Crystallisation behaviours of ferroelectric P(VDF-TrFE) ultrathin films on different substrates

Abstract

A series of ferroelectric polymer ultrathin films on different substrates were fabricated by spin coating. Thickness of the ultrathin films was easy to manipulate through tuning the polymer concentration or spin-coating speed. Crystallisation behaviours of these ferroelectric films on different substrates such as bare silicon, silicon coated with Cr or Au, were investigated by atomic force microscopy. The substrates had remarkable effect on the morphologies of the ferroelectric ultrathin films after annealing. Ferroelectric polymer ultrathin film on bare silicon grew to lamellar crystals, while the ultrathin film on silicon coated with Au came into being ‘ball-like’ crystals which were aggregated by smaller ones. The crystallisation behaviour of ferroelectric ultrathin film on silicon coated with Cr was closely related with its heat history. The film annealed immediately after fabrication generated rodlike crystals, which connected with each other. However, the one annealed after storage for a week in desiccator created spherulites, and these spherulites collided with each other and generated curved lamellae which were twisted. The different crystallisation behaviours of the ultrathin films may be due to the surface energy of different substrates. Moreover, P(VDF-TrFE) ultrathin film showed ferroelectricity although its thickness is about 10 nm.