Papers by Author: Hun Chae Jung

Abstract: ZnO is an n-type semiconductor having a hexagonal wurzite structure. ZnO exhibits good piezoelectric, photoelectric and optical properties and might be a good candidate for an electroluminescence device like an UV laser diode. But the important problems, such as substrate kinds and substrate temperature are raised its head, so they need to optimize deposit condition. Because these devices are very small and films are very thin, those are often prepared in limited quantities and shapes unsuitable for the extensive mechanical test. In this present work, ZnO thin films are prepared on the glass, GaAs (100), Si (111) and Si (100) substrates at different temperatures by the pulsed laser deposition (PLD) method. ZnO was evaluated in term of crystalline through X-ray diffraction (XRD), mechanical properties such as hardness, elastic modulus through nano-indenter. XRD measurements indicate that the substrate temperature of 200-500, 200-500, 300-500, and 300-500oC was the optimized conditions of crystalline for the glass, GaAs (100), Si (111), and Si (100) substrates, respectively. In spite of the films deposited on the different substrates, the films always show (002) orientation at the optimized conditions. Mechanical properties such as hardness and elastic modulus are influenced substrate crystallization. In case of Si (111) substrate, hardness and elastic modulus are about 10, 150GPa, respectively.

Abstract: SiC materials have excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. Therefore, in the interests of safety, we are required to measure fracture toughness of materials. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method under 20MPa using sintering additives at different temperature such as 1760oC, 1780oC, 1800oC and 1820oC. The starting powder was high purity β-SiC nano-powder with an average particle size of 30nm. Compositions of sintering additives were Al2O3 / Y2O3 = 0.7 and 1.5 (wt. %). Monolithic LPS-SiC was evaluated in terms of sintering density, hardness and fracture toughness through indentation fracture method by the Vickers hardness tester. Sintered density, hardness and fracture toughness of fabricated LPS-SiC increased with the increase of sintering temperature. They are higher than those of fabricated SiC by the chemical vapor deposition method.