C.H. Lee

Effects of annealing on the thermoelectric and microstructural properties of deformed n-type Bi2Te3-based compounds

We studied the effects of deformation and annealing of n-type 90Bi2Te3-5Sb2Te3-5Sb2Se3 thermoelectric compound. Hot-extrusion was conducted to prepare the deformed compound and then this compound was annealed at 400°C for 1–24 hr. When the undoped cast-ingot was extruded, the compound was changed from p-type to n-type due to the electrons generated during the extrusion process. For the compound extruded with SbI3-doped powders, the thermoelectric properties were also varied for the extrusion process. After annealing at 400°C more than 9 hr, the powder-extruded compound was recrystallized. This caused a decrease in carrier concentration and crystallographic anisotropy. In case of the compound extruded at the ratio of 10:1, the Seebeck coefficient α and the electrical resistivity ρ increased due to recrystallization. However, thermal conductivity κ of the compound decreased. This resulted in an increase in the figure-of-merit from 1.23 × 10−3 to 1.63 × 10−3 K−1.

Diffusion Bonding of Al 6061 Alloys Using an Eutectic Reaction of Al-Ag-Cu

In this study, a diffusion bonding of aluminium alloy A6061 was preformed using an Ag-28Cu filler metal in order to conduct eutectic brazing. Melting mechanism was surveyed. Interface behaviors of the brazed joints were observed after brazing and T6 solution treatment. Also, tensile property of the brazed joints was examined. During diffusion bonding of Al6061 alloys with Ag-28Cu filler metal, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu filler metal. It was found that the reaction layer consist of two phases formed at the interface between AA6061 and Ag-28Cu filler metal. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. Tensile strength was 300 MPa after ageing treatment at 175°C.

Distribution of the 9-bp deletion in COII/tRNA^ intergenic region of mitochondrial DNA is relatively homogeneous in east Asian populations

A deletion of one out of the two copies of 9-bp repeat sequence (CCCCCTCTA), between the cytochrome oxidase II and Iysine tranfer RNA (COII/) genes in human mitochondrial DNA (mtDNA) has been used as a polymorphic anthropological marker for people of east Asian origin, and to lesser extent, Pacific and African populations. We searched for the 9-bp deletion of the intergenic COII/ Lys region in two Korean populations (175 from Seoul and 38 from Cheju) and examine the distibution of this deletion in world populations. The 9-bp deletion was detected directly by electrophoresis of the polymerase chain reaction (PCR)-amplified nucleotide(nt) 8211-8310 mtDNA fragment. The frequencies of the 9-bp deletion were significantly different between the Seoul (16%) and Cheju (8%) populations. Examination of data from the world populations suggests a geographic gradient. The frequency reaches its highest values in some Pacific island populations and decreases along the southeast Asia-Siberia transect. In spite of this geographic gradient, Mongoloid populations including Korean, Chinese, Japanese, and Mongolian populations were relatively homo-geneous with regard to the 9-bp deletion type of the intergenic COII/ region. These results indicate Koreans are genetically related to northeast Asian populations, and have a maternal mongoloid ancestry. Therefore, the 9-bp deletion of the intergenic COII/ region will provide significant information to elucidate the historical patterns of migration of the Mongoloids.

Vacuum diffusion brazing of Al5052 alloys using Ag-28Cu insert metal

In this study, we examined brazeability of Al5052 alloys using a Ag-28Cu insert metal in vacuum condition. A high frequency induction-heating vacuum hot press was used for the brazing. Under a static pressure of 0.5 MPa and a vacuum of 5×10-5 Torr, the temperature of hot press was raised up to brazing temperature (480-590°C) at a speed of 10°C/min and held at the brazing temperature for various times. Interface behaviors of the brazed joints were observed after brazing at 480-590°C by optical microscopy and Electron Probe Micro Analyzer (EPMA). Also, bonding strength of the brazed joints was examined. During vacuum brazing of Al5052 alloys with Ag-28Cu insert metal, eutectic melts were formed by eutectic reaction between Al5052 and Ag-28Cu insert metal at about 490°C. It was found that reaction layers of two phases are formed at the interface between Al5052 and Ag-28Cu insert. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. The bonding strength of the joints increased with brazing temperature and time. The highest bonding strength was 141 MPa at 580°C, 10min.

