Abstract: The "hot spot" effect has been attracted considerable attention in surface enhanced spectroscopy and relevant fields, especially for the controllable fabrication of the dynamic "hot spot" by using the size and excitation wavelength dependent transfer effect. Herein, the coupling system of spherical dimer of gold nanoparticles and gold plate is theoretically simulated by finite element method (FEM), and the effects of excitation wavelengths and nanoparticle sizes on the electromagnetic field enhancement at different gaps of the system are systematically investigated. The results demonstrated that the two modes of surface plasmon resonance was observed. As the size of nanoparticle is 30 nm and the excitation wavelength is 450 nm~535 nm and 670 nm~950 nm, the two plasmon resonance modes were mainly dominated by a cooperative effect, and “hot spot” mainly located in the particle-particle gap. As the size of nanoparticles was increased to 85 nm or even 105 nm, a competition effect between the two plasmon resonance modes was occurred for the excitation wavelengths of 670 nm~695 nm and 725 nm~755 nm. It resulted in the transformation of “hot spot” from particle-particle to particles-gold plate gaps successfully. It was anticipated that the theoretical simulation provided an alternative approach for control and transfer on the “hot spot” and it was beneficial to design and fabricate the substrate with high performance of surface enhanced optical effect.

Key words: “Hot spots”, Surface plasmon resonance, Au nanoparticle dimer, Competition effect, Transfer effect