Low-voltage ionization of air with carbon-based materials

Polycrystalline diamond and carbon nanotubes exhibit excellent vacuum eld emission prop-erties, characterized by low turn-on voltage and high current density. Their atmospheric eld emission and ionization capabilities are reported in this paper. Highly graphitic polycrystalline diamond (HGPD) lm was grown in a plasma-enhanced chemical vapor deposition process, and its ability to ionize atmospheric air was characterized and compared against carbon nanotubes. The HGPD sample was activated by applying a moderate voltage bias (340V) for an extended period across a 10 m electrode gap. After activation, a turn-on voltage of 20 V and a sustain-able current of 10 A was observed with the same gap. Results also indicate that eld emission helps to create a moderate ionization eect without catastrophic air breakdown. A hydrogen plasma treatment is shown to restore emission current back to or even exceeding the original level, which suggests an important role of surface termination in electron emission process. Car-bon nanotubes were grown and tested but did not perform as well under similar conditions