Papers by Keyword: Raman Scattering

Abstract: The work is devoted to preparation and optical study of thin solid films of pseudo-binary AsS₃ - GeS₄ glasses, which are remarkable as topologically belonging to isostatic materials from intermediate phase (IP) region. The glasses from IP are stress free due to their structural self-organization, consequently have to be more stable and viable. To maintain the composition of the bulk source material, the films were grown via a very fast thermal vacuum evaporation of powder of relevant glasses onto optical quartz substrates. The optical properties of (GeS₄)_x(AsS₃)_1-x films (x = 0 ÷ 1) were studied by spectroscopic ellipsometry in the spectral range 0.35 ÷ 1.77 µm. It was pointed out that the films under investigation are entirely transparent in the visible and IR spectral region λ = 0.45 ÷ 1.77 µm. The refractive index follows the usual curves of a normal dispersion, reaching the maximal value around n = 3.0 at λ = 0.35 µm for AsS₃ and the minimal one around n = 1.97 at λ = 1,77 µm for Ge_17.2As_3.5S_79.3. The glass composition strongly influences the refractive index in the visible spectral range but this influence becomes must more moderate in the IR one. It was pointed out that independent on wavelength, both the extinction coefficient and refractive index nearly linearly falls with germanium concentration increase, with an exception related to ternary Ge_17.2As_3.5S_79.3, in which the extinction coefficient shifts toward higher values but the refractive index toward lower values than those expected from aforementioned linearities. The Raman spectra analysis of the studied thin films allowed explanation of this feature in terms of inhomogeneity of the Ge_17.2As_3.5S_79.3 films, caused by a great quantity of the nanoscale - separated stoichiometric As₂S₃ forming in Ge_17.2As_3.5S_79.3 films during their growing.

Abstract: In order to selectively analyze active thin layers close to surface in power devices structures, Raman scattering is necessary with UV excitation. However, the Raman spectra of GaN are usually affected by the direct bandgap photoluminescence of the material, which interferes with the Raman measurements and decreases the quality and resolution of the Raman spectra. In this work, we demonstrate experimentally that nanostructured aluminum films deposed on GaN epitaxial layers decrease the influence of the photoluminescence on the resonant Raman spectra and increase its overall spatial resolution under UV illumination.

Abstract: The features of the structure of single crystals LiNbO₃:B³⁺ (0.12 and 0.18 wt %) grown by the Czochralski method from the mixture of different genesis were studied. It was found that boron is able to incorporate into the crystal structure of lithium niobate in a trace amounts (~ 10^–4–10^–5 wt %), decreasing the concentration of structural defects Nb_Li. Thus, ordering of structural units of the cation sublattice of lithium niobate crystals grown from a congruent composition melt approach in that of stoichiometric crystals.

Abstract: One-dimensional CdZnS nanostructures have been synthesized through the sublimation. Effect of high substrate temperature on morphology, structural and optical properties of these nanostructures has been studied. X-Ray diffraction peak intensity, lattice parameters, crystallite size decreased with an increase in substrate temperature. The morphology changed with the increase in the substrate temperature. Raman Spectroscopy confirmed the existence of constituent elements in CdZnS solid solution and an increase of Zn concentration with the rise in substrate temperature. The nanostructures exhibited strong photoluminescence emission in the green light region with a substrate temperature-dependent blue shift of 53 meV in emission energy. The Stoke’s shift energy raised from 45 meV to 302 meV as the substrate temperature increased from 510 °C to 550 °C. The stoichiometric deviancies, crystallite size, and quantum confinement effects resulted into an increase in the optical band gap from 2.4 eV to 2.71 eV. The results showed that CdZnS nanostructures could be potential candidates for nanostructure based optoelectronics and photovoltaic devices.

