Micro-EDM method to fabricate three-dimensional surface textures used as SERS-active substrate

Highlights: • Novel thought was attempted to fabricate SERS active substrate by micro-EDM method. • Arrays of paraboloid-shaped micro-cavities were completed. • The surface texture can be characterized by micro-nano hierarchical structure. • R6G molecule was successfully detected under a low concentration of 10⁻⁷ M. • The surface textures exhibited good SERS performance by providing an EF > 10⁷. Based on micro electrical discharge machining (micro-EDM) method, three-dimensional surface textures were fabricated by constituting arrayed paraboloid-shaped micro-cavities on a copper template, and these surface textures were intended for surface-enhanced Raman scattering (SERS) active substrate. By lowering discharge energy, the inherent discharge craters and bulges were limited to be in nanoscale, and thereby the fabricated surface texture could be characterized as a micro-nano hierarchical structure. Raman spectra were measured on fabricated surface textures using Rhodamine 6G as the probe molecule, and results showed that the characteristic peaks of R6G molecules can be successfully identified under a low concentration of 10⁻⁷ M. In addition, the strongest Raman spectra intensity was observed on the surface texture that has the largest apparent area (S) per unit interval space (d) and per unit peak-to-valley height (h). This is mainly attributed to the fact that the surface texture with larger S/(d × h) would adsorb more probe molecules and provide higher density of SERS hot-spots. As a whole, the fabricated surface textures exhibited good SERS performances by providing an enhancement factor of greater than 10⁷. The works conducted in this study are expected to provide a novel thought to fabricate SERS-active substrate, and extend the application fields of micro-EDM technology as well.