Search

Even though organic light emitting diodes (OLED) have been achieving commercial successes, their device physics have been under debating. In this article, we develop a junction theory of organic heterojunctions, which describes the carrier accumulation dynamics in them. We derive an equation, which is the counterpart of the Mott-Schottky relation in the metal-semiconductor contact. We will show that the essence of the carrier transport control in organic devices is the control of the internal electric field and therefore the drift motion, whereas that in the semiconductors is the control of the carrier population by shifting the Fermi energy and therefore the diffusion motion. Tang's invention of organic electronic devices with layered ultrathin layers of small organic molecules was a new paradigm of controlling the carrier transport in polaron conductors rather than only a finding of the substitutes of Si semiconductors.

Carrier transport behavior in organic light emitting diode (OLED) is visualized by Modulus spectroscopy using typical layered devices ITO/α-NPD/Alq3/LiF/Al. Two techniques of Modulus analysis, Dynamic Modulus Plot (DMP) and Distributed Circuit Element (DCE) analysis are presented. The hole distribution in NPD layer is visualized by DCE model. The DMP and the DCE model show that the hole and electron transport in NPD/Alq3 devices up to 10 mA/cm2 obey not to a space charge limited current but an Ohmic conduction. It is well known that holes accumulate in NPD even below the turn-on voltage of DC current. This hole accumulation depends on both of NPD and Alq3 layer thicknesses. The voltage dependence is scaled by the Alq3 thickness, whereas the carrier density dependence by the NPD thickness. We propose a model that the accumulated holes are supplied by the thermal activation of the finite number of shallow trap sites localizing at ITO/NPD interface.

The diode operation of OLEDs is characterized by the creation of a conductive space charge region in an insulating neutral dielectric region under the voltage application. It contrasts with the semiconductor diodes, where an insulating space charge region is created in a conductive charge neutral region. We proposed a heterojunction theory based on the quasi-conductor concept to give a unified view, which gave a modified Mott-Schottky equation for OLEDs (Org. Electron. 61, 10 (2018)). Based on this theory, we proposed a new mobility evaluation method using modulus spectroscopy and reported an in-situ simultaneous evaluation of mobilities and carrier densities of carrier transporting materials in a practical OLED configuration (Jpn.J.Appl.Phys. 59(7), 071005 (2020)). However, there were invalid handlings of the boundary conditions. We carefully reconsider the connection of the electric fields through the insulating and conductive regions based on the Dynamic Modulus Plot (DMP) analysis. It is proposed that the density of the accumulated carriers is governed by the fixed interface charges rather than the Activation of Localized Carrier Source (ALCS). Despite the errors in the previous derivation, the revised theory also gave luckily the same expression of mobility as a result, to ensure the validity of the quantitative estimation in the previous report.

A preparation protocol is proposed for a reliable aptamer array utilizing an ink-jet spotter. We accumulated streptavidin and biotinylated-aptamer in this order on a biotinylated-polyethylene glycol-coated gold substrate to prepare an aptamer array. The aptamer array was prepared with an alternate spotting structure where each aptamer spot was placed between reference spots formed with blocking solution thus suppressing contamination from neighboring spots during the blocking and washing processes. Four aptamer spots were prepared in a small area of 1×4.8mm(2) with five reference spots made of blocking solution. We evaluated the thrombin binding ability of the spotted aptamer array using a multi-analysis surface plasmon resonance sensor. We prepared a disposable capillary-driven flow chip designed for on-site measurement (Miura et al., 2010) with our aptamer array and detected thrombin from phosphate-buffered saline at concentrations of 50ngmL(-1) and 1μgmL(-1) (equivalent to 1.35 and 27nM, respectively). A correlation was observed between the refractive index shift and thrombin concentration. This implies that our array preparation protocol meets the requirement for the preparation of a one-time-use chip for on-site measurement.

In-situ impedance spectroscopy (IS) observations of the photoconductivity of the carriers induced by photo-irradiation in organic hetero-junction structured photovoltaic devices are presented. In the IS measurements, the externally applied voltage and the dependence of the light intensity applied to the device were investigated. Analysis of the frequency characteristics which was measured by changing the light intensity shows there is a proportional relationship between the changes in the conductivities of the two components. The mobilities of the CuPc and C60 layers were calculated from the conductivities and were in the orders of 10﹣4 and 10﹣3 cm2/Vs, respectively.

