The characterization of SrTiO3() with MIES, UPS(HeI) and first-principles calculations

Maus‐Friedrichs, W.; Frerichs, M.; Gunhold, A.; Krischok, S.; Kempter, V.; Bihlmayer, Gustav

doi:10.1016/s0039-6028(02)01968-4

Cited by 55 publications

(49 citation statements)

References 41 publications

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“…1,13,22 -24 On bare titania the absence of Ti 3d in MIES is due to the fact that the reduced Ti species become involved in Auger neutralization processes. 13,21 However, as soon as the work function is lowered to 3.5 eV, reduced Ti species become detectable with high probability via Auger de-excitation. Indeed, reduced Ti 3C 3d species were seen with MIES from TiO 2 110 , heavily reconstructed under reducing conditions, i.e.…”

Section: Discussion and Interpretation Delocalization Of The Excess Cmentioning

confidence: 99%

MIES and UPS(HeI) studies on reduced TiO₂(110)

Krischok

Günster

Goodman

et al. 2005

Surf. Interface Anal.

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We have studied reduced TiO 2 (110) surfaces by combining metastable impact electron spectroscopy (MIES) and UPS(HeI). The reduced Ti species were preparation-induced: their number density was modified either by adsorption of K atoms or by a combined annealing/oxygen exposure procedure. The emission from the bandgap state (binding energy 0.9 eV), caused by reduced Ti 3+ 3d species, was monitored. Bandgap emission is seen clearly with UPS(HeI) and thus can be used to monitor the number density of the nearsurface reduced species. A corresponding spectral structure cannot be seen with MIES. We propose that the excess charge density introduced either by preparation-induced oxygen vacancies or by K adsorption is delocalized over several surface and subsurface Ti sites; this, together with the partial shielding of the reduced Ti species, prevents detection of the reduced Ti species with MIES.The re-oxidation and restructuring of the reduced TiO 2 (110) surface, caused by simultaneous oxygen exposure and annealing, was studied at temperatures between 400 and 770 K, again by recording the Ti 3+ 3d emission (0.9 eV bandgap state) with UPS(HeI). The surface can be completely re-oxidized by oxygen exposure at any selected annealing temperature in the range given above. Morphology changes, leading to a partially reduced surface, take place when the re-oxidized surface is further annealed at T > 600 K under reducing conditions. The results give support to the assumption that the re-oxidation is caused by the growth of additional titania whereby the Ti stems from the bulk and the oxygen originates from the gas. The restructuring of the re-oxidized surface upon annealing under reducing conditions appears to be due to diffusion of Ti interstitials to the surface.

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Section: Discussion and Interpretation Delocalization Of The Excess Cmentioning

confidence: 99%

MIES and UPS(HeI) studies on reduced TiO₂(110)

Krischok

Günster

Goodman

et al. 2005

Surf. Interface Anal.

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“…The surface work function, which can be derived from the low energy onset in the UPS spectra, corresponds to 2.7 eV. In addition to the secondary electron contributions beyond a binding energy (E B ) of 10 eV, the MIES spectrum of SrTiO 3 (100) surfaces is mainly caused by an Auger neutralization (AN) process involving O2p and Ti3d electrons [22]. The Ti 3+ 3d species form a rather narrow band, so the MIES spectrum between 9 eV ≤ E B ≤ 4 eV is similar to an AD spectrum, but shifted towards higher binding energies by 1.2 eV.…”

Section: Methodsmentioning

confidence: 99%

Nanostructures on La-doped SrTiO3 surfaces

et al. 2003

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SrTiO(3)(100) single crystals with high donor dopant concentrations (5 at% La) were annealed at 1000 degrees C for up to 150 h in ultrahigh vacuum (UHV). By applying scanning tunneling microscopy (STM) nanostructures are observed on top of the surface with typical diameters of 20 nm and typical heights of 8 nm. To characterize their electronic structure and chemical composition, the surface was analyzed by metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling spectroscopy (STS), and depth profiling Auger electron spectroscopy (AES). Investigations of the stoichiometry suggest that the secondary phases consist of LaTiO(3). We present a defect chemistry model which attempts to explain the observed effects.

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“…The most recent experimental studies on the SrTiO 3 surfaces include a combination of XPS, LEED, and time-of-flight scattering and recoil spectrometry (TOF-SARS), 23 as well as metastable impact electron spectroscopy (MIES). 24 In these recent studies, wellresolved 1×1 LEED patterns were obtained for the TiO 2 -terminated SrTiO 3 (001) surface. Simulations of the TOF-SARS azimuthal scans indicate that the O atoms are situated 0.1Å above the Ti layer (surface plane) in the case of the TiO 2 -terminated SrTiO 3 (001) surface.…”

Section: Introductionmentioning

confidence: 99%

Ab initiocalculations ofBaTiO3andPbTiO

2007

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We present and discuss the results of calculations of surface relaxations and rumplings for the (001) and (011) surfaces of BaTiO3 and PbTiO3, using a hybrid B3PW description of exchange and correlation. On the (001) surfaces, we consider both AO (A = Ba or Pb) and TiO2 terminations. In the former case, the surface AO layer is found to relax inward for both materials, while outward relaxations of all atoms in the second layer are found at both kinds of (001) terminations and for both materials. The surface relaxation energies of BaO and TiO2 terminations on BaTiO3 (001) are found to be comparable, as are those of PbO and TiO2 on PbTiO3 (001), although in both cases the relaxation energy is slightly larger for the TiO2 termination. As for the (011) surfaces, we consider three types of surfaces, terminating on a TiO layer, a Ba or Pb layer, or an O layer. Here, the relaxation energies are much larger for the TiO-terminated than for the Ba or Pb-terminated surfaces. The relaxed surface energy for the O-terminated surface is about the same as the corresponding average of the TiO and Pb-terminated surfaces on PbTiO3, but much less than the average of the TiO and Ba-terminated surfaces on BaTiO3. We predict a considerable increase of the Ti-O chemical bond covalency near the BaTiO3 and PbTiO3 (011) surface as compared to both the bulk and the (001) surface.

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The characterization of SrTiO3() with MIES, UPS(HeI) and first-principles calculations

Cited by 55 publications

References 41 publications

MIES and UPS(HeI) studies on reduced TiO₂(110)

MIES and UPS(HeI) studies on reduced TiO₂(110)

Nanostructures on La-doped SrTiO3 surfaces

Ab initiocalculations ofBaTiO3andPbTiO

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The characterization of SrTiO3() with MIES, UPS(HeI) and first-principles calculations

Cited by 55 publications

References 41 publications

MIES and UPS(HeI) studies on reduced TiO2(110)

MIES and UPS(HeI) studies on reduced TiO2(110)

Nanostructures on La-doped SrTiO3 surfaces

Ab initiocalculations ofBaTiO3andPbTiO

Contact Info

Product

Resources

About

MIES and UPS(HeI) studies on reduced TiO₂(110)

MIES and UPS(HeI) studies on reduced TiO₂(110)