The structure of chemical vapor deposited graphene substrates for graphene-enhanced Raman spectroscopy.

Defects and nanocrystalline grain structures play a critical role in graphene-enhanced Raman spectroscopy (GERS). In this study, we selected three types of few-layer, polycrystalline graphene films produced by chemical vapor deposition (CVD), and we tested them as GERS substrates. The graphene structure was controlled by decreasing the CVD temperature, thus obtaining i) polycrystalline with negligible defect density, ii) polycrystalline with high defect density, iii) nanocrystalline. We applied rhodamine 6G (R6G) as a probe molecule to investigate the Raman enhancement. Our results show that nanocrystalline graphene is the most sensitive GERS substrate, indicating that the GERS effect is primarily connected to the nanocrystalline structure, rather than to the presence of defects.