Classical beta spectra calculations are briefly described, highlighting the usual assumptions and limitations. To go beyond these usual assumptions, the numerical resolution of the Dirac equation for the atomic and beta electrons is necessary. This allowed us to determine the parameters λi involved in the theoretical shape factors exactly. A systematic comparison between theoretical and experimental shape factors led us to disqualify the usual λi = 1 assumption for all forbidden transitions. The usual ξ-approximation was proved to be incorrect for numerous first forbidden non-unique transitions, and for all higherorder non-unique transitions. A more accurate screening correction was defined and the atomic exchange effect was taken into account, an effect which is always neglected in usual calculations. The beta spectra of 63Ni and 241Pu, recently measured down to very low energies, are well reproduced in our calculations. The exchange effect was demonstrated to have a great influence on the spectral shape within this energy range.

The influence of the dose on the crystal growth and on the selectivity of the Al-CVD process has been studied. Doses were varied from 100 L to 18000 L. Selective deposition was observed, both on passivated Si vs. SiO2, as well as on bare Si vs. passivated Si. On oxide elongated crystals have been deposited with dimensions of 1200 × 60 × 60 nm.

The deposition of the ternary compound Ti-N-Si using the cold-wall CVD technique from TiCl4-NH3-SiH2Cl2 presents difficulties because of undesired powder formation in the gas-phase. For a better understanding and control of the mechanism, both simulation and experiments have been carried out to determine favorable conditions to minimize the undesired adducts. First, an original technique has been developed for the reactive injection with a double-passage nozzle specially designed. Then powders have been deliberately grown at different conditions, with their chemical compositions analyzed using X-ray diffraction spectra. Further, the flow has been modeled and compared with the results provided by means of laser sheet visualization. It is shown that the powders can be avoided with some special reactive injection schemes and by controlling the nozzle exit-substrate distance. Some useful information is also delivered on controlling the color and the composition of powders during their synthesis.