Raman enhancement of PTCDA on monolayer WSe₂

Monolayer transition metal dichalcogenide (TMD) semiconductors have garnered interest due to their direct band gap, strong excitonic effects, and valley optical selection rules. Organic semiconductors also host strongly bound excitons and allow for broadly tunable emission energies. Together, heterointerfaces of a molecular semiconductor adsorbed on a monolayer TMD are characterized by interesting effects including enhanced Raman scattering. These Raman enhancements are poorly understood but are attributed to different charge transfer mechanisms [1], [2], [3]. Here, we study a system of monolayer 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on WSe₂, chosen for its type-II band alignment. We performed low temperature Raman and photoluminescence spectroscopy and observe a large enhancement of the PTCDA Raman signal compared to monolayer PTCDA on SiO₂. The behavior of this Raman scattering is explored through electrostatic doping of the TMD and excitation energy dependence. Control over the Raman enhancement would yield new understanding of the Raman enhancement phenomena in these systems.
[1] C. Muehlethaler et al., ACS Photonics 3, 1164 (2016)
[2] Y. Lee et al., Chem. Mater. 28, 180 (2015)
[3] Y. Tan et al., Nano Lett. 17, 2621 (2017)