A combination of plasma diagnostics and Raman spectroscopy to examine plasma-graphene interactions in low-pressure argon radiofrequency plasmas

Graphene films were exposed to low-pressure capacitively coupled (E-mode) and inductively coupled (H-mode) argon radio frequency plasmas to investigate damage formation by very-low-energy ion irradiation. In the H-mode, plasma parameters were assessed by a Langmuir probe and plasma sampling mass spectrometry to determine the conditions of fixed ion fluence but with different average ion energies. The populations of argon metastable and resonant argon atoms were also measured by optical absorption spectroscopy to determine their contribution to the total energy flux during plasma treatment. In the H-mode, in which plasma-graphene interactions are dominated by ion irradiation effects, Raman spectroscopy reveals a significant rise in the D/G ratio and full width at half maximum of the G peak as well as the onset of graphene amorphization, even at very low ion energies (between 7 and 13 eV). In the E-mode characterized by comparable ion energy but much lower ion density, significant damage is also observed, a feature ascribed to the additional energy flux linked to the de-excitation of metastable argon species on the graphene surface.