Nitrogen-Terminated Polycrystalline Diamond Surfaces by Microwave Chemical Vapor Deposition: Thermal Stability, Chemical States, and Electronic Structure

In this work, we investigate the interaction of microwave (MW) N2 plasma with polycrystalline diamond surfaces. Optical emission spectroscopy (OES) was used to identify different species present in the plasma. The chemical states were investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS), and the electronic structure was investigated by ultraviolet photoelectron spectroscopy (UPS). OES showed that the MW­(N2) plasma contains mainly radical species. The nitrogen coverage is estimated to be lower than the diamond average areal density. XPS analysis showed that the nitrogen may have occupied a number of bonding configurations, while upon annealing to 800 °C, some of the incorporated nitrogen onto the diamond was stable. From the HREELS study, the N–H surface bond was stable only up to ∼600 °C. The hydrogen-terminated diamond exhibits negative electron affinity, whereas, there was an increase in the electron affinity upon the nitridation process. Even though the nitrogen concentration decreased upon annealing to 800 °C, the low energy cutoff in the electron distribution in the UP spectrum remained constant.