Temperature Coefficient of Electronic Polarizability in Thin Polymer Films Deposited on Si and SiO2 Substrates Determined via Spectroscopic Ellipsometry

Abstract

Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, their values must be determined with the greatest possible accuracy, as both have the opposite effect. In this article, we analyze changes in ellipsometric parameters resulting from changes in the thin film temperature in order to develop a data analysis method for temperature-dependent spectroscopic ellipsometry that will facilitate the accurate determination of thermo-optical parameters, including the TCEP, in polymer thin films. As practical application examples, we identified optimal spectral windows to accurately determine the thermo-optical parameters of 50 to 150 nm-thick PMMA thin films deposited on Si and SiO2 substrates. The influence of thin-film thickness on the accuracy of TOC and LTEC determination is discussed.

Thermal Transitions and Structural Characteristics of Poly(3,4-ethylenedioxythiophene/cucurbit[7]uril) Polypseudorotaxane and Polyrotaxane Thin Films

“…Further insight is provided by the construction of a phase diagram, like in our earlier works [ 23 , 24 , 25 , 47 ], by combining the DSC and VTSE results ( Figure 5 ).…”

“…The reflectance depends on the wavelength of the light and the angle of incidence as well other experimental conditions such as temperature of the sample, humidity, or pressure. It is noteworthy that the can also be determined theoretically for a specific optical system by taking into account the dielectric functions of all optical phases and their thicknesses [ 23 ]. Therefore, the complex dielectric functions , where is real and is the imaginary part of dielectric function, and the thickness of the layers of individual elements of the optical system must be ellipsometrically modeled.…”

“…Further insight is provided by the construction of a phase diagram, like in our earlier works [23][24][25]47], by combining the DSC and VTSE results (Figure 5). For the investigated PEDOT, PEDOT•CB7-PS, and PEDOT•CB7-PR thin films and powders, three characteristic temperatures are visible in the phase diagram.…”

“…Further, by combining XRD analysis of the crystallographic structure, optical studies, and surface morphologies, we expanded our knowledge, and PEDOT CB7-PS and PEDOT CB7-PR thin films were investigated in-depth beyond their previously reported properties [ 21 , 22 ]. The VTSE technique is of great interest due to its high sensitivity to various types of thermal transitions occurring in thin organic layers and good correlation with DSC data [ 23 , 24 ]. Characteristic thermal transition temperatures can be evaluated based on raw ellipsometric data, such as Ψ(T) [ 25 , 26 , 27 , 28 , 29 , 30 ], Δ(T) [ 31 , 32 , 33 , 34 , 35 ], or their derivatives [ 36 , 37 , 38 , 39 ], or derived from the analysis of temperature changes in the course of physical parameter curves, such as thin-layer thickness, refractive index, or electrical resistance [ 40 , 41 , 42 , 43 ].…”