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A method based on light scattering has been used to characterize the surface roughness of four standard kilograms made from XSH alacrite, in order to determine the root-mean-square height and the correlation length . The values of these two parameters, which have been found to lie between 2 nm and 5 nm and between 170 nm and 250 nm, respectively, show the high surface quality that it is possible to obtain by mechanical polishing of XSH alacrite. Cartographies made by light scattering, as well as and values, have shown that in spite of identical manufacturing conditions the kilograms present a significant difference in surface roughness. We have observed that the lower bases were in general rougher than the upper ones. This was explained by the different histories of the upper and lower bases. On the other hand, the same value of was found for both bases of a given kilogram. We have also found that the smoother the kilogram, the smaller the mass loss. This clearly shows the effect of surface roughness on the stability of mass standards. Finally, significant variations in the values of and have been observed after the cleaning-washing process at the Bureau International des Poids et Mesures. We have also shown that the variations noted after several successive cleaning-washings are mainly the result of the first of these. This agrees with observations made during earlier gravimetric studies.

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In order to use a power MOS transistor in the ZVS mode at high switching frequencies, the output capacitance has to be maximal and the input capacitance minimal. These characteristics available in the datasheets have to be completed if necessary tu choose the ideal transistor for application with minimal losses, and additional characterisations have to be realised in order to specify or complete the datasheets. In particular, it is necessary to be sure that all the cells of the MOS transistor can be opened in a short time before the voltage rise time at turn-off, in order to reduce as low as possible turn-off losses. The paper points out that the gate to source impedance characterises the ability of the device to turn-off very quickly and is useful to choose a MOS transistor having minimal losses in very high switching frequency ZVS applications.

On décrit une expérience dans laquelle des tranches de silicium de diamètre 10 cm ont été auto-soudées. Les interfaces ont été caractérisées au moyen de plusieurs tests différents : l'un destructif (mécanique), les autres non destructifs (optique, par imagerie dans l'infra-rouge, et acoustique) ; des diodes PN tests ont été réalisées, également dans le but d'obtenir une cartographie des décohésions. L'aire effectivement soudée est supérieure (ou au moins égale) à 80 % de la surface d'une tranche. On a étudié de manière quantitative les variations des dimensions des zones défectueuses en fonction de la température : on montre que les décohésions qui existent sur une même interface sont de deux types, selon que leurs dimensions augmentent ou, au contraire, diminuent lors d'un traitement thermique à 1 200 °C

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