Probing excitons in 2D semiconductors using an STM coupled to an optical microscope
Résumé
We introduce the use of a scanning tunneling microscope (STM) coupled to an optical microscope as a local spectroscopic probe of excitons (electron-hole pairs bound by Coulomb interaction) in two-dimensional (2D) semiconductors. The local excitation of the excitonic luminescence of 2D semiconductors using the tunnel current under the tip of an STM has long been sought after, in particular to electrically control the emission of single photons from point defects in these materials [1,2]. The excitation and emission mechanisms may involve a combination of energy transfer and injection of charge carriers into the electronic bands of the semiconductor, the creation of excitons, and processes of internal conversion to various excitonic species and complexes. We report on the observation of STM-induced excitonic luminescence (STM-L) of monolayer transition metal dichalcogenides on a transparent conductive substrate [3]. We compare the results with photoluminescence measurements to identify the emission mechanism. Thus, we demonstrate a new technique to study the excitonic and optoelectronic properties of 2D semiconductors and their heterostructures on the nanometer scale.
[1] N. Krane, et al., “Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)”. Nano Lett. 16, 5163 (2016).
[2] B. Schuler, et al., “Electrically driven photon emission from individual atomic defects in monolayer WS2”, Sci. Adv. 6, 38 (2020).
[3] D. Pommier, et al., “Scanning tunneling microscope-induced excitonic luminescence of a two-dimensional semiconductor.” Phys. Rev. Lett. 123, 027402 (2019)