The effect of parameters on the formation of ZnO nanoparticles by statistical experimental design method in vibrating milling process

Zinc oxide (ZnO) nanoparticles were synthesized by vibrating milling process. Amorphous ZnO powders prepared by the milling process were washed with water to remove NaCl, and then the powders were sintered at 300–500 °C for 2 h. In this work, statistical experimental design method was used and it was found that the particle size and size distribution of ZnO nanoparticles were dependent on the milling time and mass ratio of ball to powder. Therefore, ZnO nanoparticles with about 100 nm of mean crystallite size were obtained.     

Transport properties of Bi<Subscript>43</Subscript>Se<Subscript>4</Subscript>Te<Subscript>53</Subscript> thermoelectric alloy fabricated by mechanical grinding and pulse discharge sintering

Mechanical grinding followed by pulse discharge sintering was applied to fabricate n-type Bi₄₃Se₄Te₅₃ thermoelectric materials. Calorimetric measurements demonstrated that a Se-rich phase was developed from Bi₂(Se, Te)₃ phase after 10h of milling. However, when the milling time was extended to 25 h or longer, a Te-rich phase was formed. Hall measurements showed that the development of the Se/Te-rich phase considerably increased the carrier concentration but decreased the carrier mobility. The oxygen contamination in the smashed powders was also an important consideration for the degeneration of the figure of merit of the sintered samples.     

Selective area growth of GaN nanowires using metalorganic chemical vapor deposition on nano-patterned Si(111) formed by the etching of nano-sized Au droplets

We report on the selective area growth of GaN nanowires (NWs) on nano-patterned Si(111) substrates by metalorganic chemical vapor deposition. The nano-patterns were fabricated by the oxidation of Si followed by the etching process of Au nano-droplets. The size of formed nano-pattern on Si(111) substrate was corresponding to the size of Au nano-droplet, and the diameter of GaN NWs grown was similar to the diameter of fabricated nano-pattern. The interesting phenomenon of using the nano-patterned Si(111) substrates is the formation of very clear substrate surface even after the growth of GaN NWs. However, in the case of GaN NWs grown using Au nano-droplets, there was several nanoparticles including GaN bulk grains on the Si(111) substrates. The smooth surface morphology of nano-patterned Si(111) substrates was attributed to the presence of SiO₂ layer which prevents the formation of unnecessary GaN particles during the GaN NW growth. Therefore, we believe that nano-patterning method of Si(111) which was obtained by the oxidation of Si(111) substrate and subsequent Au etching process can be utilized to grow high-quality GaN NWs and its related nano-device applications.     

Approach to non-human species radiation dose assessment in the Republic of Korea

This paper describes the approach to non-human species radiation dose assessment in Korea. As the tentative reference organisms, one plant and seven animals were selected based on the new International Commission on Radiological Protection recommendation issued in 2007, and the size of the selected organisms was determined from the corresponding Korean endemic species. A set of 25 radionuclides was considered as a potential source term of causing radiological damage to organisms. External and internal dose conversion coefficients for the selected organisms and radionuclides were calculated by the uniform isotropic model or Monte Carlo simulation. Concentration ratios of some endemic species are being measured in laboratory experiments, in parallel with the review of existing data.     

Nanoscale fabrication of myoglobin monolayer on self-assembled DTSSP for bioelectronic device

The fabrication method of nanoscale myoglobin monolayer using chemical linker is introduced in this study because control of amount and orientation of protein immobilized on electronic device is one of main issues to be solved for the realization of biomolecular electronic device. Myoglobin, metalloprotein, is selected as active material due to its electrochemical property. To immobilize myoglobin on Au surface, 3,3-dithiobis (sulphosuccinimidyl propionate) (DTSSP) is utilized as a chemical linker. The optimum amount of protein is investigated by surface plasmon resonance (SPR). SPR and scanning tunneling microscope (STM) results confirm the nano scale protein layer formed on DTSSP self assembled monolayer (SAM) on Au surface. Protein layer on Au surface using DTSSP as chemical linker was more stable than random adsorption without linker as aspect of redox character due to the fact that myoglobin immobilized with chemical linker did not lose its redox property after long usages.     

