Estudo teórico de nanotubos de arseneto de Gálio

Abstract

Since the discovery of carbon nanotubes in 1991, and inorganic nanotubes in 1992 significant interest was shown in the study of these new forms, so as to establish a relationship between the structure and properties. Within the class of semiconductors formed by the elements of III-V groups, GaAs is considered a potential candidate to replace Si in the manufacture of electronic devices. Mainly due to the properties presented and the range of technological applications. Between among the forms in which the GaAs can be found, theoretical and experimental studies have reported the formation of clusters, ternary alloys and tubular structures obtained only in association with InAs. Among these geometries, nanotubes are those that have less information regarding the structure, stability and properties. In this sense the objective of this work is to analyze the stability of formation of GaAs nanotubes, from crystal planes (1 0 0), (1 1 0) e (1 1 1) obtained from zinc blend crystal, using algorithms developed in programming language Bash Shell of Linux. The information obtained and properties were calculated using the quantummechanical methods semi-empirical PM7 and ab initio B3LYP and HF, with 3- 21 and 6-31G basis. Considering the nanotubes obtained after optimization, these geometries tend to have greater stability compared to the respective crystal planes of origin, where models of type (1 1 0) are more stable compared to the (1 1 1) and (1 0 0), and models of type (1 0 0) geometries less stable. Through the average diameters calculated according to the type of region can establish that the models obtained from the plane (1 0 0) they have a format similar to hyperbole, where the ends have larger diameters compared to the middle, while in models of type (1 1 0) and (1 1 1) prevails the formation of conical structures, where the tips of As tend to have smaller diameter in relative to the medium and the tips of Ga. The formation of structures with asymmetric regions promotes electronic charge transfer between the atoms of Ga and As, favoring the stabilization of these geometries. For the evaluation of molecular orbitals HOMO and LUMO, it was observed that increasing the amount atoms per level, and the numbers of level, interfere directly in the Gap, where the orbital with the greatest contribution to the formation of the valence and conduction bands are the orbitals pz of Ga atoms and d orbitals of As atoms, and the calculations for more stable models using the ab initio methods B3LYP and HF, describe the formation of materials having semiconductor characteristics.