We demonstrate that under continuous single-beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering. The effect has been observed in mesoscopic materials, which possess intrinsically nonlinear properties [lithium niobate (LiNbO3), bismuth germanium oxide (Bi12GeO20; BGO), bismuth silicon oxide (Bi12GeO20; BSO)], which have a nonzero electric susceptibility of the third order, χ(3)≠0. Corroborated Raman and coherent backscattering studies demonstrate that the occurrence of both effects is conditioned by the existence of a mesoscopic morphology of the sample, which is able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, both AASRE and coherent backscattering effects are because of the Anderson localization of the light.
Surface enhanced Raman scattering (SERS) with 676.4 and 1064 nm excitations was used to investigate single-walled carbon nanotubes (SWNTs) compressed non-hydrostatically at 0.58 GPa, alone and dispersed into chemical reactive and non-reactive (SiO2 and Al2O3) host matrices. As reactive host matrices, we used inorganic compounds (KI and Ag microparticles) and aromatic hydrocarbons (biphenyl, naphthalene, p-terphenyl, phenantrene). SERS spectra indicate that by compression, SWNTs break in fragments of different size, which in turn can react or not with the host matrix. Various mechanico-chemical reactions take place. In inorganic matrices such as KI and Ag, donor-acceptor complexes are formed. Regardless of aromatic hydrocarbons type used as organic matrices, i.e. with isolated or condensed phenyl rings, a non-covalent functionalization of SWNTs is produced. Using aromatic hydrocarbons with isolated phenyl rings like biphenyl or p-terphenyl, an ionic and covalent functionalization of SWNT fragments is demonstrated by the appearance of new Raman bands at 1160 and 1458 cm-1, the latter being associated with the Ag(2) pentagonal pinch mode observed regularly in Raman spectra of C60 fullerenes. The signature for the appearance of short fragments of carbon nanotubes, behaving as closed-shell fullerenes, is observed also in photoluminescence spectra carried out on SWNTs compressed in biphenyl and p-terphenyl matrix. Additional proofs are found by transmission electron microscopy (TEM) investigations.
A new route for nanotube-based applications in molecular electronics was developed. Individual polymer strands were assembled onto single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT) by mechanical agitation. The SWNT hybrid systems have been characterized by electron microscopy (TEM, STM), optical absorption and Raman spectroscopy and a fully nondestructive technique, using electron paramagnetic resonance (EPR), has been developed to estimate the purity of MWNT soot and hybrids. It is demonstrated that solutions of the polymer are capable of suspending nanotubes indefinitely while the majority of the accompanying amorphous graphite precipitates out of solution. Electron microscopy and Raman scattering indicate that through an intercalation process, the ropes of SWNT are destroyed, resulting in individual nanotubes being well dispersed within the polymer matrix. Moreover, Raman and absorption studies suggest that the polymer interacts preferentially with nanotubes of specific diameters or a range of diameters. STM studies showed that the chiral angle of the underlying nanotube is reflected in the polymer coating, demonstrating that the lattice structure of the SWNT templates the ordering in the coating. This could lead to design of specific polymer architectures for selection of desired chiral angles, and hence specific electronic properties.
Carbon single walled nanotubes produced in high yields by the electric arc technique have been studied by several techniques including HRTEM. It is shown in particular that they have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we mainly report characterization results obtained by high resolution Raman spectroscopy. Raman spectra exhibit a very rich structure especially in the low frequency range where several components are observed. Using previous calculations, we attribute the main features to armchair tubes with (6,6) to (12,12) geometry, in agreement with the narrow diameter distribution observed by HRTEM measurements.
We discuss the production of carbon nanotubes by the electric arc-discharge method. Co-evaporation of metals, Yttrium, Lutetium, Nickel and Boron have been used with the following stoichiometry: YNi2B2C or LuNi2B2C. We have obtained singlewalled and multiwalled nanotubes and also crystalline nanoparticles embedded in glassy carbon as evidenced by HRTEM and x-ray diffraction observations. The SQUID measurements showed a superconducting transition which would mean that crystalline particles present the superconducting phases of YNi2B2C, YNi4B4C or LuNi2B2C. HRTEM investigations are corroborated by Raman spectra which exhibit the features characteristic of singlewalled nanotubes by the presence of three main peaks at approximately 1580 cm-1, approximately 1350 cm-1 and approximately 180 cm-1. Other samples present on the E2g2 mode and those assigned to glassy carbon at approximately 1350 cm-1 and approximately 1600 cm-1.
We present a temperature dependence investigation of the C equals C intramolecular phonon for both the normal and inter-ring C* equals C* labeled salts (BEDT-TTF)2I3 superconducting at Tc equals 1.5 K and 8 K. C equals C bond frequencies are found at 1467, 1493 cm-1 and 1420, 1488 cm-1 for the unlabeled and labeled crystals, respectively. We have also computed the infrared and Raman frequencies of the unlabeled and labeled BEDT-TTF molecules. In the low frequency range we found in special operating conditions a tri-iodide I3-line at 106 cm-1 in addition to those found at 36, 116, and 146 cm-1. At 8 K the Raman profile of the intense tri-iodide line at 116 cm-1 can hardly be fitted with a Lorentzian. On the other hand, we also did not succeed to fit correctly the low temperature profile of the inter-ring C equals C line with a single Lorentzian; however Fano line shapes gave satisfactory fits. Taking into account that recent results of Kini, Ferraro and Williams provided evidence of participation of lattice phonons in the pairing mechanism, our results show that intramolecular C equals C vibrations must also be considered as a possible mediation factor for superconductivity.
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