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The Keio Twin Research Center (KoTReC) was established in 2009 at Keio University to combine two longitudinal cohort projects — the Keio Twin Study (KTS) for adolescence and adulthood and the Tokyo Twin Cohort Project (ToTCoP) for infancy and childhood. KoTReC also conducted a two-time panel study of self-control and psychopathology in twin adolescence in 2012 and 2013 and three independent anonymous cross-sectional twin surveys (ToTcross) before 2012 — the ToTCross, the Junior and Senior High School Survey and the High School Survey. This article introduces the recent research designs of KoTReC and its publications.
In this paper, we discuss the characteristics of the InGaP/GaAs heterojunction phototransistors (HPTs) before and after the electrical stress at room temperature and assess the effectiveness of the emitter-ledge passivation. Although an electrical stress given to the phototransistors by keeping a collector current density of 37 A/cm2 for 1 hour at room temperature was too small to affect the room-temperature common-emitter current gain and photocurrent of both HPTs with and without the emitter-ledge passivation, they showed a significant decrease at 420 K due to the room-temperature electrical stress. Nevertheless, the room-temperature common-emitter current gain and photocurrent of the HPT with the emitter-ledge passivation were still higher than those of the HPT without the emitter-ledge passivation. The effectiveness of the emitter-ledge passivation against the electrical stress was more significant than that on the current gain in the dark. In addition to the electrical stress experiment, for a potential application of the InGaP/GaAs HPTs in space, we will irradiate the HPTs with 1-MeV electrons at the Japan Atomic Energy Agency. Both current gain and photocurrent decreased significantly after the electron irradiation. In contrast to the electrical stress, the damage due to the high-energy electron irradiation is a bulk-related phenomenon, and the emitter-ledge passivation does not seem to suppress the degradation.
The Keio Twin Research Center has conducted two longitudinal twin cohort projects and has collected three independent and anonymous twin data sets for studies of phenotypes related to psychological, socio-economic, and mental health factors. The Keio Twin Study has examined adolescent and adult cohorts, with a total of over 2,400 pairs of twins and their parents. DNA samples are available for approximately 600 of these twin pairs. The Tokyo Twin Cohort Project has followed a total of 1,600 twin pairs from infancy to early childhood. The large-scale cross-sectional twin study (CROSS) has collected data from over 4,000 twin pairs, from 3 to 26 years of age, and from two high school twin cohorts containing a total of 1,000 pairs of twins. These data sets of anonymous twin studies have mainly targeted academic performance, attitude, and social environment. The present article introduces the research designs and major findings of our center, such as genetic structures of cognitive abilities, personality traits, and academic performances, developmental effects of genes and environment on attitude, socio-cognitive ability and parenting, genes x environment interaction on attitude and conduct problem, and statistical methodological challenges and so on. We discuss the challenges in conducting twin research in Japan.
Effect of oxygen to nickel molar ratio (O2/Ni) on the crystallinity of atmospheric pressure metal organic chemical vapor deposition (APMOCVD) grown NiO at 500°C is reported. X-ray diffraction (XRD) analysis including grazing incident angle θ of 0.6°, θ-2θ, ɸ and rocking curve scan are employed for crystallographic characterization. Furthermore, surface roughness is studied by atomic force microscopy (AFM). No evidence of diffraction peaks in X-ray grazing incident angle measurement confirms that all the grown NiO films are well oriented along a certain direction. θ-2θ scan results further indicate that the samples are highly oriented only along  direction on (0001) sapphire substrates. The analysis of full width at half maximum (FWHM) of rocking curve scan of (111) plane shows that higher O2/Ni ratio results in better crystallinity. The best crystallinity is achieved with FWHM as low as 0.106° at (111) rocking curve scan corresponding to 82.57nm grain size. AFM measurement shows that NiO films grown with higher O2/Ni ratio have smoother surface morphology.
