▎ 摘　　要

Adsorbates, such as graphene nanoflakes, are always present, even in high-quality graphene. How these adsorbates affect the frictional behaviour of graphene is still largely unexplored. We perform molecular dynamics simulations to study the effect of graphene nanoflakes on the friction behaviour of a single graphene layer using a capped carbon nanotube as a probe. By changing the size of nanoflake and the probing distance between the probe tip and graphene, we observe several distinct modes of interaction between the probe and the nanoflake. Such interactions are found to drastically change the lateral and normal forces, causing a drastic change in friction behaviour. The present work indicates that abnormal phenomena, such as the irregular motion of a probing tip observed experimentally in graphene friction, could arise from the presence of adsorbates.