  Armchair graphene nanoribbons with different proportions of edge oxygen atoms
are investigated by using crystal orbital method based on density functional
theory. All the nanoribbons are energetically favorable, although buckled edges
are present. Isolated edge oxygen atoms cause semiconductor-metal transition
via introducing edge states, while adjacent edge oxygen atoms not. For the
graphene nanoribbons with all oxygen atoms on the edges, both band gap and
carrier mobility alternate with respect to the ribbon width. The carrier
mobilities are as 18%-65% large as those of the graphene nanoribbons with
hydrogen-terminated edges. These values are as large as 103 cm2V-1s-1, which
are still quite high for electronic devices. Crystal orbital analysis gives
pictorial explanations to the phenomenon.
