Wafer-scale 3D cloud-like aluminum hierarchical nanostructure for NIR SERS

Plasmonic nanomaterials with a high density of accessible hot spots over a large area are highly desirable for ultrasensitive near-infrared surface-enhanced Raman scattering (NIR SERS) sensing, especially those based on low-cost and earth-abundant noncoinage metals. Here, we report a facile thermal evaporation approach to fabricate 3D hierarchical aluminum cloud-like nanostructures decorated with nanoparticles on a wafer-sized substrate, which can provide high enhancement of Raman signals using 785 nm excitation. This enhancement is attributed to its absorption peak close to the excitation wavelength and high density of hot spots constructed by adjacent large cloud-like nanostructures and/or small nanoparticles. Systematic measurements and statistical analysis show that the obtained NIR SERS substrates exhibit high enhancement factor (1.48×105), long-term stability, and excellent reproducibility with less than 7% standard deviation over a 4-inch wafer surface. The combination of significant enhancement, long-term stability, good reproducibility, and scalable production process suggest that this type of 3D hierarchical aluminum nanostructures hold promise as a robust low-cost plasmonic material for applications in the near infrared SERS operation.