Studies of 2D Materials by Scanning Tunneling Microscopy Associated with a Light Detector

2D materials are been considered for several applications due to their new and promising mechanical, electronic and optical properties. Scanning Tunneling Microscopy (STM) is a great tool to investigate their morphology and electronic structure by means of imaging (which reaches atomic resolution) and spectroscopy. Adding a light detector to the STM provides access to the light emission that is triggered by the very local tunnel current (usually called STM induced light emission or luminescence, STML). We have developed a new light collection device compatible with an adapted low temperature UHV STM. [1] This device is based on an off axis parabolic mirror and it is designed to have high collection efficiency while keeping high spectral resolution.<br/>Using our STM equipped with such device, we studied WSe2 mechanically transferred to gold, to HOPG, and to ITO. These conducting substrates affect this transition metal dichalcogenide (TMD) in different ways.[2] After the mechanical transfer, a water interlayer isolates the TMD from gold and from ITO, but such interfacial layer was not observed for HOPG. After an annealing, light is severally quenched on the TMD over gold while on ITO the TMD preserves its emission and becomes highly doped. The TMD on HOPG was not significantly doped but was also quenched. Another study used HOPG as a support to epitaxial growth of hexagonal boron nitride (h-BN). This substrate preserved h-BN properties and both the electronic gap and light emission from defects could be determined.[3]<br/>References:<br/>[1] Ricardo Javier Peña Román et al. Review of Scientific Instruments 93, 043704, 2022.<br/>[2] Ricardo Javier Peña Román et al. Nanoscale, 12, 13460-13470, 2020.<br/>[3] Ricardo Javier Peña Román et al. 2D Mater. 8 044001, 2021.<br/>This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Projects 14/23399-9 and 2021/06893-3.