In previous papers, we introduced a novel analysis technique of the impedance spectroscopy of organic light emitting diodes to elucidate their layer-to-layer carrier dynamics and proposed a novel carrier transport model. In this article, we will discuss the carrier dynamics in the voltage region where the layer-to-layer dynamics cannot be distinguished. There appear several specific characteristic features in frequency- and voltage-dependence of complex impedance, the negative impedance, and the diffusion impedance. In the negative bias voltage region, where neither carrier injection nor accumulation occurs, conductance shows ω1/2 frequency dependence. On the other hand, at the higher voltage region where all the semicircles in Cole-Cole plot coalesce, there appear two types of negative impedance, which have ω1/2 and a Debye-like frequency dependence. We consider that the ω1/2 dependences are attributed to the diffusion impedance (Warburg impedance) coupled with and without the interfacial charge transfer reaction. The Debye-like negative impedance is attributed to the carrier trap at the interface of the Alq3 layer.

We present the impedance analysis of multi-layered organic electronic devices. We have developed a new analysis technique, Dynamic Modulus Plot (DMP), which is the combination of C-V measurement and Cole-Cole plot. It is applied to analyze the anomaly of color index change against the current density of a stacked Red/Green phosphorescent Organic Light Emitting Diode (OLED). DMP shows that electrons accumulate in the green emitting layer below the turn-on voltage. The anomaly of the color index is attributed to the quench of the triplet excitons by the electrons accumulated in the green emitting layer. The color index anomaly becomes less when the accumulation is reduced by optimizing the host material of the green emitting layer. We demonstrate that DMP is a useful method to investigate the layer-to-layer carrier dynamics of separated function devices.

Background: Different perforation rates for cervical pedicle screws by disease are expected in relation to bone quality and pedicle morphology; however, no report comparing pedicle screw perforation rate by disease had previously been published. This study investigated the perforation rates of pedicle screws inserted to cervical pedicle by disease and vertebral level using a CT-based navigation system. Materials/Methods: Fifty-three patients who underwent cervical pedicle screw insertion using CT based navigation system were studied. Diseases included rheumatoid arthritis (RA) (24 cases), destructive spondyloarthropathy (DSA) (10), cervical spondylotic myelopathy (CSM) (9), spine tumor (6), and cervical spondylotic myelopathy associated with athetoid cerebral palsy (CP) (4). Screw perforation rates for cervical pedicle screws were studied. Major perforation was defined as perforation 50% of screw diameter or more. Results: Major perforation rate by disease from C3 to C7 was as follows: spine tumor (0/24, 0%), RA (2/59, 3.4%), DSA (3/65, 4.6%), CP (2/20, 10.0%), and CSM (6/40, 15.0%). There were no clinically important complications such as vertebra arterial injury, spinal cord injury, or nerve root injury caused by any screw perforation. Major perforation rate by vertebral level was: C2(2/30, 6.7%), C3(4/49, 8.2%), C4(6/43, 14.0%), C5(1/32, 3.1%), C6(1/41, 2.4%), and C7(1/45, 2.2%), showing highest rate for C4, followed by C3. Conclusions: Cervical pedicle screw perforation rate by disease was higher in CSM compared to RA and DSA. The perforation rate by vertebral level was higher for C4 and C3, in this order.

SUMMARY We carried out degradation analysis of a blue phosphorescent organic light emitting diode by both impedance spectroscopy and transient electroluminescence (EL) spectroscopy. The number of semicircles observed in the Cole-Cole plot of the modulus became three to two after the device was operated for 567 hours. Considering the effective layer thickness of the initial and degraded devices did not change by degradation and combining the analysis of the Bode-plot of the imaginary part of the modulus, the relaxation times of emission layer and hole-blocking with electron transport layers changed to nearly the same value by the increase of the resistance of emission layer. Decay time of transient EL of the initial device was coincident with that of the degraded one. These phenomena suggest that no phosphorescence quenching sites are generated in the degraded device, but the number of the emission sites decrease by degradation.

