Propriedades estruturais e eletrônicas de nanotubos mistos de silício-germânio

Abstract

The aim of this work is perform a study about the electronic and structural properties of the mixed silicon germanium (SiGe) nanotubes. This study was performed using two different methods: one through Monte Carlo simulations and the other using first principles calculations within the density functional formalism. For the Monte Carlo simulations we used the empirical Tersoff potential and for the first principle we used the SIESTA code by solving the Khon-Sham equation in the self consistent form. The calculations were performed for two different SiGe nanotubes: the zigzag (10,0) and the armchair (6,6). We have calculated the main nanotubes properties for non defective nanotubes and when defect such as antisites and vacancies are present. Our results present that the calculated properties for the non defectives nanotubes are well reproduced using the two different methods. By the other hand, when defects are present, different results were obtained. That difference can be explained owing the fact that using first principle calculations the geometry reconstruction around the defect is easily obtained. However, due the fact that for the empirical potential, the parameters were obtained considering non defective systems a geometry reconstruction was not observed. Our result present that antisites have low formation energies and do not change the SiGe nanotube electronic properties. However, vacancies have higher and the SiGe nanotube electronic properties are strongly modified by the presence of the vacancies. Comparatively with carbon and boron nitride nanotubes this defects present lower formation energies, indicating that they probably will by found in synthesized SiGe nanotubes.