| 1. |
- CHAKAROV, DV, et al.
(författare)
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INTERACTION OF WATER WITH POTASSIUM ON GRAPHITE - A HREELS STUDY
- 1993
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 64-5, s. 279-285
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Tidskriftsartikel (refereegranskat)abstract
- Water and coadsorbed water + potassium on the basal plane of graphite were studied with high resolution electron energy loss spectroscopy (HREELS) at 85 K and after stepwise annealing up to 500 K. Water adsorbs non-dissociatively on both clean and potassium precovered surface at 85 K. The vibration spectra, together with thermal desorption spectroscopy (TDS) reveal a series of reactions within the coadsorbed layer leading to the formation of KOH, KH, and KOx and volatile products. Eventually a precursor to CO2 formation, of yet unindentified composition and observed also in K + O-2 coadsorption studies on graphite, is observed at approximate to 27 meV.
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| 2. |
- CHAKAROV, DV, et al.
(författare)
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PHOTOSTIMULATED DESORPTION OF METAL ADATOMS - POTASSIUM ON GRAPHITE
- 1994
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 311:3, s. L724-L730
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Tidskriftsartikel (refereegranskat)abstract
- Photodesorption is observed of single K atoms from a graphite surface covered with less than 1 monolayer of potassium. The desorption cross section has a threshold at homegaBAR almost-equal-to 3 eV and a maximum at homega(max)BAR almost-equal-to 4.9 eV. Polarization measurements indicate a substrate-mediated mechanism. The coverage dependence suggests that only the ionic 2D, K-phase is photoactive. The proposed mechanism includes attachment of hot electrons, photoexcited in the bulk, to the K4s adsorbate resonance of energy E(res). The band structure of graphite causes a narrow energy distribution of hot electrons, which yields homega(max)BAR almost-equal-to 2E(res).
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| 3. |
- CHAKAROV, DV, et al.
(författare)
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WATER-ADSORPTION AND COADSORPTION WITH POTASSIUM ON GRAPHITE(0001)
- 1995
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 11:4, s. 1201-1214
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Tidskriftsartikel (refereegranskat)abstract
- Water and water coadsorbed with potassium on the basal plane of graphite were studied with thermal desorption spectroscopy (TDS) and high-resolution electron energy loss spectroscopy (HREELS) in the temperature range 85-900 K. Water alone adsorbs nondissociatively on the clean graphite surface at 85 K, forming hydrogen bonded aggregates. Its structure depends both on the coverage and on substrate temperature. With increasing coverage at 85 K(0.5-1.0 monolayer (ML)) the libration mode at similar to 86 meV shows a rapid upward shift, indicating a phase transition from a 2D to a 3D structure. The transition can also be induced by annealing the low coverage structure. Water coadsorption with potassium is nonreactive or reactive, depending on temperature and potassium coverage. The nonreactive coadsorption at T-s = 85 K occurs only below a critical potassium coverage of BK less than or equal to 0.3 ML. It is characterized by substantial symmetry changes of the adsorbed water molecules, compared to the pure water adsorption, and is attributed to formation of hydrated-ion species on the surface. The surface solvation number at the lowest K coverage is three to four H2O molecules per potassium atom. K and H2O react at submonolayer coverages at 120-160 K to form surface KOH, KH, KxOy, and volatile products. The surface species gradually transforms/decomposes at elevated temperatures (200-500 K) to first form potassium-oxygen complexes that then serve as precursors to graphite oxidation to CO2 at similar to 750 K.
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| 4. |
- CHAKAROV, DV, et al.
(författare)
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WATER-ADSORPTION ON GRAPHITE(0001)
- 1995
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1109-1112
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Tidskriftsartikel (refereegranskat)abstract
- Wafer adsorption on the clean graphite (0001) surface has been studied by high-resolution electron-energy-loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). At 85 K H2O adsorbs non-dissociatively forming hydrogen-bonded aggregates. The structure and the growth mode of water clusters depend on the substrate temperature and the coverage. At all coverages, above a few per cent of a monolayer (ML), the desorption is characterized by zero-order kinetics, while the HREEL spectra reveal a threshold coverage approximately 1 ML when the average co-ordination of the H2O molecules changes. Isothermal measurements of the desorption rate and HREELS measurements at elevated temperatures suggest an irreversible phase transition from amorphous to crystalline ice at approximately 135 K.
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