The impact of carbon nanotube (CNT) incorporation into semicrystalline poly(vinylidene fluoride), PVDF, was investigated at both the macro and nanoscales. A special effort was devoted to probe the local morphology and the mechanical, ferroelectric, piezoelectric, and electrical conductivity response by means of atomic force microscopy. Incorporation of CNTs mainly induces the development of the polar γ-phase, and as a consequence, the coexistence of the γ-phase with the most stable nonpolar α-phase is observed. A maximum γ-phase content is reached at 0.7 wt % CNT loading. The spherulitic morphology of the PVDF α-phase is assessed, in conjunction with the lack of any ferroelectric response, while the presence of the polar γ-phase is confirmed, owing to clear piezoresponse signals. Local piezoelectric measurements on γ-phase domains yield a maximum effective coefficient | d| ≈ 13 pm/V, thus underlining the potential for applications of such functional PVDF-based nanocomposites in advanced piezoelectric devices. An increase in macroscopic conductivity with CNT content is observed, with a percolation threshold achieved for a composition close to 0.7 wt %. Nanoscale investigation of the electrical conductivity confirms the presence of some infinite CNT cluster homogeneously distributed over the surface. The macroscopic viscoelastic behavior of the composite reflects the reinforcing effect of CNTs, while the nanomechanical characterization yields a local contact modulus of the γ-phase domains larger than that of its α-phase counterpart, in agreement with the fact that the CNTs act as γ-phase promoters and subsequently reinforce the γ-domains.

Colossal magnetoresistive (CMR) La 0.7 Sr 0.3 MnO 3 (LSMO) thin films have been grown under tensile strains on (100)-SrTiO 3 substrates and compressive strains on (100)-LaAlO 3 and (110)-NdGaO 3 substrates by pulsed laser deposition. Using magnetic force microscopy (MFM), a "feather-like" magnetic pattern, characteristic of films with an in-plane magnetization, is observed for films deposited on both SrTiO 3 and NdGaO 3 while a "bubble" magnetic pattern, typical of films with an out-of plane magnetization, is recorded for LaAlO 3 .We show that the shape of the magnetic pattern imaged by MFM is fully correlated to the easy direction of the magnetization in the film.Electronic mail : desfeux@univ-artois.fr

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At very low temperature (450 • C), (111)-oriented and polycrystalline 0.7Pb(Mg 1/3 Nb 2/3 ) O 3 -0.3PbTiO 3 (PMN-PT) thin films have been grown on platinum (Pt) and lanthium niobate (LaNiO 3 ) bottom electrodes respectively. Macroscopic measurements reveal lower coercive fields for PMN-PT grown on LaNiO 3 compared to on platinum, while the piezoelectric coefficient d 33 is greater. At the nanometer scale, local piezoelectric hysteresis loops show that the voltages required for domain switching and piezoelectric response are the highest for PMN-PT deposited on LaNiO 3 . The electrical results can be explained by taking into account the effects induced by both electrodes on the surface morphology and structural properties of the films.

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Ferroelectric domains were investigated using piezoresponse force microscopy in superlattices composed of multiferroic BiFeO 3 and SrTiO 3 layers. Compared to single BiFeO 3 thin films, a reduction in the domains size and a suppression of the in-plane orientation of domains are observed in a superlattice of (BiFeO 3 ) 4 (SrTiO 3 ) 8 , suggesting a constrained ferroelectric domain orientation along the out-of-plane <001> direction. Such modification of domain size and orientation in BiFeO 3 -based heterostructures could play a vital role on engineering the domains and domain wall mediated functional properties necessary for device applications. 1 prellier@ensicaen.frRecent study on the strain effect on epitaxial (001) BFO thin films shows that, though the magnitude of the polarization remains unchanged, the polarization variants in BFO could be altered by strain. 9 A strain-induced out-of-plane rotation of polarization from the (111)

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