Surface roughness-correlated SERS effect on Au island-deposited substrate

Evaporation and sputtering-deposition of noble metal films on substrates are two most popular and easiest methods for creating stable surface-enhanced Raman scattering (SERS)-active metal nanoparticles (NPs). However, intrinsically low SERS effect and unclearly inherent relationship between SERS effect and surface roughness of created Au NPs make SERS-related applications are limited. Here, we present the enhanced SERS effect observed on Au nanoislands (AuNIs)-deposited substrates prepared by thermal evaporation and followed by post-annealing treatment (PAT). Experimental results indicate that the SERS intensity of Rhodamine 6G (R6G) adsorbed on AuNIs, corresponding to average particle diameter of ca. 220 nm and to mean roughness (Ra) of 50 nm, can be increased by one order of magnitude after PAT at 700 °C. Meanwhile, the AuNIs (annealed at 700 °C)-deposited silicon substrate demonstrates a large enhancement factor (EF) of 2.2 × 10⁷. The relative standard deviation is ca. 7% in SERS measurements. In addition, detailed relationships of Ra derived from analysis of atomic force microscopy (AFM) and SERS effect are correlated for metal particles smaller and larger than 300 nm.