1,720,998 research outputs found
Tuning-fork-based piezoresponse force microscopy
No full textSurface displacements of a few picometers, occurring after application of an electric potential to piezoelectric materials, can be detected and mapped with nanometer-scale lateral resolution by scanning probe methods, the most notable being piezoresponse force microscopy (PFM). Yet, absolute determination of such displacements, giving access for instance to materials' piezoelectric coefficients, are hindered by both mechanical and electrostatic side-effects, requiring complex experimental and/or post-processing procedures for carrying out reliable results. The employment of quartz tuning-fork force sensors in an intermittent contact mode PFM is able to provide measurements of electrically-induced surface displacements that are not influenced by electrostatic side-effects typical of more conventional cantilever-based PFM. The method is shown to yield piezoeffect mapping on standard ferroelectric test crystals (periodically-poled lithium niobate and triglycine sulfate), as well as on a ferroelectric polymer (PVDF), with no visible influence from the applied dc electric potential
LOCAL DIELECTRIC SPECTROSCOPY AND ITS APPLICATION TO POLYMERS
No full textThe advent of nanodielectrics, nanocomposite materials based on a polymeric matrix, and materials with physical properties ruled by interfacial effects in general demands techniques to characterize functional properties on a local scale with high spatial resolution. Scanning probe microscopies (SPMs), in their electrical modes, have emerged as indispensable tools to access physical quantities such as dielectric constant, surface potential, and static charge, with nanometer-scale lateral resolution and with surface selectivity, being influenced mainly by the outermost layer of the specimen. In this tribute, the development of various SPM electrical modes is illustrated, focusing on the measurement of dielectric permittivity and its spectroscopic extension to access the local, frequency-dependent dielectric function (local dielectric spectroscopy [LDS]). The application to nanostructured polymers in the form of ultrathin films, nanometer-scale-separated blends, and self-assembled block copolymer structures is described. LDS appears to be a promising technique for characterizing the electric properties of polymers and their composites as well as other glass formers and nanostructured systems
Noncontact friction force microscopy based on quartz tuning fork sensors
No full textNoncontact friction force microscopy (NC-FFM) measures the damping of the resonant oscillation of an atomic force microscope (AFM) tip that vibrates parallel to the sample surface at a controlled distance. By exploiting the two fundamental orthogonal vibration modes of a quartz tuning fork, such technique can be realized by all-piezoelectric sensing by simultaneously employing an AFM noncontact mode for distance control. The low noncontact-mode vibration amplitude used increases the effective interaction time for shear measurement. Application to polymeric samples shows that the dissipation contrast of NC-FFM is higher than that of the corresponding noncontact-mode phase imaging. (c) 2006 American Institute of Physics
Piezoelectric displacement mapping of compliant surfaces by constant-excitation frequency-modulation piezoresponse force microscopy
No full textA simple experimental method for piezoresponse force microscopy (PFM) measurements for reliable evaluation of piezoelectric surface displacements even on compliant surfaces is proposed based on atomic force microscopy (AFM) operated in frequency-modulation (FM) dynamic mode with constant excitation (CE), by using non-contact mode cantilevers. Surface displacement by piezoelectric effect after application of an electric potential to the conductive AFM probe translates into a likewise variation of the probe oscillation amplitude, while the related electrostatic forces mainly affect the oscillator resonant frequency, and cantilever bending is limited due to their high stiffness. Our non-contact CE-FM-PFM method is shown to reduce electrostatic force contributions as compared to contact-PFM modes. Converse piezoelectric effect mapping is demonstrated on poly(vinylidenefluoride) nanofibers obtained by electrospinning
Bilateral switching of the modulated electrooptic contrast in PLZTN ceramics RID C-3109-2009
No full textSpatial distribution of ferroelectric polarization in Pb(Zr,Ti)O-3 ceramics doped with lanthanum and niobium has been investigated using scanning electrooptic confocal microscopy. Measurement of the modulated electrooptic signal in presence of a sinusoidal electric field reveals ferroelectric domains at microscopic scale not accessible to conventional polarized optical imaging. Both electrooptic images and local electrooptic loops have been observed after applying a bias electric field to the ceramic samples, being initially non-ferroelectric macroscopically. Bilateral reversal of the electrooptic contrast during the poling cycle has been detected and explained taking into account non-180 degrees switching processes in ferroelectric grains of arbitrary orientation. (c) 2006 Elsevier Ltd. All rights reserved
