Surface modification and stability of detonation nanodiamonds in microwave gas discharge plasma

Detonation nanodiamonds (DND), with low hydrogen content, were exposed to microwave plasma generated in pure H-2, N-2, and O-2 gases and their mixtures, and investigated using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Raman, and X-ray photoelectron spectroscopies. Considerable alteration of the DND surface was observed under the plasma conditions for all used gases, but the diamond structure of the DND particle core was preserved in most cases. The stabilizing effect of H-2 in H-2/N-2 and H-2/O-2 binary gas plasmas on the DND structure and the temperature-dependent formation of various CNHx surface groups in N-2 and H-2/N-2 plasmas were observed and discussed for the first time. DND surface oxidation and etching were the main effects of O-2 plasma, whereas the N2 plasma led to DND surfaces rich in amide groups below 1073 K and nitrile groups at higher temperatures. Noticeable graphitization of the DND core structure was detected only in N-2 plasma when the substrate temperature was above 1103 K. (C) 2015 Elsevier B.V. All rights reserved.