Nanosecond Pulsed Electric Discharge Synthesis of Carbon Nanomaterials in Helium at Atmospheric Pressure from Adamantane

Nanosecond pulsed discharges in a helium-adamantane mixture at atmospheric pressure were used for the synthesis of carbon nanomaterials, using the smallest diamondoid, adamantane, as a precursor. The discharges were generated using a point-to-plane electrode with a gap distance of 1-2 mm, at room temperature, 373 and 473 K. Scanning electron microscopy of the electrodes showed the formation of carbonaceous deposits with different morphologies, while micro-Raman spectra of the deposits covering the electrodes contained features characteristic of carbon structures of varying order. To study the effect of the temperature conditions on the plasma characteristics, time-resolved optical emission spectroscopy measurements were carried out at room temperature and 456 K. The optical emission spectra showed that at room temperature the afterglow has a duration of about several microseconds, whereas at 456 K, the plasma decay is on the order of only 1 μs. This may be an indication that the carbon nanomaterials are predominantly formed in the afterglow of the nanosecond pulsed discharge, with the presence of hydrogen radicals facilitating the formation of carbonaceous materials.