Nanotribological properties of ALD-made ultrathin MoS2 influenced by film thickness and scanning velocity.

Solid-lubricanting films are usually applied to reduce friction and adhesion of micro/nanoelectromechanical systems (MEMS/NEMS). Due to the special structure, MoS2 is endowed with excellent lubricity. Layer-controlled ultrathin MoS2 films with strong interactions to the underlying substrates were prepared by atomic layer deposition (ALD) using MoCl5 and H2S and characterized by various measures. Nanotribological properties of the MoS2 films with different thicknesses were observed by an atomic force microscope (AFM) tip under various loads. In initial stage of ALD, bigger roughness induced by discontinuous nano-particles can increase friction. However, when the number of ALD cycles (NC) is more than 3, the friction force can be effectively reduced by about 40-55% because of interlayer-sliding and lower adhesion. Finally, friction properties against sliding velocities of the MoS2 films were also observed. The ultrathin MoS2 film obtained by ALD exhibits the huge application value as reducing friction surface in MEMS/NEMS.