Search

This paper reports the application of InGaN films to a polymer electrolyte cells (PEFC) stainless steel (SS) separator for the first time. Using MOCVD, InGaN films with In content of 0-1 are grown at 600 °C on sapphire and stainless steel substrates. Sputtered TiN is used as a buffer for the InGaN growth on stainless steel. For InGaN on sapphire substrates, electrical resistivity and dissolution rate in a H2SO4 solution at 60 °C are measured, and films with In content in the range 0.2-0.5 are found to have both high electric conductivity and high corrosion resistance. The anti-corrosive properties of In0.3Ga0.7N/TiN/SS structures are also confirmed by the inductively coupled plasma spectrometry (ICP) chemical analysis of the H2SO4 solution in which the In0.3Ga0.7N/TiN/SS samples are dipped for 100 h. The levels of both Ga and In atoms are under the detection limits. The I-V characteristics of a single cell using an In0.3Ga0.7N/TiN/SS separator is measured in comparison with those using bare stainless steel or carbon separators. The performance of the cell with the In0.3Ga0.7N/TiN/SS separator is much superior to that with a bare stainless steel. Compared with the cell using the carbon separator, the cell using the In0.3Ga0.7N/TiN/SS separator has a little larger ohmic loss (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on a theoretical analysis of DC and RF performances of a novel In0.1Ga0.9N/InN HEMT. A very high cut-off frequency and attractive DC characteristics have been predicted. A simple analytical model is used to explain the DC characteristics. The cut-off frequency which has been found more than 0.6 THz for a gate length of 0.1 µm is explained with low-field mobility. The maximum drain current and transconductance have been found around 1000 mA/mm and 625 mS/mm, respectively. Similar analysis have been performed for the conventional AlGaN/GaN HEMT and compared with the proposed InGaN/InN HEMT. The predicted results are found to be in good agreement with previously published results. The calculated results show that InN-based HEMT has very high cut-off frequency and transconductance when compared with the conventional GaN-based HEMT for the same gate length. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Activation of glia has been observed in various neurodegenerative diseases. Excessive production of nitric oxide (NO), as a consequence of increased inducible nitric oxide synthase (iNOS) in glia, contributes to the neurodegeneration. The enhancement of intracellular stresses such as oxidative stress and endoplasmic reticulum (ER) stress has been also implicated in several neurodegenerative disorders. During a search for compounds that regulate ER stress, a dibenzoylmethane derivative, 2,2′-dimethoxydibenzoylmethane (DBM 14-26), was identified as a novel neuroprotective agent (Takano et al. [2007] Am. J. Physiol. Cell Physiol. 293:C1884–C1894). In the present study, we found that DBM 14-26 protected cultured astrocytes from H2O2-induced cytotoxicity at lower concentrations than antioxidants, GSH and N-acetyl cysteine. DBM 14-26 prevented the productionof reactive oxygen species in the cells exposed to H2O2 as evaluated by fluorescent intensity of dichlorofluorescein. Further examination revealed that DBM 14-26 inhibited lipopolysaccharide (LPS)-induced iNOS expression and NO production. DBM 14-26 suppressed LPS-stimulated nuclear factor-κB (NF-κB) activation evaluated by p65 immunostaining and gel retardation electrophoresis. These results indicate thatDBM 14-26 protects astrocytes from oxidative stress and suppresses astrocytes activation via inhibition of NF-κB activation. Functional regulation of astrocytes by DBM 14-26 could be a therapeutic candidate for the treatment of neurodegenerative diseases. © 2011 Wiley-Liss, Inc.

