Other methods of surface analysis

Many new instruments are now available which can be used to characterize various depths of a specimen. A brief account of the use of these techniques will be presented here. 

Electron spectroscopy for chemical analysis (ESCA) is used for characterizing polymer surfaces and is also known as X-ray photoelectron spectroscopy (XPS). This method is based on the observation that electrons are emitted by atoms under X-ray irradiation. The energy of the emitted electrons yields the binding energy of the electron to the particular atom.  

Scanning electron microscopy (SEM) constitutes one of the older and one of the most widely used instruments for surface analysis. It provides a three-dimensional visual image and, thus, the quantitative analysis is relatively straightforward. 

Static secondary ion mass spectroscopy (SSIMS) ranks with XPS as one of the principal surface analytical techniques. Treatment of polymer surfaces to improve their properties with respect to wetting or water repulsion and to adhesion, is by now a standard procedure. The treatment is designed to change the chemistry of the outermost groups in the polymer without affecting bulk properties. One popular surface treatment is plasma etching. The use of SSIMS is most amenable to the surface evaluation of such treated materials. 

1 Wingate I B and Mohler J F, Textile Fabrics and their Selection, Prentice-Hall, Englewood Cliffs, NJ, 1984. 

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The impact of an ion beam on the electrode surface can result in the transfer of the kinetic energy of the ions to the surface atoms and their release into the vacuum as a wide range of species—atoms, molecules, ions, atomic aggregates (clusters), and molecular fragments. This is the effect of ion sputtering. The SIMS secondary ion mass spectrometry) method deals with the mass spectrometry of sputtered ions. The SIMS method has high analytical sensitivity and, in contrast to other methods of surface analysis, permits a study of isotopes. In materials science, the SIMS method is the third most often used method of surface analysis (after AES and XPS) it has so far been used only rarely in electrochemistry. 

The TMS rheometer has been used to study mould release in rubbers. It contains a biconical rotor (representing the mould surface). The polymer is placed in the transfer chamber, injected around the rotor and cures in situ. Fig. 1. The shear stress required to free the rotor is taken as the mould-sticking index . The rheometer has the advantage that small experimental mixes of rubber can be evaluated. Further, the rotors are easily changed, so as to evaluate changes in mould surface, and the parted surfaces are amenable to examination by XPS and other methods of surface analysis. The obvious disadvantage is that access to special equipment (the TMS rheometer) is required. The same basic concept could be adapted for the study of mould adhesion of non-elastomeric polymers. 

Prominent advantages of these methods include multi-element simultaneous analysis via commonly well-spaced spectral lines, and chemical-state information accessible via smaU, but characteristic and measurable shifts or shape changes in the lines. The stability of surface layers under photon or electron irradiation limits the possible duration of data acquisition time. Seah [20] has described a system for the intensity/energy calibration of electron spectrometers used in AES and XPS, necessary for quantitative analysis. Both AES and XPS may be made quantitative with reasonably good precision, although a great deal of care is necessary. Riviere [21] has compared AES and XPS to other methods of surface analysis (SIMS, ISS, EPMA, RAIRS). 

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