Nitrogen ion irradiation of carbon thin films using a dense plasma focus: enhanced doping and structural modifications

Abstract

Abstract Activated carbons (ACs) are widely used in supercapacitors and batteries due to their high surface area, well-developed porosity, cost-effectiveness, and scalability, making them ideal for commercial energy storage applications. In this study, carbon derived from coconut shells was processed into a thin film on a nickel substrate, synthesized via doctor blade deposition, and subjected to nitrogen ion beam irradiation (6, 12, and 24 shots) using a 3.0 kJ dense plasma focus (PF) device, operated at 2.54 kJ to produce carbon nitride. The PF device generated a high-energy ion beam (~ 72.40 keV) at 1.5 mbar within nanoseconds, with a flux of 7.2 × 10 27 ions m −2 s −1 and a fluence of 6.4 × 10 19 ions m −2 . The Lee model code estimated a nitrogen ion beam energy of 71.0 keV, closely matching the measured 72.40 keV, confirming the model’s reliability. EDX analysis revealed significant spectral changes, with nitrogen doping reaching 7.93% after 24 shots. The optimum doping content per shot is highest at lower shot counts, reaching 1.18% per shot for the 6-shot sample, and gradually decreasing with additional shots. FTIR confirmed nitrogen-related functional groups (C≡N, S − C≡N, and N = C = S), indicating successful incorporation of nitrogen. FESEM showed pores, bulges, blunt edges, and adatoms after nitrogen ion irradiation, indicating morphological changes. XRD of the 24-shot sample revealed new peaks at 52° and 76°, corresponding to the (004) and (110) planes, associated with nitrogen incorporation and surface modification. The crystallite size increased from 6.27 nm to 11.16 nm after 24 shots of nitrogen ion irradiation, indicating enhanced crystallinity. An interlayer spacing of 0.340 nm (3.40 Å), approaching the graphitic value of 3.35 Å, was observed after 24 shots, indicating the onset of graphitization. These findings confirm effective nitrogen doping and significant structural modifications.