Effects of radiation on the hardness of nanowires and nanotubes

Although it is well known that radiation can be used to harden many kinds of bulk and thin film materials, the effects of radiation on nanomaterials are much less well understood. Using molecular dynamics computer simulations, we have examined the effects of ion and electron irradiation on the mechanical properties of nanowires and nanotubes. Generally we find that for single wires and tubes, radiation softens both kinds of materials [1,2,3], but the behaviour is sometimes surprising. For instance, we have found that under tensile mechanical strain, the threshold displacement energy may, counterintuitively, increase [1]. On the other hand, in carbon nanotube bundles, multiwalled carbon nanotubes and macroscopic nanotube paper the strength of the material can strongly increase due to irradiation [4,5,6]. In this talk we will discuss the physico-chemical reasons to these effects and experimental results confirming the theoretical predictions.[1] E. Holmstr�m, L. Toikka, A. V. Krasheninnikov, and K. Nordlund, Phys. Rev. B. 82, 045420 (2010).[2] W. Ren, A. Kuronen, and K. Nordlund, Phys. Rev. B 86, 104114 (2012).[3] M. Sammalkorpi, A. Krasheninnikov, A. Kuronen, K. Nordlund, and K. Kaski, Phys. Rev. B 70, 245416 (2004)[4] M. Huhtala, A. Krasheninnikov, J. Aittoniemi, S. J. Stuart, K. Nordlund, and K. Kaski, Phys. Rev. B 70, 045404 (2004).[5] M. Sammalkorpi, A. V. Krasheninnikov, A. Kuronen, K. Nordlund, and K. Kaski, Nucl. Instr. Meth. Phys. Res. B 228, 142 (2005).[6] J. A. �str�m, A. V. Krasheninnikov, and K. Nordlund, Phys. Rev. Lett. 93, 215503 (2004)