CTAB-assisted exciton-to-trion conversion for valley contrast enhancement

In this study, we experimentally demonstrate the enhancement of valley contrast through exciton-to-trion conversion at room temperature. Cetyltrimethylammonium bromide (CTAB), a well-known organic molecule commonly used in the intercalation of 2D materials, is shown to facilitate electron transfer to a tungsten disulfide (WS₂) monolayer through chemical doping. Specifically, a 1 mM CTAB solution is drop-casted onto the WS₂ monolayer, inducing the conversion from exciton to trion emission within the material. The introduction of a trion-abundant environment in WS₂ results in a notable increase in valley contrast without the application of external bias. To the best of our knowledge, this study represents the first demonstration of valley contrast enhancement through the chemical doping of CTAB. Consequently, this research provides a detailed exploration of liquid-controlled electron doping from the perspective of valleytronics.