Search

Wireless transmission of QPSK signals at 2 THz has been demonstrated using modulator-based optical combs for the transmitter and hot electron bolometer mixers combined with phase-locked terahertz quantum cascade lasers for the receiver.

Cercospora blight caused by Cercospora asparagi routinely developed on asparagus in certain plastic hoop houses in Hiroshima Prefecture in western Japan every July to November. Stemphylium lycopersici was repeatedly isolated with C. asparagi from the blighted leaves in September 2016 and shown to be another causal agent of the blighting and added as another pathogen causing Stemphylium leaf spot of asparagus.

We have successfully demonstrated the simultaneous phase-locking of two terahertz quantum cascade lasers (THz-QCLs). These phase-locked THz-QCLs are used as local oscillators of a hot electron bolometer mixer (HEBM). The HEBM was simultaneously pumped by two phase-locked THz-QCLs for the multifrequency heterodyne detection of emission line spectra of methanol [CH3OH] at 2 THz using a gas cell. The phase-locking of THz-QCLs with arbitrary frequencies using an optical comb and a photomixer to generate THz references was also demonstrated. An advantage of this technique is that it expands the RF bandwidth of an HEBM.

We are developing a waveguide-type hot electron bolometer mixer (HEBM) at 2 THz. A membrane-type Ni-NbN HEBM device on a Si3N4 substrate was fabricated in a clean room facility of our laboratory. The membrane bridge with a size of W55 μm x L820 μm x t1 μm was supported by a Si frame with a size of 3 mm by 3 mm and a thickness of 200 μm. The device was installed in a waveguide-type mixer mount with a WR-0.51 waveguide and a diagonal horn. The measured receiver noise temperature and IF gain bandwidth are ~1,690 K in DSB and ~4 GHz which must be improved by getting the HEBM device closer to the design. We are also trying to fabricate a mixer block with a corrugated horn at 2 THz.

Fusarium asiaticum was repeatedly isolated from blighted spikes of durum wheat with head blight-like symptoms in our experimental fields in Fukuyama, Hiroshima Prefecture in western Japan, then demonstrated to be pathogenic to the crop. F. asiaticum was not previously reported as causing head blight on durum wheat, so it has been added to the pathogens causing this disease.

A soil inhabiting fungus, Ophiosphaerella korrae (J. Walker & A.M. Sm. bis) Shoemaker & C.E. Babc. has been confirmed to be pathogenic to barley, durum wheat and bread wheat of the major crops (Hong et al., 2018; Tomioka et al., 2019ab). Foliage and spikes of the affected plants early blight with root rot and ripening disorder. In this study, we revealed virulence of the fungus to rice, which is also one of the major crops. When a rice cultivar (cv. Norin No. 22) was grown in pots in artificial climate chambers after being sowed with culture discs (6 mm in diameter) of the fungus (strains MAFF150117 and MAFF150118 from bread wheat and durum wheat, respectively) on synthetic nutrient agar (SNA) (1 disc per seed), growth delay and early foliage blight (including ripening disorder) with rotting of roots and stem bases occurred. Defect rates were 22% and 84% for the plants inoculated with strains MAFF150117 and MAFF150118, respectively. Control plants simultaneously treated with aseptic SNA discs had no symptom. The fungal strains were consistently isolated from all the inoculated plants, but not from healthy controls, demonstrating that the fungal strains were virulent to rice. Additionally, a decrease tendency of grain yield without symptom on foliage and roots was detected on a rice cultivar (cv. Koshihikari that is cv. Norin No. 1 × cv. Norin No. 22) inoculated with strain MAFF150117 in another pot experiment. Ophiosphaerella korrae is also known as a pathogen causing spring dead spot or necrotic ring spot of Bermudagrass (Wetzel et al., 1999ab; Camara et al., 2000; Iriarte et al., 2004; Gullino et al., 2007; Perry et al., 2010; Sasaki et al., 2010), Kentucky bluegrass (Wetzel et al., 1999a; Camara et al., 2000, 2001; Hayakawa et al., 2004; Wong et al., 2015), Louisiana grass (Wetzel et al., 1999a; Camara et al., 2000) and Zoysiagrass (Hayakawa et al., 2004; Tredway and Butler, 2007). We will investigate varietal difference against O. korrae as well as the fungal emergent ecology in the future.[References] Camara et al. (2000) Mycologia 92:317-325 Camara et al. (2001) Mycol Res 105:41-56 Gullino et al. (2007) Pl Dis 91:1200 Hayakawa et al. (2004) J Jpn Soc Turf Sci 33 (Supplement 1):24-25 Hong et al. (2018) Pl Dis 103(1):158 Iriarte et al. (2004) Pl Dis 88:1341-1346 Perry et al. (2010) Mycopathologia 169:395-402 Sasaki et al. (2010) Jpn J Phytopathol 76(3):158 Tomioka et al. (2019a) Abstracts of papers presented at the 44th annual meeting of the pesticide science society of Japan, p 82 Tomioka et al. (2019b) Abstracts of papers presented at the 63th annual meeting of the mycological society of Japan, p 64 Tredway and Butler (2007) Pl Dis 91:1684 Wetzel et al. (1999a) Mycol Res 103:981-989 Wetzel et al. (1999b) Pl Dis 83:1160-1166 Wong et al. (2015) Pl Pathol 44:545-555

