Papers by Keyword: Raman Spectra

Abstract: Controllable modifications of overall properties of rare-earth doped glasses via gold nanoparticles (Au NPs) mediation prompted gamut research interests. Such glass systems are interesting due to their technological prospects and well as fundamental understanding of surface plasmon resonance effects at metal glass interface responsible for diverse emerging attributes. This motivate us to determine the effects of varying concentration of Au NPs on the structure and ligand field parameters of samarium (Sm³⁺⁾ doped zinc tellurite glass. Glass samples with composition (79-x)TeO₂-20ZnO-1Sm₂O₃-xAuCl₃, where 0 ≤ x ≤ 0.10 mol% are prepared using melt quenching method. X-ray diffraction pattern of all glasses confirmed their amorphous nature. Transmission electron microscopic images verified the existence of Au NPs in a glass matrix matrix with an average size of 10.52 nm. Two surface plasmons resonance band of gold are probed at 652 and 715 nm. Using the UV-Vis absorption spectral data, quantities such as nephelauxetic ratio, bonding parameter and Racah parameters are evaluated. Both bonding parameter and nephelauxetic ratio revealed a reduction with increasing concentration of Au NPs, where decrease in the ionic bonding between Sm³⁺ and surrounding ligand have clearly indicated an enhancement in the covalency. The values of Racah parameters are decreased as the concentration of Au NPs are increased. The observed reduction in the nephelauxetic function is attributed to the weakening of the localized d-electrons aroused from overlapping d-orbital and ligand orbital. Furthermore, the Raman spectra displayed the structural modification in terms of TeO₄ trigonal bipyramidal (tbp) unit, where many TeO₄ tbp units are converted into their TeO₃ trigonal pyramid (tp) counterparts. Raman bands are found to be located around 102-105 cm^-1, 420-424 cm^-1, 657-661 cm^-1 and 729-736 cm^-1. Results are analyzed and compared. Present glass composition is asserted to be useful for the development of photonic devices.

Abstract: This paper presents the results of magnetic and microstructural study of cobalt-substituted NiZn ferrite powders, Ni_0.5Zn_0.3Co_0.2Fe₂O₄, synthesized with the solid-state reaction method. The lattice parameter decreased with Co substitution, as the ionic radius of cobalt is less than that of zinc. Raman spectroscopy showed clear peaks of the A_1g, E_g, and F_2g modes, revealing cubic spinel structure and good crystallinity of the samples. The saturation magnetization reduced in the substituted sample to 50.28 emu/g at room temperature. In comparison to the bulk ferrite, the powder sample showed pronounced coercivity even at room temperature. The temperature dependence of the magnetization had superparamagnetic curvature, which yielded the effective anisotropy constant equal to 8.832 kJ/m³.

Abstract: Different nitrogen-doped 4H-SiC single crystals were grown by the physical vapor transport method through mixing nitrogen gas to the argon growth atmosphere in the composition range from 0% to 10%. The electrical properties of the crystals, including resistivity and mobility were measured by Hall effect and contactless eddy current measurements. The Raman spectra of different N-doped 4H-SiC single crystals were investigated from 173 to 473 K. The temperature and doping dependence of optical modes was analyzed with anharmonic effect. The phonon lifetime was derived from the linewidths of Raman spectra via the energy-time uncertainty relation.

Abstract: Nanocrystalline silicon (nc-Si) thin film on glass substrate is subjected to excimer laser crystallized by varying the laser energy density in the range of 50~600 mJ/cm². The effect of excimer laser crystallization on the structure of silicon film is investigated using Raman spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. The results show that polycrystalline silicon thin films can be obtained by excimer laser crystallization of nc-Si films. A laser threshold energy density of 200 mJ/cm² is estimated from the change of crystalline fraction and surface roughness of the treated films. The growth of grain is observed and the crystallization mechanism is discussed based on the super lateral growth model. The nanocrystalline silicon grains in the films act as seeds for lateral growth to large grains.