Abstract: Graphene grown by chemical vapor deposition on copper and the one transferred to Si/SiO₂ substrate were subjected to Ar ion treatment. A combination of X-ray photoelectron spectroscopy and Raman spectroscopy were used for characterization. According to XPS data sample on Si/SiO₂ appears less susceptible to sputtering under bombardment. However, the defect concentrations introduced to the transferred graphene reach up the value two orders of magnitude higher than that in as grown graphene on Cu. We attribute this difference to the influence of the non-compensated charge formed on the insulating SiO₂ layer under bombardment.

Abstract: Modifying the optical characteristics of rare earth (RE) doped inorganic glasses by stimulating surface plasmon resonance (SPR) via controlled growth of metal nanoparticles (NPs) is an outstanding quest in glass plasmonics. Glasses with composition 70TeO₂-20ZnO-10Na₂O-(x)Er₂O₃-(y)Au (x = 0.0 and 1.0 mol%; y = 0.0 and 0.6 mol% both in excess) are synthesized using melt-quenching technique and characterized. Influences of heat treatment temperature on the growth of Au NPs and their subsequent impacts on Raman spectral features modifications are inspected. The amorphous nature of glass is confirmed by using XRD. TEM reveal the non-spherical Au NPs with average diameter vary from 7.4 to 10.3 nm. Surface plasmon band is evidenced around 627 - 632 nm. Raman spectra demonstrate the presence of Er-O and Zn-O bond, anti-symmetric vibrations of Te-O-Te bonds and stretching modes of non-bonded oxygen exists in TeO₃ and TeO₃₊₁ unit. The amplifications in Raman signals by a factor of 1.39, 1.40, 0.88 and 1.29 and 1.25 corresponding to the peak centered at 262, 382, 536, 670 and 725 cm^-1 are attributed to the contribution of a surface plasmon (SP) generating a strong, localized and secondary field. The excellent features of the results suggest that our systematic method of controlled NPs growth may constitute a basis for improving the spectral features of tellurite glasses useful for the development of efficient and economic up-converted lasers.

Abstract: Mist-atomization deposition method was applied in order to grow ZnO nanoparticles on Au-seeded glass substrates acting as seeded template. Ag doped ZnO thin films were deposited on ZnO seeded templates by solution-immersion method. The influence of Ag doping content on the optical and Raman scattering properties of ZnO films were systematically investigated by UV-Vis transmittance measurement measured by ultra-violet visible spectroscopy (UV-Vis) and Raman scattering spectrum measured by Raman spectroscopy under room temperature. From UV-Vis transmittance measurement, the incorporation of Ag dopant to the ZnO makes the transmittance wavelength shifted to the shorter wavelength as compared to the pure ZnO. From Raman spectra, 4 cm^-1 downshift is observed in Ag-doped thin films as compared to pure ZnO thin films. This Raman peak shift shows that a tensile stress existed in the Ag-doped ZnO film.

Abstract: A series of aluminium doped (from 2×10¹⁶ to 8×10¹⁹ cm^-3) 4H-SiC epitaxial layers were mainly studied by Low Temperature Photoluminescence and time-resolved optical pump-probe techniques to determine the concentration of aluminium, its activation ratio, the doping related carrier lifetime, hole mobility and excess carrier diffusion length.

Abstract: The results of study of surface morphology and chemical composition of biocompatible titanium oxide and oxynitride coatings deposited by the method of reactive magnetron sputtering are presented in this paper. The distribution of coating’s fragments in size was obtained. Molecular composition of the coatings was obtained by scanning electron microscopy and Raman scattering.

Abstract: This work presents experimental evidence of the formation mechanisms of few-layer graphene (FLG) films on SiC by nickel silicidation. FLG is formed by annealing of a 40 nm thick Ni layer on 6H-SiC at 1035^ºC for 60 s, resulting in a Ni₂Si layer which may be capped by any Ni that did not react during annealing. It has been proposed that FLG forms on top of the Ni during the high temperature stage. In contrast, during cooling, carbon atoms which were released during the silicidation reaction may diffuse back towards the Ni₂Si/SiC interface to form a second FLG film. After annealing, layer-by-layer de-processing was carried out in order to unequivocally identify the FLG at each location using Atomic force microscopy (AFM) and Raman spectroscopy.