We demonstrate a remarkable improvement in the waveguiding characteristics of silicon wire waveguides, and show their application to functional optical devices. Applying a novel spot-size converter consisting of an ultrathin silicon taper and a SiON waveguide, coupling losses between silicon wire waveguide and optical fiber were greatly reduced to just 0.5 dB/coupling. Propagation losses were also reduced to less than 3 dB/cm, by smoothing the surface of the waveguide core. Some functional devices, such as photonic crystals, ring resonators, and lattice filters, were tested and showed superior optical characteristics. Enhancement of nonlinear phenomena due to a high power density effect was also observed. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(3): 42–55, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecjb.20210

This work presents our recent progress in the development of an Si wire waveguiding system for microphotonics devices. The Si wire waveguide promises size reduction and high-density integration of optical circuits due to its strong light confinement. However, large connection and propagation losses had been serious problems. We solved these problems by using a spot-size converter and improving the microfabrication technology. As a result, propagation losses as low as 2.8 dB/cm for a 400/spl times/200 nm waveguide and a coupling loss of 0.5 dB per connection were obtained. As we have the technologies for the fabrication of complex, practical optical devices using Si wire waveguides, we used them to make microphotonics devices, such as a ring resonator and lattice filter. The devices we made exhibit excellent characteristics because of the microfabrication with the precision of a few nanometers. We have also demonstrated that Si wire waveguides have great potential for use in nonlinear optical devices.

Lead intake from possible exposure routes among children residing in the Tokyo Metropolitan Area was estimated. Lead concentrations in house dust samples collected from the houses of the children and those in 24-h duplicate diet samples of the children were determined. The daily lead intake was estimated by multiplying the lead concentrations in the house dust, diet, soil and ambient air (the latter two were from the literatures) by the corresponding intake and/or inhalation rates, and summing all of the products. Bioaccessibility tests were performed on the house dust, soil and diet samples to determine the lead uptake level. Children residing in the Tokyo Metropolitan Area were estimated to be exposed to 21.5 μg of lead on a daily basis, with a maximum intake of up to 70.4 μg. The average weekly intake per kg body weight for a 5-year-old Japanese child was found to be 8.0 μg/kg bw/wk, which is below the Provisional Tolerable Weekly Intake (PTWI) of 25 μg/kg bw/wk. However, the maximum weekly intake was found to be 26 μg/kg bw/wk. House dust and soil ingestion can be the predominant routes of exposure to lead among children in Japan, and the source(s) of lead in such media must be specified to reduce the lead intake level of the children.

In this paper, a likelihood normalization method for verifying a speaker based on an HMM is proposed. In the proposed method, a speaker background model used in likelihood normalization is synthesized from the HMMs of neighboring speakers on the basis of local acoustic information expressed by the phonemes, states, and distributions of the HMMs. By this method, the statistical intermodel distance between the speaker and the background speaker in the acoustic space can be minimized and effective normalization capable of absorbing variations in the likelihood can be realized statistically. When likelihood normalization by a cohort speaker model generated on the basis of the distribution (the proposed method) was compared with the past method of using the cohort speaker model selected for speakers in speaker verifying tests using the telephone voices of 640 people (open tests without time differentials using 320 speakers and 320 impersonators), the equal error rate (EER) was reduced from 5.27% to 1.76% by the proposed method. In addition, when likelihood normalization combining a speaker-independent model and a cohort speaker model generated on the basis of the distributions was compared with a method using only a speaker-independent model in texts using the telephone voices of 100 people (open tests with a time differential of 3 months using 24 speakers and 75 impersonators), the EER was reduced from 3.41% to 2.51%, confirming the efficacy of the proposed method. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(4): 47–57, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10045

Two-dimensional photonic crystals (2D-PhCs) on oxide can be easily incorporated into photonic integrated circuits. Although an asymmetrical structure (air/PhC/oxide) is advantageous in terms of ease of fabrication, it has been pointed out that such a structure may have no photonic band gap (PBG). To clarify the characteristics of the asymmetrical structure, we calculated the band structure using the three-dimensional (3D) FDTD method and measured the transmission characteristics of a fabricated 2D Si-PhC on oxide. The calculations show that we can use a quasi-PBG even in an asymmetrical structure when the PhC thickness satisfies the single-mode condition. The measured transmission characteristics correspond to the calculated band structure and reveal the existence of a quasi-PBG. These results show that the asymmetrical 2D Si-PhC-on-oxide structure can be applied to various optical devices.