To expand the intermediate frequency (IF) band and improve the sensitivity of a hot-electron bolometer mixer (HEBM), we proposed and examined a new HEBM structure using a magnetic thin film. We found that it was possible to suppress the superconductivity of the 5-nm-thick niobium nitride (NbN) thin film by the addition of a 1.8-nm-thick nickel (Ni) thin film. It was also confirmed that the superconductivity disappeared in the Au (70 nm)/Ni (1.8 nm)/NbN (5 nm) trilayer for forming the electrodes of the HEBM. By using the magnetic thin film for the electrodes, we suggested that the superconductivity of the HEBM strip would be affected and that hot spots would be formed near the electrodes. This approach is effective for shortening the hot-electron drift length and will lead to the expansion of the IF bandwidth. We think that the new structure lowers the required local oscillator power and improves the HEBM sensitivity by suppressing the proximity effect under the electrode. The IF bandwidth of the fabricated Ni-HEBMs was evaluated at 1.9 THz. We confirmed that the IF bandwidth expands, and the evaluated bandwidths were in the range of 5.1–5.7 GHz at 4 K. Ni-HEBMs with 0.1-μm strip length were also fabricated and evaluated. The IF bandwidth was about 6.9 GHz at 4 K.

In order to design antennas for mid-infrared (MIR) hot electron bolometers (HEBs), the surface impedance of Au thin films at cryogenic temperatures was evaluated using Fourier transform infrared spectroscopy with a sample cooling system. We fabricated resonator arrays that were constructed by gold thin film strips. The length, width, and thickness of the resonators were set at 1300, 200, and 55 nm, respectively. As the temperature was lowered, the resonant frequency was shifted to the low-frequency side. By fitting the resonant frequency to simulated results, the corrected surface reactance was established for designing MIR nano-antennas. MIR HEBs with a twin-slot antenna were designed and fabricated using the corrected surface impedance. The design frequency was 61 THz. The HEBs were formed as a superconducting strip with Au antennas and electrodes. Here, the superconductivity under the Au electrodes was suppressed by a Ni thin film. For evaluating the mixer properties of the MIR HEBs, measurement setup without beam splitter was constructed. In this setup, local oscillator power was applied directly to the HEB, and we confirmed that the critical current of the HEB can be reduced to be almost zero by the LO irradiation. The HEB responses with clear polarization dependencies were also observed.

Long-term performance testes by CRIEPI (Central Research Institute for Electric Power Industry) on six industrial stacks have revealed an interesting correlation between cathode polarization loss and ohmic loss. To make clear the physicochemical meaning of this correlation, detailed analyses were made on the conductivity degradation of YSZ electrolyte in button cells and then on the ohmic losses in the industrial cells in terms of time constants which are determined from speed of the tetragonal transformation through the Y diffusion from the cubic phase to the tetragonal phase. In some cases, shorter time constants (faster degradations) were detected than those expected from the two-time-constant (with and without NiO reduction effects) model, suggesting that additional ohmic losses after subtracting the contribution from the tetragonal transformation must be caused from other sources such as cathode-degradation inducing effects. Main cathode degradations can be ascribed to sulfur poisoning due to contamination in air in the CRIEPI test site. An important feature was extracted as this cathode degradations became more severe when the gadolinium-doped ceria (GDC) interlayers were fabricated into dense film. Plausible mechanisms for cathode degradations were proposed based on the Sr/Co depletion on surface of lanthanum strontium cobalt ferrite (LSFC) in the active area. Peculiar cathode degradations found in stacks are interpreted in term of changes in surface concentration by reactions with sulfur oxide, electrochemical side reactions for water vapor emission or Sr volatilization, and diffusion of Sr/Co from inside LSCF.

