  Using full-potential density functional calculations within local density
approximation (LDA), we found mechanically tunable band-gap in ZnO monolayer
(ML-ZnO) in graphene-like honeycomb structure, by simulated application of
in-plane homogeneous biaxial strain. Unstrained ML-ZnO was found to have a
direct band gap of energy 1.68 eV within LDA; the actual band gap would be
more, since LDA is known to underestimate the gap. Within our simulated strain
limit of about plus or minus 10%, the band gap remains direct and shows a
strong non-linear variation with strain. The results may find applications in
future nano-electromechanical systems (NEMS) and nano-optomechanial systems
(NOMS).