Intermittent-contact local dielectric spectroscopy of nanostructured interfaces
No full textLocal dielectric spectroscopy (LDS) is a scanning probe method, based on dynamic-mode atomic force microscopy (AFM), to discriminate dielectric properties at surfaces with nanometer-scale lateral resolution. Until now a sub-10 nm resolution for LDS has not been documented, that would give access to the length scale of fundamental physical phenomena such as the cooperativity length related to structural arrest in glass formers (2-3 nm). In this work, LDS performed by a peculiar variant of intermittent-contact mode of AFM, named constant-excitation frequency modulation, was introduced and extensively explored in order to assess its best resolution capability. Dependence of resolution and contrast of dielectric imaging and spectroscopy on operation parameters like probe oscillation amplitude and free amplitude, the resulting frequency shift, and probe/surface distance-regulation feedback gain, were explored. By using thin films of a diblock copolymer of polystyrene (PS) and polymethylmethacrylate (PMMA), exhibiting phase separation on the nanometer scale, lateral resolution of at least 3 nm was demonstrated in both dielectric imaging and localized spectroscopy, by operating with optimized parameters. The interface within lamellar PS/PMMA was mapped, with a best width in the range between 1 and 3 nm. Changes of characteristic time of the secondary (β) relaxation process of PMMA could be tracked across the interface with PS
Enhanced crystallization kinetics in poly(ethylene terephthalate) thin films evidenced by infrared spectroscopy RID E-9799-2011 RID A-8503-2012
No full textThe cold crystallization process in poly(ethylene terephthalate) (PET) spin-coated ultrathin films was studied by infrared spectroscopy. The conformational change associated to the formation of crystal phase during annealing at 107 degrees C was measured in real time, by monitoring both intensity and frequency shift of trans and gauche conformer bands of the PET glycol segment. Enhancement of crystallization kinetics was observed in thin films deposited on amorphous silicon, with respect to a 20 mu m thick free standing film used as reference, where the fastest kinetics was observed for the thinnest (35 nm) film. Experimental findings were interpreted in terms of scarce interaction between PET films and silicon substrate, which does not provide slowing down of crystallization kinetics as observed on different substrates. This results in a dominant effect of the polymer/air interface, where faster kinetics is observed, as also confirmed by atomic force microscopy imaging, particularly on the thinnest film. Additionally, Avrami and Avramov analyses evidence a decrease of both the Avrami exponent, related to growth dimensionality, and induction time, related to delay of nucleation start, when decreasing film thickness. Therefore, the reported results enrich the description of confinement and substrate interaction effects on the cold crystallization process taking place in PET ultrathin films
Lateral resolution of electrostatic force microscopy for mapping of dielectric interfaces in ambient conditions
Full text linkThe attainable lateral resolution of electrostatic force microscopy (EFM) in an ambient air environment on dielectric materials was characterized on a reference sample comprised of two distinct, immiscible glassy polymers cut in a cross-section by ultramicrotomy. Such a sample can be modeled as two semi-infinite dielectrics with a sharp interface, presenting a quasi-ideal, sharp dielectric contrast. Electric polarizability line profiles across the interface were obtained, in both lift-mode and feedback-regulated dynamic mode EFM, as a function of probe/surface separation, for different cases of oscillation amplitudes. We find that the results do not match predictions for dielectric samples, but comply well or are even better than predicted for conductive interfaces. A resolution down to 3 nm can be obtained by operating in feedback-regulated EFM realized by adopting constant-excitation frequency-modulation mode. This suggests resolution is ruled by the closest approach distance rather than by average separation, even with probe oscillation amplitudes as high as 10 nm. For better comparison with theoretical predictions, effective probe radii and cone aperture angles were derived from approach curves, by also taking into account the finite oscillation amplitude of the probe, by exploiting a data reduction procedure previously devised for the derivation of interatomic potentials
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