Atomic layer deposition of hafnium dioxide for increasing temporal stability of silver-capped silicon nanopillar substrates used for SERS

Surface-enhanced Raman spectroscopy (SERS) is a label-free optical method employed due to its sensitivity and specificity. Metal nanoparticles are commonly used as SERS substrates for detection of molecules and any change in the metal affect the SERS performance. Silver (Ag) is a renowned plasmonic material, but it presents relatively poor chemical stability. The application of thin surface coatings has been recognized as an effective approach to enhance the chemical stability of Ag nanostructures, while preserving their desirable sensitivity. Therefore, in this study 0–13 nm thick hafnium dioxide (HfO 2 ) coatings, deposited by atomic layer deposition (ALD), have been investigated to improve the temporal stability of Ag-capped silicon nanopillar (NP) SERS substrates. Comprehensive characterization was performed, and the SERS performance were evaluated with two reporter molecules on uncoated Ag-capped NP substrates. They displayed significant variation over time, while substrates with ∼1.5 nm HfO 2 exhibited superior signal stability and noise reduction. Over a 5-month period, substrate stability was tested for detection of the nitroaromatic explosive 2,4-dinitrophenol. The limit of detection (LoD) and limit of quantification (LoQ) of uncoated Ag-capped NPs varied significantly, whereas HfO 2 -coated substrates maintained a stable SERS performance with limited variation in the LoD and LoQ, thereby ensuring consistent results.