In situ observation of the nanocrystal growth and their piezoelectric performance change in P(VDF-TrFE) films by hot stage piezoresponse force microscopy

We report the growth process of nanocrystals in spin-coated P(VDF-TrFE) films and the corresponding change in piezoelectric response by using in situ hot stage piezoresponse force microscopy (PFM). Upon annealing, irregularly shaped grains of the as-deposited film gradually grew up, and leaf-shaped grains with rather different piezoelectric response were formed above 120 °C. PFM images indicated that the individual grains in the P(VDF-TrFE) film were highly ordered nanocrystals having uniform molecular orientation, while different nanocrystals might show different molecular orientation. At 150 °C, which is higher than the Curie temperature of the material, the nanocrystals still showed a strong piezoelectric response despite the appearance of melt phase. This reveals a diffused transition in piezoelectric response that is related to the coexistence of crystalline and amorphous phases in the copolymer material. An annealing induced molecular reorientation observed by PFM was also confirmed by other charact...