Radiation damages and bubble formation of ion implanted furan-resin-derived carbon

Furan-resin-derived carbon generally produces a glass-like carbon (GC) having entangled graphene layers after high temperature heat treatments. However, furan-resin-derived carbon produced well-graphitized thin skin on surfaces after heat-treatment at 3000 °C. Since ion implantation is a useful technique for surface modification, we used them to investigate the mechanism of well-graphitized thin skin on surfaces of furan-resin-derived carbon after heat-treatment at 3000 °C. In this investigation, we observed morphological changes on Ar⁺ or Xe⁺ implanted GC surfaces using SEM&TEM and Raman spectroscopy. Ar or Xe ions were implanted into the furan-resin-derived carbon heat-treated at 3000 °C at energy of 60-160 keV at a fluence ranging from 1×10¹⁵ to 1×10¹⁷ ions/cm². Microstructural changes were examined by Raman spectroscopy. The implanted surfaces of the specimens were changed to an amorphous structure by the ion implantation. Moreover, morphological SEM&TEM observations revealed that clear bubbles with diameter of 10-80 nm were present in the Ar⁺-implanted specimen at a fluence of 1×10¹⁷ ions/cm². However, bubbles did not appear in the Ar⁺-implanted specimen at a fluence of 1×10¹⁶ ions/cm². On the other hand, bubbles with diameter of 15-30 nm were present in the Xe⁺-implanted specimens at a fluence of 1×10¹⁶ ions/cm². The Xe⁺-implanted specimens were subjected to annealing of re-heat-treatment at 3000 °C. After the annealing, the bubbles were lost in the interior of specimens by cross-sectional SEM observations. Moreover, on the implanted surfaces appeared big bubbles, which were not presented on the implanted surface before annealing. The sizes of these big bubbles were about 2-10 μm. Using Raman spectroscopy, we observed that on the surface of the big bubbles the structure was re-well-graphitized. On the surface of non-bubbled areas it was less graphitized. Thus annealing provided a restoration of the structural, but much effective only on the bubble surfaces.