ESCA Spectra

Figure 6.15 Carbon lr electron spectrum (ESCA) of the t-butyl cation. From G. A. Olah, Angew. Chem. Int. Ed., 12, 173 (1973). Reproduced by permission of Verlag Chemie, GMBH.

Fig. Vni-11. ESCA spectrum of A1 surface showing peaks for the metal, A1(0), and for surface oxidized aluminum, Al(III) (a) freshly abraided sample (b) sample after five days of ambient temperature air exposure showing increased A1(III)/A1(0) ratio due to surface oxidation. (From Instrument Products Division, E. I. du Pont de Nemours, Co., Inc.)...

The type of interaction along the interface will exert a great influence on the various properties of the composite materials. Therefore, to improve the performance of a composite material, it is absolutely necessary to characterize the structures of the interface. Some of the methods for analysis of the interface are ESCA, AES, IR-FTIR, SIMS, and SEM, etc. At present, ESCA is widely used in the surface analysis of elements and the qualitative analysis of functional groups. Figure 11 shows the ESCA spectrum of polyethylene treated with... 

Other techniques utilize various types of radiation for the investigation of polymer surfaces (Fig. 2). X-ray photoelectron spectroscopy (XPS) has been known in surface analysis for approximately 23 years and is widely applied for the analysis of the chemical composition of polymer surfaces. It is more commonly referred to as electron spectroscopy for chemical analysis (ESCA) [22]. It is a very widespread technique for surface analysis since a wide range of information can be obtained. The surface is exposed to monochromatic X-rays from e.g. a rotating anode generator or a synchrotron source and the energy spectrum of electrons emitted... 

The surface grafting of a commercial sheet of poly(ethylene tere-phtalate) was analyzed by ESCA spectra and dye adsorption. The sheets were washed with acetone to remove impurities and then grafted by irradiation for 2 and 20 min. (Figure 9). The blank sample showed no Nls peak in the ESCA spectrum. After grafting the Nls peak increased with increasing grafting time. 

The PP samples exposed to atomic oxygen show for the formation of polymer peroxy radicals (P00 ), which give almost identical ESR spectrum as in the case of ozone reaction (Fig.l). The ESCA spectra (Fig.5) indicate that atomic oxygen oxidation is more effective than ozonization. These results support our assumption that ozonization... 

XPS or ESCA (electron spectroscopy for chemical analysis) is a surface sensitive technique that only probes the outer atomic layers of a sample. It is very useful tool to study polymer surfaces [91]. An XPS spectrum is created by focusing a monochromatic beam of soft (low-energy) X-rays onto a surface. The X-rays cause electrons (photoelectrons) with characteristic energies to be ejected from an electronic core level. XPS, which may have a lateral resolution of ca. 1-10 pm, probes about the top 50 A of a surface. 

Figure 3 The Cns ESCA spectrum of two PET samples revealing the difference between a more crystalline sample exhibiting more trans C —C bonds in the glycol segment (biaxial film) and an amorphous sample rich in gauche C —C bonds (melt) in the spectral range near 286 eV. Figure reproduced from Beamson et al. [10]. Copyright 1996, with permission from Elsevier.

Direct measurement of the absolute binding energy and widths of core (X-ray) and valence (UV) bands. The core levels do not participate in bonding, hence each element gives a characteristic XPS spectrum electron spectroscopy for chemical analysis (ESCA). ESCA gives the elemental composition of the surface of a solid sample (except H), the relative amounts of each element present, its oxidation state and some information on the chemical environment around each element. In addition, it is capable of providing an estimate of the depth of a deposited overlaycr... 

The principal limitations of ESCA include the inability to detect elements present at trace concentrations within the analytical volume, and insufficient lateral resolution to characterize single micrometer-sized particles. The inability to characterize trace species is illustrated in Figure 10 for a sample of coal fly ash particles (11). The fly ash results from the noncombustible mineral components of the coal and consists largely of fused iron oxides and aluminosilicates (42). In addition, most elements are present in at least trace concentrations (22, 42), and many of these elements are highly enriched in the surface region of the particles (evidence for this will be discussed in the next section). However, the ESCA spectrum acquired over several hours of counting time indicates only the presence of detectable surface S and Ca in addition to the fly ash matrix constituents. 

Thiosulphonate structure (a) is expected to give two peaks of equal intensity corresponding to the two oxidation states in the molecule whereas the disulphoxide structure should give only one peak. ESCA spectrum shows that the thiosulphonate structure applies to the doubly oxidised cystine because two peaks of equal intensity is observed. 

The highly crosslinked nature of the polymer formed in the discharge is immediately apparent from the C,j spectrum which exhibits approximately equal quantities of the four major carbon environments CFj, CF, CF and carbon with four nearest carbon neighbors. The overall stoichiometry determined from a comparison of the F,5 and Ci peak intensities is reported to be CiFi.4. The amount of oxygen functionalities found in these polymers, due to reaction of free radical sites in the polymer with atmospheric oxidants is usually less than 0.1 atomic % and is observed in the ESCA spectrum as a small broad signal in the 0, region . ... 

Despite the fact that germanium is etched at the faster rate for a given set of plasma conditions, it does not become incorporated into the polymer matrix under the conditions of these experiments. This provides a convenient method to prepare films containing no cathode material but are essentially plasma polymerized polytetra-fluoroethylene. The small oxygen signal observed in the ESCA spectrum of this... 

The ESCA spectrum of MOT provides evidence that the electron density at N-4 is lower than at N-l and N-3 [88MI1, Ref. (28)]. 

The work reported in this chapter was conducted in 1971, at the Engineering Physics Laboratory of E. I. du Pont de Nemours and Company. This research was performed as part of the ESCA instrument development program active at that time, and was presented by Jansson and Davies (1974). An example of a deconvolved polyester spectrum obtained in the early work appeared in the review article by Herglotz and Suchan (1975). 

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