Plasma-assisted friction control of 2D MoS₂ made by atomic layer deposition

MoS₂ films as an excellent solid lubricating film can significantly decrease the friction and adhesion of nanoelectromechanical systems. Atomic layer deposition (ALD) as a surface-controlled method provides a flexible way to apply MoS₂ to complex surfaces. In this work, MoS₂ film deposited by ALD on substrates by a plasma-assisted process is used to study controlled friction. Firstly, layer-controlled MoS₂ films were fabricated by ALD from one to five layers. The friction decreases as the number of layers increases. Furthermore, the average friction force of MoS₂ deposited on Al₂O₃ substrates treated by plasma for 10 s with one ALD cycle has the lowest value. Functional groups on the substrate surface can be obtained by plasma treatment, which can control the growth of the first layer of MoS₂ in ALD so that the frictional characteristics of monolayer MoS₂ can be controlled. Finally, the effect of plasma treatment on ALD growth at the intermediate stage of MoS₂ is relatively weak. Only the monolayer MoS₂ treated by plasma can affect the growth of MoS₂ by ALD. Therefore, the controlling effect of plasma treatment on the frictional characteristics of MoS₂ deposited by ALD mainly occurs at the initial stage of growth.