Low-Variance Surface-Enhanced\nRaman Spectroscopy Using\nConfined Gold Nanoparticles over Silicon Nanocones

Abstract

Surface-enhanced Raman spectroscopy (SERS) substrates\nare of utmost\ninterest in the analyte detection of biological and chemical diagnostics.\nThis is primarily due to the ability of SERS to sensitively measure\nanalytes present in localized hot spots of the SERS nanostructures.\nIn this work, we present the formation of 67 ± 6 nm diameter\ngold nanoparticles supported by vertically aligned shell-insulated\nsilicon nanocones for ultralow variance SERS. The nanoparticles are\nobtained through discrete rotation glancing angle deposition of gold\nin an e-beam evaporating system. The morphology is assessed through\nfocused ion beam tomography, energy-dispersive X-ray spectroscopy,\nand scanning electron microscopy. The optical properties are discussed\nand evaluated through reflectance measurements and finite-difference\ntime-domain simulations. Lastly, the SERS activity is measured by\nbenzenethiol functionalization and subsequent Raman spectroscopy in\nthe surface scanning mode. We report a homogeneous analytical enhancement\nfactor of 2.2 ± 0.1 × 10⁷ (99% confidence interval\nfor <i>N</i> = 400 grid spots) and made a comparison to\nother lithographically derived assemblies used in SERS. The strikingly\nlow variance (4%) of our substrates facilitates its use for many potential\nSERS applications.