Defects in Individual Semiconducting Single Wall Carbon Nanotubes: Raman Spectroscopic and in Situ Raman Spectroelectrochemical Study
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Raman spectroscopy and in situ Raman spectroelectrochemistry have been used to study the influence of defects on the Raman spectra of semiconducting individual single-walled carbon nanotubes (SWCNTs). The defects were created intentionally on part of an originally defect-free individual semiconducting nanotube, which allowed us to analyze how defects influence this particular nanotube. The formation of defects was followed by Raman spectroscopy that showed D band intensity coming from the defective part and no D band intensity coming from the original part of the same nanotube. It is shown that the presence of defects also reduces the intensity of the symmetry-allowed Raman features. Furthermore, the changes to the Raman resonance window upon the introduction of defects are analyzed. It is demonstrated that defects lead to both a broadening of the Raman resonance profile and a decrease in the maximum intensity of the resonance profile. The in situ Raman spectroelectrochemical data show a doping dependence of the Raman features taken from the defective part of the tested SWCNT.Here we introduce balanced-detection Raman Induced Kerr Effect (BD-RIKE) as a novel coherent Raman scattering (CRS) technique which combines the advantages of stimulated Raman scattering (SRS) (absence of non-resonant background (NRB), linear scaling with the concentration) and coherent anti-Stokes Raman scattering (CARS) (background-free signal). RIKE relies on the Raman-induced birefringence occurring when the pump-Stokes frequency detuning is in resonance with a vibrational transition, leading to a polarization rotation of the Stokes field that we measure using a balanced detection configuration.
Magneto-optic Kerr effect
Raman cooling
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A time-resolved coherent anti-Stokes Raman scattering (CARS) microscope allows three-dimensional imaging based on Raman free induction decay of molecular vibration with no requirement for labeling of the sample with natural or artificial fluorophores. A major benefit of the technique is the capability to completely remove nonresonant coherent background signal from the sample and the solvent, and thus increasing the detection sensitivity of CARS microscopy significantly.
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The tuning Raman mixing effects in an optical fiber have been investigated in the frequency shift range from 656cm-1 to 1343cm-1. Many phenomena have been obser-ved experimentally, e.g., the intensity of coherent anti-Stokes Eaman scattering (CAES) is inversely proportional to that of the inverse Raman absorption (VRA), the energy distribution of SRS is influenced strongly by Raman mixing (RM). In addition to the-coherent Stokes Raman scattering (CSRS) and CARS radiations, the second order coherent Stokes Raman scattering (SOCSRS) and the second order anti-Stokes Raman scattering (SOCARS) radiations have also been observed. Finally, the experimental results are discussed.
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Coherent anti-Stokes Raman spectroscopy (CARS) was used to detect oxygen atoms (electronic Raman scattering) and oxygen molecules (rotational Raman scattering) in both hydrogen–oxygen and methane–oxygen flames. The high spectral resolution of CARS is useful for distinguishing the oxygen-atom signals from larger nearby rotational Raman signals. Saturation of the molecular CARS signal that is due to stimulated Raman scattering was observed. This effect limits the sensitivity of the CARS method.
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Since the discovery of carbon nanotubes, Raman Scattering Spectroscopy and transmission Electron Microscopy have been proved to be powerful for a detailed investigation of their properties. In TEM, a direct observation can be made, whereas Raman Scattering is used extensively to probe the different samples via their vibrational properties. In this paper, we report on recent results obtained in both single-walled carbon nanotubes (SWNTs), multiwalled-carbon nanotubes (MWNTs) and PMMA/nanotubes composites. In addition, in the case of SWNTs, we present studies carried out in Raman scattering when SERS (Surface Enhanced Raman Scattering) conditions are used. In particular, we put in evidence an increased state of disorder at the interface nanotubes/metallic support when the nanotube film thickness is decreased. Strong degradations can be observed primarily on metallic tubes with a concomitant formation of C 60 -like molecules. In the case of MWNTs, calculations of interactions between concentric tubes lead to the occurrence of low frequency vibrational modes, in good agreement with experiments.
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Abstract The line shape observed in coherent Raman scattering (CRS) with excitation under conditions of electronic resonance is discussed, For the case of A‐type scattering, the complex Raman amplitude is related directly to the molecular one‐photon absorbance of the resonance transition concerned. The basis for this relation is transform theory, a method known from spontaneous resonance Raman scattering to relate the Raman excitation profile to the observed molecular absorbance. Features of the Raman amplitude, determining the observed line shapes for coherent anti‐Stokes Raman scattering (CARS) and for coherent Stokes Raman scattering (CSRS), are discussed qualitatively. The discussion considers two typical forms in which broad molecular absorption spectra of polyatomic molecules in the condensed phases appear, Inhomogeneous broadening leads to characteristic changes of the Raman amplitude in relation to molecular absorbance in the case of CSRS (formolecules in the electronic ground state), whereas for CARS the relation derived in the homogeneous broadened case remains valid. The special advantages of the CRS technique for determining the complex non‐Raman resonant (background) susceptibility from concentration dependence are demonstrated.
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Coherent backscattering
Coherent spectroscopy
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Absorption spectrum of recently discovered single-walled 4 Å carbon nanotubes is measured. The semiempirical PM3 localized-density-matrix method is employed to evaluate the absorption spectra of three possible 4 Å single-walled carbon nanotubes, (3,3), (4,2), and (5,0). Both experimental and calculated results reveal that these nanotubes have finite optical gaps and strong anisotropic optical responses. When the electric field is perpendicular to the nanotubes, they are transparent to visible lights; and this is confirmed and explained by the calculations. Compared to the measured absorption spectrum, calculated absorption spectra are used to determine the chirality of the nanotubes synthesized in the channels of porous zeolites.
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Resonance enhancement of coherent anti-Stokes Raman scattering due to the proximity of the laser frequencies to an electronic transition has been demonstrated for dilute solutions of diphenyloctatetrane in benzene. The Raman contribution to the third order susceptibility is shown to be complex near an electronic resonance and the resulting features of the coherent anti-Stokes Raman scattering spectra are discussed in detail. This work represents one step in the demonstration that the high signal to noise ratio, fluorescence rejection, and low average power levels of the coherent anti-Stokes Raman scattering experiment can be used to advantage in Raman studies of dilute solutions and materials of biological interest.
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Raman lasing of a two-phonon Raman band in the anti-Stokes side is demonstrated. Two femtosecond light pulses with identical wavelengths are irradiated onto a SrTiO3 crystal in a cross-beam configuration. Under low excitation power, several wave-mixing signals with identical wavelengths are emitted. When the power exceeds a critical value, cascaded coherent anti-Stokes Raman scattering (CARS) signals are emitted, the frequency step of which is coincident with that of the strongest two-phonon Raman band of 2TO2.
Raman cooling
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