Ultrafast Internal Exciton Dissociation through Edge States in MoS₂ Nanosheets with Diffusion Blocking

Abstract

Edge states of two-dimensional transition-metal dichalcogenides (TMDCs) are crucial to quantum circuits and optoelectronics. However, their dynamics are pivotal but remain unclear due to the edge states being obscured by their bulk counterparts. Herein, we study the state-resolved transient absorption spectra of ball-milling-produced MoS 2 nanosheets with 10 nm lateral size with highly exposed free edges. Electron energy loss spectroscopy and first-principles calculations confirm that the edge states are located in the range from 1.23 to 1.78 eV. Upon above bandgap excitations, excitons populate and diffuse toward the boundary, where the potential gradient blocks excitons and the edge states are formed through interband transitions within 400 fs. With below bandgap excitations, edge states are slowed down to 1.1 ps due to the weakened valence orbital coupling. These results shed light on the fundamental exciton dissociation processes on the boundary of functionalized TMDCs, enabling the ground work for applications in optoelectronics and light-harvesting.

Tunable Optical Activity in Twisted Anisotropic Two-Dimensional Materials

“…They also have good performance compared to organic films and metasurfaces. The CD spectrum of the twisted BP with middle MoS 2 and hBN layers suggest that the exciton 39 present in the material can be used to tailor the optical activity (Figures S16 −17). A composite chiral material can be constructed by stacking twisted BP with other 2D materials.…”

Deep ultraviolet optical limiting materials: 2D Ti3C2 and Ti3AlC2 nanosheets

“…TMDs are arguably the most widely studied class of 2D layered materials other than graphene. TMDs exhibit typical layer-dependent tunable band gaps ranging from 1 eV (bulk) to 3 eV (monolayer), [19][20][21][22] but their larger band gaps are not suitable for mid-and far-infrared bands. 23 Black phosphorus has been regarded as the 2D material closest to graphene, and also has a thickness-dependent band gap (from 0.3 eV to 2 eV).…”

Hot Carrier Transfer in PtSe2/Graphene Enabled by the Hot Phonon Bottleneck

“…Graphene has attracted particularly strong attention as a result of its zero band gap, which results in a linear optical absorption with virtually no photon wavelength restriction. − High intrinsic carrier mobility of graphene makes it easier to combine two-dimensional (2D) transition metal dichalcogenide (TMDs) materials with narrow band gaps to make various forms of heterostructures as well as its high conductivity and efficient charge transfer (CT). − There are different CT mechanisms between graphene and TMDs, including direct electron/hole transport, , edge states, hot electron emission and tunneling effect, , etc. The CT could occur through direct transfer and the photon thermionic CT process, which could be controlled by the photon energy. , The CT processes can also be modulated by stacking order, − stacking angle, , interlayer insertion, , external field, , etc.…”

“…1−4 High intrinsic carrier mobility of graphene makes it easier to combine two-dimensional (2D) transition metal dichalcogenide (TMDs) materials with narrow band gaps to make various forms of heterostructures as well as its high conductivity and efficient charge transfer (CT). 5−9 There are different CT mechanisms between graphene and TMDs, including direct electron/hole transport, 10,11 edge states, 12 hot electron emission and tunneling effect, 13,14 etc. The CT could occur through direct transfer and the photon thermionic CT process, which could be controlled by the photon energy.…”