Crystallization and microstructure-dependent elastic moduli of ferroelectric P(VDF-TrFE) thin films

The crystallization behaviour of ferroelectric P(VDF-TrFE) copolymer thin films on various substrates has been investigated. The substrates used include bare Si for a high energy surface, and fluorinated self-assembled monolayer deposited Si and elastomer PDMS for low energy surfaces. Low energy surfaces have been found to enhance the crystallization rate. Additionally, the elastic moduli of those thin films, having thicknesses ranging from ∼30 nm to ∼1 μm, have been determined by the buckling method. The moduli have been found to depend strongly on the films microstructure, and have shown a maximum at the crystallization temperatures of 120 °C-140 °C. The films annealed at these temperatures show more than a 5× increase in modulus than that of the room-temperature dried ones. The dependence of the modulus on the film microstructure has been found to be closely related to the change in film crystallinity. The measured moduli of P(VDF-TrFE) thin films can help with the design and practical implementation of emerging applications such as flexible nonvolatile memories and piezoelectric energy harvesting devices.