Controlling oxidation degree and crystallinity to achieve high Young's modulus of graphene derivatives

Among two-dimensional materials, graphene stands out due to its exceptional electrical, optical, and mechanical properties, holding promise for various uses, such as in electronics, optoelectronics, energy storage, and energy harvesting. These properties are related to graphene structure, crystallinity, and oxidation degree. In this work, we synthesized various graphene derivatives: graphene oxide (GO), exfoliated graphene (GEX), reduced graphene oxide (rGO), and selectively oxidized graphene (SOG). Multiple characterization methods were conducted to study the chemical and mechanical properties of the few-layered graphene derivatives. The samples were suspended by spray coating on membranes with an array of circular holes to obtain the mechanical response of these free-suspended few layers by classical force-curve indentations using atomic force microscopy. The obtained values of Young's modulus ranging between 180 and 650 GPa were then correlated to oxygen functional group concentration (C/O between 2 and 9) determined by X-ray photoelectron spectroscopy and defect density quantified by Raman spectroscopy (ID/IG between 0.4 and 3.2). The mechanistic approach established a clear relationship between the mechanical response and the material's oxidation degree and crystallinity, giving insight into potential future applications.