Nano-optical imaging of 2D TMD alloys

Two-dimensional transition metal dichalcogenides (2D TMDs) are the materials of recent interest due to many promising applications. Novel materials and devices are based on the heterostructures formed by 2D TMDs. Alloys formed at TMD heterojunctions may enhance or limit the applications. It is important to characterize their optoelectronic properties with nanoscale spatial resolution. Tip-enhanced photoluminescence (TEPL) and tip-enhanced Raman scattering (TERS) techniques were used to image various TMD (MoS₂, WS₂, MoSe₂, WSe₂) alloys and heterostructures revealing detailed nanoscale features. Conventional far-field photoluminescence (PL) and Raman imaging provides highly averaged information with spectral congestion. In contrast, the TEPL and TERS methods, not limited by diffraction, provide substantial information related to nanoscale optical properties of 2D materials with resolution down to a few nanometers. The variations in the nanoscale optical properties correlating with the structural variation can provide a better understanding of the 2D TMD materials for the future development of highly efficient, flexible, lightweight optoelectronic devices.