Self-Assembly of TOPO-Derivatized Silver Nanoparticles into Multilayered Film

A novel method for transferring silver nanoparticles from aqueous solution into organic solvents such as toluene or hexane was developed. Phase-transfer reagent, tri-n-octylphosphine oxide, TOPO, provides a capping shell around Ag particles that enables concentrating nanoparticle dispersion in toluene, which is a prerequisite for successful 3D self-assembly. The dispersed particles are stable for a long period of time (at least six months). Self-assembly of high concentrations of TOPO-capped Ag particles results in a multilayered mirrorlike film formed onto glass substrates. SEM images reveal a fine-grained film consisting of 10-nm close-packed particles. The surface plasmon absorption of the 3D structure is 100 nm red-shifted compared to that of isolated particles in toluene solution, and is a result of interparticle coupling of dielectric functions of particles in near proximity. Redispersing of particles from the 3D film into toluene solution revealed a spectrum of silver particles virtually identical to that of the original solution used for the formation of the multilayered film. This confirms that the shift of surface plasmon absorption of 3D film is a result of interparticle communication/coupling.