In this work, we demonstrated a bottom-up growth of Ag/a-Si@Ag nanosphere arrays on Si to work as a high performance SERS substrate. By a solid-state dewetting process, high density Ag nanoparticle arrays were formed on the Si substrate with large-area uniformity. With well-controlled thicknesses of a-Si and Ag outer-layer coating, the SERS properties can be optimized with the inter-particle spacing of the Ag/a-Si@Ag NSs limited to several nanometers. Based on the analysis of optical properties and SERS activities to p-Tc molecules, we concluded that the optimized SERS substrate performed with both high sensitivity and large-area uniformity. A detection limit as low as 10−14 M and an enhancement factor (EF) up to 108 were obtained. Furthermore, the wafer scale large-area uniformity and reproducibility of the SERS signal were confirmed with small standard deviation, e.g., 8% at 1076 cm−1 and 9% at 1593 cm−1. The generic approach presented here can be extended to create a new class of highly sensitive SERS sensors with large-area output, and may play an important role in device design and the corresponding diverse chemical and biological detection tasks.
