Plasmonic coupling behavior of Ag–SnO₂ nanoparticle dimers

Surface plasmons exhibit broad potential in nano optics, surface enhanced spectroscopy, and optoelectronic devices owing to their strongly localized electromagnetic field enhancement. Due to the difficulty in controlling nanometer scale interparticle spacing, experimental studies addressing plasmonic coupling mechanisms in metal semiconductor systems，particularly the impact of nanometer and sub nanometer scale separations on localized surface plasmon resonance (LSPR) remain scarce. In this study, the plasmonic properties of a single silver nanoparticle, silver nanoparticle dimers, and Ag-SnO₂ heterodimers were investigated using spherical aberration corrected electron microscopy combined with high energy resolution electron energy loss spectroscopy (EELS). The results show that the intrinsic surface plasmon resonance energy of an isolated silver nanoparticle is approximately 3.24 eV. As the nearest edge to edge distance in the dimer decreases to 0.60 nm, the dominant plasmon peak red shifts to 1.67 eV, indicating strong near-field coupling. For the Ag-SnO₂ heterodimer, the main resonance peak further red shifts to 1.09 eV, demonstrating that dielectric polarization and interfacial effects are crucial in regulating plasmon energy. These findings elucidate the synergistic modulation of plasmonic behavior by interparticle separation distance and the dielectric environment, providing experimental evidence that deepens the understanding of nanoparticle coupling mechanisms and offering guidance for the design and optimization of high sensitivity sensing, photocatalytic, and nano optical devices.