Structural defects induced by Fe-ion implantation in TiO2

Abstract

X-ray photoelectron spectroscopy (XPS) and resonant x-ray emission spectroscopy (RXES) measurements of pellet and thin film forms of TiO 2 with implanted Fe ions are presented and discussed. The findings indicate that Fe-implantation in a TiO 2 pellet sample induces heterovalent cation substitution (Fe 2+ → Ti 4+ ) beneath the surface region. But in thin film samples, the clustering of Fe atoms is primarily detected. In addition to this, significant amounts of secondary phases of Fe 3+ are detected on the surface of all doped samples due to oxygen exposure. These experimental findings are compared with density functional theory (DFT) calculations of formation energies for different configurations of structural defects in the implanted TiO 2 :Fe system. According to our calculations, the clustering of Fe-atoms in TiO 2 :Fe thin films can be attributed to the formation of combined substitutional and interstitial defects. Further, the differences due to Fe doping in pellet and thin film samples can ultimately be attributed to different surface to volume ratios.

Fe ion-implanted TiO2 thin film for efficient visible-light photocatalysis

“…However, no signature of Fe-O bonding is observed and one may argue that the implantation of Fe þ ions generates more likely structural defects (vacancies, interstitials, precipitates) than substitutional Fe. 29 Despite high levels of damage even after annealing, this conclusion is largely supported by the channeling RBS data (reported below in Fig. 6), which shows no Fe substitutionality.…”

Enhanced clustering tendency of Cu-impurities with a number of oxygen vacancies in heavy carbon-loaded TiO2 - the bulk and surface morphologies

“…The employed for the model calculations supercells were including 96 atoms both for the bulk rutile-TiO 2 and for the thin-film (surface) anatase-TiO 2 , but in the latter case the supercell was used as a slab because it is the most physically feasible model of (001) TiO 2 surface [33,34]. Additionally, for the bulk morphology used in experiment both rutile and anatase polymorphic structures were theoretically tested and carefully examined, whereas for thin-film (surface) the anatase polymorphic structure was selected solely (see the reason in experimental part above).…”

“…Based on our previous theoretical experience (see Refs. [33,34]), we decided to consider as possible copper impurities the following types of defects: substitutional (S), interstitial (I) and their combination of (xS+I) type. The case of multiple defects combination was analysed and examined separately, employing different distances between various defects -i.e.…”

“…Recall, that using sample the preparation methodology, XRD, and preliminary XPS characterizations, reported in Refs. [32][33][34], the single-phase phase rutile with lattice parameters of a = 4.592Å and c = 2.960 Å and average crystallite size of about 200 nm (bulk ceramics or from now simply bulk) and single-phase anatase thin-films [32] with lattice parameters of a = 3.785Å and c = 9.487 Å were obtained.…”

Scalable approach to high coverages on oxides via iterative training of a machine‐learning algorithm

“…[46][47][48] On another hand, lattice crystal facets of oxides are more complex than metals, and form different defect sites such as oxygen vacancies and substitutional defects. [49][50][51][52] In addition, the DFT calculations for the metal oxide surfaces are more expensive than metal surfaces due to the mix of localized and delocalized electrons. [53] Therefore, relatively few theoretical works have focused on the adsorbate-adsorbate interactions over oxide surfaces" [54][55][56][57] although the several results demonstrate the importance of lateral interactions on adsorption configurations and molecular dissociation on oxides.…”