Reducing friction and wear in devices is important as a potential cost savings method for minimizing energy loss. Solid 2D materials such as molybdenum disulfide (MoS2) have gained interest because their tribological properties lend to their use as solid lubricants. Adding a single layer of MoS2 (SLM) restores a crystal lattice to amorphous interfaces, leading to incommensurate contact and increased ease of sliding. However, the nanoscopic roughness present at sliding interfaces poses a challenge to the implementation of SLM because its tribological properties depend on interactions with the supporting substrate. To understand and control the mechanical behavior of SLM in sliding contacts, it is crucial to learn how the frictional response of SLM is influenced by both the SLM-substrate interaction strength and its conformity on rough surfaces. To study this behavior, atomic force microscopy (AFM) was used to evaluate the structure of MoS2 nanosheets deposited on SiO2 surfaces that have nanoscopic roughness and controlled chemistry. Additionally, friction force microscopy (FFM) was used to investigate the tribological properties of this system. It was found that MoS2 partially conforms to nanoscopically rough surfaces, and that the conformity depends on both the layer thickness and the applied load. Friction measurements showed single layer MoS2 (SLM) on a 20 nm NP film exhibits greater friction than SLM on a 50 nm NP film because of more stick-slip motions at tip-SLM surfaces. In addition, monolayer MoS2 on functionalized substrates shows larger friction than SLM on unmodified substrates, resulting from the larger shear stress of MoS2-SAM composites. The investigation of the conformity, strain and friction of ultrathin MoS2 nanosheets on substrates with various roughness and chemistry opens the possibilities of tuning the frictional properties and using of MoS2 in nanotechnologies and catalysts.

Influences of surface chemistry and nanoscopic roughness on the frictional properties of MoS2 nanosheets

255th National Meeting (2018)

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