Improved stabilities on surface-enhanced Raman scattering-active Ag/Al ₂O₃ films on substrates

As is shown in the literature, surface-enhanced Raman scattering (SERS)-active Ag films obtained by the salting-out of Ag colloids from solutions with some salts, are popularly used to examine the structure of analytes. SERS-active Ag nanoparticles (NPs) demonstrate more significant SERS effects than Au NPs, however, problems regarding the stabilities of SERS-active Ag NPs remain to be overcome. In this work, Ag/Al₂O₃ colloids were prepared in 0.1 M HNO₃ solutions containing Al₂O ₃ NPs with higher heat capacity by sonoelectrochemical methods. SERS-active Ag/Al₂O₃ films deposited on glass slides were prepared by the addition of a saturated NaCl solution in the prepared Ag/Al ₂O₃ colloids-containing solution. In an acceptable sacrifice of Raman intensity by ca. 30% magnitude, the prepared Ag/Al ₂O₃ films markedly improved thermal stability by raising the operation temperature over 100 °C, compared to Ag films. Meanwhile, aging of SERS enhancement capability in an atmosphere of relative humidity (RH) of 50% and 20% (v/v) O₂ at 30 °C is significantly depressed using Ag/Al₂O₃ films.