Figure 1: Stripes on exfoliated graphene.

(a) Contact mode topography scan of a graphene flake on silicon oxide, showing monolayer, bilayer and trilayer regions. Scale bar, 3 μm. (b) Simultaneously recorded friction signal (upper panel), showing three distinct domains of friction labeled I, II and III. Lower panel: cartoon of the friction imaging mode. The cantilever is scanned laterally and friction between the tip and sample produces the measured torsion of the cantilever. (c) Transverse force signal (upper panel) from the same region as in b, measured by recording the torsion while scanning the cantilever longitudinally (lower panel). Surface anisotropy pushes the tip towards the local ‘easy’ axis, creating a transverse force that twists the cantilever. (d) Tapping mode topography scans of the graphene monolayer, taken within each of the three domains. Each domain is characterized by stripes of period 4.3±0.2 nm along one of three distinct axes rotationally separated by 60°. Scale bars, 20 nm. (e) Friction relative to SiO₂ for each domain as a function of clockwise sample rotation angle; zero degrees corresponds to the orientation shown in a–c. For each polar plot, the origin and circumference correspond to relative friction values of 0.15 and 0.4, respectively. Dotted lines indicate the sample rotations at which the stripes shown in d are parallel to the scan axis. The friction signal is approximately sinusoidal, with the highest friction produced when stripes are parallel to the scan axis. (f) Transverse force signal for each domain as a function of clockwise sample rotation angle. Unshaded and grey-shaded regions indicate positive and negative transverse signals, respectively. The origin of each polar plot is zero. The transverse signal for a given domain switches sign as the stripe axis rotates through the lateral axis.