| 11. |
- Shchukarev, Andrey, et al.
(author)
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XPS study of the silica–water interface
- 2004
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 137-140, s. 171-6
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Journal article (peer-reviewed)abstract
- XPS was applied to study the silica–water interface formed in NaCl solution at variable pH (2–9) and ionic strength (10–600 mM).To prevent alteration of the interface, the wet silica pastes were precooled with liquid nitrogen. After measurements under liquid nitrogen, XPS spectra were collected the next day at room temperature to follow changes at the silica surface caused by water loss.XPS data show that, at low ionic strength (<20 mM), Cl− ions could not be detected at the surface even at the lowest pH. Changes of the Na/Si atomic ratio with pH are in close agreement with the adsorption curve of OH− ions. At higher ionic strength (>100 mM), the silica surface’s point of zero charge can be determined from the Na/Cl atomic ratio. At pH 9 the amount of “free” Na+ at the surface is independent of NaCl concentration reflecting the formation of SiO---Na bonds, confirmed by O 1s spectra.Removing water from the sample surface allows determination of a “built-in” potential at the interface. Si 2p and O 1s spectra of the matrix shift to lower BE values whereas Na 1s and Cl 2p lines of the counter-ions shift to higher BE. At higher ionic strength and pH<2, shifts of Si 2p and O 1s spectra change sign, reflecting the formation of positively charged silica surfaces. The absolute value of the photoelectron line shifts for the matrix elements does not exceed 0.25 eV at any pH, whereas the shifts for counter-ions can reach 0.6 eV. The shifts decrease with increasing ionic strength, implying the formation of a more compact interface.
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| 12. |
- Öberg, Kjell, et al.
(author)
-
Comparison of monolayer films of stearic acid and methyl stearate on an Al2O3 surface
- 2001
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In: Thin Solid Films. ; 397:1-2, s. 102-8
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Journal article (peer-reviewed)abstract
- Both stearic acid and methyl stearate chemisorbs onto an oxide surface of aluminum with an asymmetric coordination of the carboxylate group as concluded from infrared (IR) spectroscopy data. Similarities in the IR spectra of the films from the two compounds suggest that the ester is bonded in the same way as the acid, and that the ester therefore undergoes hydrolysis during the surface reaction. X-Ray photoelectron spectroscopy (XPS) and IR data are interpreted in terms of self-assembled monolayer formation and a more dense film from the carboxylic acid in comparison with that from the ester.
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| 13. |
- Öberg, Kjell, et al.
(author)
-
Spectroscopic Characterization of the Bonding, Orientation, and Coverage of Copper Tetraazaphthalocyanine Monolayer Films on SiO2 Surfaces
- 2000
-
In: The Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 104:45, s. 10627-34
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Journal article (peer-reviewed)abstract
- Self-assembled monolayer films of a metallotetraazaphthalocyanine were prepared using two different reaction conditions. The films were characterized by ellipsometry, AFM, electronic absorption spectroscopy, semiempirical MO calculations, core-level XPS, and projection of a calculated structure of the chromophore onto a surface to obtain its silhouette area for comparison with surface concentration from absorption spectroscopy. A denser packing of the chromophores is found in the SAM film prepared with bromonaphthalene at 250 C as compared with the film from the more polar solvent DMF at 120 C. Data is consistent with an almost vertical orientation of the chromophores in the former film. A different number of bonds connecting the chromophore with the coupling molecule is suggested as an explanation to differences in the absorption bands for the two films.
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