Energetics of extended and finite silicon nanotubes

Full text: While nanotube research has been dominated by studies of carbon tubes, some attempts to establish the conditions for the synthesis of non-carbon tubes have also been made. The simplest test for successful tube formation is to estimate the balance between the extra energy required when forming the tube by rolling up a single atomic strip and the energy gain when all the dangling bonds at the edges of the strip are saturated. The infinite tube is stable if the energy gained is larger than the strain energy needed to bend the strip. In this paper we have investigated the energetics of hypothetical silicon nanotubes reported recently by two independent research groups. Our calculations have been carried out using the empirical Brenner potential Molecular Dynamics method for clean and hydrogenated, infinite and finite, Si tubes. The aim was to model the energetics of the Si tubes, in an analogous way to carbon tubes in order to predict their energetics and stability. Our results indicate that the model originally developed for infinite and finite clean carbon tubes can also be used for clean Si tubes. The main difference between the carbon and silicon finite tubes is that the chemical energy of the open ends of the Si tube is almost independent of the symmetry and topology of the edges. This is in sharp contrast to the carbon tubes and may result in 'symmetry selection' during the formation of the Si tubes. Such symmetry selection is not observed during the growth of carbon tubes, as correctly predicted by the model