Tungsten carbide (WC) has been suggested as a new buffer layer for the GaN-on-Si technology. We have investigated and optimized the sputtering condition of WC layer on the Si-substrate. We confirmed the suppression of the Si melt-back phenomenon. In addition, surface energy of WC/Si layer was measured to confirm the possibility as a buffer layer for GaN growth. We found that the surface energy(γ=82.46 mJ/cm²) of WC layer is very similar to that of sapphire substrate(γ=82.71 mJ/cm²). We grow GaN layer on the WC buffer by using gas-source MBE, and confirm that it is available to grow a single crystalline GaN layer.

3YSZ + (x) Al₂O₃ composites (x = 20, 40, 60, 80 wt%) were fabricated and the influences of particle sizes of Al₂O₃ on their microstructures and mechanical properties were investigated with XRD, SEM, vickers hardness and fracture toughness. Al₂O₃-3YSZ composites containing Al₂O₃ powder of a 0.3 μm and an 1.0 μm, which are here in after named as Al2O3(0.3 μm)-3YSZ and Al₂O₃ (1.0 μm)-3YSZ, respectively, were made by mixing raw materials, uni-axial pressing and sintering at 1,400℃, 1,500℃, and 1,600℃. Al₂O₃ (0.3 μm)-3YSZ composites show the higher density and the better mechanical properties than Al₂O₃ (1.0 μm)-3YSZ composites. The Vickers hardness of the Al₂O₃ (0.3 μm)-3YSZ composites show a peak value of 1,997 Hv at the content of 60 wt% Al₂O₃, which is a slightly higher value in comparison with 1,938 Hv of the Al2O3(1.0 μm)-3YSZ composite. However, the fracture toughness of Al₂O₃-3YSZ composites monotonically increases with decreasing the content of Al₂O₃ without any peak values. Al₂O₃ (0.3 μm)-3YSZ and Al₂O₃ (1.0 μm)-3YSZ composites sintered at 1,600℃ have a maximum value of a 6.9 MPa·m1/2 and a 6.2 MPa·m1/2, respectively at the composition of containing 20 wt% Al2O3. It should be noticed that the mechanical properties and the sintering density of the Al₂O₃-3YSZ composites can be enhanced by using more fine Al₂O₃ powder due to their denser microstructure and smaller grain size.

In this study, in order to develop composition ceramics for refrigeration device application, Ba(Ti_0.9Zr_0.1)O₃ composition was fabricated using conventional solid-state method. Electrocaloric effect of this ceramic was investigated using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to 150℃. Curie temperature of Ba(Ti_0.9Zr_0.1)O₃ ceramics showed 80℃. The maximum value of ?T = 0.12℃ in ambient temperature of 115℃ under 30 kV/cm was appeared. It is concluded that Ba(Ti_0.9Zr_0.1)O₃ ceramics can be applied as refrigeration device application.

Effects of pH value and deposition time on the electrical properties of (NMC) Ni-Mn-Cu-O and (NMCC) Ni-Mn-Cu-Co-O thin films were investigated. The NMC and NMCC films were prepared by spin spray method. The crystal structure and thickness of the annealed films were changed by the pH value and deposition time, respectively. A single phase of cubic spinel structure was confirmed for the annealed films deposited from solutions with pH 7.6. The resistivity of the annealed films was affected by the crystal structure and microstructure. The TCR (temperature coefficient of resistance) was dependent on the Mn³⁺/Mn⁴⁺. Typically, the resistivity of 70.5 Ω · ㎝ and TCR of -3.56%/K at room temperature were obtained for NMCC films deposited from solutions with pH 7.6 for 5 min, and annealed at 450℃ for 3 h.

Mo doped carbon (C:Mo) thin films were fabricated with various Mo target power densities by unbalanced magnetron sputtering (UBM). The effects of target power density on the surface, structural, and electrical properties of C:Mo films were investigated. UBM sputtered C:Mo thin films exhibited smooth and uniform surfaces. However, the rms surface roughness of C:Mo films were increased with the increase of target power density. Also, the resistivity value of C:Mo film as electrical properties was decreased with the increase of target power density. From the performance of organic thin filml transistor using conductive C:Mo gate electrode, the carrier mobility, threshold voltage, and on/off ratio of drain current (Ion/Ioff) showed 0.16 cm²/V·s, -6.0 V, and 7.7×10⁴, respectively.

In this study, the effect of Tb inward diffusion on the magnetic properties of the Nd-Fe-B sintered magnets was studied. After sintering of the magnets, TbF₃ slurries were dip-coated on the surface of the samples, then heat-treatment was followed for TbF₃ diffusion. The element distribution in the magnets and the diffusion profiles of Tb ions were analyzed by an EPMA (electron probe micro-analyzer). Prolonged heat treatment resulted in a deeper diffusion length of Tb ions. Coercivity of the 1^st heat-treated sample showed 21.86 kOe, while that of the 1^st, 2^nd heat-treated and annealed sample revealed 34 kOe.

