Disorder and segregation in B-C-N graphene-type layers and nanotubes: tuning the band gap

We investigate structural and electronic properties of B-C-N (boron-carbon-nitrogen) layers and nanotubes considering the positional disorder of the B, C, and N atoms, using a combination of first principles and simulated annealing calculations. During the annealing process, we find that the atoms segregate into isolated, irregularly shaped graphene islands immersed in BN. We also find that the formation of the carbon islands strongly affects the electronic properties of the materials. For instance, in the case of layers and nanotubes with the same number of B and N atoms, we find that the band gap increases during the simulated annealing. This indicates that, for a given stoichiometry, the electronic and optical properties of B-C-N layers and nanotubes can be tuned by growth kinetics. We also find that the excess of B or N atoms results in large variations in the band gap and work function.