Abstract
The mechanical, structural, electronic and magnetic properties of carbon nanotubes can be modified by electron or ion irradiation. In this work we used 25 keV He+ and Ne+ ion irradiation to study the influence of fluence and sample thickness on the irradiation-induced damage of multiwalled carbon nanotubes (MWCNTs). The irradiated areas have been characterised by correlative Raman spectroscopy and TEM imaging. In order to preclude the Raman contribution coming from the amorphous carbon support of typical TEM grids, a new methodology involving Raman inactive Au TEM grids was developed. The experimental results have been compared to SDTRIMSP simulations. Due to the small thickness of the MWCNTs, sputtering has been observed for the top and bottom side of the samples. Depending on thickness and ion species, the sputter yield is significantly higher for the bottom than the top side. For He+ and Ne+ irradiation, damage formation evolves differently, with a change in the trend of the ratio of D to G peak in the Raman spectra being observed for He+ but not for Ne+. This can be attributed to differences in stopping power and sputter behaviour.
Highlights
Carbon nanotubes (CNTs) have been investigated intensively due to their excellent properties [1]
We present a correlative approach in which ion-irradiation-induced modifications are characterised by Raman spectroscopy and TEM imaging, and the experimental results are compared to numerical simulations to explain the different observations and to discuss the irradiation of suspended vs deposited multiwalled carbon nanotubes (MWCNTs) and the influence of the thickness of a layer of suspended MWCNTs on the modifications
Raman spectra of pristine samples similar to ours were observed by Lehtinen et al for so-called bamboo MWCNTs [21], and by Ni et al [22] and Nichols et al [51] for CVD-grown MWCNTs
Summary
Carbon nanotubes (CNTs) have been investigated intensively due to their excellent properties [1]. Modifying and tuning them by electron or ion irradiation is part of these studies [2]. Irradiation-induced defects affect the elastic modulus and the tensile strength of CNTs [3]. For multiwalled carbon nanotubes (MWCNTs), the presence of a small number of defects can increase the interlayer shear strength by several orders of magnitude [4]. Single-wall carbon nanotubes (SWCNTs) have the tendency to group in bundles. By electron irradiation the different CNTs can be linked by inter-
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