Nitrogen-Terminated\nMilled Nanodiamond Surfaces by\nPlasma Exposure

This study investigates surface modifications of hydrogen-terminated\nmilled nanodiamond (H-MND) drop-cast films by microwave (MW) and radio\nfrequency (RF) nitrogen plasma exposures. The RF(N<sub>2</sub>) damaging\nplasma treatment results in the highest nitrogen adsorption (∼7.5\nat. %) followed by MW(N<sub>2</sub>) (∼4.2 at. %) and RF(N<sub>2</sub>) nondamaging (∼3.8 at. %) plasma treatments. Upon\nMW(N<sub>2</sub>) plasma exposure, nitrogen predominantly adsorbs\nin C–N/CN and NH states, whereas RF(N<sub>2</sub>)\ntreatments result in mixed C–N/CN, CN, and\nNH states, as revealed by electron spectroscopy. Crystalline edges\nstrongly influence N, H, and O adsorption onto MND and act as active\nadsorption sites. The NH(ads) concentration is notably higher on MND\nsurfaces compared to that on poly/single-crystalline surfaces, likely\nfavored by the additional bonding configuration of hydrogen on the\nMND. NH(ads) species desorbed upon vacuum annealing in the 500–700\n°C range, leaving CN adsorbed species onto the MND surfaces.\nThe nitrogen and oxygen concentration monotonically decreases with\nannealing temperatures from 300 to 1000 °C. Upon high-temperature\nannealing, partial recovery of the MND surfaces occurs, depending\non plasma exposure conditions. This study may be critical in all ex\nsitu applications influenced by the near-surface physicochemical and\nelectronic properties of nitrogen-terminated MND surfaces, such as\nNV centers in nanocrystals.