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Low-energy cluster beam deposition (LECBD) has been used to synthesize cermets with controlled size nanoparticles. In the In - system, this technique allows the formation of In nanograins uniformly distributed in the insulating matrix. Optical spectra in the range 2 to 6 eV present plasmon resonance bands which have been interpreted by Mie and Maxwell-Garnett theories. XPS measurements have shown an oxidation of a fraction of the indium particles.

In this paper, we propose a new technique for the elaboration of size controlled nanoparticles embedded in a matrix: the low-energy cluster beam deposition (LECBD). Bi-SiO x nanocermets have been prepared by codeposition of Bi neutral clusters and SiO x molecules. We present a study by transmission electron microscopy (TEM) of the structural properties of these new cermets. The clusters are generated by the gas-aggregation technique in a thermal source which produces clusters with a low energy. Then, the incident clusters do not break at the impact on the surface and conserve their size and structure. Consequently, the cermets are composed of Bi nanograins with a size distribution comparable to that of the free clusters, at low metallic concentrations. This result has been obtained for three different size distributions of the free clusters showing that the LECBD technique allows the control of the size of the embedded particles in the nanometric range. Moreover, the size and the concentration of grains are independent at metallic concentrations below 10%. This result is very important for studying the influence of these two parameters on the physical properties of granular materials.

We present a study of the first stages of growth of thin films produced by low-energy cluster beam deposition (LECBD) on graphite. Our experiments are analyzed in the framework of new models including three physical ingredients, which are the deposition, the diffusion and the aggregation of the clusters. The comparison between computer simulations of the model and the experimental structures reveals that only the incident clusters diffuse on the graphite, the clusters stick irreversibly upon contact, and allow us to quantify the diffusion of clusters on graphite. Two kinds of metallic cluster films are studied: thin films produced by deposition of antimony clusters (containing 2300 and 250 atoms) and others by deposition of gold clusters (containing about 250 atoms). In both cases, we find that the clusters, in spite of their large size, diffuse very rapidly on the surface. The different microscopic diffusion mechanisms proposed in the literature are investigated, but none is compatible with our experimental results. Finally, we suggest a collective mechanism where the cluster rotates on the surface as a rigid entity to explain our results.

We present in this work the TEM results on the nucleation and growth process of antimony particles on graphite produced by low-energy cluster beam deposition. In order to acquire more details about the first stages of film growth, we compare the experimental results with a new theoretical model named “Deposition-Diffusion-Aggregation”. Moreover this comparison allows an estimate of the diffusion coefficient D for antimony clusters of 5-nm diameter on graphite; we find D≈10−8 cm2/s.

Low Energy Cluster Beam Deposition (LECBD) has been used to synthesize cermets with controlled size nanoparticle. In the Bi-SiOx system, this technique allows the formation of Bi nanograins uniform...

The development of the Low-Energy Cluster Beam Deposition (LECBD) technique represents a new way for the synthesis of cermets. Bi-SiO x thin films have been produced by codeposition of neutral Bi clusters and SiO x molecules. A Transmission Electron Microscopy study shows that these new cermets are formed by isolated grains whose size corresponds to that of the incident clusters. This work demonstrates the main assets of this technique: homogeneity of the films, narrow size distribution of the metallic inclusions and grain size control in the nanometric range

Electrical and chemical properties of Bi films produced by low-energy cluster beam deposition (LECBD) are studied and compared with those of films made by molecular beam deposition (MBD). For LECBD Bi films, increase of roughness and decrease of film grain size explain increase of resistivity and chemical reactivity to oxygen. Two phenomena are proposed to play a role in LECBD film growth: low surface diffusion of Bi clusters (relative to Bi2) and a high barrier to cluster coalescence. The present experiments show that growth of LECBD crystallized Bi films and the film grain size can be controlled by the size distribution of incident clusters.

