Electrospun Magnetic Thin Film Max Chung, Shin-Fa Ho, and Chun-Rong Lin Abstract - a magnetic thin film composed of However, the uniform dispersion of nanoparticles to nanofibers containing Fe3O4 nanoparticles is prepared designated location turns out to be a taunting task. The with electrospinning with PVA solution. The Fe3O4 strong Van der Wall forces of nanoparticles coagulate them, nanoparticles diameter is around 8 nm, PVA solution is which in instances can be disperse by adding some polarized around 35 percent, and the voltage applied is 7 KV at 12 solvent, but changing the desired properties sometimes. cm distance. EDX confirm the existence of Fe3O4 Electrospinning is the oldest nanotechnology available nanoparticles wrapped inside the fibers, and SVM to manufacture less than ptm-diameter nanofibers [18-20]. measurements confirm magnetization. Such method can By introducing a high voltage between the spinneret and the be used to prepare magnetic thin film for sensor collecting plate, the repulsion force of the space charge on application. the ejected fluid surface overcomes the surface tension and forms thin fibers usually not possible without electric field. Keywords: thin film, electrospinning, nanoparticles The diameter of the fiber can be tuned by adjusting the applied voltage, the distance between the spinneret and the I. INTRODUCTION collector plate, and the solution concentration [21, 22]. The less than ptm diameter nanofibers may provide a Magnetic thin film is used widely in magnetic 2-dimensional carrier for nanoparticles, both for the purpose recording head [1,2], sensors [3-6], and Spintronics devices of uniform dispersion and for easy integration into macro [7-1 1]. Recently, ion beam sputtered magnetic thin film is device. If nanoparticles can be electrospun into nanofibers, also used as alignment film in LCD [12]. then the nanoparticles may be restricted to fit inside a Except for some rare method [13], most magnetic thin 200-500 nm diameter 2D structure with little chance of film are sputtered [14], and the film qualities sought after are stacking in the radial direction, and forms mm long high deposition rate, uniformity, thickness control, nanofibers that can be pick up and repositioned with an stoichiometry, and surface topology of the thin film [15]. optical microscope probe stage. So we mix Fe3O4 The magnetic property of the materials influences these nanoparticles with PVA solution, and place it in an issues strongly. The most common approach is DC electrospinning apparatus to make magnetic thin film of sputtering. DC sputtering can provide a better quality film, macro size. Section II is the experiment details of the but at very slow deposition rate. Magnetron sputtering of electrospinning process, section III describes the results magnetic materials is higher in deposition rate, but the rate is when Fe3O4 nanoparticles are added to the process, and also slower than non-magnetic target materials because the finally the conclusion. magnetic field line can not penetrate well into the sputter target. The combined effect of applied RF electric field and II. ELECTROSPINNING magnetic field from the target materials makes sputtered atoms travels in vastly different and chaotic path towards the Typical basic set up for electrospinning for nanofibers substrate and render the stoichiometry of thin film different is as shown in fig. 1. A injection syringe needle is used as from the alloy target. No matter which kinds of sputtering, spinneret, and a DC 7 KV high voltage is applied to the the oxygen adhere to the wall of the chamber constitute the spinneret with collecting plate at ground potential at 12 cm basic impurity limitation in sputtered thin film. Pulsed distance way. The 35 weight 00 PVA concentration solution Laser Deposition [16] offers better control of the is push out of the spinneret to form a Taylor cone, and then stoichiometry of the thin film produced, but is generally not accelerate towards the collector in a spiral motion. On the used in mass production. right of Fig. 1 is the typical PVA nanofibers thin film The emergence of nanotechnology brings new formed without the addition of Fe3O4 nanoparticles. The perspective to the production of magnetic thin film [17]. PVA thin film is about several cm2 in areas. The fiber Nanoparticles of magnetic materials can be produced by diameter is about 200-500 nm and the thickness is about several methods that range from 4-50 nm diameter and 50-00 ptm depending on process parameters. The fiber exhibits the unique property that small size has to offer like diameter decreases with lower PVA concentration, and controllable band gap, large surface area to volume ratio, decreases with the increase of voltage and collector distance. and concentrated density of states. There are sometimes beads in the connection between the Max Chung and Shin-Fa Ho are with the Department of fibers, but they can be removed with some special Electronic Engineering, Southern Taiwan University, E-mail: arrangement during the electrospinning process. Fig. 2 is a ,, u .~>o-e,nLw SEM picture of the PVA nanofibers. The diameter is about Chun-Rong Lin is with the Department of Mechanical Engineering, Southern Taiwan University. 1-4244-0637-4/07/$20.OO ©C2007 IEEE 309 Authorized licensed use limited to: Southern Taiwan University. Downloaded on June 18,2010 at 04:34:09 UTC from IEEE Xplore. Restrictions apply.