Adhesion effects on free-standing indentations for graphene oxide

Three-layer graphene oxide sheets rich in epoxy and hydroxyl groups were obtained by oxidation and chemical exfoliation and analyzed by free-standing indentations. This work compares the wrinkled surface behavior before and after loading and the relation with the adhesion effect. During free-standing indentation, mechano-chemical effects are presented between the tip and graphene oxide, a widely known problem that prevents obtaining accurate measurements. It is well known that adhesion is ruled by wrinkles formed by oxygen functional groups. However, this work highlights that the mechano-chemical effect decreases substantially when increasing the tip radius. The morphological and chemical characteristics of the sample were determined by scanning electron microscopy and X-ray photoelectron spectroscopy techniques.