Magnetic ordering in hexagonally bonded sheets with first-row elements.

We report first-principles total-energy electronic-structure calculations in the density-functional theory performed for hexagonally bonded honeycomb sheets consisting of B, N, and C atoms. We find that the ground state of BNC sheets with particular stoichiometry is ferromagnetic. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic ordering, leading to an argument that the BNC sheet is a manifestation of the flat-band ferromagnetism.

Atomic and electronic structures of N-incorporated Si oxides.

We present first-principles total-energy calculations on the N-incorporated Si oxides, regarded as a replacement for conventional SiO2 in device technology. We investigate the energetics, charge states, and electronic structures for various bond configurations around N. While they remain in the N-incorporated structures, the charge trap states, responsible for leakage current in SiO2, are effectively removed from the energy gap in the H-terminated structures. This shows that improvement in the electrical reliabilities of Si oxynitride films is originated not from N incorporation itself, but from the coexistence of N and H.

Energetics and electronic structures of encapsulated C60 in a carbon nanotube.

We report total-energy electronic structure calculations that provide energetics of encapsulation of C60 in the carbon nanotube and electronic structures of the resulting carbon peapods. We find that the encapsulating process is exothermic for the (10,10) nanotube, whereas the processes are endothermic for the (8,8) and (9,9) nanotubes, indicative that the minimum radius of the nanotube for the encapsulation is 6.4 A. We also find that the C(60)@(10,10) is a metal with multicarriers each of which distributes either along the nanotube or on the C60 chain. This unusual feature is due to the nearly free electron state that is inherent to hierarchical solids with sufficient space inside.