  Graphene monolayers are known to display domains of anisotropic friction with
twofold symmetry and anisotropy exceeding 200 percent. This anisotropy has been
thought to originate from periodic nanoscale ripples in the graphene sheet,
which enhance puckering around a sliding asperity to a degree determined by the
sliding direction. Here we demonstrate that these frictional domains derive not
from structural features in the graphene, but from self-assembly of atmospheric
adsorbates into a highly regular superlattice of stripes with period 4 to 6 nm.
The stripes and resulting frictional domains appear on monolayer and multilayer
graphene on a variety of substrates, as well as on exfoliated flakes of
hexagonal boron nitride. We show that the stripe-superlattices can be
reproducibly and reversibly manipulated with submicron precision using a
scanning probe microscope, allowing us to create arbitrary arrangements of
frictional domains within a single flake. Our results suggest a revised
understanding of the anisotropic friction observed in graphene and bulk
graphite in terms of atmospheric adsorbates.
