▎ 摘　　要

Graphene and graphite are generally considered as materials exhibiting friction anisotropy. However, it was demonstrated by friction force microscopy experiments that friction anisotropy most likely originates from adsorbates aligning in well-ordered stripes on graphitic surfaces. In this study, we analyzed the evolution of adsorbates on a few-layer graphene-/graphite-flake on top of a Si/SiO2-substrate after different times of storage using a multifrequency force microscopy approach. The method allows for the simultaneous in-plane and out-ofplane sample analysis as well as the discrimination of conservative and dissipative tip-sample interactions directed parallel and perpendicular to the surface and thus offers a myriad of complementary physical information. We found that friction anisotropy was observable at distinct areas of the graphene-/graphite-flake after 14 days of storage when exposed to air, albeit not throughout the whole flake, indicating different types of adsorbates. High-resolution imaging revealed that friction anisotropy occurred not only at positions where stripelike structures were visible, but also on areas which were completely covered with adsorbates. Additionally, we demonstrated that after removal of the adsorbate material by oxygen-plasma treatment, no friction anisotropy was observable on the graphene-/graphite-flake, corroborating adsorbate driven nature of friction anisotropy on graphitic surfaces.