Nitrogen-terminated milled nanodiamond surfaces by plasma exposure
Résumé
This study investigates surface modifications of hydrogen-terminated milled nanodiamond (H-MND) drop-casted films by microwave (MW) and radio frequency (RF) nitrogen plasma exposures. The RF(N2) damaging plasma treatment results in the highest nitrogen adsorption (~7.5 at.%), followed by MW(N2) (~4.2 at.%) and RF(N2) non-damaging (~3.8 at.%) plasma treatments. Upon MW(N2) plasma exposure, nitrogen predominantly adsorbs in C-N/C=N and NH states, whereas RF(N2) treatments result in mixed C-N/C=N, C≡N, and NH states, as revealed by electron spectroscopy. Crystalline edges strongly influence the N, H, and O adsorption onto MND and act as active adsorption sites. The NH(ads) concentration is notably higher on MND surfaces compared to on poly/single-crystalline surfaces, likely favored by the additional bonding configuration of hydrogen on the MND. NH(ads) species desorbed upon vacuum annealing in the 500-700 °C range, leaving a CN adsorbed species onto the MND surfaces. The nitrogen and oxygen concentration monotonically decreases with annealing temperature from 300 to 1000 °C. Upon high-temperature annealing, partial recovery of the MND surfaces occurs depending on plasma exposure conditions. This study may be critical in all ex-situ applications influenced by the near-surface physicochemical and electronic properties of nitrogen-terminated MND surfaces, such as NV centers in nanocrystals.
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