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  • 1
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    Micro-Raman investigation of pigments and carbonate phases in corals and molluscan shells (2013)
    Schweizerbart
    Details
    Publication Date: 2013-12-24
    Description: We report the results of a micro-Raman investigation, in resonance conditions, on the pigments and on the nature of the biogenic carbonate in different species of corals and marine shells of a wide variety of colours. Corallium rubrum (Anthozoa) and Stylaster roseus (Hydrozoa) show calcite and aragonite skeletons, respectively. The shells are mostly aragonitic, with the exception of bivalves of Pectinidae family which reveal a calcite/aragonite distribution. The main Raman features of the pigments (carotenoids or polyenes) show Raman dispersion (upshift of the C=C ( 1 ) and C–C ( 2 ) stretching vibration frequencies of the polyenic chain with decreasing excitation wavelength). Partially or completely demethylated polyenes with different conjugation lengths may be responsible for the colours of Corallium rubrum and of most of the marine shells. Stylaster roseus and the dark brown colours of Gibbula sp (Gastropod class) show typical bands of carotenoids, similar to those found in canthaxanthin. Overtones and combination bands are described in terms of the four fundamental vibrations of polyenes. A constant ratio between 1 and 2 frequencies, nearly independent of the Raman excitation wavelength, has been determined from a large set of data for corals and shells. A simple relationship between the main Raman frequencies and the effective conjugation length N of the polyenic chains is suggested.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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  • 2
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    The key role of micro-Raman spectroscopy in the study of ancient pottery: the case of pre-classical Jordanian ceramics from the archaeological site of Khirbet al-Batrawy (2013)
    Schweizerbart
    Details
    Publication Date: 2013-12-24
    Description: Micro-Raman (μ-Raman) spectroscopy has been used, as a preliminary and non-destructive technique, in order to investigate the mineralogical composition and to define the maximum firing temperature and redox state of the firing atmosphere of ancient ceramic materials. The studied ceramics come from the archaeological site of Khirbet al-Batrawy (north-central Jordan), dating back to the Early Bronze Age (3000–2000 B.C.). The results show that the ceramic body is composed mainly by quartz and calcite, and minor amount of feldspars and hematite. In addition, apatite and zircon, important markers to identify the provenance of raw materials, have been detected. Furthermore, the occurrence of gypsum has been related to both rehydration of anhydrite and burial alteration processes. Micro-Raman spectroscopy was helpful to investigate the nature of the pigments of these ceramics: the red colour was obtained by hematite, the dark pigment by amorphous carbon. Mineral assemblage allowed estimating the maximum firing temperature of these pottery vessels between 850 and 950 °C. The comparison of the results of μ-Raman spectroscopy and of X-ray diffraction analysis suggests that μ-Raman spectroscopy could have a key role in the study of ceramic materials, especially the characterization of archaeological ceramic samples for which manipulation and/or consumption are not allowed.
