Friction and Dissipation in Epitaxial Graphene Films

We have studied friction and dissipation in single and bilayer graphene films grown epitaxially on SiC. The friction on SiC is greatly reduced by a single layer of graphene and reduced by another factor of 2 on bilayer graphene. The friction contrast between single and bilayer graphene arises from a dramatic difference in electron-phonon coupling, which we discovered by means of angle-resolved photoemission spectroscopy. Bilayer graphene as a lubricant outperforms even graphite due to reduced adhesion.

Figure 1

(a) Friction loop (averaged over 50 lines) recorded on a boundary region of the sample with adjacent areas of single (1LG) and bilayer (2LG) films at a normal load of 172 nN. (b) Average lateral force as a function of normal load simultaneously recorded for 1LG and 2LG. (c),(d) Atomic stick-slip friction force maps recorded on adjacent 1LG and 2LG films (image size, $6\times 2{\mathrm{nm}}^2$; normal load, 181 nN; scan rate, $30\mathrm{nm}/\mathrm{s}$). (e),(f) Corresponding lateral force line profiles (positions indicated in friction force maps). The shaded regions indicate the average lateral force.

Figure 2

Kinks in the band structure of single (1LG) and bilayer (2LG) graphene. (a)–(c) Spectral function $A(\mathbf{k},\omega )$ for 2LG three dopings (in $e^{-}/{\mathrm{cm}}^2$) as indicated. The dashed lines are linear bare bands ${\omega }_b(\mathbf{k})$, the solid heavy lines are the fitted band positions ${\omega }_r(\mathbf{k})$. (d)–(f) Similar, for 1LG. (g),(h) Corresponding kink magnitude ${\omega }_r(\mathbf{k})-{\omega }_b(\mathbf{k})$ for 1LG then 2LG as a function of doping values indicated (in units of ${10}^{13}{e}^{-}/{\mathrm{cm}}^2$).

Figure 3

(a) Plot of the average lateral force as a function of normal force simultaneously recorded on the carbon-rich interface layer, single (1LG), and bilayer (2LG) graphene. (b) Normal vs average lateral force measured using the same AFM tip averaged over repeated measurements on graphite, 1LG, and 2LG.