In Situ Measurement of the Electronic Structure of Oxidized Graphene Employing Quantum-Rate Spectroscopy

Measuring the electronic structure and defect states of oxidized single-layer graphene (ox-SLG) is essential for using graphene-based materials in commercial devices. In this work, we introduce quantum-rate spectroscopy (QRS), an electronic spectroscopic method based on the principles of low-energy quantum electrodynamics, to measure the electronic structure of ox-SLGs. QRS measures the quantum capacitance of ox-SLGs in an electrolyte environment, enabling the determination of the density of states (DOS) in situ and at room temperature. This methodology not only characterizes how oxygenated functional groups modify the pristine electronic structure of graphene by resolving defect-state energies with a precision comparable to the peak-position precision of X-ray photoelectron spectroscopy (XPS) performed under high-vacuum conditions but also enables direct correlation of the DOS measured by QRS with simulations from density functional theoretical methods. Notably, this agreement suggests that epoxy groups are the dominant defects, a finding that is corroborated by Raman spectroscopy and XPS analyses. Overall, QRS emerges as a suitable and mild-condition technique for the in situ characterization of ox-SLG structures.