Linear ellipsometry

In a reflectance or ellipsometry experiment, measurements are always referred to the physical plane of incidence, as defined in Fig. 27.24. If the polarization is parallel to this plane of incidence, the parameters related to it are denoted by the subscript p. For polarization perpendicnlar to the plane, the subscript s is used. When a linearly polarized beam is reflected, one often finds that the parallel and perpendicular components nndergo changes in amplitude and phase. Thus, two beams that are in... 

As discussed above, the reflection of linearly polarized light from a surface generally produces elliptically polarized light, because the parallel and perpendicular components are reflected with different efficiencies and different phase shifts. These changes in intensity and phase angle can be analyzed to characterize the reflecting system. This approach is called ellipsometry. 

Figures 3.80(a) and (b) show the behaviour of n, k and the thickness L of a polypyrrole film during its growth on a Pt electrode in aqueous perchlorate solution obtained via in situ ellipsometry. A definite lag can be seen between the change in L and the changes in n and k. Up to c. 1.3 s the thickness of the film increases linearly with time while n and k remain constant. Between 1.3 and 2 s the growth almost tails off before increasing slowly up to 4 s and then more quickly until attaining a steady rate of increase at t > 4 s. Similarly at 1.3 s < t < 4 s both n and k increase, with n attaining a maximum value at 4 s before decreasing, while k increases at a lower rate at t > 4 s than at t < 4 s.

Figure 7.25 Set-up for ellipsometry microscopy. Incident linearly polarized light reflects on the surface and becomes eiliptically polarized. The quarter wave plate converts the polarization from elliptical to linear. The analyzer is placed such that it extinguishes all light. If the reflection properties change because a gas is adsorbed, the polarization does not match the setting of the analyzer and light passes through it. Appropriate lenses project an image of the surface onto the CCD camera (adapted from Rotermund [72]).

The adsorption kinetics from time resolved ellipsometry measurements showed two regimes (a) a diffusion controlled process at the initial stages and (b) at longer times, an exponential behavior where the arriving chain must penetrate the barrier formed by the already adsorbed chains. The experimental data indicated that the stars penetrate this barrier faster than the linear chains. 

Fig. 3.4. The geometry of an ellipsometry experiment. The linearly polarized incidence light beam becomes elliptically polarized after reflection at the sample surface. The plane of incidence is shown hatched. a is the angle of incidence...

Ellipsometry. Determination of h(u>) by KK analysis and coupled measurements of 1Z and T are affected, respectively, by the problem of the tails added to the experimental R(u>) spectra and by the need to perform 7Z and T measurements separately These problems, which introduce some uncertainty, can be solved by spectroscopic ellipsometry. The technique involves analyzing the polarization of a light beam reflected by a surface. The incident beam must be linearly polarized and its polarization should be allowed to rotate. A second linear polarizer then analyzes the reflected beam. The roles of polarizer and analyzer can be exchanged. The amplitudes of the s and p components of the reflected radiation are affected in a different way by reflection at the surface. The important function describing the process is the ellipsometric ratio p, which is defined as the polarization of the reflected wave with respect to the incident wave, expressed as the ratio between the Fresnel coefficients for p and s polarizations ... 

Ellipsometry measures the orientation of polarized light undergoing oblique reflection from a sample surface. Linearly polarized light, when reflected from a surface, will become elliptically polarized, because of presence of the thin layer of the boundary surface between two media. Dependence between optical constants of a layer and parameters of elliptically polarized light can be found on basis of the Fresnel formulas described above. 

The xxYZ component is only non-zero for chiral surfaces the value of xxyz for two enantiomers will be equal in magnitude but opfiosite in sign. As the tensor components can be complex quantities (especially near resonance), the harmonic wave can be el-liptically polarized even for a linearly polarized fundamental, just as in conventional ellipsometry. This results in a variety of interesting effects of non-linear optical activity being observable in SHG [8-13]. "ftie majcuity of observatidns of this type have been made oh chiral films [14,15]. 

Ellipsometry can also be applied to transmission measurements linear birefringence and dichroism of an anisotropic sample cause differences in amplitudes and phase shifts for waves of different polarization azimuths. Such experiments seem to be of considerable interest for partially ordered systems such as liquid crystals (cf. Sec. 4.6), here the degrees of polarization P and Ppf, reveal information related to order and reorientation processes (Korte et al., 1993 Reins et al., 1993). 

Several papers compare the properties of sulfobetaine (meth)acrylic polymers. NMR spectra and solution properties of 23a and 23b [59,60] are correlated with data from the corresponding polycarbobetaines [26]. The photophysical and solution properties of pyrene-labeled 23c were studied in terms of fluorescence emission. Addition of surfactants induces the formation of mixed micelles in aqueous solution [61]. Excluded volume effects of the unlabeled polymer were measured by light scattering [62], its adsorption on silica was studied by adsorbance measurement and ellipsometry [62,63], and the electrostimulated shift of the precipitation temperature was followed at various electric held intensities [64]. Polysulfobetaines may accelerate interionic reactions, e.g., oxidation of ferrocyanide by persulfate [65]. The thermal and dielectric properties of polysulfobetaines 23d were investigated. The flexible lateral chain of the polymers decreased Tg, for which a linear relationship with the number of C atoms was shown [66,67]. 

Boolaamphiphiles with two reactive head groups at both ends may bind in a linear or bent fashion to metal surfaces. The only example of a folded bolaamphiphiles on solid surfaces is provided by HOOC—(CH2)3o—COOH on silver. Ellipsometry yielded a surface film thickness of 20 2 A. In the reflection infrared spectra, the 2928 cm shoulder, as well as the lack of sharp bands between 1150 and 1350 cm for the progression of wagging modes indicated that the all-trans sequence length in the surface film should be much less than for the fully extended chain in the KBr pressed disk sample (Figure 6.23) . 

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