Kyu Seomoon

Fabrication of Fe-Al nanoparticles by selective oxidation of Fe-Al thin films

The possibility of a new technique for fabricating nanoparticles from thin films using selective oxidation in an atmosphere mixture of water vapor and hydrogen was investigated. Fe-5wt.%Al films were RF-sputtered and annealed in the atmosphere mixture at 900°C for up to 200 min, in order to oxidize aluminum selectively. Thermodynamics simulation showed that temperatures exceeding 800°C are necessary to prevent iron from being oxidized, as confirmed by the depth profile of XPS. As the annealing time increased, the morphology of the 200-nm Fe-Al films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. The particulate 10- to 100-nm Fe-Al films showed super-paramagnetic behavior after the oxidation. Thus, a new technique for fabricating nanoparticles was successfully introduced using selective oxidation.

Fabrication and properties of FePt thick films for alternative local field micromagnet

Growth of FePt films thicker than several tens of a micrometer was attempted on Fe substrates for the use of micromagnets. Several underlayer or intermediate layers were found to be totally ineffective to success. However, 20 μm thick FePt films on the Fe substrates were successfully grown by sputtering after HF surface treatment. (BH)max of the non-annealed film was about 10.7 MG Oe under a maximum applied field of 10 kOe. An excellent adhesion between the Fe substrate and the FePt thick films seems to be due to both improvement of surface cleanliness and roughening which enhanced the chemical and physical bonding strengths.

Effects of Gas Mixing Ratio on the Properties of Thin Films in the ZnO Synthesis by MOCVD

ZnO thin films were synthesized on Si substrates by MOCVD using diethyl zinc as a precursor. Effects of O2/DEZ gas mixing ratio on the growth rate, surface morphology, preferred orientation, and electrical properties of the ZnO thin films were investigated with SEM, XRD, and Hall measurement. The surface reflectance variations of ZnO thin films were analyzed using laser-photometer apparatus. As the O2/DEZ mixing ratio increased, growth rate and I(002)/I(101) in XRD of ZnO thin films decreased, and the crystal structure was changed from columnar to planar structure. All ZnO films deposited at various CVD conditions exhibited c-axis (002) plane preferred orientation. The electrical properties of ZnO thin films mainly depended on the carrier mobility.

Properties of Si/SiOx quantum well structure for solar cells applications

The SiOx/Si quantum wells (QWs) structures were fabricated by using the successive deposition technique, as quantum confinement device to increase the effective energy bandgap and passivation effect in Si surface for the third generation solar cell applications. In Si/SiOx QWs, the thicknesses of Si layers and SiOx layers were varied between 1 to 5 nm, respectively. The roughness of sputter-deposited Si on SiOx was less than 4 Å in the thickness of 2 nm. By using the SiOx/Si QW structures on Si surfaces, the lifetime measured by u-PCD technique increased as a result of passivated surface effects. The tunneling phenomena and good interface properties were observed in the fabricated QWs structures.