Polarity control of MOVPE InN on sapphire (0001) was investigated. Two kinds of polarity InN films on sapphire substrate by MOVPE have been prepared by controlling the substrate nitridation process and/or the LT-GaN buffer annealing process. Surface of the nitrided sapphire is a crucial factor in determining the polarity of InN film. N-polarity InN film was grown on the 1000 °C-nitrided substrate without LT-GaN buffer; while In-polarity InN film was grown on the 900 °C-nitrided substrate. In the case of InN growth with a LT-GaN buffer, buffer annealing is a crucial issue in determining the polarity of InN film. N- and In-polarity InN films were obtained on the long-time-annealed buffer and the short-time-annealed buffer, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports the crystallographic degradation of MOVPE InN during the growth. Using FWHMs of X-ray rocking curve, tilt ((0002)) and twist ((10-10)) angle distributions are evaluated and effects of the major growth parameters, such as growth temperature, growth time and with/without GaN buffer in the degradation, are revealed. With increasing either thickness of grown InN or growth temperature up to 600 °C, the tilt angle distribution is markedly increased, indicating the crystallographic degradation of grown films. The use of a GaN buffer reduces such degradation. Since the twist angle distribution is scarcely changed by such growth parameters, the destruction of InN crystals during growth and annealing is concluded to be anisotropic. The trends of the crystallographic degradation revealed here are in good agreement with those for the electrical and optical degradation previously reported. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An experimental study has been made on the correlation between the fabrication conditions for 3c-SiC/Si (111) template and electrical and crystallographic properties of InN films grown on the templates. The template has been prepared by C+-ion implantation into Si (111). Although the 3c-SiC layers show a large (170 arcmin) FWHM of XRC (111) diffraction, InN films with a considerably small (about 50 arcmin) FWHMs for (0002) and (10-10) diffraction are grown on the layers. A lower implantation dose brings a smaller XRC FWHMs for 3c-SiC. The post implantation annealing is found to be effective to improve the quality of the 3c-SiC layer and, therefore, to improve the quality of InN films. Hall mobility in InN is found to be markedly increased by decreasing FWHM of InN (0002) diffraction. The best data of carrier concentration and Hall mobility are 6.2×1018 cm–3 and 630 cm2/Vs, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An InN film is grown using an ArF excimer laser assisted-MOVPE where a high NH3 decomposition rate condition is realized because of the effective dissociation of NH3 by the ArF laser. Grown films show unusual phenomena such that amount of metallic In involved in a grown InN film is increased with increasing NH3 flow rate during the growth. Through the annealing of grown InN films in the NH3 flow, it is revealed that the photolysis of NH3 by the ArF laser irradiation causes the decomposition of InN and, as a result of it, the formation of In droplets. The direction of the source gases injection during the growth, perpendicular or parallel to the substrate surface, has a significant effect on the formation of metallic In. Compared with the perpendicular injection, the parallel injection can suppress the formation of In droplets and allow us to grow InN at a higher temperature. A high density of atomic hydrogen (H) generated by the photolysis of NH3 seems to take nitrogen atoms away from InN, leaving metallic In on the surface. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on the catalyst-assisted metal-organic vapor phase epitaxy (CA-MOVPE) growth of InN with an independent control of catalyst temperature. When the catalyst temperature is increased above the growth temperature of InN, the grain size becomes large and full width at half maximum (FWHM) of X-ray rocking curve (XRC) is drastically decreased The migration of precursors is highly enhanced and the crystal quality is improved by CA-MOVPE with an independent heating system of the catalyst. This CA-MOVPE system will open the possibility of the growth of high-quality InN and In containing alloys especially with the higher In content (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on the MOVPE growth of InN and InxGa1-xN with x up to ∼0.4 on AlN/Si (111) substrates. Good quality InN films are grown after a pretreatment of the substrate surface at 1000 °C in NH3. While pretreatment of the substrate surface in N2results the In droplet formation. Single-crystalline InxGa1-xN films with x up to ∼0.4 are successfully grown on Si (111) substrates without phase separation and metallic In incorporation by changing the growth temperature and TMI/(TMI+TEG) molar ratio. Comparative study between the AlN/Si (111) and GaN/α-Al2O3(0001) substrates shows that the quality of InN, GaN and InGaN with low In contents depends on the quality of the underlying layer. While the quality of InGaN at the intermediate In content range hardly depends on of the underlying layer/substrate. These works will allow us towards the fabrication of the future InGaN-Si tandem cell using MOVPE. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-temperature (∼600 °C) MOVPE growth of GaN is investigated using a catalyst to enhance NH3 decomposition rate. As a catalyst, Ir is employed in this study. Significant differences in electrical properties between samples grown with and without catalyst are observed. The sample grown at 600 °C without catalyst shows a high resistivity (106 Ωcm) and a low carrier concentration (1011 cm-3). The low carrier concentration is seemed to be due to the compensation by the carbon impurity known as a deep level acceptor, since the activation energy for such sample is closed to that for carbon-doped GaN. The employment of the catalyst results in the improvement of crystalline quality of low-temperature grown GaN. As a result of this study, we have found that the catalyst-assisted MOVPE has significant effects on the suppression of impurity (mainly carbon) incorporation and the improvement of crystalline quality of GaN grown films. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This report shows the effect of Cp2Mg supply on MOVPE growth behavior of InN. At low growth temperature (∼600 °C), the formation of adducts occurred, which degenerates the crystal quality. With increasing the growth temperature, the adduct formation was suppressed because the decomposition of Cp2Mg was enhanced and thus the incorporation of carbon into the film was suppressed. The use of Cp2Mg during InN growth increases the growth rate in the lateral direction. Non-doped InN film grown on GaN buffer has an In-face of the top side. On the other hand, the inversion domains seems to be formed in the highly Mg-doped InN. Tilt distribution decreases from 65 to 30 arcmin with the increase of Cp2Mg/TMI molar ratio 0 to 0.06. The donor is produced in highly Mg-doped MOVPE-grown InN (Cp2Mg/TMI molar ratio > 0.005). Therefore, the effect of Cp2Mg supply on MOVPE growth behavior of InN is found to improve a macro-scale crystal quality but also produces the donor (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports the deterioration of nitrogen (N)-face of wurtzite InN in the NH3 ambient near the growth temperature. Using an atmospheric-pressure MOVPE system, both In-polar and N-polar InN are grown by controlling the nitridation temperature of a sapphire substrate. The N-face has a much larger etching rate (40 nm/h) compared with that of the In-face (14 nm/h). From the PL measurement from the front surface and the rear surface through the sapphire substrate, it is shown that the N-face of both In- and N-polar films shows a marked intensity reduction and a large blue shift of PL spectrum. These facts show that the N-face of InN is very unstable and deteriorates in the NH3 ambient. The deterioration becomes severer at a temperature higher than 550 °C. Since such a PL shift is due to the Burstein-Moss effect, the result indicates that the high density of donor-type defects are preferentially introduced on the N-face of InN. Further investigations will be needed to clarify whether such instability of N-face in the NH3 ambient is related to the poorer quality of MOVPE InN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have found that the material quality of MOVPE InN can be markedly improved after the annealing in the air at around 300 °C. By the annealing in the air, carrier concentration is reduced by about one order of magnitude. In accordance with the carrier reduction, PL intensity is increased and PL peak energy is shifted to the lower energy side by about 0.06 eV for the film annealed for 3 h. The reduction of carrier concentration is also conformed by the shift of LO phonon-plasmon coupled mode in the Raman spectrum. The FWHM of the E2 (high) mode is decreased, indicating that the crystalline quality is slightly improved by the annealing. Since the FWHM of X-ray rocking curve is not changed after the annealing, the improvement by the annealing is concluded not to be in macroscopic scale but microscopic scale. No improvements are found for the samples annealed in the N2 flow. No data that show the chemical oxidation of InN are also found. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

