All-Optical Reconfigurable Excitonic Charge States in Monolayer MoS₂

Abstract

Excitons are quasi-particles composed of electron–hole pairs through Coulomb interaction. Due to the atomic-thin thickness, they are tightly bound in monolayer transition metal dichalcogenides (TMDs) and dominate their optical properties. The capability to manipulate the excitonic behavior can significantly influence the photon emission or carrier transport performance of TMD-based devices. However, on-demand and region-selective manipulation of the excitonic states in a reversible manner remains challenging so far. Herein, harnessing the coordinated effect of femtosecond-laser-driven atomic defect generation, interfacial electron transfer, and surface molecular desorption/adsorption, we develop an all-optical approach to manipulate the charge states of excitons in monolayer molybdenum disulfide (MoS2). Through steering the laser beam, we demonstrate reconfigurable optical encoding of the excitonic charge states (between neutral and negative states) on a single MoS2 flake. Our technique can be extended to other TMDs materials, which will guide the design of all-optical and reconfigurable TMD-based optoelectronic and nanophotonic devices.

Optical Modification of Two-Dimensional Materials: From Atomic to Electronic Scale

“…from the surrounding environment can also provide excessive charges, leading to ∼10 times decrease of the recombination rate of excitons in monolayer MoS 2 . 141 Regarding this problem, Huang et al 81 used a fs laser to reversibly switch the excitons in monolayer MoS 2 between the Via the modulation of exciton state, the laser can indirectly influence other physical properties of 2D materials, for example, the electroabsorption and magnetism modulation. 142,143 Recently, Xu et al reported the tuning of spin−spin interactions between moire-trapped carriers through optical excitation, which yielded ferromagnetic order in WS 2 /WSe 2 moireś uperlattices.…”

“…from the surrounding environment can also provide excessive charges, leading to ∼10 times decrease of the recombination rate of excitons in monolayer MoS 2 . Regarding this problem, Huang et al used a fs laser to reversibly switch the excitons in monolayer MoS 2 between the neutral and charged states in an ambient environment. Figure (c) summarizes the PL evolution the MoS 2 monolayer under fs laser irradiation.…”

“…The excitation of electron under light illumination can be harnessed in both optoelectronic and nanophotonic devices, e.g., single photon source, − TMD laser − and photodetector. − Moreover, the light-driven coherent oscillation of free electron in graphene allows excitation of surface plasmons in the mid-infrared regime, leading to the creation of atomic-thin plasmonic materials. − On the other hand, a lot of new physical and chemical phenomena are observed during the light–2D materials interaction. For example, the magnetic-optical Kerr effect, − laser tuning of the excitonic state, , photoconductivity, , and laser-driven phase transition. ,, The insightful understanding of such phenomena allows us to modify the morphology, the composition, and the atomic structure of 2D materials. This provides new strategies to manipulate the optical, thermal, or electrical properties of 2D materials on demand and further extend their applications.…”

Super-Resolution Exciton Imaging of Nanobubbles in 2D Semiconductors with Near-Field Nanophotoluminescence Microscopy

“…Two-dimensional (2D) semiconductors, such as transition metal dichalcogenides (TMDs) with the chemical formula MX 2 (where M = Mo, W, Ru, ... and X = S, Se, Te, ...), 1,2 have emerged as promising nanomaterials for next-generation chipscale optoelectronic devices due to their fascinating properties such as indirect-to-direct bandgap transition, 1 strong Coulomb interaction, 3 and valley-specific circular dichroism. 4 Since the bandgaps of monolayer TMDs (1L-TMDs) are sensitive to the dielectric environment, 5,6 mechanical strain, 7 and external perturbation, 8 such 2D semiconductors provide ideal platforms for manipulating light−matter interaction at the nanoscale, which has spawned many applications such as solar cells, 9 light-emitting devices, 10 and photodetectors. 11 Nowadays, the industrial production of 2D semiconductors is becoming possible with the development of large-scale production techniques such as chemical vapor deposition (CVD).…”

Nanoscale Manipulation of Exciton–Trion Interconversion in a MoSe2 Monolayer via Tip-Enhanced Cavity-Spectroscopy

“…Recently, the phenomenon of exciton-to-trion conversion in 2D semiconductors has attracted significant attention. − Trions offer distinct advantages over neutral excitons for optoelectronic device applications. Trions are responsive to external bias, enabling electrical control over their spatial distribution, a feature that can be harnessed in the development of trion-based integrated circuits. − Additionally, trions have relatively shorter lifetimes and lower binding energies compared to excitons, making them conducive to the development of highly efficient photovoltaics, such as trion-based photocurrent devices and solar cells. − To enhance the rate of exciton-to-trion conversion and improve the performance of trionic devices, plasmonic nanostructures are considered an ideal platform. ,, Plasmonic structures can induce hot electron generation, facilitate electron funneling, and reduce trion lifetimes, thus enhancing the functionality, selectivity, and sensitivity of such devices. ,, …”