Modification of mechanical properties of vertical graphene sheets via fluorination

Abstract

We report systematically tuning the mechanical properties of vertical graphene (VG) sheets through fluorination. VG sheets were synthesized using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and were functionalized through exposure to xenon difluoride (XeF₂) gas. An atomic force microscopy technique, PeakForce Quantitative Nanomechanical Mapping (QNM®), was used to measure the mechanical properties of the VG sheets. We show that fluorination can significantly enhance the reduced modulus of surfaces comprised of VG sheets. Samples with only ∼3.5% fluorine had a reduced modulus approximately eight times higher than unfunctionalized VG sheets, which is attributed to sp² to sp³ conversion and a change of the C–C bond length after functionalization. Fluorination also decreased the energy dissipation of the VG sheets and reduced their adhesion to the AFM tip. This method represents a unique approach towards modification of the mechanical properties of nanostructures without a significant increase in weight or change of the VG sheet morphology.