Figure 1: STM/S of MBE-grown WSe₂.

(a) STM topographic image (size: 75 × 75 nm², sample bias: 2.4 V) of a MBE-grown WSe₂ sample on highly ordered pyrolytic graphite with the nominal coverage of 1.2 MLs, revealing dominantly ML WSe₂, bilayer (BL) and trilayer (TL) islands. Inset: an atomic resolution image (size: 7.5 × 7.5 nm², sample bias: −1.5 V) of ML WSe₂. (b) STS spectrum (averaged over 50 scans) taken at a fixed position on a defect-free ML WSe₂, revealing an energy gap of 2.59 eV. (c) Topographic STM image and (d) STS map of ML WSe₂ measured simultaneously at −1.5 eV (size: 14 × 14 nm²). The white dashed circles in (c) mark two point defects, which show darker contrast in (d). The inset in (d) is the FT-STS map showing the reciprocal lattice (the points labelled by G). The first Brillouin zone (the white dashed hexagon) and its high symmetry points (K and M) are also shown for reference.