We report the existence of broad and weakly asymmetric features in the high-energy (G) Raman modes of freely suspended metallic carbon nanotubes of defined chiral index. A significant variation in peak width (from 12 cm-1 to 110 cm-1) is observed as a function of the nanotube's chiral structure. When the nanotubes are electrostatically gated, the peak widths decrease. The broadness of the Raman features is understood as the consequence of coupling of the phonon to electron-hole pairs, the strength of which varies with the nanotube chiral index and the position of the Fermi energy.
We present an analysis of deep-UV Raman measurements of graphite, graphene and carbon nanotubes. For excitation energies above the strong optical absorption peak at the $M$ point in the Brillouin zone ($\approx 4.7\,\text{eV}$), we partially suppress double-resonant scattering processes and observe the two-phonon density of states of carbon nanomaterials. The measured peaks are assigned to contributions from LO, TO, and LA phonon branches, supported by calculations of the phonon dispersion. Moreover, we gain access to the infrared-active $E_{1u}$ mode in graphite. By lowering the excitation en…
We present a resonance Raman study of the disorder-induced D mode in a sample highly enriched with semiconducting (9,7) single-walled carbon nanotubes in the excitation energy range of 1.49 - 2.05 eV. The intensity of the D mode shows a resonance behavior near the optical transition of the (9,7) tube. The well-known dispersion of the D-mode frequency, on the other hand, is not observed at the resonance, but only above a certain excitation energy. We explain our results by numerical simulations of the D-mode spectra.
We used tip-enhanced Raman spectroscopy to study the diameter-dependent Raman modes in a contacted carbon nanotube rope. We show that with the near-field tip enhancement a large number of nanotubes within a rope can be identified, even if the nanotube modes can not be distinguished in the far-field signal. Several metallic and semiconducting nanotubes can be identified and assigned to nanotube families. Additionally, we provide a tentative chiral index assignment.
Chirality distribution and transition energies of carbon nanotubes
从孤立的纳米管上的共振拉曼散射，我们得到的光学跃迁能量，径向呼吸模式的频率和拉曼强度的金属和半导体管。我们仅根据第三近邻紧束缚Kataura图明确地指定了大约50个纳米管的手性指数（n_1，n_2），并发现omega_RBM= 214.4 cm ^-1 nm/d+18.7 cm ^-1。与发光实验相反，我们观察到所有的手性，包括锯齿管。拉曼强度有一个系统的手性角依赖性确认最近的从头计算。
We present a high sensitivity single-monochromator Raman spectrometer which allows operation with a tunable laser source. The instrument is based on the modification of a commercial Raman spectrometer; such instruments operate with holographic Rayleigh filters which also act as a laser mirrors and are usually considered as inherently narrow-band. In our design, the two tasks are separated and the filter can be freely rotated without much effect on the light alignment. Since rotation shifts the filter passband, this modification allows tunable operation with efficient stray light filtering down…
Electronic and optoelectronic devices based on thin films of carbon nanotubes are currently limited by the presence of metallic nanotubes. Here we present a novel approach based on nanotube alkyl functionalization to physically remove the metallic nanotubes from such network devices. The process relies on preferential thermal desorption of the alkyls from the semiconducting nanotubes and the subsequent dissolution and selective removal of the metallic nanotubes in chloroform. The approach is versatile and is applied to devices post-fabrication.
The appearance of a broad peak at $\sim$1550 cm$^{-1}$ (G$^{-}$ peak) in carbon nanotube resonant Raman scattering spectra has been conventionally attributed to the presence of metallic nanotubes. Here, we present resonant Raman measurements on macroscopic nanotube ensembles enriched in armchair species prepared through density gradient ultracentrifugation. Our data clearly demonstrate that the broad G$^{-}$ mode is absent for armchair structures and appears only when the excitation laser is resonant with non-armchair "metals." Due to the large number ($\sim$10$^{10}$) of nanotubes across seve…
We demonstrate that AC arc discharge under de-ionized water which has been recently used for carbon nanotubes (CNT) production can be modified to increase the quantity and quality of carbon nanotubes by applying a magnetic field. The carbon soot thus obtained was analyzed using SEM, TEM and Raman spectroscopy. The Raman scattering measurements showed interesting results. Radial breathing modes (RBM) were observed in the Raman data in the range 150 - 700 cm-1. The presence of RBM is good enough indication of the presence of the carbon nanotubes in the soot collected by us. The RBM data was anal…
We have used resonant Raman scattering spectroscopy to fully analyze the relative abundances of different (n,m) species in single-walled carbon nanotube samples that are metallically enriched by density gradient ultracentrifugation. Strikingly, the data clearly show that our density gradient ultracentrifugation process enriches the metallic fractions in armchair and near-armchair species. We observe that armchair carbon nanotubes constitute more than 50% of each (2n + m) family.
