image: (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) Dark-field scattering spectrums of above gap-mode nanocavity with various thicknesses of PE layers. (c) The dark-field spectrum of fixed nanocavities was measured with different positions of MoS₂. view more
Credit: by Bao-Ying Wen, Jing-Yu Wang, Tai-Long Shen, Zhen-Wei Zhu, Peng-Cheng Guan, Jia-Sheng Lin, Wei Peng, Wei-Wei Cai, Huaizhou Jin, Qing-Chi Xu, Zhi-Lin Yang, Zhong-Qun Tian, and Jian-Feng Li
Light-matter interaction in plasmonic nanocavities has attracted great attention due to its fundamental importance and enormous potential applications in nanophotonics. Recently, a widespread interest focused on the nanoscale spatial distributions of light-matter interaction whose coupling modes mainly depend on two system compositions’ characteristics: optical cavities and emitters. Meanwhile，the gap-mode plasmonic nanocavity has a proper mode volume, and can manipulate the light at the nanoscale and respond quickly to the changes in the system, so it has attracted extensive attention of researchers. However, the nanogap in such systems is extremely narrow and usually (sub)nanometer scale. Presently, few studies on the vertical distribution of the actual system coupling in plasmonic nanocavities.
In a new paper published in Light Science & Application, a team of scientists, led by Professor Jian-Feng Li from Department of Physics, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China and co-workers have 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. They established a system with the Rabi splitting of 62 meV by coupling of the A exciton for MoS2 and gap-mode plasmonic nanocavities. Then, using the polyelectrolyte as the spacer layer, MoS2 was embedded in the different lon-gitudinal positions at nanoscale of coupling strength in nanocavity for accu-rately probing the different longitudinal distribution. Further, they found that the photoluminescence enhancement factor also changes with the longitudinal distribution. And they achieved the largest enhancement factor of photolu-minescence for 2800 times in this structure, which is comparable with other works. This novel method provides insight into the light-matter interaction and a possible strategy for the rational design of plasmonic nanocavities utilizing coupling processes. We believe that this research is appealing to a broad range of scientific communities in the fields of nanophotonics and provide potential guiding significance for future photonic devices.
The nanogap of gap mode plasmonic nanocavities is very small and often is (sub)nanoscale, there is no effective measurement method, so it is extremely difficult to detect distribution within the nanogap. These scientists develop a novel method to probe the longitudinal distribution of this nanogap:
“We used polyelectrolyte as spacer and monolayer MoS2 as emitter to embed the nanoscale coupling into different longitudinal positions of the plasmon nanocavity to accurately detect the longitudinal positions at nanoscale for coupling strength in nanocavity.”
“We inserted MoS2 into the gap-mode plasmonic nanocavities structure. By adjusting the thickness of the polyelectrolyte layer, to obtain various plasmon resonance frequencies. Meanwhile, the normalized dark-field scattering spectrums show peaks splitting with a characteristic dip at the wavelength of the A excitons (black line), which indicates the coherent coupling with plasmon-exciton interaction. We also found that under the fixed nanocavities, the coupling strength is sensitive to the position of the exciton, and the spatial resolution is ~1 nm. The difference in dark-field splitting degree when MoS2 is located at different positions in nanocavities implies the different coherent interaction strength between excitons and plasmons in the nanocavity. At the same time, we also studied the photoluminescence at different positions of this system and found that when the coupling strength of this system is the largest, the enhancement factor is the highest, reaching 2800 times. It is further proved that the influence of the strength of the plasmon-exciton interaction on the system's luminous ability.”
“This work provides insight for further exploration and regulation of the interaction between excitons and plasmons in the plasmonic nanocavity. And we believe that this research is appealing to a broad range of scientific communities in the fields of nanophotonics and provide potential guiding significance for future photonic devices.” the scientists forecast.
Journal
Light Science & Applications