Gap-Surface Plasmon-Enhanced Photoluminescence of InSe

2D materials, with distinct characteristics compared to their conventional bulk counterparts, have been a popular topic in various optoelectronic research fields. Herein, indium selenide (InSe), a monochalcogenide van der Waals layered semiconductor, which has been studied due to its thickness dependent optical characteristics is explored. For InSe to be used as a versatile light source, enhancing the emission of InSe is required. Here, enhanced photoluminescence (PL) from multi-layer InSe is demonstrated using a gap plasmon induced between Ag nanocube dimer and an Au substrate. Such plasmonic structures support multiple resonances, one of those overlapping with InSe's band edge PL emission. The calculated Purcell factor shows a 200-fold increase on the short edge of nanocube dimers. Experimentally, PL enhancement of 6-fold is demonstrated at room temperature. In addition, a method for determining the thickness of 2D materials via dark-field spectroscopy using white light illumination is shown. This study paves the way for the incorporation of 2D InSe into nanophotonic structures.