Study of the electronic structure of TiO2(110) and Cs/TiO2(110) with metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (HeI)

Brause, M.; Skordas, Spyridon; Kempter, V.

doi:10.1016/s0039-6028(99)01052-3

Cited by 45 publications

(41 citation statements)

References 32 publications

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“…20 As discussed in detail in Ref. 13, the emission from bare titania is due to the resonance ionization-Auger neutralization process sequence whereby the He Ł probe atom is first resonantly ionized; its re-neutralization involves two O 2p electrons, one of which is emitted. 11,12 Superimposed on the resulting structure (between 10 and 16 eV) is a contribution of secondary and scattered electrons.…”

Section: The Mies Resultsmentioning

confidence: 99%

“…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%

“…The procedure to calibrate the K coverage is described elsewhere for Cs/TiO 2 110 . 13 The sample can be cooled with liquid nitrogen and heated by electron bombardment. The temperature was measured with a thermocouple in direct contact with the front of the single crystal.…”

Section: Methodsmentioning

confidence: 99%

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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: The Mies Resultsmentioning

confidence: 99%

Section: Discussion and Interpretation Delocalization Of The Excess Cmentioning

confidence: 99%

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

Krischok

Günster

Goodman

et al. 2005

Surf. Interface Anal.

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“…23,24 The particular processes taking place on titania precovered by >0.5 ML of K and Cs have been identified previously. 11,12 In that work it has been established that the He Ł interaction with the alkali adsorbates causes a pronounced structure due to auto detachment. The energy scales in the figures are adjusted in such a way that electrons emitted from the Fermi level (denoted by E F ), i.e.…”

Section: Methodsmentioning

confidence: 99%

“…The UPS(HeI) technique is insensitive to the amount of charge of 2s character remaining at the adsorbate. However, for Cs and K/TiO 2 (110) 11,12 metastable-induced electron spectroscopy (MIES) has been demonstrated to be well suited to study this topic. In particular, MIES is rather sensitive to the presence of s-electrons at the adsorbate core.…”

Section: Introductionmentioning

confidence: 99%

Lithium adsorption on TiO₂: studies with electron spectroscopies (MIES and UPS)

Krischok

Schaefer

Höfft

et al. 2005

Surf. Interface Anal.

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The adsorption of lithium atoms on rutile TiO 2 (110) single crystals was studied with metastable-induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) between 130 K and room temperature. Some auxiliary measurements on W(110) required for data interpretation are also reported. At 130 K ionic adsorption at titania prevails up to 0.3 monolayer equivalents (MLE) as judged from the weak Li(2s) emission in MIES for these exposures. The reduction of the Ti 4+ cation is manifested by the growth of an occupied bandgap state in UPS: the alkali s-electron is transferred to a near-surface cation, thereby reducing it to Ti 3+ 3d. The transfer of the s-electron is responsible for the observed work function decrease up to ∼0.5 MLE coverage. From the analysis of the UPS Ti 3+ 3d signal, as well as from the Li(2s) emission, it is concluded that the degree of ionicity of the adsorbed Li decreases from 100% at 0.3 MLE to 40% at 0.7 MLE. Above 0.5 MLE the MIES spectra are dominated by an Li(2s)-induced peak indicating the presence of Li with an at least partially filled 2s orbital. At temperatures above 160 K this peak is almost absent. Excluding Li desorption at these temperatures, we suggest that Li moves into or below the rutile TiO 2 (110) surface above 160 K. Lithium insertion into the surface and intercalation are discussed.

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A study of the electronic structure and reactivity of V/TiO2(110) with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS)

Lee

Zając²,

Goodman

2006

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The interaction of vanadium with TiO 2 (110) surface was studied with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) under ultrahigh vacuum (UHV) conditions. A strong interaction between vanadium and TiO 2 is observed with the addition of the first vanadium layer. Adsorption and reaction of ethanol to ethylene were investigated with MIES, UPS and temperature programmed desorption (TPD) and found to be sensitive to the surface electronic structure. In particular the temperature of ethylene evolution decreased by $100 K with a change in the vanadium coverage from 0.5 to 5 ML.

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Study of the electronic structure of TiO2(110) and Cs/TiO2(110) with metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (HeI)

Cited by 45 publications

References 32 publications

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

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

Lithium adsorption on TiO₂: studies with electron spectroscopies (MIES and UPS)

A study of the electronic structure and reactivity of V/TiO2(110) with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS)

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Study of the electronic structure of TiO2(110) and Cs/TiO2(110) with metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (HeI)

Cited by 45 publications

References 32 publications

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

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

Lithium adsorption on TiO2: studies with electron spectroscopies (MIES and UPS)

A study of the electronic structure and reactivity of V/TiO2(110) with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS)

Contact Info

Product

Resources

About

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

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

Lithium adsorption on TiO₂: studies with electron spectroscopies (MIES and UPS)