Hydroxyl-functionalized ZnO monolayers for optoelectronic devices: Atomic structures and electronic properties

Two-dimensional materials have been extensively investigated both experimentally and theoretically due to their appealing physical/chemical properties. Zinc oxide (ZnO) monolayers, as typical two-dimensional materials, have also aroused wide concern. However, the improper bandgap or nonmagnetic limits their applications in optoelectronic or spintronic devices. Herein, based on first-principles calculations, the effects of individual hydroxyl adsorption and hydroxyl group functionalization on the atomic and electronic structures of ZnO monolayers are investigated. The results demonstrated that the most stable structure for individual hydroxyl on the ZnO monolayer is the one in which the hydroxyl is adsorbed on the top of the hollow site with an adsorption energy of −1.448 eV. Furthermore, hydroxyl could easily aggregate on ZnO monolayer with increasing of hydroxyl coverage and form epoxy groups. Upon hydroxyl group functionalization, ZnO monolayers exhibit mechanical and thermal stability. Moreover, OH–ZnO and ZnO–OH monolayers exhibit magnetic semiconductors, while OH–ZnO–OH monolayers are nonmagnetic semiconductor. Additionally, the band gaps of ZnO monolayer with hydroxyl group functionalization could be effectively modulated via applying the strain. This study opens a new avenue for preparing potential high-performance ZnO-based optoelectronic devices.