Two doses (1013 and 1015 cm−2) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.
Cladding tubes are structural parts of nuclear plants, submitted to complex thermomechanical loadings. Thus, it is necessary to know and predict their behaviour to preserve their integrity and to enhance their lifetime. Therefore, a new experimental device has been developed to control the load path under multi-axial load conditions. The apparatus is designed to determine the thermomechanical behaviour of zirconium alloys used for cladding tubes. First results are presented. Creep tests with different biaxial loadings were performed. Results are analysed in terms of thermal expansion and of creep strain. The anisotropy of the material is revealed and iso-creep strain curves are given.
The efficiency of solar energy conversion in a photovoltaic device consisting of an infinite number of solar cells is examined in detail. A mathematical analysis of the complicated functional dependence of the efficiency on temperature and light concentration ratio is presented. Although an infinite tandem seems, at first sight, only of academic interest, it is shown that the various approximate expressions obtained for the complicated efficiency function can give some more insight into the basic limits of the photovoltaic conversion, and can enable easy predictions of an upper limit of the efficiency of tandem structures with a finite number of solar cells.
High performance, compact planar lightwave circuit based triplexers have been built and tested. The triplexers utilize lasers, photodiodes and filters that have been adapted to enable passive optical assembly of the triplexer, 02005 Optical Society o f America OCIS codes: (130.3120) integrated optics devices (230.0250) optoelectronics ' IntroductionPassive optical networks (PONS) are beginning to be mass deployed in high speed Fiber to the Home (FTTH) access networks. These networks utilize bidirectionaI optical modules that allow downstream and upstream traffic to share a single fiber. In the case where voice, data, and video services are provided on the access network, the optical module on the subscriber side is a triplexer that has two downstream receivers and one upstream laser. The most widely used waveIength plan uses the band from 1550-1560 nm for downstream video, 1480-1500 nm for downstream data, and 1260-1360 nm for upstream data. A triplexer typically consists of a data photodiode and transimpedance amp, a video photodiode, a 13 10 nm band laser and monitor photodiode, and WDM filters to separate the various optical wavelengths. Proper operation of the triplexer requires a high level of optical isolation from the WDM filters as well as effective suppression of stray light. Because every subscriber has a triplexer as part of the Optical Network Termination (ONT) equipment, cost is also an extremely important parameter for triplexers.In this paper we describe a pIanar lightwave circuit (PLC) based triplexer that achieves high levels of performance fiom a compact design that is built entirely using passive optical assembly methods. Planar Lightwave Circuit Triplexer Design . .A PLC based optical triplexer can be viewed as being built from five distinct functional elements. The optical waveguide network provides optical connectivity between the other main elements. The remaining four elements are the Iaser, PDs (3 per triplexer), the WDM filters (two per triplexer), and the optical fiber. A challenge in designing a PLC based ttiplexer is the design of the interfaces between the optical waveguides and these other elements. In this section, we describe ow designs for the key elements and the interfaces. The optical waveguide network used in the triplexer is primarily based on silica waveguides formed on a silicon substrate [ 1 ,a]. The Filter yA Laser Data. PD MPD
Fe-implanted Si-wafers have been oxidized at 900 °C and 1100 °C in order to investigate the behaviour of Fe atoms at the growing SiO2/Si interface and the impact on the integrity of microelectronic devices of an involuntary Fe contamination before or during the oxidation process. As-implanted and oxidized wafers have been characterized using secondary ion mass spectroscopy, atom probe tomography, and high-resolution transmission electron microscopy. Experimental results were compared to calculated implantation profiles and simulated images. Successive steps of iron disilicide precipitation and oxidation were evidenced during the silicon oxidation process. The formation of characteristic pyramidal-shaped defects, at the SiO2/Si interface, was notably found to correlate with the presence of β-FeSi2 precipitates. Taking into account the competitive oxidation of these precipitates and of the surrounding silicon matrix, dynamic mechanisms are proposed to model the observed microstructural evolution of the SiO2/Si interface, during the growth of the silicon oxide layer.
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