| Low-energy electron diffraction after oxidising and reducing treatments | All patterns showed a c(6x2) reconstruction with two domains rotated 90° relative to each other; the reconstruction remained stable after the subsequent UHV reducing treatment |
|---|---|
| XPS atomic composition after oxidising and reducing treatments and 100 ML H₂O adsorption at room temperature, Al Kα | 0.05 wt.% Nb, oxidised: Sr 22 at.%, O 60 at.%, Ti 17 at.%, C 1 at.%; 0.05 wt.% Nb, reduced: Sr 21 at.%, O 60 at.%, Ti 18 at.%, C 1 at.%; 0.7 wt.% Nb, oxidised: Sr 22 at.%, O 57 at.%, Ti 16 at.%, C 4 at.%; 0.7 wt.% Nb, reduced: Sr 22 at.%, O 58 at.%, Ti 16 at.%, C 4 at.% |
| Sr3d XPS, Al Kα, Eₖ ~1350 eV | Single doublet representing the bulk SrTiO₃ environment; fixed spin-orbit splitting 1.75 eV; bulk FWHM approximately 0.80 eV |
| Surface-sensitive Sr3d XPS, Eₖ = 600 eV and 150 eV | Two additional surface components shifted by 0.6 eV and 1.1 eV toward higher binding energies relative to the bulk peak; both were significantly enhanced at Eₖ = 150 eV. The +1.1 eV peak was assigned to the reconstructed SrO overlayer and the +0.6 eV component to other surface oxide and hydroxylated species (SrOHₓ). Upon water exposure, the +0.6 eV feature intensity increased at the expense of the bulk and +1.1 eV SrO components |
| Surface-sensitive O1s XPS, Eₖ ~150 eV | Low-doped samples: hydroxyl contribution around 12 at.% (± 1 %); 0.7 wt.% Nb-doped samples: higher hydroxyl contribution, with 21 at.% (± 1 %) for the reduced sample |
| XPS valence-band maximum after 100 ML H₂O exposure at room temperature | 2.90 eV below the Fermi level for the oxidised samples and 3.15 eV below the Fermi level for the reduced samples |
| UPS He II after 100 ML H₂O exposure at room temperature | Surface states from the Fermi level to the valence-band maximum; a slope at 2–3 eV attributed to O2p–Ti3d hybridised states increased in intensity with higher Nb doping; additional Ti3d-derived intensity occurred around 0.5 eV. In-gap states were visible around ~0.5 eV; features occurred around ~2 eV, ~4.5 eV, ~7 eV, ~8 eV, ~10 eV, and ~13 eV |
| XAS | O K-edge: t2g ~530 eV and eg ~532 eV; Ti L-edge: t2g ~457 eV and eg ~463 eV |
| XAS, XPS and UPS Fermi-level position | 0.3 eV below the conduction-band minimum for oxidised samples and 0.05 eV below it for reduced samples; reduction shifted the Fermi level by 0.25 eV |
| Ti2p and O1s XPS fit ratios after oxidising and reducing treatments | 0.05 wt.% Nb, oxidised: Ti³⁺/Ti⁴⁺ 2.4 %, OH/(OH + O) 10.9 %; 0.7 wt.% Nb, oxidised: 3.0 %, 10.6 %; 0.05 wt.% Nb, reduced: 2.3 %, 10.8 %; 0.7 wt.% Nb, reduced: 3.2 %, 11.9 % |
| UPS He II work function, −3 V bias, before and after 100 ML H₂O adsorption at room temperature | 0.05 wt.% Nb, oxidised: 4.2 eV before, 4.4 eV after; 0.7 wt.% Nb, oxidised: 4.4 eV before, 4.6 eV after; 0.05 wt.% Nb, reduced: 5.7 eV before, 4.6 eV after; 0.7 wt.% Nb, reduced: 5.8 eV before, 4.7 eV after |
Marie Neumann, Virginia Pérez-Dieste, Jan Philipp Hofmann. “In-gap states enhance the hydroxylation of c(6x2) terminated SrTiO₃.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15001261/v2
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