Local temperature control of hybrid plasmonic nano-antennas

Local enhanced heat generation in plasmonic nano-antennas caused by the finite conductivity of metals can cause local super-heating areas, a disadvantage to the normal work of nano-antennas. In this work, an approach to simultaneously enabling near-field intensity enhancement at the operating wavelength in the visible and local operating temperature control of hybrid plasmonic antennas is studied. Results show that the operating temperature for the pure Au or Ag nanoparticles (NP) is very high at a low intensity of incident light in vacuum, owing to a negligible thermal radiation dissipation in the infrared region. Thus, different dielectric spheres (i.e., Al₂O₃, SiO₂, and TiO₂) were introduced to enhance the thermal radiation dissipation of the hybrid plasmonic antennas. The hybrid antennas obtained greater absorption ability and near-field enhancement compared to pure plasmonic NPs. Additionally, the hybrid antennas showed great thermal emittance capability compared to pure plasmonic NPs. The Ag–TiO₂ hybrid antenna obtained the lowest temperature increase among the three hybrid systems while maintaining the highest near-field enhancement. The sharp absorption peaks or near-field enhancement spectra of the Ag–TiO₂ hybrid antennas can be attributed to the excitation of the whispering gallery mode coupled with the surface plasmon mode, resulting in an enhanced absorption or near-field enhancement. The absorption cross section, the near-field intensity enhancement, and the thermal emittance of the Ag–TiO₂ hybrid antennas increase with the size of the TiO₂ sphere. A saturation value exists for the TiO₂ sphere size to reduce the temperature increase at a specific intensity of incident light. In addition, air convection with the consideration of size effect also can further reduce the operating temperature of the hybrid antenna.