Nano and Sub-Micro Scale Optical Characterization of Transition Metal Dichalcogenide Nanoribbons by AFM-Optical Spectroscopy

Two-dimensional (2D) transition metal dichalcogenide (TMDC) nanoribbons have attracted significant interest recently due to their intriguing optical, magnetic, and electronic properties, all of which can be controlled by manipulating their edges and ribbon width via quantum confinement. The specific termination, structure, strain, or defects at the edges play crucial roles in shaping the characteristics of TMDC ribbons. For instance, MoS₂ exhibits distinct signals in second harmonic generation (SHG) for S-zigzag versus S-Mo Klain edges. However, understanding the correlation between optical properties and intricate ribbon edges is challenging largely due to the diffraction limits of conventional optical techniques. The integration of optical spectroscopy with an atomic force microscope (AFM) allows for nanoscale optical imaging by enhancing the optical signal through plasmonic confinement between the metallic AFM tip and the sample. The techniques could reveal more detail on the impact of the edge on the ribbons. In this study, we focus on optical nano-imaging of TMDC nanoribbons using tip-enhanced photoluminescence and second harmonic generation. Our observations reveal variations in emission energy across different locations on the ribbons, indicating the influence of defects and edges on photoexcited exciton and trion energies in TMDC ribbons. To delve deeper into the effects of ribbon edges, we conducted polarization-resolved SHG experiments both with and without the application of an external magnetic field. The results not only shed light on the influence of edges but also offer opportunities to tune and manipulate the optical and magnetic properties of these nanoribbons.