Plasma-free hydrogenation of oxygen-terminated polycrystalline diamond as determined by circular transmission line measurements (CTLM)

We developed a process to fully hydrogen-terminate diamond by annealing in forming gas. The surface was characterized using circular transmission line measurements (CTLMs) to evaluate the onset and degree of hydrogen termination. No hydrogenation occurred at temperatures at or below 500 °C. Hydrogenation occurs after annealing for 5 min at temperatures between 600 and 1000 °C, with complete hydrogenation achieved at 1000 °C, which showed the same sheet resistance as diamond terminated in a hydrogen plasma. Annealing at temperatures lower than 1000 °C resulted in only partial hydrogenation but can be compensated by increasing the anneal time. At temperatures exceeding 1100 °C, the sheet resistance suddenly and drastically increases, indicating instability of a hydrogen-terminated diamond surface at elevated temperatures under forming gas. The activation energy was determined to be $1.20 eV$⁠. SEM inspection showed that annealing in hydrogen produced significantly reduced surface roughness compared to diamond surfaces hydrogenated in a H₂ plasma.