Hreshchuk O. Relationship between morphological and structural features of metallic nanostructures with effects of Raman scattering enhancement

Dissertation represents results of studies of morphological and structural features of gold nanostructures with the effects of surface-enhancing Raman scattering (SERS) of analyte molecules. Effective SERS substrates, which are films based on nanoparticles (NP) of core-shell type - Au-SiO2, SiO2-Au, have been developed and investigated. It is established that for SERS substrates based on Au-/SiO2 nanostructures, the Raman signal enhancement is 102-103 (depending on the thickness of the shell), and for SiO2-Au - 104-105 (depending on the concentration of gold NP, on the SiO2 surface shell). The significant increase supposed by high increase of effective surface on which gold NP are deposited, as well as by the presence in the system of "hot spots" with high electric field strength. Two types of effective SERS substrates based on "nanostars" have been developed and investigated. It is demonstrated that by changing the size of the nucleus and the edge of the NP in the process of their synthesis, it is possible to adjust the parameters of plasmon absorption band of SERS substrates to the required laser excitation wavelength to realize the best resonant conditions of SERS. The correlation between results of the experimental data and theoretically modeled distribution of the EM field near the NP was found. It is established that the SERS signal gain from substrates based on gold “nanostars” 105 - 106. It is established that type II substrates can be used for the diagnosis of living tissues, since besides plasmon absorption band with a maximum at 600 nm, they are characterized by a band with a maximum at 1000 nm, which goes into the tissue transparency window. The morphological and optical properties of SERS substrates formed by interference photolithography have been investigated. The effect of significant increase in Raman scattering efficiency from analyte molecules due to annealing of such nanostructures with pre-deposited molecules was revealed. It is established that after annealing at T = 420 оС, the morphological homogeneity of nanostructures improves, their sizes and morphology changes respectively the half-width of the plasmon absorption band decreases and its maximum shifts from 670 to 600 nm. SERS substrates made by thermal deposition of metals have been developed and investigated. It has been shown that by thermal annealing of such films in the temperature range from 200 to 450oC it is possible to adjust the position of the plasmon absorption band to the required wavelength for resonance with exciting laser radiation. It has been demonstrated that this type of SERS substrate effectively amplifies the SERS signal from rhodamine 6G and crystalline violet molecules.