Cu ions irradiation-induced defects in graphene and their effects on optical properties

The radiation-induced damage in graphene irradiated with 8-MeV Cu²⁺ ions at fluences varying from 1 × 10¹⁵ ions/cm² to 1 × 10¹⁶ ions/cm² was studied. The samples were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectra analysis. The number of point defects was observed to increase with the ion fluence until the adjacent point defects started to merge, forming individual amorphous regions. Then a critical stage, when the metallic nature of graphene was transformed into semiconducting, was reached for the first time in an ion beam irradiated graphene. It was noticed that further increase of the ion fluence results in a total conversion of the crystalline graphene structure into the massively disordered layer with decreased optical absorption. Density function theory calculations supported obtained experimental results.