XPS spectroscopy

Watanabe and Ohnishi [39] have proposed another model for the polymer consumption rate (in place of Eq. 2) and have also integrated their model to obtain the time dependence of the oxide thickness. Time dependent oxide thickness measurement in the transient regime is the clearest way to test the kinetic assumptions in these models however, neither model has been subjected to experimental verification in the transient regime. Equation 9 may be used to obtain time dependent oxide thickness estimates from the time dependence of the total thickness loss, but such results have not been published. Hartney et al. [42] have recently used variable angle XPS spectroscopy to determine the time dependence of the oxide thickness for two organosilicon polymers and several etching conditions. They did not present kinetic model fits to their results, nor did they compare their results to time dependent thickness estimates from the material balance (Eq. 9). More research on the transient regime is needed to determine the validity of Eq. 10 or the comparable result for the kinetic model presented by Watanabe and Ohnishi [39]. 

The parameters of treatment were chosen since these led to the most pronounced changes of polymer surface in our previous experiments [70-74]. It was observed elsewhere that plasma treatment of polymer macromolecules results in their cleavage, ablation, alterations of chemical structure and thus affects surface properties e g. solubility [75]. The chemical structure of modified polyethylene (PE) was characterized by FTIR and XPS spectroscopy. Exposition to discharge leads to cleavage of polymeric chains and C-H bonds followed by generation of free radicals which easily oxidize [10,76]. By FTIR spectroscopy the presence of new oxidized structures within whole specimen volume can be detected. IR spectra in the 1710-1745 cm" interval [71,77] from PE, exposed to... 

The power of XPS-spectroscopy must be seen in the fast and efficient control of the homogeneity of an isolated protein. Commercial samples are sometimes not homogeneous enough or tend to show age dependent deterioration. These can readily be seen by XPS. When rapid and thorough isolation of a protein can be accomplished, no oxidised sulphur species are seen. A good example proved to be Cd, Zn-thionein which had no active redox metals. 

The applications of XPS-spectroscopy in practical chemistry are manifold and we can only touch some typical results in order to exemplify the potential of this technique. A more complete picture can be obtained by consulting the references listed in Table 2. As can be seen, nearly all elements of the periodic table have been investigated by XPS and the chemical shifts reported in the literature might help with the interpretation of data and can give a feeling, whether a problem is suitable for XPS-spectroscopy. 

In a similar experiment, immobilisation of a-chymotrypsin (AC) on PE films [253] was studied using high resolution XPS spectroscopy. The atomic concentration changes upon functionalisation and immobilisation affirmed the successful derivatisation and immobilisation reactions. 

Nefedov, V.I. XPS-spectroscopy of chemicals, Chemistry, Moscow (1984) [in Russian]. 

The mechanisms of the oxidation of solvents such as THF and PC were studied by several groups, utilizing FTIR and XPS spectroscopy [107-109] and on-line mass spectrometry (DEMS-differential, electrochemical mass spectroscopy [110-112]). For example, using ex situ FTIR spectroscopy, Lacaze et al. [46] showed that THF in FiC104 solutions are polymerized on electrodes biased to high potentials. The proposed mechanism involves oxidation of C104 as an initial step, as shown in Scheme 7 [46,102], ESR measurements also support such a mechanism. However, there are also suggestions for possible direct oxidation... 

FIGURE 27 Diagram representing the states of oxidation of ruthenium as a function of the 02 exposure (in mbar x s) and temperature. The patterned areas were determined on the basis of a large set of 02-TD spectra (Blume et al., 2004 Bottcher and Niehus, 1999a,b). The black squares indicate the (exposure-T) space, when the system was characterized by XP spectroscopy and microscopy (Blume et al., 2005 Bottcher et al., 2002b). The ball models illustrate schematically the distribution of oxygen in the various states of oxidation of the sample. 

As catalysis is by nature a surface phenomenon, XPS spectroscopy seems ideal for studying the solids involved. The interpretation of the data is, however, somewhat complex and usually requires taking the results of other techniques into consideration. 

Borasio M, Rodriguez de la Euente O, Rupprechter G, Ereund H-J (2005) In situ studies of methanol decomposition and oxidation on Pd(lll) by PM-IRAS and XPS spectroscopy. J Phys Chem B Lett 109 17791... 

Rupprechter G, Kaichev VV, Unterhalt H, Morkel M, Bukhtiyarov VI (2004) CO dissociation and CO hydrogenation on smooth and ion-bombarded Pd(lll) SFG and XPS spectroscopy at mbar pressures. Appl Surf Sci 235 26... 

Morkel M, Kaichev VV, Rupprechter G, Freund H-J, Prosvirin IP, Bukhtiyarov VI (2004) Methanol dehydrogenation and formation of carbonaceous overlayers on Pd(lll) studied by high-pressure SFG and XPS spectroscopy. J Phys Chem B 108 12955... 

Readers should note that other analytical techniques also exist for investigating the elemental make up of samples, such as CHN analysers (especially for compositional analysis of pure organic chemicals) and X-ray fluorescence (XRF) instruments, and techniques such as X-ray photoelectron (XPS) spectroscopy are available for surface-specific analysis, but expensive. 

The material, calcined at different temperatures and under different atmospheres was studied by XPS analysis in order to determine the surface composition and the oxidation state of tin, vanadium and antimony in each of the samples. Table 4 reports the atomic percentage of tin, vanadium and antimony in the various ca ysts the bulk atomic ratio analysis is made by atomic absorption and the surface atomic ratio by XPS spectroscopy. 

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