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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 optical properties of bimetallic silver-gold clusters are investigated in the size range 1.9--2.8 nm. Clusters, produced by laser vaporization of an alloy target Au-Ag (50%-50% atomic composition) are embedded with a low concentration in an alumina matrix. The mixed particles have the same stoichiometry as the rod. Absorption spectra exhibit a plasmon resonance band between those of pure Au and Ag embedded clusters, shifting towards higher energies with decreasing cluster size. Theoretical calculations in the frame of the time-dependent-local-density-approximation, including an inner skin of ineffective screening and the porosity of the matrix, are in good agreement with experimental results.

The alloying behaviour of antimony molecules Sb4 into nanometre size indium clusters deposited on amorphous carbon has been studied by transmission electron microscopy and selected area electron diffraction for morphological and structural characterizations, and by energy dispersive X-ray spectroscopy for analysis of composition. First, large indium clusters containing about 1700 atoms (mean diameter = 4.4 nm) formed by the gas aggregation technique in a thermal source are deposited on amorphous carbon. Nucleation and growth mechanisms lead to the formation of indium particles randomly dispersed on the substrate. Then antimony molecules evaporated at various thicknesses are deposited on to the indium aggregates. These two successive depositions have been performed at room temperature. A dissolution of antimony atoms into the indium particles takes place and InSb compound is successfully formed. InSb particles as produced have the zinc-blende structure (sphalerite type) which is the structure of t...

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.

The optical properties of nanocomposite thin films of gold and silver clusters embedded in an alumina matrix have been investigated. The samples have been characterized by several techniques in order to determine their composition, morphology and cluster size distribution. Ellipsometry and photoabsorption measurements have been performed. The differences in the optical properties of the various samples reflect finite size effects. Time Dependent Local-Density-Approximation (TDLDA) calculations, taking into account the d-electrons and matrix screening effects, are consistent with observed size evolutions of the Mie frequency. Low frequency Roman scattering spectra exhibit a strong size-dependent band related to quadrupolar vibration modes of the clusters.

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.

Nanostructured films of cobalt and nickel have been prepared using the low-energy neutral cluster beam deposition technique on various substrates. The nucleation-and-growth process of the films has been studied by in-situ electrical conductivity measurements and transmission electron microscopy observations. Complementary results obtained from X-ray diffraction and absorption measurements on films 100 nm thick confirm the nanostructured morphologies of both Co and Ni films consisting of a random stacking of well crystallized fcc grains having a diameter of around 3–4 nm. In terms of magnetic properties the granular structure leads to films which roughly behave like amorphous ferromagnets but with local order of the extent of a grain. From magnetization measurements and ferromagnetic resonance experiments which showed spin-wave oscillations, the magnetic parameters characteristic of the cluster-assembled films (i.e. magnetocrystalline anisotropy and intergrain exchange coupling energies) have been...

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...

Single crystals of LiNbO3 with y- and z-cut orientations were irradiated at GANIL with 3.37 MeV/amu 238U ions at a fluence ranging from 1.0 × 1011 to 4.0 × 1011 ions.cm−2. The damage resulting from these irradiations at high electronic stopping powers (> 10 KeV/nm) consists mainly of amorphous tracks. After irradiation the samples were implanted with europium ions of 70 keV energy at a fixed fluence of 5 × 1016 ions. Subsequent annealings in air, in the range 700–1100°C, were applied to investigate the influence of the pre-irradiation damage on the thermal evolution of Eu implanted LiNbO3 crystals. Rutherford Backscattering Spectrometry (RBS) results clearly show that the existence of the amorphous tracks enhances the europium diffusion. An anisotropy effect has been observed in the diffusion process.

Single crystals of lithium niobate (LiNbO3) with y‐cut orientation were irradiated at GANIL with 5.17 MeV/amu 155Gd ions at a fluence ranging from 1.5×1011 to 6.0×1011 ions cm−2. After irradiation the samples were implanted with europium ions of 70 keV energy at a fixed fluence of 5×1016 ions cm−2. Both irradiations and implantations were performed at room temperature. Thermal treatments in air, in the range 300–1100 °C, were applied to investigate the influence of the preirradiation damage on the thermal evolution of Eu implanted LiNbO3 crystals. Transmission electron microscopy micrographs exhibit the amorphous track formed by high‐energy irradiations. Rutherford backscattering spectrometry results show that these amorphous tracks enhance the europium diffusion in depth of the LiNbO3. A diffusion coefficient and an activation energy were estimated to be about 4.2×10−15 cm2 s−1 and 0.42 eV, respectively.

Nanocrystallized films of iron have been elaborated using for the first time the Low Energy Cluster Beam Deposition techniques. Structural characterizations have shown that the grain size distribution is very narrow and centered around 5 nm. The grain shape is almost spherical. Moreover, the density of the films is around 62% of bulk iron. Magnetic properties of the samples were studied using Mossbauer spectroscopy, ferromagnetic resonance and SQUID magnetometry. Experimental results have been quantitatively interpreted in the framework of the Random Anisotropy Model, with an exponential correlation of anisotropy directions extending up to 5 nm. In particular, the anisotropy and inter-grains exchange coupling energies have been determined.

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

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.

