Raman spectroscopy is an extremely sensitive and effective method for studying the structure of macromolecules and their changes. The specially designed SERS substrates are one of the ways to enhance Raman signals. Such substrates can significantly increase the sensitivity of optical diagnostics of materials in the ultra-small quantities. It is important for different applications in science, industry and human activity. At present time, the problem of design and optimization of the different substrates for enhance Raman signals remains relevant. The periodic structures on base of, both metal gratings on a dielectric substrate and metal gratings on a metal substrate can be used as SERS-substrates.
In this work, modeling of the distribution of an electromagnetic field and an enhanced factor by periodic structures consisting of rectangular diffraction metal (silver) gratings on a dielectric (polycarbonate) and metal (silver) substrates have been carried out for excitation wavelengths of 532 nm (Nd: YAG laser on the second harmonics), 633 nm (He-Ne-laser) and 785 nm (diode laser) for maximum enhancing of Raman signals. The optimal grating parameters are determined which provide maximum concentration of electromagnetic field for these wavelengths of exciting radiation. The modeling results showed that maximum enhanced field is obtained for the given wavelength and grating period only at certain values of the grating thickness and the filling factor. Periodic structures on the basis of the metal grating on the metal substrate showed significantly higher enhance of the electromagnetic field (90 units) compared to structures based on the metal grating on the dielectric substrate (15 units). Consequently, such structures are more suitable for effective application as SERS- substrates.
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