Masahiko Yoshiura

TSC of polyaniline thin film

We report the results of thermally stimulated current (TSC) measurements of polyaniline thin films with electric conducting or insulating property and the latest application of the analytical estimation methods for TSC signals.

Charging property and charge trap parameters in porous polypropylene film using thermally stimulated current

The heat resisting property of charge storage resins is required. It is well known that the charge storage of a polymer is influenced by the charge carrier traps. Charge trap parameters and charging property of porous and solid polypropylene (PP) films were studied using thermally stimulated current (TSC). We proposed already the Asymptotic Estimation Method (AEM) to evaluate trap parameters such as the energy depth of the trap Et and the escape frequency factor ν from TSC spectrum caused by multiple carrier traps, separately. To describe the ν- Et correlation, the trap sites caused by the porous structure were evaluated in the range of 1.0–1.1 eV. In addition, the ν values for those trap sites were found to be in the range 1011–1012 S−1. A comparison of surface potential decay revealed that drawing treatment caused discharge property by heating and the porous structure in the PP film induced charge storage stability.

Environmental Design for Muscle Cell Culture with Magnetic Field

Control methodology on cell culture has been studied for regenerative medicine and micro-actuator in an interdisciplinary research field. Environment has been designed around cultured muscle cells with a magnetic field, and an effect of the magnetic field at an extremely low frequency on proliferation and orientation of cultured skeletal muscle cells has been studied in vitro. Skeletal muscle cells were isolated from a hind-limb quadriceps, and cultured on a dish coated with collagen. The culture dishes were placed parallel to the uniform alternating magnetic field, which was generated with a solenoid coil. The result shows that the cultured skeletal muscle cells tend to align to the direction of the magnetic field at the extremely low frequency.

Behavior of the discrete energy states

A study comparing composite thermally stimulated current (TSC) curves that usually are measured by the single heating method, and partial curves from repeated heating and cooling processes, is reported. For this purpose, both the auto-separation (As) and reconstruction (Re) methods are necessary. The former enables us to separate accurately composite curves obtained by one heating process into several TSC curves with a single relaxation process. The latter enables us to reconstruct TSC curves from partial curves obtained by repeated heating and cooling, even if they had no observed peak. Both methods apply a theory, using the fundamental element that was defined originally to be the smallest quantity and a coordinate determined arbitrarily on the measured TSC curves. The current type of charge compensation equation that makes accurate RC procedure possible was first proposed. From detailed analysis, it was confirmed that an electron trap and a hole trap are produced simultaneously in a naphthacene doped anthracene single crystal. Analysis suggests that repeated heating and cooling influences both trap sites and that the indirect transport mechanisms via discrete state-to-state charge transfer processes is not negligible.

Proposal of reconstructing method of partial TSC curves to some full curves for accurate evaluation

An original theory that three parameters, the energy depths of carrier traps E/sub t/, the escape frequency factor /spl nu/ and the density of carrier trap site n, can be theoretically evaluated with high accuracy from partial TSC curves is proposed. How the standard can be constructed has been a most important resultant point.

Influence of heat-treatment of traps examined by using the thermally stimutated current and the dielectric characteristics of carbon-black-filled polyimide film

The influence of heat-treatment on the thermal deterioration of carbon-black-filling polyimide film (CBPI film) was examined by thermally stimulated current (TSC) measurement. CBPI film used for experiment had about 0.01 of tan δ and about 5.7 of relative permittivity. The conductivity of the film was about 1016 S/cm and was stable for a temperature change. When CBPI film was heat-treated, the conductivity became thermal active form. The thermal deterioration of a carbon black structure was occurred, because the tan δ was increased about 20 times in comparison with that of the film before the heat-treatment. Four kind of charge traps were also observed in the TSC spectrum of the CBPI film.

Evaluation of energy depth of traps in PA/BaTiO3 composite film by TSC measurements

Recently, composite films of polymer and inorganic-filler are required as a key material for further downsizing of electronic devices such as a capacitor. We have studied, through thermally stimulated current (TSC) measurement, to explain the effects of trap levels on electrical conduction and charging properties of Polyamide(PA)/BaTiO<inf>3</inf> composite films. TSC measurements were performed from 150 K to 350 K. TSC signals were detected for PA, 20 vol% filled PA, and 40vol% filled PA. Trap parameters were accurately evaluated through asymptotic estimation method (AEM). The values of energy depth of charge trap (E<inf>t</inf>) for PA, 20 vol% filled PA, and 40vol% filled PA were estimated 0.654 eV, 0.647 eV, and 0.625 eV, respectively. Escape frequency factors (υ) were also estimated 5.28 × 10⁸ S⁻¹, 1.87 × 10⁷ S⁻¹, and 3.22 × 10⁷ S⁻¹, respectively. It was revealed that BaTiO<inf>3</inf> filled in PA films reduced both Et value and υ.

Thermally stimulated current of polyaniline thin films

TSDC of a polyaniline thin film was measured with an electrode system (mica/ITO/EB film/ITO/mica). The comparative study of TSC and TSDC spectra revealed that both spectra contained two component current curves and the cause of the currents were different, though detailed mechanism of the current generation is still not clear.

Photoconduction of polyaniline thin films

The intrinsic and the extrinsic photoconduction were observed in the surface regions of doped and undoped polyaniline films, respectively. The difference of the photoconduction between hole and electron was not observed in the present experimental conditions.

Behavior of the discrete states observed through detailed analyses of TSC curves

In order to make the electronic transport mechanism in organic substances clear in detail, the thermally stimulated current (TSC) method is very effective. From the TSC method, three parameters such as an energy depth E/sub t/ [eV] of the carrier trap site, a preexponential parameter (or an escape frequency factor) /spl nu/ [s/sup -1/] and a charge carrier density n/sub t/ [m/sup -3/] relating to the phenomena, can be estimated. We have completed some theories that enable us to analyze in detail TSC data obtained experimentally. One of them, the asymptotic estimation method (AEM) originally proposed by us, enables us to evaluate these three parameters accurately. And this has been expanded extensively to estimate 3N parameters, through an exact auto-separation (AS) method of various composite TSC curves and through the reconstruction (RC) method of TSC curves with no peak obtained by partially repeated heating cooling procedures. Where N is the number of the single TSC curve of the first-order included in the objects. The fine advantages are that these expanded theories have higher accuracy than 4 significant figures. Then, detail analyses of discrete states became possible by using both methods.