Papers by Keyword: Raman Spectra

Abstract: In this work we investigate and analyze phase composition and structure parameters of the nanocomposites obtained by the melt-based impregnation of porous opal matrices with dielectrics prospective for optoelectronics applications Bi₁₂GeO₂₀ and NaBi (MoO₄)₂. The embedded material is formed inside opal pores as nanocrystals with an average linear size not exceeding 50 nm and modified lattice parameters. In the case of impregnating opals with Bi₁₂GeO₂₀, new additional compounds are produced and transformation of opal matrix from amorphous to crystalline state is observed. These effects are discussed in the framework of the interaction of bismuth cations with the surface of the 285 nm SiO₂ particles that compose opal matrix. No stoichiometry deviations and new phases are detected in “opal-NaBi (MoO₄)₂” composite.

Abstract: Controllable mechanical properties of highly performed Poly (L-lactide acid) (PLLA) monofilaments with oriented molecular structure could widen their applications, especially in biomedical field. Herein, different heat treatments were applied to regulate the degree of molecular relaxation of oriented PLLA monofilaments to tune their mechanical properties. These filaments were manufactured by melting spun and solid-state drawing processes. Then, they were processed by different heat treatments, including annealing, normalizing, and quenching. As the cooling time extension, an obvious molecular orientation loss in filaments happened and increased regularly, and it could reach up to about 35.1% maximumly. However, molecules only in crystal phase were limitedly affected. As a result, mechanical performances of these filaments exhibited a corresponding change after heat treatments. Young’s modulus and elongation at break were promoted after all kinds of post-processes and increased with longer cooling time gradually. But breaking strength showed a contrast change. It means that different heat treatments could be effective avenues to control mechanical properties of oriented PLLA materials by altering the orientation structure.

Abstract: Investigation of the reaction kinetics between Ni film and 4H-SiC substrate at temperatures which are usually used for ohmic contacts formation provides valuable insights into the studies on fundamental properties of ohmic contacts to 4H-SiC, which are limiting the switching speed, energy efficiency and high-temperature thermal stability of SiC MOSFETs. High Resolution Scanning Electron Microscope (HRSEM) and Raman spectroscopy were used to elaborately characterize the interfacial reaction products under various annealing conditions and to assess the thicknesses of reaction diffusion layers. The square of reaction layer thicknesses versus time followed parabolic law and the apparent active energy of interfacial reaction was derived as 1.5 eV (145 kJ/mol). For Raman spectra, the intensity ratio of two Raman peaks for each nickel silicide detected varied monotonically with temperature in the same trend, indicating that crystal quality of nickel silicide film was improved with annealing temperature rising at micron scale. The red-shift of Ni₂Si peak locations at about 140 cm^-1 with temperature was suggestive of the polycrystalline Ni₂Si film with weaker stress/strain status. Moreover, the in-plane size of graphite cluster aggregating at top surface increased with annealing temperature rising until about 1000°C, which is detrimental to the ohmic contacts from the perspective of device applications.

Abstract: In this work 3,5 Bis(Tri fluro methyl)Benzyl amine phenyl alanine a monmer molecule is DFT theoretically optimized to get the structural insight of the molecule. Band gap energy, Mullikan atomic charges, DOS spectral analysis, HOMO - LUMO, Electrostatic surface potential , molecular electrostatic potential and theoretical Raman spectral analysis is computed and compared with the experimental data .Since this molecule shows self assembly similar to peptide molecules it is quite interesting to analyze its structure based on theory and experimental the results suggests the H –boding interactions between the molecules is the key mechanism. The band energy from DOS plots suggests the molecular interactions through π-π .The possibility of the self assembly is explained further from Raman spectral studies that tells the mode specific interaction among the molecules..

Abstract: The article is devoted to the method of obtaining a diamond-like coating on a silicon substrate by laser ablation of a glassy carbon target in a vacuum. The presented technology makes it possible to achieve the synthesis of wear-resistant thin-film coatings with a thickness of about 200 nm. The diagnostics of the obtained coating was carried out using probe microscopy, the chemical and phase composition was estimated by the Raman spectra.

