Electric double layer in porous media is studied with direct numerical simulations of the Nernst-Planck-Poisson equation. The time evolution of the charging process of the electric double-layer along a straight pore is first studied, and confirm that the time evolution obeys a power law of the exponent 1/2. We find that the diffusion constant increases effectively by the effect of the width of the pore. Next it is found that the time evolution of the charging process in fractal porous media obeys a power law, and the exponent alpha is related to the fracton dimension. Finally, we propose a coupled map lattice model for the creation of pore structures by gas activation processes, and perform numerical simulation of the charging dynamics of the electric double layer.

β-FeSi2 thin films were epitaxially grown on p-type Si(111) substrates at a substrate temperature of 560 °C and Ar pressure of 2.66 × 10−1 Pa by radio-frequency magnetron sputtering (RFMS) using a sintered FeSi2 target, without postannealing. The resultant n-type β-FeSi2/p-type Si heterojunctions were evaluated as near-infrared photodiodes. Three epitaxial variants of β-FeSi2 were confirmed by X-ray diffraction analysis. The heterojunctions exhibited typical rectifying action at room temperature. At 300 K, the heterojunctions showed a substantial leakage current and minimal response for irradiation of near-infrared light. At 50 K, the leakage current was markedly reduced and the ratio of the photocurrent to dark current was considerably enhanced. The detectivity at 50 K was estimated to be 3.0 × 1011 cm Hz1/2/W at a zero bias voltage. Their photodetection was inferior to those of similar heterojunctions prepared using facing-target direct-current sputtering (FTDCS) in our previous study. This inferiority is likely because β-FeSi2 films prepared using RFMS are located in plasma and are damaged by it.

The electric double layer around fractal electrodes is studied with direct numerical simulations of the Nernst-Planck equation coupled with the Poisson equation. The capacitance and the relaxation time obey a power law as a function of the system size, the temperature, and the concentration. The time evolution of the charging process exhibits a stretched exponential law, and the exponent beta is numerically evaluated.

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The quantum contact through which the electronic conductance is quantized by 2e 2 /h was chemically formed in a beaker. This preparation method needed only conventional tools in a common laboratory. Quasi-two-dimensional zinc fractal was used as an electrode, which was electrochemically synthesized at an immiscible interface between water and 4-methyl-2-pentanone. The electronic conductance through the colliding atomic bridge between the zinc fractal and a copper ring electrode surrounding this 2D fractal was quantized at room temperature.

Undoped and C-doped n-type β-FeSi2 thin films were epitaxially grown on p-type Si substrates by sputtering and their heterojunction diode performances were experimentally studied. The near-infrared photodetection, at a wavelength of 1.3 m, in these heterojunction diodes was clearly improved as compared to the heterojunctions comprising undoped-β-FeSi2. From X-ray diffraction and Raman spectroscopic measurements, there were no evident structural differences between the undoped and C-doped films. C-doping hardly affects the crystallization and epitaxial growth of β-FeSi2. The enhancement in the diode performance by C-doping might be owing to C atoms terminating dangling bonds and compensating defects in β-FeSi2 crystals.

Abstract-The fabrication of n-type β-FeSi 2 /p-type Si hetero junctions was accomplished by FTDC Sat a substrate temperature of 600°Cwithout post-annealing. Their currentvoltage characteristic curves were measured at low temperatures ranging from 300 K down to 50 K. In order to examine the mechanism of carrier transport in the hetero junctions using thermionic emission theory, the ideality factor was estimated from the slope of the linear part of forward lnJ-V characteristic curves. In the temperature range from 300 K down to 225 K, the ideality factor was 1.23 at 300 K and increased to 2.02 at 225 K. The ideality factor values 2 implied that the mechanism of carrier transport was governed by a recombination process. In the temperature range from 200 K down to 50 K, the ideality factor was 3.34 at 200 K and increased to 15.56at 50 K. Parameter A was calculated to be constant. The temperature dependent ideality factor, together with the constant value of parameter A, implied that the predominant mechanism of carrier transport was a trap-assisted multi-step tunneling process. At highly applied forward bias voltage, the mechanism of carrier transport was changed to a space charge limited current process.

We prepared n-type nanocrystalline iron disilicide (NC-FeSi2)/intrinsic (i) ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C)/p-type Si heterojunctions and evaluated as photodiodes. UNCD/a-C and NC-FeSi2 films were deposited by coaxial arc plasma deposition and pulsed laser deposition, respectively. The capacitance-voltage and current-voltage characteristics of heterojunctions were measured at room temperature. The inserted i-UNCD/a-C layer to form pin heterojunctions reduced the capacitance and dark current as compared with those in the case of pn heterojunctions. The build-in potential of heterojunctions was estimated to be 1.2 eV. The prepared heterojunctions showed typical rectifying action and a response for an illumination with a 6 mW, 1.31 μm laser. The recombination process is the predominant mechanism of current transport in the heterojunctions. The dynamic resistance area product and detectivity were 1.54 × 103 Ω cm2 and 5.0 × 108 cmHz1/2/W at-1 V. The evident improvement in the device performance was demonstrated, which should be due to the reduction of dark current by i-UNCD/a-C layer.