Nanotribological properties of 2-D MoS2 on different substrates made by atomic layer deposition (ALD)

The friction influence of 2-D molybdenum disulfide (MoS 2 ) films deposited on different substrates (Si, SiO 2 and Al 2 O 3 ) by atomic layer deposition (ALD) has been investigated. All of the three substrates showed a trend of decreasing friction with increasing number of layers of MoS 2 , but the friction leveled off for more than 6 layers samples. Comparing these 2-D MoS 2 films with each other, MoS 2 on the Al 2 O 3 possesses the lowest friction, while MoS 2 on the Si possesses the highest one, owing to effect of substrate on the specific self-limiting reaction in ALD process. At the same time, the friction of the monolayer MoS 2 is strongest affected by sulfur deficient. As the number of layers increases, the influence of the substrate on the friction of MoS 2 can be approximately characterized by the work of adhesion. Greater work of adhesion corresponds to a higher friction force. When the thickness is more than 6 layers, the substrate effect disappears gradually. Moreover, the friction of 2-D MoS 2 could be controlled near linearly by changing plasma treatment time within the range from 1 to 20 s, which suggests a possible way for the friction control of 2-D MoS 2 on different substrate quasi-qualitatively or even qualitatively.