Nobutaka Tanigaki

Two-dimensional array of silver nanoparticles

Abstract The silver salts of fatty acids were thermally decomposed at 250°C in an atmosphere of nitrogen to form silver nanoparticles with a size of 5 nm. The particles suspended in toluene put on a hydrophilic surface of the plasma-polymerized film of osmium tetraoxide and on a water surface to form a two-dimensional array. The nanoparticles repelled each other with a distance of 2.8–3.5 nm depending on the length of the alkyl chain. The surface pressure–area isotherms were measured to confirm the condensation mechanism of two-dimensional arrangement of nano-particles surrounded by alkyl moieties.

Fullerene/cobalt porphyrin hybrid nanosheets with ambipolar charge transporting characteristics.

A novel supramolecular nanoarchitecture, comprising C(60)/Co porphyrin nanosheets, was prepared by a simple liquid-liquid interfacial precipitation method and fully characterized by means of optical microscopy, AFM, STEM, TEM, and XRD. It is established that the highly crystalline C(60)/Co porphyrin nanosheets have a simple (1:1) stoichiometry, and when incorporated in bottom-gate, bottom-contact field-effect transistors (FETs), they show ambipolar charge transport characteristics.

Highly polarized polymer light-emitting diodes utilizing friction-transferred poly(9,9-dioctylfluorene) thin films

Polarized polymer light-emitting diodes (PLEDs) have been constructed utilizing friction-transferred poly(9,9-dioctylfluorene) (PFO) thin films. The friction transfer technique allows oriented PFO to be deposited directly onto an indium tin oxide anode without an alignment layer such as polyimide. Polarized absorption and photoluminescence spectra revealed that the polymer backbones are highly aligned in the friction direction. We fabricated PLEDs consisting of friction-transferred PFO as an emissive layer, vacuum-deposited bathocuproine as an electron transport and hole-blocking layer, and a vacuum-deposited LiF∕Al cathode. Highly polarized blue emission with an integrated polarization ratio of 31 and a luminance of up to 300cd∕m2 was observed from the PLEDs.

Highly efficient polarized polymer light-emitting diodes utilizing oriented films of β-phase poly(9,9-dioctylfluorene)

Uniaxially oriented films of β-phase poly(9,9-dioctylfluorene) (PFO) were realized by a friction-transfer technique followed by thermal annealing and vapor treatments. Absorption and photoluminescence (PL) spectra show the characteristics of β-phase: an additional absorption peak at 433nm and redshifted PL peaks compared with those of the usual nematic (N) phase. We fabricated polarized polymer light-emitting diodes utilizing oriented films of β-phase PFO. Highly polarized β-phase emission with an integrated polarization ratio of 51 was observed from the devices. The efficiency of the devices based on β-phase reached 2.0cd∕A, which is two times higher than that based on N-phase.

Oriented thin films of conjugated polymers : polysilanes and polyphenylenes

Abstract In this paper, preparation of uniaxially oriented films of conjugated polymers, polysilanes and poly(p-phenylenes) (PPP) is investigated. Highly oriented thin films of poly(dimethylsilane) (PDMS) were prepared by the friction transfer method. The properties of PDMS films strongly depend on the preparation temperature. At a temperature higher than 210°C, uniform ultrathin films with extremely high orientation were obtained. It is considered that the friction transfer is related to the disorder (hexagonal) phase of PDMS. Other polysilanes, such as poly(diethylsilane) (PDES), poly(di-n-hexylsilane) (PDHS), poly(di-n-butylsilane) and poly(methylphenylsilane) also afforded oriented films by the same method. Oriented films of PPP were prepared by the friction transfer method. The thin films of the polymers were characterized mainly by ultraviolet absorption spectroscopy. The friction-transferred PDMS and PPP had abilities of orienting other materials. The films of polysilanes, such as PDHS, which were cast on the oriented PDMS from solution, were oriented along the PDMS chain direction. Oriented films of some oligophenylenes were obtained by vapor deposition or cast on the friction-transferred PPP. When the friction-transferred PPP film was immersed into the reaction mixture, a newly oriented PPP film were polymerized on the friction-transferred PPP films.

Polymer field-effect transistors by a drawing method

We demonstrated the polymer field-effect transistors (FETs) utilizing regioregular poly(3-alkylthiophene)s (P3AT) films prepared by a drawing method. The P3AT film exhibited large optical dichroic ratio, which originated in the polymer backbones aligned to the drawing direction. In-plane anisotropy and enhancement of FET characteristics have been observed that are caused by molecular alignment. In the case of poly(3-dodecylthiophene), the hole mobility along the drawing direction was enhanced by a factor of 25 compared with that of spin-coated film.

Highly oriented films of poly(dimethylsilylene) by friction deposition

Highly oriented films of poly(dimethylsilylene) on smooth substrates such as glass and quartz plates were prepared by the friction deposition technique. The structure of the oriented film was characterized by polarized optical microscopy, transmission electron microscopy and polarized ultraviolet absorption spectroscopy. The polymer backbone in the film was parallel to the sliding direction. The orientation was confirmed to be dependent on the temperature of substrates during deposition.

Control of growth mechanism and optical properties of p-sexiphenyl thin films on ionic crystal substrates

Abstract Phenylene oligomers, which are low molecular weight materials of the π-conjugated polymer of poly(p-phenylene), PPP, have been examined for their unique electrical and optical properties. Recently, the vacuum-deposited thin films of oligophenylenes were applied to light-emitting diodes (LED), non-linear optical (NLO) devices, etc. In this study, highly crystalline p-sexiphenyl (6P) thin films were prepared on an ionic crystal substrate (potassium chloride, KCl) by using organic molecular beam deposition technique. The crystal structure, molecular orientation and morphology of thin films prepared at different temperatures were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). It was confirmed that 6P rod-like and planar crystals having the preferential molecular orientations to KCl substrate surface were epitaxially grown. Then, preferential parallel orientations of 6P onto KCl surface formed at low temperatures of 14°C and 50°C and normal ones formed at high temperature of 150°C. Further, it was confirmed that the optical properties of 6P thin films were strongly influenced by the molecular orientations in crystals formed onto KCl substrate surface.

Crystallization Dynamics of Organolead Halide Perovskite by Real-Time X-ray Diffraction

We analyzed the crystallization process of the CH3NH3PbI3 perovskite by observing real-time X-ray diffraction immediately after combining a PbI2 thin film with a CH3NH3I solution. A detailed analysis of the transformation kinetics demonstrated the fractal diffusion of the CH3NH3I solution into the PbI2 film. Moreover, the perovskite crystal was found to be initially oriented based on the PbI2 crystal orientation but to gradually transition to a random orientation. The fluctuating characteristics of the crystallization process of perovskites, such as fractal penetration and orientational transformation, should be controlled to allow the fabrication of high-quality perovskite crystals. The characteristic reaction dynamics observed in this study should assist in establishing reproducible fabrication processes for perovskite solar cells.

One-Dimensional Growth of Phenylene Oligomer Single Crystals on Friction-Transferred Poly(p-phenylene) Film

One-dimensionally oriented thin crystals of a phenylene oligomer, p-sexiphenylene (6P), are grown on the poly( p-phenylene) (PPP) film prepared by the friction-transfer method. The 6P molecules tend to grow epitaxially on the (001) planes of alkali halides and the molecular axis is parallel to the directions of alkali halides. The needle crystals orient along two directions. On the other hand, 6P stands on quartz plates with random orientations. The slender crystals of 6P formed on the friction-transferred PPP on alkali halides and quartz plates confirm that the uniaxial orientation has anisotropic optical properties.