Toward a thermally robust operando surface-enhanced raman spectroscopy substrate

The work presented here describes the first steps toward designing a thermally robust surface-enhanced Raman spectroscopy (SERS) substrate with the potential to conduct in situ monitoring of catalytic reactions. Nanosphere lithography (NSL) fabricated SERS substrates were coated with thin (0.2-1.0 nm) films of atomic layer deposited (ALD) Al ₂O ₃. The thermal stability of these substrates was examined at various temperatures (100-500°C) and over time (up to 6 h) in nitrogen. The results showed that ALD Al ₂O ₃ coated nanoparticles maintained their original geometry significantly better than the bare Ag nanoparticles. While experiments showed that thicker ALD Al ₂O ₃ coatings resulted in the most stable nanoparticle structure, ALD Al ₂O ₃ coatings as thin as 0.2 nm resulted in thermally robust nanostructures as well. Additionally, the ALD Al ₂O ₃ coated nanoparticles were heated under propane to mimic reaction conditions. These experiments showed that while the nanoparticle geometries were not as stable under reducing atmosphere conditions, they were much more stable than uncoated nanoparticles and therefore have the potential to be used for SERS monitoring of reactions conducted at elevated temperatures.