Search results for "RAMAN"
showing 10 items of 1328 documents
Review on Raman scattering in semiconductor nanowires: I. theory
2013
Raman scattering is a nondestructive technique that is able to supply information on the crystal and electronic structures, strain, temperature, phonon-phonon, and electron-phonon interaction. In the particular case of semiconductor nanowires, Raman scattering provides addi- tional information related to surfaces. Although correct, a theoretical approach to analyze the surface optical modes loses critical information when retardation is neglected. A comparison of the retarded and unretarded approaches clarifies the role of the electric and magnetic polarization in the Raman selection rules. Since most III-V compounds growing in the zincblende phase change their crystal structure to wurtzite…
Strain effects and phonon-plasmon coupled modes in Si-doped AlN
2009
The E 2h and A 1 (LO) phonon modes of AlN films grown on sapphire are analyzed by Raman scattering as a function of silicon doping for concentrations covering from 5.5 x 10 19 cm ―3 to 5.2 x 10 21 cm ―3 . For high doping levels the appearance of a mode around 520 cm ―1 indicates the precipitation of crystalline silicon in the samples and its inhomogeneous incorporation to the AlN layer. The frequency of this mode shifts to lower energies with doping, indicating that the silicon crystals are embedded in the AlN lattice and under tensile strain. On the other hand, the AlN phonon modes are blue-shifted due to the compressive strain as a result of the silicon incorporation. This strain is parti…
Structural and Vibrational Properties of Corundum-type In2O3 Nanocrystals under Compression
2017
[EN] This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12 14 GPa. The different stability range found in nanocrystallin…
High-pressure Raman scattering of the stretching mode in nitrogen along the 300-K isotherm
1996
We present Raman scattering studies of the vibrational band of nitrogen at room temperature between 1 and 31 GPa allowing a detailed line-shape analysis. For the fluid and \ensuremath{\beta} phases the vibrational linewidths compare to dephasing rates ${\mathit{T}}_{2}^{\mathrm{\ensuremath{-}}1}$ determined by experiments in the time domain. The \ensuremath{\delta}-\ensuremath{\epsilon} transition is unmistakably marked by a drop of the vibrational linewidths around 17 GPa. A further transition into the \ensuremath{\eta} phase around 20 GPa proposed from previous Raman results can be ruled out. Additionally, clear evidence is found for a dynamical freezing of the ${\mathrm{N}}_{2}$ molecule…
Micro- and nano-diamond particles in carbon spherules found in soil samples
2008
Carbonaceous spherules of millimeter size diameter and found in the upper soils throughout Europe are investigated by TEM, including SAED, HRTEM and EELS, and Raman spectroscopy. The spherules consist primarily of carbon and have an open cell-like internal structure. Most of the carbon appears in an amorphous state, but different morphologies of nano- and microdiamond particles have also been discovered including flake shapes. The latter observation, together with the original findings of some of these spherules in crater-like structures in the landscape and including severely deformed rocks with some spherules being embedded in the fused crust of excavated rocks, points towards unique cond…
The influence of Al doping on the photocatalytic activity of nanostructured ZnO: The role of adsorbed water
2018
Abstract Al doped ZnO nanoparticles (labeled as x% A-ZnO, x = 0.0, 0.5, 1.0, and 1.5) were synthesized by a simple sol-gel method, characterized and tested as photocatalysts for the degradation of a model compound under UV-light irradiation. Diffuse reflectance spectroscopy (DRS) and photoelectrochemical analysis have been performed to evidence their optical and electronic behavior. The structural features of the powders were highlighted by means of specific surface area (SSA) analysis, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopy. Al doping results in enhanced photocatalytic activity of the modified powders with respect to pure ZnO. In particular, the h…
Enhancement of calcium copper titanium oxide photoelectrochemical performance using boron nitride nanosheets
2020
International audience; Photoelectrochemical water splitting under visible light has attracted attention for renewable hydrogen production. Despite prevalent investigations, many challenges still hindered an efficient energy conversion, such as enhancing the reaction efficiency in visible light. Thus controlling the photoelectrode materials is an essential step in designing new materials for water splitting. CaCu3Ti4O12 (CCTO) has received great attention as photocatalyst under solar light due to its combined band gap as result of the presence in its structure of TiO2 active in UV light and CuO active under visible light. In this work, a cubic CCTO with different amount of exfoliated hexago…
Corundum type indium oxide nanostructures: ambient pressure synthesis from InOOH, and optical and photocatalytic properties
2016
A simple, cost effective, surfactant free and scalable synthesis of rhombohedral In2O3 (rh-In2O3) nanostructures with controllable size and shape has been developed under ambient pressure by thermal dehydration of InOOH nanostructures. The InOOH nanostructures have been prepared by solvothermal reaction between indium nitrate hydrate with tetramethylammonium hydroxide (TMAH) in anhydrous methanol at 140 °C without any surfactant. The structure and morphology of the nanostructures have been characterized in detail by X-ray powder diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The studies reveal that highly crystalline nanostructures of In…
Photoactivity under visible light of metal loaded TiO2 catalysts prepared by low frequency ultrasound treatment
2017
Abstract Visible-light responsive bare and metal loaded (Pt, Ag, Rh, Pd) TiO 2 photocatalysts were prepared by using a simple ultrasound treatment. This method induced bulk oxygen deficiency resulting in a narrowing bandgap (from 3.18 to 3.04 eV) and in visible light absorption. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area (SSA) and pore size distribution (PSD), UV–vis diffuse reflectance spectroscopy (DRS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was evaluated by using the 4-nitrophenol oxidation reaction and the photocatalytic oxidation of glucose w…
Influence of calcination on the structural properties of earth abundant Cu2ZnSnS4
2021
Abstract In the present work, we report on the synthesis of nano-crystalline kesterite copper zinc tin sulfide (CZTS) in powder form and the post-annealing process at high temperatures (calcination), and study their physical properties. We have successfully synthesized CZTS by direct fusion, and the resulting material was crushed to obtain a fine powder. Then, the resulting powder was calcined at high temperatures: 800–1000 ∘C. The calcined samples have been characterized with a number of different structural: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical techniques: photoluminescence (PL), Raman and diffuse reflectance spectr…