We are developing a hot electron bolometer mixer (HEBM) at 2 THz for the atmospheric observations. We demonstrated an integrated HEB mixer in a cryostat with a cryogenic local oscillator (LO). An alignment of the LO into an HEB mixer was made using a cryogenic rotator. We have detected a beat note using this receiver system at 2 THz.

We have measured the absorption and Raman spectral change induced by the irradiation of e-beam. By the irradiation of e-beam on SWNTs thin films, the intensity of defect related Raman band increase, and the peak energy of IR absorption bands shift to the higher energy side. These results indicate that the origin of infrared band is due to the plasmon resonance of finite-length SWNT. We have estimated the effective tube length and defect density from IR absorption peak energy.

We proposed a terahertz (THz) communication system operating in the 3 THz range using an optical-comb-based THz source and a heterodyne receiver system using a hot electron bolometer mixer (HEBM) along with a quantum cascade laser (QCL) operating at 3 THz for a local oscillator. The THz source is composed of a Mach-Zehnder-modulator-based flat comb generator (MZ-FCG), and a uni-traveling-carrier photodiode (UTC-PD). By using a phase-locked loop (PLL) system, the oscillation frequency of the QCL was highly stabilized. By using this system, generation and detection of coherent THz carriers in the 3 THz range have been demonstrated, which had a phase noise of -70 dBc/Hz at an offset frequency of 100 kHz.

We have demonstrated the phase-locking of a THz quantum cascade laser (THz-QCL) toward the realization of an accurate and stable local oscillator for a high-resolution receiver. The beat note between the THz-QCL and a THz reference was obtained by heterodyne mixing in a superconducting hot electron bolometer mixer (HEBM) and used for stabilizing the phase of 3.1 THz radiation from the THz-QCL. The phase-locked 3.1 THz radiation was fully evaluated with a superlattice harmonic mixer operating in the THz band, and this revealed that the THz-QCL synchronized with the microwave reference with a fractional frequency instability of 3×10 -15 at an averaging time of 100 s, corresponding to a center frequency deviation within 1 mHz, and the imposed phase noises during the heterodyne mixing were negligibly small.

We have proposed using nanoantennas with superconducting detector to improve the response performance of infrared detectors. Dipole nanoantennas that have an NbN load resistance were fabricated to evaluate the antenna properties. By using electromagnetic simulation, the antenna length was set at 2400 nm for the operation around 7-μm wavelength. The antennas were evaluated by using Fourier transform infrared spectroscopy. In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm -1 . The results of the simulation qualitatively agreed with the results of the experiment. The antenna effective area was also evaluated, and the area was estimated to be approximately 5.4 μm 2 at 1420 cm -1 . We have fabricated a prototype of midinfrared (MIR) photodetectors that were formed with 45 dipole antennas with an NbN strip. The antennas were placed within an area of 20 × 20 μm 2 , and they were connected by bias line in series. By the irradiation of MIR (λ = 4.9 μm) light, the responses with high polarization dependence values caused by antenna effect were observed.

To improve the response performance of superconducting infrared detectors, we propose using a photonic antenna with a microdetector in conjunction with a nanostructure. In this paper, we report on the evaluated properties of a slot antenna and microstrip lines for the design of a midinfrared detector with a phased-array nanoslot antenna. We also explain the fabrication process for the detector. The antenna and microstrip line were designed for operation at a wave center near 5 μm. By measuring spectral reflectance characteristics, clear absorption by the antenna and the microstrip resonator was observed. To evaluate the validity of our process, we fabricated a midinfrared detector, which has structures composed of slot antennas and microstrip lines. We confirmed that the superconductivity of the superconducting detector was generally maintained in good condition after the fabrication process of midinfrared detectors.

Ear rot with white or pink mold was found on corn (Zea mays L.). A species of Fusarium, not registered previously as a pathogen causing Gibberella ear rot of corn in Japan, was isolated from the rotted ear. The isolates, identified as F. asiaticum based on morphological characteristics and nucleotide sequences, caused white or pink mold on corn ear after inoculation. Moreover, the 3-acetyl deoxynivalenol chemotype and the nivalenol chemotype were found in the isolates. We propose to include F. asiaticum as one of the pathogens causing Gibberella ear rot of corn in Japan.

