Analysis by XPS

Watts JF, Wolstenholme J (2003) An introduction to surface analysis by XPS and AES. Wiley, Rexdale... 

Analysis by XPS after incorporation of the linear or dendritic cationic polymers showed an increase in the atom % N consistent with incorporation of an N-rich polycation. The polyvalent interactions between the cationic polyelectrolytes and the poly(sodium acrylate)graftson PE were stable to Soxhlet extraction with 95% ethanol, repeated acid/base treatment, and soaking or sonication in isopropanol and THE However, in these cases, simple acid treatment did not release the cationic polymer as was the case with PAA/Au grafts even though grafting in both cases was reportedly ionic and not covalent. 

In conclusion we emphasize that the final chemical composition of the surface films covering Li electrodes in solutions is the result of a delicate balance between several competing reduction processes of solvent, salt anion, and contaminants. In this section we emphasize the role of salt reduction processes. However, each solution has to be studied separately since the above balance is determined by factors such as salt concentration, the nature of the solvent, contamination level, etc., all of which differ from system to system. Table 4 presents element analysis by XPS of surface films formed on freshly prepared Li electrodes in several solutions. It demonstrates how the impact of salt reduction on the Li surface chemistry depends on the solution composition and the storage time. (The atomic percentage of fluorine on the surface is a good measure for the impact of the salt.)... 

Table 4 Element Analysis (by XPS) of Li Electrodes Prepared and Stored in Alkyl Carbonate Solutions... 

J. F. Watts and J. Wolstenholme, An Introduction to Surface Analysis by XPS and AES , John Wiley Sons, Chichester, England, 2003. 

The analysis by XPS of the fresh catalysts shows the presence of the chloride ion peak (Cl - 198.4 eV). The presence of chlorine species in metal... 

Hori et al. pointed out that the deactivation takes place due to the presence of heavy metal impurities originally contained in chemical reagents used as the electrolytes. Heavy metal ions in the electrolyte solution are cathodically reduced and deposited on the electrode surface during the CO2 reduction, deteriorating the electrocatalytic properties of metal electrodes. They apphed a classically established technique of preelectrolysis to purification of electrolyte solutions since their early works. Frese also referred to the impurity heavy metals, and mentioned the presence of Fe and Zn on the Cu electrode after electrolysis on the basis of the surface analysis by XPS. The importance of the purity of the electrolyte solution was mentioned in Section I1.2(zz) as well. The mechanism of the deactivation was recently established, and sununarized below. ... 

The analysis by XPS of the fresh catalysts shows the presence of the chloride ion peak (Cl 2p3/Jt - 198.4 eV). The presence of chlorine species in metal catalysts prepared from metal chlorides has already been reported, indicating the difficulty of eliminating all the Cl by Hs treatment, despite the fact that TPR showed practically complete reduction of the metal (ref. 12). Actually, only a small amount of this Cl modifies the electronic density of metal atoms, leading to the formation of electron-defficient metal species (MT ) on the surface (refs. 11-13), which we have detected by XPS. The rest of the chlorine may remain as HCl or can substitute OH groups attached to the carbon support. These findings can be explained if one accepts that, in the presence of H2, the HCl is held by the carbon carrier, but it car back-migrate to the vicinity of the metal after H2 removal. Table 2 also summarizes the metal/carbon atomic ratios (M/C). As this ratio is an estimate of metal dispersion, a parallelism exists between the experimental M/C XPS ratios and the corresponding values obtained by H2 chemisorption. 

Surface analysis by XPS is accomplished by irradiating a sample with monoenergetic soft x-rays and energy analysing the electrons emitted. MgKa x-rays (1253.6 eV) or AlKa x-rays (1486.6 eV) are usually used [27]. The basic principle of the XPS technique is depicted in Figure 3.1 [24]. An incident x-ray photon (hv) causes an electron to be ejected from one of the core-electronic levels. The photoemitted core-electron... 

In essence there are two potential ways in which the interphase region can be approached either by the use of systems based on real adhesives or organic coatings to create a model interphase, or by the sectioning, by some means or other, to expose the interphase region prior to analysis by XPS or ToF-SIMS. In this paper the use of both approaches, which have been widely explored in the author s laboratory over the last three decades, will be described. 

Quantitative Anaiysis. Quantitative analysis by XPS can be used to determine the relative concentrations of components of a sample. Either peak area or peak height sensitivity factors can be used, but the latter approach is more accurate. 

D. Briggs, Ed., Polymer Surface Analysis by XPS and Static SIMS, Cambridge University Press, Cambridge, 1998. 

Readers who are interested in delving a little deeper into polymer surface analysis by XPS are guided to the followdng works. Miller et al. (1986) produced a review of biomaterial applications for XPS with a heavy emphasis upon the theoretical aspects of the technique. A useful handbook for all aspects of XPS and Auger spectroscopies was edited by Briggs and Seah (1990). 

The analysis by XPS can confirm that the ZnO was always present initially on the surface of zinc although the probe had not been exposed in the ehamber. A very thin film of this oxide forms instantaneously by chemical oxidation on the zine surfaee in contact with clean air at room temperature. This film does not affeet the later eleetroehemical corrosion process [5]. Once the humidity layer is established, zinc hydroxide is rapidly formed on the ZnO film via an electrochemical mechanism. Generally, it is considered that hydroxides are the initial compounds in zinc atmospheric corrosion studies [5, 15]. 

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