THERMOPHYSICAL MEASUREMENTS AND INTERFACIAL ADHESION STUDIES IN ULTRATHIN POLYMER-FILMS USING HOMODYNE PHOTOTHERMAL SPECTROMETRY

Homodyne laser photopyroelectric spectrometry (PPES) is a new photothe rmal detection scheme which uses electronic mixing to downshift a high -frequency swept wave photothermal response into a bandwidth of approx imately one kilohertz. A rapid photopyroelectric impulse response is r ecovered from the downshifted component at high time resolution and is used, here, in two different geometries, to probe the thermal and int erfacial properties of assemblies composed of submicron-thickness poly mer films deposited on the metallized surface of a pyroelectric thin-f ilm detector. In the thermal transmission mode geometry, the sample is excited by irradiation in a very thin opaque surface layer, and the t ransit time of a heat pulse through the sample to the pyroelectric tra nsducer can be used to obtain a thickness or thermal diffusivity measu rement. By the use of an inverse mode geometry, a metal/polymer interf ace is excited by irradiation of an optically transparent polymer thin -film sample attached to the metallized surface of the pyroelectric tr ansducer. Heat flow at short distances from the bond interface can be monitored by the pyroelectric effect through the high time resolution of the homodyne photopyroelectric measurement. The combination of info rmation obtained in these two geometries with an analysis of the therm al wave reflections which occur at interfaces between materials of dis similar thermal effusivity can be used to evaluate relative interfacia l adhesion between the metal and polymer layer.