In superconducting spintronics, ferromagnetic \pi Josephson junctions are attractive for qubits, cryogenic memory, and phase shifters in logic circuits, offering reduced cell size and superior coherence and scalability. This study demonstrates such junctions based on niobium nitride, which can be grown epitaxially on MgO and is compatible with existing hardware. Its results provide physical insight into superconducting spintronics, as well as an interesting component for applications in quantum information processing.

Simultaneous stabilization of two quantum cascade lasers operated at 2 and 3 THz has been demonstrated by using a multi-frequency THz source based on Mach-Zehnder-modulator-based flat comb generator (MZ-FCG) combined with a programmable optical filter.

We have developed a phase-locking system of a terahertz quantum cascade laser (THz-QCL) using a hot electron bolometer mixer (HEBM) and a terahertz reference such as an amplifier/multiplier chain (AMC) or an optical-comb generator followed by a UTC-PD. We have demonstrated simultaneous phase-locking of two THz-QCLs. The phase-locked THz-QCLs can be used as local oscillators (LOs) of an HEBM. This technique is useful for atmospheric and astronomical observations.

A novel technique that is capable of discriminating absorption variations by measuring angular distribution of diffuse reflected light is presented for semi-infinite two-layered isotropic diffusive media. By using Monte-Carlo simulation, it was found that, in principle, the technique is useful to discriminate absorption variations caused in individual layers. This capability was validated in terms of partial path length as well as spatial sensitivity distribution.

To improve the response performance of superconducting infrared detectors, we propose using a photonic antenna with a micro-detector in conjunction with a nano-structure. In this paper, we report evaluation results that show the basic characteristics of a photonic antenna in the mid-infrared region. The antenna consists of a nano-slot antenna and a thin-film load resistance placed in the center of the antenna. The antennas were designed for operation at approximately several tens of THz by using an electromagnetic simulator. Through measurements of the spectral reflectance characteristics, clear absorptions caused by the antenna properties were observed at approximately 50 THz, and high polarization dependencies were also observed. The results of the simulation qualitatively agreed with the results of the experiment. The effective area of the antenna was also evaluated and was found to be approximately 3.5 μm2 at 54 THz.

Fructans can act as cryoprotectants and contribute to freezing tolerance in plant species, such as in members of the grass subfamily Pooideae that includes Triticeae species and forage grasses. To elucidate the relationship of freezing tolerance, carbohydrate composition and degree of polymerization (DP) of fructans, we generated transgenic plants in the model grass species Brachypodium distachyon that expressed cDNAs for sucrose:fructan 6-fructosyltransferases (6-SFTs) with different enzymatic properties: one cDNA encoded PpFT1 from timothy grass (Phleum pratense), an enzyme that produces high-DP levans; a second cDNA encoded wft1 from wheat (Triticum aestivum), an enzyme that produces low-DP levans. Transgenic lines expressing PpFT1 and wft1 showed retarded growth; this effect was particularly notable in the PpFT1 transgenic lines. When grown at 22 A degrees C, both types of transgenic line showed little or no accumulation of fructans. However, after a cold treatment, wft1 transgenic plants accumulated fructans with DP = 3-40, whereas PpFT1 transgenic plants accumulated fructans with higher DPs (20 to the separation limit). The different compositions of the accumulated fructans in the two types of transgenic line were correlated with the differences in the enzymatic properties of the overexpressed 6-SFTs. Transgenic lines expressing PpFT1 accumulated greater amounts of mono- and disaccharides than wild type and wft1 expressing lines. Examination of leaf blades showed that after cold acclimation, PpFT1 overexpression increased tolerance to freezing; by contrast, the freezing tolerance of the wft1 expressing lines was the same as that of wild type plants. These results provide new insights into the relationship of the composition of water-soluble carbohydrates and the DP of fructans to freezing tolerance in plants.

