Subnanometer Thick Native sp² Carbon on Oxidized Diamond Surfaces

Oxygen-terminated diamond has a wide breadth of applications, which include stabilizing near-surface color centers, semiconductor devices, and biological sensors. Despite the vast literature on characterizing functionalization groups on diamond, the chemical composition of the shallowest portion of the surface (<1 nm) is challenging to probe with conventional techniques like XPS and FTIR. In this work, we demonstrate the use of angle-resolved XPS to probe the first ten nanometers of both oxygen and hydrogen terminated (100) single-crystalline diamond grown via chemical vapor deposition (CVD). With the use of consistent peak-fitting methods, the peak identities and relative peak binding energies were identified for sp² carbon, ether, hydroxyl, carbonyl, and C-H groups for both of these diamond surface terminations. For the oxygen-terminated sample, we also quantified the thickness of the sp² carbon layer situated on top of the bulk sp³ diamond bonded carbon to be 0.3 ± 0.1 nm, based on the analysis of the Auger electron spectra and D-parameter calculations. These results indicate that the majority of the oxygen is bonded to the sp² carbon layer on the diamond, and not directly to the sp³ diamond bonded carbon.