Study The Surface-Enhanced Raman Scattering On Ag/Graphene Substrates

Surface-enhanced Raman Scattering(SERS)has been used as a powerful tool for detecting the structures of molecules in many fields such as materials,biosensing,chemistry,and physics.To date,graphene with noble metals have been a hot research topic for SERS;much attention was paid to change the structures of metal materials and hybrids for getting stronger SERS intensity and prolonging the working life.However,the defects would inevitably generate on graphene during the process of preparation.The foundational groups of defects are electronegative and they can lead to the divergence of metal distribution,which would affect the intensity for Raman singal.Few researchers have discussed the ways that the defects in graphene affect the SERS activity of hybrids.We prepared the graphene with different defects and discussed the relationship between the defects and the SERS intensity.The method for experiment as follow:(1)Graphene with different amounts of defects has been prepared by chemical vapor deposition(CVD)by controlling the flow rate of hydrogen.The Raman spectra show that the sample G100(the graphene grow with 100 sccm of hydrogen)contains much more defects than others.The layers of graphene are increased with increasing the flow rate of hydrogen.The XPS spectra show the percentage of C-O bonds reached its maximum for G100.(2)Ag nanoparticles(NPs)were deposited on graphene substrates by magnetron sputtering.The SEM was used for analyzing the size and morphology of Ag NPs.It is observed that the sizes of Ag NPs become larger when the flow rate of hydrogen is increased from 10 to 100 sccm and the distances between adjacent Ag NPs get smaller.The sizes of Ag NPs sharply become sand the distances between adjacent Ag NPs turn to larger when the flow of hydrogen exceeds 100 sccm.(3)The sample of G100-Ag shows the strongest SERS singal.Therefore,the graphene is a few layers and contains abundant C-O bonds when using hydrogen less than 100 sccm during the CVD growth.The SERS EF,the percentage of C-O bonds,and the percentages of distances between adjancent Ag NPs less than 10 nm have the similar changing trend.It is considered that the C-O bonds in graphene have the ability to provide active sites to absorb Ag atoms or clusters to create growth cores for Ag NPS,which would be developed to form “hot spots” for SERS.