抄録
Graphene is a two-dimensional material with a sp2-carbon network. Its outstanding characteristics such as very-high electron mobility for field effect transistors [1] and gas-barrier properties have been remarked [2]. To improve these characteristics like impurity doping or find new one, the development of its modification methods is indispensable; however, the current ones might destroy or reduce properties: implantation, adsorption, and chemical modification. We have been using low-energy ion attack of photoemission-assisted Townsend discharge (PATD) plasma [3]. PATD is a discharge style of our photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD) system, which is a DC plasma system with the aid of UV-photoemission. In conventional radio-frequency discharge plasma, a sheath electric field may cause irreversible and severe damage to graphene. 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, we can expect precisely-controlled graphene by PATD.
Figure 1 shows Raman spectra of graphene sheets treated by PATD plasma at 800 Pa and 300 V in a 100-sccm argon flow. The D band, which represents disorder of the graphene sheet and is observed around 1340 cm-1, is controlled by quantity of electric charge passed. Treatment in a low electric charge (Fig. 1(b)) suppresses the D band, suggesting that minute and precise control is accomplished on graphene.
References: [1] S. Takabayashi et al., Diamond Relat. Mater. 22, 118 (2012); [2] S. Ogawa et al., J. Phys. Chem. Lett. 11, 9159 (2020); [3] T. Takami et al., e-J. Surf. Sci. Nanotechnol. 7, 882 (2009).
