Direct Writing\nof SERS Substrates Using Femtosecond\nLaser Pulses

Abstract

Achieving a high-density, repeatable, and uniform distribution\nof “hotspots” across the entire surface-enhanced Raman\nscattering (SERS) substrate is a current challenge in facilitating\nthe efficient preparation of large-area SERS substrates. In this study,\nwe aim to produce homogeneous surface-enhanced Raman scattering (SERS)\nsubstrates based on the strong interaction between femtosecond laser\npulses and a thin film of colloidal gold nanoparticles (AuNPs). The\nSERS substrate we obtained consists of irregularly shaped and sharp-edged\ngold nanoparticle aggregates with specially extruding features; meanwhile,\na large number of three-dimensional AuNP stacks are produced. The\nadvantages of such configurations lie in the production of a high\ndensity of hotspots, which can significantly improve the SERS performance.\nWhen the laser fluence is 5.6 mJ/cm², the substrate exhibits\nthe best SERS enhancement effect, and a strong SERS signal can still\nbe observed when testing the concentration of R6G at 10^–8 mol/L. The enhancement factor of such SERS substrates prepared using\nfemtosecond laser direct writing is increased by 3 orders of magnitude\ncompared to the conventional furnace annealing process. Furthermore,\nthe relative standard deviation for the intensities of the SERS signals\nwas measured to be 5.1% over an area of 50 × 50 μm², indicating a highly homogeneous SERS performance and excellent\npotential for practical applications.