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Bimetallic cobalt–samarium nanoparticles are prepared in the gas phase using a combined laser vaporization-rare gas condensation source and subsequently deposited on various substrates or embedded in non-magnetic metallic matrix using the Low Energy Cluster Beam Deposition technique (LECBD). Structural and magnetic characterizations from assemblies of isolated clusters, reveal Co – Sm clusters with a mean diameter around 3.5 nm, and a loss of magnetization compared to the bulk SmCo 5 phase, probably due to an amorphous state associated to a segregation of the samarium atoms at the cluster surface. Annealing in ultra high vacuum up to 820 K considerably improves the crystallinity and the homogeneity of the mixed clusters leading to a significant increase of the magnetic anisotropy and consequently of the blocking temperature, as large as 400 K, without significantly increasing the mean size (around 6 nm). Such results seem promising for applications to high density memory devices and spintronics.

International audience; The optical properties of nanocomposite thin films of gold, silver and bimetallic silver-gold clusters embedded in a porous alumina matrix have been investigated in the size range 2–6.7 nm. The metallic particles are produced by laser vaporization of either an Au0.5Ag0.5 alloy or a pure metal target whereas the dielectric matrix is evaporated by an electron gun. Samples involving a low metal concentration have been characterized by several complementary techniques in order to determine their composition, morphology and cluster size distribution. The mixed particles have the same stoichiometry as the target rod. Optical absorption spectra exhibit a surface plasmon resonance whose position is shifting with cluster mean size, giving evidence of finite size effects. Theoretical calculations in the framework of Time-Dependent-Local-Density-Approximation (TDLDA), taking into account an inner skin of ineffective screening and the porosity of the matrix, are consistent with observed size evolutions of the Mie frequency in each type of sample.

The behaviour of gold atoms that alloy into amorphous antimony (aSb) islands is studied by transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS). In a first step, antimony thin films are produced by low-energy cluster beam deposition (LECBD). The antimony clusters (of diameter ≈5 nm, with 2300 atoms) are generated in a thermal source by the gas aggregation technique and deposited onto highly-oriented pyrolitic graphite (HOPG). For cluster submonolayer coverage (

Alloying of gold atoms into nanometer-sized antimony clusters deposited on highly oriented pyrolitic graphite (HOPG) has been studied by transmission electron microscopy (TEM) for morphological and structural characterisations and by energy dispersive X-ray spectroscopy (EDX) for analysis of composition. First, large antimony clusters (≈5.4 nm) generated by the gas aggregation technique in a thermal source were deposited on HOPG. These antimony clusters diffused on graphite and formed, by collision and irreversible sticking, ramified islands the density of which can be predicted, prior to deposition, with suitable cluster flux and substrate temperature. Then, the gold atoms were evaporated at various mean thicknesses on the same Sb N –HOPG substrate. For this post-deposition of gold, the morphology of the deposit was quite different, depending on the evaporation method (Knudsen cell heated by electron bombardment or spiral tungsten filament heated by the Joule effect): ramified islands of Sb–Au alloys plus gold supported particles when using the first method and only ramified Sb–Au islands for the second one. In this paper, we give an explanation of these two different morphologies and we study the alloy formation versus the gold content.

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.