Fructans are water-soluble fructose oligomers and polymers that are accumulated in many plants, especially the C3 temperate grasses. Fructan accumulation enhances cold and drought tolerance in grasses, and the increased soluble carbohydrates improve forage quality, especially the nutritional value animals can gain from these grasses. The C4 grasses yield high biomass but their inability to accumulate fructans coupled with their low water-soluble carbohydrate (WSC) content are limiting factors for the forage quality of these grasses. The aim of this study was to produce fructans and increase the total soluble sugar content by introducing and expressing fructan biosynthesis genes in a C4 grass, bahiagrass (Paspalum notatum Flugge). Using particle bombardment, we transformed bahiagrass with a wheat-derived sucrose:sucrose 1-fructosyltransferase (1-SST) gene and a sucrose:fructan 6-fructosyltransferase (6-SFT) gene, both of which were regulated by the cauliflower mosaic virus (CaMV) 35S promoter. Transcripts of the 1-SST and 6-SFT genes were detected in six out of 12 transgenic plants carrying both genes. Transgenic bahiagrass plants expressing the 1-SST and 6-SFT genes accumulated 1-kestose and nystose. Although further polymerization of fructose units by 6-SFT activity was not detected in transgenic plants, the total soluble sugar content increased. These results suggest that transgenic bahiagrass plants expressing wheat fructosyltransferase genes created a new metabolic pathway for fructan biosynthesis, which is an important requirement for producing fructans in C4 forage grasses with the objective of increasing the total soluble sugar content of these plants. This is the first report of introducing plant-derived fructosyltransferases with the goal of increasing fructan accumulation in C4 forage grasses.

The power generation properties of a solid oxide fuel cell (SOFC) were studied for various fuel velocities in the anode channel of a tubular solid oxide fuel cell. In order to achieve high power density at low temperatures, a tubular structure and LaGaO 3 -based oxide thin film electrolyte on an anode substrate were adopted. It was found that the tubular SOFC showed a higher voltage at the fuel inlet side with higher fuel velocities. The fuel velocity was increased by inserting a cylindrical-shaped inner rod into the tubular cell. The cell potential was increased from 0.815 to 0.867 V when the rod was inserted at 0.2 A/cm 2 with a fuel utilization ( U f ) of 70%. The impedance analysis suggested that the ohmic loss and diffusion overpotential decreased with increasing fuel velocity. Moreover, the effects of fuel velocity on the current distribution were analyzed by numerical simulation using the “FLUENT” code. The results indicated that the current density at the fuel inlet part increased as the fuel velocity became higher; thus, the current density distribution was dependent on fuel velocity. Higher fuel velocity seems to be effective in removing the water generated in the anode pores in the substrate due to its high fluid shear force. Hence, the hydrogen was easily diffused to the three-phase boundary at the fuel inlet part resulting in the improved current density.

By using frequency-stabilized multi-frequency terahertz (THz) source system composed of a Mach-Zehnder-modulator-based flat comb generator, simultaneous phase-locking of two quantum cascade lasers was successfully demonstrated.

We have proposed using nano-antennas to improve the response performance of infrared detectors. Prototypes of mid-infrared superconducting hot electron bolometer formed by a twin-slot-antenna with an NbN strip were fabricated. By the irradiation of mid-infrared (λ=4.89 μm) pulsed light, clear polarization dependency of responses was observed. When the HEB was biased close to the critical current, the detector output synchronized with the trigger signal was observed. The output waveforms were composed of voltage pulse trains, and the half width of the pulse was evaluated about 0.3 nsec.

We have developed a superconducting low noise heterodyne receiver at 3-THz band based on a hot electron bolometer mixer (HEBM) with a phase-locked THz Quantum Cascade Laser (THz-QCL) as a local oscillator for atmospheric or astronomical observations. We have demonstrated gas cell measurement of emission line spectra of methanol [CH 3 OH] at 3.7-THz band. We have also measured methanol line at 2.07-THz band.

NICT has commenced development of an accurate and stable frequency standard for THz frequency band. We succeeded in phase-locking a single-mode 3THz quantum cascade laser (THz-QCL) to a THz reference. Using the phase-locked THz-QCL and a hot electron bolometer mixer, a THz wave generated by photomixing was evaluated. The result showed that the phase-locked THz-QCL and the optically generated THz wave had the same sability as the microwave references at the 10−15 level and also that imposed noises during heterodyne mixing were negligibly small.

This study discusses the electromagnetic modeling of fatigue cracks in plant environment to improve accuracy of depth sizing with eddy current testing. For the purpose, the factors that influence eddy current signals of fatigue cracks are evaluated. Here, martensitic layer and oxide fillings in fatigue cracks are focused on as influencing factors, and oxides are systematically filled in fatigue cracks by thermal treatment. The measured EC signals change depending on the presence and type of filling oxides. Numerical simulations are conducted to discuss the electromagnetic modeling of cracks with oxide fillings. The types of oxides in the cracks are identified by Raman spectroscopy, and the martensitic layers in vicinity of crack faces are observed by magnetic force microscopy. These results support for the electromagnetic model of environmental fatigue cracks developed in this study.