We propose two photonic crystal structures that can be created by combining nanolithography with alternating-layer deposition. Photonic band calculations suggest that a drilled alternating-layer photonic crystal combining two-dimensional (2D) alternating multilayers and an array of vertically drilled holes may achieve a full photonic bandgap. In addition, a 3D/2D/3D cross-dimensional photonic crystal, which sandwiches a 2D photonic crystal slab between three-dimensional (3D) alternating-layer photonic crystals, should provide better vertical confinement of light than a conventional index guiding slab. Fabrication techniques based on existing technologies (electron beam lithography, bias sputtering, and low-pressure ECR etching) require very few process steps. Our preliminary fabrication suggests that, by refining these technologies, we will be able to realize photonic crystals.

The broadband Raman conversion of femtosecond-light pulses to the anti-Stokes side is demonstrated. A 130 fs light pulse from a Ti:sapphire-based regenerative amplifier system is divided into two light pulses. They are focused on a SrTiO3 crystal with a finite cross angle. Over 24 higher-order coherent anti-Stokes Raman scattering signals are observed, which cover from near infrared to green. These higher-order coherent anti-Stokes Raman scattering (CARS) signals come from the resonant excitation of two-phonon waves. The results offer a possibility of an all solid-state anti-Stokes Raman shifter covering an extremely broadband tunable range.

A newly developed technique for high voltage surface potential imaging having high resolution capability using Scanning Electrostatic Force Microscope(SEFM) is described. It can measure both electrostatic surface potential distribution of several hundred volts on the dielectric film and topography independently and simultaneously in high resolution of some tens of μm, in the air, quantitatively and without affecting charge distribution. The result of measuring surface potential distribution formed by spark discharge on a dielectric film is shown and compared to the results by a conventional electrostatic voltmeter and by toner method.

The purpose of this study was to compare the effectiveness of dental checkups incorporating tooth-brushing instruction (TBI) with that of conventional dental checkups. A team consisting of one dentist and three dental hygienists saw an average of 60 employees per day on-site at an airline company. The patient's teeth were stained with a disclosing tablet and the results recorded on a Plaque Control Record (PCR) chart. The patient was then given TBI. After recording the relevant data, including TBI given and PCR scores, the charts were stored. Checkups were performed in a total of 3,854 patients between 2001 and 2005 and changes in annual scores investigated. In addition, annual shifts in mean score in patients receiving checkups over all five years were compared with those in patients receiving checkups for the first time in each of the five years. The mean score in patients receiving a checkup in 2001 was 35.1%, declining by 2.6 points to 32.5% in 2005. Among patients receiving checkups over all five years, the mean score in 2001 was 34.0%, declining by 11.2 points to 22.8% in 2005. Over the five-year period, the mean score in patients receiving checkups was 34.1%. In patients receiving checkups over all five years, the proportion with PCR scores

The authors point out that a TEOS/O/sub 3/-oxide layer used as an interlevel dielectric enhances hot-carrier degradation of MOSFETs due to the water-related components (water and/or silanols) contained in the layer. This results mainly from enhanced hot-electron trapping in the gate oxide and also from interface-trap generation. By applying an ECR-SiO/sub 2/ layer under the TEOS/O/sub 3/-oxide layer, tolerance against hot-carrier damage is improved to the level of MOSFETs without the TEOS/O/sub 3/ oxide. From ESR measurement results, it is found that the spin density of the ECR-SiO/sub 2/ film under the TEOS/O/sub 3/ oxide is two orders lower than that of the ECR-SiO/sub 2/ film only. It is suggested that the dangling bonds in the ECR-SiO/sub 2/ film effectively trap water diffusing from the water-containing overlayer. >

The second-order Raman bands of SrTiO(3) are excited under two-color cross-beam configuration using femto-second laser pulses. Raman-inactive one-phonon waves are generated by the coherently excited large amplitude two-phonon wave. The one-phonon waves are observed as a train of visible light spots, the frequency steps of which are coincident with the frequencies of the one-phonon modes. In order to understand the mechanism, a model of three-wave interaction among one two-phonon wave and two one-phonon waves is proposed.

