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Raman Scattering Measurements (raman + scattering_measurement)
Selected AbstractsUltraviolet and visible Raman spectroscopic investigations of nanocrystalline carbon thin films grown by bias-assisted hot-filament chemical vapor depositionJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2003S. Gupta Abstract The structural bonding in a series of nanocrystalline carbon thin films grown under different substrate biasing conditions was analyzed using Raman spectroscopy in both the visible and ultraviolet (uv) regimes of the spectrum. The nanocrystalline carbon thin films studied were deposited by the hot-filament chemical vapor deposition (HFCVD) technique using a 2% concentration of methane in hydrogen. The films were deposited on molybdenum substrates under various substrate biasing conditions. A positive bias (forward) produced a continuous flow of electrons from the filament on to the substrate, whereas a negative bias (negative) caused the substrate to be bombarded with positive ions. Films were also grown under no bias, for comparison. Differences in the Raman spectra obtained with visible (,L = 514.5 nm) and uv (,L = 244.0 nm) excitation sources were investigated. Apart from the basic features consisting of D and G bands at around 1360 and 1580 cm,1 in the case of visible Raman spectra, an extra feature at around 1060 cm,1, denoted a T band, appeared in the uv Raman spectra only. Hence, uv Raman scattering measurements clearly revealed the presence of sp3 -bonded carbon atoms. The position and its intensity ratio with respect to the G peak [(I(T)/I(G)] were used to provide a reliable means to measure the sp3 C bonding fraction, which is both semi-quantitative and non-destructive. The sp3 content estimated within the microstructure of n-C thin films was found to be around 60,80%. Further, probing the samples with two different photons (visible and uv) allowed us to estimate qualitatively the amount and clustering of sp2 sites. This technique provided a fast and reliable microstructural characterization of disordered carbons. The dispersion in the Raman features is specific to each carbon system and, therefore, can be used as a fingerprint. These findings point at the similarities of bias-assisted HFCVD nanocrystalline carbon (n-C) materials and the tetrahedrally bonded amorphous carbon (ta -C) materials grown by ion-beam assisted deposition (IBAD). Copyright © 2003 John Wiley & Sons, Ltd. [source] Phase Transformations in the High-Temperature Form of Pure and TiO2 -Stabilized Ta2O5JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Geoff L. Brennecka The high-temperature forms of undoped tantalum pentoxide (H-100Ta2O5) and TiO2,modified Ta2O5 (H-92Ta2O5,8TiO2) were investigated by in situ synchrotron X-ray diffraction and Raman scattering measurements. Two unquenchable and reversible phase transformations were observed in pure H-Ta2O5, while only one was detected for TiO2 -stabilized H-Ta2O5. Diffraction studies were consistent with displasive transformations, but hot-stage Raman spectroscopy indicated the existence of transient intermediate forms during the transformations. Use of complementary techniques enabled the reinterpretation of phase transformations in light of a newly proposed crystal structure model for H-Ta2O5,1 and emphasized the structural contributions of the oxygen sublattice. [source] Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X-ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Shin-ichi Nakashima Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X-ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics. [source] Electrical Conductivity and Lattice Defects in Nanocrystalline Cerium Oxide Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Toshio Suzuki The results of the electrical conductivity and Raman scattering measurements of CeO2 thin films obtained by a polymeric precursor spin-coating technique are presented. The electrical conductivity has been studied as a function of temperature and oxygen activity and correlated with the grain size. When compared with microcrystalline samples, nanocrystalline materials show enhanced electronic conductivity. The transition from extrinsic to intrinsic type of conductivity has been observed as the grain size decreases to <100 nm, which appears to be related to a decrease in the enthalpy of oxygen vacancy formation in CeO2. Raman spectroscopy has been used to analyze the crystalline quality as a function of grain size. A direct comparison has been made between the defect concentration calculated from coherence length and nonstoichiometry determined from electrical measurements. [source] Dispersing silicon nanoparticles in a stirred media mill , investigating the evolution of morphology, structure and oxide formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007A. Reindl Abstract Silicon nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions (in regard to aggregation) of Si nanoparticles were produced after 6 hours of dispersing. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy as a function of dispersing time. The average crystallite size decreased from about 18 nm down to about 10 nm within 24 hours of milling as determined by X-ray diffraction and Raman scattering measurements. In addition careful analysis of the Raman spectra revealed a decrease of the crystalline volume fraction from 75% down to 24% and a corresponding increase of the amorphous phase. The microstructural development with varying crystallite size and crystalline volume fraction was directly confirmed by transmission electron microscopy measurements. Elemental analysis showed an increase of oxygen content that was directly proportional to the increase in specific surface area of the silicon nanoparticles during the dispersing process. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscopy that indicated vibrational bands of HSi,Si3,xOx, SiOx, and residual 1-butanol. The final product of the dispersing process seems to be a two-phase mixture of amorphous Si and Si nanocrystallites covered with SiOx on the surface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and properties of In/p-Cu(In1,xGax)(S1,ySey)2 surface-barrier structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009Ellen Zaretskaya Abstract Cu(In1,xGax)(S1,ySey)2 (CIGSS) thin films were prepared by the simultaneous selenizarion/sulfurization of Cu-In-Ga metallic alloys. Full characterizations have been carried out using XRD, SEM, EDX, AES and Raman scattering measurements. Photosensitive In/p -CIGSS surface-barrier rectifying structures were created by thermal deposition of pure Incontacts onto the surface of the CIGSS as grown films. The influences of the thin films chemical composition and the illumination conditions on the photo-electric parameters of In/p -CIGSS structures were studied. Analysis of the results showed the availability of the prepared CIGSS films for creation of high efficiency thin films photovoltaic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||