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2 Journal of Achievements in Materials and Manufacturing Engineering

2 2006

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Surface modification of PBO fiber by electrostatic discharge for composites

100%

Wu G. M. , Shyng Y. T.

tom Vol. 17, nr 1-2

169--172

Purpose: PBO fibers provide great potential applications as reinforcement fibers for advanced composites due to the excellent thermal resistance and specific stiffness and strength. However, the interfacial adhesion between reinforcing fiber and polymer matrix in a composite system is a primary factor for the stress transfer from matrix to fiber. In this paper, the effects of surface treatment on the modification of PBO fiber and its composite materials have been investigated using electrostatic discharge under atmospheric pressure. The surface treatment process has been designed to improve fiber/matrix interfacial bonding quality while providing minimum alteration to the bulk characteristics of the reinforcement fiber. Design/methodology/approach: Both as-spun (AS) and high-modulus (HM) PBO fibers were surface treated and characterized in this study. The characterization techniques included scanning electron microscopy, MTS tensile tester, dynamic contact angle analysis system and microbond pull-out tests. Findings: The results showed that PBO fibers exhibited -10% reduction in tensile strength after the proposed treatment process. The AS fiber surface free energy could be increased from 49.90 mJ/m2 to 65.42 mJ/m2(+31%) and the HM fiber surface free energy could be increased from 46.20 mJ/m2 to 65.36 mJ/m2 (+41%). The interfacial shear strength between PBO fiber and the epoxy matrix was improved to 41.6 MPa (+20%) for AS fiber system, and it improved to 40.1 MPa (+23%) for HM fiber system. The composite failure mode also shifted from fiber/matrix interface adhesive failure to partly cohesive failure. Research limitations/implications: The composite interfacial shear strength was improved through the increased surface free energy of PBO fiber. The more cohesive failure mode allowed more energy to be dissipated during failure. Originality/value: The proposed electrostatic discharge treatment process could improve the surface characteristics of PBO fiber and the applications in advanced composites.

Defect structures in InGaN/GaN multiple quantum wells on Si(111) substrates

100%

Wu G. M. , Kao Y. L.

tom Vol. 18, nr 1-2

195--198

Purpose: Nitrides are compound semiconductor nanomaterials that are suitable for use in light-emitting diodes. It has been desired to grow high quality gallium nitride crystal thin film on silicon substrates because silicon substrates have the advantages of low cost, large wafer size, and good electrical and thermal conductivity. However, the higher defect density can limit the industrial applications due to lower quantum efficiency. The purpose of this study has been to investigate the crystal defect structure within InGaN/GaN multiple quantum wells on Si(111) substrates. In addition, the variation in quantum well thickness was also explained by the selective area growth model. Design/methodology/approach: InGaN/GaN nano-structures were prepared by metal-organic chemical vapor phase epitaxy (MOVPE) using composite buffer layers. The crystal defect structures in the buried multiple quantum wells on both (0001) and {10-11} sidewalls were carefully studied by transmission electron microscopy. Previous studies on sapphire substrates have been compared and discussed. Findings: The V defect structures have been found in InGaN/GaN multiple quantum wells on Si(111) substrates. A simplified structural model with increasing barrier thickness has been reported. The barrier thickness increased on both (0001) and {10-11} facets along thin film growth. A decreased fill factor based on the selective area growth model was proposed. In addition, the average thin film growth rate was found to be four times higher along (0001) than that along {10-11} facet. As the number of multiple quantum wells increased, the barier thickness increasing was also intensified. Research limitations/implications: The understanding in defect structure could help to modify the processing and design parameters. Originality/value: The V-defect structure and model were reported for the first time using silicon substrates. The different growth rates along defect structures were quantified. High quality gallium nitride crystal could be manufactured along with better substrate design.