Spectroscopic property complex refractive index

In order to calculate the optical generation rates in the organic absorbers (see appendix 1), it is necessary to determine the complex refractive index n = n + ik of all layers. The most useful method to obtain this data is spectroscopic ellipsometry, which allows us to determine the real part n and imaginary part k of the refractive index. The general measurement principle of ellipsometry is to measure the polarization of an output beam after the polarized input beam has interacted with the sample. From the change in polarization we derive the optical properties of the layer by fitting the measured output polarization to a model of the optical response of the material [144]. 

The multi-wavelength ellipsometiy (i.e., spectroscopic elhpsome-try) can characterize spectroscopic property of the passive oxide. Figure 24 indicates spectra of the complex refractive index, N2 = 2 - j 2, of the passive oxide formed on iron at 1.43 V vs. reversible hydrogen electrode at the same solution (RHE) in pH 8.4 borate solution and in pH 3.1 phosphate solution for 1 In Fig. 24, the thickness of the passive oxide was estimated at each wavelength of incident light. The measurement and estimation were made by the 3-parameter method. Similar results were also reported by Cahan et al. " ... 

Figure 24. Spectra of complex refractive index, 7 2 = 2 j 2 for th passive oxide formed at 1.43 V vs. RHE in pH 8.4 borate and pH 3.1 phosphate solution for 1 h. The Ni was calculated from multi-wavelength ellipsometry with the film thickness. Reprint from T. Ohtsuka, K. Azumi, and N. Sato , A spectroscopic Property of the Passive Film on Iron by 3-parameter Reflectometry , Denki Kagaku, 51 (1983) 155, Copyright 1983 with permission from The Electrochemical Soc. of Japan.

Light striking a dielectric interface can undergo a number of processes, the most important of which are reflection, absorption, and scattering. In a spectroscopic experiment, the intensity of light incident on a surface, Iq, is compared to that which has been transmitted through the medium, T = Iq/I, scattered from the medium S = IJIq or reflected from the medium, where R = IJI. A material s optical parameters (i.e., reflectivity, transmissivity, and absorbtivity) are described by the Fresnel equations which define these properties in terms of the materials refractive index, n, where n = n, + ik or complex dielectric constant e = + ik. These two parameters are interrelated since n = Ve. Fresnel also... 

An important difference exists between a solution and a thin film on a substrate as a sample for infrared measurement. In a solution, chemical species randomly change their positions and orientations, whereas molecules in a thin film on a substrate cannot move freely and have fixed orientations as a result of interactions between molecules and with the substrate. The molecular orientation is associated with a quantity which is called permittivity in electromagnetics or refractive index in optics. Both permittivity and refractive index are complex quantities that have components representing their anisotropic properties. It is necessary to consider these quantities in order to deal with the spectroscopic properties of an oriented thin film. 

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