Large area hexagonal boron nitride coatings for SERS applications with silver nanoparticles

Hexagonal boron nitride (hBN) is a two-dimensional, wide-bandgap semiconductor which has a honeycomb like structure similar to that of graphene. hBN sheets has been shown to be highly effective in protecting metals against oxidation at high temperatures. Recently, atomically thin layers of two-dimensional (2D) materials, namely graphene and hexagonal Boron Nitride (hBN) have been used for passivating metallic nanoparticles for SERS applications. Mono- to few layers of graphene and hBN were shown to be highly effective in protecting metal nanoparticles, whilst preserving electro-magnetic hot spots. We report on wafer-scale growth of hexagonal boron nitride (hBN) on sapphire substrates using metal organic vapor phase epitaxy. The properties and characteristics of hBN layers studied using different techniques like Raman spectroscopy, atomic force microscopy and transmission electron microscopy are reported here. Furthermore, we utilize large area hBN, for passivating silver nanoparticles (Ag NPs) and validate its use for SERS. Ag NPs are known to yield highest sensitivity for SERS, but are prone to rapid oxidation in ambient conditions, and hence not utilized extensively. Here, we show that oxidation of Ag NPs can be prevented by hBN coatings and its SERS activity can be retained even after thermal annealing in air