Figure 3: Valence band, spatially-resolved photoemission electron spectroscopy and μ-ARPES.

(a) Spectromicroscopic investigation of the single- and double-layer MoS₂ islands on HOPG. Kinetic-energy-filtered PEEM images are obtained with the photon energy of 100 eV. Photoelectron energy analyzer is tuned to the binding energy of 1.8 eV at which a clear photoemission intensity contrast is observed between the single- and double-layer MoS₂ due to the difference in the bandgap size. (b) Spatially-resolved angle-integrated valence-band photoemission spectra for a single-layer MoS₂ island (A), double-layer MoS₂ area formed by two overlapping islands (B) and the HOPG substrate (C). Difference in the position of the VBM for the single- and double-layer MoS₂ is consistent with changes in the bandgap size observed in STS. The HOPG spectrum intensity is scaled-down by a factor of two to enhance the visibility of the MoS₂ spectra. (c) Momentum-resolved μ-ARPES spectra measured along the Γ-M high-symmetry direction at the locations labeled Area 1 and 2 in (a). Lateral resolution in the μ-ARPES measurement mode is approximately 5 μm, and for this reason some contribution from the HOPG substrate can be seen in the image. Strongly-hybridized Mo d_z² and S-p_z states, centered at the binding energy of approximately 2.3 eV at the Γ-point, show a clear broadening and shift towards E_F at the area containing the double-layer MoS₂.