We report the observation of four-wave mixing phenomenon in a simple silicon wire waveguide at the optical powers normally employed in communications systems. The maximum conversion efficiency is about -35 dB in the case of a 1.58-cm-long silicon wire waveguide. The nonlinear refractive index coefficient is found to be 9×10-18 m2/W. This value is not negligible for dense wavelength division multiplexing components, because it predicts the possibility of large crosstalk. On the other hand, with longer waveguide lengths with smaller propagation loss, it would be possible to utilize just a simple silicon wire for practical wavelength conversion. We demonstrate the wavelength conversion for data rate of 10-Gbps using a 5.8-cm-long silicon wire. These characteristics are attributed to the extremely small core of silicon wire waveguides.

A broadband spectral comb is generated around the third harmonics of incident light with the nondegenerate, impulsively stimulated Raman scattering technique using ultrashort light pulses. The comb has a spectral width of more than 4000 cm(-1), and its envelope becomes smooth as the light powers are increased. It consists of discrete lines, the spacing of which is equal to the frequency of the Raman-active phonon mode, even though the frequency of the phonon mode is far smaller than the frequency difference between the two incident light pulses. The multiline structure is generated with multiwave mixing by exchange of the impulsively stimulated phonon among the signals.

Multicolored light pulses are generated with high efficiency in the visible region by injecting two ultrashort light pulses with infrared frequencies into orthoferrite ${\mathrm{YFeO}}_{3}$ single crystals. The spectrum of the multicolored light pulses consists of third harmonics of two beams and higher-order coherent anti-Stokes Raman scattering. This is generated by the excitation of a phonon in the crystal resonating to the frequency difference of two incident beams. The spectrum of the emitted light signals covers a frequency region wider than $5000{\mathrm{cm}}^{\ensuremath{-}1}$ with the same frequency separation equal to that of the coherently driven phonons.

We experimentally demonstrate the structural tuning of the waveguiding modes of line defects in photonic crystal slabs. By tuning the defect widths, we realized efficient single-mode waveguides that operate within photonic band gap frequencies in SOI photonic crystal slabs. The observed waveguiding characteristics agree very well with 3D finite- difference time-domain calculations. The propagation loss of the line defect waveguides is experimentally determined to be 6 dB/mm. In addition, we measure group velocity dispersion of line defects by using Fabry-Perot resonance of the sample. Extremely large group dispersion is observed, and the traveling speed of light is reduced down to 1/100 of the light velocity in air.

We propose a new three-dimensional photonic crystal structure or drilled alternating-layer photonic crystal (DALPC), which can be fabricated by a combination of the deposition of alternating layers of dielectric films and one-time dry etching. Our band calculation predicts that the DALPC has a photonic band gap (PBG) in all directions. We fabricated a Si/SiO2 DALPC by electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. We measured the light transmission of the DALPC sample in both the in-plane and vertical directions. We observed a transmission minimum around the 1.4-µm-wavelength for all measured directions and TE/TM polarizations, which demonstrated a potential of the DALPC as a three-dimensional PBG material.

Low-energy photoelectron spectroscopy combined with photoelectron yield spectroscopy was developed to investigate the buried organic interfaces in the practical device thickness. Ultralow background signal and charging durability were achieved by utilizing monochromatic low-energy photons. C60/rubrene/Au interfaces were studied as a prototypical system of organic solar cells. The low density of gap states was detected in the rubrene film and a small feature due to the C60-induced morphological change was observed in the C60/rubrene interface.