Abstract: The dream to have multifunctional materials has triggered an intense study of multiferroicity, i.e. of materials in which magnetic and electric polarizations are simultaneously present and strongly coupled. Here we study TbMnO₃, a perovskite manganite exhibiting multiferroicity. It has an incommensurate antiferromagnetic ordering transition at 41 K and a transition into a multiferroic spin spiral state at 26 K. In this study, Raman spectroscopy has been used to elucidate the nature of the excitations related to phase transitions. We show that the optical phonons in TbMnO₃ resemble the phonon characteristics typical for perovskite manganites, corresponding to MnO₆ octahedral vibrations. The appearance of a new low energy modes at 32 cm^-1, 40 cm^-1, and 63 cm^-1 observed below 41 K signifies the antiferromagentic ordering in TbMnO₃. The 32 cm^{- 1} and 63 cm^-1 are interpreted as spin ordering activated phonon while the 40 cm^-1 is interpreted as spin ordering induced splitting of Tb quasi doublet cystal field level.

Abstract: Single crystalline high quality α-Mn₂O₃ nanorods and sea-urchins assembled with pen-type nanoneedles have been successfully synthesized by template-free hydrothermal route. The variation in hydrothermal temperature has affected the morphology of the α-Mn₂O₃ sea-urchin assembled with the nanoneedles noticeably. The influence of temperature change on the thickness, crystallinity, surface morphology and optical properties of α-Mn₂O₃ has been characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Raman Spectroscopy (RS) and UV-visible Spectroscopy. The results showed that in our experimental conditions, single crystalline nanorods of the α-Mn₂O₃ were obtained at a low temperature of 180 °C, while single crystalline sea-urchin assembled with pen-type nanoneedles were obtained by increasing the temperature to 280 °C. Nanorods and sea-urchin assembled with pen-type nanoneedles obtained had the well defined morphology and crystalline quality. The sea-urchin synthesized at 280 °C exhibited more than 90% absorption in UV-visible spectrum.

Abstract: Ce_0.8Pr_0.2-xSm_xO_2-δ(x=0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 19 nm and 28 nm. The Raman spectra analysis reveals that the solid solution Ce_0.8Pr_0.2-xSm_xO_2-δ has a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Sm in Ce_0.8Pr_0.2-xSm_xO_2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce_0.8Pr_0.15Sm_0.05O_2-δ is higher than that of single rare earth doped ceria Ce_0.83Sm_0.17O_2-y. The results also show that Ce_0.8Pr_0.15Sm_0.05O_2-δ possess maximum conductivity. At 600 °C, the conductivity is 1.20×10^-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce_0.8Pr_0.15Sm_0.05O_2-δ.

Abstract: Ce_0.8Pr_0.2–xNd_xO_2-δ(x = 0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 20 nm and 25 nm. The Raman spectra analysis reveals that the solid solution Ce_0.8Pr_0.2–xNd_xO_2-δ has a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Nd in Ce_0.8Pr_0.2–xNd_xO_2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce_0.8Pr_0.18Nd_0.02O_2-δ is higher than that of single rare earth doped ceria Ce_0.83Sm_0.17O_2−y. The results also show that Ce_0.8Pr_0.18Nd_0.02O_2-δ possess maximum conductivity. At 600 °C, the conductivity is 1.85×10^-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce_0.8Pr_0.18Nd_0.02O_2-δ.

Abstract: There is much fluorescence for impurities on the variation cashmere fiber surface; the characteristic of the Raman spectrum is not obvious. Based on the orthogonal principle, variation cashmere fiber is purified by soaking in different component water/organic solvents, and cleaning with ultrasonic wave. Through measuring and analyzing the Raman spectrum, we confirm the optimal organic solvent system, soaking time and temperature for the cleanse technology of variation cashmere. The result shows that, the variation cashmere fiber is soaked in diethyl ether/aqueous organic solvent in the optimal condition, the Raman spectrum appears good peak-area ratio, and we get cleanest variation cashmere fiber.

Abstract: The XRD patterns of Strontium Titanate (SrTiO₃) prepared by direct current arc discharge plasma technique show that the well crystallized cubic structure. A Raman spectra study is performed to investigate SrTiO₃ ceramics and powders compared with earlier investigations. The observed Raman spectra in this work have been interpreted primarily as second order and derived from combinations, overtones and differences of phonon frequencies.