Redox Photochemistry on Van Der Waals Surfaces for Reversible Doping in 2D Materials

Abstract

Despite the van der Waals (vdW) surfaces are usually chemically inert, un‐destructive, scalable, and reversible redox reactions are introduced on the vdW surfaces of 2D anisotropic semiconductors ReX2 (X = S or Se) facilitated by simple photochemistry. Ultraviolet (UV) light (with humid) and laser exposure can reversibly oxidize and reduce rhenium disulfide (ReS2) and rhenium diselenide (ReSe2), respectively, yielding a pronounced doping effect with good control. Evidenced by Raman spectroscopy, dynamic force microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy, the grafting and removal of covalently functionalized oxygen groups on the perfect vdW surfaces are confirmed. The optical and electrical properties can be thereby reversibly tunable in wide ranges. Such optical direct‐writing and rewritable capability via solvent/contaminant‐free approach for chemical doping are compelling in the coming era of 2D materials.

Precision Chemistry in Two-Dimensional Materials: Adding, Removing, and Replacing the Atoms at Will

“…Such grafted oxygen can act as a hole donor to ReS 2 , resulting in p-doping behavior. 5 Similar chemical grafting was also observed in bilayer graphene after exposure to XeF 2 , as evidenced by cross-sectional HRTEM, and F atoms were found to be bound to each graphene layer from both sides after fluorination. 10…”

“…The hole-doping effect is evidenced by the observation of ambipolar charge-transport behavior in the FET configuration devices. 5…”

“…(b) Schematic illustration of the reversible photochemistry method, showing the UV treatment in a moist environment and the laser irradiation recovery process. (Adapted from ref . Copyright 2021 Wiley.…”

“…To address such an issue, another way is to graft the dopant atoms onto the van der Waals surface through a gentler procedure instead of accessing the 2D lattice. For instance, under ultraviolet light irradiation with controlled humidity, highly oxidative O 3 and oxygen-related radicals can be created and quickly react with the 2D ReS 2 or ReSe 2 lattice, resulting in the grafting of oxygen radicals on the van der Waals surface, which would act as a hole donor to the 2D materials, as evidenced by the p-doping behavior in the field-effect transistor device results . More interestingly, a laser annealing treatment can be used to remove such covalent oxidation on the vdW surface without generating any atomic defects, and the optical and electric transport performance can simultaneously recover to the pristine status (Figure b).…”

“…While these oxygen radicals are removed by laser annealing, the current and mobility show reliable recovery. The hole-doping effect is evidenced by the observation of ambipolar charge-transport behavior in the FET configuration devices …”