1,722,113 research outputs found
Theory of adsorption and surfactant effect of Sb on Ag(111)
Full text linkWe present first-principles studies of the adsorption of Sb and Ag on clean and Sb-covered Ag(111). For Sb, the substitutional adsorption site is found to be greatly favored with respect to on-surface fcc sites and to subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag. We propose that the experimentally reported surfactant effect of Sb is due to Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high density of Ag islands which coalesce into regular layers
TOWARDS AN UNDERSTANDING OF SURFACTANT ACTION IN THE EPITAXIAL-GROWTH OF METALS - THE CASE OF SB ON AG(111)
No full textWe address the role of ''surfactant'' adsorbates in determining changes in the homoepitaxial growth mode of metals, discussing the case of Sb on Ag (111). From ab initio calculations, we extract evidence that the mechanism operative in this system is that Sb induces an irregular shape and an increase in density of the growing Ag islands, and an ensuing increase of the number of attempts for an adatom to descend to a lower terrace. This results from a combination of peculiar properties of this system: Sb is adsorbed in substitutional surface sites, leading to the formation of a Sb-Ag surface alloy; deposited Ag has reduced mobility on Sb-covered Ag (111), from which follows a higher nucleation probability. The island shape is irregular since the surface alloy is disordered. Surface seggregation of Sb once the growing layer is completed furthers the phenomenon for many deposited Ag layers. Our explanation of the surfactant action of Sb on Ag (111) does not require a reduction of the downstep diffusion barrier, which may, however, be a concurrent factor helpful to interlayer mass transport and layer-by-layer growth
A development tool for analog fuzzy controllers: Features and Applications
No full textThis paper describes an integrated development tool for analog fuzzy controllers which exploits analog hardware implementation and fuzzy logic flexibility to allow an easy and extremely low-costsynthesis of non-linear control laws.The core of the final implementation is a modular general-purpose analog fuzzy engine (AFE) withgood speed performance and built-in temperature compensation. To ease fieldprototyping, a digitally-programmable version of AFE is provided with a software layer computing thebiasing voltages needed by the circuit to fit numerical data and/or linguistic rulesspecified by the users. Once that the application is fine-tuned, a further software module isable to generate an optimized version of AFE dedicated to the task. An example application show that this approachcan lead to the implementation of effective analog controllers, fulfilling industrial requirements
Novel Diffusion Mechanism on the GaAs(001) Surface: The Role of Adatom-Dimer Interaction
No full textBridging the length and time scales: from ab initio electronic structure calculations to macroscopic proportions
No full textChapter 5.6. Highly Porous Components
No full textHighly porous ceramics with a porosity > 55 vol% are used in various engineering applications. The most important among them are filtration (molten metals, particulate from diesel exhaust gases), radiant burners, catalyst supports, gas sorption, biomedical devices, kiln furniture, reinforcement for metal matrix composites, bioreactors, thermal protection systems, supports for space mirrors, components in solid oxide fuel cells, lightweight sandwich structures, and heat exchangers. Ti chapter will describe the production of highly porous compnents via a wide range of processing methods
- …
