Silver-coated polydiacetylene nanocrystals fabricated using surfactants as binder

A method of fabricating polydiacetylene (PDA) nanocrystals covered with silver nanoparticles was established using surfactant as a binder between the PDA core and silver nanoparticles, and the linear optical properties were examined in relation with their structure. Noble metal-coated PDA nanocrystals are expected to enlarge effective third-order nonlinear optical susceptibility χ⁽³⁾. due to the enhancement of the optical electric field induced by localized surface plasmon. The well-defined PDA nanocrystal cores were first prepared by the conventional reprecipitation method. The following two-step reduction, namely, seed deposition and seed growth, enabled higher silver coverage on the surface of PDA nanocrystals. In particular, silver deposition succeeded by employing an anionic surfactant, because of electrostatic attraction with silver cations. It was also important to optimize concentration and the affinity of surfactant for PDA. The extinction spectra of the PDA nanocrystals covered with silver exhibited a strong localized surface plasmon peak of silver, distinct from the already-reported inverse core-shell-type structure, which would contribute to efficient enhancement of χ⁽³⁾.