Figure 2: STM/STS characterization of MoS2 films.

(a) and (b) STM topography showing one monolayer, two monolayer and three monolayer thick terraces of MoS₂ (V = +1.75 V, I = 10 pA) where the underlying graphite can be seen in the bottom part of (b) (V = +3.0 V, I = 250 pA). The scale bar represents 50 nm. (c) and (d) show atomic resolution topographies of the HOPG substrate (V = +1.0 V, I = 200 pA) and the MoS₂ monolayer (V = −0.8 V, I = 10 pA), respectively. The insets reveal the fast Fourier transform where the white circles are drawn as a guide to show the peaks associated with the atomic lattice. The blue circles in (d) are drawn as a guide to show the peaks associated with the Moiré lattice. The scale bars in (c) and (d) represent 3 nm. (e) A cartoon depicting the super modulation resulting from the top Sulfur atoms of MoS2 (S-S direction), and the top Carbon atoms of the HOPG (C-C direction) at a relative angle of 11 degrees. This misalignment of film and substrate produces a Moiré lattice with an 18 degree angle relative to the S-S direction of MoS₂. (f) Scanning tunneling spectroscopy spectra averaged over several different locations per layer reveal a reduction in the bandgap with increasing layer number (set point: V = + 1.5 V, I = 200 pA). (g) Valence and conduction band edges in panel (f) are magnified to highlight their evolution with layer number.