Mesoscopic elastic properties of cluster-assembled carbon films

– The mesoscopic elastic response of cluster-assembled carbon films was measured by Brillouin light scattering. The values of bulk modulus and shear modulus were estimated from the shifts of both surface and bulk phonon peaks. The most basic mechanical properties of these new materials were so investigated down to the scale of a few hundreds of nanometers. The shear modulus is found in the range of that of crystalline graphite, whereas the bulk modulus and Poisson’s ratio are significantly different. The results agree with the mainly sp coordinated granular structure shown by Raman spectroscopy. Recently the use of carbon clusters and nanotubes as building blocks for the synthesis of nanocrystalline and composite materials with unusual elastic properties has been suggested [1][3] and several experiments to identify possible synthetic routes have been reported [4], [2], [5]. In particular several authors have suggested that the assembling of carbon clusters could be used to produce an entire new class of porous materials with interesting structural and functional properties [4]-[7]. Cluster beam deposition has been proposed to deposit nanocrystalline carbon thin films where the sp-sp content could be controlled by the choice of the precursor clusters [4], [5]. The nanoand meso-porosity resulting from cluster stacking with reduced fragmentation could give origin to a material with interesting mechanical, acoustic, thermal and electronic properties. Experimental characterization and theoretical modellization of cluster-assembled materials have to face the problem of cluster coalescence and of their organization in structures spanning length scales from the nanometer up to the micrometer. The different structures in which the precursor clusters are organized need experimental probes sensitive to the different length scales typical of intra-cluster and inter-cluster interactions. For carbon-based materials, Raman