MRS Meetings and Events

 

NM02.06.02 2022 MRS Spring Meeting

Directing Exciton Propagation in Monolayer TMDCs Through Patterned Dielectric Substrates

When and Where

May 11, 2022
8:45am - 9:00am

Hawai'i Convention Center, Level 3, 303B

Presenter

Co-Author(s)

Jonas Zipfel1,Boyce Chang1,Daria Blach2,Kenji Watanabe3,Takashi Taniguchi3,Edward Barnard1,Ricardo Ruiz1,Archana Raja1

Lawrence Berkeley National Laboratory1,Purdue University2,National Institute for Materials Science3

Abstract

Jonas Zipfel1,Boyce Chang1,Daria Blach2,Kenji Watanabe3,Takashi Taniguchi3,Edward Barnard1,Ricardo Ruiz1,Archana Raja1

Lawrence Berkeley National Laboratory1,Purdue University2,National Institute for Materials Science3
The formation of tightly bound excitons, dominating the electro-optical response of two-dimensional semiconductor materials, such as monolayers of transition metal dichalcogenides (TMDCs), have attracted attention in the solid-state community for the past decade due to a plethora of novel physical properties connected to their strong light-matter coupling, high binding energies and intriguing spin-valley physics. Yet, the local control of exciton propagation and the manipulation of their transport has manifested as a particular challenge so far. Although excitons in monolayer TMDCs are known to be quite mobile with observed diffusion coefficients up to 1-3 cm<sup>2</sup>/s [1,2], their lack of charge precludes common ways of creating directed transport by applying an electrical potential gradient. However, an alternative route for creating such potentials may be found within their inherent two-dimensional nature since the electrostatically bound excitons are particularly susceptible to changes in their local dielectric environment [3,4]. This opens a novel and convenient way to tailor the excitonic energy landscape in a controlled and non-invasive way, envisioning directed exciton propagation along a well-defined energy pathway created from dielectric patterns obtained through artificial, nanostructured substrates.<br/>In our work we couple monolayers of WSe<sub>2</sub> to nano-patterned substrates with abrupt, repetitive changes in their dielectric constants created through ultra-sharp interfaces of alternating materials. The structures are conveniently created via block copolymer lithography and subsequent atomic layer deposition on large areas, easily scalable to 100's of micrometers in either direction, while achieving nano-pattern dimensions as small as 20nm. From a wide palette of possible patterns that can be fabricated, our initial, prototypical substrates of choice are 50nm interdigitated oxide/air line-grids. This pattern transfers into steep and narrow potential trenches in the excitonic energy landscape through distinct, local dielectric screening, creating a single preferred direction for the excitons to propagate along. We employ time and spatially resolved micro-spectroscopies to systematically monitor exciton propagation across this engineered energy landscape via the phonon-assisted PL emission from long-lived states at cryogenic temperatures.<br/>[1] N. S. Ginsberg and W. A. Tisdale, Annual Review of Physical Chemistry <b>71</b>, 1 (2020); 10.1146/annurev-physchem-052516-050703.<br/>[2] K. Wagner<i> et al.</i>, Physical Review Letters <b>127</b>, 76801 (2021); 10.1103/PhysRevLett.127.076801.<br/>[3] D. Rhodes, S. H. Chae, R. Ribeiro-Palau, and J. Hone, Nature Materials <b>18</b>, 541 (2019); 10.1038/s41563-019-0366-8.<br/>[4] M. I. B. Utama<i> et al.</i>, Nature Electronics <b>2</b>, 60 (2019); 10.1038/s41928-019-0207-4.

Keywords

dielectric properties | nanostructure | van der Waals

Symposium Organizers

Archana Raja, Lawrence Berkeley National Laboratory
Diana Qiu, Yale University
Arend van der Zande, University of Illinois at Urbana Champaign
Stephen Wu, University of Rochester

Publishing Alliance

MRS publishes with Springer Nature