Study of substrate temperature effects on carbon thin film coating on SS316 in DC glow-discharge plasma

In tokamak reactors, plasma-facing components require low-Z coatings, such as carbon, to minimize impurity generation and reduce plasma contamination. Coating is typically performed during short shutdown periods, and shorter deposition times are preferred due to operational costs and limited maintenance windows. Low deposition temperature is a critical parameter affecting film quality, and this study investigates the optimal low-temperature condition to achieve high-quality carbon films within a short deposition time. Carburizing of SS316 substrates by direct current glow-discharge (DCGD) plasma was performed at different substrate temperatures. Methane and helium were used as the precursor and buffer gases, respectively. A treatment time of 90 min was applied to all samples in order to investigate the effect of temperature on coating properties at relatively short processing times. The morphology and structure of the coatings were characterized using normal and grazing-incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX; spot, mapping, and line-scan modes), and Raman spectroscopy. The Raman spectrum at 100 °C indicates an amorphous hydrogenated carbon layer with a sp³ /sp² band intensity ratio of 0.53, which is not observed at the other investigated temperatures. White surface particles were observed on the exposed specimens; EDX spot and line-scan analyses confirmed that these features are carbon-rich compounds. Normal and grazing-incidence XRD analyses show the formation of a small amount of S-phase in the treated layer. On the basis of these results, the optimal carbon deposition temperature for the first wall of a tokamak is identified as 300 °C. • SS316 was carburized by methane DC glow-discharge plasma. • Carbon coatings were deposited at 100–500 °C for 90 min. • Structural evolution was studied using XRD, SEM, EDX, and Raman spectroscopy. • Hydrogenated amorphous carbon formed at low temperatures. • Limited S-phase formation and surface crystallite refinement were observed. • A uniform carbonized layer was obtained at 300 °C.