On The Interaction Of Channeling/Segmentation Cracks Of Coating: Study On The Critical Spacing

Channeling/segmentation cracks may arise in the coating subjected to in-plane tensile stress. The interaction between these multiple cracks, say the effect of the spacing between two adjacent cracks oil the behaviors of channels themselves and the interface around the interface corners, attracts wide interest. However, if the spacing is greater than a specific magniture,, namely the Critical Spacing (CS), there should be no interaction between such channeling/segmentation cracks. In this study, file mechanism of the effect of the crack spacing oil the interfacial stress around the interface corner will be Interpreted firstly. Then the existence of the CS will be verified and the relationship between the CS and the so-called stress transfer length Ill coating will be established for plane strain condition. Finally, the dependence of the stress transfer length, simultaneously of the CS, on the sensitive parameters will be investigated with finite element method and expressed with a simple empirical formula. (C) 2007 Elsevier Ltd. All rights reserved.

Narrow-channel-spacing 32-channel arrayed-waveguide-grating multiplexer with an innovative alignment method

A 32-channel 50-GHz spaced arrayed-waveguide grating with our innovative configuration has been designed and fabricated. The performance of the device has been fully tested by using a tunable laser light source, optical power meter, and polarization controller. The insertion loss (IS) of the device is 4.2 similar to 7.4 dB. The crosstalk is about -28 clB. The IS uniformity is less than 3.2 dB. With our configuration, the performance of the device has been enhanced effectively and the difficulty in alignment process has been decreased obviously. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

A base-emitter self-aligned multi-finger Si1-xGex/Si power heterojunction bipolar transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-aligned large-area multi-linger configuration power SiGe heterojunction bipolar transistor (HBT) device (with an emitter area of about 880 mu m(2)) is fabricated with 2 mu m double-mesa technology. The maximum dc current gain is 226.1. The collector-emitter junction breakdown voltage BVCEO is 10 V and the collector-base junction breakdown voltage BVCBO is 16 V with collector doping concentration of 1 x 10(17) cm(-3) and thickness of 400 nm. The device exhibited a maximum oscillation frequency f(max) of 35.5 GHz and a cut-off frequency f(T) of 24.9 GHz at a dc bias point of I-C = 70 mA and the voltage between collector and emitter is V-CE = 3 V. Load pull measurements in class-A operation of the SiGe HBT are performed at 1.9 GHz with input power ranging from 0 dBm to 21 dBm. A maximum output power of 29.9 dBm (about 977 mW) is obtained at an input power of 18.5 dBm with a gain of 11.47 dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, f(max) and f(T) are improved by about 83.9% and 38.3%, respectively.

Emitter of hetero-junction solar cells created using pulsed rapid thermal annealing

In this paper, we use a pulsed rapid thermal processing (RTP) approach to create an emitter layer of hetero-junction solar cell. The process parameters and crystallization behaviour are studied. The structural, optical and electric properties of the crystallized films are also investigated. Both the depth of PN junction and the conductivity of the emitter layer increase with the number of RTP pulses increasing. Simulation results show that efficiencies of such solar cells can exceed 15% with a lower interface recombination rate, but the highest efficiency is 11.65% in our experiments.

Photoluminescence investigation of charge build-up process in the emitter of a double-barrier resonant tunneling structure

Charge build-up process in the emitter of a double-barrier resonant tunneling structure is studied by using photoluminescence spectroscopy. Clear evidence is obtained that the charge accumulation in the emitter keeps almost constant with bias voltages in the resonant regime, while it increases remarkably with bias voltages beyond resonant regime. The optical results are in good agreement with the electrical measurement. It is demonstrated that the band gap renormalization plays a certain rob in the experiment.

Influence of Inter-Fiber Spacing and Interfacial Adhesion on Failure of Multi-Fiber Model Composites: Experiment and Numerical Analysis

The uniaxial tension experiments on glass-fiber-reinforced epoxy matrix composites reveal that the fragmentations of fibers display vertically aligned fracture, clustered fracture, coordinated fracture, and random fracture with the increase of inter-fiber spacing. The finite element analysis indicates that the fragmentations of fibers displaying different phenomena are due to the stress concentration as well as the inherent randomness of fiber defects, which is the dominant factor. The experimental results show that matrices adjacent to the fiber breakpoints all exhibit birefringent-whitening patterns for the composites with different interfacial adhesion strengths. The larger the extent of the interfacial debonding, the less the domain of the birefringent-whitening patterns. The numerical analysis indicates that the orientation of the matrix adjacent to a fiber breakpoint is caused by the interfacial shear stress, resulting in the birefringent-whitening patterns. The area of shear stress concentrations decides on the domain of the birefringent-whitening patterns.

Hybrid metal-base transistor with base of sulfonated polyaniline and fullerene emitter

We demonstrate hybrid vertical architecture transistors that operate like metal-base transistors, using n-type silicon as the collector, sulfonated polyaniline as the base, and C-60 fullerene as the emitter. Electrical measurements suggest that the sulfonated polyaniline base effectively screens the emitter from electric field variations occurring in the collector leading to the metal-base transistor behavior.

