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The phase formation in planar binary systems is discussed in terms of the diffusion-kinetic approach. Application to Pt and Ni silicide thin and thick films confirms this approach and permits to interpret experimental data in terms of the physical mechanisms involved. A temperature-dependent critical thicknessW c for the transition of a compound to its subsequent one is discussed and expressed in terms of the activation energies for the growth and reaction rate.

A new method of dental fluorine prophylaxis based on the chemical reaction induced by UV irradiation in dental enamel has been presented. Fluorine ions from a gel topic can be retained to the dental apatite in the lamp-irradiated samples at about 70% and in the laser-irradiated samples at about 80% of the maximum deposited value. The19F(p,α)16O nuclear reaction was used to measure the fluorine concentrations in the first 3 μm of the enamel of healthy teeth before and after the gel topic applications with and without UV irradiation. This method of dental prefenction resolves the problem of the traditional fluorine prophylaxis which brings fluorine in the enamel without binding the apatite.

The growth kinetics of NiSi has been evaluated by depositing a Ni film on and Si substrates. X-ray diffraction and MeV4He+ backscattering have been used to identify the compounds formed and to measure their thicknesses. Carbon and oxygen impurities have been detected with Auger electron spectrometry with Ar sputtering. During thermal annealing Ni2Si is formed first, while NiSi appears only after the total exhaustion of the Ni film. It has been found that, on both Si substrates, the thickness of NiSi increases with the square root of time. Different growth rates have been observed for the two different Si orientations. The activation energy in the (300÷370)°C temperature range is 1.83 eV for NiSi grown on and 1.23 eV for NiSi on Si. The two competing mechanisms of Ni diffusion through NiSi by grain boundary and by substitutional processes are correlated with the different microcrystalline structure of the NiSi silicide layers grown on different Si-oriented substrates.