Atmospheric pressure synthesis of diamondoids by plasmas generated inside a microfluidic reactor

Diamond molecules, so-called "diamondoids", have shown a high potential for various nanotechnology applications, however the elaboration - especially of larger diamondoids - by organic chemical synthesis is complicated or even impossible. Plasma synthesis represents another possible approach, but the detailed diamondoid growth mechanisms in pulsed laser or electric discharges are still not understood. This study investigates the effect of plasma gas chemistry on the synthesis of diamantane from adamantane and possible reaction intermediates, using dielectric barrier discharge (DBD) microplasmas generated inside continuous flow quartz microreactors. The DBDs were realized in argon-hydrogen-methane mixtures, and adamantane was used as a nucleus for the diamondoid growth. Gas chromatography-mass spectrometry (GC-MS) was used for sample analysis, and optical emission spectroscopy was employed for probing the electric discharges. From the GC-MS measurements, the synthesis of diamantane could be confirmed, the yield of diamantane increasing with the amount of hydrogen. In contrast, the addition of methane did not have any marked effect on the synthesis. The results suggest that hydrogen plays a similar role for the growth of diamondoids as in the synthesis of diamond by chemical vapor deposition, i.e. abstraction of hydrogen terminations from the diamondoid surface.