Nonlinear ellipsometry

In this chapter we review some of the most important developments in recent years in connection with the use of optical teclmiques for the characterization of surfaces. We start with an overview of the different approaches available to tire use of IR spectroscopy. Next, we briefly introduce some new optical characterization methods that rely on the use of lasers, including nonlinear spectroscopies. The following section addresses the use of x-rays for diffraction studies aimed at structural detenninations. Lastly, passing reference is made to other optical teclmiques such as ellipsometry and NMR, and to spectroscopies that only partly depend on photons. 

Optical properties of electronic and magnetic systems were discussed in talks by R. Hicken (Electron relaxation in metals by femtosecond ellipsometry) and R. Pisarev (Nonlinear optical spectroscopy). 

Ellipsometry and nonlinear optics have proven their sensitivity in studying monolayer thickness and molecular orientation, but generally the anisotropic nature of the interface makes results rather difficult to interpret [20-22], In many cases, these methods were limited in their potential to supply information about biophysical issues such as head group structure, enzyme secondary structure, and the orientation of ordered regions. 

In the previous subsections we briefly introduced some nonlinear techniques of Raman spectroscopy. Besides stimulated Raman spectroscopy, Raman gain spectroscopy, inverse Raman spectroscopy, and CARS, several other special techniques such as the Raman-induced Kerr effect [361] or coherent Raman ellipsometry [362] also offer attractive alternatives to conventional Raman spectroscopy. 

Thin layers of electrochemically deposited metals and thin polymer layers deposited on electrode surfaces can be conveniently studied by ellipsometry combined with other electrochemical experiments. Electrocrystallization of nickel was studied by Abyaneh, Visscher, and Barendrecht with ellipsometry and simultaneous amperometric measurements. The initial changes in A and ij/ showed nonlinear variations with the deposition time (Fig. 12), which is apparently abnormal, indicating a marked deviation of the optical properties of the deposited film from the bulk metal properties. The observed trend was explained by theoretical calculations using equations of effective medium theory (see Section IV.4 for effective medium theory) for hemispherical growth of the nucleation centers. The observed ellipsometry data clearly demonstrate that in the initial stage of nonuniform deposition the measured parameters, ij/ in particular, can change in a... 

Finally, application of other methods of analysis can be recommended. Many of the previous electrochemical studies devoted to conducting polymers were carried out in combination with radiotracer technique, AC electrogravimetry, quartz-crystal microbalance, surface plasmon resonance, and even ellipsometry, and atomic-force microscopy. In this context application of emerging experimental techniques such as local EIS and nonlinear impedance analysis may also be recommended. 

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