Fracture and mechanical properties of nanotubes and nanowires

During the last two decades there has been an increasing progress in the synthesis and characterization of various nanoscale materials. These materials are of great interest because they show unique properties related to their small size and large surface-to-volume ratio. For instance, it is known that the tensile strength of carbon nanotubes is at least 10 times greater than that of steel. In the present study, the fracture, mechanical and thermal properties of nanoscale materials are investigated using the ab initio molecular dynamics (TBMD) [M. Menon, et al. Phys. Rev. B 70 (2004) 125313; M. Menon, et al. Phys. Rev. B 75 (2007) 155435] and the quantum mechanical statistical moment method (QMSMM) [Vu Van Hung, J. Lee, K. Masuda-Jindo, J. Phys. Chem. Solids 67 (2006) 682; Vu Van Hung, K. Masuda-Jindo, Nruyen Thi Hoa, J. Mat. Res. 22 (2007) 2230; K. Masuda-Jindo, Vu Van Hung, P.E.A. Turchi, Sol. Stat. Phenomena 138 (2008) 209]. We investigate the electronic structures and electronic (quantum) transport properties of carbon-related nanoscale materials, i.e., carbon nanotubes (CNTs), graphenes, Si, SiC nanowires (with and without atomistic defects), in comparison with those of bulk materials. Particular attention will be paid to the effects of polymorphic atomistic defects (Stone-Walles, 5-7-7-5, and combinations of 5-7 defects, adatoms, kinks, cracks) on the properties of nanoscale materials. Thermal lattice expansion coefficients, linear elastic moduli, specific heat, yield strength and fracture behaviors are studied, including the anharmonicity of thermal lattice vibrations. We will show that strength, thermodynamic and electronic properties of the nanoscale materials are quite different from those of the corresponding bulk materials.