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The diffusion-assisted coextrusion process is introduced as a method to fabricate graded-index plastic optical fibers (GI-POFs). In this process, two or more polymeric materials containing additives for refractive index modification are fed separately into a coextrusion die where a concentric multilayer structure is formed. Subsequently, the diffusion of additives takes place in a diffusion zone, creating a nonequilibrium concentration profile, and hence the refractive index profile. A theoretical analysis for the prediction of the refractive index profile obtainable by this process indicates that it is difficult to obtain a near-parabolic refractive index profile unless a very large residence time in the diffusion zone is provided. However, significant changes in the refractive index profile can be induced by adopting a multilayer approach. Furthermore, the bandwidth estimated by the ray analysis indicates that a small variation of the refractive index profile created by the additive diffusion can result in a significant increase in the bandwidth, suggesting that the diffusion-assisted coextrusion process is a viable method to fabricate GI-POFs with a bandwidth higher than 400 Mbits/s for 100 m.

Chemical mechanical polishing (CMP) is widely adopted in producing excellent local and global planarization of microelectronic devices. However, the fundamental mechanisms of material removal and the interactions of the chemical and mechanical effects are not well understood. In the present paper, the contact area of a pad with a wafer is measured in dry and wet conditions in different pH solutions using optical microscopy and Fourier transform infrared spectroscopy, respectively. Pad surface mechanical properties in dry and wet states are also investigated using atomic force microscopy. The results indicate a significant difference in pad surface mechanical properties between dry and wet states, which could be correlated with the CMP removal rates.

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Extensional flow of a bicomponent two-layer slot cast coextrusion process has been studied. A Newtonian and an upper-convected Maxwell fluid were considered to be the two layers, respectively, and the two-layer flow was assumed to be steady and isothermal. This choice was made as a simple model for a system which consists of two distinctly different fluids in terms of their extensional behaviors. Present study considered only the draw-down region where the film thickness changes slowly with the distance from the die exit. For this region, asymptotic solutions could be obtained for two limiting cases in which the elasticity effect of the Maxwell fluid layer is small and the applied tension at the take-off is large, respectively. When the elasticity effect is small, the melt thickness and the velocity profiles are exponential as in the case of a Newtonian single-layer flow. When the applied tension is large, on the other hand, the velocity profile is shown to be near linear. Furthermore, the viscoelasticity effect of the Maxwell fluid layer becomes so dominant that it dictates the mechanics of the coextrusion flow even when its flow rate and shear viscosity may be much smaller than those of the Newtonian layer.