Fig. 2: SPM characterization of monolayer MoS2 islands on HOPG.
a Schematic of SPM measurements process. b AFM image of a typical triangular MoS2 island, showing no obvious brightness differences between the edge and the bulk. The profile line (yellow) shows an apparent height of 0.70 nm of the triangular flake, corresponding to the single-layer MoS2 feature. c STM image of the triangular MoS2 island grown alongside the edge of the substrate terrace, clearly showing the electronic edge states with a brim of very high conductance along the island edges. The profile line (yellow) also shows a significant protrusion at the edge. The apparent height of the triangular flake is 0.72 nm, consistent with the AFM measurement in b. d Zoomed-in STM image of the area indicated by the dark-blue rectangle in c. Inset: atomic resolution image of MoS2 obtained from the area indicated by the white dashed square. e dI/dV spectra taken across the MoS2 edge from HOPG to the bulk MoS2. The color of the curves is consisted with the color of marked positions in the inset. The tunneling spectrum (#3) acquired at the MoS2 edge shows clearly electronic states (marked by pink) around Fermi level, revealing its metallic feature. STM scanning parameters: U = −1.0 V, I = 100 pA (c) and (d) U = −1.0 V, I = 800 pA for the inset.
