Photoemission and HREELS study of K adsorption on TiO<sub>2</sub>(100)

Thomas, Andrew G.; Hardman, P.J.; Muryn, Christopher A.; Dhariwal, H.S.; Prime, A F; Thornton, G.; Román, E.; Segovia, J.L. de

doi:10.1039/ft9959103569

Cited by 37 publications

(8 citation statements)

References 16 publications

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“…It is predominantly composed of O 2p orbitals which extend from 0 eV ͑fixed to be the VBM͒ to about Ϫ7 eV in good agreement with the experimental bandwidth of 6-6.5 eV. [22][23][24][25] The most striking changes to the DOS that occur upon adsorption of K are the appearance of two new peaks labeled A and B in Fig. 4.…”

Section: Resultssupporting

confidence: 65%

“…Feature A is due to the K 3p state which lies about 8 eV below the valence band in excellent agreement with photoemission studies which reveal a peak at 8-9 eV below the valence band minimum. 24,25 Feature B is spin polarized and appears about 1 eV above the VBM and is due to d orbitals localized almost entirely on the reduced surface Ti (3) ion. Similar band gap states are observed experimentally at about 3 eV above the VBM.…”

Section: Resultsmentioning

confidence: 99%

“…This state is associated with a new peak in the electronic DOS about 1 eV above the VBM. States have been observed about 3 eV above the VBM in TiO 2 samples reduced by either adsorption of alkali metals [22][23][24][25]28,55 or by the creation of oxygen vacancies. 14,7,28 Spin-polarized states at a similar energy with respect to the VBM were found in recent theoretical investigations of potassium adsorption on the ͑110͒ surface 52 and on oxygen deficient ͑110͒ surfaces in which both DFT and HF approaches were used.…”

Section: B the Nature Of The Electronic Statementioning

confidence: 96%

“…1, [22][23][24][25][26][27][28] Low energy electron diffraction ͑LEED͒ data indicate that K adsorption on the ͑100͒ surface at half-monolayer coverage results in an ordered c(2ϫ2) geometry. 22 This is confirmed by surface x-ray absorption fine structure ͑SEXAFS͒ studies which also probe the local geometry of the adsorption site.…”

Section: Introductionmentioning

confidence: 99%

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First-principles study of potassium adsorption onTiO2surfaces

1999

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We present an ab initio study of alkali metal adsorption on metal oxide surfaces. We have investigated the changes that occur to the structure and electronic properties of the rutile TiO 2 ͑100͒ surface when a 1 2 monolayer of potassium atoms is adsorbed. The K atoms are reduced to K ϩ ions as charge transfer occurs from the K 3s orbital to localized Ti 3d orbitals at the surface of the substrate. The occupied Ti 3d states lie about 1 eV above the O 2 p valence band maximum in agreement with recent photoemission studies. The Ti 3d states are spin polarized and are similar to those found at oxygen deficient TiO 2 surfaces. The geometric structure also undergoes significant relaxation as the lattice is polarized around the reduced Ti sites. The calculated surface structure is in excellent agreement with x-ray adsorption data. ͓S0163-1829͑99͒04224-1͔

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Section: Resultssupporting

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Section: B the Nature Of The Electronic Statementioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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First-principles study of potassium adsorption onTiO2surfaces

1999

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“…4 -9 For brevity we have mentioned only studies on TiO 2 (110), although the same behaviour is found for adsorption on TiO 2 (100) as well. 10 This has been interpreted as a charge flow from the adsorbate to Ti cations mediated by surface oxygen. In the photoemission spectra, the occurrence of the charge transfer is manifested by the presence of an occupied gap state with Ti 3d character and a significant decrease of the surface work function similar to that observed for alkali adsorption on metals.…”

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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