Key Engineering Materials Vols. 321-323

Abstract: Thermal diffusivity of nonstoichiometric PrMnO3 and NdMnO3 phases were measured by laser flash method from room temperature to 1100 K, in addition to the data of electrical conductivity, thermal analysis and high temperature X-ray diffractometry to detect the phase transition. The thermal diffusivity curve varied with increasing temperature and showed a clear anomaly with a sudden dip at the phase transition temperature. The transition temperature decreases with oxygen nonstoichiometry in each phase.

Abstract: Polymer light emitting diodes (PLEDs) with ITO/PEDOT:PSS/MEH-PPV/LiF/Al structures were prepared by spin coating method on the patterned ITO(indium tin oxide)/glass substrates. MEH-PPV [Poly(2-methoxy-5(2-ethylhexoxy)-1,4-phenylenevinyle)] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)]
polymers were used as the light emitting and hole transport materials. The dependence of the plasma treatment of ITO anode films on the optical and electrical properties of the PLEDs was investigated. The sheet resistances increased with increasing the plasma intensities from 40W to 300W in RF power. In contrast, the surface roughness was improved as the plasma intensity increased. The maximum current density and luminance were found to be about 97.5 mA/
and 55 cd/m2 at 8 V for the PLED sample coated on ITO/glass substrate with plasma treatment of 100W for 30s under 40 mtorr O2 pressure.

Abstract: To fabricate a (110) silicon hard master, we used anisotropic wet etching. The etching chemical for the silicon wafer was a TMAH 25% solution. We fabricated a 1x4 multimode planar waveguide splitter using the silicon hard master. Organic-inorganic hybrid materials were used as core and cladding layers of the planar waveguide splitter. The 15 μm-thick under-cladding layer was coated on a silicon substrate and baked. After the core layer was coated on the under-cladding layer, the core pattern was formed by using a hot embossing process at 100 °C and 1-3 kg/cm2. The propagation loss of the planar waveguide was 0.4 dB/cm and the insertion loss of the 1x4 planar waveguide splitter was 11.2 dB at the total splitter length of 3.5 cm.

Abstract: A feasibility test for real-time fine particle measurements in vacuum semiconductor processing equipment has been conducted. The approach in monitoring particles in process equipment is an installation of a sensor at a critical location inside the process equipment (hence the term ‘in-situ’) to track free particle levels in real-time. Common method for particle detection in a process chamber today is a use of test wafer with a laser wafer scanner. However, this method does not give a real time information of the particle status in the process chamber. In this paper, a new method has been developed to detect particles in real time in vacuum system for particles smaller than an optical method can detect. The system consists of a particle charging region and a particle detection region in a vacuum system. Particles with 50nm are successfully detected at about 10 torr region.

Abstract: In this paper, elastic moduli of nanostructured alumina are evaluated by simultaneous measurement of longitudinal and shear wave velocities using mode-converted ultrasound in scanning acoustic microscope (SAM). Mode-converted longitudinal and shear waves inside alumina sample are captured to calculate acoustic wave velocities and determine elastic constants such as Young’s modulus and Bulk modulus. Al2O3 nanostructured alumina samples are formed by compacting micro-sized Al2O3 powder with nano-sized Al2O3 powder from 10wt% to 50wt%, and tested by SAM to investigate elastic moduli. A correlation is found from experiment that the more percentage of nano-particles are added, the higher elastic moduli are obtained. It is also shown that the mode-converted ultrasound is sensitive enough to characterize mechanical modulus of nanostructured alumina quantitatively.

Abstract: Electron beam welding (EBW) has an important role in industrial applications such as semi-conductor and LCD manufactures because of its high performance and accuracy. Since the operation is done in a vacuum room, it is very difficult to test the weldability as well as the correct welding area of the specimen. In this study, a measurement system of the EBW was developed based on the 3-axis LVDT controlled table. In addition, the algorithm to tracking the welding line has been developed. The weldability of the aluminum specimen was tested by a newly developed measurement system with ultrasonic C-scan inspection.

Abstract: The thermal fatigue properties of the solder joints with various underfills were evaluated by thermal shock test. Flip chip package with electroless nickel-immersion gold plated on Cu pad of FR-4 substrate and the Sn-37Pb solder ball was used. The thermal fatigue crack initiated at the edges of interface between solder and silicon die. The fatigue property of package with underfill, which has a higher glass transition temperature (Tg) and lower coefficient of thermal expansion (CTE) value was better than that of package with underfill having a lower Tg and higher CTE.

Abstract: In the present study, an investigation has been carried out on the friction stir welding (FSW) of two magnesium alloys. Hot-rolled and Die-casting plates of AZ type magnesium alloys were successfully joined by friction stir welding. AZ31B-H24 and AZ91C-F plates with the thickness of 4mm were used, and the microstructural development in stir zone (SZ) was investigated using optical and scanning electron microscopes. Hardness of SZ in AZ31B-H24 alloy has been slightly decreased due to the coarse structure. On the other hand, Hardness of SZ in AZ91C-F alloy has been remarkably increased due to very fine recrystallized grain structure. The result of EPMA showed Al Solid solution hardening by Solid solution of β intermetallic compound to α-Mg. While tensile strength of the FSWelded AZ31B-H24 alloy showed about 80% values compare to Base metal, AZ91C-F showed about 68% values due to strongly affected by formation of the intermetallic compounds, β-Al12Mg17.

Abstract: The purpose of this study is to find out the method to detect AE signals at around the notch tip and to evaluate the AE signal characteristics for the basemetal, PWHT(post weld heat treatment) and weldment specimens of SA-516 steel during bend test. AE signals were produced in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed by PWHT specimen and basemetal. More AE signals were produced from the weldment because of the oxides, and discontinuous mechanical properties. The stronger AE signal strength, amplitude and more AE event counts for the weldment were shown.

Abstract: Conventionally, shielded-metal arc welding (SMAW) process has been applied to join pipes of reactor coolant loop, which caused defects and lot of loss in time and cost due to excessive heat input in joining section. Recently, narrow-gap welding (NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet commonly used, because safety of NGW process is not fully proven. In the present paper, welded coupons are made of stainless steel. They are manufactured under different processes; general welding (GW), and repair welding after GW. Performed are various mechanical tests to investigate microstructure, tensile strength and so on. It is verified that the mechanical properties of stainless steel are slightly changed after repair welding process. It is also found from stress corrosion cracking tests that the failure time of repair welding is shorter than that of general welding.