Rapid and flexible construction of inverted silicon architectures with nanogaps as high-performance SERS substrates

Abstract

Three-dimensional (3D) plasmonic nanostructures act as excellent surface-enhanced Raman spectroscopy (SERS) substrates for detecting trace analytes. Nevertheless, an efficient 3D architecture and the optimal fabrication route remain to be uncovered to further raise the performance of 3D SERS substrates and expand application horizons. This work reports a cost-effective and flexible route to fabricate 3D inverted silicon (Si) architectures with nanogaps that are difficult to achieve by conventional lithography towards SERS applications. Finite-difference time-domain simulations demonstrated that the distribution of electrical field depended significantly on the architecture and layout of inverted pyramids. Several parameters including volume ratio of HF/HNO3 mixtures, indentation force and etching time were evaluated to determine optimal fabrication process of inverted Si architecture. Based on an electrochemical dissolution model and molecular dynamic simulations, the rapid selective etching can be ascribed to nanocrystals in amorphous Si (a-Si) regions, and distorted Si beneath a-Si layer. SERS detection illustrated an impressive sensitivity and excellent reproducibility, and the practical applicability of as-prepared SERS substrates was demonstrated by detecting malachite green residues from different water environments as well as fish tissues and scales. The proposed selective etching provides a brand-new route for manufacturing high-performance 3D architecture substrates for SERS applications.