Formation of a highly doped ultra-thin amorphous carbon layer by ion bombardment of graphene

Ion bombardment of graphene leads to the formation of defects which may be used to tune properties of the graphene based devices. In this work, however, we present that the presence of the graphene layer on a surface of a sample has a significant impact on the ion bombardment process: broken sp² bonds react with the incoming ions and trap them close to the surface of the sample, preventing a standard ion implantation. For an ion bombardment with a low impact energy and significant dose (in the range of 10¹⁴ atoms cm^-2) an amorphization of the graphene layer is observed but at the same time, most of the incoming ions do not penetrate the sample but stop at the surface, thus forming a highly doped ultra-thin amorphous carbon layer. The effect may be used to create thin layers containing desired atoms if no other technique is available. This approach is particularly useful for secondary ion mass spectrometry where a high concentration of Cs at the surface of a sample significantly enhances the negative ionization probability, allowing it to reach better detection limits.