*2.2. Deposition of Thin Films*

Water–methanol solutions in a volume ratio of 20:80 and concentrations of 1 and 2 wt.% were used for deposition of acetal modified PVA films. Thin polymer films were deposited by spin-coating method at a rotation speed of 4000 rpm and time of 60 s using 0.250 mL of the solution. After deposition, the films were annealed in air for 30 min at 60 and 180 ◦C. For comparison, films of neat PVA were also prepared by depositing 2 and 5 wt.% water solution of PVA to achieve the same film thicknesses as in the case of modified films. Silicon wafers and Au–Pd covered optical glass plates were used as substrates. The Au–Pd sublayers with Au:Pd ratio of 80:20 and thickness of 30 nm were deposited on glass substrates by cathode sputtering of gold/palladium target (Quorum Technologies, Lewes, UK) for

60 s under vacuum 4 <sup>×</sup> 10−<sup>2</sup> mbar using Mini Sputter Coater SC7620 system (Quorum Technologies, Lewes, UK).

Polymer thin films composites (polymer doped with SiO2 particles) were spin-coated on silicon wafers (0.250 mL solution at concentration of 1 wt.%, 4000 rpm, 60 s) and post-annealed at 60 ◦C for 30 min.
