Strong substrate effect in local poling of ultrathin ferroelectric polymerfilms

By locally poling and measuring ultrathin films of the ferroelectric copoly mer vinylidenefluoride/trifluoroethylene (VDF/TrFE), we show that the subst rates on which these films are adsorbed play a strong role in orienting and poling the films. We carried out both poling and measurements using the Au -coated probe tip of the cantilever of an atomic force microscope. For ultr athin films of about 20 nm of the copolymer spin-coated on graphite, only a fraction of the thickness of the copolymer film can be repoled, so that th e net local piezoelectric effect is enhanced or reduced, depending upon whe ther poling is parallel or antiparallel to that induced by the substrate, r espectively. For sufficiently thick films, this substrate effect is negligi ble. The apparent lateral resolution with which information can be stored b y poling in ultrathin films depends strongly on the film thickness and poli ng direction with respect to the substrate effect. (C) 1999 Elsevier Scienc e S.A. All rights reserved.