    Print ISSN: 0935-1221
    Electronic ISSN: 1617-4011
    Topics: Geosciences
    Published by Schweizerbart
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  • 3
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    Raman spectroscopy of (Ca,Mg)MgSi2O6 clinopyroxenes (2012)
    Mineralogical Society of America
    Details
    Publication Date: 2012-08-01
    Description: The Raman spectra of eight clinopyroxenes synthesized along the join diopside-clinoenstatite (Di-Cen, CaMgSi 2 O 6 -Mg 2 Si 2 O 6 ) were measured. The splitting of the 670 cm –1 mode of the A g symmetry, observed in the composition Di 52 En 48 to clinoenstatite, was interpreted as evidence of a C 2/ c-P 2 1 / c phase transition. The transition was also revealed by deviation from the linear dependence of the peak position vs. composition and by the appearance of several new peaks in the samples richer in clinoenstatite. Analysis of peak positions vs. structural changes suggests that for the M2 polyhedron, in which Ca substitution for Mg occurs, a different deformation mechanism acts in Ca richer and poorer P 2 1 / c pyroxenes, and that Ca richer P 2 1 / c pyroxenes deform with the same mechanism as C 2/ c pyroxenes. The frequency of the peak at 670 cm –1 was found to change linearly with the kinking angle of the tetrahedral chains for C 2/ c and of the B chain for P 2 1 / c , whereas the position of the peak ascribed to the A chain was little affected by the kinking angle. Peak broadening in C 2/ c Ca-rich homogeneous pyroxenes was interpreted to be a consequence of the positional disorder of the Ca and Mg in the M2 cavity: peak broadening increases with increasing Mg content for peaks assigned to M2-O vibrations, but it changes little for peaks assigned to chain bending, which suggests that cation substitution in the M2 cavity occurs with little interaction with the silicate chain. Furthermore peak broadening was observed in intermediate pyroxenes as a consequence of mottled textures, antiphase domains, and compositional inhomogeneity.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 4
    Electronic Resource
    Electronic Resource
    Raman scattering study of residual strain in GaAs/InP heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4156-4160 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Raman spectroscopy study on highly mismatched GaAs layers with thickness ranging from 15 nm to 6.6 μm and grown by metal-organic vapor-phase epitaxy on InP (001) substrates, is reported. Both LO and TO GaAs phonons have been observed in backscattering and Brewster geometries. In the thinnest samples large frequency red shifts with respect to the bulk are measured indicating large residual tensile strains. The Raman measurements agree with x-ray-diffraction measurements and confirm that layers thinner than 30 nm exhibit a 3D growth mechanism as suggested by transmission electron microscopy investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355997
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  • 5
    Electronic Resource
    Electronic Resource
    Morphological characterization and strain release of GaAs/InAs (001) heterostructures (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 957-959 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface morphology of GaAs layers on (001) InAs substrates, grown by MOVPE at temperatures in the range 500–650 °C and for times from a few seconds to minutes, has been observed by atomic force microscopy. Information on the strain release and on the surface quality has been obtained by Raman scattering and high resolution x-ray diffraction measurements. Large islands with different shapes and facets are generally formed and only at 550 °C is a quasi-2D growth observed. At the highest growth temperatures InxGa1−xAs is detected at the interface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117094
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  • 6
    Electronic Resource
    Electronic Resource
    Phonon confinement effects in the Raman scattering by TiO2 nanocrystals (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 73-75 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocrystalline TiO2 has been obtained by a sol-gel process by controlling the crystal size through the water/alkoxide ratio. Raman spectra of anatase nanocrystals with average sizes of 9.5–13.4 nm are reported and the correlation between the Raman band shape (peak position and linewidth) of the main feature at 144 cm−1 and the crystals dimension is discussed. While in this system a minor role is played by nonstoichiometry and pressure effects, a model based on the phonon confinement, which takes into account the size distribution as determined by the transmission electron microscopy images, correctly reproduces the Raman band shape change. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120648
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation and Raman spectroscopy of Zn x Cd1−x In2S4 mixed cation layered compounds (1983)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 2044-2049 
    Details
    ISSN: 0392-6737
    Keywords: Infra-red and Raman spectra and scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Sono riportati i risultati sulla crescita e la caratterizzazione dinamico-strutturale delle fasi lamellari che si formano nei composti quaternari misti Zn x Cd1−x In2S4. Gli esperimenti evidenziano la formazione di due fasi politipiche.
    Abstract: Резюме Обсуждается выращивание и проводится структурный и динамическии анализ слоистых фаз, которые образуются в четырехкомпонентных смешанных соединениях Zn x Cd1−x In2S4. Эксперименты показывают, что образуются две фазы.
