Imaging two-dimensional materials at the nanoscale: insights, challenges, opportunities, and advanced techniques in tip-enhanced spectroscopy.

The nanoscale imaging of two-dimensional (2D) materials is critical for understanding their fundamental properties and potential uses in novel technological applications. Tip-enhanced spectroscopic (TES) studies on 2D materials have thus far been very fruitful, discovering heterogeneities once invisible to conventional imaging, and demonstrating light-matter interactions with the potential for new avenues in opto-electronic material control. Recent advances in this domain have pushed the boundaries of TES and its capabilities. Optimized fabrication methods, improved measurement systems, and innovative nano-optical techniques are all being actively demonstrated, providing excitement for future science approaching the horizon. This review serves to highlight new developments for advanced techniques in TES, discussing the state of TES on 2D materials and how it has shaped a need for such developments. Challenges in this domain that continue to linger will be discussed, as well as opportunities that remain waiting to be explored.