Microthermal Probing of Ultrathin Polymer Films

We present the results of microthermal studies of ultrathin polymeric films deposited on a silicon substrate. We propose the procedure for microthermal analysis of ultrathin polymer films, elucidate limits of applicability of this technique to study their microthermal properties, and observe the thermomechanical response during local heating for films with thicknesses above 10 nm. The glass transition temperature of ultrathin polystyrene (PS) films deduced from experiments decreases for film thicknesses below 200 nm. For the thinnest PS film with clearly detectable response(25nm), the glass transition temperature is 20 °C below its bulk value. Our estimation of heat dissipation in the tip–surface contact area supports the conclusion that the observed micro-thermal-analysis response for polymer films is associated mainly with temperature-induced elastic variation of the contact area.