3,448 research outputs found
Dramatic improvement of performance of visible hydrogenated amorphous silicon carbide based p-i-n thin-film light-emitting diodes by two-step hydrogenation
No full textThe effects of two-step hydrogenation on the performance of visible p-i-n thin-film light-emitting diode (TFLED) have been investigated. The TFLEDs were fabricated by a photochemical vapor deposition (CVD) method, A hydrogenation process was performed in two steps: One was an in situ hydrogenation process using a photo-CVD system and the other an ex situ hydrogenation process using a plasma apparatus after TFLED fabrication. It was found that the performance of visible a-SiC:H-based p-i-n TFLEDs was drastically improved by a two-step hydrogenation process. The threshold voltage decreased by about 3 V, the electroluminescence peak shifted towards a shorter wavelength, from 680 to 590 nm, add the brightness increased from 1.3 to 128 cd/m(2). (C) 1996 American Institute of Physics
Stabilization of approximately feedback linearizable systems using singular perturbation
No full textWe consider a stabilization problem of approximately feedback linearizable systems. We introduce a perturbation parameter by applying high-gain feedback and use both the feedback linearization method and the singular perturbation method for the controller design. Through this, we can overcome the rigorous conditions of the feedback linearization method and can reduce the dimension of the slow model of the singularly perturbed system
Hydrogen passivation of visible p-i-n type thin-film light-emitting diodes
No full textThe effects of hydrogen passivation on the performance of visible p-i-n thin-film light-emitting diodes (TFLEDs) have been investigated. The TFLEDs were fabricated using a photochemical vapor deposition method. The hydrogenation process was performed using an inductively coupled plasma system at a rf power of 800 W and a process pressure of 20 mTorr for 30 min. It was found that hydrogenation dramatically improved the performance of these TFLEDs. The threshold voltage was decreased by about 1 V, the electroluminescence (EL) peak shifted from 704.5 to 689 nm, the EL intensity increased by a factor of 3, and the brightness-increased from 1 to 24 cd/m(2) by 24 times. (C) 1996 American Institute of Physics
Ex situ hydrogen passivation effect of visible p-i-n type thin-film light-emitting diode characteristics
No full textThe effect of ex situ hydrogen passivation process on the performance of visible hydrogenated amorphous silicon carbide (a-SiC:H)-based p-i-n type thin-film light-emitting diodes has been investigated. An ex situ hydrogen passivation process dramatically improved the device performance; that is, the threshold voltage decreased by about 5 V, the electroluminescence (EL) intensity increased by a factor of about 3, and the EL peak shifted toward a short wavelength from 700 to 600 nm, resulting in an increase of the brightness from 1 cd/m(2) to 35 cd/m(2). This improvement of device performance is caused by the passivation of interface states in the p/i and i/n interfaces as well as midgap states in the luminescent active intrinsic a-SiC:H layer by hydrogen atoms. A process time dependence of the ex situ hydrogen passivation effect on the device performance also has been studied. (C) 1997 American Institute of Physics
Hydrogenation time dependence of a-SiC:H-based P-I-N thin film visible light-emitting diode characteristics
No full textThe hydrogenation time dependence of hydrogenation effects on the performance of a-SiC:H-based p-i-n thin film light-emitting diodes (TFLEDs) in the visible range has been investigated. It was found that hydrogenation markedly improved the device performance, and that increasing the hydrogenation time beyond a saturation point degraded the device performance; that is, as compared with the performance of a TFLED hydrogenated for a short time (similar to 15 min), the threshold voltage increased slightly, the EL peak shifted towards a longer wavelength, and the brightness decreased. In particular; after hydrogenation for 45 min, the brightness decreased to 15 cd/m(2)
Local structure of LiB3O5 single crystal from Li-7 nuclear magnetic resonance
No full textThe local structure of LiB3O5 single crystal was investigated with Li-7 (I=3/2) nuclear magnetic resonance measurements. We observed four different spectra, which could be divided into two groups corresponding to two kinds of lithium atoms, Li-A and Li-B, lying at crystallographically equivalent sites and magnetically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature and are e(2)qQ/h=143+/-1 kHz and eta=0.6+/-0.1 for Li-7. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have the same principal values of the electric field gradient tensor, but different orientations, and originate from magnetically inequivalent sites. Also, the Li-7 spin-lattice relaxation rate was measured, and the measured relaxation rate was found to be proportional to the temperature. The temperature-dependent single phonon process is considered to be more effective than the Raman process for nuclear quadrupole relaxation. In addition, we discuss the correlation between the asymmetry parameter and the largest nonlinear optical coefficient. (C) 2003 American Institute of Physics
ACOUSTIC CHARACTERISTICS OF AN EXPANSION CHAMBER WITH CONSTANT MASS-FLOW AND STEADY TEMPERATURE-GRADIENT (THEORY AND NUMERICAL-SIMULATION)
No full textAn empirical relationship between optical properties and the nuclear quadrupole coupling parameters in the boron sites in the nonlinear optical CsLiB6O10
No full textThe rotation patterns of the nuclear magnetic resonance of B-11 (I = 3/2) in a nonlinear optical CsLiB6O10 single crystal were measured in three mutually perpendicular crystal planes. We observed sixteen different spectra which could be divided into two groups corresponding to two kinds of boron atoms, B(1) and B(2), having different boron-oxygen rings and lying at crystallographically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature for the first time. For the 4-coordinated B(1), e(2)qQ/h = 0.23 +/- 0.03 MHz and eta = 0.456 +/- 0.004, and for the 3-coordinated B(2), e(2)qQ/h = 2.58 +/- 0.03 MHz and eta = 0.276 +/- 0.004. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have different principal values of the electric field gradient tensor and originate from magnetically inequivalent sites. The principal Z-axis of the EFG tensor nearly coincides with the normal to the plane of the boron-oxygen triangle. We found an interesting correlation between the asymmetry parameter and the largest nonlinear optical coefficient
Stability analysis and control of non-standard nonlinear singularly perturbed system
No full textStability analysis and control of a non-standard nonlinear singularly perturbed system are studied. A non-standard form in which linear and nonlinear parts coexist is considered and a transformation using linear parts is suggested. On the basis of this transformation, the non-standard form is changed into a quasi-standard form, which is similar to a standard form. For the transformed system, the stability conditions under which the system is exponentially stable for the sufficiently small perturbation parameter epsilon are found. Using this analysis, a stabilising controller is designed. The practical aspects of the scheme proposed are illustrated through the control of a series DC motor
Thermal characteristics of organoclay and their effects upon the formation of polypropylene/organoclay nanocomposites
No full textWe have examined thermal characteristics of two types of organically modified montmorillonite (OMMT) with different alkylammonium cations and their effects upon the formation of PP nanocomposite, when using a maleic anhydride grafted polypropylene oligomer (maPP) as a compatibilizer. The microstructure of the composite has been characterized by X-ray diffraction (XRD) analysis, transmission electron microscopy and Fourier transform infrared spectroscopy. OMMT showed the decrease of the interlayer spacing at the processing temperature, due to the release of organic ion by thermal decomposition. Thermal characteristics of OMMTs depended greatly on the interlayer structure of OMMT. When the OMMT with small interlayer spacing and less organophilicity was used, PP composite resulted in the only partial exfoliation due to thermal decomposition of the clay layers
- …
