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 microtherma l analysis of ultrathin polymer films, elucidate limits of applicability of this technique to study their microthermal properties, and observe the the rmomechanical response during local heating fbr films with thicknesses abov e 10 nm. The glass transition temperature of ultrathin polystyrene (PS) fil ms deduced from experiments decreases for film thicknesses below 200 nm. Fo r the thinnest PS film with clearly detectable response (25 nm), the glass transition temperature is 20 degreesC 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 ass ociated mainly with temperature-induced elastic variation of the contact ar ea.