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Strong exciton-photon coupling has been observed in a highly oriented organic single crystal microcavity. This microcavity consists of a thiophene/phenylene co-oligomer (TPCO) single crystal laminated on a high-reflection distributed Bragg reflector. In the TPCO crystal, molecular transition dipole was strongly polarized along a certain horizontal directions with respect to the main crystal plane. This dipole polarization causes significantly large anisotropies in the exciton transition and optical constants. Especially the anisotropic exciton transition was found to provide the strong enhancement in the coupling with the cavity mode, which was demonstrated by a Rabi splitting energy as large as ∼100 meV even in the "half-vertical cavity surface emitting lasing" microcavity structure. [ABSTRACT FROM AUTHOR]

We have fabricated optical devices using an organic semiconductor crystal as an emission layer in combination with a two-dimensional (2D) inorganic diffraction grating used as an optical cavity. We formed the inorganic diffraction grating by wet etching of aluminum-doped zinc oxide (AZO) under a 2D cyclic olefin copolymer (COC) diffraction grating used as a mask. The COC diffraction grating was fabricated by nanoimprint lithography. The AZO diffraction grating was composed of convex prominences arranged in a triangular lattice. The organic crystal placed on the AZO diffraction grating indicated narrowed peaks in its emission spectrum under ultraviolet light excitation. These are detected parallel to the crystal plane. The peaks were shifted by rotating the optical devices around the normal to the crystal plane, which reflected the rotational symmetries of the triangular lattice through 60°. [ABSTRACT FROM AUTHOR]

Vertical-cavity organic lasers are fabricated with melt-grown crystals of a cyano-substituted thiophene-phenylene co-oligomer. Due to lying molecular orientation, surface-emitting lasing is achieved even in the half-cavity crystal grown on a distributed Bragg reflector (DBR) under optical pumping at room temperature. Anticrossing splits in angle-resolved photoluminescence spectra suggest the formation of exciton-polaritons between the cavity photons and the confined Frenkel excitons. By constructing the full-cavity structure sandwiched between the top and bottom DBRs, the lasing threshold is reduced to one order, which is as low as that of the half cavity. Around the threshold, the time profile of the full-cavity emission is collapsed to a pulsed shape accompanied by a finite turn-on delay. We discuss these observed characteristics in terms of a polariton contribution to the conventional photon lasing. [ABSTRACT FROM AUTHOR]

We have achieved to observe vertical cavity surface emitting lasing (VCSEL) from an optically pumped organic single crystal. A vapor-grown thiophene/phenylene co-oligomer (TPCO) single crystal with in-plane polarization component was used as the gain medium in an optical microcavity. Since the top and bottom surfaces of the TPCO crystal serve as high-quality resonators, well-defined Fabry-Pérot resonance is achieved. Furthermore, by using high reflectivity distributed Bragg reflector as the cavity resonator, we have observed lasing emissions with a line width of 0.9 nm and a threshold of ~3 mJ/cm². The VCSEL-type optical feedback configuration demonstrated in this study is expected to be one of the available means to realize the electrically pumped organic laser device. [ABSTRACT FROM AUTHOR]

Autologous bone grafts remain the gold standard for the treatment of congenital craniofacial disorders; however, there are potential problems including donor site morbidity and limitations to the amount of bone that can be harvested. Recent studies suggest that granulocyte colony-stimulating factor (G-CSF) promotes fracture healing or osteogenesis. The purpose of the present study was to investigate whether topically applied G-CSF can stimulate the osteoconductive properties of beta-tricalcium phosphate (β-TCP) in a rat calvarial defect model. A total of 27 calvarial defects 5mm in diameter were randomly divided into nine groups, which were treated with various combinations of a β-TCP disc and G-CSF in solution formor controlled release system using gelatin hydrogel. Histologic and histomorphometric analyses were performed at eight weeks postoperatively. The controlled release of low-dose (1 μg and 5 μg) G-CSF significantly enhanced new bone formation when combined with a β-TCP disc. Moreover, administration of 5 μg G-CSF using a controlled release system significantly promoted the biodegradable properties of β-TCP. In conclusion, the controlled release of 5 μg G-CSF significantly enhanced the osteoconductive and biodegradable properties of β-TCP. The combination of GCSF slow-release and β-TCP is a novel and promising approach for treating pediatric craniofacial bone defects. [ABSTRACT FROM AUTHOR]

