Probing the Role of Plasmonic Enhancement in Quantum Emission in Single-Layer WSe₂ Nanoribbons on Au Nanocones

Transition metal dichalcogenides (TMD) are a class of 2D semiconductors that host intense light-matter interactions. Using chemical vapor deposition with a nickel catalyst, single-layer (1L) TMD nanoribbons are grown that have distinct structural and electronic properties to their 2D crystallites because of their quasi-1D geometry. When 1L-WSe₂nanoribbons are draped over arrays of Au nanocones, strain-induced exciton localization occurs. At these strained sites, the photoluminescence intensity is dramatically increased at room temperature and single-photon emitters emerge at cryogenic temperatures. In addition to the effect of strain, due to the subwavelength size of the Au nanocones, a localized surface plasmon resonance (LSPR) is present that can provide Purcell enhancement of the emitters as well as local field enhancement of the excitation field at the apex of the nanocone. COMSOL finite element modeling of the nanocones shows the resonance of the LSPR occurs at approximately 625 nm, which is ideal for excitation enhancement of strain-localized states near the cone apex. Here, we conduct excitation energy dependent spectroscopy and photoluminescence lifetime analysis to probe for signatures of both excitation enhancement and Purcell enhancement in the system. By sweeping the energy at which the strained regions of the 1L-WSe₂nanocones are excited and collecting the integrated intensity of the photoluminescence, we obtain an excitation spectra of many strain-localized emitters. This excitation spectrum and the statistical distribution of excited state lifetimes are then compared to both unstrained 1L-WSe₂ as well as locally strained 1L-WSe₂ emitters that do not have plasmonic stressors. By comparing these systems, we can identify signatures of nearfield excitation enhancement as well as Purcell enhancement. These studies provide insight into how the combined effects of strain and nanoplasmonics can increase the brightness of 1L-WSe₂ nanoribbon-based quantum light sources for application in a BB84 quantum key distribution protocol testbed.