▎ 摘　　要

We examined the effects of outgassing from the walls of the reaction chamber on the synthesis of graphene by plasma-assisted chemical vapor deposition at low carbon concentrations. The actual partial pressures of CH4 and H2O during graphene synthesis were measured directly by mass spectrometry. The results showed that the actual partial pressures of the various gas species differed for each batch, even though the control parameters for the gas supplies were kept constant, resulting in graphene devices with different electrical properties. The plasma cleaning of the chamber walls prior to the graphene synthesis process effectively increased the uniformity of the electrical properties of devices formed using the thus-synthesized graphene samples; this was attributable to the stabilization of the conditions for outgassing from the chamber walls. (C) 2016 Elsevier Ltd. All rights reserved.