Search

We investigate the effects of volatile additives in solutions used to prepare thin-film transistors (TFTs) of regioregular poly(3-hexylthiophene) (P3HT). We use the additives trifluoromethylbenzene (TFMB) and methylcyclohexane (MCH) because they are poor solvents for P3HT. The additives improve the performance of the resulting TFTs when the boiling point (Tb) of the major solvent, carbon tetrachloride, is lower than that of the additive. The maximum mobility is (4.0 ± 0.9) × 10-2 cm2V-1s-1, which is 6.1 times larger than that of TFTs prepared without TFMB or MCH added to the solution; the on/off ratio and the subthreshold slope were also improved. The relative Tb of the solvent and the additive affected the film formation with the amount of TFMB or MCH remaining at the final stage of thin film deposition influencing the precipitation of P3HT aggregates. [ABSTRACT FROM AUTHOR]

The authors report that thermal treatment effect on various N,N′-dialkyl-3,4,9,10-perylene tetracarbxylic diimides [PTCDI-Cn, alkyl-dodecyl (n=12), butadecyl (n=14), octadecyl (n=18)] thin-film transistors (TFTs) depends on the substituted alkyl chain length. It is clearly demonstrated that there are two kinds of molecular movements during the thermal treatment on PTCDI films; molecular rearrangement in the same layer and molecular migration from the lower layer to the upper layer. The former is directly related to the grain growth and can be controllable by applying an external electric field. The latter is also related not only to the grain growth but also to the formation of cracks between grains. These two movements show opposite dependence on the alkyl chain length during the thermal treatment; the former is more active in longer alkyl chain, but the latter in shorter one. However, they also have opposite effect to TFT performance, and PTCDI films with longer alkyl chains have great advantage on TFT performance for the thermal treatment. Consequently, PTCDI-C18 TFTs show the highest electron mobility as large as 1.2 cm2/V s after the thermal treatment at 140 °C. [ABSTRACT FROM AUTHOR]

To directly observe the behavior of single molecules in real time and space, the x-ray methodology, diffracted x-ray tracking, has been proposed. This system monitors the spots of a diffracted x ray from individual nanocrystals, which are labeled with the individual single molecules. To operate single molecular detection systems with x rays, it is necessary to fabricate dispersive nanocrystals and observe the diffracted spots from the nanocrystals. We succeeded in fabrications of dispersive one-dimensional (Mo/Si) nanocrystals with diameters of approximately 25 nm using reactive ion etching. Furthermore, we monitored well-defined diffracted x-ray spots from Mo/Si nanocrystals (2.5 bilayers: Mo/Si/Mo/Si/Mo, d-space = 5.0 nm) in real time (2.0 ms). [ABSTRACT FROM AUTHOR]

Reports on the effect of low energy helium[sup+] ion-beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Measurement of film thickness on each sample in a region bombarded by ions and a region shadowed from ions; Effect of ion current density upon pyrene film structure; Chemical reaction induced by ion irradiation.

Provides information on a study concerning the fluorescence characterization of polymeric materials, methyl methacrylate films using excimer laser as an ablation source. Experiment; Effect of ablation on properties of polymer films; Fluorescence dynamics.

We found a tunable lasing action of dye-doped glass films using a distributed feedback (DFB) resonator composed of gold (Au) nanoparticles. The Au-DFB resonators having various periodic spacings of 400-600 nm were fabricated by photoreduction of chloroauric ions doped in silica/ titania sSiO2 /TiO2d sol-gel films using two-beam interference of a He-Cd laser. After lamination of a SiO2 /TiO2 film containing Rhodamine B sRBd, the device was pumped with a frequency-doubled yttrium aluminum garnet laser. As compared to the amplified spontaneous emission [full width at half maximum (FWHM) ~20 nm] from a RB-doped film without DFB, the laminated device indicated feedback-gained narrowing of the emission (FWHM~1 nm). Moreover, their peak wavelengths were shifted according to the tuned spacing of the Au-DFB resonator. [ABSTRACT FROM AUTHOR]

The authors have investigated the direct relationship between the fluorescence lifetime (FL) and the transient photoluminescence (PL) response of organic materials to examine the applicability of organic light-emitting diodes as light sources for optical communications. Transient PL responses of organic materials with different FLs were measured as a frequency dependence of PL intensity pumped by a modulated violet laser diode. The authors have revealed that the cutoff frequency of PL intensity is significantly related to FL of an organic film. The -3 dB cutoff frequency of 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DSB) has reached about 160 MHz, which is much higher than that of other organic materials. This is because the FL of DSB is shortest among all the organic materials used in this study. [ABSTRACT FROM AUTHOR]

We have demonstrated that single crystals of a thiophene/phenylene co-oligomer [α, ω-bis-biphenyl-4-yl-terthiophene (BP3T)] show interesting photonic aspects: (1) the self-waveguided amplified spontaneous light emissions with a comparable low threshold of 8 μJ/cm2 to other optimized organic solid-state laser systems, and (2) the laser oscillation based on the optical self-confinement effect in the crystals. We have also presented electroluminescence from the crystals based on bipolar injection and the crystals’ tolerance for intense current driving. These achievements strongly imply that BP3T crystals are a promising candidate for organic laser diodes. [ABSTRACT FROM AUTHOR]

Photopumping measurements for the dilute thin films of the representative proton-transfer laser dye, 2-(2-hydroxyphenyl)benzothiazole (HBT) revealed that it exhibited better stimulated-emission performance, especially at the high doping level of 26 wt %. This suggests that HBT has an ability to form high gain media, in addition to an inherent potential for widely tuning gain wavelength. Both are advantageous for overcoming the polaron-absorption problem that is a major obstacle to making organic laser diodes. [ABSTRACT FROM AUTHOR]

