Effect of orientational order of tris(8-hydroxyquinolinato)aluminum(III) on electroabsorption

The electroabsorption (EA) spectrum was analyzed in terms of the orientational order of tris(8-hydroxyquinolinato)aluminum(III) (Alq₃) molecules, where the orientational order parameter P_n(cosθ) (θ: the tilt angle of molecule; P_n: nth Legendre polynomial; : thermodynamic average) was used to quantify the anisotropic orientational order of Alq₃. It was shown that the EA intensity is a function of S₁ and S₂ at the modulation frequency ω, whilst it is a function of S₂ at the second-harmonic frequency 2ω. The EA spectrum for the vacuum deposited Alq₃ was obtained from the optical transmittance measurement. The results suggested that the spontaneous polarization of Alq₃ is generated in the evaporated films.     

THERMAL AND FREEZING STRAINS ON A FACE OF WET SANDSTONE SAMPLES UNDER A SUBZERO TEMPERATURE CYCLE

Some laboratory tests showed rather strange hysteresis loops in strain–temperature space, where the strains were measured with a strain gauge on the surface of a wet cubic rock sample under a subzero temperature cycle. This report gives introductory remarks and the first result on a new project launched by the present authors. The project is intended to make clear the major mechanisms responsible for the unexpected hysteresis loops in the strain–temperature diagram, in which an abrupt increase in strains appeared at a halfway point of the cooling process at higher cooling rates. The hysteresis loops suggest that various thermal and mechanical (or physical) phenomena take place within the rock sample; some possible candidates of causes behind the phenomena are discussed and a hypothesis associated with them is proposed. Furthermore, to separate an unexpected part of the hysteresis loop from its “regular” part, thermal strains on the surface of a spherical sample under a temperature cycle are calculated within the framework of linear thermoelasticity. The equivalence between strains on the surface of a cubic sample and that of a spherical one is discussed.     

Probing carrier behavior in organic semiconductor device by electric field induced optical second harmonic generation measurement

Electric field induced optical second harmonic generation (EFISHG) measurement is capable of probing carrier motions in organic devices. By measuring nonlinear polarization induced in active layer of organic devices, the carrier motion is visualized. After summarizing the conventional SHG measurement as a tool for material characterization, we show that the EFISHG is a way for probing carrier motions, and thus extends the potentiality of the conventional SHG measurement. We employ the EFISHG measurement to probe carrier behaviors in double-layer metal-insulator–metal diodes, e.g., Au/TIPS-pentacene/PI/ITO diodes, and demonstrate how the time-resolved SHG measurement probes carrier motion in the diodes, in terms of the I–V and C–V characteristics. Results give an insightful picture on the carrier injection, and the succeeding carrier transport.     

Energetic alignment in nontoxic SnS quantum dot-sensitized solar cell employing spiro-OMeTAD as the solid-state electrolyte

An environmentally friendly solid-state quantum dot sensitized solar cell (ss-QDSSC) was prepared by combining colloidal SnS QDs as the sensitizer and organic hole scavenger spiro-OMeTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene) as the solid-state electrolyte, and the energy alignment of SnS and TiO₂ was investigated. The bandgap of colloidal SnS QDs increased with decreasing particle size from 14 to 4 nm due to an upshift of the conduction band and a downshift of the valence band. In TiO₂/SnS heterojunctions, the conduction band minimum (CBM) difference between TiO₂ and SnS was as large as ～0.8 eV; this difference decreased with decreasing particle size, but was sufficient for electron injection from SnS nanoparticles of any size into TiO₂. Meanwhile, the sensitizer regeneration driving force, that is, the difference between the valence band maximum (VBM) of SnS and the work function of the electrolyte, showed an opposite behaviour with the SnS size due to a downward shift of the SnS VB. Consequently, smaller SnS QDs should result in a more efficient charge transfer in heterojunctions, revealing the advantages of QDs vs larger particles as sensitizers. This prediction was confirmed by the improved photovoltaic performance of ss-QDSSCs modified with SnS nanoparticles, which peaked for 5–6 nm sized SnS nanoparticles due to the balance between electron injection and sunlight absorption.     

