Fig. 2: Characterizations of exfoliated MoS₂ monolayers from crystal powders.

a Photograph of MoS₂ crystal powders used for electrochemical molecular intercalation. The average particle size of the powder is ~10 µm. b The atomic force microscopy (AFM) image of 2D monolayer nanosheets exfoliated from crystal powders. Scale bar, 2 µm. c Liquid-state photoluminescence spectrum of powder-exfoliated MoS₂ monolayers dispersed in dichloroethane with bis(trifluoromethane)sulfonimide (TFSI) treatment. Insets are the photographs of the ink solution with and without ultraviolet light illumination. The term “a.u.” denotes “arbitrary units”. PL photoluminescence. d I_d–V_gs transfer characteristics of 20 individual MoS₂ transistors based on 2D nanosheets exfoliated from crystal powders. Inset is the statistical distribution of the mobility values for these transistors. V_ds = 1 V. I_d, drain current; V_gs, gate-source voltage; V_ds, drain-source voltage. e Photograph of a piece of MoS₂ bulk single crystal. f The AFM image of 2D monolayer nanosheets exfoliated from the bulk single crystal. Scale bar, 2 µm. g Photoluminescence spectrum of bulk-crystal-exfoliated MoS₂ monolayers dispersed in dichloroethane with TFSI treatment. Insets are the photographs of the ink solution with and without ultraviolet light illumination. h I_d–V_gs transfer characteristics of 20 individual MoS₂ transistors based on 2D nanosheets exfoliated from large-piece single crystal. Inset is the statistical distribution of the mobility values for these transistors. V_ds = 1 V. i Transmission electron microscopy (TEM) image of an individual MoS₂ nanosheet exfoliated from crystal powders. Inset is the corresponding selected-area electron diffraction pattern of this MoS₂ nanosheet. Scale bar, 1 µm. j X-ray photoelectron spectra (XPS) analysis of the MoS₂ nanosheets exfoliated from crystal powders. k The thickness distribution of powder-exfoliated MoS₂ monolayer nanosheets measured by AFM. Inset is the schematic illustration of an inorganic monolayer capped by organic molecules with a thickness of ~2.8 nm. l Raman spectra of 10 individual MoS₂ nanosheets. The red dotted lines indicate the position of the A_1g and E_2g peaks of the Raman spectra.