Subnanometric control of coupling between WS$_2$ monolayers with a molecular spacer

TL;DR

This study demonstrates how a spin-cast organic molecular spacer can precisely control interlayer coupling in WS$_2$ monolayer heterostructures, enabling tunable optical properties and potential applications in nanoscale devices.

Contribution

It introduces a novel method of using molecular spacers to achieve subnanometric control over interlayer interactions in 2D heterostructures.

Findings

Interlayer coupling can be tuned by adjusting molecular spacer thickness.

Valence-band splitting depends on spacer thickness, affecting exciton energies.

Molecular spacers enable precise control over optical properties of monolayer stacks.

Abstract

Stacking monolayer semiconductors into heterostructures allows for control of their optical and electronic properties, offering advantages for nanoscale electronics, optoelectronics, and photonics. Specifically, adding a thin spacer between monolayers can yield bulk materials that retain interesting monolayer properties, such as a direct bandgap and a high emission quantum efficiency. The interaction mechanisms between monolayers, including interlayer coupling, charge transfer, and energy transfer, might be tuned through subnanometric control over the spacer thickness. Traditional spacer materials like bulk oxides or other layered materials can suffer from poor material interfaces or inhomogeneous thickness over large areas. Here, we use a spin-cast organic molecular spacer to adjust interlayer coupling in WS$_2$ monolayer stacks. We vary the molecular spacer thickness to tune the interlayer distance, significantly altering the optical properties of the resulting organic-inorganic heterostructures. Additionally, we demonstrate a dependence of the valence-band splitting on molecular spacer thickness manifested as a change in the energy difference between A and B excitons resulting from spin-orbit coupling and interlayer interactions. Our results illustrate the potential of molecular spacers to tailor the properties of monolayer heterostructures. This accessible approach opens new routes to advance atomically thin devices and could enable sensing technologies at the subnanometer scale.