Strong magnetic resonances and largely enhanced second-harmonic generation of colloidal MoS 2 and ReS 2 @Au nanoantennas with assembled 2D nanosheets.

Colloidal disk-like and sphere-like MoS ₂ nanoantennas are synthesized. They consist of curly and interlaced 2D nanosheets. The resonance peak of the MoS ₂ nanoantennas can be tuned from 500 to 900 nm by adjusting the size and shape. The strong magnetic and electric resonances of the dielectric antennas are revealed by theoretical calculations with Mie theory. The second harmonic generation (SHG) of the exfoliated nanosheets and the synthesized nanodisks and nanospheres is investigated and compared by scanning the excitation laser wavelength. SHG enhancement of 52 fold is observed for the spherical nanoantennas at 400 nm, which is attributed to the nanoantenna-enhanced two-photon resonance excitation of the D exciton of MoS ₂ monolayers. Moreover, ReS ₂ @Au plasmon-dielectric hybrid nanoantennas are also synthesized. The SHG of Au nanoparticles is enhanced 8.5 times by the coupling of the two types of nanoantennas. This new class of optical nanoantennas consisting of 2D materials and exhibiting unique linear and nonlinear optical responses will bring promising applications ranging from nonlinear photonics to photochemistry.