Shelf time effect on SERS effectiveness of silver nanorod prepared by OAD technique

Recent developments in silver nanorods, fabricated by oblique-angle deposition (OAD) technique, have provide a great ability to produce high gain enhancement, reproducible, uniform response, and low-cost surface-enhanced Raman scattering (SERS) substrates. However, shelf-time stability, while not well studied, of this type of the substrates has been a primary concern for future SERS applications. Therefore, this work aimed to provide a better understanding of the shelf-time effect, within a normal laboratory storage condition, on the stability of SERS effectiveness for the OAD-based silver nanorods. For this purpose, SERS substrates consisting of the silver nanorods were prepared by an electron-beam metal evaporator, based on the OAD technique. The prepared substrates were systematically kept in laboratory storage for an experimental period of one month in order to represent their shelf life. When methylene blue molecules, previously exposed on the SERS surface, were used as probing reference, SERS spectra of such molecules were periodically recorded. Subsequently, gain enhancement factors were calculated from the measured spectra to monitor the change in effectiveness of the SERS substrates under prolonged storage time. Auger electron spectroscopy (AES) was performed to investigate degradation in the SERS effectiveness from an accumulation of residual contaminants from ambient air onto the substrate surface. In addition, an effect of ion etching was further investigated in an attempt to remove the adsorbed molecules. Our discovery confirmed that the SERS effectiveness was recovered by the ion treatment, which efficiently extended the SERS shelf life for practical applications.