Synthesis of nanodiamonds and diamondoids by dielectric barrier discharges generated in supercritical xenon

Nanodiamond and diamondoids were synthesized by dielectric barrier discharge plasmas (applied voltage $\sim 2 - 8\,\mathrm{kV_{p-p}}$, frequency $5 - 10\,\mathrm{kHz}$) generated in supercritical xenon close to the critical point ($T_{\mathrm crit} = 289.7\,\mathrm{K}$, $p_{\mathrm crit} = 5.84\,\mathrm{MPa}$), using adamantane as a precursor. The synthesized materials were characterized by micro-Raman spectroscopy, which permitted to confirm the presence of sp$^3$ hybridized bonds. Matrix assisted laser desorption ionization mass spectrometry and gas chromatography - mass spectrometry were used to identify the synthesized materials. The most frequent peaks were those that could be attributed to hexamantane (C$_{4n+6}$H$_{4n+12}$, $n = 6$), but also peaks that could be attributed to other higher order diamondoids consisting of $n = 2 - 15$ of fused adamantane cages.