Simultaneous Determination of Refractive Index and Thickness of Submicron Optical Polymer Films from Transmission Spectra

Abstract

High-transparency polymers, called optical polymers (OPs), are used in many thin-film devices, for which the knowledge of film thickness (h) and refractive index (n) is generally required. Spectrophotometry is a cost-effective, simple and fast non-destructive method often used to determine these parameters simultaneously, but its application is limited to films where h > 500 nm. Here, a simple spectrophotometric method is reported to obtain simultaneously the n and h of a sub-micron OP film (down to values of a few tenths of a nm) from its transmission spectrum. The method is valid for any OP where the n dispersion curve follows a two-coefficient Cauchy function and complies with a certain equation involving n at two different wavelengths. Remarkably, such an equation is determined through the analysis of n data for a wide set of commercial OPs, and its general validity is demonstrated. Films of various OPs (pristine or doped with fluorescent compounds), typically used in applications such as thin-film organic lasers, are prepared, and n and h are simultaneously determined with the proposed procedure. The success of the method is confirmed with variable-angle spectroscopic ellipsometry.

Peri‐Acenoacene for Solution Processed Distributed Feedback Laser: The Effect of 1,2‐Oxaborine Doping

“…The film thickness (h f ) was determined from the interference pattern present in the transparent region of the absorption spectrum by using an optical method. [33] The DFB resonators were manufactured using a multistep method previously reported: [28,34] 1) the photoresist layer was spin-coated over the active film from a hot water solution (40 °C) of the DCG (2.2 wt%); 2) the 1D grating was recorded by HL, in which an interferometric pattern generated by combining the direct light from an argon laser (I-308C, Coherent) emitting at 364 nm with that reflected on a mirror forming 90° with the sample holder is registered on the photoresist; 3) the DCG layer was desensitized in a cool water bath (15 °C) and the latent hologram was converted into a relief grating by dry etching the unexposed areas with an oxygen plasma using a surface treatment machine (Zepto, Diener Electronic). The depth of the resulting grating was d = 90 nm and the duty cycle was 0.75.…”

Donor–acceptor naphthalimides and peryleneimides for all-solution-processed thin film lasers

“…This thickness was chosen to be the maximum one that only supports fundamental modes in the waveguide with a high confinement factor ( Γ ∼ 90%) 34,36 and was measured using the interference pattern formed in the transparent window of the absorption spectrum. 46,47…”

Neutron Reflectometry Studies of the Hydrated Structure of Polymer Thin Films

“…To aid in these calculations, databases with tabulated refractive indices exist for the more commonly used materials. However, the polymer films, that were studied in this work have no such data available, so ( ) of the films were modelled using the Cauchy formula 133 , that is commonly used for transparent layers. To calculate the optical properties of mixtures of the various materials, effective media approximations are employed 134 .…”