Unraveling the Near- and Far-Field Relationship of 2D Surface-Enhanced Raman Spectroscopy Substrates Using Wavelength-Scan Surface-Enhanced Raman Excitation Spectroscopy

Lithographic and nonlithographic two-dimensional (2D) substrates for surface-enhanced Raman spectroscopy (SERS) have gained enormous popularity as analytical platforms for detection and identification of various analytes. However, their near- and far-field properties in most cases remain poorly understood. We have previously developed a metal nanopillar film over nanospheres (FON) platform exhibiting Raman enhancement factors of ∼10⁷. These substrates have a reproducible and predictable localized surface plasmon resonance throughout the entire visible region and much of the near-IR region of the electromagnetic spectrum. Extending upon these results, we have utilized wavelength-scan surface-enhanced Raman excitation spectroscopy to unravel the relationship between near- and far-field properties of FON surface-enhanced Raman spectroscopy substrates. We examined by scanning electron microscopy FONs fabricated by either stationary (ST-FONs) or spun (SP-FONs) metal deposition to examine the interrelationships of nanoscale structure and near- and far-fied properties. We demonstrate that the line width and spectral position of the far-field and near-field resonances of ST- and SP-FONs directly depend on the nanofeature distribution at the metallic surface. In particular, we show that the actual nanofeature morphology and distribution directly impact the spectral alignment of the far-field and near-field resonances.