A team of nanotechnology researchers from the University of Pennsylvania and Columbia University has used friction force microscopy to determine the nanoscale frictional characteristics of four atomically-thin materials, discovering a universal characteristic for these very different materials. Friction across these thin sheets increases as the number of atomic layers decreases, all the way down to one layer of atoms. This friction increase was surprising as there previously was no theory to predict this behavior.
The team tested the nanotribological, or nano-scale frictional properties, of graphene, molybdenum disulfide (MoS2), hexagonal-BN (h-BN) and niobium diselenide (NbSe2) down to single atomic sheets. The team literally shaved off atomic-scale amounts of each material onto a silicon oxide substrate and compared their findings to the bulk counterparts. Each material exhibited the same basic frictional behavior despite having electronic properties that vary from metallic to semiconducting to insulating.
The results may also have practical implications for the design of nanomechanical devices that use graphene, which is one of the strongest materials known. It may also help researchers understand the macroscopic behavior of graphite, MoS2 and BN, which are used as common lubricants to reduce friction and wear in machines and devices.
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