Figure 3. Comparing surface roughness of monolayer MoS₂ on different substrates.

(a) LEEM images of MoS₂ flakes sitting on top of a holey Si substrate. (b) Optical image of an MoS₂ flake on SiO₂ with hBN buffer in between. Markers in (a,b) indicate positions where detailed LEED spot profile analyses were done. (c) explains the mechanism that causes broadening of the observed LEED diffraction pattern. A rough surface produces diffraction beams which spread out as a cones perpendicular to the sample surface, causing increased broadening with increasing incident electron energy. (d) The FWHM of the specular (00) diffraction beam–σ, with respect to the incident electron wave vector k_⊥. Superimposed on the resonant features due to few-layer effects, the overall linear increase in σ indicates a high degree of surface roughness of the MoS₂ on bare Si and SiO₂. A smaller slope in suspended MoS₂ shows a much reduced, but non-zero surface roughness in suspended samples, while the hBN buffer results in yet another order of magnitude decrease in surface roughness.