Effect of substrate temperature on poly(methyl methacrylate) nanocomposite thin films deposited by matrix assisted pulsed laser evaporation

The effects of substrate heating on thin films deposited by matrix assisted pulsed laser evaporation (MAPLE) were investigated. Substrates were heated at temperatures ranging from 315 to 425 K during depositions of neat poly(methyl methacrylate) (PMMA) and PMMA–carbon nanotube (CNT) composite thin films. Scanning electron microscopy (SEM) was used to examine the surface morphology of deposited films, while gel permeation chromatography (GPC) was used to determine the extent of photon-induced degradation in the molecular weight of deposited polymer. Significant reductions in molecular weight were observed. Further information regarding the degradation behavior was obtained from differential scanning calorimetry (DSC), where the glass transition temperatures (Tg) of native and MAPLE deposited PMMA samples were measured. A decrease in the surface roughness of deposited films was observed with increasing substrate temperature for both neat PMMA and PMMA–CNT composite films. At temperatures significantly lower than the measured Tg for the as-received PMMA, features in deposited films began to take on a disc-like structure. DSC analysis of the deposited species shows a decrease in Tg relative to the as-received material. This reduction in Tg is attributed to the degradation of the native polymer during the MAPLE process, as shown by GPC results. Surface roughness effects in both the neat polymer and composite films show a continuous decrease in roughness as a function of temperature, as observed by both profilometry and SEM. The final roughnesses of the composite films were significantly greater than those of the pure polymer films. It is speculated that this is the result of CNT agglomeration within the starting target solutions.