Progress in sidewall morphology smoothing of Si wire waveguides by thermal oxidization was observed using a focused-ion-beam (FIB) transmission-electron-microscopy technique. The roughness of Si∕SiO2 interface was drastically reduced with increasing oxidation time and temperature. Deformation of the cross-sectional profile of the waveguides was observed with secondary electron images of scanning FIB irradiation. The initial rectangular profile is transformed due to stress concentration at the rectangle corners at oxidation temperatures of 900 and 1000°C. In contrast, at 1100°C, the profile maintains the original rectangular profile due to the stress release by the viscous flowing of SiO2. These results indicate that the optimum oxidation condition for the Si wire waveguide has been found, which provides an extremely smooth sidewall without deformation of the cross-sectional profile.

Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for 1.5-microm infrared systems. The waveguide's low-loss bends with 2.5-microm radius reduce the total length of the filter to less than 100 microm and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.

The water‐blocking effect of plasma chemical vapor deposition (CVD) SiO2 film is investigated. Using electron spin resonance measurements, point defects in the electron cyclotron resonance (ECR) plasma CVD SiO2 used in this work can be identified as dangling bonds belonging to Si atoms. The defect density is reduced by capping water‐containing film on it, suggesting that the defect is capable of trapping water. The hot‐carrier degradation in a metal‐oxide‐semiconductor (MOS) device is successfully prevented when ECR plasma CVD SiO2 is used as a water‐blocking layer that keeps water in the overlayer from diffusing to the gate oxide. This result indicates that ECR plasma CVD SiO2 effectively blocks water due to the water trapping ability of the Si dangling bonds.

A new three-dimensional photonic crystal structure is designed to simplify fabrication. A calculation of the band structure predicts that this photonic crystal has a complete photonic band gap in all directions. The entire three-dimensional periodic structure, except for the vertically drilled holes, is formed by automatic shaping during bias sputtering deposition. The fabrication technologies used to construct this photonic crystal are electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. Our preliminary fabrication reveals that each technology can be controlled well enough to lead to the creation of a photonic band gap material for an optical communication wavelength.

A nondispersive vacuum ultraviolet atomic absorption spectrophotometer for mercury has been developed. A mercury electrodeless discharge lamp (EDL), which provided a significant radiant flux at both the main resonance line at 185.0 nm and the resonance-intercombination line at 253.7 nm, was utilized with a nitrogen-purged system and a CsI phototube. Because of its spectral response, the CsI phototube allowed it to measure effectively the mercury atomic absorption only at 185.0 nm. The dependence of the atomic absorption sensitivity on the EDL operational power was similar to that in a dispersive system. Since the nondispersive system allowed operation of the EDL with lower power compared with the dispersive system, better sensitivity could be obtained owing to less self-absorption of the resonance line. Furthermore, the low fluctuation noise of the light source led to a lower detection limit. The sensitivity and detection limit were 0.077 and 0.014 ng, respectively, and the relative standard deviation for 0.05 ng mercury was at most about 5.8%.

Results Four authors of academic hospitals designed and are now performing on this trial supported by Stryker Japan after permission of Institutional Review Board of each hospital. Candidates are female patients with an age between 10 to 19 with adolescent idiopathic scoliosis which are planned to have surgical treatment by segmental pedicle screw system. Curve profile should be Lenke type 1 to 3, over 45 degrees of the main curve by the Cobb method. We get written informed consent from patients and parents. Exclusion criteria are patients who cannot understand Japanese, patients who have had previous spinal surgery, patients who are pregnant, patient who have allergy to nickel, chrome, or titanium, etc. Randomization to cobalt-chrome rod or titanium rod is performed with a web-based register adjusted by age, the Cobb angle of the main curve in standing, that in active bending, and the Risser grade. We set a total of 80 cases after power calculation by past reports. Placement of pedicle screws and techniques of correction maneuver are to be reported. Radiographic parameters by X-ray, CT scan, and MRI at preoperative time, post operative time, and one-year after surgery are to be analyzed. Questionnaires of patient-reported outcome by SRS-22, SF-12, and SJ-27 (AIS-specifc outcome made by Japanese Scoliosis Society) are asked to fill at preoperative time, six-month after surgery, and one-year after surgery.