Iron-related defect levels in SrTiO3 measured by photoelectron paramagnetic resonance spectroscopy

Abstract

Shift of surface Fermi level position toward the conduction band minimum by crystal defects near GaAs(001) surfaceThe optical absorption of defect centers in SrTiO 3 substrates grown by the Vernuil method are investigated using photoinduced electron paramagnetic resonance ͑photo-EPR͒ at room temperature. As received samples revealed EPR signatures for Fe 3+ , Cr 3+ , Mn 4+ , and an iron-oxygen vacancy complex, Fe 3+ V O . An anneal in dry oxygen at 800°C decreased the intensity of all of the centers except, Mn 4+ . More significantly, the anneal induced a new charge state of Fe, Fe 5+ . Photo-EPR data of the annealed samples were interpreted in terms of two defect levels, the 4+ to 5+ transition of Fe ͑Fe 4+/5+ ͒ at 2.5 eV below the conduction band edge and the 3+ to 4+ transition of the iron-oxygen vacancy complex ͑Fe 3+/4+ V O ͒ at 1.2 eV above the valence band edge. The former is consistent with reported defect levels and the latter provides a modified value based on measurements over a larger portion of the band gap than had been reported previously.

Band-structure modulation of SrTiO3 by hydrogenation for enhanced photoactivity

“…The signal 6 in Fig. 5(a) corresponds to Fe 3+ ions in axis crystal field, that is, Fe 3+ at the Ti site with one of the six oxygen ions in the first nearest shell missing, sometimes written as Fe 3+ -V O [31][32][33]. It is seen that with the increasing hydrogenation, the EPR signals diminish steadily and finally disappear.…”

“…The signals 1 to 5 in Fig. 5(a) correspond to Fe 3+ ions in cubic crystal field, that is, Fe 3+ at the Ti site with six oxygen ions in the first [31][32][33]. The signal 6 in Fig.…”

Nonradical Oxidation of Pollutants with Single-Atom-Fe(III)-Activated Persulfate: Fe(V) Being the Possible Intermediate Oxidant

“…When mixed with the PDS solution, the signal became much stronger and slightly shifted ( g = 2.0032). The much stronger ESR signal probably arose from the conversion of Fe­(III) to Fe­(V), which has more active single electrons in its 3d 3 orbitals. , …”

“…EPR analysis has been applied to characterize Fe 5+ formed in metal oxides during thermal annealing. 41 Here, the EPR spectra of PDS/Fe−N−C, and PDS and Fe−N−C alone in pure water were recorded at room temperature (Figure S8, Supporting Information). PDS alone gave nearly no EPR signal.…”

P-type conductivity in annealed strontium titanate

“…Prior electron paramagnetic resonance (EPR) studies have shown that as-received samples contain Fe 3+ . 6,17 After the vacuum anneal, UV/visible spectra show the well-known Fe 4+ peak at 430 nm (Fig. 3).…”