介电衬底上利用常压 CVD 直接生长石墨烯复合纳米银表面增强拉曼研究

Raman spectrum is used to feed back the stretching, vibration, and rotation of molecules, thereby transmitting structural information of molecules. The rotation and vibration of each molecular bond are determined by the type of molecule, and different molecules will transmit different signals. Based on such properties, Raman spectrum can be used for molecular identification and determination of substances. However, in practical applications, the concentration of the molecules to be tested is often relatively low, and the scattering intensity is too low for traditional Raman spectrum. Some molecules to be detected also have strong fluorescent signals, which will mask the Raman signal of the molecule. Moreover, traditional Raman has a lower limit of detection, and the limit value is relatively high. The emergence of surface enhanced Raman spectrum (SERS) technology solves the problem of low sensitivity of traditional Raman, which can be detected at the molecular level. SERS substrates are usually fabricated by metal nanoparticles, which can achieve electromagnetic enhancement through localized "hot spots". The composite of metal nanoparticles and graphene is a hot and emerging direction. Among them, nano-silver has the best enhancement effect for SERS substrate. The introduction of graphene makes the SERS substrate more stable and weakens the fluorescence background. However, traditional composite SERS substrates usually use low pressure chemical vapor deposition to fabricate graphene on copper foil, needing to be transferred to combine with nanoparticles. Wet etching and transfer will cause certain damage to the graphene, and there will also be chemicals residues, thus affecting the application effect of graphene. In addition, the graphene transfer is a time-consuming process, which makes the application of graphene cumbersome. Therefore, the work aims to design a novel substrate (Ag/G/SiO₂) for SERS. Graphene was grown on SiO₂ dielectric substrate by APCVD, which was free from transfer and combined with nano-silver to prepare SERS substrate. The growth quality of graphene was controlled by adjusting the time of feeding the ethanol carbon source, and the best enhancement effect of graphene under the optimal growth time was explored. In this work, APCVD could improve the growth rate of graphene while ensuring the quality of graphene. Growing graphene directly on SiO₂ avoided transfer process and reduced damage and chemical pollution to graphene, thus ensuring high-quality applications of graphene. At the same time, the same experimental method was used to prepare graphene on catalytic metal copper foil. After transfer process, a SERS substrate (Transfer-G/Ag/SiO₂) composited with transferred graphene and nano-silver was prepared, which was used to evaluate the rapidly prepared Ag/G/SiO₂. The performance of the two substrates was measured by the SERS of a 10^‒6 mol/L R6G probe molecule with a Raman test platform under a low power 532 nm laser. The enhancement factor (EF) of the two substrates was calculated, the EF of the optimal Ag/G/SiO₂ substrate was 9.23×10⁵, and the EF of the Transfer-G/Ag/SiO₂ substrate was 9.93×10⁵. The stability of Ag/G/SiO₂ was tested as well. The RSD values of the characteristic peaks at 611 cm^‒1, 1 362 cm^‒1 and 1 648 cm^‒1 were 9.80%, 14.08% and 18.18%, respectively, which were lower than 20%, and even the RSD values at 611 cm^‒1 and 1 362 cm^‒1 were lower than 10% and 15%. Compared with Transfer-G(Cu)/Ag/SiO₂ substrate prepared by traditional methods, the SERS effect of Ag/G/SiO₂ substrate is also significant, which is shown in the following aspects: The enhancement factors of the two substrates are basically the same, and they both have good thermal stability, uniformity and high repeatability. This improves the performance of Ag/G/SiO₂ substrate and provides a feasible method for rapid preparation of high-performance SERS substrate.