Emission gain narrowing has been observed for single crystals of a thiophene/phenylene co-oligomer. The hexagon flake crystals were placed on a quartz substrate with the crystals’ face in close contact with the substrate plane. These crystals were irradiated with a N[sub 2] laser with a 337.1 nm wavelength at a repetition rate 10 Hz that tuned its intensity to 100–1150 μJ/cm[sup 2]. The emission gain narrowing takes place at 21490 (465.4 nm) and 20220 cm[sup -1] (494.5 nm) with increased intensities, with their half width at half maxima reaching ∼50 cm[sup -1]. On the basis of the nonlinear relationship between the emission peak intensities and the laser light intensity, the gain narrowing has been attributed to the amplified spontaneous emission. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied transparent organic light-emitting diodes, which had a transparent top electrode deposited by sputtering, for possible application to a transparent light-emitting display. In the fabrication of a transparent electrode on an organic layer, steps must be taken to reduce the damage incurred by the organic layer during the sputter deposition process. We report the results of our study where we found that we could reduce the damage to the organic layer by suppressing the temperature rise of substrate resulting from the intermittent plasma irradiation. We also found that a thin film of metal acethylacetonate complexes [Mt(acac)[sub 2]] is useful as a buffer layer to prevent an underlying emission layer from incurring damage in the sputter process. In previous reports, a thin film of copper phthalocyanine (CuPc) was used as an electron injective buffer layer. However, the absorption of the CuPc Q bands at λ=620 and 665 nm decreased the total optical transmission of the device. Transmittance in the visible region of our device reached ∼90%, because Mt(acac)[sub 2] has no absorption properties that reduce the transmittance of visible light. The device using Ni(acac)[sub 2] as a buffer layer showed better electron injection properties and luminance of 1500 cd/m[sup 2] than the one using CuPc. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines 200 nanometer x 2 millimeter array of organic light-emitting diodes (OLED) and their electroluminescent (EL) properties. Fabrication of lines and spaces using the phase shift mask; Observation of anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED.

We have evaluated a synthetic red fluorescent dye, 6-methyl-3-[3-(1,1,6,6-tetramethyl-10-oxo2,3,5,6-tetrahydro-1H,4H,10H-11 -oxa-3a-aza-benzo[de]anthracen-9-yl)-acryloyl]-pyran-2,4-dione (AAAP), as a dopant for an organic light-emitting diode (LED). Bright emission of a good red (maximum luminance: 5600 cd/m2, chromaticity coordinates: x=0.63, y=0.36) was obtained. The device consisted of ITO/TPD(50 nm)/Alq[sub 3] doped with AAAP(1.5 mol %,15 nm)/bOXDF(20 nm)/Alq[sub 3](25 nm)/Mg:Ag (ITO: indium tin oxide, TPD: N, N[sup ′]-diphenyl- N,N′-di(3-methylphenyl)-1, 1′biphenyl-4,4′-diamine, Alq[sub 3]: tris (8-hydroxyquinolinato)-aluminum (III), bOXDF:2,2-bis[5-(4-biphenyl)-1,3,4-oxadiazole-2-yl-4,1 -phenylene]-hexafluoropropane). The bands of fluorescence of the Alq[sub 3] host and of absorption of the AAAP dopant overlap in an advantageous way, and insertion of the bOXDF layer between the emission layer, doped with AAAP, and Alq[sub 3] layer, made for a device with good properties. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report an organic solid-state distributed feedback laser consisting of an organic active layer and a Bragg grating without morphological change. The active layer consists of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostryl)-4H-pyran as a laser dye, tris(8hydroxyquinoline) aluminum as a host, and poly(methyl methacrylate) as a binder. The threshold and linewidth of the laser are 400 μJ/cm2 and 1.5 nm, respectively. With this laser, the Bragg grating exists out of the active layer and the grating surface is flat, which are very important for device fabrication and electric driving of the laser. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electroluminescent (EL) behavior has been evaluated in a cell which contained molecular dispersion of 1,4-bis(N,N-diphenylaminophenyl-1,3,4-oxadiazolyl)benzene (OXD) in a low-molecularweight liquid crystal, 4-octyloxy-4[sup ′]-cyanobiphenyl (8OCB). EL emission was observed above the temperature where the OXD/8OCB mixture showed a liquid-crystalline phase. Furthermore, we fabricated an EL device which consisted of interdigital electrodes coated onto a glass substrate. It was found that the EL emission from the device was highly polarized. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have succeeded in fabricating a thick-film organic light emitting diode having a doped hole transport layer (DHTL). The basic cell structure is anode DHTL/emitter layer/cathode. The DHTL is composed of a hole transporting polycarbonate polymer (PC-TPB-DEG) and tris(4-bromophenyl)aminium hexachloroantimonate (TBAHA) as a dopant. As an emitter, we used tris(8-hydroxyquinoline) aluminum (Alq). With a 650-nm-thick DHTL, the device showed considerable reduction in cell resistance compared with an anode/nondoped HTL/Alq/cathode device with the same HTL thickness. Although the electroluminescent quantum efficiency &Fgr;[sub L] was rather low in the doped device, we should be able to increase it by interposing a thin tetraphenylbendidine (TPB) layer between the DHTL and the emitter layer while keeping the driving voltage low. The anode/DHTL (650 nm)/TPB(50 nm)/Alq(50 nm)/cathode showed luminance of more than 4004 cd/m[sup 2] at 10.0 V and 220 mA/cm[sup 2]. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]