The low-energy cluster beam deposition technique (LECBD) is applied to produce cluster assembled films with hitherto unknown nanostructured morphologies and properties. Neutral clusters having the very low energy gained in the supersonic expansion at the exit of the inert gas condensation-type source are deposited without fragmentation upon impact on the substrate. Depending on the deposition conditions (nature, size and flux of incident clusters, nature and temperature of the substrate, vacuum conditions), granular nanostructures resulting from the diffusion and coalescence of supported clusters are obtained with materials of any type (covalent or metallic). A critical size for coalescence limits the supported grain size and, finally, highly porous thick films growing by random stacking of nanoparticles are obtained. A recent model developed by combining several dynamical processes simultaneously occurring on the substrate (deposition - diffusion - aggregation, DDA) is used to simulate the cluster assembled film morphology in good agreement with the experimental observations. Examples of novel materials obtained by LECBD are presented to illustrate the interesting potentialities of the technique. In the case of covalent materials such as carbon and silicon, 'amorphon'-type disordered structures, different from the conventional amorphous structures (a-C and a-Si), are obtained with some unique properties. With transition metal (Fe, Co and Ni) cluster assembled films, a specific magnetic behaviour, resulting from the competition between the intrinsic properties of the grains (magnetocrystalline anisotropy) and the interactions between grains, is observed. Also, films of clusters embedded in various co-deposited matrices are produced in order to control the interactions between grains via the matrix materials (insulating, conducting ...). Interesting optical properties (from metallic clusters in ) or giant magnetoresistance effects (from Co clusters in silver) are reported for such systems, emphasizing the future role of LECBD in various fields of applications such as optical and optoelectronic nanostructures, magnetic and magneto-optic nanostructures and quantum devices.

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

The growth of Bi films obtained by low-energy cluster beam deposition (LECBD) is compared to those obtained by classical molecular beam deposition (MBD). For these two deposition techniques, significant differences in the very first stages of growth are presented. From transmission electron microscopy (TEM) observations, we show that the morphology of Bi thin films is sensitive to the size of incident clusters. The influence of incident cluster size on particle number density, diameter of supported particles and coverage rate is studied in the range of cluster size: 2–1100 atoms. The increase of roughness and decrease of the grain size are observed for Bi thick films (equivalent thickness teq about 40 nm) produced by LECBD compared to those produced by MBD.

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

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.

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.

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.

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.

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.

Mixed $({\mathrm{Au}}_{x}{\mathrm{Ag}}_{1\ensuremath{-}x}{)}_{n}$ clusters of various relative compositions are produced in a laser vaporization source, and embedded in an alumina matrix. The size and concentration effects in the optical properties are investigated for different stoichiometries (from $x=0$ up to 1 in steps of 0.25), in the diameter range 1.5\char21{}5 nm for which the size evolution is ruled by quantum effects. For a given size, we measure a steady evolution of the surface plasmon frequency versus x. For a given relative composition, the blueshift (relative to the prediction of Mie's theory), damping, and broadening of the resonance all become more important as the size decreases and as the gold concentration increases. These spectra are compared with model calculations, based on the time-dependent local-density-approximation formalism, including both the porosity of the matrix and an inner skin of reduced ionic-core polarizability. Two models are introduced to describe the effective dielectric function of the ionic background in the bimetallic cluster. Agreement between experimental results and both models is discussed.

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.

The low-energy cluster beam deposition (LECBD) technique is used to deposit gold nanoclusters preformed in the gas phase on functionalized graphite substrates (highly oriented pyrolitic graphite (HOPG)), to prepare 2D- organized arrays of cluster assembled dots. Functionalized HOPG substrates are obtained using the focused ion beam (FIB) nanoengraving technique to pattern 2D-organized arrays of defects (nanoholes, nanobumps) which act as traps for the diffusing clusters. Depending on the deposition conditions (nature, size and fluence of the deposited clusters) and the functionalized substrates (nature and size of the FIB-induced defects, geometry of the 2D array of defects and temperature during deposition) high-quality quantum-dot arrays can be obtained with well controlled and reproducible morphologies. Kinetic Monte Carlo simulations of the cluster deposition experiments on functionalized substrates allow us to obtain quite good fits of the experimental images performed by tapping mode atomic force microscopy (TMAFM), leading to systematic investigations of the best conditions to realize high-quality quantum dots systems. This combined top-down-bottom-up approach (LECBD-FIB) seems a promising method for preparing high-integration-density devices (∼Tbit cm −2 ) well suited for future applications to data storage, nanoelectronics, nano-optics, nanomagnetic systems.

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.