First-principles study on the structural and electronic properties of AlNCx nanosheet

The structural and electronic properties of a hydrogen terminated hexagonally AlN nanoribbon with 6 zigzag Al–N chains across the ribbon width (6-ZAlNNR) and the hexagonally bonded hetero-sheets AlNCx (x=2,4,6x=2,4,6) consisting of AlN and graphite strips with zigzag shaped borders have been investigated systemically by using the first-principles. The results show that in 6-ZAlNNR, the states of the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) at zone boundary Z are edge states whose charges are localized at edge Al and N atoms, respectively. Introducing the graphite strip Cx and increasing its width lead to the LUCB and HOVB getting closer with each other especially in flat dispersion region around the zone boundary Jy, thus decreasing in the energy gap of the hetero-sheets AlNC2, AlNC4 and AlNC6 successively. Similar to the edge states existing in zigzag edged AlNNR, the flat dispersion border states also exist in the zigzag borders of hexagonally networked hetero-sheets AlNCx. Unlike the edge states whose charges are localized at one of the edge atoms, the border states are localized at two atoms of the borders with either bonding or antibonding character.

► In 6-ZAlNNR, the states of the LUCB and HOVB at zone boundary Z are edge states.
► The flat dispersion border states exist in zigzag borders of hetero-sheets AlNCx.
► The energy gap of hetero-sheets decreases for AlNC2, AlNC4 and AlNC6 successively.
► The border states localized at two atoms of the border are bonding or antibonding.