Ion-Engineered Nanostructuring of MoO ₃ –Ag–Au Multilayer Surfaces as SERS Substrates for the Detection of Organic Molecules

Surface-enhanced Raman spectroscopy (SERS) is a potent, label-free method for highly sensitive molecular detection. We illustrate the ion-beam engineering of MoO 3 –Ag–Au multilayer plasmonic substrates to improve SERS performance. Orthorhombic α-MoO 3 microflakes were produced via chemical vapor deposition (CVD) on Si/SiO 2 substrates. Thin films of Ag (5 nm) and Au (5 nm) were thermally evaporated onto the MoO 3 flakes, and the samples were subjected to 100 MeV Ag 8+ swift heavy ion irradiation at fluences of 3 × 10 11 and 3 × 10 12 ions/cm 2 . Irradiation causes dewetting of metal films, prompting structural and morphological changes that result in the formation of dispersed Ag–Au nanoparticles, enhanced surface roughness, and defect generation within the MoO 3 lattice. X-ray diffraction (XRD) verifies the α-MoO 3 phase; field emission scanning electron microscopy (FESEM) elucidates nanoparticle formation and surface reorganization; Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose vibrational alterations and binding-energy shifts in Mo 3d, indicative of oxygen vacancies (V_O) and partial reduction of Mo. SERS measurements of molecular probes demonstrate significantly increased Raman intensities following ion irradiation. Finite-difference time-domain (FDTD) simulations assess localized surface plasmon resonance (LSPR) and near-field enhancement linked to the nanoparticle–flake configuration, while density functional theory (DFT) calculations of the electronic structure and density of states (DOS) validate the involvement of V_O in facilitating charge-transfer interactions. Experimental and theoretical evidence suggests that targeted swift-ion irradiation adjusts both electromagnetic and chemical enhancement mechanisms in MoO 3 –Ag–Au multilayer nanostructures, offering a reliable method for creating tunable, high-performance SERS substrates for ultrasensitive molecular detection.