Manipulating the light-matter interactions in plasmonic nanocavities at 1 nm spatial resolution

Abstract

The light-matter interaction between plasmonic nanocavity and exciton at the sub-diffraction limit is a central research field in nanophotonics. Here, we demonstrated the vertical distribution of the light-matter interactions at ~1 nm spatial resolution by coupling A excitons of MoS₂ and gap-mode plasmonic nanocavities. Moreover, we observed the significant photoluminescence (PL) enhancement factor reaching up to 2800 times, which is attributed to the Purcell effect and large local density of states in gap-mode plasmonic nanocavities. Meanwhile, the theoretical calculations are well reproduced and support the experimental results.

Fig. 1. The characterization of gap-mode plasmonic nanocavity.

a The schematic diagram of the gap-mode nanocavity, which consists of a Au film, a Ag nanocube, a monolayer MoS₂, and PE spacer layers. b Scanning electron microscope (SEM) image of Ag nanocubes with 80 ± 3 nm (scale bar 100 nm). The inset is a transmission electron microscope (TEM) image of an Ag nanocube(scale bar 20 nm). c Bright-field image and d the corresponding dark-field scattering image of monolayer MoS₂ with gap-mode nanocavities (scale bar 5 μm). The inset is the AFM height profile of monolayer MoS₂ on PE-coated Au film

Fig. 2. The dark-field scattering spectrums study of plasmon-exciton system with different thicknesses of PE layers.

a Dark-field scattering spectrums of above gap-mode nanocavity with various thicknesses of PE layers. b The energy of the upper branch hybrid state energy (red) and the lower branch hybrid state energy (blue) as a function of detuning

Fig. 3. The dark-field scattering spectrums study and theoretically calculation for electromagnetic field distribution of plasmon-exciton system with the same thickness PE layers.

a Schematic diagram of MoS₂ at the above nanocavities with the thickness of 5 PE layers. b The dark-field spectrum of nanocavities was measured with different positions of MoS₂. c Distribution of the x, y, z-component of the electric field in the XY planes situated at 5th position in Fig. 3a with MoS₂ is background index-only material, normalized to the incident electric field

Fig. 4. The PL spectrum study of monolayer MoS₂ at the above gap-mode nanocavity with the same thickness of PE layers.

a PL spectra of monolayer MoS₂ with (red) and without (black) gap-mode nanocavity. b The blue line is the enhancement factor of the PL at different positions; the red line is the LDOS at different positions