SILVER ION EXCHANGED SODA-LIME GLASSES FOR SERS PLATFORMS

Ion exchange in silver nitrate is gaining an increasing interest in plasmonics due to the possibility to induce the formation of silver nanoparticles in the glass matrix by an ad-hoc thermal post-process. Here we report the application of this technology in soda-lime glasses for the fabrication of SERS platforms both in planar and fiber configurations. Commercially available soda-lime glass (SLG) slides of dimensions (75 mm × 25 mm × 1.3 mm) and composition (in wt.%) 73.24% SiO2, 14.07% Na2O, 6,45% CaO, 4.08% MgO, 1.46% Al2O3, 0.18%, K2O and 0.09% Fe2O3 supplied by Gold Star, Chance Propper LTD. were used as substrates. After a standard cleaning procedure, the glass samples were immersed for 4 h in a molten salt bath of NaNO3:AgNO3 (95:5 mol.%) mixture at the temperature of 390 °C. Then, the resulting silver ion-exchanged glass samples (labelled as SLG1, SLG2, SLG3 and SLG4) were annealed at 550 °C for the different time intervals of 45 min and 3, 6 and 16 h, respectively. Finally, the annealed specimens were etched in 4% HF solution in order to remove about 350 nm of material and expose the Ag nanoparticles for SERS applications Commercially glass bar made available by Effetre Murano s.r.l., with a composition of 70,06% SiO2, 17,53% Na20, 8,87% CaO, 3,54% K2O, and Fe2O3 traces of around 0.27%, was drawn at the Polytechnic of Turin in order to obtain an optical fiber with a diameter of around 130 ?m. The tip of the fiber was ion- exchanged under the same conditions of molten salt and temperature already adopted for the planar samples. The ion-exchange duration was around 4 h and 30 min. Subsequently, the fiber tip was annealed at the temperature of 550 °C for 45 min. Atomic Force Microscopy (AFM), UV-Visible (UV-Vis) and SERS characterization of the aforementioned nanocomposite substrates showed the presence of Ag nanoparticles ranging in size from few nm to a few tens of nm, depending on the annealing conditions. SERS effect was observed on the fiber tip covered by 4- mercaptobenzoic acid (MBT) at 10-6 M by using a micro-Raman spectrometer with a 638 nm excitation wavelength, a 50xLWD objective and a 1200 gr/mm grating.