Electronic and optical properties of beryllium chalcogenides/silicon heterostructures

We have calculated electronic and optical properties of Si/BeSe$_{0.41}$Te$_{0.59}$ heterostructures by a semiempirical $sp^{3}s^{*}$ tight-binding method. Tight-binding parameters and band bowing of BeSe$_{0.41}$Te$_{0.59}$ are considered through a recent model for highly mismatched semiconductor alloys. The band bowing and the measurements of conduction band offset lead to a type II heterostucture for Si/BeSe$_{0.41}$Te$_{0.59}$ with conduction band minimum in the Si layer and valence band maximum in the BeSe$_{0.41}$Te$_{0.59}$ layer. The electronic structure and optical properties of various (Si$_{2})_{n }$/(BeSe$_{0.41}$Te$_{0.59})_{m}$ [001] superlattices have been considered. Two bands of interface states were found within the bandgap of bulk Si. Our calculations indicate that the optical edges are below the fundamental bandgap of bulk Si and the transitions are optically allowed.Comment: 16 pager, 7 figure

Finite element dynamic simulation of whole rallying car structure: Towards better understanding of structural dynamics during side impact

Side impact accidents against a tree or pole remain the most dangerous accident scenarios in rally cars. Statistical data shows that 52% of the fatalities between 2004 and 2009 concern crashes against a rigid pole by the track sides, whilst among those more than 60% were side impacts. Despite the present scientific efforts, rallying cars side impacts are still among the least understood primarily due to limited space between the occupant and door sill, evolving safety regulations and vehicle dynamics. In this study, finite element dynamic characteristics of the whole car were studied. The finite element model consisted of the whole car structure and 241 parts including the engines, tyres and the suspension members with 4 different element types and 7 material models. All structural parts were modelled as low-carbon steel with the piecewise- linear-plasticity material model (mat 24). The tyres were modelled with the Blatz-Ko rubber material (mat 07) whilst also rigid and other materials (mat 020, 01, 09, S01 and S02) were used to represent different parts of the model, as the suspension members, suspension links and the engine. A rollcage and two racing seats were modelled with four-node shell elements and the use of piecewise-linear-plasticity and composite-damage materials respectively. A semi- cylindrical pole of 200mm diameter was also designed and modelled as a rigid body. The model was used to first investigate the dynamics of the crash, and later run a wide range of simulations and parametric studies in the cage, the car's floor and the seats. The important findings from the study are presented, conclusions drawn and scope for further development outlined

Cellulose-Based Bio- and Nanocomposites: A Review

Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper

Confinement d'ions dans une cage cylindrique à champ quadrupolaire HF. Application à la spectrométrie de masse - II. Partie expérimentale

In a first paper we gave a theoretical treatment of the confinement of ions in a cylindrical trap of quadrupolar symmetry with special application to mass spectrometry. The present paper deals with experimental results. A resonance ion detection system is employed which due to its selectivity, permits the use of the optimum operating point in the stability diagram and so selectivity is improved. A comparison of the results obtained with the trap and those obtained with a commercial spectrometer, the simple Riber quadrupole « Miniquade Q-63 » shows the advantages and disadvantages of the cylindrical trap.Cet article fait suite à une partie théorique traitant le confinement d'ions à l'intérieur d'une cage cylindrique à champ quadrupolaire HF, en vue d'application à l'analyse de gaz résiduels par spectrométrie de masse. La détection des ions confinés est faite par une méthode de résonance qui grâce à sa sélectivité, permet de se placer au point optimum du diagramme de stabilité, ce qui améliore la sensibilité. Une comparaison entre les résultats obtenus avec cette cage et ceux que l'on obtient en utilisant un spectromètre commercial, le quadrupôle simplifié Riber « Miniquade Q-63 » montre les avantages et inconvénients d'utilisation de la cage cylindrique

Room and low temperature electrical measurements for the interface characterization of titanium disilicides on silicon from multilayer titanium/silicon structures

The interface of titanium disilicides TiSi2 on silicon formed by electron gun evaporation of silicon/titanium multilayers and subsequent annealing is characterised using current-voltage measurements on specially prepared Schottky diodes in the whole temperature range from room temperature down to 77K. In particular, the influence of the bilayer Si/Ti thickness ratio, ranging between 2 and 3, on the barrier height of the diodes is studied and compared with the case of a diode formed by deposition of a single titanium layer and further annealing. The activation energies derived from the low temperature measurements have shown that the interface of the sample prepared with single layer deposition is more rough than the case of the sample prepared with deposition of multilayers using a bilayer thickness ratio Si/Ti=2.5 which is close to the calculated value for the stoichiometric films

Confinement d'ions dans une cage cylindrique à champ quadrupolaire HF. Application à la spectrométrie de masse - I. Partie théorique

In a first part, we study the conditions of confinement of ions in an RF electric field of quadrupolar symmetry in a cylindrical ion trap. The conditions of confinement of a maximum number of ions, created in the volume of the trap, are calculated. Ions are created by an electronic beam in the volume of the trap. The trajectories of ionizing electrons are determined. Mean ionization cross sections are also calculated for ions most frequently encountered. Field imperfections limit the maximum obtainable resolution when a method of detection by resonance absorption is used. In a second article, experimental results obtained by use of the cylindrical ion trap will be given.Dans cette première partie, on étudie les conditions de confinement d'ions par un champ électrique HF à symétrie quadrupolaire dans une cage cylindrique, en vue d'application à la spectrométrie de masse. Les conditions de confinement d'un nombre maximum d'ions sont calculées. Les ions étant créés à l'intérieur du volume de la cage, le faisceau électronique est influencé par le champ de confinement. On détermine l'allure du faisceau électronique, puis on calcule une section efficace moyenne d'ionisation et on en déduit un facteur de correction permettant de comparer entre eux les pics ioniques les plus fréquemment rencontrés. On montre enfin que les imperfections du champ quadrupolaire limitent la résolution en masses, lorsqu'on utilise une méthode de détection des ions par absorption résonnante d'énergie. Dans un deuxième article, on donnera les résultats expérimentaux obtenus en utilisant la cage cylindrique

Investigation on a microring laser coupled with phase-section bus waveguide as a tunable transmitter for application in future optical/wireless hybrid networks

In this paper, semiconductor microring lasers with integrated phase sections in the bus waveguide are numerically evaluated, using a dynamic multimode laser model, and investigated as low-cost, integrated, potential tunable directly modulated transmitters for future hybrid optical-wireless networks. The effect of optical feedback through bus waveguide is revealed as a promising mechanism for improving nonlinear distortion. Additionally, tunability is achieved with the aid of phase-tuning. The underlying laser dynamics beyond this behavior are analyzed. © 2010 Elsevier B.V. All rights reserved