Available from ESCA

Although as will become apparent if we consider any one level of information available from ESCA and compare this with that available from the most competitive of the other available spectroscopic technique for the particular case in question, it is invariably the case that ESCA compares relatively unfavourably. The most distinctive feature of ESCA as a spectroscopic tool however which sets it apart from any other is the large range of available information levels and these are shown in Table 2. For a fuller description see Ref.2. ... 

Basic Types of Information Available From ESCA Studies APPLICATIONS OF ESCA TO STUDIES OF STRUCTURE AND BONDING IN POLYMERS... 

Basic Types of Information Available From ESCA Studies... 

If the hierarchy of information levels available in ESCA were limited to those discussed in detail in the proceeding sections the technique would clearly be extremely useful and versatile in many applications. It is evident, however, that for systems in which only a single core level is available for study and for which no chemical shifts are apparent that the range of applications of the the technique to such systems would be limited. Fortunately ESCA is a much more interesting and subtle technique and such systems are encompassed when we consider the information available from the direct study of low energy shake up satellites. 

Before the advent of ultraviolet photoelectron spectroscopy and ESCA, experimental evidence on the energy density was mainly available from static magnetic susceptibility and specific heat measurements (134). These provide information on the density of states at the Fermi level and it is impossible to base any conclusions on such experimental information with regard to the shapes of the d-bands in the alloys. It is currently believed that there is very little transfer of d-electrons between the atoms. If an increase in the number of d-electrons on a particular atom does occur, it is due to transfer of electrons from the s,p-band to the lower d-band. This is, of course, related to the difference in electronegativity of the alloying components (135a, 135b). 

Figure 1 shows schematically the typical data levels and variable experimental parameters which can be employed in the application of ESCA to polymeric systems. Figure 2 indicates how, many of the information levels available from the ESCA experiment may be used to study the time and temperature dependent behavior of polymer surface phenomena. Many of the contributions to this book deal with specific applications with an emphasis on one or other of the information levels available from the ESCA technique. Before considering specific applications of our own we may profitably highlight recent developments which point the way forward for applications in the next decade. 

The information levels available from a single ESCA experiment endow the technique with wide ranging applicability in the study of the surface structure of polymers, of surface modification and reactivity in general and of interfacial synthesis. In the present article we consider two representative applications of the technique to research programmes of considerable current technological importance namely the plasma synthesis of ultrathin polymer films and the environmental modification of polymers studied from the surface aspect. Before considering these topics, however, we briefly consider some recent experiments pertinent to the quantification of ESCA data namely the measurement of electron mean free paths as a function of kinetic energy. ... 

This result is contrary to what has been deduced from other studies of the norbornyl ion in strong acid media. Accordingly, we now turn to a reappraisal of the available ESCA, H-nmr, C-nmr, kinetic, Raman, quenching and isotope studies that have been brought to bear on the structural problem. 

First, because of the large energy difference, this method is completely insensitive to chemical binding effects. While other conventional surface analysis techniques which are sensitive to the chemical state are unquestionably frequently required, it is also true that methods thus dependent on the chemical state may suffer from difficulties in calibration, particularly in transition regions where an element is found in more than one chemical state. Energetic ion beam analysis, on the other hand, offers an absolute technique independent of these effects. As such, this technique and other conventional techniques (e.g. Auger, ESCA etc.) may often prove to be complementary, each supplying information not available by the other techniques. 

The organic dielectrics known as polyimides have been studied extensively by a variety of bulk characterizational techniques as a perusal of the literature will illustrate. Little has been published on their surface properties. X-ray photoelectron spectroscopy (ESCA) has been extremely useful for polymer characterization (, 7, ), In a previous paper ( ), we have reported the ESCA spectra of structurally different polyimides derived from both commercially available polyamic acid resins (DuPont s PI5878, PI2525, PI2550), and from laboratory synthesized polyamic acid resins. 

X-ray photoelectron spectroscopy (XPS), early called ESCA (electron spectroscopy for chemical analysis) in the pioneering works of Siegbahn [23], is currently the most widely used surface analytical technique. The popularity of this technique comes from the exceptional combination of compositional and chemical information that it provided, its easy of operation, and the ready availability of commercial equipments. 

---