Thermal Diffusivity of Metallic Thin Films: Au, Sn, Mo, and Al/Ti Alloy

The thermal diffusivity of Au, Sn, Mo, and Al_0.97Ti_0.03 alloy thin films, which are commonly used in microelectromechanical (MEMs) system applications, is measured by two independent methods — the ac calorimetric and photothermal mirage methods. Both methods yield similar results of the thin-film thermal conductivity, but the uncertainty of the mirage technique is found to be relatively large because of the large temperature increase during the measurement. The measured thermal diffusivities of the thin films are generally lower than those of the same bulk material. Especially, the Al_0.97Ti_0.03 thin film shows a pronounced thermal conductivity drop compared with bulk Al, which is believed to be mainly due to impurity scattering. Comparison of the thermal conductivity with the electrical conductivity measured by the standard four-probe technique indicates that the relation of thermal and electrical conductivities follows the Wiedemann–Franz law for the case of Au and Sn thin films. However, the Lorentz number is significantly larger than the theoretical prediction for the case of Al_0.97Ti_0.03 and Mo thin films.     

Application of Au-Sn eutectic bonding in hermetic radio-frequency microelectromechanical system wafer level packaging

Development of packaging is one of the critical issues toward realizing commercialization of radio-frequency-microelectromechanical system (RF-MEMS) devices. The RF-MEMS package should be designed to have small size, hermetic protection, good RF performance, and high reliability. In addition, packaging should be conducted at sufficiently low temperature. In this paper, a low-temperature hermetic wafer level packaging scheme for the RF-MEMS devices is presented. For hermetic sealing, Au-Sn eutectic bonding technology at temperatures below 300°C is used. Au-Sn multilayer metallization with a square loop of 70 μm in width is performed. The electrical feed-through is achieved by the vertical through-hole via filling with electroplated Cu. The size of the MEMS package is 1 mm × 1 mm × 700 μm. The shear strength and hermeticity of the package satisfies the requirements of MIL-STD-883F. Any organic gases or contamination are not observed inside the package. The total insertion loss for the packaging is 0.075 dB at 2 GHz. Furthermore, the robustness of the package is demonstrated by observing no performance degradation and physical damage of the package after several reliability tests.     

Supercritical Carbon Dioxide debinding in metal injection molding (MIM) process

The conventional debinding process in metal injection molding (MIM) is critical, environmentally unfriendly and time consuming. On the other hand, supercritical debinding is thought to be an effective method appropriate for eliminating the aforementioned inconvenience in the prior art. In this paper, supercritical debinding is compared with the conventional wicking debinding process. The binder removal rates in supercritical CO₂ have been measured at 333.15 K, 348.15 K, and 358.15 K in the pressure range from 20 MPa to 28 MPa. After sintering, the surface of the silver bodies were observed by using SEM. When the supercritical CO₂ debinding was carried out at 348.15 K, all the paraffin wax (71 wt% of binder mixture) was removed in 2 hours under 28 MPa and in 2.5 hours under 25 MPa. We also studied the cosolvent effects on the binder removal rate in the supercritical CO₂ debinding. It was found that the addition of non-polar cosolvent (n-hexane) dramatically improves the binder removal rate (more than 2 times) for the paraffin wax-based binder system. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Formation of Barrier Ribs for Plasma Display Panels via Powder-Blasting Process: Part II, Effects of Powder-Blasting Angle

The effects of powder-blasting angle on the powder-blasting rate of a thick film prepared using a tape-casting technique were investigated. The results revealed that the etching rate was sensitive to the angle of powder blasting. The mechanism of this dependency was discussed based on brittle fracture and erosion caused by the powders blasted on the surface of the film. In addition, a new processing route for barrier ribs for plasma display panels was attempted, using the sensitive dependency of the etching characteristics on the powder-blasting angle. It was demonstrated that the ribs could be processed successfully using layers having different etching rates.