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ABSTRACT Nanostructured carbon films have been grown by deposition of supersonic cluster beams. A novel pulsed microplasma cluster source allows to obtain cluster beams of high intensity and stability. Cluster growth and beam formation have been charaterized. Separation effects typical of supersonic expansions cause inhomogeneities of cluster distribution in the beam, depending on their masses. This effect, observed for the first time, has been carefully characterized. The deposited films have a low density porous structure based on nanometer-size grains. The coordination is essentially three-fold with a large number of defects. Film density, morphology and surface roughness can be controlled by varying the precursor cluster mass distribution. Applications of cluster-assembled carbon films will be presented. INTRODUCTION The physico-chemical properties of carbon thin films are mainly influenced by the coexistence of different atomic coordination, degree of crystallinity, texture, voids, surface roughness. These features, in systems assembled atom by atom, are largely determined by the kinetic energy of the ions impinging on the substrate during the film growth [1-3]. The use of carbon nanoparticles instead of atoms as building blocks, can open new possibilities for the synthesis of materials with a controlled structure and porosity on a mesoscopic and nanoscopic scale [4-6]. Supersonic cluster beam deposition (SCBD) is, in principle, a very promising technique for the growth of nanostructured carbon films with interesting structural and functional properties [7, 8]. With this technique it is possible to generate highly collimated beams containing clusters with a mass distribution ranging from few atoms to several thousands. The incident energy of clusters accelerated in a supersonic expansion is such that massive fragmentation is prevented and the clusters retain their individuality on the substrate. Although very promising, the use of SCBD is still limited by requirements on cluster sources in terms of intensity, stability, tunability and transferability. Recently we have developed a pulsed microplasma cluster source (PMCS) which overcomes many of the problems encountered in SCBD, providing long-term stability, high intensity and control on cluster mass distribution [9]. Using PMCS we have deposited cluster-assembled carbon films characterized by a porous granular structure. The films contain fullerene- and tubulene-like structures embedded in an amorphous matrix. The growth process via SCBD can be described as a random stacking of particles as for ballistic deposition [10]: structure, density and morphology of the films can be controlled by varying the precursor distribution. Several characteristic length scales influence the functional and the structural properties of this material, the principal parameter to control these length scales is the size of the clusters and their mass distribution. 75 Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society

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