Eung-Suek Lee

Silver-plated carbon nanotubes for silver/conducting polymer composites

Carbon nanotubes (CNTs) have advantages as conductive fillers due to their large aspect ratio and excellent conductivity. In this study, a novel silver/conducting polymer composite was developed by the incorporation of silver-plated CNTs. It is important to achieve a homogeneous dispersion of nanotubes and to improve the interfacial bonding to utilize the excellent properties of reinforcements in the matrix material. The homogeneous dispersion of nanotubes was achieved by an acid treatment process, and the interfacial contact was improved by electroless silver plating around nanotubes. The resistivity of the silver/conducting polymer composite was decreased by 83% by the addition of silver-plated single-walled carbon nanotubes. Conductive bumps were also screen-printed to demonstrate the capability of the composite as electrical interconnects for multi-layer printed circuit boards.

Functionalized nano-silver particles assembled on one-dimensional nanotube scaffolds for ultra-highly conductive silver/polymer composites

A novel silver/polymer composite with electrical conductivity (2.5 × 105 S cm−1) higher than that of bulk tungsten was developed through the addition of a small amount of multi-walled carbon nanotubes decorated with glutaric acid functionalized nano-silver particles (1.5 wt%). The nanotubes were used as one-dimensional conductive scaffolds constructing an effective electrical network among micron-sized silver powders.

Environment-favorable applications for carbon nanotubes

Polymer-based conductive pastes have been actively investigated as possible replacements for lead-based solders in electronic circuits. However, potential for increasing the electrical conductivity of polymer composites reinforced by metallic fillers is limited because of the generally poor contacts.1, 2 Although metallic fillers generate electrical paths in the polymer matrix, poor contacts prevent the electrical conductivity of metal/polymer composites from reaching the levels usually achieved for bulk metals.2 Therefore, the efficiency of the electrical network (a key parameter for increasing its conductivity) is largely dependent on network morphology and junction quality. We have significantly improved the electrical conductivity of silver (Ag)/polymer composites by incorporating multiwalled carbon nanotubes (MWNTs) decorated with self-assembled nano-Ag particles with an average size of 5nm.2 We functionalized the nano-Ag particles with phenyl rings—see Figure 1(a)— which can lead to homogeneous dispersion and attachment to MWNTs through the – interaction (‘stacking’) without detrimental effects on the MWNTs’ electrical and mechanical properties.3–6 We additionally functionalized the nano-Ag particles on MWNTs with glutaric acid (g-Ag-MWNTs) to prevent oxidation.2 Figure 1(b) shows that MWNTs coated with such particles form an effective electrical network based on micrometer-sized silver powders. We employed the tubes as 1D scaffolds and improved the contact interface by attaching nano-Ag particles. The conductivity achieved for the composite (2:5 105S/cm) was even higher than that of bulk tungsten (1:9 105S/cm), and we successfully screen printed electrical interconnects: see Figure 1(c).2 This novel composite might find Figure 1. (a) Electrical-network formation by glutaric-acidfunctionalized nano-silver particles attached to multiwalled carbon nanotubes (g-Ag-MWNTs).2 (b) Transmission-electron-microscope image of solid contacts between micrometer-sized silver powders and g-Ag-MWNTs after annealing at 185C for 1h. (c) Screen-printed electrical interconnects.