Abstract: Nanocomposite in the form of a porous matrix SiO₂ with average pore size of 320 nm filled with barium titanate nanoparticles in paraelectric cubic phase was obtained. Shift of the stretching vibration of Si–O–Si to higher frequencies caused by increased strengthening of the network in the matrices has been observed. Also demonstrated that decrease in the intensity of the absorption relating to Si–O(H) stretching vibration relative to Si-O(−Si) stretching vibration. Raman scattering spectra demonstrate the presence of both a cubic and a tetragonal ferroelectric crystalline phase in the filler nanoparticles. Thus, the mechanical deformation of nanoparticles in the pores of the matrix can lead to a change in the crystalline phase of the filler.

Abstract: Ultra-nanocrystalline diamond films were prepared by a microwave plasma-enhanced chemical vapor deposition reactor using CH₄/H₂ gas mixture with a power as low as 650 W. The effects of CH₄ concentration on nanostructure of the films and gas-phase species in plasma were investigated. The CH₄ concentrations of 1.5%, 3.0%, 3.5%, and 4.0% were used and balanced with H₂ to a total flow rate of 200 sccm. Morphology and composition of the films were characterized by SEM, Raman spectroscopy and Auger spectroscopy. The gas-phase species and electron density in the plasma were explored by optical emission spectroscopy and plasma-impedance measurement. The increasing CH₄ concentration from 1.5% to 4.0% increased C₂H_x species and decreased electron density. Phase of the film transform from nano- into ultranano- diamond phase but the growth rate revealingly decreased from 300 to 210 nm/h. Raman spectra indicate the higher CH₄ concentration promted phase of the film transiton from NCD to UNCD. While Auger spectra revealed that UNCD film deposited with 4.0%CH₄ was composed of 90.52% diamond phase but only 9.48% of graphite phase. The relation between phase transformation of the films and growth mechnism controlled by gas-phase species in the plasma will be dissused.

Abstract: The study of glass components influence on the physical and chemical properties of As–S–Se–I glasses has the potential to help design glasses with the required properties. A change of certain glass properties upon the introduction of selenium into AsSI glass was demonstrated. Non-stoichiometric compounds along the As₂S₃-AsI₃-Se diagram section were investigated by differential thermal analysis, ultrasonic measurements, dilatometric measurements. It has been shown that the introduction of selenium decreases the glass solubility in water. Change in the glass properties with the change in the short-range structure studied by Raman spectroscopy was shown. These glasses can be used for creation of immersion lenses and optical adhesives which change radiation characteristics of mid-IR LEDs.

Abstract: The Raman spectroscopy is used to identify and determine the content of the components of a GdOCl − GdCl₃ • 6H₂O mixture. It can be used for analytical control of the composition and detection of undesirable oxygen-containing impurities in chloride reaction media in the preparation of rare-earth metals.

Abstract: Obtaining enhanced up-conversion efficiency in rare earth ions doped inorganic glass by means of noble metal nanoparticles (NPs) embedment remains challenging. For the first time, we report the combined effects of silver (Ag) and titania (TiO₂) NPs embedment on the structural and absorption characteristics of dysprosium (Dy³⁺) doped tellurite glass. Transparent and thermally stable glass samples were prepared using conventional melt quenching method and characterized via spectroscopic techniques. The production of the strong electric field in the proximity of Dy³⁺ ion due to the localized surface plasmon (LSP) of embedded metallic NPs was found to improve the glass absorption properties. The effects of bimetallic NPs in changing the structure and absorption properties were found to be better than singly included metallic NP (either Ag or TiO₂). This improvement in the absorption behavior was attributed to the combined LSP resonance (LSPR) effects of Ag and TiO₂ NPs which transferred strong local electric field into the Dy³⁺ ions positioned in their vicinity. The UV-Vis-NIR spectra revealed six absorption bands centerted at 1690, 1283, 1097, 904, 800 and 755 nm which were allocated to the transition from ⁶H_15/2 ground state to various excited states (⁶H_11/2, ⁶F_11/2, ⁶F_9/2, ⁶F_7/2, ⁶F_5/2 and ⁶F_3/2) of Dy³⁺ ion. Furthermore, the Raman spectra of such bimetallic NPs included glass system exhibited Raman peak shift accompanied by intensity variations when compared to the glass system with only one type of NPs incorporation. This enhancement in the Raman signal was ascribed to the LSPR mediated mechansim. The synthesized glass comporition was asserted to be prospective for devices.