deposition can enhance the magnetic proporties further and the annealing time has an optimal value of20min. The coercivity of the sample deposited under800℃and annealed for20min is608Oe.The results of this article can also be applied to the self-assembly of the other magnetic particles and the preparation of other Co-based RE-TM alloys.