Experimental observation and characterization of amorphous carbon generated in graphene on gold nanoparticles

The interaction of graphene with gold nanoparticles is investigated using transmission electron microscopy. We observe gold-nanoparticle-mediated etching of graphene flakes, often leading to hole formation. Further, using a combination of high-angle annular dark field imaging and electron energy loss spectroscopy, we highlight that the catalytic effects of gold nanoparticles on graphene lead to the formation of amorphous carbon layers. From the extracted diffractograms, we observe regions with diffraction halos as well as some regions with a weak tetrahedral motif. Using independently performed Raman measurements, we confirm the presence of tetrahedral amorphous carbon as well as mixed graphitic-amorphous regions. For the amorphous carbon regions with mixed sp²-sp³ states, the Raman G peak is red-shifted to 1564 cm^-1 and an I _D/I _G ratio of 0.63 indicates less than 20% sp³ content. For the tetrahedral amorphous carbon regions, we observe that the Raman G peak is at 1580 cm^-1, close to that of monolayer graphene. However, there is no Raman D peak, i.e., I _D/I _G = 0, which indicates close to 100% sp³ content. The translation of the Raman G peak location and the I _D/I _G ratios is on par with the amorphization trajectory analysis of Ferrari and Robertson (Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 14095) and validates the conversion route of graphite to amorphous carbon to tetrahedral amorphous carbon. The presented method provides a promising pathway for creating defect-induced amorphous carbon at room temperature, which has a broader impact on the electronics and semiconductor industries.