Graphene nanoribbons are prepared inside boron nitride nanotubes by liquid phase encapsulation and subsequent annealing of 1,2,4-trichlorobenzene. The product is imaged with high resolution transmission electron microscopy, and characterized by optical absorption and Raman spectroscopy. Carbon-containing material is detected inside the boron nitride nanotubes with energy-dispersive x-ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM). The observed structures twist under the electron beam and the characteristic features of nanoribbons appear in the Raman spectra.
The Raman response of new structures grown after filling SWCNTs with ferrocene and transformation at moderate high temperatures is demonstrated to be very strong, even stronger than the response from the tubes. Transmission electron microscopy demonstrates that the new objects are flat and exhibit a structure similar to short fragments of nanoribbons. The growth process is controlled by two different activation energies for low and high transformation temperatures, respectively. Immediately after filling Raman pattern from a precursor molecule are detected. Two different types of nanoribbons w…
Fano resonance spectra for the G band in metallic carbon nanotubes are calculated as a function of laser excitation energy in which the origin of the resonance is given by an interference between the continuous electronic Raman spectra and the discrete phonon spectra. We found that the second-order scattering process of the non-zero q electron-electron interaction is more relevant to the continuous spectra rather than the q = 0 first-order process because the q = 0 direct Coulomb interaction vanishes due to the symmetry of the two sublattices of a nanotube. We also show that the RBM spectra of…
The electronic transport properties of a metallic carbon nanotube with the five-seven disclination pair characterized by a lattice distortion vector are investigated. The influence of the disclination dipole includes induced curvature and mixing of two sublattices. Both these factors are taken into account via a self-consistent perturbation approach. The conductance and the Fano factor are calculated within the transfer-matrix technique. PACS: 73.63.Fg, 72.80.Rj, 72.10.Fk
Phonon softening phenomena of the $Γ$ point optical modes including the longitudinal optical mode, transverse optical mode and radial breathing mode in "metallic" single wall carbon nanotubes are reviewed from a theoretical point of view. The effect of the curvature-induced mini-energy gap on the phonon softening which depends on the Fermi energy and chirality of the nanotube is the main subject of this article. We adopt an effective-mass model with a deformation-induced gauge field which provides us with a unified way to discuss the curvature effect and the electron-phonon interaction.
Rabi waves have been experimentally registered for the first time by Raman scattering studies of zigzag nanotubes, produced by high energy ion beam modification of natural diamond single crystals. Antiferroelectric spin wave resonance has been detected for the first time in Raman spectroscopy practice in given samples. Substantial qualitative and quantitative changes in Raman spectra in dependence on propagation direction of laser excitation wave have been found.
Growing graphene nanoribbons from small organic molecules encapsulated in carbon nanotubes can result in products with uniform width and chirality. We propose a method based on encapsulation of 1,2,4-trichlorobenzene from the liquid phase and subsequent annealing. This procedure results in graphene nanoribbons several tens of nanometers long. The presence of nanoribbons was proven by Raman spectra both on macroscopic samples and on the nanoscale by tip-enhanced Raman scattering and high-resolution transmission electron microscopic images.
