Su Jeong Suh

A Control of the Nanopore Regularity in Alumina Layer

This study placed a focus on fabrication factors and surface morphology characteristics to obtain anodic alumina layers with ordered nanopore arrays using two-step anodization process. The regularity of nanopore arrangement in anodic alumina was prepared in oxalic acid at 40 V. The regular array was shown to be more strongly dependent on the time of first anodization than that of second anodization. The widening process of oxide surface in H3PO4 solution clearly exhibits that the nanopore diameter of the alumina layer subjected to widening time increased linearly at a rate of 0.6 nm/min at 30°C, and 0.8 nm/min at 40°C. The pore arrays in anodic alumina were analyzed by SEM.

Exchange anisotropy and thermal stability of Mn-Ir-Pt exchange-biased layers

The exchange coupling and the microstructures of the Ta/(Ni-Fe,Co-Fe)/Mn-Ir-Pt/Ta multilayers have been investigated by varying the compositions of Mn-Ir-Pt film. For exchange-bias layer (EBL) comprising NiFe/CoFe/Mn/sub 79.7/Ir/sub 18.4/Pt/sub 1.9/ structures, the exchange bias field (H/sub ex/) of 441 Oe (exchange energy Jex of 0.236 erg/cm/sup 2/) and the blocking temperature (T/sub b/) of 260/spl deg/C was obtained. In addition, it is found that the Mn-Ir-Pt EBLs have the polycrystalline structure and [111] texture. The crystallographic structure of the Mn-Ir-Pt film was face centered cubic (FCC).

A Study on Anodic TiO2 Photocatalyst for Water Purification

The microstructure and photocatalytic characteristics of anodic TiO2 film have been investigated for applications in waste water treatment. The major structure of the fabricated anodic TiO2 film consisted of porous cell structure, of which the main crystal structure bas been found to be anatase type. The photocatalytic efficiencies of anodized TiO2 were evaluated by the degradation rate of aniline blue and the chemical states of anodic film were estimated by P2P spectrum. The reaction order and the rate constant for degradation of dye have been determined to be first dimension and 1.608410-4s. Due to the high bonding strength between TiO2 film, and the substrate and the high specific surface area, the anodized TiO2 can be used as efficient photocatalyst with high reactivity for waste water treatment and water purification.

Origin of Thermal Stability of IrMn Based Specular Spin Valve Type GMR Multilayer

By using the sputtering process, we made the IrMn based specular spin valve system, whose nano-oxide layer (NOL) was formed by natural oxidation. After thermal annealing at 305 and 410 °C, the thermal stability of the specular spin valve was observed. We found that the highest magnetoresistance (MR) ratio of about 12 % MR was produced after optimum annealing at 305 °C but the sample annealed at 410 °C also had a high MR ratio about 10 %. It is superior to other studies at this temperature. Based on the AES and XPS results, we could conclude that this enhanced thermal stability was due to the stable Cu layer between the pinned layer and free layer and to the NOL as a diffusion barrier for the Mn.