Kenji Omote

Temperature dependence of elastic, dielectric, and piezoelectric properties of “single crystalline’’ films of vinylidene fluoride trifluoroethylene copolymer

Elastic, dielectric, and piezoelectric constant matrix elements of a “single crystalline’’ (SC) film of vinylidene fluoride trifluoroethylene copolymer, P(VDF/TrFE), in which the orthorhombic [001] and [110] axes of fully extended chain crystals are preferentially oriented parallel to the stretching axis and normal to the surface, respectively, were measured at temperatures ranging from 10 K to the Curie point (402–404 K) by using a piezoelectric resonance method. All of the electromechanical coupling factors (k31, k32, k33, k24, and k15) are larger than those of conventional lamellar crystalline films. Some of the matrix elements for a P(VDF/TrFE) single crystal are derived from the measured values of constant matrix elements for the SC film. Some features characteristic of the SC film are revealed. The SC film has a large Young’s modulus for the stretching direction (1/s11) (121 GPa at 10 K). The properties related to the molecular motions along the chain axis, such as 1/s11, shear stiffness constant c5...

Formation of ‘‘single crystalline films’’ of ferroelectric copolymers of vinylidene fluoride and trifluoroethylene

We find that a highly double‐oriented film of practically unlimited size can be obtained from a uniaxially drawn film of P(VDF/TrFE) by crystallization in the paraelectric phase with its surfaces free from any constraint other than tensile stress along the chain axis. The c axis (the chain axis) and the [110] axis in the orthorhombic system of the poled crystalline film are parallel to the stretching axis and perpendicular to the film plane, respectively. Contrary to conventional crystalline polymer films, the present film has no amorphous region and no lamellar crystal. The film exhibits highly anisotropic characteristics in optical, mechanical, and piezoelectric properties.

Chain motions in the paraelectric phase in single crystalline films of vinylidene fluoride and trifluoroethylene copolymer P(VDF/TrFE)

An anomalously large dielectric constant and a long relaxation time along the chain axis were first observed in the paraelectric phase of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. Dielectric, X-ray scattering and shear sound velocity studies consistently show that the anomalous phenomena arise from the characteristic motion of a chain molecule of T G T G ′ chain conformation in the crystal: the chain in the paraelectric phase rotates independently of neighboring chains, and, in the chain, a T G T G ′ sequence, whose length increases around the Curie temperature, undergoes the flip-flop motion. The crystal in the paraelectric phase is a liquid crystal of 1D liquid and 2D solid.

Effects of Ion Energy Control on Production of Nitrogen–C60 Compounds by Ion Implantation

Nitrogen–C60 compounds such as azafullerene (C59N) and nitrogen-atom-encapsulated fullerene (N@C60) are produced by implanting nitrogen ions into C60 thin films on a substrate immersed in an electron cyclotron resonance plasma under a mirror magnetic field. Each compound is found to be synthesized, depending on the ion energy provided by the potential difference between the substrate and the plasma. The optimum energy for C59N synthesis is approximately 40–50 eV, and the amount of C59N decreases in an ion energy range larger than 50 eV. In contrast, an ion energy larger than 20 eV is required for N@C60 synthesis.

Shear piezoelectric properties of vinylidene fluoride trifluoroethylene copolymer, and its application to transverse ultrasonic transducers

Shear piezoelectric properties of a vinylidene fluoride trifluoroethylene copolymer [P(VDF/TrFE)] have been studied in a temperature range from 10 to 350 K. The shear electromechanical coupling factors k15 and k24 at 290 K are found to be 0.19 and 0.20, respectively, the values being largest among the piezoelectric polymers known at present. The factors k15 and k24 remain constant below 200 K, while k24 increases and k15 decreases above 200 K. The effectiveness of P(VDF/TrFE) as a transverse ultrasonic transducer material was demonstrated by measurements of transverse sound velocities and absorptions in aluminum and poly(methyl methacrylate) with P(VDF/TrFE) shear transducers.

