Search results for "RAMAN"
showing 10 items of 1328 documents
Interfacial disorder of graphene grown at high temperatures on 4H-SiC(000-1)
2016
This paper presents an investigation of the morphological and structural properties of graphene (Gr) grown on SiC(000-1) by thermal treatments at high temperatures (from 1850 to 1950 °C) in Ar at atmospheric pressure. Atomic force microscopy and micro-Raman spectroscopy showed that the grown Gr films are laterally inhomogeneous in the number of layers, and that regions with different stacking-type (coupled or decoupled Gr films) can coexist in the same sample. Scanning transmission electron microscopy and electron energy loss spectroscopy shoed that a nm-thick C-Si-O amorphous layer is present at the interface between Gr and SiC. Basing on these structural results, the mechanisms of Gr grow…
THz nanocrystal acoustic vibrations from ZrO2 3D supercrystals
2013
International audience; We report sharp low-frequency Raman spectral features of supercrystals synthesized via the "benzyl alcohol route" and consisting of either yttrium-stabilized or pure zirconia (ZrO2) nanocrystals. In situ formed benzoate species control the nanocrystal growth and act as organic glue leading to the assembly of the nanocrystals in highly ordered 3D supercrystals. We attribute some Raman peaks to THz acoustic vibrations of individual nanocrystals which are only weakly coupled due to the strong acoustic mismatch between the capping ligands and the nanocrystals. Peak positions are consistent with nanocrystal sizes estimated from transmission electron microscopy and X-ray p…
Structural anisotropy and annealing-induced nanoscale atomic rearrangements in metamict titanite
2012
The structural state of metamict titanite was studied by Raman spectroscopy, complementary high-resolution transmission electron microscopy, and single-crystal X-ray diffraction. The results show that Raman scattering collected from metamict titanite is highly anisotropic, which is typical of single crystals. But surprisingly, the observed Raman-scattering dependence on the sample orientation is much more pronounced for heavily metamict than for weakly metamict titanite samples. These radiation-induced anisotropic effects are related to the specific atomic arrangements in metamict titanite. The Raman spectra collected in backscattering geometry from a plane nearly perpendicular to the chain…
A new route to grow oxide nanostructures based on metal displacement deposition. Lanthanides oxy/hydroxides growth
2012
Abstract A metal displacement reaction has been used in order to cause precipitation of oxide nanostructures within pores of anodic alumina membrane (AAM) templates. Here, we focus on the displacement deposition of LnO/OH (Ln = La, Ce, Sm, Er) nanostructures using Zn as sacrificial anode, employing a specific cell arrangement where a galvanic couple was formed between zinc anode and the Au thin layer covering template pore bottom. Progress of displacement deposition reaction into template channels was monitored measuring the open circuit potential as well as pH changes of the electrolyte. A progressive de-activation of the anode surface was observed for long deposition times, caused by depo…
Physicochemical characterization and photoelectrochemical analysis of iron oxide films
2013
Iron oxide films with a nanoporous structure were grown by anodizing sputter-deposited Fe in a fluoride containing ethylene glycol solution and annealed under air exposure at different temperatures. X-ray diffraction and Raman spectroscopy allowed to identify the presence of hematite and/or magnetite after thermal treatment for films annealed at T ≥ 400 °C under air exposure. According to GDOES compositional depth profiles, the thermal treatment sensitively reduced the amount of fluoride species incorporated into the film during the anodizing process. A band gap value of ~2.0 eV was estimated for all the investigated layers, while a flat band potential dependent on both the growth condition…
The influence of thickness, interpore distance and compositional structure on the optical properties of self-ordered anodic aluminum oxide films
2016
Highly ordered anodic aluminum oxide (AAO) films were fabricated using a two-step anodization process in oxalic acid, sulfuric acid, or ethylene glycol containing sulfuric acid, which are important in design of nanostructured optical devices. The morphology and UV-Vis reflectance spectroscopy of these films were analyzed. The morphological parameters of the AAO films, such as the thickness, pore diameter, interpore distance, porosity, pore arrangement regularity, and anodization electrolyte, were adjusted in order to study the effect of these parameters on the UV-Vis reflectance properties of these films. Raman spectroscopy measurements were then utilized to better understand the chemical d…
Structural, vibrational and electronic properties in the glass-crystal transition of thin films Sb70Te30 doped with Sn
2020
Abstract Antimony-telluride based phase-change materials doped with Sn have been proposed to be ideal materials for improving the performance of phase-change memories. It is well known that Sb70Te30 thin films show a sharp fall in the electrical resistance in a narrow temperature range when heating. Therefore, it is interesting to study the effect of adding Sn into this composition. In this work, undoped and Sn-doped Sb–Te thin films of composition Snx[Sb0.70Te0.30]100-x, with x = 0.0, 2.5, 5.0 and 7.5 at. %, have been obtained by pulsed laser deposition. Their electrical resistance has been measured while heating from room temperature to 650 K. A sharp fall in the electrical resistance, as…
High-pressure Raman investigation of high index facets bounded alpha-Fe2O3 pseudocubic crystals
2021
[EN] High index facet bounded alpha-Fe2O3 pseudocubic crystals has gained the attention of the scientific community due to its promising electrochemical sensing response towards aqueous ammonia. The structural stability of alpha-Fe2O3 pseudocubic crystals is investigated through high-pressure Raman spectroscopy up to 22.2 GPa, and those results are compared with our ab initio theoretical calculations. The symmetry of the experimental Raman-active modes has been assigned by comparison with theoretical data. In addition to the Raman-active modes, two additional Raman features are also detected, whose intensity increases with compression. The origin of these two additional peaks addressed in t…
The structural properties of GaN insertions in GaN/AlN nanocolumn heterostructures.
2009
The strain state of 1 and 2.5 nm thick GaN insertions in GaN/AlN nanocolumn heterostructures has been studied by means of a combination of high resolution transmission electron microscopy, Raman spectroscopy and theoretical modeling. It is found that 2.5 nm thick GaN insertions are partially relaxed, which has been attributed to the presence of dislocations in the external AlN capping layer, in close relationship with the morphology of GaN insertions and with the AlN capping mechanism. The observed plastic relaxation in AlN is consistent with the small critical thickness expected for GaN/AlN radial heterostructures.
Polarized multiplex coherent anti-Stokes Raman scattering using a picosecond laser and a fiber supercontinuum
2011
International audience; We perform multiplex coherent anti-Stokes Raman scattering (CARS) micro-spectroscopy with a picosecond pulsed laser and a broadband supercontinuum (SC) generated in photonic crystal fiber. CARS signal stability is achieved using an active fiber coupler that avoids thermal and mechanical drifts. We obtain multiplex CARS spectra for test liquids in the 600–2000 cm−1 spectral range. In addition we investigate the polarization dependence of the CARS spectra when rotating the pump beam linear polarization state relative to the linearly polarized broad stokes SC. From these polarization measurements we deduce the Raman depolarization ratio, the resonant versus nonresonant …