AVS 52nd International Symposium
    Thin Films Monday Sessions
       Session TF-MoP

Paper TF-MoP13
Controlled Synthesis and Magnetic Properties of Iron Oxide Particles Formed by Thermal Decomposition of Rapidly Expanded Supercritical Solutions

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Aspects of Thin Films Poster Session
Presenter: D.R. Miller, University of California, San Diego
Authors: S. De Dea, University of California, San Diego
D. Graziani, University of California, San Diego
D.R. Miller, University of California, San Diego
R.E. Continetti, University of California, San Diego
Correspondent: Click to Email
Films of iron oxide fine magnetic particles were synthesized by rapidly expanding a supercritical solution (RESS) of ferric acetylacetonate (FeAA) and CO@sub 2@ onto a hot silicon wafer. The temperature of the substrate was set at a value such that thermal decomposition of the solute would occur at the silicon surface with subsequent formation of iron oxide particles in an oxidizing atmosphere. We present the details of the RESS apparatus and initial data on the FeAA/CO@sub 2@ system and the deposited thin films. In the RESS process particle morphology and composition can be controlled by adjusting process parameters such as pre-expansion temperature, pressure and composition of initial solution, temperature of the substrate, nozzle to substrate distance, and expansion chamber pressure and composition. In the process design and utilization of RESS it is very important to acquire accurate solubility data and then to monitor the composition of the expanding solution. For this purpose a spectroscopic view cell was introduced in the RESS system, prior to the expansion, to allow both equilibrium solubility as well as on-line concentration measurements. Obtained solubility data will be presented and compared with predicted solubility from the Peng-Robinson equation of state. The deposited particles were analyzed with SEM, XRD, EDX and a SQUID based magnetometer. It was found that smaller nanoparticles were formed when the RESS expansion was into the vacuum. The effect of the supersonic expansion jet structure on particle morphology will be discussed. EDX and XRD showed that complete decomposition of FeAA occurred at the silicon surface and that the particles consisted of a mixture of crystalline Fe@sub 2@O@sub3@ and Fe@sub 3@O@sub 4@. Magnetization measurements were performed at different temperatures and they showed that the particles have ferromagnetic properties. Results for the coercive field as well as saturated and remanent magnetization will be presented.