1：Experimental Design and Method Selection:

The study involved the production of Ag/ZnO, ZnO/Ag bilayers, and ZnO/Ag/ZnO multilayers by vacuum thermal evaporation. The role of thickness of the individual layers in the range of 5-50 nm was investigated.

2：Sample Selection and Data Sources:

Thin films of Ag and ZnO were deposited on glass substrates. The thickness of the films was measured using a quartz crystal thickness monitor.

3：List of Experimental Equipment and Materials:

UV-VIS-NIR spectrophotometer (Elico model No. SL 159), powder X-ray diffractometer (XRD) (Philips PW 1830 with Cu Kα radiation), confocal micro-Raman spectrometer (Alpha 300 of Witec, Germany), atomic force microscope (NT-MDT Model Solver Pro), Edinburgh UV-VIS-NIR (FLS 980) spectrometer.

4：Experimental Procedures and Operational Workflow:

The films were deposited on glass substrates by resistive thermal evaporation. The substrates were cleaned with acetone and ethanol and then rinsed with ethanol in an ultrasonic cleaner prior to each deposition. The spectral transmission curves were recorded, and the crystal structure of the films was obtained from XRD. Raman spectra were recorded, and atomic force microscope images were acquired.

5：Data Analysis Methods:

The SERS spectra were background subtracted with an appropriate polynomial fitting followed by smoothing the spectrum by adjacent averaging function. The enhancement factors (EF) were calculated using the relationship between the intensities of selected Raman peak of R6G molecule collected over the SERS active substrate and non-resonant substrate.