Evaluation of microstructural evolution of glassy carbon induced by helium implantation and annealing

The effects of helium ion (He +2 ) implantation into glassy carbon (GC) were systematically investigated. He +2 ions with an energy range of 17 keV were implanted into GC to fluences of 10 16 , 10 17 and 10 18 cm -2 at room temperature (RT). The as-implanted GC samples were subsequently vacuum annealed at 300 o C, 500 o C, and 800 o C for 1 hour. Structural evolution of GC was characterized using Raman spectroscopy and transmission electron microscopy (TEM). A fluence-dependent trend in displacement per atom (dpa) and He concentration was observed. Raman spectroscopy revealed progressive structural disorder and amorphization at fluences 10 17 and 10 18 cm -2 , marked by merging and redshifts of the D and G peaks, indicating tensile strain in the carbon matrix. Partial recovery of D/G peak separation and crystalline order was observed, especially at 800 o C for the 10 16 cm -2 fluence. TEM micrographs showed a confined damaged region of about 130 nm, with distinct defect aggregation towards the bulk for fluences of 10 16 cm -2 and 10 17 cm -2 , whereas the defect aggregation appeared in two regions for the fluences of 10 18 cm -2 . At this high fluence, bubble-like structures were observed upon annealing, indicating He accumulation and pressurization within the carbon matrix. This observation reveals a nonlinear dispersion and saturation effect. The bubbles contributed to the localized distribution of the lattice structure. Overall, annealing at 800 °C facilitated partial microstructural recovery, particularly for samples implanted to fluences of 10 16 cm -2 and 10 17 cm -2 .