Polarized light reflectance measurements polarizers

Reflectance measurements involve measurements of the intensity of light reflected from a flat specular surface of an electrode in a spectroelectrochemical cell. The incident light is polarized either parallel (p) or perpendicular s) to the plane of incidence, as shown in Fig. 27.24. A detector monitors the intensity of the reflected beam. The light is monochromatic, but the spectrometers usually can be tuned over large wavelength ranges. There are excellent reviews of reflectance by McIntyre (1973) and Plieth et al. (1992). 

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

The attenuated total reflection (ATR) method measures the reflection coefficients of vertically and horizontally polarized light reflected from a polymer layer adsorbed on a transparent surface63. These coefficients allow the thickness of the adsorbed layer and the polymer concentration in it to be determined. 

Theoretical consideration of the IR spectroscopy of monolayers adsorbed on a metal surface showed that the reflection-absorption spectrum is measured most efficiently at high angles of incidence, and that only parallel component of incident light gives measurable absorption species (23). Figure 4 presents a schematic description of a monomolecular film on a mirror, with the incident light and direction of the polarization. Figure 5 presents, in detail, an alkyl thiol molecule on a metal surface. Note the direction of the different transition dipoles. Thus, while both the... 

Examination of light reflected from surface films. Apparatus for measuring the ellipticity of polarization of the light reflected from surfaces covered by films is described by Freundlich and others,8 Bouhet,9 and... 

Ellipsometry measures the relative attenuation and phase shift of polarized light reflected from a polymer-coated surface. The Drude equations (Drude, 1889a,b, 1890 Stromberg et ai, 1963 McCrackin and Colson, 1964) relate the attenuation and phase shift to the average refractive index and thickness tel of an equivalent homogeneous film. Interpretation of fel in terms of the actual refractive index distribution or the polymer distribution [Pg.189]

This salt (NPrQn, /V-propylquinolinium) consists of tetramerized TCNQ chains. It undergoes a phase transition at 220 K which is considered to be a second-order metal-to-semiconductor transition. Optical reflectivity measurements on crystals, with the light polarized in the chain direction, indicate that the charge distribution on the TCNQ sites in the tetrads is less uniform at 100 K than at 300 K. This is as in TEA(TCNQ)2 (see Section III.A.3). However, estimation of this charge distribution from the bond lengths at 300 K [38] gives ambiguous results for this material [63]. 

In Fig. 7.2 the optical and detection part of the experimental setup is schematically drawn. The film is illuminated by an argon-ion laser about 10 mm above the surface of the soap solution in the reservoir. The laser operates in the TEMqo mode (multimode) at 514.5 or 488 run, at a power between 100 and 300 mW. The light is polarized perpendicular to the plane of incidence. The lens L, with a focal distance of 60 cm, is placed about 40 cm from the film so that the incident beam is slightly focused on the film. The diaphragm system D, which is positioned after the incoming window (see Fig. 7.1), is used to remove unwanted stray light. The specularly reflected light is measured by means of a photodiode, which can be set at fixed positions such that Bq =45°, 60°, or 75°. 

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