Field Evaporation Of Zno: A First-Principles Study

With recent advances in atom probe tomography of insulators and semiconductors, there is a need to understand high electrostatic field effects in these materials as well as the details of field evaporation. We use density functional theory to study field effects in ZnO clusters calculating the potential energy curves, the local field distribution, the polarizability, and the dielectric constant as a function of field strength. We confirm that, as in MgO, the HOMO-LUMO gap of a ZnO cluster closes at the evaporation field strength signaling field-induced metallization of the insulator. Following the structural changes in the cluster at the evaporation field strength, we can identify the field evaporated species, in particular, we show that the most abundant ion, Zn2+, is NOT post-ionized but leaves the surface as 2+ largely confirming the experimental observations. Our results also help to explain problems related to stoichiometry in the mass spectra measured in atom probe tomography. (C) 2015 AIP Publishing LLC.