Electron emission from ferroelectric copolymer thin films of vinylidene fluoride and trifluoroethylene

Electron emission from ferroelectric copolymer thin films consisting of vinylidene fluoride and trifluoroethylene (PVDF-TrFE) are reported. The ∼3μm thick copolymer thin films were deposited by spin coating and were then annealed to improve their crystallinity. The as-annealed films exhibited an electron emission capability, as anticipated; an emission charge within the range from 122to308pC∕cycle occurs at a positive excitation voltage with different excitation frequencies. It was found that the electron emission process of the PVDF-TrFE thin films differs from the conventional ferroelectric electron emission. A possible emission mechanism is proposed, which suggests that an amorphous phase in the polymer films plays an important role in trapping and emitting electrons.

Performance of Multilayered Ultrasonic Transducers Comprising Vinylidene Fluoride and Trifluoroethylene Copolymer Films and Ferroelectric Ceramic Plates.

Frequency and impulse response characteristics of multilayered ultrasonic transducers comprising forward films of vinylidene fluoride and trifluoroethylene copolymer (P(VDF-TrFE)) and backward ferroelectric ceramic plates of lead-zirconate-titanate (PZT) and a backing load, are studied both theoretically and experimentally. These transducers can be driven in three operation modes: (1) P(VDF-TrFE) as a transmitter and a receiver, (2) PZT as a transmitter and a receiver, and (3) PZT as a transmitter and P(VDF-TrFE) as a receiver. It is found that, owing to the great difference in their acoustic and dielectric properties, PZT plates and P(VDF-TrFE) films operate independently at different frequencies, and that, in operation mode (3), the multilayered transducers exhibit broad frequency bandwidth or shorter impulse response characteristics with high sensitivity and high S/N ratio.

Measurements of electronic transport properties of single-walled carbon nanotubes encapsulating alkali-metals and C60 fullerenes via plasma ion irradiation

We report on the measurements of the electronic transport properties of Cs-encapsulated single-walled carbon nanotubes (SWNTs), Li-encapsulated SWNTs, and C60-encapsulated SWNTs synthesized by plasma ion irradiation method. After fabricating field-effect transistor (FET) configurations using pristine and plasma-ion-irradiated SWNTs, the electronic transport properties of these devices are investigated in vacuum at room temperature. As a result, C60-encapsulated SWNTs give rise to a p-type semiconducting property as pristine SWNTs do. On the other hand, it is clearly observed that Cs-encapsulated SWNTs exhibit n-type transport behavior. Moreover, Li-encapsulated SWNTs show an ambipolar transport property with both n-type and p-type characteristics. Thus, the electronic properties of SWNTs are found to be successfully controlled by plasma ion irradiation.

Properties of transverse ultrasonic transducers of ferroelectric polymers working in thickness shear modes

Shear piezoelectric properties of poly(vinylidene fluoride) (PVDF) and copolymer of vinylidene fluoride and trifluoroethylene [P(VDF/TrFE)] have been studied precisely in a wide temperature range from 10 to 400 K. It was found that these polymers have the shear electromechanical coupling factors k/sub 15/ and k/sub 24/ large enough to be utilized for transverse ultrasonic transducers operating in a wide frequency range and in a wide temperature range below 400 K. Shear mode ultrasonic transducers of P(VDF/TrFE) were fabricated and their performances were studied both experimentally and theoretically. The shear polymer transducers are useful for generation and detection of transverse ultrasonic waves.

Temperature Dependence of Shear Piezoelectric Properties of Poly(vinylidene fluoride) Studied by Piezoelectric Resonance Method.

Elastic and dielectric anisotropies, and shear piezoelectric properties of uniaxially oriented poly(vinylidene fluoride) (PVDF) were determined in the temperature range from 10 K to 400 K by a piezoelectric resonance method. The shear piezoelectric stress constant e24 increases above the primary dispersion temperature, while e15 decreases markedly and tends to zero at 390 K: e24 and e15 are, respectively, 28 mC/m2 and 38 mC/m2 at 10 K, and 48 mC/m2 and 15 mC/m2 at 295 K (where the coordinate axes X and Z in the film refer to the stretching axis and poling axis, respectively). The temperature dependences of e24 and e15 are analyzed on the basis of the model in which the crystalline and amorphous phases are combined in series and parallel along the chain axis. The analysis shows that e15 in the crystalline phase decreases considerably above the primary dispersion temperature, whereas e24 in the crystalline phase increases with increasing temperature.