Ion Flux-Induced Effects on the Nanoscale Morphology of Poly(dimethylsiloxane): Implications for Tunable SERS Response

Micro and nanoscale patterning of polymeric surfaces has attracted considerable interest due to its relevance in flexible electronics, biosensing devices, optical components, and surface-enhanced Raman scattering (SERS) substrates. We investigate the evolution of nanoscale surface morphology in polydimethylsiloxane (PDMS) under low-energy ion irradiation, focusing on the role of ion flux. While ion-beam-induced patterning in polymers has been widely studied, the flux-dependent mechanisms governing stress generation and wrinkle formation at the nanoscale in PDMS remain largely unexplored. Our results reveal a strong flux dependence in surface morphology and wrinkle development. At lower beam currents, corresponding to ion fluxes ∼10 14 ions cm –2 s –1, longer irradiation times allow viscoelastic relaxation and radical recombination, thereby limiting compressive stress buildup and producing weakly developed wrinkles. In contrast, higher beam currents, corresponding to ion fluxes ∼10 15 ions cm –2 s –1, promote rapid ion-induced surface stiffening, enabling efficient compressive stress accumulation and the formation of well-defined wrinkle patterns. In contrast, crystalline Si irradiated under identical conditions shows negligible surface morphological evolution, underscoring the fundamentally different response of polymeric and crystalline materials. Nanomechanical measurements reveal a clear increase in the Young’s modulus of the irradiated surface layer, from 1.5 MPa (pristine) to 11 MPa upon irradiation indicating progressive stiffening with ion exposure. Complementary X-ray photoelectron spectroscopy confirms the formation of a silica-like SiO x layer confined within the ion penetration depth, establishing the chemical origin of the mechanical modification. Finally, SERS measurements on the patterned surfaces show a systematic dependence of enhancement, albeit small, on beam current, demonstrating that ion-beam-driven morphology control provides a versatile route to engineer functional nanostructured SERS-active polymer substrates.