21 research outputs found
Extrinsic localized excitons in patterned 2D semiconductors
We demonstrate a new localized excitonic state in patterned monolayer 2D
semiconductors. This state is not associated with lattice disorder but is
extrinsic, i.e. results from external molecules on the material surface. The
signature of an exciton associated with that state is observed in the
photoluminescence spectrum after electron beam exposure of several 2D
semiconductors. The localized state, which is distinguished by non-linear power
dependence, survives up to room temperature and is patternable down to 20 nm
resolution. We probe the response of the new exciton to the changes of electron
energy, nanomechanical cleaning, and encapsulation via multiple microscopic,
spectroscopic, and computational techniques. All these approaches suggest that
the state does not originate from irradiation-induced structural defects or
spatially non-uniform strain, as commonly assumed. Instead, we show that it is
extrinsic, likely a charge transfer exciton associated with the organic
substance deposited onto the 2D semiconductor. By demonstrating that structural
defects are not required for the formation of localized excitons, our work
opens new possibilities for further understanding of these states and using
them for example in chemical sensing and quantum technologies