Title: Friction between incommensurate crystals

Author: J. Friedel and P -G de Gennes

Bibliographic details: Philosophical Magazine, Volume 87, Number 1, 1 January 2007, pp. 39-49(11)

Abstract: We present an overview of friction processes expected between two ideal crystals of strong layers (graphite, MoS2, etc.) when one crystal is rotated with respect to the other by a certain angle θ. We assume perfect conditions: no impurities; no preexisting dislocations in the bulk of the crystals; slow gliding velocities. Two regimes show up: (a) Weak coupling when , where are typical intra- (inter-) layer interactions. Here we expect weak friction, controlled by two-phonon processes, and analyzed by Sokoloff et al. However, we point out that surface waves at the interface also play a role. (b) Strong coupling where two orthogonal sets of screw disclinations should build up in the contact plane, as shown long ago by F.C. Frank. Here (to a first approximation) the dislocations are arranged in ladders, and we expect solid friction with a Peierls-Nabarro threshold stress.

Notes: A paper that needs careful reading (which, I haven’t done yet).

Note added on August 8, 2007A follow-up paper in Philosophical Magazine Letters.