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Supported bimetallic Pd-Pt clusters with a well-defined stoichiometry are produced using a laser-vaporization source. Free clusters are also studied by time-of-flight mass spectrometry and photofragmentation. The supported clusters are characterized by energy dispersive x-ray analysis. The low binding energy of palladium atoms compared to that of platinum is clearly demonstrated in both free and supported clusters. The reactivity is briefly discussed.

The morphology of supported Bi particles is studied using the technique of profile imaging at atomic resolution. These particles show a crystallized Bi core surrounded by an amorphous (or liquid) material. For small supported particles (diameter of the Bi core, about 6-9 nm) observed by high-resolution electron microscopy at room temperature, the lattice fringe orientation changes very rapidly during the observation. This fluctuating evolution is attributed to atomic rearrangements of the particle induced by the microscope electron beam. During this evolution, a decrease in the size of the crystallized Bi core is sometimes observed for the smaller particles.

To determine if the first stages of growth of indium deposits obtained by low-energy cluster beam deposition (LECBD) can be studied despite the oxidation of the smallest in supported aggregates, transmission electron microscopy (TEM), Auger electron spectroscopy (AES) with high spatial resolution and electron energy loss spectroscopy (EELS) experiments have been carried out. According to the analysis of the experimental results, a surface oxidation of In supported aggregates occurs during transfer into air between the deposition and the analysis systems. The oxidation of the deposits obtained after transfer through air may be neglected for a first analysis of TEM results to study nucleation and growth of indium aggregates.

The systematic study of the first stages of antimony growth on amorphous carbon substrates is inhibited by the oxidation of the deposit during transfer through air from the evaporating chamber to the analysis system. To prevent the oxidation of the deposit, the sample is coated in situ with carbon. Under these conditions, transmission electron microscopy and high resolution transmission electron microscopy show that antimony deposits on amorphous carbon supports are amorphous in the first stages of growth. This work shows for the first time that, even for a very low thickness where antimony is considered amorphous, some crystalline antimony aggregates exist on the support. These aggregates are assumed to act as nucleation centres for the crystallization of continuous antimony films which occurs when the equivalent thickness is larger than a critical thickness.

Small bismuth particles have been formed on amorphous carbon films by molecular beam deposition. The pressure during the deposition was less than 1 × 10−4 Pa. At low thicknesses (

In order to understand the differences existing between films obtained with a classical molecular beam deposition (MBD) and the new low-energy cluster beam deposition (LECBD), transmission electron microscopy has been used to characterize the first stages of antimony LECBD. Antimony deposits are discontinuous and amorphous up to 2nm in thickness. They are formed with isolated amorphous antimony particles surrounded by an amorphous antimony oxide shell. Moreover, under electron beam exposure in the microscope, an amorphous-crystal transformation has been observed in the oxide shell. Electron irradiation induces the formation of a crystallized antimony oxide (Sb2O3) around the amorphous antimony core.

Indium deposits on amorphous carbon grids have been produced by atomic deposition in a vacuum chamber evacuated at a pressure of 1 × 10 −4 Pa. Deposits of 2 nm thickness corresponding to 7.6 × 10 15 atoms cm −2 appear to be formed from small isolated amorphous aggregates. In situ thermal annealing in a transmission electron microscope induces an amorphous-crystalline phase transformation. A similar phase change caused by the electron beam of the microscope is also observed, at an atomic scale, by high resolution electron microscopy. In both cases the phase obtained after transformation is In 2 O 3 .

Small bismuth clusters with a narrow size distribution (two to ten atoms) were produced by the inert-gas condensation technique and deposited at room temperature on an amorphous carbon film. We have shown that the growth process involves the formation of large particles (diameter from 1·5 to 20 nm). The larger particles have been characterized by high-resolution transmission electron microscopy. These particles are formed with a single-crystal core edged by an amorphous shell. Cluster images in the [2201], [0001] and [0110] directions are presented and compared with simulated images of bismuth single crystal.

Bismuth clusters are produced by the inert gas condensation technique. The cluster beam is analysed by time of flight mass spectrometry and is simultaneously deposited on an amorphous carbon film. We compare two kinds of deposition: molecular beam and free clusters deposition (18 A mean size). Cluster deposition exhibits a larger mean particle size on the support. The two kinds of deposition may be correlated with the Schmeisser’s law.

Small bismuth clusters with narrow size distribution (2→ 10 atoms) were generated in an inert gas condensation source and vacuum deposited, at room temperature, on amorphous carbon. The deposit has been characterized by Transmission Electron Microscopy (TEM) which has shown a growth process involving the formation of large particles: diameter from 1.5 to 20 nm. Axial illumination lattice imaging with a high resolution electron microscope has been performed. Particles of about 20 nm diameter have been formed with a single crystalline core edged by an amorphous shell. Cluster images in the [2201] direction are presented in detail and compared with simulated images of bismuth single crystal.

Transmission electron microscopy studies have recently shown that low-energy cluster-beam deposition allows the formation of higher-quality films compared with the classical molecular-beam deposition. This work presents preliminary results obtained with antimony deposits.