SERS substrates based on self-organized dimple nanostructures on polyethylene naphthalate films produced via oxygen ion beam sputtering.

[Display omitted] • Dimple nanostructures are formed on PEN films using a one-step IBS. • Nanotip size, geometry controllable by varying ion-irradiation energy density. • Nanotips with spacing under 10 nm effectively enhanced SERS signal. • IBS process has potential for use in roll-to-roll manufacture of SERS substrates. Surface-enhanced Raman spectroscopy (SERS) utilizes metal nanostructures to enhance the intensity of Raman signals. Although many methods have been developed for fabricating SERS nanostructures, most involve multiple steps. Herein, we employed oxygen ion beam sputtering (IBS), a one-step technique suitable for processing flexible substrates in roll-to-roll processes for mass production, Specifically, one-step oxygen IBS was used to fabricate self-organized dimple nanostructures, whose area and roughness could be controlled using the ion irradiation energy density, on the surfaces of polyethylene naphthalate films. Gold nano-tips for SERS were subsequently obtained by evaporating gold onto the dimple nanostructures. Finite-difference time-domain (FDTD) simulations revealed that nano-tip structures with spacings of less than 10 nm increased the localized E-field enhancement, which improved the SERS signal. Fabrication at a low energy density (5.8 J/cm2) produced more nano-tips with spacings of less than 10 nm, corresponding to a density of 61.4 nano-tips/μm2. SERS analysis conducted with methylene blue at 638 nm and 785 nm demonstrated that the Raman signal intensity was stronger for SERS substrates fabricated with low energy density (5.8 J/cm2) than for substrates fabricated with high energy density (17.3 J/cm2), because of the high density of nano-tips on the former substrate. [ABSTRACT FROM AUTHOR]