Strain-mediated growth dynamics and electronic structure evolution of Ag films on MoS2(0001) by low-energy electron microscopy

The growth morphology and electronic properties of epitaxial Ag(111) films on MoS₂(0001) surfaces have been investigated using selected-area low-energy electron diffraction, low-energy electron microscopy, and density functional theory. The growth dynamics of Ag(111) films evolve with thickness, unveiling an intriguing growth mechanism. The films display strained pseudomorphic growth for lower coverages, while relaxed flat Ag(111) films form for nominal coverages exceeding 2.5 ML, following the Stranski-Krastanov growth mode. The strain relaxation leads to the nucleation of two-dimensional Ag islands with steep-edged flat (111) tops, while for higher nominal coverages, the island morphology evolves to rooflike islands with a flat Ag(111) top and faceted sides. The side facets were identified as {100}, {110}, and 1̄11 planes by reciprocal space mapping using facet diffraction spots. With increasing thickness, these islands coalesce, eventually covering the entire MoS₂ surface. Further, the variations in the surface work function and unoccupied density of states for different film coverages are studied, providing insights into the relationship between strain, surface morphology, and electronic properties. These films' structural, morphological, and electronic state evolutions as a function of the annealing temperatures have also been detailed. Notably, annealing above 400 ^∘C leads to forming fully discrete Ag islands while retaining the characteristic rooflike morphology, highlighting the high thermal stability of these facet planes.