To determine the extent of brain damage in children with spastic diplegia, we analyzed the true midsagittal magnetic resonance imaging findings for the corpus callosum in 43 children with spastic diplegia and in 69 neurologically normal children. In the normal children, the thicknesses of the genu, midbody, splenium and the entire corpus callosum were found to increase with age, while the ratios of the thickness of the splenium and of the midbody to the length were constant, regardless of age. Both ratios were significantly reduced in diplegic children and the ratio for the splenium was highly correlated with the extent of motor impairment. Assessment of the morphometric changes in the corpus callosum using magnetic resonance imaging may contribute to the determination of the extent of brain damage in diplegic children.

This paper reports the effect of oxygen supply on MOVPE InN growth at high temperature (∼650 °C). It is noted that the deterioration occurs near the interface, and InN film becomes porous layer during growth. When we supply oxygen in the reactor (O2/NH3 ratio is 0∼0.018%), atomic hydrogen is reduced by reacting oxygen and the porous layer is decreased. Our study reveals that the porous layer is produced by atomic hydrogen. It is important to reduce the atomic hydrogen in the reactor. The oxygen suppresses the deterioration of the film during growth. The carrier concentration increases with the increase of oxygen supply. However, not only oxygen but also defect density due to oxygen is responsible for a higher carrier concentration. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper indicates an evidence for the deterioration of the MOVPE InN during the growth at high temperature (∼650 °C). It is noted that the deterioration occurs near the interface and InN film becomes porous layer during the further growth. The porous layer has high electron density. The rate-limiting process of N-face InN decomposition depends on atomic hydrogen. The atomic hydrogen produced by the decomposition of NH3 is responsible for the deterioration of InN film. The crystal quality of InN improves with decreasing the porous layer which is important for MOVPE InN. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, we demonstrated that antibodies reactive with a common beta 1 subunit (CD29) of the VLA family of antigens could synergize with CD3 but not CD2 in inducing CD4 cell proliferation in a serum-free culture system. The extent of activation was similar to that obtained when CD4 cells were cultured with anti-CD3 plus fibronectin. The proliferative response induced via the CD3-CD29 pathway was associated with the interleukin (IL) 2 autocrine pathway, including IL 2 production and IL 2 receptor expression. Specifically, cross-linking of VLA-5, but not other members of the VLA family of antigens with the CD3 molecule induced strong CD4 cell activation. However, cross-linking of CD3 with other cell surface antigens such as CD4 did not induce CD4 cell activation in this serum-free culture system. The above results strongly suggest that the VLA/CD29 family of antigens may play an important role in regulating CD4 T cell activation via the CD3-T cell receptor pathway.

The synthesis of a number of ring-substituted phenyl isopropenyl ketones and their polymerization with styrene is reported. The ultraviolet absorption spectra of the polymers are analogous to those of ring-substituted acetophenones and valerophenones. The quantum yields of the Norrish type II photoreaction were estimated in 1,2-dichloroethane solution at 364 nm by automatic viscometry. These quantum yields are comparable to those of substituted butyrophenones and valerophenones, in that relatively high quantum yields were obtained for the unsubstituted and p-chloro-substituted compounds with low yields for p-amino and p-hydroxy compounds. The p-nitro-substituted compound gives no type II reaction, presumably because the excitation becomes localized on the nitro groups which photolyzes by a mechanism which does not involve chain scission. The implications of these studies on possible applications to photoimaging are discussed.