Modification of the Surface Structure of Carbon Materials under Ion Irradiation

The study is devoted to the effect of high-intensity deuterium ion fluxes (on the order of 1024 ions/(m2 s)) on the surface of anisotropic carbon-based materials-pyrolytic graphite and a carbon composite containing fibers based on polyacrylonitrile with an "onion-skin" structure. It was shown that fragmentation of surface graphene layers during irradiation with high-intensity deuterium ion fluxes, along with the resulting compressive stresses, leads to the bending of the detached surface graphene layers and the formation of a system of hills. Upon further irradiation, the reverse process occurs: on the slopes of these hills, graphene layers parallel to the surface are formed, while at their peaks, crystals with layers also parallel to the surface appear. When the side surface of carbon fibers with an "onion-skin" structure is irradiated, transverse corrugations form perpendicular to the fiber axis if ions penetrating the surface induce compressive stresses, leading to fragmentation and bending of the near-surface layers, and if the degree of structural damage to the fiber is sufficient for repeated ion emission. Longitudinal folds parallel to the fiber axis are observed when, at a significant penetration depth of the irradiating ions, the stress maximum forms at a certain depth, while the damage to the surface layers is insufficient for the release of implanted ions. In this case, the surface deformation mechanism of the fiber is similar to that of blister formation. The ion irradiation of fiber ends leads to their protrusion above the matrix surface and the recrystallization of the exposed regions. The graphene planes of the resulting crystals are oriented perpendicular to the fiber axis. The results of this study indicate that, regardless of the original orientation of the graphene layers in the sample and the direction of the ion flux, the target undergoes sequential, mutually perpendicular transformations upon irradiation.