Structure Control and Analysis of Graphene by Photoemission-assisted Townsend Discharge Plasma*

Graphene is a two-dimensional material with a sp²-carbon network. Its outstanding characteristics such as very-high electron mobility and gas-barrier properties have been remarked. To improve its characteristics and find new one, atomic-scale modification and analysis are required. However, the existing modification methods may destroy or reduce the properties: implantation, adsorption, and chemical modification. We have been using low-energy ion attack of photoemission-assisted Townsend discharge (PATD) plasma. PATD is generated with the aid of UV-photoemission in our photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD) system. In conventional radio-frequency discharge plasma, a sheath electric field may cause severe damage to graphene. However, PATD can give atomic-scale modification to graphene without destroying it.

Moreover, in convensional radio-frequency discharge plasma, because of the displacement current, both current and voltage are difficult to measure independently and precisely. Power in watt, which is a product of current and voltage, is used as a variable. However, the current is an extensive variable and is a factor of kinetics of chemical reactions; The voltage is an intensive variable and is a factor of thermodynamics. Thus, the unit of power cannot investigate what a reaction is selected and how preferentially the reaction is dealt with. Our PATD can analyze them because it is a DC plasma where current and voltage are measured independently with an appropriate current magnitude.