Genetic variations in six candidate genes for insulin resistance in Korean essential hypertensives

Hypertension is a complex disease with strong genetic influences. Essential hypertension has been shown to be associated with insulin resistance. To clarify the genetic basis of insulin resistance in hypertension, case‐control association studies were performed to examine candidate genes for insulin resistance in hypertension. Polymorphisms investigated were the BstO I polymorphism of the (β3‐adrenergic receptor (ADRB3) gene, the Xba I polymorphism of the glycogen synthase (GS Y) gene, the Dde I polymorphism of the protein phosphatase 1 G subuit (PP1G) gene, the BstE II polymorphism of the glucagon receptor (GCG‐R) gene, the Pst I polymorphism of the insulin (INS) gene and the Acc I polymorphism of the glucokinase (GCK) gene. No significant differences were observed in the distribution of alleles and genotypes of the ADRB3, GS Y, PP1G, GCG‐R, INS, and GCK genes between hypertensive and normotensive groups. Although the frequencies in each of these polymorphisms were not significantly different between essential hypertensive and normotensive individuals, our results may provide additional information for linkage analysis and associative studies of disorders in carbohydrate metabolism or in cardiovascular disease.

Plasma etching for the application to low-k dielectrics devices

We present a study of the photoresist (PR) etching and the low-k materials damage using a ferrite-core inductively coupled plasma (ICP) etcher, in order to develop an etching process for the low-k dielectric devices. We reveal that the N2/O2 flow ratio and bias power affected the PR etching rate. By Fourier transform infrared spectroscopy and HF dipping test, we investigated the effect of the gas flow ratio and bias power on the amount of etching damage to the low-k material.

Orientation Distribution in Bi2Te3-Based Compound Prepared by Spark Plasma Sintering

P-type Bi0.5Sb1.5Te3 compounds doped with 3wt.% Te were fabricated by spark plasma sintering after mixing large powders(PL) and small powders(PS). We could obtained the highest figure of merit(Zc) of 2.89×10-3/K in sintered compound mixed to PL:PS=80:20. This resulted from the increase of orientation by large powders(PS) and the reduce of pores by small powders. The figure of merit(Zc) of the sintered compound using only small powders(PS) showed lower value of 2.67×10-3/K compared with that of sintered compound mixed to PL:PS=80:20 due to the increase of electrical resistivity.

Structural and optical properties of annealed Ga2O3 films on Si(111) substrates

Abstract An investigation has been made into the structural and optical properties of gallium oxide Ga2O3 films grown on Si(111) substrates by the metal organic chemical vapour deposition (MOCVD) technique, and annealed in the temperature range 750–1050°C. Post-deposition annealing of amorphous Ga2O3 was found to generate b phase grains. Photoluminescence spectra indicated that the annealed Ga2O3 films had a blue-green emission at 470 nm and an ultraviolet emission at 365 nm.

Catalyst-Free Growth of Tin Oxide One-Dimensional Nanostructures on Silicon Nitride Substrates

We have obtained one-dimensional (1D) nanomaterials of tin oxide (SnO2) on silicon nitride (Si3N4)-coated Si substrates by carrying out the thermal evaporation of solid Sn powders and varying the substrate temperature in an Ar/O2 ambient gas. We analyzed the samples with scanning electron microscopy, X-ray diffraction, transmission electron microscopy and photoluminescence (PL). Reactions at a lower substrate temperature gave rise to thinner 1D structures. The obtained 1D nanomaterials were single crystalline with a tetragonal rutile structure. We proposed a vapor-solid process as the growth mechanism for SnO2 nanorods. The PL spectrum exhibited visible light emission.

Development of Eco-flux laminated strip for air atmosphere brazing

The purpose of this study is to introduce and discuss flux laminated strip. Flux laminated strip can be used for air atmosphere brazing. The new product is fabricated by four processes: embossing of strip; multi bending of embossed strip; flux injection; and resizing of the material. This flux laminated strip exhibits similar melting characteristics to flux cored and flux coated alloys. The flux laminated strip eliminates the need for a separate fluxing operation that is typically needed when using bulk alloy. The product ensures the correct amount of flux during the brazing process and reduces the post-braze clean time. The ability to produce a quality joint while reducing the amount of pre-braze and post-braze operations make flux laminated strip an innovative Eco-braze-materials.