Directing exciton propagation in monolayer TMDCs through patterned dielectric substrates*

The local control of exciton transport in monolayer TMDCs has manifested as a particular challenge so far. Although these excitons are known to be quite mobile  [1,2], their lack of charge precludes common ways to create directed transport via electrical potentials. An alternative route to this may be found in their inherent 2D nature since these excitons are particularly susceptible to their local dielectric environment [3,4]. This opens a novel way to tailor the excitonic energy landscape, envisioning directed exciton propagation along a defined energy pathway created from dielectric patterns through nanostructured substrates.

Here, we couple monolayers of WSe₂ to nano-patterned substrates with abrupt changes in their dielectric constants from ultra-sharp interfaces of alternating materials. The structures are created via block copolymer lithography and atomic layer deposition on large areas, scalable to 100’s of µm in either direction, with pattern dimensions down to 20nm. Our substrates of choice are 50nm interdigitated oxide/air line-grids. This transfers into narrow potential trenches in the excitonic energy landscape through distinct, local dielectric screening, creating a preferred direction for exciton propagation. We use time and spatially resolved micro-spectroscopies to monitor exciton transport across this engineered energy landscape via the phonon-assisted PL emission from long-lived states at cryogenic temperatures.

[1]   Annual Review of Physical Chemistry 71, 1 (2020).

[2]   Physical Review Letters 127, 76801 (2021)

[3]   Nature Materials 18, 541 (2019)

[4]   Nature Electronics 2, 60 (2019)