Tailoring the sp2/sp3 carbon composition for surface enhancement in Raman scattering

Carbon materials exhibit great potential in the application of surface-enhanced Raman scattering (SERS). In this work, the approaches of tailoring the sp2/sp3 carbon using chemical vapor deposition (CVD) and chemical terminations using surface modification were carried out in order to improve the SERS properties of carbon materials. With increasing the methane gas flow in CVD process, amorphous sp2 carbon was added into nanocrystalline diamond films. At high methane concentration, diamond/graphite (D/G) nanosheet films with a porous structure were formed with diamond nanosheet as a core and multilayer graphite as a shell. The adsorbed R6G molecules exhibit an increase in Raman signals with increasing the methane concentration. With oxidizing the D/G samples by modified Hummers method, the Raman signals are further increased with a detection limit of 10-8 mol/L and an enhancement factor of about 7 × 106. The Raman and XPS results indicate that such Raman enhancement is attributed to the CO groups formed on the conductive graphite, the π-π stacking interaction between the probe molecule and the graphite and the presence of the porous structure. The oxidized D/G films exhibit high mechanical strength and recyclability after repeated detection-cleaning process, which are urgently needed for practical SERS application.