Frictional Characteristics of Atomically Thin Sheets

Thin Friction The rubbing motion between two surfaces is always hindered by friction, which is caused by continuous contacting and attraction between the surfaces. These interactions may only occur over a distance of a few nanometers, but what happens when the interacting materials are only that thick? Lee et al. (p. 76; see the Perspective by Müser and Shakhvorostov) explored the frictional properties of a silicon tip in contact with four atomically thin quasi–two dimensional materials with different electrical properties. For all the materials, the friction was seen to increase as the thickness of the film decreased, both for flakes supported by substrates and for regions placed above holes that formed freely suspended membranes. Placing graphene on mica, to which it strongly adheres, suppressed this trend. For these thin, weakly adhered films, out-of-plane buckling is likely to dominate the frictional response, which leads to this universal behavior. A universal trend is observed for the friction properties of thin films on weakly adhering substrates. 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.

[1]  J. Sader,et al.  Calibration of rectangular atomic force microscope cantilevers , 1999 .

[2]  Bharat Bhushan,et al.  Atomic‐scale and microscale friction studies of graphite and diamond using friction force microscopy , 1994 .

[3]  Andre K. Geim,et al.  Two-dimensional atomic crystals. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[4]  L. Prandtl,et al.  Ein Gedankenmodell zur kinetischen Theorie der festen Körper , 1928 .

[5]  Paul L. McEuen,et al.  Nanomechanical oscillations in a single-C60 transistor , 2000, Nature.

[6]  M Cieplak,et al.  Molecular Origins of Friction: The Force on Adsorbed Layers , 1994, Science.

[7]  A. Volokitin,et al.  Electronic friction of physisorbed molecules , 1995 .

[8]  W. Sawyer,et al.  Transition from thermal to athermal friction under cryogenic conditions. , 2009, Physical review letters.

[9]  Fujita,et al.  Edge state in graphene ribbons: Nanometer size effect and edge shape dependence. , 1996, Physical review. B, Condensed matter.

[10]  A. Rydberg,et al.  Lateral force calibration of an atomic force microscope with a diamagnetic levitation spring system , 2006 .

[11]  M. Müser.  Structural lubricity: Role of dimension and symmetry , 2003 .

[12]  A. Bostwick,et al.  Friction and dissipation in epitaxial graphene films. , 2009, Physical review letters.

[13]  L. Marks,et al.  A predictive analytical friction model from basic theories of interfaces, contacts and dislocations , 2007 .

[14]  K. Shull.  Contact mechanics and the adhesion of soft solids , 2002 .

[15]  G. McClelland,et al.  Atomic-scale friction of a tungsten tip on a graphite surface. , 1987, Physical review letters.

[16]  K. Shepard,et al.  Current saturation in zero-bandgap, top-gated graphene field-effect transistors. , 2008, Nature nanotechnology.

[17]  P. Kim,et al.  Energy band-gap engineering of graphene nanoribbons. , 2007, Physical review letters.

[18]  J. M. van Ruitenbeek,et al.  Formation and manipulation of a metallic wire of single gold atoms , 1998, Nature.

[19]  In-Ha Sung,et al.  Predictions and observations of multiple slip modes in atomic-scale friction. , 2006, Physical review letters.

[20]  SUPARNA DUTTASINHA,et al.  Graphene: Status and Prospects , 2009, Science.

[21]  Kishi,et al.  Atomic-scale friction observed with a two-dimensional frictional-force microscope. , 1995, Physical review. B, Condensed matter.

[22]  I. Szlufarska,et al.  Recent advances in single-asperity nanotribology , 2008 .

[23]  Andre K. Geim,et al.  Electric Field Effect in Atomically Thin Carbon Films , 2004, Science.

[24]  K. Kamaras,et al.  Anomalies in thickness measurements of graphene and few layer graphite crystals by tapping mode atomic force microscopy , 2008, 0812.0690.

[25]  Andre K. Geim,et al.  Raman spectrum of graphene and graphene layers. , 2006, Physical review letters.