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Optical properties of mixed clusters Ni/Ag, Co/Ag, and Ni/Au of 2-5 nm in diameter, produced by laser vaporization and embedded in an alumina matrix, are investigated. The first part is devoted to (Ni x Ag 1 - x ) n clusters whose photoabsorption spectra reveal a surface plasmon resonance, damped, broadened, and blue-shifted as compared to pure silver clusters. For a given mean size, a blueshift of the resonance band as well as a damping and broadening with increasing nickel proportion is observed, in good qualitative agreement with classical predictions, assuming a Ni-core/Ag-shell geometry. This core-shell structure is confirmed by low energy ion spectroscopy measurements showing that the cluster surface is essentially composed of silver. For a given composition, the size evolution of the plasmon band consists of a damping and broadening with decreasing size whereas no clear shift is noticed. Although the classical predictions, including the surface scattering limited mean free path contribution of the conduction electrons in the silver shell, account well for the size effects, inhomogeneous effects (size, shape, and local porosity) also contribute to the broadening and damping of the resonance in experiment. The second part concerns the optical properties of (Co 0 . 5 Ag 0 . 5 ) n and (Ni 0 . 5 Au 0 . 5 ) n clusters. The size evolution of the optical properties of (Co 0 . 5 Ag 0 . 5 ) n clusters is similar to that of (Ni 0 . 5 Ag 0 . 5 ) n clusters, with in addition, a weak blueshift of the resonance with decreasing size. As for the (Ni 0 . 5 Au 0 . 5 ) n clusters, their optical spectra do not display a marked resonance. The comparison with a core-shell model including a size dependent damping constant in the gold or silver shell gives a good understanding of these features for the two systems Co/Ag and Ni/Au.

The escape depth of the secondary ions resulting from electronic sputtering of fast heavy ions in inorganic thin films has been investigated. Chromium layers deposited onto SiO 2 substrate as well as SiO x layers deposited onto chromium substrate have been characterised by secondary ion emission mass spectrometry (SIMS) in combination with time-of-flight (TOF) mass analysis (also referred to as HSF-SIMS [B.U.R. Sundqvist, in: Sputtering by Particle Bombardment III, eds. R. Behrisch and K. Wittmaack (Springer, Berlin, Heidelberg, 1991) p. 257]). These crossed experiments lead to a value around 1 nm for SiO x layers and 0.5 nm for Cr layers. On the other hand, HSF-SIMS can be used to correlate the intensity of the secondary ion emission to the film coverage rate (Θ) and (or) the morphology of particular films like those produced by low energy cluster beam deposition (LECBD). Using Sb deposits, the non-linear relationship between ion emission and Θ is interpreted in terms of sputtering enhancement in the individual supported clusters.

Magnesium oxide and lithium fluoride single crystals are implanted with metallic ions (Na + , Rb + ) and subsequently annealed to form small metallic precipitates of sodium or rubidium embedded in the insulating matrix. They are reimplanted at low dose rate with the same particles and analyzed using optical absorption measurements and transmission electron microscopy. In MgO samples, the metallic precipitates are dissolved in the lattice and they all disappear for doses of the order of 10 15 ions cm −2 , whereas, to the contrary, in LiF the precipitation increases. This result seems to indicate the strong influence of intrinsic defects on the atomic mixing process.

It has previously been shown that high fluence Na implantation into MgO crystals followed by annealing leads to the formation of metallic Na precipitates. We have studied the effect of a subsequent low-fluence Na implantation on such precipitates, i.e., the effect of Na damage cascades whose size is comparable to that of the precipitates. Optical spectroscopy experiments and in situ transmission electron microscopy (TEM) experiments performed on-line with the Orsay ion implantor are both discussed. It is shown that simple ballistic ion beam mixing cannot account for the results. The latter indicate that damage-induced mixing at the host matrix-precipitate interface leads to drastic changes in the precipitate composition, presumably due to in-diffusion of oxygen (and possibly Mg) into the precipitate volume.