Complex refractive index calculated from reflectance measurements

The reflectivity spectra R(E) and the reflectivity-EXAFS Xr(E) = R(E) — Rq(E)]/R()(E) are similar, but not identical, to the absorption spectra and x(E) obtained in transmission mode. R(E) is related to the complex refraction index n(E) = 1 — 8(E) — ifl(E) and P(E) to the absorption coefficient /i(E) by ji fil/An. P and 8 are related to each other by a Kramers-Kronig transformation, p and 8 may be also separated in an oscillatory (A/ , AS) and non-oscillatory part (P0,80) and may be used to calculate Xr- This is, briefly, how the reflectivity EXAFS may be calculated from n(E). which itself can be obtained by experimental transmission EXAFS of standards, or by calculation with the help of commercial programs such as FEFF [109] with the parameters Rj, Nj and a, which characterize the near range order. The fit of the simulated to measured reflectivity yields then a set of appropriate structure parameters. This method of data evaluation has been developed and has been applied to a few oxide covered metal electrodes [110, 111], Fig. 48 depicts a condensed scheme of the necessary procedures for data evaluation. 

Figures 7 and 8 show two different designs with a different number of layers in the metal-dielectric AR part of the structure, along with their calculated performances (reflectance and luminance spectra). The complex refractive index of all layers were measured from films deposited in the same conditions as our devices. When compared to the performance of a conventional OLED shown in Fig. 3(b) and (c), we see that the new designs reduce the reflectance to 2% and less, which is 25 times less than that of a typical OLED, and that the emission is of the same order of magnitude.

The optical absorption coefficient a, calculated from the complex refractive index or dielectric constant of the film on Pt, exhibits two peaks at 3 00 and 365 mm, as pointed out by McIntyre and Kolb on the basis of their specular reflectance spectroscopic measurements over the wavelength range... 

As described in detail in Chapter 8, calculations based on the Kramers-Kronig relations give the real and imaginary parts of a complex refractive index (n(v) and k(v) see Section 1.2.4) from a reflection spectrum measured by the method of specular reflection from a... 

The difficulty in this calculation is that measured reflection results are often not easily available over the whole frequency range. Therefore, an interpolation of the data to values of low (0 eV) and high (w 1000 eV) energy values may be required [33]. With known values of 7i hv) and (])(hv), e"(ci)) and e"(complex refractive index n = n + in" and complex dielectric function e = e + ie" ... 

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