▎ 摘　　要

We show that ripples observed in free-standing graphene sheets can be explained as a consequence of adsorbed OH molecules sitting on random sites. The adsorbates cause the bonds between carbon atoms to lengthen slightly. Static buckles then result from a mechanism like the one that leads to buckling of leaves. Buckles caused by roughly 20% coverage of adsorbates are consistent with experimental observations. Copyright (C) EPLA, 2009