Tuning the plasmon shift and local electric field distribution of gold nanodumbbell: The effect of surface curvature transition from positive to negative

The localized surface plasmon resonance (LSPR) properties and local electric field distributions of the gold nanodumbbell are theoretically studied by using the finite-difference time-domain (FDTD) calculation. The decrease of both positive curvature radius in the spherical end and the negative curvature radius in the midsection results in the absorption peak corresponding to longitudinal plasmon mode red shifts distinctly. However, the transverse plasmonic absorption peak is not sensitive to the change of the curvature radii. The physical mechanism has been illuminated by studying the shape transformation dependent local field distribution between nanorod and nanodimer. It has been found that the decrease of the radii of curvature leads to the dumbbell-shaped particle transforming to a dimer-like structure, while the change in inter-particle plasmon coupling results in the “hot spots” of the local field migrating from the spherical ends to the midsection of the particle. There is an associated red shift of longitudinal LSPR. These results indicate that the transition of surface curvature between positive and negative greatly affects the surface charge distribution, local field enhancement and plasmon coupling.