Study of the influence of structural defects in the properties of carbon nanotube / Estudo da influência de defeitos estruturais nas propriedades de nanotubos de carbono

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

We have investigated the influence of defects on structural, electronic and mechanical properties of single-walled carbon nanotubes (SWCNT), bundles of nanotubes and multi-walled carbon nanotubes (MWCNT). All our results were obtained with the first principles theory of total energy - Density Functional theory (DFT). We have investigated the structural properties of four defects in single-walled nanotubes: Stone-Wales (5577), monovacancy and two divacancies (585) and (555777). We show the behavior of the formation energy as a function of tube diameter for all structures. In this study, we have observed that divacancies have a stability reversal, when we compare the formation energies of these defects in nanotubes and graphene and, moreover, they are the most important defects in the modification of transport properties of SWCNT. We have studied the stability and transport properties of these systems. The defect 585 is less stable in graphene due to two breaks bonds in pentagons. We have observed that the 555777 becomes more stable than the 585, for armchair (zigzag) with a diameter of about 40 °A (53 °A), respectively. We have studied the structural and mechanics properties of bundles of carbon nanotubes with vacancy-vacancy defects, V¹2 and V² 2 . Due to carbon nanotube geometric structure these defects have lower formation energy than in graphene. These defects can form connections between the walls of this bunldes and we present how this imperfection can change the shear modulus of this nanotubes. We have also studied the barrier to form the connection with the method Nudged Elastic Band- NEB. Finally, we have investigated the structural and mechanical properties of multiwalled nanotubes (MWCNT) with defects like vacancy-interstitial (Wigner defect) and vacancy-vacancy (V¹2 and V² 2 defects). We show that this system have several possibilities for the Wigner defect. We observed that the more stable of all vacancyinterstitial defect is the case of the system that have a pentagon in the inner tube and the pentagon atoms participate in the connection (Wigner-Ia defect). We have studied the stability of these defects in two concentrations (½d = 0.082 [def.°A1] and ½d = 0.164 [def.°A1]). In the study of mechanical properties in these systems, we observe the improvements in shear modulus by a factor of up to 15, compared with the system without connection. When we doubled the concentration of defects the shear modulus increases by a factor of 3. We present a study of load transfer between the walls of DWCNT through the connections and we show that depending on the concentration of defects, the load transfer could be up to 75% of the maximum load.

ASSUNTO(S)

structural and mechanics properties structural defects carbon nanotubes computation simulation nanotubos de carbono física do estado sólido propriendades estruturais e mecânicas density functional theory teoria do funcional da densidade solid state physics defeitos estruturais simulação computacional

ACESSO AO ARTIGO

Documentos Relacionados