The use of UV rather than X-radiation

If UV radiation (photon energies typically of 20-40 cV) were to be used rather than X-rays to excite emission from the valence band, the resultant spectra might be mote intense, but since the photoelectrons would have much lower kinetic energies the spectra would correspond to emission from the outer surface layers only. The process would therefore be particularly sensitive to the presence of impurities and contamination on the surface. In addition, UV excitation involves transition probabilities and ionization cross-sections different from those appearing in X-ray excitation, which has the consequence that spectral analysis by calculation has to include both ground and virtual states, and is therefore more difficult. 

Speetrum of the fiber coated with a very thin layer of matrix material = S. It is e.vsential that the. spectrum of the underlying fiber can be seen in the XPS data, to make sure that the buried interface is within the sampling depth. 

If there is chemical interaction at the fiber/matrix interface, 

In the latter case the spectrum of the interface region can be found from a difference spectrum (29). that is, by subtracting M and F from S. 

An example of this approach is illustrated in Fig. 19. The difference spectrum (d) is the result of subtraction of the spectra (a) of an oxidized carbon fiber and (b) of a phenolic matrix from the total spectrum (c) of the fiber and matrix coupled with a titanium alkoxide coupling agent (TOT=tetrakis(2-ethylhexyl)ti-tanate) 151). The difference spectrum is characteristic of the -O-TiRi-O- group which might be formed by reaction of the titanium alkoxide with both the oxidized fiber surface and the phenolic resin according to the scheme. 

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