Nanocarbon materials have been synthesized by pulsed laser ablation (532 nm; 52 J/cm2; 7 ns; 10 Hz) of highly oriented pyrolytic graphite in adamantane-dissolved supercritical xenon at a temperature T = 290.2 K and pressure p = 5.86 MPa. Micro-Raman spectroscopy of the products revealed the presence of hydrocarbons possessing sp3 hybridized bonds also found in diamond structures. The synthesis of diamantane was confirmed by gas chromatography-mass spectrometry. The same measurements also indicate the possible synthesis of other diamondoids up to octamantane. Thus, laser ablation in supercritical fluids is proposed as one practical method of synthesizing diamondoids.

Diamondoid molecules were synthesized from adamantane (C10H16) using low-temperature plasmas generated in supercritical xenon. The carbon content of the synthesized materials was verified by energy dispersive X-ray spectroscopy, while micro-Raman spectroscopy measurements confirmed that the synthesized materials contained sp3 bonds, the features in the Raman spectra being similar to those found in the Raman spectra of higher order diamondoids. Mass peaks at m/z = 396 were most abundant and might be attributed to C30H36 isomers of hexamantane. The synthesis of this particular type of diamondoid is explained by the fewer necessary cleavages of C–C bonds or C–H occurring to form the diamondoid.

Diamondoids were synthesized by dielectric barrier discharges in supercritical xenon containing dissolved adamantane, which served as a precursor. The synthesis of diamantane was confirmed by gas chromatography mass spectrometry measurements, in addition to energy-dispersive X-ray spectroscopy and micro-Raman spectroscopy measurements. Moreover, the possible synthesis of two higher-order diamondoids, pentamantane and decamantane, with molecular weights of 330 and 456, respectively, is indicated from the selective ion monitoring mode. The largest production yield was obtained in the vicinity of the critical point.

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