-Au (111) Moiré Heterostructure at Sub Nanometer Scale

For the first time, the effects of strain and optical excitations are studied in tandem at the sub nanometer (nm) scale in a monolayer MoS₂-Au (111) heterostructure. The imperfect topography of the Au (111) surface at its domain edges induces non-uniform, sub nm scale strain in the MoS₂ monolayer above the Au (111) substrate. The experimental local density of states (LDOS) of the strained region is significantly enhanced between 400 meV and 1200 meV and exhibits an overall energy downshift relative to that of the unstrained region. These effects are explained by density functional theory and molecular dynamics simulations of strained MoS₂ configurations that demonstrate energy downshifts near the high-symmetry momentum K and Q points in the first Brillouin zone along with a decrease in the effective mass at each valley for tensile strain. Next, measurements under 515 nm continuous wave light are conducted to investigate the non- equilibrium behavior of the sample. While strong charge transfer effects between the Au (111) and MoS₂ quench any optical effect in unstrained areas, the LDOS in the strained regions exhibits significant light-induced modification: an effective upward energy shift. This can be explained by a local accumulation of excitons near the K and Q regions due to the strain renormalized electronic bandstructure. These results pave the path forward for fine tuning the LDOS of 2D materials by strain and optical excitations.