Patterned ferro-, pyro- and piezoelectricity in poly(vinylidene fluoride) by means of a laser-induced irreversible beta ->alpha phase transformation

Materials with patterned pyro- or piezoelectricity are useful for a range of applications such as sensor arrays with reduced cross talk between individual elements, piezoelectric gratings for direction-sensitive acoustic-wave detection/emission, or motion-sensitive pyroelectric sensors. Here, the successful patterning of pyro- and piezoelectric poly(vinylidene fluoride) (PVDF) films, by controlled scanning of a focused laser beam across their top electrodes, is reported. The resulting patterns are based on the differences between the ferroelectric polar beta phase and the paraelectric nonpolar alpha phase of PVDF. Nonpolar alpha-phase areas are generated in a poled beta-PVDF film through a local heating process that yields a beta-->alpha phase transition throughout the thickness of the film. An important feature of this process is the fact that the PVDF film remains intact and can still be used even in applications that require free-standing films. Infrared spectroscopy and pyroelectrical depth profiling are employed to prove the beta-->alpha phase transition and the accompanying pyroelectricity pattern, respectively. (C) 2002 American Institute of Physics.