We experimentally study the surface roughness and the lateral friction force in single-layer MoS2 crystals deposited on different substrates: SiO2, mica, and hexagonal boron nitride (h-BN). Roughness and sliding friction measurements are performed by atomic force microscopy. We find a strong dependence of the MoS2 roughness on the underlying substrate material, being h-BN the substrate which better preserves the flatness of the MoS2 crystal. The lateral friction also lowers as the roughness decreases, and attains its lowest value for MoS2 flakes on h-BN substrates. However, it is still higher than for the surface of a bulk MoS2 crystal, which we attribute to the deformation of the flake due to competing tip-to-flake and flake-to-substrate interactions.
Single-layer MoS2 roughness and sliding friction quenching by interaction with atomically flat substrates
J. Quereda, A. Castellanos-Gomez, N. Agraït, G. Rubio-Bollinger; Single-layer MoS2 roughness and sliding friction quenching by interaction with atomically flat substrates. Appl. Phys. Lett. 4 August 2014; 105 (5): 053111. https://doi.org/10.1063/1.4892650
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