The basic experimental features of voltage jump V J, between two adjacent branches in stacked Bi2Sr2CaCu2Ox intrinsic Josephson junctions (IJJs) are discussed. The temperature dependence of the V J normalized to its value at 4.2 K, V J( T )/ V J(4.2K), exhibited a downward deviation from a BCS temperature dependence of gap voltage. In this study, we assume that the critical current I c, much smaller than that expected from the Ambegaokar-Baratoff (AB) theory is the intrinsic feature for IJJs. To interpret the V J( T ) characteristics, the linear approximation for the subgap quasiparticle current is also examined and a linear subgap resistance model is proposed as follows: R J,sg( T )= R J,sg(0)/[1+exp( k o( T - T c/2)], where k o is constant. Under these assumptions, the voltage jump is given by V J( T )= R J,sg( T ) x I c( T ). The normalized V J( T )/ V J(4.2) characteristics for all samples with different V J and I c values are well explained using this model.

We fabricated Bi2Sr2CaCu2Ox (Bi-2212) SQUIDs with two stacks of intrinsic Josephson junctions by an acid-treatment process. The stacks were fabricated from a single crystal of Bi-2212. The in-plane loop of a dc-SQUID was surrounded by an acid-treated product, which was produced by immersing the Bi-2212 single crystal in dilute hydrochloric acid (pH=1.65). The critical aspect of this process is that the surrounding acid-treated product (BiOCl) is transparent. The SQUID exhibited a large hysteresis with a ratio of the critical current to the return current of 0.4 at 77 K. Applying a magnetic field modulated the critical current of a dc-SQUID for fields of up to about 10 G. In addition, we fabricated dc-SQUIDs attached to a shunt resistor, which exhibited nonhysteretic current-voltage characteristics. Appling a magnetic field modulated the voltage; the maximum voltage modulation was about 30 μV at 77 K.

To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antenna's center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed.

Bipolar charge transporting block copolymer composing of carbazole and oxadiazole monomers as hole and electron transporting units, respectively, was synthesized by nitroxide mediated radical polymerization. It is found that the current efficiency significantly increased with the addition of the block copolymer in the device based on polymer blend system. AFM measurement revealed that a phase-separated structure in the polymer blend layer changed to suitable morphology in the presence of block copolymer.

Despite their close association with human activities, plant pathogenic fungi have rarely been found in archaeological excavations. We report here that a fungus was closely associated with human activities even in prehistoric times. Sclerotium-like objects were found at historical sites (4000 to 400 BP) on the island of Hokkaido, northern Japan. They were spherical, 0.3-1.0 mm in diameter, and had a medulla and rind. Some had leaf fragments on the surface or a protuberance that resembled emerging sporocarp primordia. These traits indicated that they were sclerotia of the snow mold fungus, Typhula ishikariensis biotype B.

A series of hole and electron transporting random and block copolymers consisting of triphenylamine moiety as a hole transporting unit and oxadiazole moiety as an electron transporting unit have been prepared via a nitroxide mediated radical polymerization. Oxadiazole monomers with t-butyl or trifluoromethyl groups, 2 and 7, respectively, were used for copolymerization. Photoluminescent measurements of polymers revealed that the formation of the exciplex between triphenylamine and oxadiazole units tends to occur in the order of random copolymers, block copolymers, and polymer blends, implying phase-separated morphologies in block or blend systems. The polymers were applied for OLED devices, and we found that the morphology in the polymer layer critically affected device performance. The block copolymer comprising hole and electron transporting units with the composition of 14/86 showed the highest external quantum efficiency over 10%.

The block copolymers consisting of 2,7-dimethoxycarbazole- and oxadiazole-containing segments as hole and electron transporting units, respectively, were synthesized by NMRP manner. OLED devices were fabricated using block copolymer, random copolymer, and polymer blend for matrix of the emitting layer with Ir(ppy) 3 as a phosphorescent dopant in order to investigate morphological effect on the performance. From the finding that the block copolymer system overwhelmed the others in EQE, we assumed that a morphology with dimethoxycarbazole units assembled to the surface of PEDOT:PSS played a considerable role for effective recombination of charges as well as sufficient charge injection into the emitting layer.