Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006