Nanocarbon Hybrid Films of Reduced Graphene Oxide and N-Doped Graphene Quantum Dots as a Metal-Free Platform for Graphene-Enhanced Raman Scattering

Hybrid films of reduced graphene oxide (RGO) and nitrogen-doped graphene quantum dots (N-GQDs) were obtained by processing colloidal dispersions of graphene oxide (GO) and N-GQDs. N-GQDs/RGO films with well-dispersed nanophases were prepared by mechanical spraying of an 80:20 v/v ratio of N-GQDs:GO dispersion on glass substrates at 315 °C. In contrast, multilayer assemblies of N-GQDs/RGO films resulted from the two-step process consisting of a GO film prepared by spin coating on a glass substrate and the subsequent mechanical spraying of the N-GQD dispersion at 300 °C. The nanostructured array was studied using scanning electron microscopy and transmission electron microscopy, showing that the preparation method impacts film morphology and the crystalline structure. The structure and chemical composition of the N-GQDs/RGO hybrid films studied by spectroscopy techniques, such as Raman microscopy and X-ray photoelectron spectroscopy, showed the distribution of N-GQDs in the hybrid film. The assembly of nanocarbons in the resulting hybrid films impacts their optoelectronic and electrochemical properties. Recently, it was observed that graphene itself provides significant enhancement of the Raman signal and the so-called graphene-enhanced Raman scattering (GERS). We tested the N-GQDs/RGO hybrid films as substrates for GERS using crystal violet and methyl blue showing an enhancement factor (EF) of 103 and 102, respectively. In the future, the GERS effect will be a new technology to develop better-performing Raman-based analytical devices that avoid using expensive noble metals.