Isotope Engineering of Carbon Nanotube Systems

Abstract

The synthesis of a unique isotope engineered system, double-wall carbon nanotubes with natural carbon outer and highly 13C enriched inner walls, is reported from isotope enriched fullerenes encapsulated in single-wall carbon nanotubes (SWCNTs). The material allows the observation of the D line of the highly defect-free inner tubes that can be related to a curvature induced enhancement of the electron-phonon coupling. Ab initio calculations explain the inhomogeneous broadening of inner tube Raman modes due to the distribution of different isotopes. Nuclear magnetic resonance shows a significant contrast of the isotope enriched inner SWCNTs compared to other carbon phases and provides a macroscopic measure of the inner tube mass content. The high curvature of the small diameter inner tubes manifests in an increased distribution of the chemical shift tensor components.

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

“…Significant efforts have been devoted to produce and study isotope-enriched graphene-related materials [4][5][6][7][8][9][10][11][12][13]. For instance, isotope labeling provided direct evidence that the growth mechanism of graphene is substrate dependent and, furthermore, shed light on the rational design of chemical vapor deposition (CVD) synthesis methods [4][5][6][7][8].…”

Encapsulating C59N azafullerenes inside single‐wall carbon nanotubes

“…The filling efficiency for C 60 using the toluene stirring method was found to yield 48(1) % filling of the total available volume by comparing the Raman signal with the previous calibration [24]. This corresponds to ∼6 % fraction of the total sample mass as the 100 % encapsulation corresponds to 13 % mass fraction of the encapsulated fullerenes [23].…”

“…This, however, can not be used to measure the encapsulation efficiency as Raman intensities depend on the strength of the Raman resonance enhancement and the Raman scattering matrix elements [21]. For C 60 peapods the Raman signal was calibrated with independent and carbon number sensitive measurements: EELS studies gave the total number of C 60 related and non-C 60 related carbons [22] and the mass of encapsulated C 60 s was determined from NMR studies using 13 C enriched fullerenes [23]. In the current case, neither methods can be employed and we determined the filling efficiency for the azafullerene by encapsulating a mixture of the azafullerene and C 60 .…”

Reducing the thermal conductivity of carbon nanotubes below the random isotope limit

“…Nevertheless, there are ways to achieve nanotubes where the isotopic concentration is distributed in a segmented way. One of them consists in synthesizing nanotubes from C 60 peapods 11,12 .…”