Morphology and magnetism of CoPd coverage on MoS2 flakes/SiO2

Abstract

CoPd alloy nanostructures and thin films were deposited on MoS2 flakes through e-beam evaporation at a high temperature (HT) (500 K) and at room temperature (RT) (300 K). In HT growth, CoPd nanoparticles assembled at the edge of the MoS2 flake. The nanoparticles formed parallel chains at the edge of each layer in multilayered MoS2. As indicated by the quenched photoluminescence, HT deposition resulted in a flat CoPd coverage with a roughness of ≤±0.5 nm on a MoS2 terrace. By contrast, RT growth led to a relatively rough CoPd thin film on MoS2 (roughness ≤±2 nm). The film comprised a merged nanoparticle assembly. The MoS2/SiO2 step edge played a crucial role in magnetic domain pinning such that the magnetic coercivity (Hc) of Pd/Co/MoS2 was smaller than that of Pd/Co/SiO2. Similarly, RT CoPd (8 nm)/MoS2 exhibited a parallelogram-shaped hysteresis loop with a relatively small Hc value compared with that of the square hysteresis loops of RT CoPd (8 nm)/SiO2. The hydrogenation of RT CoPd (8 nm)/MoS2 resulted in reversible Hc enhancement.