Development of plasmonics-active SERS substrates on a wafer scale for chemical and biological sensing applications

Abstract

This paper describes the fabrication of highly efficient plasmonics-active SERS substrates -having metallic nanowire structures with pointed geometries and sub-5 nm gap between the metallic nanowires enabling concentration of high EM fields in these regions -on a wafer-scale by a reproducible process that is compatible with large-scale development of these substrates. These SERS substrates were employed for detecting chemical and biological molecules of interest. IntroductionSurface-enhanced Raman scattering (SERS) is one of the most powerful spectroscopic tools employed for noninvasive and non-destructive detection of biomedical species and chemical or biological molecules (1-11). The challenges lie in developing novel SERS materials and substrates that not only achieve SERS enhancement factors that are as large as possible but can also be developed in a reliable and repeatable manner. Another challenge lies in the development of these substrates over a large area, such as entire 4, 6, or 12 inch wafers, and still capturing the functionalities of large SERS enhancement factors and reproducibility of the SERS substrates. Based on models developed and theoretical calculations, we fabricated highly efficient plasmonics-active one-dimensional (1D) and two-dimensional (2D) nanowire structures, on entire 4-inch wafers, for achieving a substantial electromagnetic enhancement of the SERS signals. Moreover, we were able to fabricate sub-5 nm nano-scale gaps in these SERS substrates over the entire 4-inch wafer (the first time this is being reported) by a process that is not time consuming or expensive and that is compatible with large-scale development of these SERS substrates on a wafer-scale and the existing silicon technology. Each 4-inch wafer was cleaved into hundreds of sensor chips for SERS based chemical and biological detection.