Nanoscale Thermal AFM of Polymers: Transient Heat Flow Effects

Thermal transport around the nanoscale contact area between the heated atomic force microscopy (AFM) probe tip and specimen under investigation si a central issue in scanning thermal microscopy (SThM) Polarized light microscopy and AFM imaging of the temperatuer-induced crystallization of poly(ethylen terephthalate) (PET) films in the region near the tip were used in this study to unveil the lateral heat transport The radius of the observed lateral surface isotherm at 133 degrees C ranged from 2 2 +/- 0 5 to 18 7 +/- 0 5 mu m for tip-polymer interface temperatures between 200 and 300 degrees C with contact times varying from 20 to 120 s, respectively in additon , the heat transport into polymer films was assessed by measurements of the thermal expansion of poly(dimethy siloxane) (PDMS) films with variable thickness on silicon supports Our data showed that heat transport in the specimen normal (z) direction occured to depths exceeding 1000 mu m using representative non steady SThM conditions (i e, heating from 40 to 180 degrees C at a rate of 10 degrees C s(-1)) On the basis of experimental results, a 1D steady stae model for heat transport was developed, which shows the temperature profile close to the tip-polymer contact The model also indicates that <= 1% of the total power generated in the heater area, which is embedded in the cantilever end, is transported into the polymer through the tip-polymer contact interface Our results complement recent efforts in the evaluation and improvement of existing theoretical models for thermal AFM, as well as advance further developments of SThM for nanoscale thermal materials characterization and/or manipulation via scanning thermal lithography (SThL)