The metallic nickel (Ni) deposited on an n-Si substrate with resistivity of 4 – 6 Ω∙cm was oxidized by the ultra-violet (UV) oxidation technique to form a p-NiO/n-Si heterojunction diode. The rectifying current-voltage (I-V) characteristic confirmed formation of a pn junction. The capacitance-voltage (C-V) characteristic further identified an abrupt p+n junction between NiO and n-Si. The photocurrent increased with the increased wavelength of laser under illumination of the diode. The voltage-dependent photocurrent suggests that the carriers generated in the depletion region of Si was effectively collected but not outside the depletion region. A low diffusion length of holes was attributed to Ni diffusion in Si caused by the substrate heating during the UV oxidation.
We have successfully formed high-quality nanoporous NiO films by the hydrothermal technique and observed intense ultraviolet (UV) luminescence at room temperature. The SEM image reveals nanoporous NiO films with pore diameters from 70 to 500 nm. The results of XRD, Micro Raman and FTIR characterizations confirm the cubic structure of NiO. The optical band gaps estimated from the absorption spectrum are found to be 3.86 and 4.51 eV. The former is similar to that of bulk NiO, while the latter is much higher than that of bulk NiO. The increased band gap was attributed to the quantum confinement in the NiO nanocrystals, which may be present in the nanoporous NiO film. The room-temperature photoluminescence (PL) spectrum shows a peak of intense luminescence at 3.70 eV and several other peaks in the UV and near-UVwavelength regions. The intense UV luminescence at 3.70 eV was associated with the near band-edge emission and the others with defect-related emission. The high-quality wall of nanoporous NiO with a large surface-to-volume ratio provided the intense UV emission.
Photosynthetic membrane proteins convert solar light into chemical energy in
a significantly high efficiency. Up-to-date reports of the photosynthetic
bacterium suggest that such effective light conversion is due to the energy
transfer between two light-harvesting (LH) protein complexes that are
patterned in two dimensions. In this report, LH complex isolated from
Rb. sphaeroides was immobilized onto a patterned gold
surface with self-assembled monolayers (SAMs) and lipid bilayers at two main
objectives: (1) micron-scale patterning of LH complex, and (2) prevention of
quenching for pattern observation.
The reliability of InP/InGaAs heterojunction bipolar transistors (HBTs) with highly carbon-doped and zinc-doped InGaAs base layers grown by metal-organic vapor phase epitaxy has been investigated. The Raman spectroscopy reveals that the post-growth annealing for the carbon-doped InGaAs base improves the crystallinity to become as good as that of the zinc-doped InGaAs base. However, the photoluminescence intensity remains lower than that of the zinc-doped InGaAs even after the post-growth annealing. The current gains of the carbon- and zinc-doped base InP/InGaAs HBTs are 63 and 75, respectively, and they are affected by the base crystallinity. After the 15-min current stress test, the current gains decreased by 40 and 3% from the initial current gains for zinc- and carbon-doped base HBTs, respectively, are observed. These results indicate that the carbon-doped base HBT is much more reliable than that of zinc-doped base HBT, though it has a lower current gain.
Tin-dioxide (SnO2) ultra-small nanorods (UNR) have been successfully synthesized using the novel micellar technique. From transmission electron microscopy, the average diameter and length of the UNRs are estimated to be 1.3 nm and 5.0 nm, respectively. The crystal structure of the SnO2 UNRs was found to be tetragonal from the glazing incidence x-ray diffraction. The optical band gap estimated from the absorption spectrum is blue-shifted by 1 eV from that of bulk (3.64 eV). The photoluminescence spectrum shows two groups of peaks each with several fine peaks, one in the wavelength range of 270 – 370 nm and the other in the range of 380 – 500 nm which are due to the strong quantum confinement effect.
