Radiation damage to multi-walled carbon nanotubes and their Raman vibrational modes

Since their discovery in 1991 by Iijima, carbon nanotubes (CNTs) have been of great interest, both from a fundamental point of view and for future applications. As recent experimental and theoretical studies demonstrate, irradiation of CNTs with energetic particles can successfully be used for nano-engineering, e.g., for creating molecular junctions between the nanotubes, making nanotube-based quantum dots and composite materials with enhanced mechanical properties. In this work, the Raman spectroscopy investigation of nanotube defects created by irradiation of Ar+ ions with various energies and doses was presented. In order to obtain more informative data, scanning electron microscope and thermal gravimetric analysis were carried out. Sheet resistivity of samples was also measured with the standard four-point probe technique. From the results, it was evident that the intensity ratio of the ‘D band’ at around 1300 cm-1 to the intensity of the ‘G band’ at 1590 cm-1, relative intensity of the D to G bands increases with enhancement of the irradiation dose. Comparing the intensity ratio $\boldsymbol {I}_{\mathbf {D^{\boldsymbol {\prime }}}}\boldsymbol {/}\boldsymbol {I}_{\mathbf {G } }$ (the D $^{\boldsymbol {\prime }}$ band was assigned to the lattice defects which occur inside the graphene atomic layer and induces a break in the two-dimensional translational symmetry) with I D / I G tend to decide the D $^{\boldsymbol {\prime }}$ band treated as a defect. Electrical measurements showed that resistance of samples increases with enhancement of irradiation dose, clearly due to creation of more defects.