Physical and chemical properties of films prepared by Low-Energy Cluster Beam Deposition (LECBD) are presented, discussed and compared to those of films obtained by other conventional deposition techniques. LECBD films are formed by the stacking of individual grains corresponding roughly to the incident free clusters. This original structure suggests that LECBD is promising for technological and theoretical applications. Film properties strongly related to the mean grain size can be controlled with this original technique. This work shows several examples showing the assets of LECBD: ultrathin sintered films, high surface-volume ratio or continuous ultrathin films, new structures of metallic deposits. Used as a tool to obtain experimental data to study fractal 2D models or to elaborate deposits to study quantum size effects, this deposition technique would be original, efficient and sometimes essential in many research areas

Low energy cluster beam deposition allows the preparation of thin films that cannot be prepared by usual deposition techniques. We show here that low energy cluster beam deposition allows the preparation of continuous amorphous antimony thin films, contrary to the usual molecular beam deposition technique. These stable continuous amorphous films had never been obtained at room temperature. The study has been carried out by combining electrical measurements and transmission electron microscopy observations.

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.

We show that cluster deposition, contrary to atomic or molecular deposition, makes it possible to experimentally approximate to several 2D theoretical models (percolation, cluster-cluster aggregation). Concerning percolation, molecular deposition seems to simulate bond correlated percolation whereas free-cluster deposition is close to geometrical site percolation. The low mobility of the clusters can explain these features. In different experimental conditions, cluster deposition allows to perform 2D cluster-cluster aggregation experiments.

We show that antimony thin films present two percolation transitions. The first corresponds to the well-known insulator-conductor transition already observed in other metallic films. The second corresponds to the crystallization of the film and may be compared to invasion percolation.

We have correlated electrical measurements and transmission electron microscopy observations of ultrathin antimony films. The obtained results allow us to understand the crystallization of antimony. It seems that, at room temperature, the critical thickness below which no complete crystallization is possible corresponds to the percolation threshold.

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.

Effects of low-energy cluster beam deposition (LECBD) on the growth of thin films are presented. According to TEM results, LECBD antimony films are the result of random packing of the incident clusters. We show that the “pavement of the surface substrate” previously observed in the first stage of film growth is still a valid model for thick films. With low compactness and the high roughness which characterize LECBD films, specific applications are suggested.

We have prepared continuous amorphous antimony thin films by low‐energy cluster beam deposition. Contrary to the antimony films prepared by molecular beam deposition, this new technique allows preparation of continuous amorphous films which are stable at room temperature. This study has been carried out by combining electrical measurements and transmission electron microscopy observations.

We present a quantitative study of the diffusion of spherical antimony clusters deposited on graphite surfaces. The experimental structures obtained during deposition are compared to predictions of recent computer models, and very good agreement is found. From this comparison we can obtain the diffusion coefficient of large antimony clusters containing around 2300 atoms moving on a graphite substrate: we find ${D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}D}_{0}\mathrm{exp}({\ensuremath{-}E}_{a}/{k}_{B}T)$ with ${D}_{0}\ensuremath{\approx}1.6\ifmmode\times\else\texttimes\fi{}{10}^{4}{\mathrm{cm}}^{2}/\mathrm{s}$ and ${E}_{a}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.7\ifmmode\pm\else\textpm\fi{}0.1\mathrm{eV}$. This large value of ${D}_{0}$ suggests that the diffusion cannot be explained by a simple atomic activated process, but may rather involve collective motions of the atoms of the cluster.

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.

Direct observation of the infinite percolation cluster at the percolation threshold is shown. We use crystallization propagation in an amorphous thin film. The morphological analysis of the infinite cluster shows good agreement with that predicted by percolation theory. The crystallization process can be described using an invasion percolation model in a fractal network. At the macroscopic scale, crystallization induces a double percolation.

The excited Rydberg states of Na2 are observed for very high n values up to 70. Four series nd 1Δg, nd 1Πg, nd 1Σg+, and ns 1Σg+ are identified and their quantum defects are measured. At high n values the observed spectrum is completely modified by the decoupling between the electronic angular momentum l of the Rydberg electron and the internuclear axis (l uncoupling). A perturbation model is developed to treat this phenomenon and appears sufficient to account for the main features such as interference effects in the electric dipole transition to the Rydberg series. Finally the Na2+ ion molecular constants are deduced.

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 result is interpreted by the p character of the bonding as in aluminum. The fragmentation processes are studied and discussed. The behavior of the ionization potential explains why the evaporation of neutral monomers is an unlikely channel in the dissociation processes. Finally doubly charged indium clusters are detected for n≥15 and their ionization threshold is determined. Triply charged clusters are also observed.

