The excellent mechanical properties of carbon nanotubes are being exploited in a growing number of applications from ballistic armour to nanoelectronics. However, measurements of these properties have not achieved the values predicted by theory due to a combination of artifacts introduced during sample preparation and inadequate measurements. Here we report multiwalled carbon nanotubes with a mean fracture strength >100 GPa, which exceeds earlier observations by a factor of approximately three. These results are in excellent agreement with quantum-mechanical estimates for nanotubes containing only an occasional vacancy defect, and are ∼80% of the values expected for defect-free tubes. This performance is made possible by omitting chemical treatments from the sample preparation process, thus avoiding the formation of defects. High-resolution imaging was used to directly determine the number of fractured shells and the chirality of the outer shell. Electron irradiation at 200 keV for 10, 100 and 1,800 s led to improvements in the maximum sustainable loads by factors of 2.4, 7.9 and 11.6 compared with non-irradiated samples of similar diameter. This effect is attributed to crosslinking between the shells. Computer simulations also illustrate the effects of various irradiation-induced crosslinking defects on load sharing between the shells.
Bibliographical noteFunding Information:
Financial support for this work was provided by the National Science Foundation (CMMI 0555734 and CHE-0550497) and the Office of Naval Research (N000140710905 and N000140810108). The tests were performed at the Electron Probe Instrumentation Centre (EPIC) at Northwestern University. The authors thank I. Petrov and E. Olson for their contribution in the development of the in situ TEM holder. G.C.S. and S.L.M. acknowledge the NASA University Research, Engineering and Technology Institute on Bio Inspired Materials (NCC-1-02037). P.Z., and use of the Centre for Nanoscale Materials at Argonne National Laboratory, were supported by the Department of Energy (DE-AC02-06CH11357).