The GaN layer was typical III-V nitride semiconductor and was grown on the sapphire substrate which cheap and convenient. However, sapphire substrate is non-conductivity, low thermal conductivity and has large lattice mismatch with the GaN layer. In this paper, the poly GaN epilayer was grown by HVPE on the metallic compound graphite substrate with good heat dissipation, high thermal and electrical conductivity. We tried to observe the growth mechanism of the GaN epilayer grown on the amorphous metallic compound graphite substrate. The HCl and NH3 gas were flowed to grow the GaN epilayer.
The temperature of source zone and growth zone in the HVPE system was set at 850oC and 1090oC, respectively. The GaN epilayer grown on the metallic compound graphite substrate was observed by SEM, EDS, XRD measurement.
In this study, the reflectivity characteristics of Ag nano-coating grown by electroless plating were investigated in order to use as the reflecting plate of BLU (Back Light Unit) in the LCD (Liquid Crystal Display) or LED (Light Emitting Diode) display equipment. The microstructure of Ag nano-coating was polycrystalline nano-structure that consisted of Ag nano-crystals to be reduced and precipitated, and the size of reduced nano-crystals increased as the thickness of nano-coating increased. The reflectivity of Ag nano-coating in the visible light decreased as the thickness of nano-coating increased and the reduction of reflectivity was more severe in the short wavelength region of visible light. The decrease of reflectivity was closely related to the size of Ag nano-crystal and was thought to be due to the larger surface roughness of larger nano-coating thickness. Therefore, the finer Ag nano-crystals and thinner nano-coating thickness could be favorable for the higher reflectivity of Ag nano-coating grown by electroless plating.
Vanadium oxide thin films were deposited on c-Al2O3 (001) substrate by in-situ RF magnetron sputtering.
Oxygen partial pressure was adjusted to prepare thermochromic VO2 phase. X-ray diffraction patterns and scanning electron microscopy convincingly showed that plate-like V2O5 grains were changed into round-shape VO2 grains as oxygen partial pressure decreased. After the optimized deposition conditions were fixed, the effect of substrate temperature and orientation on the optical properties of VO2 thin films was analyzed.
IR cut-off thin films consisted of ATO nanoparticles were successfully fabricated by sol-gel method. The coating solution was synthesized with organic/inorganic hybrid binder and ATO colloidal solution and ATO thin films were coated on a slide glass with the withdrawal speed of 5~40 mm/s. As the withdrawal speed increased from 5 mm/s to 40 mm/s, the thickness of coating thin films also increased from 1.05 μm to 4.25 μm and the IR cut-off in wavelength of 780~2500 nm increased from 49.5 % to 66.7 %. In addition, the pencil hardness of ATO thin films dried at 80oC was ca. 5H and the coating films were not removed after a cross cutter tape test because of the hybrid binder synthesized with tetraethylorthosilicate and methyltrimethoxysilane. The surface morphologies, optical properties and film thickness of prepared thin films with a different withdrawal speed were measured by field emission scanning electron microscope (FESEM),UV-Vis spectrophotometer, and Dektak.
Pure-carbon materials such as graphite, graphene, carbon nanotubes, and diamond have very high thermal conductivities. The reported thermal conductivity of graphene is in the range 3000~5000W/m-K at room temperature. Here,we developed graphene/cu foam hybrid type heat spreader to obtain higher thermal conductivity than Cu foam. Hybrid materials were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and thermal conductivity measurement system; LFA (Laser Flash Analysis @ LFA 447, NETZSCH). We suggest that excellent thermal properties of graphene/cu foam hybrid structures are beneficial for all proposed electrical applications and can lead to a thermal management application.
Granular bamboo-derived active carbons (AC) were impregnated (or coated) with TiO2 nano crystalline powders.
The photocatalytic activity of the TiO2-impregnated active carbons (TiO2/AC) were determined on the basis of the degradation rate of methylene-blue aqueous solution under UV irradiation. The active compounds of TiO2 were impregnated onto the AC under moderate hydrothermal conditions (≤ 200oC, pH 11). The mean size of TiO2 particles calculated from BET surface area were found to be as 50 nm. The TiO2 precipitates were coated on the cavities or pores on the surfaces of highly activated carbons. Since the hydrothermal process led to a lowering of the on-set temperature of the anatase-torutile transition of TiO2 as low as 200oC, TiO2 crystallites of a pure anatase or a mixed form with rutile were successfully coated on the AC depending on the synthesis temperatures.
Translucent opal glass was fabricated in order to substitute polycarbonate diffuser of LED lighting for the purpose of improving the durability problem. Calcium phosphate was used for the opacifier of opal glass and melted at 1550oC for 2 hrs in electric furnace. Because opal glass was made by phase separation and growth of opacifier grains during cooling procedure after forming of melted glass, we identified the effect of opaque properties by the change of forming and cooling temperature, as R.T. (room temperature), 850oC, 1100oC and 1200oC. As the results, it had excellent optical properties for the diffuser of LED lighting in the fabricated sample of forming and cooling at 1200oC, with no dazzling from direct light by high haze value over 82 % and low parallel transmittance value under 10 %. For the thermal properties, it had expressed thermal expansion coefficient of 6.352 × 10−6/oC and softening point of 839oC.
Cobalt aluminate (CoAl2O4) is a highly stable pigment with excellent resistance to light, weather, etc., which has resulted in widespread use as a ceramic pigment. Due to the unique optical characteristics, CoAl2O4 is generally used as a coloring agent to decorate porcelain products, glass, paints and plastics. Here, CoAl2O4 pigments were synthesized by polymerized complex method and solid state reaction. Then CoAl2O4 pigment were grinded using the attrition milling with 1 mm size zirconia ball for 3 hours. The attrition milling process was performed at the constant speed of 800 rpm and ball to powder weight ratio (BPR) was 100 : 1. The characteristics of synthesized pigment were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and CIE L*a*b*. The XRD patterns of CoAl2O4 show single phase spinel structure. The particle size of CoAl2O4 measured by FE-SEM, TEM and PSA analysis was in the range of 100~200 nm. The blue color of obtained CoAl2O4 pigments could be confirmed through CIE L*a*b* measurement.