Exciton tuning in monolayer WSe 2 via substrate induced electron doping.

We report large exciton tuning in WSe 2 monolayers via substrate induced non-degenerate doping. We observe a redshift of ∼62 meV for the A exciton together with a 1-2 orders of magnitude photoluminescence (PL) quenching when the monolayer WSe 2 is brought in contact with highly oriented pyrolytic graphite (HOPG) compared to dielectric substrates such as hBN and SiO 2 . As the evidence of doping from HOPG to WSe 2 , a drastic increase of the intensity ratio of trions to neutral excitons was observed. Using a systematic PL and Kelvin probe force microscopy (KPFM) investigation on WSe 2 /HOPG, WSe 2 /hBN, and WSe 2 /graphene, we conclude that this unique excitonic behavior is induced by electron doping from the substrate. Our results propose a simple yet efficient way for exciton tuning in monolayer WSe 2 , which plays a central role in the fundamental understanding and further device development.