High piezoelectric activity in nonpoled thin films prepared by vapor deposition polymerization

A simple dry process in vacuum was developed for the preparation of polyamide, polyimide, and polyurea thin films on the basis of the conventional vapor deposition technique; this method was termed vapor deposition polymerization (VDP). Pyroelectric and piezoelectric properties have been observed for the polyurea thin films prepared by the VDP method with a poling treatment. Instead of the above conventional poling method, we have proposed a new method, "surface energy poling". A polar structure can be constructed spontaneously in a thin film when a polar polymer is sandwiched between two materials with higher and lower surface energies. In this paper, we discuss piezoelectric behavior in nonpoled thin films of aromatic polyurea prepared by the VDP method, i.e., synthesized by simultaneous deposition of a diamine monomer and a diisocyanate monomer in vacuum without a conventional poling process.