P. Melinon

Comparison between selenium and tellurium clusters

Selenium and tellurium clusters are produced by the inert gas condensation technique. The mass spectra of both species are completely different and reveal different properties. In selenium, a periodicity of 6–7 is observed and may be interpreted by the binding energy between small cyclic molecules. Moreover, it was very difficult to obtained large clusters probably because the binding energy between these molecules is very small. In tellurium, these periodic structures do not exist and large clusters are easily obtained in nucleation conditions where only small selenium clusters are present. These results are discussed and a simple nucleation model is used to illustrate this different behavior. Finally these clusters properties are correlated to the bulk structure of both materials.

Luminescence and Raman characterization of molecular and nanocrystalline silicon clusters

Abstract Silicon clusters prepared by low energy cluster beam deposition exhibit visible luminescence similar to that observed in porous silicon. The structure and properties are characterized by different complementary techniques with a special emphasis on Raman spectroscopy. The comparison with silicon clathrates structures is promising. The validity of the confinement model in a size range down to a few angstroms is discussed.

Experimental studies on selenium cluster structures

In this paper, we report properties of selenium clusters produced by vapor condensation technique. Impact electronic ionization is performed on clusters in the size range from 2 to 36 atoms. The measured ionization potentials exhibit small oscillation corresponding to the wiggles observed on the mass distribution. An attempt to connect these experimental observations with the geometrical structure of the molecules is made in the discussion.

Study of selenium clusters. Evidence of packing structure

The aim of this paper is to study the properties of selenium clusters produced by vapor condensation technique. Simulation of nucleation process up to 50 atoms are in favour of a structure close to the amorphous structure. Doubly charged clusters are also obtained in the mass spectra.

Structure of small rare earth clusters

Rare earth clusters are produced by the inert gas condensation technique. The observed size distribution shows large peaks atn=13, 19, 23, 26, 29, 32, 34, 37, 39, 45, ... The beginning of this sequence (up to 34) has been already observed in argon clusters and recently by our group in barium clusters; this sequence may be interpreted in terms of icosahedral structures corresponding to the addition of caps on a core icosahedron of 13 atoms.

Diamond-like carbon films produced by cluster deposition

Carbon clusters with selected size distributions centered around C 20 , C 60 and C 900 produced with a laser vaporization source have been deposited on various substrates at room temperature to produce films with thicknesses as large as 100 nm. C 20 have been choosen for its nearly pure sp 3 hybridization, C 900 for its quasi pure sp 2 bonding character and C 60 for its mixed state. Structures and properties of the films were characterized using various complementary techniques : atomic force microscopy, electron diffraction, Raman scattering, Electron energy loss spectroscopy, X-ray absorption near edge structure, Fourier transform infrared spectroscopy and Auger electron spectroscopy. The results show that the low energy cluster beam deposition allows to growth films in which the particular structures and properties of the free clusters can be conserved. The attractive field of applications of this technique concerns the possibility of realising Diamond-like thin films with controlled hybridization (sp 3 -sp 2 ) and nanostructure from amorphous diamond to amorphous graphite.

Electronic and chemical properties of indium clusters

Indium clusters are produced by the inert gas condensation technique. The ionization potentials are found higher for small clusters than for the Indium atom. This is explained by the p character of the bonding as in Aluminium. Doubly charge clusters are also observed and fragmentation processes discussed. Finally small Indium clusters 3 < n < 9 are found very reactive with hydrocarbon.