Ferromagnetic metal-polymer nanocomposites for magnetic sensing applications

xiii, 156 leaves : ill. ; 30 cm.PolyU Library Call No.: [THS] LG51 .H577M AP 2008 KwongIn this project, cobalt and polytetrafluoroethylene (PTFE) composite films were fabricated by Pulsed Laser Deposition technique (PLD) with the use of split target. The composition of the films was changed by varying the pulse irradiation ratio of the metal and polymer targets. The deposited samples consist of cobalt particles of sizes about 5 nm and irregular shaped PTFE particles of size larger than 200 nm in a well connected PTFE polymer matrix. The cobalt-PTFE composite films exhibit a room temperature magnetoresistance (MR) change of about 5% at 10 kOe. A significant enhancement of MR value to 6% was achieved at 20 K at 8 kOe. The blocking temperature of the sample was obtained to be about 90 K. Possible explanations of the observed experimental results are suggested. Cost-effective and simple magnetic sensor applicable in device industries prepared by this method is anticipated. Fabrication of cobalt nanoparticles has been successfully demonstrated by PLAL technique in 3 kinds of solvent with detailed discussions. Superhydrophobic PTFE thin films for fabricating self-cleaning surfaces were successfully fabricated by PLD technique. A large contact angle of about 170o and low sliding angle was achieved. Detailed discussions and explanations were presented. Fabrication of cobalt hydroxide nanoplatelets at room temperature by an innovative method, simply using sodium hydroxide (NaOH) solution to react with a PLD prepared pure cobalt thin film, was presented. The morphology of the nanoplatelets and the crystal structure were characterized. This method provides a simple, relatively fast and clean method to produce nano-sized cobalt hydroxide for using in real applications.Department of Applied PhysicsM.Phil., Dept. of Applied Physics, The Hong Kong Polytechnic University, 200