Capacitance-Voltage (C-V) hysteresis was observed in the Metal-Oxide-Semiconductor (MOS) capacitor with silicon nanocrystals. The MOS capacitor was fabricated by thermal oxidation of Si nanocrystals, which were deposited on an ultra-thin thermal oxide grown previously on a p-type Si substrate. The Si nanocrystals were deposited by the gas evaporation technique with a supersonic jet nozzle. The size uniformity and the crystallinity of the Si nanocrystals are found to be better than those fabricated by the conventional gas evaporation technique. The C-V hysteresis in the MOS capacitor is attributed to electron charging and discharging of the nanocrystals by direct tunneling though the ultra-thin oxide between the nanocrystals and the substrate. The flat-band voltage shift observed during the C-V measurement depends on the size and density of the nanocrystals and also on the magnitude of the positive gate bias for charging. The retention characteristic is also discussed.
The ultrafine particles with diameters in the order of 10 nm were deposited onto Si and SiO2 substrates by evaporation of Ge in a pure hydrogen atmosphere. Although the as-deposited Ge ultrafine particles do not show any detectable luminescence, they emit blue light after being exposed to the UV light for a long time. The blue light is strong enough to be seen with the naked eye even under a room light. The photooxidation, unique to the Ge ultrafine particles, has been identified as a major factor contributing to the blue light emission.
The oxygen-containing silicon (Si) ultrafine particles have been deposited onto Si and SiO2 substrates by evaporation of Si powder in an oxygen-containing argon atmosphere. The asdeposited Si ultrafine particles exposed to the ultraviolet light emit blue light, which is strong enough to be seen with the naked eye. The blue light emission is associated with a broad photoluminescence (PL) peak at 2.7 eV, which is attributed to radiative recombination via a radiative recombination center. The proposed model with one radiative and two nonradiative recombination centers well explains the temperature-dependent PL peak intensity.
The Raman scattering from LO phonon–plasmon coupled (LOPC) mode in heavily carbon doped p–type InxGa1–xAs grown by metalorganic molecular beam epitaxy (MOMBE) was studied experimentally. Only one LOPC mode appears between the GaAs–like and InAs–like LO modes was observed. The peak position of the LOPC mode is near the GaAs–like TO mode frequency, and is not sensitive to the hole concentration. The intensity of the mode increases with increasing the carrier concentration while the two LO modes decrease and become unvisible under the higher doping level. The hole concentration dependence of the linewidth and intensity of the LOPC mode is very similar to that in p–type GaAs. It was shown that the plasmon damping effect plays a dominant role in the p–type doping case.
We have successfully grown undoped GaAs of very high resistivity on Si by MOCVD. The back and side edges of the Si substrate were coated with a Si3N4/SiO2 stacked layer to suppress Si incorporation Into GaAs by the gas phase transport mechanism during MOCVD growth. A 3- μm-thick GaAs layer was grown on this Si substrate at 750 °C in an atmospheric MOCVD reactor using the two-step growth technique. The electron concentration measured by a Polaron C-V profiler is 3xl0l4 cm−3, as low as that of GaAs grown on GaAs substrate, up to the depth of 1.5 μm from the surface.
We discuss room temperature CW operation of AlGaAs/GaAs SQW lasers and GaAs MESFETs with good pinch-off characteristic on SiO2 -back coated Si. The all-MOCVD-grown,SQW laser on Si with thermal-cycle annealing, which has the EPD of 1.5 × 107 cm−2, has the threshold current as low as 55 mA (1.41 kA/cm2) under CW operation at room temperature. The pinch-off and the sidegating effect characteristics of GaAs MESFETs on Si have been improved by using SiO2-back coating of Si and higher growth temperature. The maximum transconductance of 160 mS/mm has been obtained for the MESFET with a 2.5 × 15 µm gate. The main origin of sidegating effect associates with the channel layer-undoped GaAs layer beneath it interface. The SiO2 -back coating is found effective to obtain a lower background electron concentration in undoped GaAs layer and to control doping of the active layer in GaAs/Si.
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