Construction Of SERS Substrates Fulled With Nanobowl Gaps

In surface-enhanced Raman scattering (SERS), nanometer gap junctions betweenparticles and their sharp surface protrusions are known as ‘‘hot spots’’. These “hotspots” can pruduce extremely intense local electromagnetic fields, thereby resulting inenormous SERS enhancements. In recent years, great efforts have been devoted to theconstruction of “hot spots” in order to maximize SERS enhancements. However, thepreparation of a SERS substrate with abundant, easy-to-construct, and reproduciblenanogaps still remains to be a great challenge due to the complex preparationprocesses and high cost. Therefore, the research interest of this thesis is focusing onthe construction of the novel SERS substrate fulled with nanobowl gaps. The mainresearch contents and results are outlined as follows:(1) Au@SiO2nanoparticles with core sizes of30,55, and80nm and shellthickness of4nm and those with shell thicknesses of4,8,12nm and core size of55nm were successfully synthesized.(2) Submonolayer and monolayer Au@SiO2nanoparticle arrays assembled on aconductive gold surface were used as template, through which a thin gold film of ca.32nm was electrodeposited on the gold surface and partially embedded the Au@SiO2nanoparticles. After removal of the SiO2shell by dissolving, new SERS substrateswith abundant nanobowl gaps were prepared. This SERS substrate generates strong,stable, and reproducible Raman signal. Its construction process is simple, low-costand requires no special equipments, but the created gaps have a high precision. Theexperimentally determined average SERS enhancement factors (EFs) of the newSERS substrates are about105, consistent with the theoretical EF simulated usingthree-dimensional finite difference time-domain method (3D-FDTD) method.(3) Au@SiO2NPs with three core sizes of30,55, and80nm and the same shellthickness of4nm and those with three shell thicknesses of4,8, and12nm and thesame core size of55nm were used to build the novel SERS substrates and to explorehow core size and shell thickness affect their SERS signals. We found that the coresize has no obvious influence on the surface enhancement of the novel substrates.However, we failed to reveal how shell thickness, i.e., the hot spot size, affects thesurface enhancement of the novel substrates because the core particle were moreeasily detached from the created bowl with the increase of shell thickness.