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  • Polymer and Materials Science  (6)
Materialart
Erscheinungszeitraum
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 471-471 
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 21 (1994), S. 643-649 
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Chemisorption of ammonia on the acid sites located at the outer surface of dealuminated mordenites has been investigated by x-ray photoelectron spectroscopy. The N 1s level of chemisorbed ammonia results from the overlapping of three components occurring near 402.4, 400.5 and 399.1 eV. From the N 1s binding energy of NH4+- exchanged mordenite and values reported in the literature for pyridine adsorbed on Brönsted and Lewis acid sites, the components at 402.5 and 399.1 eV are assigned to ammonia in interaction with Si-OH-Al framework groups and with Lewis acid sites, respectively. Based on XPS N/Al ratios and infrared results, the component at 400.5 eV is attributed to ammonia chemisorbed on silanol groups. The surface concentration of the three types of acid sites is estimated from the decomposition of the N 1s peaks. Evidence for the presence of surface extra-framework Al in dealuminated mordenites is provided and the influence of these Al species on the outer surface acidity is discussed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 11 (1988), S. 478-486 
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Yeast cells, Saccharomyces cerevisiae and carlsbergensis, have been analysed by XPS.A preparation and analysis procedure was developed in order to minimize contamination and re-arrangements of the cell surface. The use of an external standard of silica permitted the absolute surface concentrations to be estimated and the influences of sample preparation procedure on surface roughness and chemical composition of the cell surface to be evaluated separately. The selected procedure consisted of washing the cells in distilled water, freezing a pellet in liquid nitrogen, freeze-drying at 268 K, mounting the obtained powder in a trough and pressing the surface.Repeated analyses on a given yeast strain enable the variances linked to the main steps of the preparation procedure for each surface element to be evaluated; thereby, confidence intervals can be given for any small set of XPS data. Freeze-drying is the main source of variation and samples which have to be compared should be freeze-dried together. The reproducibility of the surface concentration decreases in the order C, O, N, P and is much better for the N/P ratio than for N or P alone.The neutrality of the XPS preparation and analysis procedure towards the yeast cell surface is supported by the correlation obtained for ten yeast strains between the surface N/P ratio (dehydrated state) and the electrophoretic mobility at pH 4 (hydrated state). This gives confidence in the ability of XPS to investigate a biological surface. The surface specificity of XPS is illustrated by the very low O/C (0.39) and N/C (0.1) concentration ratios which denote a high proportion of lipids at the cell surface (60-70%), in contrast with the low proportion in the whole cell wall (8%).
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The relative analyser transmission functions of two different XPS spectrometers (VG ESCA-3 Mk II and SSI X-Probe of Fisons) have been determined experimentally by several methods presented in the literature. The transmission function of the VG ESCA-3 Mk II can be expressed as T ∝ Ea(Ea/Ek)n, where n is close to 0.8. The transmission function T of the SSI X-Probe cannot be presented as a separate function of Ea and Ek and it is expressed as \documentclass{article}\pagestyle{empty}\begin{document}$$ T \propto \,\,E_{\rm a} (E_{\rm a} /E_{\rm k})^n,\,{\rm where}\,\,n = 0.5594\, + \,0.6072\,\log (E_{\rm a} /E_{\rm k})\, + \,0.3309\,\log ^2 (E_{\rm a} E_{\rm k}) $$\end{document}The possible influence of the efficiency D of the detector on the determined transmission functions is discussed. The advantages and disadvantages of the methods used are pointed out, together with their limitations and potential applications. The results show that some methods can only be applied to spectrometers such as the VG ESCA-3 Mk II in which n is a constant or depends only on Ek. The method proposed by Hemminger et al. [Surf. Interface Anal. 15, 323 (1990)] has been shown to be applicable to both spectrometers but a systematic error can be introduced when D is not constant. Such a systematic error can be reduced by another method but this method can only be applied to spectrometers in which the transmission function is known for a given analyser energy.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 15 (1990), S. 344-346 
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: In this paper, the stationary charging voltage of human dental enamel samples due to photoelectron ejection in an x-ray photoelectron spectrometer is related to the amount of material adsorbed from commercially available mouthrinses and the adsorbed layer thickness. A clear relationship was observed between the charging voltage versus the C/Ca elemental surface concentration ratio, taken as a measure of the amount of adsorbed material. Consequently, a similar relationship was found between charging versus adsorbed layer thickness.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The first principles model (FPM) has been compared with other quantitative approaches by using many standard samples. As a first step, the applicability of the theoretical dependence of IC 1s/ICKVV on the reduced thickness (x) of a hydrocarbon surface contamination layer was checked and shown to be approximately correct only in the middle range of x. A semi-empirical relation between IC 1s/ICKVV and x has been developed. The advantage of this relation over that previously developed in the literature is that the transmission function of our spectrometer is well characterized. The reduced thickness calculated using this semi-empirical relation has been shown to be close to the real value. The comparison of atomic ratios calculated using these quantitative approaches has shown that the best approach is the FPM. For the samples investigated in this work, the introduction of the anisotropy parameter L is not necessary: in most cases, the influence of L is smaller than the observed errors; and in certain cases where the difference of L values is large, more consistent results are obtained when L is ignored. The FPM approach provides consistent results not only when an inter-comparison is made between different spectrometers but also when, within a given machine, the analysis conditions are varied. The accuracy of this approach is relatively good (with errors 〈15%) and holds true even when comparing peaks separated by more than 1000 eV. Finally, the comparison of results obtained with different previously determined transmission functions has allowed us to test the applicability of the methods used for the determination of these transmission functions (see Part I).
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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