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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.

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We report the synthesis and characterization of well-defined CoPt clusters with a mean diameter of 3 nm, produced in ultrahigh vacuum conditions following a physical route. Samples made of diluted layers of CoPt clusters embedded in amorphous carbon have been studied by transmission electron microscopy. Highresolution observations have revealed the appearance of L1 0 chemical order upon annealing, even for clusters witha2nmdiameter, without cluster coalescence. The magnetic properties of both chemically disordered and ordered CoPt clusters embedded in amorphous carbon have then been measured by x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry. Despite a striking change of the Co magnetic moment, the magnetic anisotropy of chemically ordered nanoparticles increases, with respect to the chemically disordered A1 phase, in much lower proportions than what is observed for the bulk.

The interaction between a monokinetic and mass resolved low-energy gold cluster beam and a gold ͑111͒ surface is studied in detail at room temperature by means of molecular dynamics. The model makes use of the classical second moment tight-binding approximation to estimate the interatomic forces. A model is described to account for the electron-phonon coupling. Clusters of the nanometer size are modeled to slow down one after the other on the gold surface until a nanostructured layer about 7 nm thick is formed. The cluster slowing down is studied in detail and the consequences of the diffusionless accumulation of clusters on the surface is investigated. The first impinging clusters undergo pronounced epitaxy with the substrate surface although defects of various kinds can take place in them. The further cluster slowing down stimulates the annihilation of these defects. A pronounced surface roughness indicates no significant coalescence. As the slowing down proceeds further, cluster layers become increasingly defective and highly stressed. This stress field propagates into the first cluster layer, inducing lattice distortions. The memory of the surface orientation is progressively lost as the deposited layer thickness increases. The cluster assembled is characterized by numerous cavities of the nanometer size that may be interconnected and form nanopores. Incident conditions are found to play an important role, which motivates a realistic comparison between simulated and real experiments.

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Measurements and calculations have shown significant disagreement regarding the sign and variations of the thermal expansion coefficient (TEC) of graphene α(T ). Here we report dedicated Raman scattering experiments conducted for graphene monolayers deposited on silicon nitride substrates and over the broad temperature range 150-900 K. The relation between those measurements for the G band and the graphene TEC, which involves correcting the measured signal for the mismatch contribution of the substrate, is analyzed based on various theoretical candidates for α(T ). Contrary to calculations in the quasiharmonic approximation, a many-body potential reparametrized for graphene correctly reproduces experimental data. These results indicate that the TEC is more likely to be positive above room temperature.

The formation of gold films obtained by low-energy cluster beam deposition at room temperature in ultrahigh vacuum on a gold ͑111͒ surface has been analyzed in situ by scanning probe microscopy. Neither diffusion of the clusters on the surface, nor coalescence between clusters has been detected. The films are formed by a random pavement of the surface and as a consequence submonolayer films are composed by three-dimensional isolated particles, whereas multilayer films exhibit a nanostructured morphology. Moleculardynamics simulations, using the same size distribution of incident clusters as in the experiment, reveal the influence of the impact energy on the film morphology. For a low kinetic energy of the incident clusters ͑0.25 eV/atom͒, the simulated morphology is in excellent agreement with experimental measurements.