A Dithienylbenzothiadiazole Pure Red Molecular Emitter with Electron Transport and Exciton Self-Confinement for Nondoped Organic Red-Light-Emitting Diodes

An amorphous photoluminescent material based on a dithienylbenzothiadiazole structure has been used for the fabrication of organic red-light-emitting diodes. The synergistic effects of the electron-transport ability and exciton confinement of the emitting material allow for the fabrication of efficient pure-red-light-emitting devices without a hole blocker.

High gain in hybrid transistors with BAlq(3)/Alq(3) isotype heterostructure emitter

We report the fabrication of permeable metal-base transistors based on bis(2-methyl-8-quinolinolato-N1,O8)-(1,1'-biphenyl-4-olato) aluminum (BAlq(3))/tri(8-hydroxyquinoline) aluminum (Alq(3)) isotype heterostructure as emitter layer. In this transistor, n-Si was used as the collector, LiF/Al as the emitter electrode, and Au/Al bilayer metal as the base. We show that the leakage current is greatly reduced in Al/n-Si/Au/Al/BAlq(3)/Alq(3)/LiF/Al devices with respect to Al/n-Si/Au/Al/Alq(3)/LiF/Al devices due to the utilization of BAlq(3)/Alq(3) isotype heterostructure emitter, leading to high common-base and common-emitter current gains at low driving voltages.

Hybrid permeable metal-base transistor with large common-emitter current gain and low operational voltage

We demonstrate the suitability of N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), an organic semiconductor widely used in organic light-emitting diodes (OLEDs), for high-gain, low operational voltage nanostructured vertical-architecture transistors, which operate as permeable-base transistors. By introducing vanadium oxide (V2O5) between the injecting metal and NPB layer at the transistor emitter, we reduced the emitter operational voltage.

Improved color purity and efficiency by a coguest emitter system in doped red light-emitting devices

We demonstrate red organic light-emitting diodes (OLEDs) with improved color purity and electroluminescence (EL) efficiency by codoping a green fluorescent sensitizer 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1, 1, 7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-ij)quinolizin-11-one (C545T) as the second dopant and a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the lumophore into tris(8-hydroquinoline) aluminum (Alq(3)) host. It was found that the C545 T dopant did not by itself emit but assisted the carrier trapping from the host Alq(3) to the red emitting dopant. The red OLEDs realized by this approach not only kept the purity of the emission color, but also significantly improved the EL efficiency. The current efficiency and power efficiency, respectively, reached 12 cd/A at a current density of 0.3 mA/cm(2) and 10lm/W at a current density of 0.02 mA/cm(2), which are enhanced by 1.4 and 2.6 times compared with devices where the emissive layer is composed of the DCJTB doped Alq(3), and a stable red emission (chromaticity coordinates: x = 0.64, y = 0.36) was obtained in a wide range of voltage. Our results indicate that the coguest system is a promising method for obtaining high-efficiency red OLEDs.

High gain in hybrid transistors with vanadium oxide/tris(8-hydroxyquinoline) aluminum emitter

We report the electrical characterization of hybrid permeable-base transistors with tris(8-hydroxyquinoline) aluminum as emitter layer. These transistors were constructed presenting an Al/n-Si/Au/Alq(3)/V2O5/Al structure. We investigate the influence of the V2O5 layer thickness and demonstrate that these devices present high common-base and common-emitter current gain, and can be operated at very low driving voltages, lower than 1 V, in both, common-base and common-emitter modes.

Electrolummescence from (5)Do -> F-7(J) and D-5(1) -> F-7(J) (J=0-4) transitions with a europium complex as emitter

Electroluminescence (EL) devices with Eu(HTH)(3)phen [HTH: 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione, phen: I 10-phenanthroline] as an emissive centre were fabricated using vacuum evaporation. In addition to the Eu3+ 5D0 --> F-7(J) (J = 0-4) lines that were visible in the photoluminescence signal, the device also showed strong emission from the D-5(1) --> F-7(J) (J = 0-4) transitions. The enhanced emission from the D-5(1) F-7(J) (J = 0-4) transitions was attributed to the increased excitation intensity in the EL device. The luminescence lifetimes of the 5 D, and 5 Do levels were measured to be 0.6 mus and 866 mus, respectively.

A hydroxyphenyloxadiazole lithium complex as a highly efficient blue emitter and interface material in organic light-emitting diodes

We synthesized a hydroxyphenyloxadiazole lithium complex (LiOXD) as a blue light-emitting and electron injection/transport material to be used in double-layer organic electroluminescent devices. Devices with the concise configuration of ITO/TPD/LiOXD/Al showed bright blue EL emission centered at 468 nm with a maximum luminance of 2900 cd m(-2). A current efficiency of 3.9 cd A(-1) and power efficiency of 1.1 lm W-1 were obtained. LiOXD was also examined as an interface material. The efficiency of an ITO/NPB/Alq(3)/Al device increased considerably when LiOXD was inserted between Alq(3) and aluminium. The improvement of the device characteristics with LiOXD approached that observed with the dielectric LiF salt.

Organic electroluminescent devices using rare earth complex Eu(DBM)(3) as an emitter

Eu3+ narrow band emitting EL device with PPV, Alq(3) as hole and electron transportation layers has been prepared. The emitting layer, which consists of PVK, Eu(DBM)(3) and PBD is formed by spin-casting method. A maximum luminance of 52cd.m(-2) is achieved from the device.