Adsorption structures of catechol on the ZnO(10-10) surface

The details of catechol interacting with the ZnO surfaces are critical for understanding how the organic chro-mophores anchor on and hence functionalize the ZnO materials. In this work, we apply low-temperature scan-ning tunneling microscopy (LT-STM) in combination with density functional theory (DFT) calculations to investigate the adsorption state and interface charge transfer of catechol on a ZnO(10-10) surface. For the molecules deposited at liquid nitrogen temperature, the fully-protonated (FP) status prevails in the isolated molecules despite the synergistic formation of half-protonated (HP) and fully-deprotonated (FD) ones. However, annealing to elevated temperature drives all the molecules to assemble into either linear or a c(2 x 2) super-structure composed of only FD catechols. Such spontaneous deprotonation of catechol is different from the predicted water-assisted process and plays critical roles in switching the catechol from electron acceptors to electron donors relative to the ZnO surface. These results may bring new insights into the design of optoelec-tronic and biomedical applications of the ZnO-organic compositional system.

Automated summary

In this study, the adsorption state and interface charge transfer of catechol on a ZnO(10-10) surface were investigated using low-temperature scanning tunneling microscopy and density functional theory calculations. The results showed that annealing at elevated temperature induced spontaneous deprotonation of catechol, which played a critical role in switching the molecule from an electron acceptor to an electron donor relative to the ZnO surface.