Single Type of Nanocavity Structure Enhances Light Outcouplings from Various Two-Dimensional Materials by over 100-Fold

In this study we developed a method, using a simple two-layer nanocavity structure, to significantly enhance light outcoupling from two-dimensional (2D) materials. Because the surface electric fields (E-fields) of the nanocavities were enhanced greatly over ultrabroadband regimes, the excitation of various 2D materials with laser light and their Raman and photoluminescence (PL) light emissions were all enhanced dramatically while maintaining band-to-band ratios and peak positions precisely. At the same time, the optical visibility of the 2D materials was also enhanced significantly over a broad spectral regime. Using a single type of Ag/SiO2 nanocavity structure, we obtained a 475-fold, equal enhancement in the intensities of the main Raman peaks of single layer graphene (SLG) and more than a 350-fold increase in the intensities of both the Raman and PL signals of single-layer tungsten disulfide (WS2). Notably, the light outcouplings of these 2D materials were enhanced dramatically without any spectral distortion generated by the nanocavity. Moreover, a nanocavity structure prepared from a nonplasmonic metal reflector also enhanced the light outcoupling from 2D materials by over 200-fold. Combined with Raman and PL spectroscopy, such simple nanocavity structures appear to have great applicability for precise and reliable investigations, providing abundant structural information, of a variety of 2D materials.