Local Structure of Fe Impurity Atoms in ZnO: Bulk versus Surface

Abstract

By studying Fe-doped ZnO pellets and thin films with various x-ray spectroscopic techniques, and complementing this with density functional theory calculations, we find that Fedoping in bulk ZnO induces isovalent (and isostructural) cation substitution (Fe 2+ → Zn 2+ ).In contrast to this, Fe-doping near the surface produces both isovalent and heterovalent substitution (Fe 3+ → Zn 2+ ). The calculations performed herein suggest that the most likely defect structure is the single or double substitution of Zn with Fe, although, if additional oxygen is available, then Fe substitution with interstitial oxygen is even more energetically favourable.Furthermore, it is found that ferromagnetic states are energetically unfavourable, and ferromagnetic ordering is likely to be realized only through the formation of a secondary phase (i.e.ZnFe 2 O 4 ), or codoping with Cu.

Mixed Substitution in P‐Doped Anatase TiO2 Probed by XPS and DFT

“…We performed the DFT‐calculations by employing the SIESTA pseudopotential code well described in Ref. because this technique has been successfully applied in the previous studies of doped semiconductors . We used the Perdew–Burke–Ernzerhof variant of the generalized gradient approximation (GGA‐PBE) for the exchange‐correlation potential with a full optimization of the atomic positions.…”

XPS and DFT study of pulsed Bi-implantation of bulk and thin-films of ZnO—The role of oxygen imperfections

“…The density-functional theory (DFT) calculations were performed using the SIESTA pseudopotential code [22] as had been previously used for related studies of impurities in the bulk and thin-film semiconductors [13][14][15]. All calculations were made using the Perdew-Burke-Ernzerhof variant of the generalized gradient approximation (GGA-PBE) [23] for the exchangecorrelation potential.…”

Pleomorphic structural imperfections caused by pulsed Bi-implantation in the bulk and thin-film morphologies of TiO2

“…The average temperature of the samples during ion implantation did not exceed 295 °C in this case. The chemical purity of the initial and Bi-implanted TiO 2 samples was additionally qualified with the help of PHI XPS Versaprobe 500 spectrometer (ULVAC-Physical Electronics, USA), applying Al X-ray Kα radiation (1486.6 eV) [17]. The same XPS system had been employed for the core-level and valence band analysis of the samples under study.…”

“…The density-functional theory (DFT) calculations were performed using the SIESTA pseudopotential code [18][19] as had been previously utilized with a success for related studies of impurities in the bulk and thin-film semiconductors [17]. All calculations were made using the Perdew-Burke-Ernzerhof variant of the generalized gradient approximation (GGA-PBE) [19] for the exchange-correlation potential.…”

“…For the modeling of anatase-TiO 2 surface we applied the same supercell as a slab ( Fig. 2d) which is feasible model of (001) surface of titanium dioxide [17].…”