Thermal transport in ultrathin fluoropolymer films

Polymers are industrially interesting materials that may contribute inexpensive solutions to nanoscale thermal transport and its numerous applications. In particular, polymers exhibit a shift in their thermal properties when confined to nanometer scales. For instance, ultrathin polymers having thicknesses comparable to the radius of gyration, show a suppression of anharmonicity near the glass transition temperature, which itself is different from the bulk. While thermal properties have been extensively studied for a variety of thick polymers, published thermal conductivity measurements for thin polymer films typically cover thicknesses greater than 100 nm. In this work, time-domain thermoreflectance (TDTR) measurements on fluoropolymer films that are 2.1 to 65 nm thick show an increase in thermal conductivity with decreasing thickness and suggest that a kinetic picture of phonons is over-simplistic when considering ultrathin polymer films with sub-100 nm confinement. This thesis details the work done on measuring the thermal conductivity of ultrathin amorphous fluoropolymer films deposited on Si using a plasma polymerization process. The films are characterized for density, stiffness and composition as a way to shed some light on structural changes that occur with decreasing polymer thicknesses. We show that the increase in thermal conductivity for these amorphous polymers follows the change in film stiffness with different thicknesses and compares well to the minimum thermal conductivity model of amorphous films