Abstract
Plasmonic nanostructures strongly localize electric fields on their surfaces via the collective oscillations of conducting electrons under stimulation by incident light at certain wavelength. Molecules adsorbed onto such surfaces experiences a strongly enhanced electric field due to the localized surface plasmon resonance (LSPR), which amplifies the Raman scattering signal from these molecules. This phenomenon is referred to as surface enhanced Raman scattering (SERS). Further enhancements in the Raman intensity have been achieved by designing plasmonic nanostructures with a controlled size, shape, composition, and arrangement. This review paper focuses on the theory and analyses the influence of protective coating with oxide materials an isolated plasmonic metal nanostructures. Starting with a brief description of the basic principles underlying LSPR and SERS, we compare two plasmonic metals, two dielectric materials and the effect of changing individual parameters of the nanostructure on output enhanced Raman signal.
Highlights
Surface-enhanced Raman scattering (SERS)For a direct, label free and non destructive characterization of molecules, vibrational spectroscopes are efficient interesting techniques
One way is to add nanostructured metallic film under irradiation and localized surface plasmon resonance (LSPR) at wavelength λLSP R will appear, meaning the appearance of surface waves corresponding to a collective oscillation of the excited conductive electrons or plasmons and local electromagnetic field will be induced
From the literature λLSP R should be located at some intermediate energy between the excitation λ0 and Raman λR electromagnetic fields to provide the maximum enhancement of the two factors [1, 4]
Summary
Label free and non destructive characterization of molecules, vibrational spectroscopes are efficient interesting techniques. Based on the determination of molecular or crystalline vibrations, Raman scattering provides many information about the studied object whatever is its nature (liquid, solid or gas). Detection of low concentrated molecules requires metallic surface nanostructure that promote enhanced Raman scattering (SERS). The second process results in the enhancement of the Raman scattered signal ER from probe molecule (at λR) at the vicinity of the nanoparticle surface and it’s called re-radiation process. Where I0 the Raman signal intensity scattered by the molecule If these two wavelengths λ0 and λR are close to each other it is considered that this two factors are approximately equal. From the literature λLSP R should be located at some intermediate energy between the excitation λ0 and Raman λR electromagnetic fields to provide the maximum enhancement of the two factors [1, 4]. Where Nsurf is the number of molecules bound to the enhancing metallic substrate, INRS is normal Raman intensity and Nvol is number of molecules in the excitation volume
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