Researchers at the Russian Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences developed a tomography imaging procedure that facilitates the visualization of defects on graphene layers by mapping the surface. This is a unique use of a traditionally medical imaging method to materials at the atomic scale, that may help improve existing characterization and defect-location methods.
The scientists concentrated on a specific contrast agent - soluble palladium complex - that can selectively attach to defect areas on the surface of carbon materials. his attachment results in the formation of nanoparticles that can be detected using an electron microscope. The binding of the agent is stronger in areas where the carbon center is more reactive, and the reactivity centers and defect sites can be mapped in high resolution and excellent contrast. Also, this procedure distinguished defects not only by the differences in their morphology, but also by their varying chemical reactivity. Therefore, this imaging approach enables the chemical reactivity to be visualized with spatial resolution. In their research, the scientists showed that more than 2,000 reactive centers can be located per 1 μm2 of the surface area of regular carbon material. The study pointed out the spatial complexity of the carbon material at the nanoscale level. Mapping of surface defect density showed substantial gradients and variations across the surface area, which may possess a kind of organized structures of defects.