Thickness Dependence and In Situ Studies of Nanomechanical Properties of Polymer Thin Films Upon Gas-Polymer Interaction using Amplitude Modulation Frequency Modulation (AMFM) Atomic Force Microscopy (AFM)

Polymer thin films are used for several applications and their thickness reduction is most important in future generation storage devices when they are used as dielectrics. Thickness reduction inevitably affects the quality of the polymer films. Furthermore, for environment safety these polymers are also used for the adsorption of the Volatile organic compounds (VOCs). Understanding the nanomechanical properties of thin polymer films and the effect of their interactions with VOCs on these properties is important in several applications like environment monitoring systems in closed spaces, sensors, electronics and packaging systems. In the present work we try to study the effect of thickness on the nanomechanical properties of polymer thin films in two different forms; deposited on the substrate and free standing films using Amplitude Modulation Frequency Modulation (AMFM) Atomic Force Microrscopy (AFM). The study has been done for polymer films of polystyrene and polymethacrylate deposited on the substrate and as free standing films. Changes in the measurement of Young’s modulus of the polymer when it is free standing and deposited on the substrates were observed with respect to the thickness of the film. It has been observed that as the thickness of the film is reduced the young’s modulus measured for the two forms of the films do not match. The causes of changes have been discussed based on the interaction of tip with the free-standing and substrate deposited films. Furthermore, it is observed that the interaction of VOCs is quite different in both cases which is analyzed based on the changes observed in young’s modulus by AMFM measurement. AMFM is a unique technique to study nanoscale viscoelastic properties of polymers. It can map the elastic properties of materials with unprecedented spatial resolution. In AMFM, conventional amplitude modulation and frequency modulation modes are combined to measure viscoelastic properties of materials with sub-10 nm resolution. The results have been discussed highlighting the importance and uniqueness of AMFM techniques in such measurements.