Probing carbon isotope effects on the Raman spectra of graphene with different C-13 concentrations

A resonance Raman study of graphene samples with different C-13 isotopic concentrations and using different laser excitation energies is presented. The main Raman peaks (D, G, G*, and 2D) of graphene were measured and the dependence of their frequencies on the isotope atomic mass follows a simple harmonic oscillator relation. The G* and 2D double-resonance peak positions were measured as a function of the laser energy, and we observed that the slopes of the laser energy dependence are the same independently of isotope concentration. This result shows that isotopic substitution does not alter the electron and phonon dispersions near the K point of the graphene Brillouin zone. From the linewidth of G and 2D Raman peaks, we have also obtained a dependence of the phonon lifetime on the C-13 isotope concentrationopen

Applications of the Rietveld method to quantify the crystalline phases of Portland cement clinker doped with nickel and chromium

The effects of chromium or nickel oxide additions on the composition of Portland clinker were investigated by X-ray powder diffraction associated with pattern analysis by the Rietveld method. The co-processing of industrial waste in Portland cement plants is an alternative solution to the problem of final disposal of hazardous waste. Industrial waste containing chromium or nickel is hazardous and is difficult to dispose of. It was observed that in concentrations up to 1% in mass, the chromium or nickel oxide additions do not cause significant alterations in Portland clinker composition. (C) 2008 International Centre for Diffraction Data

Resonant Raman spectroscopy of graphene grown on copper substrates

A study of resonant Raman spectroscopy of the as-grown graphene on copper foils is presented. Different laser energies have been used to excite the sample, in order to obtain the dependence of the Raman features (intensities, frequencies and line widths) on the laser energy. We show that the normalised spectra acquired using green laser lines are more intense, with a maximum around 2.3 eV. Moreover, the results show a broader 2D (or G') band when a UV laser is used to excite the sample, which is explained by the manifestation of the trigonal warping effect in the dispersion of electrons and phonons around the Dirac point

Sorting of single-walled carbon nanotubes by amphiphiles molecules adsorption studied by resonant Raman excitation profile

International audienceAdsorption of specifically designed polyaromatic amphiphiles were used to sort HjPCo single-walled carbon nanotubes (SWNTs) with different helicities. The sorting is investigated by resonant Raman excitation profiles. Chiral indexes (n and m) of SWNTs present in our samples are determined by fitting the Raman peaks observed in the radial breathing modes region (RBM). Scanning over an excitation energy range between 2 and 2.2 eV with a 0.01 eV step allows to investigate mainly two families of metallic nanotubes (2n + m = 24 and 2n + m = 27). The transition energies of nanotubes measured from the Raman spectra differ from the calculated ones, leading to useful corrections of the Kataura plot. The results also display significant differences between the sorted and the reference samples, meaning that discrimination between SWNTs of different properties is possible. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

The double-resonance Raman spectra in single-chirality (n, m) carbon nanotubes

Single-chirality (n, m) carbon nanotubes exhibit the same richness in physics of graphene including an additional phenomenon: the quantum confinement of electrons and phonons along the nanotubes circumference. Raman spectroscopy has been employed for almost 20 years to study carbon nanotubes, but the effect of the quantum confinement on the double-resonance (DR) Raman process in a single- chirality carbon nanotube was not yet understood. In this work, Raman spectra of the 2D band in enriched nanotube samples were measured using more than 70 laser excitation lines in the visible range (1.87e2.71 eV), and simulations of the D and 2D Raman spectra of single-chirality nanotubes were performed considering the quantum confinement along the nanotube circumference. We show that each single-chirality nanotube exhibits a series of non-dispersive D and 2D Raman peaks, which are not necessarily enhanced by resonances with optical transitions between van Hove singularities. Our results provide a complete explanation of the DR Raman spectrum, including the D and 2D bands, at the specificity level of a single-chirality nanotube, and will allow for the correct interpretation of the DR spectra of carbon nanotubes in samples containing a distribution of different (n, m) nanotube species

Origin of the color in cobalt-doped quartz.

Synthetic Co-doped quartz was grown hydrothermally in steel autoclaves at the Technological Center of Minas Gerais (CETEC), Brazil. The quartz samples, originally yellow in the as-grown state acquired blue coloration after prolonged heat treatment times at 500?C near the alpha?beta transition temperature. UV?VIS?NIR absorption spectroscopy shows the characteristic spectra of Co3+ before heat treatment. After heat treatment, the optical absorption spectrum is dominated by two split-triplet bands the Wrst in the near infrared region centered at about 6,700 cm?1 (1,490 nm) and the second in the visible spectral range at about 16,900 cm?1 (590 nm). Both split-triplet bands are typical for Co2+ ions in tetrahedral coordination environments. From the absence of electron paramagnetic resonance (EPR) spectra, we conclude that the Co2+ found in the optical absorption spectra of the blue quartz is not due to an isolated structural site in the quartz lattice. Instead, the blue color is associated with electronic transitions of Co2+ in small inclusions in which the Co site has tetrahedral symmetry. The non-observation of polarizationdepend optical absorption spectra is also in agreement with this model. The results for Co2+ in quartz are diVerent from Co-bearing spinel and staurolite and other silicates like orthopyroxene, olivine, and beryls. The formation process of the color center is discussed

Incorporation of multi wall carbon nanotubes into glass-surfaces via laser-treatment

Carbon nanotubes (CNT) are interesting candidates for the reinforcement in robust composites and for conducting fillers in polymers due to their fascinating electronic and mechanical properties. For the first time, we report the incorporation of multi walled carbon nanotubes (MWNTs) into silica-glass surfaces by means of partial surface-melting caused by a continuous wave Nd:YAG laser. MWNTs were detected being well incorporated in the silica-surface. The composites are characterized using scanning electron microscopy (SEM) and Raman-spectroscopy. A model for the composite-formation is proposed based on heatabsorption by MWNTs and a partial melting of the silica-surface.Peer reviewe

Raman and infrared spectroscopic investigations of a ferroelastic phase transition in Ba2ZnTeO6 double perovskite.

The low-temperature vibrational properties of B a 2 ZnTe O 6 double-perovskite ceramics obtained by the solid-state route were investigated by Raman scattering and Fourier-transform infrared reflectivity. We found that this material undergoes a reversible ferroelastic phase transition at around 140 K, well compatible with a recently proposed rhombohedral-to-monoclinic structural change that would occur below 165 K. Complementary calorimetric measurements showed that the phase transition has a first-order character, with an entropy jump compatible with a displacive mechanism. The vibrational spectra show clearly the splitting of the doubly degenerate E modes into nondegenerate representations of the low-symmetry phase. In particular, the lowest-frequency Raman mode presents soft-mode behavior and splits below the critical temperature, confirming the in-plane ferroelastic deformation in the low-temperature phase