Field evaporation of ZnO: A first-principles study

Abstract

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.

Quantitative analysis of doped/undoped ZnO nanomaterials using laser assisted atom probe tomography: Influence of the analysis parameters

“…At high laser pulse energies, the surface electric field is strong enough to ionize only zinc atoms and not oxygen atoms leading to the oxygen deficiency. This is in agreement with the recent work of Xia et al, 38 which show by first-principles calculation approach that Zn atoms are first evaporated. It is suggested that the Zn evaporation leads to an O enrichment.…”

“…Moreover, at higher field, the zinc atoms can evaporate between or after pulses causing lower detection of zinc atoms. Note that this behaviour at very high field (Zn 2þ /Zn þ ratio more than 4) is not described in the work of Xia et al 38 The same variations in concentration have been also observed for Eu and N-doped ZnO nanomaterials. Concentration of Eu dopants was decreased by the increase in the field as it was seen previously for Zn.…”

Direct Observation of Nanoparticulate Goethite Recrystallization by Atom Probe Analysis of Isotopic Tracers

“…In this case, ALD of ZnO was selected for encapsulation as part of a sandwich structure, with additional layers of PVD ZnO above and below to provide a sufficient “bulk” material for cross-section lift-out and specimen shaping. Zinc oxide is a wide band gap semiconductor that is known to field-evaporate well under UV laser-assisted atom probe analysis. , Previous analyses of ZnO nanorods indicated that no significant peaks are present in the 27–29 Da range, where the Fe 2+ peaks critical to this study are located . Also, the evaporation fields for ZnO and goethite appear to be similar, based upon charge state and tip radius/voltage comparisons between a natural bulk goethite sample and ZnO.…”

“…Zinc oxide is a wide band gap semiconductor that is known to field-evaporate well under UV laser-assisted atom probe analysis. 44,45 Previous analyses of ZnO nanorods indicated that no significant peaks are present in the 27−29 Da range, where the Fe 2+ peaks critical to this study are located. 46 Also, the evaporation fields for ZnO and goethite appear to be similar, based upon charge state and tip radius/voltage comparisons between a natural bulk goethite sample and ZnO.…”

Impact of extreme electrical fields on charge density distributions in Al3Sc alloy

“…Interestingly, in nonmetals, the electric field is distributed across the sample, while in metals only the surface layer is affected due to field expulsion. 26 Thus, a cluster of a few layers is sufficient for modeling the field evaporation of conducting materials.…”