Bending Modulus of CVD Grown Multi-walled Carbon Nanotubes (MWNTs)

We have measured the bending modulus of several different CVD grown MWNTs using a vibrating reed technique. The MWNTs are produced from a thermal decomposition of three different precursors: (i) xylene/ferrocene, (ii) xylene/ferrocene/melamine (nitrogen-doped), and (iii) trimethylamine (TMA)/ferrocene. The first two precursors are used to compare the mechanical properties of typical CVD-grown to bamboo-type MWNTs. Nanotubes prepared using the third precursor shows relatively fewer walls ($\sim $ 4-20 compared to $\sim $15-40) and defects compared to those prepared from the xylene/ferrocene mixture. The resonant frequencies of these nanotubes were measured optically and electronically in air using a dark field light microscope. The diameters of these nanotubes range from 50 -- 160 nm as determined from TEM and the average length is $\sim $ 10 microns. For the xylene/ferrocene and trimethylamine/ferrocene tubes, the average bending modulus is estimated to be 0.1 and 0.3 TPa, respectively. However, the bending modulus for the nitrogen-doped tubes is $\sim $9 GPa which is significantly lower compared to regular MWNTs implying that the bending modulus decreases with an increase in wall defects.