(305d) Electrically Controllable Plasmonic Behavior of Gold Nanocube@Polyaniline Core/Shell Nanostructures

Noble metal nanoparticles, especially those made from gold and silver, have attracted significant attention because of their unique localized surface plasmon resonance (LSPR) properties that can be exploited in various applications such as photocatalysis, solar cells, and sensing. Even though specific plasmonic properties can be obtained through well-established synthesis techniques, it is difficult to modulate LSPR peak position and cross-section intensity in a real-time manner. Here, we demonstrate the electrically tunable plasmonic behavior of hybrid core/shell nanostructures composed of gold nanocube (AuNC) cores and electroactive polyaniline (PANI) shells. The oxidation state of the PANI shells was reversibly changed by applying an electrical potential, which resulted in a refractive index change of the PANI shells. Consequently, a significant LSPR shift was achieved with high reversibility and stability. Because of its unique core/shell structure, with AuNC cores and electroactive PANI shells in close contact, a high LSPR shift (24 nm) is achieved. Finite-difference time-domain (FDTD) computer simulations show that the electromagnetic field decay length of the core AuNC is an important parameter in the design core/shell nanostructures; the most efficient LSPR modulation was obtained for PANI shells thinner than the electromagnetic field decay length of the gold nanoparticles. Single particle studies showed that the PANI shell acts as a physical barrier between adjacent nanoparticles as well as an electroactive medium, which prevents plasmonic coupling while providing a variable refractive index medium.