Temperature-modulated ellipsometry for the measurement of dynamic expansion of nanoscale thin films

Direct characterization of the chemco-physical properties of nanometer-thick thin films is essential for understanding and optimizing their performance to meet the evolving demands of nanodevice applications. Herein, temperature-modulated ellipsometry was demonstrated as a capable technique for measuring the dynamic expansion of nanoscale thin polymer films, enabling the direct assessment of both reversible and irreversible processes associated with thermal transitions. A sinusoidal plus linear temperature modulation protocol was implemented to induce oscillatory thickness variations in the thin film, and a spectroscopic ellipsometer was employed for the real-time measurement of dynamic expansion. The reversing thermal expansion (αr), which is related to intrinsic molecular dynamics, was determined from the amplitude of the thickness oscillations in response to temperature variations. By contrast, the apparent thermal expansion (αapp), which encompasses contributions from both reversible and irreversible processes (e.g., degradation), was obtained from the response to a linear temperature ramp. Their difference (Θ = αapp - αr) reflects the contribution of irreversible processes to film expansion. This technique provides a multidimensional assessment of the various processes occurring in thin films, making it a valuable tool for a wide range of modern technological applications.