Hydrothermal synthesis of silver nanoshells: formation and plasmon hybridization

Silver nanoshells with varying diameters are synthesized using Polyacrylamide (PAM) in a controllable way by the hydrothermal process followed by calcinations to investigate the plasmon hybridization. At relatively lower hydrothermal temperature (T-H similar to 415 K), an assembly of silver nanoparticles (NPs) along the PAM chain is formed exhibiting transverse (453 nm) and longitudinal (949 nm) surface plasmon resonance (SPR) peaks. With increasing T-H (similar to 510 K), this assembly of NPs disrupt into segments and create a homogeneous phase of PAM-silver composites, which upon cooling form globules due to agglomeration. During calcinations at 650 K, PAM is degraded into several gases (NH3, CO2, and water vapor) to form nanobubbles, which are trapped inside the globule and coalescence into a single bubble as a result; the molten state containing the NPs forms a spherical shell to minimize the surface energy. The absorption spectra are de-convoluted into three peaks, which are attributed to the hybridization between anti-bonding and bonding SPR modes of individual nanoshells.