The Ag thin film of YBCO (yttrium barium copper oxide) CC (coated conductor) protect the YBCO layer and, at the same time, affects the electrical characteristics of the YBCO CC. Therefore, YBCO CC with the commercialization of the Ag thin film layers makes it easy to establish a process, it can lead to a variety of characteristic changes in YBCO CC. In this paper, plasma surface treatment was carried out to facilitate the deposition of the Ag thin film and the deposition process of YBCO CC. Surface roughness from the test results was increased as the time of the plasma surface treatment increased from 5 to 20 minutes. On the other hand, the surface roughness was decreased for the time of the plasma surface treatment over 20 minutes. Furthermore, after depositing, the increasing of deposit amount and reduced lifting phenomenon showed a similar tendency with the rise time of surface roughness.

In this paper, the fault current limiting characteristics of the flux-lock type SFCL (superconducting fault current limiter) using magnetic application circuit were analyzed. The flux-lock type SFCL has the structure to install the magnetic application circuit, which can increase the resistance of HTSC (high-TC superconducting element comprising) the SFCL. To analyze the fault current limiting effect of the flux-lock type SFCL through the magnetic flux application circuit, the flux-lock type SFCL either with the magnetic flux circuit or without the magnetic flux circuit was constructed and the fault current limiting characteristics of the SFCL were compared each other through the short-circuit tests.

In this study, the physical and optical properties of ZnS:Mn2+ Quantum Dot prepared by wet-process condition with Mn/Zn ratio was valuated. The powder characteristics and optical behavior were investigated through XRD, TEM and Photo spectrometer exicted by various UV light source. We found the main peak of ZnS (111) was shifted by 0.8 degree to low angle position with increasing stirring energy from 200 RPM to 600 RPM, which is thought to be the increase of lattice defects during wet process. The photo luminescence at 600 RPM shows also higher blue intensity which is well correlated with XRD results. With increasing Mn/Zn ratio, the PL intensity become higher and shifed by 8.5nm to right side, by the increment of substitutional Mn²⁺ ions.

We report the studies on the red organic phosphor by using perylene bisimide derivatives. Even though perylene bisimide derivatives have excellent thermal stability and luminous efficiency, they have low solubility in organic solvents. In this research, modified perylene bisimide derivative, N,N`-Bis(4-bromo-2, 6-diisopropylphenyl)- 1, 6, 7, 12-tetraphenoxyperylene-3, 4, 9, 10-tetracarboxyl bisimide (1C), has been prepared by the reaction of phenol with N,N`-Bis(4-bromo-2, 6-diisopropylphenyl)-1, 6, 7, 12-tetrachloroperylene-3, 4, 9, 10-tetracarboxyl bisimide (1B) in presence of DMF, at 70℃. The synthesized (1C) was characterized by using 1H-NMR, FT-IR, UV/V is spectroscopy, and TGA. The absorbtion and emission of (1C) was shown at 576 nm and 610 nm in UV/V is spectrum. In TGA thermogram, (1C) showed good thermal stability without significant weight loss to 220℃. And in the solubility analysis, (1C) with phenoxy group showed the good solubility in general organic solvents. The blended films of (1C) with PMMA (polymethyl methacrylate) at different weight % concentration such as 10, 5, 1 weight % have been prepared. The blended film was shown at 616 nm when monitored at 450 nm in PL emission spectra.

The effect of low temperature (250℃) heat treatment after electron irradiation (irradiation time = 30, 180, 300s) on the chemical bonding and electrical properties of ZnO thin films prepared using a sol-gel process were examined. XPS (X-ray photoelectron spectroscopy) analysis showed that the electron beam irradiation decreased the concentration of M-O bonding and increased the OH bonding. As a result of the electron beam irradiation, the carrier concentration of ZnO films increased. The on/off ratio was maintained at ~10⁵ and the VTH values shifted negatively from 11 to 1 V. As the irradiation time increased from 0 to 300s, the calculated S. S. (subthreshold swing) of ZnO TFTs increased from 1.03 to 3.69 V/decade. These values are superior when compared the sample heat-treated at 400℃ representing on/off ratio of ~10² and S. S. value of 10.40 V/decade.

CNT (carbon nanotube) resistors with low resistance and negative TCR (temperature coefficient of resistance) were fabricated with yarned CNT (carbon nanotube) fibers. The CNT fibers were prepared by yarning CNTs grown on the silicone substrate by CVD (chemical vapor deposition) method. The CNT resistors were fabricated by winding CNT fibers on the surface of ceramic rod. Both metal terminals were connected with the CNT fiber wound on the ceramic rod. We measured electrical resistance and thermal stability with the number of CNT fibers wound. The CNT resistor system shows linearly decreased resistance with the number of CNTs wound on the ceramic rod and saturated at 20 strands. The CNT resistor system has negative TCR between -1,000 ~ -2,000 ppm/℃ and stable frequency properties under 100 kHz.