Polarized light reflectance measurements

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. 

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]

The technique of reflectance optical microscopy has proven to be invaluable in the analyses and characterization of fossil fuels, in particular coal materials and petroleum-containing source rocks. The technique involves the measurement of the percentage of white polarized light reflected from a polished surface of a coal specimen using oil immersion and analyzed within the microscope. This percentage value gives a measure of the aromaticity of the carbonaceous matter which constitutes coal and rock materials. Table 2.1 contains specific... 

In ellipsometry monochromatic light such as from a He-Ne laser, is passed through a polarizer, rotated by passing through a compensator before it impinges on the interface to be studied [142]. The reflected beam will be elliptically polarized and is measured by a polarization analyzer. In null ellipsometry, the polarizer, compensator, and analyzer are rotated to produce maximum extinction. The phase shift between the parallel and perpendicular components A and the ratio of the amplitudes of these components, tan are related to the polarizer and analyzer angles p and a, respectively. The changes in A and when a film is present can be related in an implicit form to the complex index of refraction and thickness of the film. 

The principal of measurement is shown schematically in Fig. 4.61. Linear polarized light is reflected from a sample surface which must be flat and sufficiently reflecting. The state of polarization of the incident light is changed, by reflection, into ellipti-... 

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). 

If a sample is excited with polarized light and emission is measured through a second set of polarizers parallel and perpendicular to the first polarizer, the ratio of the two emission signals reflects the rotatory freedom of the chromophore. In practice, binding of a second molecule to the labeled one can be detected if the size of the chromophore complex increases considerably. The advantage of this method is that no changes in quantum yield are necessary for the observation of the binding reaction. 

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. 

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