Annealing and 4-MBA Co-mediated controllable fabrication of Ag nanograss for high-performance SERS detection

Surface-enhanced Raman spectroscopy (SERS) holds great promise for trace molecular detection, yet its practical application is constrained by the lack of scalable substrates with high-density plasmonic hot spots. In this work, we propose a facile and efficient strategy to fabricate silver nanoflowers (Ag-NFs) and silver nanograss (Ag-NGs) featuring high-density hot spots that derive from abundant cavities and nanogaps generated by interlaced nanosheet networks. Using multilayer-film-based strategy, the spatial arrangement and morphological evolution of Ag nanostructures grown from[Ag/SiO₂]₄ multilayer stacks can be tailored by adjusting the annealing temperature and interlayer SiO₂ thickness. The formation of Ag-NGs that derives from[Ag (50 nm)/SiO₂ (5 nm)]₄ multilayer annealed at 600 °C is governed by two key factors during thermal annealing: the physically confining barrier of SiO₂ interlayers that inhibits severe agglomeration of Ag clusters, and 4-mercaptobenzoic acid (4-MBA) which functions as a mediator to guide growth of Ag nanosheets. The optimized SERS performance for Ag-NGs is attributed to synergistic plasmonic field amplification enabled by abundant cavities and tips of interlaced Ag nanosheet, as confirmed by COMSOL simulations. This facile fabrication method allows scalable, batch-reproducible synthesis of interwoven Ag nanosheets, providing a promising strategy for high-sensitivity SERS substrates for environmental trace analysis and plasmonic sensing devices.