Fabrication of carbon nanomaterials by atmospheric pressure microplasma

Atmospheric pressure microplasma was produced in a scanning electron microscope (SEM) chamber for synthesising carbon nanomaterials. The SEM observation is convenient for both adjusting the gap length and observing the electrode surface before and after experiments. After adjusting the gap length, the electrodes were housed in a small removable gas cell equipped in the SEM chamber and CH₄ discharge gas was introduced into the gas cell. It was found that the discharge was pulsated automatically because of slow discharge through a large ballast resistor and fast discharge through gas breakdown, even though a DC voltage was applied. The peak pulse current density was almost 60 kA cm², the peak power density in the microplasma volume was approximately 555 MW cm³ and the pulse width was 10 ns typically. Spherical and nanotube-like carbon nanomaterials were found on the cathode surface after microplasma discharge for 1-5 s. With the discharge time increasing, the spherical substance changes into nanotube-like carbon nanomaterials.