Frictional Characteristics of Atomically Thin Sheets

• Published in: Science (American Association for the Advancement of Science) Vol. 328; no. 5974; pp. 76 - 80
• Main Authors: Lee, Changgu, Li, Qunyang, Kalb, William, Liu, Xin-Zhou, Berger, Helmuth, Carpick, Robert W, Hone, James
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 02.04.2010; The American Association for the Advancement of Science
• Subjects: Adhesion; Atoms & subatomic particles; Bending; Boron; boron nitride; Condensed matter: structure, mechanical and thermal properties; Crystal lattices; elastic deformation; Exact sciences and technology; finite element analysis; Friction; Graphene; Graphite; Material properties; Materials; Materials science; Mechanical and acoustical properties; Mica; microscopy; Molybdenum; molybdenum disulfide; Nanoscience; Niobium; Physical properties of thin films, nonelectronic; Physics; silica; Sliding; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Atomic force microscopy; Molybdenum sulfide; Slip; Boron nitride; Nanostructures; Elastic deformation; Thin films; Thickness; Finite element method; Nanometer scale; Friction; Stick slip; Graphene; Atomistic model; Silicon oxides; Niobium selenides; Modelling
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.1184167

Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS₂), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS₂ exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length-dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets' increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.