Mass spectrometry facilitates the precise control of N2 plasma surface treatment for carbon materials

Low-pressure plasma treatments are performed in a novel reactor that combines radio frequency inductively coupled plasma with direct-current bias at the chamber wall, allowing for independent control of the ion flux and energy at the small area grounded electrode with the treated sample. An energy-selective mass spectrometry is integrated at the grounded electrode for measuring the composition and energies of ions arriving at the sample during the treatment process. The capability of the system to treat sensitive materials is demonstrated through the N 2 plasma treatment of single-layer graphene under varying ion energies obtained by changing reactor pressures and demonstrating that ions with energies of 5 to 23 eV are responsible for inducing structural defects in the material. On the contrary, higher ion energy, controlled by an application of a direct-current bias, is needed to enhance the catalytic properties of carbon papers in plasma treatment. This work facilitates a more comprehensive understanding of N 2 plasma treatment on carbon-based material surfaces and provides a theoretical foundation for prospective applications of plasma technologies. • A novel plasma reactor, allowing for independent control of the ion flux and energy, is reported. • Low-pressure N 2 plasma treatments for two types of carbon materials were studied. • The working pressure and additional DC bias were varied to modulate the ion-flux energy distribution function of N 2 plasma. • Ions with energies of 5 to 23 eV in plasma are responsible for inducing structural defects in single-layer graphene. • A higher ion energy than 23 eV is necessary for enhancing the ORR catalytic properties of carbon paper.