| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 93 === Ag/Pd nanoparticles have been synthesized with a reactive alcohol-type surfactant, sodium dodecyl sulfate (SDS), without the presence of an external reducing agent. Both UV-vis absorption spectra and X-ray diffraction patterns for the bimetallic and physical mixtures of individual nanoparticles revealed the formation of bimetallic structure. Based on this method, an ordered 3D grapelike nanostructure was formed possibly due to transformation of the liquid crystal phase of the micelles. Data from the energy dispersive X-ray analysis show that the composition of bimetallic nanoparticle is approximately equal to the feeding solution. Furthermore, the SDS-stabilized Ag/Pd nanoparticles exhibit distinct catalytic activity for electroless copper deposition and may become a substitute for conventional palladium system which is expensive and unstable in operation.
Although SDS-stabilized Ag/Pd nanoparticles possessed good catalytic activity, its adhesion to the substrate was found less than satisfactory. Therefore, another improved system of Ag/Pd nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) was developed. The PVP-stabilized Ag/Pd nanoparticles have been successfully synthesized in various molar ratios. The transmission electron microscopy (TEM) images show the diameters of Ag/Pd nanoparticles increased with increasing Pd molar ratios. UV-vis absorption spectra, X-ray diffraction patterns (XRD) and energy-dispersive X-ray analysis (EDX) all confirmed the formation of bimetallic structure. Additionally, the results of energy dispersive X-ray analysis (EDX) showed that the average composition of bimetallic nanoparticle was approximately equal to the feeding solution while the results of X-ray photoelectron spectroscopy (XPS) revealed the surface was palladium-rich, implying an inhomogeneous alloy structure. The Ag/Pd (3/7) nanoparticles show potential to be a new activator for electroless copper deposition. Furthermore, the surface composition and the thickness of adsorbed polymer have pronounced effect on catalytic activity. The activity of Ag/Pd nanoparticles declines in lockstep with the increasing PVP molecular weight. Moreover, the copper can be successfully deposited onto 0.25 pattern wafer.
The effect of PVP and its role in the formation process of Ag/Pd nanoparticles were also investigated. Based on our study, the functional group of PVP has week interaction with Pd2+ ions, inducing a negative shift of the mixed potential. Ag+ ions have priority to be reduced over Pd2+ ions in the formation of Ag/Pd nanoparticles. The presence of PVP will hinder both Pd2+ and Ag+ ions. However, the steric obstacle effect of PVP would be more pronounced for Pd2+ ions and thus Pd2+ ions are more difficult to diffuse through the polymeric barrier in the particles’ growth stage. Accordingly, Pd2+ ions tend to deposit onto the preformed nuclei at a latter stage, rendering a palladium-rich surface structure of Ag/Pd nanoparticles. Moreover, the steric barrier of PVP would be less effective with increasing molecular weight possibly owing to the decreasing number of molecules.
The feasibility of Ag/Pd nanoparticles as activator for electroless copper deposition was finally carried out. The crystalline structure of electroless Cu film was found unaffected by the type of activators. In addition, the Ag/Pd (3/7) nanoparticles had the shortest induction period and thus exhibited the highest activity, which demonstrated its potential to be a novel activator for electroless deposition.
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