Cover story: Li SS, Fang YN, Wang JF. Control of light–matter interactions in two- dimensional materials with nanoparticle-on-mirror structures. Opto-Electron Sci 3, 240011 (2024).

Light–matter interactions in two-dimensional (2D) materials have aroused intense interest in the past decades. Nanoparticle-on-mirror (NPoM) structures, constructed from plasmonic nanoparticles on a smooth metal film with a nanospacer in between, offer a good platform for enhancing light–matter interactions in diverse 2D materials with atomic thicknesses. 

The NPoM structure can confine optical fields with surprisingly low loss and with volumes below 1 cubic nanometer, which is highly desired for various optical modulation. In addition, the nanocavity in the NPoM structure can be well defined by controlling the thickness of sandwiching 2D materials. This precise control has led to the observation of various intriguing phenomena in the hybrid system. For example, plasmon–exciton coupling in the hybrid structure can be tailored across the weak to ultrastrong coupling regimes, with room-temperature splitting features in the photoluminescence spectra. The ultraconfined plasmonic field combined with the atomic spacing also enables rich nonlinear optical effects and quantum tunneling in relaxed conditions. Future studies on integrating NPoM structures with diverse 2D materials will certainly deepen our understanding of the unique optoelectronic processes in 2D materials and provide enormous opportunities for designing devices to be employed in solar energy harvesting, sensing, optics/optoelectronics, and quantum nanophotonics.