Influence of the Morphology on the Functionalization of Graphene Nanoplatelets Analyzed by Comparative Photoelectron Spectroscopy with Soft and Hard X‐Rays

Since its isolation, graphene has received growing attention from academia and industry due to its unique properties. However, the “what is my material” barrier hinders further commercialization. X‐ray photoelectron spectroscopy (XPS) is considered as a method of choice for the determination of the elemental and chemical composition. In this work the influence of the morphology of graphene particles on the XPS results is studied and investigated as a function of X‐ray energy, using conventional XPS with Al Kα radiation and hard X‐ray photoemission spectroscopy (HAXPES) using Cr Kα radiation. Thereby, the information depth is varied between 10 and 30 nm. For this purpose, two commercial powders containing graphene nanoplatelets with lateral dimensions of either ≈100 nm or in the micrometer range are compared. These larger ones exist as stack of graphene layers which is inspected with scanning electron microscopy. Both kinds of particles are then functionalized with either oxygen or fluorine. The size of the graphene particles is found to influence the degree of functionalization. Only the combination of XPS and HAXPES allows to detect the functionalization at the outermost surface of the particles or even of the stacks and to provide new insights into the functionalization process. Functionalization is a crucial process for the application of graphene in composites or as sensors. Comparative hard and conventional X‐ray photoelectron spectra with different information depths provide new possibilities for quantifying and localizing the functional elements like oxygen or fluorine in graphitic particles which consists of small, rounded particles, or stack of flakes.