We present a theoretical model to describe the double-resonant scattering process in arbitrary carbon nanotubes. We use this approach to investigate the defect-induced $D$ mode in CNTs and unravel the dependence of the $D$-mode frequency on the CNT diameter and on the energy of the resonant optical transition. Our approach is based on the symmetry of the hexagonal lattice and geometric considerations, hence the method is independent of the exact model that is chosen to describe the electronic band structure or the phonon dispersion. We finally clarify the diameter dependence of this Raman mode…
The functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) with luminescent sp$^{3}$ defects creates red-shifted emission features in the near-infrared and boosts their photoluminescence quantum yields (PLQYs). While multiple synthetic routes for the selective introduction of sp$^{3}$ defects have been developed, a convenient metric to precisely quantify the number of defects on a SWCNT lattice is not available. Here, we present a direct and simple quantification protocol based on a linear correlation of the integrated Raman D/G$^{+}$ signal ratios and defect densities as ex…
Controlling the bandgap of carbon nanostructures is key to the development and mainstream application of carbon-based nanoelectronic devices. We report density functional theory calculations of the effect of silicon impurities on the electronic properties of carbon nanotubes (CNTs). We have found that Si adatoms open up a bandgap in intrinsically metallic CNTs even when the linear density of Si atoms is low enough that they do not create a bonded adatom chain. The bandgap opened in metallic CNTs can range between 0.10 eV and 0.47 eV, depending on adsorption site, linear density of Si adatoms, …
We develop a continuous theory of low-frequency dynamics for nanotubes with truly two-dimensional (2D) walls constituted by single-atom monolayer. In this frame topological bending elasticity of the monolayer is not related to its vanishing macroscopic thickness. The proposed approach predicts completely new sound dispersions and radius dependences of non-resonant Raman-active modes frequencies in single-walled carbon nanotubes (SWCNT). Resulting relations are suitable for nanotubes identification and more complete or alternative characterization. The theory is also applied to describe the low…
Single-walled carbon nanotubes (SWNTs) with five different C13/C12 isotope compositions and well-separated Raman peaks have been synthesized and conjugated to five targeting ligands in order to impart molecular specificity. Multiplexed Raman imaging of live cells has been carried out by highly specific staining of cells with a five-color mixture of SWNTs. Ex vivo multiplexed Raman imaging of tumor samples uncovers a surprising up-regulation of epidermal growth factor receptor (EGFR) on LS174T colon cancer cells from cell culture to in vivo tumor growth. This is the first time five-color multip…
Mixtures containing different weight ratios of single wall carbon nanotubes (SWCNT) and double wall carbon nanotubes (DWCNT) were prepared and studied by in-situ Raman spectroelectrochemistry. Two components of the G-prime mode in the Raman spectra, which can be resolved at high electrode potentials, were assigned to the signals from inner tubes of DWCNT and outer tubes of DWCNT together with SWCNT. The dependence of the ratios of these two components of the G-prime mode on the nominal amount of SWCNT and DWCNT in the samples was simulated so that the residual amount of SWCNT in the original D…
We have studied the coherent dynamics of G-band phonons in single-walled carbon nanotubes through impulsive stimulated Stokes and anti-Stokes Raman scattering. The probe energy dependence of phonon amplitude as well as preferential occurrence between Stokes and anti-Stokes components in response to chirped-pulse excitation are well explained within our model. The temperature dependence of the observed dephasing rate clearly exhibits a thermally-activated component, with an activation energy that coincides with the frequency of the radial breathing mode (RBM). This fact provides a clear picture…
QED-model for multichain coupled qubit system, proposed in \cite{Part1}, was confirmed by Raman scattering studies of quasi-1D carbon zigzag-shaped nanotubes (CZSNTs), produced by high energy ion beam modification of natural diamond single crystals. Multichain coupled qubit system represents itself Su-Schriffer-Heeger $σ$-polaron lattice, formed in CZSNTs plus quantized external electromagnetic (EM) field. New quantum optics phenomenon - Rabi waves, predicted in \cite{Slepyan_Yerchak} has experimentally been identified for the first time. It is shown, that Raman spectra in quasi-1D CZSNTs are …
Long linear carbon-chains have been attracting intense interest arising from the remarkable properties predicted and their potential applications in future nanotechnology. Here we comprehensively interrogate the excitonic transitions and the associated relaxation dynamics of nanotube confined long linear carbon-chains by using steady state and time-resolved Raman spectroscopies. The exciton relaxation dynamics on the confined carbon-chains occurs on a hundreds of picoseconds timescale, in strong contrast to the host dynamics that occurs on a few picosecond timescale. A prominent time-resolved …
We investigated the atomic structures, Raman spectroscopic and electrical transport properties of individual graphene nanoribbons (GNRs, widths ~10-30 nm) derived from sonochemical unzipping of multi-walled carbon nanotubes (MWNTs). Aberration-corrected transmission electron microscopy (TEM) revealed a high percentage of two-layer (2L) GNRs and some single layer ribbons. The layer-layer stacking angles ranged from 0o to 30o including average chiral angles near 30o (armchair orientation) or 0o (zigzag orientation). A large fraction of GNRs with bent and smooth edges was observed, while the rest…
The interaction of double wall carbon nanotubes (DWCNTs) and the conducting polymer poly(3,4-ethylenedioxythiphene/polystyrenesulfonate (PEDOT/PSS) was studied by in-situ Raman spectroelectrochemistry. The mixing of DWCNTs with PEDOT/PSS caused a partial doping of the outer tube of DWCNTs, which was indicated by the relative change of the Raman intensity of the DWCNTs features. On the other hand, the bands corresponding to inner tubes of DWCNTs and to the polymer were almost untouched by assembling both species into a composite. The in situ Raman spectroelectrochemical experiments have shown t…