Iron and copper thin metallic films (thickness ≤ 100 nm) deposited on sapphire substrates (α-Al2O3) were mixed at room temperature by various rare gas ions (Ne, Ar, Kr and Xe) in large energy and dose ranges. Microstructural and chemical characterization of the mixed interfaces were performed using three complementary techniques: high resolution transmission electron microscopy (HRTEM), X-ray photoemission spectroscopy (XPS) and conversion electron Mossbauer spectrometry (CEMS) in the particular case of Fe/Al2O3 samples. The final atom distributions at the mixed interface are the result of the ballistic phase of mixing and no long range diffusion of mixed elements in Al2O3 has been observed. The result is a very narrow and damaged interface (amorphous or not in the case of Fe/Al2O3 or Cu/Al2O3, respectively) containing a very high concentration of metallic atom recoils. The composition and nature of this interfacial layer, which completely depends on the energy deposition at the interface, which is controlled by the mixing parameters (mass of the incident ion, energy and fluence) are the origin of the spectacular adhesion enhancement observed. In the particular case of the Fe/Al2O3 interface, the formation of iron recoils in Al2O3 in the Fe2+ state and the formation of the spinel phase seem to be correlated with the quality of the interfacial joint in terms of adhesion. Thermal annealings in a low temperature range (< 600°C) promote the spinel phase formation and produce an additional positive effect on adhesion.

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.

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.

Metallic iron layers (~ 60 nm) deposited on sapphire substrates have been mixed at room temperature with various ions (Ne, Ar, Kr, Xe) in wide dose and energy ranges. Microstructural characterization of the interface has been performed at the atomic scale using high-resolution transmission electron microscopy observations on cross-sectioned samples. Complementary measurements with conversion electron Mossbauer spectrometry (CEMS) and X-ray photoelectron spectrometry (XPS) give chemical information on the nature of the nonequilibrium phases formed at the interface. The mixed zone at the interface concerns few atomic planes and no long-range diffusion takes place at room temperature in those metal-ceramic systems. A significant enhancement of adhesion has been measured by the pin pull test for the mixed samples with a strong dependence on the energy deposition at the interface. These results will be discussed taking into account the microstructural and physicochemical aspects as well as the energy deposition in individual cascades during the primary ballistic phase (~ 10 −13 s) of the ion beam mixing process.

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.

The ion beam mixing technique is well adapted to treat metal-ceramic interfaces under low temperature and non-equilibrium conditions. Using this technique, we have mixed Cu-Al2O3 and Fe-Al2O1 interfaces in order to improve the adhesion. Cu and Fe metallic layers having thicknesses of less than ~ 100 nm were deposited on optical grade polished surfaces of sapphire substrates. Ion beam mixing experiments were performed at room temperature with xenon, krypton, argon, and neon ions of various energies and fluences ranging from 1015 to 4 x 1016 ions per cm2. A linear increase of adhesion with ion mixing was observed for all the ions and systems studied. A strong dependence of adhesion on the energy transfer, controlled by the nature and energy of the incident ions, was observed, allowing us to optimize the adhesion enhancement in the particular case of the Nebombarded Fe-Al2O3 interface. The microstructural and chemical effects induced at the interface during the ballistic phase of the mixing process responsib...

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 .

Etude de la possibilite de formation d'un verre du systeme Fe-Ti par melange par faisceau d'ions des multicouches. On opere a 300 K pour trois compositions: Fe 83 Ti 17 (pres du point eutectique) et Fe 2 Ti et FeTi (composition a l'equilibre)eTUDE DE L

The phenomenon of irradiation enhanced adhesion of thin copper films deposited on sapphire has been studied. After irradiation of copper-sapphire interfaces with 1.5 MeV energy xenon ions. the bonding between metal and clean ceramic has been dramatically improved. This continuous adhesion enhancement has been measured as a function of ion dose from 5 × 1015 up to 3 × 1016 ions/cm2 by pin pull test experiments. The adhesion force measured after mixing with 3 × 1016 ions/cm2 is six times larger than for the unmixed sample. According to alpha particle Rutherford backscattering analysis, the copper-sapphire interface remains abrupt, even after 3 × 1015 ions/cm2. So, in order to clarify the mechanism responsible for such enhancement of adhesion, microstructural characterization of the interfaces has been performed at an atomic scale using high resolution transmission electron microscopy (HRTEM). These observations have shown that the copper-sapphire interface has been modified within a thin region (a few atomic planes) in which the interface roughness has clearly increased. The width of this interfacial region corresponds rather well to that deduced form the calculation of the recoil atom distributions induced during the ballistic stage of the incident ion interaction. Thus, no long range diffusion seems to occur after this primary stage in this metal-ceramic system. In the absence of any interfacial compound induced by irradiation between copper and sapphire, the increase in roughness of the interface has been assumed to be one of the parameters promoting the copper-sapphire adhesion enhancement. One of the most interesting results in ion beam mixing applied to metal-ceramic systems arises from the experimental result that ion beam irradiation often induces an enhancement of adhesion between the metallic film and the substrate. This effect has been clearly shown [3–5] on different combinations of metal and ceramic materials with a wide range of mixing conditions, i.e. by varying the nature and the energy of the incoming particle.

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.

International audience; For Abstract see ChemInform Abstract in Full Text.

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 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.