Chemistry of the shallow surface of isolated nanodiamonds probed by synchrotron X-ray photoemission

Nanodiamonds (NDs) are under active investigation for their unique properties and potential applications in energy harvesting, quantum technologies, and nanomedicine. The surface chemistry of NDs significantly influences their semiconducting behavior, colloidal properties, and interactions with water and light. To gain deeper insights into these properties, this study employs synchrotron X-ray photoelectron spectroscopy (XPS) to investigate the shallow surface chemistry of isolated nanodiamonds in an aerodynamic jet. Employing a photon energy of 360 eV, we probed the surface of nanodiamonds with a depth of 0.3 nm. Based on the collected data, the band diagrams of the nanoparticles have been established, reporting the expected differences in electron affinity between the two surface chemistries. Interestingly, both Ox-MNDs and H-MNDs showed fairly similar C 1s core level signatures, a phenomenon discussed in detail within the article, including the effect of residual water molecules. This raises important questions about the true interface formed with water molecules when NDs are in an aqueous suspension, particularly in the context of their use as photocatalysts.