Surface morphology, magnetism and chemical state of Fe coverage on MoS ₂ substrate

The surface morphology, magnetism and chemical state of Fe coverage on the surface of molybdenum disulfide (MoS ₂ ) were investigated using scanning tunneling microscopy, magneto-optical Kerr effect, and depth-profiling X-ray photoemission spectroscopy (XPS). Fe deposition on the MoS ₂ substrate resulted in a nanoparticle array with the particle size ranged few nanometers (∼3±1 nm). For low-coverage Fe deposition <6 ML, nanoparticles were well-separated and long-range magnetic ordering was absent at room temperature. When the Fe coverage was increased, in-plane magnetic anisotropy was observed and the magnetic coercivity increased monotonically. The depth-profiling XPS showed the presence of a pure Fe state without observable chemical shift at the Fe/MoS ₂ interface. The XPS measurement of Pd/2 ML Fe/MoS ₂ also confirmed the dominance of the pure Fe state at the interface. The increase in Fe coverage changed the morphology from a nanoparticle array to a continuous coverage, leading to the onset of the ferromagnetic ordering and the transition from continuous surface oxidation to a bilayer structure.