Frictional characteristics of atomically thin sheets.

Area of Science:

• Materials Science
• Nanotechnology
• Tribology

Background:

• Atomically thin 2D materials exhibit unique properties compared to their bulk counterparts.
• Understanding nanoscale friction is crucial for designing advanced micro- and nano-electromechanical systems.
• Frictional behavior of layered materials on substrates is complex and depends on various factors.

Purpose of the Study:

• To investigate the effect of layer thickness on nanoscale friction for various 2D materials.
• To compare the frictional characteristics of atomically thin sheets with their bulk forms.
• To elucidate the underlying mechanisms governing nanoscale friction in 2D materials.

Main Methods:

• Friction Force Microscopy (FFM) was employed to measure nanoscale friction.
• Atomically thin sheets of graphene, MoS2, NbSe2, and hBN were exfoliated onto silicon oxide substrates.
• Finite Element Modeling (FEM) was used to analyze elastic deformation effects.

Main Results:

• Friction monotonically increased as the number of layers decreased for all tested 2D materials.
• This thickness-dependent friction trend was observed on weakly adherent substrates but suppressed by strong substrate binding.
• Graphene and MoS2 showed atomic lattice stick-slip friction, with thinnest sheets exhibiting sliding-length-dependent static friction.

Conclusions:

• The observed nanoscale friction trend is attributed to increased susceptibility to out-of-plane elastic deformation in thinner sheets.
• The findings suggest a universal characteristic of nanoscale friction for 2D materials weakly bound to substrates.
• Strong substrate interaction can significantly alter or suppress thickness-dependent frictional behavior.