Variation of the mechanical properties of pulsed laser deposited PMMA films during annealing

The structural and mechanical properties of polymethyl methacrylate (PMMA) thin films produced by pulsed laser deposition in ultra-high vacuum were investigated by infrared spectroscopy, electron microscopy, size-exclusion chromatography and microhardness measurements. After preparation, the film hardness and elastic modulus are found to be increased. This is caused by a reduced chain length of the polymer film to values of 5800 g/mol and by cross links of an amount of about 20% of the polymer, while the chemical structure of the deposited films is comparable to the target material. During annealing, relaxation processes lead to a reduction of the film hardness, without changing the cross-linked part in the samples.