Fig. 1. Schematic diagram of a dielectric/metal core-shell placed above a gold film.

Fig. 2. (a) Scheme of plasmon hybridization picture of the core-shell on gold film; (b) scattering spectrum of core-shell particles on gold film. The inset of panel (b) shows the z-component of the electric field in xy plane.

Fig. 3. (a) Longitudinal optical force F_z exerted on the core-shell on gold film. The electric-field intensity enhancement factor map of the core-shell on gold film at wavelengths of (b) 540, (c) 670, (d) 790, and (e) 830 nm, respectively.

Fig. 4. (a) Scattering spectra of the core-shell on gold film; (b) longitudinal optical force spectra of the core-shell on gold film; (c) maximum longitudinal optical force and the average electric-field intensity enhancement factor as a function of gap size for the core-shell on gold film.

Fig. 5. (a) Scattering spectra of the core-shell on gold film; (b) longitudinal optical force spectra of the core-shell on gold film; (c) maximum longitudinal optical force as well as the average electric-field intensity enhancement factor as a function of dielectric core radius for the core-shell on gold film.

Fig. 6. (a) Scattering spectra of the core-shell on gold film; (b) longitudinal optical force spectra of the core-shell on gold film; (c) maximum longitudinal optical force and the average electric-field intensity enhancement factor as a function of index for the core-shell on gold film.