The thiophene/phenylene co-oligomers are ranked as a newly occurring class of organic semiconductors. The materials are characterised by that thiophenes and phenylenes are hybridised at the molecular level with their various mutual arrangements. These molecular arrangements produce peculiar morphological features in the solid state and excellent electronic and optical properties. In this review article we outline those characteristics in light of the structure/property relationship with central emphasis upon the crystal structure and its relevance to the leading-edge optoelectronic functionalities. These topics are most suitably approached by device studies including field-effect transistors and light-emitting devices. We describe the device characteristics in close connection with current-injected lasers. [ABSTRACT FROM AUTHOR]

We synthesized a novel small-molecule organic semiconductor, which is soluble in organic solvents at room temperature under normal pressure. We demonstrated that its high-quality crystalline films can be directly grown on substrates using various solution techniques such as solution casting, slow evaporation, and edge casting. We applied crystals to FETs with a bottom- or top-contact configuration, revealing that the carrier mobility ranged from ∼10−4 to ∼10−2 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

We applied the top-gate configuration to organic light-emitting transistors (OLETs) having an organic semiconductor crystal and an aluminum-doped zinc oxide (AZO) layer. The AZO layer was inserted between a quartz substrate and the organic crystal. The devices had the top-contact configuration where gold and an alloy of magnesium and silver were used for the contacts. Silver and Parylene C® were used for a gate contact and a gate insulator for the top-gate configuration, respectively. These OLETs showed more efficient current injection at low voltages than both the devices without a gate contact and the devices having the bottom-gate configuration. The present results indicate that the top-gate configuration is effective for improving the crystal OLET characteristics. [ABSTRACT FROM AUTHOR]

We have directly fabricated a diffraction grating onto platelike single crystals made of an organic semiconducting oligomer by electron beam lithography followed by reactive-ion etching. The decrease in the grating period resulted in photoexcited spectrally narrowed emission peaks related to the first-order diffraction from the crystal edge without outstanding quenching of the crystal. This work is expected to lead to the realization of organic semiconductor lasers. [ABSTRACT FROM AUTHOR]

We improved organic light-emitting transistors (OLETs) characterized by aluminum-doped zinc oxide (AZO) layer insertion between organic and gate insulator layers using organic oligomer semiconductor crystals. (i) To ensure firm contact between the crystal and the AZO layer, we shaped the AZO layer into a rectangle (250 × 500 µm2) and covered it with a vapor-phase-grown crystal. (ii) To enhance contact between the crystal and the AZO layer, we placed the crystal used as a mask on the patternless AZO layer and etched parts of AZO not covered with the crystal with hydrochloric acid vapor. We completed OLETs by forming electron- and hole-injection contacts on the crystal. We modified these contacts with an oxide and/or a carbonate. The devices showed bright light emission from the part of the crystal sandwiched between the electron- and hole-injection contacts located on the AZO layer. [ABSTRACT FROM AUTHOR]

We incorporated a dual-gate structure into organic crystal field-effect transistors (OCFETs). An organic semiconductor crystal was laminated on the comb-shaped interdigitated Cr/Au source and drain that were preliminarily deposited on SiO2 (used as a bottom-gate insulator) covering Si (a bottom-gate contact). On top of the crystal, we successively formed a parylene top-gate insulator and an Au top-gate contact. High hole mobilities were observed by applying voltages to both gate contacts and by applying a certain voltage to the top-gate contact with the bottom-gate contact floated. The drain currents of dual-gate devices are larger than those of single-gate devices with only the bottom-gate contact. Dual-gate OCFETs produce light emissions with the application of alternating-current (AC) voltages to both gate contacts. The dual-gate OCFETs require gate voltages lower than those of single-gate devices. These results indicate that dual-gate structures are useful for realizing high hole mobilities and current-injected light emissions by facilitating carrier injections into the OCFETs. [ABSTRACT FROM AUTHOR]