SURFACE DIPOLE ORDERING OF SUBMICRON POLYDIPHENYLENEPHTHALIDE FILMS

This paper considers the problem of surface dipole ordering of thin polymer layers with nanometer range thicknesses. We have experimentally studied submicron dielectric films of electrically active polydiphenylenephthalide polymer composed of molecules that included a side phthalide group with a relatively large dipole moment. The interest to this polymer is caused by an abnormally high conductivity at the polymer/polymer interface which was previously associated with possible superficial ordering of the phthalide groups. Using the methods of piezoresponse force microscopy we have explored the surface of submicron films synthesized by centrifugation. We have detected a manifestation of spontaneous polarization indicating the ordering of dipoles. Also, in order to determine the bulk and surface contributions to the polarization of the films we have studied the polarization and relaxation in samples of different thicknesses. With a reduction of the thickness the piezoelectric response of the signal increases and electrically generated domains acquire ideal radial shapes. This confirms that the surface layers of the polymer film make the predominant contribution to orientation processes. Polarization switching occurs in the films, manifested by the change of the piezoelectric response signal contrast when fields of different polarity are applied. We use these surface phenomena to explain the unique electronic properties of the boundaries of polar organic dielectrics.

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