Craze yielding and fracture mechanism in PE/PS/PE laminated films

The change in polystyrene (PS) layer thickness, which has been simultaneously determined during post-yield deformation, shows that crazing is the basic mechanism of toughening in all laminated films, and that shear deformation supplements the contribution of crazing especially for samples with high polyethylene (PE) volume fractions. Crazes formed in PS layers in the laminated films are slender and regular compared with the short and lenticular crazes formed in bulk PS film. When PE volume fraction increased, craze advance speed decreased because of the reduction of the stress concentration effect at craze tips. The life-time of the first mature craze to be formed at a given strain rate increased with PE volume fraction because the PE supporting the mature crazes could effectively inhibit craze rupture and blunt out the propagating crack by absorbing the stored elastic energy in the PS layer that would have been dissipated as fracture surface energy.     

Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

High-reliability GaAs-AlGaAs HBTs by MBE with Be base doping andInGaAs emitter contacts

The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5×10⁸ h at 125°C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology     

Alpha-particle-induced charge collection in p-n junction diodes insemi-insulating GaAs substrates

The bias and angle dependences of the alpha-particle-induced charge collected by GaAs p-n junction diodes are investigated. These diodes, in which the n-layer overlays the p-layer, are fabricated in a semi-insulating GaAs substrate by Si and Mg ion implantation. ²⁴¹ Am placed in a vacuum is used as an alpha-particle source with an initial energy of 4.03 MeV and a fluence of 5.4×10^-5/s/μm². The results show that the collected charge is nearly independent of the applied bias. This bias independence may be further evidence that the charge funneling process is not important in semi-insulating GaAs. A model not incorporating funneling can explain the measured angular dependence. Based on this model, the design principle for the buried p-layer structure is discussed     

Magnesium interlayered diamond coating on silicon

Diamond thin films have been deposited using hot filament chemical vapour deposition technique on manually scratched p-Si(1 0 0) substrate, with and without magnesium interlayer. In spite of magnesium melting point being lower (T_m = 649 °C) than the growth temperature of the substrate (T_s  750 °C) used in these experiments, it was found that high quality diamond films could be grown on Mg covered substrate. A liquid substrate is probably generated during the diamond film growth. Raman spectroscopy analysis exhibited only the triply degenerate, zone centre optical phonon peak at 1333 cm⁻¹ indicating that nearly stress free crystallites were present. Broadening of the Raman peak (11.76 cm⁻¹) indicates that some small crystallites also are present. Scanning electron and atomic force microscopy accompanied by X-ray diffraction analysis where used to compare the details of diamond film growth directly on scratched Si(1 0 0) and Mg interlayered scratched Si(1 0 0) substrates.     

A self-stabilizing ring orientation algorithm with a smaller numberof processor states

A distributed system is said to be self-stabilizing if it will eventually reach a legitimate system state regardless of its initial state. Because of this property, a self-stabilizing system is extremely robust against failures; it tolerates any finite number of transient failures. The ring orientation problem for a ring is the problem of all the processors agreeing on a common ring direction. This paper focuses on the problem of designing a deterministic self-stabilizing ring orientation system with a small number of processor states under the distributed daemon. Because of the impossibility of symmetry breaking, under the distributed daemon, no such systems exist when the number n of processors is even. Provided that n is odd, the best known upper bound on the number of states is 256 in the link-register model, and eight in the state-reading model. We improve the bound down to 6³=216 in the link-register model     

Analysis and modeling of char particle combustion with heat and multicomponent mass transfer

A char combustion model suitable for a large-scale boiler/gasifier simulation, which considers the variation of physical quantities in the radial direction of char particles, is developed and examined. The structural evolution within particles is formulated using the basic concept of the random pore model while simultaneously considering particle shrinkage. To reduce the computational cost, a new approximate analytical boundary condition is applied to the particle surface, which is approximately derived from the Stefan–Maxwell equations. The boundary condition showed reasonably good agreement with direct numerical integration with a fine grid resolution by the finite difference method under arbitrary conditions. The model was applied to combustion in a drop tube furnace and showed qualitatively good agreement with experiments, including for the burnout behavior in the late stages. It is revealed that the profiles of the oxygen mole fraction, conversion, and combustion rate have considerably different characteristics in small and large particles. This means that a model that considers one total conversion for each particle is insufficient to describe the state of particles. Since our char combustion model requires only one fitting parameter, which is determined from information on the internal geometry of char particles, it is useful for performing numerical simulations.     

Future prospect of remote Cat-CVD on the basis of the production, transportation and detection of H atoms

The future prospect of remote Cat-CVD, in which the decomposition and the deposition chambers are separated, is discussed on the basis of the absolute density measurements of H atoms. It is now well recognized that uniform deposition is possible on a large area without plasma damages by Cat-CVD. However, we may not overlook the demerits in Cat-CVD. One of the demerits is the poisoning of the catalyzer surfaces by the material gases, both temporary and permanent. One technique to overcome this problem is remote Cat-CVD. The question is how to separate the decomposition and deposition areas. If the separation is not enough, there should be back diffusion of the material gases, which will poison the catalyzers. If the separation is too tight, radicals may not effuse out from the decomposition chamber. These problems are discussed and it is shown that SiO₂ coating to reduce the radical recombination rates on walls is promising. The possibility of the polytetrafluoroethene coating by Cat-CVD is also discussed.