Synthesis and properties of macromer-grafted polymers for noncovalent functionalization of multiwalled carbon nanotubes

We prepared macromer-grafted polymers (MGPs) containing suitable polymer side chains for improving solubility and pyrene units for improving adsorption on multiwalled carbon nanotube (MWCNT) surfaces, and demonstrated that these MGPs act as MWCNT solubilizers that improve solubility of MWCNTs in typically poor solvents such as alkanes and that improve flowability of polymer/MWCNT composites. The polydimethylsiloxane (PDMS)-MGPs, synthesized using PDMS macromers and pyrene-containing monomers, improved solubility of MWCNTs not only in chloroform but also in hexane, which is a poor solvent for MWCNTs. Moreover, the addition of PDMS-MGP-adsorbed MWCNTs (MWCNT/PDMS-MGPs) to epoxy resin monomers or polybutylene terephthalate (PBT) drastically reduced the viscosity of the obtained epoxy resin monomer/MWCNT/PDMS-MGP mixtures and PBT/MWCNT/PDMS-MGP composites in comparison to the epoxy resin monomer/MWCNT mixtures and PBT/MWCNT composites, respectively. The viscosity of PBT/MWCNT/PDMS-MGP composites including ?1 vol% of MWCNTs, in particular, was almost equal to that of pristine PBT.     

Trajectory control of controlled-PM linear synchronous motor magnetic levitation vehicle—FEM dynamics simulations and experiments in mass-reduced-control mode

A novel magnetic levitation train system can be constructed by using a long-stator controlled-PM linear synchronous motor having propulsion and attractive-mode levitation functions and minimum loss. Realizing this system requires simplifying manufacture of the long-stator guideway. In the long-stator on the ground, semiclosed large slots are adapted and designed for one-turn coils of a waveform to be easily installed. The large slots cause the PM LSM detent forces to give strong influences on dynamic operations of the running vehicle. A two-dimensional FEM used for the dynamics simulations is capable of precisely analyzing the detent forces produced between the stator teeth and the PMs. This paper presents FEM dynamics simulations and experiments in mass-reduced-control mode of a 1/2 scale model magnetic levitation vehicle supported by small rubber rollers. The simulation model developed here includes the vehicle speed performance, position sensors and drag force due to friction between rubber roller and rail. The detent force problem in propulsion motion is successfully solved by adapting the feedback control of the vehicle propulsion based on the I₁₀-controlled method. The trajectory control is thus accomplished for the vehicle to follow speed and position patterns. The dynamics simulations are verified from the experiments. The simulation program proposed here enables us to investigate the magnetic levitation train system, including LSM design and vehicle dynamic operations.     

Preparation of chiral poly(diacetylene) films from 10,12-pentacosadiynoic acid using circularly polarized light

By irradiating evaporated 10,12-pentacosadiynoic acid (p-DA) monomer film with circularly polarized light (CPL), we prepared chiral poly(diacetylene) [PDA] film. The circular dichroism (CD) was obtained reproducibly, depending on the rotational direction of the CPL. The induced chirality showed the dependence on the substrate temperature used for the preparation of evaporated p-DA monomer films, and it was stable after the transition to red-phase by annealing. Results suggest that side chain of polymer made a significant contribution to the formation of red-phase chiral PDA.     

Carrier injection from polypyrrole coated gold electrode in pentacene field effect transistors

Carrier injection characteristics of conjugated polymer coated gold (Au) electrode were investigated. Using pentacene field effect transistors (FETs) with Au electrodes covered with polypyrrole (PPy) film deposited electrochemically from an aqueous electrolyte solution of HCl or PTSA (1 M) containing pyrrole monomer, transient microscopic optical second harmonic generation (TRM-SHG) measurements were carried out. Transfer characteristics of the transistors suggested that the injection of holes was assisted by the deposited polymer film improving the hole injection efficiency. The TRM-SHG results well supported the results of the electrical measurements, and we anticipate that polypyrrole could be a potential candidate as an electrode material in polymer electronics.