Ultra-thin Sputtered Silver Films for Ultrasensitive SERS Detection: Synergistic Roles of Electromagnetic and Chemical Enhancement Mechanisms

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© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.This study presents the fabrication and optimization of ultrathin silver (Ag) films by low-power DC magnetron sputtering for surface-enhanced Raman spectroscopy (SERS) applications, with emphasis on the synergistic roles of electromagnetic (EM) and chemical enhancement (CE) mechanisms. Ag nanostructures were deposited onto glass substrates with controlled deposition durations (10–300 s), enabling the formation of tunable morphologies ranging from isolated nanoparticles to quasi-continuous nanostructured films. Structural and optical analyses revealed that an ~ 8.2 nm-thick Ag film exhibits optimal SERS performance due to its interconnected architecture, high surface asymmetry, and enhanced plasmonic coupling. SERS measurements were conducted using two cationic dyes—Rhodamine 6G (R6G) and Rhodamine B (RhB)—selected for their well-characterized Raman signatures and distinct surface adsorption behaviors. The optimized Ag substrate achieved enhancement factors in the range of 10⁶–10⁹ and detection limits down to 7 × 10⁻12M. Wavelength-dependent experiments using 532 nm and 633 nm excitation revealed strong SERS responses at both wavelengths, with maximal enhancement observed at 633 nm due to superior resonance alignment with the localized surface plasmon modes of the film. Electromagnetic field estimations based on UV–Vis absorbance correlated well with experimental trends, confirming EM as the dominant mechanism. Nonetheless, energy-level alignment between the Ag Fermi level and the molecular orbitals of the dyes, particularly for R6G, supports a secondary contribution from CE, driven by charge-transfer interactions and electrostatic adsorption. These findings demonstrate that the concurrent optimization of nanostructure, plasmonic response, and analyte–surface interaction is essential for enhancing both EM and CE effects. The substrate also enabled detection of Escherichia coli, underscoring its potential for biosensing at ultra-trace levels.

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