Optimizing silver‐capped silicon nanopillars to simultaneously realize macroscopic, practical‐level SERS signal reproducibility and high enhancement at low costs

Abstract

The ideal surface‐enhanced Raman spectroscopy (SERS) substrate should fulfil the following: (a) predictable SERS enhancement, (b) macroscale SERS signal uniformity, and (c) suitability for mass production at low costs. Macroscale SERS uniformity and reproducibility at practical levels are big obstacles, which have been preventing most SERS substrates from reliable sensing applications. We have previously shown that SERS‐active nanopillar structures, fabricated by lithography‐free processes, exhibit high average SERS enhancements and are mass producible. Here, we report an optimized process and show that the improved structures exhibit unrivalled macroscale SERS uniformities (RSD: ∼2.5% in millimeter scale, ∼7% in wafer scale) and reproducibility (RSD: ∼1.5% across 3 wafers), while at the same time exhibiting a very large average SERS enhancement factor of >108. The obtained SERS uniformity (~2.5% RSD in millimeter scale) is the best to date measured on large‐area solid SERS substrates. Fast and reproducible SERS analysis of trans‐1,2‐bis (4‐pyridyl) ethylene down to 4 × 10−13 mol is demonstrated using the optimized structures. We emphasize that achieving simultaneously macroscopic, practical‐level SERS signal reproducibility and high enhancement via a lithography‐free process is a notable advance towards industrialization of substrate‐based SERS sensors.

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…K. Wu et al presented research aimed at optimizing silver‐capped silicon nanopillars to simultaneously realize macroscopic, practical‐level SERS signal reproducibility and high enhancement at low costs. They note that achieving simultaneously macroscopic, practical‐level SERS signal reproducibility and high enhancement via a lithography‐free process is a significant advance towards industrialization of substrate‐based SERS sensors . J.‐L.…”

Optimizing noncontact oxygen‐plasma treatment to improve the performance of a top‐down nanofabricated surface enhanced Raman spectroscopy substrate with structurally responsive, high‐aspect‐ratio nanopillar array

“…The SERS enhancement for the as‐supplied nanopillar array substrates is determined by the array and metal coating parameters [ 7,33,34 ] set, within fabrication tolerances, by the manufacturer. Relative gains with oxygen‐plasma treatment will furthermore depend on the degree and nature of the contamination and how well the optical sampling is matched to the substrate structure and analyte disposition.…”

Wafer‐Scale Polymer‐Based Transparent Nanocorals with Excellent Nanoplasmonic Photothermal Stability for High‐Power and Superfast SERS Imaging

“…Maskless RIE using mixed SF 6 and O 2 plasma is frequently employed to produce other state‐of‐the‐art wafer‐scale SERS substrates, such as the widely used metal‐capped silicon nanopillars . It, however, usually causes significant structural inhomogeneity across the wafer, due to pronounced macroloading effect, leading to poor yield and nonuniform SERS signals . Macroloading effect means that etch rate becomes slower with more exposed etch area, due to depletion of etchant.…”

“…The different colors of the nanopillar substrate with ring patterns indicate structural inhomogeneity across the wafer, caused by macroloading effect during RIE. This leads to poor yield and inconsistent SERS performance across the wafer …”