Diphenylsiloxane–dimethylsiloxane copolymer: Optical functions from 191 to 1688 nm (0.735–6.491 eV) by spectroscopic ellipsometry

We report the optical functions of diphenylsiloxane-dimethylsiloxane (DPS-DMS) copolymer as determined from reflection spectroscopic ellipsometry (SE) and transmission ultraviolet-visible data, which were generated over 191–1688 nm from a commercial sample of DPS-DMS. This material is a random, linear copolymer terminated with silanol groups that is a liquid at room temperature and pressure. Both reflection and transmission measurements required special experimental considerations. The reflection SE measurements utilized the “rough-surface” method, wherein the liquid was poured onto a roughened (frosted) glass slide, which scatters the reflected light leaving only the reflection from the liquid surface. That is, there is effectively no substrate or material beneath the liquid that affects the ellipsometry measurements or that needs to be modeled. Transmission measurements were obtained via a dual cuvette approach to eliminate the effects of the cuvettes. The reflection data provided the refractive index across the entire spectral range as well as the extinction coefficient at ultraviolet wavelengths. The transmission measurements provided input for the extinction coefficients at visible and near infrared wavelengths, where the liquid is transparent or semitransparent. The reflected SE data were modeled using a Sellmeier dispersion model and six Gaussian oscillators plus a surface roughness layer. This produced a good fit with a mean squared error (MSE) of 2.41. For example, we obtained the following n(λ) values, where λ is the wavelength in nanometers: n(300) = 1.534, n(500) = 1.477, and n(1000) = 1.458. As expected, the refractive index of DPS-DMS is higher than that of liquid polydimethylsiloxane.