Irradiation effects of graphene and thin layer graphite induced by swift heavy ions

Graphene and thin graphite films deposited on SiO₂/Si are irradiated by swift heavy ions (²⁰⁹Bi, 9.5 MeV/u) with the fluences in a range of 10¹¹ ions/cm²–10¹² ions/cm² at room temperature. Both pristine and irradiated samples are investigated by Raman spectroscopy. For pristine graphite films, the "blue shift" of 2D bond and the "red shift" of G bond with the decrease of thickness are found in the Raman spectra. For both irradiated graphene and thin graphite films, the disorder-induced D peak and D' peak are detected at the fluence above a threshold Φ_th. The thinner the film, the lower the Φ_th is. In this work, the graphite films thicker than 60 nm reveal defect free via the absence of a D bond signal under the swift heavy ion irradiation till the fluence of 2.6×10¹² ions/cm². For graphite films thinner than 6 nm, the area ratios between D peak and G peak increase sharply with reducing film thickness. It concludes that it is much easier to induce defects in thinner films than in thicker ones by swift heavy ions. The intensities of the D peak and D' peak increase with increasing ion fluence, which predicts the continuous impacting of swift heavy ions can lead to the increasing of defects in samples. Different defect types are detected in graphite films of different thickness values. The main defect types are discussed via the various intensity ratios between the D peak and D' peak (H_D/H_D').