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The effect of plasmonic nanostructures (NSs) on the Raman spectra and underlying structural changes in thin chalcogenide films is investigated. Several tens of nanometers thick As2S3 and Se films were deposited by thermal sputtering on glass and surface-enhanced Raman spectroscopy (SERS) substrates based on gold nanostructures for comparison. The films on glass were practically not detectable by the Raman spectroscopy. Using gold NSs as the substrates enabled reliable registration of the Raman spectra of both the As2S3 and Se films. The registered Raman spectra contained all the features usually present in the films with the thicknesses ~1 μm or more. Based on our analysis of the spectra obtained at different excitation wavelengths, we may conclude that the SERS chemical mechanism makes the main contribution to the enhancement of the Raman signal from chalcogenide films. Adjustment of the parameters of SERS substrates to tune their plasmon band position in resonance with the excitation laser radiation enables increasing the plasmonic enhancement contribution. Besides the effect of enhancement, localized plasmon resonance in the gold NSs causes local heating of the chalcogenide film around them leading to local structural transformations, which can be controlled using the Raman spectra. [ABSTRACT FROM AUTHOR]

Biomorphic carbon matrices (BCMs) were produced by pyrolysis from wood species of different forest and garden trees, after which the as-prepared BCMs were converted to SiC ceramics through their impregnation with liquid silicon and further heat-treatment. Both types of obtained samples were studied by scanning electron microscopy (SEM), Raman scattering (RS), and electron spin resonance (ESR) methods. The SEM data reveal that all BCM samples contain large (10–50 μm) and small (1–5 μm) micro-pores with surface densities ∼109 m−2 and 1011 m−2, respectively. Analysis of RS allowed to estimate carbon cluster sizes of about 5–11 nm depending on the sample type. The study of the electronic structure using ESR spectroscopy is carried out for BCM and SiC ceramics samples. Using theoretical analysis of the ESR spectra, it was found that spin resonance in BCMs is due to the contribution of three spin systems: free electron spins, "pseudo-free" electron spins from the tail of density states below the conduction band, and localized spins at dangling carbon bonds (DCBs). Their contributions depend on the ratio of different structural phases such as sp2-hybridized graphite-like carbon network and amorphous carbon phase. For most BCM samples, the large ESR line width is dramatically narrowed when samples are pumped out due to the exclusion of the broadening effect of molecular oxygen. The transformation of BCM into SiC by impregnation with liquid silicon can be clearly traced in the Raman spectra and in the ESR spectra. It is established that the electronic properties of synthesized SiC ceramics are due to the presence of residual graphite-like carbon nanoclusters. [ABSTRACT FROM AUTHOR]

Laterally ordered gold nanoisland arrays made using interference lithography has been investigated in this work as SERS substrates. The developed substrates demonstrate performance in enhancing Raman signal of common dye analyte (crystal violet (CV)) comparable to commercial SERS substrates, with the lowest detectable concentration of CV ~10−6…10−7 M. They can be reused after heat treatment at 300 °C without any drop of performance. Furthermore, we found a principal difference in the effect of annealing of SERS substrates before deposition of the analyte molecules and additional in situ annealing (with molecules) on the intensity of Raman signal. Possible physical origin of the latter effect has been discussed. [ABSTRACT FROM AUTHOR]

Using the method of chemical synthesis, effective SERS substrates were developed, which were the films of gold nanoparticles possessing the form of stars. The peculiarity of star-shaped nanoparticles is that they could enhance the electric field of the radiating dipole not only by setting the frequency of the plasmon absorption band at the frequency of the exciting laser radiation, but additionally due to significant contribution to Raman scattering of the so-called "hot spots" that exist at the edges of the stars. "Nanostar"-based films were prepared using both direct deposition of gold nanoparticles from colloidal solution on the glass substrate and on the layer of polycation of polydiallyldimethyl ammonium bromide on the surface of glass substrates. Surface morphology of the obtained films was investigated using scanning electron microscopy. Plasmon absorption spectra were obtained using the method of optical absorption. Variation of geometrical parameters inherent to these nanostructures allows configuring the position of the plasmonic absorption band maximum close to the laser excitation wavelength. The coefficient of enhancement of Raman signal was evaluated for Rhodamine 6G molecules deposited on the designed SERS substrates (for different wavelengths of the exciting laser radiation, namely: λ = 633, 532 and 457 nm). [ABSTRACT FROM AUTHOR]

The efficient SERS (surface enhanced Raman scattering) substrates that are films of nanoparticles (NP) of the "core--shell" type, where the core of SiO2, and the shell of gold nanoparticles, were developed in this work. Application of scanning electron microscopy and optical absorption enabled to find correlation between surface morphology of nanostructures and position of the plasmon absorption band. It helped to adjust the latter to the wavelength of exciting laser radiation. It has been shown that the designed nanostructures are able to enhance electric field of an emitting dipole not only due to adjustment of the band frequency for plasmon absorption to the wavelength of exciting laser radiation but also due to contribution of the so-called "hot spots" to enhancement of electric field scattering. Analysis of characteristics inherent to SERS substrates with nanostructures of the soil core -- Au shell type has shown that they enhance the Raman signal by 5 orders higher as compared with the substrates based on SiO2 nanospheres not covered with gold nanoparticles. [ABSTRACT FROM AUTHOR]

Optical constants of Cu2ZnSnS414 thin films formed using thermal annealing of pre-deposited layers of copper, zinc and tin sulphides on glass substrates at different temperatures and ambient atmosphere were determined. It has been shown that films grown at lower temperatures have the tetragonal structure of kesterite, and the corresponding value of the optical band gap is 1.47 eV. [ABSTRACT FROM AUTHOR]