▎ 摘　　要

Narrow zigzag graphene nanoribbons are found to have exceptional electronic and magnetic properties but difficult to fabricate. We show by density-functional calculations and an elastic mechanical model that oxygen atoms have strong energetic favorability to adsorb on small-diameter carbon nanotubes and form unzipped C-O-C epoxy chains along a direction of minimum angle to the tube axis. With other oxygen atoms further attacking, the unzipping epoxy chain formed on the energy-optimum direction of the nanotube is broken into carbonyl pairs. These results promise that unique zigzag graphene nanoribbons could be fabricated by oxidization of small-diameter carbon nanotubes with arbitrary chiralities according to the minimum energy principle.