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Register a new userTailored nano-antennas for directional Raman studies of individual carbon nanotubes
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We exploit the near field enhancement of nano-antennas to investigate the Raman spectra of otherwise not optically detectable carbon nanotubes (CNTs). We demonstrate that a top-down fabrication approach is particularly promising when applied to CNTs, owing to the sharp dependence of the scattered intensity on the angle between incident light polarization and CNT axis. In contrast to tip enhancement techniques, our method enables us to control the light polarization in the sample plane, locally amplifying and rotating the incident field and hence optimizing the Raman signal. Such promising features are confirmed by numerical simulations presented here. The relative ease of fabrication and alignment makes this technique suitable for the realization of integrated devices that combine scanning probe, optical, and transport characterization.
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We report experimental measurements of electronic Raman scattering under resonant conditions by electrons in individual single-walled carbon nanotubes (SWNTs). The inelastic Raman scattering at low frequency range reveals a single particle excitation feature and the dispersion of electronic structure around the center of Brillouin zone of a semiconducting SWNT (14, 13) is extracted.
In this paper, we investigate the low frequency Raman spectra of multi-wall carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency Raman modes are unambiguously identified on purified samples thanks to the small internal diameter of the MWNT. We propose a model to describe these modes. They originate from the radial breathing vibrations of the individual walls coupled through the Van der Waals interaction between adjacent concentric walls. The intensity of the modes is described in the framework of bond polarization theory. Using this model and the structural characteristics of the nanotubes obtained from transmission electron microscopy allows to simulate the experimental low frequency Raman spectra with an excellent agreement. It suggests that Raman spectroscopy can be as useful regarding the characterization of MWNT as it is in the case of single-wall nanotubes.
We report a measurement on quantum capacitance of individual semiconducting and small band gap SWNTs. The observed quantum capacitance is remarkably smaller than that originating from density of states and it implies a strong electron correlation in SWNTs.
With the empirical bond polarizability model, the nonresonant Raman spectra of the chiral and achiral single-wall carbon nanotubes (SWCNTs) under uniaxial and torsional strains have been systematically studied by textit{ab initio} method. It is found that both the frequencies and the intensities of the low-frequency Raman active modes almost do not change in the deformed nanotubes, while their high-frequency part shifts obviously. Especially, the high-frequency part shifts linearly with the uniaxial tensile strain, and two kinds of different shift slopes are found for any kind of SWCNTs. More interestingly, new Raman peaks are found in the nonresonant Raman spectra under torsional strain, which are explained by a) the symmetry breaking and b) the effect of bond rotation and the anisotropy of the polarizability induced by bond stretching.
The electronic Raman scattering (ERS) features of single-walled carbon nanotubes (SWNTs) can reveal a wealth of information about their electronic structures, but have previously been thought to appear exclusively in metallic (M-) but not in semiconducting (S-) SWNTs. We report the experimental observation of the ERS features with an accuracy of 1 meV in suspended S-SWNTs, the processes of which are accomplished via the available high-energy electron-hole pairs. The ERS features can facilitate further systematic studies on the properties of SWNT, both metallic and semiconducting, with defined chirality.
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