Lead clusters are produced by the inert gas condensation technique. The fragmentation of singly and doubly charged clusters is studied as a function of the electron energy. For singly charged clusters our results indicate the successive loss of neutral atoms. For doubly charged clusters, the smallest observed cluster corresponds to the smallest neutral cluster generated in the beam. Moreover, we show that the critical size previously observed at nc= 31 may be explained by fragmentation processes.

Iodine clusters are obtained by free expansion of iodine vapour. The I2 molecule is then photodissociated by a cw laser in the nozzle expansion region. Hot dissociated 1 atoms partially prevent nucleation, allowing accurate probing of the nucleation region. Moreover, I atoms can act as germs for the formation of odd clusters I2n-1, leading to an increase of the ratio (number of I2n-1+/number of I2n+).

Barium clusters are produced by the inert-gas condensation technique. The observed size distribution shows large peaks at n=13, 19, 23, 26, 29, 32, as well for singly charged clusters as for doubly and triply charged clusters. These results can be interpreted by icosahedral close-packing structures, similar to those observed in noble-gas clusters.

The electronic structure of small selenium aggregates Sen > (2 < n < 10) has been calculated using the CNDO method on a complete basis 4s, 4p, 4d. The energy per bond, the ionization potentials (IP) and the electronic affinities (EA) are given as a function of the aggregate size. The IP and EA converge to a common value which approaches the work function of bulk metal. The calculated gap is in good agreement with recent experimental determinations.

The velocities of bismuth clusters produced by the inert gas condensation technique have been measured by the time of flight spectrometer. A large velocity slip has been observed between the helium carrier gas and the clusters. The translational temperature of helium has been also measured. Although the fragmentation phenomena associated with electron impact ionization precludes a precise determination of the temperature of the clusters, this temperature can be roughly estimated and our results show that a partial mass selection of neutral clusters by a velocity selector is possible.

Autoionizing Rydberg states are observed by optical-optical double resonance under high resolution. An intense n d 1 Δ g Rydberg series (12 ⪯ n ⪯ 30) is assigned and the quantum defects measured. Molecular constants of the Na + 2 ground state are obtained by extrapolation of the Rydberg series. and the ionization potential of tile Na 2 , molecule is deduced.

Molecular clusters Hgx (2x (2

Mass spectra of Agn aggregates (2 I(Ag2n+). Doubly charged clusters have also been detected and evidence exists for a Coulomb explosion mechanism.

By observing the behaviour of the vapour phase of antimony at different temperatures it has been possible to outline the different ionization processes of the monoatomic and polyatomic species. Particularly, we have found evidence for the existence of triatomic molecules in the vapour phase and we have found their ionization potential to be 7.50 ± 0.13 eV. From the ionization efficiency curves we have deduced a set of critical potential values and, by combination with out ionization potential values, we have obtained the dissociation energies of the molecules and ions.

Resume Les processus d'ionisation a haute temperature des vapeurs monoatomiques de Au, Cu, Sn, In, Zn, Cd et Hg ont ete etudies a l'aide d'une cellule de Knudsen couplee a une source d'ionisation du type Fox. La structure fine des courbes d'efficacite d'ionisation a pu etre determinee par l'etude de leur evolution en fonction de la temperature. Les courbes d'efficacite d'ionisation ont ete representees avec leur courbe derivee seconde respective. Ces dernieres permettent une determination precise du premier potentiel d'ionisation ainsi que des potentiels critiques, dont les valeurs sont, dans la plupart des cas, en bon accord avec celles deduites des courbes derivees premieres relatives aux courbes d'efficacite d'ionisation obtenues par impact photonique. Des processus d'ionisation ont ete proposes mettant notamment en evidence la contribution preponderante de phenomenes d'autoionisation.

Bismuth clusters are produced by the inert gas condensation technique. The clusters velocity is studied systematically as a function of the helium pressure. A large velocity slip is observed between He and the clusters. This velocity slip depends on the mass cluster and allows us to select in size the neutral clusters. Moreover this mass selectivity enables us to study the fragmentation of bismuth clusters (as a function of the ionizing energy).

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.