    Notes: Summary We report on the growth and the structural and dynamical analysis of the layered phases which are formed in Zn x Cd1−x In2S4 quaternary mixed compounds. The experiments show that two polytypic phases are formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457907
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  • 8
    Electronic Resource
    Electronic Resource
    Raman scattering in defect chalcopyrite crystals (1983)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 2050-2057 
    Details
    ISSN: 0392-6737
    Keywords: Infra-red and Raman spectra and scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si riportano i risultati ottenuti da misure di scattering Raman sulle calcopiriti difettive CdGa2Se4, CdGa2S4 e ZnGa2S4. Lo spettro fononico è consistente con il gruppo spaziale $$I\bar 4$$ . Il confronto fra fononi corrispondenti suggerisce un semplice modello per la dinamica vibrazionale. Si presentano anche risultati preliminari sul composto misto Cd x Zn1−x Ga2S4 e in condizioni di risonanza su CdGa2Se4.
    Abstract: Резюме Сообщаются результаты измерений Рамановского рассеяния в дефектных соединениях халькопирита CdGa2Se4, CdGa2S4, ZnGa2S4. Фононная картина соответствует $$I\bar 4$$ пространственной группе. Сравнение мезду соответствующими фононами позволяет предположить простую модель для вибрационной динамики. Приводятся предварительные результаты для Рамановского рассеяния в смешанном соединении Cd x Zn1−x Ga2S4 и для резонансного условия в CdGa2Se4.
    Notes: Summary Raman-scattering measurements on the defect chalcopyrite compounds CdGa2Se4, CdGa2S4, ZnGa2S4 are reported. The phonon picture is consistent with the $$I\bar 4$$ space group. A comparison between corresponding phonons suggests a simple model for the vibrational dynamics. Preliminary Raman results in the mixed compound Cd x Zn1−x Ga2S4 and in resonance conditions in CdGa2Se4 are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457908
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  • 9
    Electronic Resource
    Electronic Resource
    XAFS characterization of the structural site of Yb in synthetic pyrope and grossular garnets (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 251-256 
    Details
    ISSN: 1432-2021
    Keywords: Key words XAFS ; Ytterbium ; Garnet ; Pyrope ; Grossular
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The incorporation and site preference of minor amounts (about 1 wt%) of Yb3+ in synthetic pyrope (Mg3Al2Si3O12) and grossular (Ca3Al2Si3O12) garnet were studied by X-ray Absorption Fine-Structure (XAFS) Spectroscopy. The measurements, performed in the temperature range 77–343 K at both Yb LI- and LIII-edges, demonstrate that Yb3+ enters the garnet structure and is located in the dodecahedral site in both samples. The coordination environment of Yb3+ in the two samples was compared to that of the X-site cation in end-member synthetic pyrope and grossular and in Yb3Al5O12 as determined by single-crystal X-ray diffraction. The local geometry around Yb3+ is different from that of Mg and Ca in the bulk of the garnet, and also from that of Yb3+ in Yb3Al5O12. Τhe XAFS results indicate that, (1) structural relaxation occurs around Yb3+ in the garnet structure; (2) the host garnet matrix exerts a major structural control on the incorporation of Yb3+, and (3) minor amounts of Yb3+ in garnet are located in structural sites and not in ill-defined defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050184
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  • 10
    Electronic Resource
    Electronic Resource
    A temperature dependent X-ray Absorption Fine Structure study of dynamic X-site disorder in almandine: a comparison to diffraction data (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 200-205 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  X-ray Absorption Fine-Structure (XAFS) measurements in the temperature range 20-473K at the Fe K-edge of synthetic almandine (Fe3Al2Si3O12) allow us to determine the temperature dependence of the XAFS Debye-Waller (DW) factors for each of the two crystallographically independent Fe−O bond distances (Fe(1)−O and Fe(2)−O). The vibrational anisotropy of Fe2+ in the dodecahedral X-site has been documented. The XAFS DW factor of the longer Fe(2)−O bond is larger and has a greater T-dependence than the shorter Fe(1)−O bond, which remains constant over the measured T range. The XAFS DW factors are compared with the uncorrelated part of the DW factors derived from a single-crystal X-ray diffraction (XRD) study on almandine and are interpreted on the basis of the Einstein model. A comparison with diffraction data shows that the shorter Fe(1)–O bond is significantly affected by correlation in the atomic displacements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050033
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