Takeshi Mikayama

Au/Poly(3-methylthiophene)/10-(p-nitrobenzyl)-2(10H)-phenazinone/Al organic hetero-junction photovoltaic device

Abstract We proposed a novel concept of organic two-layer photovoltaic devices with D– σ –A molecule (Donor subunit– σ bond–Acceptor subunit)/conducting polymer heterojunction. Au/PMeT (poly(3-methylthiophene))/NBPN (10-( p -nitrobenzyl)-2(10H)-phenazinone)/Al was fabricated as a prototype of D– σ –A/polymer photovoltaic device. The power conversion efficiency of this photodiode was 5.1 × 10 −2 % under white illumination (8.46 mW/cm 2 ). This value was larger than that of PMeT Schottky photodiode. This fact suggests that the concept of D– σ –A/polymer photovoltaic device is effective.

Nanometre-scale photoelectric characteristics of a molecular device monolayer

We constructed monolayer Langmuir–Blodgett (LB) films using a novel molecule C37H40N4O4 synthesized by us. This molecule is a long-chain alkyl derivative with a dinitrobenzene moiety (acceptor subunit) and a dihydrophenazine moiety (donor subunit) bridged by a methylene group with a constant distance and bond angle between the acceptor and donor groups. It behaves as a unimolecular device with control of the potential between the donor and acceptor subunits. We transferred the monolayer film onto a Au(111) substrate and measured nanometre-scale electrical characteristics in the dark or in an evanescent field. Rectifying characteristics and increasing photoconductivity were observed.

Search for a d-Wave Chiral-Glass Transition in Granular High- T c Superconductor (Sr 0.7Ca 0.3) 0.95CuO 2- x

We have studied the behavior of second-order nonlinear susceptibility χ (2) of an infinite-layer superconductor (Sr 0.7 Ca 0.3 ) 0.95 CuO 2- x to search for the chiral-glass state predicted by Kawamura for a d -wave ceramic. The linear and nonlinear susceptibilities are composed of the measured harmonic susceptibilities up to the seventh-order harmonics. The second-order nonlinear susceptibility χ (2) shows a negative peak but oscillates as a function of temperature near T c . This is not consistent with the prediction based on a chiral-glass transition. The Bean critical-state model explains the observed χ (2) behavior well. It is necessary to avoid the effect of vortex pinning to find a chiral-glass transition.

Analysis of localized vibration of nitrogen in silicon

Abstract Normal modes of local vibration of nitrogen in CZ silicon are analyzed by using the molecular orbital calculation. Wavenumber and dipole are compared to the observed infrared absorption spectra. It is confirmed that the observed peaks at 963 and 764 cm−1 are due to a normal vibration mode of antisymmetric stretch of BF3-type planar four-atom molecule and H2O-type nonlinear three-atom molecule, respectively. Those modes in the N–N–O structure and N–N–O–O structure were identified and the 1026 cm−1 peak was assigned to the Si–O–Si vibration. The results help to establish the total nitrogen concentration in CZ-Si.

Observation of monolayers of a long-chain alkyl dihydrophenazine derivative for a photoelectric molecular device by atomic force microscopy

Abstract We constructed high-quality monolayer Langmuir-Blodgett (LB) films using a novel molecule C37H50N4O4 synthesized by us. This molecule is the long-chain alkyl derivative which has dinitrobenzene moiety (acceptor unit) and dihydrophenazine one (donor unit) bridged by methylene group with constant distance and bond angle to behave as unimolecular photoelectric device with the control of the potential between donor and acceptor subunits. We transferred the monolayer film onto a mica plate and succeeded in getting molecular images by atomic force micoscopy.

Rectifying and Photovoltaic Effects of Organic Hetero-Junction Films Based on Fluorenone Derivatives/Poly (3-Methylthiophene) Prepared by Electrochemical Polymerization and Undoping

The eletrooxidative polymerization of 3-methylthiophene is a convenient method to synthesize an electroconducting polymer poly(3-methylthiophene) (PMeT) in form of a thin solid film incorporated by the counter anion from the supporting electrolytes as a dopant. Electropolymerized PMeT is konwn to be very stable toward oxygen, moisture and temperature in both their doped and undoped state. The thickness of these films, the amount of dopant and the properties of the films can be easily controlled electrochemically[1]. We have proposed dry organic hetero-junction devices based on electron transfer reaction between an organic dye molecule and PMeT [2]. Wet devices based on electron transfer reaction have been already accomplished by many reseachers, but these devices have complex structure. Our dry device is very simple. We expect that these devices should not behave like a conventional semiconductor device base on band theory and that they might be a next coming origanic molecular devices.

Kim Critical State in Twinned YBa2Cu3O7 Single Crystal

We have investigated the role of twin boundaries in a high-quality YBa2Cu3O7 single crystal. The fundamental and harmonic susceptibilities were measured as functions of temperature in a parallel field of H ac+H dc sinωt to the c axis. The results are in excellent agreement with those calculated from the simplified Kim model of critical current density (J c = k/|H i |). This type of field dependence of J c is expected for the weak-link network. Twin boundaries in YBa2Cu3O7 single crystal are likely to act as weak links in a field on the order of 1 mT.

Complex susceptibility of infinite-layer superconductor (Sr0.7Ca0.3)0.95CuO2−x

We studied the complex susceptibility χ′ − iχ″1 and the third-harmonic susceptibility χ′3 − iχ″3, of the infinite-layer superconductor (Sr0.7Ca0.3)0.95CuO2−x by using a two-position susceptometer and compared with that of other oxide superconductors. Both χ′1 and χ″1 are very sensitive to the amplitude of ac magnetic field Hac. This indicates that weak links are dominant in specifying the local magnetic field in the (Sr0.7Ca0.3)0.95CuO2−x samples although they were prepared at 830°C for 4 h under very high pressure (7 GPa). Onset temperature of χ′1 somewhat higher than that of χ″1, indicating the existence of the London-like field penetration regime. The harmonic susceptibility was not well explained by the critical-state model. As predicted from the d-wave symmetry, χ′3 diverges positively in the superconducting transition.